NOTABLE SCIENTISTS

A TO Z OF

PHYSICISTS

DARRYL J. LEITER, PH.D.Former Senior Research Associate,

NASA, Goddard Space Flight Center, Greenbelt, Maryland

withSHARON L. LEITER, PH.D.

Research Consultant, RAND Corporation, Washington, D.C., and Santa Monica, California

A TO Z OF PHYSICISTS

Notable Scientists

Copyright © 2003 by Darryl J. Leiter, Ph.D.

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For Jacob, who will see further

If I have seen further than other men, it is because I have stood on theshoulders of giants.

—Isaac Newton

The most beautiful thing we can experience is the mysterious. It is thesource of all true art and science.

—Albert Einstein

A great truth is a truth whose opposite is also a great truth.—Niels Bohr

If you want to learn about nature, to appreciate nature, it is necessaryto understand the language that she speaks in.

—Richard P. Feynman

CONTENTS

List of Entries viiAcknowledgments ix

Introduction xi

Entries A to Z 1

Entries by Field 349Entries by Country of Birth 353

Entries by Country of Major Scientific Activity 355Entries by Year of Birth 358

Chronology 360Bibliography 364

Index 373

Alferov, Zhores IvanovichAlfvén, Hannes Olof GöstaAlvarez, Luis W.Ampère, André-MarieAnderson, Carl DavidAnderson, Philip WarrenÅngstrom, Anders JonasArchimedesBardeen, JohnBarkla, Charles GloverBecquerel, Antoine-HenriBernoulli, DanielBethe, Hans AlbrechtBhabha, Homi JehangirBlackett, Patrick Maynard

Stuart, LordBloch, FelixBloembergen, NicolaasBohr, Niels Henrik DavidBoltzmann, LudwigBorn, MaxBridgman, Percy WilliamsBroglie, Louis-Victor-Pierre,

prince deCarnot, Nicolas Léonard SadiCavendish, HenryChadwick, Sir JamesChandrasekhar, SubramanyanCherenkov, Pavel AlekseyevichChu, Steven

Clausius, Rudolf JuliusEmmanuel

Cockcroft, John DouglasCompton, Arthur HollyCoulomb, Charles-Augustin deCurie, MarieDavisson, Clinton JosephDirac, Paul Adrien MauriceDoppler, ChristianDyson, FreemanEinstein, AlbertFaraday, MichaelFermi, EnricoFeynman, Richard PhillipsFitch, Val LogsdonFitzGerald, George FrancisFizeau, Armand-Hippolyte-

LouisFoucault, Jean-Bernard-LéonFranck, JamesFraunhofer, Joseph vonFresnel, Augustin-JeanGabor, DennisGalilei, GalileoGamow, GeorgeGauss, Johann Carl FriedrichGeiger, Hans WilhelmGell-Mann, MurrayGlaser, Donald ArthurGlashow, Sheldon Lee

Goeppert-Mayer, MariaGertrude

Hawking, StephenHeisenberg, WernerHelmholtz, Hermann Ludwig

Ferdinand vonHenry, JosephHertz, Heinrich Rudolf’t Hooft, GerardHooke, RobertHuygens, ChristiaanJosephson, Brian DavidJoule, James PrescottKamerlingh Onnes, HeikeKapitsa, Pyotr LeonidovichKelvin, Lord (William

Thomson)Kilby, Jack St. ClairKirchhoff, Gustav RobertKroemer, HerbertKusch, PolykarpLamb, Willis Eugene Jr.Landau, Lev DavidovichLandé, AlfredLangevin, PaulLaue, Max Theodor Felix vonLederman, Leon M.Lee, Tsung-DaoLenard, Philipp vonLenz, Heinrich Friedrich Emil

vii

LIST OF ENTRIES

viii A to Z of Physicists

Lorentz, Hendrik AntoonMach, ErnstMaxwell, James ClerkMeitner, LiseMichelson, Albert AbrahamMillikan, Robert AndrewsMössbauer, Rudolf LudwigMott, Sir Nevill FrancisNe’eman, YuvalNernst, WaltherNewton, Sir IsaacOhm, Georg SimonOppenheimer, J. RobertØrsted, Hans ChristianPauli, WolfgangPenzias, Arno AllanPerrin, Jean-BaptistePlanck, Max Ernest LudwigPoynting, John HenryPurcell, Edward MillsRabi, Isidor IsaacRaman, Sir Chandrasekhara

VenkataRamsey, Norman F.Rayleigh, Lord (John William

Strutt)

Reines, FrederickRichter, BurtonRöntgen, Wilhelm ConradRubbia, CarloRutherford, ErnestRydberg, Johannes RobertSakharov, Andrei

DmitriyevichSalam, AbdusSchawlow, Arthur LeonardSchrieffer, John RobertSchrödinger, ErwinSchwinger, Julian SeymourSegrè, Emilio GinoShockley, William BradfordSnell, WillibrordSommerfeld, Arnold Johannes

WilhelmStark, JohannesStefan, JosefStern, OttoStokes, George GabrielTaylor, Joseph H., Jr.Teller, EdwardTesla, NikolaThomson, Joseph John (J. J.)

Ting, Samuel Chao ChungTomonaga, Sin-ItiroTownes, Charles HardVan Allen, JamesVan de Graaff, Robert JemisonVan Vleck, John HousbrookVeltman, Martinus J. G.Volta, Alessandro Guiseppe

Antonio AnastasioWeber, Wilhelm EduardWeinberg, StevenWheeler, John ArchibaldWien, Wilhelm (Carl Werner

Otto Fritz Franz)Wigner, Eugene PaulWilson, Charles Thomson

ReesWu, Chien-ShiungYang, Chen NingYoung, ThomasYukawa, HidekiZeeman, Pieter

ix

ACKNOWLEDGMENTS

My primary debt of gratitude is to my wifeand colleague, Dr. Sharon L. Leiter, for

her invaluable contributions to the creation ofthis work. The essays in this book took shape asa result of the ongoing dialogue between us, be-tween scientist and layman, which challengedme to find clear and precise expression for thecomplex ideas of modern physics.

Thanks go to my editor, Frank K. Darm-stadt, for his patience and guidance in preparingthe manuscript, and to my agent, Jodie Rhodes,for making the opportunity to write this bookavailable to me.

I would also like to thank Heather Lindsayat the Emilio Segrè Photo Archives of theAmerican Institute of Physics for her kindnessand competence in helping us obtain the pho-tographs in this volume.

Finally, I am grateful to my colleagues inthe physics community for many insightful dis-cussions involving conceptual and historical de-velopments in physics.

xi

Ato Z of Physicists is an up-to-date biograph-ical dictionary containing profiles of 150

of the most illustrious figures in the history ofphysics. It provides a comprehensive and acces-sible guide to the men and women behind theideas that have shaped the modern vision ofphysical reality.

These biographical essays, focusing on indi-vidual struggles and achievements, never losesight of the communal nature of physics: theways in which the lives and works of physicistsare interconnected. They give brief yet detailedexplanations of each physicist’s key discoveriesand of how they grew out of previous findingsand established the ground for future break-throughs. Anyone wanting to know at a glance“who did what” in physics will find the answeras well as in-depth explanations of the work it-self in this volume. Each entry concludes with abrief list of suggested further reading, enablingthe student to delve more deeply into the lifeand contributions of a given subject.

The stories of the men and women in thisvolume tell of astounding insights, happy acci-dents, and perseverance rewarded, as well asfruitless quests, misinterpretations, and frustra-tions. Whatever their individual differences,however, physicists are people with “wind intheir sails.” The common desire of physicistsfrom all lands and ages to play a part in the evo-lution of an ultimate explanation of physical re-

ality—as well as the belief that such an expla-nation is possible, that is, that nature is funda-mentally orderly and comprehensible—imbuestheir lives with a rare spiritual and intellectualexcitement.

The history of physics is one of repeated“paradigm shifts,” in which an established pic-ture of the universe is replaced by another,more far-reaching vision. Thus, Galileo’s under-standing of physical laws was modified and par-tially replaced by the discoveries of Sir IsaacNewton, whose “classical” physics was over-turned by the “quantum” physics of Niels Bohrand the “relativistic” universe of Albert Ein-stein. In each instance, the prior physical modelwas not so much invalidated as shown to applyto a circumscribed level of reality, beneathwhich a deeper one was revealed. The directionof these revolutionary shifts has been towardthe world of the infinitesimally small. When atlast their existence was accepted by the major-ity of physicists, atoms were found to consist ofelementary particles, which in turn compriseeven smaller “quarks.”

Few if any physicists living today believethat the “final answer” to the question of na-ture’s fundamental structure has been found. In-deed, the quest for a “unified field theory” or“theory of everything” is the hallmark of con-temporary physics. For this reason, the next edi-tion of this volume will doubtless contain the

INTRODUCTION

story of individuals and discoveries that funda-mentally modify what we know now.

Limits of time and resources made it impos-sible for me to include a great many figures whobelong in this book; the fact that this is an agewhen physicists work as large teams, writing 35-author papers, only heightened the problem ofinclusiveness. Regretfully, I have omitted physi-cists whose work is well established, advocatesof promising theories that have yet to be ac-cepted by the physics community, as well asphysicists whose careers were not marked by alasting discovery, but whose dedication to re-search and teaching created the vital mediumout of which such discoveries emerge.

THE ENTRIES

Entries are arranged alphabetically by surname,with each entry listed under the name by whichthe entrant is most commonly known. The typ-ical entry provides the following information:

Entry Head: Name, birth/death dates,field(s) of specialization, and nationality.

Essay: Essays range in length from 500 to2000 words, with most averaging around 1200words. Each contains basic biographical infor-mation—date and place of birth, family infor-mation, educational background, positionsheld, prizes awarded, and so on—but the great-est attention is given to the entrant’s work.Names in small capital letters within the essaysprovide easy reference to other people repre-sented in the book. All direct quotations, unlessotherwise noted, are the physicist’s own words.In addition, entries conclude with FurtherReading, sources the reader who is interested infollowing up on a person or his/her work cancheck.

In addition to the alphabetical list of physi-cists, readers searching for names of individualsfrom specific countries can consult the nation-ality index, which organizes entrants by countryof birth and/or citizenship. The subject indexlists scientists by field. Finally, the Chronologylists entrants by their birth and death dates.

xii A to Z of Physicists

A� Alferov, Zhores Ivanovich

(1930– )RussianExperimentalist, Solid State Physicist

Zhores Alferov is a major figure in solid statephysics, whose groundbreaking work on semi-conductors led to the creation of the physics ofmodern miniaturized electronic devices such ascell phones, pagers, and compact disc (CD)players. For this work he shared the 2000 NobelPrize in physics with two other pioneers in infor-mation and communications technology, HER-BERT KROEMER and JACK ST. CLAIR KILBY.

He was born on March 15, 1930, in Vitebsk,Belorussia, in what was then the Soviet Union,to Anna Vladimirovna, a librarian and head of apublic organization of homemakers, and IvanKarpovich, a factory director and a CommunistParty member, who told Zhores and his brothertales of his exploits in the civil war. He attendeda boys’ school in Minsk, which had been devas-tated in World War II, where an inspiringphysics teacher helped him find his calling andadvised him to apply for admission to the cele-brated V. I. Ulyanov [Lenin] ElectrotechnicalInstitute in Leningrad (now Saint Petersburg).Although he found theoretical physics “easyenough,” he was attracted to laboratory workand began the research on semiconductors, that

is, materials such as silicon or germanium thathave a resistivity midway between that of con-ductors and that of insulators, that wouldbecome his life’s work. In 1952 he graduatedfrom the Department of Electronics, after com-pleting a thesis on the problem of obtaining thinfilms.

He was offered the opportunity to stay onbut instead accepted a position at the Physico-Technical Institute in Leningrad, under theleadership of Abram F. Ioffe in 1953 as a juniorresearcher in the recently organized semicon-ductor laboratory. He considered this “luckychance” to work with the elite of his chosen fieldthe cause of his “happy scientific career.” By May1953, the first Soviet transistor receivers hadbeen developed and Alferov began to compre-hend the significance of the technology for elec-tronic devices as well as basic research. Withinthe next few years his group developed the firstSoviet high-power germanium rectifiers and ger-manium and silicon photodiodes, used in mod-ern electronic devices. He was part of the teamthat developed a special semiconductor devicefor the first Soviet atomic submarine in 1958.

He received his candidate’s degree (some-where between American master’s and doctoraldegrees) from the Ioffe Institute (formerly thePhysico-Technical Institute) in 1961. At thispoint, he became involved with heterostruc-

1

tures and semiconductor lasers. Because earlytransistors were relatively low-powered andslow, semiconductor transistors based on het-erostructures were proposed as a way of increas-ing amplification and achieving higherfrequencies and power. Such a heterostructureconsists of two semiconductors whose atomicstructures fit one another well, but that havedifferent electronic properties. Kroemer had for-mulated these ideas theoretically in a 1957paper. Alferov understood that semiconductorphysics would be developing on the basis of het-ero- rather than homostructures and led hisgroup at the Ioffe Institute in the race todevelop this technology before Bell Telephone,IBM, and RCA could do so.

During this period of intense research, herose steadily in rank at the Ioffe Institute,becoming a senior researcher in 1964 and headof his laboratory in 1967. That year he marriedTamara Darskaya, a researcher at a large spaceenterprise, with whom he would have two chil-dren. By 1969 his group had mastered all theideas on control of the electron and light fluxesin classical heterostructures based on the arsenidgallium–arsenid aluminum heterostructure.

During his first trip to the United States in1969, Alferov spoke about his group’s recentdevelopment of low-threshold room tempera-ture lasers. He electrified his audience when heexplained how they had obtained the continu-ous wave regime by developing an optical fiberwith low losses—a breakthrough that resultedin the discovery and rapid development of opti-cal fiber communication. He was able to visitBell Labs and IBM and later wrote of his rela-tionship with the giant American firms as “arare example of open and friendly competitionbetween laboratories belonging to the antago-nistic great powers.”

Semiconductor heterostructures have beenimportant to the development of lasers, light-emitting diodes, modulators, and solar panels.The semiconductor laser is based on the recom-

bination of electrons and holes, emitting pho-tons (particles of light). If the density of thesephotons becomes sufficiently high, they maybegin to move in rhythm with each other andform a phase-coherent state, that is, laser light.The first semiconductor lasers had low efficiencyand could only shine in short pulses. Both Kroe-mer and Alferov had suggested in 1963 that theconcentration of electrons, holes, and photonswould become much higher if they were con-fined to a thin semiconductor layer between twoothers—a double heterojunction. Despite a lackof the most advanced equipment, in May 1970, afew weeks earlier than their American competi-tors, Alferov’s group succeeded in producing alaser that operated continuously and that didnot require troublesome cooling.

After receiving his doctorate from the IoffeInstitute in 1970, Alferov spent six months in1971 in the United States, working in the semi-conductor devices lab at the University ofIllinois. In 1973, he became professor of opto-electronics at the Saint Petersburg State Elec-trotechnical Institute (the new name of theUlyanov Institute). In 1987 he was electeddirector of the Ioffe Institute and in 1988 wasappointed dean of the faculty of physics andtechnology at Saint Petersburg Technical Uni-versity. He was elected a corresponding memberof the Union of Soviet Socialist Republics(USSR) Academy of Sciences in 1972 and a fullmember in 1979. Since 1989 he has been vicepresident of the USSR (now Russian) Academyof Sciences and president of its Saint PetersburgScientific Center.

In the tumultuous period since the SovietUnion collapsed in 1991, Alferov has beendeeply concerned with the plight of Russia’sseverely underfunded scientific community. In1995, to protect the Academy of Sciences, hebecame a deputy of the State Duma (Russianparliament) and won fame as a leading advocatefor educational funding programs. When he wonthe 2000 Nobel Prize he donated a third of his

2 Alferov, Zhores Ivanovich

winnings for the support of Russian educationand science. He believes that

If Russia is to be a great power, it will be, notbecause of its nuclear potential, faith in Godor the president, or Western investment, butthanks to the labor of the nation, faith inknowledge and science and the mainte-nance and development of scientific poten-tial and education.

Alferov’s work has led to spectacular scien-tific breakthroughs in which the advanced mate-rials and tools of microelectronics are being usedfor studies in nanoscience and investigations ofquantum effects. The impact of Alferov’s researchon the modern world of electronics and communi-cation has been enormous. Lasers and light-emit-ting diodes (LEDs) have been further developed inmany stages. Without the heterostructure laser,today we would not have had optical broadbandlinks, CD players, laser printers, bar code readers,laser pointers, and numerous scientific instru-ments. LEDs are used in displays of all kinds,including traffic signals, and may eventuallyreplace lightbulbs altogether. In recent years, ithas been possible to make LEDs and lasers thatcover the full visible wavelength range, includingblue light. Today, high-speed transistors are foundin cellular phones and in their base stations, insatellite dishes and links. There they are part ofdevices that amplify weak signals from outer spaceor from a faraway cellular phone without drown-ing in the noise of the receiver itself.

Alferov is currently editor in chief of theRussian journal Technical Physics Letters and amember of the editorial board of the Russianjournal Science and Life. He is the author of fourbooks, 400 articles, and 50 inventions involvingsemiconductor technology.

Further ReadingNoll, A. Michael. Principles of Modern Communications Tech-

nology. Boston and London: Artech House, 2001.

� Alfvén, Hannes Olof Gösta(1908–1995)SwedishPlasma Physicist, Astrophysicist

Hannes Alfvén was the founder of the modernfield of plasma physics, the study of electricallyconducting gases, and the father of the branch ofplasma physics known as magnetohydrodynam-ics (MHD), the study of plasmas in magneticfields. He was honored for this work with the1970 Nobel Prize in physics.

Alfvén was born on May 30, 1908, inNorrkoping, Sweden, to Anna-Clara Romanusand Johannes Alfvén, both physicians. Heattended the University of Uppsala and earned aPh.D. in 1934 for a dissertation on ultrashortelectromagnetic waves; in that year, he wasappointed lecturer in physics at Uppsala. In1935, he married Kerstin Maria Erikson, withwhom he would share a 67-year marriage thatwould produce five children.

He became a research physicist, in 1937, atthe Nobel Institute in Stockholm, where hebegan his groundbreaking work in plasmaphysics. Plasmas are highly ionized gases con-taining both free positive ions and free electrons.The dominant state of matter in the universe,they are rare on Earth, but abundant in stars,galaxies, and intergalactic space. Alfvén studiedplasma physics primarily within the context ofastrophysics, beginning with an attempt toexplain the phenomenon of sunspots by investi-gating the interaction of electrical and magneticfields with plasmas. He formulated the frozen-in-flux theorem, which postulates that under cer-tain conditions, a plasma is bound to themagnetic lines of flux passing through it. On thebasis of this theorem he then postulated the exis-tence of the galactic magnetic field, which nowforms the basis for cosmic magnetism, using theidea to explain the origin of cosmic rays.

In the early 1930s, most physicists believedthat cosmic rays were gamma rays that permeated

Alfvén, Hannes Olof Gösta 3

the whole universe. But when cosmic rays werediscovered to be charged particles, Alfvén made aunique proposal: if the galaxy contained a large-scale magnetic field, then cosmic rays could movein spiral orbits within the galaxy, because of theforces exerted by the magnetic field. He arguedthat there could be a magnetic field pervading theentire galaxy if plasma were spread throughoutthe galaxy. This plasma could carry the electricalcurrents that would then create the galactic mag-netic field. Whereas this intuitive hypothesis wasfirst dismissed on the grounds that interstellarspace was known to be a vacuum incapable ofsupporting electrical currents and particle beams,it was later accepted by physicists and becamevery fashionable in the 1980s and 1990s.

Alfvén was the first to devise the guidingcenter approximation, a widely used techniquethat enables the complex spiral movement of acharged particle in a magnetic field to be calcu-lated with relative ease. In 1939, using this tech-nique, Alfvén proposed a theory to explainauroras and magnetic storms that would exert aprofound influence on future attempts by physi-cists to understand the Earth’s magnetosphere.At the time, the renowned space scientist Syd-ney Chapman argued that the currents involvedwere restricted to flow only in the ionospherewith no downflowing currents. Alfvén chal-lenged this widely accepted theory by champi-oning the ideas of the Norwegian scientistKristian Birkeland, who believed that electriccurrents flowing down along the Earth’s mag-netic fields into the atmosphere were the causeof the aurora and polar magnetic disturbances.Alfvén won the debate decades later, in 1974,when Earth satellites were able to measure andobserve the downflowing currents for the firsttime. In a similar manner many of Alfvén’s the-ories about the solar system were disputed formany years and only vindicated as late as the1980s, through measurements of cometary andplanetary magnetospheres by artificial satellitesand space probes.

In 1940, Alfvén joined the Royal Instituteof Technology, Stockholm, and became profes-sor of electronics at the Royal Institute in 1945.In 1942, he hypothesized that a form of electro-magnetic plasma wave (now called the Alfvénwave) could propagate through plasma, a phe-nomenon that was, in fact, later observed byother physicists in plasmas and in liquid metals.On purely physical grounds he concluded thatan electromagnetic wave could propagatethrough a highly conducting medium such as theionized gas of the Sun, or in plasmas anywhere.Since his hypothesis contradicted JAMES CLERK

MAXWELL’s theory of electromagnetism, initiallyno one took it seriously. It was, after all, “wellknown” that electromagnetic waves could pene-trate only a very short distance into a conductorand that as the resistance of a conductor becamesmaller and smaller, the depth of penetration ofan electromagnetic wave would approach zero.Thus, with an ideal electrical conductor, therecould be no penetration of electromagnetic radi-ation. Alfvén’s proposal of a form of electromag-netic wave that could propagate in a perfectconductor with no attenuation or reflection wasignored. However, in 1948, when Alfvén lec-tured on it at the University of Chicago, ENRICO

FERMI agreed with the conclusions of Alfvén’swork and it became widely accepted.

Also in 1942 Alfvén put forth a theory ofthe origin of the planets in the solar system,sometimes called the Alfvén theory, whichhypothesizes that planets were formed from thematerial captured by the Sun from an interstellarcloud of gas and dust. The theory envisages thefollowing series of events: As atoms were drawntoward the Sun, they became ionized and influ-enced by the Sun’s magnetic field. Then, in theplane of the solar equator, the ions condensedinto small particles, which, in turn, coalesced toform the planets. Although Alfvén’s theory didnot adequately explain the formation of theinner planets, it was important in suggesting therole of MHD in the origin of the solar system.

4 Alfvén, Hannes Olof Gösta

In 1950, together with his colleague N.Herlofson, Alfvén was the first to identify non-thermal radiation from astronomical sources assynchrotron radiation, which is produced by fast-moving electrons in the presence of magneticfields. The recognition that the synchrotronmechanism of radiation is important in celestialobjects proved extremely productive in astro-physics, since nearly all the radiation recorded byradio telescopes derives from this mechanism.

It was in the 1960s that Alfvén formulatedhis opposition to the big bang theory of cos-mology. He wrote, “I have never thought thatyou could obtain the extremely clumpy, hetero-geneous universe we have today, stronglyaffected by plasma processes, from the smooth,homogeneous one of the Big Bang, dominatedby gravitation.”

Instead of the big bang theory, in which theuniverse is created out of nothing, in a fieryexplosion, at a fixed moment in time, he postu-lated the plasma universe, an evolving universewithout beginning or end. He believed that theappeal of the big bang was rooted in its mytho-logical approach, in which a perfect principle issought, on the basis of which “the gods” createdthe universe. He juxtaposed to this, what hecalled a scientific, empirical approach, reasoningthat, since we never observe something emerg-ing from nothing, there is no reason to assumethat this occurred in the distant past. On theother hand, since we now see an evolving uni-verse, plasma cosmology assumes that the uni-verse has always existed and evolved and willcontinue to do so for an infinite time to come.Today big bang theory continues to be more per-suasive to the great majority of physicists, inlarge part as a result of the observation of thecosmic background radiation that permeates theuniverse, believed to be a remnant of the initialexplosion. However, Alfvén’s theory continuesto attract a small dissident minority.

Around this time, in addition to his scien-tific debates, Alfvén became embroiled in polit-

ical controversies. He was a writer of popular sci-ence books, sometimes with the collaboration ofhis wife, Kerstin Maria Erikson Alfvén, and in1966 he published, under the pseudonym OlafJohannesson, The Great Computer, a pointedpolitical–scientific satire in which the planet istaken over by computers. In Alfvén’s hands, thispopular science fiction theme became a vehiclefor ridiculing the growing infatuation of govern-ment and business with computers, as well as forattacking a large part of the Swedish scientificestablishment. The book succeeded in greatlyantagonizing the objects of its pointed critique.By the following year, Alfvén’s quarrel with theSwedish government, particularly his condem-nation of Sweden’s nuclear research program forallocating insufficient funds for projects onpeaceful uses of thermonuclear energy, becamebitter enough for him to decide to leave Sweden.He was immediately offered two positions—onein the United States and the other in the SovietUnion. After two months in the Soviet Union,he became a professor at the University of Cali-fornia, San Diego. Eventually, he reconciled hisdifferences with the Swedish scientific bureau-cracy and divided his time between the RoyalInstitute and the University of California.

In 1970, he shared the Nobel Prize withLouis-Eugène-Félix Néel. He was president ofthe Pugwash Conference on Science and WorldAffairs and became a leading advocate of armscontrol.

In spite of such recognition, for much of hiscareer his ideas were dismissed or treated withcondescension, forcing him to publish inobscure journals.

Alfvén’s contentious career was balanced byhis private life—his happy marriage and large,accomplished family; his zest for travel; and hisphysical vitality. He died on April 2, 1995, inStockholm, at the age of 86.

Alfvén was a controversial figure, regarded bya few as “the Galileo of the late 20th century” andby many as a heretic for his rejection of the big

Alfvén, Hannes Olof Gösta 5

bang theory. Yet his contributions to physics aremany and undeniable and are today being appliedin the development of particle beam accelerators,controlled thermonuclear fusion, rocket propul-sion, and the braking of reentering space vehicles.Applications of his research in space scienceinclude explanations of the Van Allen radiationbelt, the reduction of the Earth’s magnetic fieldduring magnetic storms, the magnetosphere (aprotective plasma envelope surrounding theEarth), the formation of comet tails, the forma-tion of the solar system, the dynamics of plasmasin our galaxy, and the fundamental nature of theuniverse itself. His numerous contributions to thisfield are reflected in the concepts that bear hisname, including the Alfvén wave, Alfvén speed,and Alfvén limit.

See also GAMOW, GEORGE; PENZIAS, ARNO;VAN ALLEN, JAMES ALFRED.

Further ReadingAlfvén, Hannes. On the Origin of the Solar System.

Westport, Conn.: Greenwood Press, 1973.———. Worlds-Antiworlds: Antimatter in Cosmology.

New York: W. H. Freeman, 1966.

� Alvarez, Luis W.(1911–1988)AmericanExperimental Physicist, ParticlePhysicist, Electronic Engineer

Luis W. Alvarez was an experimentalist ofextraordinary scope and ability, who won the1968 Nobel Prize in physics for his developmentof the hydrogen bubble chamber, which led togreat advances in the discovery of high-energyunstable states of nuclear particles.

He was born in San Francisco on July 13,1911, the son of Walter C. and Harriet SmythAlvarez. His father was a physician and researcherin physiology; by the time he was 10, Luis coulduse all the tools of his father’s shop and wire up

electrical circuits. Alvarez would later credit hisfather’s role in nurturing his scientific creativity:

He advised me to sit every few monthsin my reading chair for an entireevening, close my eyes and try to thinkof new problems to solve. I took hisadvice very seriously and have beenglad ever since that I did.

In 1925, the family moved to Minnesota,when Walter Alvarez joined the staff of theMayo Clinic in Rochester. Luis spent two highschool summers as an apprentice in the clinic’sinstrument shop.

When he enrolled at the University ofChicago, he intended to study chemistry butfound himself fascinated by physics instead. Hewas particularly drawn to optics; his native talentwas nourished by ALBERT ABRAHAM MICHELSON’soptical technicians. He earned his B.S., M.S., andPh.D. in physics from the University of Chicagoin 1932, 1934, and 1936, respectively. He wouldlater describe his training at Chicago as “atro-cious,” adding, however, “I could build anythingout of metal or glass, and I had the enormous con-fidence to be expected of a Robinson Crusoe whohad spent three years on a desert island.”

In 1934, he began flying, soloing with justthree hours of dual instruction. Over the next 50years, he would log more than a thousand hoursas a pilot. In 1936, he married Geraldine Smith-wyck, with whom he had two children, Walterand Jean. Beginning in 1936, he spent his entirecareer at the University of California at Berkeleyas professor of physics; there he would laterbecome Professor Emeritus in 1978. In 1936,Ernest Lawrence, who would become a closefriend, invited him to join the Berkeley Radia-tion Laboratory. There he spent a year immers-ing himself in the literature on nuclear physicsand attended Lawrence’s weekly journal club—atradition he would continue for decades in hisown home.

6 Alvarez, Luis W.

In 1937 Alvarez gave the first experimentaldemonstration of the existence of the K-shellelectron capture process by nuclei. Anotherearly development was a method for producingbeams of very slow neutrons, which led to inves-tigation of neutron scattering and to the firstmeasurement of the magnetic moment of theneutron. Just before the beginning of World WarII, he discovered 3H (tritium), best known as aningredient of thermonuclear weapons, and He3(helium three), which became important in low-temperature physics.

During the World War II years, Alvarezplayed a key role in radar research and develop-ment at the Massachusetts Institute of Technol-ogy. He invented the system known as Vixen,which permitted radar-equipped aircraft todestroy surfaced German submarines. He and hisgroup developed ground-controlled approach(GCA) radar, which allowed ordinary aircraftand pilots to land at night and in poor visibility.He also made important contributions to themicrowave early warning system and the Eagleblind bombing system.

Then, after working with ENRICO FERMI atthe Metallurgical Laboratory at the Universityof Chicago on the first nuclear reactor, Alvarezjoined the Manhattan Project team at LosAlamos under J. ROBERT OPPENHEIMER. Hemade one of his most important contributions inthe critical 1944–1945 period before the end ofthe war, when he invented capacitor-dischargebridgewire detonators. These allow the simulta-neous initiation of the multiple high-explosive“lenses” required to generate the implosion sys-tem needed for the development of the pluto-nium version of the atomic bomb. After the war,he returned to Berkeley and designed and con-structed the first operational linear accelerator.He was also deeply involved in the effort to builda large deuteron accelerator for the productionof plutonium for nuclear weapons at theLawrence Laboratory, where he was associatedirector of the Lawrence Radiation Laboratory

in 1949–1959 and 1975–1978. At this point inhis life he married his second wife, the formerresearch assistant Janet L. Landis; they had twochildren, Donald and Helen.

During this period Alvarez began to concen-trate on the development and use of large, liquidhydrogen bubble chambers, in order to trackunstable nuclear particles. Such particles disin-tegrate rapidly into other particles and are sominute that they can be identified only by thetracks they leave behind them as they move. Inhigh-energy accelerators, these particles move atnear light speeds. Although the particle life spanmight be only 10,000th of 1 millionth of a sec-ond, the track acquires a length of several cen-timeters. The pattern of tracks thus becomesvery complicated. Interpreting them correctlyrequires advanced experimental techniques.Alvarez extended the idea of the liquid heliumbubble chamber invented by DONALD ARTHUR

GLASER and developed the hydrogen bubblechamber, an invaluable instrument for this kindof investigation.

The hydrogen bubble chamber containsmany hundreds of liters of liquid hydrogenreduced to a temperature of –2500°C. When theparticle passes through the chamber, the liquidhydrogen is warmed to its boiling point alongthe particle’s track. In the particle’s wake are atrail of bubbles that can be photographed whilestill very small. The photos reproduce the pathof the particle. Because the chamber containsonly hydrogen, all reactions must occur withhydrogen nuclei, which for high-energy pro-cesses are essentially protons. This fact consider-ably simplifies the interpretation of the particleproduction and decay phenomenon. Alvarezand his group constructed a series of increasinglydelicate automatic scanning and measuringinstruments for transferring the informationfrom the photographic film into a state that canbe analyzed by computer. Using these newlydeveloped hydrogen bubble chamber tech-niques, they were able to discover a large

Alvarez, Luis W. 7

number of “fundamental nuclear particle reso-nances.” This work on particle physics withhydrogen bubble chambers garnered Alvarez the1968 Nobel Prize in physics.

As an inventor, Alvarez was often the onewho, many years after their inception, took hisown ideas into production. This was true for hisstabilized optical system for binoculars or cam-eras, invented in 1963 and produced 20 yearslater as a stabilizing zoom lens for shoulder-heldvideo cameras, and for his variable-power lens,invented in 1971 and first marketed byPolaroid in 1986. He realized profits from hismore than 40 patented inventions only a fewyears before his death in his Berkeley home onAugust 31, 1988.

Alvarez was a path breaker in high-energyparticle physics, a consummate engineer andtechnologist who made vital contributions tocivil and military aviation, as well as a radicalthinker whose intellectual curiosity and talentfor experiment continually led him in newdirections. Among his more exotic ventureswas the x-raying of the great pyramid of Cheopsby the use of cosmic X-ray muons, whichrevealed that the pyramid had no hiddenchamber. He was also the first person to suggestthat the extinction of the dinosaurs 65 millionyears ago was due to a collision of a giant cometwith the Earth. Alvarez’s controversialdinosaur extinction theory was later confirmedby geological observations, which discoveredhigh levels of minerals characteristic of thecomet over the surface of the Earth. This, inturn, led to the discovery of the location of thegiant comet’s crater under the waters of theYucatan peninsula.

See also GELL-MANN, MURRAY.

Further ReadingAlvarez, Luis W. Adventures of a Physicist. New York:

Basic Books, 1978.Trower, W. Peter, ed. Discovering Alvarez. Chicago

and London: University of Chicago Press, 1987.

� Ampère, André-Marie(1775–1836)FrenchTheoretical and Experimental Physicist(Electrodynamics), MathematicalPhysicist

André-Marie Ampère founded a new branch ofphysics that he named electrodynamics: the studyof the relationship between mechanical forcesand electric and magnetic forces. In his honorthe unit of electric current is called the ampereor amp.

He was born in Polémieux, near Lyons,France, on January 22, 1775. The man whowould later teach physics, mathematics, andchemistry had no formal education. Ampère’sfather was a wealthy merchant, who, in additionto having his son privately tutored, was person-ally involved in his education and inspired inhim a passionate desire to learn. Ampère’s caringand protective family imbued in him both anoptimistic belief in the fruits of scientific inves-tigation, which was characteristic of the En-lightenment, and a devotion to Catholicism. Hewas apparently something of a prodigy, master-ing mathematical texts independently, at anearly age.

When he was 18, however, his peacefulworld of study and family affection was shatteredby the advent of the French Revolution. In1793, Lyons was captured by the RepublicanArmy, and his beloved father, who was a wealthycity official, was guillotined. A devastatedAndré-Marie put down his books on mathemat-ics and would not return to them for 18 months.When he met his future wife, Julie, he began tocome to life again.

In 1802 Ampère published his first treatise,The Mathematical Theory of Games, an earlycontribution to probability theory, and wasappointed professor of physics and chemistry atthe École Centrale in Bourg. Later that year, hebecame professor of mathematics at the Lycée in

8 Ampère, André-Marie

Lyons. Ampère’s career was thriving, but anotherof the personal tragedies that would haunt his lifewas about to occur: his young wife, whose healthhad been steadily declining, died in 1804. Thegrieving Ampère left Lyon with its sad memoriesfor the intellectual excitement of Paris.

He quickly found a position as an assistantlecturer in mathematical analysis at the ÉcolePolytechnique in Paris, and, four years later, hewas promoted to professor of mathematics. Oncemore his personal life formed a dark counter-point to his professional activities. He remarriedin August 1806 but had already separated fromhis second wife by the time their daughter wasborn 11 months later. Meanwhile, his talent hadbeen recognized by Napoleon, who in 1808appointed him inspector-general of the newlyformed university system, a post he held until hisdeath. He also taught philosophy at the Univer-sity of Paris in 1918, became assistant professorof astronomy in 1920, and was appointed to thechair of experimental physics at the Collège deFrance in 1824.

Ampère’s intellectual voracity and versatil-ity continued unabated; between 1805 and hisfamous work on electrodynamics in the 1820s,he studied psychology, philosophy, physics, andchemistry. In 1820, the Danish physicist HANS

CHRISTIAN ØRSTED demonstrated his discoverythat a magnetic needle is deflected when thecurrent in a nearby wire is flowing, therebyshowing evidence of a relationship betweenelectricity and magnetism. Ampère witnessed arestaging of Ørsted’s demonstration in Paristhat same year. Within a week he had preparedthe first of several papers that would describe anew branch of physics revealed by Ørsted’swork. Ampère called it electrodynamics, todifferentiate it from the electrostatics ofCHARLES AUGUSTIN COULOMB. Central to histhinking was a relationship that came to beknown as Ampère’s law, a mathematicaldescription of the magnetic force between twoelectric currents. It shows that two parallel

wires carrying electric currents in the samedirection attract each other, whereas two paral-lel wires carrying electric currents in oppositedirections repel one another. Specifically,Ampère’s law relates the magnetic force pro-duced by two parallel current-carrying conduc-tors to the product of their currents divided bythe square of the distance between the conduc-tors. Today, Ampère’s law is usually stated inthe form of calculus: the line integral of themagnetic field around an arbitrarily chosenpath is proportional to the net electric currentenclosed by the path.

Ampère also predicted and demonstratedthat a helical “coil” of wire (which he named asolenoid) behaves as a bar magnet when carryingan electric current. The numerous experimentshe performed enabled him to explain known elec-tromagnetic phenomena and predict new ones. Inaddition, Ampère pioneered the development ofmeasuring techniques for electricity, inventing aninstrument using a free-moving needle to measurethe strength of the current. This was the proto-type of what we know today as the galvanometer.

He also tried to develop a theory to explainelectromagnetism, proposing that magnetism ismerely electricity in motion. Prompted by hisclose friend AUGUSTUS FRESNEL, one of the orig-inators of the wave theory of light, he suggestedthat molecules are surrounded by a perpetualelectric current.

Ampère culminated his groundbreakingstudies with the publication in 1827 of hisMemoir on the Mathematical Theory of Electro-dynamic Phenomena, Uniquely Deduced fromExperience, in which he enunciated precisemathematical formulations of electrodynamics,notably Ampère’s law.

He died of pneumonia at the age of 61, onJune 10, 1836, while on an inspection tour ofMarseille. The epitaph on his gravestone reads,Tandem felix (Happy at last).

Ampère was honored by election as a fellowof the Royal Society in 1827. His name is

Ampère, André-Marie 9

inscribed, along with those of 71 other promi-nent French scientists, on the Eiffel Tower. TheRue Ampère, a street in the 17th arrondisementin Paris, and the Mons Ampère, a feature of thelunar landscape, have been named for him.

More than any other scientist, Ampère wasresponsible for creating the discipline of electro-dynamics. Decades later Ampère’s law becamean integral part of JAMES CLERK MAXWELL’s uni-fied theory of electrodynamics.

Further ReadingDarrigol, Olivier. Electrodynamics from Ampère to Ein-

stein. Oxford: Oxford University Press, 2000.Hofmann, James R. André-Marie Ampère: Enlighten-

ment and Electrodynamics. London: CambridgeUniversity Press, 1966.

� Anderson, Carl David(1905–1991)AmericanExperimentalist, Particle Physicist

Carl David Anderson built an enhanced cloudchamber with which he discovered the positiveelectron or positron, an achievement that gar-nered him the 1936 Nobel Prize in physics, aswell as the positive and negative muon (or mumeson).

He was born in New York City on Septem-ber 3, 1905, the son of Swedish immigrants, andattended the California Institute of Technology,where he received a B.Sc. in physics and engi-neering in 1927. He was awarded a Ph.D. in1930 for a dissertation on the space distributionof photoelectrons emitted from various gases as aresult of irradiation with X rays. Although hisnominal dissertation director was ROBERT MIL-LIKAN, who had accurately determined thecharge of the electron, Anderson complained,“Not once in the three years of my graduate the-sis work did he visit my laboratory or discuss thework with me.”

Anderson would remain at Caltech for therest of his career. In 1930 he became a researchfellow working with Millikan’s research teamand began to study gamma rays and cosmic rays.Anderson built and ran the Caltech MagnetCloud Chamber: a special type of cloud chamberthat was divided by a lead plate in order to slowthe particles sufficiently for their paths to beaccurately determined. He used it to measure theenergies of cosmic and gamma rays, by measur-ing the curvature of their paths, in strong mag-netic fields (up to about 24,000 gauss or 2.4tesla). In 1932, he announced that he hadobtained “dramatic and completely unexpected”results: approximately equal numbers of posi-tively and negatively charged particles, whereonly electrons had been expected. He also notedthat in many cases several negative and positiveparticles were simultaneously projected from thesame center. At first he assumed that the posi-tive particles were protons; however, it turnedout that their mass was identical to that of elec-trons (as opposed to the much heavier protons),and so he called them positive electrons. Hewent on to suggest the name positrons for theseantimatter particles. The previous year PAUL

ADRIEN MAURICE DIRAC, on the basis of his rel-ativistic theory of the atom, had predicted theexistence of a positive electron when he discov-ered that the mathematical description of theelectron contained twice as many states as wereexpected. Working with his first graduate stu-dent, Seth Neddermeyer, Anderson also showedthat positrons can be produced by irradiation ofvarious materials with gamma rays. In 1932 and1933, LORD STUART BLACKETT, SIR JAMES

CHADWICK, and the Joliot-Curies indepen-dently confirmed the existence of the positronand later elucidated some of its properties.

In 1933, Anderson was promoted to assis-tant professor of physics at Caltech. Three yearslater, when he shared the 1936 Nobel Prize withVictor Hess, the discoverer of cosmic rays, hewas the youngest physicist ever to be so honored.

10 Anderson, Carl David

That same year he contributed to the dis-covery of another elementary particle, themuon. He and Neddermeyer transported theirmagnet cloud chamber to the summit of PikesPeak, Colorado, in order to obtain more intense,higher-energy cosmic rays. After a summer atPikes Peak, they analyzed their results and foundthat the positive and negative tracks were differ-ent from those made by electrons and protonsand appeared to have been made by a particlewith an intermediate mass. They proposed thatthe high-altitude tracks were new, unknown par-ticles and called them mesotrons, because oftheir “middle” mass; the name was later short-ened to meson. At first Anderson thought thatthis was the particle previously predicted byHIDEKI YUKAWA, which was supposed to hold thenucleus together and carry the strong nuclearforce. Further studies, however, showed that itdid not readily interact with the nucleus andtherefore could not be Yukawa’s particle. Ander-son’s particle is now called the mu meson to dis-tinguish it from the pi meson.

When World War II broke out, Andersonturned down an offer to direct development ofthe atomic bomb, “on purely economic grounds,”and the job went to J. ROBERT OPPENHEIMER. Inthe autobiography he would write in his 70s, heobserves:

I believe my greatest contribution tothe World War II effort was my inabilityto take part in the development of theatomic bomb. Thinking so brings mepeace of mind.

Instead, he worked on the development ofrocket launchers at Caltech and, in 1944, super-vised the installation of the first rocket launch-ers on Allied planes.

After the war, in 1946, he married LorraineBergman, with whom he had two sons, Marshalland David. He served as full professor at Caltechuntil his retirement in 1976, when he became

professor emeritus. He died on January 11, 1991,after a brief illness, at the age of 85.

Carl Anderson played a major role in thediscovery of new elementary particles andpointed the way to the existence of antimatter.His discovery of the positron led to the predic-tion of other antiparticles, such as the antipro-ton discovered by EMILIO SEGRÈ in 1955. Todaythe existence of antimatter—an antiparticle forall particles—is universally accepted.

See also WILSON, CHARLES THOMSON REES.

Further ReadingWeiss, Richard J., ed. The Discovery of Anti-Matter:

The Autobiography of Carl David Anderson, theYoungest Man to Win the Nobel Prize. Series inPopular Science, Vol. 2. Singapore: World Sci-entific, 1999.

Anderson, Carl David 11

Carl David Anderson discovered the positive electron,or positron, as well as the positive and negative muon.(NARA, courtesy AIP Emilio Segrè Visual Archives)

� Anderson, Philip Warren(1923– )AmericanTheoretical Physicist, Solid StatePhysicist

Philip Warren Anderson shared the 1977 NobelPrize in physics with JOHN HOUSBROOK VAN

VLECK and NEVILL FRANCIS MOTT for his theo-retical work on the behavior of electrons in mag-netic, noncrystalline solids.

He was born in Indianapolis on December13, 1923; shortly afterward, Harry WarrenAnderson, his father, became a professor of plantpathology at the University of Illinois inUrbana, where Philip spent his childhood andadolescence. He spent his happiest hours withthe families of his parents’ friends, enjoying hik-ing and camping and developing the politicalconsciousness that would make him an oppo-nent of McCarthyism, a supporter of liberalcauses, an opponent of the Vietnam War, and ascientist who refused to engage in classifiedresearch. Although the physicists among hisfather’s friends encouraged him, he initiallyintended to major in mathematics when heentered Harvard University, in 1940, on a full-support National Scholarship. The world was atwar and physics students were urged to concen-trate on a field with immediate applications,such as “electronic physics.” After earning hisB.A., summa cum laude, in 1943, he spent thenext two years doing antenna engineering workat the Harvard Naval Research Laboratories inWashington, D.C.

Returning to Harvard in 1945, he plungedinto a series of stimulating courses, includingthose of JULIAN SEYMOUR SCHWINGER. Heearned his M.S. in 1947 and that same year mar-ried Joyce Gothwaite, who soon presented himwith a daughter, Susan. He received his Ph.D.in 1949 from Harvard, after completing his dis-sertation under Van Vleck, on the pressurebroadening of spectral lines in microwave,

infrared, and optical spectroscopy. (Pressurebroadening refers to the increase in the width ofa spectrum line resulting from collisionsbetween atoms and molecules in a gas thatoccur as the gas pressure increases.)

In 1949, he went to work at Bell Laborato-ries in Murray Hill, New Jersey, where he joineda stellar theoretical group, which included JOHN

BARDEEN, the coinventor of the transistor. Fromhis Bell colleagues, Anderson learned about fer-romagnetism (the magnetism of substancescaused by a domain structure, that is, a materialregion in which all the atomic magnetic fieldspoint the same way), crystallography, and solidstate physics. At the Kyoto InternationalPhysics Conference in 1953 he gained a lastingadmiration for Japanese culture and met NevillMott, whose work he admired.

In the late 1950s, Anderson developed atheory that explained superexchange: the cou-pling of spins of two magnetic atoms in a crystalthrough their interaction with a nonmagneticatom located between them. He was then able toapply the Bardeen–Cooper–Schrieffer (BCS)theory of superconductivity to explain theeffects of impurities on the properties of super-conductors. Working with a French graduatestudent, Pierre Morel, Anderson studied theJosephson effect, an electrical effect associatedwith pairs of superconductors. He went on todevelop the theoretical treatments of antiferro-magnetics (paramagnetic substances with asmall susceptibility to the external magneticfield, which behave as ferromagnetic substanceswhen their temperature is changed), ferro-electrics (crystalline compounds having naturalspontaneous electric polarization that can bereversed by the application of an electric field),and superconductors.

During this same period, Anderson did hisimportant work on disordered systems. In crys-talline materials, the atoms form regular lattices,which greatly facilitate the theoretical treat-ment. In disordered materials, the regularity is

12 Anderson, Philip Warren

lacking so that there is no lattice whatsoever, as,for instance, in glass; this makes it very hard totreat such materials theoretically. In 1958,Anderson published a paper in which he showedunder what conditions an electron in a disor-dered system can either move through the sys-tem as a whole or be more or less tied to aspecific position as a localized electron. Mottdrew the attention of solid state physicists to thispaper, which became one of the cornerstones inthe understanding of the electric conductivity indisordered systems. Anderson would return tothe subject of disordered media in the early1970s, working on low-temperature properties ofglass and later studying spin glasses.

In the early 1960s, Anderson developed amodel of the interatomic effects that influencethe magnetic properties of metals and alloys(now called the Anderson model) to describethe effect of the presence of an impurity atom ina metal. He also devised a method of describingthe movements of impurities within crystallinesubstances, a method now known as Andersonlocalization. He also studied the relationshipsamong the phenomena of superconductivity,superfluidity, and laser action, all of whichinvolve coherent waves of matter or energy, andpredicted the possibility of superfluid states ofhelium 3, an isotope of helium. On the morepractical side he performed research on thesemiconducting properties of inexpensive, disor-dered glassy solids. His studies of these materialsindicated the possibility that they could be usedin place of the expensive crystalline semicon-ductors now used in many electronic devices,such as computer memories, electronic switches,and solar energy converters.

In 1967, through the efforts of Mott, Ander-son obtained a “permanent visiting professorship”at the Cavendish Laboratories at Cambridge Uni-versity. For the next eight years he and Joycedivided their time between Cambridge and NewJersey. Anderson headed the Theory of Con-densed Matter Group at Cambridge, which he

recalls as “eight productive and exciting years,spiced with warm encounters with students, visi-tors, and associates from literally the four cornersof the Earth.”

In 1975, the Cambridge appointment wasreplaced by a part-time appointment as JosephHenry Professor of Physics at Princeton Univer-sity. The following year he became ConsultingDirector of Research at Bell, and he would laterassist ARNO ALLAN PENZIAS in the difficultyears of restructuring that followed the breakupof the Bell Laboratory system. In 1977, Ander-son received the Nobel Prize in physics fordeveloping Van Vleck’s ideas about how localmagnetic moments can occur in metals, such assilver or copper, that in pure form are not mag-netic at all.

The years following the Nobel Prize wereproductive ones for Anderson. He retired fromBell in 1984 and took up full-time duties atPrinceton. During this fertile period he and hiscolleagues at Princeton revitalized localizationtheory in solid state physics by developing a scal-ing theory that made it into a quantitativeexperimental science.

A longtime proponent of “small science,” inthe late 1980s Anderson became a controversialfigure in the physics community when heargued before Congress against funding for theproposed superconducting super collider to bebuilt in Texas at a cost of $8 billion. He believedthe project would yield neither practical bene-fits nor any fundamental truths that could notbe gained elsewhere and more cheaply. WhenCongress killed the plan in 1993, Anderson saidhe was only sorry that Congress had allowed theproject to go on for so long. He was also an out-spoken critic of “Star Wars,” the Reagan admin-istration plan to build a satellite-based missiledefense system.

In 1986, he became deeply involved withthe Sante Fe Institute, a new interdisciplinaryinstitution dedicated to emerging scientific syn-theses, especially those involving the sciences of

Anderson, Philip Warren 13

complexity. The following year, news of a newclass of “high-temperature” superconductorsgalvanized the world of many-body quantumphysics, leading Anderson to reexamine olderideas and search for new ones. He found that hewas able to account for most of the wide varietyof unexpected anomalies observed in thesematerials by invoking a new two-dimensionalstate of matter and a new mechanism for elec-tron pairing called deconfinement.

The amazing range of Anderson’s researchin solid state physics has spanned the topics ofspectral line broadening, exchange interactionsin insulators, the Josephson effect, quantumcoherence, superconductors, and nuclear theory.Experimental confirmation continues to supportthe predictions of Anderson’s theory of high-temperature superconductors, which is expectedto find many new scientific applications in the21st century.

See also JOSEPHSON, BRIAN DAVID; SCHRIEF-FER, JOHN ROBERT.

Further ReadingVidali, Gianfranco. Superconductivity: The Next Revo-

lution? Cambridge: Cambridge University Press,1993.

� Ångstrom, Anders Jonas(1814–1874)SwedishSpectroscopist, Astronomer

Anders Ångstrom is known as the father of spec-troscopy, the branch of physics that studies lightby using a prism or diffraction grating to spreadout the light into its range of individual colors orspectrum.

Ångstrom was born in Logdo, Sweden, onAugust 13, 1814, the son of a chaplain. Heattended the University of Uppsala, where heobtained his doctorate in physics in 1839. Thatsame year, he became a lecturer at the university

and, four years later, an observer at the UppsalaObservatory. His first significant research pro-ject involved the development of a method ofmeasuring heat conductivity, which enabledhim to demonstrate that it was proportional toelectrical conductivity.

He published Optical Investigations, his mostimportant work, in 1853; in it he presented hisprinciple of spectral analysis. He had studied elec-tric arcs and discovered that they yield two spec-tra, one superimposed on the other. The first wasemitted from the metal of the electrode itself, thesecond from the gas through which the sparkpassed. He was also able to demonstrate that a hotgas emits light at the same frequency as it absorbsit when it is cooled. Ångstrom had established hisreputation and was elected to the chair of physicsat the University of Uppsala in 1958.

Ångstrom’s early work provided the basisfor the spectrum analysis that would occupyhim for the rest of his life. In 1862 heannounced his hypothesis—which would laterbe confirmed—that the Sun’s atmosphere con-tains hydrogen. The solar spectrum was his pri-mary interest, but in 1867 he also became thefirst person to study the spectrum of the auroraborealis, the spectacular display of blue, pink,red, orange, and yellow light seen in the nightsky in the Northern Hemisphere during the falland winter. He used a spectroscope consistingof a simple triangular prism, which broke up thewhite light passing through it into a rainbow-like band of colors known as a spectrum. Look-ing through this prism with the aid of atelescope, he showed that the light of theaurora borealis differed from that of the Sun.He thus reached the momentous conclusionthat no two substances have the same spectrumand, therefore, that any substance can be iden-tified by its spectrum.

In 1868 he published his famous Researcheson the Solar Spectrum, which contained measure-ments of the wavelengths of more than 1,000lines in the Sun’s spectrum, known as Fraunhofer

14 Ångstrom, Anders Jonas

lines, measured to six significant figures in unitsof 100 millionths of a centimeter (10–8 cm).

Another of his important achievements washis atlas of the normal solar spectrum, publishedin 1869, which became a standard referencetool. He remained at the University of Uppsalauntil his death on June 21, 1874.

Ångstrom’s legacy is visible in the work ofcontemporary astronomers and astrophysicists,who still identify elements found in starsthrough the use of spectroscopy.

The unit of measure for the wavelength oflight, officially adopted in 1907, is called theangstrom in his honor. Signified by Å and equalto one hundred millionth of a centimeter (10 –8

cm), the angstrom serves as a convenient unitthat can be used to specify radiation wave-lengths, which enables physicists to avoid writ-ing large numbers of zeroes, when discussing thewavelength of light.

See also FRAUNHOFER, JOSEPH VON.

Further ReadingBeckman, Olof. Ångstrom: Father and Son. Acta Uni-

versitatis Upsaliensis, C. Organisation Och His-toria, No. 60. Uppsala, Sweden: Coronet Books,1997.

� Archimedes(c. 287–212 B.C.)GreekTheoretician and Experimentalist(Mechanics, Hydrostatics),Mathematician, Astronomer

Archimedes is widely viewed as the greatest sci-entist of the ancient world. As a physicist, he iscredited with establishing the fields of statics, abranch of mechanics dealing with the forces onan object or in a system in equilibrium, andhydrostatics, the study of fluids (liquids andgases) in equilibrium. He is most famous forArchimedes’ principle, which offered the first

scientific explanation of what makes solidobjects float.

Only a handful of facts about Archimedes’life have been established with certainty. Thebiography of him written by his friend Heraclei-des has been lost. What remains for historiansto draw on are Archimedes’ nine survivingmathematical treatises, which he published inthe form of correspondence with the leadingmathematicians of his time (including theAlexandrian scholars Conan of Samos andEratosthenes of Cyrene); the accounts of his lifeleft by his Greek contemporaries; and storiesfrom Plutarch, Livy, and others. He was widelyknown during his lifetime, mainly because of hisinventions that were used in war. The impres-sion his mechanical genius made on the popularimagination gave rise to numerous legends,which today are viewed by most historians asapocryphal.

Archimedes is believed to have been bornin 287 B.C., in Syracuse, Sicily, then a Greekcolony. The date has been based on the claim ofa 12th-century historian that he died at age 75,and then working backward from the date of hisdeath in 212 B.C., which is reliably established.His father was Phidias, an astronomer; the fam-ily was a noble one, possibly related to that ofKing Hieron II of Syracuse. As a young man, hetraveled to Alexandria, then a great capital oflearning for mathematics, and studied underConon and other mathematicians, who hadbeen students of Euclid. Most disciples wouldremain in Alexandria, but Archimedes returnedto Syracuse, where he spent the rest of his lifestudying mathematics and physics, divertinghimself by designing the numerous mechanicaldevices that earned him widespread renown.

The boldness and originality of Archimedes’mathematical work are tempered by its extremerigor and adherence to the highest standards ofthe geometry of his time. Among his mostimportant results was the determination of thevalue of π. He made the most accurate predic-

Archimedes 15

tion of his time about the value of π, bracketingits value within the upper and lower limits givenby 223/71 = 3.14085 > π > 3.1429 = 220/70.What is more amazing is the fact that the aver-age of Archimedes’ upper and lower limits onthe value of π is 3.1419, less than three parts inten thousand different from the modern approx-imation given: π = 3.1416. In an attempt toimprove Greek numerical notation, he devisedan ingenious system for the expression of verylarge numbers. In his treatise The Sandreckoner,he proposed a number system capable of express-ing very large numbers. He then used this num-ber system to estimate the number of grains ofsand in the universe as given by the number1063. In this manner he showed that large num-bers could be considered and handled effectively.He also invented methods to solve cubic equa-tions and to determine square roots by approxi-mation. Most impressively, he devised formulasto determine the surface areas and volume ofcurved surfaces and solids, a topic that antici-pated the development of the integral calculus2,000 years later by Newton and Leibniz.

As a physicist Archimedes is credited withestablishing the fields of statics of objects andhydrostatics of fluids. In statics he worked outthe rigorous mathematical proofs behind theprinciple of the lever and the compound pul-ley—mechanical devices that can multiply theeffects of forces. Although the scientists of histime were familiar with the use of the lever,Archimedes was the first to show that the ratioof the effort applied to the load raised by a leveris equal to the inverse ratio of the distances ofthe effort and load from the pivot or fulcrumabout which the lever rotates. He is said to haveclaimed that if he could stand at a great enoughdistance, he could use a lever to move the world.In response to this, King Hieron purportedlyissued him the lesser challenge of showing thathe could move a very heavy object with ease.Archimedes allegedly responded by easily mov-ing a ship, laden with passengers, crew, and

cargo, which a number of men had struggledmightily to lift out of the harbor onto dry land.Sitting at a distance from the ship, he is said tohave used a compound pulley to pull it over theland as if it were gliding through water.

His two-volume treatise on hydrostatics, OnFloating Bodies, is the first known work on thetopic and survives only partly in Greek, the restin medieval Latin translation from the Greek.The first book contains his most famous result,the Archimedes’ principle, which states that theupward force on an object totally or partly sub-merged in a fluid is equal to the weight of fluiddisplaced by the object. He is said to havebecome engrossed in the problem of floatingbodies when King Hieron ordered that his newcrown be evaluated to see whether it was puregold, without damaging the object. In what isprobably the most famous Archimedes story, thegreat scientist is said to have been watchingwater overflow from the bath he was immersedin when the idea now known as Archimedes’principle dawned on him. So jubilant was he,legend relates, that he ran through the townnaked, crying, “Eureka!” (“I’ve got it!”). Whathe had grasped was that if the gold of the king’scrown had been mixed with silver, which is lessdense, then in order to have an equal weight tothat of a purely golden crown, the king’s crownwould have to have a greater volume and there-fore would displace more water than that of apurely golden crown. Unfortunately, as the storygoes, this method proved that the crown con-tained silver and the unlucky goldsmith was putto death by the king.

In antiquity Archimedes was also known asan astounding astronomer, although little isknown of this side of his activities. According tothe Greek biographer Plutarch, Archimedeschose to publish only the results of his theoreti-cal researches because he deemed only theseworthy of serious consideration. But his interestin mechanics deeply influenced his mathemati-cal thinking. In this context he wrote works on

16 Archimedes

theoretical mechanics and hydrostatics, and histreatise Method Concerning Mathematical Theo-rems shows that his intuitive mechanical reason-ing was an essential tool leading to his discoveryof new mathematical theorems. He wrote:

Certain things first became clear to meby a mechanical method, although theyhad to be proved by geometry afterwardsbecause their investigation by the saidmethod did not furnish actual proof. Butit is of course easier, when we have previ-ously acquired, by the [mechanical]method, some knowledge of the ques-tions, to supply the proof than it is to findwithout any previous knowledge.

Inventions attributed to him include adesign for a model planetarium able to showthe movement of the Sun, Moon, planets, andpossibly constellations across the sky. Ciceroreports that when Marcellus sacked Syracuse,he took this planetarium as booty. He is alsocredited with the Archimedes screw, an augurpump used to raise water for irrigation, which isstill used in many parts of the world. He report-edly invented it during his days in Egypt,although it is also possible that he borrowed theidea from others in Egypt.

The most dramatic of his inventions, how-ever, were instruments of war. At the urging ofKing Hieron, he transformed his playfulmechanical diagrams into viable machines.Some of these proved invaluable during theRoman siege of Syracuse from 212 to 215 B.C.,when Archimedes’ weapons allegedly set fire tothe ships of the Roman fleet under Marcellusand made them capsize. This held the Romans atbay for a long time, although they eventuallysucceeded in sacking the city, an operation inwhich Archimedes met his end. Plutarch givesthree different versions of his death, all of whichpicture him killed while absorbed in scientificpursuits. In one version, despite orders to spare

him, Archimedes was killed on the spot by aRoman soldier when he was ordered to leave hisstudy, where he was contemplating a mathemat-ics problem. He left instructions for his tomb tobe marked with a sphere inscribed in a cylinder,together with the formula for the ratio of theirvolumes—since he considered this discovery hisgreatest achievement. Cicero found the tomb,overgrown with vegetation, a century and a halfafter Archimedes’ death.

Given the magnitude and originality ofArchimedes’ achievements, it is ironic that hisinfluence remained so small and undeveloped inancient times. His work was not widely knownin antiquity and did not lead directly to otheradvances at that time. However, his legacy waspreserved by Byzantium and Islam, inspiringimportant work by medieval Islamic mathemati-cians, and from there it spread to Europe fromthe 12th century onward. The greatest impact ofhis work on later mathematicians occurred inthe late 16th and early 17th centuries, afterwhich it had a profound impact on the history ofscience. In particular, Archimedes’ method offinding mathematical proof to substantiateexperiment and observation became the methodof modern science introduced by GALILEO

GALILEI. Galileo published a study of the behav-ior of bodies in water, Bodies That Stay AtopWater or Move Within It, in which he champi-oned Archimedes’ law of buoyancy, which statesthat the buoyant force on a body in water isequal to the weight of the water displaced.

Further ReadingArchimedes. The Works of Archimedes. New York:

Dover Publications, 2002.Ipsen, D. C. Archimedes: Greatest Scientist of the

Ancient World. Hillside, N.J.: Enslow, 1988.Lafferty, Peter. Archimedes. New York: Bookwright

Press, 1991.Stein, Sherman. Archimedes: What Did He Do Besides

Cry Eureka? Washington, D.C.: The Mathemat-ical Association of America, 1999.

Archimedes 17

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� Bardeen, John(1908–1991)AmericanTheoretical Physicist, Solid StatePhysicist, Electrical Engineer

John Bardeen was a giant of solid state physics,whose greatest achievements were the inventionof the transistor, with WILLIAM BRADFORD

SHOCKLEY and Walter Battrain, and the devel-opment of a comprehensive theory of supercon-ductivity, with JOHN ROBERT SCHRIEFFER andLeon Cooper. These contributions made himthe first person to win two Nobel Prizes inphysics, in 1956 and 1972.

He was born on May 23, 1908, in Madison,Wisconsin, the second of five children born toCharles Russell Bardeen and Althea Harmer.His father was the first graduate of the JohnsHopkins Medical School and founder of theMedical School of the University of Wisconsin;his mother had studied art at the Pratt Institutein Brooklyn, New York, and practiced interiordesign in Chicago. John attended elementaryand secondary schools in Madison. His bril-liance was immediately apparent, and he wasskipped from third grade to junior high. Thedeath of his mother of cancer when he was 12was a devastating blow. He managed to con-tinue his studies, however, and entered the

University of Wisconsin at age 15. He chose tomajor in engineering, both because of his loveof mathematics and because he had no desire tobe an academic as his father was.

He received a B.S. in electrical engineer-ing in 1928 and an M.S. the following year, atthe University of Wisconsin. Between 1928and 1930, he was a graduate assistant, examin-ing mathematical problems of antennas andworking on applied geophysics. The GreatDepression had begun and jobs were scarce. Hemanaged to get hired by Gulf Research inPittsburgh, where he worked on mathematicalmodeling of magnetic and gravitational oilprospecting surveys. This was an excitingperiod when geophysical methods were firstbeing applied to oil prospecting. But Bardeen,who kept abreast of advances in physics, wasincreasingly drawn to pure science. In 1933, hegave up his industrial career and enrolled forgraduate work at Princeton University withEUGENE PAUL WIGNER. At Princeton he wasintroduced to the rapidly developing field ofsolid state physics. Bardeen was fascinated bythe work of such physicists as Wigner and Fred-erick Seitz, who were using the new quantummechanics to help understand how semicon-ductors worked. He finished his dissertation onthe theory of the work function of metals in1935.

From 1935 to 1938 he was a junior fellow atHarvard University, where he worked with JOHN

HOUSBROOK VAN VLECK and PERCY WILLIAMS

BRIDGMAN. In 1938, he married Jane Maxwell, abiologist who taught at a girls’ high school nearBoston. It was to be an enduring union thatwould produce three children and six grandchil-dren. From 1938 to 1941, he was an assistantprofessor at the University of Minnesota. DuringWorld War II, between 1941 and 1945, hereturned to applied physics at the Naval Ord-nance Laboratory in Washington, D.C., wherehe investigated ways to protect U.S. ships andsubmarines from magnetic mines and torpedoes.In 1945 he joined the newly formed researchgroup in solid state physics, which included Wal-ter Brittain and was directed by William Shock-ley, at the Bell Telephone Laboratories in

Murray Hill, New Jersey, where his research onsemiconductors led in 1947 to the developmentof the transistor. Physicists first understood theelectrical properties of semiconductors in thelate 1930s, when they became aware of the roleof low concentrations of impurities in control-ling the number of mobile charge carriers inmaterials. Current rectification (i.e., the conver-sion of oscillating current into direct current) atmetal–semiconductor junctions had long beenknown, but the next step required was to pro-duce amplification analogous to that achievedby vacuum tube technology. Shockley’s groupbegan a program to control the number of chargecarriers at semiconductor surfaces by varying theelectric field.

Bardeen and Brittain worked together har-moniously, as Brittain designed the experimentsand Bardeen worked out theoretical explana-tions for the results. In the spring of 1947,Shockley asked them to investigate the reasonfor the failure of an amplifier he had designed,which was based on a crystal of silicon, laterreplaced by germanium. By observing Brittain’sexperiments, Bardeen realized that the assump-tion they had been making—that electrical cur-rent traveled through all parts of the germaniumin the same way—was incorrect. On the con-trary, electrons behave differently at the surfaceof the metal. If they could control what was hap-pening at the surface, the amplifier should work.They demonstrated the effects of amplificationof two metal contacts 0.05 mm apart on a ger-manium surface. Large variations of the poweroutput through one contact were observed inresponse to tiny changes in the current throughthe other. On December 23, 1947, they suc-ceeded in building the first point-contact tran-sistor, the forerunner of the many complexdevices now available through silicon chip tech-nology. Bardeen, Brittain, and Shockley wereawarded the Nobel Prize for this work in 1956.

In 1951, Bardeen left Bell and moved to theUniversity of Illinois, where, with the graduate

Bardeen, John 19

John Bardeen invented the transistor and developed acomprehensive theory of superconductivity. (AIPEmilio Segrè Visual Archives)

student Bob Schrieffer and postdoctoral studentLeon Cooper, he developed the microscopictheory of superconductivity, known as theBardeen–Cooper–Schrieffer (BCS) theory. In1911, HEIKE KAMMERLINGH ONNES had firstobserved zero electrical resistance in some met-als below a critical temperature. Since thenphysicists had looked for a microscopic inter-pretation of this phenomenon of superconduc-tivity. The methods that were successful inexplaining the electric properties of normalmetals were unable to predict the effect. At verylow temperatures, metals were still expected tohave a finite resistance due to scattering ofmobile electrons by the ions in the crystal lat-tice. Bardeen’s solution to this problem was toshow that electrons pair up through an attrac-tive interaction, and that zero resistivity occurswhen the thermal energy available is insuffi-cient to break the pair apart.

Thus, for electrons embedded in a crystal,the normal Coulomb repulsion can be compen-sated for by this pairing effect when the tem-perature is below the critical value. The ioncores in the crystal lattice respond to the pres-ence of a nearby electron, and the motion mayresult in the attraction of another electron tothe ion. The net effect is an attraction betweentwo electrons through the response of the ionsin the solid. The BCS theory was based on theidea that the interaction between the electronsand the lattice leads to the formation of boundpairs of electrons, called Cooper pairs. The dif-ferent pairs are strongly coupled to each other;this leads to a complex collective pattern inwhich a considerable fraction of the total num-ber of conduction electrons are coupled to forma superconducting state. Because of the charac-teristic coupling of all the electrons, one can-not break up a single pair of electrons withoutalso perturbing all the others, and this processrequires an amount of energy that must exceeda critical value. Many of the remarkable quali-ties of superconductors can be understood qual-

itatively from the structure of this correlatedmany-electron state.

The comprehensive BCS theory has theability to explain all known properties associ-ated with superconductivity. Although applica-tions of superconductivity to magnets andmotors were possible without the BCS theory,the theory is important for strategies to increasethe critical temperature as much as possible,since, if it could be raised above liquid nitrogentemperature, the economics of superconductiv-ity would be transformed. In addition, the the-ory was an essential prerequisite for theprediction of Josephson junction tunneling,which has important applications in magne-tometers and computers and in determinationof the fundamental constants of physics. TheBCS theory has had profound effects on nearlyevery field of physics from elementary particleto nuclear physics and from helium liquids toneutron stars. Bardeen and his two colleaguesshared the Nobel Prize in physics for their the-ory in 1972.

During this period of intense theoreticalwork, he continued to be actively interested inengineering and technology. In 1951 he becamea consultant for the Xerox Corporation (calledHaloid at the time), and he continued work withthem throughout their development as a tech-nological giant. From 1961 to 1974, he was amember of the Board of Directors of the XeroxCorporation. He also was a consultant for Gen-eral Electric Corporation for many years and forother technology firms.

In 1975 he became professor emeritus at Illi-nois, where he began working on theories for liq-uid helium 3 that have analogies with the BCStheory. He lived out the rest of his life inUrbana, Illinois, teaching, researching, andplaying his favorite game, golf. He died in 1991at the age of 82.

During his 60-year scientific career, Bardeenmade important contributions to virtually everyaspect of condensed matter physics, from his

20 Bardeen, John

early work on the electronic behavior of metals,the surface properties of semiconductors, andthe theory of diffusion of atoms in crystals to hislater work on quasi-one-dimensional metals. Inhis 83d year he continued to publish original sci-entific papers. Both of Bardeen’s NobelPrize–winning achievements have had a revolu-tionary impact on computer technology. Theinvention of the transistor led directly to thedevelopment of the integrated circuit and thenthe microchip.

See also JOSEPHSON, BRIAN DAVID; KILBY,JACK ST. CLAIR.

Further ReadingBernstein, Jeremy. Three Degrees Above Zero: Bell Labs

in the Information Age. New York: Scribner &Sons, 1984.

Riordan, Michael, and Lillian Hoddeson. CrystalFire: The Invention of the Transistor and the Birthof the Information Age. New York: W. W. Nor-ton, 1998.

� Barkla, Charles Glover(1877–1944)BritishExperimentalist (X-ray Scattering), SolidState Physicist, Quantum Physicist

Charles Glover Barkla made important ex-periments involving the scattering of X rays,proving that they are a form of transverse elec-tromagnetic radiation like that of visible light.He received many honors for this work, includ-ing the 1917 Nobel Prize in physics “for hisdiscovery of the characteristic X-radiation ofthe elements.”

He was born on June 7, 1877, in Widnes,Lancashire, where his father, J. M. Barkla, wassecretary to the Atlas Chemical Company. Hefirst studied at the Liverpool Institute and thenentered University College in Liverpool in 1895;there he studied physics under Oliver Lodge, a

pioneer in radio. He earned a bachelor’s degree in1898 with highest honors and, a year later, a mas-ter’s degree. A prestigious research scholarshipenabled him to attend Trinity College, Cam-bridge, in the autumn of 1899 and to work at theCavendish Laboratory under JOSEPH JOHN (J. J.)THOMSON, who had recently discovered thatcathode rays consisted of electrons. Barkla’s firstoriginal experiment measured the velocity ofelectromagnetic waves traveling along wires ofdifferent thickness and composition.

He transferred to King’s College, Cam-bridge, in 1900, to pursue another passion—choral singing—but also continued his physicsresearch. It had been known since 1897 thatwhen X rays fall on any substance, whether solid,liquid, or gas, they cause a secondary radiation tobe emitted. As were many physicists of the day,Barkla was drawn to investigating this phe-nomenon, which would become the primaryfocus of his career. In 1902, he returned to Uni-versity College in Liverpool, as Oliver LodgeFellow. The following year he published his firstpaper on secondary X radiation, in which heannounced his discovery that the secondaryradiation emitted from gases of elements with alow atomic mass has the same average wave-length as that of the primary X-ray beam imping-ing on the gas. More importantly, he showedthat the amount of secondary radiation pro-duced is proportional to the atomic mass of thegas. This work represented a significant earlyadvance in the development of the concept ofatomic number.

In research completed in 1904, for which hereceived a doctorate, he found that the heavy ele-ments produced secondary radiation of a greaterwavelength than that of the primary X-ray beam,a process that would later be explained byARTHUR HOLLY COMPTON. Further, by demon-strating that X rays can be partially polarized, ascan visible light, Barkla proved that they are aform of transverse electromagnetic radiation thatobeys JAMES CLERK MAXWELL’s equations.

Barkla, Charles Glover 21

In 1907, after being appointed as a lecturer atLiverpool, he married Mary Esther Cowell, withwhom he had two sons and one daughter. Thatyear he did his most important research, with hiscolleague C. A. Sadler. They discovered, in theprocess of X-ray scattering, that the secondaryradiation is homogeneous and that the radiationfrom the heavier elements is of two kinds: oneconsisting of X rays scattered unchanged and theother a fluorescent radiation whose propertieswere related to the particular substance involved.They were also able to show that these character-istic X-ray radiations (i.e., of a specific wave-length associated with a particular substance)were monochromatic, that is, contained one fre-quency. Barkla discovered two types of character-istic X-ray emissions: the K series (for the morepenetrating emissions) and the L series (for theless penetrating). A later prediction that otherseries of secondary emissions might exist was jus-tified when an M series with even lower penetrat-ing power than the K series was discovered.

In 1909 Barkla became professor of physicsat Kings College, London, and in 1913 hebecame professor of natural philosophy at Edin-burgh University. In the years that followed hereceived many honors for this work, all culmi-nating in the 1917 Nobel Prize in physics.

The last years of his life were saddened bythe death of his youngest son, Flight LieutenantMichael Barkla, a brilliant scholar, who waskilled in action in 1943. Barkla remained atEdinburgh University until his death at hishome, Braidwood, in Edinburgh, on October 23,1944, at the age of 67.

Barkla made valuable contributions to ourunderstanding of the absorption and photo-graphic action of X rays. Building on Barkla’slater work, Compton demonstrated the relation-ship between the characteristic X radiation, awave, and the corpuscular radiation, a particle,accompanying it. His work also showed both theapplicability and the limitations of quantumtheory in relation to X rays.

See also RÖNTGEN, WILHELM CONRAD.

Further ReadingKnoll, Glenn Frederick. Radiation Detection and Mea-

surement. 3d ed. New York: John Wiley & Sons,1999.

� Becquerel, Antoine-Henri(1852–1908)FrenchExperimentalist (Radioactivity)

Antoine-Henri Becquerel changed the courseof modern physics by his accidental discoveryin 1896 of natural radioactivity, the sponta-neous emission of radiation by a material. Forthis achievement he shared the 1903 NobelPrize with Pierre Curie and MARIE CURIE, whofurther investigated Becquerel’s discovery.

He was born in Paris on December 15, 1852,into a family of physicists: Antoine César, hisgrandfather, had made important contributionsin electrochemistry; Alexander Edmond, hisfather, was a professor of applied physics who haddevoted his career to the study of luminescence.The young Becquerel was trained as an engineerat the École Polytechnique and École des Pontset Chaussées and, in 1875, began doing researchinto the behavior of polarized light in crystals. Hemarried the daughter of a civil engineer, withwhom he had a son, who would also become aphysicist. From 1878 on, he held the post of assis-tant at the National Museum of Natural Historyin Paris and took over his father’s job as chair ofapplied physics at the Conservatoire des Arts etMétiers. In 1888, he received the doctor of sci-ences degree for a dissertation on the absorptionof light by crystals. He became a member of theFrench Academy of Sciences in 1889 and a pro-fessor of applied physics at the museum in 1892and at the École Polytechnique in 1895.

In his research, Becquerel had taken up hisfather’s studies of luminescence, which encom-

22 Becquerel, Antoine-Henri

passes fluorescence, the emission of light onlyduring stimulation by external radiation, andphosphorescence, the light that persists after theexternal radiation ceases. An exciting new pathof inquiry was suggested to him in 1896, the yearthat WILHELM CONRAD RÖNTGEN discovered Xrays. At a meeting of the academy, Becquerelheard the mathematician Henri Poincarédescribe how X rays were emitted from a fluores-cent spot on the glass cathode ray tube used byRöntgen. Becquerel had the idea that X raysmight be produced naturally by fluorescent crys-tals. To test his hypothesis he placed some crys-tals of a double sulfate of uranium and potassiumon a photographic plate wrapped in paper andput it in sunlight to make the crystals fluoresce.Observing that the plate he developed wasfogged, Becquerel concluded, “The phosphores-cent substance in question emits radiation whichpenetrates paper opaque to light.” He assumedthat the Sun’s energy was being absorbed by theuranium, which then emitted X rays.

Becquerel conscientiously set about repeat-ing his experiment, only to find himself hinderedby the Paris weather: the sky was cloudy and thecrystals could not fluoresce without sunlight.There was nothing to do but put the wrappedplate and the crystals into a drawer and wait.When for several days the clouds refused to part,Becquerel, whether from impatience or curiosity,decided to develop the plates anyway. Instead ofthe faint images he expected to appear, he wasamazed to discover images that were quite dis-tinct; the plates had been strongly exposed toradiation. He concluded that this phenomenonwas not related to fluorescence, but was a contin-uous and natural emission by the crystals.

Studying the radiation, he found that itbehaved in the same way as X rays: that is, itpenetrated matter and ionized air. He showedthat the radiation was due to the presence of ura-nium in the crystals and subsequently found thata disk of pure uranium is also highly radioactive.Searching for other radioactive materials, the

Curies discovered polonium and radium, whichare even more radioactive, in 1898. In 1900,Becquerel subjected the radiation from radiumto a magnetic field and demonstrated that radia-tion emitted by uranium shared certain charac-teristics with X rays; however, unlike X rays, itcould be deflected by a magnetic field and there-fore must consist of charged particles. He alsoshowed that radioactivity transforms one ele-ment into another. He discovered that radioac-tivity could be removed from a radioactivematerial by chemical action, but was subse-quently regained by the material.

In 1900, Becquerel was made an officer ofthe Legion of Honor, and he won the NobelPrize in physics in 1903. Subsequently, hebecame vice president (1906) and president(1908) of the Academy of Sciences. He died onAugust 25, 1908, in Le Croisic, France.

The implications of Becquerel’s revolution-ary discovery of radioactivity would be realizedin 1902–1903, when ERNEST RUTHERFORD

explained it as the spontaneous transmutation ofelements. The study of radioactivity itself wasthereby transformed into the modern science ofnuclear physics, which would give birth tonuclear medicine, nuclear reactors, and nuclearweapons.

See also THOMSON, JOSEPH JOHN (J. J.).

Further ReadingBadash, Lawrence. “The Discovery of Radioactivity.”

Physics Today February 1996, pp. 21–26.

� Bernoulli, Daniel(1700–1782)Dutch/SwissTheoretical and Experimental Physicist(Hydrodynamics), MathematicalPhysicist

Daniel Bernoulli was an early pioneer of hydro-dynamics, who also laid the groundwork for the

Bernoulli, Daniel 23

later development of the kinetic theory of gases.He is famous for discovering what has come tobe called the Bernoulli effect, the relationbetween the pressure in a steadily flowing fluidand its velocity, which is crucial to an under-standing of how airplanes fly.

He was born in Groningen, the Nether-lands, on February 8, 1800, into a family of bril-liant, fiercely competitive mathematicians,which included his father, Johann; his uncle;and two brothers. When Daniel was five, thefamily returned to Basel, Switzerland, theirnative city, where Johann took over the chair inmathematics after the death of its previous occu-pant, his brother Jakob. Johann was determinedto steer Daniel away from a career in mathemat-ics, allegedly because it paid poorly, and plannedto prepare him to be a merchant. First, however,he sent him at age 13 to the University of Baselto study logic and philosophy. When his son’spassion for mathematics persisted, Johannagreed to tutor him. It was Johann who intro-duced him to the theory of conservation ofenergy, which would later lead Daniel to hisimportant work on the mathematical theory offluid flow. When he had given up on making hisson a merchant, Johann ordered him to studymedicine. Daniel dutifully pursued a medicaldegree in Heidelberg, Strasbourg, and Basel,where he obtained a doctorate in 1721 with athesis on respiration, in which he applied math-ematical physics to medicine. Attracted to thework of the British physician William Harvey onblood as a fluid, he did research on blood flowand pressure, which combined his interests inmathematics and fluids.

Upon graduation, Bernoulli hoped to be anacademician as his father was but was unable toobtain a position. Instead, at age 23, he set outfor Padua, Italy, to study practical medicine.When illness led to enforced solitude, he spenthis time studying mathematics and in 1724 pub-lished his first mathematical work, on probabil-ity. The following year he designed an hourglass

for a ship that would flow even in stormyweather and won the first of a series of 10 prizesawarded by the Paris Academy for papers onsuch diverse topics as marine technology, navi-gation, oceanography, astrology, and medicine.He returned home to Basel that year and found aletter from Empress Catherine the Great, invit-ing him to become professor of mathematics inSaint Petersburg, Russia. To make the proposalmore attractive, she offered a second position forhis brother Nicolaus. The brothers accepted, butwithin eight months, Nicolaus was dead oftuberculosis. Grieving and oppressed by theharsh climate, Bernoulli wrote to his father,expressing his intention to return home. At thispoint Johann sent him his star student LeonardEuler to assist him in his work. Bernoulliremained in Russia, embarking on what wouldbe a lifelong collaboration with the brilliantyoung mathematician.

From 1727, when Euler arrived, until 1733,when Bernoulli left Saint Petersburg, heenjoyed his most fruitful period. Probing therelationship between the speed at which bloodflows and its pressure, he performed experi-ments that involved puncturing the wall of apipe with a small open-ended straw and notingthat the height to which the fluid rose in thestraw was related to the fluid’s pressure in thepipe. Soon European physicians were measuringblood pressure by sticking point-ended glassdirectly into their patients’ arteries. In 1896 anItalian doctor would discover the less painfulblood pressure cuff used today. However,Bernoulli’s original method of measuring thepressure in a flowing fluid is still used in modernaircraft to measure the speed of the air passingthe plane, that is, its air speed.

In Saint Petersburg, Bernoulli completed hismost famous work, Hydrodynamica, a theoreticaland practical study of equilibrium, pressure, andvelocity in fluids, which relied on his earlierwork on conservation of energy; it would be pub-lished, after years of polishing, in 1738. When

24 Bernoulli, Daniel

Bernoulli wrote his magnum opus, scientistsknew that a moving body exchanges its kineticenergy for potential energy when it gains alti-tude. Bernoulli had the insight that in a similarway, a moving fluid exchanges its kinetic energyfor pressure. From these principles he developedthe principle of what is now known as theBernoulli effect, which states that the pressure ofa fluid depends inversely on its velocity: thepressure decreases as the velocity increases.Thus, the Bernoulli effect, which governs fluidflow and has many applications, is a conse-quence of conservation of energy. Applied toaerodynamics, it explains how a moving wingwhose cross section has the shape of an airfoil(curved on the top, flat on the bottom) experi-ences the lifting force that allows an airplane tofly. The curve of the wing is designed to create afaster flow of air over the top of the wing thanover the bottom. As a result of the Bernoullieffect, the air pressure over the top of the wing islower than the air pressure beneath the wing. Inthis way, the wing is pushed upward, enabling anairplane to fly.

In his Hydrodynamica Bernoulli alsoattempted to construct a mathematical descrip-tion of the behavior of gases, based on theassumption that they are composed of tiny parti-cles. By producing an equation of state, that is,an equation that relates the pressure, tempera-ture, and volume of a gas, he was able to relateatmospheric pressure to altitude. This was thefirst step toward the kinetic theory of gases thatwould be developed a century later.

Despite his productive collaboration withEuler, Bernoulli was unhappy in Saint Peters-burg. In 1734, he returned to Basel to lecture,first on botany and later on physiology—the onlypost he could get at the time. He would continueto correspond with Euler, who put many ofBernoulli’s physical insights into rigorous mathe-matical form. When Bernoulli and his fatherwere declared joint winners of the ParisAcademy’s Grand Prize that year, the father,

enraged that his son had been judged his equal,broke off relations with him. Bernoulli stayed inBasel, barred from his father’s house. A year afterpublication of Hydrodynamica, his father pub-lished Hydraulica, based on his son’s work butwritten as if his son’s work had been based on his.Europe, however, gave the younger Bernoulli thecredit he was due, electing him to most of theleading scientific societies of his day. In 1750,Bernoulli at last became professor of physics atBasel, where he would remain for the next 26years, giving a series of memorable physics lec-tures during which he performed actual experi-ments. In research that advanced the field ofmathematical physics, he developed SIR ISAAC

NEWTON’s theories and used them together withthe more powerful calculus of Gottfried Leibnitz.

Bernoulli died on March 17, 1782, in Basel,where he was buried. An imaginative scientistwith broad interests, Bernoulli helped launchthe field of hydrodynamics, anticipated thekinetic theory of gases, and discovered a funda-mental principle of aerodynamics.

Further ReadingVischer, D. “Daniel Bernoulli and Leonard Euler: The

Advent of Hydromechanics,” in Gunther Gar-brecht, ed., Hydraulics and Hydraulic Research: AHistorical Review. Rotterdam and Boston:Balkema, 1987, pp. 145–156.

� Bethe, Hans Albrecht(1906– )German/AmericanTheoretician, Nuclear Physicist,Astrophysicist, Solid State Physicist

During his long and brilliant career, Hans Bethehas made numerous contributions to both funda-mental and applied science. His early work laidthe foundation for nuclear physics and explainedthe dynamics of the energy of stars. DuringWorld War II, he headed the theoretical group

Bethe, Hans Albrecht 25

at Los Alamos, New Mexico, that developed theatomic bomb. He later came to epitomize thesocially responsible scientist, working tirelesslyin the interests of nuclear disarmament.

Hans Albrecht Bethe was born on July 2,1906, in Strasbourg, Germany (now France), theson of a university professor. He studied at theUniversity of Frankfurt for two years and thentransferred to the University of Munich, wherehe worked under the eminent ARTHUR SOMMER-FELD. He earned a Ph.D. in 1928 for a disserta-tion on electron diffraction, which continues tobe used by physicists for interpreting observa-tional data.

During the next five years, Bethe’s workflourished within the exciting European physicsworld, which was discovering the secrets of theatom through the insights of the new quantummechanics. He lectured at the universities ofFrankfurt, Munich, and Tubingen and workedwith ENRICO FERMI in Rome. His research onatomic physics and scattering theory resulted in ahighly successful theory of inelastic collisionsbetween fast particles and atoms. Bethe’s theorydetermined the stopping power of matter for fastcharged particles, thereby enabling nuclear physi-cists to study radiation effects in matter. He thenlooked at more energetic collisions, calculatingthe Bremsstrahlung (braking radiation), that is,the radiation emitted by relativistic electrons(electrons moving nearly as fast as the speed oflight) as they are slowed during the process of col-liding with charged particles in matter. He alsostudied the production of electron–positron pairsby high-energy gamma rays.

As were those of so many outstanding physi-cists of his generation, Bethe’s career in Ger-many was derailed by the rise of Hitler. In 1933he moved to England, where he would remainfor two years, first at Manchester University andthen at Bristol University. In 1935 he emigratedto the United States, where he would become anaturalized citizen. Cornell University in Ithaca,New York, was to become his academic home

from 1937 until his retirement in 1975, when hebecame professor emeritus.

During the mid- and late 1930s, Bethe con-tinued his research on atomic nuclei. In 1934, hefirst formulated his theory of the deuteron (thenucleus of an atom of deuterium: a combinationof a proton and a neutron. (Deuterium is a natu-rally occurring stable isotope of hydrogen; it isknown as heavy hydrogen.) The following yearhe went on to resolve contradictions in thenuclear mass scale. His theoretical investiga-tions of nuclear reactions enabled him to predictmany reaction cross sections. He also gave amore precise quantitative form to NIELS HENRIK

DAVID BOHR’s theory of the compound nucleus.Bethe summarized his own work and other theo-retical and experimental studies in nuclearphysics in three articles in the Reviews of ModernPhysics, which became the basic textbook fornuclear physicists.

Bethe’s fundamental work on nuclear reac-tions led him to the discovery of the nuclear pro-cesses that supply stellar energy, a problem thathad remained unsolved since LORD KELVIN

(WILLIAM THOMSON) and HERMANN VON

HELMHOLTZ had drawn attention to it 75 yearsearlier. The riddle was an old one: how has itbeen possible for the stars, including our Sun, toemit light and heat without exhausting theirenergy sources? Bethe determined that the mostimportant nuclear reaction in the brilliant starsis the carbon–nitrogen cycle, whereas the Sunand fainter stars mainly use the proton–protonreaction. Equally important, he was able toexclude other possible nuclear reactions. Hewould receive the 1967 Nobel Prize in physicsfor this groundbreaking work.

The years of Bethe’s great discoveries alsosaw the onset of World War II. From 1943 to1946, the emphasis of his work would be on themilitary applications of modern physics. Afterworking on the development of radar at the Mas-sachusetts Institute of Technology in Cambridge,he joined the Manhattan Project, which Pres.

26 Bethe, Hans Albrecht

Franklin Delano Roosevelt had charged with themission of developing on atomic bomb. As direc-tor of the Theoretical Physics Division at LosAlamos, Bethe played an important role in thework that led to the first successful atomic bombtest in the New Mexico desert in July 1945.

Throughout his long career, Bethe has beenan amazingly versatile theoretical physicist. Inthe late 1940s, he was the first to explain theLamb shift, a frequency shift in atoms thatrevealed the fundamental quantum nature of

electrodynamic processes in the hydrogen spec-trum. This work laid the foundation for themodern development of quantum electrodynam-ics. Later on, he collaborated on the scattering ofpi mesons (the quanta of the nuclear force) andon their production by photon processes. Healso worked on solid state theory, investigatingthe splitting of atomic energy levels when anatom is inserted into a crystal. He made studiesof the theory of metals and developed a theory oforder and disorder in alloys. In astrophysics, he

Bethe, Hans Albrecht 27

Hans Bethe laid the foundation for nuclear physics, explained the dynamics of stars, and headed the theoreticalgroup that developed the atomic bomb. (AIP Emilio Segrè Visual Archives, Marshak Collection)

made important contributions to the under-standing of the explosions of giant stars calledsupernovae and helped to formulate the theoryof neutron stars, the dense remnants of super-nova explosions in which the gravitational forceis so strong that protons fuse with electrons toform neutrons.

In addition to continuing his scientificresearch, Bethe has devoted himself to fightingfor a sane international policy for controllingthe nuclear weapons he had helped to create. Hewas instrumental in founding the Bulletin ofAtomic Scientists and frequently contributed toit. Bethe served as delegate to the first Interna-tional Test Ban Conference in Geneva in 1958.His efforts were recognized in 1961 when he waschosen for the Atomic Energy Commission’sprestigious Enrico Fermi Award. He thenbecame the principal science adviser to the U.S.government during the negotiations on the 1963Nuclear Test Ban Treaty. Through his writingsand lectures on the nuclear threat, he has raisedpublic awareness and been a leader in the effortsof scientists to take social responsibility for thefruits of their inventions.

In the latter decades of his career, Bethe haswritten and spoken extensively on aspects of theenergy crisis: the finite amount of energy on Earththat will be available to a growing population andthe more immediate problem of maintaining asupply of gasoline to power automobiles. He is asupporter of a nonnuclear future, when peoplewill rely on solar energy in all its forms.

See also LAMB, WILLIS E.

Further ReadingBernstein, Jeremy. Hans Bethe, Prophet of Energy. New

York: Basic Books, 1980.Bethe, Hans Albrecht. The Road from Los Alamos,

Masters of Modern Physics. New York: SpringerVerlag, 1991.

Schweber, Silvan S. In the Shadow of the Bomb.Princeton, N.J.: Princeton University Press,2000.

� Bhabha, Homi Jehangir(1909–1966)IndianTheoretician, Particle Physicist

Homi Jehangir Bhabha was a brilliant theoreti-cian whose best-known contribution to particlephysics is an accurate expression of a cross sec-tion (i.e., the probability) of the quantum elec-trodynamic scattering of positrons by electrons,what is now called Bhabha scattering. He wasalso the chief architect of India’s atomic energyprogram, a seminal figure in the development ofa world-class cadre of Indian scientists afterWorld War II, and a prominent advocate for thecause of peaceful uses of atomic energy.

He was born on October 30, 1909, in Bom-bay, into a wealthy Parsi family with a long tra-dition of learning and service to the country.The Bhabha family cultivated interests in thefine arts, particularly Western classical musicand painting, all of which became an essentialpart of Homi Bhabha’s quest for a vivid, richexistence. As a young man, he wrote:

I know quite clearly what I want out ofmy life. Life and my emotions are theonly things I am conscious of. I love theconsciousness of life and I want as muchof it as I can get. But the span of one’slife is limited. What comes after deathno one knows. Nor do I care. Since,therefore, I cannot increase the contentof life by increasing its duration, I willincrease it by increasing its intensity.

He attended the Cathedral and John Con-nom Schools in Bombay. Then, after passing theentrance exam at age 16 in 1927, he traveled toEngland, where he planned to study mechanicalengineering at Gonville and Caius College atCambridge University. Both his father and hisuncle, Sir Dorab J. Tata, wanted him to becomean engineer so that he could eventually join the

28 Bhabha, Homi Jehangir

Tata Iron and Steel Company in Jamshedpur.But events turned out quite differently. At Cam-bridge, PAUL ADRIEN MAURICE DIRAC, who dis-covered the quantum mechanical equation thatdescribed relativistic electrons and that led tothe prediction of antimatter electrons orpositrons, was his tutor in mathematics. In 1928,Bhabha wrote to his father:

I seriously say to you that . . . a job as anengineer is . . . totally foreign to mynature and radically opposed to my tem-perament and opinions. Physics is myline. I know I shall do great thingshere . . . I am burning with a desire to dophysics.

After the young man earned his first-classhonors degree in engineering in 1930, hisfather relented and Bhabha joined theCavendish Laboratories in Cambridge, wherehe received a Ph.D. in theoretical physics in1935. During this time the Cavendish was atthe height of its golden age under the director-ship of ERNEST RUTHERFORD. In the single yearof 1932, SIR JAMES CHADWICK demonstratedthe existence of the neutron; JOHN DOUGLAS

COCKCROFT produced the artificial disintegra-tion of light elements by bombarding themwith high-speed protons; and LORD PATRICK

MAYNARD STUART BLACKETT invented acounter-cloud chamber that would demonstratethe production of positron and electron pairs.Working in this revolutionary atmosphere,Bhabha made major contributions to the earlydevelopment of quantum electrodynamics(QED), the study of the interaction of elec-trons and the electromagnetic field. His firstpaper was on the absorption of high-energygamma rays in matter. A primary gamma raydissipates its energy in the formation of elec-tron showers. In 1935, he became the firstphysicist to use the QED formalism to deter-mine the cross section (the probability) of elec-

trons scattering on positrons—a phenomenonthat is now known as Bhabha scattering.

After this important work, Bhabha focused onthe study of cosmic rays and, in a classic paperwritten with W. Heitler in 1937, suggested thatthe highly penetrating particles detected atground level could not be electrons (nine yearslater these highly penetrating particles were in factfound to be mu mesons). In his paper with Heitlerhe described how primary cosmic rays from spaceinteract with the upper atmosphere to produceparticles observed at the ground level and was ableto explain how the cosmic ray showers were pro-duced by the cascade production of gamma raysand electron–positron pairs. In 1938, he proposeda classic method of confirming the time dilationeffect of the special theory of relativity by measur-ing the lifetimes of cosmic ray particles striking theatmosphere at very high speeds. Their lifetimeswere found to be prolonged by exactly the amountpredicted by relativity. This impressive body ofresearch led to his election to the prestigious RoyalSociety in 1940, when he was only 30.

Bhabha remained at Cambridge until 1939,when he returned to India for what was to be abrief visit. He was in India when World War IIbroke out, however, and found it impossible toreturn to Cambridge. A readership was createdfor him as head of the cosmic rays department atthe Bangalore Institute of Science, under thedirectorship of the great Indian physicist SIR

CHANDRASEKHARA VENKATA RAMAN. Ramanwas influential in Bhabha’s decision to remain inIndia to advance the development of scienceand technology there.

In 1943, he became president of the physicssection of the Indian Science Congress. Thefollowing year, he proposed the establishment ofan institute for training scientists in advancedphysics and stimulating physics research forapplication to industrial development. Realiz-ing the need for an institute devoted entirely tofundamental research, he wrote for funding to aclose family friend, J. D. R. Tata, whose family

Bhabha, Homi Jehangir 29

had pioneered projects in metallurgy, powergeneration, and science and engineering educa-tion in the early 20th century. In 1945, hebecame the first director of the Tata Institute ofFundamental Research (TIFR) in Bombay, apost he held for the rest of his life. TIFR becamethe training ground for a team of experts forIndia’s atomic energy program. Since Bhabhawas also an accomplished artist and architect,under his supervision not only did science pros-per, but so did the edifice itself: aestheticallydesigned, it was surrounded by beautiful lawnsand gardens, at Land’s End in Bombay, facingthe Arabian Sea.

The other great institute he established wasthe Atomic Energy Establishment in Trombay,renamed after his death the Bhabha AtomicResearch Center (BARC).

In 1948 he wrote to the Indian president,Jawaharlal Nehru, proposing the establishmentof an atomic energy commission (AEC). InAugust 1948 the Indian Atomic Energy Act waspromulgated and the AEC was established. Formore than 20 years (1944 to 1966), he ledIndia’s atomic energy program, advancing hispriorities: surveying of natural resources; devel-opment of basic sciences—physics, chemistry,and biology; and creation of a program forinstrumentation, particularly in electronics. Hewas determined that India would be self-suffi-cient in supplying the experts necessary tonuclear energy production.

Bhabha also became an important figure inthe international science community. He servedas president of the first United Nations Confer-ence on the Peaceful Uses of Atomic Energy,held in Geneva in 1955. He was president of theInternational Union of Pure and AppliedPhysics from 1960 to 1963.

He died tragically in a plane crash on MountBlanc in the French Alps, on January 24, 1966,while on his way to Vienna to attend a meetingof the Scientific Advisory Committee of theInternational Atomic Energy Agency. He wasmourned by his peers, not only as a distinguishedtheorist, but also as one of those rare beings inwhom scientific and artistic excellence, as wellas love of country and a strong sense of interna-tionalism, harmoniously coexist.

See also EINSTEIN, ALBERT; MILLIKAN, ROBERT

ANDREWS; WILSON, CHARLES THOMAS REES.

Further ReadingAbraham, Itty. The Making of the Indian Atomic Bomb:

Science, Secrecy, and the Postcolonial State. NewYork: St. Martin’s Press, 1998.

Venkataraman, G. Bhabha and His Magnificent Obses-sions. Hyderabad, India: University Press, 1994.

30 Bhabha, Homi Jehangir

Homi Jehangir Bhabha formulated the quantumelectrodynamic theory of electron-positron scatteringand was the chief architect of India’s atomic energyprogram. (AIP Emilio Segrè Visual Archives, PhysicsToday Collection)

� Blackett, Patrick Maynard Stuart,Lord(1897–1974)BritishExperimentalist, Atomic Physicist,Particle Physicist

Patrick Blackett made the first photograph of anatomic transmutation and in the early 1920sdeveloped the cloud chamber, invented in 1911by CHARLES THOMSON REES WILSON, into aninvaluable instrument for studying nuclear reac-tions. These achievements garnered him the1948 Nobel Prize in physics. His discovery of thephenomenon of pair production of positrons andelectrons in cosmic rays provided the first evi-dence of ALBERT EINSTEIN’s theory that mass andenergy are equivalent.

He was born on November 18, 1897, inCroydon, Surrey, the son of Arthur StuartBlackett. He joined the Royal Navy in 1912 as anaval cadet. During World War I, he took partin the battles of the Falkland Islands and Jut-land and designed a revolutionary new gun-sight. Attracted to science, he resigned from thenavy when the war ended with the rank of lieu-tenant and began to study science at CambridgeUniversity, where he received a B.A. in 1921.At Cambridge’s Cavendish Laboratory, hebegan working under ERNEST RUTHERFORD oncloud chambers.

In 1924, he married Constanza Bayon, withwhom he had a son and a daughter, and in thesame year he obtained the first photos of anatomic transmutation, which was of nitrogeninto an oxygen isotope. In 1919, he explainedthe transmutation of elements from experimentsin which nitrogen was bombarded with alphaparticles. The oxygen atoms and protons pro-duced were detected by scintillations in a screenof zinc sulfide. He used a cloud chamber to pho-tograph the tracks formed by these particles, tak-ing more than 20,000 pictures and recordingabout 400,000 tracks. Of these, eight showed

that a nuclear reaction had taken place, con-firming Rutherford’s explanation of the trans-mutation process. His accurate measurementsshowed that the course of a collision betweenatomic nuclei always follows the laws of conser-vation of momentum and energy, provided thatthe mass–energy relationship given by the the-ory of relativity is also taken into account.

Blackett continued to develop the cloudchamber and in 1932, with a young Italian physi-cist, Guiseppe Occhialini, designed the counter-controlled cloud chamber, a brilliant inventionin which cosmic rays could photograph them-selves. The counter-controlled cloud chamberwas activated when simultaneous dischargesoccurred as the result of an electrically chargedparticle’s passing through two geiger counters,placed above and below the cloud chamber. Thismade the cloud chamber vastly more efficientand reduced the huge number of required obser-vations. Early in 1933, this device confirmed theexistence of the positron (or positive electron)proposed by CARL DAVID ANDERSON and alsodemonstrated the existence of pair production,the generation of positrons and electrons directlyfrom the interaction of gamma rays with heavynuclei. The observation of pair production wasthe first evidence that matter may be createdfrom energy, as Einstein had predicted in his the-ory of special relativity. Blackett and Occhialinialso performed experiments demonstrating thereverse process of pair annihilation, in which apositron–electron pair are transformed intogamma radiation, thus converting mass back intoenergy. In the interpretation of these experi-ments, they were guided by PAUL ADRIEN MAU-RICE DIRAC’s quantum theory of the electron.

In 1933, Blackett became a professor ofphysics at Birkbeck College, London, and in1935, he moved to the University of Manch-ester. He continued his cosmic ray studies,attracting a distinguished group of researchersaround him. This work was interrupted byWorld War II, when he joined the Instrument

Blackett, Patrick Maynard Stuart, Lord 31

Section of the Royal Aircraft Establishment.Early in 1940 he became scientific adviser tothe Coastal Command and started the analyticstudy of the anti-U-boat war. He later contin-ued this work as director of Naval OperationalResearch at the Admiralty. Blackett served asadviser to the Anti-Aircraft Command and,during the Blitz of London, was involved inantiaircraft operations.

After the war Blackett returned to univer-sity life. At Manchester, his research team mademany important discoveries about cosmic rays,including the discovery, in 1947, of the first twoof what became known as strange particles: alarge family of intrinsically unstable particleswith a life span of 10–10 second and a massgreater than that of a proton, which undergo aseries of elementary particle decays.

In 1948 Blackett’s speculations about theisotropy of cosmic rays led him to studies of theorigin of the interstellar magnetic field and ofthe magnetic field of the Earth and Sun.These, in turn, led him to study the Earth’smagnetic field and particularly the phe-nomenon of rock magnetism. In 1953, he wasappointed head of the physics department atthe Imperial College of Science and Technol-ogy, London, where he built up a research teamto investigate the phenomenon. After hisretirement in 1963, he was instrumental in theestablishment of the Ministry of Technology.He became president of the Royal Society in1965 and a life peer in 1969. He died on July13, 1974.

Blackett’s pioneering discoveries providedthe first evidence of Einstein’s theory that massand energy are equivalent and laid the founda-tion for modern experimental high-energy parti-cle physics.

Further ReadingBlackett, Patrick Maynard Stuart. Fear, War, and the

Bomb: Military and Political Consequences ofAtomic Energy. New York: McGraw-Hill, 1949.

� Bloch, Felix(1905–1983)Swiss/AmericanExperimentalist, Quantum Theorist(Statistical Mechanics), Solid StatePhysicist

Felix Bloch was a major figure in 20th-centuryphysics, who was among the first to demonstratethe power of quantum mechanics to illuminatemany hitherto mysterious physical phenomena.He did groundbreaking work in the quantumtheory of metals and solids, discovering whatcame to be called Bloch walls, which separatemagnetic domains in ferromagnetic materialssuch as iron. He shared the 1952 Nobel Prize inphysics with EDWARD MILLS PURCELL for theirsimultaneous independent discovery of thenuclear magnetic resonance.

He was born in Zurich, Switzerland, on Octo-ber 23, 1905, to Gustav Bloch, a wholesale graindealer, and Agnes Mayer Bloch, Gustav’s cousinfrom Vienna. Living in Zurich, where he devel-oped his lifetime love of mountains, from 1912 to1918, he attended primary and secondary school.His childhood was marred by the death of his 12-year-old sister, who had been his main support indealing with painful feelings of exclusion atschool. He loved the clarity and beauty of mathe-matics and was also drawn to music. In 1924, hepassed the Matura, the final examination, whichwas the passport to a higher education.

Since his ambition was to become an engi-neer, he enrolled at the Federal Institute ofTechnology in Zurich. After a year, however, heknew he wanted to study physics and transferredto the division of mathematics and physics, inwhich his professors, including ERWIN

SCHRÖDINGER and Peter Debye, introduced himto the new wave theory of quantum mechanics.By now Bloch’s interests were enthusiasticallydirected toward theoretical physics. WhenSchrödinger left Zurich in 1927, Bloch trans-ferred to the University of Leipzig, where he

32 Bloch, Felix

studied with Schrödinger’s rival in the quest fora theoretical formulation of quantum mechan-ics, WERNER HEISENBERG. He received a Ph.D.in 1928 for a dissertation in which he investi-gated the quantum mechanics of electrons incrystals and developed the theory of metallicconduction.

After spending the 1930–1931 academicyear with Heisenberg at Leipzig, he wrote amajor paper on ferromagnetism, in which hedeveloped the concept that came to be calledBloch walls. Earlier researchers had done exper-iments on the process of magnetization in ferro-magnets, including the phenomenon ofmagnetic domain structure, that is, localizedmagnetic regions in a metallic material. Under-standing this process required understanding theboundary wall between domains and the mannerin which it moved. Bloch was able to determinetheoretically the thickness and structure of themagnetic domain boundary wall and predictedthat in a distance as small as a few hundredangstroms the magnetization could reversedirection. Many years later it became possible toobserve this progress experimentally.

In 1931, Bloch also worked with NIELS HEN-RIK DAVID BOHR at his institute in Copenhagen.Bohr had long been interested in stoppingpower: that is, the loss of energy of a chargedparticle as it passes through matter. Since writ-ing an important paper on the topic in 1913, inwhich he presented a classical calculation, Bohrhoped to improve his theory to agree moreclosely with observed losses of alpha and betaparticles. In a 1930 paper based on quantummechanics, HANS ALBRECHT BETHE came upwith a better fit between theory and observation.Bloch was able to explain the discrepancybetween their results in a 1933 paper, showingthat their calculations were opposite limitingapproaches corresponding to the different waysin which the phase of the quantum wave func-tion varied as the particle passed near an atom.The equation describing the stopping of charged

particles in matter became known as theBethe–Bloch formula.

As did many physicists of Jewish descent,Bloch chose to leave Germany in 1933, whenHitler’s Nazi regime came to power. Learningthat his name was on a list of “displaced schol-ars,” that year he went to Rome on a RockefellerFellowship, and there he worked at ENRICO

FERMI’s institute at the University of Rome. Hethen accepted an offer from Stanford University,where he was able to realize what had been agrowing inclination to do experimental physics.

The neutron had been discovered in 1932and the physics of neutron interactions was juststarting to be explored. Suspecting that the neu-tron had a magnetic moment, that is, a measureof the strength of a magnet, he drew on hisexpertise in ferromagnetism and devised amethod for polarizing neutrons in a ferromag-netic material. In his first studies, using anextremely simple neutron source, he discoveredthat a direct proof of the magnetic moment offree neutrons could be obtained through thestrength of its magnetic field observing magneticscattering of neutrons in a ferromagnetic sub-stance such as iron. In a 1936 paper, in which hefirst described the theory of magnetic scatteringof neutrons, Bloch showed how the scatteringcould lead to a beam of polarized neutrons. Fur-ther, he demonstrated how it was possible to dis-tinguish the atomic scattering from the nuclearscattering by temperature variations of the ferro-magnetic material in which the neutrons werescattered. From such experiments on neutronscattering at small angles, he was able to deter-mine the magnetic moment of the neutronexperimentally.

Developing these ideas, in 1939 he collabo-rated with LUIS W. ALVAREZ in conducting afamous experiment at the Berkeley cyclotron, inwhich they were able to determine the magneticmoment of the neutron with an accuracy ofabout 1 percent. That year, on the way to ameeting of the American Physical Society in

Bloch, Felix 33

Washington, D.C., Bloch met Dr. Lore Misch, afellow physicist and refugee from Germany.They married in Las Vegas on March 14, 1940.Their lifelong union produced four children,who would present them with 11 grandchildren.

When World War II began, Bloch becameinvolved in the initial work on atomic energy atStanford. Invited to Los Alamos by J. ROBERT

OPPENHEIMER, he worked on the implosionmethod suggested by Seth Neddermeyer. Lateron, he worked on radar countermeasures at Har-vard University, which exposed him to the lat-est developments in electronics. When hereturned to Stanford after the war, in 1945, heapplied this new knowledge to his earlier workon the magnetic moment of the neutron anddeveloped innovative approaches to the studyof nuclear moments.

By then, ISIDOR ISAAC RABI had theoreti-cally determined that magnetic resonance, asso-ciated with groups of atoms shot through aregion of strong magnet fields as a beam, was ameasurable phenomenon. But instruments capa-ble of measuring magnetic resonance in liquidsor solids had not yet been designed. Bloch’s solidgrasp of quantum mechanics, particularly thequantum mechanics of solids, uniquely qualifiedhim to solve this problem. With W. W. Hansenand M. E. Packard, he devised a new methodthat used an electromagnetic procedure (ini-tially called nuclear magnetic induction) for thestudy of nuclear moments in solids, liquids, orgases. He developed a phenomenologicaldescription for the frequency of precession (i.e.,rotation), of the nuclear magnetic moments ofneutrons and the electromagnetic signals thatwould be emitted from them in the nuclear mag-netic induction process, using formulas thatbecame known as the Bloch equations.

Only a few weeks after successfully perform-ing this work, he learned that Purcell and hisHarvard collaborators had independently madethe same discovery, using a resonance methodinvolving energy absorption of radiation in a

cavity. The name nuclear magnetic resonance(NMR) was given to both methods for measur-ing nuclear magnetic moments, and Bloch andPurcell shared the 1952 Nobel Prize in physics.

After his groundbreaking discovery, Blochdevoted himself to investigations using his newmethod. He succeeded in combining it with hisearlier work on the magnetic moment of theneutron to allow him to measure that quantitywith a high degree of accuracy. In 1954, Blochspent a year as the first director general of theEuropean Center for Nuclear Research (CERN)in Geneva. The work, which was largely admin-istrative, was not to his liking, and he returnedto Stanford eager to continue his studies ofnuclear magnetism. He joined his colleagues indesigning and building the Stanford LinearAccelerator Center.

In 1961, he was appointed Max Stein Pro-fessor of Physics at Stanford. Throughout theearly 1960s, after the announcement of theBardeen–Cooper–Schrieffer (BCS) theory ofsuperconductivity, he returned to his old interestin the theory of superconductivity, which hewanted to simplify in order to clarify the physicalprocesses involved. In his farewell speech aspresident of the American Physical Society in1966, he spoke of his unfulfilled hopes to findthat simplicity. His last research papers dealtwith superconductivity and presented a simpli-fied discussion of the Josephson effect.

On retiring, Bloch began writing a book onstatistical mechanics. Although it was unfin-ished at the time of his death, it was completedby a colleague on the basis of his notes and pub-lished as Fundamentals of Statistical Mechanics,which is regarded as an insightful, elegantly writ-ten account of the subject. He died suddenly of aheart attack on September 10, 1983, and wasburied on a mountainside overlooking Zurich.

Bloch’s breakthrough discovery of the pro-cess of nuclear magnetic resonance led to manyunanticipated scientific and practical applica-tions: in addition to its intended role in evaluat-

34 Bloch, Felix

ing nuclear magnetic moments, NMR becamean essential spectroscopic tool used in structuraland dynamic studies in chemistry. More impor-tantly, in medicine, NMR was developed byP. C. Lauterburg and others into magnetic reso-nance imaging (MRI), which dramaticallyimproved upon the traditional X ray and rivaledthe successful computer-assisted tomographiceffect known as computed tomography (CT) orCT scanning.

See also BARDEEN, JOHN; CHADWICK, SIR

JAMES; SCHRIEFFER, JOHN ROBERT; JOSEPHSON,BRIAN DAVID.

Further ReadingHofstadter, Robert. “Felix Bloch,” in Biographical

Memoirs. Vol. 64. Washington, D.C.: NationalAcademy Press, 1994, pp. 34–71.

� Bloembergen, Nicolaas(1920– )Dutch/AmericanTheoretical and Experimental Physicist,Laser Spectroscopist

Nicolaas Bloembergen made his mark on 20th-century physics through his contributions to thetechnology of the laser, the revolutionary devicethat creates and amplifies a narrow, intensebeam of coherent light, and its forerunner, themaser. His three-level crystal maser proved strik-ingly more powerful than earlier gaseous masersand became the most widely used microwaveamplifier. Bloembergen went on to develop laserspectroscopy, which allows high-precision obser-vations of atomic structure. On the basis of hislaser spectroscopic studies, he established thetheoretical foundation for the science of nonlin-ear optics, a new theoretical approach to theanalysis of how high-intensity coherent electro-magnetic radiation interacts with matter.Bloembergen also did seminal work in nuclearmagnetic resonance.

Bloembergen was born on March 11, 1920,in Dordrecht, the Netherlands, the second of sixchildren born to Auke Bloembergen, who was achemical engineer, and Sophia Maria Quint,who had a degree that qualified her to teachFrench but instead devoted herself to familyduties. Before Nicolaas reached school age, thefamily moved to Bilthoven, a suburb of Utrecht,where, he recalls, “We were brought up in theProtestant work ethic characteristic of theDutch provinces.” Encouragement of intellec-tual attainments and a level of frugality beyondthat required by family income were twin pillarsof his childhood. However, his parents alsourged him to participate in field hockey, watersports, and skating on the Dutch waterways,rather than sit constantly over his books. At theage of 12 he entered the municipal gymnasiumin Utrecht, whose rigid curriculum emphasizedthe humanities; he did not discover his love ofscience until the last years of secondary school.He describes his choice of physics as “probablybased on the fact that I found it the most diffi-cult and most challenging subject.”

In 1938, he entered the University ofUtrecht, where he was allowed to assist in theresearch of a graduate student, G. A. W. Rutgers,with whom he published his first paper, “On theStraggling of Alpha Particles in Solid Matter,” in1940. That same year, however, the Nazisinvaded the Netherlands, and Bloembergen’smentor, Professor L. S. Ornstein, was forced toleave the university in 1941. He managed toobtain the Dutch equivalent of a master’s degreein science degree just before the university wasclosed completely in 1943. For the next twoyears, until the war’s conclusion in 1945, hewent into hiding, “eating tulip bulbs” and read-ing about quantum mechanics “by the light of astorm lamp.”

At war’s end, he was accepted to do graduatework by Harvard University, and, with the helpof his father and the Dutch government, he leftbehind the devastation of Europe. His arrival at

Bloembergen, Nicolaas 35

Harvard coincided with the detection, by E. M.PURCELL, R. V. Pound, and Henry Torrey, ofnuclear magnetic resonance (NMR) in con-densed matter (an effect that results when wavesof radio frequency are absorbed by the nuclei ofmatter in a strong external magnetic field).Bloembergen was accepted as a graduate assis-tant to develop the early NMR apparatus. At thetime the field of NMR in solids, liquids, andgases was unexplored, and Bloembergen and hisHarvard colleagues gathered a rich harvest offindings, which they published in 1948 in alandmark paper, “Relaxation Effects in NuclearMagnetic Resonance,” in The Physical Review.Bloembergen did part of this work back in theNetherlands, at the Kammerlingh Onnes Labo-ratory in Leiden, in 1947 and 1948; there he dis-covered the nuclear spin relaxation mechanismby conduction electrons in metals and by param-agnetic impurities in ionic crystals, the phe-nomenon of spin diffusion, and the large shiftsinduced by internal magnetic fields in paramag-netic crystals. He was the first physicist to mea-sure NMR relaxation times, that is, the decaytime of the NMR process, accurately and discov-ered that NMR relaxation times could be mea-sured in seconds or fractions of seconds. Thisresult made NMR a practical research tool, withapplications in chemistry, medicine, andphysics, including a method for analyzing thestructure of molecules and for producing thecontrast needed to create images of tissues in thehuman body. Bloembergen wrote his doctoralthesis, “Nuclear Magnetic Relaxation,” usingthese same materials, and submitted it, in 1948,to the University of Leiden, where he hadalready filled all his other requirements for thePh.D.

During a vacation trip with the PhysicsClub in Leiden, in the summer of 1948, he metHuberta Deliana Brink (known as Deli), apremed student, whom he married in Amster-dam in 1950. The young couple immigrated tothe United States, where they would raise three

children and become citizens in 1958. With Delias “a source of light in my life,” he picked up hiscareer at Harvard. While a junior fellow there hebroadened his experimental background toinclude microwave spectroscopy and somenuclear physics at the Harvard cyclotron; how-ever, he preferred “the smaller-scale experimentsof spectroscopy, where an individual or a fewresearchers at most, can master all aspects of theproblem.” Thus, in 1951, he returned to NMRresearch; his group made a number of significantdiscoveries that led Bloembergen to propose athree-level solid state maser in 1956.

He did not try to build a working laser, afterCHARLES HARD TOWNES and ARTHUR

LEONARD SCHAWLOW published their proposalfor an optical maser, doubting that a small aca-demic lab with no previous experience in opticscould succeed. He did, however, recognize in1961 that his laboratory could take advantageof some of the new research opportunities madepossible by laser instrumentation. His groupstarted a program in a field that became knownas nonlinear optics, the study of the behavior ofhigh-intensity coherent radiation in matter,and published their early results in a 1965monograph. Nonlinear optical methods ofspectroscopy are based on the mixing of two ormore high-intensity coherent light waves in anoptically active medium for which the princi-ple of superposition, valid for ordinary electro-magnetic radiation, breaks down. Bloembergenand his group demonstrated this type of nonlin-ear optical phenomenon shortly after the laserwas introduced and comprehensively exploredthe theory describing it around the same time.Bloembergen’s method of nonlinear four-wavemixing, in which three coherent light wavesact together in generating a fourth coherentlight wave, made it possible to generate laserlight far outside the visible range, in both theinfrared and the ultraviolet spectra. Thisgreatly extended the range of wavelengthsaccessible to laser spectroscopy studies. One

36 Bloembergen, Nicolaas

example of this is a special form of four-wavemixing called coherent anti–Stokes Ramanscattering (CARS), which has been applied instudies of widely differing kinds—from opti-mization of combustion processes in automo-bile engines to the study of the transport ofchemical elements in biological tissues. For thisseminal work Bloembergen shared the 1981Nobel Prize in physics with Schawlow, thecoinventor of the laser.

While performing this work Bloembergenenjoyed a rich academic life at Harvard, includ-ing innumerable travels abroad.

He served on a 1986 committee to studyPresident Ronald Reagan’s “Star Wars” programand concluded that, in order for it to work, adecade of laser weapon research would beneeded. The committee’s findings confirmed thescientific community’s “gut feeling” that it wasnot practical.

In addition to writing monographs onnuclear magnetic relation and nonlinear optics,he has published over 300 papers in scientificjournals. In June 1990 he retired from the facultyat Harvard and became professor emeritus. Heand his wife had a special feeling for Tucson, soafter his retirement from Harvard, in 1991 hebecame an unpaid professor of physics at theUniversity of Arizona, Tucson, where he contin-ues to pursue research at the university’s opticalinstitute. Also in 1991, he served as president ofthe American Physical Society.

Bloembergen’s theoretical and experimentalwork with masers and lasers led to a vast spec-trum of practical applications, from surgicaltechniques to boring and cutting of metal to thedevelopment of fiber optics. In a 1998 talk, heforesaw an increasing laser use in scientificapplications, noting that there is currently an“enormous push” for high-powered semiconduc-tor lasers.

See also RABI, ISIDOR ISAAC; RAMAN, SIR

CHANDRASEKHARA VENKATA; STOKES, GEORGE

GABRIEL.

Further ReadingBloembergen, Nicolaas. Encounters in Magnetic Reso-

nances: Selected Papers of Nicolaas Bloembergen.River Edge, N.J.: World Scientific, 1996.

———. Encounters in Nonlinear Optics: SelectedPapers of Nicolaas Bloembergen (with Commen-tary). River Edge, N.J.: World Scientific, 1996.

———. Nonlinear Optics. 4th ed. River Edge, N.J.:World Scientific, 1996.

� Bohr, Niels Henrik David(1885–1962)DanishTheoretical Physicist, QuantumTheorist, Philosopher of Science

Among the revolutionary geniuses of 20th-cen-tury physics, the name of Niels Bohr, whosemodel of the atom laid the basis for quantummechanics, is second only to that of ALBERT EIN-STEIN. By wedding MAX PLANCK’s notion of dis-crete quanta of energy to ERNEST RUTHERFORD’snuclear model of the atom, Bohr opened thedoor to a description of material processes atodds not only with the determinism of classicalphysics, but with what many, Einstein included,considered to be a coherent, existentially palat-able vision of nature.

Niels Henrik David Bohr was born on Octo-ber 7, 1885, in Copenhagen, Denmark, into afamily remarkable for its intellectual attain-ments: his mother, Ellen Adler Bohr, was amember of a wealthy Jewish family, prominentin Danish banking and parliamentary circles,and his father, Christian Bohr, was a professor ofphysiology at the University of Copenhagen,known for his work on the physical and chemi-cal aspects of respiration. Niels was consideredless brilliant than his younger brother, Harold,who became a renowned mathematician. But hewasted no time in distinguishing himself: threeyears after entering the University of Copen-hagen in 1903, he won a gold medal from the

Bohr, Niels Henrik David 37

Royal Danish Academy of Sciences for his theo-retical analysis of vibrations of water jets as ameans of determining surface tension. Heremained in Copenhagen until 1911, when hereceived a doctorate for a theory explainingelectron behavior in metals.

In 1912, he traveled to England, to continuehis research in Cambridge with JOSEPH JOHN (J.J.) THOMSON, the discoverer of the electron.When Thomson proved indifferent to his ideas,Bohr moved to Manchester to work with ErnestRutherford, who was making important contri-butions to the theory of the atom. Rutherfordhad proposed that atoms consist of electronsorbiting a positively charged nucleus. But it wasnot understood how electrons could continually

orbit the nucleus without radiating energy, asclassical physics demanded. According to JAMES

CLERK MAXWELL’s equations, orbiting electronswould be accelerating and continuously emit-ting electromagnetic radiation; this processwould cause them to spiral into the nucleus inabout a trillionth of a second. In contradistinc-tion to the classical prediction, however, thehydrogen atom was extremely stable.

With Rutherford as his inspiration and men-tor, Bohr set about explaining this discrepancy.He began with MAX ERNEST LUDWIG PLANCK’s1900 theory that energy is emitted in discretepackets or quanta and applied it to Rutherford’snuclear atom. Bohr postulated that electrons areconfined to a certain number of stable orbits, inwhich they neither emit nor absorb energy. Onlywhen it jumps from one discrete orbit to a lowerone does the electron lose energy: it sends off anindividual photon (particle of light). Since anelectron in the innermost orbit has no orbit withless energy to jump to, the atom remains stable.Bohr’s theory explained many of the spectral linesfor hydrogen and helium, but he hesitated to pub-lish his results, fearing that no one would takehim seriously unless he explained the spectra ofall the elements. It was Rutherford who persuadedhim that the ability to explain hydrogen andhelium would be quite enough to make his modelcredible. Indeed, when Bohr’s three papers on thestructure of the hydrogen atom and on heavieratoms appeared in 1913, they had a profound,unsettling effect. Many of Bohr’s contemporariesbalked at accepting so bizarre a picture of theatomic world. But new spectroscopic measure-ments and other experiments confirmed Bohr’stheory, and in 1914 direct evidence for the exis-tence of such discrete states was found.

In 1916, the University of Copenhagenappointed him to the chair of theoreticalphysics. When he made known his plans toreturn to “more ideal” research conditions inEngland, the Danish university created theInstitute of Theoretical Physics for him (now

38 Bohr, Niels Henrik David

Niels Henrik David Bohr laid the foundation for thetheory of quantum mechanics, an enormouslysuccessful description of physical processes that is atodds with classical determinism. (Princeton University,AIP Emilio Segrè Visual Archives)

the Niels Bohr Institute for Astronomy, Physicsand Geophysics). In 1921, a year before hereceived the Nobel Prize in physics, he wasappointed its director, a post he would retain forthe rest of his life. The institute became a meccafor theoretical physicists, who traveled from allover the world to debate the meaning of the newphysics, and the birthplace of what came to becalled the Copenhagen school. While still in his20s, Bohr found himself at the very center of thequantum mechanical revolution. Bohr and hiscolleagues, including WOLFGANG PAULI andWERNER HEISENBERG, brainstormed tirelessly insearch of a physical interpretation of the newmathematical description of nature. The resultwas the Copenhagen interpretation of quantummechanics, which introduced a radical assump-tion into physical thinking: because the quan-tum interaction between the “observer” and the“objects to be observed” can never be ignored atthe microscopic level, microphysical processesare fundamentally random and probabilistic.Bohr enunciated one of the startling implica-tions of this hypothesis in his complementarityprinciple, which states that an electron can beregarded as a particle or wave phenomenon, andboth characterizations are equally valid, depend-ing on the experimental circumstances:

Evidence obtained under different ex-perimental conditions cannot be com-prehended within a single picture butmust be regarded as complementary inthe sense that only the totality of thephenomena exhausts the possible infor-mation about the phenomenon.

In the early 1920s, Bohr sought to develop aconsistent quantum theory that would supersedeclassical mechanics and electrodynamics at theatomic level. During this period of intense andwide-ranging exploration, he formulated hisprinciple of correspondence, a philosophicalguideline for selection of new physical theories,

requiring that they explain all the phenomenafor which a preceding theory is valid. Since clas-sical mechanics had met all challenges untilphysicists began to examine the atom itself,Bohr insisted that quantum mechanics, to bevalid, must do what the old physics did—andmore: it must describe atomic phenomena cor-rectly and be applicable to conventional phe-nomena, as well. In 1923, he announced thatthe new physics could do just that:

Notwithstanding the fundamental de-parture from the ideas of the classicaltheory of mechanics and electrodynam-ics involved in these postulates, it hasbeen possible to trace a connectionbetween the radiation emitted by theatom and the motion of the particleswhich exhibits a far-reaching analogy tothat claimed by the classical ideas of theorigin of radiation. Indeed, in a suitablelimit the frequencies calculated by thetwo very different methods would agreeexactly.

If Bohr’s view of quantum theory graduallywon almost universal acceptance, one converthe never succeeded in winning, though not forlack of trying, was Einstein. The Bohr–Einsteindebates of the 1920s and 1930s are legendary.Einstein, who could never accept the probabilis-tic nature of quantum mechanics, produced aseries of gedanken (thought) experimentsdesigned to disprove the theory. Bohr wouldthen attempt to expose the flaws in Einstein’sreasoning. To Einstein’s insistence that “Goddoes not play dice with the universe,” Bohrwould counter, “Einstein, stop telling God whatto do!” But if Bohr accepted the strangeness ofthe theory he had helped bring into being, hisattitude toward it was anything but complacent.“Anyone who is not dizzy after his first acquain-tance with the quantum of action,” he said, “hasnot understood a word.”

Bohr, Niels Henrik David 39

In the 1930s, Bohr’s interests turned tonuclear physics and in 1939 he proposed the liq-uid-droplet model for the nucleus, which proveda key to understanding many nuclear processes:Nucleons (neutrons and protons) behave asmolecules do in a drop of liquid. If given enoughextra energy (by absorbing a neutron), thespherical nucleus may be distorted into a dumb-bell shape and then split at the neck into twonearly equal fragments, releasing energy. In thisway Bohr, working with JOHN A. WHEELER, wasable to explain why a heavy nucleus couldundergo fission after the capture of a neutron.Bohr validated his theory when he correctly pre-dicted that the nuclei of uranium-235 and ura-nium-238 would behave differently, since thenumber of neutrons in each nucleus is odd andeven, respectively.

During World War II, Bohr was active in theDanish resistance movement; in 1943, he escapedwith his family to Sweden and then to England,where he and his son, Aage, took part in the pro-ject for making a nuclear fission bomb. He accom-panied the British research team to Los Alamosand made significant contributions to physicalresearch on the U.S. atomic bomb. After the war,Bohr became a prominent advocate for control ofnuclear weapons, pleading, in a famous 1950 openletter to the United Nations, for an “open world”and exhorting Roosevelt and Churchill to strivefor international cooperation. His passionateadvocacy won him the first U.S. Atoms for PeaceAward in 1957. He was instrumental in creatingthe European Center for Nuclear Research(CERN), Geneva, in 1952.

In his last years Bohr remained a staunchdefender of the Copenhagen interpretation ofquantum mechanics and published articles inwhich he related the quantum mechanical idea ofcomplementarity to aspects of human life andthought. Bohr’s unique approach to science andphilosophy, his openness to new ideas, and will-ingness to learn from even the most junior of hiscolleagues left a lasting imprint on the generation

of physicists who followed him. Until his death inCopenhagen on November 18, 1962, he remaineda spirited participant in the great physics debateshe had played so central a role in initiating.

Further ReadingPais, Abraham. Niels Bohr’s Times: In Physics, Philoso-

phy, and Polity. Oxford: Oxford University Press,1991.

Ruhla, Charles. The Physics of Chance: From BlaisePascal to Niels Bohr. Oxford: Oxford UniversityPress, 1992.

Spangenburg, Ray, and Diane K. Moser. Niels Bohr:Gentle Genius of Denmark. New York: Facts OnFile, 1995.

Whitaker, Andrew. Einstein, Bohr and the QuantumDilemma. Cambridge: Cambridge UniversityPress, 1996.

� Boltzmann, Ludwig(1844–1906)AustrianTheoretical Physicist (StatisticalMechanics, Electromagnetism,Thermodynamics)

Ludwig Boltzmann was an intuitive geniuswhose belief in the existence of an underlyingatomic structure in nature, governed by the lawsof probability, helped set the course for 20th-century physics. An embattled figure, whoseideas contradicted the scientific dogmas of histimes and who died before his theories were val-idated, Boltzmann redefined the very nature oftheoretical physics and paved the way for thestatistical theory of quantum mechanics.

Boltzmann was born in Vienna on February20, 1844, and received his early education inLinz and Vienna. He studied at the University ofVienna at a time when the fundamentals of ther-modynamics and electromagnetism were beingestablished. Over the next 40 years, he wouldmake vital contributions to these fields. In 1859,

40 Boltzmann, Ludwig

while still a student in Vienna, he published hisfirst paper, on the kinetic theory of gases. Hewent on to write a thesis on that subject, underthe supervision of JOSEF STEFAN, the discovererof a fundamental law of radiation, and receivedhis Ph.D. in 1866.

The following year Boltzmann became Ste-fan’s assistant at the Physikalisches Institut inVienna. Building on the work of JAMES CLERK

MAXWELL, in 1868 he published a groundbreak-ing paper on thermal equilibrium in gases. Byexamining the distribution of energy among col-liding gas molecules, Boltzmann derived anexponential formula, later known as theMaxwell–Boltzmann distribution, to describethe distribution of molecules. This formularelates the mean total energy of a molecule to itstemperature, in terms of a fundamental constantk, which came to be known as the Boltzmannconstant. This seminal work formed the basis ofthe new field of statistical mechanics, whichplayed a major role in the later discoveries ofMAX ERNEST LUDWIG PLANCK and others.

Over the next several years Boltzmannwould move restlessly from one academic post toanother. From 1869 to 1873, he was professor oftheoretical physics at the University of Graz;from 1873 to 1876, professor of mathematics atVienna; in 1876, he returned to Graz, this timeas professor of experimental physics, andremained there until 1879.

During this period, Boltzmann published amathematical description of the tendency of agas to reach a point of equilibrium as the mostprobable state. This famous equation, S = k logW (which was later engraved on his tombstone),describes the relationship between entropy andprobability.

During the 1880s, he was director of thePhysikalisches Institut in Vienna. During histenure there, Boltzmann developed the work ofhis former mentor, Josef Stefan. Stefan hadexperimentally derived the law of blackbodyradiation, showing that the energy radiated by a

black body is proportional to the fourth power ofits absolute temperature. In 1884, Boltzmannproposed a theoretical formulation for it, subse-quently known as the Stefan–Boltzmann law,based on the second law of thermodynamics andMaxwell’s electromagnetic theory.

Between 1889 and 1902, Boltzmann wouldoccupy academic posts in Munich, Vienna, andLeipzig. He is said to have joked that he movedaround so much because he had been born dur-ing the final hours of a Mardi Gras. A morelikely explanation of his wandering is what wewould today term a manic–depressive nature,aggravated by years of scientific jousting.

It was during these years that Boltzmannbecame embroiled in what is now known as theatomist–energeticist debate. With no technol-ogy available to verify their existence at the turnof the century, atoms had been relegated by mostphysicists to the realm of speculation. ERNST

MACH, Boltzmann’s leading opponent, wasamong these. For Mach the purpose of sciencewas to measure and demonstrate only that whichit could observe. Mach and his colleagues werecontent to measure the expansion of gases andempirically deduce a simple law relating temper-ature, pressure, and volume. They were not fazedby their inability to explain why these propertieswere related in this particular way. Boltzmann,on the other hand, believed that by hypothesiz-ing a dynamic submolecular world of collidingatoms he could explain why gas expands and byhow much. It was the atoms’ incessant move-ment that produced the properties of gas, Boltz-mann said: the greater the speed of the atoms,the higher the gas temperature; the greater thenumber of collisions of atoms against the walls ofa container, the greater its pressure. Boltzmann’satomic model enabled him to understand theability of hot gas to push on a piston in a steamengine, thereby converting energy into mechan-ical work. His statistical methods of evaluatingthe variations in the movements of molecules ina gas demonstrated that reliable physical laws

Boltzmann, Ludwig 41

could be built on probability. Boltzmann consid-erably broadened the definition of what it meantto be a theoretical physicist and paved the wayfor the nondeterministic microscopic descrip-tion of nature soon to be proposed by the archi-tects of quantum mechanics.

Despite continued opposition to his ideas,Boltzmann’s career flourished. In Vienna, his lec-tures on the philosophy of science became so pop-ular it was necessary to move them to the biggestlecture hall available; his fame even reached thepalace of Franz Josef and earned him an invitationto visit. In 1904, he traveled to the United States.He lectured at the World’s Fair in Saint Louis andvisited Stanford and Berkeley, continuing todefend his belief in atomic structure. Sadly, hefailed to realize that the new discoveries concern-ing radiation that he learned about on this visitwere about to prove his theories correct.

Ludwig Boltzmann committed suicide, hang-ing himself while his wife and daughter wereswimming, at Duino, near Trieste, on September5, 1906. A short time later, the discovery ofBrownian motion led to a near-universal accep-tance of his kinetic and statistical theories.

See also EINSTEIN, ALBERT.

Further ReadingCercignani, Carlo. Ludwig Boltzmann: The Man Who

Trusted Atoms. Oxford: Oxford University Press,1998.

Lindley, David. Boltzmann’s Atom: The Great DebateThat Launched a Revolution in Physics. New York:Free Press, 2000.

� Born, Max(1882–1970)German/BritishTheoretical Physicist, QuantumTheorist, Solid State Physicist

Max Born is best known for his distinctive con-tributions to the revolution in subatomic physics

of the 1920s. It was Born who, in 1924, anointedthe new physics quantum mechanics. The follow-ing year, along with his students, WERNER

HEISENBERG and Pascual Jordan, he formulatedmatrix mechanics, the first mathematical systemcapable of explaining the behavior of electronsin an atom. Most importantly, his statisticalinterpretation of subatomic events, which sug-gests that a fundamental randomness is inherentin the laws of nature, became the defining fea-ture of the Copenhagen interpretation of whatthe equations of quantum mechanics actually“mean.”

He was born on December 11, 1882, in Bres-lau, Germany, now Wroclaw, Poland, into awealthy Jewish family. His mother, Margarete,née Kauffmann, was part of a family of Silesianindustrialists. Gustav, his father, was a professor ofanatomy at the University of Breslau, where Maxwould enroll after completing his studies at KonigWilhelm’s Gymnasium. Born’s studies would takehim from Breslau to Heidelberg, Zurich, and,finally, the University of Göttingen, where, in1907, he was awarded a doctorate in physics andastronomy. He married Hedwig Ehrenberg in1913 and had three children with her.

When World War I broke out, Born joinedthe German army and was assigned to a researchunit in which he worked on the problem of soundranging. He also found time to study the theoryof crystals and publish his first book, Dynamics ofCrystal Lattices. After briefly holding academicpositions in Göttingen and Berlin, he wasappointed professor of physics at Frankfurt-am-Main in 1919. While there, he applied his workon the lattice energies of crystals (the energygiven out when gaseous ions join together toform a solid crystal lattice) to the formation ofalkali metal chlorides. By calculating the ener-gies involved in lattice formation, from whichthe properties of crystals may be derived, he madea seminal contribution to solid state physics.

In 1921, Born moved from Frankfurt to amore prestigious post in Göttingen and, during

42 Born, Max

his 12 years there, made it an internationalcenter for theoretical physics rivaled only byNIELS HENRIK DAVID BOHR’s Institute for Theo-retical Physics in Copenhagen. It was in Göt-tingen, with Heisenberg as his assistant, thatBorn did his most important work, on the elec-tronic structure of atoms. In 1913, Bohr hadpublished his theory of the atom, based on MAX

ERNEST LUDWIG PLANCK’s 1900 theory thatenergy is emitted in discrete packets or quanta.In Bohr’s model, electrons rotating around thenucleus of an atom are confined to a certainnumber of stable orbits, emitting quanta ofenergy only when jumping to a lower orbit. Themodel proved highly productive, explainingmany of the spectral lines for hydrogen andhelium, but it had an ad hoc quality, which leftphysicists wondering about the guiding princi-ple behind it. In 1925, Heisenberg returned toGöttingen after a year working with Bohr inCopenhagen and offered an approach to theproblem. Together with Born and Jordan, hedeveloped a mathematical system that explainedthe features of the atom. Their famous “three-man paper,” published that year, introducedmatrix mechanics, the first precise mathemati-cal description of the workings of the atom. Bymathematical treatment of values withinmatrices or arrays, the frequencies of the linesin the hydrogen spectrum were obtained.

The next year, however, matrix mechanicswas challenged by ERWIN SCHRÖDINGER’s wavefunction, a mathematical expression for LOUIS-VICTOR-PIERRE, PRINCE DE BROGLIE’s, 1923 dis-covery that electrons do not occupy orbits butexist in standing waves around the nucleus.Schrödinger’s approach, which he called wavemechanics, with its more familiar concepts andequations and its ability to allow visualization ofthe atom, rapidly became the theory of choice.Born made an important contribution to wavemechanics with his Born approximation method,a mathematical technique for solving the Schröd-inger equation (i.e., computing the behavior of

subatomic particles) that continues to be used inhigh-energy physics.

However, his most fundamental work grewfrom the attempt to answer the “big question”posed by quantum mechanics: what is the phys-ical reality described by the wave function?Born came up with the disturbing, revolution-ary notion that the Schrödinger wave equationdescribed not a matter wave existing in spaceand time, but a wave of probabilities. Accord-ing to this statistical interpretation, whenphysicists measure the location of an electron,the probability of finding it in each regiondepends on the magnitude of its wave functionthere. The traditional, deterministic view ofnature posited that someone shooting at a tar-get can, in principle, aim the shot so that it willbe certain to hit the target in the middle. InBorn’s view, that kind of certainty is no longerpossible; we can only predict the probabilitiesthat certain events will occur. On the basis of alarge number of shots, we can determine thatthe average point of impact will be in the mid-dle of the target. Whereas the implications ofthese quantum statistic mechanical effects maybe trivial on the macroscopic level, they arefundamental for subatomic phenomena, sug-gesting a randomness inherent in the very lawsof nature. Born’s statistical interpretation ofthe wave function quickly became a corner-stone of the Copenhagen interpretation: alongwith the work of Jordan in Göttingen and PAUL

ADRIEN MAURICE DIRAC in Cambridge, Eng-land, on the unified equations known as trans-formation theory, it appeared to complete themathematical foundations of the new quantummechanics.

Born’s fruitful years in Göttingen came to anunnatural end, however, when he was forced toflee Nazi Germany in 1933. He continued hiscareer in England, first as a lecturer at Cam-bridge and then at Edinburgh University, where,in 1936, he was appointed professor of naturalphilosophy. He became a British citizen in 1939

Born, Max 43

and returned to Germany when he retired in1953. The following year he was awarded theNobel Prize in physics for his contributions toquantum mechanics.

When he died in Göttingen on January 5,1970, he was the recipient of numerous presti-gious awards and the author of more than 360publications, including textbooks and mono-graphs for physics students and experts, as well assome popular science books.

Max Born’s legacy to modern physics is adynamic one, which continues to be debated.Schrödinger himself was never comfortable withBorn’s interpretation of his equation; he devisedhis famous Cat Paradox, a thought experimentwhose outcome leaves the cat in question bothdead and alive to show the absurdity of applying

probability to the macroscopic world. And no stu-dent of physics is unfamiliar with Einstein’s objec-tion: “I cannot believe that God plays dice.” EvenBorn, who declared in his autobiography that“theoretical physics is actual philosophy,” specu-lated that, despite the predictive success ofquantum mechanics, “something,” although inac-cessible to the observer, may yet exist beneath thelaws of probability:

If God made the world a perfect mecha-nism, He has at least conceded so muchto our imperfect intellect that in order topredict little parts of it, we need notsolve innumerable differential equations,but can use dice with fair success.

The inability of the Copenhagen interpreta-tion to answer the question of “what liesbeneath” left the field open to successive gener-ations of physicists to probe this mystery, whichlies at the heart of quantum mechanics.

Further ReadingBorn, Max. My Life. New York: Scribner’s, 1978.Born, Max, R. J. Blin-Stoyle, and J. M. Radcliffe.

Atomic Physics. New York: Dover, 1989.Born, Max, Gunther Leibfried, and Walter Biem. Ein-

stein’s Theory of Relativity. New York: Dover,1989.

Pagels, Heinz R. Cosmic Code: Quantum Physics as theLaw of Nature. New York: Simon & Schuster,1982.

� Bridgman, Percy Williams(1882–1961)AmericanExperimentalist (High-Temperature andHigh-Pressure Physics), Philosopher ofScience

Percy Williams Bridgman did pioneering workon the behavior of materials at high tempera-

44 Bridgman, Percy Williams

Max Born is best known for his statistical interpretationof subatomic events, which suggests that a fundamentalrandomness is built into the laws of nature. (AIP EmilioSegrè Visual Archives, Gift of Jost Lemmerich)

ture and high pressure, for which he won the1946 Nobel Prize in physics. He is, however,most famous for his work in the philosophy ofmodern physics as founder of the school of oper-ationalism, an approach that stresses the pri-macy of the physical operations of measurementin physical research.

He was born on April 21, 1882, in Cam-bridge, Massachusetts, the son of a journalistwho wrote on social and political issues. Hereceived his early education at public schools inthe nearby town of Newton. In 1900, he enteredHarvard University, and four years later hereceived his bachelor’s degree. In 1908, hereceived a Ph.D. from Harvard and joined itsfaculty. Harvard would remain his academichome for the rest of his life, making him aninstructor in 1910, assistant professor in 1913,and full professor in 1919. In 1912, he marriedOlive Ware, with whom he had a daughter, Jane,and a son, Robert.

Working at Harvard’s Jefferson ResearchLaboratory, Bridgman quickly demonstrated hisunusual skill in operating machine tools andmanipulating glass. He began doing experi-ments involving static high-pressure effects onmaterials at pressures of 6500 atmospheres (oneatmosphere = 14.7 lb/in). In these experimentsBridgman had to invent his own equipment.This work led to his invention of a type of gas-ket seal in which the pressure in the gasketalways exceeds that in the pressurized fluidwithin the gasket. This resulted in a gasketwith a self-sealing closure property that madehigher pressures possible. Using this new devicein an experimental apparatus made of newtypes of steels and metals with heat-resistantcompounds, he was able to increase the pres-sure in his experiments to 400,000 atmo-spheres. At these extraordinarily high pressureshe measured the compressibility of liquids andthe physical properties of solids, such as electri-cal resistance. He discovered new high-pressureforms of ice and new phenomena such as the

rearrangement of electrons in cesium at a cer-tain transition pressure.

Bridgman also did pioneering work indevising a technique to synthesize diamonds,which he later used to synthesize many moreminerals. Because the pressures and tempera-tures he achieved in his experiments simulatedthose deep beneath the ground, his discoveriesyielded insights into the physical processes thattake place within the Earth. This led to thedevelopment of a new school of geology basedon his experimental work at high temperatureand high pressure.

Bridgman was a loner, wholly dedicated toresearch, who disliked lecturing. His teachingexperience, however, made him aware of theambiguities of scientific language and causedhim to shift his attention to the philosophy ofscience. In 1927, he became Hollis Professor ofMathematics and Philosophy at Harvard andpublished his most influential work, The Logicof Modern Physics, in which he developed hisphilosophy of operationalism. His fundamentalargument was that in order to be meaningful,physical concepts must be defined in terms ofthe physical operations involved in their mea-surement:

The concept of length involves as muchas and nothing more than the set ofoperations by which length is deter-mined. . . . [T]he concept is synonymouswith a corresponding set of operations.

Bridgman was an influential and prolificwriter, publishing more than 260 papers. In1931, he published Physics of High Pressure,which became a classic in the field. His otherbooks include The Nature of Physical Theory,1936; The Nature of Thermodynamics, 1941, andReflections of a Physicist, 1955.

From 1950 to 1954, Bridgman was HigginsProfessor at Harvard. He then retired andbecame professor emeritus. On August 10, 1961,

Bridgman, Percy Williams 45

dying of cancer, he killed himself at his home inRandolph, New Hampshire.

A bold intelligence, Bridgman is famous forhis aphorism “There is no adequate defense,except stupidity, against the impact of a newidea.” For all his attempts to define the nature ofphysical discovery systematically, he never lostsight of its essentially unpredictable nature:

In his attack on his specific problem [theworking scientist] suffers no inhibitionsof precedent or authority, but is com-pletely free to adopt any course that hisingenuity is capable of suggesting tohim. No one standing on the outsidecan predict what the individual scientistwill do or what method he will follow. Inshort, science is what scientists do, andthere are as many scientific methods asthere are individual scientists.

Further ReadingBridgman, Percy Williams. The Logic of Modern

Physics. New York: Macmillan, 1961.

� Broglie, Louis-Victor-Pierre-Raymond, prince de(1892–1987)FrenchTheoretical Physicist, QuantumTheorist

Louis-Victor-Pierre, prince de Broglie, made hisgroundbreaking contribution to modern physicswhile still a graduate student at the Sorbonne(University of Paris) in 1924. In 1905, ALBERT

EINSTEIN had shown that light, long understoodby physicists to be a wave, can behave as a parti-cle under certain conditions. Building on thiswork, the young Broglie demonstrated that inaddition to light, atomic particles have a dualnature. This wave–particle duality was acceptedas a fundamental principle governing the struc-

ture of the atom and was subsequently used byERWIN SCHRÖDINGER to develop the wave equa-tion for the quantum mechanics of atomic struc-ture. De Broglie’s discovery earned him the 1929Nobel Prize in physics.

The man whose full name and title wasLouis-Victor-Pierre Raymond, duc de Broglie wasborn on August 15, 1892, in Dieppe, France, thesecond son of an ancient aristocratic family. Atthe age of 18 he entered the Sorbonne, intendingto earn a degree that would help prepare him for adiplomatic career. But the lure of physics proveddecisive; as did his older brother, Maurice, whowas a pioneer in the study of X-ray spectra, deBroglie broke family tradition and earned a degreein science, in 1913. His studies were interruptedby World War I. He was fortunate, however, in hisassignment to a radio unit stationed at the EiffelTower, where he had spare time to devote to thestudy of technical problems. At the end of the warhe resumed his studies at the Sorbonne, specializ-ing in theoretical physics. He took a special inter-est in the study of problems involving quanta, theterm introduced by the German physicist MAX

ERNEST LUDWIG PLANCK in 1900, when he dis-covered that certain experimental results could beunderstood only if energy were emitted andabsorbed in discrete packets or quanta. This was arevolutionary vision, challenging the classicalNewtonian view that energy could have anyvalue and was transmitted in a continuous stream.ALBERT EINSTEIN was among the first physicists toaccept this paradigm-shattering hypothesis. In1905, he used the idea of quanta to explain thephotoelectric effect. Light, he said, was composednot only of waves, but also of particles, which henamed photons.

Broglie’s breakthrough into the nature ofmatter built on Planck’s and Einstein’s work. In1923, he published a brief note in the journalComptes Rendus, containing an idea that was torevolutionize our understanding of the physicalworld at the most fundamental level. He beganwith the assumption that a particle of mass m is

46 Broglie, Louis-Victor-Pierre-Raymond, prince de

always associated with an internal clock tickingwith frequency ν. He noted that relativity the-ory predicts that when such a particle is set inmotion, its total energy increases, tending toinfinity as the speed of light is approached. Sim-ilarly, the frequency of the clock’s ticking slowsdown. However, in quantum mechanics, adecrease in frequency is related to a decrease inthe energy of the particle. This apparent contra-diction between the tendency of the relativisticenergy to increase and that of the quantumenergy to decrease troubled de Broglie.

A year later, in 1924, Broglie published theresolution of this apparent contradiction in thefirst chapter of his doctoral thesis, by postulatingthat a wave always accompanies the motion of aparticle. He argued that the wave aspect associ-ated with quantum mechanical particles is aninherently relativistic phenomenon. Using theorbits of the electron in the quantum model of thehydrogen atom developed by NIELS HENRIK DAVID

BOHR as his example, he suggested that relativis-tic effects are not inconsequential in determiningthe electronic properties of the hydrogen atom,even though the speed of the orbiting electron issignificantly less than the speed of light.

In 1927, experimental evidence for deBroglie’s theory was discovered independently byresearchers in the United States and GreatBritain. They performed experiments that pro-duced electron wave diffraction patterns similarto the diffraction patterns associated with lightwaves, thus showing that particles can producean effect that had until then been exclusive toelectromagnetic waves such as light and X rays.Such waves are known as matter waves. For par-ticles to be described as waves they must satisfy apartial differential equation known as a waveequation. De Broglie’s attempt to develop such awave equation in 1926 proved unsatisfactory. Itfell to Schrödinger to succeed where de Brogliehad failed; that same year, he unveiled his famousSchrödinger equation, a wave equation that pre-dicted known experimental results on atoms.

After receiving his doctorate, de Brogliestayed on at the Sorbonne until 1928. In 1929,the Swedish Academy of Sciences conferred onhim the Nobel Prize in physics for his discoveryof the wave nature of electrons. He moved tothe Henri Poincaré Institute in Paris in 1932 asprofessor of theoretical physics and remainedthere until 1962. In 1956, he received the goldmedal of the French National ScientificResearch Center. During this period he was alsoa senior adviser on the development of atomicenergy in France.

From 1930 to 1950, de Broglie turned hisattention to the extensions of wave mechanics:PAUL ADRIEN MAURICE DIRAC’s electron theory,the new quantum theory of light, the generaltheory of spin particles, and applications of wavemechanics to nuclear physics. Not until 1951did he return to the study of the wave equationhe had developed in 1926, which attempted togive a causal interpretation to wave mechanicsin terms of classical space and time. Throughouthis life, de Broglie was concerned with the fun-damental question of whether the statisticalresults of physics are all that there is to be knownor whether there is an underlying, completelydetermined reality that experimental techniquesare as yet inadequate to discern. Early in hiscareer, he was inclined to accept the almost uni-versal adherence of physicists to the purely prob-abilistic interpretation of MAX BORN, Bohr, andWERNER HEISENBERG. Like Einstein, however,he was constitutionally unable to live with it. Inhis later years he expressed the belief that “thestatistical theories hide a completely determinedand ascertainable reality behind variables,which elude our experimental techniques.”

De Broglie’s discovery of the wave–particleduality enabled physicists to view Einstein’s con-viction that matter and energy can be convertedinto one another as fundamental to the structureof nature. The study of matter waves led notonly to a much deeper understanding of thenature of the atom, but also to explanations of

Broglie, Louis-Victor-Pierre-Raymond, prince de 47

chemical bonds and to the practical applicationof electron waves in electron microscopes.

See also DAVISSON, CLINTON; JOSEPH; THOM-SON, JOSEPH JOHN (J. J.).

Further ReadingAchinstein, Peter. Particles and Waves: Historical

Essays in the Philosophy of Science. Oxford: OxfordUniversity Press, 1994.

Van der Merwe, Alwyn. Waves and Particles in Lightand Matter. Boston: Kluwer Academic, 1994.

Wheaton, Bruce R. The Tiger and the Shark: EmpiricalRoots of Wave–Particle Dualism. Cambridge:Cambridge University Press, 1990.

48 Broglie, Louis-Victor-Pierre-Raymond, prince de

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� Carnot, Nicolas Léonard Sadi(1796–1832)FrenchTheoretical Physicist (Thermodynamics)

Sadi Carnot was a pioneer in the field of thermo-dynamics, whose search for more efficient steamengines led him to fundamental discoveries aboutthe relationship between work and heat.

He was born in Paris on June 1, 1796, theeldest son of an illustrious, erudite family, andnamed after the medieval Persian poet andphilosopher Sa’di of Shiraz. This was a time ofpolitical upheaval, and Lazare, his father, was atthe center of events as a member of the Direc-tory, the French revolutionary government. Dur-ing Sadi’s early childhood Lazare’s politicalcareer underwent dramatic reversals, as he wasforced into exile and later commanded to returnand become Napoleon’s minister of war. Whenshortly afterward he was made to resign, he tookcharge of his son’s education, giving him a solidgrounding in mathematics and science, music,and languages. The young Sadi attended theÉcole Polytechnique in Paris, whose facultyboasted such scientific luminaries as SiméonDenis Poisson, ANDRÉ-MARIE AMPÈRE, andFrançois Arago, who exposed him to the newestideas in physics and chemistry, between 1812and 1814. By this time, Napoleon’s armies were

in retreat, foreign armies had entered France,and Sadi and his classmates engaged in skir-mishes on the outskirts of Paris in an unsuccess-ful attempt to turn back the invaders. In 1815,Lazare fled to Germany, where he would remainfor the rest of his life, while his son remained inFrance, preparing himself for a career as a mili-tary engineer at the École Genie in Metz.

When he graduated in 1816, Carnot wasfirst assigned to inspect fortifications. In 1819,he managed to transfer to the office of the gen-eral staff in Paris, and soon afterward he retiredon half-pay, in order to pursue his varied inter-ests, which included industrial development,mathematics, and the fine arts. As he becameincreasingly fascinated with the design of steamengines, he was led to explore basic questionsabout the nature and dynamics of heat. Carnotembarked on his most fertile period, which cul-minated, in 1824, in the publication of his clas-sic work, Reflections on the Motive Power of Heat.Even in this most fundamental scientific inquiry,patriotic considerations played a role. It was anEnglishman, James Watt, who had invented thesteam engine, and England continued to outdis-tance France in its development of this versatile,if inefficient (it had an efficiency of only 6 per-cent) workhorse. Carnot’s desire to create theoptimal steam engine design was at least partlymotivated by his belief that France’s failure to

make adequate use of steam had contributed toits political downfall. When he presented thiswork formally to the Académie des Sciences, itwas given an enthusiastic reception but wasignored until a decade later, in 1834, whenEmile Clapeyron, a railroad engineer, quotedand extended his results.

In Reflections Carnot strove to determinewhether there was a fixed limit to the work asteam engine could produce. He was in search ofa theory applicable to all kinds of heat engines.Carnot noted that a steam engine producesmotive power when heat flow “falls” from thehigher temperature of the boiler to the lowertemperature of the condenser, analogously to theway water, when falling, provides power in awater wheel. On this basis, he developed anequation, now known as Carnot’s theorem,which showed that the maximal amount of workan engine using a hot gas can produce dependsonly on the absolute temperature difference ofthe gas as it flows through the engine from theboiler to the condenser. He was also able to showthat the maximal amount of work obtained isindependent of (1) whether the temperaturedrops rapidly or slowly or in a number of stagesand (2) the nature of the gas used in the engine.Carnot’s work established a scientific basis forsteam engine design. His experimental data ledhim to recommend that steam be used over alarge temperature interval and with minimallosses due to conduction or friction.

Carnot arrived at his theorem by consider-ing the case of an ideal heat engine engaged in areversible cyclic process now known as theCarnot cycle. For a cyclic process to be com-pletely reversible (an idealization), no work isdone in overcoming friction at any stage and noheat is lost to the surroundings. In the Carnotcycle a quantity of gas undergoes a combinationof two basic processes that produce work andconsume heat: (1) an isothermal process thattakes place at a constant temperature and (2) anadiabatic process in which heat can neither

enter nor leave the system, so any work donechanges the internal energy and hence the tem-perature of the system. In the Carnot cycle anideal gas (i.e., a gas whose internal energydepends only on the absolute temperature) isfirst allowed to expand isothermally to do work,absorbing heat in the process, and then adiabat-ically expanded again without transfer of heatbut with a temperature drop. The gas is thencompressed isothermally, heat being given off,and finally it is returned to its original conditionby another adiabatic compression, accompaniedby a rise in temperature.

In terms of this series of operations Carnotwas able to show that even an ideal engine can-not convert into mechanical energy all the heatsupplied to it since some of the heat energy mustbe expelled in the process. Hence, Carnot’s lawstates that no real, physical engine can be moreefficient than an ideal reversible engine workingwithin the same range of temperature.

During the time that he developed his the-orem, Carnot still believed in the caloric theoryof heat, which held that heat was a form of fluid.However, unpublished notes, discovered in1878, showed that Carnot was beginning tobelieve heat was energy that could change intowork. He had calculated a conversion constantfor heat and work, indicating that he believedthat the total quantity of energy in the universewas constant. In essence, he had thought outthe basics of the first law of thermodynamics,conservation of energy. He proposed experi-ments for observing the temperature effects offriction in fluids, some of which were identicalwith those performed by JAMES PRESCOTT

JOULE 20 years later.Sadly, Carnot had little time to continue

his research; he died suddenly in a cholera epi-demic in Paris on August 24, 1832, at the age of36. According to the custom of the times, hispersonal belongings, including most of hisnotes, were burned. He would be largely forgot-ten until LORD KELVIN (WILLIAM THOMSON)

50 Carnot, Nicolas Léonard Sadi

confirmed his conclusions and published themin his Account of Carnot’s Theorem in 1849.Carnot’s work formed the basis for Kelvin’s andRUDOLF JULIUS EMMANUEL CLAUSIUS’s deriva-tions of the second law of thermodynamics, orentropy. In his short but brilliant career Carnotmade seminal contributions to both pure andapplied physics, laying the foundations onwhich the modern science of thermodynamicswould be built.

Further ReadingCarnot, Sadi. Reflections on the Motive Power of Heat.

R. H. Thurston, ed. Translation of 1897 original.New York: John Wiley, 1990.

Van Ness, H. S. Understanding Thermodynamics. NewYork: Dover, 1983.

� Cavendish, Henry(1731–1810)BritishExperimentalist (Gravitation,Electromagnetism), Physical Chemist

Henry Cavendish devised an ingenious methodfor determining the gravitational constant,which allowed him to make the first accuratemeasurements of the mass and density of theEarth. He did pioneering work in electricity andwas the first to recognize hydrogen as a distinctsubstance and to show that water is composed ofhydrogen and oxygen. Because of his exactingstandards and refusal to make public any resultsthat failed to meet them, Cavendish publishedvery little of his prodigious output. For this rea-son, his influence on subsequent researchers wasfar less than it might have been.

He was born in Nice, France, where hismother had traveled to improve her health, onOctober 10, 1731. Descended from the dukes ofDevonshire and Kent, he was the first son ofLord Charles Cavendish, a well-known experi-mental scientist. His mother died when he was

only two, after giving birth to his brother, Fred-erick. After receiving his early education athome, Cavendish entered the Hackney Semi-nary at age 11. In 1749, he began his studies atPeterhouse College, Cambridge University; heleft four years later without a degree, a commonenough practice in his day. He took the custom-ary “grand tour” of Europe with his brotherbefore settling down in the family house inSoho, London, with his father.

Encouraged by his father to pursue scientificresearch, Cavendish became a vital member ofthe scientific community and was elected to theRoyal Society in 1760. Despite his immense,inherited wealth, he lived simply and chose tosocialize only with other scientists. He appearedto be terrified of women and instructed hisfemale servants to stay out of sight if theywanted to keep their jobs. His long bachelor lifewould be devoted wholly to science. In 1783, hisfather died and left him an inheritance thatmade him one of the wealthiest men in Europe.He then moved to a villa in Clapham Common,where he established a well-equipped laboratoryand library. Apart from such expenses, however,he maintained his frugal way of life, spendingnothing on himself and neglecting his appear-ance.

In 1776, Cavendish published his first paper,which demonstrated the existence of hydrogen,a discovery that earned him the Royal Society’sCopley Medal. He had arrived at his discoveryby using a quantitative approach, which charac-terized most of his research. By calculating thedensities of hydrogen gas and ordinary air, heshowed that they are entirely different sub-stances.

For the rest of his life, however, he publishedrarely. His most significant publications were atheoretical study of electricity (1771), a demon-stration of the synthesis of water (1784), and thedetermination of the gravitational constant(1798). In his 1771 paper on the nature of elec-tricity, he assumed that electricity was an elec-

Cavendish, Henry 51

tric fluid. This was the beginning of a decade ofwork on the subject, in which he strove to donothing less than explain all electrical phenom-ena and produce a sequel to SIR ISAAC NEW-TON’s great work, The Principia. Cavendish’saccomplishments were substantial: the discoverythat electrical fields obey the inverse square lawas well as important work on conductivity, inwhich he compared the electrical conductivitiesof equivalent solutions of electrolytes and for-mulated a variant of GEORG SIMON OHM’s law.His ideas on electricity predated those ofCHARLES AUGUSTIN COULOMB and MICHAEL

FARADAY, although his experiments would notbe known until a century later, when JAMES

CLERK MAXWELL published them. HadCavendish published them, he doubtless wouldhave accelerated progress in that field.

In 1798, he announced that he had mea-sured Newton’s gravitational constant, the con-stant of proportionality in the equationexpressing Newton’s law of universal gravita-tion. Since this law contained two unknowns—the gravitational constant and the mass of theEarth—determining one would determine theother. In what has become known as theCavendish experiment he used an apparatusconsisting of a delicate suspended rod with twosmall lead spheres attached to each end. Heplaced two large immobile spheres in a line at anangle to the rod. Because of the gravitationalattraction of the large spheres, the small spherestwisted the rod toward them. By observing theperiod of oscillation set up in the rod, Cavendishdetermined the gravitational constant and con-sequently was able to measure the density of theEarth (about five and one-half times that ofwater) and its mass (6 × 1024 kg). So sensitivewas his apparatus, no one was able to producemore accurate measurements for over a century.

Cavendish died alone in his London homeon February 24, 1810, at the age of 79, afterannouncing to his valet, “Mind what I say. I amgoing to die,” and giving him precise instruc-

tions on how to deal with the event. Only afterhis death did the cornucopia of scientificmanuscripts he left behind reveal the immensescope of the research he had done over a span of60 years and his stature as one of the greatest of18th-century physicists. The illustrious CavendishLaboratory at Cambridge University was namedin his honor.

Further ReadingJungnickel, Christa, and Russell K. McCormach, eds.

Cavendish: The Experimental Life. Bucknell, Pa.:Bucknell University Press, 1999.

Maxwell, James Clerk, ed. The Electrical Researches ofthe Honourable Henry Cavendish. London: FrankCass, 1967.

McCormach, Russell K. Cavendish. Newark, Del.:American Philosophical Society, 1996.

� Chadwick, Sir James(1891–1974)BritishExperimentalist, Particle Theorist,Nuclear Physicist

Sir James Chadwick was a British experimental-ist who won the 1935 Nobel Prize in physics forhis discovery, three years earlier, of the neutron,a particle with no charge made up of a protonand an electron. This discovery, which has beenhailed as the beginning of nuclear physics, leddirectly to nuclear fission and the developmentof the atomic bomb.

Born in Cheshire, England, on October 20,1891, James Chadwick was the son of JohnJoseph Chadwick and Anne Mary Knowles. Hereceived his secondary education in Manchesterand entered Manchester University in 1908.Chadwick is said to have intended to major inmathematics, but when he accidentally enteredthe line of registering physics majors was too shyto admit the error. On receiving his degree inphysics in 1911, he continued at Manchester,

52 Chadwick, Sir James

doing research with ERNEST RUTHERFORD onthe emission of gamma rays from radioactivematerials. Intent on gaining more research expe-rience, he left for Berlin in 1913, to work withHANS WILHELM GEIGER. During this apprentice-ship, he became the first to demonstrate thatbeta particles (particles emitted in a type ofradioactive decay known as beta decay) possess arange of energies up to a characteristic maximalvalue of the nucleus. Chadwick soon found him-self a hostage of World War I; considered anenemy alien, he was kept at a stable, which hadbeen transformed into an internment camp, forthe duration of the war. While there he some-how managed to conduct research on the ioniza-tion present during the oxidation of phosphorusand the photochemical reaction between chlo-rine and carbon monoxide.

After his release in 1919, Chadwick ac-cepted Rutherford’s invitation to join him at theCavendish Laboratory in Cambridge, where hewould remain until 1935. While in Liverpool, hemet and married, in 1925, Aileen Stewart-Brown and had twin daughters with her. Thatyear Rutherford had produced the first artificialnuclear transformation: by bombarding nitrogenwith alpha particles (particles emitted in a typeof radioactive decay known as alpha decay) hehad produced atom disintegration. Workingtogether the two men observed the transmuta-tion of other light elements by means of alphaparticle bombardment and studied the proper-ties and structure of atomic nuclei. On the basisof this work Chadwick established the equiva-lence of atomic number and charge.

Chadwick’s most significant achievement,in the words of the Nobel Prize Committee, “bya combination of intuition, logical thought, andexperimental research [proving] the existence ofthe neutron and establishing its properties,”occurred in 1932. Rutherford had hypothesizedthe existence of a neutral particle with the sameweight as a proton as early as 1920. Lacking elec-tric charge, such particles would be difficult to

detect. Chadwick attacked the problem butmade little progress until 1930, when theresearchers Walter Bothe and Herbert Beckerdescribed an unusually penetrating type ofgamma ray (a form of electromagnetic radiationemitted by atomic nuclei) produced by bom-barding the metal beryllium with alpha particles.Because of the properties of this radiation,Chadwick guessed that it represented notgamma rays, but Rutherford’s neutral particle,made up of a proton and an electron and there-fore having a mass slightly greater than that of aproton. Since the mass of the beryllium nucleus

Chadwick, Sir James 53

Sir James Chadwick discovered the neutron, a nuclearparticle with zero electric charge. His discovery leddirectly to nuclear fission and ultimately to the atomicbomb. (AIP Emilio Segrè Visual Archives, William G.Meyers Collection)

had not yet been measured, he devised an exper-iment in which boron was bombarded withalpha particles. This bombardment producedneutrons. Chadwick confirmed that the neu-tron’s mass was slightly greater than the proton’s,on the basis of the mass of the boron nucleus andother elements and the properties involved. Theneutron provided physicists with an incompara-ble tool for investigating the atom. Since neu-trons are devoid of electric charge, they need notovercome the considerable electric forces pre-sent in the nuclei of heavy atoms and thereforeare capable of penetrating and splitting thenuclei of even the heaviest elements. Thus,Chadwick’s work with neutrons paved the wayto the fission of uranium 235 and the creation ofthe atomic bomb.

The year of his great discovery Chadwickbecame professor of physics at the University ofLiverpool, where he ordered the construction ofa cyclotron that he would use to investigate thenuclear disintegration of the light elements.When World War II began, he was one of thefirst in Great Britain to urge the possibility ofdeveloping an atomic bomb. He directed theBritish atomic bomb effort at Liverpool and in1943 moved to Los Alamos to head the Britishteam participating in the Manhattan Project.He was knighted in 1945 after his return to Liv-erpool, where he developed a research school innuclear physics. In 1948 he became Master ofGonville and Caius College at Cambridge andremained there until his retirement a decadelater. He died on July 24, 1974.

Chadwick’s discovery of the neutron sig-naled the beginning of nuclear physics andinspired ENRICO FERMI to study nuclear reac-tions produced by neutrons, leading to the dis-covery of nuclear fission.

Further ReadingBrown, Andrew P. The Neutron and the Bomb: A Biog-

raphy of Sir James Chadwick. Oxford: OxfordUniversity Press, 1997.

� Chandrasekhar, Subramanyan(1910–1995)IndianTheoretical Physicist, Astrophysicist

Subramanyan Chandrasekhar laid the basis formodern astrophysics with his theories about theevolution of stars, which led to the concept ofblack holes. He was part of the pioneering gen-eration that melded physics and astronomy intoa dynamic, unified discipline. His career illus-trates the formidable barriers faced by any physi-cist whose work represents a paradigm shift—afundamental change in the way we view physicalreality. Despite the public ridicule that greetedthe theories he began developing in the 1930s,while still a student, Chandrasekhar’s work waseventually recognized as fundamental to theunderstanding of how stars are born, live, anddie. When he died in 1995, he had been awardedthe 1983 Nobel Prize in physics for this work andwas widely hailed as an astrophysicist who hadforever changed the way we look at the universe.

The man known as Chandra to his friendsand colleagues (the name means “moon” or“luminous” in Sanskrit) was born on October 13,1910, in Lahore, in colonial India, now a part ofPakistan. His was a highly educated SouthIndian family, which would boast the only otherIndian Nobel Laureate in physics, his uncle, SIR

CHANDRASEKHARA VENKATA RAMAN. Hisfather, C. S. Ayyar, was employed by the Indianrailways, which transferred the family to Madraswhen Chandrasekhar was eight. The oldest boyin a family of three boys and five girls, he washome schooled by his parents and private tutorsuntil the age of 12. Once enrolled in a regularschool, he developed a passionate interest inmathematics. He was a precocious student, whoentered Presidency College in India at the age of15. There he met the English physicist ARNOLD

JOHANNES WILHELM SOMMERFELD, who exposedhim to the new quantum mechanics. Reading allhe could find on this revolutionary theory, he

54 Chandrasekhar, Subramanyan

came across a 1926 article, “On Dense Matter,”by R. H. Fowler, a professor at Cambridge Uni-versity, which would lead him to begin develop-ing his first original ideas and to leave India in1930, at 19, to study in England.

Fowler’s article removed a daunting road-block to scientific understanding of so-calledwhite dwarfs or collapsed stars, that is, stars near-ing the end of their lives. In the 1920s, the workof Arthur Eddington, the most eminent astro-physicist of the time, had led to a quandaryknown as the Eddington paradox. Eddingtonbelieved that as a star continued gradually tocool, by radiating heat into interstellar space, itmust gradually shrink. The star must ultimatelyturn cold and then support itself not by thermalpressure, but rather by the only other type ofpressure known in 1925: that found in solidobjects such as rocks, which is due to repulsionbetween adjacent atoms. Such “rock pressure”was possible only if the star’s matter had a den-sity like that of a rock: a few grams per cubic cen-timeter. This, however, was 10,000 times lessthan the density of white dwarf stars like SiriusB! In order to reexpand to the lesser density ofrock and thereby be able to support itself when itturned cold, a white dwarf star would have to doenormous work against its own gravity. Physi-cists knew of no energy supply inside the staradequate for such work.

Fowler resolved this paradox by replacingthe physical laws Eddington had used with thenew quantum mechanics. He ascribed the pres-sure inside Sirius B and other white dwarf, not toheat, but to a quantum mechanical phe-nomenon known as the degenerate motion ofelectrons or electron degeneracy. This degener-ate motion is a consequence of a feature of mat-ter that Newtonian physicists never dreamed of:the wave–particle duality. An electron insidethe very dense matter of a white dwarf star has ashort wavelength and accompanying highenergy, which implies rapid motion. This meansthat the electron must fly around inside its cell,

behaving as an erratic, high-speed mutant: half-particle, half-wave. Physicists say that the elec-tron is degenerate, and they call the pressurethat its erratic high-speed motion produces elec-tron degeneracy pressure. Fowler concluded thatwhen a white dwarf like Sirius B cools off, itneed not reexpand to the density of rock in orderto support itself; rather, it continues to be sup-ported quite satisfactorily by quantum degener-acy pressure at its own density of 4 million gramsper cubic centimeter.

On his long sea voyage to England, Chan-drasekhar applied the effects of ALBERT EIN-STEIN’s special relativity and the new quantummechanics to Fowler’s work. He calculated thelimiting mass for collapsing stars to becomewhite dwarfs as less than 1.44 solar masses. Thisvalue became known as the Chandrasekharlimit. If the mass of the star exceeds this limit,Chandrasekhar concluded, its gravity will over-come pressure inside the star, which will con-tinue to collapse into a very dense object,which would later become known as a blackhole. In Cambridge, Chandrasekhar refined hisdiscovery. Yet, when he presented it in 1935 ata meeting of the Royal Astronomical Society,Eddington, who had been highly supportive ofChandrasekhar’s research, criticized him indevastating terms. The older scientist’s lifework had demonstrated that all stars, regardlessof their mass, had stable configurations and, intheir final life stage, became white dwarfs.Chandrasekhar’s contention that there was alimit to the mass of a star in its old age wasanathema to him. Unfortunately, Eddington’scredibility was far greater than that of Chan-drasekhar, a young unknown and a foreigner toboot. Humiliated but still believing in his work,Chandrasekhar succeeded in having a numberof famous physicists confirm his calculations.Nonetheless, decades would pass before thephysics community would accept the Chan-drasekhar limit and make it the basis for thetheory of black holes.

Chandrasekhar, Subramanyan 55

After failing to find a position in England,where Eddington’s influence prevailed, or inIndia, where he was the victim of academicinfighting, Chandrasekhar was invited to workat the University of Chicago’s Yerkes Observa-tory in 1937. Chandrasekhar gladly acceptedbut first returned to India to marry LalithaDoraiswamy, who had been a fellow physics stu-dent at Presidency College. She would sharehis 58 years at the University of Chicago as abeloved teacher and researcher.

Eventually, the Chandrasekhar limit wasuniversally accepted, even by Eddington, withwhom he made peace, but the pain of that con-flict with his former mentor was sufficient forhim to abandon research on the black holefates of massive stars for nearly 40 years. Duringthis time he laid many of the foundations ofmodern astrophysics: the theories of stars andtheir pulsations, of galaxies, and of interstellargas clouds, to name but a few. But his enduringfascination with the fates of massive stars ledhim to build upon the efforts of a younger gen-eration of astrophysicists that, from 1964 to1975, had created the “golden age” of blackhole research. Black holes were found to bedynamic objects with enormous energies,whose gravitational and other properties,according to general relativity, could be pre-dicted from just three numbers: the hole’s mass,its rate of spin, and its electric charge. Only afew of these properties were known in 1975,when Chandrasekhar took up the exhilaratingchallenge of computing all the remaining ones,a task to which his formidable mathematicalskills proved to be equal. Eight years later, atage 73, he completed his task and publishedThe Mathematical Theory of Black Holes—ATreatise, which will be a mathematical hand-book for black hole researchers for decades tocome, enabling them to extract methods forsolving black hole problems in general. Thatsame year Chandrasekhar was honored for “histheoretical studies of the physical processes of

importance to the structure and evolution ofthe stars” by the Nobel Prize in physics.

Four years after his death of a heart attackin 1995, at the age of 84, the National Aero-nautics and Space Administration’s (NASA’s)Advanced X-Ray Astrophysics Facility (AXAF),which was launched and deployed in July1999 by the space shuttle Columbia, wasrenamed the Chandra X-Ray Observatory in hishonor. Referred to by astrophysicists simply as“Chandra,” it combines high resolution, a largecollecting area, and sensitivity to higher energyX rays, to study extremely faint sources, some-times strongly absorbed, in crowded fields.

See also BROGLIE, LOUIS-VICTOR-PIERRE,PRINCE DE; WHEELER, JOHN ARCHIBALD.

Further ReadingChandrasekhar, S. An Introduction to the Study of Stel-

lar Structure. New York, Dover, 1989.Srinivasan, G. ed. Chandrasekhar: The Man behind the

Legend—Chandra Remembered. Chicago: Uni-versity of Chicago Press, 2000.

Thorne, Kip S. “The Mystery of the White Dwarfs”and “The Golden Age,” in Black Holes and TimeWarps: Einstein’s Outrageous Legacy. New Yorkand London: W. W. Norton, 1994, pp. 140–163and pp. 258–299.

Wali, Kamewashar C. Chandra: A Biography of S.Chandrasekhar. Chicago: University of ChicagoPress, 1992.

———, ed. From White Dwarfs to Black Holes: TheLegacy of S. Chandrasekhar. Singapore: WorldScientific, 2000.

� Cherenkov, Pavel Alekseyevich(1904–1990)RussianExperimentalist, Particle Physicist

Pavel Alekseyevich Cherenkov discovered whatcame to be known as the Cherenkov effect orCherenkov radiation, associated with the char-

56 Cherenkov, Pavel Alekseyevich

acteristic electromagnetic radiation that is emit-ted by charged atomic particles moving atvelocities higher than the speed of light in atransparent medium. His discovery earned him ashare of the 1958 Nobel Prize in physics andled to the invention of the Cherenkov detector,which proved to be of great importance forexperimentation in nuclear physics and the studyof cosmic rays.

Cherenkov was born on July 18, 1904, inthe Voronezh region in the northern part of theRussian Empire. His parents, Aleksey and MariaCherenkov, were peasants. After a youth markedby war and revolution, he studied physics andmathematics at Voronezh University and gradu-ated in 1928. Two years later, he was appointed asenior scientist at the renowned Lebedev Insti-tute of Physics in Moscow, in what had becomethe Soviet Union. That year, he married MaryaPutintseva, the daughter of a Russian literatureprofessor, with whom he would have two chil-dren, a son, Aleksey, and a daughter, Elena.

In 1934, the eminent physicist Sergey Vav-ilov assigned as his thesis work the study of whathappens when the radiation from a radium sourcepenetrates into and is absorbed in different fluids.Others had done this before Cherenkov and hadobserved what he observed: the emission of bluelight from a bottle of water subjected to radioac-tive bombardment. In the past, however, physi-cists who had seen the bluish glow thought it wasa manifestation of fluorescence (i.e., the absorp-tion of energy by atoms, followed by a short-livedemission of electromagnetic radiation, as the par-ticles move to lower energy states).

Cherenkov, however, was not persuadedthat what he was looking at was fluorescence. Tobegin with, using experiments with distilledwater, he found that the radiation continuedafter the exciting source had been removed; hadhe been looking at fluorescence, the radiationwould have stopped. Investigating further, heshowed that the light was caused by fast sec-ondary electrons produced by the radiation.

Cherenkov was able to create the effect by irra-diating the liquid with the electrons alone. Hehad discovered a new phenomenon, laterdubbed the Cherenkov effect, in which acharged particle that is emitted in radioactivedecay with velocity greater than the speed oflight in the medium (which is smaller than thespeed of light in a vacuum) generates a “shockwave” of photons in the blue light range. It isoften compared to the sonic boom of a jet flyingfaster than the speed of sound.

Cherenkov published his findings in Rus-sian periodicals between 1934 and 1937.Although his papers established the generalproperties of the newly discovered radiation,they did not provide a mathematical descrip-tion of the effect. This was done by two ofCherenkov’s colleagues, Igor YevgenyevichTamm and Il’ya Milhailovich Frank, withwhom he would later share the 1958 NobelPrize in physics. Tamm and Frank’s mathemati-cally rigorous formulation explained how a fastelectron passing through a liquid could give riseto the type of radiation Cherenkov hadobserved. As does the bow wave of a ship thatmoves through the water with a velocityexceeding that of the waves, they explained, acharged particle passing through a mediumwith a velocity greater than that of the light inthe medium creates the subatomic equivalentof a “bow wave,” causing the medium to glow asthe movement of the electrons outdistances thelight. None of this contradicts ALBERT EIN-STEIN’s theory that nothing can exceed thespeed of light, since this applies only to thespeed of light in a vacuum or in empty space. Ina medium such as water or a transparent solid,the speed of light is less than in a vacuum andvaries with the wavelength.

Cherenkov radiation propagates as a conewhose opening angle depends on the particlespeed. When this cone of radiation hits a flatsurface, a characteristic circular ring of light isseen. In the 1950s, Cherenkov circular rings of

Cherenkov, Pavel Alekseyevich 57

light were photographed by Valentin Zrelovusing proton beams at the Joint Institute forNuclear Research (JINR), Dubna, near Moscow.

This work led to the development of theCherenkov detector, an instrument based on theCherenkov effect, capable of registering the pas-sage of single particles through a transparentmedium, if the particles have a velocity suffi-ciently high to exceed the speed of light in themedium. As a particle detector, the Cherenkovcounter had the advantage of suitability for useas a device for detecting fast particles and deter-mining their speeds, as well as distinguishingbetween particles of different speeds. It workedin the following fashion: for a given transparentmedium, the light associated with Cherenkovradiation is emitted only in directions inclinedat a certain angle to the direction of the parti-cles’ momentum. Thus, for a given transparentmedium, by simply measuring the angle betweenthe radiation and the path of the particles,physicists can measure the particles’ speed. Thisnew type of radiation detector became one of themost important instruments used in particleaccelerators. It has become a standard piece ofequipment in atomic research for observing theexistence and velocity of high-speed particles,including cosmic rays.

Cherenkov was eventually made a sectionleader at the Lebedev Institute and received adoctoral degree from the institute in 1940. Hewas named professor of experimental physics in1953 and taught at several institutes of higherlearning for many years. In 1959, he was put incharge of the photomeson processes laboratory.

In the latter part of his career, Cherenkovworked on cosmic rays and on the design of largeparticle accelerators. He shared in the work ofdevelopment and construction of electron accel-erators and in investigations of photonuclearand photomeson reactions. He died on January6, 1990.

Cherenkov’s insightful discovery strikinglydemonstrates how a relatively simple observa-

tion, thoroughly investigated and traced to itsfundamental dynamics, can lead to importantfindings and open up new paths to research. TheCherenkov effect played a key role in the 1955discovery of the antiproton. Cherenkov detec-tors are used in nuclear medicine and continueto be used extensively in modern high-energyparticle accelerator experiments to determinethe nature of unified particle theories and thestructure of the early universe.

See also REINES, FREDERICK; RUBBIA, CARLOS.

Further ReadingJelley, J. V. Cherenkov Radiation and Its Applications.

Oxford, N.Y.: Pergamon Press, 1958.

� Chu, Steven(1948– )AmericanExperimentalist, Atomic Physicist,Biophysicist

Steven Chu is a brilliant and versatile experi-mentalist, who was awarded the 1997 NobelPrize in physics, with Claude Cohen-Tannoudjiand William D. Phillips, for his pioneeringresearch in cooling and trapping atoms by usinglaser light.

He was born on February 29, 1948, in SaintLouis, Maryland, the middle son of Ju Chin Chu,an American-educated chemical engineer, andChing Chen Li, an economist. With China in astate of political turmoil, in 1945 the Chusdecided to start their family in the United Statesand eventually settled in Garden City, NewYork, near the Brooklyn Polytechnic Institute,where Ju Chin Chu taught. Although there wereonly two other Chinese families in the town, theChus chose to live there because of the highquality of the public schools.

As a child he found joy in building plasticmodel airplanes and warships, eventually gradu-ating to “constructing devices of unknown pur-

58 Chu, Steven

pose where the main design criterion was tomaximize the number of moving parts and over-all size.” Developing an interest in varioussports, he taught himself to play tennis by read-ing a book.

Chu describes himself as the “academicblack sheep” of the family, whose “mediocre” per-formance was no match for his older brother’s.He found relief from the tedium of memorizationin the problem solving approach of a geometrycourse and, during his senior year, in two well-taught classes in advanced placement physicsand calculus. Encouraged to experiment, he cap-italized on his years of experience in buildingdevices and constructed a physical pendulum,designed to measure gravity. Chu has remarked,“Ironically, twenty-five years later, I was todevelop a refined version of this measurement,using laser cooled atoms in an atomic fountaininterferometer.”

Rejected by the Ivy League schools, “becauseof my relatively lackluster A– average,” heattended the University of Rochester, New York.There, he was inspired by a course that used TheFeynman Lectures in Physics, which proved thedecisive factor in his choice of physics over mathas a major. When he graduated in 1970 with aB.S. in physics and an A.B. in math, his ambitionwas to become a theoretical physicist. But at theUniversity of California, Berkeley, where he pur-sued his graduate studies, he soon realized hewould be happiest as an experimentalist. Work-ing with Eugene Commins, he defined an excit-ing experimental thesis topic: the search for aparity-violating effect in atomic transitions asso-ciated with the Z0 particle, a neutral mediator ofthe weak force predicted by the electroweak the-ory, a unified theory of quantum electrodynamicsand the weak interactions developed by STEVEN

WEINBERG, ABDUS SALAM, and SHELDON LEE

GLASHOW. Although Chu and his grad studentcolleagues were eventually scooped by a group atthe Stanford Linear Collider, their observation ofparity nonconservation in atomic transitions was

nonetheless one of the earliest confirmations ofthe electroweak theory. After receiving a doctor-ate in 1976 and working for two years as a post-doctoral fellow at Berkeley, he was invited to jointhe physics faculty as an assistant professor. Fear-ful of inbreeding, however, the departmentallowed him to take a leave of absence beforestarting his own group at Berkeley. Chu saw this“as a wonderful opportunity to broaden myself.”

In 1978, he joined the staff of Bell Laborato-ries in Murray Hill, New Jersey, where he wasgiven the freedom to devote himself exclusivelyto research in an atmosphere permeated with“the joy and excitement of doing science”:

The cramped labs and office cubiclesforced us to interact with each otherand follow each other’s progress. Theanimated discussions were commonduring and after seminars and at lunchand continued on the tennis courts andat parties. The atmosphere was too elec-tric to abandon and I never returned toBerkeley.

At Bell, in 1982, Chu and Allen Mills didthe first laser spectroscopy of positronium, anatom made up of an electron and its antiparti-cle (a positron). Physicists had long been tryingto obtain a precise measurement of this mostbasic of atoms in order to test the predictions ofquantum electrodynamics. Chu and Mills mea-sured the 1s-2s energy level splitting of positro-nium to an accuracy of a few parts per billion.They went on to measure the correspondingtransition in muonium, an atom consisting of amuon and an electron.

In 1983, when he became head of the quan-tum electronics research department at AT&TBell Laboratories, Holmdel, New Jersey, Chu’sinterests had broadened considerably. Duringthis period he accidentally discovered what helater called “a counterintuitive” pulse-propaga-tion effect while using picosecond laser tech-

Chu, Steven 59

niques to examine the possibility of using exci-tons (quasi particles associated with solid statephenomena) as a means for observing metal-insulator transitions.

Then, in 1985, spurred by conversations withhis colleague Art Ashkin, Chu led his group tothe discovery of how first to cool and then to trapgaseous atoms with laser light. Since temperatureis defined by the average random speed of thegaseous atoms, cooling the atoms reduces theiraverage random speed in this gas phase. Employ-ing a method called Doppler cooling, Chu’s teamused an array of intersecting laser beams to createan effect they called “optical molasses,” in whichthe average random speed of target atoms wasreduced from about 4000 kilometers per hour toabout one kilometer per hour, as if the atoms weremoving through thick molasses. When thismethod was used, the temperature of the slowedatoms approached –273.15 °C, the absolute zeroof temperature. Chu considers the underlyingdynamics of this process “quite simple”:

When an atom absorbs a photon fromthe laser, it absorbs the momentum ofthe photon. And every time it absorbs aphoton, the velocity slows down by threecentimeters a second. It then re-radiatesthe photon with no preferred direction;what this means is if you average overmany photon absorptions, the atom con-stantly gets momentum kicks in thedirection of the laser beam. . . . [T]heatom can absorb a photon and re-radiateit in about 30 nanoseconds. So, in thecourse of one second, you can get a prettysubstantial force on the atom, somethinglike 100,000 times the force of gravity.This means that over the course of a mil-lisecond you can slow an atom to an ant’scrawl.

However, since gravity will cause atoms tofall out of the optical molasses in about one sec-

ond, Chu and his coworkers had to find a way ofactually trapping them. Once more using lasersand magnetic coils, they developed their magne-tooptical trap (MOT) by creating a force greaterthan gravity, which drew the atoms into themiddle of the trap to enable them to capture andstudy the chilled atoms. Phillips and Cohen-Tanoudji expanded Chu’s work, devising ways touse lasers to trap atoms at temperatures evencloser to absolute zero.

Atomic traps make it possible to study atomswith great accuracy and to determine their innerstructure. They allow scientists to improve theaccuracy of atomic clocks used in space naviga-tion, to construct atomic interferometers that canprecisely measure gravitational forces, and todesign atomic lasers that can be used to manipu-late electronic circuits at an extremely fine scale.In the future they may well play a key role in theconstruction of quantum computers.

After doing this major work, Chu felt theneed to “spawn scientific progeny” and left his“cozy ivory tower” at Bell to join the faculty ofStanford University in 1987. Since then he hasenjoyed working with a large number of “extraor-dinary” students on a wide range of problems. Hisgroup has demonstrated the first atomic fountainclock, which has exceeded the short-term stabil-ity of atomic clocks maintained by standards lab-oratories, and developed an atom interferometer,which has exceeded the accuracy of the mostaccurate commercial inertial sensors.

A year after his arrival, he developed theoptical tweezer method of manipulating indi-vidual deoxyribonuclei acid (DNA) molecules.On the basis of Ashkin’s demonstration thatthe atomic trap also works on tiny glass spheresembedded in water, Chu attached micrometer-sized polystyrene spheres to the ends of theDNA molecule. Using this technique of simul-taneously visualizing and manipulating singlebio molecules, his group has used single DNAmolecules to examine various problems inpolymer science. They discovered molecular

60 Chu, Steven

individualism, which unexpectedly showedthat identical molecules in the same initialstate will choose distinct pathways to a newequilibrium state.

He is currently the Theodore and FrancesGeballe Professor of Physics at Stanford Univer-sity, where he pursues a wide variety of researchinterests in experimental atomic physics, quan-tum electronics, laser physics, biophysics, andpolymer physics.

See also SCHAWLOW, ARTHUR LEONARD;TOWNES, CHARLES HARD.

Further ReadingChu, Steven. “Laser Trapping of Neutral Particles,”

Scientific American, February 1992, p. 71.Metcalf, Harold J., et al., eds. Laser Cooling. New

York: Springer-Verlag, 1999.

� Clausius, Rudolf Julius Emmanuel(1822–1888)PrussianTheoretical Physicist (Thermodynamics)

Rudolf Clausius discovered the second law ofthermodynamics, otherwise known as the law ofentropy, which states that heat cannot flowspontaneously from a cooler body to a hotterone. His espousal of the mechanical theory ofheat and his penetrating insights into the rela-tionship between heat and work created thefoundations of modern thermodynamics.

He was born in Koslin in Prussia, nowKoszalin in Poland, on January 2, 1822, the sixthson in a large family. As a boy he attended asmall local school run by his father, who was alsoa minister, before going on to the gymnasium inStettin. He attended the University of Berlin,concentrating in mathematics and physics, andreceived his degree in 1844; after graduating, hetaught advanced classes in those subjects at agymnasium. He was awarded a Ph.D. from theUniversity of Halle in 1848.

When Clausius began his research on heatand thermodynamics, the caloric theory was gen-erally accepted. It was based on two axioms: (1)heat in the universe is conserved and (2) heat ina substance is a function of the state of the sub-stance. Using JAMES PRESCOTT JOULE’s experi-mental evidence, Clausius showed that bothaxioms were false and replaced them with twolaws of thermodynamics. The first law, conserva-tion of energy, states that the total energy of asystem and its surroundings remains constant,even if it changes from one energy form toanother. This means that heat and work areequivalent, since whenever work is done by heat,an equivalent amount of heat energy is con-sumed. Clausius then went on to formulate thesecond law of thermodynamics, in an 1850 paper,published in Annalen der Physik, that establishedthe foundations of modern thermodynamics.Drawing on NICOLAS LÉONARD SADI CARNOT’sand LORD KELVIN’s (WILLIAM THOMSON) con-cept of the continuous dissipation of energy, hedeveloped the concept of entropy, which is ameasure of disorder and of the extent to whichenergy can be converted into work. The greaterthe entropy, the less energy is available for work.Clausius identified two sources of entropy: theconversion of heat to work and the transfer ofheat from high to low temperatures, which is thenormal behavior of heat and produces positiveentropy. He rejected the opposite process—thespontaneous flow of heat from low to high tem-peratures (which would produce negativeentropy)—as contrary to the normal behavior ofheat. Since the change in entropy could be onlyzero, in a reversible process, or positive, in anirreversible process, he concluded that entropyinevitably increases in the universe.

After publishing the 1850 paper that estab-lished his reputation, Clausius took a teachingposition at the Royal Artillery and EngineeringSchool in Berlin. He would stay there for fiveyears, before leaving his beloved Germany forSwitzerland, where he had been offered a double

Clausius, Rudolf Julius Emmanuel 61

post—as professor of physics at the Zurich Poly-technic and at the University of Zurich. Therehe pursued his work on the laws of thermody-namics, over the next 15 years, publishing eightmore papers, in which he refined his ideas andmathematical formulations. In his 1865 paper heelegantly defined the first and second laws as fol-lows: (1) the energy of the universe is constant;(2) the entropy of the universe tends toward amaximum. He improved the mathematical treat-ment of HERMANN LUDWIG FERDINAND VON

HELMHOLTZ’s law on the conservation of energyand jointly formulated the Clausius–Clapeyronequations, which describe the relationshipbetween pressure and temperature for matterundergoing a change of state.

While in Zurich, Clausius began to branchout in other directions as well. He studied therelationship between thermodynamics and thekinetic theory of gases, which JAMES CLERK

MAXWELL and LUDWIG BOLTZMANN had devel-oped, and made numerous contributions to thattheory. At the same time, he delved into thetheory of electrolysis, correctly proposing thatan electric current could induce the dissociationof materials.

In 1859, he married a German woman, Adel-heid Rimpan, who would bear him six children.Enjoying the stimulation of Zurich’s distinguishedscientific community, Clausius more than oncerefused positions in Germany. Not until 1867 didhe succumb to homesickness and accept a posi-tion as professor of physics at the University ofWarzburg. Two years later, he would exchangethis position for the physics chair in Bonn.

The serenity of his academic life would soonbe shattered by the outbreak of the Franco-Prus-sian War in 1870. A German patriot, Clausiuswas not one to shirk his duties. He organized avolunteer ambulance service, working side byside with his students on the major battlefields ofthe war. While carrying out his mission of mercy,which earned him an Iron Cross, Clausiusreceived a serious leg wound, which would cause

him pain for the rest of his life. During thisperiod, his wife died in childbirth, leaving himsole responsibility for their large brood. Clausiusappears to have coped bravely with these set-backs, taking up riding to strengthen his leg,raising his children warmly and conscientiously,and eventually remarrying. If he was under-standably less productive in the later half of hiscareer, he nonetheless continued to work untilhis final illness, holding his physics chair atBonn until his death on August 24, 1888. Hismany honors included the British Royal Soci-ety’s Copley Medal in 1879.

A brilliant theorist, Clausius was instrumen-tal in establishing theoretical physics as a recog-nized discipline. His seminal work led toimportant developments in thermodynamics, sta-tistical mechanics, and the kinetic theory of gases.

See also HELMHOLTZ, HERMANN LUDWIG

FERDINAND VON.

Further ReadingCardwell, D. S. L. From Watt to Clausius: The Rise of

Thermodynamics in the Early Industrial Age. Cor-nell, N.Y.: Cornell University Press, 1971.

Dugdale, J. S. Entropy and Its Physical Meaning. Lon-don: Taylor & Francis, 1996.

Von Baeyer, Hans Christian. Warmth Disperses andTime Passes: A History of Heat. New York: Mod-ern Library, 1999.

� Cockcroft, John Douglas(1897–1967)BritishExperimentalist, Nuclear Physicist

In collaboration with Ernest Walton, John Dou-glas Cockcroft built the first particle accelerator,which produced the first nuclear transformationsby means of artificially accelerated particles, in1932. For this achievement, which led to newinsights into the properties of atomic nuclei, theyshared the 1951 Nobel Prize in physics.

62 Cockcroft, John Douglas

He was born in Todmorden, Yorkshire, onMay 27, 1897, into a family that had beeninvolved in cotton manufacturing for several gen-erations. In 1914, he entered Manchester Univer-sity, planning to study mathematics, whenEngland became embroiled in World War I.Cockcroft promptly volunteered for war serviceand did not resume his studies until the end ofhostilities, in 1918. After serving as a signals offi-cer in the Royal Field Artillery, Cockcroft foundhimself drawn to the study of electrical engineer-ing; he enrolled in Manchester’s College of Tech-nology, where he earned a master’s degree intechnical science in 1922. He served a two-yearapprenticeship with an electrical company beforeenrolling at Saint John’s College, at CambridgeUniversity, where he returned to his study ofmathematics, receiving a B.A. in 1924. The fol-lowing year he married Eunice Elizabeth Crab-tree, with whom he would have four daughtersand a son.

Cockcroft’s career blossomed at Cambridgewhen he went to work at the Cavendish Labora-tory, assisting the great nuclear physicist ERNEST

RUTHERFORD, who had attracted a group of brightyoung scientists to work with him. Amongthem was the visiting Russian physicist PYOTR

LEONIDOVICH KAPITSA, who collaborated withCockcroft on the development of intense mag-netic fields and low temperatures. Cockcroft’smost important collaboration, however, would bewith Walton. By the late 1920s, Rutherford hadperformed the first artificial transformation of oneelement into another, by bombarding the nuclei ofcertain light elements with alpha particles andtracking the results in a cloud chamber. He found,however, that bombardment with alpha particleshad its limits, because large nuclei repelled themwithout disintegrating. Cockcroft’s electricalengineering expertise, unavailable to most nu-clear physicists, helped him to find a way to over-come this barrier. Working with Walton, heconstructed a voltage multiplier that built up acharge of 710,000 volts and accelerated protons

in a beam through a tube containing a high vac-uum. With this instrument they produced theirfirst artificial transformation in 1932. Beginningwith the transformation of lithium into helium,they confirmed the production of helium nucleiby observing their tracks in a cloud chamber.They went on to disintegrate other elementssuch as boron.

In 1929, Cockcroft was elected to a fellow-ship at Saint John’s College. He later served invarious capacities at Cambridge, including Jack-sonian Professor of Natural Philosophy. Whenglobal war erupted once again, in 1939, Cockcroftwent to work on the application of radar to coastand air defense problems, becoming head of theAir Defense Research and Development Estab-lishment. In 1944, he took over the constructionof the first nuclear reactor in Canada. When thewar ended he returned to England and becamethe nation’s first director of the Atomic EnergyResearch Establishment in Hartwell. He wasknighted in 1948 and in 1959 became master atChurchill College, Cambridge. From 1954 to1959, he was a scientific research member of theU. K. Atomic Energy Authority.

He received the Atoms for Peace Award in1961 and became president of the Pugwash Con-ference, a gathering of distinguished scientistsfrom around the world to express concern overnuclear developments. He died in Cambridge onSeptember 18, 1967.

The voltage multiplier invented by Cock-croft and Walton was the prototype for the moreadvanced particle accelerators, such as thecyclotron, by means of which the world of sub-atomic particles would be revealed, in ever greaterdetail, over the course of the next century.

See also VAN DE GRAAFF, ROBERT JEMISON;WILSON, CHARLES THOMSON REES.

Further ReadingWilson, Edmund J. An Introduction to Particle Acceler-

ators. Oxford: Oxford University Press, 2001.

Cockcroft, John Douglas 63

� Compton, Arthur Holly(1892–1962)AmericanExperimentalist (Electromagnetism),Particle Physicist

Arthur Holly Compton won the 1927 NobelPrize in physics for his discovery of what came tobe known as the Compton effect, a quantummechanical explanation of the phenomenon inwhich high-energy electromagnetic waves suchas X rays undergo an increase in wavelengthafter being scattered by electrons. This work,which was recognized as experimental proof thatelectromagnetic radiation is quantized, possess-ing both classical wavelike properties and parti-clelike photon properties, was a foundation ofthe new field of quantum electrodynamics. As amember of the Manhattan Project, Comptonalso played a major role in the development ofthe atomic bomb.

He was born on September 10, 1892, inWooster, Ohio, into an educated, pious family.His father was a Presbyterian minister and pro-fessor of philosophy at the College of Wooster,his mother a Mennonite, dedicated to mission-ary causes, who had been the 1939 Mother ofthe Year. While choosing a science career, likehis older brother, Karl, Arthur maintained thefamily tradition of religious dedication. Heattended the College of Wooster, where heearned a bachelor’s degree in 1913. He thenwent on to Princeton University for postgradu-ate study, earning a master’s degree in 1914 anda Ph.D. in 1916. Here he devised an elegantmethod for demonstrating the Earth’s rotation.In 1916, he married Betty Charity McCloskey,with whom he would have two sons. Then hespent a year as an instructor of physics at theUniversity of Minnesota. His next position wasas a research engineer with the WestinghouseLamp Company in Pittsburgh. In 1919, he leftfor Cambridge University, England, as aNational Research Council Fellow; there he

worked with ERNEST RUTHERFORD at theCavendish Laboratory on the properties of scat-tered gamma rays.

In these experiments he discovered thatscattering X rays on a graphite block loweredtheir energy, thereby increasing their wave-length. This phenomenon was clearly unlikethe scattering of classical waves, in which thewavelength remains the same when it bouncesoff a surface. Since the groundbreaking work ofJAMES CLERK MAXWELL, the classical wavenature of electromagnetic radiation had beenfirmly established. Then, in 1905, ALBERT EIN-STEIN announced his theory of the photoelec-tric effect: that light is simultaneously a waveand a particle he called a photon. In this con-text Compton conjectured that the X rays mustbe acting as light particles or photons, that is,transferring their energy to the graphite elec-trons with which they collide. Theoretically,Compton treated the X-ray scattering as beingdue to a collision between a quantum of theelectromagnetic field (i.e., a photon) and anelectron, the latter regarded as a free particleinitially at rest. Then, conservation of energyand momentum required the photon to transferenergy and momentum to the electron, causingthe wavelength of the photon to increase.Compton’s discovery confirmed the particlenature of the photon and placed the quantumprediction of wave–particle duality on a firmexperimental foundation. In the same set ofexperiments he also discovered the phe-nomenon of complete reflection of X rays andtheir total polarization, which led to a moreaccurate determination of the number of elec-trons in an atom.

In 1923, he moved to the University ofChicago as professor of physics, and four yearslater he shared the 1927 Nobel Prize withCHARLES THOMSOM REES WILSON, the discov-erer of the cloud chamber.

In the 1930s, the emphasis of his researchshifted to cosmic rays, whose nature physicists

64 Compton, Arthur Holly

were then debating: are they a form of electro-magnetic radiation that passes in undeflectedstraight lines from outer space through theEarth’s magnetic field, as ROBERT ANDREWS MIL-LIKAN suggested? Or are they streams of chargedparticles, which would, therefore, be deflectedalong curved paths as they traversed the Earth’smagnetic field, as the German physicist WaltherBothe believed? To attempt to settle the ques-tion, Compton carried out measurements atthousands of locations around the world andfound conclusive evidence that cosmic rays mustconsist of charged particles.

In 1941, finding himself unable to embracethe pacifism of his mother’s Mennonite creed, heagreed to serve as chairman of the NationalAcademy of Sciences Committee to EvaluateUse of Atomic Energy in War, organized at theUniversity of Chicago, which included ENRICO

FERMI, Leo Szilard, and EUGENE PAUL WIGNER.Compton designed methods of isolating fission-able plutonium and, with Fermi, produced a self-sustaining nuclear chain reaction, which led tothe development of the atomic bomb. He alsoplayed a role in the government’s decision to usethe bomb. He was responsible for the appoint-ment of J. ROBERT OPPENHEIMER to head theatomic bomb project, and afterward he defendedOppenheimer’s loyalty to the United States,when, during the postwar McCarthy era, he wasinvestigated by the House Un-American Activi-ties Committee.

In 1945, at the war’s conclusion, Comptonreturned to Saint Louis as chancellor, a posi-tion he held until 1954, when he became pro-fessor of natural philosophy. He retired in 1961,when he became Distinguished Service Profes-sor of Natural Philosophy at Washington Uni-versity. He died on March 15, 1962, inBerkeley, California.

A prolific writer, he wrote several books onsocial and moral issues, including The Freedom ofMan (1935), The Human Meaning of Science(1940), and Atomic Quest—a Personal Narrative

(1956), in addition to his numerous technicalpublications.

Discovery of the Compton effect played animportant role in the development of quantumelectrodynamics, in which the electromagneticfield itself behaves according to the rules ofquantum mechanics. The orbiting ComptonGamma Ray Observatory, named in his honor,was launched on April 5, 1991, and returned toEarth on June 5, 2000. It conducted experimentsthat relied on the intricate understanding of theinteraction of matter and high-energy gammarays that Compton discovered in his ground-breaking experiments.

See also BARKLA, CHARLES GLOVER; RÖNT-GEN, WILHELM CONRAD.

Compton, Arthur Holly 65

Arthur Holly Compton discovered the Compton effect,a quantum mechanical effect in which high-energy Xrays increase in wavelength after scattering byelectrons. (AIP Emilio Segrè Visual Archives)

Further ReadingAllison, Samuel K. “Arthur Holly Compton.” Bio-

graphical Memoirs Nat. Ac. Sci, 38: 81, 1965.Compton, Arthur Holly. Atomic Quest—a Personal

Narrative. Oxford: Oxford University Press,1956.

———. The Cosmos of Arthur Holly Compton. NewYork: Knopf, 1967.

� Coulomb, Charles-Augustin de(1736–1806)FrenchTheoretician and Experimentalist(Electromagnetism, Electrostatics,Mechanics)

Charles Augustin Coulomb pioneered the sci-ence of electrostatics and established the lawsgoverning electric charges. In recognition of hisachievement the unit of electric charge is namedthe coulomb.

He was born on June 14, 1736, inAngoulême, in southwestern France, into awealthy family, active in legal and governmentalcircles. When Charles was a boy, the familymoved to Paris, where he received a solidgrounding in both the sciences and the humani-ties at the Collège Mazarin. He then entered theEngineering School in Mezières and graduated in1761 as a military engineer with the rank of firstlieutenant in the engineering corps.

Over the next 20 years he traveled exten-sively with the corps, working on projectsinvolving engineering, structural design, fortifi-cations, and soil mechanics. He spent eight years(1764–1772) on Martinique in the West Indies,when the island was attacked by both Britishand Dutch fleets, and took charge of building anew fort.

In 1773, he returned to France, toBouchain, where he began to write importantwork on applied mechanics. In the first paper hedelivered before the Académie des Sciences in

Paris, he discussed the influence of friction andcohesion in problems of statics. At his next post-ing, in Cherbourg, he wrote a famous paper onthe magnetic compass, which contained his firstwork on the torsion balance, a device heinvented for measuring very small forces by thetorsion (twist) they cause in a fiber or a wire. Hewas the first to show physicists how the torsionsuspension could provide a method of accuratelymeasuring extremely small forces. Sent toRochefort in 1779, he continued his study ofmechanics, using Rochefort’s shipyards as labo-ratories for his experiments. He wrote a majorwork on friction, The Theory of Simple Machines,which won him the Grand Prix from theAcadémie des Sciences in 1781. In this classicwork he virtually created the science of friction,extending knowledge of the effects of frictioncaused by factors such as lubrication and differ-ences in materials and loads.

The recognition Coulomb received for thiswork enabled him to leave engineering projectsbehind him and to devote himself to physics. Hewas elected to the mechanics section of theAcadémie and moved to Paris, where he obtaineda permanent position. Between 1785 and 1791,Coulomb wrote seven important treatises onelectricity and magnetism and submitted themto the academie. In these treatises, influenced bythe work of Joseph Priestley on electrical repul-sion, he developed a theory of attraction andrepulsion: that bodies with the same electricalcharge repel each other, whereas bodies withopposite electrical charge attract each other. Heexamined perfect conductors and insulators(dielectrics) and concluded that a perfect dielec-tric does not exist in nature, since, above a cer-tain limit, every substance conducts electricity.He treated the electrical force in a manner simi-lar to the way SIR ISAAC NEWTON treated gravi-tational force, that is, as an action at a distance.Coulomb’s major contribution was in electro-statics, the study of time-independent electricfields, in which he made extensive use of an

66 Coulomb, Charles-Augustin de

adapted version of his torsion balance. Coulombperformed his experiment by using certain rea-sonable assumptions, namely, (1) that the elec-trical forces behave as if concentrated on a pointand (2) that the dimensions of the bodies aresmall compared with the distance betweenthem. Under these conditions he found that theforce between two electric charges on these bod-ies was proportional to the product of thecharges and inversely proportional to the squareof the distance between their centers; this rela-tionship became known as Coulomb’s law.Coulomb also investigated the distribution ofelectric charge over a body and found that it islocated only on the surface of the charged bodyand not in its interior.

In other work, Coulomb demonstrated theinverse square law of repulsion and attractionin like and unlike magnetic poles. He wrote atotal 25 papers between 1781 and 1806, work-ing closely with other eminent scientists of thetime. His life was also filled with the prepara-tion of hundreds of committee reports for theacademie, with his engineering consulting, andwith his multifaceted service to the Frenchgovernment. At different times, Coulombfound himself in charge of the education inpublic schools, hospital reform, care of theroyal fountains, and administration of thewater supply of Paris. From 1802 to 1806, asinspector general of public education, he wasmainly responsible for setting up lycées (sec-ondary schools) throughout France.

When, in 1789, the French Revolution ledto the reorganization of many institutions,Coulomb retired from the engineering corps,and he withdrew to his country home to con-tinue his research in 1791. He would return toParis a few years later, when the abolishedAcadémie des Sciences was replaced by theInstitut de France in 1795. Coulomb became itspresident in 1801. The following year, he mar-ried Louise Françoise LeProust Desormais, whohad already borne him two sons. Four years

later, on August 23, 1806, at the age of 70, hedied in Paris.

Coulomb’s work established electrostatics asan exact science. A century later Coulomb’s lawwould become an important component of theunified theory of electrodynamics developed byJAMES CLERK MAXWELL.

Further ReadingStewart, C., ed., Coulomb and the Evolution of Physics

and Engineering in Eighteenth Century France.Princeton, N.J.: Princeton University Press,1971.

� Curie, Marie(1867–1934)Polish/FrenchExperimentalist (Radioactivity), PhysicalChemist

Marie Curie was a brilliant and dedicated exper-imentalist, who, with her husband, Pierre, inves-tigated the atomic process first observed byANTOINE-HENRI BECQUEREL, which she namedradioactivity, and discovered two new chemicalelements, polonium and radium. She was notonly the first woman to win a Nobel Prize—shewon two, in physics and in chemistry.

She was born Marya Sklodowska onNovember 7, 1867, in Warsaw, Poland, the fifthand youngest child of Vladislav, a professor ofmathematics and physics, and Bronislava, apianist, singer, and schoolteacher. Poland wasthen under Russian dominance and theSklodowskis were obliged to hide their strongfeelings of Polish patriotism. Marya’s childhoodwas marked by the death of her mother of tuber-culosis, when Marya was 10. She graduated atthe top of her high school class at the age of 15and then worked for eight years as governess forthe children of wealthy families. During thisperiod, she never lost sight of her goals, studyingmathematics and physics in her spare time and

Curie, Marie 67

attending a clandestine university run by Polishprofessors in defiance of the Russian occupiers.With her salary, she helped her older sister,Bronya, pay her tuition at the Sorbonne (theUniversity of Paris), where she was studying tobe a physician. When Bronya in turn, afterobtaining her medical degree in 1891, sent forher, the 24-year-old Marya promptly changedher name to its French form, Marie, andlaunched her studies of science and math at theSorbonne. Although Bronya helped out, Marieled a Spartan existence in an unheated attic,where her diet consisted primarily of bread, but-ter, and tea. She managed to graduate at the topof her class in the spring of 1893, with the equiv-alent of a master’s degree in physics. Whengranted a generous fellowship, she was able tocontinue her studies, earning a master’s degree inmathematics the following year.

In 1894, she went to work for a Frenchindustrial society and, while looking for ade-quate laboratory conditions, met Pierre Curie,the laboratory director of the Municipal Schoolof Industrial Physics and Chemistry in Paris.Eight years her senior and already established asa physicist, Pierre persuaded her to remain withhim in Paris instead of returning to Poland.They married in 1895, just after Pierre hadearned his doctorate and become a full professor.Their union would be fruitful on the personallevel—their first daughter, Irène (later the sci-entist Irène Joliot-Curie), was born in 1897 anda second, Eve, in 1904—and spectacular on thescientific.

Marie was determined to pursue a Ph.D.and, for her doctoral research, decided to followup on Becquerel’s 1896 observation that the ele-ment uranium spontaneously emitted radiation.She discovered that the intensity of the radia-tion was in direct proportion to the amount ofthe uranium in her sample, and nothing she didto alter the uranium (such as combining it withother elements or subjecting it to light, heat, orcold) affected the rays. This led her to hypothe-

size that the rays were the result of somethinghappening within the atom itself, which was dueto a process she called radioactivity.

Next she tested minerals that containeduranium or thorium and found that pitch-blende (a mineral that contains uranium) gaveoff four times as much radiation as would beexpected from the amount of uranium it con-tained. This led her to believe that the mineralmust contain other elements that also give offradiation. In April 1898, she published a paperannouncing the radioactivity of thorium andspeculating that an even more strongly radioac-tive element existed.

At this point Pierre abandoned his ownphysics research to collaborate with Marie onhers. The Curies embarked on what Marie wouldlater describe as the happiest time in their lifetogether, doing rigorous work, at their ownexpense, in a makeshift lab, lacking heat or ven-tilation. They focused their investigations onpitchblende because it emitted the strongestrays. Using a painstaking refining method inwhich tons of the material had to be refined toobtain a tiny sample of radioactive material,they quickly succeeded in isolating a substancefrom pitchblende that was 400 times more activethan uranium. Marie called it polonium, inhonor of her native Poland. They soon found asecond, even more radioactive element, andcalled it radium.

Although the Curies announced their dis-covery on December 26, 1898, it was not untilSeptember 1902 that they finally produced0.0035 ounce (0.1 g) of pure radium chloride—enough to confirm the existence of radium.When, in June 1903, Marie described thisresearch to her doctoral committee, she had thepleasure of hearing that hers was the greatestcontribution ever to be made by a dissertation.That fall she won the 1903 Nobel Prize inphysics, which she shared with her husband andBecquerel. With the public imagination cap-tured by their discovery, the Curies now enjoyed

68 Curie, Marie

international renown and enough money to easesome of their financial burdens. The Sorbonnecreated a new professorship for Pierre in 1904and promised to build an excellent laboratory forhim and Marie.

This spiral of good fortune ended tragicallywhen Pierre was killed on April 19, 1906, as heabsentmindedly stepped in front of a horse-drawn wagon. With two small daughters to sup-port, Marie found the strength to master hergrief and persuaded the Sorbonne to hire her asits first woman professor. Two years later she waspromoted to full professor. She independentlycontinued the research she and Pierre had donetogether, setting out to refute the critics’ claimthat radium was not really an element, by pro-ducing pure radium and pure polonium. In 1911,after four years of exacting work, she succeededin producing radium as a pure metal. That yearshe won a second Nobel Prize, this time inchemistry, for her discovery and isolation ofradium and polonium.

By 1914, she was the head of two laborato-ries, one in her native Warsaw and one at theSorbonne called the Radium Institute. Unableto continue her research during World War I,she supported the French war effort by organiz-ing a fleet of wagons, which were called “littleCuries,” to carry portable X-ray equipment tobattle sites. With her characteristic energy anddedication, she opened 200 X-ray stations thatexamined over a million soldiers. When the warended, she campaigned during a 1920 tour of theUnited States and again in 1929, to raise moneyfor a hospital and laboratory devoted to radiol-ogy, the branch of medicine that uses X rays andradium to diagnose and treat disease. She usedher celebrity status to campaign for the RadiumInstitute and other causes she believed in, serv-ing on the council of the League of Nations andon its international committee on intellectualcooperation.

As the 1920s drew to a close, a number ofdebilitating symptoms, including fatigue, dizzi-

ness, low-grade fever, humming in her ears,and a progressive loss of eyesight, becameCurie’s constant companions. Although shewas aware that many colleagues had sufferedsimilarly and died, for a long time, she refusedto attribute their deaths to the element sheand Pierre had discovered—radium. When shedid finally admit radium’s role, she continuedto work with it. When doctors discovered shehad leukemia, they concealed the news fromthe public and from her. She succumbed tothe disease on July 4, 1934, at the mountainsanatorium where she had gone to recuperate.Ironically, one of the enduring applications ofher work has been in the treatment of cancerwith radiation.

Curie, Marie 69

Marie Curie discovered the phenomenon ofradioactivity and two new chemical elements,polonium and radium. (AIP Emilio Segrè VisualArchives, W. F. Meggars Collection)

A devoted scientist, whom fame could notdistract from the profound pleasures of her labo-ratory, she once said:

A scientist in his laboratory is not a meretechnician: he is also a child confrontingnatural phenomena that impress him asthough they were fairy tales.

Marie Curie lived to see her work give riseto the field of atomic physics. In 1995, herremains, together with her husband’s, were

enshrined in the Pantheon, the memorial to thenation’s “great men,” in Paris. She was the firstwoman to be so honored.

Further ReadingCurie, Eve. Madame Curie. New York: Doubleday,

1937.Pasachoff, Naomi. Marie Curie and the Science of

Radioactivity. Oxford: Oxford University Press,1997.

Quinn, Susan. Marie Curie: A Life. New York: Simon& Schuster, 1995.

70 Curie, Marie

71

D� Davisson, Clinton Joseph

(1881–1958)AmericanExperimentalist, Particle Physicist

Clinton Joseph Davisson shared the 1937 NobelPrize in physics with George Thomson as thefirst to observe experimentally the wave natureof the electron, thereby confirming LOUIS-VICTOR-PIERRE, PRINCE DE BROGLIE’s theory ofthe wave–particle duality of subatomic particles.

He was born in Bloomington, Illinois, onOctober 22, 1881, to Joseph Davisson, an artisan,and Mary Calvert, a schoolteacher. He attendedBloomington public schools and, in 1902, won ascholarship on the basis of his mastery of mathe-matics and physics to the University of Chicago.There he studied under ROBERT ANDREWS MIL-LIKAN, the first physicist to measure the charge ofthe electron, who was impressed with his abili-ties. For financial reasons, however, Davissonhad to leave school and return to his hometown,where he began working for the telephone com-pany. In 1904, Millikan came to his rescue by rec-ommending him for an assistantship in physics atPurdue University. In June of that year, he wasable to return to Chicago, where he remaineduntil, in 1905, once more thanks to Millikan, hebecame a part-time instructor of physics atPrinceton University. Continuing to study for his

degree, he earned a B.Sc. in 1908, from Chicago.In 1911, a fellowship in physics at Princetonenabled him to complete a Ph. D. from Chicago,for his thesis “The Thermal Emission of PositiveIons from Alkaline Earth Salts.” That same year,he married Charlotte Sara Richardson, the sisterof his thesis adviser; they would have three sonsand one daughter together.

From 1912 to 1917, Davisson was an instruc-tor in the physics department at the CarnegieInstitute of Technology in Pittsburgh. Duringthis period he spent the summer of 1913 at theprestigious Cavendish Laboratory, CambridgeUniversity, working under JOSEPH JOHN (J. J.)THOMSON, the discoverer of the electron. Whenthe United States entered World War I in 1917,Davisson tried to enlist in the army but wasrejected. He worked instead for the engineeringdepartment of the Western Electric Company,which later became Bell Telephone Laboratories,in New York City. Initially this was a war assign-ment, but Davisson decided to stay on, resigninghis position as assistant professor at Carnegie.

While he was working on an experimentinvolving the reflection of electrons from metal sur-faces under electron bombardment in April 1925,an accidental explosion caused a nickel target hewas studying to become heavily oxidized. Heremoved the coating of oxide by heating thenickel. As he continued working, he made an

intriguing observation: a change had taken place inthe angle of reflection of electrons from the nickelsurface. Davisson and his assistant Lester Germersought a possible cause and finally attributed thechange to the recrystallization of the nickel; it wasprobable, they conjectured, that in the reheatingprocess many small crystals in the nickel surfacehad converted into several large crystals. The fol-lowing year, however, while enjoying a “secondhoneymoon” with Charlotte in London, Davissonattended a conference that dealt with the new rel-ativistic particle–wave theory of the electrondeveloped by de Broglie. In his theory, the Frenchphysicist had found a simple relationship betweenthe velocity of the particle and the wavelength ofthe “wave-packet” associated with this particle.The greater the velocity of the particle, the shorterthe wavelength. If the velocity of the particle isknown, it is then possible, by using de Broglie’s for-mula, to calculate the wavelength, and vice versa.Once aware of de Broglie’s revolutionary new the-ory that electrons have wave properties, Davissonno longer found the recrystallization hypothesis sopersuasive. He knew that X-ray diffraction hadalready been observed in crystals. Was it not likely,he reasoned, that the effects he had observed weredue to the diffraction of electron waves in theplanes of atoms in the nickel crystals?

Upon his return to the United States, heand Germer devised an experiment using a sim-ple nickel crystal. The atoms were in a cubic lat-tice with atoms at the apex of cubes, and theelectrons were directed at the plane of atoms at45 degrees to the regular end plane. Electrons ofa known velocity were directed at this plane,and those emitted were recorded by an electrondetection apparatus. In January 1927, the resultsthey obtained indicated that for incident elec-trons of a certain velocity, electron diffractionoccurred, producing outgoing beams that couldbe related to the interplanar distance. The wave-length of the beams could then be determinedand used, together with the known velocity ofthe electrons, to confirm de Broglie’s hypothesis.

Four months later, George Thomson, theson of J. J. Thomson, working independently atAberdeen University, Scotland, with differentexperimental apparatus, made the same discov-ery. For their definitive confirmation of the par-ticle–wave duality of subatomic particles,Davisson and Thomsom would share the 1937Nobel Prize in physics.

From 1930 to 1937, Davisson focused on thetheory of electron optics, seeking ways to applyit to engineering problems. He also studied thescattering and reflection of very slow electronsby metals. During World War II, he investigatedthe theory of electronic devices, as well as aseries of problems in the field of crystal physics.

Davisson remained with Bell TelephoneLaboratories for 29 years, retiring in 1946, whenhe became visiting professor of physics at theUniversity of Virginia, Charlottesville. Heretired in 1949 and died in Charlottesville, onFebruary 1, 1958, at the age of 76.

Davisson’s groundbreaking experiments, byconfirming the de Broglie hypothesis that a quan-tum wave–particle duality is inherent in matter,opened the door to the new world of quantummechanics and elementary particle physics.

See also LAUE, MAX-THEODOR FELIX VON.

Further ReadingMadey, Theodore E., and William C. Brown. History of

Vacuum Science and Technology: A Special VolumeCommemorating the 30th Anniversary of the Ameri-can Vacuum Society. Philadelphia: ISI Press, 1984.

� Dirac, Paul Adrien Maurice(1902–1984)BritishTheoretical Physicist, QuantumTheorist, Particle Physicist

Paul Dirac ranks among the most original andcreative thinkers in the history of physics. Hismost important contribution was the Dirac

72 Dirac, Paul Adrien Maurice

equation, which reconciled quantum mechanicsand special relativity, expanded the quantummechanical model of the atom to include spinand magnetism, and led to the prediction ofantimatter. For these seminal achievements inquantum mechanics and particle theory he wasawarded the 1933 Nobel Prize in physics.

Paul Adrien Maurice Dirac was born onAugust 8, 1902, in Bristol, England, the middleof three children born to Charles Dirac, who hademigrated from Switzerland, and Florence Han-nah Holten, an Englishwoman from Cornwall.They did not make a particularly happy family.Charles Dirac, who taught French at a secondaryschool, insisted that only French be spoken atdinner, so that Paul was the only one to dinewith him. When his older brother later commit-ted suicide, Paul’s estrangement from the fatherhe held responsible was complete; he invitedonly his mother to his anointment as a NobelPrize laureate. Paul suffered throughout his lifefrom shyness in social situations and a verbal ret-icence that gave rise to a body of “Dirac stories.”One of the most famous of these tells how heintended to turn down the Nobel Prize in 1933in order to avoid the publicity. He changed hismind only when ERNEST RUTHERFORD assuredhim there would be more publicity if he refusedthe prize.

Dirac attended Merchant Venturer’s Sec-ondary School in Bristol, before enrolling atBristol University, where he studied electricalengineering. He received a B.Sc. degree in 1921and was accepted for graduate study at Cam-bridge. Financial problems forced him to post-pone matriculation for two more years, duringwhich he studied mathematics at Bristol. AtCambridge, he worked with Cambridge’s lead-ing theoretician, Ralph Fowler, who introducedhim to Rutherford and NIELS HENRIK DAVID

BOHR’s work on the structure of the atom andsupervised his work on statistical mechanics. Hewas an unusually prolific graduate student, pub-lishing no fewer than 11 papers on statistical

mechanics and quantum theory. He earned aPh.D. in 1926 for his thesis “Quantum Mechan-ics,” in which he formulated a mathematicallyconsistent general theory of quantum mech-anics in correspondence with Hamiltonianmechanics. The following year he became a Fel-low of Saint John’s College. As Paul Dirac wasestablishing himself as a physicist of genius, hisbrother, Reginald, took his life. The tragedyseems to have only intensified Dirac’s tendencytoward social isolation.

He began to travel extensively, makingnumerous trips to the Soviet Union, as well as toCopenhagen and Göttingen, where he workedwith the leading lights of quantum mechanics:Bohr, WOLFGANG PAULI, MAX BORN, andWERNER HEISENBERG. Both Heisenberg andERWIN SCHRÖDINGER had just published rivaltheories, later to be proved mathematically equiv-alent, which provided a conceptual foundationfor Bohr’s quantum model of the atom. Dirac wasdisturbed by the nonrelativistic form of theSchrödinger–Heisenberg quantum theory andwanted to integrate it with Einstein’s special rela-tivity. In 1928, he succeeded in doing so with hisrenowned Dirac equation, which allowed him toformulate the relativistic theory of the electron.The Dirac equation, which is still used widelytoday, was both mathematically elegant andbreathtakingly productive. It led to a more com-plex model of the electron by endowing it with anintrinsic quantized rotation property, known asspin, which generated an intrinsic magnetic fieldaround the electron. Until Dirac, the unit ofquantization was integer multiples of Planck’sconstant. The Dirac equation implied half-inte-gers of Planck’s constant for the intrinsic spin ofthe electron. It gave a quantitative explanation ofthe Compton effect, which describes the wayphotons and electrons collide and scatter off eachother. It also accounted perfectly for certainanomalies in the spectrum of atomic hydrogen.

Two years later, in 1930, Dirac published thefirst edition of his classic book, Principles of

Dirac, Paul Adrien Maurice 73

Quantum Mechanics. In its final chapters, he firstapplied the rules of quantum mechanics to theelectromagnetic field. His rudimentary calcula-tions would become the basis for what laterbecame known as quantum electrodynamics(QED), the study of the quantum mechanicalinteraction of electrons and photons.

The following year his relativistic theory ofthe atom would yield an even more astonishingprediction: the existence of a positron or posi-tive electron. Dirac’s prediction was motivatedby his discovery that the mathematics describingthe electron contained twice as many states aswere expected. He proposed that the positiveenergy states described the electron, and thatthe negative energy states described a particle

with a mass equal to that of an electron but withan opposite (positive) charge of equal strength:that is, an antiparticle of the electron. Whenindependent experiments by CARL DAVID

ANDERSON and LORD PATRICK MAYNARD STU-ART BLACKETT, in 1932 and 1933, confirmedthat a positron could be produced by a photon,Dirac was invited to share the 1933 Nobel Prizewith Schrödinger. His discovery of the positronled to the prediction of other antiparticles, suchas the antiproton discovered by EMILIO GINO

SEGRÈ in 1955. Today the existence of antimat-ter—an antiparticle for all particles—is univer-sally accepted.

With the recognition of his work, Diracwas invited, in 1932, to become Lucasian Pro-fessor of Mathematics at Cambridge, a post lastheld by SIR ISAAC NEWTON. He would retainthis position until 1969. In 1934, he visited theInstitute for Advanced Study at Princeton,where he met the eminent Hungarian physicistEUGENE PAUL WIGNER at a time when MargitBalasz, Wigner’s sister, who lived in Budapest,happened to be visiting him. An acquaintancewas struck up, and, in 1937, Paul and Margitwere married. They had two daughters together.In addition, Paul adopted Margit’s daughter andson from a previous marriage, one of whom,Gabriel Andrew Dirac, became a famous puremathematician.

Dirac’s work continued to yield importantinsights. In 1938, he published his famous paperon classical electron theory, which presented anelegant mathematical formulation of two issuesnot well understood at the time: mass renormal-ization and radiative reaction. He was led to yetanother significant discovery when he noticedthat particles with half-integral spins (i.e., theelectron) that obeyed the Pauli exclusion prin-ciple also obeyed statistical rules different fromthose of particles with integer spin, such as thephoton. Dirac worked out the statistics for theseparticles (now called fermions), only to learnthat ENRICO FERMI had already done so. History

74 Dirac, Paul Adrien Maurice

Paul Dirac discovered the wave equation for a spinningelectron, which reconciled quantum mechanics andspecial relativity and ultimately led to the prediction ofantimatter. (AIP Emilio Segrè Visual Archives, Ramseyand Musprat Collection)

has credited both men: Fermi–Dirac statisticscontinue to be useful in nuclear and solid statephysics (in determining the distribution of elec-trons at different energy levels).

During World War II, as a consultant to agroup in Birmingham working on atomic energy,Dirac worked on uranium separation andnuclear weapons. He retained his academic postin Cambridge until 1969, when he moved to theUnited States; in 1971, he became professor ofphysics at Florida State University.

In 1973 and 1975, Dirac gave a series ofnotable lectures in Leningrad on the large num-ber hypothesis. He had published his first paperon this subject in 1937; now, in his later years, itonce more absorbed his attention. The theorydeals with pure, dimensionless numbers such asthe ratio of the electrical and gravitationalforces between an electron and a proton, whichis 1039. This ratio happens to represent the age ofthe universe expressed in terms of atomic units.If there is some meaningful connection betweenthese two values, there must be a connectionbetween the age of the universe and either theelectric force or the gravitational force. Thisimplies that the gravitational force may not be aconstant but is decreasing at a rate proportionalto the rate of aging of the universe. The largenumber hypothesis also points to the intriguingrelated fact that the number of particles in theuniverse, which is 1078, is equal to the square ofthe age of the universe. This suggests that mattermay be being continuously created.

In addition to his numerous, fundamentalcontributions to quantum mechanics, particletheory, and cosmology, Dirac bequeathed tophysics his unique aesthetics: a conviction thatbeauty or mathematical elegance is inseparablefrom scientific truth. Subsequent generationsof physicists have been inspired and challengedby his 1963 assertion in Scientific American that

it is more important to have beauty inone’s equations than to have them fit

experiment. . . . If one is working from thepoint of view of getting beauty in one’sequations, and if one has really a soundinsight, one is on a sure line of progress. Ifthere is not complete agreement betweenthe results of one’s work and experiment,one should not allow oneself to be toodiscouraged, because the discrepancymay well be due to minor features that arenot properly taken into account and thatwill get cleared up with further develop-ment of the theory.

Paul Dirac died in Tallahassee, Florida, onOctober 20, 1984, after a long illness.

See also COMPTON, ARTHUR HOLLY; FEYN-MAN, RICHARD PHILLIPS; PLANCK, MAX ERNEST

LUDWIG; SCHWINGER, JULIAN SEYMOUR.

Further ReadingDirac, Paul A. M. The Principles of Quantum Mechanics.

Vol. 27. Oxford: Oxford University Press, 1982.Fraser, Gordon. Antimatter: The Ultimate Mirror.

Cambridge: Cambridge University Press, 2000.Kursunoglu, Behram N., and Eugene Wigner, eds.

Paul Adrien Maurice Dirac: Reminiscences About aGreat Physicist. Cambridge: Cambridge Univer-sity Press, 1987.

Pais, Abraham, et al., eds. Paul Dirac, the Man and HisWork. Cambridge: Cambridge University Press,1998.

� Doppler, Christian(1803–1853)AustrianTheoretical Physicist (Acoustics, Optics)

Christian Doppler discovered the so-calledDoppler effect, an apparent change in the fre-quency of a wave motion caused by relativemotion between the source and the observer. Itwas quickly and easily verified with respect tosound waves, for which the frequency increases

Doppler, Christian 75

as source and observer are in motion toward oneanother and decreases as they are in motionaway from one another. The Doppler effectwould have its greatest impact, however, whenapplied to light waves by astronomers, whofound in it an indispensable tool for measuringthe velocities and distances of celestial bodies.

Christian Doppler was born in Salzburg,Austria, on November 29, 1803, into a familythat had operated a successful stone-masonrybusiness since 1674. He was heir to a family tra-dition that decreed the son would take over thefamily business, but for the frail Christian, a lessphysically arduous path seemed advisable. Heprogressed from primary school in Salzburg tosecondary school in Linz, where his talent formathematics was increasingly evident. Upongraduating, he attended the Polytechnic Insti-tute in Vienna from 1822 to 1825; there he con-tinued to excel in mathematics and otherstudies. He then returned to his native city,where he attended lectures at the SalzburgLyceum and continued his studies privatelywhile tutoring in physics and math.

By 1819, Doppler was back in Vienna,where he studied higher mathematics, mechan-ics, and astronomy at the university and gradu-ated in 1833. Remaining in Vienna to work asassistant to the professor of higher mathematicsand mechanics, A. Burg, he wrote his firstpapers on math and electricity. Doppler, who,at 30, was somewhat older than most assistants,began seeking a permanent academic post. Inthe Austro-Hungarian Empire of that timeaspiring academics had to compete for vacantprofessorships (a term applied to secondary aswell as university teaching positions) by takingstate exams and giving demonstration lectures.Doppler entered several of these competitions,on both the secondary school and universitylevels, while supporting himself as a book-keeper at a cotton-spinning factory.

When success continued to elude him, hedecided to emigrate to the United States in

1835. But he did an abrupt about-face, justbefore setting out, when a job teaching mathe-matics at the Technical Secondary School inPrague was offered to him, two years after he hadcompeted for it. Doppler accepted, glad to haveany teaching position, even if it was not the onehe dreamed of. He competed for a job teachingadvanced mathematics in Prague, but the closesthe came to realizing his ambitions was a four-hour-a-week teaching assignment at a technicalcollege. He had married in 1836 and was gratefulfor the extra income. Not until 1841 would heobtain a professorship in mathematics at theState Technical Academy in Prague. At thesame time, his research was producing excitingresults.

On May 25, 1842, at a meeting of the RoyalBohemian Society of Sciences, Doppler read hispaper “On the Colored Light of the Double Starsand Certain Other Stars of the Heavens.” Herehe first presented what came to be called theDoppler effect, the relation of the frequency of asource to its velocity relative to an observer.Doppler derived his principle by treating bothlight and sound as longitudinal waves in theether and matter, respectively. He pointed outthat sound waves from a source moving towardan observer reach the observer at a greater fre-quency than if the source is stationary, thusincreasing the observed frequency and raisingthe pitch of the sound. Similarly, sound wavesfrom a source moving away from the observerreach the observer more slowly, resulting in adecreased frequency and a lowering of pitch. In1845, the first experimental test of Doppler’sprinciple was made at Utrecht in the Nether-lands. A locomotive was used to carry a group oftrumpeters in an open carriage back and forthpast a second group of musicians, who jotteddown the pitch of the notes being played. Thevariation of pitch produced by the motion of thetrumpeters verified Doppler’s equations for thecase of sound waves. He would later publish animproved version of his principle, which took

76 Doppler, Christian

into account both the motion of the source andthe motion of the observer.

In the 1842 paper, Doppler hypothesizedthat his principle would apply to any wavemotion, including motion of light waves, andpredicted that this would be of particular valueto astronomers.

Time would prove Doppler eminently cor-rect. In 1848 ARMAND-HIPPOLYTE-LOUIS FIZEAU

suggested that applying the Doppler principle toobserved shifts in the spectral lines of stars wouldenable astronomers to determine their motion.Twenty years later, William Huggins applied thisidea when he determined that Sirius was movingaway from our solar system by detecting a smallred shift, that is, a displacement of lines towardthe red end of the visible spectrum, where wave-lengths are longer. This is caused by the Dopplereffect and indicates that the observed body ismoving away from the Earth. Later observationsfound that the spectra of some astronomicalobjects show a blue shift, indicating movementtoward the observer. Both red and blue shiftsbecame known as Doppler shifts.

While making his important discovery,Doppler was finding his long-desired professor-ship, involving the examination of hundreds ofstudents in different scientific and mathematicalareas, more than he could handle. In 1844, withhis health failing, he requested a leave. Hewould not return to teaching until 1846. Thefollowing year he eagerly accepted a professor-ship of mathematics, physics, and mechanics atthe Academy of Mines and Forests in BanskaStiavnica. Only a year later political unrestthroughout the Austro-Hungarian Empireforced him to uproot himself once more. Thatyear he was elected to membership in theAcademy of Sciences in Vienna and wasawarded an honorary doctorate from the Uni-versity of Prague. With a solid reputation as aresearcher established, he then returned toVienna and in 1850 became director of the newPhysical Institute and professor of experimental

physics at the Royal Imperial University ofVienna. This was the apogee of his career. Hislung problems steadily worsened until, inNovember 1852, he traveled to Venice, seekingthe healing influence of the warmer climate. Hisdevoted wife, who had remained in Vienna withtheir three sons and two daughters, rushed to hisside when it became clear that he was failing.She was with him when he died in Venice onMarch 17, 1853.

Doppler’s legacy is most readily reflected inits impact on astronomy, in which, applied tothe case of light waves, measuring the Dopplershift of celestial bodies remains a fundamentalmethod of estimating their relative velocitiesand distances. When, in 1929, Edwin Hubblelinked the velocity of a galaxy to its distancefrom Earth, it became possible to use the redshift to determine, not only the distances ofgalaxies, but, ultimately, the size and structure ofthe universe.

Further ReadingEden, Alan. The Search for Christian Doppler. New

York: Springer-Verlag, 1992.

� Dyson, Freeman(1923– )British/AmericanTheoretician, Quantum Field Theorist,Mathematical Physicist

Freeman Dyson was a brilliant theorist andmathematician, who discovered the “RosettaStone,” capable of harmonizing the relativisticquantum field theoretic language developed byJULIAN SEYMOUR SCHWINGER and SIN-ITIRO

TOMANAGA with the space time diagrammaticlanguage of RICHARD PHILLIPS FEYNMAN into acoherent theory of quantum electrodynamics(QED). In the latter part of his career, he hasbecome famous for his speculative work on thepossibility of life on other planets.

Dyson, Freeman 77

Dyson was born on December 15, 1923, inCrowthorne, Berkshire, England, the secondchild of Sir George Dyson, a gifted composer andconductor, who eventually directed the BritishRoyal College of Music in London, and MildredLucy Dyson, a highly educated woman who hadbeen trained as a lawyer. Dyson spoke of hisupbringing by parents who began raising theirfamily in their 40s as “more like being withgrandparents in their own fashion. It was moreintellectual than physical.” Encouraged toexplore the arts, Dyson wrote a futuristic novel,“Sir Phillip Roberts’s Erolunar Collision,”inspired by Jules Verne, when he was nine; itstale of a mission to the Moon that is aborted forlack of funding is a blend of science fiction andsocial satire. He was sent to Twyford, a boardingschool, when he was nine and, by age 12, he hadwon first place in the scholarship exams toWinchester, which had the reputation of beingthe best mathematical school in England’s pub-lic school system. He read popular books aboutALBERT EINSTEIN and relativity and becameincreasingly obsessed with mathematics, teach-ing himself calculus and most of complex func-tion theory from the Encyclopaedia Britannica.

After graduating from Winchester in thesummer of 1941, with England already at war, heenrolled at Trinity College, Cambridge Univer-sity, where England’s greatest mathematicianswere then to be found and where PAUL ADRIEN

MAURICE DIRAC was the leading light in physics.In 1943, however, his education was interruptedby the British war effort. He was a pacifist in theGandhi tradition and considered declaring him-self a conscientious objector. But the courageousexample of the people of his country in theirstruggle to survive inspired him to do his part.He allowed himself to be recruited into theRoyal Air Force Bomber Command at HighWycombe, where he spent his time performingfutile statistical studies on the safety and efficacyof the British strategic bombing campaign,which were ignored by the military bureaucracy.

His frustration and sense of impotence at hisinability to minimize bomber losses wouldremain with him for many years.

At the war’s conclusion, Dyson accepted ajob as a demonstrator in mathematics at ImperialCollege, London, but subsequently left mathe-matics, which he had come to view as an intrigu-ing game, for the “reality” of physics, in which hefelt the true challenges lay. When he returned tohis studies at Cambridge in 1946, he immersedhimself in physics and earned a B.A. Feeling thatthe United States was the only place to pursue hisnew field, he decided to do his graduate studies atCornell University, in order to work with HANS

ALBRECHT BETHE. When he arrived at Cornell in1947, he quickly became involved in a moment ofhigh drama in the world of physics.

Bethe had just returned from the ShelterIsland conference at which WILLIS EUGENE

LAMB JR. had announced the observation of ahighly significant experimental discrepancyfrom the predictions of Dirac’s long-acceptedtheory, which physicists used to calculate theenergy levels of the atom. In his experimentLamb shone a beam of microwaves onto a hotwisp of hydrogen gas blowing from an oven. Hefound that two fine structure levels in the nextlowest group, which should have coincidedwith the Dirac theory, were in reality shiftedrelative to each other by a certain amount (theLamb shift). He measured it with great accu-racy and later made similar measurements onheavy hydrogen. On the basis of this experi-mental discovery Bethe and other quantumtheorists such as Schwinger, Feynman, andTomonaga began to realize that what was miss-ing from Dirac’s theory was a proper interpreta-tion of the unwieldy concept of theself-interaction of the electron, which by itsvery nature contained infinities, thus prevent-ing a straightforward physical interpretation.

When the electromagnetic field is quan-tized, according to the rules of quantum mech-anics, particles of light called photons are

78 Dyson, Freeman

generated. At the heart of the quantum electro-dynamic process is the quantum exchange forcethrough which different electrons interact byexchanging photons with each other; in thiscontext an electron can also exchange a photonwith itself. How were physicists to deal with thisself-interaction? QED, as it was formulated inthe mid-1940s, was not considered to be a rela-tivistically covariant formalism (i.e., it was notformally compatible with the rules of special rel-ativity). This lack of relativistic covariance pre-vented a unique mathematical interpretation ofthe physical effects of self-interaction.

Schwinger changed all this when he discov-ered a relativistically covariant form for QED.This enabled him to introduce the concept ofrenormalization, which allowed a consistent math-ematical interpretation of the self-energy infinities.On the physical level, renormalization impliedthat physical particles are surrounded by a cloud of“virtual particles,” that is, ghostly particles thatexist within the context of the uncertainty princi-ple, whose energy, momentum, and charge modifythe physical appearance of the bare original parti-cle. In applying the method of renormalizationSchwinger found that the self-energy infinitiescould be subtracted out. This led to a fully consis-tent relativistic theory of quantum electrodynam-ics, which explained the Lamb shift as due to thevirtual particle modification of the Coulomb forcebetween the electron and the proton in the hydro-gen atom. Using his new relativistically covariantQED formalism with renormalization, Schwingerwas also able to calculate the anomalous magneticmoment of the electron.

In the midst of this revolutionary turmoil,Dyson arrived at Cornell as a graduate studentwith a glowing reputation as a mathematician.Since Bethe had been the first to calculate theLamb shift theoretically, on the basis of a non-relativistic approximation to electron theory, hegave Dyson the problem of developing a morerigorous version of the Lamb shift in the contextof a relativistic electron theory, which ignored

the electron’s spin. Dyson found that an exactrelativistic calculation could be carried out with-out impossible complication and gave a finiteanswer in agreement with Bethe’s earlier approx-imate Lamb shift calculation.

While at Cornell, Dyson learned aboutSchwinger’s new version of QED secondhand,from Victor Weisskopf. He was already forming afriendship with the young Richard Feynman,who had come up with an alternate approach tothe problems besetting QED, radically differentfrom Schwinger’s but equally effective. He usedspace-time diagrams, easily visualized spacetimeanalogs of the complicated mathematical expres-

Dyson, Freeman 79

Freeman Dyson proposed the S-matrix theory ofquantum electrodynamics (QED), which unified therelativistic quantum field theory of Julian S.Schwinger and Sin-Itiro Tomanaga with the space-time diagram theory of Richard P. Feynman. (AIPEmilio Segrè Visual Archives)

sions needed to describe the quantum probabili-ties of the behavior of electrons, positrons, andphotons. His idea of a diagrammatic approach toQED resulted in a highly effective computationalscheme. Instead of quantum field operators, hisfundamental building blocks were particle pro-cesses in space-time. Feynman’s diagrams visual-ized the construction of the quantum mechanicalprobabilities associated with fundamental quan-tum processes in terms of the space-time trajecto-ries of real and virtual particles. More importantly,this space-time diagrammatic formulation of QEDhad the great advantage of simplifying all of theintricate calculations needed by Schwinger andTomonaga to predict such interactions in their for-mulation of QED.

Feynman’s space-time diagrammatic approachto QED intrigued Dyson but seemed magical tohim. It troubled him that Feynman was merelywriting down answers instead of solving equationsin the usual way. Dyson began to conceive hismission as synthesizing these rival theories ofQED. In the summer of 1948, Dyson and Feyn-man drove cross-country together, becoming inti-mate friends. Dyson then spent the summer inAnn Arbor, listening to Schwinger lecture, andcame away feeling that Schwinger’s theory was“unbelievably complicated.” At summer’s end, heleft Ann Arbor to continue his graduate studies atthe Institute of Advanced Study at Princeton,where J. ROBERT OPPENHEIMER was director. Onthe 48-hour bus ride from Ann Arbor to Prince-ton, he had an epiphany—the answer to theproblem he had been pondering all year. He wroteto his family that his work

consisted of a unification of radiationtheory, combining the advantageousfeatures of the two theories put forth bySchwinger and Feynman. Now it hap-pened that Schwinger and Feynmantalk such completely different lan-guages, that neither of them is able tounderstand properly what the other is

doing. It also happened that I wasalmost the only young man in the worldwho had worked with the Schwingertheory from the beginning and had alsohad long personal contact with Feyn-man at Cornell, so I had a uniqueopportunity to put the two together.

Without consulting Oppenheimer, he sentoff a paper to Physical Review in which he syn-thesized Feynman’s and Schwinger’s work. Thisseminal 1949 paper, “The S-Matrix in QuantumElectrodynamics,” formed the basis on whichfuture physicists would devote themselves toproblems of renormalization, doing calculationsof staggering complexity. Dyson had found themathematical common ground betweenSchwinger and Feynman by focusing his atten-tion on the so-called scattering matrix, or Smatrix, which described the probability of all ofthe possible quantum electrodynamic scatteringinteractions that could occur in spacetime. Byusing the S-matrix, Dyson derived Feynman’sdiagrams from Schwinger’s more complex quan-tum field operator language. He did this bydevising a graphical technique, which enabledhim to show that there was a one-to-one corre-spondence between the S-matrix elements of hisgraphs and those of the Feynman spacetime dia-grams. Thus, the Dyson graphs provided a meansof accurately and unambiguously cataloging thearrays of probabilities corresponding to variousFeynman spacetime diagrams. Dyson’s formula-tion was more reliable than Feynman’s and moreusable than Schwinger’s. Despite initial opposi-tion by Oppenheimer and others, in January1949, at the American Physical Society confer-ence in New York city, the Feynman-Dysonmethod, as it came to be called, was enthusiasti-cally endorsed. Dyson became an overnightcelebrity and was offered half a dozen jobs.

In 1949, he returned to England, where hewas awarded a prestigious Royal Society WarrenResearch Fellowship at the University of Birm-

80 Dyson, Freeman

ingham, where he obtained the Ph.D. he hadneglected to earn at Cornell. Returning for ayear at Princeton, Dyson met and fell in lovewith Verena Haefeli. Then, after a brief periodin Europe, in May 1950, he agreed to succeedFeynman as professor of physics at Cornell. Laterthat year he and Verena were married. In 1952,finding that he did not like the professorial life,he moved to the Princeton institute as a perma-nent member. He became a U.S. citizen in 1957,the same year his wife, with whom he had beguna large family, left him. With this cataclysm inhis personal life, an era in his scientific lifeended, as well. Dyson would never again workon QED or devote himself to the exploration offundamental physics problems.

In the late 1950s, he took leave from Prince-ton in order to join the Orion Project researchteam, which was attempting to build a crewedspacecraft and send it to Mars. Dyson describeshis Orion period as one of the happiest times ofhis life. The project, conceived at the GeneralDynamics Corporation by former ManhattanProject scientists who were eager to find peace-ful uses for nuclear power, aimed to create apropulsion system that would allow humanbeings to explore the entire solar system. Theproposed vehicle, which would have been pro-pelled into space by several repeated nuclearexplosions, never made it to the launch pad andwas declared defunct in 1965. (The Nuclear TestBan Treaty of 1963 outlawed it.) Dysonattributed its demise to scientific conservatism.

In the early 1960s, he became a member ofthe U.S. Arms Control and DisarmamentAgency (ACDA) and took part in test bannegotiations. Later in the 1960s, he chaired theFederation of American Scientists, an organiza-tion founded in 1945 as the Federation ofAtomic Scientists by Oppenheimer and LosAlamos colleagues to address the dangers of thenuclear age.

In addition he has long advocated theexploration and colonization by earthlings of the

solar system and beyond and has studied ways ofsearching for intelligent life. He is well knownfor his theories about advanced civilizationsbeing able to take a planet like Jupiter apart tobuild a star-bound biosphere (known in sciencefiction as a Dyson sphere).

Dyson has said that his real life began at age45, when he began publishing a series of booksinterpreting science to the general public. Theseinclude Disturbing the Universe, an autobio-graphical account (1979); Weapons and Hope,reflections on nuclear disarmament (1984); Ori-gins of Life (1985); Infinite in All Directions(1988); and The Sun, the Genome, and the Inter-net, his exploration of the most important tech-nologies for the 21st century.

Dyson’s great achievement in synthesizingthe work of Schwinger and Feynman gave thephysics community easy access to the calcula-tional techniques of QED and thus was the keyto innumerable future breakthroughs. A com-plex man and thinker, Dyson has defined hisrelationship to science differently at differenttimes of his life. Calling himself “an artist withmathematical tools,” he has likened the plea-sures of doing mathematical physics with thoseof writing a novel, “where you as author havecomplete control over the characters . . . a self-contained world where you understand every-thing, the parts and the whole.”

See also KUSCH, POLYKARP.

Further ReadingDyson, Freeman. Disturbing the Universe. Cambridge,

Mass.: Perseus Books, 2001.———. Imagined Worlds. Cambridge, Mass.: Harvard

University Press, 1998.———. The Sun, the Genome, and the Internet: Tools

of Scientific Revolutions. Oxford: Oxford Univer-sity Press, 2000.

Schweber, Silvan S. QED and the Men Who Made It:Dyson, Feynman, Schwinger, and Tomonaga.Princeton, N.J.: Princeton University Press,1994.

Dyson, Freeman 81

E

82

� Einstein, Albert(1879–1955)German/AmericanTheoretical Physicist, Relativist,Quantum Theorist, Philosopher ofScience

Albert Einstein’s extraordinary life in physicswas a quest for nothing less than to “know howGod created this world,” to uncover the funda-mental, unifying laws of the universe. In this hesucceeded more than any scientist before him,with the possible exception of SIR ISAAC NEW-TON. His theories of special and general relativ-ity grew out of the paradoxes facing physicists asthe 20th century began: the cracks in the seem-ingly solid walls of the house of classicalmechanics that Newton and his successors hadbuilt. Revolutionary ideas about the nature ofspace, time, and matter were in the air that turn-of-the-century physicists breathed, but only adaring leap of intuition and imagination wouldunify and transform them into a new vision ofphysical reality. This astounding insight into theworkings of nature was the essence of Einstein’sgenius. Early in his career, it led him to discover-ies that confirmed the existence of atoms,launched quantum mechanics, demolished clas-sical Newtonian notions of absolute space andtime, redefined gravitation, and revolutionized

cosmology. In Einstein’s later years, however, thesame sense of inner rightness that guided him tothese discoveries led him to reject quantummechanics and to search futilely for a theory thatwould unify electromagnetic and gravitationalforces.

Little in Einstein’s early years presaged hisfuture greatness. Born in Ulm, in Wurttemberg,Germany, on March 14, 1879, into a Jewish fam-ily, he moved to Munich six weeks after hisbirth, when his father’s business ventures failed.Late in speaking, he talked slowly, pausing toconsider what he would say. When he was fouror five, his father showed him a magnetic com-pass, which convinced him that there was“something behind things, something deeplyhidden.” As a boy, he sang hymns praising God,which he had composed himself, on his way toschool. But at 12, reading a book on Euclideanplane geometry, his religious impulse took theform it would retain all his life: a sense of pro-found wonder before the natural universe. YoungAlbert did not extend this sense of awe to secu-lar authorities, however. He was a rebellious, dis-ruptive student at his Munich gymnasium,where successful students learned by memorizingand doing what they were told. Albert preferredto study at home and, at 15, quit school andrejoined his family, who had moved once again,in Italy. The following year he failed the

entrance examination to the Swiss Federal Poly-technic in Zurich, Switzerland, and was obligedto beef up his math knowledge at a preparatoryschool in Arrau, Switzerland.

It was in Arrau, walking along the river, thatAlbert began the relentless questioning ofnature’s laws that he would pursue all his life. Heasked himself an almost childlike question,What would he see if he were to chase a beam oflight at the velocity of light? He knew that New-tonian physics would say that he could catch upwith the beam of light and would then observe itas a spatially oscillatory electromagnetic field atrest. But experience told him that no such thingcould ever be observed, an assertion verified bythe great JAMES CLERK MAXWELL, whose famousequations for a unified electromagnetic fieldindicated that velocity is inherent in light.Albert’s gedanken experiment (thought experi-ment) led him to a fork in the road: he must giveup either Maxwell’s equations or Newton’s lawsof motion. For the moment, he would live withthis paradox.

The next year, he passed his entrance examsand began his studies at the polytechnic. Whenhis physics professor, Heinrich Weber, an old-fashioned classical physicist, ignored the giantsof electromagnetic field theory, Maxwell andMICHAEL FARADAY, Albert began skippingWeber’s classes and reading physics on his own.When he was not hanging out in coffee houses,playing his violin, or spending time with one ofthe few women physics students, Mileva Maric,he conducted experiments in the polytechnic’slaboratories, one of which ended in an explosionthat almost cost him a hand. He managed to passhis exams and graduate in 1900 with unexcep-tional grades.

Having failed to impress his professors, whomight have eased his way into the university sys-tem, he floundered at first, taking low-payingteaching jobs. When he was offered a well-paidpost as a patent clerk in the Swiss Patent Officein Bern, in 1901, he grabbed it and became a

Swiss citizen. By 1903, he was in a position tomarry Mileva, who had, meanwhile, given birthto an illegitimate daughter, Lieserl, andentrusted her to the care of relatives in Serbia.Albert never knew his daughter, whose fate hasremained a mystery. Over the next few years,Mileva and Albert would have two sons, HansAlbert and Edward. Albert would work as atechnical expert at the patent office until 1909,years he would later remember as “my best timeof all.” In his friend and coworker Michael Bessohe had an ideal sounding board for the physicstheories he dreamed up in his spare time. It wasBesso who steered him to the work of ERNST

MACH, one of the few leading scientists to ques-

Einstein, Albert 83

Albert Einstein’s theories of special and generalrelativity demolished classical Newtonian notions ofabsolute space and time, redefined gravitation, andrevolutionized cosmology. (AIP Emilio Segrè VisualArchives, Bundy Library)

tion the Newtonian paradigm that underlay thebelief in an ether, the mysterious fluid pervadingall of space, in which electromagnetic waveswere said to propagate. To Mach, the ether was a“metaphysical obscurity.” Observation, heinsisted, was the only way for scientists to know.As a corollary, he held that space was no abstractthing, but an expression of interrelationshipsamong events: “All masses and all velocities, andconsequently all forces, are relative.” AlthoughMach would later deny his role as the progenitorof relativity, his influence on the young Einsteinwas profound. By 1905, Albert’s thoughts beganto crystallize. That year he obtained a doctoraldegree from the University of Zurich and pub-lished three papers—on Brownian motion, thephotoelectric effect, and special relativity. Eachunraveled a mystery that had stumped the bestscientific minds.

Einstein’s first paper had a major impact onthe running debate between physicists of theatomist and energeticist schools. In 1827, RobertBrown had observed through a microscope therandom motion of small particles in a fluid: themotion of the particles increases when the tem-perature increases but decreases if larger particlesare used. Since then physicists had been trying toexplain the phenomenon. To the energeticists,who rejected the concept of atoms and thought ofall matter as continuous, Brownian motion, withits discrete bumps, was disturbing. Einstein onlyincreased their consternation when he explainedthe phenomenon as the effect of large numbers ofmolecules bombarding the particles. His assump-tions allowed him to predict the movement andsize of the particles, values that were later verifiedexperimentally by the French physicist JEAN-BAP-TISTE PERRIN. Experiments based on this workwere used to obtain an accurate value of the Avo-gadro number, which is the number of atoms inone mole of a substance, and the first accuratevalues of atomic size. Einstein had struck a deci-sive blow in favor of the theory that matter iscomposed of atoms.

In his second classic paper, Einsteinaddressed himself to a puzzle surrounding theso-called photoelectric effect, the ejection ofelectrons from the surface of a substance by radi-ation. In the classical theory of electromag-netism, light was viewed as a wave. Maxwell’sequations for the electromagnetic field predictedthat when light waves fall on a metal surface, theenergy of the electrons that are ejected dependson the intensity as well as the frequency of thelight. But the experiment that produced thephotoelectric effect showed that the energy ofthe electrons ejected is quantized according tothe frequency and not the intensity of the light.

In 1900 MAX ERNEST LUDWIG PLANCK,while studying blackbodies (objects that do notreflect surface light and are thus perfect emittersand absorbers of radiation at all frequencies),had discovered a formula that related the energyof the radiation to its frequency. This was hisfamous blackbody radiation law, which pre-dicted that E = hv, where E is the energy, h is anumber known as Planck’s constant, and v is thefrequency of radiation. He was led to the realiza-tion that a sound derivation of his law couldonly be based on the postulate that the energy ofradiation is emitted and absorbed, not continu-ously, but in discrete packets, which he calledquanta. Planck postulated that the materialoscillators in the walls of the blackbody hadunits of energy that were quantized in terms ofthe frequency of light, but he did not quantizethe light itself.

It was Einstein who took that step, generaliz-ing from Planck’s quantum postulate. Suppose,he said, the light itself is quantized according toits frequency. Light then would consist of parti-cles, which he called light quanta or photons. Heused Planck’s constant as a way to determine theenergy of these light particles, suggesting that thekinetic energy of each electron is equal to the dif-ference in the incident energy and the lightenergy needed to overcome the threshold ofemission. The equation expressing this is known

84 Einstein, Albert

as Einstein’s photoelectric law. This work wouldearn him the Nobel Prize in physics 16 yearslater, in 1921. It would also mark the beginningof his long friendship with Planck, who dislikedthe quantum idea he himself had fathered asmuch as Einstein had. For years Einstein wouldstruggle in vain to understand how the classicalMaxwell’s equations could consistently producehis light quanta. The key to this enigma would befound 30 years later by RICHARD PHILLIPS FEYN-MAN, JULIAN SEYMOUR SCHWINGER, and others,in the form of quantum electrodynamics, a the-ory that Einstein never accepted.

Although solving the enigma of Brownianmotion and discovering that light has a particleproperty were no small achievements, they palednext to the sweeping discoveries enunciated inEinstein’s third 1905 paper, “On the Electrody-namics of Moving Bodies,” which unveiled thetheory of special relativity. Nineteenth-centuryphysicists had amassed a growing body of knowl-edge indicating that the behavior of light andother electromagnetic radiation regularly con-tradicts classical Newtonian physics. Since1881, they had been living with the results ofthe Michelson–Morley experiment, which con-clusively demonstrated that the velocity of lightis constant and does not vary with the motion ofeither the source or the observer. Designed tomeasure the effect of the ether, the mysteriousmedium pervading the universe, in which lightwaves were thought to be propagated, theMichelson–Morley experiment appeared to dis-prove the ether’s very existence. A number oftheories arose, attempting to rescue this pillar ofthe Newtonian universe, including the brashidea, arrived at independently by HENDRIK

ANTON LORENTZ and GEORGE FRANCIS

FITZGERALD, that objects moving through theether contract slightly in the direction of theirmotion and thereby hide the effect of the changein the velocity of light.

As for Einstein, the lack of an ether was nota problem but an opportunity to propose the

central tenet of special relativity: since there isno frame of reference against which absolutemotion can be measured, all motion can only bemeasured as relative to the observer. He furtherproposed that the velocity of light is constantand does not depend on the motion of theobserver. From these two postulates and someelementary algebra, he concluded that when anobject is in uniform motion relative to anobserver, length decreases and time slows by theamount postulated by Lorentz, while the inertialmass of particles increases. At ordinary veloci-ties, the magnitude of these effects is negligibleand Newton’s laws still apply. But at velocitiesapproaching that of light, they become substan-tial. To quantify this strange state of affairs, Ein-stein found that he could use the Lorentztransformations, a group of equations that math-ematically predict the increase of mass, shorten-ing of length, and dilation of time for an objecttraveling at near the speed of light, while thevelocity of light is always the same. Many yearslater, Einstein’s conclusions on time dilation,length contraction, and mass increase would beconfirmed by observations of fast-moving sub-atomic particles and cosmic rays.

Since an object moving at the velocity oflight would appear to an observer to have zerolength and infinite mass, while time would standstill, Einstein concluded that an object cannotmove at a velocity equal to or greater than thevelocity of light. Answering the question he hadasked himself in Arrau, at age 16, he concludedthat one could never catch up with a beam oflight. Maxwell’s equations, which stated that thevelocity of light was constant, were correct,whereas the ether and Newton’s absolute spacewere superfluous. There was no need for any pre-ferred universal frame of reference. What matterare observable events, and no event can beobserved until the light that communicates itreaches the observer. If space and time had beenthe absolutes in Newton’s universe, the speed oflight was the only absolute in Einstein’s. Indeed,

Einstein, Albert 85

no velocity greater than that of light has everbeen detected.

In the process of exploring the furtherimplications of special relativity, Einstein wasled, in 1907, to the discovery that mass isequivalent to energy, which he expressed inwhat is undoubtedly the most famous equationever written: E = mc2, or energy equals masstimes the square of the speed of light. Giventhe magnitude of the speed of light, Einstein’sequation revealed that an enormous amount ofenergy is stored as mass. It would provide thekey to both nuclear power and nuclearweapons, although such applications were farfrom Einstein’s mind at the time.

Special relativity would undergo a vital evo-lution in 1908 when Einstein’s former professorat the polytechnic, the brilliant mathematicianHerbert Minkowski, expressed Einstein’s ideas interms of a geometric form: a four-dimensionalcontinuum made up of three dimensions of spaceand one of time: Minkowski space or spacetime. Ifthis interpretation helped make relativityacceptable to most physicists, it led Einsteinhimself to remark, “Since the mathematicianshave invaded the theory of relativity, I do notunderstand it myself anymore.”

With the lay public, not to mention a goodmany scientists, confounded by special relativ-ity, recognition was not immediate. Einsteinwas brusquely rejected when he applied for anacademic job at the University of Bern. But by1909 his discoveries were gaining appreciationin the scientific community. Einstein wasoffered a junior professorship at the Universityof Zurich. As his reputation grew, in 1911 hebecame a full professor, first in Prague, and, in1912, in Zurich. Then in 1914, just as war wasbreaking out in Europe, Einstein moved hisfamily to Berlin, where he had been offered apost, without teaching duties, as director of theKaiser Wilhelm Institute.

By this time, Einstein was nearing the endof his eight-year struggle to make the theory of

relativity generally applicable by consideringnot only systems that are in uniform motionbut also those that are accelerating. The specialtheory dealt with inertial mass, which is theresistance objects offer to change in their stateof motion. Inertial mass is what you feel whenyou glide a bowling ball along the floor. Gravi-tational mass is what you feel when you lift it.Yet, for some reason, the inertial and gravita-tional masses of any given object are equiva-lent. Moreover, because they are equivalent,they cancel each other out. Since GALILEO

GALILEI’s discovery that an apple and a cannon-ball fall at the same velocity, scientists hadbeen aware of this. But what had struck Galileoand Newton as mere coincidence appeared toEinstein in a different light.

He had begun his relentless pursuit of a rela-tivistic theory of gravity in 1907. In his famouselevator gedanken experiment, he had shown thatpeople in a sealed elevator would be unable todetermine whether they were in a real gravita-tional field or just feeling the inertial forces dueto acceleration. Einstein would later call thisidea, known as the principle of equivalence, “thehappiest thought of my life.” Einstein reasonedthat if the effects of gravity are identical to thoseof acceleration, gravitation itself might beregarded as locally equivalent.

In this context he investigated the effect ofgravitation on light and in 1911 concluded thatlight rays would be bent in a gravitational field.He realized, however, that if gravitation were aform of acceleration, the new theory wouldrequire something other than the four-dimen-sional Euclidean geometry that underlay thespacetime continuum of special relativity. More-over, to prevent reintroducing the concept ofthe ether, the mathematical formalism had to beexpressed in a covariant manner, that is, one inwhich the physical laws seen by observers arenot tied to a preferred frame of reference. In1912, Einstein enlisted his friend Marcel Gross-man to find a way of expressing the new theory

86 Einstein, Albert

in terms of a new mathematical language calledcovariant tensor calculus.

Despite many setbacks, by 1915, Einsteinhad developed these ideas into the general theoryof relativity, which states that masses distort thestructure of spacetime and that this distortionproduces the effects of gravitation. Matter curvesspace, and what we call gravitation is only theacceleration of objects as they fall along their tra-jectories in curved spacetime. The ability of thisnew formulation to account for a phenomenonthat Newton’s theory could not—the anomalouspart of the perihelion in Mercury’s orbit—con-vinced Einstein himself that his theory was cor-rect. He had only a handful of supporters,however, during the chaotic years of World WarI. When not involved in scientific research, Ein-stein was embroiled in pacifist activities and abitter separation from Mileva, who returned toZurich with their two sons. When his divorcewas finalized in 1919, Einstein married his cousinand longtime mistress Elsa Einstein.

That same year, his theory of general rela-tivity would achieve spectacular recognition.The English astronomer Arthur Eddingtontraveled to Brazil to observe a solar eclipse, hop-ing to confirm general relativity’s predictionthat the apparent position of stars would shiftwhen they are seen near the Sun because itsintense gravity would bend the light rays fromthe stars as they pass the Sun. When Eddingtonannounced that the apparent bending of thelight rays seen from the stars was offset to justthe degree predicted by general relativity, Ein-stein became an overnight internationalcelebrity. General relativity was further con-firmed in 1925, when its prediction that a redshift is produced if light passes through a stronggravitational field was observed.

General relativity gave an exciting newanswer to the age-old question, What existsbeyond the edge of the universe? Since gravity islinked to the geometry of a curved four-dimen-sional space-time, the universe can be both infi-

nite in four dimensions and bounded in three, tothose who observe it from a three-dimensionaluniverse. Since matter warps three-dimensionalspace, the total of the mass in all the galaxies inthe universe may be sufficient to cause three-dimensional space to close around them.

Despite burgeoning recognition of his rela-tivity theory, the conservative Nobel Prize com-mittee awarded Einstein the 1921 prize for hiswork on the photoelectric effect. Einstein wouldspend the next decade traveling widely—withinEurope, to the United States, to Palestine, andto South America—explaining his theories tomostly rapt audiences. The 20s was also the timewhen Einstein would commence his lifelongdebate with the adherents of the new quantummechanics. As early as 1909 Einstein hadpointed to the need to reconcile the particle andwave theories of light. It would be LOUIS-VIC-TOR-PIERRE, PRINCE DE BROGLIE, who in 1923,using Einstein’s mass–energy equation andPlanck’s quantum theory, would find a way todescribe the wave nature of a particle. WhereasEinstein was supportive of de Broglie’s work, herejected its further development by ERWIN

SCHRÖDINGER, WERNER HEISENBERG, NIELS

HENRICK DAVID BOHR, and others, into a theoryexpressed in terms of probabilities, which essen-tially banished microscopic causality in space-time. For Einstein the revolutionary, this wasone revolution too many, signaling the end ofphysics itself. His meeting with Bohr in 1927 atthe Solvay Conference marked the beginning ofa famous series of debates between the twogiants, in which Einstein would present agedanken experiment designed to debunk quan-tum theory, which Bohr would then proceed todemolish. For Einstein, the great stumblingblock was the principle of indeterminacy: “Goddoes not play dice,” he told Bohr, who replied,“Einstein, stop telling God what to do.” To thisday the conceptual and mathematical incompat-ibility of relativity and quantum mechanics hasnot been resolved.

Einstein, Albert 87

With Hitler’s ascendance to power in 1933,the heady period of discovery and unfettereddebate in European physics came to an end.That year Einstein emigrated to the UnitedStates, accepting a position at Princeton Uni-versity’s Institute for Advanced Study, where hewould remain for the rest of his life. His secondwife, Elsa, died in 1936, and he never remarried.In 1939, with the Hungarian physicist Leo Szi-lard, he wrote to President Roosevelt, informinghim that Hitler had the ability to build anatomic bomb, an admonition that led to theestablishment of the Manhattan Project. WhenWorld War II ended, Einstein was tormented byhis role in the development of the Americanatomic bomb and campaigned actively to abol-ish nuclear weapons. In 1952, Einstein, who hadhelped establish the Hebrew University ofJerusalem, was offered the presidency of Israel.He refused, believing he was temperamentallyunsuited for the job. He eloquently described thetwo poles of his nature:

My passionate sense of social justice andsocial responsibility has always con-trasted oddly with my pronounced lackof need for direct contact with otherhuman beings and human communities.I am truly a “lone traveler” and havenever belonged to my country, my home,my friends, or even my immediate family,with my whole heart; in the face of allthese ties, I have never lost a sense of dis-tance and a need for solitude.

In the solitude of his later years, believingthat “God is subtle, but he is not malicious,” Ein-stein labored tirelessly to plumb that subtlety,seeking a theory that would unify gravity andelectromagnetism. This time the mystery did notyield to him.

Albert Einstein died in Princeton on April18, 1955, when an aneurysm in his abdominal

aorta burst. He was cremated that day at 4 P.M. inTrenton, New Jersey. His ashes were scattered ata nearby river.

After Einstein, the mathematical languageof relativity became the stuff of which all thelaws of physics would have to be constructed.From then on, one of the key tests of any newphysical law would be whether it could be writ-ten in a “relativistic form,” capable of satisfyingthe fundamental structure of space and time thatEinstein had revealed.

See also BOLTZMANN, LUDWIG; DOPPLER,CHRISTIAN; MICHELSON, ALBERT ABRAHAM;OPPENHEIMER, J. ROBERT.

Further ReadingAczel, Amir D. God’s Equation: Einstein, Relativity, and

the Expanding Universe. New York: Dell, 2000.Balibar, Françoise. Einstein: Decoding the Universe.

New York: Harry N. Abrams, 2001.Bernstein, Jeremy. Albert Einstein and the Frontiers of

Physics. Oxford: Oxford University Press, 1996.Bodanus, David. E = mc2: A Biography of the World’s

Most Famous Equation. New York: Walker, 2000.Brian, Denis. Einstein: A Life. New York: John Wiley

& Sons, 1997.Calder, Nigel. Einstein’s Universe. New York: Random

House, 1990.Einstein, Albert. The Expanded Quotable Einstein,

Alice Calaprice, ed. Princeton, N.J.: PrincetonUniversity Press, 2000.

———. Ideas and Opinions. New York: RandomHouse, 1988.

———. Out of My Later Years. Secaucus, N.J.: CarolPublishing Group, 1972.

Howard, Donald R., and John Stachel, eds. Einstein:The Formative Years 1879–1909. Boston:Birkhauser, 1986.

Overbye, John. Einstein in Love. New York: Viking,2000.

Pais, Abraham. Subtle Is the Lord . . . the Science andthe Life of Albert Einstein. Oxford: Oxford Uni-versity Press, 1982.

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89

� Faraday, Michael(1791–1867)BritishTheoretical and Experimental Physicist(Electromagnetism), Physical Chemist

Michael Faraday was among the greatest 19th-century physicists to engage in the quest tounderstand electromagnetism and to harnesselectricity for human ends. His experimentalwork led him to discover electromagnetic induc-tion and invent the electric motor, the electricgenerator, and the transformer. As a theorist,Faraday introduced the concept of force fields toexplain the relationship of electricity and mag-netism, replacing the time-honored idea ofaction at a distance. This new paradigm woulddominate every aspect of modern physics.

Nothing in the circumstances of MichaelFaraday’s birth, on September 22, 1791, in New-ington, Surrey, England, pointed to his illustri-ous future. His father, a poor blacksmith, wouldleave for London that same year to seek work.As a boy, Michael learned to read and write butwas given little formal education and had a weakgrounding in mathematics. When he was 14 hewas apprenticed to a bookbinder and booksellerin London. It was there that his eclectic scien-tific training began. Encouraged to read,Michael devoured every book on science he

could find in the shop and was soon performinghis own crude experiments on electricity. Read-ing the works of the eminent French chemistAntoine Lavoisier sparked his fascination withchemistry. His bookbinding training helped himdevelop the manual dexterity that he would useto good purpose as an experimenter.

The young Faraday also took advantage ofthe educational opportunities London had tooffer. In 1810, he was introduced to the CityPhilosophical Society, in which he received abasic education in science. He also began toattend the lecture series sponsored by the RoyalInstitution. In 1812, after listening to lecturespresented by Sir Humphry Davy, the Britishchemist, Faraday managed to get himself hired asthe great man’s laboratory assistant. The follow-ing year, he accompanied him to France and Italy,where he was exposed to the latest advances inscientific research and attended lectures by someof Europe’s most renowned researchers, includingthe pioneer of current electricity, ALESSANDRO

GUISEPPE ANTONIO ANASTASIO VOLTA.When he returned to London Faraday

embarked on a 20-year period at the Royal Insti-tution when he would make most of his pioneer-ing discoveries in electricity and chemistry. Atthe beginning he concentrated on chemistry,developing a method for liquefying chlorine andisolating benzene, a compound now widely used

in chemical products. He combined his interestsin chemistry and electricity in the study of elec-trolysis, the production of chemical changethrough certain conducting liquids, that is, elec-trolytes, and in 1834 formulated what becameknown as Faraday’s laws of electrolysis, whichstate that (1) the amount of chemical change pro-duced is proportional to the charge passed, and(2) the amount of chemical change produced by agiven charge depends on the ion concerned.

His great work in electromagnetism began in1820, when the Danish physicist HANS CHRIS-TIAN ØRSTED discovered that a current in a wiredeflects a magnetic needle. When Faradayrepeated this experiment he found that a magnetalso exerts a force on a wire carrying an electriccurrent. Faraday explained the orientation ofØrsted’s compass by stating that circular lines ofmagnetic force are produced around the wire, ahypothesis he demonstrated by devising an appa-ratus that would cause a magnet to revolve aroundan electric current. In 1821, Faraday showed howelectric and magnetic forces could be convertedinto mechanical motion by positioning a current-carrying wire between the north and south polesof a horseshoe magnet. The interaction of forcesmade the wire rotate, thus creating a simple elec-tric motor. He demonstrated the followingdynamics: (1) If a current flows in a wire close to amagnet that is not fastened down, the magnetmoves. (2) If a current flows in a wire close to amagnet that is fastened down, the wire moves. Byshowing that either the conductor or the magnetcould be made to move, Faraday had demon-strated with stunning simplicity that electricalenergy could be converted into motive force.

Faraday’s fame grew, eventually eclipsing thatof his mentor Davy, who felt that his own role inFaraday’s discoveries had been ignored. In 1824,he was elected as a member of the Royal Society,England’s premier scientific organization. The fol-lowing year he began to popularize sciencethrough his lectures at the Royal Institution, anactivity he would engage in throughout his career.

In 1831, Faraday embarked on the ground-breaking work that would lead him to the dis-covery of electromagnetic induction, that is, theproduction of electricity by means of varyingmagnetic intensity. He was not the first todemonstrate the phenomenon, but the first tounderstand its meaning. Seven years earlier,François Arago had found that a rotating non-magnetic copper disk caused the deflection of amagnetic needle placed above it. Nobody at thetime could explain what was happening. ThenFaraday performed the following experiment:using a ring of soft iron wrapped in two windingsof insulated wire, he connected one wire to agalvanometer (which measures electric current)and the other to a battery. At first it appearedthat nothing had happened. But when the cir-cuit was broken and reconnected, the gal-vanometer recorded the pulse of an electriccurrent. Faraday realized that an induced currentwas produced while the intensity of the magne-tized iron ring was rising or falling: that is, achanging magnetic field can induce a current.(At the same time another American physicist,JOSEPH HENRY, made the same discovery butcould not spare time from his teaching to publishhis findings.) The device Faraday constructed todemonstrate induction was the first transformer,or mechanism for changing the voltage suppliedby an electrical current. Faraday made anothergreat discovery when he realized that the motionof the copper wheel relative to the magnet inArago’s experiment caused an electric current toflow in the disk, which in turn set up a magneticfield and deflected the magnet. He built a simi-lar device in which the current produced couldbe led off; this was the first electric generator.

Throughout the 1830s Faraday’s string ofdiscoveries showed no signs of abating. In 1832,he showed that the flow of electrostatic chargegives rise to the same effects as electric currents,thus proving that there is no basic differencebetween them. Then, in 1837, he investigatedelectrostatic force and demonstrated that it con-

90 Faraday, Michael

Fermi, Enrico 91

sists of a field of curved lines of force, and thatdifferent substances take up different amounts ofelectric charge when subjected to an electricfield. This led Faraday to conceive of specificinductive capacity.

Faraday explained magnetism in terms oflines of force, which stretch out in all directions,flowing out of the north pole and into the southpole of a magnet. He knew little mathematicsand found this concrete approach to the descrip-tion of electricity and magnetism much moreuseful than the equations for the force betweencharges or currents in terms of an action at a dis-tance. The field concept allowed the electricand magnetic forces to be clearly visualized andformed the basis for the mathematical descrip-tion of electricity and magnetism, known todayas electromagnetic theory.

Faraday suggested that the propagation oflight through space consisted of vibrations in thefield lines of electromagnetic force. He alsofound that when light passes through a medium,a magnetic field rotates the plane of polarizationof the light. This is now known as the Faradayeffect. His concepts of electric and magneticfields were put into rigorous mathematical forma generation later by JAMES CLERK MAXWELL,who showed that light is, in fact, an oscillatorydisturbance in the electromagnetic field lines,just as Faraday had predicted.

Another aspect of Faraday’s work, whichillustrates his prescience, was his suggestion thata link between gravitation and electromag-netism may exist. Such a link was observed 70years later in a test of ALBERT EINSTEIN’s generaltheory of relativity, when light rays passing nearthe Sun were found to be deflected.

By 1850, Faraday’s years of brilliant scien-tific invention had ended. He abandonedresearch and then lecturing, retiring in 1858 ona small pension. Faraday was a deeply religiousman, whose principles would not allow him totake part in preparation of poison gas for use inthe Crimean War. Despite his fame, he remained

modest, refusing to be knighted or receive hon-orary degrees. He died on August 25, 1867, inthe Hampton Court apartment that had beengiven to him by Queen Victoria.

He is honored by the use of his name in thefarad, the Système International d’Unités (SI)unit of capacitance, and the Faraday constant,the quantity of electricity needed to liberate astandard amount of substance in electrolysis.

Faraday’s extraordinary ability to visualizeand pictorially represent physical processesunderlay his discoveries of basic laws, which leddirectly to the age of electricity. His special geniusenabled him to visualize not only his experimen-tal apparatus (the coil and the magnet), but alsothe invisible field that surrounds it and conveysthe electromagnetic force. His introduction of theconcept of a field of force may well be his greatestcontribution to modern science.

Further ReadingCantor, Geoffrey, David Gooding, and Frank A. James.

Michael Faraday. Amherst, N.Y.: PrometheusBooks, 1996.

Day, Peter, compiler. The Philosopher’s Tree: A Selec-tion of Michael Faraday’s Writings. Bristol, Eng-land: Institute of Physics, 1999.

Keithley, Joseph F. The Story of Electrical and MagneticMeasurements: From Early Days to the Beginningsof the 20th Century. New York: Wiley-IEEE Press.1998.

Ludwig, Charles. Michael Faraday: Father of Electron-ics. Scottdale, Pa.: Herald Press, 1978.

Russell, Colin Archibald. Michael Faraday: Physics andFaith. Oxford: Oxford University Press, 2000.

� Fermi, Enrico(1901–1954)Italian/AmericanTheoretician and Experimentalist,Particle Theorist, Nuclear Physicist

Enrico Fermi was the last great physicist to wearthe double hat of theorist and experimentalist

92 Fermi, Enrico

before the explosion of knowledge after 1900forced physicists to specialize. His early researchin using slow neutrons to produce new radioactiveelements won him a Nobel Prize in physics in1938. His theory of radioactivity, known as betadecay, introduced the last of the four basic forcesknown in nature: gravity, electromagnetism, and,operating within the nucleus of the atom, thestrong force and Fermi’s weak force. His mostfamous achievement was the creation of the firstknown chain reaction in a nuclear reactor, whichled to both the atomic bomb and the productionof nuclear power for peaceful purposes.

Enrico Fermi was born in Rome on Septem-ber 19, 1901, the youngest of the three childrenof Alberto Fermi, an administrator with the Ital-

ian national railroad, and Ida de Gattis. He dis-covered physics at age 14, when, stunned by thedeath of his older brother, he took refuge in read-ing from cover to cover two old volumes of ele-mentary physics that he had chanced to find. Hewas a prodigy in secondary school, composing anessay for university admission that was deemedworthy of a doctoral examination. In 1918, heentered the elite Reale Scuola Normale Superior,associated with the University of Pisa. Fermireceived his Ph.D. four years later, at age 21, for athesis on X rays. His subsequent postdoctoralstudy at Göttingen University, where he workedunder MAX BORN among such leaders of thequantum revolution as WOLFGANG PAULI andWERNER HEISENBERG, was perhaps the only timein his career when his own talents were eclipsed.

In 1924, Fermi accepted a position as lec-turer in mathematics at the University of Flo-rence. There he published a paper on thebehavior of perfect gases, which spurred thephysics department at the University of Rome tomake him an offer; Fermi accepted, becoming afull professor of theoretical physics at age 25.Intent on reviving Italian physics, he set aboutattracting the best young minds to Rome.

He soon developed a statistical method forpredicting the characteristics of electronsaccording to Pauli’s exclusion principle, whichstates that no two subatomic particles can bedescribed with the same quantum numbers.Fermi–Dirac statistics, as they came to beknown, continue to be useful in nuclear andsolid state physics, for example, to determine thedistribution of electrons at different energy lev-els. Particles with half-integer spins, such as theelectron, that obey Fermi–Dirac statistics, werelater named fermions.

Fermi gained national recognition for his1928 book Introduction to Atomic Physics, thefirst textbook on modern physics to appear inItaly, and the following year became theyoungest member of the prestigious RoyalAcademy of Italy.

Enrico Fermi developed the theory of radioactivityknown as beta decay, which is based on a weak forceacting within the nucleus of the atom. He also createdthe first known chain reaction in a nuclear reactor. (AIPEmilio Segrè Visual Archives, Bainbridge Collection)

In the 1930s he engaged in experimentalwork that yielded some of his most importantresults and earned him an international reputa-tion. In 1930, Pauli had proposed that the emis-sion of an electron in beta decay is accompaniedby the production of an unknown particle.Pauli’s particle had neither charge nor mass; as aresult, it had never been detected. In 1934,Fermi experimentally confirmed Pauli’s hypoth-esis and dubbed the new particle the neutrino.That same year Frederik and Irène Joliot-Curiediscovered artificial radioactivity, using alphaparticle bombardment. Learning of their work,Fermi began producing new radioactive isotopesby neutron bombardment. He found that a blockof paraffin wax or a jacket of water around theneutron source produced slow, or “thermal,”neutrons, which are more effective in producingsuch elements. This work garnered him the 1938Nobel Prize in physics.

Receiving the Nobel Prize proved to be morethan an honor for Fermi; it saved his life. In1928, he had married a Jewish woman, Laura,with whom he had two children. As Italian anti-Semitism grew during the 1930s, under BenitoMussolini’s fascist regime, the Fermis’ life becameincreasingly precarious. Taking the opportunityto leave Italy for the Nobel Prize ceremonies,they emigrated to the United States.

Their new home was in New York, whereFermi received a position at Columbia Univer-sity. Together with two eminent Hungarianémigrés, Leo Szilard and EUGENE PAUL WIGNER,Fermi wrote a famous letter to Franklin DelanoRoosevelt, warning him of the danger of Hitler’sscientists’ applying the principle of the nuclearchain reaction to the production of an atomicbomb. Roosevelt acted on the warning, andFermi and Szilard soon found themselves work-ing on the development of a nuclear reactor atColumbia.

Continuing his work on the fission of ura-nium induced by neutrons, Fermi constructed anelegantly simple machine that he called an

“atomic pile.” It had a moderator consisting of apile of purified graphite blocks, to slow the neu-trons, with holes drilled in them to take rods ofenriched uranium. Other neutron-absorbingrods of cadmium, called control rods, could belowered into or withdrawn from the pile to limitthe number of slow neutrons available to initiatethe fission of uranium.

In 1941, when the Manhattan Project con-solidated its operations at the University ofChicago, Fermi and his team moved there andbegan building a nuclear reactor on the univer-sity’s squash court. On December 2, 1942, thecontrol rods were withdrawn for the first time andthe reactor began to work, powered by the firstself-sustaining nuclear chain reaction. It was theforerunner of the modern nuclear reactor, whichreleases the basic binding energy of matter.

Fermi moved to Los Alamos, New Mexico,and, with ARTHUR HOLLY COMPTON, led theteam that constructed an atomic bomb, whichused the same nuclear reaction process, but nowwithout control mechanisms. This bomb pro-duced a nuclear explosion in July 1945 at Alam-ogordo Air Base, New Mexico. Fermi used asimple experiment to estimate its explosiveyield: he dropped scraps of paper both before theexplosion and afterward, when the blast windarrived, and compared their displacement. A fewweeks later atom bombs were dropped onHiroshima and Nagasaki, in Japan.

After the war Fermi, who had become aU.S. citizen in 1944, returned to the Universityof Chicago as Distinguished-Service Professor ofNuclear Studies. There he continued hisresearch on the basic properties of nuclear parti-cles, focusing on mesons, which are the quan-tized form of the force that holds the nucleustogether. He also played a key role in the con-struction of the university’s synchrocyclotronparticle accelerator.

In 1949, he argued against U.S. develop-ment of the hydrogen bomb, calling it “aweapon, which in practical effect is almost one

Fermi, Enrico 93

of genocide.” The warning went unheeded.Fermi died prematurely in Chicago of stomachcancer on November 28, 1954, but his name andhis achievements have been honored in manyways: element number 100, discovered in 1955,was named fermium. The Fermi is a unit oflength used in atomic and nuclear physics, andthe Fermi level is the energy level in a solid atwhich a quantum state would be equally likely tobe empty or to contain an electron. Finally, thehighly prestigious Fermi Award, which he him-self received shortly before his death, was estab-lished in his honor.

See also DIRAC, PAUL ADRIEN MAURICE.

Further ReadingCooper, Dan. Enrico Fermi and the Revolutions in Mod-

ern Physics. Oxford: Oxford University Press,1998.

Fermi, Laura. Atoms in the Family: My Life with EnricoFermi. Chicago: University of Chicago Press,1994.

Segrè, Emilio. Enrico Fermi, Physicist. Chicago: Uni-versity of Chicago Press, 1995.

� Feynman, Richard Phillips(1918–1988)AmericanTheoretician, Quantum Field Theorist,Particle Physicist

Richard P. Feynman was the brilliant, charismaticarchitect of the modern space-time diagram for-mulation of quantum electrodynamics (QED),the theory that describes the quantum interactionof electrons with electromagnetic fields. For thiswork he shared the 1965 Nobel Prize in physicswith JULIAN SEYMOUR SCHWINGER and SIN-ITIRO TOMONAGA.

He was born on May 11, 1918, in New YorkCity, the descendant of Russian and Polish Jewswho had immigrated to the United States in thelate 19th century. His father, Melville, had

attended a homeopathic medicine institute butchose not to practice, engaging instead in aseries of precarious business ventures. Hestrongly influenced his young son’s approach toproblem-solving activities, stressing that whatmattered was not facts per se, but the process offinding things out. His mother, Lucille Phillips,was born in New York, into a family of prosper-ous, assimilated Jews, and attended the broadlyhumanistic Ethical Culture School. Feynmancredited her for teaching him that “the highestforms of understanding we can achieve arelaughter and human compassion.” When Feyn-man was four or five, a baby brother died shortlyafter birth. His sister, Jean, was born when hewas nine; she, too, would become a physicist.Feynman grew up in Far Rockaway, Queens,where he had excellent instruction in chemistryand mathematics in the public schools. In addi-tion to impressive mathematical skills, he mani-fested an early mechanical aptitude: he startedcollecting old radios for use in his “personal lab-oratory” at age 10 and by age 12 was repairing hisneighbors’ radios.

As an undergraduate at the MassachusettsInstitute of Technology in Cambridge, he wrotea thesis proposing an original and enduringapproach to calculating forces in molecules.After graduating in 1939, he continued his stud-ies at Princeton University, earning a Ph.D. in1942 for a thesis directed by JOHN ARCHIBALD

WHEELER, in which he put forth a theory ofadvanced and retarded electromagnetic interac-tions that travel backward and forward in time.This relativistic “action-at-a-distance” approachto electromagnetism attempted to replace thewave-oriented electromagnetic picture of JAMES

CLERK MAXWELL with one based entirely on par-ticle interactions mapped in space and time. Hedeveloped an approach to quantizing the theorygoverned by the principle of least action, a tech-nique that minimized a quantity that was equalto the energy multiplied by the time associatedwith the physical processes. Feynman’s method

94 Feynman, Richard Phillips

calculated all the probabilities of all the possiblepaths a particle could take in moving from onespace-time point to another. His first lecture onthis subject at Princeton was intriguing enoughto attract ALBERT EINSTEIN, WOLFGANG PAULI,and John von Neumann to the audience.

Shortly after receiving his doctorate, overhis parents’ objections, he married his first love,Arlene Greenbaum, who was ill with tuberculo-sis. She was with him, in nearby sanitoriums,when, during World War II, he joined the Man-hattan Project to build the atomic bomb, work-ing first at Princeton, New Jersey, then at LosAlamos (1943–1945). When Arlene’s healthdeteriorated rapidly and she died, Feynmanburied his sorrow in research. He became theyoungest group leader in the theoretical divi-sion, headed by HANS ALBRECHT BETHE, withwhom he devised the formula for predicting theenergy yield of a nuclear explosive. He was alsoin charge of the project’s primitive computingeffort, using a hybrid of new calculatingmachines and human workers to try to processthe vast amounts of numerical computationrequired by the project. At Los Alamos, heflouted military discipline with a series of eccen-tric practical jokes, exposing the inadequatesecurity by breaking into safes where atom bombplans were stored. Present at the first test of anatomic bomb on July 16, 1945, at Alamogordo,New Mexico, he was initially euphoric but lateranxious about the deadly force that he and hiscolleagues had unleashed.

From 1945 to 1950, Feynman was at CornellUniversity as professor of theoretical physics;there he returned to his research on formulatinga consistent theory of QED. He was present atthe Shelter Island conference in 1947 when thefoundations of QED were shaken by two keyexperimental results. In 1947, WILLIS EUGENE

LAMB, working in ISIDOR ISAAC RABI’s labora-tory at Columbia University, began experimen-tal investigations that would have a profoundimpact on the formulation of QED. Applying

the art of spectroscopy with unprecedented pre-cision, he shone a beam of microwaves onto ahot wisp of hydrogen gas blowing from an oven.He found that two fine structure levels in thenext lowest group, which should have coincidedwith the Dirac theory, were in reality shifted rel-ative to each other by a certain amount (theLamb shift). A second flaw in the Dirac theorywas found that same year in the same Columbialab, by POLYKARP KUSCH, who discovered a tinydiscrepancy from what the theory predictedwhen he made highly accurate measurements ofthe magnetic moment of the electron. On thelast day of the Shelter Island meeting, which hedescribed 20 years later as the most importantconference in his life, Feynman lectured on hisspacetime approach to quantum mechanics andbecame stimulated once more to address theproblems of QED.

After Shelter Island Schwinger, Tomonaga,and other quantum field theorists such as Bethebegan to realize that what was missing fromDirac’s theory was a proper interpretation of theunwieldy concept of the self-interaction of theelectron, which by its very nature contained

Feynman, Richard Phillips 95

Richard P. Feynman created the modern space-timediagram formulation of quantum electrodynamics(QED), the theory that describes the quantuminteraction of electrons with electromagnetic fields.(AIP Emilio Segrè Visual Archives, Photo by ChristopherSykes)

infinities, thus preventing a straightforwardphysical interpretation. When the electromag-netic field is quantized, according to the rules ofquantum mechanics, particles of light calledphotons are generated. At the heart of the quan-tum electrodynamic process is the quantumexchange force through which different elec-trons interact by exchanging photons with eachother; an electron can also exchange a photonwith itself.

How were physicists to deal with this self-interaction? QED, as it was formulated in themid-1940s, was not considered to be a relativis-tically covariant formalism (that is, it was notformally compatible with the rules of special rel-ativity). This lack of relativistic covariance pre-cluded a unique mathematical interpretation ofthe physical effects of self-interaction. Schwingerchanged all this when he discovered a relativis-tically covariant form for QED. In doing so, heintroduced the concept of renormalization,which allowed a consistent mathematical inter-pretation of the self-energy infinities. On thephysical level, renormalization implied thatphysical particles are surrounded by a cloud of“virtual particles,” ghostly particles existingwithin the context of the uncertainty principle,whose energy, momentum, and charge modifythe physical appearance of the bare original par-ticle. In applying the method of renormalizationSchwinger found that the self-energy infinitiescould be subtracted out. This led to a fully con-sistent relativistic theory of quantum electrody-namics, which explained the Lamb shift as dueto the virtual particle modification of theCoulomb force between the electron and theproton in the hydrogen atom.

Feynman’s intuitive space-time diagram for-mulation of QED was radically different fromSchwinger’s approach. By 1948, he had com-pleted this construction. In the process he intro-duced the idea of Feynman diagrams, easilyvisualized spacetime analogs of the complicatedmathematical expressions needed to describe

the quantum probabilities of the behavior ofelectrons, positrons, and photons. His idea of adiagrammatic approach to QED, whichstemmed from his earlier work with Wheeler onan action-at-a-distance formulation of electro-dynamics, resulted in a highly effective compu-tational scheme. Instead of quantum fieldoperators, his fundamental building blocks wereparticle processes in spacetime. Feynman’s dia-grams visualized the construction of the quan-tum mechanical probabilities associated withfundamental quantum processes in terms of thespacetime trajectories of real and virtual parti-cles. More importantly, Feynman’s formulationof QED had the great advantage of simplifyingall of the intricate calculations needed bySchwinger and Tomonaga to predict such inter-actions in their formulation of QED.

Feynman first presented his space-time dia-grams at the 1948 Pocono conference attendedby the elite of theoretical physics, who had justlistened to Schwinger’s elegant mathematicalarguments. Prominent physicists such as NIELS

HENRIK DAVID BOHR, EDWARD TELLER, and PAUL

ADRIEN MAURICE DIRAC were mystified andunconvinced by Feynman’s original and intu-itive presentation. Later a new generation ofphysicists would see matters differently. FREE-MAN DYSON, who had befriended Feynman atCornell, called Feynman diagrams “this wonder-ful vision of the world as a woven texture ofworld lines in space and time, with everythingmoving freely . . . a unifying principle that wouldeither explain everything or explain nothing.”In 1949, Feynman sent off a paper with the fullversion of the diagrams, which discussed the“fundamental interaction”: a ladderlike diagramthat showed two electrons moving forward inspacetime interacting by exchanging a single“virtual” photon. By 1950, the relative simplic-ity of the Feynman diagrams began to over-shadow the more intimidating operator QEDmethods of Schwinger and a flood of papersbegan to cite Feynman.

96 Feynman, Richard Phillips

At first, Feynman diagrams seemed to beunrelated to the relativistic quantum operatorfield formulation of QED developed bySchwinger and Tomonaga. This perceptionchanged dramatically when Dyson was able todemonstrate that Feynman’s diagrammatic resultsand insights were directly derivable from thequantum probability matrix (called the S matrix)formulation of Schwinger and Tomonaga. Dysonwas also able to use the Feynman diagrams toshow that mass and charge renormalizationremoved all the infinities from the S matrix ofQED to all orders of approximation. Further, hedemonstrated how Feynman formalism made iteasy to make predictions about observable phe-nomena associated with the anomalous magneticmoment of the electron and the Lamb shift. TheFeynman diagrammatic method allowed Dyson toprove that renormalized QED was a consistentquantum field theory.

In 1950, Feynman accepted a professorshipof theoretical physics at the California Instituteof Technology, where he remained for the rest ofhis life. In the early 1950s, he provided a quan-tum mechanical explanation for the Sovietphysicist LEV DAVIDOVICH LANDAU’s theory ofsuperfluidity: the bizarre, frictionless behavior ofliquid helium at temperatures near absolute zero.In 1952, Feynman was a visiting professor at theUniversity of Rio de Janeiro, Brazil, where helectured on electromagnetism for 10 months,while preparing to parade in the carnival of asamba school in Copacabana. After this exhila-rating period, he returned to the United States,and in June 1952 he married Mary Louise Bell ofNeodesha, Kansas, whom he had met at Cornell.The marriage lasted only four years.

In 1958, Feynman contributed to the theoryof nuclear interactions with MURRAY GELL-MANN. They devised a theory that accounted formost of the phenomena associated with theweak force, which is the force at work inradioactive decay. Their theory, which is basedon the asymmetrical “handedness” of particle

spin, has proved extremely productive in mod-ern particle physics.

On September 24, 1960, Feynman marriedGweneth Howarth, a native of Yorkshire, Eng-land, with whom he would have two children,Carl (born in 1962) and Michelle (adopted in1968). In 1968, while working with experi-menters at the Stanford Linear Accelerator onthe scattering of high-energy electrons by pho-tons, he invented a theory of partons, or hypo-thetical hard particles inside the nucleus of theatom, that helped lead to the theory of quarks.

Feynman’s lectures at Caltech evolved intothe books Quantum Electrodynamics (1961) andThe Theory of Fundamental Processes (1961).Then, between 1963 and 1965, he published hisclassic textbook based on his introductoryphysics course, The Feynman Lectures on Physics.Two additional books, also distilled from his lec-tures, The Character of Physical Law (1965) andQED: The Strange Theory of Light and Matter(1985), contain his views on a range of subjects,including quantum mechanics, the scientificmethod, the relationship between science andreligion, and the role of beauty and uncertaintyin scientific knowledge.

After the explosion of the National Aero-nautics and Space Administration’s (NASA’s)space shuttle Challenger in 1988, he wasappointed to the council investigating the causeof the disaster. In typical Feynman fashion, heswept away bureaucratic constraints and identi-fied the cause as the failure of an o ring in theunusually cold launch-pad temperatures bydunking a similar O ring in a glass of ice water infront of other committee members to emphasizehis conclusion.

After a five-year battle against abdominalcancer, he died in 1988, at the age of 69. Col-orful and iconoclastic, brilliant and unconven-tional in his thinking, Richard Feynmanenjoyed a level of esteem within the physicscommunity that was unique, even in a disci-pline given to mythologizing the great. His

Feynman, Richard Phillips 97

space-time diagram formulation of QED hasremained valid, leading to far-reaching conse-quences. His invention of Feynman diagrams, apictorial representation of the quantum proba-bility for particle interactions in spacetime,adopted by the world of science as the basiclanguage of quantum physics, continues to per-meate many areas of theoretical physics in the21st century.

Further ReadingFeynman, Richard. The Meaning of It All: Thoughts of

a Citizen Scientist. Reading, Mass.: Addison Wes-ley, 1995.

———. QED: The Strange Theory of Light and Matter.Princeton, N.J.: Princeton University Press,1985.

Feynman, Richard, and R. Leighton. Surely You’reJoking, Mr. Feynman: Adventures of a CuriousCharacter. New York: W. W. Norton, 1997.

Gleick, James. Genius: The Life and Science of RichardFeynman. New York: Pantheon Books, RandomHouse, 1992.

Leighton, R. Tuva or Bust! Richard Feynman’s LastJourney. New York: W. W. Norton, 1991.

Mehra, J. The Beat of a Different Drum: The Life andScience of Richard P. Feynman. Oxford: OxfordUniversity Press, 1994.

� Fitch, Val Logsdon(1923– )AmericanExperimentalist, Particle Physicist

Val Logsdon Fitch won the 1980 Nobel Prize inphysics, together with James W. Cronin, for the1964 discovery of charge parity (CP) violationsin the decay of neutral K mesons, one of theapproximately 100 particles turned up by giantparticle accelerators in the 1950s and 1960s.Fitch’s experiment disproved the long-held the-ory that particle interactions should always beindifferent to the direction of time.

He was born on March 10, 1923, on a cattleranch in sparsely populated Cherry County,Nebraska, not far from a Sioux reservation andthe site of the battle of Wounded Knee. He wasthe youngest of three children born to Fred Fitch,who had acquired a ranch of four square miles bythe time he was 20, and Frances Logsdon, a localschoolteacher. Fred Fitch could speak the Siouxlanguage and was made an honorary chieftain inrecognition of “his friendly interests on theirbehalf.” Injured by a fall from a horse shortly afterVal’s birth, he was forced to leave the manage-ment of the ranch to others and move his familyto nearby Gordon, where he became an insur-ance broker. His son would remember less theromance of ranching, than the hard, mundanework of keeping things in repair.

After attending public schools in Gordon,Fitch served in the United States Army duringWorld War II and was sent to Los Alamos, NewMexico, to work on the Manhattan Project forthe development of the atomic bomb. The expe-rience proved a turning point, deflecting himfrom his original interest in chemistry. In histhree years of working in a laboratory there, hehad the chance to interact with such giants ofphysics as NIELS HENRIK DAVID BOHR, SIR JAMES

CHADWICK, ENRICO FERMI, ISIDOR ISAAC RABI,and Richard Tolman, and to learn the basictechniques of experimental physics.

After the war, he completed the work for abachelor’s degree in electrical engineering atMcGill University in Montreal in 1948. Hethen went to Columbia University for his grad-uate studies, at the time when its Nevis Labora-tory Cyclotron was beginning operation.Working under Jim Rainwater, for his thesis hedid pioneering experiments conducted at theCyclotron on µ-mesic atoms and received aPh.D. in 1954.

That year, he joined the faculty of PrincetonUniversity, where he pursued his latest interest,the decay properties of subatomic particles, con-centrating on strange particles and K mesons.

98 Fitch, Val Logsdon

For the next 20 years, most often working with asmall group of students, he studied K mesons.

When Fitch began his work, there werethree known symmetry principles in particlephysics: (1) the principle of charge symmetry(C), which states that the laws of nature areexactly alike for both antimatter and matter; (2)the principle of parity symmetry (P), whichstates that fundamental laws have exact mirrorsymmetry; and (3) the principle of time-reversalsymmetry (T), which states that fundamentallaws do not change when all motions arereversed. T-symmetry is equivalent to the com-bination of charge and parity (CP) symmetries.The neutral K mesons are most suitable for test-ing the validity of the combination of chargeand parity. All three symmetries separately existin electromagnetic, strong, and gravitationalinteractions.

In 1957, the theorists TSUNG-DAO LEE andCHEN NING YANG and the experimentalistCHIEN-SHIUNG WU showed that left hand–righthand symmetry is violated in the weak interac-tions and hence that exact mirror symmetry (P)is violated in the weak interactions. The weakinteractions also violated the symmetry princi-ple associated with (C): that laws of nature areexactly alike for matter and antimatter. How-ever, in the weak interactions, the two effects ofC and P symmetry violations canceled eachother out, thus preserving the CP symmetry,which was equivalent to the T symmetry. Time-reversal symmetry is valid for all processes gov-erned by electromagnetic forces and is thus acornerstone of chemistry. Similarly, T = CP sym-metry is also presumed to be valid for the strongforce, the weak force, and gravity.

Earlier, in 1955, MURRAY GELL-MANN andAbraham Pais had analyzed the neutral K-mesons and found that they had a new physicalproperty called strangeness, which can maketheir decay properties ambivalent with respectto matter and antimatter. If perfect symmetrywere to prevail, a K-meson would have to decay

into antimatter in exactly half the cases and intomatter in the other half. Lee, Yang, and Wu’sdiscovery of P violation left open the possibilityof CP = T violations.

In 1964, Fitch conducted experimentalstudies with Cronin at the Brookhaven NationalLaboratory to test whether the decay of Kmesons could violate CP symmetry. In order tofind out whether CP violating decay of K mesonsoccurred, they used the Alternating GradientSynchrotron proton accelerator, to produce abeam of neutral K mesons. Then, using a spe-cially designed large and complicated detectorarray, they recorded and measured with greatprecision the radioactive decay of the neutral Kmesons in flight. The type of K meson they stud-ied decayed into one-half ordinary matter andone-half antimatter. They found that two of athousand of these K meson decays did in factviolate the CP symmetry.

Fitch and Cronin’s experiment demon-strated that left hand–right hand asymmetry isnot always completely compensated for by trans-forming matter to antimatter while maintainingleft–right symmetry. They interpreted the resultsof their experiment, which were confirmed by along series of subsequent experiments, as a smallbut clear lack of CP = T symmetry.

A few years after Fitch had done his ground-breaking work, his life was marred with tragedy:his wife, Elise Cunningham, with whom he hadtwo sons, died in 1972. Four years after herdeath, he married Daisy Harper, who addedthree stepchildren to his life. That same year, hewas made head of the physics department atPrinceton. Fitch has stayed involved in elemen-tary particle research and continues to expresshis belief that “the delights and challenges ofunexpected discovery will continue always.”

The results of Fitch’s experiments forcedphysicists to abandon the long-held principle oftime-reversal T invariance and explained whymatter and antimatter did not immediatelyannihilate one another during the big bang ori-

Fitch, Val Logsdon 99

gin of the universe. It is now believed that a netpositive amount of matter was created in the bigbang only because of a CP = T symmetry viola-tion in the particle decay processes in the earlyuniverse. This allowed matter to gain an edgeover antimatter.

See also DIRAC, PAUL ADRIEN MAURICE.

Further ReadingWilson, Jane, ed. All in Our Time: The Reminiscences

of 12 Nuclear Physicists. Chicago Bulletin of theAtomic Scientists, 1975.

� FitzGerald, George Francis(1851–1901)IrishTheoretical Physicist(Electromagnetism)

George Francis FitzGerald was a gifted mathe-matical physicist best known for what is nowcalled the Lorentz–FitzGerald contractionhypothesis. Developed independently byFitzGerald and HENDRIK ANTOON LORENTZ, thehypothesis was an ingenious attempt to explainaway the negative result of the Michelson–Mor-ley experiment, which was inconsistent with theexistence of the ether.

FitzGerald was born on August 3, 1851, inDublin, into a family of clerics and intellectuals.His father, William FitzGerald, was a minister inthe Irish Protestant Church and rector at SaintAnn’s in Dublin when George was born andwould later become a bishop. The boy was tutoredat home by the sister of the mathematicianGeorge Boole, who noted his strong mathemati-cal aptitude, great inventiveness for mechanicalconstructions, and skills as an observer. When hewas only 16, he entered Trinity College inDublin, where he concentrated on mathematicsand experimental science, as well as pursuingathletics and social activities. When he gradu-ated four years later, in 1871, he was recognized

as the outstanding student in mathematics andexperimental science.

For the next six years, he devoted himself tothe study of mathematics and physics, in prepa-ration for the competition for a fellowship fromTrinity College. It was during this period, in1873, that JAMES CLERK MAXWELL published hisTreatise on Electricity and Magnetism. In this sum-mary work Maxwell presented the four partialdifferential equations, now known as Maxwell’sequations, that demonstrated that electricityand magnetism are aspects of a single electro-magnetic field, and that light itself is a variety ofthis field. FitzGerald, as did Lorentz and HEIN-RICH RUDOLF HERTZ, with whom he exchangedideas over the years, insightfully perceived thatMaxwell’s work provided a jumping-off point forfurther discoveries and began exploring direc-tions for developing the theory.

FitzGerald published a paper on the electro-magnetic theory of the reflection and refractionof light and sent it to Maxwell, who commentedthat Lorentz was developing his ideas in the samegeneral direction. In 1883, on the basis of hisown research, he predicted that a rapidly oscillat-ing (alternating) electric current would produceelectromagnetic waves, adding that he himself“did not see any feasible way of detecting theinduced resonance.” This would be left to Hertz,who in the late 1880s conducted his early exper-iments with radio. FitzGerald drew Hertz’s workto the attention of the scientific community inBritain, announcing that Hertz had “observedthe interference of electromagnetic waves, quiteanalogous to those of light.”

By this time FitzGerald had won his fellow-ship, on his second try in 1877, and had becomeErasmus Smith Professor of Natural and Experi-mental Philosophy at Trinity College in 1881.He would remain at Trinity for the rest of his lifeand do his most important work there. The pathto this contribution, once more, originated withMaxwell, who, in the last year of his life, hadsuggested an experiment that would be carried

100 FitzGerald, George Francis

out in the 1880s by ALBERT ABRAHAM MICHEL-SON and Edward Morley. Using an ingeniousoptical system capable of making extremely pre-cise measurements, Michelson and Morleyattempted to measure the ether, a hypotheticalmedium in which light waves were thought topropagate. The idea was to measure changes inthe speed of light, on the basis of the interfer-ence patterns created when a light beam wassplit in two and the separated beams guidedalong perpendicular paths and then recom-bined. When no changes in the speed of lightwere observed, physicists scrambled to find aplausible explanation, that would not involverelinquishing their long-held belief in the exis-tence of the ether.

FitzGerald proposed that the null result ofthe Michelson–Morley experiment could beexplained by assuming that the length of anobject moving through the ether contracts inthe direction of the motion. He further sug-gested that light emitted by such an object doeshave a different velocity but travels over ashorter path and thus seems to have a constantvelocity regardless of the direction of motion.Only an observer outside the moving systemwould be aware of the reduction in light veloc-ity; within the system the contraction would alsoaffect the measuring instruments and result inno change in the perceived velocity. He workedout a simple mathematical relationship to showhow velocity affects physical dimensions.Lorentz independently arrived at the same ideain 1895, giving a more detailed description ofwhat became known as the Lorentz–FitzGeraldcontraction hypothesis. Each man readilyacknowledged the contribution of the other. In1905, four years after FitzGerald’s death, thecontraction hypothesis was given a differentinterpretation and incorporated into ALBERT

EINSTEIN’s theory of relativity.In addition to his research, FitzGerald was

deeply involved in educational issues in Ireland.At Trinity, he waged a long-running battle to

increase the amount of teaching of experimentalphysics and advocated expanding the role of theuniversity to “teach mankind,” rather than theelite few. He served as a commissioner of nationaleducation, working to reform primary educationin Ireland by introducing more opportunities todo experimental work into the curriculum.

In 1883, he married Harriette Mary Jellett,daughter of the Reverend J. H. Jellett, provost ofTrinity College. During the eight years of theirmarriage, the couple had eight children, threesons and five daughters. In 1900, FitzGeraldexperienced intestinal problems and, despitesurgery, died, in Dublin, on February 22, 1901, atthe age of 49.

FitzGerald was honored in his lifetime byelection in 1883 as a Fellow of the Royal Society,which awarded him its Royal Medal in 1899 forhis contributions to optics and electrodynamics.He was an important transitional figure, whosebold idea that objects moving at very highspeeds contract, conceived in the context of SIR

ISAAC NEWTON’s universe, would provide a step-ping-stone to Einstein’s.

Further ReadingWhittaker, E. “G. F. FitzGerald.” Scientific American

185(5): 93–98, 1953.

� Fizeau, Armand-Hippolyte-Louis(1819–1896)FrenchExperimentalist (Optics), Astronomer

Louis Fizeau was a brilliant experimental physi-cist who made the first measurements of thespeed of light on the Earth’s surface and, concur-rently with JEAN BERNARD LÉON FOUCAULT,showed that light travels faster in air than inwater, thus confirming the wave theory of light.He also discovered the fact that the relativemotion of a star affects the position of the linesin its spectrum.

Fizeau, Armand-Hippolyte-Louis 101

Fizeau was born in Paris on September 23,1819, at Nanteuil, Seine-et-Marne, into awealthy family. As a young man, he hoped to fol-low the career of his father, an illustrious physi-cian and professor of pathology at the ParisFaculty of Medicine. When poor health pre-vented him from pursuing this course, he turnedinstead to physics, studying optics at the Collègede France and working with François Arago atthe Paris Observatory.

Arago would inspire Fizeau to study the newscience of photography, which led him to inventa method of increasing the permanence ofdaguerreotypes in 1839. Then, in 1845, in col-laboration with Foucault, he made the firstdetailed photographs of the Sun. Fizeau and Fou-cault went on to investigate the interference oflight rays and showed that the spacing of theinterference fringes was proportional to thewavelength of the light. In 1847, they discov-ered that heat rays from the Sun undergo inter-ference, thus showing that radiant heat also hasa wave nature.

That same year, he and Foucault went theirseparate ways; each took up Arago’s suggestionfor an experiment to determine whether lighttravels faster in air than in water—a questionthat would settle the heated debate betweensupporters of AUGUSTIN JEAN FRESNEL’s andTHOMAS YOUNG’s position that light is a waveand the majority of physicists, who advocatedthe particle theory of light. Whereas Foucaultadopted Arago’s suggestion that a rotating mir-ror method be used, Fizeau tried a less complexmethod, which featured a rotating toothedwheel, with over a hundred teeth, rotating hun-dreds of times a second, and two mirrors situatedover five miles apart. He shone a light through agap between the teeth of a rapidly rotatingtoothed wheel. A mirror reflected the lightthrough the same gap to the second mirror.Fizeau varied the speed of the wheel, therebydetermining the speed at which the wheel wasspinning too fast for the light to pass back and

forth through the same gap. Since he alreadyknew the distance the light traveled, and sincethe speed of rotation of the wheel determinedthe time the light took to travel back and forththrough the gap, he was able to divide the dis-tance by time to get the speed of light. In thisway, in 1849, he made the first measurement ofthe speed of light, putting it at 315,000 kilome-ters per second (about 5% larger than the cur-rently accepted modern value). The followingyear, working with Louis Breguet and using arotating-mirror method, he measured the com-parative speed of light in air and water. As didFoucault, who had just done a similar experi-ment, he discovered that light moves faster in airthan in water, thus coming down on the side ofthe wave theory of light.

While performing these historical experi-ments, Fizeau also made a landmark contribu-tion to astronomy when in 1848 he proposed(independently of the work of CHRISTIAN

DOPPLER) that a moving light source such as astar undergoes a change in observed frequencythat can be detected by a shift in its spectrallines. This meant that stars moving away fromthe Earth would show a red shift in their spec-tral lines, whereas those moving toward theEarth would show a blue shift. Fizeau’s methodis used extensively today to determine thedistances of galaxies and other astrophysicalphenomena

In 1851, returning to his investigation oflight, he conducted an experiment that measuredthe amount of ether drift of light waves in a mov-ing, transparent medium. He exactly reproducedFresnel’s formula for the velocity of ether drift ofwaves in a moving, medium. This effect was laterexplained, without the concept of the ether, inthe context of the theory of relativity.

Fizeau died in Venteuil, France, on Septem-ber 18, 1896. His most far-reaching contribu-tion to physics was the development ofexperimental methods to determine both thespeed and the wave nature of light, which sub-

102 Fizeau, Armand-Hippolyte-Louis

sequently led to the development of special rel-ativity.

Further ReadingBuchwald, Jed Z. The Rise of the Wave Theory of Light:

Optical Theory and Experiment in the Early Nine-teenth Century. Chicago: University of ChicagoPress, 1989.

� Foucault, Jean-Bernard-Léon(1819–1868)FrenchExperimentalist (ClassicalElectrodynamics, Optics), Astronomer

Jean Foucault is famous for inventing the gyro-scope and developing the Foucault pendulum,with which he demonstrated the rotation of theEarth. He made the first accurate measurementof the speed of light and validated the wave the-ory of light by showing that light moves faster inair than in water.

Born in Paris on September 19, 1819, he wasa sickly child who was educated at home. As ayoung man, he began to study medicine, with theintention of becoming a surgeon, but soon foundhimself more strongly drawn toward science. Hebegan his scientific career as what we wouldtoday call a free-lancer, writing scientific text-books and newspaper articles on scientific mat-ters, while performing his experiments at home.

Foucault’s first piece of original researchwould prove to be a gateway to a more far-reaching achievement than he anticipated.Collaborating with ARMAND-HIPPOLYTE-LOUIS

FIZEAU, he used the photographic techniques ofthe time to take the first detailed pictures of thesurface of the Sun in 1845. In Foucault’s timephotography was in its infancy. For the longexposures then required he used a clockworkpendulum device to turn the camera slowly sothat it would follow the Sun. He noticed thatthe pendulum device was behaving strangely,

in that it tended to remain in the same swingplane when rotated. This observation led himto demonstrate experimentally the Earth’s rota-tion: he showed that a pendulum maintains thesame swing plane relative to the Earth’s axis,and as a result the swing plane appears to rotateslowly as the Earth turns beneath it. He firstperformed this experiment at home in 1851,before making a spectacular demonstration bysuspending a 200-foot pendulum that traced itspath in sand on the floor from the dome of thePanthéon in Paris. The pendulum continued toswing in a single plane as the Earth rotatedbeneath it and left a series of traces in the sandthat revealed its motion. The slow clockwiseveering of the swing plane of the pendulumdemonstrated that the Earth was slowly turningcounterclockwise beneath it.

Although the fact of the Earth’s rotationwas universally accepted by then, Foucaultoffered the first actual demonstration of thisphenomenon, ending a quest that had begun inGALILEO GALILEI’s time two centuries earlier.Since the back and forth movement of a pendu-lum is actually a form of rotation, Foucault’sexperiment led him to realize that a body rotat-ing in one direction would behave in a similarmanner as a pendulum. In 1852, this realizationled him to invent the gyroscope, a body rotatingin one direction only, in one plane of rotation.His discovery of the nature of the movements ofthe pendulum and gyroscope demonstrated theeffects that conservation of angular momentumhad on rotating bodies in motion over theEarth’s surface.

At the same time Foucault devised experi-ments to determine accurately the value of thespeed of light and to discover whether light con-sisted of waves or particles. Both he and Fizeau,following a suggestion of François Arago,attempted to find the comparative speed of lightin air and water. According to the physics of thetime, if light traveled faster in water, the particletheory of light would be vindicated. Conversely, if

Foucault, Jean-Bernard-Léon 103

light traveled faster in air, the wave theory of lightwould be confirmed. Foucault made his measure-ments by reflecting a beam of light from a rotatingmirror to a stationary mirror and back again to therotating mirror. The time taken by the light totravel this path caused a deflection of the image.The deflection would be greater if the light trav-eled through a medium that slowed its velocity.The more the medium slowed the velocity, thegreater the deflection. In 1849, in competitionwith Foucault, Fizeau developed a slightly differ-ent method, involving a rotating toothed wheel,which yielded a moderately accurate value for thespeed of light. In 1850, using the rotating-mirrormethod, Foucault showed that light travels fasterin air than in water, just ahead of Fizeau’s makingthe same discovery. In 1862, Foucault refined hisrotating mirror technique and made the firsthighly accurate measurement of the speed oflight. He performed the first terrestrial measure-ment of the speed of light in absolute units: kilo-meters per second. The value he obtained in thisway, 298,000 kilometers per second, remainswithin 1 percent of the results obtained today bymore advanced methods.

With a solid scientific reputation estab-lished by his pendulum exposition, in 1855, Fou-cault was able to transfer his experiments fromhis home to the Paris Observatory, where hewould make several important contributions topractical astronomy. He died of a brain disease inParis on February 11, 1868, at age 49.

Foucault’s original and exacting experimentsresulted in enduring contributions to severalareas of theoretical and applied physics. His pre-cise measurement of the speed of light in air andwater confirmed the wave nature of light. Hisinvention of the gyroscope was applied in thenavigational gyrocompass and automatic stabiliz-ers in ships and aircraft. Every major sciencemuseum has a Foucault pendulum on display.

Further ReadingTobin, W. “Léon Foucault.” Scientific American, July

1998, pp. 52–59.

Tobin, W., and A. B. Pippard. “Foucault, His Pendu-lum and the Rotation of the Earth.” Interdisci-plinary Science Reviews, 19 (1994): 326–337.

� Franck, James(1882–1964)German/AmericanAtomic Physicist, Quantum Theorist,Physical Chemist, Biophysicist

James Franck and his collaborator, Gustav Hertz,performed experiments that provided convinc-ing evidence for the quantum theory and thequantum model of the atom, developed, respec-tively, by MAX ERNEST LUDWIG PLANCK andNIELS HENDRIK DAVID BOHR. This work earnedthem the 1925 Nobel Prize in physics. Franckparticipated in the development of the atomicbomb but was a leading advocating for demon-strating it in an uninhabited area, rather thandropping it on Japan, without warning.

Franck was born on August 26, 1882, inHamburg, Germany, into a well-to-do Jewishbanking family. His father, who denigratedFranck’s pursuing a scientific career, sent him tothe University of Heidelberg in 1901 to preparehimself to join the family firm by studying lawand economics. Franck was saved by his friend-ship with another wealthy Jewish youth, MAX

BORN, whose parents fully approved of his deci-sion to pursue physics. Franck’s father was gradu-ally converted to their point of view. Initially achemistry student, he went on to study physicsat the University of Berlin, where he earned aPh.D. in 1906 for a dissertation on the kineticsof electrons, atoms, and molecules and themobility of ions in gases.

In 1911, Franck married Ingrid Jefferson ofGöteborg, Sweden, with whom he would havetwo daughters, Dagmar and Lisa. He lectured atthe University of Berlin from 1911 to 1918, tak-ing time out to participate in World War I, andwas awarded an Iron Cross, first class, for his ser-

104 Franck, James

vice. After the war he became the head of thephysical chemistry division at the Kaiser Wil-helm Institute, where he worked on the theoryof gases. In 1920, he became professor of experi-mental physics and director of the Second Insti-tute for Experimental Physics at the Universityof Göttingen. Franck emerged as an inspiringteacher of such brilliant students as the futureNobel Prize winner PATRICK MAYNARD STUART,LORD BLACKETT and the man who would spear-head the development of the U.S. atomic bomb,J. ROBERT OPPENHEIMER. Between 1920 and1933, Göttingen became an international centerfor the new quantum physics and Franck’s oldfriend Max Born was then head of Göttingen’sInstitute of Theoretical Physics. The two collab-orated on molecular processes, developing theirclassic potential energy diagrams found in physi-cal chemistry textbooks. Franck went on to cal-culate the dissociation energy of molecules byextrapolating data on the vibration of moleculesobtained from spectra. Later on Edward Condoninterpreted this method in terms of quantummechanical wave mechanics, formulating whatbecame known as the Franck–Condon principle.

At Göttingen, Franck did his most impor-tant work in collaboration with Gustav LudwigHertz, studying collisions of free electrons in var-ious noble gases. In these experiments they dis-covered that for certain inelastic collisionsbetween electrons and atoms energy can betransferred from the electrons to the atoms onlyin discrete amounts. In particular for the mer-cury atom, they found that electrons acceptenergy only in quantum units of 4.9 electronvolts (an electron volt is the kinetic energygained by an electron that is moving through adifference in electric potential of one volt). Foran inelastic collision (a collision in which anelectron transfers energy to the mercury atom),the electron needs kinetic energy in excess of 4.9electron volts. The inelastic transfer of the elec-tron’s energy to the mercury atoms was thenrevealed by the fact that the atoms became

excited, and that state caused them to emit lightat a specific wavelength of 2537 Å. This resultoffered the first experimental proof of Planck’squantum hypothesis that E = h�, where E is thechange in energy, h is Planck’s constant, and � isthe frequency of light emitted. These experi-ments also confirmed the existence of the dis-crete energy levels postulated by Bohr in histheory of the atom. In 1925, Franck shared theNobel Prize in physics with Hertz for this work.

When the Nazis came to power in 1933,Franck, though Jewish, was allowed to keep hispost because of his outstanding military servicein World War I. He was, however, instructed tofire his Jewish colleagues. Franck refused andresigned in open protest against the regime’sracist policies. He left Germany with his familyand settled in Baltimore, Maryland, where hebecame a professor at Johns Hopkins Univer-sity. He remained there until 1935, when hewent to the Niels Bohr Institute in Copen-hagen, Denmark, for a year as visiting professor.He then returned to the United States and, in1938, moved to the University of Chicago.During World War II, Franck was director ofthe Chemistry Division of the MetallurgicalLaboratory at the University of Chicago, whichwas the center of the Manhattan Project todevelop an atomic bomb. He headed a group ofatomic scientists in preparing the “FranckReport” for the U.S. War Department; it urgedan open demonstration of the atomic bomb inan uninhabited place, instead of dropping itwithout warning on Japan. Although the reportwas not heeded, it remains an important testi-mony to the social conscience of scientistsattempting to circumscribe the destructiveimpact of their wartime work.

In 1946, several years after the death of hisfirst wife, he married Hertha Sponer, who was aprofessor of physics at Duke University inDurham, North Carolina. In 1947, at age 65, hebecame professor emeritus at the University ofChicago, but he continued his work as head of

Franck, James 105

the university’s photosynthesis research groupuntil 1956.

He died in Germany on a visit to friends inGöttingen, where he and Born had been madehonorary citizens, on May 21, 1964, at the ageof 81.

Franck is remembered for both his contribu-tions to the development of quantum mechanicsand his personal courage in taking difficultmoral stands that he believed to be compatiblewith his responsibility as a physicist.

Further ReadingGamow, George. Thirty Years That Shook Physics: The

Story of Quantum Theory. New York: Dover, 1985.Walker, J. Samuel. Prompt and Utter Destruction: Tru-

man and the Use of Atomic Bombs Against Japan.Chapel Hill: University of North Carolina Press,1997.

� Fraunhofer, Joseph von(1787–1826)GermanTheoretician (Optics), Spectroscopist,Astronomer

A self-taught theoretician and a master ofapplied optics, Joseph von Fraunhofer inventedthe first spectroscope, an instrument for produc-ing and analyzing spectra, and established Ger-many as the world leader in the production ofscientific and optical instruments. His nameentered the lexicon of physics when the darklines in the spectra of the Sun and stars, whichhe was the first to investigate, were namedFraunhofer lines.

He was born on March 6, 1787, in Straub-ing, Bavaria, the 11th child of Franz XaverFraunhofer, a glazier. From the beginning, his lifewas directed toward the skillful making andrefining of objects. His formal schooling wasbrief. At age 10, after losing his mother, hebegan helping out in his father’s glazing work-

shop. A year later his father died and he becamean apprentice to a glazier in Munich, then thecapital of Bavaria. His master trained him wellbut forbade him to engage in the reading andstudies he craved. A happy accident, however,changed his life. When the house he was work-ing in collapsed around him but left him unin-jured, he came to the notice of both the futureking, Maximilian I, who helped him financially,and an influential politician and businessmannamed Joseph Utzschneider, who gave himbooks and exposed him to ideas in physics andoptics. At the age of 19, he found employmentin the optical shop of the Munich PhilosophicalInstrument Company, producers of scientificinstruments. Working under a master glazier, heperfected his skills and became an expert in boththe theory of optics and its practical applica-tions. He was a great success within the com-pany, which made him a director in 1811.

In the area of lens making, Fraunhoferapplied his knowledge of optical theory to theconstruction of lenses with the smallest possi-ble degree of aberration. Rather than using thetrial-and-error approach that was typical atthat time, he attacked the problem conceptu-ally, working out the dispersion power andrefractive index of different kinds of opticalglass. Using glass prisms he invented the firstspectroscope capable of scientific study of spec-tra and was able to make very accurate mea-surements of the dispersion and refractiveproperties of various kinds of glass.

In 1814, while trying to obtain more accu-rate values of the dispersion power and refractiveindex of various kinds of optical glass, he used amonochromatic light source consisting of aflame that contained two bright yellow spectrallines. By comparing the effect of the light fromthe flame to that of the light from the Sun hefound that the solar spectrum contained 574dark spectral lines between the red and violetends of the spectrum. Later, in 1859, GUSTAV

ROBERT KIRCHHOFF would explain that these

106 Fraunhofer, Joseph von

dark spectral lines, called Fraunhofer lines, weredue to the absorption of light by sodium andother elements present in the Sun’s atmosphere.Using this interpretation, Kirchhoff was able toidentify other elements in the Sun’s spectrumand developed the law that states that the ratioof the emission line and absorption line power ofall material bodies is the same at a given temper-ature and a given wavelength of radiation pro-duced. He went on to demonstrate the existencein the Sun of many chemical elements isolatedon Earth and to argue that the Sun primarilycomprises a hot, incandescent liquid.

In 1821, Fraunhofer perfected anotherimportant invention: a diffraction grating thatwas able to decompose white light into its spec-tral components. He was able to do this by firstlooking at the patterns produced by light whenit is diffracted through a single slit and thendetermining the relationship between the dis-persion angles of the light and the width of theslit. He then built a diffraction grating, using alarge number of slits consisting of 260 parallelwires, and made the first study of spectra pro-duced by the diffraction grating method. Usingthe diffraction grating to study the dark spectrallines from the Sun, he noted that the dispersionof the spectra is greater with a diffraction gratingthan with a prism. Then by examining the rela-tionship between the spectral dispersion and theseparation of the wires in the grating, he con-cluded that the dispersion is inversely related tothe distance between successive slits in the grat-ing. By measuring the dispersion, he was able todetermine the wavelengths of light of specificcolors and the dark lines. In addition to diffrac-tion gratings he constructed reflection gratingsin order to study the effect of diffraction onoblique rays. Finally, by using the wave theory oflight, Fraunhofer was able to derive a generalform of the diffraction grating equation that isstill in use today.

For this groundbreaking work Fraunhoferwas recognized as a leader in the field of optics,

and in 1823 he became director of the PhysicsMuseum of the Bavarian Academy of Sciencesin Munich. The following year he was knightedand elected as a member of the Civil Order ofthe Bavarian Crown. Tragically only two yearslater, at the age of 39, he contracted tuberculosisand he died in Munich on June 7, 1826.

Fraunhofer left a rich legacy to manybranches of physics, from astronomy to thestructure of the atom. Spectroscopy became avital tool used by modern physicists to under-stand atomic structure.

Further ReadingJackson, Myles W. Spectrum of Belief: Joseph von

Fraunhofer and the Craft of Precision Optics.Transformations: Studies in the History of Sci-ence and Technology. Cambridge, Mass.: MITPress, 2000.

� Fresnel, Augustin-Jean(1788–1827)FrenchTheoretical and Experimental Physicist(Optics)

The deft mathematical analysis of Augustin-Jean Fresnel persuaded his contemporaries toabandon the prevailing Newtonian theory thatlight consists of particles in favor of his owntransverse wave theory of light. By applying hisnew ideas on light, he developed a revolutionarylens design that came to be known as the Fresnellens, which still has applications today, fromlighthouses to stage spotlights to the solar panelson spacecraft.

He was born on May 10, 1788, in Broglie,Normandy, in France, into a religious family andreceived home schooling until the age of 12. Hethen studied at the École Centrale in Caen,where he was introduced to science. In 1804,he entered the École Polytechnique in Paris;there he received a solid grounding in mathe-

Fresnel, Augustin-Jean 107

matics and, two years later, went on to theÉcole des Pont et Chaussées, where he studiedfor three years, in preparation for an engineer-ing career. Upon graduating, he worked as acivil engineer for the government. It was dur-ing this period that he developed an interest inoptics and, thanks to unforeseen political cir-cumstances, found he had plenty of time topursue research in this field. In 1815, whenNapoleon returned to France from exile in Elba,Fresnel, calling the former emperor’s homecom-ing “an attack against civilization,” protestedvigorously, despite his precarious health. Placedunder house arrest in Normandy, he embarkedupon the work that would persuade his peers toreconsider totally their point of view about opti-cal phenomena.

At the end of the 19th century physics wasdominated by SIR ISAAC NEWTON’s particle the-ory of light, which the great 17th century physi-cist had extrapolated from his particle laws formatter. Fresnel disliked Newton’s theory of light,both because of its failure to explain such basicoptical phenomena as the interference effectand because of its lack of the simplicity he val-ued in a theory. Using his mathematical prowess,intuition, and skills as an experimentalist, heundertook an ambitious project to “create a rev-olution in science.”

One of the major challenges for optics inFresnel’s time was to interpret diffraction, thetendency of light images to become fuzzy aroundthe edges, within the context of a mathemati-cally solid wave theory. In 1815, Fresnel demon-strated mathematically that the dimensions oflight and dark bands produced by diffractioncould be related to the wavelength of the light, ifone assumed that light consisted of waves. In1816, the new theory enabled him to predict theintensity of the “fuzziness” or fringes.

His second major challenge was to inter-pret polarization, the tendency of light wavesto vibrate in directions perpendicular to thedirection of wave propagation. Earlier, the

Dutch physicist CHRISTIAAN HUYGENS hadproposed that light consists of longitudinalwaves analogous to sound waves. Huygens’slight wave theory made it possible to interpretrefraction and reflection. It also allowed him toexplain, as the light particle theory could not,how two light rays can intersect without caus-ing each other to deviate from their paths. Itfailed, however, to explain light polarization.And, like the particle theory, the longitudinalwave theory could not explain double refrac-tion, the splitting of incident transmitted lightinto two beams, each polarized perpendicularlyto the other. Working with the French physi-cist François Arago, Fresnel showed that polar-ized light could be refracted through twodifferent angles because one ray would consistof waves oscillating in one plane and the otherray would consist of waves oscillating in a planeperpendicular to the plane of the first. Hismathematical analysis led him to conclude in1821 that polarization could occur only if lightconsists of transverse waves. Fresnel’s ex-planation of polarized light was later carriedbeyond the visible spectrum in JAMES CLERK

MAXWELL’s theory of electromagnetism.By this time, Napoleon had departed French

shores once more and Fresnel was back on thejob as a civil engineer. Despite having to relegatescientific research to his spare time, he contin-ued to do important work. He designed whatcame to be called the Fresnel lens, which hasone surface cut in steps so that transmitted lightis refracted just as it would be if a much thicker,heavier, and more expensive conventional lenswere used. Designed to replace mirrors in light-houses, Fresnel lenses have myriad uses today.

Fresnel went on to unify the mysterious flu-ids Newton had postulated to account for thephenomena of heat, electricity, magnetism, andlight into a single universal fluid, that is, anether, whose modifications explained the differ-ent observed physical phenomena. At the sug-gestion of Arago, Fresnel undertook research on

108 Fresnel, Augustin-Jean

the aberration of starlight, an effect tied to theannual movement of the Earth in its orbit,which makes starlight seem to slant, altering theapparent position of the stars hour by hour. Theaberration of starlight causes the light from starsto describe an ellipse over the course of a year.This aberration effect, which is constant for allstars, led Fresnel to conjecture that the move-ment of light emitted by all stars is uniform, anidea contrary to Newton’s theory, in which par-ticles of light emitted by different stars have dif-ferent speeds. Fresnel succeeded in explainingthis phenomenon by proposing that the etherwas partially dragged by the Earth’s movement.

Although Fresnel’s light wave theory gainedmany adherents, the question of whether lightconsisted of particles or waves awaited experi-mental demonstration. Fresnel never learnedthe answer since, continually plagued by illhealth, he died of tuberculosis in Ville-d’Avray,near Paris, on July 14, 1827, at the age of 39,before a decisive experiment could be per-formed. He had been elected to the Académiedes Sciences in 1823 and awarded the RumfordMedal of the Royal Society just before his death.

More than two decades after Fresnel’s death,at the request of Arago, ARMAND-HIPPOLYTE-LOUIS FIZEAU and JEAN-BERNARD-LÉON FOU-CAULT independently conducted experimentsthat determined whether a light wave movesmore rapidly in air than in water, as the wavetheory predicted, or, on the contrary, morerapidly in water than in air, as the particle theorypredicted. The former proved to be the case andFresnel’s wave theory was validated.

By developing his ideas on the wave natureof light into a comprehensive mathematical the-ory, Fresnel determined properties that everyfuture theory of light would have to satisfy andcreated the groundwork for the later work ofMaxwell.

Further ReadingBuchwald, Jed Z. The Rise of the Wave Theory of Light:

Optical Theory and Experiment in the Early Nine-teenth Century. Chicago: University of ChicagoPress, 1989.

Silverman, Mark P. Waves and Grains. Princeton,N.J.: Princeton University Press, 1998.

Fresnel, Augustin-Jean 109

110

G� Gabor, Dennis

(1900–1979)Hungarian/BritishTheoretician and Experimentalist(Holography, Information Theory)

Dennis Gabor is known as the father of hologra-phy, a method of producing three-dimensionalimages by using laser light. Although lasers,which are necessary to producing a hologram,would not be invented until 1960, Gabor con-ceived and fully elucidated the nature of holo-grams in 1948. He received the 1971 Nobel Prizein physics for this work.

He was born in Budapest on January 5,1900, the oldest son of Bertalan Gabor, directorof a mining company, and his wife, Adrienne.He fell in love with physics at the age of 15 and,with his brother George, set up a small labora-tory at home, where they duplicated experi-ments on X rays and radioactivity. However, hechose to pursue engineering instead of physics,which was not yet a profession in Hungary,studying first at the Technical University inBudapest and then at the Technische Hoch-schule of Berlin in Charlottenberg, where hereceived his diploma in 1924. Nonetheless, asoften as he could, he would “sneak over” to theUniversity of Berlin, where ALBERT EINSTEIN,MAX ERNEST LUDWIG PLANCK, WALTHER

NERNST, and MAX THEODOR FELIX VON LAUE

were then in residence. Although Gabor wasofficially an engineer, most of his work was inapplied physics. In 1927, he was awarded a Ph.D.for developing one of the first high-speed cath-ode ray oscillographs, devices that monitor oscil-lating currents in high-voltage transmissionlines. While doing this work, he also developedthe first iron-shrouded magnetic electron lens.He then joined the firm of Seimens and Halshein Berlin, where he invented a high-pressurequartz mercury lamp with superheated vapor anda molybdenum tape seal, which is now exten-sively used in street lamps.

When the Nazis came to power in 1933,Gabor fled Germany and, after a short time inHungary, left for England, where he remainedfor the rest of his life, becoming a British citizen.He first worked at the British Thomson-Hous-ton Company in Rugby as a research engineerand in 1936 married Marjorie Louise Butler. Heremained at Thomson-Houston until 1948. Dur-ing the postwar years he wrote his first papers oncommunication theory and developed a systemof stereoscopic cinematography.

In 1948, Gabor carried out the basic experi-ments in holography, which at the time wascalled wavefront reconstruction. He would latercall this “an exercise in serendipity,” the art oflooking for something and finding something

else. His original goal was to develop animproved electron microscope that used elec-trons instead of light rays, one capable of resolv-ing atomic lattices and seeing single atoms. Hestudied the idea of coherent beams of light (i.e.,light that contains a single frequency of oscilla-tion), in which all the waves are exactly in phasewith each other. Gabor noted that a coherentbeam reflected from an object should travel avarying number of wavelengths to an observer,depending on the distance to the surface of theobject. In this context he realized that a beam ofcoherent light reflected from an object shouldcontain information on the shape of the object.

In Gabor’s holographic method the beam ofcoherent light reflected from the object and thebeam of coherent light emitted directly from thecoherent light source are simultaneously recordedon a photographic film plate. The superpositionof the two coherent beams produces an interfer-ence pattern on the photographic film plate.

The interference pattern produced dependson the amplitude and phase of the light wavesin the reflected beam at the surface of the plate,which in turn depend on the distance of eachpart of the plate from each part of the object.The interference pattern thus contains infor-mation on the shape of the object. The inter-ference pattern, called a hologram, appears onthe film as an apparently meaningless patternof whirls when the plate is developed. How-ever, when the hologram is placed in a beam ofcoherent light and the viewer looks throughthe hologram, the interference pattern of thetwo beams is deconstructed and a three-dimen-sional image of the object is seen (i.e., if theviewer moves, a different perspective of theobject is obtained). Gabor invented thismethod before coherent light sources becameavailable, calling it holography from the Greekholos, meaning “whole.” In three papers pub-lished between 1948 and 1952, he laid out anexact analysis of the method. Holography madeits breakthrough when the first laser was

invented in 1960. This is because the laser gen-erates continuous coherent light wave trains ofsuch length that one can reconstruct the depthin the holographic image. Twenty years afterdoing his pioneering work in the developmentof holography Gabor would be awarded the1971 Nobel Prize in physics.

In 1949, he joined the faculty of the ImperialCollege of Science and Technology in London.With young doctoral students as collaborators, heworked on many interesting and challengingproblems: he constructed an advanced version ofthe Wilson cloud chamber and made a number ofinventions, including a holographic microscope;an electron-velocity spectroscope; an analogcomputer that was a universal, nonlinear “learn-ing” predictor, recognizer, and stimulator of timeseries; a flat, thin color television tube; and a newtype of thermionic converter. He also did work oncommunication theory, plasma theory, and mag-netron theory.

Finally, in 1958, Gabor became professor ofapplied electron physics at Imperial College, atwhich point his interest shifted to a study of thefuture of industrial civilization. He wrote:

I became more and more convincedthat a serious mismatch has developedbetween technology and our socialinstitutions, and that inventive mindsought to consider social inventions astheir first priority.

He developed these ideas in three books:Inventing the Future, 1963; Innovations, 1970;and The Mature Society, 1972.

Gabor retired in 1967 and became a seniorresearch fellow and a staff scientist of CBS Lab-oratories, Stamford, Connecticut, where heworked on many new schemes of communica-tion and display. From 1967 until his death inLondon on February 8, 1979, he was ProfessorEmeritus of applied electron physics at the Uni-versity of London.

Gabor, Dennis 111

Gabor’s invention of holography continuesto have a profound impact on the developmentof technology. With its ability to determine anobject’s point in space to a fraction of a lightwavelength, the hologram has enriched opticalmeasurement techniques. Many physics andengineering applications have been found forholography, and in the future we may see thedevelopment of holographic computers andholographic three-dimensional television ormotion pictures.

See also TOWNES, CHARLES HARD.

Further ReadingGabor, Dennis. Innovations: Scientific, Technological and

Social. Oxford: Oxford University Press, 1970.Kock, Winston E. Lasers and Holography: An Introduc-

tion to Coherent Optics. New York: Dover, 1981.

� Galilei, Galileo(1564–1642)ItalianTheoretical and Experimental Physicist,Astronomer, Mathematician

Galileo Galilei was called “the father of modernphysics—indeed of modern science altogether”by ALBERT EINSTEIN. Over the course of his longand stormy career, he established the modern sci-entific method of deducing mathematical laws toexplain the results of experiment and observa-tion. His discovery of the properties of the pendu-lum, his invention of the first crude thermometer,and his formulation of the laws governing themotion of falling bodies all flowed from theseprinciples. In astronomy, the enhanced telescopeshe constructed enabled him to observe the heav-ens in unprecedented detail and led him toespouse the Copernican theory that the Earthrevolves around the Sun. His subsequent prosecu-tion by the Inquisition enthroned him in the pop-ular imagination as a defender of scientific truthagainst the dogmas of religious authority. Galileo

himself, however, was a devout Catholic who sawno conflict in the truths of religion and science.

He was born in Pisa on February 15, 1564,and given, as was not uncommon at the time, afirst name based on the family name. His father,Vincenzio Galilei, was a musician who per-formed experiments to test mathematical for-mulations on the properties of music and anadvocate of using reasoned argument ratherthan authority to prove one’s point. He had hisson tutored privately in Pisa and, in 1575,when the family moved to Florence, sent himto study at a nearby monastery. Galileoremained there until 1581; at the age of 17, hereturned to Pisa, where, at his father’s urging,he took up the study of medicine at the univer-sity. When it became clear that Galileo wasmore attracted to mathematics, Vincenzioallowed him to be tutored by the Tuscan courtmathematician. Galileo the son made his firstimportant discovery: by using his pulse to timethe swing of a lamp in the Cathedral of Pisa, heobserved that a pendulum always swings backand forth in the same period of time, regardlessof the amplitude of the swing.

When Galileo returned home to Florence in1585, he had not earned a formal academicdegree. The following year he extendedARCHIMEDES’ work in hydrostatics by inventingan improved version of the hydrostatic balancefor measuring specific gravity. In 1589, he wasback at the University of Pisa, a professor ofmathematics at age 25. He lost no time inattacking Aristotle’s belief that the speed of afalling object is determined by its weight.According to legend, Galileo dropped two can-non balls of different weights from the LeaningTower of Pisa; they hit the ground together,demonstrating that unequal weights fall at thesame speed. He published his first ideas onmotion in De Motu (On motion) in 1590. InPisa he also invented one of the first scientificmeasuring instruments: a primitive thermometerconsisting of a bulb of air that expanded or con-

112 Galilei, Galileo

tracted as the temperature changed, causing thelevel of a column of water to rise and fall.Despite these achievements, his attacks on Aris-totle had antagonized his colleagues and his con-tract was not renewed.

In 1592, friends found him a better positionas professor of mathematics at the University ofPadua, where he would flourish over the next 17years. In 1599, he met a 21-year-old courtesan,Marina Gamba, who would bear him a son andtwo daughters. Galileo, who never married,would end his liaison with Marina when he leftPadua but remain a devoted father all his life.His family responsibilities led him to market amilitary compass he had invented. He also man-aged to continue his motion studies, determin-ing the law of falling bodies: the distance fallenby a body is proportional to the square of thetime of descent. From this he was able to deducethat neglecting air resistance, all bodies fall withthe same acceleration in a gravitational field. Itwas this ability to separate out the significantcomponents of an experiment to determinewhat was fundamental to the investigation thatmade him the first modern scientist.

In 1609, on learning that a Dutchmannamed Hans Lippershey had invented the tele-scope the year before, Galileo immediately set towork improving the instrument. Using a tele-scope that magnified up to 20 times, he madethe celestial observations that would revolution-ize astronomy: he discovered the mountains ofthe Moon, sunspots, the phases of Venus, andthe four largest (Galilean) satellites of Jupiter.He also noted that Saturn had an oval shape, anobservation that CHRISTIAAN HUYGENS latershowed to be caused by its rings, and that theMilky Way is composed of stars. When he pub-lished his findings in Sidereus nuncius (The starrymessenger) in 1610, the book caused a sensationthroughout Europe. Galileo was offered a life-long position in Padua but returned to his nativeFlorence instead, as mathematician and philoso-pher to the grand duke of Tuscany.

In Florence, in 1612, he returned to his ear-lier work on hydrostatics. He published a studyof the behavior of bodies in water, Bodies ThatStay Atop Water or Move Within It, in which hechampioned Archimedes’ law of buoyancy,which states that the buoyant force on a body inwater is equal to the weight of the water dis-placed. In 1613, he published his treatise onsunspots, Sunspot Letters, in which he arguedthat the spots were on or near the Sun’s surfaceand not, as the German Jesuit ChristophScheiner proposed, the Sun’s satellites.

Meanwhile, his work in both mechanics andastronomy was yielding new arguments forCopernicus’ heliocentric theory, which Galileohad always favored. Anti-Copernicans arguedthat the Earth must be stationary, since birds andclouds would fall off a turning or moving Earth,just as, unanchored objects would fall off a mov-ing carousel. But, on the basis of his motion stud-

Galilei, Galileo 113

Galileo Galilei established the modern scientific methodand was the first to provide experimental support for theCopernican theory that the Earth revolves around theSun. (AIP Emilio Segrè Visual Archives)

ies, Galileo conjectured that a horizontal compo-nent of motion provided by the Earth alwaysexists to keep such objects in position, eventhough they are not attached to the ground. Fur-thermore, Galileo had found that when seenthrough a telescope, Venus showed phases likethose of the Moon and therefore must orbit theSun, not the Earth. This left astronomers with achoice of either the Copernican system or theEarth-centered model proposed by Tycho Brahe,in which everything but the Earth and Moonrevolves around the Sun, which in turn revolvesaround the Earth. Most astronomers favored theEarth-centered model, and Galileo increased theranks of his enemies by using all his formidablemathematical and verbal skills to ridicule them.In 1616, however, the Catholic Church bannedall work on the Copernican theory, forcingGalileo to make a tactical retreat. That year hewrote his Theory on the Tides, in which he usedthe two Copernican motions—the Earth’s dailyrotation on its own axis and its annual revolutionaround the Sun—to explain the tides. Through-out his life he would disdain the hypothesis thatthe Moon caused the tides, considering it taintedwith occultism and astrology.

In 1623, Galileo published Il saggiatore (Theassayer), in which he set forth his philosophy ofthe nature of physical reality and modern scien-tific inquiry:

The grand book of the universe . . . can-not be read until we have learnt the lan-guage and become familiar with thecharacters in which it is written. It iswritten in mathematical language, andthe letters are triangles, circles andother geometric figures, without whichmeans it is humanly impossible to com-prehend a single word.

Il saggiatore was about to be printed when alongtime admirer and patron, Mafeo CardinalBarberini, was chosen to become Pope Urban

VIII. Galileo had time to dedicate the work to thenew pope; he then set out for Rome and succeededin obtaining Urban’s permission to present argu-ments for the rival geocentric and heliocentricpositions, so long as Copernicus’ theory wastreated as a mere hypothesis. It was not until 1632that Galileo published his Dialogue Concerning theTwo Chief World Systems: Ptolemaic and Coperni-can. The book was banned and Galileo was takento Rome to stand trial for heresy in April 1633.Although Galileo may have believed his ownclaim that he had been even-handed in his pre-sentation, most readers would agree with theInquisition’s view that he had used observationsand experiments to favor Copernicus. Legend hasit that when forced to abjure his belief that theEarth moves around the Sun, he muttered, “Eppursi muove” (Yet it does move). On the margins ofhis copy of the Dialogue he wrote: “In questions ofscience, the authority of a thousand is not worththe humble reasoning of a single individual.”

Galileo’s sentence of life imprisonment wascommuted to house arrest at his villa at Arcetrinear Florence for the rest of his life. Although hisfinal years were saddened by the death of hisbeloved daughter, Sister Maria Celeste, in 1634,and the loss of his eyesight in 1637, he continuedto work, with the help of an assistant, and pub-lished his most important book, Discourses andMathematical Discoveries Concerning Two New Sci-ences, in Leiden, Holland, in 1638. In it hesummed up his life’s work in motion studies. Herejected the idea that a force is necessary to sustainmotion and showed that a body in uniform hori-zontal motion will continue moving. He realizedthat this will occur only in a vacuum, and that airresistance always causes a uniform terminal veloc-ity to be reached. He demonstrated that gravitynot only causes a body to fall, but also determinesthe motion of rising bodies, and furthermore thatgravity extends to the center of the Earth. He thenshowed that the motion of a projectile is made upof two components: uniform motion in a horizon-tal direction and vertical motion under the down-

114 Galilei, Galileo

ward acceleration due to gravity. He also deduced,by combining horizontal and vertical motion, thatthe trajectory of a projectile is a parabola.

Galileo’s second “new science” was engineer-ing, particularly the science of structures, in whichhe pointed out that the dimensions of a structureare important to its stability: a small structure willstand, whereas a larger structure of the same rela-tive dimensions may collapse. Using the law oflevers, he went on to examine the strengths of thematerials necessary to support structures.

In his last years, Galileo designed a pendu-lum clock. He died at Arcetri on January 8,1642. Galileo’s work formed the basis for thesubsequent development of classical mechanicsand observational astronomy. His work inmotion studies would be developed by SIR ISAAC

NEWTON into a full understanding of inertia, thelaws of motion, and gravitation.

Further ReadingDrake, Stillman. Galileo at Work: His Scientific Biogra-

phy. Chicago: University of Chicago Press, 1978.Galileo. Discoveries and Opinions of Galileo: Including

the Starry Messenger (1610), Letter to the GrandDuchess Christina (1615), and Excerpts from Letterson Sunspots (1613), The Assayer (1623). StillmanDrake, Translator. Based on work by Galileo. NewYork: Doubleday & Company, 1989.

Reston, James. Galileo: A Life. New York: Harper-Collins, 1994.

Sobel, Dava. Galileo’s Daughter: A Historical Memoir ofScience, Faith, and Love. New York: Walker,1999.

� Gamow, George(1904–1968)Russian/AmericanTheoretical Physicist, Nuclear Physicist,Cosmologist

George Gamow is famous for the theoreticalwork that led to discovery of the first evidence

supporting the big bang theory of the origin ofthe universe. In 1948, he predicted that if theuniverse had begun with a fiery explosion, thena cosmic microwave background radiationwould remain. Seventeen years later, Gamow’sprediction was confirmed, when ARNO ALLAN

PENZIAS and Robert Wilson, using a horn-shaped radio antenna, detected an unchangingnoise that pervaded all of space.

Born in Odessa, Ukraine, on March 4, 1904,Gamow attended local schools. His father’s giftof a telescope when George was 13 sparked hisinterest in astronomy. In 1922, he enteredNovorossiya University in Odessa; he thentransferred to Leningrad State University, wherehe studied optics and cosmology, earning a Ph.D.in 1928.

In 1926, Gamow traveled to Germany toattend summer school at the University of Göt-tingen, where he did his first important researchin nuclear physics. Attempting to formulate atheory of alpha particle decay, he constructed amodel in which the new quantum mechanicswas applied to the study of nuclear structure forthe first time. He explained why uranium nucleicould not be penetrated by alpha particles (ion-ized atoms of helium) that have twice the energyof the alpha particles emitted by the nuclei. Hishypothesis was that this was due to a “Coulombpotential barrier” generated by the repulsion ofthe electrostatic Coulomb forces that actedbetween the uranium nuclei and the alpha parti-cles. In classical mechanics, charged subatomicparticles like protons, when hurled against theCoulomb barrier, had no chance of penetratingit. In quantum mechanics, however, because ofthe uncertainty principle, protons can some-times penetrate the Coulomb barrier by tunnel-ing through it. In 1928, Gamow appliedquantum probabilities to the question of nuclearfusion in stars and found that alpha particlescould surmount the Coulomb barrier by quan-tum tunneling, which now stood revealed as themechanism by which the stars shine.

Gamow, George 115

That year, on the basis of this work, NIELS

HENRIK DAVID BOHR, the guiding spirit of quan-tum mechanics, invited Gamow to his Instituteof Theoretical Physics in Copenhagen, where hecontinued his work on nuclear physics andbegan to study nuclear reactions in stars. ThereGamow worked on the liquid drop model ofnuclear structure, in which the nucleus wasregarded as a collection of alpha particles thatinteracted via strong nuclear and Coulombforces. Ultimately, the liquid drop model of thenucleus was used to develop the present theoryof nuclear fission and fusion.

In 1929, as a Rockefeller Fellow, he workedwith ERNEST RUTHERFORD at the Cavendish

Laboratory, Cambridge, England, calculatingthe energy required to split a nucleus by usingartificially accelerated protons. This work leddirectly to the 1932 construction, by JOHN

DOUGLAS COCKCROFT and Ernest Watson, of alinear accelerator, in which protons were usedto disintegrate boron and lithium, resulting inthe production of helium. This was the firstexperimentally produced transmutation gener-ated without the use of radioactive materials.

In 1930, Gamow engaged in furtherresearch in Copenhagen. Then in 1931 hereturned to the Soviet Union and marriedLyubov Vokhminzeva, with whom he wouldhave a son, Rustem Igor. His career as a Sovietphysicist was thriving: in 1931, he became pro-fessor of physics at Leningrad State University aswell as head of research at the Academy of Sci-ences in Leningrad. But that same year, he wasmade aware of the limits on his freedom whenthe Soviet Union denied him permission toattend a conference on nuclear physics in Rome.In 1933, he was allowed to travel to the SolvayConference in Brussels, where he defected to theWest. After spending some time in Europe, as afellow at the Pierre Curie Institute in Paris andvisiting professor at the University of London,he traveled to the United States.

His first American home was in Washing-ton, D.C., where he assumed the chair of physicsat George Washington University, in 1934. Hewas able to offer a position at George Washing-ton to another distinguished émigré, EDWARD

TELLER, thus taking him to the United Statesbefore the war. A fruitful collaboration beganbetween the two physicists, who, in 1936,announced their discovery of the Gamow–Tellerselection rule for beta decay, the process inwhich radioactive transmutations of matter fromone element to another occur.

Much of Gamow’s later work centeredaround the immense question that had longintrigued him: the origin of the universe. In1938, he contributed to the interpretation of

116 Gamow, George

George Gamow is famous for his theoretical work thatled to discovery of the first evidence supporting the bigbang theory of the origin of the universe. (AIP EmilioSegrè Visual Archives)

the Hertzsprung–Russell diagram, which plotsthe spectral classes (or colors) of stars againsttheir brightness. Using this technique, heexamined the origin of nebulae and the produc-tion of energy occurring in the internal struc-ture of red giant stars and, in the early 1940s,published his neutrino theory of supernovae inwhich he examined neutrino emission duringstellar explosions.

Gamow made his most fundamental contri-bution, however, in 1948, when he presentedevidence in support of the big bang model of theexpanding universe. At the time, the two com-peting cosmological theories were the steadystate theory, which held that the universe was asit had always been; homogenous in space andtime, and the big bang theory, which arose fromEdwin Hubble’s 1929 finding that the galaxiesare rapidly moving away from each other. Sup-porters of the big bang theory argued that galax-ies must have been closer to one another in thepast and that, in the furthest reaches of thepast—the cataclysmic moment in which the uni-verse was created some 15 billion years ago—they were merged in a single, infinitely dense,hot mass. In Gamow’s view these conditionsmust have existed in order for atomic nuclei tofuse into different combinations, thereby creat-ing chemical elements. He reasoned that if theuniverse had been expanding and cooling sincethe big bang, it would not have cooled com-pletely. For this reason, the radiation emitted bythe initial cosmic explosion should still be pre-sent in the universe at a lower but nonethelessobservable frequency. In particular the photonscarrying the energy of the big bang, having origi-nated in the wavelengths of light, ought to havebeen redshifted by the subsequent expansion ofthe universe into the lower frequencies of elec-tromagnetic energy called microwave radio radi-ation. On the basis of this idea, Gamow and hiscolleagues estimated that the universe todayshould be permeated by an ocean of photons withan ambient absolute temperature of about three

kelvin (3 K). At the time, this prediction wasimpossible to verify, since radio astronomy was inits infancy. But in 1965, Penzias and Wilson werehaving trouble accounting for a persistent hiss ina microwave horn Bell Laboratories had built forsatellite communication experiments. When thePrinceton physicist Robert Dicke made themaware of Gamow’s work, they realized thatGamow’s refined estimate of 2.7 K was just thetemperature of this unwanted noise. They hadstumbled across confirmation of Gamow’s cosmicbackground radiation hypothesis, which, in turn,provided evidence for the big bang. Penzias andWilson, rather than Gamow, received the NobelPrize for the work, but Gamow’s seminal role inthis historical discovery is universally recognized.

In 1948, the year of his great work in cos-mology, Gamow’s career took a radically differ-ent direction. After gaining a top secret securityclearance, he went to work on the hydrogenbomb project at Los Alamos, New Mexico,where he collaborated closely with Teller on thedesign of the weapon.

Another major turning point in his lifeoccurred in the mid-1950s, when he becameinterested in molecular biochemistry and con-tributed to the solution of the genetic code.Gamow’s theory was found to be correct, and in1961 the genetic code was understood. In 1956,he divorced his first wife and left George Wash-ington University to become professor ofphysics at the University of Colorado. Two yearslater he married Barbara Perkins. He remainedat Colorado until his death in Boulder onAugust 20, 1968.

Later in life, Gamow became famous as theauthor of popular science books, especially his Mr.Tompkins series. Others included One, Two,Three . . . Infinity (1947), The Creation of the Uni-verse (1951), The Atom and Its Nucleus (1961),and Gravity (1962).

George Gamow was a major figure in 20th-century physics, whose personality and intellectleft an indelible impression on the physicists of

Gamow, George 117

his time. Unconventional and charismatic, hewas known for his wit and irreverence towardhuman affairs, while retaining his sense of awebefore nature. His curiosity about how the uni-verse began moved the physics community agiant step closer to unraveling that mystery.

See also COULOMB, CHARLES AUGUSTIN;HEISENBERG, WERNER; MEITNER, LISE.

Further ReadingGamow, George. The Creation of the Universe. New

York: Mentor, 1951.———. Mr. Tompkins in Paperback. Canto Series.

Cambridge: Press Syndicate of the University ofCambridge, 1968.

———. My World Line: An Informal Autobiography.New York: Viking Penguin, 1970.

———. Thirty Years That Shook Physics. Garden City,N.Y.: Anchor, 1966.

� Gauss, Johann Carl Friedrich(1777–1855)GermanMathematical Physicist(Electromagnetism, TerrestrialMagnetism), Astronomer

Johann Gauss was a scientific virtuoso, mostfamous for his seminal work in mathematics. Asa physicist, he made substantial contributions inthe fields of electromagnetism and terrestrialmagnetism, deriving a method for defining mag-netic units and formulating Gauss’s law, whichwas later used to simplify the mathematical for-mulation of JAMES CLERK MAXWELL’s equationsfor the electromagnetic field.

Gauss was born on April 30, 1777, into avery poor and uneducated family in Brunswick,Germany. He was a child prodigy, who taughthimself to read and do arithmetic and who wasdoing calculations before he had learned to talk.Upon entering school, Gauss offered proof of thegenius that would rescue him from his humble

beginnings, presenting a masterfully simple solu-tion to the problem of adding up any set ofwhole numbers. His reputation spread, and, atthe age of 14, he was given a stipend by the dukeof Brunswick, so that he could devote himself toscience. Before his 25th birthday, Gauss wouldbe famous for his work in mathematics andastronomy.

When Gauss entered the Brunswick Col-legium Carolinum in 1792, he already pos-sessed a superior scientific and classicaleducation. He spent three years there, duringwhich he independently discovered Bode’s lawof planetary distances, the binomial theoremfor rational exponents, and the arithmetic–geo-metric mean, as well as the law of quadraticreciprocity and the prime number theorem. In1795, he went on to the University of Göttin-gen, where he constructed a 17-sided regularpolygon, using only a ruler and compass, thefirst construction of a regular figure in moderntimes. Leaving Göttingen in 1798 without adegree, he returned to Brunswick, where helived on another stipend from the duke. Hereceived a degree in 1799, for a dissertationsubmitted to the University of Helmsted on thefundamental theory of algebra.

Gauss now entered upon a period ofrenowned discoveries. Continuing to pursue hismathematical research, in 1801, he publishedhis famous work, Arithmetic Disquisitions, most ofwhich was devoted to number theory. That sameyear, he made a remarkable prediction of theposition in which the asteroid Ceres could befound. Ceres was the first asteroid to be locatedby astronomers, who later lost track of it. Whenit was rediscovered, it turned out to be exactlywhere Gauss, using his least squares approxima-tion method, had calculated it would be.

For the next few years Gauss’s personal lifeunderwent a series of triumphs and reversals. Hemarried his beloved first wife, Johanna Ostoff,on October 9, 1805. The following year, how-ever, he lost his patron when the duke of

118 Gauss, Johann Carl Friedrich

Brunswick was killed fighting Napoleon. Forcedto seek a paying job, Gauss became director ofthe Göttingen Observatory in 1807, a positionhe would retain for the next 47 years, until hisdeath at age 78. In 1808, Gauss’s father died, andthe next year his wife died giving birth to theirsecond son, who died soon afterward. Distraughtand left with a son to raise, he married Johanna’sbest friend, Minna, the next year. They hadthree children, although the match seems tohave been a marriage of convenience.

Despite personal tragedy, and the politicalturmoil of the times—the French Revolution,the Napoleonic period, and democratic revolu-tions in Germany—external events neverseemed to lessen the flow of Gauss’s scholarlyoutput. In 1809, he published his second book,the two-volume Theory of the Motion of a Celes-tial Body Following an Elliptical Orbit Around theSun, in which he discussed conic sections andelliptic orbits and showed how to refine the esti-mate of a planet’s orbit. He published severalworks on mathematical subjects and worked onthe construction of a new observatory, whichwas completed in 1816. The following year hebegan important work at the observatory in thefield of geodesy. Asked to conduct a geodesicsurvey of the state of Hanover, he created newand improved surveying methods, inventing theheliotrope in 1821 to reflect an image of theSun to mark positions over long distances; itworked by reflecting the Sun’s rays by using adesign of mirrors and a small telescope. Gausspublished over 70 papers on geodesy between1820 and 1830.

In 1825, he experienced heart problems;since surveying work was physically rigorousand mathematical breakthroughs no longercame so easily to him, he sought a new researchdirection. In 1831, the year that his second wifedied after a long illness, he began working inthe field of terrestrial magnetism in collabora-tion with WILHELM EDUARD WEBER, who hadjust arrived in Göttingen as a physics professor.

The two men carried out a worldwide magneticsurvey from which, in 1839, Gauss derived amathematical formula expressing magnetism atany location.

During their six productive years together,Gauss and Weber also studied electromag-netism. In 1833, they constructed a moving-needle telegraph similar to that later developedby Charles Wheatstone. However, Gauss failedto scour up financial support for his telegraph,and it was abandoned. Their theoretical workwas more successful. Believing that all unitsshould be assembled from a few basic or abso-lute units, that is, length, mass, and time,Gauss and Weber derived units for magnetism;the centimeter–gram–second (CGS) unit formagnetic flux density was called the gauss. (Ithas now been replaced by the tesla in the Sys-tème International d’Unités [SI] system, whichdoes, however, derive a full set of units fromseven basic units in accordance with Gauss’sideas.)

During this period, he formulated whatcame to be known as Gauss’s law, as follows: ifthe electric flux through an area is defined as thevalue of the electric field multiplied by the areaof a surface perpendicular to the field, then thetotal of the electric flux out of a closed surface isproportional to the electric charge enclosed.This is a general law applying to any closed sur-face, for example, a sphere, and represents a lan-guage that can be used to simplify theformulation of Maxwell’s equations for the elec-tromagnetic field.

After a political dispute forced Weber toleave Göttingen, Gauss’s productivity decreased.He did no more magnetic research but contin-ued astronomical observations and mathemati-cal investigations. His students included thegreat mathematician G. F. B. Riemann. In hislater years he made a fortune through shrewdinvestments in bonds issued by private compa-nies. Gauss died in his sleep, of heart disease, inGöttingen on February 23, 1855.

Gauss, Johann Carl Friedrich 119

A versatile genius, he once described therestless process of discovery that fueled his long,productive career:

When I have clarified and exhausted asubject, then I turn away from it, inorder to go into darkness again. Thenever satisfied man is so strange, if hehas completed a structure, then it is notin order to dwell in it peacefully, but inorder to begin another.

See also MAXWELL, JAMES CLERK.

Further ReadingBühler, W. K. Gauss: A Biographical Study. New York:

Springer-Verlag, 1987.

� Geiger, Hans Wilhelm(1882–1945)GermanExperimentalist, Nuclear Physicist

Hans Wilhelm Geiger helped lay the foundationsof nuclear physics by inventing the Geigercounter, the first instrument capable of detectingand determining the quantity of radioactivity.

Geiger was born in Neustadt, Rheinland-Pfalz, on September 30, 1882, the son of a philol-ogist. He studied physics at the Universities ofMunich and Erlangen and received a Ph.D. fromErlangen in 1906 for a dissertation on electricaldischarges in gases. That year he went to Englandand became a research assistant at the Universityof Manchester, where he worked under ERNEST

RUTHERFORD from 1907 to 1912. His early post-doctoral work involved the application of hisexpertise in electrical charges in gases to radioac-tive decay.

While working with Rutherford, in 1908,Geiger developed the first version of his ground-breaking invention: a device that counted alphaparticles, which are emitted in the type of

radioactive decay known as alpha decay. Theinstrument consisted of a metal tube containing agas (usually argon) at low pressure and a thin wirein the center of the tube. A high voltage wasapplied between the wire and the tube. When analpha particle arrived through a window at oneend of the tube, it caused the gas to ionize andproduced a momentary flow of current. The elec-trical signals that resulted from this process corre-sponded to the number of alpha particles enteringthe tube. The counter enabled Geiger to showthat approximately 3.4 × 1010 alpha particles areemitted per second by a gram of radium, and thateach alpha particle has a positive charge, withtwice the value of the electron charge. Rutherfordlater demonstrated that the doubly charged alphaparticle was in fact a helium nucleus.

Later, Ernest Marsden joined the group as aresearch assistant. In 1909, he and Geiger stud-ied the interactions of alpha particles fromradium with metal reflectors. Although a smallnumber of alpha particles were deflected atwide angles to the beam, most alpha particlespassed straight through the metal. They foundthat the deflection of the alpha particles was afunction of the material of which the reflectorwas made: as the atomic weight of that materialdecreased, so did the amount of deflection. Toshow that the deflection was unrelated to thethickness of metal reflectors, they experi-mented with deflectors of varying thickness.This research led Rutherford to propose, in1911, that the atom consists of a central posi-tively charged nucleus surrounded by electronshells. In Rutherford’s model of the atom, thedeflection of the alpha particles occurs whenthe positively charged particle interacts withthe positively charged nuclei in the metal andis deflected by repulsive forces. The mathemat-ical relationship between the amount of alphascattering and atomic weight was later formu-lated by Geiger and Marsden.

In 1910 and 1911, Geiger and Rutherfordstudied the relationship between the range of an

120 Geiger, Hans Wilhelm

alpha particle and its velocity and examined thevarious disintegration products of uranium.They determined the relationship between therange of an alpha particle and the radioactiveconstant, together with John Nuttall.

Geiger returned to Germany in 1912 tobecome head of the Radioactivity Laboratoriesof the Physikalische Technische Reichsanstaltin Berlin. There he established a successfulresearch group, which included SIR JAMES

CHADWICK, who would later discover the neu-tron. He embarked upon the task of refining hisradiation counter and created an instrumentcapable of detecting beta particles and otherkinds of radiation. When World War I brokeout, Geiger served in the German artillery; hereturned to his position in Berlin at the war’sconclusion. He remained there until 1925, whenhe decided to accept a position as professor ofphysics at the University of Kiel. In 1928, col-laborating with Walther Müller, he developed amore advanced version of the Geiger counter,known as the Geiger–Müller counter, which hasthe advantage of emitting audible clicks, inresponse to radioactivity, that are recorded auto-matically. He used this instrument to confirmthe Compton effect, that is, photon–electronscattering, in 1925. Four years later, he movedagain, this time to the University of Tübingen.From 1931 on, he devoted himself to the studyof cosmic rays. In 1936, he became head of thephysics department at the Technical Universityof Charlottenberg-Berlin and editor of theZeitschrift für Physik.

Geiger’s fortunes declined during WorldWar II, as he was debilitated by illness andthereby forced to slow the pace of his research.After the war, when the Allies occupied Ger-many, he lost his home and possessions. He diedon September 24, 1945, in Potsdam.

By discovering an accurate way of detectingradiation, Geiger made an invaluable contribu-tion to the development of nuclear physics.

See also COMPTON, ARTHUR HOLLY.

Further ReadingStoner, Donald R., and Buford Guy. Geiger Counter.

New York: American Institute of Physics/Ameri-can Association of Physics Teachers, 1975.

� Gell-Mann, Murray(1929– )AmericanTheoretician, Particle Physicist

Murray Gell-Mann revolutionized our under-standing of the subatomic world by his boldreconstruction of the fundamental assumptionsof elementary particle physics. His “eightfoldway” theory described the nuclear force interms of a new fundamental quantity calledstrangeness, which obeyed a new kind of sym-metry principle (called Unitary SymmetrySU[3]). This new theory presupposed a morebasic elementary particle, which Gell-Manncalled a quark, hidden inside the protons andneutrons of the nucleus. On the basis of thisinsight, he was able to impose order on thechaos of the particle zoo that was created by thediscovery, in high-energy particle acceleratorexperiments, of some 100 excited states of par-ticles associated with the atomic nucleus. Thescope of his achievement was recognized in hisselection as the sole winner of the 1969 NobelPrize in physics.

He was born in New York City on Septem-ber 15, 1929. His father, Arthur, was a Jewishimmigrant from Austria, who learned Englishso well that he opened an English languageschool for immigrants in the early 1920s. Buthe was plagued by business failures andimposed his disappointment, perfectionism,and frustration on his precocious younger son.Gell-Mann’s older brother taught him to readand awakened his love of language, science,and art. Known as “Wonder Boy” and “MostStudious” to his classmates at Columbia Gram-mar, a private school on the Upper West Side

Gell-Mann, Murray 121

of New York, Gell-Mann entered Yale Univer-sity at age 15 and received a B.Sc. in 1948.With an innate talent for many subjects, hedid not immediately gravitate to physics.Shortly before his 19th birthday, he wasaccepted for graduate studies at the Mas-sachusetts Institute of Technology (MIT) inCambridge by Victor Weisskopf and arrivedjust in time to watch the competition in quan-tum electrodynamics between the theorists

JULIAN SEYMOUR SCHWINGER at Harvard andRICHARD PHILLIPS FEYNMAN at Cornell.

After receiving a Ph.D. from MIT in 1951,he spent a year at Princeton University’s Insti-tute for Advanced Study. He then moved on tothe University of Chicago, where he joinedENRICO FERMI’s group and over the next fouryears rose in the ranks from instructor to associ-ate professor. It was during this period that hewas led to his great work by focusing on a puz-

122 Gell-Mann, Murray

Murray Gell-Mann described the nuclear force in terms of a new fundamental quantity called strangeness, whichacts in accordance with a symmetry principle called Unitary Symmetry SU3, which presupposes elementaryparticles called quarks hidden inside the protons and neutrons of the nucleus. (AIP Emilio Segrè Visual Archives,Physics Today Collection)

zling phenomenon in particle physics: the largenumber of new excited nuclear states (new par-ticles) generated by high-energy particle accel-erators appeared quickly but disappearedslowly. This suggested that their creation reliedon the strong forces inside the atomic nucleusand that their demise was controlled by theweak forces associated with the slow processesof radioactive decay.

In his quest to understand how this processworked, Gell-Mann proposed a new physicalattribute, which he called “strangeness,” a quan-tity analogous to electric charge, which obeyedthe unitary symmetry principle called SU(3).Whereas in electromagnetic particle collisions,electric charge is conserved—the total going inequals the total going out—strangeness is con-served in strong and electromagnetic interac-tions, but not in weak interactions. In thistheory, strong interactions create a pair of parti-cles with equal and opposite values ofstrangeness, which cancel each other out. Theseparated members of such a pair cannot sponta-neously decay through a strong interaction,because that would violate conservation ofstrangeness. Thus, the slower weak interaction,in which the violation of conservation ofstrangeness is allowed to occur, takes over andcauses radioactive decay of the particles.

The idea of a theory of nuclear force basedon a limited conservation of strangeness provedto be an organizing principle. The unitary sym-metry (SU[3]) inherent in Gell-Mann’s conceptof strangeness led him directly to his eightfoldway, a method of sorting all known particles,according to certain general characteristics, intoeight “families.” In calling this grouping theeightfold way, he was alluding tongue in cheekto Buddhism’s teaching that there are eightattributes of right living. The logic of his systemwas so tight that it revealed the obvious missingfamily members. In 1953, Gell-Mann publisheda series of papers predicting specific, as yet undis-covered new particles, as well as other particles

he insisted could not be discovered. His timingcould not have been better. Successive experi-ments confirmed each of his positive predictionsand did not contradict the negative ones.

In 1955, Gell-Mann married the archaeolo-gist J. Margaret Dow, of Birmingham, England,with whom he would share a marriage of over 25years and raise two children, Elizabeth Sarah andNicholas Webster. The following year he movedto the California Institute of Technology, wherehis most intense collaboration would be with hisnew colleague, Richard Feynman. The personaldifferences between these two giants of theoreti-cal physics, Feynman’s earthiness and disdain offormality versus Gell-Mann’s high-brow, intel-lectually polished manner, as well as their com-peting research styles and theoretical ideas,became legendary. Despite their rivalries, theymanaged to work together and, in 1958, deviseda theory that accounted for many of the phe-nomena associated with the weak force—theforce at work in radioactive decay. In a jointpaper, they extended the underlying principlesbeyond beta decay to other classes of particleinteraction, a proposal that experiments wouldvalidate many years later. They also suggestedthe idea that a new kind of current (analogous toelectric current, a flow of charge) should be con-served. This concept was later developed andbecame a basic tool of high-energy physics.

Picking up the thread of his earlier break-throughs in particle physics, that is, the successof his SU(3) symmetry structure, to explain thenuclear force and produce the eightfold way,Gell-Mann now addressed himself to the ques-tion, What is the basic building block (calledthe irreducible representation) of this symmetry?His answer, given in 1964, when George Zweigcame up with a similar solution, was an as yetundiscovered particle that had three differentmanifestations (hadrons), each holding a frac-tion of a charge. Gell-Mann gave them thewhimsical name quarks (rhymes with corks) andwas later pleased to associate this nomenclature

Gell-Mann, Murray 123

with a line in James Joyce’s Finnegan’s Wake:“Three quarks for Muster Mark!” Quarks werethe building blocks of all of the new excited par-ticle states, including the more stable neutronand the proton. Initially, Gell-Mann suggestedthat hadrons were composed of three quarks orantiquarks, called up, down, and strange (u, d, s),with spin 1/2 and electric charges 2/3, –1/3,–1/3, respectively. (That year, SHELDON LEE

GLASHOW proposed that a fourth, charm quarkwas needed to complete the theory. Later, beautyand truth quarks were added.)

Physicists debated, Were quarks real or meremathematical quirks? Fractional charge seemedan outrageous suggestion at first—it had neverbeen observed. For this reason, the introductionof quarks was treated more as a mathematicalidea than as a proposal for an actual physicalobject. Gell-Mann himself, who had little usefor philosophy, refused to participate in thisdebate. Whatever the nature of his abstractinvention, its predictions continued to be con-firmed by particle accelerator experiments.

In terms of the new SU(3) symmetry, thequarks inside the protons and neutrons in thenucleus were permanently confined by forcesresulting from the quantum exchange of mas-sive vector particles called gluons. Following ananalogy with quantum electrodynamics (QED)theory, Gell-Mann and others later constructedthe quantum field theory of quarks and gluons,called quantum chromodynamics (QCD), whichcan account for all the nuclear particles andtheir strong interactions.

In 1992, 11 years after losing his wife, Mar-garet, to cancer, Gell-Mann married MarciaSouthwick of Boston. Shortly afterward, hebecame a professor and Distinguished Fellow atthe Santa Fe Institute, where he pursues hisinterests in natural history, biological evolution,the history of language, and the study of creativethinking. Over the succeeding decade, after dis-covering the simplicity underlying nature’s com-plexity, Gell-Mann turned to the mystery of

complex adaptive systems, which learn or evolveby utilizing acquired information. He deals withthese issues in his book The Quark and the Jaguar:Adventures in the Simple and the Complex, inwhich he relates the basic laws of physics to thecomplex diversity of the natural world.

He is also concerned about policy mattersrelated to world environmental quality (includingconservation of biological diversity), restraint inpopulation growth, sustainable economic devel-opment, and stability of the world political system.

By developing the quark theory of thestrong interactions, Gell-Mann redefined theconcept of an elementary particle and openedthe door for physicists to create what is knowntoday as the Standard Model, a global unifica-tion of the electroweak theory with the quantumchromodynamic SU(3) strong interaction the-ory. Even this theory, however, is not complete;the search for a unified particle “theory of every-thing” continues today.

See also LEDERMAN, LEON M.; SALAM,ABDUS; WEINBERG, STEVEN.

Further ReadingGell-Mann, Murray. The Quark and the Jaguar: Adven-

tures in the Simple and the Complex. New York: W.H. Freeman, 1994.

Johnson, George. Strange Beauty: Murray Gell-Mannand the Revolution in Twentieth-Century Physics.New York: Alfred A. Knopf, 1999.

Kane, Gordon. The Particle Garden: Our Universe asUnderstood by Particle Physicists. Cambridge,Mass.: Perseus, 1995.

� Glaser, Donald Arthur(1926– )AmericanExperimentalist, Nuclear Physicist,Particle Physicist, Biophysicist

Donald Arthur Glaser received the 1960 NobelPrize in physics for his invention of the bubble

124 Glaser, Donald Arthur

chamber, a device that gave nuclear physicists apowerful new tool for investigating elementaryparticles.

He was born on September 21, 1926, inCleveland, Ohio, to Lena Glaser, a homemaker,and William Glaser, a businessman. After attend-ing public schools in Cleveland Heights, Ohio,he entered the Case Institute of Technology; hegraduated with a bachelor’s degree in physics andmathematics in 1946. He spent the springsemester of that year teaching math at Casebefore beginning his graduate studies at the Cali-fornia Institute of Technology. His doctoral the-sis was an experimental study of the momentumspectrum of high-energy cosmic rays and mesonsat sea level, which he completed in 1949.

After receiving a Ph.D. in 1950, he joinedthe physics faculty at the University of Michi-gan, in Ann Arbor, where he remained until1957. During this period, his research focusedon elementary particles. He was especiallyinterested in the strange particles, the transientparticles generated in the high-energy colli-sions of nuclei, and sought new methods ofdetecting and recording their presence in ele-mentary particle processes. Initially, he experi-mented with the cloud chamber, which hadbeen developed in the 1920s by the Britishphysicist CHARLES THOMSON REES WILSON. Itcontained a saturated vapor that condensed asa series of liquid droplets along the ionized pathleft by a particle crossing the chamber. Thecloud chamber played an enormous role in the“golden age of nuclear physics” during the1930s, when the nuclear particles being inves-tigated had energy ranges on the order of a fewmillion electron volts. With advances in parti-cle accelerators, such as the one built at theEuropean Nuclear Research Center (CERN) inGeneva, in the early 1950s, nuclear physicistsbegan to deal with fast high-energy particles,with energies more than 1000 times larger thanthose earlier obtainable, which would bemissed by the cloud chamber.

In 1952, Glaser solved this problem whenhe built his first bubble chamber, in which parti-cle tracks are composed of small gas bubbles in aliquid. It consisted of a vessel only a few cen-timeters across containing superheated liquidether under pressure. When the pressure wasreleased suddenly, particles traversing the cham-ber left tracks consisting of streams of small bub-bles formed when the liquid boiled locally. Thetracks were photographed by using a high-speedcamera. In later bubble chambers, supercooledliquid hydrogen was substituted for ether, andchambers two meters across are now in use.Glaser worked on the development of varioustypes of bubble chambers for experiments inhigh-energy nuclear physics.

He also did experiments on elementary parti-cles at two giant accelerators, the Cosmotron ofthe Brookhaven National Laboratory in New Yorkand the Bevatron at the Lawrence Radiation Lab-oratory in California, which yielded informationon the lifetime, decay modes, and spins of strangeparticles, as well as differential cross sections forthe production of these particles by pions.

In 1959, Glaser accepted an appointment atthe University of California, where he switchedhis research focus from physics to molecularbiology. In 1960, he won the Nobel Prize andmarried Ruth Bonnie Thompson. He laterbecame professor of physics and biology in 1964.

Because it allowed the physics communityto exploit the gigantic atomic accelerators in theUnited States, Western Europe, and Russia,Glaser’s invention of the bubble chamber had anenormous impact on nuclear and particlephysics. The bubble chamber has allowed largeresearch teams to make rapid progress in investi-gating the strange new particles that are formed,transformed, and annihilated when the beamfrom these machines is directed into the cham-ber. This has led to a greater understanding ofthe structure of nuclear particles and the inter-nal quantum forces that allow them to be cre-ated and destroyed inside atomic nuclei.

Glaser, Donald Arthur 125

See also RICHTER, BURTON; RUBBIA, CARLO;TING, SAMUEL; CHAO CHUNG.

Further ReadingWilson, E. J. N. An Introduction to Particle Accelera-

tors. Oxford: Oxford University Press, 2001.

� Glashow, Sheldon Lee(1932– )AmericanTheoretician, Particle Physicist,Quantum Field Theorist

Sheldon Lee Glashow shared the 1976 NobelPrize in physics with ABDUS SALAM and STEVEN

WEINBERG for his contributions to the creationof the electroweak theory, a quantum field the-ory that unifies the electromagnetic and weakforces. In particular, he predicted the existenceof the fourth, “charmed” quark, which was nec-essary to generalize the electroweak theory intowhat is now known as the Standard Model ofelectromagnetic, weak, and strong interactions.He has remained active in the quest for a GrandUnified Theory (GUT) capable of synthesizingall four interactions—the weak, electromag-netic, strong, and gravitational—within thecontext of quantum field theory.

He was born on December 5, 1932, in NewYork City to Lewis Glashow and Bella RubinGlashow, who had immigrated to the UnitedStates in the early years of the century to escapeanti-Semitism in tsarist Russia. Lewis Glashowbecame a successful plumber and secured a com-fortable, middle-class life for his family. Havinghad no opportunity to obtain a higher educa-tion, Lewis and Bella were determined that theirchildren would. “In comfort and in love,” Shel-don would later recall, “we were taught the joysof knowledge and of work well-done.” His broth-ers chose medicine and dentistry; Sheldon knewfrom an early age that he would be a scientist,and his parents encouraged him in this direc-

tion. His father built a basement lab for him,where he explored aspects of chemistry and biol-ogy and played with frogs.

He attended the highly competitive BronxHigh School of Science, where his talentedschoolmates included Steven Weinberg, whobecame a close friend. His interests soon shiftedfrom biology to physics. Glashow, Weinberg, andGary Feinberg, who also became a physicist,taught each other relativity and quantummechanics on the subway ride to school. In hisNobel Prize speech, Glashow would thank thesefriends “for making me learn too much too soon ofwhat I might otherwise not have learned at all.”Gregarious, easy-going, anything but a “grind,” heseemed to learn physics effortlessly. In his senioryear, Glashow was named a finalist in the nation-wide Westinghouse Science Talent Search.

Graduating in 1950, Glashow and Weinbergwent on to Cornell University together; theirclass included the mathematical physicistDaniel Kleitman, who would become Glashow’sbrother-in-law. Glashow was disappointed withthe lackluster faculty and turned in a mediocreperformance in his classes; he received a bache-lor’s degree in 1954. Matters improved consider-ably when he enrolled at Harvard University forhis graduate studies. At Harvard, he absorbedthe belief that the weak and electromagneticforces could be explained by a single, unifiedgauge theory from his thesis adviser, JULIAN SEY-MOUR SCHWINGER. In his thesis “The VectorMeson in Elementary Particle Decay,” Glashowfirst explored the possibility of an electroweaksynthesis. In 1958, when Glashow completed hiswork, he and Schwinger planned to write apaper on the topic, but one of them lost the firstdraft and somehow the project was dropped.

After finishing the work for which hewould receive a Ph.D. in 1959, Glashow won aNational Science Foundation Post-DoctoralFellowship, which he hoped would take him toMoscow, to work with Igor Tamm at the Lebe-dev Institute. These were the cold war years,

126 Glashow, Sheldon Lee

however, and his visa never materialized.Instead, working at the Niels Bohr Institute inCopenhagen, he was able to construct a unifiedYang–Mills theory (a generalization of quantumelectrodynamics [QED]) of the weak and elec-tromagnetic interactions, which contained theSU(2) × U(1) symmetry structure of whatwould later be called the electroweak theory.However, the theory had the drawback of con-taining infinities. Glashow tried to renormalizehis equations to get rid of the infinities and,once convinced he had done so, presented hisresults at a conference in London in the springof 1959. Abdus Salam, an expert on renormal-

ization, who with John Ward had been tryingunsuccessfully to do the same thing, was in theaudience; he lost little time in invalidatingGlashow’s results. Undeterred, Glashow contin-ued to look for links between the weak and elec-tromagnetic forces.

During his stay in Europe, he met MURRAY

GELL-MANN, who became a champion of hisideas. Gell-Mann presented his theory on thealgebraic structure of weak interactions at a 1960conference in Rochester, New York, and arrangedfor his protégé to become a research fellow at theCalifornia Institute of Technology. Soon after-ward, Gell-Mann invented the “eightfold way”

Glashow, Sheldon Lee 127

Sheldon Lee Glashow predicted the existence of the fourth, “charmed” quark, necessary for what is now known asthe Standard Model of electromagnetic, weak, and strong interactions. (AIP Emilio Segrè Visual Archives, PhysicsToday Collection)

method of grouping elementary particles, whichGlashow studied for several years.

In 1961, he became an assistant professor atStanford University and, independent of Wein-berg and Salam, published a paper, “Partial Sym-metries of Weak Interactions.” In it, he pointedout “remarkable parallels” between electromag-netism and the weak force, depicting them aslinked by a broken symmetry, and predicted theexistence of the W and Z force-carrying parti-cles. These previously undetected particleswould play a significant role in experimentaltests of the unified electroweak theory, butGlashow could not predict their masses, with theresult that the experimenters were in the dark asto what to look for.

The next year, he moved on to the Univer-sity of California, Berkeley, as an associate pro-fessor; he remained there until 1966. During thistime, he continued to develop the phenomeno-logical successes of the SU(3) symmetry appliedto the various species of quarks, which werelabeled in terms of their flavors (up quark, downquark, strange quark, etc.), and attempted tounderstand the departures from exact symmetryas a consequence of spontaneous symmetrybreaking. Then, in 1964, he became aware of thework of Peter Higgs, demonstrating that thespontaneous symmetry breaking effects of scalarfields, coupled to Yang–Mills gauge theory, couldcreate new kinds of force-carrying particles,some of them massive. This led Glashow to spec-ulate that if the virtual particles that carry theelectromagnetic and weak forces (known collec-tively as the intermediate vector boson W and Zparticles) were related by a broken symmetrythrough a coupling to a scalar Higgs field, itmight be possible to estimate their masses interms of the unified, more symmetrical forcefrom which the two forces were thought tohave arisen.

During this same period, Weinberg andSalam, independently of Glashow and of oneanother, devised similar electroweak theories.

All three theories, however, had the limitationthat they could only be applied to leptons, aclass of particles that includes electrons and neu-trinos, but not to protons and neutrons.Glashow, who in 1966 became Eugene HigginsProfessor of Physics at Harvard, studied variousmeans of extending the electroweak theory toinclude the hadronic class of particles, which,according to Gell-Mann’s SU(3) symmetry, wasmade up of quarks such as protons, neutrons, andmesons. In order to do so, he found it necessaryto postulate the existence of a flavor for Gell-Mann’s quarks, which he called charm. In 1969,with John Iliopolos and Luciano Maiani hedeveloped the arguments that predicted theexistence of charmed hadrons built out ofcharmed quarks. The prediction would not beverified until 1974, when SAMUEL CHAO

CHUNG TING and BURTON RICHTER indepen-dently discovered the J/psi particle.

Over the next two years, this extendedversion of the unified electroweak theoryattracted scant attention since, unlike QED, ithad not yet been shown to be renormalizable(i.e., capable of being altered by a mathemati-cal procedure that cancels the unwantedinfinities in a quantum field theory by intro-ducing the appropriate renormalization con-stants). All this changed in 1971, when theDutch physicist GERARD ’T HOOFT used com-puter algebra techniques to prove that theextended electroweak theory coupled to aHiggs scalar field with spontaneous symmetrybreaking was indeed renormalizable. This tech-nique showed that the theory was viable andimmediately attracted the attention of the par-ticle physics community. Although experimen-tal verification of the electroweak theorywould not occur until 1983, ’t Hooft’s proof wasthe final step that led the Nobel Committee toaward Weinberg, Salam, and Glashow the1979 prize in physics.

In the intervening years between the for-mulation of the electroweak theory and its

128 Glashow, Sheldon Lee

international recognition, Glashow pushed hisideas further. In 1974, he and his Harvard col-league Howard Georgi correctly predicted thatthe effects of charmed quarks would be discov-ered in neutrino physics and in particle pro-duction processes generated by high-energyelectron positron annihilation. Continuingtheir fruitful collaboration, they suggested thata connection analogous to that between theelectromagnetic and weak forces might beforged with the strong force. Their proposed“grand unification” of three of the four forces inthe universe differed in one essential way fromthat of the electroweak theory; whereas theelectroweak theory argued that the electromag-netic and weak forces crystallized out of theirsymmetric union when the temperature of theuniverse dropped to about a 1015 K above abso-lute zero, Georgi and Glashow showed that theunion of the electroweak force with the strongforce would have been apparent only at a tem-perature some 1012 times higher. From the pointof view of energy, this is about 1015 times themass of the proton or about four orders of mag-nitude less than the Planck mass (the massenergy at which ALBERT EINSTEIN’s gravitationtheory must be quantized). Thus, their idea of aGUT boldly took theoretical physics into anenergy realm beyond that which anyone haddared explore, namely, that of the early uni-verse, when the quantization of gravity becameimportant.

In his Nobel Prize speech, Glashow com-mented on the relationship of the extendedelectroweak theory (which by then had becomeknown as the Standard Model) and GUTs:

While keeping an open mind with respectto the source of the next big breakthrough,Glashow has pursued his own vigorous path as aresearcher and educator. He has written a num-ber of technical and popular science books,including Lie Algebras in Particle Physics, withHoward Georgi (1999); The Charm of Physics(1995); From Alchemy to Quarks: The Study of

Physics as a Liberal Art (1994); and Interactions:A Journey Through the Mind of a Particle Physicistand the Matter of This World, with Ben Bova(1988). His most recent book project deals witha favorite activity of his: solving physics prob-lems while engaged in a game of billiards.

He has had visiting professorships to CERN,the University of Marseilles, the MassachusettsInstitute of Technology, Texas A&M University,and Boston University. He has also been a con-sultant to the Brookhaven National Laboratoryand affiliated senior scientist at the University ofHouston.

He lives with his wife, the former JoanShirley Alexander, whom he married in 1972 andwith whom he has had four children. In recentyears, he has moved to Boston University, wherehe is Arthur G. B. Metcalf Professor of Physics.

Glashow’s current work involves grand uni-fied theories and the search for antimatter in theuniverse, focusing on the theoretical conse-quences of such a discovery. He continues tobelieve that there will always be another funda-mental discovery just around the corner:

Can we really believe that nature’s bag oftricks has run out? Have we finallyreached the point where there is nolonger a new particle, a “fifth” force, or abewildering new phenomena to observe?Of course not. Let the show go on!

See also NE’EMAN, YUVAL; RUBBIA, CARLO;VELTMAN, MARTINUS J.G.

Further ReadingCrease, Robert P. The Second Creation: Makers of the

Revolution in Twentieth-Century Physics. Rutgers,N.J.: Rutgers University Press, 1995.

Glashow, Sheldon L. The Charm of Physics. New York:Springer-Verlag, 1991.

———. Interactions: A Journey Through the Mind of aParticle Physicist and the Matter of This World.New York: Warner Books, 1988.

Glashow, Sheldon Lee 129

� Goeppert-Mayer, Maria Gertrude(1906–1972)German/AmericanTheoretical Physicist, Nuclear Physicist,Physical Chemist

Maria Goeppert-Mayer was a brilliant theoreti-cal physicist who developed a shell model theorythat explained the arrangement of the protonsand neutrons in the atomic nucleus. After a life-time of underrecognition, she was awarded theNobel Prize in physics in 1963 for this work, thesecond woman to be honored in this way.

She was born on June 28, 1906, in Katowice,Germany (now part of Poland), into a family ofacademics: seven generations of university pro-fessors. Her father, Friedrich, a pediatrician,moved the family to Göttingen, when Maria wasfour, on his appointment to the medical facultyat the University of Göttingen. Maria inheritedher scientific bent from her father, whom sheidolized, and a love of music and social life fromher mother. In 1924, after attending a smallwomen’s preparatory school, she was admitted tothe University of Göttingen, which had very fewwomen students in those years. She began study-ing mathematics, but Göttingen was then arenowned world physics center. Intrigued by theexciting developments of atomic physics and thenew quantum mechanics, she changed her majorin 1927. Working under the great quantum theo-rist MAX BORN, in 1930, she completed her Ph.D.thesis, in which she calculated the probabilitythat an electron orbiting an atomic nucleuswould emit a two-photon state of light as itjumped to an orbit closer to the nucleus. Thisbold result would be experimentally confirmed30 years later.

While Maria was a graduate student, herfather died and her mother began to take inboarders, one of whom was an American chem-istry student, Joseph Edward Mayer, whomMaria married in 1930. The young couplemoved to the United States, where Joseph

became an assistant professor of chemistry atJohns Hopkins University in Baltimore. Becauseof the antinepotism laws common at the time,which forbade the hiring of both husband andwife, as well as the economic hardship of theGreat Depression, Johns Hopkins could not offerher a paying academic job. Her only income wasfrom helping a professor with his German corre-spondence; but she kept doing physics, for thesheer love of it. Encouraged by her husband, shebegan to explore physical chemistry and did sig-nificant research in that area.

In 1933, the year she became a naturalizedU.S. citizen, her daughter Maria Anne was born.When her child was four, she began workingwith her husband on a textbook on statisticalmechanics describing the behavior of molecules,which was eventually published in 1940. In1938, just before her husband took a job atColumbia University, she gave birth to her sec-ond child, Peter.

As World War II loomed, Goeppert-Mayerand her husband joined a group of expatriate sci-entists who urged the United States to developan atomic bomb. She was offered her first paidwork as a scientist to search for ways to separatethe bomb’s potential fuel, the radioactive form ofuranium, from the more common, nonradioac-tive form. However, her work had little directeffect on the bomb project.

In early 1946, she and her husband wereinvited to join the University of Chicago’s newInstitute for Nuclear Studies (later the EnricoFermi Institute), where the faculty includedEDWARD TELLER and ENRICO FERMI. Goeppert-Mayer was made an unsalaried associate profes-sor and earned a part-time salary as a seniorresearcher at the Argonne National Laboratory.The Chicago group was one of the most brilliantgatherings of scientists in the 20th century. Afrequent topic of their weekly seminars was thearrangement of protons and neutrons in theatomic nucleus. At the time, the most com-monly accepted model of the atomic nucleus

130 Goeppert-Mayer, Maria Gertrude

pictured it as something like a drop of water, inwhich protons and neutrons moved randomly.However, physicists also knew that electronsorbited the atomic nucleus in distinct layerscalled shells, and by analogy some physicists hadsuggested that the protons and neutrons in theatomic nucleus might also be arranged in shells.They based their supposition on findings madein the period between 1920 and 1930 that pro-tons and neutrons each formed particularly sta-ble systems in an atomic nucleus when thenumber of either kind of nucleon was one of theso-called magic numbers: 2, 8, 20, 50, 82, and126. Several physicists tried to interpret thesemagic numbers by analogy with NIELS HENRIK

DAVID BOHR’s successful explanation of the peri-odic table of the elements. In this picture it wasthen assumed that the nucleons move in orbitsin a common field of force and that these orbitsare arranged in so-called shells that are energet-ically well separated. The magic numbers shouldcorrespond to completed shells of nucleons.Although this interpretation was successful forlight nuclei, it could only explain the first threemagic numbers (2, 8, 20), and for many years nofurther physical or mathematical evidence wasfound to support the shell model of the nucleus.

In 1946, while working with Edward Telleron a theory of the origin of chemical elements,Goeppert-Mayer noticed that elements whosenuclei contained certain numbers of protons orneutrons (i.e., magic numbers again) wereunusually abundant and stable, never undergo-ing radioactive decay. Searching for the reasonfor these magic numbers, she hypothesized thatthey had some relation to the arrangement ofprotons and neutrons in shells. She proposedthat just as filled electron shells prevented ele-ments from reacting chemically, the magic num-ber of protons and neutrons represented thefilled shells in the nucleus that prevented atomsfrom breaking down radioactively. In this picturethe nucleus was like an onion with the protonsand neutrons revolving around each other in

layers. The magic numbers represented the mostabundant elements because in these elementsthe nuclear particles were very tightly boundtogether, moving in a clockwise–counterclock-wise pattern. These tightly fitting nuclei wouldnot change properties with any other elements,and that was why such elements as tin and leadwere so abundant.

The way to prove her idea occurred toGoeppert-Mayer in a discussion with EnricoFermi when he asked her whether there wereany possibility that spin-orbit coupling mightplay an important role in the shell model of thenucleus. Spin-orbit coupling is a processwhereby the direction in which a particle spinshelps determine which orbit or shell it willoccupy. Whereas spin-orbit coupling amongelectrons is weak, Goeppert-Mayer realized thatif it were powerful in the nucleus, requiring

Goeppert-Mayer, Maria Gertrude 131

Maria Gertrude Goeppert-Mayer developed the nuclearshell model theory, which explained the arrangement ofthe protons and neutrons in the atomic nucleus. (AIPEmilio Segrè Visual Archives, Physics Today Collection)

much more energy for particles to spin in onedirection than in the other, it could explain hermagic numbers and prove that nuclear particlesare arranged in shells. Her idea was that anucleon’s energy should differ when it “spins” inthe same direction from that when it spins in theopposite direction as it revolves around thenucleus. Fermi’s question was the key to unlock-ing this brilliant insight. Ten minutes after heasked it, she was bombarding him with themathematical proof of her theory.

Her landmark paper on this topic, publishedin 1948, marked the beginning of a new era inthe acceptance of the shell model. Goeppert-Mayer had given convincing evidence for theexistence of the higher magic numbers, noting,moreover, that experiments strongly supportedthe existence of the closed nuclear shells. Atabout the same time, Hans D. Jensen, a Germanphysicist, developed and published a similar idea.The two physicists met in 1950 and five yearslater published their important book ElementaryTheory of Nuclear Shell Structure. Her achieve-ments at last opened academic doors, and, in1959, both Goeppert-Mayer and her husbandwere invited to join the faculty of the Universityof California at La Jolla in San Diego, California.

Although a few months later, she suffered astroke, she was able to continue her research,refining her shell model theory of the nucleus.

In 1963, she shared the Nobel Prize inphysics with Jensen and EUGENE PAUL WIGNER,the second woman, after MARIE CURIE, to attainthat distinction. She died of heart disease onFebruary 20, 1972, at the age of 65, in La Jolla.

Goeppert-Mayer’s work created new insightinto the nature of nuclear structure, the processof radioactive transformation of the elements,and the properties of the forces that can holdnuclei together in closed nuclear shells. Theexistence of such closed shell nuclei, which can-not radioactively transform into other elements,explains why there is an abundance of stable ele-ments in nature.

Further ReadingDash, Joan. A Life of One’s Own. New York: Harper &

Row, 1973, pp. 231–346.McGrayne, Sharon Bertsch. Nobel Prize Women in

Science: Their Lives, Struggles, and MomentousDiscoveries. New York: Birch Lane Press, 1993.

Sachs, Robert. Maria Goeppert-Mayer, 1906–1972, aBiographical Memoir. Washington, D.C.: NationalAcademy of Sciences, 1979.

132 Goeppert-Mayer, Marie Gertrude

H

133

� Hawking, Stephen(1942– )BritishTheoretician, Relativist, Astrophysicist,Cosmologist

One of the best known physicists alive today,Stephen Hawking developed groundbreakingmathematical theorems delineating the physicalrequirements dictated by general relativity forthe astrophysical formation of black holes. Helater shocked the physics community with hisdiscovery of a physical mechanism that requiredthat black holes must always emit radiation(known as Hawking radiation), leading to theireventual evaporation. His ideas on cosmologyhave deeply influenced our current understand-ing of space and time, black holes, and the originof the universe.

Hawking was born on January 8, 1942, inOxford, England, where his mother hadretreated from the family’s London home toescape the German bombing during World WarII. Soon afterward, they returned to London,where Stephen’s father worked as a medicalresearcher. When Stephen was eight, his fathertook a job at the Institute for Medical Studies inMill Hill and the family moved to Saint Albans,about 20 miles north of London, to shorten hiscommute. Stephen first attended the Saint

Albans School for Girls (where boys up to theage of 10 were accepted) then transferred toSaint Albans School, at age 11.

He wanted to study mathematics, but hisfather was determined he should attend his almamater, University College, at Oxford, which didnot have a mathematics fellow. So it was that,on winning a scholarship, he studied physics andnatural science instead. At Oxford, where theprevailing attitude was that “you were supposedto be brilliant without effort,” he coasted forthree years, without working very hard, and justmanaged to obtain a first-class honors degree innatural science.

He continued on to Cambridge University todo research in cosmology and general relativityunder Dennis Sciama. But during his firstsemester, the clumsiness and unexplained falls hehad begun to experience during his last year atOxford grew more worrisome. Persuaded by hismother to see a doctor, he underwent a series ofdiagnostic tests. The verdict was amyotrophic lat-eral sclerosis (ALS), popularly known as LouGehrig’s disease, a degenerative, incurable neuro-muscular illness. Hawking had just turned 21.Although the doctors offered him no hope and notreatment, he found his own source of strength:

My dreams at that time were very dis-turbed. Before my condition had been

diagnosed, I had been very bored withlife. There had not seemed to be any-thing worth doing. But shortly after Icame out of hospital, I dreamt that I wasgoing to be executed. I suddenly realizedthere were a lot of things I could do if Iwere reprieved. . . . I found to my sur-prise that I was enjoying life in the pre-sent more than before.

Hawking fell in love with Jane Wilde,whom he had met just before learning his diag-nosis and soon became engaged to her. With

something to work for, he returned to Cam-bridge, continued his research, and earned adoctorate in 1966. He became a research fellowand later a professorial fellow at Cambridge’sGonville and Caius College. In 1973, he left theInstitute of Astronomy and joined the Depart-ment of Applied Mathematics and TheoreticalPhysics, where, since 1979, he has held thehighly prestigious post of Lucasian Professor ofMathematics, once filled by SIR ISAAC NEWTON.

Between 1965 and 1970, Hawking worked onthe thorny issue of singularities in classical gravita-tional theory. A singularity is a hypotheticalregion in space in which gravitational forces causematter to be infinitely compressed and space andtime to become infinitely distorted. Singularitiesseemed to be associated with the gravitational col-lapse process described by ALBERT EINSTEIN’s gen-eral theory of relativity. In collaboration withRoger Penrose, Hawking developed a series of rea-sonable mathematical physics theorems thatshowed that the general theory of relativity con-tained singularities, which implied that space andtime would have a beginning in the big bang andan end in black holes. The development of thesePenrose–Hawking theorems led relativistic astro-physicists to devise new mathematical techniquesfor studying this area of cosmology.

From 1972 to 1975, stimulated by a series ofmeetings and discussions with Kip Thorne and theeminent Russian physicist Yakov Zeldovich,Hawking made a startling discovery. By effecting a“partial marriage” between quantum field theoryand general relativity, he showed that black holesmust always emit radiation. This was perhaps hismost spectacular achievement: the discovery thatblack holes are not really black; rather, they emitevery possible type of elementary particle withinthe thermal spectrum of a hot body, ultimatelyending their lives in a general explosion.

During this same period Hawking studiedthe creation of the universe and postulated thatafter the big bang, many objects as heavy as 109

tons but only the size of a proton were created.

134 Hawking, Stephen

Stephen Hawking developed theorems delineating thephysical requirements for the astrophysical formation ofblack holes. His ideas have deeply influenced ourcurrent understanding of space and time and the originof the universe. (AIP Emilio Segrè Visual Archives,Physics Today Collection)

Because of their large gravitational attraction,these primordial mini black holes would be gov-erned by general relativity, but their subatomicsize would require them to obey the laws ofquantum mechanics. To date, however, observa-tional searches for the characteristic Hawkingradiation emitted by these primordial blackholes have not been successful.

Hawking’s next major work was a logicalcontinuation of this partial marriage of quantumfield theory and general relativity. In 1983, withJim Hartle of Santa Barbara, he made theremarkable proposal that our universe and all itcontains are in a unique quantum state havingno boundary or edge. The no-boundary universeis one in which the universe does not start witha singularity. The hypothesis uses the Americanphysicist RICHARD PHILLIPS FEYNMAN’s idea oftreating quantum mechanics as a “sum over his-tories,” meaning that a particle does not haveone history in spacetime but instead followsevery possible path to reach its current state. Bysumming these histories—a difficult process thatmust be done by treating time as imaginary—you can find the probability that the particlepasses through a particular point.

Hawking and Hartle then wedded this ideato general relativity’s view that gravity is just aconsequence of curved spacetime. Under classi-cal general relativity, the universe either has tobe infinitely old or has to have started at a sin-gularity. But Hawking and Hartle’s proposalraises a third possibility—that the universe isfinite but had no initial singularity to produce aboundary. The geometry of the no-boundaryuniverse would be similar to the geometry of thesurface of a sphere, except that it would havefour dimensions instead of two. You can travelcompletely around Earth’s surface, for instance,without ever encountering an edge. In this anal-ogy, unfolding in imaginary time, Earth’s NorthPole represents the big bang, marking the start ofthe universe. However, just as the North Pole isnot a singularity, neither is the big bang.

As Hawking writes:

Both time and space are finite in extent,but they don’t have any boundary oredge . . . there would be no singularities,and the laws of science would holdeverywhere, including at the beginningof the universe.

In the mid-1970s, when he did this impor-tant work, despite his physical handicaps, Hawk-ing was managing to lead a rich professional andpersonal life. He and Jane had three children, anduntil 1974, with Jane’s help, he was relativelyindependent. However, as his condition pro-gressed, the couple employed outside help,including a live-in research assistant and part-time nurses. In 1984, Hawking completed the firstdraft of what would be his phenomenally sellingpopular science book, A Brief History of Time.

But the following year, while visiting thegiant particle accelerator at the European Centerfor Nuclear Research (CERN) in Geneva,Hawking contracted pneumonia, underwent atracheotomy, and lost his voice. His speech hadbecome increasingly slurred over the years, butnow it was gone altogether. David Mason, ofCambridge Adaptive Communication, fitted asmall portable computer and a speech synthesizerto his wheelchair. Using this system, he has writ-ten books and papers and given a large number ofscientific and technical talks. After 25 years ofmarriage, Stephen and Jane divorced. He subse-quently married Elaine Mason, one of his nurses.

His technical books include The Large ScaleStructure of Spacetime, with G. F. R. Ellis (1989);General Relativity: An Einstein Centenary Survey,with W. Israel (1980); 300 Years of Gravitation,with W. Israel (1990), and The Nature of Spaceand Time, with Ruger Penrose (1996). His popu-lar books include A Brief History of Time (1998),Black Holes and Baby Universes and Other Essays(1994), Stephen Hawking’s Universe: The CosmosExplained (1998), The Universe in a Nutshell

Hawking, Stephen 135

(2001), The Theory of Everything, (2002), TheFuture of Spacetime (2002), and On the Shouldersof Giants: The Great Works of Physics and Astron-omy (2002).

Hawking continues to do research, write,and travel all around the world to lecture. InJanuary 2002, physicists gathered at CambridgeUniversity to honor him on his 60th birthday.

Although Hawking modestly dismisses talkof himself as a “modern day Einstein” as mediahype, there is no doubt about the substantialcontributions he has made, both to astrophysicsand to cosmology, and to the popular fascinationwith these frontiers of knowledge. With clarityand incisive humor, he has consistently raisedissues that lie on the boundary between physicsand philosophy.

See also CHANDRASEKHAR, SUBRAMANYAN;GAMOW, GEORGE; WHEELER, JOHN ARCHIBALD.

Further ReadingHawking, Steven. A Brief History of Time: From the

Big Bang to Black Holes. New York: BantamBooks, 1998.

———. The Future of Spacetime. New York: W. W.Norton, 2002.

———. Stephen Hawking’s Universe: The CosmosExplained. New York: Basic Books, 1998.

———. The Universe in a Nutshell. New York: Ban-tam Books, 2002.

� Heisenberg, Werner(1901–1976)GermanTheoretical Physicist, QuantumTheorist

One of the greatest of 20th-century physicists,Werner Heisenberg is recognized as the founderof quantum mechanics. His most famous discov-ery was the uncertainty principle, which intro-duced the notion of probability into thecomplex of startling ideas on which the structure

of a quantum mechanical view of nature wasbeing built. For this dubious feat—deprivingphysics of modern science’s most hallowed tenet,the deterministic idea of cause and effect—hewas awarded the 1932 Nobel Prize in physics. IfHeisenberg was fortunate to begin his career at atime of exciting breakthroughs in physics, thehistorical circumstances of his middle yearsposed agonizing choices. Choosing to remain inhis beloved Germany through the Nazi era, hemanaged to avoid internment as a “white Jew”and eventually played a major role in the failedattempt to develop a German atomic bomb. Theprice he may have paid for his survival remainscontroversial to this day.

Werner Karl Heisenberg was born onDecember 5, 1901, in Würzberg, in the southernGerman state of Bavaria. His father, AugustHeisenberg, was professor of Greek at the Uni-versity of Munich; his mother, Anna, who con-verted from Catholicism to her husband’sLutheranism, was the daughter of the principalof the gymnasium Werner and his older brother,Erwin, would attend. Erwin later became achemist. As a prestigious academic family, theHeisenbergs participated in the cultural andsocial life of the upper middle class.

In 1911, Werner entered the MaximiliansGymnasium in Munich; nine years later he wouldgraduate at the top of his class. But these school-boy years were anything but idyllic: the outbreakof World War I produced danger and physicaldeprivation. Heisenberg’s generation, which wasindoctrinated with German nationalism, feltbetrayed by their elders when Germany wasdefeated in 1918 and the monarchy collapsed.Heisenberg appears to have found refuge frompolitical and social turmoil in two parallel, butquite different, directions. The first was his fasci-nation with the mathematics of the number sys-tem, because, he said, “It’s clear, everything is sothat you can understand it to the bottom.” Thesecond was his role as leader of a small group ofyounger boys, associated with the New Boy

136 Heisenberg, Werner

Scouts, who sought the essence of German culturein nature, music, and poetry. His “boys” would bethe companions of his leisure, hiking and campingin and around Germany with him, until Hitlerbanned all independent youth groups in 1933.

Upon entering the University of Munich in1920, Heisenberg decided to study theoreticalphysics under ARNOLD JOHANNES WILHELM

SOMMERFELD and soon produced a publishablecontribution to the early quantum mechanics ofthe atom. He formed a lasting friendship withWOLFGANG PAULI, who, in 1922, began to castdoubt on NIELS HENRIK DAVID BOHR’s results.Completing his doctoral dissertation on turbu-lence in fluid streams in 1923, Heisenberg becameMAX BORN’s assistant at Göttingen. From 1924to 1925, he took a leave of absence to work withBohr in Copenhagen. In later years, he describedhis apprenticeship by saying, “I learned opti-mism from Sommerfeld, mathematics at Göttin-gen, and physics from Bohr.”

During these dynamic years in Munich,Göttingen, and Copenhagen, Heisenbergattacked the three areas of research in which thefailure of theory to explain experimental resultshad led to talk of a “crisis” in quantum theory:the study of light emitted and absorbed by atoms(spectroscopy), the predicted properties of atomsand molecules, and the question of whether lightbehaved as a wave or a particle. Heisenberg wasless interested in creating a picture of what hap-pens inside the atom than in finding a mathe-matical system that explained the features of theatom—in this case the position of the spectrallines of hydrogen, the simplest atom. Since theelectron orbits in atoms could not be observed,Heisenberg tried to develop a quantum mechan-ics without them. He relied instead on what canbe observed, namely, the light emitted andabsorbed by atoms. He used a modification ofthe quantum rules to explain the anomalousZeeman effect, in which single spectral linessplit into groups of closely spaced lines in astrong magnetic field. Information about atomic

structure can be deduced from the separation ofthese lines. His collaboration with Born andBorn’s other assistant, Pascual Jordan, resulted ina famous “three-man paper” in 1925, introduc-ing a system called matrix mechanics. By math-ematical treatment of values within matrices orarrays, the frequencies of the lines in the hydro-gen spectrum were obtained. Heisenberg hadformulated the first precise mathematicaldescription of the workings of the atom, thusbecoming the founder of quantum mechanics.

The next year, however, Heisenberg’s formu-lation was challenged when ERWIN SCHRÖDINGER

presented a system of wave mechanics that

Heisenberg, Werner 137

Werner Heisenberg’s uncertainty principle introducedthe notion of probability into the complex ideas onwhich the structure of a quantum mechanical view ofnature was being built. (AIP Emilio Segrè VisualArchives. Photo by A.B. Truckeri)

accounted mathematically for the 1923 discoveryof LOUIS VICTOR-PIERRE, PRINCE DE BROGLIE, thatelectrons do not occupy orbits but exist in stand-ing waves around the nucleus. Wave mechanics,with its more familiar concepts and equations andits ability to visualize the atom, rapidly became thetheory of choice. In May 1926, Schrödinger pub-lished an article proving that wave and matrixmechanics were equivalent mathematically, whileclaiming the superiority of wave mechanics.Heisenberg’s opinion, expressed in a letter toPauli, was unambiguous:

The more I think about the physicalportion of Schrödinger’s theory, themore repulsive I find it. . . . WhatSchrödinger writes about the visibilityof his theory “is probably not quiteright,” in other words it’s crap.

With the addition of Born’s statistical inter-pretation of the wave function and the unifiedequations known as transformation theory, cre-ated by Jordan in Göttingen and PAUL ADRIEN

MAURICE DIRAC in Cambridge, England, themathematical foundation of the new quantummechanics seemed complete. The search was onfor an “interpretation” of the mathematics capableof linking observations in the macroscopic world,in which classical physics prevails, to events andprocesses in the quantum world of the atom.

In February 1927, Heisenberg, by uncover-ing a problem in the way physicists could mea-sure basic physical variables appearing inquantum equations, formulated his famousuncertainty principle:

The more precisely the position (of anatom) is determined, the less preciselythe momentum is known in thisinstant, and vice versa.

Heisenberg showed that this uncertainty,sometimes referred to as the principle of indeter-minacy, is not the fault of the experimentalist,

but inherent in quantum mechanics. Hence, theuncertainty principle negates cause and effect,maintaining that the result of an action can onlybe expressed in terms of the probability that acertain effect will occur. Heisenberg’s revolution-ary idea, together with Bohr’s complementarityprinciple and Schrödinger’s wave function,became the cornerstones of the Copenhageninterpretation of quantum mechanics. Over theprotests of so prominent a holdout as ALBERT

EINSTEIN, who could not accept the notion ofprobability, the Copenhagen interpretation wasaccepted by the greater part of the internationalphysics community.

At the historic Solvay Physics Conferenceheld in Brussels in October 1927, Heisenbergdeclared the new quantum mechanics to becomplete and irrevocable. At the end of his life,looking back at this time, he would say that thenext five years

looked so wonderful that we often spokeof them as the golden age of atomicphysics. The great obstacles that hadoccupied all our efforts in the precedingyears had been cleared out of the way;the gate to an entirely new field, thequantum mechanics of the atomic shells,stood wide open, and fresh fruits seemedready for the picking.

Heisenberg’s personal prospects couldhardly have been better: Only 25, he had justbeen offered the Chair of Theoretical Physics atthe University of Leipzig. That very year, hemade another major breakthrough by solvingthe mystery of ferromagnetism. By using thePauli exclusion principle, which states that notwo electrons can have four identical quantumnumbers, he proved that ferromagnetism iscaused by electrostatic interaction between theelectrons. Heisenberg would remain at Leipziguntil 1942 and make it a first-rate internationalresearch center. Collaborating with Pauli andothers, he made important progress in joining

138 Heisenberg, Werner

quantum mechanics and relativity theory into arelativistic quantum theory of “fields” (such aselectromagnetic or material fields). At a timewhen high-energy particle accelerators did notyet exist, he and Dirac pioneered high-energyphysics research by examining the highly ener-getic particles entering the Earth’s atmospherefrom outer space (cosmic rays).

When Hitler gained power in 1933 andattacked relativity theory and quantum mechan-ics as “Jewish physics,” Heisenberg, who hadmade the decision to remain in his homeland,defended the new physics and tried to preservewhat was left of German science. But in 1937,Heisenberg found himself the target of attack.Branded by an official newspaper as a “represen-tative of Judaism in German spiritual life whomust be eliminated just as the Jews themselves,”he endured a frightening year-long investiga-tion, which ended in his exoneration. In thatyear, he met and married Elisabeth Schumacher,a student of German literature, who was to bearhim seven children.

Heisenberg went on to serve as director ofthe Kaiser Wilhelm Institute for Physics inBerlin from 1942 to 1945 and led Germany’satomic research effort. Given its preeminence innuclear fission research, Germany might wellhave developed an effective nuclear weaponsprogram. The fact that it did not may have beendue simply to lack of resources. But Heisenberg’sdefenders suggest that he was reluctant to handthe Nazis nuclear weapons and sabotaged theeffort by diverting research to peaceful uses ofnuclear energy. Historians continue to debatethe issue hotly.

After the war, he was briefly interned inBritain along with other leading German scien-tists. From 1946 to 1970, he directed MaxPlanck Institute for Physics and Astrophysics inMunich. Even though his collaboration withPauli to find a consistent unified quantum the-ory of elementary particles failed, he was suc-cessful in making his institute an internationallyrenowned research center. In his later years, he

wrote two books on the philosophy of physics:Physics and Philosophy (1962) and Physics andBeyond (1971). He died of cancer at his home inMunich on February 1, 1976.

Further ReadingCassidy, David. “Heisenberg, Uncertainty and the

Quantum Revolution.” Scientific American 266:106–112.

———. Uncertainty: The Life and Science of WernerHeisenberg. New York: W. H. Freeman, 1992.

Heisenberg, Werner. The Physicist’s Conception ofNature. Westport, Conn.: Greenwood, 1970.

Rose, Paul Lawrence. Heisenberg and the Nazi AtomicBomb Project: A Study in German Culture. Berke-ley: University of California Press, 1998.

� Helmholtz, Hermann Ludwig Ferdinand von(1821–1894)GermanTheoretician (Thermodynamics,Hydrodynamics, Optics, Acoustics),Physical Chemist

Hermann Helmholtz’s major contribution tophysics is generally considered to be the first pre-cise formulation of the law of conservation ofenergy. However, his impact on 19th-centuryscience transcends the value of any specific dis-covery. A polymath of great intellectual range,deeply concerned with the implications of sci-ence for philosophy and culture, Helmholtz wasthe dominant figure in German science in themid-19th century.

He began his life in Potsdam on August 31,1821, the eldest of four children born to a motherwho descended from William Penn, the founderof Pennsylvania, and a father who taught philos-ophy and literature at the local gymnasium. Adelicate child, Hermann eagerly absorbed theerudition showered on him by his father. In addi-tion to imbuing in him a love of the fine arts, hisfather taught him Latin, Greek, Hebrew, French,

Helmholtz, Hermann Ludwig Ferdinand von 139

Italian, and Arabic. As a student at his father’sgymnasium, Hermann showed a talent forphysics. The family was poor, however, and, sincescholarships were awarded only in popular fields,Hermann decided to study medicine. In exchangefor financial aid, he obligated himself to 10 yearsof service as an army doctor. In 1838, he enteredthe Friedrich Wilhelm Institute of Medicine andSurgery in Berlin. In his spare time, he attendedcourses at the university on chemistry, studiedadvanced mathematics on his own, and becamean expert pianist.

His research career began in 1841 with workon a dissertation on the relationship betweennerve fibers and nerve cells of invertebrates. Inthis work, he rejected the accepted view that liv-ing things possess an innate vital force, arguingthat life processes obey the same principles thatgovern nonliving systems. Physiology, he pro-posed, should be based wholly on the principlesof physics and chemistry. After receiving anM.D. in 1842, he became a surgeon with his reg-iment in Potsdam, where he spent all his timeconducting experiments in the laboratory hehad set up in the barracks.

In 1847, Helmholtz published an importantpaper, presenting the mathematical principlesbehind the principle of conservation of energy. Hederived a general equation in which the kineticenergy of a moving body is equal to the product ofthe force and distance through which the forcemoves to bring about the energy change. Thisequation could be applied in many fields to showthat energy is always conserved. It led to formula-tion of the first law of thermodynamics, whichstates that the total energy of a system and its sur-roundings remains constant even if it changesfrom one form of energy to another. He demon-strated that in various situations—collisions,expansion of gases, muscle contraction—in whichenergy appears to be lost, it is in fact convertedinto heat energy. Helmholtz examined the appli-cations of this work in such fields as electrostatics,galvanic phenomena, and electrodynamics.

The quick recognition of Helmholtz’s valu-able work led to his early release from his militaryduties, in 1848. The following year he marriedOlga Von Velten and settled down to an aca-demic career as associate professor of physiologyat Konigsberg University. While there, he devel-oped the three-color theory of vision firstproposed, in 1801, by THOMAS YOUNG, demon-strating that a single primary color must alsoaffect retinal structures sensitive to the otherprimary colors. This hypothesis successfullyexplained the color of after-images and the effectsof color blindness. He also developed the oph-thalmoscope, which is used to examine the retina,and the ophthalmometer, which measures thecurvature of the eye.

In 1855, Helmholtz moved to Bonn tobecome professor of anatomy and physiology;there he made important discoveries in thephysiology of vision and hearing by studyingnerve impulses. He would move yet again, in1858, to become professor of physiology at theUniversity of Heidelberg. That same year, hewrote an important paper on hydrodynamics, inwhich he established the mathematical princi-ples that define motion in a vortex.

Helmholtz’s first years at Heidelberg werebeset with personal losses. First, his father diedin 1858, and then, at the end of 1859, his ailingwife died. Left to raise two young children on hisown, Helmholtz remarried within 18 months.His second wife, Anna von Mohl, the daughterof another professor at Heidelberg, was muchyounger than he. Worldly and handsome, shewould bear him three children as well as expand-ing his social world.

His next major work was an 1862 study onacoustics, examining musical theory and theperception of sound. He explained the origin ofmusic on the basis of fundamental physiologicalprinciples. He also formulated a theory of hear-ing, correctly suggesting that structures withinthe inner ear resonate at particular frequenciesso that both pitch and tone can be perceived.

140 Helmholtz, Hermann Ludwig Ferdinand von

Around 1866, he began to move away fromphysiology and more toward physics, engaging inthe heated discussions on the properties of non-Euclidean space that preoccupied many scien-tists in the late 19th century.

In 1871, Helmholtz accepted the chair ofphysics at the University of Berlin, where heworked on thermodynamics in physical chem-istry and attempted to establish a mechanicalfoundation for thermodynamics. Throughout the1870s he was embroiled in debates with WILHELM

EDUARD WEBER on the compatibility of Weber’selectrodynamics with the principle of conserva-tion of energy. The question became moot when,in the 1880s, JAMES CLERK MAXWELL’s theory ofelectrodynamics was widely accepted. Helmholtzthen derived Maxwell’s equations from the leastaction principle, a mathematical technique forderiving field equations.

In 1882, he derived an expression thatrelates the total energy of a system to its freeenergy (which is the portion that can be con-verted to forms other than heat) and to its tem-perature and entropy. His findings enabledchemists to determine the direction of a chem-ical reaction. In 1887, he became director ofthe new Physical-Technical Institute of Berlin.This was the last post he would hold. After aperiod of poor health, he died in Berlin onSeptember 8, 1894.

In his staggeringly diverse inquiries, HermannHelmholtz pursued his lifelong ambition to under-stand the unifying principles in nature, as well asthe subjective sources of knowledge—the senseorgans—that mediate experience. He was the bril-liant representative of a generation who emphati-cally rejected metaphysics in favor of mathematicsand mechanics. Among the countless students heinfluenced, not the least was HEINRICH RUDOLF

HERTZ, whom he set upon the path that wouldlead him to the discovery of radio waves.

A classical physicist himself, Helmholtzwould inspire the generation who would createthe revolutions of relativity and quantum

mechanics, imbuing them with his high mathe-matical and experimental standards.

Further ReadingCahan, David, ed. Hermann Von Helmholtz and the

Foundations of Nineteenth-Century Science. Cali-fornia Studies in the History of Science, No. 12.Berkeley: University of California Press, 1993.

Helmholtz, Hermann Von, and David Cahan, eds. Sci-ence and Culture: Popular and Philosophical Essays.Chicago: University of Chicago Press, 1995.

� Henry, Joseph(1797–1878)AmericanExperimental Physicist(Electromagnetism)

Joseph Henry was the greatest experimentalphysicist in America in the mid-19th century.His most enduring work was in the field of elec-tromagnetism; he built extremely large electro-magnets and independently discovered thedynamics of electromagnetic induction at thesame time as MICHAEL FARADAY was makingsimilar discoveries in Great Britain. Henry’swork with electromagnetism played a crucialrole in Samuel F. B. Morse’s invention of thetelegraph. Later in his career, as the first secre-tary of the Smithsonian Institution, he played apivotal role in the organization and develop-ment of American science.

Joseph Henry’s life exemplified the Ameri-can ideal of the self-made person who rises toeminence from modest origins. Born on Decem-ber 17, 1797, in Albany, New York to AnnAlexander and William Henry, a day laborer ofScottish descent, he received little schoolingand was obliged to work in a general store afterschool hours. At age 13, he was apprenticed to awatchmaker, learning skills that would laterserve him well in the physics laboratory. In 1819,he was able to enroll in the Albany Academy, a

Henry, Joseph 141

school for boys from the elementary grades up tothe college level, which charged no tuition. Itwas here that his lifelong fascination with sci-ence was born. By 1822, Henry had alreadybecome a teaching assistant in science courses.He left the Albany Academy in 1822 andworked as a schoolteacher for a time, beforereturning, in 1826, as professor of mathematicsand natural philosophy. In spite of spending upto seven hours a day in the lecture hall, he foundtime to begin his research on electromagnetism.

When Henry set to work, the Danish physi-cist HANS CHRISTIAN ØRSTED had alreadyannounced his seminal experiment in which anelectric current generated a magnetic force.Ørsted’s work launched the great age of electro-magnetic research in Europe, spearheaded byANDRÉ-MARIE AMPÈRE in France and Faraday inGreat Britain. Henry began his own research byusing the skills he had learned as a watchmaker’sapprentice to construct electromagnets ofunprecedented strength. By insulating the wireinstead of the iron core, he was able to wrap alarge number of turns of wire around the core;the resulting magnet, built for Yale University,was capable of lifting more than 2000 pounds,while requiring relatively small electric currents.

While experimenting with such magnets,Henry discovered mutual induction—the induc-tion of electric currents by a moving or changingmagnetic field—the principle behind the trans-former and the generator. He was unaware of thework of Faraday, who independently discoveredmutual induction and published his resultsbefore Henry, with his heavy teaching load,managed to do so. If Faraday is credited with dis-covering induction, Henry nonetheless made anentirely unique discovery: noticing that a largespark was generated when an electric circuit wasbroken, he deduced the property known as self-induction, a phenomenon that acts to prevent acurrent from changing. If a current is flowing,self-induction keeps it flowing; if an electromo-tive force is applied, self-induction prevents

current from increasing. He found that self-induction depends on the configuration of thecircuit, especially the coiling of the wire. He alsodiscovered how to make non-self-inductivewindings by folding the wire back on itself.

The early 1830s were years of personal andprofessional growth. In 1830, he married HarrietAlexander. The following year he publishedseminal papers on his experiments on electro-magnetism and his invention of an oscillatingelectromagnetic motor, the first demonstrationof continuous motion produced by magneticattraction and repulsion. In 1832, Henry becameprofessor of natural philosophy at the College ofNew Jersey, later Princeton University, a post hewould retain until 1848. He was a popularinstructor, who taught not only physics, but alsochemistry, geology, mineralogy, astronomy, andarchitecture.

At Princeton, lighter teaching responsibili-ties and the company of stimulating colleaguesnurtured his research. Continuing to work onmagnets, Henry built one for Princeton thatcould lift 3500 pounds. He also invented the firstprimitive magnetic relay by rigging a wire tosend signals from his laboratory to his home oncampus, a distance of one mile. This system,whereby Henry sent signals to his wife, used aremote electromagnet to close a switch in orderto generate a stronger local circuit. It was similarto the arrangement Morse used in his telegraphand may thus be considered a prototype of thathistory-making invention.

In the following years, as Henry becameunwillingly involved as a witness in the legalchallenges of other inventors to Morse’s rightsto the patent for the telegraph, his own role increating Morse’s machinery became an issue.Henry never said he had invented the tele-graph, but he correctly claimed credit for dis-covering its basic underlying principles and fordemonstrating, in his laboratory and lecturehall, that an electromagnetic telegraph was pos-sible. The two men would argue bitterly about

142 Henry, Joseph

issues of scientific and technological priority forthe rest of their lives.

In 1837, Henry traveled to Europe, wherehe met Faraday, Wheatstone, and other Britishscientists, and he returned with new equip-ment for his experiments. The following yearhe discovered that by rearranging his electricalcoils, he could either step-up or step-down thevoltage of a current. This innovation perfectedthe magnetic induction mechanism, pavingthe way for what is now known as a trans-former. Four years later, he discovered thatelectrical induction could be detected overlong distances, an observation that would leadto radio transmission.

Henry was a remarkably versatile and pro-lific investigator, publishing papers in astro-physics and terrestrial magnetism, optics andacoustics, and founding the field of appliedacoustics in the United States. But he truncatedhis life as a researcher prematurely in 1846,when he agreed to serve as the first secretary ofthe Smithsonian Institution, created byCongress for “the increase and diffusion ofknowledge.” He made the decision reluctantly,commenting, “If I go, I will probably exchangepermanent fame for transient reputation.”Under his leadership, the Smithsonian becamethe premier American institution for organizingand developing science.

As a “public scientist,” Henry undertookmany services to the nation. In 1848, he orga-nized and supported a corps of volunteer weatherobservers, a highly successful venture that led tothe creation of the U.S. Weather Bureau. From1849 to 1850, he was president of the AmericanAssociation for the Advancement of Science.From 1852 to 1878, he took charge of experi-ments and testing for the U.S. Light-HouseBoard, responsible for the construction andrepair of lighthouses, making it into a center forapplied research in optics, thermodynamics, andacoustics. He served as President Lincoln’s chieftechnical adviser during the Civil War. From

1868 to 1878, Henry was president of theNational Academy of Sciences. When JosephHenry died on May 13, 1878, in Washington,D.C., his funeral was attended by the U.S. presi-dent and numerous illustrious government offi-cials and scientists.

By demonstrating the ability of electricity todo useful work through an electromagnet, Henrylaid the foundation of the 19th-century commu-nications revolution. His name has been hon-ored in many ways, most notably in 1893, whenthe standard electrical unit of inductive resis-tance was named the henry.

Further ReadingCoulson, Thomas. Joseph Henry: His Life and Work.

Princeton, N.J.: Princeton University Press,1950.

Moyer, Albert E. Joseph Henry: The Rise of an Ameri-can Scientist. Washington, D.C.: SmithsonianInstitution Press, 1997.

� Hertz, Heinrich Rudolf(1857–1894)GermanExperimentalist (ClassicalElectromagnetism)

Heinrich Hertz experimentally confirmed the elec-tromagnetic theory of JAMES CLERK MAXWELL,who in 1873 had predicted the existence of elec-tromagnetic waves that traveled at the speed oflight. In the process, he discovered radio wavesand paved the way to the invention of the radioand the wireless telegraph.

He was born in Hamburg, on February 22,1857, the son of a prominent lawyer and legisla-tor. He showed an early interest in understand-ing how things work and by the age of twelvehad equipped his own workshop. At age 15, heentered the Johanneum Gymnasium. Threeyears later, having decided on an engineeringcareer, he moved to Frankfurt to gain some prac-

Hertz, Heinrich Rudolf 143

tical experience in that profession. In 1876 hemoved to Dresden to prepare for the state exam-inations that would officially qualify him as anengineer. But his studies were interrupted by ayear of compulsory military service, duringwhich time he decided that his true calling wasin pure science. When he was discharged heentered Munich University with the intentionof studying mathematics but soon switched hisfield of concentration to physics.

In 1878, he transferred to the University ofBerlin and studied under GUSTAV ROBERT

KIRCHHOFF and HERMANN LUDWIG FERDINAND

VON HELMHOLTZ. The latter quickly recognizedhis abilities and became his mentor. In 1880,after receiving a Ph.D. magna cum laude for atheoretical study of electromagnetic inductionin rotating conductors, Hertz remained in Berlinto work as Helmholtz’s assistant. The next stepin his academic career was to gain experience asa lecturer; with this in mind, in 1881, Hertzmoved again, this time to the University of Kiel.Four years later, he accepted a position as profes-sor of physics at the Polytechnic in Karlsruheand the following year married Elizabeth Doll,daughter of a Karlsruhe professor, who wouldbear him two daughters. It was in Karlsruhe in1888, that Hertz would perform his history-mak-ing experiments designed to test the validity ofMaxwell’s theory of electromagnetism.

Maxwell’s equations had demonstrated thatelectricity and magnetism are aspects of a singleelectromagnetic field, and that light itself is avariety of this field. In his 1873 Treatise on Elec-tricity and Magnetism he established that light hasa radiation pressure and suggested that a wholefamily of electromagnetic radiations must exist, ofwhich light is only one. According to Maxwell’stheory, waves exist in space and travel with afinite velocity, as opposed to the prevailing viewthat electric effects are examples of action at a dis-tance: that electricity travels infinitely fast.

To test Maxwell’s predictions, Hertz used anoscillator made of polished brass knobs, each

connected to an induction coil and separated bya tiny gap over which sparks could leap. He rea-soned that if Maxwell’s predictions were correct,electromagnetic waves would be transmittedduring each series of sparks. To confirm this, hemade a simple receiver of looped wire. At theends of the loop were small knobs separated by atiny gap. The receiver was placed several yardsfrom the oscillator. According to Maxwell’s the-ory, if electromagnetic waves were spreadingfrom the oscillator sparks, they would induce acurrent in the loop that would send sparks acrossthe gap. This occurred when Hertz turned on theoscillator, producing the first transmission andreception of electromagnetic waves.

Hertz’s oscillator experiments demonstratedwhat Maxwell had only theorized: that the veloc-ity of radio waves is equal to the velocity of light.This proved that radio waves are a form of light.The experiments also demonstrated how to makeelectric and magnetic fields detach themselvesfrom wires and move through space freely. WhenHertz described his experiments in 13 papers andpublished them in 1893, they were successfullyrepeated around the world. As a result, Maxwell’stheory was universally accepted.

Sadly, in the very year that he did hisgroundbreaking experimental work, Hertz beganto suffer from a toothache, which proved to bethe first symptom of the degenerative bone dis-ease that would cut short his brilliant career. In1889, he accepted an appointment as professorof physics in Bonn, succeeding the great RUDOLF

JULIUS EMMANUEL CLAUSIUS. His healthsteadily worsened and on January 1, 1894, at age36, in Bonn, he died of blood poisoning.

Hertz’s discovery of radio waves would leadto a revolution in communication, triggering theinvention of the wireless telegraph and of radio,as well as paving the way for radar and televi-sion. In his honor the unit of frequency of anelectromagnetic wave, which is equal to onecomplete vibration or cycle per second, is calledthe hertz.

144 Hertz, Heinrich Rudolf

Further ReadingBaird, David, Alfred Nordman, and R. I. Hughes, eds.

Heinrich Hertz: Classical Physicist, ModernPhilosopher. Boston: Kluwer Academic, 1997.

Buchwald, Jed Z. The Creation of Scientific Effects:Heinrich Hertz and Electric Waves. Chicago:Chicago University Press, 1994.

Susskind, Charles. Heinrich Hertz: A Short Life. SanFrancisco: San Francisco Press, 1995.

Susskind, Charles, Johanna Hertz, and MathildeHertz. Heinrich Hertz: Memoirs, Letters, Diaries.San Francisco: San Francisco Press, 1977.

� ‘t Hooft, Gerard(1946– )DutchTheoretician, Quantum Field Theorist

Gerard ’t Hooft shared the 1999 Nobel Prize inphysics with MARTINUS J. G. VELTMAN forproving that the quantum structure of elec-troweak interactions is renormalizable. In sodoing, he placed particle physics on a firmermathematical foundation, showing how thetheory could be applied in precise calculationsof finite physical quantities that could be usedto predict the properties of new particles. Par-ticle accelerator experiments in Europe andthe United States have recently confirmedmany of the calculated results. This work,which used algebraic computer algorithms,also stimulated the development of superfastquantum computers.

Gerard ’t Hooft was born on July 5, 1946, inDen Helder, the Netherlands, into a familyboasting a number of eminent scientists: hisgrand-uncle, Fritz Zernike, won the 1953 NobelPrize in biology for his invention of the phasecontact microscope; his grandfather, PieterNicolaas von Kampen, was a famous zoologist atthe University of Leiden; and his uncle, Nico-laas Godfried van Kampren, was a professor oftheoretical physics at the State University of

Utrecht. From early childhood, Gerard had anatural inclination toward pure science, to thedismay of his father, a naval engineer, whohoped his son would study engineering. ’THooft grew up in the Hague, with his father;his mother, who was a French teacher; and histwo sisters.

’T Hooft received his secondary educationat the Dalton Lyceum in the Hague, where hefollowed the classical track, which requiredGreek and Latin, because he was attracted bythe challenge of it. Already drawn to physics,he was inspired by his high school physicsteacher, who would spur his students to deeperthinking by saying, “If there were any realgeniuses in this class, then they could haveargued as follows. . . .” When he was 16, he com-peted in the Dutch National Math Olympiadand, to his own considerable amazement (hewas aware of having made several errors), wonsecond prize.

After passing his final high school exams in1964, ’t Hooft enrolled at the State Universityof Utrecht. At his father’s urging, he joined themost elite student organization, enduring thehumiliating initiation rituals. He was also amember of the university’s renowned rowingteam and its science club, as well as an orga-nizer of a national congress for science stu-dents. Although all of this was time-consuming,it failed to lessen his preoccupation withphysics. His uncle–professor invited him intothe Theoretical Physics Institute, an informalarrangement of three houses next to a canal,where, he recalls, “I adored the discussions andthe laughter.”

Despite the reservations of his uncle, he wasdetermined to study elementary particles, whichhe perceived as “the heart of physics.” Fortu-nately, a new professor of theoretical physics,Martinus Veltman, specialized in particle theory.When “Tini,” as everyone called Veltman, took’t Hooft on as his student, the first material hegave him to study was a paper by CHEN NING

‘t Hooft, Gerard 145

YANG and Robert Mills, telling him, “This stuffyou must know.” ’T Hooft found the work “beau-tiful, elegant, and unique.” In 1950, Yang andMills had shown that the quantum electrody-namic (QED) formalism, developed earlier byJULIAN SEYMOUR SCHWINGER, RICHARD PHILLIPS

FEYNMAN, and SIN-ITIRO TOMONAGA, could begeneralized to include internal dynamic symme-tries that were more general than the standardspacetime C (charge), P (parity), and T (time-reversal) symmetries.

In the early 1960s, STEVEN WEINBERG,SHELDON LEE GLASHOW, and ABDUS SALAM

used this new generalization of QED to unifythe electroweak forces into one quantum for-malism. At the heart of their quest was the fas-cinating phenomenon of so-called brokensymmetries, which seemed to permeate mat-ter—asymmetric relations that have sponta-neously arisen from the functioning of symmetriclaws (for instance, the asymmetric crystal struc-ture of ice that freezes out from the symmetricliquid structure of water when the temperaturebecomes low enough).

They were aware of the fact that in theearly 1960s Peter Higgs had published papersdemonstrating that spontaneous symmetrybreaking events could create new kinds offorce-carrying particles, some of them massive.This led them to speculate that if the virtualparticles that carry the electromagnetic andweak forces (known collectively as the inter-mediate vector boson W and Z particles) wererelated by a broken symmetry, it might be pos-sible to estimate their masses in terms of theunified, more symmetrical force from which thetwo forces were thought to have arisen. Work-ing independently, each constructed a unifiedquantum field theory of electromagnetic andweak interactions (a quantum electroweak the-ory) that could make a verifiable prediction ofthe approximate masses of the required tripletW and the singlet Z particles needed todescribe the weak interactions.

However, in the beginning the physics com-munity found it difficult to accept the elec-troweak theory. This was because when theytried to use the theory to calculate the propertiesof the W and Z particles (which were the carri-ers of the weak force associated with radioactiv-ity) and many other physical quantities, thetheory predicted nonsensical infinite results.The situation resembled that of the 1930s,before Tomonaga, Schwinger, and Feynman“renormalized” QED, that is, found a mathemat-ical way to eliminate the infinities.

Meanwhile, in the Netherlands, Veltmanhad not given up hope of renormalizing theorieslike the electroweak theory. At the end of the1960s, he had developed a computer programcalled “Schoonschip,” which, using symbols,performed algebraic simplifications of the com-plicated expressions that all quantum field theo-ries result in when quantitative calculations areperformed. Twenty years earlier, Feynman hadsystematized the calculation problem with hisdiagrams. Veltman believed in the possibility offinding a way of renormalizing the theory, andhis computer program was the cornerstone of thecomprehensive work of testing different ideas.

When ’t Hooft chose a topic for his Ph.D.thesis in 1969, nothing appealed more to hisimagination than the problem Veltman wasworking on: renormalization of the so-calledYang–Mills non-Abelian gauge field theories,which at the time were being applied to thestudy of the weak interactions. In 1971, ’t Hooftsucceeded in this task and published two articlesdescribing his breakthrough. However, it was thesecond paper, in which he renormalized masslessYang–Mills fields for theories using the Higgsspontaneous symmetry breaking mechanism togenerate the masses of the fields, that attractedworld attention. First, ’t Hooft verified hisresults, using Veltman’s computer program;when this was done, the two men were able towork out a detailed calculation of the renormal-ization method. The renormalized non-Abelian

146 ‘t Hooft, Gerard

gauge theory of electroweak interaction was nowa functioning theoretical machinery capable ofperforming precise calculations. They presentedtheir results at a 1971 international particlephysics conference in Amsterdam.

’T Hooft received his Ph.D. for this work in1972 and that year married Albertha (Betteke) A.Schik, who had studied medicine at Utrecht Uni-versity. The couple began their married life at theEuropean Center for Nuclear Research (CERN),Geneva, where Gerard had a fellowship and Bet-teke began training to be a specialist in anesthesia.’T Hooft recalls this as an exciting time:

Veltman also came to CERN, andtogether we refined our method forYang–Mills theories. We were delightedwith the great impact that our theorieshad. From 1971 onwards, all theories forthe weak interactions that were proposedwere Yang–Mills theories. Experimentswere set up aimed at selecting out whichof these Yang–Mills theories were correct.

The reaction of the physics community isnicely summed up by the physicist Kenneth Lane:

For a decade, people didn’t know how tocalculate beyond the most elementarylevel with the Glashow–Salam–Wein-berg model. It was impossible. And so themodel was more or less forgotten. ThenGerard and his thesis advisor, Tini Velt-man, showed how to do it. Their findingscame out in 1971, and it was a bombshell.Everybody immediately jumped onto thistheory, and over the next decade itbecame clear that the Glashow, Wein-berg, and Salam model was correct.Experiments verified it in every detail.

The decisive experiments were first made byCARLO RUBBIA and his team at CERN in 1981.Two years later, in 1983, they announced the

discovery of the triplet W and singlet Z particles,which had been based on signals from detectorsspecially designed for this purpose.

As his work made possible a new physicalunderstanding of the subatomic world, ’t Hooft’spersonal and professional life flourished. In1974, he returned to Utrecht, where he wasmade assistant professor. Two years later, he wasa visiting professor at Harvard and Stanford,where he worked on problems related to quan-tum chromodynamics (QCD), including theissue of quark confinement. In the meantime,his family was growing: his daughter, SaskiaAnne, was born in Boston; his second daughter,Ellen Marga, was born in 1978, in Utrecht,where ’t Hooft became a full professor.

He and Veltman went on to calculate themass of the top quark, the heavier of the twoquarks in the third family of what became knownas the Standard Model. Many years later, in 1995,the top quark was observed directly for the firsttime at the Fermi Laboratory in Batavia, Illinois.Another highly important element of the modelis the existence of a massive Higgs particle, whichhas not yet been observed. Physicists hope thatthe Large Hadron Collider (LHC), to be com-pleted at CERN around 2005, will do the job.

’T Hooft’s books include Under the Spell ofthe Gauge Principle (1994), In Search of the Ulti-mate Building Blocks (1997), and Introduction toGeneral Relativity (2001).

’T Hooft is currently professor of theoreticalphysics at both the Spinoza Institute and theInstitute for Theoretical Physics at the Univer-sity of Utrecht, where his research focuses onmagnetic monopoles, gauge theory in elemen-tary particle physics, quantum gravity andmicroscopic black holes, and other fundamentalaspects of quantum physics.

As do other physicists who have greatly con-tributed to the Standard Model of elementaryparticles, ’t Hooft believes that, despite itsimmense productivity, it must eventually bereplaced by a deeper understanding, involving a

‘t Hooft, Gerard 147

new paradigm about the nature of space and time,and incorporation of the gravitational force. Hewrites, “To me, Nature is a big jigsaw puzzle, and Isee it as my task to try to fit the pieces together.”

See also BETHE, HANS ALBRECHT; DYSON,FREEMAN; GELL-MANN, MURRAY.

Further Reading’T Hooft, Gerard. In Search of the Ultimate Building

Blocks. Cambridge: Cambridge University Press,1997.

———. Under the Spell of the Gauge Principle. Singa-pore: World Scientific, 1994.

� Hooke, Robert(1635–1703)BritishTheoretician and Experimentalist(Classical Mechanics, Gravitation,Optics), Astronomer

Robert Hooke was a brilliant and versatile 17th-century scientist, who is best known for thederivation of Hooke’s law of elasticity, whichstates that the stress placed on an elastic body isproportional to the strain produced.

He was born on July 18, 1635, in Freshwa-ter, Isle of Wight. Poor health prevented himfrom preparing for the ecclesiastical career hisfather, who was a church curate, had plannedfor him. When his father died in 1648, Hookewent to London and was educated at Westmin-ster School, where he studied ancient lan-guages, learned to play the organ, and masteredthe first six books of Euclid’s Elements in a week.

At age 18 he went on to Oxford University,where he joined an outstanding group of youngscientists. In 1658, while working for RobertBoyle, he constructed an improved version of theair pump of Otto Guericke, which led, four yearslater, to Boyle’s formulation of his famous law,defining the relationships among the temperature,pressure, and volume of a gas. By the time Hooke

received an M.A. in 1663, he and most of hisOxford colleagues had moved to London, where,in 1662, they established what would becomeEngland’s most prestigious organization of schol-ars, the Royal Society. At first, Hooke served ascurator of experiments at the society, a paid postthat involved the presentation of several newexperiments at every weekly meeting. Thiscaused him to know a little bit about a lot ofthings. He would later become a fellow of thesociety and one of its secretaries. In the mid-1660s he accepted two posts he would hold forthe rest of his life: lecturer in mechanics for theRoyal Society and professor of geometry at Gre-sham College in London. A fine architect, healso served as London’s city surveyor and waschief assistant to Christopher Wren in rebuild-ing London after the Great Fire of 1666.

Hooke enjoyed a prolific 40-year career inLondon as a natural philosopher, as physicistswere called then. In 1665, he published Micro-graphia, the book that would establish his inter-national reputation. The first important work onmicroscopy, it contained observations made withmagnifying lenses, some of very small objects,others of astronomical bodies, including a seriesof observations of lunar craters with speculationsabout their origin. It was in this work, whichcontained a number of discoveries in biology,that Hooke used the term cell to describe theempty spaces in the structure of cork; modernbiology would adopt the term to denote a livingunit of protoplasm. In Micrographia Hooke alsoput forth the controversial idea, which hademerged from his observations of spectral colorsand patterns in thin films, that light might havea wave nature. He would develop this idea in1672, by suggesting what AUGUSTIN-JEAN FRES-NEL would prove almost 150 years later, in 1821,namely, that the vibrations in light might be per-pendicular to the direction of propagation.

Another major focus of Hooke’s research wasgravitation, a phenomenon that absorbed himfor more than 20 years. In 1664, he made the sug-

148 Hooke, Robert

gestion that astronomical bodies are pulled intoorbits around larger bodies by a gravitationalforce directed toward the center of the largerbody. He developed this idea into a theory ofplanetary motion in his 1674 publication Attemptto Prove the Motion of the Earth, which correctlyproposed that planets are held in their orbitsthrough a balance between an outward centrifu-gal force and an inward gravitational attractionto the Sun. In 1679, he wrote to SIR ISAAC NEW-TON, suggesting that this attraction would varyinversely as the square of the distance from theSun. When, in 1687, Newton published his lawof universal gravitation, which built upon theseideas, Hooke, who seems to have been constantlyembroiled in disputes over who should be cred-ited with a discovery, was angry and embittered.

The most important discovery, indisputablyhis, was what came to be known as Hooke’s law.Enunciated in 1678, the principle, which grewfrom his longtime interest in the physical prop-erties of springs, states that the stress placed onan elastic body is proportional to the strain pro-duced. Hooke’s law has important practicalapplications in both physics and the physicaldesign of mechanical devices of machines.

Hooke himself was no mean designer ofinstruments. Over the course of his career, heinvented the compound microscope; a wheelbarometer, which registered air pressure with amoving pointer; a weather clock, which recordedsuch factors as air pressure and temperature ona revolving drum; the universal, or Hooke’s,joint, found in all cars; and the balance wheelin watches.

In 1696, Hooke’s health began to deterio-rate. He died in London on March 3, 1703.

Hooke was an outstanding example of the“Renaissance physicists” of his time: he madesubstantial original contributions to a stunningvariety of fields and stimulated the thinking ofhis colleagues, most prominently, Newton’s ideason gravitation.

See also CARNOT, NICOLAS LÉONARD SADI.

Further ReadingDrake, Ellen Tan. Restless Genius: Robert Hooke and

His Earthly Thoughts. Oxford: Oxford UniversityPress, 1996.

Nichols, Richard. Robert Hooke and the Royal Society.Philadelphia: Trans-Atlantic, 1999.

� Huygens, Christiaan(1629–1695)DutchMathematical Physicist (Optics,Classical Mechanics), Astronomer

Christiaan Huygens was a brilliant physicist andmathematician who is best known for develop-ing the first wave theory of light, which wouldbe further developed by 19th-century physicistsfrom AUGUSTIN-JEAN FRESNEL to JAMES CLERK

MAXWELL. An extraordinarily versatile scientist,Huygens also explained the mechanics of thependulum and invented the pendulum clock,created improved telescopes, and made impor-tant advances in pure and applied mathematicsand in mechanics. He was the first astronomer torecognize the rings of Saturn and discover itssatellite Titan.

Huygens was born on April 14, 1629, at theHague, in the Netherlands, into a cultured fam-ily prominent in diplomatic circles. He was edu-cated at home by his erudite, multitalentedfather, Constantin. In 1645, he entered the Uni-versity of Leiden, where he studied mathematicsand law until 1647. Intending to pursue a diplo-matic career, he then went on to study law foranother two years at the College of Orange inBreda. But in 1649, after returning from a diplo-matic mission in Denmark, he decided not toenter his father’s profession after all. Huygenssenior provided him with an ample allowance,which enabled him for the next 16 years todevote himself to his scientific pursuits.

During this period Huygens applied newmathematical techniques to physical problems.

Huygens, Christiaan 149

Motivated by disbelief in René Descartes’s lawsof impact, he carried out studies on impact andcollisions, using the idea of relative frames of ref-erence and considering the motion of one bodyrelative to that of another. He discovered thelaw of conservation of momentum, stating it interms of the conservation of the center of gravityof a system of bodies under impact. He then wasable to prove by experiment that the momentumin a fixed direction before the collision of twobodies is equal to the momentum after the colli-sion. In addition, he showed that the kineticenergy of motion of a system of particles is con-served in an elastic collision.

In 1655, Huygens and his brother began tomake telescopes of high technical quality, devis-ing a better way of grinding and polishing lenses.That year he discovered Titan, the largest satel-lite of Saturn, and determined its period of rota-tion. The next year he solved the problem ofwhat had appeared to be the “arms of Saturn,”ingeniously deducing that they must be the pro-file view of a ring surrounding the planet. Astelescopes improved, Huygens’s observationswere confirmed, and by 1665 his theory wasaccepted by the important astronomers of theday. In the early 1660s, he traveled to Paris andLondon, where he met the leading scientists andshowed the English his telescopes, which provedsuperior to their own. He was elected to thenewly formed Royal Society of London in 1663.

In 1657, Huygens developed and patented aclock regulated by a pendulum, which greatlyincreased the accuracy of time measurements.By 1658, major towns in the Netherlands hadpendulum tower clocks. He had been drawn tothis work by both the need in astronomy foraccurate timekeeping and in navigation fordetermination of longitude at sea. For the latterpurpose, he built several pendulum clocks,which underwent sea trials in 1662 and 1668.He would work on theories related, first, to thesimple pendulum and, second, to harmonicallyoscillating systems, throughout the rest of his

life; eventually he solved the problem of thecompound pendulum.

In 1659, Huygens studied centrifugal forceand showed its similarity to gravitational force.He also derived the law of centrifugal force foruniform circular motion. During the same period,he studied projectiles and gravity, developingGALILEO GALILEI’s ideas. Later, in the 1670s,studying motion in resisting media, he becameconvinced by experiment that the resistance insuch media as air is proportional to the square ofthe velocity. In London, at the Royal Society, hemet SIR ISAAC NEWTON. Although admiringNewton, Huygens was unconvinced by his the-ory of universal gravitation, since he did notbelieve that two different masses could attractone another if there were nothing between them.

In 1666, when the Académie Royale desSciences was founded, Huygens was invited toParis, to join; he assumed leadership of thegroup, on the basis of his knowledge of how theRoyal Society operated in England. Supportedby a generous pension by King Louis XIV, helived and worked in luxurious quarters at theBibliothèque Royale for 15 years, frequentlytraveling abroad. In 1671, when Louis XIVinvaded the Netherlands, Huygens found him-self in a country at war with his own. Like manyscientists of this era, Huygens considered himselfabove political wars; with the help of his friends,he stayed on in Paris and continued his work.

Huygens is most famous for his wave theoryof light, which he published in 1678. In it hepresented what is now known as Huygens’s prin-ciple: an expanding sphere of light behaves as ifeach point on the wave front were a new sourceof radiation of the same frequency and phase.He used this principle to explain reflection andrefraction, showing that refraction is related todiffering velocities of light in media. He thenused this argument as a counter to Newton’sparticle theory of light. The essence of Huy-gens’s theory was that light is transmitted as apulse through the ether, which sets up a whole

150 Huygens, Christiaan

Huygens, Christiaan 151

train of vibrations in the ether. However, as suc-cessful as this approach was, he could not use hisideas to explain the phenomenon of polariza-tion of light.

In the final years of his life, he composedone of the earliest discussions of extraterrestriallife, published posthumously in 1698. He wasfrequently ill and returned home to the Hague,where he died on July 8, 1695.

Huygens was one of the foremost scientistsand mathematicians of his day. In physics, hiswave theory of light would be recognized as the

forerunner of theories challenging Newton’s par-ticle theory of light, which, in turn, led the wayto modern theories of electromagnetism.

Further ReadingStruik, Dirk Jan. The Land of Stevin and Huygens: A

Sketch of Science and Technology in the DutchRepublic During the Golden Century. Dordrecht,Netherlands: D. Reidel, 1982.

Yoder, Joella G. Unrolling Time: Christiaan Huygensand the Mathematization of Nature. Cambridge:Cambridge University Press, 1988.

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� Josephson, Brian David(1940– )WelshTheoretician, Solid State Physicist,Condensed Matter Theorist

Brian David Josephson discovered the phenom-enon of superconducting quantum tunneling,which later became known as the Josephson effect,when he was a 22-year-old graduate student. Apartfrom its important role in the theory of supercon-ductors, the discovery of the Josephson effect ledto major scientific breakthroughs in the develop-ment of computer technology and earned Joseph-son a share in the 1973 Nobel Prize in physics.

He was born on January 4, 1940, in Cardiff,Glamorgan, in Wales, where he attended thepublic schools. After graduating from CardiffHigh School, he entered Trinity College, Cam-bridge University; while still an undergraduate,he published an important paper, which dealtwith certain aspects of the special theory of rela-tivity and the Mössbauer effect. He earned abachelor’s degree in 1960 and two years later waselected a fellow at Trinity. A brilliant and exact-ing student, he was a source of discomfort to hisprofessors, who would politely inform them,after class, of any errors they had made.

In graduate school Josephson’s embryonicinterest in superconductivity (the absence of

electric resistance of certain materials at lowtemperatures) took wing when he noticed someunique connections between solid state theoryand his own experimental work on superconduc-tivity. He was led to calculate the current due toquantum mechanical tunneling across a thinstrip of insulator between two superconductors.He began to explore the properties of a junctionbetween two superconductors, which laterbecame known as a Josephson junction. In thiswork he extended earlier work by Leo Esaki andIvar Giaever on quantum tunneling, the phe-nomenon by which electron quantum wavefunctions can penetrate solids. He showed theo-retically that an electron current between twosuperconductors could flow across an insulatinglayer without the application of a voltage as aresult of quantum tunneling. On the other hand,when a voltage was applied, the current stoppedflowing and oscillated at high frequency. Thefrequency of the oscillating quantum tunnelingcurrent is very precisely related to fundamentalconstants of physics and can be used to deter-mine most accurately the ratio of Planck’s con-stant to the charge on the electron and toestablish a highly accurate voltage standard.This phenomenon, now called the Josephsoneffect, can also be used as a generator of radia-tion, particularly in the microwave and farinfrared regions.

When Josephson published his discovery,it was disputed by no less an authority thanJOHN BARDEEN, the most renowned solid statephysicist of his time, who had invented thetransistor and developed the comprehensivemicroscopic theory of superconductivity, theBardeen–Cooper–Schrieffer (BCS) theory,announced in 1957. This led to a face-to-facedebate by the two men in London in 1962. Butthe question was eventually resolved by laterexperimental results in which Josephson’s pre-dictions were verified. Ironically the experi-mental confirmation of Josephson’s discoveryultimately reinforced the BCS theory.

Although Josephson makes his permanentacademic home at Cambridge, where he was madeassistant director of research in 1967 and full pro-fessor of physics in 1972 in the United States. Inthe early 1980s, Josephson was involved in themathematical modeling of intelligence. By apply-ing the Josephson effect, in 1980, researchers atIBM assembled an experimental computer switchstructure that permitted switching speeds from 10to 100 times faster than those possible with con-ventional silicon-based chips, vastly increasingdata processing capabilities.

Josephson shared the 1973 Nobel Prize inphysics with Esaki and Giaever “for their discov-eries regarding tunneling phenomena in solids.”

A few years before he was awarded the NobelPrize, Josephson became interested in the possiblerelevance of Eastern mysticism to scientificunderstanding. Josephson is currently director ofthe Mind–Matter Unification Project of the The-ory of Condensed Matter Group at the CavendishLaboratory, Cambridge, which he describes as“concerned primarily with the attempt to under-stand from the viewpoint of the theoretical physi-cist, what may loosely be characterized asintelligent processes in nature associated withbrain function or with some other natural pro-cess.” He has published many articles on con-sciousness, including paranormal phenomena.

Josephson’s insight into superconductingquantum tunneling theory has had profound

consequences for experimental and theoreticalphysics. Quantum interference effects are thebasis of superconducting quantum interferencedevices (SQUIDs), which can act as ultrasensi-tive magnetometers capable of detecting tinygeophysical anomalies in the Earth’s magneticfield as well as the anomaly caused by the pres-ence of submarines hidden in the ocean. Finally,the experimental use of the Josephson effect hasmade the phase of the macroscopic quantumwave function accessible to experimental controland has raised the science of metrology (the sci-ence of measuring the values of the fundamentalconstants of physics) to the extraordinary preci-sion of one part in 1019, thus strengthening thefoundations of physics. In the future, Josephson’sdiscovery may also have an important impact onthe development of artificial intelligence.

See also DOPPLER, CHRISTIAN; EINSTEIN,ALBERT; MÖSSBAUER, RUDOLF LUDWIG; SCHRI-EFFER, JOHN ROBERT.

Further ReadingJosephson, B. D. “The History of the Discovery of

Weakly Coupled Supercomputers.” In PhysicistsLook Back: Studies in the History of Physics, editedby J. Roche. Bristol, England: Adam Hilger,1990. Institute of Physics Publishing.

McDonald, Donald G. “The Nobel Laureate Versusthe Graduate Student.” Physics Today July 1991,pp. 46–51.

Utts, Jessica, and Brian D. Josephson. “The Paranor-mal: The Evidence and Its Implications for Con-sciousness.” Times Higher Education SupplementApril 5, 1996, p. v.

� Joule, James Prescott(1818–1889)BritishExperimentalist (Thermodynamics)

James Prescott Joule was an ingenious experimen-talist, who collaborated with LORD KELVIN

Joule, James Prescott 153

(WILLIAM THOMSON) in developing a thermody-namic theory of gases and discovered what is nowknown as Joule’s law, which defines the relation-ship between heat and electricity. His highlyaccurate measurements of the mechanical equiv-alent of heat were later used by RUDOLF JULIUS

EMMANUEL CLAUSIUS to formulate the first law ofthermodynamics, conservation of energy.

Joule was born on December 24, 1818, inSalford, England, into a family whose wealthderived from operating a brewery. Described as ashy and delicate child, he received his only for-mal education, in elementary mathematics, nat-ural philosophy, and chemistry, at homebetween 1833 and 1837. Although his lack ofadvanced mathematical training would laterlimit his role in developing the theory of ther-modynamics, it did nothing to dim the luster ofhis experiments, the first of which he performedin a laboratory at the family brewery.

At the peak of his career, between 1837 and1847, Joule conducted a series of diverse andhighly accurate experiments. The first of theserelated the chemical and electrical energyexpended to the heat produced in metallic con-ductors and voltaic and electrolytic cells. Pub-lished between 1840 and 1843, Joule’s resultsestablished the relationship between heat andelectricity that came to be known as Joule’s law.It states that the heat produced in a conductor ofresistance r by a current i is equal to i2r/second.

Joule’s next experiments investigated therelationship between heat and mechanicalenergy. In one of these he built a small electro-magnet to show that electrical energy generatedby mechanical energy in a dynamo can produceheat, a form of energy. Later, in his famous pad-dle-wheel experiment, he measured the rise intemperature of water agitated by paddles drivenby falling weights. This showed that the kineticenergy of the weights as they fell existed as heatenergy in the water. This last experiment hasbecome the best-known method for determiningthe mechanical equivalent of heat, which veri-

fied that in physical processes energy cannot becreated or destroyed, but only changed into dif-ferent forms. Clausius would use Joule’s results informulating this principle as the first law of ther-modynamics, conservation of energy. The cur-rently accepted value of the mechanicalequivalent of heat is 4.1868 joules/calorie. (Thejoule is the unit of all forms of energy and isdefined as the energy expended when a force ofone newton moves through a distance of onemeter. The calorie is the heat energy required toheat one gram of water by one degree Celsius.)

When Joule first presented his results on themechanical equivalent of heat, they wereresisted by many of his peers, who found it diffi-cult to believe he could make such accuratemeasurements. He had a critically importantally, however, in Lord Kelvin (then WilliamThomson), who recognized that Joule’s experi-mental prowess was just what he needed to but-tress his own theoretical work. In 1847, theyembarked on a collaboration, which resulted, in1852, in the discovery of the Joule–Kelvineffect: the decrease in temperature in a gas whenit expands in a vacuum. This is caused by theconversion of heat into work done by themolecules in overcoming attractive forcesbetween them as they move apart. It was toprove vital to techniques in the liquefaction ofgases and in low-temperature physics.

The acceptance of Joule’s work led to hiselection in 1850 to the Royal Society, whichawarded him its prestigious Copeley Medal in1866. Throughout his career, Joule’s familywealth had allowed him to work as an indepen-dent researcher, without taking on an academicposition. When his funds did run out in 1878,Queen Victoria rescued him with a state pen-sion. After a long illness he died in Sale,Cheshire, on October 11, 1889.

Joule was a pivotal figure in the develop-ment of thermodynamics in the mid-19th cen-tury. His major contribution to physics was thedemonstration, through a body of precise exper-

154 Joule, James Prescott

Joule, James Prescott 155

iments, that the ratio of equivalence of the dif-ferent forms of energy is independent of the pro-cess in which one form of energy is convertedinto another and of the materials involved.

See also CARNOT, NICOLAS LÉONARD SADI.

Further ReadingVon Baeyer, Hans Christian. Warmth Disperses and

Time Passes: A History of Heat. New York: Mod-ern Library, 1999.

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� Kamerlingh Onnes, Heike(1853–1926)DutchExperimentalist (Low-TemperaturePhysics, Superconductivity)

Heike Kamerlingh Onnes was a pioneer of low-temperature physics, whose success in producingliquid helium made it possible to study the proper-ties of matter at temperatures close to absolute zeroon the Kelvin scale. He received the 1913 NobelPrize in physics for this work, which then led himto discover superconductivity, the total lack ofelectrical resistance in some materials when theyapproach a temperature near absolute zero.

He was born on September 21, 1853, inGroningen, the Netherlands, to Anna GerdinaCoers, the daughter of an architect, and HarmKamerlingh Onnes, the owner of a brick works.After attending secondary school in his nativetown, at age 17 he entered the University ofGroningen to study physics and mathematics.He won two prizes there for his studies on thenature of the chemical bond. From 1871 to1873, he studied in Heidelberg, under the Ger-man physicists GUSTAV ROBERT KIRCHHOFF

and Robert Bunsen. Upon his return toGroningen, he wrote his doctoral dissertation,“New Proofs of the Rotation of the Earth,” inwhich he showed that JEAN-BERNARD-LÉON

FOUCAULT’s famous pendulum experimentbelongs to a larger group of experimental phe-nomena that can be used to prove that theEarth rotates.

In 1878, Kamerlingh Onnes became anassistant at the Polytechnic in Delft, whereJohannes van der Waals aroused his interest inthe properties of matter at low temperatures. In1881, he published a paper, “General Theory ofLiquids,” that dealt with the kinetic theory of theliquid state. This marked the beginning of hislifelong study of the properties of matter at lowtemperatures. During this period he formulatedhis methodological approach to physics, whichemphasized the importance of quantitativeresearch. “Knowledge through measurement”became his famous maxim. In the attempt toobtain experimental evidence to support van derWaals’s theories on equations of state for gases,he investigated the equations of states of matterof liquids and gases over a wide range of pressuresand temperatures and studied their general ther-modynamic properties. His goal was to findexperimental evidence for the atomic theory ofmatter and for van der Waals’s corpuscular the-ory of gases at low temperatures.

In 1882, Kamerlingh Onnes became profes-sor of experimental physics at the University ofLeiden, which became his academic home, and,in 1887, he married Maria Bijleveld, with whom

he had a son, Albert. In 1894, he founded hisfamous Cryogenic Laboratory in Leiden, whichsoon became a renowned world center for low-temperature physics. In this laboratory, he firstapplied the cascade method for cooling gases,developed by James Dewar; finally, in 1908, hesucceeded in liquefying helium by using theJoule–Kelvin effect, a process in which the tem-perature of a gas decreases when it expands in avacuum. This effect is caused by the conversionof heat into work done by the molecules inovercoming attractive forces between them asthey move apart. By lowering the temperatureof helium to 0.9 K, he reached the nearestapproach to absolute zero then achieved. Healso constructed “cold baths” with liquidhelium, which enabled him to study the proper-ties of matter at temperatures between 4.3 and1.15 K, very close to absolute zero.

Then Kamerlingh Onnes surpassed thesetechnical achievements and studied how matterbehaves at even lower temperatures. In 1910, hesucceeded in lowering the temperature of liquidhelium to 0.8 K. LORD KELVIN (WILLIAM THOM-SON) had postulated in 1902 that as the tempera-ture approached absolute zero, electrical resistancewould increase. In 1911, Kamerlingh Onnes foundthe reverse to be true: that is, the electrical resis-tance of a conductor decreases and finally vanishesas temperature approaches absolute zero. Thisphenomenon, for which he became most famous,was later called superconductivity. His interest inthe technical application of low-temperaturephysics to the industrial and commercial uses ofrefrigeration led him to study magneto-opticalproperties at low temperatures of such metals asmercury, lead, nickel, and manganese–iron alloys.

Known for his personal charm and human-ity, Kamerlingh Onnes, working with his wifeduring and after World War I, assisted starvingchildren in war-torn countries. His health hadalways been delicate. He retired in 1924 anddied in Leiden, after a short illness, on February21, 1926.

The research done by Kamerlingh Onnesessentially created the field of low-temperaturephysics. Since properties of matter at very lowtemperatures differ fundamentally from thoseat normal temperatures, knowledge of thesechanges was crucial in answering basic questionson the nature of matter at the molecular, atomic,and subatomic levels. His systematic research onsuperconductivity was also of great importanceto the theory of electrical conduction in solids.Superconducting materials have helped scien-tists make many important advances. For exam-ple, superconducting magnets play a crucial rolein the particle accelerators physicists use tostudy subatomic particles. The KamerlinghOnnes Laboratory in Leiden, named in hishonor, is the leading world center for research inlow-temperature physics.

See also JOULE, JAMES PRESCOTT; KAPITSA,PYOTR LEONIDOVICH; LANDAU, LEV DAVIDOVICH.

Further ReadingGoudaroulis, Y., and Gavrolu, K., eds. Through Mea-

surement to Knowledge: The Selected Papers ofHeike Kamerling Onnes. Dordrecht, Netherlands:Kluwer, 1991.

� Kapitsa, Pyotr Leonidovich(1894–1984)RussianExperimentalist (Low-TemperaturePhysics)

Pyotr Leonidovich Kapitsa won the 1978 NobelPrize in physics for his fundamental discoveriesin low-temperature physics, which relates to theproperties of materials at temperatures nearabsolute zero on the Kelvin scale. Best known forhis work on the superfluidity of liquid helium,Kapitsa is recognized for both his contributionsto the development of physics in England andthe Soviet Union and his role as an interna-tional advocate for peace and disarmament.

Kapitsa, Pyotr Leonidovich 157

He was born in Kronstadt, near Saint Peters-burg, Russia, on July 8, 1894, into an educated,prosperous family. His father, Leonid PetrovichKapitsa, was a military engineer; his mother,Olga Yeronimovna Stebnitskaya, worked as aneducator and researcher in the area of folklore.Kapitsa studied under the eminent Russianphysicist A. F. Joffe at the Petrograd PolytechnicInstitute and earned a Ph.D. in 1919. During thistumultuous period of revolution and civil war,Kapitsa’s wife and two small children died in a fluepidemic. In the aftermath of this tragedy, atJoffe’s urging, he left for England, to do his grad-uate work under ERNEST RUTHERFORD at theCavendish Laboratory in Cambridge.

Kapitsa arrived at a time of great intellectualexcitement at Cambridge. The charming, dedi-cated young Russian became Rutherford’sfavorite pupil and mixed with such brilliantyoung physicists as JOHN DOUGLAS COCKCROFT,SIR JAMES CHADWICK, and LORD PATRICK MAY-NARD STUART BLACKETT. Put off by the formal-ity of British academic life, he founded “theKapitsa Club,” in which unfettered discussionwas the rule. In his first important piece of work,he developed methods for obtaining strong mag-netic fields of transient duration.

By 1924, Kapitsa was deputy director ofmagnetic research at the Cavendish. That year,using specially constructed accumulator batter-ies and switching gear, he performed experi-ments that allowed him to pass very largeelectric currents through a coil with a very smallinternal volume for very brief periods. Using thisexperimental technique, he was able to generatea very large transient magnetic field: 5,000,000gauss (the centimeter–gram–second unit formagnetic flux density), a record for magneticfield intensity that was not surpassed for 30years. He kept on improving this technique and,in 1927, by short-circuiting an alternating cur-rent generator of special construction, he wasable to generate large magnetic field intensitiesfor longer times in larger volumes of space.

Kapitsa’s career and personal life were flour-ishing. In 1927, he was married a second time, toAnna Alekseyevna Krylova, with whom he hadtwo sons, Sergey and Andrey. He was elected afellow of Trinity College, Cambridge, in 1925,and a fellow of the Royal Society, in 1929. WithR. H. Fowler, he founded and edited an interna-tional series of physics monographs. In 1930, hebecame director of the Royal Society Mond Lab-oratory in Cambridge, which had been builtespecially for him, and began his most signifi-cant research, on liquid helium, one of the mostuseful means for attaining low temperatures,which was first produced by HEIKE KAMERLINGH

ONNES in 1908.In 1934, while working in his laboratory,

Kapitsa invented and designed an originaldevice for liquefying helium, which cooled thegas by periodically controlled expansions. Forthe first time a machine could produce liquidhelium in large quantities without previous cool-ing with liquid hydrogen. This device was thefoundation for the subsequent importantadvances made in low-temperature physics.

In the autumn of 1934, Kapitsa’s life as a dis-tinguished member of the British physics com-munity abruptly ended, when he went to theSoviet Union for a conference and was notallowed to return to Cambridge. On Stalin’sorders, his passport was confiscated by a statethat considered his services too valuable to beshared with the West. Kapitsa was a patrioticRussian, with a “friendly” attitude toward therevolution. Although depressed at first, he man-aged to accept his situation and devoted himselfto the advancement of Soviet science. In 1936,he was made director of the S. I. Vavilov Insti-tute for Physical Problems of the SovietAcademy of Sciences in Moscow, and, the fol-lowing year, he persuaded the Soviet physicistLEV DAVIDOVICH LANDAU to head the theorydivision of his institute. With Rutherford’s help,the Soviet Union purchased the Mond Labora-tory, which was transported to Kapitsa in

158 Kapitsa, Pyotr Leonidovich

Moscow. His friendship with Cockcroft andother English scientists kept the link betweenEuropean and Soviet physics alive even duringthe worst years of Communist oppression.

During this period, Kapitsa developed anew method for the production of liquid oxygenwith a low-pressure cycle by using a specialhigh-efficiency turboexpansion device. Thiswork and its application were of great impor-tance to the Soviet Union, particularly in theproduction of steel. The highly efficient radialcompressed gas turboengine he developed stillserves as a world model for modern large-scaleoxygen production plants. Kapitsa was also oneof the first to study the unusual properties of aform of liquid helium that exists below 2.2 Kcalled helium II. Because liquid helium II con-ducts heat far more rapidly than copper, whichis the best heat conductor at room temperature,it flows very easily with a viscosity far less thanthat of any other liquid or gas. By 1938, Kapitsawas able to show that helium II had such greatinternal mobility and negligible or vanishingviscosity that it could be characterized as asuperfluid (a term he coined). During the nextfew years, his experiments on the properties ofthe helium II superfluid indicated that it was ina macroscopic or coherent “quantum state” andtherefore could be considered to be a “quantumfluid” with zero entropy: that is, that it has aperfect atomic order. Kapitsa published his find-ings on the superfluidity of helium II in 1941.Meanwhile, Landau successfully worked on acomprehensive theory of superfluidity, earningthe 1962 Nobel Prize in physics.

During World War II, Kapitsa headed thegovernment department in charge of oxygen pro-duction. However, in 1946, he refused to work onthe development of nuclear weapons. He wasplaced under house arrest until Stalin died, in1953, and the head of his secret service, LavrentyBeria, was arrested, in 1955. Kapitsa was not idleduring his years of confinement. He worked onhigh-power electronics, inventing high-power

microwave generators. He also discovered a newkind of continuous high-pressure plasma dis-charge with electron temperatures greater than1,000,000 K. In 1955, when he was once moremade director of the Vavilov Institute, instead ofreturning to his work on low temperatures, hecontinued to study high-power electronics andplasma physics. In the 1950s, he worked on balllightning, a puzzling phenomenon in whichhigh-energy plasma maintains itself for a muchlonger period than seems likely. Kapitsa remainedhead of the Vavilov Institute until his death in1984. He received the Nobel Prize in 1978, atthe age of 84.

Kapitsa became a well-known public figure,highly respected for his personal courage. He wasa member of the Soviet National Committee ofthe Pugwash Conference of scientists devoted topeace and disarmament and received theFrédéric Joliot-Curie Silver Medal of the WorldPeace Committee in 1959. During the worstyears of repression, he defended his colleagues,saving some of them from death in the camps.The writer C. P. Snow, who knew him in hisCambridge days, wrote that only when Kapitsahad returned to the Soviet Union did he and hisother English colleagues realize

how strong a character he was; how brave he was; and fundamentally what a goodman. . . . If he hadn’t existed, the worldwould have been worse: that is an epitaphthat most of us would like, but don’t deserve.

See also KELVIN, LORD (WILLIAM THOMSON).

Further ReadingBadash, Lawrence. Kapitsa, Rutherford, and the Krem-

lin. New Haven, Conn.: Yale University Press,1985.

Boag, J. W., P. E. Rubinin, and D. Shoenberg, eds.Kapitsa in Cambridge and Moscow: Life and Let-ters of a Russian Physicist. Amsterdam: ElsevierScience, 1990.

Kapitsa, Pyotr Leonidovich 159

� Kelvin, Lord (William Thomson)(1824–1907)IrishTheoretical Physicist (Thermodynamics,Classical Electromagnetism)

William Thomson, better known as Lord Kelvin,was a great 19th-century physicist who first pro-posed the use of an absolute scale of temperature.The Kelvin temperature scale has the enormousadvantage over other temperature scales such asthe Celsius scale of defining its zero point inde-pendently of the freezing point of a specific sub-stance such as water. It became an invaluabletool in the study of the thermodynamics of gases.The basic unit of thermodynamic temperaturewas named the kelvin in his honor, with absolutezero being equal to zero Kelvin (0 K).

William Thomson was born on July 26,1824, in Belfast, Ireland. He lost his motherwhen he was six but had a close relationshipwith his father, a professor of mathematics atBelfast University. Studying with his father,William became an accomplished mathemati-cian at a very early age. When he was eight, thefamily moved to Glasgow, Scotland, where hisfather became a professor of mathematics atGlasgow University. Since it was commonpractice for universities to compete with sec-ondary schools for the best pupils, William wasable to enroll at Glasgow University at age 10.There he studied astronomy, chemistry, andnatural philosophy, as physics was then called,which included the study of heat, electricity,and magnetism. At age 17, he went on to Cam-bridge and graduated four years later at the topof his class.

After a trip to Paris, he returned to Glasgow,where, with his father’s help, he was appointedprofessor of natural science at the university. Aninnovative pedagogue, he created the first labo-ratory in a British university. Shortly after hisappointment, he began a collaboration withGEORGE GABRIEL STOKES, which would con-

tinue for more than 50 years. Their initial workon hydrodynamics led to Kelvin’s discovery, in1847, that the distribution of electrostatic forcein a region and the distribution of heat througha solid are mathematically equivalent. He con-cluded that electrical and magnetic fields aredistributed in the same way that energy movesthrough an elastic solid. JAMES CLERK MAXWELL

would later successfully develop these ideas intohis unified electromagnetic theory.

The following year, in 1848, Kelvin wouldmake his most important contribution, whichgrew out of his early interest in the Frenchmathematical approach to physics. While doingresearch in Paris he had learned of the researchof NICOLAS LÉONARD SADI CARNOT on theability of heat to do work. By analyzing Carnot’stheory, which explains the amount of work pro-duced by an engine using an ideal gas governedonly by the temperature at which it operates,Kelvin developed the idea of an absolute tem-perature scale in which the temperature repre-sents the total energy of a body. Unlike theCelsius scale, in which 0°C is defined as thefreezing point of water, Kelvin’s scale definedabsolute zero as the point at which all vibra-tional motion associated with heat in the gasvanishes. He did this by considering a perfectgas, that is, a gas of molecules of zero dimensionwhose pressure depends only on its temperature.Absolute zero was reached when the volume ofthe perfect gas vanished. This was an idealiza-tion, since, in reality, the volume of a gas doesnot wholly disappear. But real gases approxi-mate perfect gases for some range of tempera-ture and their volume decreases as thetemperatures decreases, if the pressure is heldconstant. In this manner Kelvin determinedthat absolute zero 0 K occurred at –273°C,showing that Carnot’s theory was correct ifabsolute temperatures were used.

Where Kelvin parted ways with Carnot,however, was on the question of what heat actu-ally is. Carnot held the prevalent belief that

160 Kelvin, Lord

heat is a fluid, whereas Kelvin believed it to bea form of motion and supported JAMES

PRESCOTT JOULE’s mechanical theory of heat. In1851, he announced that Carnot’s theory andthe mechanical theory of heat were compatible,if one accepted that heat cannot pass sponta-neously from a cooler body to a hotter one. Inthis way Kelvin found his own path to what isnow known as the second law of thermodynam-ics, which RUDOLF JULIUS EMMANUEL CLAU-SIUS had independently discovered a yearearlier. In 1852, Kelvin suggested that mechan-ical energy dissipates as heat, an idea that Clau-sius later developed into the theory of entropy, ameasure of the disorder of a system.

In 1852, Kelvin, the brilliant theorist, andJoule, the ingenious experimentalist, began along, fruitful collaboration. Together they for-mulated the Joule–Thomson effect, whichdescribes the decrease in temperature in a gaswhen it expands in a vacuum. The effect,which is caused by the work done as the gasmolecules move apart, had great import in theliquefaction of gases. Joule’s ideas on heatwould change Kelvin’s, leading him to believein a dynamical theory of heat, which he wouldapply to electricity and magnetism. “Whateverelectricity is,” Kelvin said in 1856, “it seemsquite certain that electricity in motion is heat,and that a certain alignment of the axes of rev-olution in this motion is magnetism.”

Kelvin also expanded the discoveries madeby MICHAEL FARADAY into a full theory of elec-tromagnetism. He derived an expression for theenergy possessed by a circuit carrying a currentand developed a theory of oscillating circuitsthat was experimentally verified in 1857. Thisapproach was later used to generate and analyzethe production of radio waves.

Kelvin’s work on electricity and magnetismhelped Maxwell develop his theory of electro-magnetism. Still, when it was published, Kelvindid not fully support its tenets. In fact, in the lat-ter part of his career, he seemed to be on the los-

ing side of many arguments: he refused to acceptthe concept of atoms, opposed Darwin’s theories,speculated incorrectly as to the age of the Sunand the Earth, and opposed ERNEST RUTHER-FORD’s ideas on radioactivity.

Kelvin joined a group of industrialists in themid-1850s on a project to lay a submarine cablebetween Ireland and Newfoundland. He pointedout that a fast rate of signaling could only beachieved by using low voltages, which wouldrequire very sensitive detection equipment suchas the mirror galvanometer that he had invented.When his advice was finally heeded on the thirdtry, in 1866, the first transatlantic cable workedbeautifully. That year he was knighted for thiswork and became Lord Kelvin. As a furtherreward for his involvement in the cable project,he amassed a considerable personal fortune. In1899, he retired from Glasgow; he died at hisestate in Largs, Ayrshire, Scotland, on December17, 1907.

Kelvin’s discoveries were crucial to the twomain areas of research of 19th-century physics.His absolute scale of temperature became one ofthe foundations of thermodynamics. His insightsinto the nature of electricity and magnetismplaced stepping-stones along the road leading toMaxwell’s comprehensive formulation of anelectromagnetic theory.

See also HERTZ, HEINRICH RUDOLF.

Further ReadingBurchfield, Joe D. Lord Kelvin and the Age of the Earth.

Chicago: University of Chicago Press, 1990.Shachtman, Tom. Absolute Zero and the Conquest of

Cold. New York: Mariner Books, 2000.Smith, Crosbie, and M. Norton Wise. Energy and

Empire: A Biographical Study of Lord Kelvin. Cam-bridge: Cambridge University Press, 1989.

Thompson, Silvanus P. The Life of Lord Kelvin. NewYork: Chelsea, 1977.

Tunbridge, P. Lord Kelvin: His Influence on Electrical Mea-surements and Units. IEE History of TechnologySeries, No. 18. London: Peter Peregrinus, 1991.

Kelvin, Lord 161

� Kilby, Jack St. Clair(1923– )AmericanSolid State Physicist, Electrical Engineer

Jack St. Clair Kilby had an enormous impact onthe world through his invention of the integratedcircuit, also known as the microchip, which gaverise to the microelectronics revolution. His workwas rewarded with a 2000 Nobel Prize in physics.

The man who would clear a path toward thecomputer age and space exploration was born onNovember 8, 1923, in Great Bend, Kansas, andgrew up in the midst of what he called “theindustrious descendants of the western settlers ofthe American Great Plains.” His father ran asmall electric company and had customersthroughout the rural western part of Kansas.Kilby traces his decision to pursue electronics towatching his father use an amateur radio to keepin touch with customers who had lost theirpower and phone service during an ice storm. Asa teenager in the 1940s, he was a fan of broadcastradio and particularly enjoyed band music, alove that stayed with him all his life.

After high school graduation, he majored inelectrical engineering at the University of Illi-nois, where he also took courses in vacuum tubeengineering physics. He received a B.S. in 1947,a year before Bell Laboratories announced theinvention of the transistor. He later observedthat this “meant that my vacuum tube classeswere about to become obsolete, but it offeredgreat opportunities to put my physics studies togood use.” He took a job with Centralab, anelectronics manufacturer in Milwaukee, Wis-consin, that made parts for radios, televisions,and hearing aids; there he was responsible forthe design of ceramic-base silk screen circuitboards. At the same time, he took eveningclasses at the University of Wisconsin andearned a master’s degree in electrical engineer-ing in 1950. In 1952, Centralab sent him to atransistor symposium at Bell Labs, where he was

able to see firsthand the work of the transistorinventors JOHN BARDEEN, Walter Brattain, andWILLIAM BRADFORD SHOCKLEY.

In 1958, he left Milwaukee and moved withhis wife to Dallas, Texas, where he went to workfor Texas Instruments. The company put him towork on electronic component miniaturization,looking for ways to produce smaller and moreeffective electrical components. Electrical engi-neers were aware of the potential of digital com-puters but faced the challenge of what wasknown as the “tyranny of numbers”: the expo-nentially increasing number of componentsrequired to design improved circuits and thephysical limitations derived from the number ofcomponents that could be assembled together.In the summer of 1958, while the rest of thestaff was on vacation and he had the laboratoryto himself, Kilby worked on this problem. Hefound his solution in the monolithic (formedfrom a single crystal) integrated circuit. Ratherthan design smaller components, he was able tofabricate entire networks of discrete compo-nents—resistors, capacitors, distributed capaci-tors, and transistors—in a single sequence bylaying them into a single crystal, or chip of asemiconducting material. On September 12,Kilby was able to demonstrate that an inte-grated circuit worked.

At the same time, Robert Noyce, a researchengineer who had founded his own company,Fairchild Semiconductor Corporation, foundthe same solution, using a different manufactur-ing process. Fairchild and Texas Instrumentsthen engaged in more than 10 years of litigation,which was finally resolved in the late 1960swhen the firms decided to cross-license theirtechnologies. Both Kilby and Noyce wereawarded the National Medal of Science (1969),and both were inducted into the NationalInventors Hall of Fame (1982).

When, 42 years after the invention of theintegrated circuit, Kilby shared the 2000 NobelPrize in physics with the semiconductor pioneers

162 Kilby, Jack St. Clair

ZHORES IVANOVICH ALFEROV and HERBERT

KROEMER, he paid tribute to his colleague:

While Robert [Noyce] and I followedour own paths, we worked hard togetherto achieve commercial acceptance forintegrated circuits. If he were still liv-ing, I have no doubt he would haveshared this prize.

Kilby, who was known in the corridors ofTexas Instruments as “the humble giant,” becauseof his height (he is six feet six inches tall) andunassuming manner, would later express hisastonishment at the fruits of his invention:

What we didn’t realize then was thatthe integrated circuit would reduce thecost of electronic functions by a factorof a million to one. . . . Nothing hadever done that for anything before.

After proving that integrated circuits werepossible, he headed teams that built the first mili-tary systems and the first computer incorporatingintegrated circuits. He also worked on teams thatinvented the handheld calculator and the thermalprinter, which was used in portable data terminals.

In 1970, Kilby took a leave of absence fromTexas Instruments and worked on a method toapply silicon technology to help generate elec-trical power from sunlight. From 1978 to 1984,he was a Distinguished Professor of ElectricalEngineering at Texas A&M University. He offi-cially retired from Texas Instruments in the1980s but has maintained a strong involvementwith the company. Texas Instruments named astate-of-the-art digital chip research center inhis honor in 1997. He is married and has twodaughters and five granddaughters.

Kilby’s invention of the integrated circuit isone of the most important discoveries in the his-tory of technology. Today chips that are beingmade contain nearly a billion bits of memories or

logic gates in processors—the brains of computers.Integrated circuit chips containing programmabledigital signal processors and analog componentsare also used in mobile phones, enabling them toplace calls at costs per transistor roughly the sameas those for simple memory chips.

Further ReadingQueisser, Hans. The Conquest of the Microchip. Cam-

bridge, Mass.: Harvard University Press, 1988.Reid, T. R. The Chip: How Two Americans Invented the

Microchip and Launched a Revolution. New York:Simon & Schuster, 1984.

Warshofsky, Fred. The Chip War: The Battle for theWorld of Tomorrow. New York: Charles Scribner’sSons, 1984.

� Kirchhoff, Gustav Robert(1824–1887)GermanTheorist and Experimentalist(Electromagnetism, Spectroscopy,Thermodynamics)

Gustav Kirchhoff’s most far-reaching contribu-tion to physics was his discovery of a fundamen-tal law of electromagnetic radiation, which ledto his development of the concept of a perfectblackbody, an object that does not reflect anysurface light and is therefore a perfect emitterand absorber of radiation at all frequencies. Inaddition, together with Robert Bunsen, hefounded the science of spectroscopy, which ledto the discovery of several new chemical ele-ments and to methods of determining the com-position of stars and the structure of the atom.He also did important work in electromag-netism, discovering the laws that govern theflow of electricity in electrical networks.

Kirchhoff’s distinguished career unfoldedwithin a period of national prosperity and stabil-ity that was reflected in a thriving academic com-munity. He was born in Königsberg, Germany, on

Kirchhoff, Gustav Robert 163

March 12, 1824, into a family with a strong tradi-tion of service to the Prussian state. He attendedthe University of Königsberg, where he was intro-duced to the new science of electromagnetismand exposed to the ideas and methods of the lead-ing French school of mathematical physics.While still a student, he made an important con-tribution to electrical circuit theory when heextended Ohm’s law, which formulates the rela-tionships of current, electromotive force (volt-age), and resistance to networks of conductors.He went on to derive what came to be known asKirchhoff’s laws, a set of rules for calculatingunknown currents, resistances, and voltages in anelectric circuit. In later work on electricity, Kirch-hoff would demonstrate that electrostatic poten-tial is identical to electromotive force, thusunifying the theories of static charges and electriccurrents. He would also show that an oscillatingcurrent is propagated in a conductor of zero resis-tance at the velocity of light, a discovery thatwould play an important role in the development,in the 1860s, of the electromagnetic theory oflight by JAMES CLERK MAXWELL.

Kirchhoff graduated from the University ofKönigsberg in 1847 and the same year marriedClara Richelot, the daughter of one of his pro-fessors. The following year he began his teach-ing career, as a lecturer at the University ofBerlin. A master of mathematical analysis, whoinsisted on clear-cut logical formulation ofphysical ideas directly based on observed data,Kirchhoff became a leading figure in the flower-ing of theoretical physics in Germany. In 1850,he became professor of physics in Breslau, wherehe met Robert Bunsen, the inventor of the Bun-sen burner. The two men began a dynamic col-laboration, and, in 1852, Bunsen arranged forKirchhoff to join him on the physics faculty ofthe University of Heidelberg. In Heidelberg’sstimulating atmosphere, dominated by thegreat HERMANN LUDWIG FERDINAND VON

HELMHOLTZ Kirchhoff, partly in collaborationwith Bunsen, made his greatest contributions.

Bunsen had been interested in how chemi-cals emitted and absorbed light; Kirchhoff hadfocused on the way substances acted whenburned or heated to incandescence. In the1850s, Bunsen had developed his famous gasburner, which emitted a colorless flame, andused it to investigate the distinctive colors thatmetals and their salts produce in a flame. Heused colored solutions and glass filters to distin-guish the colors in a partly successful attempt toidentify the substances by the colors they pro-duced. Kirchhoff pointed out to Bunsen that hecould accurately identify the colors by using aprism to produce spectra of the colored flames.They developed the spectroscope, a prism-baseddevice that separated light into its primary chro-matic components (i.e., its spectrum), and, in1860, discovered that each of the elements pre-sent in a substance has a characteristic set ofspectral emission lines. They then began study-ing the spectral “signature” of various chemicalelements in gaseous form. By using this spectralanalysis, Bunsen discovered two new elements:cesium in 1860 and rubidium in 1861.

In 1859, Kirchhoff made another importantdiscovery, while investigating spectroscopy as ananalytic tool. He noticed that certain dark spotsin the Sun’s spectrum were intensified if the sun-light passed through a sodium flame. JEAN

BERNARD LÉON FOUCAULT had made this discov-ery 10 years earlier but had not followed up on it.Kirchhoff hypothesized that the sodium flamewas absorbing light from the sunlight of the samecolor that it emitted and explained that the darklines, known as Fraunhofer lines, were due to theabsorption of light by sodium and other elementspresent in the Sun’s atmosphere. He identifiedother elements in the Sun’s spectrum in this wayand developed a law, which states that the ratioof the emission line power to absorption linepower of all material bodies is the same at a giventemperature and a given wavelength of radiationproduced. He went on to demonstrate the exis-tence in the Sun of many chemical elements iso-

164 Kirchhoff, Gustav Robert

lated on Earth and to argue that the Sun ismainly composed of a hot, incandescent liquid.Further, he firmly established the hot gaseousnature of the solar atmosphere and produced thefirst detailed map of the solar system.

From this, Kirchhoff went on in, 1862, toderive the concept of a perfect blackbody, anobject that absorbs all the energy that falls uponit, and, because it reflects no light, appears blackto an observer. It is also a perfect emitter, and inthis context Kirchhoff proved that the energyemitted E depends only on the temperature Tand the frequency v of the emitted energy: E =J(T, v). He challenged physicists to find thefunction J. In 1900, MAX ERNEST LUDWIG

PLANCK guessed the correct formula for the Jfunction but in so doing was forced to hypothe-size that the energy was emitted, not continu-ously, but in discrete packets, which he namedquanta. Thus began the revolution that wouldresult in the quantum theory.

Kirchhoff’s Heidelberg life was marred bythe death of his wife in 1869. Left with two sonsand two daughters, in 1872, he married LuiseBrommel. By 1875, he was too ill to continueexperimental work and accepted a chair in theo-retical physics in Berlin. He was disabled by anaccident, which obliged him to use crutches or awheelchair. In 1886, he was forced by illness toretire, and he died in Berlin on October 17, 1887.

Through his seminal work in electromag-netism, blackbody radiation, and spectroscopy,Kirchhoff made enduring contributions to mod-ern physics. Although he was a classical physi-cist to the core, his work on blackbodies wouldlead a new generation of physicists to the dis-covery of quantum mechanics.

See also FRAUNHOFER, JOSEPH VON; OHM,GEORG SIMON.

Further ReadingHearnshaw, J. B. The Analysis of Starlight: One Hun-

dred and Fifty Years of Astronomical Spectroscopy.Cambridge: Cambridge University Press, 1990.

Kuhn, Thomas. Black-Body Radiation and the QuantumDiscontinuity, 1894–1912. Oxford: Oxford Uni-versity Press, 1978.

� Kroemer, Herbert(1928– )GermanTheoretical Physicist andExperimentalist, Solid State Physicist

Herbert Kroemer is a pioneer in the field ofsemiconductor theory, who first elucidated theidea of heterostructures and their potential foropening up laser and transistor technology. Inrecognition of this work, which laid the founda-tion for today’s revolution in information andcommunication technology, he shared the 2000Nobel Prize in physics with ZHORES IVANOVICH

ALFEROV and JACK ST. CLAIR KILBY.Kroemer was born on August 25, 1928, in

Weimar, Germany. His father was a civil servant,his mother “a classical German housewife.” Bothwere members of families of skilled artisans andhad no high school education but wanted thebest education for their children and pushedthem to achieve. Herbert had no problem doingso: he “breezed through 12 years of schools almosteffortlessly” but was often bored and entertainedhimself by disturbing the class. His high schoolphysics teacher overcame this problem by enlist-ing him to help teach the subject. Upon graduat-ing in 1947, he entered the University of Jena inEast Germany, where he was inspired by thephysics lectures of Friedrich Hund. These wereprecarious years, when political oppression underthe Communist regime caused many of his fellowstudents to flee to the West or to “disappear” intothe German branch of Stalin’s system of forcedlabor camps. While spending a summer as a stu-dent at the Siemens company, Kroemer took theopportunity to escape to West Berlin via one ofthe empty return flights of planes participating inthe Berlin airlift.

Kroemer, Herbert 165

After being grilled by such notable profes-sors as WOLFGANG PAULI, he was admitted to theUniversity of Göttingen, which he described as“intellectually a wonderful place.” When theexperimentalist he wanted to work with turnedout to have a long waiting list, he set the direc-tion of his career by signing on with a theorist,Fritz Sauter, for his diploma thesis. Sauter had aprofound influence on Kroemer’s developmentas a physicist, teaching him that

you had to be able to go back and forth[between the physical concept and themathematical formulation] with ease.Yet, in the last analysis, concepts tookpriority over formalism, the latter wassimply an (indispensable) means to anend.

Taking NIELS HENRIK DAVID BOHR as his“personal role model,” he never developed into a“hard-core Theorist with a capital T,” butbecame basically a conceptualist, who remainedacutely aware of his limitations as a formalist.

For his diploma thesis, Kroemer chose toextend the 1939 work of WILLIAM BRADFORD

SHOCKLEY on the nature of surface states in one-dimensional potentials. While he was engagedin this research, Sauter urged him to write up atalk he had given on hot-electron effects in thenewly invented transistor and submit it as hisdoctoral dissertation. Thus, Kroemer received aPh.D. in theoretical physics, in 1952, before his24th birthday, from the University of Göttingen.

Despite this academic success, he had nohopes for a university career. Virtually no newpositions for theoretical physicists were being cre-ated in Germany, and the prospects in industrywere similarly dim. He managed to be hired as a“house theorist” by the small semiconductorresearch group at the Central Telecommunica-tions Laboratory of the German postal service.There he was given the freedom to choose his ownproblems and lecture to his experimentalist and

technologist colleagues, an experience that madehim into what he termed “an applied theorist.”

By focusing on the problem of overcomingthe severe frequency limitations of the new tran-sistors, Kroemer was led directly to the idea ofheterostructures: two semiconductors whoseatomic structures fit one another well but thathave different electronic properties. He was thefirst to point out the significant performanceadvantages that can be gained in various semi-conductor devices by incorporating heterostruc-tures into them. In a 1954 paper, he firstoutlined the principles of his heterostructurebipolar transistor (HBT). After coming to theUnited States, where he joined RCA Laborato-ries in Princeton, New Jersey, in 1954, hereturned to his research on heterojunctions. In aseminal 1957 theoretical paper, he set forth thebasic design principles for all heterostructures.

In 1963, while working at Varian Associatesin Palo Alto, California, Kroemer proposed theconcept of the double-heterostructure laser, thecentral concept in the field of semiconductorlasers, without which that field would not exist.He proposed that the concentration of elec-trons, holes, and photons would become muchhigher if they were confined to a thin semicon-ductor layer between two others—a doubleheterojunction. His Nobel Prize–winning con-tributions can be traced directly to these earlypapers. But his paper was rejected, in 1963, and,when finally published, ignored. Varian refusedto fund his work on the new kind of laser, believ-ing that it had no practical applications. For thenext decade, Kroemer worked on hot-electronnegative resistance effects, playing no role in thetechnological realization of the laser. It wasAlferov and his group at the Ioffe Institute inLeningrad who, in May 1970, first produced alaser that operated continuously, without requir-ing complex cooling measures.

Kroemer left Varian in 1966 and, two yearslater, joined the University of Colorado, wherehe resumed his work on heterostructures. After

166 Kroemer, Herbert

moving to the University of California in SantaBarbara, he developed a powerful new methodto determine physical properties of the het-erostructure interface. In 1976, he began assem-bling a large illustrious team of scientists for thestudy of the physics and technology of com-pound semiconductors and devices based onthem. During this period, he became a strongadvocate for developing the full potential of “thedevice that started it all,” the heterostructurebipolar transistor.

Today the use of heterostructures continuesto dominate the design of compound semicon-ductors—not just lasers and light-emitting diodes(LEDs), but integrated circuits as well—and theyare even invading mainstream silicon circuittechnology. In addition, Kroemer’s work on het-erostructures has led to spectacular scientificbreakthroughs in which the advanced materialsand tools of microelectronics are being used forstudies in nanoscience and of quantum effects.The impact of this research on the modern worldof electronics and communication has beenenormous. Lasers and light-emitting diodes havebeen further developed in many stages. Withoutthe heterostructure laser, today we would nothave had optical broadband links, compact disc(CD) players, laser printers, bar code readers,laser pointers, and numerous scientific instru-ments. LEDs are used in displays of all kinds,including traffic signals. In recent years, it hasbeen possible to make LEDs and lasers that coverthe full visible wavelength range, including bluelight. Today, high-speed transistors are found incellular phones and in their base stations, insatellite dishes and in links. There they are partof devices that amplify weak signals from outerspace or from a faraway cellular phone withoutdrowning in the noise of the receiver itself.

Kroemer later turned to experimental workand became one of the pioneers in molecularbeam epitaxy, a method used to apply new mate-rial surfaces on silicon interfaces. Describing him-self as “an opportunist—and not at all ashamed of

it,” Kroemer continues to work on a wide varietyof problems in semiconductor physics, includingthe superlattice Bloch oscillator, “an excitingcombination of heterostructures and hot electronphysics,” and superconducting weak links.

See also BARDEEN, JOHN; BLOCH, FELIX.

Further ReadingKroemer, Herbert. “Heterostructures for Everything:

Device Principle of the 1980’s?” Japanese Journalof Applied Physics, 20 (suppl. 20–21): 9–13, 1981.

Riordan, Michael, and Lillian Hoddeson. The Inventionof the Transistor and the Birth of the Information Age.New York: W. W. Norton & Company, 1998.

� Kusch, Polykarp(1911–1993)AmericanExperimentalist, Quantum Physicist

Polykarp Kusch was an ingenious experimental-ist who won the 1955 Nobel Prize in physics “forhis precise determination of the magneticmoment of the electron.” His discovery had aprofound impact on the development of thetheory of the interaction of electrons andelectromagnetic radiation, known as quantumelectrodynamics (QED).

Kusch was born on January 16, 1911, inBlankenberg, Germany, the son of a Lutheranclergyman. The family immigrated to the UnitedStates the following year and settled in the Mid-west, where Kusch received his early education.He became a U.S. citizen in 1922. After enteringthe Case Institute of Technology, Cleveland,Ohio, intending to major in chemistry, he soonrealized that his interests lay elsewhere; heearned a B.S. in physics in 1931. For the next fiveyears, he pursued his graduate studies at the Uni-versity of Illinois, where he received an M.A. in1933 and a Ph.D. in 1936, for a thesis on opticalmolecular spectroscopy directed by F. WheelerLoomis. He then did postdoctoral work at the

Kusch, Polykarp 167

University of Minnesota, working with John T.Tate on problems in mass spectroscopy.

In 1937, Kusch began his long career as amember of the physics department at ColumbiaUniversity, where he became known as a capti-vating teacher, who delivered his intense, well-thought out lectures in what was known as “theKusch whisper,” a loud, deep, inspirationalvoice. From the beginning, he worked closelywith ISIDOR ISAAC RABI on his investigations ofatomic, molecular, and nuclear phenomena viathe molecular beam method. Following thework of Rabi, Kusch focused his research on theuse of externally applied electric and magnetic

fields on atomic and molecular beams as amethod to conduct detailed studies of the inter-actions of particles and molecules.

During World War II, Kusch put hisresearch on atomic and molecular beams asideand studied the use of microwave generators forradar at the Westinghouse Electric Corpora-tion, the Bell Telephone Laboratories, and theColumbia Radiation Laboratories. His work inthese laboratories taught him about microwavemethods and was crucial to his future applica-tions of vacuum tube technology to a broadspan of experiments.

Back at Columbia full time after the war, hebecame immersed in research on atomic andmolecular beams and did his most importantwork: the experimental observation of theanomalous magnetic moment of the electron andprecise determination of its magnitude. The elec-tron had long been known to be capable of actingas a small magnet whose strength, as measured byits magnetic moment, according to PAUL ADRIEN

MAURICE DIRAC’s theory of the electron, wasequal to a quantity known as the Bohr magneton.However, at the beginning of 1947, Rabi and hiscollaborators found that the hyperfine structureof the electron in external magnetic fields didnot entirely conform to the predictions of Dirac’stheory. The physicist Gregory Breit hypothesizedthat this might be due to the fact that the valueof the magnetic moment of the electron waslarger than the value of one Bohr magneton aspredicted by the Dirac equation.

Building on this insight, in 1947, Kuschmade a series of scrupulously accurate atomicbeam experiments that confirmed Breit’shypothesis: the magnetic moment of the elec-tron was, indeed, larger than the Bohr magnetonby about one part in a thousand. Kusch used anextremely refined technique involving atomicbeams in order to reveal this tiny difference inthe value of the magnetic moment of the elec-tron. Later, he would use molecular beam tech-niques in experimental studies in chemical

168 Kusch, Polykarp

Polykarp Kusch’s precise determination of the magneticmoment of the electron had a profound impact on thedevelopment of quantum electrodynamics. (AIP EmilioSegrè Visual Archives, Physics Today Collection)

physics. As did the Lamb shift, discovered byWILLIS EUGENE LAMB in the Columbia lab thatsame year, the tiny discrepancy that Kuschdetected led the theorists JULIAN SEYMOUR

SCHWINGER, RICHARD PHILLIPS FEYNMAN, andFREEMAN DYSON to reformulate QED, the the-ory of the interaction of electrons and electro-magnetic radiation, radically. Lamb and Kuschwould share the 1955 Nobel Prize in physics.

In 1949, Kusch was made full professor atColumbia. He later was director of the Radia-tion Lab, as well as its academic vice presidentand provost. In the latter part of his career, hebecame deeply involved with problems of sci-ence education. From 1962 to 1965, he servedon the Board of the Institute for ScientificInformation in Philadelphia.

Kusch was married to Edith Starr McRoberts,with whom he had three children. A year afterher death in 1959, he married Betty Pezzoni. In1971, he retired from Columbia and became a

member of the physics department at the Uni-versity of Dallas, Texas, for the next decade.After a series of strokes, he died on March 20,1993, at his home in Dallas at the age of 82.

Kusch’s experimental discovery of theminuscule anomaly in the magnetic moment ofthe electron, along with the detection of theLamb shift, provided the impetus for the theoret-ical breakthrough that led to the development ofmodern renormalized quantum electrodynamics.

See also BOHR, NIELS HENRIK DAVID.

Further ReadingKusch, P. “The Magnetic Moment of the Electron.”

In Nobel Lectures on Physics. New York: Elsevier,1964, pp. 298–310.

Schweber, Silvan S. QED and the Men Who Made It:Dyson, Feynman, Schwinger, and Lamb, WillisEugene Tomonaga. Princeton, N.J.: PrincetonUniversity Press, 1994.

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� Lamb, Willis Eugene Jr.(1913– )AmericanTheoretical and Experimental Physicist,Quantum Physicist

Willis Eugene Lamb Jr. manifested a rare combi-nation of theoretical and experimental prowessin his discovery of what came to be called theLamb shift, an anomaly in the fine structure ofthe hydrogen spectrum. For this work, which hadprofound implications for the development ofquantum electrodynamics, he shared the 1955Nobel Prize in physics with POLYKARP KUSCH.

He was born on July 12, 1913, in Los Ange-les, California, the son of Willis Eugene Lamb, atelephone engineer, and Marie Helen Metcalf,originally from Nebraska. After attending publicschools in Oakland and Los Angeles, he enteredthe University of California at Berkeley in 1930;four years later he graduated with a B.S. inchemistry. He then “switched to the other sideof the sidewalk,” doing his graduate work atBerkeley in theoretical physics. Working underJ. ROBERT OPPENHEIMER, he earned a Ph.D. in1938 for a thesis on the electromagnetic proper-ties of nuclear systems.

Lamb then joined the faculty of ColumbiaUniversity, New York, and the following yearmarried Ursula Schaefer, a student from Ger-

many. Over the next 10 years, he rose frominstructor to full professor. From 1943 to 1951,he was also associated with the Columbia Radia-tion Laboratory. During World War II, he didextensive work on radar technique, whichimproved upon ISIDOR ISAAC RABI’s magneticresonance method.

Lamb won his Nobel Prize for the discoveryhe made, while heading a group at the Columbialab after the war, of an anomaly in the fine struc-ture of the hydrogen spectrum. The workfocused on the hydrogen atom, in which a singleelectron moves around the nucleus in one of aseries of orbits, each having a definite energy.These energy levels exhibit a fine structure,which means that they are arranged in groups ofneighboring levels, the groups widely separated.In 1928, PAUL ADRIEN MAURICE DIRAC hadoffered an explanation of the fine structure, longthought to be correct: a theory of the electronbased on relativity and quantum theory. Overthe next decade, physicists used optical methodsto check Dirac’s theory of the fine structure;although these studies suggested some flaw inthe theory, no definite results emerged.

In 1947, after a thorough theoretical analy-sis, Lamb began his experimental investigations,using a modified Rabi resonance method.Applying the art of spectroscopy with unprece-dented precision, he shone a beam of

microwaves onto a hot wisp of hydrogen gasblowing from an oven. He found that two finestructure levels in the next lowest group of finestructure levels, which should have coincidedwith the Dirac theory, were in reality shifted rel-ative to each other by a certain amount (theLamb shift). He measured the shift with greataccuracy and later made similar measurementson heavy hydrogen. When Lamb announced hisnews to the participants of the 1947 ShelterIsland (New York) Conference, they were unset-

tled by this stunning example of the truism thatprogress in science occurs when experiment con-tradicts theory. The comment of JULIAN SEY-MOUR SCHWINGER, a leading theorist of thetime, reveals the level of shock and surprise:“The facts were incredible—to be told that thesacred Dirac theory was breaking down all overthe place.” Quantum theorists would later real-ize that what was missing from Dirac’s theory wasthe unwieldy concept of the self-interaction ofthe electron, which by its very nature contained

Lamb, Willis Eugene 171

Willis Eugene Lamb Jr. discovered an anomaly in the fine structure of the hydrogen spectrum that had profoundimplications for the development of quantum electrodynamics. (AIP Emilio Segrè Visual Archives)

infinities, thereby preventing a straightforwardphysical interpretation.

At the heart of the quantum electrodynamicprocess is the quantum exchange force by whichelectrons can interact by exchanging photonswith each other. However, an electron can alsoexchange a photon with itself. Encouraged byLamb’s groundbreaking experiment, HANS

ALBRECHT BETHE, Schwinger, RICHARD PHILLIPS

FEYNMAN, and SIN-ITIRO TOMONAGA were stimu-lated to develop the method of renormalization, inwhich the self-energy infinities could be sub-tracted out. This led to a fully consistent relativis-tic theory of quantum electrodynamics, in whichboth the electron and the electromagnetic fieldwere quantized. It explained the Lamb shift as dueto the modification of the Coulomb force betweenthe electron and the proton in the hydrogen atom.This modification was caused by the finite part ofthe quantum electrodynamic self-interaction,which was left after the infinite part was sub-tracted by the renormalization process.

Lamb has been on the physics faculty ofStanford University, Harvard University, OxfordUniversity, and Yale University. Since 1974 hehas been affiliated with the University of Ari-zona’s Optical Science Center and Departmentof Physics, and from 1983 on with its ArizonaResearch Laboratories. He became Regents Pro-fessor at Arizona in 1989.

Lamb’s research has spanned a large numberof subjects, including the theory of the interac-tions of neutrons and matter, field theories ofnuclear structure, theories of beta decay, rangesof fission fragments, fluctuations in cosmic rayshowers, pair production processes, order–disor-der problems, ejection of electrons by metastableatoms, quadrupole interactions in molecules,diamagnetic corrections for nuclear resonanceexperiments, theory and design of magnetonoscillators, theory of a microwave spectroscope,study of the fine structure of hydrogen, deu-terium, and helium, and theory of electrody-namic energy level displacements.

At the age of 87, he was still walking a mileeach morning to his work at the Optical Sci-ences Center in Tucson.

Lamb’s discovery had a profound impact onthe theorists of his time and resulted in aparadigm shift leading to the reshaping of thequantum theory of the interaction of electronsand electromagnetic radiation. The implicationsof the seemingly tiny effect associated with theLamb shift probed the depths of the process inwhich the quantum theory is applied to electro-magnetic fields and led to what is now known asquantum electrodynamics.

Further ReadingLamb, Willis E. “The Fine Structure of Hydrogen,”

Laurie M. Brown and Lillian Hoddeson, eds. inThe Birth of Particle Physics. Cambridge: Cam-bridge University Press, 1983.

Schweber, Silvan S. QED and the Men Who Made It:Dyson, Feynman, Schwinger, and Tomonaga.Princeton, N.J.: Princeton University Press, 1994.

� Landau, Lev Davidovich(1908–1968)RussianLow-Temperature, Atomic, Nuclear,Plasma, Solid State, and QuantumPhysicist; Relativist

Lev Davidovich Landau was a brilliant theoristwhose research and teaching raised theoreticalphysics in the Soviet Union to new levels. Therange of his discoveries influenced all branchesof theoretical physics, from fluid mechanics toquantum field theory. His theoretical explana-tion of why liquid helium is a superfluid earnedhim the 1962 Nobel Prize in physics.

Landau was born in Baku, Azerbaijan, Rus-sian Empire, on January 22, 1908, into a scientif-ically oriented Jewish family. His father was anengineer, who worked in the Baku oil industry;his mother, a physician, who did research in

172 Landau, Lev Davidovich

physiology. Lev was a mathematical prodigy andfinished his secondary studies at age 13. Tooyoung to attend university, he studied physicsand chemistry at the Baku Economical Techni-cal School for a year before enrolling inLeningrad State University. After graduating in1927, at the age of 19, he worked at theLeningrad Physico-Technical Institute (knownas Phystech). At that time, the most excitingwork in physics was being done in Europe, andLandau had the opportunity to interact with itfirsthand. Between 1929 and 1931, he traveledto Göttingen, Leipzig, Zurich, and Cambridge.But his most formative stay was in Copenhagen,where he worked at NIELS HENRIK DAVID BOHR’sInstitute of Theoretical Physics, developing thenew quantum mechanics. From then on hebecame a disciple of Bohr, whose work wouldhave a powerful impact on his subsequentresearch, which involved applying the quantumparadigm to all realms of theoretical physics.

In 1930, Landau published a quantum theo-retical study on the behavior of free electrons ina magnetic field that drew him instant interna-tional recognition. It proved essential to anunderstanding of the properties of metals.Working in collaboration with his students,after he returned to the Soviet Union, he wasable to uncover important new theoreticalresults about the structure of magnetic sub-stances and superconductors and new insightsinto the quantum theory of phase transforma-tions and thermodynamical fluctuations. In1932, he became the head of the Theory Divi-sion of the Ukrainian Physical-Technical Insti-tute in Kharkov, Ukraine. Under hisleadership, it became the center of theoreticalphysics in the Soviet Union. Three years later,he became head physicist at the Kharkov GorkyState University and began collaboration withE. M. Lifshits on classic texts on theoreticalphysics. Studying under Landau was no smallachievement: to be accepted a student had tomaster what Landau called “the theoretical

minimum,” which meant basic knowledge of allfields of theoretical physics.

In 1937, Landau left Kharkov for Moscow tobecome head of the Theory Division of PYOTR

LEONIDOVICH KAPITSA’s Institute of PhysicalProblems and teach at Moscow University. Thatyear he married K. T. Drobanzeva, with whomhe would have a son, Igor, who would become anexperimental physicist. The late 1930s, how-ever, was the height of the Stalinist purges,known as the Terror, and Landau soon becameone of its victims. Swept up in the dragnet ofrandom, groundless arrests, in April 1938, hewas taken into custody and convicted of being a“German spy.” After a year in prison, he was seri-ously ill, and Kapitsa, whose work on behalf ofSoviet physics was much valued by Stalin, was

Landau, Lev Davidovich 173

Lev Davidovich Landau was a Russian physicistwhose discoveries influenced all branches oftheoretical physics, from fluid mechanics to quantumfield theory. (AIP Emilio Segrè Visual Archives,Physics Today Collection)

determined to save him. He handed the dictatora desperate ultimatum, saying that he, Kapitsa,would resign all his posts if Landau was notreleased immediately. Kapitsa won his gambleand Stalin assented. Although Landau wouldlater be honored as a Hero of Socialist Labor, hisyouthful devotion to Communism did not sur-vive this episode.

After Kapitsa’s discovery, in 1938, of thesuperfluidity of liquid helium II, Landau beganresearch that would lead him to a complete theoryof the “quantum liquids” at temperatures nearabsolute zero. Helium gas had previously been liq-uefied by cooling to about 4 K above absolute zero.However, subsequent experiments by Kapitsa indi-cated that when cooled another 2 K, liquid heliumwas transformed into a new state, called liquidhelium II, whose high thermal conductivityallowed it to flow without friction through veryfine capillaries and slits that almost completelyprevent the flow of all other liquids. Kapitsainvented the term superfluid to describe the physi-cal flow properties of liquid helium II. On the basisof these experiments Landau set out to explainsuperfluidity in terms not of single atoms, but ofthe quantized states of motion of the whole liquid.He began by looking at the fluid in its ground stateof absolute zero temperature. He theoreticallydescribed the excited states of the superfluid interms of quantum states that he called quasi parti-cles. He then used Kapitsa’s experimental resultsto deduce the quantum mechanical properties ofthe quasi particles. Landau’s theory, from whichthe properties of the superfluid could be calcu-lated, was later confirmed in 1957 by studies of thescattering of neutrons in liquid helium II andearned him the Nobel Prize in physics in 1962.

His papers of 1941–1947 are devoted to thetheory of the quantum liquids of the Bose type,to which the superfluid liquid helium (the usualisotope 4He) belongs. Between 1956 and 1958,he formulated the theory of the quantum liquidsof the Fermi type, among which liquid helium orisotope 3He belongs.

In 1962, the year he won the Nobel Prize,Landau was in a car accident that left himunconscious for six weeks. Several times doctorsdeclared him clinically dead. Although he didregain consciousness and lived for another sixyears, he was never again capable of creativework. He died in Moscow on April 1, 1968.

Landau is famous for the major discoverieshe made in low-temperature, atomic, nuclear,and plasma physics. He will always be remem-bered for his uncanny ability to see to the core ofa physical problem with a unique physical intu-ition that he was able to apply to almost all areasof theoretical physics.

Further ReadingAdronikashvili, Elevter. Reflections on Liquid Helium.

Melville, N.Y.: American Institute of Physics,1998.

Khalatnikov, I. M., ed. Landau, the Physicist and theMan: Recollections of L. D. Landau. Oxford:Oxford University Press, 1989.

Livanova, Anna Mikhailovna. Landau: A GreatPhysicist and Teacher. Oxford: Oxford UniversityPress, 1980.

� Landé, Alfred(1888–1976)German/AmericanTheoretical Physicist, QuantumTheorist

Alfred Landé was a theoretical physicist bestknown for discovering the g-formula, whichrelates the ratio of the magnetic moment of anatom to the angular momentum of the electriccurrent loops that generate it. This fundamentaldiscovery enabled physicists to determine thefine as well as the superfine structure of the opti-cal and X-ray spectra of atomic systems.

Landé was born on December 18, 1888, inElberfeld, in the Rhine region of Germany.Landé’s father served as deputy head of the

174 Landé, Alfred

provincial government in Duesseldorf for a time.The family was a cultured one, imbuing himwith a deep love of music. His early fascinationwith science encompassed cosmology, the studyof crystals and minerals, chemistry, and electric-ity. His superiority in mathematics and physicsled his high school teachers to consider himsomething of a prodigy. He studied at the Uni-versities of Marburg and Göttingen, where hebecame an assistant to the great mathematicianDavid Hilbert. He went on to earn his Ph.D. atthe University of Munich in 1914, workingunder ARNOLD JOHANNES WILHELM SOMMER-FELD, an influential and revered member of thecommunity of European-born physicists whoproduced the quantum revolution in the firstthird of the 20th century. Unlike Sommerfeldand other visionary physicists, who regarded thenew quantum theory and its wave–particle dual-ity as a radical paradigm shift, however, Landétried to understand the quantum mystery as agap in classical mechanics.

When World War I began, Landé enlistedfor service with the Red Cross and worked in ahospital for a few years. Later MAX BORN, one ofthe pioneers of quantum mechanics, managedto have him transferred to one of the few scien-tific sections of the army, a weapons develop-ment center in Berlin, where he worked underBorn on sound detection methods. The twophysicists did not confine their collaborationto war-related research, but moved into theabstract domain of the new quantum theory.Together they reached the conclusion thatNIELS HENRIK DAVID BOHR’s 1913 quantummechanical model of the atom, which was lim-ited to electron orbits moving in the same plane(in analogy to the solar system), was inade-quate, since they found evidence that the elec-tron orbits must be inclined toward each other.They published a paper stating these results,which were experimentally justified in 1918,arousing widespread interest and controversy inthe physics community.

The following year Landé became a lecturerat the University of Frankfurt, where he wouldremain until 1922. This would be one of themost important periods of his scientific life. Hevisited Bohr at his institute in Copenhagen todiscuss the Zeeman effect, the splitting of spec-tral lines in an intense magnetic field, whichhad been discovered by PIETER ZEEMAN, in1897. He was able to pursue this issue further,when, in 1922, he was appointed associate pro-fessor of theoretical physics at the University ofTübingen, then the most renowned center foratomic spectroscopy in Germany. That year hemarried Elisabeth Grünewald, with whom hewould have two sons, Arnold and Carl.

In 1923, Landé became famous for publishinga formula (known as the g-formula) expressing afactor known as the Landé splitting factor as afunction of the quantum numbers of the station-ary state of the atom. The Landé splitting factordetermined the ratio of the magnetic moment ofan atom to its intrinsic angular momentum, mea-sured in quantum units of Bohr magnetons, whichequals eh/4πmc, where e is the charge on an elec-tron, h is the Planck constant, m is the electronrest mass, and c is the speed of light. On the basisof this fundamental discovery physicists were ableto determine the fine and superfine structures ofthe optical and X-ray spectra of atomic systems.Landé went on to collaborate with Louis Paschenand others to analyze in great detail the fine struc-ture of the line spectra and the further splitting ofthe lines under the action of magnetic fields ofincreasing strength. He formulated the lawsobeyed by the frequencies and intensities of thelines in terms of the sets of spectroscopic quantumnumbers, which could take on either integral orhalf-integral values.

As the Nazi regime was rising to power in1931, Landé, who had visited Columbus, Ohio,in 1929 and 1930, left Germany for the UnitedStates and became a professor of theoreticalphysics at Columbus State University. Heremained there for the rest of his life. His son

Landé, Alfred 175

Arnold became a surgeon in Minneapolis, andhis son Carl became a professor of politics at theUniversity of Kansas.

Despite his many significant contributionsto the quantum theory of atomic structure, tothe very end of his career Landé remainedopposed to the wave–particle duality interpreta-tion of quantum mechanics. In support of thisconservative point of view he claimed

Today, after endless repetition, a dualnature of matter may seem as obviousand indisputable to the experts as theimmobility of the earth seemed toGalileo’s learned colleagues who refusedto look through his telescope because itmight make them dizzy.

He died in October 1976 in Columbus, Ohio.See also AMPÈRE, ANDRÉ-MARIE; BROGLIE,

LOUIS-VICTOR PIERRE, PRINCE DE.

Further ReadingBorn, Max. Atomic Physics. 8th Ed. New York: Dover

Books, 1989, pp. 161–164.Herzberg, Gerhard. Atomic Spectra and Atomic Struc-

ture. New York: Dover, 1944.

� Langevin, Paul(1872–1946)FrenchTheoretician, Experimentalist(Acoustics, Condensed Matter),Mathematical Physicist

Paul Langevin, the foremost mathematicalphysicist of his time in France, is most renownedfor his invention of a method for generatingultrasonic waves. Langevin’s invention becamethe basis of modern techniques of sonar: amethod of finding the range and bearing of anobject (target) by transmitting high-frequencysounds and detecting their echoes on their

return. He also performed important work onparamagnetic and diamagnetic forces.

Langevin was born in Paris on January 23,1872. He attended the École Lavoisier and theÉcole de Physiques et de Chimie Industrielles,where Pierre Curie was his laboratory supervisor.He entered the Sorbonne in 1891, and took aone-year leave, in 1893, to serve in the military. In1894, he entered the École Normale Superieure,where he studied under JEAN-BAPTISTE PERRIN. In1897, he won an award that allowed him to spenda year at the Cavendish Laboratory in Cambridge,England, then under the direction of the greatatomic physicist ERNEST RUTHERFORD; there heworked under JOSEPH JOHN (J. J.) THOMSON, thediscoverer of the electron.

Langevin received a Ph.D., in 1902, forwork on gaseous ionization done partly at Cam-bridge and partly under Pierre Curie. In Paris, hespent a lot of time in Perrin’s lab and was sweptup in the excitement of the early years of thestudy of radioactivity and ionizing radiation. Hejoined the faculty of the Collège de France in1902 and, two years later, was made professor ofphysics. He remained there until 1909, when theSorbonne offered him a similar position.

Langevin’s early work at the Cavendish andthe Sorbonne on the analysis of secondary emis-sion of X rays from metals exposed to radiationresulted in his discovery of secondary electronsfrom irradiated metals. He was also interested inthe dynamics of ionized gases, particularly themobility of positive and negative ions; in 1903,he published a theory for their recombination atdifferent pressures.

In 1905, ALBERT EINSTEIN published hisgroundbreaking paper on special relativity.Langevin would become deeply interested in Ein-stein’s work on space and time and a firm believerin the theory of the equivalence of mass andenergy. However, it was another paper Einsteinpublished that year, on Brownian motion, theincessant random movement of microscopic par-ticles in a liquid, that would influence Langevin’s

176 Langevin, Paul

own seminal work on paramagnetic (weak attrac-tive) and diamagnetic (weak repulsive) phenom-ena in gases. In 1895, Pierre Curie had shownexperimentally that the susceptibility of a param-agnetic substance to an external magnetic fieldvaries inversely with temperature. Ten years later,in 1905, when Langevin produced a model basedon statistical mechanics to explain this phe-nomenon, he was influenced by Einstein’s pro-posal that Brownian motion was due toimbalances in the forces on a particle resultingfrom molecular impacts from the liquid. Einstein’sexplanation led Langevin to hypothesize thatwhen an externally applied magnetic field wasabsent, the alignment of molecular moments in aparamagnetic substance would be random; con-versely, when such a field was present, the align-ment would be nonrandom. The greater thetemperature, however, the greater the thermalmotion of the molecules, and thus the greater thedisturbance to their alignment by the magneticfield. This theory was extremely useful in describ-ing molecular fluctuations in other systems,including in nonequilibrium thermodynamics.

Langevin went on to propose that the mag-netic properties of a substance are determined bythe valence electrons, the specific orbital elec-trons that atomic elements have available toshare when forming into molecular compounds.Langevin extended his description of magnetismin terms of electron theory to account for dia-magnetism. He showed how a magnetic fieldwould affect the motion of electrons in themolecules to produce a moment that is opposedto the field. This enabled predictions to be madeconcerning the temperature-independence ofthis phenomenon and allowed estimates to bemade of the size of electron orbits.

In 1911, Langevin, whose work had beeninstrumental in verifying Einstein’s atomic theo-ries, published one of the earliest popularaccounts of relativity, L’evolution de l’espace et dutemps (The evolution of space and time). His sci-entific career was flourishing, but his personal

life was in disarray. Unhappily married and thefather of four children, he became romanticallyinvolved with MARIE CURIE, who had been wid-owed in 1906, when Pierre Curie was run overand killed by a carriage in the street. Langevin’swife, Jeanne, arranged for their love letters to bepilfered and published in the French press. Scan-dal broke out on the eve of the First Solvay Con-ference in Brussels, which both physicists wereattending, nearly overwhelming the burningissues of the new quantum mechanics the con-ference was called to address. Although his affairwith Curie did not last, Langevin obtained adivorce. Later, in 1921, he would become amember of the Solvay International PhysicsInstitute and, in 1928, be elected its president.

Pan-European scientific gatherings such asthe Solvay Conference were interrupted withthe outbreak of World War I, in 1914. But thewar years, when he worked on military tech-nologies, led Langevin to his seminal discoverieson piezoelectricity, the electric current producedby some crystals and ceramic materials whenthey are subjected to mechanical pressure.Building on the research of other physicists,which showed that the reflection of ultrasonicwaves from objects could be used to locate them,he developed an improved technique for accu-rate detection and location of submarines. Histechnique was based on the use of high-fre-quency radio circuitry to oscillate piezoelectriccrystals and thus obtain ultrasonic waves at highintensity. Within a few years, this approach ledhim to a practical system for the echolocation ofsubmarines, which became the basis of modernsonar and is used for scientific as well as militarypurposes. In 1917, he pioneered the use of thepiezoelectric effect, that is, the generation of asmall potential difference across certain materi-als when they are subjected to a stress, as well asvacuum tube amplifiers in underwater soundingequipment, the first use of electronics in thisway. In 1918, this new technology enabled himto receive echoes from a submarine as deep as1800 meters. This work continued after the war,

Langevin, Paul 177

leading to the development of sonar transducers,circuits, systems, and materials.

In 1940, after the German occupation ofFrance, Langevin became director of the ÉcoleMunicipale de Physique et de Chimie Indus-trielle, where he had been teaching in 1902.However, the Nazis soon arrested him for his out-spoken antifascist views. He was first imprisonedin Fresnes and later placed under house arrest inTroyes. After the execution of his son-in-law anddeportation of his daughter to Auschwitz (whichshe survived), he was forced to escape to Switzer-land in 1944. Langevin returned to Paris laterthat year and resumed his directorship of his oldschool. He died soon after in Paris on December19, 1946. The Institute Max von Laue–PaulLangevin was established in Grenoble, France, in1967, in honor of him and German physicist MAX

THEODOR FELIX VON LAUE, as a symbol of postwarcooperation between France and Germany.

Langevin’s genius as a theoretical physicistwas recognized by Einstein, who wrote thatLangevin had all the tools for the developmentof the special theory of relativity at his disposal,and that if he had not proposed the theory him-self, Langevin would have done so. Equally tal-ented as an experimentalist, Langevin, throughhis research on the piezoelectric effect, initiatedthe modern ultrasonic era.

Further ReadingGraff, K. F. “A History of Ultrasonics,” in Warren

Mason, ed. Physical Acoustics. Vol. 1. New York:Academic Press, 1981.

� Laue, Max Theodor Felix von(1879–1960)GermanTheoretician (Electromagnetism),Relativist, Solid State Physicist

Max von Laue was a brilliant theoretician whoplayed an important role in several crucial

developments in the early part of the 20th cen-tury. One of ALBERT EINSTEIN’s earliest follow-ers, he produced evidence strengthening thetheory of relativity, thereby hastening its accep-tance. In 1912, through his discovery of X-raydiffraction in crystals, he simultaneously revealedthe nature of X rays and crystals and laid thefoundations of X-ray crystallography. This work,described by Einstein as one of the most beauti-ful discoveries in physics, won him the 1914Nobel Prize in physics.

He was born in Pfaffendorf, near Koblenz,on October 9, 1879, to Julius and WilhelmineLaue. His father was an official in the Germanmilitary administration, who was raised to therank of the hereditary nobility in 1913, thusbecoming “von Laue.” The nature of his father’swork led Max to spend his childhood movingbetween a number of German towns, includingStrasbourg. He studied briefly at the Universityof Strasbourg, before transferring to the Univer-sity of Göttingen, where he specialized in theo-retical physics. He spent a semester at theUniversity of Munich and, in 1902, continuedhis studies at the University of Berlin. There,working under the founder of quantum theory,MAX ERNEST LUDWIG PLANCK, he earned hisPh.D. the following year for a dissertation onlight interference phenomena between plane-parallel plates. He then returned to Göttingen,where he spent two years studying art and earneda teaching certificate in 1905.

That year Laue became an assistant toPlanck at the Institute of Theoretical Physics inBerlin, where the two physicists began whatwould be a long, productive collaboration. Dur-ing his four years in Berlin, Laue qualified asa lecturer. He worked on the application ofentropy to radiation fields and on the thermody-namic significance of the coherence of lightwaves. Inspired by Planck’s relativity seminar, hebegan writing to Einstein, with whom he devel-oped a close friendship. When, in 1906, he vis-ited him at his patent office in Bern, Laue

178 Laue, Max Theodor Felix von

emerged feeling he had met the “revolutionary”who had “overturned all of mechanics and elec-trodynamics.” He developed a proof for Ein-stein’s special theory of relativity based onoptics. His proof used ARMAND HIPPOLYTE LOUIS

FIZEAU’s 1851 experimental verification of a the-ory developed earlier by AUGUSTIN JEAN FRES-NEL that hypothesized that the speed of light isaffected by the motion of water. This theoryseemed to be at odds with the prime assertion ofspecial relativity, that is, that the speed of light isa constant independent of the motion of theobserver. However, Laue showed that Fresnel’stheory could be derived in a manner consistentwith special relativity. In this way, Fizeau’sexperiment provided confirmation of relativity,contributing greatly to its rapid acceptance. Inaddition, Laue published the first monograph onEinstein’s special theory of relativity, which hewould expand in 1919 to include the generaltheory of relativity; both monographs werereprinted several times.

In 1909, Laue became a lecturer at the Insti-tute of Theoretical Physics at the Universityof Munich, then under the direction of therenowned ARNOLD JOHANNES WILHELM SOM-MERFELD; in the following year he married Mag-dalena Degen, with whom he would have twochildren. In Munich, Laue began his research onthe nature of X rays, which were only vaguelyunderstood at the time. X rays were thought to beextremely short electromagnetic waves. Becauseof their short wavelengths, the problem physi-cists confronted in measuring them was that nograting sufficiently fine to diffract them could beartificially produced. Laue found his measuringinstrument in nature. He hypothesized that crys-tals, known to consist of orderly arrays of atoms,could be used as superfine gratings, providing amedium in which X rays would form some kind ofdiffraction or interference pattern.

In the spring of 1912, when he had movedto the University of Zurich, Laue’s proposal wastested by Sommerfeld’s graduate students. They

bombarded copper sulfate crystals with X raysand produced a photographic plate with a darkcentral patch representing X rays that had pene-trated straight through the crystal surrounded bya multilayered halo of regularly spaced spots rep-resenting diffracted X rays. The results wereannounced to the Bavarian Academy of Scienceless than two weeks later along with Laue’smathematical formulation, the “theory ofdiffraction in a three-dimensional grating.” Thedemonstration of the nature of crystal structureand of X rays by the same experiment was widelyacclaimed and promptly led to Laue’s selectionas the 1914 Nobel laureate in physics.

His fame established, Laue was offered andaccepted a full professorship at the University ofFrankfurt. By this time, however, Europe was inthe grip of World War I; from 1916 on, Laueworked at the University of Würzburg, develop-ing communication equipment for the Germanarmy. When hostilities ceased, he exchangedteaching positions with MAX BORN and becameprofessor of theoretical physics at the Univer-sity of Berlin, where he expanded his originaltheory of X-ray diffraction. Laue had initiallyconsidered only the interaction between theatoms in the crystal and the radiation waves,but he now included a correction for the forcesacting between the atoms. This correctionaccounted for the slight deviations that hadalready been noticed. Although Laue did notparticipate directly in the development of quan-tum theory, he did incorporate the discovery ofelectron wave particle interference into hisdiffraction theory.

In 1914, the Kaiser-Wilhelm Institute ofPhysics in Dahlem, a suburb of Berlin, had beenfounded with Einstein as first director. Lauenow became second in charge, dealing withmost of the administrative work of the institute,particularly its financing. In this way he had astrong influence on the direction of Germanphysics in the 1920s and early 1930s, advancingimportant discoveries in theoretical physics.

Laue, Max Theodor Felix von 179

Laue’s eminence in the scientific community ofGermany was recognized in 1932, when he wasawarded the Max Planck Medal by the GermanPhysical Society.

However, in 1933, the rise of Hitler andthe resulting persecution of Jewish scientistssuch as Einstein became intolerable to Laue. Byvirtue of his protest he lost his influence withinGermany’s scientific establishment. In 1943, heresigned in protest from his position as profes-sor at University of Berlin. When Berlin wasbombed in 1944, he moved to Hechingen,along with the Kaiser Wilhelm Institute. Whenthe Allies invaded Germany, his acts of civiccourage and refusal to participate in the devel-opment of a German atomic bomb did notexempt him from internment in England, alongwith nine other German atomic physicists.During this dark period, he continued hisresearch and wrote a history of physics, whichwas translated into many languages and hadseveral editions.

In 1946, Laue returned to Germany andhelped rebuild German science, becoming act-ing director of the Max Planck Institute in Göt-tingen and professor at the university there. Healso did some important work on the effect ofmagnetic fields on superconductivity, publishing12 papers and a book on the subject between1937 and 1947. In 1951, he became director ofthe Fritz Haber Institute for Physical Chemistryin Berlin, where he focused on research on X-rayoptics. In 1958, he retired but continued hisresearch. At the age of 80, he died on April 23,1960, of injuries sustained in a car accident,when he collided with an inexperienced motor-cyclist on the way to his Berlin laboratory.

A deeply religious man, esteemed by his col-leagues for both his intellect and his moralintegrity, he exerted a strong, positive influenceon German physicists during the catastrophicyears of World War II and its aftermath. TheInstitute Max von Laue–Paul Langevin wasestablished in Grenoble, France, in 1967, in

honor of him and the French physicist PAUL

LANGEVIN, as a symbol of postwar cooperationbetween France and Germany.

The reverberations of Laue’s discovery thatX rays were waves of light that obeyed Maxwell’sequations were felt in physics, chemistry, andbiology. His work gave rise to two entirely newbranches of science: X-ray crystallography,which led to the determination of the structureof (DNA), and X-ray spectroscopy, which led toexact measurement of the wavelength of X raysand to advances in atomic theory.

See also MAXWELL, JAMES CLERK; RÖNTGEN,WILHELM CONRAD.

Further ReadingHammond, Christopher. The Basics of Crystallography

and Diffraction. Oxford: Oxford University Press,2001.

Mendelssohn, Kurt. The World of Walther Nernst: TheRise and Fall of German Science, 1864–1941.Pittsburgh: University of Pittsburgh Press, 1973.

� Lederman, Leon M.(1922– )AmericanExperimentalist, Particle Physicist

Leon M. Lederman shared the 1988 Nobel Prizein physics with Melvin Schwartz and Jack Stein-berger for the invention of the neutrino beammethod and the demonstration of the doubletstructure of the electron and of the muon (bothnow known as leptons). They arrived at this dis-covery by observing that the weak interactiondecay processes associated with electrons andmuons involved electron neutrinos and muonneutrinos, respectively.

He was born on July 15, 1922, in New YorkCity, the son of Jewish immigrants. His father,Morris Lederman, who earned his living by oper-ating a hand laundry, had a profound respect foreducation. Leon would later trace the beginning

180 Lederman, Leon M.

of his passion for science to the reading of sci-ence books:

I got hold of a book in big print that waswritten by Einstein in the 1930s, whichpresented science as a detective story.And I loved that presentation.

Lederman attended Manhattan publicschools, where he was inspired by “absolutelymagnificent teachers.” He entered the City Col-lege of New York as a chemistry major, but, by thetime he graduated in 1943 with a degree in chem-istry, he had lost his enthusiasm for the subject,“because of all the smells, that was one thing,”and found physics to be “simpler somehow,cleaner.” With the country embroiled in WorldWar II, he was obliged to put off further studies.For the next three years, he served in the UnitedStates Army, rising to the rank of second lieu-tenant in the Signal Corps. On discharge, heentered Columbia University’s graduate programin physics, headed by ISIDOR ISAAC RABI, theinventor of the technique of nuclear magneticresonance. In 1948, Lederman began workingwith Eugene T. Booth, director of Columbia’s pro-ject to construct a 385-million-electron-volt(Mev) synchrocyclotron (a device for accelerat-ing particles to high energies) at its Nevis Labora-tory. Lederman’s thesis assignment was to build aWilson cloud chamber, the first instrument todetect the tracks of atomic particles. He wasawarded the Ph.D. in 1951 for this work andasked to stay on at Columbia, which remained hisacademic home for the next 28 years. During thistime he directed the work of 50 Ph.D. candidates.

In 1958, after being promoted to full profes-sor, Lederman took his first sabbatical at the Euro-pean Center for Nuclear Research (CERN),where he organized a group to do the “g-2” exper-iment, designed to measure the anomalous mag-netic moment of elementary particles. He wouldcontinue to participate in CERN collaborationsthrough the 1970s. Between 1961 and 1978, he

was director of the Nevis Lab. In 1979, he becamedirector of the Fermi National Accelerator Labo-ratory, where he supervised the construction andutilization of the first superconducting syn-chrotron, which became the highest-energyaccelerator in the world at that time. Althoughhe was a guest scientist at many laboratories, mostof his important research was done at Nevis,Brookhaven National Accelerator Laboratory onLong Island, New York, CERN, and Fermilab.

Lederman’s Nobel Prize–winning work wascarried out in the early 1960s. The experimentwas planned when Lederman, Melvin Schwartz,and Jack Steinberger were associated withColumbia University and was carried out with thealternating gradient synchrotron at Brookhaven.The work led to discoveries that opened entirelynew opportunities for research into the innermoststructure and dynamics of matter. It removed twobig obstacles to research into the weak forces (1)by inventing an experimental method for thestudy of weak forces at high energies and (2) bydiscovering that the weak interaction of radioac-tive decay is associated with at least two kindsof neutrinos. One neutrino belongs with theelectron, the other neutrino with the muon (arelatively heavy charged elementary particle, dis-covered in cosmic radiation in the late 1930s byCARL DAVID ANDERSON). The current elemen-tary particle theory of electroweak interactions,which uses a doublet grouping of electron withelectron neutrino and muon with muon neutrino,has its roots in this discovery.

Neutrinos are elementary particles with nocharge and zero or almost zero rest mass. They areghostlike particles, which undergo only weakinteractions. Classified as leptons with the elec-tron and the muon, they are fermions with spin1/2. In 1927 the electron neutrino’s existence waspostulated by WOLFGANG PAULI. Lederman andhis colleagues transformed the ghostly neutrinointo an active research tool by inventing amethod that generated a beam of high-energyneutrinos from the interactions occurring in

Lederman, Leon M. 181

high-energy proton particle accelerators. Usingthis method, they found that neutrino beamscould reveal the hard inner structure of nucleons.

At Columbia, where TSUNG-DAO LEE andCHEN NING YANG had discovered that the law ofparity was violated in the weak interactions, theproblem Lederman’s group addressed was devel-oping a feasible method of studying the effect ofweak forces at high energies. Previously, it hadbeen possible to study only low-energy sponta-neous processes of radioactive decay. Hence,beams of electrons, protons, and neutrons hadproved unusable. Schwartz proposed using abeam of neutrinos, and for the next two yearsthe three collaborators worked on creating a suf-ficiently intense beam of high-energy neutrinosfree of all other particles, as well as on designinga detector for measuring high-energy neutrinoreactions. Their method was to generate a high-energy muon neutrino beam as the by-product ofthe decay processes associated with high-energyproton collisions and let these muon neutrinosinteract with matter. If the muon neutrinos werethe same as electron neutrinos, then equal num-bers of electrons and muons would be generatedby these neutrino interactions. What theyfound, however, was that their high-energy neu-trino beam created only muons. This resultproved that the weak interaction of radioactivedecay is associated with at least two kinds ofneutrinos, an electron neutrino at low energiesand a muon neutrino at high energies.

Lederman’s first wife was Florence Gordon,with whom he had three children. He is nowmarried to Ellen Lederman. After retiring fromFermilab in 1989, he became professor of physicsat the University of Chicago. That year he wasappointed science adviser to the governor ofIllinois. He helped organize the Teachers’Academy for Mathematics and Science, designedto bolster the skills of teachers in the Chicagopublic schools. He helped found and is on theboard of trustees of the Illinois Mathematics andScience Academy, a residential public school for

gifted children. In 1991, he became president ofthe American Association for the Advancementof Science. Lederman has also developed collab-orations with Latin American scientists and beena crusader for science education for gifted chil-dren as well as for public understanding of sci-ence. He has served on the boards of directors ofseveral museums, schools, science organizations,and government agencies.

Lederman’s invention of the high-energyneutrino beam method, which led to the discov-ery that electrons and muons have their ownneutrinos, laid the experimental foundation fortheoretical development of the unified theory ofelectroweak interactions. This theory laterbecame important for quark research thatyielded a deeper understanding of the strongnuclear interactions.

In his later years, Lederman, in his charac-teristically witty, incisive manner, expressed hisview of the way science works:

You get to be a part of the establishmentby blowing it up. . . . Because every timeyou destroy the established dogma . . .the accepted body of knowledge, you aregoing to get something better to take itsplace. . . . Although nobody likes his owntheory to be overturned . . . at some pointdeep down inside the scientist will creepin and say, gee, but this gives the possi-bility of a different theory, which mighteven be better.

See also GELL-MANN, MURRAY; GLASHOW,SHELDON LEE; SALAM, ABDUS; WEINBERG,STEVEN.

Further ReadingLederman, Leon M., and David N. Schramm. From

Quarks to the Cosmos: Tools of Discovery. NewYork: W. H. Freeman, 1995.

Lederman, Leon M., and Dick Teresi. The God Parti-cle: If the Universe Is the Answer, What Is theQuestion? New York: Houghton Mifflin, 1993.

182 Lederman, Leon M.

� Lee, Tsung-Dao(1926– )Chinese/AmericanTheoretical Physicist, Particle Physicist

Tsung-Dao Lee is a world-renowned theoreti-cian who, together with CHEN NING YANG, pre-dicted that conservation of parity is violated inthe weak interactions of the atomic nucleus.Their discovery led to significant developmentsin particle theory and won them the 1957 NobelPrize in physics. Only 31 years of age at the time,Lee became the second youngest physicist to beawarded the Nobel Prize.

Lee was born on November 24, 1926, inShanghai, China, the third of six children bornto Tsing Kong Lee, a businessman, and MingChang Chang. He attended the Kiangsi MiddleSchool in Kanchow, Kiangsi, graduated in 1943,and entered the National Chekiang Universityin Kweichow province. When the Japaneseinvasion forced him to flee to Kunming, Yunan,he enrolled at the National Southwest Univer-sity, where he met his future collaborator, Yang.

Lee entered the United States, in 1946, on ascholarship from the Chinese government.Although he had never formally earned anundergraduate degree, he enrolled in graduatestudies in physics at the University of Chicago,where his friend Yang was also enrolled. Heearned a Ph.D. in 1950, working under the emi-nent Indian-born astrophysicist SUBRAMANYAN

CHANDRASEKHAR, for his dissertation “Hydro-gen Content of White Dwarf Stars.” That year hemarried (Jeanette) Hui Chung Chin, a formeruniversity student, with whom he would havetwo sons, James and Stephen. After spending afew months as a research associate at YerkesAstronomical Observatory, in Lake Geneva,Wisconsin, from 1950 to 1951, he was a researchassociate and lecturer at the University of Cali-fornia in Berkeley. He then accepted a fellowshipto the Institute of Advanced Study in Princetonand became a member of the staff. He was

appointed assistant professor of physics atColumbia University in 1953, promoted to asso-ciate professor in 1955 and to professor in 1956(at age 29, he was then the youngest professor onthe faculty). By this time Lee had a substantialreputation, for his work in statistical mechanicsand in nuclear and atomic physics.

In June 1956, Yang collaborated with Leeon a paper that raised the question of whetherparity, the assumption that nature makes no dis-tinction between left and right, is conserved inweak interactions. At the time physicists uni-versally believed that physical reactions wouldbe the same (i.e., have parity, or equality)whether the particles involved in them had aright-handed or a left-handed spin (i.e., thequantized rotation property). If the physicalprocess proceeds in exactly the same way whenreferred to an inverted coordinate system, thenparity is said to be conserved. If, on the con-trary, the process has definite left- or right-handedness, then parity is not conserved in thatphysical process. This law of conservation ofparity was explicitly formulated in the early1930s by the Hungarian-born physicist EUGENE

PAUL WIGNER and became a component ofquantum mechanics.

The strong forces that hold atoms togetherand the electromagnetic forces that are responsi-ble for chemical reactions obey the law of parityconservation. Since these are the dominant forcesin most physical processes, physicists assumed thatparity conservation was an inviolable natural law.In the early 1950s, applying the principle of con-servation of parity to individual subatomic parti-cles and their interactions had proved highlysuccessful in accounting for the behavior of thoseparticles. By the end of 1955, however, a puzzlingcontradiction between the parity principle andthe other principles employed to order the ever-growing number of subatomic particles hademerged. In particular, questions were raised byresults beginning to pour forth from the manyhigh-energy accelerators built in the United

Lee, Tsung-Dao 183

States after World War II, indicating that oneform of radioactive decay appeared to violate theconservation of parity law. One of the newly dis-covered mesons—the so-called K meson—seemedto exhibit decay modes into configurations withdiffering parity. Exploring this paradox from everyconceivable perspective, Lee and Yang discoveredthat contrary to what had been assumed, there wasno experimental evidence against parity noncon-servation in the weak interactions. The experi-ments that had been done, it turned out, were notrelevant to the question. In their landmark 1956Physical Review paper, “Question of Parity Conser-vation in Weak Interactions,” Lee and Yang made

the startling proposal that the universally acceptedconservation of parity law might not hold true inweak nuclear interactions, which include radioac-tive decay.

Their suggestions for experiments capable ofdeciding the issue were immediately taken up byCHIEN-SHIUNG WU at the cryogenic laboratoryof the National Bureau of Standards in Wash-ington, D.C. Testing radioactive cobalt atoms attemperatures approaching absolute zero, Wufound the evidence Lee and Yang were lookingfor: the law of parity did not apply to weak inter-actions. Shortly after her announcement in Jan-uary 1957, other experimentalists confirmed herresults. In the wake of this paradigm revolutiongenerated by the three Chinese American physi-cists, Lee and Yang were awarded the NobelPrize in physics that very year.

In 1960, Lee became professor of physics atthe Institute of Advanced Study, Princeton; hereturned to Columbia in 1963 to assume the firstEnrico Fermi Professorship in physics. Since1964 he has also made significant contributionsto the explanation of the violations of time-reversal invariance that occur during certainweak interactions.

As did Yang, Lee became deeply involvedin the development of Chinese science, andspecifically its integration into world science.Working together with the Chinese Academyof Sciences, he founded the China Center ofAdvanced Science and Technology World Lab-oratory in 1989. Since then he has traveled toChina every year to participate in internationalacademic exchanges.

Through his brilliant insights, Lee has madeinvaluable contributions to the modern formula-tion of symmetry principles in particle physics.The renowned American physicist J. ROBERT

OPPENHEIMER described Lee’s work as character-ized by “a remarkable freshness, versatility, andstyle.” As a 77-year-old professor at ColumbiaUniversity, Lee summarized his relationship tohis work in a statement of moving simplicity:

184 Lee, Tsung-Dao

Tsung-Dao Lee together with Chen Ning Yang predictedthat conservation of parity is violated in the weakinteractions of the atomic nucleus. Only 31 years ofage at the time, Lee became the second youngestphysicist to be awarded the Nobel Prize. (AIP MeggarsGallery of Nobel Laureates)

To me, scientific research is as important asbreathing, and it equals my life.

Further ReadingBernstein, Jeremy. A Comprehensible World: On Mod-

ern Science and Its Origins. New York: RandomHouse, 1967.

Boorse, H. A., and L. Motz, eds. The World of theAtom. New York: Basic Books, 1966.

� Lenard, Philipp von(1862–1947)Hungarian/GermanExperimental and Theoretical Physicist,Atomic Physicist

Philipp von Lenard is most famous for developingan ingenious experiment involving a cathode raytube with a thin aluminum window that permit-ted the rays to be studied as they escaped into theopen air. The results of this research, which ledhim to conclude that the volume of an atom ismainly composed of empty space, contributed tothe conception of Rutherford’s planetary model ofthe atom and earned Lenard the 1905 Nobel Prizein physics. His pioneering work on the photoelec-tric effect was influential in ALBERT EINSTEIN’sformulation of the theory of light quanta.

He was born in Pressburg, Hungary (nowBratislava, Slovakia), on June 7, 1862. His fam-ily was originally from the Tyrol, and Lenard wasstrongly drawn to German culture. After brieflystudying at the University of Budapest, he wentto Germany, where he studied physics at theUniversity of Heidelberg under Robert Bunsen,the inventor of the Bunsen burner, and at theUniversity of Berlin under the eminent HER-MANN LUDWIG FERDINAND VON HELMHOLTZ. In1886, he received a Ph.D. from Heidelberg,where he remained for the next three years.

In 1891, Lenard became assistant to HEIN-RICH RUDOLF HERTZ, the discoverer of radiowaves, at the University of Bonn, where he did his

first original research in mechanics, on the oscilla-tion of precipitated water drops. He also workedon luminescence and phosphorescence. He thenbegan his work on cathode rays, the phenomenonthat produced a fluorescent glow when most of theair was pumped out of a glass tube with wiresembedded at either end and a high voltage wassent across it. At the time physicists were askingwhether cathode rays were charged particles orsome undefined wavelike process in the ether. In1892, after reading William Crookes’s 1879 paperon the movement of cathode rays inside dischargetubes, Lenard became interested in designing anexperiment that would allow cathode rays to beexamined outside discharge tubes. Hertz suggestedthat Lenard construct a cathode ray tube with athin sheet of aluminum serving as a window, nowcalled the Lenard window, to contain the vacuum,while releasing the cathode rays. Lenard experi-mented with windows made of aluminum foil ofvarying thickness and in 1894 published resultsthat revealed the amazing discovery that the cath-ode rays could move about 8 cm in the air afterpassing through the thin aluminum window. Inthis experiment he found that the cathode raysdecreased in number as the distance from the tubeincreased and was able to show that the ability ofa material to absorb cathode rays depends on itsdensity. The experimental finding that cathoderays were able to pass through the aluminum foilled him to the hypothesis that the volume that theatoms occupied in the metal consisted of a largeamount of empty space. This result proved crucialto JOSEPH JOHN (J. J.) THOMSON in his discoverythat cathode rays were really electrons: particlesthat had to have a mass much smaller than themass of any atom. Lenard had hoped to make thatdiscovery himself and was embittered whenThomson beat him to it. Subsequent experimentsby others measured the charge directly and con-firmed Lenard’s conclusions.

After his groundbreaking work on cathoderays, Lenard accepted an associate professorshipat the University of Breslau and in 1895 became

Lenard, Philipp von 185

professor of physics in Aachen. In 1896, hebecame professor of theoretical physics at Hei-delberg, and in 1898, he became professor ofexperimental physics at the University of Kiel.

In 1901, on the basis of his cathode rayexperiments, he concluded that the part of theatom where the mass was mostly concentratedconsisted of neutral doublets, or “dynamides,” ofnegative and positive electricity, which werevery small and separated by wide spaces and hada number equal to the atomic mass. On the basisof this idea he estimated that the solid matter inthe atom was about one billionth of the wholeatom. This work was influential in HENDRIK

ANTOON LORENTZ’s formulation of his theory ofelectrons and, 10 years later, in ERNEST RUTHER-FORD’s proposal of his planetary model of theatom, which incorporates this basic structure.

From 1902 onward, Lenard studied photo-electricity and worked on extending Hertz’sresearch on the photoelectric effect. In the latterexperiments he was able to show that negativeelectricity can be released from metals by expo-sure to ultraviolet light. He later found that thiselectricity was identical in properties to cathoderays (later known as electrons). He also was ableto show experimentally that the number of elec-trons projected is proportional to the energy car-ried by the incident light, whereas the electronspeed or kinetic energy varies inversely with thewavelength of the incident light while remainingindependent of its energy. However, it was Ein-stein who was able to explain the photoelectriceffect successfully, in 1905, using the quantumtheory rejected by Lenard, by postulating thatlight consists of particles of energy, which hecalled photons.

Lenard married Katharina Schlehner andbetween 1907 and 1931 settled in Heidelberg,as professor of experimental physics. In 1924,he became a dedicated follower of Hitler’sNational Socialist Party, which rewarded hiszeal by making him the “Chief of Aryan [orGerman] Physics.” He spent his later years

reviling Jewish scientists such as Einstein,whom he never forgave for discovering and giv-ing his name to the theory of light quanta,which explained Lenard’s results.

Antagonistic by nature, Lenard in his bookGreat Men of Science (1934) omitted such figuresas WILHELM CONRAD RÖNTGEN, who had used atube that Lenard had designed to discover X raysbut had failed to credit him. Lenard felt under-rated by the physics community, despite his NobelPrize and a great many lesser honors. He died inMesselhausen, Germany, on May 20, 1947.

Lenard left a mixed legacy to physics. Hemade substantial contributions to atomic physicsbut will also be remembered as one of the veryfew distinguished physicists to embrace Nazism.

See also MILLIKAN, ROBERT ANDREWS.

Further ReadingKeller, Peter. The Cathode Ray Tube: Technology, His-

tory, and Applications. New York: PalisadesBooks, 1992.

� Lenz, Heinrich Friedrich Emil(1804–1865)RussianTheoretical and Experimental Physicist(Classical Electromagnetism,Geophysics)

Heinrich Lenz was a Russian physicist whocontributed a significant chapter to the evolv-ing story of electromagnetism that physiciststhroughout Europe were piecing together inthe 1800s. The fundamental law that he dis-covered, which later became known as Lenz’slaw, revealed that the phenomenon of electro-magnetic induction, as described earlier byMICHAEL FARADAY, obeyed the law of conser-vation of energy.

Lenz was born in Dorpat, now Tartu, Esto-nia, on February 12, 1804. After completing hissecondary education at the age of 16, he

186 Lenz, Heinrich Friedrich Emil

entered the University of Dorpat, where hestudied chemistry and physics. In 1923, whilestill a student, he managed to obtain the post ofgeophysical scientist on Otto von Kotzebue’sthird expedition around the world. For the nextthree years he took advantage of this uniqueopportunity to investigate geophysical phe-nomena. He studied climatic conditions suchas barometric pressure, finding the areas ofmaximal and minimal pressure that exist in theTropics and determining the overall climaticpattern. He also made extremely accurate mea-surements of the salinity, temperature, and spe-cific gravity of seawater. He discovered areas ofmaximal salinity on both sides of the equator inthe Atlantic and Pacific Oceans and estab-lished the differences in salinity between theseoceans and the Indian Ocean. On a later expe-dition, to the Caucasus in southern Russia in1829, he studied the area’s natural resources,measured mountain heights, and measured thelevel of the Caspian Sea. No one would obtainobservations of the ocean more accurate thanLenz’s until the next century.

When he returned to Saint Petersburg, withhis expedition findings to his credit, Lenz wasadmitted to the prestigious Saint PetersburgAcademy of Science, on an apprentice level; by1834, he would rise to the status of full academi-cian. He began to study electromagnetism in1831, after Faraday and JOSEPH HENRY indepen-dently discovered electromagnetic induction.His first major discovery, published in 1833, wasthe famous Lenz’s law, which states that thedirection of a current that is induced by an elec-tromagnetic force always opposes the directionof the electromagnetic force that produces it.This occurs because a current induced by a mov-ing magnet or coil flows in such a direction thatit, in turn, induces a magnetic field that opposesthe motion of the magnet or coil inducing thecurrent.

Lenz described the dynamics of this processas follows: thrusting a pole of a permanent bar

magnet through a coil of wire induces an electriccurrent in the coil; the current in turn sets up amagnetic field around the coil, making it a mag-net. Lenz’s law indicates the direction of theinduced current. Because like magnetic polesrepel each other, when the north pole of the barmagnet approaches the coil, the induced currentflows in such a way as to make the side of the coilnearer the pole of the bar magnet itself a northpole to oppose the approaching bar magnet.When the bar magnet is withdrawn from thecoil, the induced current reverses itself, and thenear side of the coil becomes a south pole to pro-duce an attracting force on the receding barmagnet. A small amount of work, therefore, isdone in pushing the magnet into the coil and inpulling it out against the magnetic effect of theinduced current. The small amount of energyrepresented by this work manifests itself as aslight heating effect, the result of the inducedcurrent’s encountering resistance in the materialof the coil. Lenz’s law thus upholds the generalprinciple of the conservation of energy. If thecurrent were induced in the opposite direction,its action would spontaneously draw the barmagnet into the coil in addition to producingthe heating effect, thereby violating conserva-tion of energy.

In 1833, Lenz investigated the way electri-cal resistance of metals changes with tempera-ture and showed that an increase in temperatureincreased resistance. Around the same time, hestudied the heat generated by current flowing inmetals and discovered, independently of JAMES

PRESCOTT JOULE, the law now known as Joule’slaw, which describes the proportional relation-ship between the production of heat and thesquare of the current. In the context of theseexperiments, he worked on establishing the unitfor the measurement of resistance.

During the same period, he also worked onthe application of certain theoretical physicsprinciples to engineering design and on formula-tion of programs for geographical expeditions. In

Lenz, Heinrich Friedrich Emil 187

1836, he became a professor at Saint PetersburgUniversity and from 1840 to 1843 was dean ofmathematics and physics. He authored a numberof very successful books. Lenz died of a strokejust before his 61st birthday, while on vacationin Rome, on February 10, 1865.

Lenz’s law helped HERMANN LUDWIG FERDI-NAND VON HELMHOLZ formulate the law of con-servation of energy. It is applied today inelectrical machines such as generators and elec-tric motors.

Further ReadingKeithley, Joseph F. The Story of Electrical and Magnetic

Measurements: From Early Days to the Beginningsof the 20th Century. New York: Wiley-IEEE Press,1998.

� Lorentz, Hendrik Antoon(1853–1928)DutchTheoretical Physicist (ClassicalElectromagnetism, Optics), Relativist

Hendrik Lorentz extended JAMES CLERK MAX-WELL’s theory of electromagnetism by proposingthat since light is generated by oscillating elec-tric currents, the presence of a strong magneticfield would have an effect on the charged parti-cles that make up the oscillating currents.Specifically, it would result in a splitting ofspectral lines by causing the wavelengths of thelines to vary. In 1896, his student PIETER ZEE-MAN experimentally confirmed Lorentz’s the-ory, and they shared the Nobel Prize in physicsin 1902. Of equal importance, Lorentz devel-oped a set of equations that mathematicallypredicted the increase of mass, shortening oflength, and dilation of time for a physicalobject in motion with velocities ranging fromzero to the speed of light. These equations,which later became known as the Lorentztransformation, played a major role in ALBERT

EINSTEIN’s development of the theory of specialrelativity.

Lorentz was born in Arnhem, the Nether-lands, on July 18, 1853. His childhood wasmarked by the death of his mother when he wasfour and his businessman father’s remarriage fiveyears later. Hendrik was educated at localschools and entered the University of Leiden in1870; in less than two years he had earned theB.Sc. degree in mathematics and physics. He leftLeiden at the age of 19 to return to Arnhem as anight school teacher, while writing his Ph.D.thesis, which refined the electromagnetic theoryof James Clerk Maxwell so that it more satisfac-torily explained the reflection and refraction oflight. He received his degree in 1875 at the ageof 22.

When Lorentz was 24, in 1878, he assumedthe chair of theoretical physics, newly createdfor him, at Leiden, where he would remain forthe next 39 years. In 1881, he married AlettaCatharina Kaiser. The couple had a son and twodaughters, one of whom became a physicist.During that time he published an essay on therelationship between the velocity of light in amedium and the density and composition of themedium. The resulting formula, developedalmost simultaneously by the Danish physicistLudwig Lorenz, has become known as theLorenz–Lorentz formula.

In the process of attempting to develop aunified theory to explain the relationship ofelectricity, magnetism, and light, Lorentz pro-posed that if electromagnetic radiation is pro-duced by the oscillation of electric charges, thesource of light might be traced to the oscillationof charges inherent in atoms of matter. If thiswere the case, a strong magnetic field shouldhave an effect on the oscillations and thus onthe wavelength of the light generated. The the-ory was confirmed in 1896 by the discovery ofthe Zeeman effect, in which a magnetic fieldsplits spectral lines. This made it possible toapply the molecular theory to the theory of elec-

188 Lorentz, Hendrik Antoon

tricity and to explain the behavior of light wavespassing through moving transparent bodies.

Lorentz’s electron theory was not successfulin explaining the null result of the Michel-son–Morley experiment that attempted to mea-sure the “luminiferous ether,” the hypotheticalmedium in which light waves were thought topropagate. The experimenters had hoped tomeasure the ether by observing changes in thespeed of light on the basis of interference pat-terns created when a light beam was split in twoand the separated beams were guided along per-pendicular paths and then recombined. To theirdismay, no changes in the speed of light wereobserved. In an attempt to salvage the conceptof the ether, Lorentz and the Irish physicistFRANCIS GEORGE FITZGERALD, working inde-pendently, developed the idea, now known asthe Lorentz–FitzGerald contraction hypothesis,that the length of an object moving through theether contracts in the direction of the motion.When Lorentz heard of FitzGerald’s work, hewas glad to have an ally, commenting, “I havebeen rather laughed at for my idea over here.”Both were scrupulous in acknowledging oneanother’s work, each believing that the otherhad published first.

In 1899, Lorentz showed that the Lorentz–FitzGerald contraction resulted from a processdelineated in a group of equations, which becameknown as Lorentz transformations, that mathe-matically predict the increase of mass, shorteningof length, and dilation of time for an object trav-eling at near the speed of light. Taken together,they compose the revolutionary picture of spaceand time that Einstein would present in 1905 inhis theory of special relativity. Einstein wouldbase his theory on two postulates: (1) the laws ofphysics take the same form in all inertial frames;(2) in any inertial frame, the velocity of light c isthe same whether the light is emitted by a bodyat rest or by a body in uniform motion. Fromthese he deduced both the Lorentz transforma-tions and the Lorentz–FitzGerald contraction.

However, even though Lorentz was recog-nized as a major contributor to the mathematicsof special relativity, he himself never felt com-fortable with Einstein’s conclusions:

[I find] a certain satisfaction in the olderinterpretation according to which theether possesses some substantiality,space and time can be sharply separated,and simultaneity without further speci-fication can be spoken of.

His attitude toward the second great physi-cal revolution of the day, quantum mechanics,was similarly conservative. In 1911, he chairedthe first Solvay Conference in Brussels, whichmet to consider the problem of having two dif-ferent approaches, classical and quantum

Lorentz, Hendrik Antoon 189

Hendrik Lorentz developed a set of equations, laterknown as the Lorentz transformation, that played amajor role in Albert Einstein’s development of the theoryof special relativity. (AIP Emilio Segrè Visual Archives)

physics. His private hope was that it would bepossible somehow to reincorporate quantumtheory into classical physics.

From 1912, when he accepted a double posi-tion as curator at the Teyler Institute in Haarlemand secretary of the Dutch Society of Sciences,onward, Lorentz continued at Leiden as extraordi-nary professor, delivering his famous Mondaymorning lectures for the rest of his life. In 1919, heassumed a leading role in the project to reclaim theZuyderzee in the Netherlands, a great work ofhydraulic engineering. His theoretical calculationsplayed an important role in the project. Enjoyinggreat prestige in Dutch governmental circles, heinitiated steps leading to the creation of a societyfor applied scientific research. In 1923, he was

elected to membership in the International Com-mittee of Intellectual Cooperation of the League ofNations and became its chairman in 1925.

He died in Haarlem on February 5, 1928. Onthe day he was buried the state telegraph andtelephone services in Holland were suspended forthree hours as a tribute to “the greatest man Hol-land has produced in our time.” The renownedBritish physicist ERNEST RUTHERFORD deliveredan appreciative graveside oration.

See also MICHELSON, ALBERT ABRAHAM.

Further ReadingDe Haas-Lorentz, G. L. H. A. Lorentz: Impressions of

His Life and Work. Amsterdam: North-Holland,1957.

190 Lorentz, Hendrik Antoon

M

191

� Mach, Ernst(1838–1916)AustrianExperimentalist (Optics, Acoustics,Classical Mechanics), Philosopher ofScience

Ernst Mach was a brilliant experimentalist, whois best known for deducing the Mach number,the ratio of the velocity of an object to thevelocity of sound, which plays a crucial role inaerodynamics. Mach was an important figure inturn-of-the-century controversies about the verynature of matter. He was the leading advocatefor the energeticist point of view, which rejectedthe belief of the atomists that matter is com-posed of invisible atoms. His study of the subjec-tive factors in scientific observations, which ledhim to question the Newtonian assumption thatspace and time are absolute, influenced ALBERT

EINSTEIN’s development of the general theoryof relativity.

Ernst Mach was born in Chirlitz-Turas inthe Austro-Hungarian Empire (now Moravia)on February 18, 1838. His parents educated himat home until he was 14, when he was sent to thelocal gymnasium (high school). He entered theUniversity of Vienna at 17 and designed opticaland acoustic experiments to study the then-controversial Doppler effect: the relationship

between the perceived frequency of sound andthe motion of the observer relative to that of thesource. After receiving his Ph.D. in 1860, at age22, he stayed on in Vienna teaching mechanicsand physics until 1864.

While Mach was in Vienna his exposure tothe work of Gustav Fechner on the physiologicalprocesses of perception launched him on a life-long quest to understand the physiological, psy-chological, and sensory dynamics that shape theacquisition of scientific knowledge. In 1863, hepublished a book on psychophysics. The follow-ing year he was appointed professor of mathe-matics at the University of Graz, where he wouldremain for three years. Lacking both equipmentand funding for physics experiments, he contin-ued to study vision, hearing, and the subjectivesense of time.

Mach’s most important work would bedone, between 1867 and 1895, at Charles Uni-versity in Prague, where, as professor of experi-mental physics, he would carry out a broadspectrum of studies, which resulted in 90 publi-cations and six books. His experimental workfocused mainly on acoustics and physical optics,including studies of interference, diffraction,polarization, and refraction of light in differentmedia. During this period he developed opticaland photographic techniques for the measure-ment of sound waves and wave propagation. In

1887, he published work on the photography ofprojectiles in flight, which showed the shockwave produced by the gas around the tip of theprojectile. Mach determined that the anglebetween the direction of motion and the shockwave varies with the speed of the projectile: theflow of gas changes its character when the pro-jectile reaches the speed of sound. He then for-mulated what came to be called the Machnumber to describe the ratio of the velocity ofan object to the speed of sound in the mediumin which the object is moving. The Mach num-ber would become a central concept of aerody-namics, particularly of supersonic flight. Thus,an aircraft flying at twice the speed of sound inair is said to be flying at Mach 2.

It was also in Prague, in 1883, that Machwould publish his most influential book, TheDevelopment of Mechanics, which contains hiscritique of Newtonian physics. Although othersbefore him had challenged Newton’s concept ofabsolute space and time, Mach’s incisive treatisehad a strong impact, appearing as it did just afterJAMES CLERK MAXWELL’S work on the electro-magnetic field had challenged the mechanisticconception of the world. Mach’s central argu-ment, for which he offered precise evidence, wasthat all measurements of spatial distances, timeintervals, motion velocities, and masses of physi-cal objects are basically measurements of relativequantities. Mach’s contention that mass is not anabsolute measure of matter but is conditioned bythe surrounding environment is called the Machprinciple. It states that an object cannot haveinertia in a universe devoid of all other objects,since inertia depends on the reciprocal interac-tion of objects, however distant. Einstein, whowrote of the book’s “profound influence” on him,searched for a mathematical expression of theMach principle. But Mach disliked the theory ofgeneral relativity and was far from pleased to seehis own work praised as its predecessor. Heintended to write a book criticizing Einstein’swork but never managed to do so.

At the same time, Mach found himselfembroiled in another of the central controversiesof the day: the atomist–energeticist debate. Hisconviction that phenomena under scientificinvestigation can be understood only in terms ofexperiences, or “sensations,” present in the obser-vation of phenomena led him to insist that noscientific hypothesis is admissible unless it isempirically viable. His scorn for hypotheticalentities that could be neither seen nor testedexperimentally made him vehemently opposethose physicists who were reaching for a deeperexplanation of what they saw in the laboratory bypostulating a dynamic submolecular world of col-liding atoms. “I don’t believe in atoms,” he bluntlytold LUDWIG BOLTZMANN, the leading atomist,in January 1897 at a meeting of the ImperialAcademy of Sciences in Vienna. As it happened,Mach was wrong about the atom, whose exis-tence would soon be demonstrated by ERNEST

RUTHERFORD and whose properties would beexplored by the new quantum mechanics. Hisview of scientific discovery was validated, how-ever, since precise mathematical and statisticalmeasurement would be required to prove theatom’s existence.

In 1895, Mach returned to the University ofVienna as professor of inductive philosophy. Twoyears later, he suffered a stroke that paralyzed hisright side. Despite this, he continued to doresearch until 1901, when he was appointed tothe Austrian parliament, a post he held for 12years. He continued to lecture and write inretirement, publishing Knowledge and Error in1905 and an autobiography in 1910.

In 1913 he moved to his son’s home nearMunich, where he continued to write books. Hedied there a day after his 78th birthday, onFebruary 19, 1916. He is remembered not onlyfor his ingenious and exacting experimentalstudies, but for his contributions to the debateover the nature of scientific investigation, whichcontinues to this day.

See also DOPPLER, CHRISTIAN.

192 Mach, Ernst

Further ReadingCohen, R. S., ed. Boston Studies in the Philosophy of Sci-

ence. Vol. 6. Ernst Mach: Physicist and Philosopher,Boston: Kluwer Academic, 1975.

Lindley, David. Boltzmann’s Atom: The Great DebateThat Launched a Revolution in Physics. New York:Free Press, 2000.

� Maxwell, James Clerk(1831–1879)ScottishTheoretical Physicist (ClassicalElectromagnetism, Optics,Thermodynamics)

James Clerk Maxwell is considered the greatesttheoretical physicist of the 19th century. Hebrilliantly synthesized the key findings of hispredecessors in four equations that unified thedescription of electromagnetic processes. In sodoing he discovered that light consists of elec-tromagnetic waves and led the way to explo-ration of the whole spectrum of electromagneticradiation. A multifaceted genius who made fun-damental contributions to the study of everyproblem he addressed, he also formulated thestatistical kinetic theory of gases, solved themystery of Saturn’s rings, and discovered theprinciples governing color vision.

Maxwell was born in Edinburgh, Scotland,on November 13, 1831, but spent his boyhoodon his family’s country estate in Glenlair. Fromhis earliest years he showed a high degree ofcuriosity and a passion for finding out howthings worked. After his mother died, plans forhis home education were dropped and the boywas sent to Edinburgh Academy, where he stud-ied from age 10 to age 16. A shy, solitary boy,absorbed in mathematical and mechanical pur-suits, Maxwell quickly proved to be a precocious,prize-winning student. When he was only 14, hediscovered an original method for drawing a per-fect oval based on his generalization of the defi-

nition of an ellipse and submitted his work, inhis first paper, to the Royal Society of Edinburghin 1846.

Upon graduating from the academy in 1847,he entered the University of Edinburgh and, stillan undergraduate, began doing independentresearch on the theory of color. In 1849, buildingon the work of THOMAS YOUNG and HERMANN

LUDWIG FERDINAND VON HELMHOLTZ, he demon-strated that colors could be built up from mixturesof the three primary colors—red, green, andblue—by spinning disks containing sectors ofthese colors in various sizes. He would developthis work for many years, inventing a color box inwhich the primary colors could be selected fromthe Sun’s spectrum and combined. This modelexplained how all colors are produced by addingand subtracting the primary colors. Turning to theproblem of color vision, he confirmed Young’stheory that the eye has three kinds of receptorssensitive to the primary colors and showed thatcolor blindness is due to defects in the receptors.The culmination of his investigations wouldoccur in 1861, when he produced the first colorphotograph to use a three-color process.

In 1850, Maxwell went on to study at Cam-bridge. He graduated with a degree in mathe-matics from Trinity College in 1854 and wasawarded a fellowship allowing him to continuehis work at Cambridge. Maxwell’s genius for pur-suing several research problems at once wasalready evident. In 1856, Maxwell moved toScotland in order to be near his ailing father andbecame professor of natural philosophy atMarischal College, Aberdeen. He competed forthe Adams Prize offered by Cambridge on 1857,awarded to whoever could offer a satisfactoryexplanation for the rings of Saturn that wouldresult in a stable structure. He won the prize byshowing that whereas a solid ring would collapseand a fluid ring would break up, stability couldbe achieved if the rings consisted of numeroussmall solid particles, an explanation now con-firmed by the Voyager spacecraft.

Maxwell, James Clerk 193

In 1859, he married Katherine Mary Dewar,daughter of the head of Marischal College; hethen moved to London in 1860 as professor ofnatural philosophy and astronomy at King’s Col-lege. There he continued the work begun atCambridge, in 1855–1856, when he had estab-lished the foundation for his most importantwork by providing a mathematical formulationfor MICHAEL FARADAY’s theory that electric andmagnetic effects result from field lines of forcethat surround conductors and magnets. His sem-inal paper, “On Faraday’s Lines of Force,” hadcompared the behavior of the lines of force withthe flow of an incompressible fluid. This modelimplied the existence of a medium in which thefield lines were established.

Over the next 15 years, Maxwell would pub-lish a series of papers in which, step by step, hedeveloped the four field equations that describethe physics of electrodynamics. He continued todevelop the incompressible fluid model for themedium, assuming that it contained rotating vor-tices corresponding to magnetic fields separatedby cells corresponding to electric fields. By con-sidering how the motion of the vortices and cellscould produce magnetic and electric fields, heexplained all previously known effects of electro-magnetism. In Maxwell’s formulation, Coulomb’slaw required two equations for the electric field,and Ampère’s law and Faraday’s law required twomore for the magnetic field. Thus, Maxwell’sequations showed that (1) unlike charges attracteach other; like charges repel (Coulomb’s law);(2) there are no single, isolated magnetic poles (ifthere is a north, there will be a correspondingsouth pole) (Ampère’s law); (3) electrical cur-rents can cause magnetic fields (Ampère’s law);and (4) changing magnetic fields can causechanging electric fields (Faraday’s law).

However, Maxwell noted that these equa-tions were not symmetrical in the manner inwhich electric and magnetic fields entered intothem. To correct this, he postulated that if achanging magnetic field could produce a chang-

ing electric field, then symmetry required that achanging electric field could produce a changingmagnetic field. This implied a new phe-nomenon, namely, that an oscillating combina-tion of transverse electric and magnetic fieldscould propagate through space at the speed oflight. This led Maxwell to claim that light, infact, is a form of electromagnetic radiation:

We can scarcely avoid the conclusionthat light consists in the transverseundulations of the same medium, whichis the cause of electric and magneticphenomena.

Maxwell’s equations demonstrated thatelectricity and magnetism are aspects of a singleelectromagnetic field, and that light itself is avariety of this field. In this way he unified whathad been the separate studies of electricity, mag-netism, and optics. In his 1873 Treatise on Elec-tricity and Magnetism he summarized all of hiswork on the subject, establishing that light has aradiation pressure and suggesting that a wholefamily of electromagnetic radiations must exist,of which light is only one. This prediction wasconfirmed in 1888 when HEINRICH RUDOLF

HERTZ discovered the existence of radio waves,which move at the speed of light.

At the same time that he was developing hisideas on electromagnetic theory, Maxwell con-tinued work begun at Aberdeen in 1860 on thekinetic theory of gases. He built on the work ofRUDOLF JULIUS EMMANUEL CLAUSIUS, who in1857–1858 had shown that a gas must consist ofmolecules in constant motion colliding witheach other and the walls of the container. Hearrived at a formula to express the distribution ofvelocity in gas molecules, relating it to tempera-ture and thus demonstrating that heat resides inthe motion of molecules.

His kinetic theory did not fully explain heatconduction, and it was modified by LUDWIG

BOLTZMANN in 1868, resulting in what became

194 Maxwell, James Clerk

known as the Maxwell–Boltzmann distributionlaw. Maxwell also accurately estimated the sizeof molecules and invented a method of separat-ing gases in a centrifuge. In addition, the kinetictheory had an important impact on the questionof the validity of the second law of thermody-namics, which states that heat cannot sponta-neously flow from a cooler body to a hotter one.For example, when two connected containers ofgases have the same temperature, it is statisticallypossible for the molecules to diffuse spontaneouslyso that the faster-moving molecules all concen-trate in one container while the slower moleculesgather in the other, making the first container hot-ter and the second colder. Maxwell conceived thishypothesis, known as Maxwell’s demon. Eventhough this process is statistically possible it ishighly unlikely. In this context, the second law isnot absolute but only highly probable.

In 1865, Maxwell’s father died, and hereturned to his family estate in Glenlair, Scot-land, and devoted himself to research. He madeperiodic trips to Cambridge. In 1871, he was per-suaded to move to Cambridge, where he becamethe first professor of experimental physics andset up the Cavendish Laboratory, which openedin 1874. He continued his lectures there until1879, when he contracted cancer. That summer,he returned to Glenlair to be with his wife, whowas also ill. He died at age 48, on November 5,1879, in Cambridge.

The four partial differential equations nowknown as Maxwell’s equations are among thegreat achievements of 19th-century mathemat-ics. The year before Maxwell died, he suggestedan experiment for measuring the effect of theether. This inspired ALBERT ABRAHAM MICHEL-SON and Edward Morley to carry out theirfamous experiment in the 1880s, the results ofwhich disproved the existence of the ether, themedium in which light waves were thought tobe propagated. The discovery that there was noether did not discredit Maxwell’s work. Hisequations and descriptions of electromagnetic

waves remained valid even though the wavesrequire no medium. They paved the way for thediscovery of special relativity and of the spec-trum of electromagnetic radiation, such as Xrays and gamma rays, that is at the core of mod-ern physics.

See also AMPÈRE, ANDRÉ-MARIE; COULOMB,CHARLES-AUGUSTIN DE; EINSTEIN, ALBERT.

Further ReadingHarman, Peter M. The Natural Philosophy of James

Clerk Maxwell. Cambridge: Cambridge Univer-sity Press, 1998.

Hendry, John. James Clerk Maxwell and the Theory ofthe Electromagnetic Field. Bristol: England: Insti-tute of Physics, 1986.

Hunt, Bruce J. The Maxwellians. Ithaca, N.Y.: CornellUniversity Press, 1995.

� Meitner, Lise(1878–1968)Austrian/SwedishExperimentalist (Radioactivity),Nuclear Physicist

Lise Meitner is famous for research she per-formed in 1938, which correctly interpreted anddescribed the splitting or fission of the uraniumnucleus under neutron bombardment. Thisresult was pivotal to the development of nuclearphysics. Ironically she was deprived of the NobelPrize for this achievement, which went to OttoHahn, who had done the initial splitting experi-ment but had incorrectly interpreted the results.

She was born on November 7, 1878, thethird of eight children born to Philipp Meitner,a wealthy lawyer, and Hedwig, the mother towhom she owed her love of music. She wouldlater say of her childhood in this cultured Jew-ish family,

Even today I am filled with deep grati-tude for the unusual goodness of my par-

Meitner, Lise 195

ents, and the extraordinarily stimulatingintellectual atmosphere in which my sis-ters and brothers and I grew up.

Lise showed an early interest in science and,choosing MARIE CURIE as her heroine, aspired tobecome a physicist and study radioactivity. Herparents, however, insisted she qualify as a Frenchteacher, so she could support herself, before shestudied physics. After passing the examinationin French, she entered the University of Viennain 1901.

In 1905, she completed a thesis on thephysics of thermal conduction under the direc-

tion of LUDWIG BOLTZMANN and became thesecond woman to receive a Ph.D. in physics fromthe university.

In 1907, Meitner entered the University ofBerlin to study under MAX ERNEST LUDWIG

PLANCK, the founder of quantum mechanics.There she met Otto Hahn, a chemist, who waslooking for someone to work with him onradioactivity at the Kaiser Wilhelm Institute ofChemistry in Dalhem. When Hahn’s supervisorrefused to allow a woman to work in his labora-tory, she and Hahn set up a small lab in a car-penter’s workroom. Following in the footsteps ofANTOINE-HENRI BECQUEREL and Marie Curie,they set out to analyze the physical properties ofradioactive substances. Hahn’s main interest wasthe discovery of new elements, whereas Meitnerwanted to examine radiation emissions. Togetherthey determined the beta emission spectra ofnumerous nuclear isotopes. By 1912, Meitnerwas a member of the Kaiser Wilhelm Instituteand an assistant to Planck at the Berlin Instituteof Theoretical Physics.

When World War I broke out in 1914, Hahnremained at the university doing war researchwhile Meitner joined the Austrian army as an X-ray technician. During this period she continuedsporadic work with Hahn, arranging her leave tocoincide with his. In 1918, they announced theirdiscovery of a new element, protactinium, thesecond heaviest element then known, whichmade them famous. Meitner later won the Leib-niz Medal from the Berlin Academy of Scienceand the Leiben Prize from the Austrian Academyof Science and became head of a new departmentin radioactive physics at the Kaiser WilhelmInstitute. In 1922, she was made a lecturer at theUniversity of Berlin, where four years later shebecame Germany’s first woman to be appointed afull physics professor. Einstein called her “theGerman Marie Curie.”

Working on her own during this period, shestudied the relationship between nuclear betaand gamma radiation and the basis for the con-

196 Meitner, Lise

Lise Meitner correctly interpreted and described thesplitting or fission of the uranium nucleus underneutron bombardment, a pivotal discovery in thedevelopment of nuclear physics. (AIP Emilio SegrèVisual Archives, Herzfeld Collection)

tinuous beta spectrum and correctly determinedthat beta particles are electrons ejected from thenucleus. On the basis of conservation of energyand momentum, WOLFGANG PAULI, using theseresults, realized that there had to be a third neu-tral particle in the process of atomic decay; thisinsight led him to postulate the existence of theneutrino. Meitner was also the first to describethe atomic emission of Auger electrons, whichoccurs when an electron rather than a photon isemitted after one electron drops from a higher toa lower electron shell in the atom.

After 1933, when the Nazis rose to power,Meitner stayed in Berlin, despite the growingofficial anti-Semitism, because she was pro-tected by her Austrian citizenship. Remainingintensely involved in her research, she used aWilson cloud chamber to photograph positronproduction by gamma radiation. In 1935, sheand Hahn resumed their collaboration andbegan to study the effects of neutron bombard-ment on uranium. ENRICO FERMI had shown thatthe nucleus of an atom, under the right condi-tions, could capture a neutron and emit a betaparticle, thus becoming an atom of the nextheaviest element. Meitner and Hahn wanted toconfirm these results and use the neutron bom-bardment on uranium to produce transuranicelements, that is, elements with atomic numbersgreater than that of uranium (92). They used ahydrogen sulfide precipitation method toremove elements with atomic numbers between84 and 92 from their neutron-irradiated sampleof uranium and succeeded in finding evidencefor existence of elements with atomic numbersof 93, 94, 95, and 96.

In 1938, the Nazis annexed Austria anddeprived Meitner of Austrian citizenship, forcingher to become a German Jew subject to Germanlaws. With her life in danger, she escaped to Hol-land, with the help of Dutch scientists and a fam-ily heirloom diamond ring from Hahn, who“wanted her to be provided for in an emergency.”Shortly afterward, she moved to Denmark, as the

guest of NIELS HENRIK DAVID BOHR. She thenaccepted a position Bohr had found for her, at theNobel Physical Institute in Stockholm, where acyclotron was being built. Not knowing theSwedish language and suffering from the loneli-ness of exile, however, she found it difficult tofocus on her work. Meanwhile, she got word fromHahn that he and his new partner, a young Ger-man chemist named Fritz Strassmann, had foundthat the radioactive elements produced by neu-tron bombardment of uranium had propertieslike those of radium. But if Hahn was excited atthe prospect of discovering new elements, Meit-ner found the energetic reactions necessary toproduce such new elements unexpected andincreasingly hard to explain. From Stockholm,she asked him for firm chemical evidence of theidentities of the products.

Delving further, Hahn and Strassmann weresurprised to learn that the neutron bombard-ment had produced not transuranic elements butthree isotopes of barium, which has an atomicnumber of 56. Hahn asked Meitner whether shecould explain this. Meitner and her nephew,Otto Frisch, who was working at Bohr’s institutein Copenhagen, realized that Hahn and Strass-mann’s results indicated that the uraniumnucleus had been split into smaller fragments.They found that Hahn’s results could beexplained if, rather than simply adding or sub-tracting a particle or two from the uraniumnucleus, Hahn had split it almost in half. Doingso would produce barium and krypton, a gaseouselement that would be harder to detect.

Their result was startling, since physicistshad thought splitting atomic nuclei was not pos-sible because of the very powerful forces thatheld the nucleus together. Most thought thenucleus was like a drop of water, held together bythe equivalent of surface tension: the electriccharge of a heavy nucleus generates a repulsiveforce that partially offsets the attractive nuclearforce. Recalling that the repulsive force of thenuclear electric charge, that is, the atomic num-

Meitner, Lise 197

ber, diminishes this surface tension, Meitner andFrisch calculated that at an atomic number ofabout 100 the surface tension of the nucleus dis-appears; therefore, uranium at 92 must be fairlyclose to that instability. For these reasons theyconcluded that the uranium nucleus might be“very wobbly, like a large, thin-walled balloonfilled with water,” and under these conditions asingle neutron could cause it to split apart, a pro-cess they named nuclear fission.

They had also discovered the reason no ele-ments beyond uranium exist naturally in theworld: the electric and nuclear forces workingagainst each other in the nucleus eventuallycancel each other out. They also calculated,according to Einstein’s relativity equation, E =mc2, which shows how to convert mass intoenergy, that splitting a uranium nucleus shouldrelease 200 million electron volts, 20 milliontimes more than an equivalent amount of TNT.(An electron volt is the energy necessary toaccelerate an electron through a potential differ-ence of one volt). This energy, which would bereleased in the form of radiation and heat, wouldnot be obvious in samples of uranium as small asthose Hahn had used, but it could be detectedwith the right instruments. Frisch duplicated theexperiment and found evidence of this form ofnuclear energy.

In January 1939, Frisch and Meitner pub-lished two papers describing their analysis, inwhich they expressed the idealistic hope thattheir work would herald a “promised land ofatomic energy.” Instead, it set in motion a series ofdiscoveries leading to the development of the firstnuclear reactor in 1942 and the development ofthe atomic bomb in 1945. Although Frisch didbecome a part of that effort, Meitner herself livedin semiretirement in neutral Sweden duringWorld War II and refused to participate in atomicbomb research. She hoped that such a weaponwould not be feasible and was devastated when itwas successfully developed and dropped on Japan.After this, her remaining hope was that the real-

ity of nuclear devastation would make humanityrealize there must be an end to war.

Ironically, in 1944, Hahn won the NobelPrize in chemistry for his work on nuclear fis-sion, and, although he never did anything tocorrect the injustice of Meitner’s work’s beingoverlooked, they remained friends. In 1947, theSwedish Atomic Energy Commission estab-lished a laboratory for Meitner at the RoyalInstitute of Technology. Later she moved to theRoyal Swedish Academy of Engineering Sci-ence, to work on an experimental nuclear reac-tor. In 1949, she became a Swedish citizen andwas awarded the Max Planck Medal. She con-tinued to study the nature of fission products andcontributed to the design of an experimentwhereby fission products of uranium could becollected. Later she performed cyclotronresearch on the production of new radioactivespecies, which led to the development of theshell model of the nucleus.

In 1960, Meitner retired and settled inCambridge, England, to be near Frisch, whotaught there. Finally, in 1966, she became thefirst woman to receive the Fermi Award from theU.S. Atomic Energy Commission, which sheshared with Hahn and Strassmann.

Lise Meitner was a brilliant scientist whomade great contributions to nuclear physics, aswell as a humanist who lived according to herconvictions. In old age, she wrote:

I believe all young people think abouthow they would like their life todevelop. When I did so I alwaysarrived at the conclusion that life neednot be easy provided only that it wasnot empty. And this wish I have beengranted.

She died in Cambridge on October 27,1968, just before her 90th birthday. In 1982,when element 109 was created, it was namedmeitnerium in her honor.

198 Meitner, Lise

Further ReadingFrisch, Otto. What Little I Remember. Cambridge:

Cambridge University Press, 1991.Rife, Patricia. Lise Meitner and the Dawn of the Nuclear

Age. Cambridge, Mass.: Birkhauser, 1998.Sime, Ruth Lewin. Lise Meitner: A Life in Physics.

Berkeley: University of California Press, 1996.

� Michelson, Albert Abraham(1852–1931)AmericanExperimental Physicist (Optics)

Albert Michelson was the great experimentalistwho, together with Edward Morley, performedthe classic Michelson–Morley experiment forlight waves, which disproved the existence ofthe ether, the mysterious medium in which lightwaves were thought to propagate. With theinstrument he designed for this experiment, theinterferometer, Michelson pioneered a new fieldcapable of making a broad range of highly exactmeasurements. He developed extremely sensi-tive optical equipment, which enabled him tomake very precise measurements of the velocityof light. When, in 1907, he won the Nobel Prizein physics for these achievements, he becamethe first American to be honored in this way.

Michelson was born in Strelno, Prussia(now Poland), on December 19, 1852, the son ofa Jewish merchant, who escaped persecution byemigrating with his family to the United Stateswhen Albert was two years old. The familystarted out in New York and eventually settledin Virginia City, Nevada, and San Francisco,where his father’s business interests prosperedand Albert attended school. When his fatherheard of an opportunity for his son to gainadmission to the United States Naval Academyin Annapolis, Albert duly applied but was notselected. The young man pleaded his case beforePresident Ulysses S. Grant, who ordered that hebe admitted in 1869. But Michelson was not des-

tined for a naval career. In a class of 29, heplaced first in optics, 25th in seamanship. Whenhe graduated in 1873, he was ordered aboard theUSS Monongahela, a sailing ship, for a two-yearvoyage through the Caribbean and down to Rio.After his return in 1875 he was appointed as aninstructor in physics and chemistry at the NavalAcademy. Two years later, he married MargaretMcLean Heminway, with whom he would havethree children. (Michelson would later divorceher, remarry, and have three more children withhis second wife.)

From this time on, he would devote his lifeto science. Fascinated by the problem of measur-ing the speed of light, he would create ever morerefined instruments for achieving his goal. Hemade his first attempt in 1878, at Annapolis,when he improved the rotating-mirror method ofJEAN-BERNARD-LÉON FOUCAULT to determinethe velocity of light. Michelson made his mea-surement by timing a flash of light travelingbetween mirrors. Using very high-quality lensesand mirrors to focus and reflect the beam of light,he found that light moved at a velocity of186,355 miles per second, with a possible error of±30 miles per second or so. This measurementwas 20 times more accurate than Foucault’s andremained the best to be obtained for a genera-tion; when it was improved upon, in the 1920s,Michelson was the one who improved it, by mak-ing very precise measurements over a 23-milepath between two mountain peaks in California.

Although his work at Annapolis had givenhim renown, Michelson decided he needed agreater mastery of optics before attacking thenext challenge he had set for himself: the mea-surement of the ether. Between 1880 and 1882,he pursued postgraduate studies in Berlin underHERMANN LUDWIG FERDINAND VAN HELMHOLTZ

and later in Paris. It was in Berlin, in 1881, thatMichelson built his first interferometer, in orderto carry out an experiment suggested by JAMES

CLERK MAXWELL in 1878. Maxwell, as did mostphysicists, believed that light waves, by analogy

Michelson, Albert Abraham 199

with sound waves propagating through the atmo-sphere, move through the ether, a materialmedium that surrounds and permeates all space,including outer space. To date, however, no onehad figured out how to measure it.

Michelson’s ingenious optical system wasdesigned to do just that. It consisted of an L-shaped apparatus in which a beam of light wassplit in two. The separated beams were guidedalong perpendicular paths of identical lengthand then recombined in such a way that thebeams “interfered” with each other: that is, thedirections and distances of their light paths wereso closely meshed that the beams could interactand create observable interference fringes. If theEarth was moving through a universal ether, thetimes needed by the two parts of the split light

beam to transverse a sample of the ether currentfrom perpendicular directions should differslightly, and that difference should be detectablein the resulting pattern of interference fringes.Since the Earth is revolving about its axis as wellas moving around the Sun, the flow of ether seenin the laboratory should be periodically chang-ing and hence the speed of light should bechanging as well. This change in the speed oflight should cause the interference fringes inMichelson’s interferometer to shift in a periodicmanner, which should be observable.

To his consternation, Michelson coulddetect no change in the interference pattern,neither in this first experiment, nor in 1885 or1887, when he repeated the experiment, using amore sensitive interferometer built with Morley.The results of the Michelson–Morley experi-ments were paradoxical in term of Newtonianphysics and triggered passionate debate. Evi-dently, the speed of light plus any other addedvelocity was still equal only to the speed of light.

To explain this, fundamental and long-heldphysical ideas had to be reexamined. Some physi-cists continued to believe in the ether and claimedits effect could not be detected because it movedwith the Earth. However, this was disproved bystellar aberration experiments performed byOliver Lodge in 1893. A more promising theorywas put forth by GEORGE FRANCIS FITZGERALD,who suggested that objects moving through theether contract slightly in the direction of theirmotion and thereby hide the effect of the changein the velocity of light. A radically different inter-pretation of the FitzGerald contraction hypothesiswould become part of the special theory of relativ-ity proposed by ALBERT EINSTEIN in 1905. Michel-son, however, believed that the physics of his daywas founded on a rock and was skeptical of theo-ries that promised to overthrow its basic tenets:

The more important fundamental lawsand facts of physical science have allbeen discovered, and these are now so

200 Michelson, Albert Abraham

Albert Abraham Michelson performed the classicMichelson–Morley experiment for light waves, whichdisproved the existence of the ether in which lightwaves were thought to be propagated. (AIP EmilioSegrè Visual Archives, Michelson Museum)

firmly established that the possibility oftheir ever being fully supplanted in con-sequence of new discoveries is exceed-ingly remote. . . . Our future discoveriesmust be looked for in the sixth place ofdecimals.

When he returned to the United States, dis-appointed by the results of his experiments, heleft the navy and took up a position as professorof physics at the Case School of Applied Sciencein Cleveland, Ohio. In 1889, he joined thephysics department at Clark University inWorcester, Massachusetts, where, in 1892, heand Morley redefined the length of the standardmeter kept in Paris in terms of a certain numberof wavelengths of monochromatic light, using ared line in the cadmium spectrum. This methodof defining the standard unit of length was finallyadopted in 1960, and a krypton line is now used.

Michelson made his final academic shift in1892, accepting an appointment as professor ofphysics at the University of Chicago, where hewould remain until 1929. During these years hedeveloped his interferometer into a precise instru-ment for measuring the diameters of heavenlybodies and in 1920 announced the size of thegiant star Betelgeuse, the first star to be measured.

He died on May 9, 1931, in Pasadena, Cali-fornia. Earlier that year Einstein had paid himtribute:

Dr. Michelson, it was you who led thephysicists into new paths, and throughyour marvelous experimental workpaved the way for the development ofthe theory of relativity.

The Michelson–Morley experiment wasperhaps the most significant in the history of sci-ence. It marked a turning point in theoreticalphysics, demonstrating the counterintuitive factthat the velocity of light is constant, indepen-dent of the motion of the observer. Despite his

desire to preserve the foundations of 19th-cen-tury physics, Michelson’s gift for extremely pre-cise experimental work ignited a revolutionarychain of advances in physics, which woulddestroy the theory of the luminescent ether andcreate the groundwork for relativity.

Further ReadingJaffe, Bernard. Michelson and the Speed of Light. Gar-

den City, N.Y.: Doubleday, 1960.Livingston, Dorothy Michelson. Master of Light: A

Biography of Albert A. Michelson. New York:Scribner, 1973.

� Millikan, Robert Andrews(1868–1953)AmericanExperimentalist, Atomic Physicist

Robert Andrews Millikan performed the famousoil droplet experiment, which represented thefirst accurate determination of the charge on theelectron. For this achievement, as well as for hismeasurement of Planck’s constant, he wasawarded the Nobel Prize in physics in 1923.

He was born on March 22, 1868, in Morri-son, Illinois, the second son of the ReverendSilas Franklin Millikan, a minister, and MaryJane Andrews Millikan, a former dean of womenat Olivet College. His Scottish–Irish ancestorshad pioneered in settling the Midwest. He had arural childhood, helping out on the family farm.At 14, he worked 10-hour days during the sum-mer at a local barrel head factory, earning a dol-lar a day. After graduating from Maquoketa HighSchool in Iowa, he entered Oberlin College in1886; there his Greek professor sparked hisinterest in physics. A 12-week physics course,which he would later call “a complete loss,” washis only formal physics instruction at Oberlin. Itwas apparently enough, however, to win him anoffer to teach elementary physics there; heneeded the money and accepted. After earning a

Millikan, Robert Andrews 201

B.A. from Oberlin in 1891 and an M.A. in 1893,he embarked on graduate study at ColumbiaUniversity, which would award him a Ph.D. inphysics in 1895.

Millikan then spent some time in Germany,studying with MAX ERNEST LUDWIG PLANCK inBerlin and WALTHER NERNST in Göttingen. Hemarried Greta Erwin Blanchard, with whomhe would have three sons. In 1896, Millikanaccepted an appointment as assistant professorof physics at the University of Chicago, where,in 1906, he was made associate professor and,four years later, full professor.

In 1908, Millikan began constructingexperiments to measure the charge on the elec-tron. His approach was conceptually simple buthard to achieve in practice, and it took him fiveyears of trying before he was able to determinethe electron’s charge. He first investigated therate at which water droplets fall when exposedto an electric field. He began by filling a cloudchamber with ions generated by X rays. He thenrapidly let air back into the cloud chamber,causing tiny water droplets to condense aroundthe ionized particles. Next, by applying an elec-trostatic field and observing the behavior of thewater droplets, he was able to measure the rateat which the water drops either fell, under theinfluence of gravity alone, or were balanced,under the influence of gravity plus an electricfield. Since the ionized droplets would absorbmultiple integers of the electronic charge, thevalue of which he was trying to determine, thestrength of the electric field required to coun-teract the gravitational force on the dropletswould also be an integral multiple of the elec-tronic charge. By measuring a range of values ofthe electric field needed to balance a large num-ber of different size droplets against gravity, andthen calculating the least common integralmultiple of these values, he could determine thevalue of the electronic charge.

By 1909, Millikan had an approximate valuefor the electronic charge, but the water droplets

evaporated too quickly to make precise measure-ment possible, so he switched to oil droplets,which were much more stable. In his experimenthe produced oil droplets with variable charge,which fell through fine holes in the upper of twocharged metal plates. He measured the range ofvalues of the electric field needed to balance alarge number of different charged oil dropletsagainst gravity. Then, calculating the least com-mon integral multiple of these values, he foundthat the charges on the droplets were integralmultiples of the charge on the electron. The factthat the oil droplets did not evaporate allowedhim to determine the value of the electroniccharge more accurately than in his previous workwith water droplets. The calculations Millikanobtained from his work with oil droplets, whichhe completed in 1913, were used for many yearsto measure the charge of the electron.

During this period Millikan also studied thephotoelectric effect, investigating ALBERT EIN-STEIN’s hypothesis that the kinetic energy of anelectron emitted by incident radiation is propor-tional to the frequency of the radiation multi-plied by Planck’s constant, another fundamentalconstant in nature. He found a way to performhis experiments on photoelectricity when heobserved that alkali metals are sensitive to a verywide range of electromagnetic frequencies. Afterworking for three years to improve the sensitivityof his apparatus, in 1916, he was able to validateEinstein’s 1905 equation, thereby obtaining anaccurate value for Planck’s constant. This estab-lished beyond doubt the validity of Einstein’s lin-ear relationship between energy and frequency,as well as the photon hypothesis underlying thenature of Einstein’s photoelectric equation.

During World War I, Millikan was directorof research for the National Research Council,which was involved in defense research. Hehelped develop submarine detection anddestruction devices. In 1921, he moved fromChicago to Pasadena, where he became directorof the Norman Bridge Laboratory at the Califor-

202 Millikan, Robert Andrews

nia Institute of Technology. In the 1920s, hestudied the ultraviolet spectra of many elements,extending the frequency range and identifyingmany new spectral lines. In 1925, he began athorough study of cosmic rays, which he namedafter proving that they originated in outer space,a hypothesis first put forth by V. F. Hess, who dis-covered them in 1912. Millikan was skeptical ofthis hypothesis until he himself proved it exper-imentally. He did this by comparing the inten-sity of ionization in two lakes at differentaltitudes and in the process was able to demon-strate that the rays producing the ionizationmust have passed through the atmosphere fromabove and could not have originated on Earth.

However, the nature of cosmic rays remaineda puzzle. At first Millikan argued that in the hydro-gen clouds in interstellar space hydrogen atoms arebeing continually fused together to producehelium and heavier elements, releasing a largeamount of energy in the form of photons. Thehypothesis was widely accepted until 1929, whenit was shown that the primary cosmic rays consistmostly of hydrogen and helium nuclei. Later Mil-likan asserted that cosmic rays are electromagneticwaves, but ARTHUR HOLLY COMPTON disprovedthis in 1934 when he demonstrated that they con-sist of charged particles.

Millikan remained the head of the NormanBridge Laboratory until 1945, when he retired.A prolific author, he wrote, among other books,Science and Life (1924); Evolution in Science andReligion (1927); Science and the New Civilization(1930); Time, Matter, and Values (1932); Elec-trons, Protons, Photons, Neutrons, Mesotrons, andCosmic Rays (1947); and Autobiography (1950).He was a religious philosopher and lectured onthe reconciliation of science and religion. Hedied in Pasadena on December 19, 1953.

Millikan’s experimental genius led him todiscover accurate ways to determine two of themost fundamental constants of modern physics:the charge on the electron and the value ofPlanck’s constant.

See also COULOMB, CHARLES-AUGUSTIN DE;WILSON, CHARLES THOMSON REES.

Further ReadingKargon, Robert H. The Rise of Robert Millikan: Portrait

of a Life in American Science. Ithaca, N.Y.: Cor-nell University Press, 1982.

Millikan, Robert Andrews, and I. Bernard Cohen.Autobiography of Robert A. Millikan. Manchester,N.H.: Ayer, 1980.

� Mössbauer, Rudolf Ludwig(1929– )GermanExperimentalist, Particle Physicist

Rudolf Ludwig Mössbauer won the 1961 NobelPrize in physics for his discovery of what came tobe known as the Mössbauer effect, the recoil-freeresonance absorption of gamma radiation byatoms in a crystal. Mössbauer’s discovery spawnedthe enormously productive field of Mössbauerspectroscopy, which, in addition to providing anaccurate method for the experimental verifica-tion of ALBERT EINSTEIN’s theory of relativity,continues to find applications as a research tool ina wide spectrum of scientific fields.

He was born on January 31, 1929, inMunich, to Ludwig Mössbauer and Erna Ernst.After completing his secondary studies inMunich in 1948, he took a year’s break from hisschooling, working in industrial laboratories.He then began his physics studies at theMunich Institute of Technology and receivedhis undergraduate degree in 1952. Over thenext two years Mössbauer completed his mas-ter’s thesis at the Institute’s Laboratory ofApplied Physics. From 1955 to 1957, heworked on his doctoral thesis, carrying out aseries of experiments in Heidelberg at the MaxPlanck Institute for Medical Research; hereceived a Ph.D. in 1958. At the suggestion ofhis thesis adviser, Professor Maier-Leibnitz, he

Mössbauer, Rudolf Ludwig 203

investigated resonance absorption and hadsome unexpected results, which he investigatedsystematically. That year he announced theMössbauer effect, which he discovered duringhis postdoctoral research.

Physicists had long known that incomingradio waves can only be received if the receiver istuned to the same frequency as the sender. Underthese conditions it is said that resonance absorp-tion is taking place. In 1953, Mössbauer tried toobserve the corresponding phenomenon forgamma rays impinging on nuclei. The methodwas to allow gamma radiation from some kind ofnuclei to act on other nuclei of exactly the samekind. The absorption of a gamma ray by anatomic nucleus usually causes it to recoil, therebyaffecting the wavelength of the reemitted ray.Mössbauer discovered that at low temperaturescrystals absorb gamma rays of a specific wave-length and resonate, so that the crystal as a wholerecoils while the nuclei do not. Mössbauer’sexperiment showed that after an atomic nucleusemits a gamma ray photon (during radioactivedecay), the absorption of the momentum of theatom by the whole of its crystal lattice occursbecause the atom is so firmly bound to the lattice.The same effect occurs with the absorption ofgamma rays. Because of the very small width ofthe gamma ray absorption lines, the resonanceabsorption in the crystal is very sharp. Moreimportantly, in terms of practical applications,the resonance absorption can be influenced bythe Doppler effect associated with the moving ofthe source or the absorber of the gamma radia-tion at velocities that can be as slow as a few mil-limeters per hour. This essentially recoillessnuclear resonance absorption became known asthe Mössbauer effect. A lengthening of thegamma ray wavelength in a gravitational field,verifying the predictions of the general theory ofrelativity, was observed experimentally in 1960.

Mössbauer traveled to the United States in1960 and, the following year, became professorof physics at the California Institute of Tech-

nology, Pasadena, where he continued his stud-ies of gamma absorption. He simultaneouslyheld a professorship at Munich. He marriedElisabeth Pritz, with whom he had two chil-dren, Peter and Regine.

Because the link between the Mössbauereffect and the electron structure of the sample canbe exploited in the study of many types of materi-als, it is used primarily to study the electron struc-ture of materials. Other important applicationsinvolve measuring the separation and displace-ment of nuclear energy levels that occur in solidsas a result of the influence of the environmentsurrounding the nucleus. Mössbauer spectroscopyis extremely versatile and can also be used in solidstate physics, surface physics, medicine, chem-istry, biochemistry, and geology.

See also BETHE, HANS ALBRECHT; DOPPLER,CHRISTIAN; FERMI, ENRICO; RUTHERFORD,ERNEST.

Further ReadingFraunfelder, H. The Mössbauer Effect. New York:

W. A. Benjamin, 1963.Maddock, Alfred G. Mössbauer Spectroscopy: Princi-

ples and Applications of the Techniques. West Sus-sex, England: Horwood, 1998.

� Mott, Sir Nevill Francis(1905–1996)BritishTheoretical Physicist, Solid StatePhysicist

Sir Nevill Francis Mott was a pioneer in solidstate physics, who shared the 1977 Nobel Prizein physics with JOHN HOUSBROOK VAN VLECK

and PHILIP WARREN ANDERSON for his work onthe electromagnetic properties of noncrystalline,or amorphous, semiconductors.

He was born on September 30, 1905, inLeeds, England, to Charles Francis Mott and Lil-lian Mary Reynolds, who had met as students

204 Mott, Sir Nevill Francis

working under JOSEPH JOHN (J. J.) THOMSON atthe Cavendish Laboratory at Cambridge Univer-sity. The spirit of discovery ran in his family: Hisgreat-grandfather was Sir John Richardson, thearctic explorer. Mott attended Clifton College,Bristol, before going on to Cambridge’s SaintJohn’s College in 1923; there he majored inmathematics and physics. He found himselfbored by laboratory experiments and was farmore excited by the revolutionary developmentsin theoretical physics. His study of the new quan-tum theory was a formative moment in his devel-opment as a physicist; throughout his career, hewould apply the intuitive understanding of itsformalism he gained in those years. After earninga bachelor’s degree in 1927, he spent a year inCopenhagen working with NIELS HENRIK DAVID

BOHR, the father of quantum theory. He thenwent on to the University of Göttingen, theother major center of the new physics, and per-formed calculations there that predicted howquantum mechanics modified ERNEST RUTHER-FORD’s classical model of the scattering of alphaparticles with helium atoms. These quantum pre-dictions were later verified experimentally by thework of SIR JAMES CHADWICK.

In 1929, Mott spent a year as lecturer atManchester University, working with LawrenceBragg, a pioneer in X-ray diffraction; he thenwas invited back to Cambridge’s Gonville andCaius College in 1930. That year he earned amaster’s degree and married Ruth EleanorHorder, with whom he would have two daugh-ters. He spent three years in Cambridge, workingon problems in nuclear physics. Because of com-plications associated with the absence of hisadviser, Ralph Fowler, Mott left without earninga Ph.D. However, Cambridge would make goodthis unfortunate omission in 1995 by awardinghim an honorary doctorate.

In 1933, he moved to the University of Bris-tol to become Melvin Wills Professor of Theoret-ical Physics; at Bristol he switched from nuclearto solid state physics and built one of the leading

groups in the new field. There he worked on met-als and metal alloys, semiconductors and photo-graphic emulsions. He devised the theoreticaldescription of the effect of light on a photo-graphic emulsion at the atomic level. He and R.W. Gurney proposed the first complete theory ofthe process that occurs when a photographic filmis exposed to light, which was built on thehypothesis that light produces free electrons andholes that roam around the crystal. When theyrun into imperfections—dislocations or foreignatoms—the electrons become trapped. They thenattract interstitial silver ions to form silver atomsand produce the latent image. In the presence ofa developer, the entire grain may be catalyzed intofree silver by the initially formed specks of silver.

Mott described his research in a series ofbooks that are still widely used, including TheTheory of Atomic Collisions, with Harrie Massie(1934); The Theory of Properties of the Metalsand Alloys, with Harry Jones (1936); and Elec-tronic Processes in Ionic Crystals, with R. W.Gurney (1940).

During World War II, Mott headed a theo-retical physics group at Fort Halstead, workingon problems related to munitions, such as defor-mation in metals due to projectiles. His socialconsciousness was aroused during this period,and in 1946 he helped to found the Atomic Sci-entists’ Association, organized to inform thepublic about the realities of atomic energy. Healso became an active member of the PugwashConference, the international group set up toexplore ways of preventing nuclear war.

Mott remained at the University of Bristoluntil 1948, when he became director of theHenry Herbert Wills Physical Laboratories, alsoin Bristol. From 1954 to 1971, he was CavendishProfessor of Physics at Cambridge, where he nur-tured the impressive growth of solid state physicsand radio astronomy. He also became master ofhis Cambridge college, Gonville and Caius, from1959 to 1966 and played a leading role in thereform of science education in Great Britain.

Mott, Sir Nevill Francis 205

When he gave up the exhausting duties of hismaster’s position, he was once more able toengage in research and became interested in thenew field of noncrystalline semiconductors(materials whose resistive properties lie some-where between those of a metal and those of aninsulator). Mott’s studies of electrical conductionin various metals led him to explore the conduc-tivity potential of amorphous materials (i.e.,materials with irregular atomic structures). WhenMott attacked the problem, the electronic struc-ture of crystalline solids had for some time beenunderstood, in terms of the effects of diffractionfrom the translationally symmetric lattice. Butsolid state physicists did not know how to applythis description to amorphous materials such asglass, which have no such symmetry. Could such adisordered material be an electrical conductor?What determined whether a material could be ametal or an insulator? To answer these fundamen-tal questions, Mott began collaborating withPhilip Anderson, then at Bell Laboratories inNew Jersey, enabling him to work several years atthe Cavendish as a visiting professor. Togetherthey devised a theoretical framework for therapidly increasing pool of experimental data.

In their Nobel Prize–winning work Mott andhis colleagues developed the quantum theorydescribing the transitions that glass and otheramorphous substances can make between electri-cally conductive (metallic) states and insulating(nonmetallic) states, thereby functioning as semi-conductors. In their groundbreaking researchthey discovered special electrical characteristicsin glassy amorphous semiconductors and formu-lated fundamental laws of behavior for theirmaterials. These glassy substances, which are rel-atively simple and cheap to produce, eventuallyreplaced the more expensive crystalline semicon-ductors in many electronic switching and mem-ory devices. This development ultimately led tothe manufacture of more affordable personal com-puters, pocket calculators, copying machines, andother similar devices. Amorphous semiconduc-

tors also provided a source of cheap and reliablematerial that could be used to improve the perfor-mance of electronic circuits, increasing computermemory severalfold. The use of amorphous semi-conductors has also led to a revolution in thetransistor industry. More efficient photovoltaiccells, based on these materials, were producedwith the capacity to convert solar energy intoelectricity; this advance opened the way for awide range of new developments in electronics,including cheaper methods of solar heating.

In 1978, Mott became president of the Lon-don-based scientific publishing house Taylor &Francis, Ltd. He was Senior Research Fellow atImperial College, London, from 1971 to 1973and in 1971 published his important book MetalInsulator Transitions. He also wrote an autobiog-raphy, A Life in Science, and collaborated withseveral others on a science–religion interface,Can Scientists Believe?

In his later years, Mott’s overriding researchinterest was the field of high-temperaturesuperconductors, which were discovered in1986. He became professor emeritus at Cam-bridge and retired to Milton Keynes, Bucking-ham, where he died at the age of 91 on August8, 1996.

Nevill Mott shaped the course of solid statephysics from the time of its emergence as anindependent field in the 1920s, when the tech-niques of quantum mechanics first enabledphysicists to study the behavior of matter in thesolid state. His work on noncrystalline amor-phous semiconductors in the 1970s helped makesolid state physics into a force for rapid techno-logical development.

Further ReadingMott, Nevill. A Life in Science. London: Taylor &

Francis, 1987.Mott, N. F., and A. S. Alexandrov, eds. Sir Nevill

Mott—65 Years in Physics. World ScientificSeries in 20th Century Physics, Vol. 12. Singa-pore: World Scientific, 1995.

206 Mott, Sir Nevill Francis

207

N� Ne’eman, Yuval

(1925– )IsraeliTheoretician, Particle Physicist

Yuval Ne’eman is an eminent physicist, who in1961 independently originated the theory ofunitary symmetry, SU(3), for classifying thehuge array of high-energy unstable particles dis-covered in the 1950s and 1960s. At the sametime, MURRAY GELL-MANN independently madethe same discovery and gave it the enduringname the “eightfold way.” Later, Ne’eman andGell-Mann collaborated on a book on the sub-ject of SU(3) symmetry and elementary parti-cles. Parallel to his life in science, Ne’eman hashad an important and controversial career as anIsraeli soldier, a pioneer in developing Israel’snuclear capability, and a politician and policy-maker on the far Right of the political spectrum.

Ne’eman was born on May 14, 1925, in TelAviv, in what was then Palestine, to Gedalia andZipora Ne’eman. He received a B.Sc. degree inengineering in 1945, and a diploma in mechani-cal engineering in 1946, from the Israeli Insti-tute of Technology (the Technion) in Haifa. Heworked as a hydrodynamical design engineer at apump factory during these years. Ne’eman inter-rupted his studies to join Israel’s struggle tobecome a sovereign state; as an activist working

against the British, he was a member of the Jew-ish underground known as the Hagana. Hefought in the War of Independence in 1948 as aninfantry commander. When the war ended withthe formation of the Israeli state, he resumed hisstudies while continuing to serve with the IsraeliDefense Forces (IDF).

On June 28, 1951, Ne’eman married DvoraRubinstein, with whom he had three children.The couple traveled to Paris, where he receiveda diploma in military engineering, in 1952, fromthe École de Guerre (war college). Advancingthrough the ranks of the IDF, he became acolonel in 1955. As his military career pro-gressed, he served as deputy director of the intel-ligence division of the IDF from 1955 to 1957and as military attaché to London from 1958 to1960. While in London, he studied at the Impe-rial College of Science and Technology, wherehis general adviser was ABDUS SALAM, one ofthe founders of the electroweak theory. In 1961,in his doctoral thesis, working independently ofGell-Mann, who made the same discovery thatyear, Ne’eman uncovered the basic symmetry ofthe subatomic particles, known as the unitarysymmetry SU(3), which later became known asthe eightfold way.

In his quest to understand how the new par-ticle SU(3) symmetry worked, Ne’eman proposeda new physical attribute (which Gell-Mann in

his independent, equivalent work calledstrangeness) of the strong interactions analogousto electric charge. Whereas in electromagneticparticle collisions electric charge is con-served—the total going in equals the total goingout—Ne’eman assumed that strangeness is con-served in strong and electromagnetic interac-tions, but not in weak interactions. In thistheory, strong interactions create a pair of parti-cles with equal and opposite values ofstrangeness, which cancel out each other. Theseparated members of such a pair cannot sponta-neously decay through a strong interaction,because that action would violate conservationof strangeness. Thus, the slower weak interac-tion, in which the violation of conservation ofstrangeness is allowed to occur, takes over andcauses radioactive decay of the particles.

The idea of a theory of nuclear force basedon a limited conservation of strangeness provedto be an organizing principle. The unitary sym-metry SU(3) inherent in the concept ofstrangeness led Gell-Mann and Ne’emandirectly to a method of sorting all known parti-cles, according to certain general characteristics,into eight “families.” The logic of this systemwas so tight that it revealed the obvious missingfamily members. In 1953, Gell-Mann publisheda series of papers predicting specific, as yet undis-covered new particles, as well as other particleshe insisted could not be discovered. His timingcould not have been better. Successive experi-ments confirmed each of his positive predictionsand failed to contradict the negative ones.

Ne’eman and Gell-Mann continued to workalong the same logical trajectory. As Ne’emanexplains:

After Gell-Mann and I came out withour theory, the question arose of why theparticles follow this particular order. In1962, I wrote a paper together withHaim Goldberg-Ophir in which we pro-posed a structural explanation: the exis-

tence of three kinds of fundamental“building blocks” which make up pro-tons and neutrons within the atomicnucleus (proton = aab, neutron = abb,omega minus = ccc, and so on). The fol-lowing year, this model was improvedupon by Gell-Mann, and independentlyby George Zweig, and Gell-Mannnamed the building blocks “quarks.”

From 1961 to 1963, Ne’eman was sciencedirector of the Soreq Research Institute, part ofIsrael’s Atomic Energy Commission. In 1963, hearrived for two years as a visiting professor at theCalifornia Institute of Technology, where hebecame a good friend of RICHARD PHILLIPS FEYN-MAN, who, along with Gell-Mann, was Caltech’sleading light. This gave him a ringside seat forwhat he called “the childish fight” into which thepassionate collaboration of the eminent Ameri-can physicists degenerated. Ne’eman publishedThe Eightfold Way with Gell-Mann in 1964.

Ne’eman then returned to Israel, where,from 1965 to 1972, he was founder and head ofTel Aviv University’s School of Physics andAstronomy. From 1971 to 1975, he served aspresident of the university. At the same time,Ne’eman became increasingly involved innational concerns, serving from 1974 to 1976 asIsrael’s chief defense scientist. He has been aninfluential voice in the debate on Israel’s pre-ferred security borders. In 1981, he became amember of the Knesset, Israel’s parliament; heserved as Israel’s minister of science and devel-opment from 1982 to 1984, and again from 1990to 1992, when he also served as minister ofenergy. He founded the Israeli Space Agency in1983 and has served as its director. From 1979 to1997, he was director of the Mortimer and Ray-mond Sackler Institute of Advanced Studies. Hewas chairman of the Mediterranean-Dead SeaCanal Committee, in which he directed theplanning of 110-kilometer canal that supplieshydroelectric power to the region.

208 Ne’eman, Yuval

Ne’eman is an associate at the InternationalCenter for Theoretical Physics, Trieste, Italy;and a member of the Israeli and American Phys-ical Societies and the Institute of Strategic Stud-ies, London. A prolific author, he has writtenThe Past Decade in Particle Theory, coedited withE. C. G. Sudarshan (1973); Group TheoreticalMethods in Physics, coedited with L. Horwitz(1980); To Fulfill a Vision (1981); Membranes andOther Extendons, written with Elena Eizenberg(1992); and The Particle Hunters, written withYoram Kirsh (1996), among other titles.

Dividing his time between Israel and theUnited States, from 1968 to 1990, he was directorof the Center for Particle Theory at the Univer-sity of Texas, Austin, where he continues to be amember of the faculty. As a member of the Insti-tute for Advanced Studies at Tel Aviv University,he also participates extensively in the activities ofthe Inter-University Center for Terrorism Stud-ies, established in 1997, in Washington, D.C.,and Holon, Israel, to study the nature and impactof international and domestic terrorism.

Further ReadingNe’eman, Yuval, and Murray Gell-Mann. The Eight-

fold Way. Cambridge, Mass.: Perseus, 2000.Ne’eman, Yuval, and Yoram Kirsh. The Particle Hunters.

Cambridge: Cambridge University Press, 1996.

� Nernst, Walther(1864–1941)PrussianExperimentalist (Thermodynamics),Physical Chemist

Walther Nernst was a remarkable physicist andphysical chemist, who discovered the third law ofthermodynamics, also known as the Nernst heattheorem, which states that the entropy of a puresubstance tends to zero as its thermodynamic tem-perature approaches zero. He received the NobelPrize in chemistry for this work in 1920.

Nernst was born in Briesen, West Prussia,on June 25, 1864, the son of a district judge. Heobtained his early schooling in Graudentz andthen attended the Universities of Zurich, Berlin,and Graz, where he studied physics and mathe-matics. He then went on to study in Wurtzburg,where in 1887 he received a doctorate for a the-sis on electromotive forces produced by mag-netism in heated metal plates. His first positionwas at Leipzig University, where he joined a dis-tinguished company of physical chemists. In1892, he married Emma Lohmeyer. They hadtwo sons, both of whom would be killed inWorld War I, and three daughters.

In 1894, Nernst accepted the chair in phys-ical chemistry in Göttingen, where he foundedthe Institute for Physical Chemistry and Electro-chemistry and became its director. Always look-ing for industrial applications of physicalresearch, Nernst produced ingenious devices. In1898, he invented a metallic-filament lamp,known as the Nernst lamp. A link between thecarbon lamp and the incandescent lamp, it wassuperseded by the development of tatalum andtungsten filaments. He also invented an electri-cal piano, which replaced the sounding boardwith radio amplifiers.

Having rapidly developed a reputation forbrilliance as well as egocentricity, Nernstaccepted a position at the University of Berlin,as professor of chemistry and physics, in 1905.With his students he made many importantphysical and chemical measurements, includingdeterminations of specific heats of solids at verylow temperatures and of vapor densities at hightemperatures. All these were considered fromthe point of view of the quantum hypothesis.

During this period, Nernst made his NobelPrize–winning contribution, completing thefoundations of thermodynamics, which hadbeen laid in the mid-19th-century. In 1847,HERMANN LUDWIG FERDINAND VON HELM-HOLTZ had derived a general equation that ledto the first law of thermodynamics, which states

Nernst, Walther 209

that the total energy of a system and its sur-roundings remain constant even if it changesfrom one form of energy to another. Then, in1850, RUDOLF JULIUS EMMANUEL CLAUSIUS

had formulated the second law of thermody-namics, the law of entropy, which states thatheat cannot spontaneously pass from a cooler toa hotter body.

Nernst’s third law of thermodynamics, for-mulated in 1906, states that it is impossible tocool a body to absolute zero by any physical pro-cess. Although one can approach absolute zero,one cannot actually reach this limit. If one couldreach absolute zero, all bodies would have thesame entropy. Nernst and his collaboratorstested his theorem by measuring the specificheats and other thermodynamic quantities of anumber of substances at low temperatures. Byearly 1910, they found that specific heats notonly decreased with lowering temperature, asNernst had proposed, but appeared to bedecreasing to zero. This outcome had been pre-dicted by ALBERT EINSTEIN three years earlier onthe basis of the quantum hypothesis.

Through his colleague MAX ERNEST LUD-WIG PLANCK, Nernst made the acquaintance ofEinstein. He and Planck would later be instru-mental in luring Einstein to the University ofBerlin in 1914. Nernst played an important rolein organizing the first of the Solvay Conferences,in which the best minds of physics would grapplewith the mysteries of the newly emerging quan-tum theory.

Nernst made fundamental contributions inelectrochemistry, osmotic pressure, the theory ofsolutions, solid state chemistry, thermochem-istry, electroacoustics, and photochemistry. Hewrote numerous monographs on these topics aswell as a standard textbook, Introduction to theMathematical Study of the Natural Sciences. Hebecame director of the new Physical ChemistryInstitute in 1924, a position he held until hisretirement in 1933. He died in Berlin onNovember 8, 1941.

As the founder of modern physical chem-istry, Nernst was an important figure in the tran-sition from classical to modern physical science.

Further ReadingBarkan, Diana. Nernst: Architect of Physical Revolu-

tion. Cambridge, Mass.: Cambridge UniversityPress, 1999.

Mendelssohn, Kurt. The World of Walther Nernst: TheRise and Fall of German Science, 1864–1941.Pittsburgh: University of Pittsburgh, 1973.

� Newton, Sir Isaac(1642–1727)BritishMathematical Physicist (Mechanics,Gravitation), Experimentalist (Optics),Astronomer

Sir Isaac Newton launched the modern age ofscientific discovery and invention that contin-ues to this day. His was a rare genius, capable ofcreating the mathematical tools—the calcu-lus—he needed to pursue his physical investiga-tions. His three laws of motion and his law ofgravitation, clearly defining the nature of mass,weight, force, and acceleration, remain thefoundation of our understanding of the mechan-ical dynamics of the macroscopic world. Hismathematical description of gravitational forcegave a physical basis to the Sun-centered uni-verse proposed by Copernicus and defended byGALILEO GALILEI and erased the artificial bound-ary separating terrestrial and celestial events.His breakthroughs in optics, including the dis-covery that white light is composed of a spec-trum of colors and the invention of thereflecting telescope, would suffice to secure theplace of a lesser figure in the annals of physics; inNewton’s case, they rank among the secondaryachievements of an unparalleled career.

Isaac Newton was born in Woolsthorpe, inLincolnshire, England, on December 25, 1642,

210 Newton, Sir Isaac

by the old Julian calendar, the year Galileo died.His father, an illiterate but propertied farmer,had died three months earlier and Isaac himself,a premature, sickly baby, surprised everyone bysurviving. His mother’s remarriage to a wealthy,elderly clergyman in the next town, when Isaacwas three, was a blow to the boy. Left in the careof grandparents, who treated him as an orphan,he found solace in making drawings and diagramsof mechanical things and in executing a few, suchas water clocks, kites with fiery lanterns attached,and a model mill powered by a mouse. He wassent to school in nearby Grantham at age 12 butforced to withdraw four years later when hisnewly widowed mother demanded his services asmanager of her estate. When Isaac proved whollyunsuited to the task, an uncle succeeded in reen-rolling him at school, where he studied for hisuniversity entrance examinations.

In 1661, Newton entered Trinity College,Cambridge, where, despite his mother’s wealth,he was obliged to work his way through the firstthree years by waiting tables and cleaning roomsfor better subsidized students. He wrote, in ajournal of his thoughts, “Plato is my friend, Aris-totle is my friend, but my best friend is truth.”He plunged avidly into his studies and in 1664was elected a scholar, a status that included fouryears of financial support. But the bubonicplague would interrupt his university career.Spreading across Europe, it reached Cambridgein 1665, forcing the university to close its doors.

Newton would later call the next two years,spent at home in seclusion, “the prime of my agefor invention.” In light of what he accomplished,this seems an understatement. During this periodhe laid the foundations of differential and inte-gral calculus, which he called the “method offluxions.” Newton was led to invent this newbranch of mathematics by his desire to describemotion using analytic geometry. The problemwas that plane geometry was capable of describ-ing only linear motion. To solve this problem, hereasoned that, by dividing the straight lines of a

polygon into infinitesimally smaller straight-linesegments, a circle would result in the limit of aninfinitely large number of line segments of van-ishingly small length. From this insight flowedthe calculus, the algebra of infinitesimal quanti-ties, which enabled him to describe curvilinearmotion mathematically.

The calculus was the mathematical lan-guage in which he would express his theory ofuniversal dynamics. And, indeed, it was duringthis extraordinary two-year period that Newtonexperienced his major physical insights: he for-mulated the three laws of motion and the essen-tials of his gravitation theory, in addition tocompleting important work on optics. Amaz-ingly, however, he would not share his findingswith the world until several years later. True to

Newton, Sir Isaac 211

Isaac Newton launched the modern age of scientificdiscovery and invention. Newton’s three laws ofmotion and his law of gravitation remain thefoundation of our understanding of the mechanicaldynamics of the macroscopic world. (AIP Emilio SegrèVisual Archives, Physics Today Collection)

his own complex personal dynamics, the with-drawn young man, fearing criticism and cherish-ing his “peace of mind,” was roused to publishonly with external encouragement, most fre-quently someone else’s claiming credit for whatNewton knew he had already discovered. Atsuch times, he would defend his claim to pri-macy fiercely and even ruthlessly.

Thus, the publication in 1667 by NicolasMercator of a book with some methods for deal-ing with infinite series spurred Newton to writehis own treatise, De Analysi, expounding hisown wider-ranging mathematical results. By nowhe was back in Cambridge and had been electeda fellow of Trinity College. It was his mentorIsaac Barrow who disseminated Newton’s workto the mathematics community, establishing theyoung man’s reputation. When Barrow resignedas Lucasian Professor of Mathematics in 1669 topursue divinity studies, Newton, age 26, wasgiven this prestigious chair. Newton wouldremain at Cambridge for almost 30 years, livingmodestly and never marrying. An indifferentlecturer, whose classes were sparsely attended,Newton devoted his days and nights to his soli-tary studies, which, in addition to physics andmathematics, included chemistry, alchemy, the-ology, and mysticism. Newton would remain apassionate student of theology all his life, assert-ing the existence of a deity as the “first cause” ofall natural phenomena.

Despite his quest for anonymity Newtonsoon became famous for his invention of thereflecting telescope. In need of a telescope forobserving the motion of comets and planets,Newton was dissatisfied with the Galilean-stylerefractor telescope, then the only one in use,which had a large lens at the front end to gatherlight. Refractors tended to introduce spuriouscolors (i.e., chromatic aberration); to eliminatethis, Newton used a mirror instead of a lens tocollect light. The resulting efficient and inex-pensive instrument became the most populartelescope in the world and remains the proto-

type of today’s huge astronomical reflecting tele-scopes. When, in 1672, Newton presented oneto the Royal Society, the most influential ofnumerous scientific societies that were formed inthe 17th century, it elected him a fellow andurged him to write a paper on his work in optics.Newton obliged, at last publishing the results ofhis 1665–1666 experiments with light and color.He reported that sunlight, when passed througha prism, dispersed into a spectrum of colors;when passed through a second prism, the colorsin the spectrum combined and once moreformed white light. In this way he proved thatcolors are a property of light and not of theprism. He also investigated other optical phe-nomena including thin film interference effectssuch as Newton’s rings. Although this paper wasgenerally well received, criticism by the eminentROBERT HOOKE made Newton once more recoilfrom the ordeal of publishing. Later Hookewould claim that Newton had stolen some of hisoptical results. Newton’s response was to waituntil Hooke was dead before publishing hisOpticks in 1704.

Given his aversion to subjecting his work topublic scrutiny, Newton might never have pub-lished his most important findings without theintervention of the eminent astronomer EdmondHalley, who urged him to write his magnum opusand then saw that it was published. Over a two- tothree-year period, between 1684 and 1686, New-ton wrote his Mathematical Principles of NaturalPhilosophy, known today as the Principia, whichwas published in 1687. Here, in what is consid-ered the greatest scientific treatise ever written,Newton proposed his laws of motion, and, mostcentrally, the theory of gravity. In developing hissystem, he built upon a synthesis of Kepler’s lawsof planetary motion and Galileo’s laws of motionand gravitation. He would later say

If I have seen further than other men, itis because I have stood on the shouldersof giants.

212 Newton, Sir Isaac

Newton “saw further” by divining the unify-ing physical principles underlying his predeces-sors’ observations. He invented the concept ofmass, a physical property of every object in theuniverse, and said that all objects with mass pos-sess inertia, the tendency to resist any change inits state of motion. In his first law, the law of iner-tia, he states: “Every body remains at rest or inuniform motion in a straight line unless it is com-pelled to change that state.” Here Newton affirmsGalileo’s contention, contradicting Aristotle,that no force is needed to sustain an object inmotion. In Newton’s universe, when an object isset in motion or changes its velocity or directionof motion, a force is responsible. Newton definedforce in his second law, the law of acceleration,which states, “A force accelerates a body by anamount proportional to its mass.” Since accelera-tion is the rate of change of velocity with time,the law can be stated as, Force equals mass timesacceleration or F = ma. Newton’s third law ofmotion states, “To every action there always existsan equal and opposite reaction.” The force ofaction and the counterforce of reaction are alwaysmutual; that formulation indicated how objectscould be made to move and led to the law of con-servation of momentum.

Newton then took these concepts and, bywedding them to his theory of the universality ofthe gravitational force, explained the dynamicsof the entire solar system, validating Kepler’slaws of planetary motion. According to legend,Newton saw an apple fall in his orchard around1665–1666, thought of it in terms of an attractivegravitational force toward the Earth, and realizedthe same force might extend as far as the Moon.He was familiar with Galileo’s work on projectilesand suggested that the Moon’s motion in orbitcould be understood as a natural extension of thattheory. Since the law of inertia tells us that theMoon would move in a straight line unless actedupon by an outside force, Newton reasoned that aforce—gravity—is acting on it. Calculating theforce needed to hold the Moon in its orbit, as

compared with the force pulling an object to theground, he deduced his famous inverse-square lawof gravitation: “The force of gravitational attrac-tion between two bodies is proportional to theirmasses, and decreases with increasing distancebetween them, as the inverse of the square of thatdistance, so if the distance is doubled, the force isdown by a factor of four.” In order for the law towork, Newton had made the key assumption thatgravity emanates from the center of the Earth.Using exact computation, he calculated the rela-tive masses of heavenly bodies from their gravita-tional forces. Since comets were shown to obeythe same laws, he conjectured that they mightperiodically return. Using his law of action–reac-tion, he was also able to describe the tides asresulting from the gravitational pull of both theSun and the Moon: the action force holds theMoon in its orbit; the reaction force of gravityfrom the Moon moves the tides around the Earth.However, he never pretended to understand whatactually caused gravitation, suggesting to thosewho found the idea of attraction across emptyspace objectionable that it might be caused by theimpact of unseen particles.

The publication of the Principia had anelectrifying effect throughout Europe andturned Newton into a figure of awe and rever-ence. After its appearance he seems to havegrown bored with Cambridge. As a firm oppo-nent of the attempt by King James II to makethe universities into Catholic institutions, hewas elected a member of Parliament for theUniversity of Cambridge to the ConventionParliament of 1689 and sat again in 1701–1702.The excessive strain of his studies and theattendant disputes caused him to suffer severedepression in 1692, when he was described ashaving “lost his reason.”

Four years later, in 1696, he moved to Lon-don as Warden of the Royal Mint. In 1699, hebecame Master of the Mint, an office he retaineduntil his death. The Royal Society of Londonfirst elected him president in 1703 and annually

Newton, Sir Isaac 213

reelected for the rest of his life. He was knightedby Queen Anne in 1705.

His major work, Opticks, in which hesummed up his life’s work on light, appeared in1704. Although he held that light rays were cor-puscular in nature, he integrated into his ideasthe concept of periodicity, holding that “etherwaves” were associated with light corpuscles. Thecorpuscle concept lent itself to an analysis byforces and established an analogy between theaction of material bodies and that of light, rein-forcing the universalizing tendency of the Prin-cipia. However, in the 1800s, the investigation ofinterference effects by THOMAS YOUNG led tothe establishment of the wave theory of light.

As Newtonian science gained acceptance inEurope, he became the most highly esteemednatural philosopher in Europe. His last decadeswere spent revising his major works, polishinghis studies of ancient history, and defendinghimself against critics, such as Leibnitz, withwhom he engaged in bitter dispute over who hadinvented the calculus. He died at age 84 onMarch 20, 1727, and was buried with great pompin Westminster Abbey.

Newton seemed to understand that his workheralded the beginning of an era in which thescientific method would continue to unlock thebasic laws governing the universe. He wrote:

To myself I seem to have been only likea boy playing on the seashore and

diverting myself in now and then find-ing a smoother pebble or a prettier shellthan ordinary, whilst the great ocean oftruth lay all unexplored before me.

Despite this apparent modesty, Newtonwould have been pleased, but not altogether sur-prised, to hear the reply of Apollo 8 astronaut BillAnders who was asked who was “driving” thespacecraft to the Moon by his eight-year-old son.“I think,” said the astronaut, “Isaac Newton isdoing most of the driving now.”

Further ReadingBerlinski, David. Newton’s Gift: How Sir Isaac Newton

Unlocked the System of the World. New York: FreePress, 2000.

Fauvel, John, ed. Let Newton Be! Oxford: OxfordUniversity Press, 1988.

Ferris, Timothy. “Newton’s Reach,” in Coming of Agein the Milky Way. New York: William Morrow,1988, pp. 103–122.

Newton, Isaac. The Principia: Mathematical Principlesof Natural Philosophy. Translated by BernardCohen and Anne Whitman. Berkeley: Univer-sity of California Press, 1999.

Speyer, Edward. Six Roads from Newton: Great Discov-eries in Physics. Wiley Popular Science. NewYork: John Wiley & Sons, 1996.

Westfall, Richard S. Never At Rest: A Biography ofIsaac Newton. Cambridge: Cambridge UniversityPress, 1983.

214 Newton, Sir Isaac

O� Ohm, Georg Simon

(1789–1854)BavarianTheoretical and Experimental Physicist(Classical Electromagnetism)

Georg Simon Ohm’s formulation of the relation-ship between current, electromotive force (volt-age), and resistance, known as Ohm’s law, was aseminal contribution to the understanding ofelectricity and opened the door to an era ofinvention in which scientists could design elec-tric circuits for specific functions. Although hisname would later be synonymous with the unitof resistance (the ohm), he was underappreci-ated in his lifetime and frustrated in his aca-demic ambitions.

Ohm was born in Erlangen, Bavaria (nowGermany), on March 16, 1789. His Protestantparents had no formal education, but Ohm wasfortunate in his father, a self-educated masterlocksmith who gave his children a solid educa-tion in mathematics, physics, chemistry, andphilosophy. Young Georg gained far more fromthis home schooling than he did from the unin-spiring, learning-by-rote methods used at theErlangen Gymnasium, where he was sent at age11 for his secondary education.

On entering the University of Erlangen in1803, the future pioneer of the theory of elec-

tricity dissipated his opportunity for highereducation in a nonstop round of social plea-sures, which included dancing, ice-skating, andplaying billiards. His irate father demandedthat he drop out after three semesters and senthim to earn his living as a schoolteacher andprivate tutor in Switzerland. During his years inSwitzerland, Ohm, guided by a former profes-sor, carried out an exhaustive program of inde-pendent mathematical study, reading the worksof Euler, Laplace, and Lacroix, among others.The fact that he was awarded his Ph.D. inOctober 1811, after returning to the Universityof Erlangen in April of that same year, givessome idea of how well he succeeded in master-ing the material independently.

Although the university immediately en-gaged him as an unpaid lecturer, an unimpededpath to the scholarly career he desired was not tobe. Ohm was forced to take on a paying job as ateacher in a mediocre school in Bamberg. In 1817,he found a somewhat better position in Cologne,teaching mathematics and physics at the JesuitGymnasium. Ohm doggedly pursued his self-education, reading the work of the French math-ematicians and acquainting himself with currentwork on electricity. In 1820, when the Danishphysicist HANS CHRISTIAN ØRSTED announcedhis groundbreaking discovery that an electric cur-rent can generate a magnetic force, Ohm began

215

using the gymnasium’s well-equipped physics lab-oratory to perform his own experiments.

His work would culminate in 1825, when, atage 36, Ohm published his first paper, examiningthe decrease in the magnetic force produced by acurrent flowing in a wire as the length of thewire increases. He used a voltaic pile (electricbattery) to produce a current and connected dif-ferent lengths of wire to it; he then measured themagnetic force that was generated by the cur-rent, using the magnetic needle of a galvanome-ter. In this way, that is, by measuring themagnetic force, he was, in fact, measuring theelectric current flowing in the wire. The resultsconfirmed his expectations: a longer wire pro-duced a greater loss in the magnetic force. Thisimplied that a longer wire had a smaller currentflowing in it and, therefore, had greater resis-tance, the term coined by Ohm to designate theopposition of the material to the flow of charge.

In 1826, he repeated this experiment, thistime generating the current by using a thermo-couple (a pair of wires of different conductors,welded or soldered at one end, used to measuretemperature). This technique had the advantageof producing a constant electric current, as dis-tinct from the fluctuating current produced by thevoltaic pile. He found that the magnetic force wasequal to the electromotive force produced by thethermocouple divided by the length of the wireplus the resistance of the remainder of the circuit,including the thermocouple itself. He expressedhis findings in terms known today as Ohm’s law,which states that the current is equal to the elec-tromotive force divided by the overall resistanceof the circuit.

In the context of this experiment, Ohmpointed out that an electric current flowsthrough a conductor of varying resistance to pro-duce a potential difference, just as heat flowsthrough a conductor of varying conductivityfrom one temperature to another to produce atemperature difference. In 1827, Ohm publishedhis results and his complete theory of electricity

in his great work, Die Galvanische Kett, mahtem-atisch bearbeitet (The Galvanic circuit, investi-gated mathematically).

Despite the immense importance of Ohm’swork, recognition by the scientific communitycontinued to elude him. Few of his peers werecapable of understanding his mathematics, andthose few German physicists who could appreci-ate the rigor of Ohm’s formulations doubted thecorrectness of his approach. Ohm remained aschoolteacher, in Berlin, until 1833, when hemoved to Nuremberg and became a professor ofphysics at the respectable but undistinguishedPolytechnic Institute.

Recognition, when it was finally given him,began in England. In 1841, Ohm was awardedthe Royal Society’s Copley Medal. In 1849, hebegan to lecture at the University of Munich.He finally became a professor of physics at theuniversity in 1852 but died only two years laterin Munich on July 6, 1854.

Ohm’s law, together with the laws of elec-trodynamics discovered by ANDRÉ-MARIE

AMPÈRE at about the same time, pioneered theway to future theoretical investigation of elec-tricity. His name is remembered in both the unitof resistance, the ohm, and its inverse, the unitof conductivity, the mho, Ohm spelled back-ward, also called the siemens.

Using Ohm’s law, scientists could for thefirst time calculate the amounts of current, volt-age, and resistance in electric currents, measur-ing changes in one of these variables throughchanges in the others.

Further ReadingJungnickel, Christa, and Russell McCormmach. Intel-

lectual Mastery of Nature: Theoretical Physics fromOhm to Einstein: The Torch of Mathematics,1800–1870. Vol. 1. Chicago: University ofChicago Press, 1986.

Keithley, Joseph F. The Story of Magnetic Measure-ments: From Early Days to the Beginning of the 20thCentury. New York: Wiley-IEEE Press, 1998.

216 Ohm, Georg Simon

� Oppenheimer, J. Robert(1904–1967)AmericanTheoretical Physicist, QuantumTheorist, Atomic Physicist, NuclearPhysicist

J. Robert Oppenheimer was a brilliant theoreti-cal physicist who made important contributionsto quantum mechanics and nurtured the devel-opment of an outstanding theoretical physicscommunity at the University of California,Berkeley. His name is forever associated with thedevelopment of the first atomic bomb in LosAlamos, New Mexico, where he was director ofthe Manhattan Project, and, in particular, withthe moral and ethical controversies faced byphysicists who participated in the creation ofweapons of mass destruction.

He was born in New York City on April 22,1904, the elder of Ella and Julius Oppenheimer’stwo sons. His father was a German Jew whoimmigrated to the United States at the age of 17and made a fortune importing textiles. Robertwas a frail, studious child, who would laterdescribe himself as an “unctuous, repulsivelygood little boy,” whose schooling failed to pre-pare him for life’s cruelties. He attended the Eth-ical Culture School in New York, which wasfounded on the principle “Man must assumeresponsibility for the direction of his life and des-tiny.” His interest in science was sparked by hisgrandfather’s gift of a mineral collection. At age12, the precocious child gave a lecture at theNew York Mineralogical Club.

Oppenheimer entered Harvard Universityin 1922 and graduated summa cum laude inonly three years. He would later describe hisundergraduate years as the most exciting of hislife, when he “intellectually looted the col-lege,” usually taking six courses and auditingfour. He had a talent for languages, excelling inLatin, Greek, French, and German. He pub-lished poetry and studied Eastern philoso-

phies—subjects he would pursue all his life.While majoring in chemistry, he was quicklydrawn to understanding the physics that under-lay the chemistry and began working in the lab-oratory of the future physics Nobel laureatePERCY WILLIAMS BRIDGMAN.

On the strength of a letter from Bridgman,who did not conceal the fact that Oppenheimer’sstrengths were analytical, not experimental, hewas accepted by the Cavendish Laboratory at theUniversity of Cambridge. He sailed to England in1925, an exhilarating time for a young physicistto be in Europe. Postwar work on quantum the-ory was just getting under way, and Oppen-heimer’s work at the laboratory, which, under the

Oppenheimer, J. Robert 217

J. Robert Oppenheimer made important contributionsto quantum mechanics. His name is forever associatedwith the development of the first atomic bomb inLos Alamos, New Mexico. (AIP Emilio Segrè VisualArchives and Los Alamos Scientific Laboratory)

direction of ERNEST RUTHERFORD, was interna-tionally renowned for its pioneering studies onatomic physics, exposed him to the latest ideas.His acquaintance with NIELS HENRIK DAVID

BOHR, the guiding spirit of quantum mechanics,was the turning point in his decision to commithimself to theoretical physics.

Oppenheimer had already published twopapers on quantum mechanics when he acceptedMAX BORN’s invitation to study in Göttingen,Germany, in 1926. He earned his Ph.D. there in1927 with the dissertation “On the QuantumTheory of Continuous Spectra,” which waspublished in the prestigious German journalZeitschrift fur Physik. The professor in charge ofhis oral examination is said to have expressedrelief when the ordeal was over, fearing that theprobing Oppenheimer was about to question him.Between 1926 and 1929, the young physicistpublished 16 papers. Together with Born hedeveloped the quantum theory of molecules.When he returned to the United States, at age25, he enjoyed an international reputation.

Awarded a National Research Fellowship,he headed back to Europe, honing his mathe-matical skills with Paul Ehrenfest in Leiden andhis analytical edge with WOLFGANG PAULI inZurich. In 1929, he was appointed assistant pro-fessor at both the California Institute of Tech-nology (CalTech) and the University ofCalifornia at Berkeley. For the next 13 years hewould commute between these two campuses,inspiring a generation of physicists and trans-forming the face of American physics. Under hischarismatic leadership, an outstanding group ofresearchers attacked the problems of theoreticalphysics with an intensity previously unknown atAmerican universities. His most importantresearch involved the study of the relativisticequations for the atom developed by PAUL

ADRIEN MAURICE DIRAC. In 1930, Oppenheimershowed that the Dirac equation predicted that apositively charged particle with the mass of anelectron could exist. This particle, detected in

1932 and called the positron, was the first exam-ple of antimatter. He also did research on theenergy processes of subatomic particles, includ-ing electrons, positrons, neutrons, and mesons.In addition, his analyses anticipated many laterfinds in astrophysics, including neutron stars andblack holes.

During these California years, in the earlythirties, Oppenheimer’s political consciousnesswas awakened by the rise of fascism in Europe.He became deeply concerned about the fate ofJews in Germany, where he had relatives, manyof whom he would later help to escape. Heformed friendships with Spanish students whowere Communists and in 1936 he sided with therepublic during the Spanish Civil War. Hewould stop short of joining the CommunistParty, however, finding he could make “nosense” of its dogma.

In 1939 Oppenheimer met his future wife,Katherine Puening, known as Kitty, who wouldbear him a son and a daughter. Also in that yearBohr, who had escaped from Denmark to Eng-land, brought word that the Germans had splitthe atom. ALBERT EINSTEIN and Leo Szilardwrote their famous letter warning PresidentFranklin Delano Roosevelt that the Nazis couldbe the first to make a nuclear bomb. When Roo-sevelt established the Manhattan Project in1942, giving the United States Army responsi-bility for the joint efforts of British and U.S.physicists to develop an atomic bomb, Oppen-heimer became its director. In 1943, he set up anew research station at Los Alamos, New Mex-ico, where he assembled a team of first-rate sci-entific minds, including HANS ALBRECHT

BETHE, ENRICO FERMI, and EDWARD TELLER. Thequality of Oppenheimer’s supervision of themore than 3,000 people working at Los Alamosis generally believed to have been a crucial fac-tor in the project’s success. According to Teller,

Oppenheimer was probably the best labdirector I have ever seen, because of the

218 Oppenheimer, J. Robert

great mobility of his mind, because ofhis successful effort to know about prac-tically everything important inventedin the laboratory, and also because of hisunusual psychological insight.

On July 16, 1945, Oppenheimer was presentat “Trinity,” the first test of an atomic bomb, inthe New Mexico desert. He described his initialreaction with masterful understatement: “Weknew the world would not be the same.” Withthree other scientists who had been consultedon how to deploy the bomb, Oppenheimer rec-ommended that a populated “military target” beselected. Within a month, two bombs weredropped on Nagasaki and Hiroshima, leading tothe Japanese surrender on August 10, 1945.Oppenheimer would later write:

I have no remorse about the making ofthe bomb and Trinity. That was doneright. As for how we used it . . . I do nothave the feeling that it was doneright. . . . Our government should haveacted with more foresight and clarity intelling the world and Japan what thebomb meant.

After the war, as chairman of the UnitedStates Atomic Energy Commission (AEC),Oppenheimer continued to experience the limitsof his influence over the technology he hadplayed so central a role in developing. Along withmost members of the commission, he opposed thecreation of a hydrogen bomb. But when the Sovi-ets exploded a nuclear device in the summer of1949, President Truman gave the H-bomb projecta green light. Although Oppenheimer’s offer toresign was not accepted, his opposition to thehydrogen bomb was to have dramatic conse-quences. In 1953, in the heat of the McCarthyera, when anti-Communist hysteria reigned,Oppenheimer was accused of having Communistsympathies. The Federation of American Scien-

tists rushed to his defense, to no avail. PresidentEisenhower ordered he be stripped of his securityclearance, and Oppenheimer’s influence onnational science policy came to an end.

In the eyes of the world, Oppenheimer hascome to epitomize the plight of the scientist,attempting to assume moral responsibility forthe consequences of his discoveries, whobecomes the target of a witch-hunt. Yet there isa darker side to Oppenheimer’s struggle; fouryears earlier, in 1949, perhaps wishing to shoreup his own position, he had joined forces withthe witchhunters, denouncing several of his col-leagues as Communist sympathizers before theHouse Un-American Activities Committee.

In his last years, as director of the Instituteof Advanced Study at Princeton, Oppenheimerdevoted much of his time to writing about theproblems of intellectual ethics and morality. In1963, President Johnson awarded him theEnrico Fermi Prize, the highest award the AECconfers, as an attempt to make amends for hisunjust treatment. In 1966, he retired fromPrinceton, where he died on February 18 of thefollowing year, of throat cancer. His final printedwords were “Science is not everything, but sci-ence is very beautiful.”

See also FEYNMAN, RICHARD PHILLIPS; RABI,ISIDOR ISAAC.

Further ReadingHerken, Gregg. Brotherhood of the Bomb: The Tangled

Lives and Loyalties of Robert Oppenheimer, ErnestLawrence and Edward Teller. New York: HenryHolt, 2002.

Rhodes, Richard. Dark Sun: The Making of the Hydro-gen Bomb. New York: Simon & Schuster, 1995.

———. The Making of the Atomic Bomb. New York:Simon & Schuster, 1986.

Schweber, Silvan S. In the Shadow of the Bomb. Prince-ton, N.J.: Princeton University Press, 2000.

Smith, Alice K., and Charles Weiner, eds. RobertOppenheimer: Letters and Recollections. Cam-bridge, Mass.: Harvard University Press, 1980.

Oppenheimer, J. Robert 219

� Ørsted, Hans Christian(1777–1851)DanishExperimental Physicist (ClassicalElectromagnetism), Physical Chemist

Hans Christian Ørsted exhilarated the Europeanscientific community in July 1820 with theannouncement of his discovery that an electriccurrent produces a magnetic field. Physicists,among them ANDRÉ-MARIE AMPÈRE, lost notime following up on Ørsted’s groundbreakingwork, developing the fields of electromagnetismand electrodynamics.

The man who would initiate the mainthrust of 19th-century physics was educated as apharmacist. At the age of 17, he moved toCopenhagen from Rudkøbing, Langeland, Den-mark, where he had been born on August 14,1777. His studies at the University of Copen-hagen represented his first experience of formaleducation. He entered the university in 1794,earned a doctorate in pharmacology in threeyears, and settled down to practice his profes-sion. But two years later he abandoned pharma-ceutical work for an extensive tour of Europe.When he returned, he began to exercise his tal-ent as a teacher, successfully offering a series ofpublic lectures. Ørsted lived in an age in whichspecialization was far less developed than in ourown, and when it was common for scientists toteach and do research in more than one field. In1806, presumably on the strength of his teachingabilities, he became a professor of physics at theUniversity of Copenhagen, a position he wouldretain until 1829.

In the late 18th century, interest in mag-netism was spurred, in part, by the need for acompass that would be accurate near the polarregions and could thus be used in the search forthe Northwest Passage (a sea passage throughthe Arctic regions of North America that wouldconnect the Atlantic and Pacific Oceans).Ørsted began seeking the connection between

electricity and magnetism around 1813, philo-sophically convinced that all forces in naturehave a unified essence and can therefore beconverted into one another. As early as 1600,William Gilbert, a pioneer of magnetism, hadproposed such a connection. In Ørsted’s time,many physicists looked for a magnetic force act-ing in the direction of the electric current butfailed to find it. Ørsted succeeded because hehypothesized that the magnetic force would beacting in a direction perpendicular to that ofthe current.

Ørsted performed his history-making exper-iment before a lecture hall filled with his stu-dents, in April 1820. The demonstration was asimple one: he placed a compass needle beneatha wire connected to a battery. The needle movedfaintly toward the wire. Ørsted was convinced ofhis success but, given the small size of the effect,proceeded cautiously. Not until July, after per-forming further experiments showing that acircular magnetic force, which aligns itself per-pendicular to the current, is produced aroundthe wire, did he report his findings to Europe’sleading scientific journals. Here at last was defi-nite experimental evidence of the relationshipbetween electricity and magnetism. Withinweeks of learning of Ørsted’s results, Ampère inFrance would develop a mathematical descrip-tion of the magnetic force between two electriccurrents, founding the new science of electrody-namics. The race to develop a unified theory ofelectrodynamics was on, although Ørsted him-self would play no further role in it.

In 1829, he left his university post tobecome director of the Polytechnic Institute inCopenhagen, where he remained until his deathon March 2, 1851. As a teacher and writer, heplayed a dynamic role in elevating the level ofscientific education and research in Denmark.In 1824, he founded a society devoted to thespread of scientific knowledge among the gen-eral public, the Danish Society for the Promo-tion of Natural Science. His name was given to

220 Ørsted, Hans Christian

the oersted (symbol Oe), the unit of magnetic-field strength in the centimeter–gram–secondsystem of physical units.

Further ReadingJelved, Karen, ed. Selected Scientific Works of Hans

Christian Ørsted. Princeton, N.J.: Princeton Uni-versity Press, 1998.

Keithley, Joseph F. The Story of Magnetic Measure-ments: From Early Days to the Beginning of the20th Century. New York: Wiley-IEEE Press,1998.

Ørsted, Hans Christian 221

P� Pauli, Wolfgang

(1900–1958)Austrian-born SwissTheoretical Physicist, QuantumTheorist, Particle Physicist

Wolfgang Pauli was one of the pioneering gener-ation of 20th-century physicists who discoveredand refined the basic principles of atomic behav-ior as revealed by the laws of quantum mechan-ics. His most far-reaching contributions flowedfrom his insight that no two electrons in an atomcan occupy the same energy state. Enunciated in1925, the Pauli exclusion principle, as it came tobe called, explained numerous phenomena onboth the atomic and nuclear levels and garneredPauli the 1945 Nobel Prize in physics. He is alsofamous for his 1930 prediction of the existence ofthe neutrino, a particle without charge or mass,which was discovered almost 30 years later.

Wolfgang Pauli was born in Vienna on April25, 1900. His father, a physician and professor ofchemistry at the University of Vienna, was ofJewish origin but had his son baptized aCatholic. His godfather was the famous Austrianphysicist ERNST MACH. A precocious highschool student in Vienna, Wolfgang entered theUniversity of Munich in 1918, having alreadymastered both special and general relativity.Encouraged by his professor, the eminent

ARNOLD JOHANNES WILHELM SOMMERFELD,Pauli wrote the first comprehensive monographon the subject, a 200-page work, whichprompted ALBERT EINSTEIN himself to observe,“Whoever studies this mature and grandly con-ceived work might not believe that its author isa twenty-one year old man.” The Munich yearswere formative for Pauli. It was then that he wasexposed to ideas far stranger than those he hadfound in Einstein’s work. As he would laterrecall, “I was not spared the shock, which everyphysicist accustomed to the classical way ofthinking experienced when he came to knowNiels Bohr’s basic postulate of quantum theoryfor the first time.”

He formed a lifelong friendship withWERNER HEISENBERG, whose uncertainty princi-ple would add the notion of nondeterminacy tothe startling picture of nature emerging fromquantum mechanics in the 1920s. Their longand copious correspondence would later be pub-lished, providing a wealth of insights into one ofthe most exciting periods in the history ofphysics. Pauli received a doctorate in 1922 for athesis, supervised by Sommerfeld, on the quan-tum theory of ionized molecular hydrogen.

That same year he went to Göttingen as anassistant to MAX BORN but soon moved toCopenhagen to study with NIELS HENRIK DAVID

BOHR; there he began, in his own words, “a new

222

phase of my scientific life.” When he returned toGermany in 1923, accepting a position at theUniversity of Hamburg as a lecturer, his expo-sure to Bohr’s work on the structure of the atomand the problems that work was encounteringhad become the focus of his research.

Bohr’s model of the atom, modified by Som-merfeld, proposed that the electrons of an atomare arranged in groups, which have differentmean distances from the nucleus and are eachcharacterized by three quantum numbers, whichdescribe the rotation of the electron around thenucleus. Problems with the model arose whenthese numbers failed to account for magneticanomalies in matter. Pauli solved the problem byadding a fourth quantum number to the threealready in use (n, l, and m). This number, s,would represent the electron’s rotation aroundan axis through its own center of gravity, whatcame to be called spin, and would have two pos-sible values: +1/2 or –1/2. Building on thishypothesis, in 1925, he enunciated his Pauliexclusion principle, which stated that no twoelectrons in the same atom could have the samevalues for their four quantum numbers. One ofthese quantum numbers describes one of the twopossible directions for the electron’s intrinsicspin. Thus, two electrons that are in the sameenergy level as described by the other threequantum numbers are differentiated from eachother because they have opposite spins. Theexclusion principle proved essential not only inexplaining atomic structure: by uncovering thesignificance of ordering elements by their atomicnumber, it provided an explanation for the peri-odic table of the elements.

Pauli’s important work led to his appoint-ment, in 1928, as professor of experimentalphysics at the Federal Institute of Technology,Zurich, a position he would hold for the rest ofhis life. During the years before World War II,Pauli developed the institute into a vibrantinternational center for physical research. Atthe beginning of his Zurich years he made

another major contribution in his prediction ofa new elementary particle: the neutrino. Pauli’shypothetical particle was offered as a solutionto the dilemma posed by the observation thatelectrons appeared to be emitted in a continu-ous stream whereas theory called for a discon-tinuous spectrum. Pauli accounted for thisdiscrepancy by proposing that the emission ofan electron in beta decay is accompanied bythe production of an unknown particle.Because Pauli’s particle had neither charge normass, the model explained why it had neverbeen detected. It was ENRICO FERMI who in1934 confirmed Pauli’s view and dubbed the

Pauli, Wolfgang 223

Wolfgang Pauli discovered the fact that no twoelectrons in an atom can occupy the same energy state.Known as the Pauli exclusion principle, it explainednumerous phenomena on both the atomic and thenuclear level. (AIP Emilio Segrè Visual Archives)

new particle the neutrino. Two years beforePauli’s premature death, on December 15,1958, in Zurich, his prediction was experimen-tally validated by the American physicistsFREDERICK REINES and Clyde L. Cowan, whorecognized neutrinos by their impact with sub-nuclear particles in mineral water.

Pauli left Europe when hostilities broke outand spent the war years in the United States, atthe Institute for Advanced Study, Princeton. Heacquired both Swiss and U.S. citizenship andspent his later years in Princeton and in Zurich.

An intuitively gifted scientist, universallyrespected by colleagues such as Bohr and Heisen-berg, who relied on his advice, Pauli was also alifelong student of the great Swiss psychoanalystCarl Gustav Jung. When his brief first marriagefailed in 1929, Pauli underwent analysis withJung and later continued corresponding withhim. In 1952, Jung and Pauli coauthored TheExplanation of Nature and the Psyche, which dis-cusses the influence of Jungian archetypes on thework of the great astronomer Johannes Kepler.

Further ReadingHermann, A. Wolfgang Pauli: Scientific Correspondence

with Bohr, Einstein, Heisenberg. Vol. 191. NewYork: Springer-Verlag, 1979.

Laurikainen, Kalervo Vihtori. Beyond the Atom: Philo-sophical Thought of Wolfgang Pauli. New York:Springer-Verlag, 1988.

Pauli, Wolfgang, et al., eds. Writings on Physics andPhilosophy. New York: Springer-Verlag, 1994.

� Penzias, Arno Allan(1933– )German/AmericanExperimentalist, Radio Astronomer,Astrophysicist

Arno Allen Penzias shared the 1978 Nobel Prizein physics with Robert W. Wilson for their dis-covery of cosmic microwave background radia-

tion, which provided strong support for the bigbang theory of the origin of the universe.

He was born into a Jewish family on April26, 1933, in Munich, Germany, the year theNazis rose to power. Until the age of six, he was,in his own words, “an adored child in a closely-knit middle class family.” The mirage of safetyevaporated when the family was rounded up,along with other Jews of Polish origin, for depor-tation to Poland. The Poles refused to acceptmore immigrants and the family was returned toMunich, but from that point on they thoughtonly of emigrating to America. When he was six,Arno and his little brother were put on a trainfor England, where they were soon joined bytheir parents. Within six months, the familysailed for America, arriving in January 1940 inNew York, where his father found carpentrywork and the boys attended public schools in theBronx. Arno went on to attend Brooklyn Tech-nical High School, a specialized public schoolfor highly promising students. He then studiedphysics at the City College of New York, whichhad long been a gateway to the middle class forstruggling immigrants, and graduated in 1954 inthe top 10 percent of his class. He married hislifelong partner, Anne Pearl Barras, with whomhe would have three children, and spent the nexttwo years as a radar officer in the United StatesSignal Corps. In 1956, his army experience qual-ified him for a research assistantship in theColumbia Radiation Laboratory, where excitingresearch in microwave physics was under way.Working under CHARLES HARD TOWNES, the dis-coverer of the maser and the laser, he built amaser amplifier in a radio astronomy experimentand completed his Ph.D. thesis in 1961.

Penzias then took a job with Bell Laborato-ries in Holmdel, New Jersey, anticipating that itwould be a temporary position. Instead, Bellbecame his professional home for the next 37years. He started out doing research in radio com-munications and participated in the pioneeringEcho and Telstar communication satellite experi-

224 Penzias, Arno Allan

ments. In 1963, he was joined in his research inradio astronomy by Robert Wilson, a youngphysicist from the California Institute of Tech-nology, with whom he formed his historic partner-ship. Taking over the state-of-the-art horn-shapedradio antenna that had been used for radio com-munication with Echo and Telstar, the two mensoon detected a faint microwave signal withunique properties. The signal corresponded to theradiation emitted from a blackbody with a temper-ature of three degrees above absolute zero, per-vaded all of space, and never wavered over time.They looked into the possibility that the noise wasoriginating in the antenna itself—which hadbeen clogged by pigeon dung. But, even when theoffending matter had been removed, the signalpersisted. When other possible sources—such asthe Milky Way and the Sun—had been systemat-ically eliminated, they became aware, in 1965,through discussions with the Princeton physicistRobert H. Dicke, of an electrifying explanationfor their findings: the big bang theory of cosmiccreation.

At the time, there were two competing cos-mological theories. The steady-state theory,espoused by Hermann Bondi, Thomas Gold, andFred Hoyle, held that the universe was as it hadalways been: homogeneous in space and time.The big bang theory arose from Edwin Hubble’s1929 finding that the galaxies are rapidly mov-ing away from each other. This led physicistssuch as GEORGE GAMOW to argue that galaxiesmust have been closer to one another in the pastand that in the farthest reaches of the past—thecataclysmic moment in which the universe wascreated some 15 billion years ago—they weremerged in a single, infinitely dense, hot mass.This theory postulated that a background radia-tion at three Kelvin had survived from theinfancy of the universe and pervaded all ofspace. Penzias’s and Wilson’s mysterious signalfit the big bang’s prediction in every respect.Their findings offered hard experimental evi-dence for the big bang theory, a result that hasheld up until the present day.

From the mid-1960s, Penzias served as a the-sis advisor to Princeton graduate students inastrophysics, while continuing to do research atBell. During this period he focused on researchin interstellar chemistry and discovered the pres-ence of key chemicals in interstellar space.Using the techniques he had pioneered, he wasable to observe millimeter-wave radio spectraemanating from carbon monoxide and severalother simple molecules in the dusty clouds ininterstellar space. In 1973, working with KeithJefferts, Penzias made the amazing discovery ofthe existence of deuterium (heavy hydrogen) inouter space, which earned the nickname “Arno’swhite whale”—a reference to Moby Dick, theelusive whale in Herman Melville’s great novel.

Between 1972 and 1982, Penzias continuedthe academic side of his career as a visiting mem-ber of the astrophysics department at PrincetonUniversity. But in the early 1970s, he becameincreasingly involved in managerial responsibil-ities at Bell Labs. He became head of the RadioPhysics Research Department in 1972 and, fouryears later, director of the Radio Research Lab,devoted to understanding radio and its commu-nication applications. Shortly after receiving hisNobel Prize in 1978, he was promoted oncemore, to executive director of the Communica-tions Sciences Research Division.

The year 1981 was a watershed: Penzias’sscientific research career came to an abrupt endwhen the Justice Department and AT&Tdecided to settle their antitrust case by breakingup the Bell Laboratory system. Penzias agreed toserve as vice president of research, a position heheld for 14 years, a crucial period when Bell LabsResearch was attempting to transform itself intoa competitive market player while trying tomaintain its scientific excellence. He left thatjob in 1995, to become vice president of AT&TBell Laboratories.

At this time he turned from scientific researchto exploration of the impact of technology onsociety. A prolific writer, in addition to over 100

Penzias, Arno Allan 225

scientific papers, he published two books, two sci-ence fiction stories, and numerous technical andbusiness articles. Penzias describes his first book,Ideas and Information, which examines the impactof information technology on business and society,as a depiction of computers “as a wonderful tool forhuman beings, but a dreadful role model.” DigitalHarmony, his second book, envisions machinesthat will work in harmony with each other, theirhuman users, and the natural environment. Itexplores how emerging technologies will changethe way people work and live. As vice-chairmanof the Committee of Concerned Scientists, hedevotes much time to defending the rights of sci-entists living under repressive regimes.

The discovery of the cosmic microwavebackground by Penzias and Wilson turned thestudy of cosmology into a respected, empiricalscience. On November 18, 1989, the NationalAeronautics and Space Administration (NASA)sent the Cosmic Microwave Background Explorer(COBE) satellite into orbit to carry out moreadvanced studies of this phenomenon and itsclues to the nature and history of the universe.

Further ReadingPenzias, Arno. Digital Harmony: Business, Technology

and Life After Paperwork. New York: Harper Busi-ness, 1995.

Penzias, Arno Allan. Ideas and Information: Managingin a High-Tech World. New York: W. W. Norton,1989.

Silk, Joseph. The Big Bang. New York: Henry Holt,2000.

� Perrin, Jean-Baptiste(1870–1942)FrenchExperimentalist, Physical Chemist,Atomic Physicist

Jean Perrin was a great experimentalist, whoproduced the first empirical evidence for the

existence of atoms by observation of Brownianmotion, the random, continuous movement ofparticles in a liquid. His groundbreaking workended the passionate dispute that had longdivided physicists over whether matter is funda-mentally continuous or is made up of particle-like atoms and won him the 1926 Nobel Prize inphysics.

Perrin was born in Lille, France, on Septem-ber 30, 1870. His father was a member of a fam-ily of peasants in the Lorraine region and servedas an infantry officer. He received his early edu-cation in Lyons and Paris; in 1891, he enteredthe École Normale Superieure, where he earnedhis doctorate six years later. During these years,he began his research into cathode rays: the phe-nomenon that produced a fluorescent glowwhen most of the air was pumped out of a glasstube with wires embedded at each end and ahigh voltage was sent across it.

At the time physicists were questioningwhether cathode rays were charged particles orsome undefined wavelike phenomenon in theether. To investigate this issue Perrin designedexperiments in which cathode rays that were gen-erated in discharge tubes were allowed to pene-trate thin sheets of glass or aluminum andcollected in a hollow cylinder produced a negativecharge on a fluorescent screen onto which thecathode rays were focused. As the negative chargewas increased, the intensity of fluorescence fell.The finding that they could be slowed by an elec-tric field demonstrated that the cathode rays wereparticle-like and carried a negative electric charge.In these experiments Perrin was also able to estab-lish crude values for the charge-to-mass ratio of anelectron, e/m. Later on, when the measurement ofthe e/m ratio of cathode rays was improved uponby the classic experiments of JOSEPH JOHN (J. J.)THOMSON, the identification of cathode rays withthe existence of the first elementary particle, theelectron, was firmly established.

In 1897, he began a lectureship in physicalchemistry at the Sorbonne, where, 12 years later,

226 Perrin, Jean-Baptiste

he published his most important contribution,work on atomic theory. These were the yearswhen what is now known as the atomist–ener-geticist debate was at its height. Because therewas no technology available to verify their exis-tence at the turn of the century, atoms had beenrelegated by most physicists to the realm of spec-ulation. ERNST MACH was the leading advocatefor this energeticist school of thought. For Machthe purpose of science was to measure and demon-strate only that which it can observe. Mach andhis colleagues were content to measure theexpansion of gases and empirically deduce a sim-ple law relating temperature, pressure, and vol-ume. They were not disturbed by their inabilityto explain why these properties were related inthis particular way. LUDWIG BOLTZMANN, theleading atomist, on the other hand, believed thatby hypothesizing a dynamic submolecular worldof colliding atoms he could explain why gasexpands and by how much. The starting point forPerrin’s research was the work of Robert Brown,who in 1827 had observed through a microscopethe random motion of small grains in a fluid, aphenomenon that became known as Brownianmotion. Brown noted that the motion of the par-ticles increased when the temperature increasedbut decreased when larger particles were used. Toenergeticists who believed in continuous matter,Brownian motion, with its discrete bumps, wasparticularly disturbing. In one of his landmark1905 papers, ALBERT EINSTEIN increased the con-sternation of the energeticists when he explainedthe phenomenon of Brownian motion as theeffect of large numbers of molecules bombardingthe particles in a manner that allowed him topredict the movement and size of the particles.

Four years later, Perrin was able to verifyEinstein’s explanation experimentally. Perrinreasoned that since both the grains and thewater molecules were very small, both wouldbehave as gas molecules and the principles of thekinetic theory of gases could be used to explaintheir collision process. In his classic experiment

he used gamboge particles obtained from veg-etable sap, and the distribution of these sus-pended particles in a container was analyzed bydepth. He found that their number decreasedexponentially with height. Using principles pro-posed in Einstein’s paper on Brownian motion,he was able to deduce a definite value for theAvogadro number (the number of particles inone mole of a substance) that agreed substan-tially with experimental values obtained inother ways. The fact that the Avogadro numbercould be accurately determined in this experi-ment showed that Brownian motion implied theexistence of atoms. Although atoms were notvisible, Perrin’s results were accepted as defini-tive proof of their existence.

In 1910, Perrin was made a full professor ofphysical chemistry at the Sorbonne, but his aca-demic life was soon interrupted by World War I.Between 1914 and 1918, he served as an officerin the engineer corps. Afterward, he returned tothe Sorbonne, where he continued to pursue hisresearch. He had a deep interest in astrophysicsand, in 1920, published results demonstratingthat only the fusion of hydrogen atoms intohelium atoms can account for the origin of solarenergy. In addition, during the 1930s, he wasinstrumental in creating several vital scientificinstitutions: the National Scientific ResearchCenter, which offered talented French scientistsan alternative to hard-to-obtain university posi-tions; the Palace of Discovery; the Institute ofAstrophysics in Paris; the Institute of Physicaland Chemical Biology; and the large Observa-tory in Haute Provence.

In 1926 he received the Nobel Prize inphysics and became a Commander of the Legionof Honor, Commander of the British Empire,and of the Belgian Order of Leopold.

A prolific author of books and scientificpapers, he was especially known for his 1913work Les Atomes, explicating the body of exper-imental evidence, of which his own work was sovital a part, that established the existence of

Perrin, Jean-Baptiste 227

atoms. In that work, Perrin eloquently charac-terized the nature of his own achievement:

To divine . . . the existence and proper-ties of objects that still lie outside ourken, to explain the complications of the vis-ible in terms of invisible simplicity, is thefunction of the intuitive intelligencewhich, thanks to men like Dalton andBoltzmann, has given us the doctrine ofatoms.

Perrin remained at the Sorbonne until1940, but his outspoken opposition to the occu-pying Nazi regime forced him to flee to theUnited States in December 1941. Soon after-ward he became ill and died in New York Cityon April 17, 1942. After the war, in 1948,France paid homage to him by carrying home hisremains on the battleship Jeanne d’Arc and bury-ing them in the Panthéon.

Further ReadingPerrin, Jean. Atoms. Reprint ed. Woodbridge, Conn.:

Ox Bow Press, 1990.

� Planck, Max Ernest Ludwig(1858–1947)GermanTheoretical Physicist(Electromagnetism), Quantum Theorist

The work of Max Planck laid the foundation forthe paradigm shift that ushered in the era of mod-ern physics: the discovery of a world of discrete,discontinuous “quanta” of energy beneath theapparent continuity of classical Newtonianmechanics. The inescapable logic that led him, in1900, to postulate the universal constant innature that came to be known as Planck’s con-stant led directly to the formulation of quantummechanics 20 years later. Planck himself, whoseintellectual roots were firmly planted in 19th-

century notions of the absolute nature of physicallaws, only reluctantly accepted the implicationsof the discovery that earned him the 1918 NobelPrize in physics.

Max Ernest Ludwig Planck was born onApril 23, 1858, in Kiel, Germany, into a dis-tinguished scholarly family with a long historyof devotion to church and state. When hisfather, a renowned law professor, accepted aposition at the University of Munich, youngMax entered the city’s famous MaximilianGymnasium, where he excelled in all subjects.Graduating at 17, he was torn between a careerin music, which remained a passion through-out his life, and one in physics. He chosephysics because, he explained, “The outsideworld is something independent from man,something absolute, and the quest for the lawswhich apply to this absolute appeared to me asthe most sublime scientific pursuit in life.”Inspired by the discovery that “pure reasoningcan enable man to gain an insight into themechanism of the world,” Planck resolved todevote his life to theoretical physics when itwas not yet a formal discipline.

As a student at the University of Munich,he encountered the attitude, not uncommonamong physicists of the time, that the study ofphysics was essentially a dead end, since every-thing of importance had already been discov-ered. Following his own interests, Planck foundthis idea to be anything but accurate. His fasci-nation with absolutes in nature led him to focuson the laws of thermodynamics, which, in turn,led him to the problem of blackbody radiation.Classical physics thought of radiation (light) asa continuous wave in a field. Physicists knewthat whereas the color of a cool object is due toits surface light, that is, the reflected light emit-ted by an external source, a heated object glowswith the light inside it. In this context, in1859–1960, GUSTAV ROBERT KIRCHHOFF intro-duced the idealized concept of a blackbody: anobject that does not reflect any surface light

228 Planck, Max Ernest Ludwig

and is, therefore, a perfect emitter and absorberof radiation at all frequencies. Blackbody radia-tion is the full spectrum of light frequenciesinside a heated body that has no surface reflec-tion. By the 1890s, classical physicists hadmade several experimental and theoreticalapproaches to determining spectral energy dis-tribution: a curve showing how much lightenergy is emitted at different frequencies for agiven temperature of the blackbody. A formuladerived by Planck’s colleague WILHELM (CARL

WERNER OTTO FRITZ FRANZ) WIEN provedvalid only at high frequencies, and a similarequation found by LORD RAYLEIGH (JOHN

WILLIAM STRUTT) was accurate only at low fre-quencies. In 1900, at the age of 42, Planck suc-ceeded in combining these two equations,producing a formula that related the energy ofthe radiation to its frequency.

But, while the physics community hailedPlanck’s radiation law as indisputably correct,Planck himself was uneasy with the fact that itwas based on nothing more solid than a “luckyintuition.” Before it could be taken seriously,he believed, it had to be derived from firstprinciples. No other episode in Planck’s careerbetter illustrates his uncompromising scientificintegrity. In order to ground his derivation inphysical principles, he had to relinquish his cher-ished belief in the absolute nature of the secondlaw of thermodynamics (entropy) in favor ofLUDWIG BOLTZMANN’s statistical interpretationof that law. His second unwelcome realizationwas that a sound derivation could only be basedon the postulate that the energy of radiation isemitted and absorbed not continuously, but indiscrete packets, which he called quanta. Heassumed that the energy of quanta of light wasproportional to the frequency of the light: that is,the higher the frequency, the higher the energy.The proportionality constant in this relationshipbetween the quantum energy of radiation andthe frequency of light emitted turned out to be auniversal constant, which kept showing up for all

kinds of blackbodies and all temperatures. Thisnumber, 6.626, 196 × 10–34 J/s (joules per sec-ond), came to be called Planck’s constant; it isdesignated by the symbol h.

The fact that Planck’s constant was not zero,but had a small finite value, gradually led physi-cists to understand that the world of the verysmall, the microphysical world, could not bedescribed by classical Newtonian mechanics. Noone greeted this revelation with less enthusiasmthan Planck himself did. Over the years hedevoted his efforts to undercutting the newquantum mechanics but succeeded only in con-firming its necessity.

Planck’s law of radiation set the stage forlater applications of the paradigm shift that light

Planck, Max Ernest Ludwig 229

Max Ernest Ludwig Planck created the foundation forthe idea of the quantum hypothesis: the discovery of aworld of discrete, discontinuous quanta of energybeneath the apparent continuity of classical Newtonianmechanics. (AIP Emilio Segrè Visual Archives)

energy is quantized. In 1905, ALBERT EINSTEIN

used it in his explanation of the photoelectriceffect. Light, he said, was composed not only ofwaves, but also of particles, which he named pho-tons. In 1913, NIELS HENRIK DAVID BOHR appliedthe quantum theory to the structure of thehydrogen atom. By the 1920s, quantum mechan-ics had evolved into a full system.

But Planck would play no further role inthe revolution he had inadvertently ignited. Asprofessor of physics at the University of Berlin,from 1989 until his retirement in 1926, hemade contributions to optics, thermodynamics,statistical mechanics, and physical chemistry.In his later years, he turned to philosophicalwritings, in which he rejected the quantummechanical view that observer and observedare inextricably linked and continued to seenature as existing in total independence ofhuman beings. As did Einstein and ERWIN

SCHRÖDINGER, he found the quantum mechan-icaI view of matter as statistical and non-deterministic alien to his most deeply heldconvictions about the nature of reality.

If the physics of the new century wasuncongenial to Planck’s worldview, its historywas nothing less than personally devastating tohim. In 1909, he lost his much-loved first wife,Marie Merck, who had borne him two sons andtwin daughters. The next year he marriedMarga von Hoesslin, with whom he had a son.But he was to witness the tragic deaths of fourof his children. His twin daughters, Margereteand Emma, died in childbirth in 1917 and1919, respectively. Remaining in Germanythroughout two world wars, he saw his eldestson, Karl, killed in action in 1916. When theNazis gained power, Planck did what he couldto preserve German physics, pleading withHitler directly to reverse his racist policies.Throughout these trials, Planck had beenupheld by his stoicism and religious conviction.But when, in 1945, his youngest son, Erwin,who had been implicated in an attempt to

assassinate Hitler, was brutally executed by theGestapo, Planck lost the will to live. He died in1947, at the age of 89, in Göttingen.

Further ReadingHeilbron, J. L. The Dilemmas of an Upright Man: Max

Planck and the Fortunes of Germany. Cambridge,Mass.: Harvard University Press, 2000.

Klein, M. J. “Max Planck and the Beginnings ofQuantum Theory.” Archive for History of ExactSciences 1: 459–479, 1962.

Planck, Max. A Survey of Physical Theory. New York:Dover, 1994.

� Poynting, John Henry(1852–1914)BritishTheoretician and Experimentalist(Classical Electromagnetism,Gravitation)

John Henry Poynting is famous for his discoveryof the Poynting vector, a key element in theelectromagnetic conservation of energy equa-tion. In this formulation, Poynting determinedthe rate of outward flow of electromagneticenergy from a volume containing charge andcurrents. He also produced a measurement of SIR

ISAAC NEWTON’s gravitational constant, whichremains accurate today.

He was born in Monton, Lancashire, nearManchester, on September 9, 1852, andattended the secondary school where his fathertaught. In 1867, he entered Owens College inManchester (later Manchester University),where he earned a bachelor of science degree in1872. He did his graduate work at Trinity Col-lege, Cambridge University, from 1872 to 1876and, on completing his studies, served as aphysics demonstrator at Owens College.

Then, in 1878, Poynting had the opportu-nity to work as a researcher at the CavendishLaboratories in Cambridge under the great

230 Poynting, John Henry

JAMES CLERK MAXWELL, who had produced acomprehensive theory of electromagnetism. Heworked with Maxwell until 1880, when hebecame professor of physics at Mason College,Birmingham (later Birmingham University). AtBirmingham, in 1884, he made his own signifi-cant contribution to electromagnetism, when hepublished his paper “On the Transfer of Energyin the Electromagnetic Field.” It contained anequation (which he worked out by usingMaxwell’s electromagnetic field theory), bywhich the magnitude and direction of the flowof electromagnetic energy—later called thePoynting vector—can be determined. Mathe-matically, the Poynting vector is given by

S = (1/µ)EB sin θ

where S is the Poynting vector, µ is the perme-ability of the medium, E is the strength of theelectric field vector, B is the strength of the mag-netic field vector, and θ is the angle between theelectric and magnetic field vectors. Interestingly,Poynting’s work did not assume the existence ofan ether, the all-pervasive cosmic “wind” inwhich electromagnetic waves were thought topropagate by most physicists of the time; insteadhe used the concept of flux of electricity betweenlines of force, suggested by MICHAEL FARADAY.

Poynting made his second important contri-bution to physics in 1891, when he published theresults of an extensive series of experiments,begun during his Cambridge days, designed tomeasure Newton’s gravitational constant (on thebasis of which the Earth’s mean density can becalculated). Poynting’s results, which heobtained by using an ordinary beam balance, arealmost identical with the numbers acceptedtoday. In 1895, Charles Boys improved uponPoynting’s experimental method by using aquartz fiber torsion balance. Poynting used Boys’sapparatus for several later studies of his own, suchas the measurement of radiation pressure.

In 1903, he did important work on radiationin which he hypothesized that the Sun’s radia-

tion causes small particles orbiting the Sun tomove increasingly closer to the Sun, until theyeventually fall into it. This discovery, which isnow known as the Poynting–Robertson effect,was later developed and related to the theory ofrelativity by the American physicist HowardRobertson. Poynting also devised a method formeasuring the radiation pressure from a body,which can be used to determine the absolutetemperature of celestial objects.

Poynting remained at the University ofBirmingham until his death on March 30, 1914,in Birmingham, of diabetes-related causes.

Poynting’s work, by determining the man-ner in which conservation of electromagneticenergy occurred in Maxwell’s equations, was avital stepping stone in the confirmation and ver-ification of Maxwell’s electromagnetic theory.

Further ReadingSchultz Slusher, Harold, and Stephen J. Robertson.

The Age of the Solar System: A Study of the Poynt-ing–Robertson Effect and Extinction of Interplane-tary Dust. El Cajon, Calif.: Institute for CreativeResearch, 1982.

� Purcell, Edward Mills(1912–1997)AmericanNuclear Physicist, Solid State Physicist,Astrophysicist, Biophysicist

Edward Mills Purcell’s 1945 discovery, with hiscolleagues Henry C. Torrey and Robert V.Pound, of nuclear magnetic resonance (NMR)led to his sharing of the 1952 Nobel Prize inphysics with FELIX BLOCH, who had made thesame discovery by using a different approach.His other famous achievement was detection ofthe emission of 21-cm-wavelength radiationfrom atomic hydrogen in interstellar space,which became a fundamental measuring tool inastrophysics.

Purcell, Edward Mills 231

He was born on August 30, 1912 in Tay-lorville, Illinois, to Mary Elizabeth Mills, a highschool Latin teacher, and Edward A. Purcell, themanager of a local telephone company. Whenhe was 14, the family moved to nearby Matoon,Illinois, where his father became general man-ager of the Illinois Southeastern TelephoneCompany. His father’s involvement in the tele-phone industry played an important role in hislife, providing him with discarded equipment toinvestigate and exposing him to the scientificarticles in the Bell System Technical Journal. Hewould later describe these as “a glimpse intosome kind of wonderful world where electricityand mathematics and engineering and nice dia-grams all came together.”

Purcell entered Purdue University in 1929,intending to become an electrical engineer. Butwhen Karl Lark-Horovitz became head of thephysics department, the study of physics at Pur-due flourished and Purcell signed up for a courseof independent study. His professor set him towork rebuilding a spectrometer and an electrom-eter to measure nuclear half-lives, an experiencethat heightened his growing fascination withphysics. It solidified when Lark-Horovitz let himtake part in experimental research on electrondiffraction. After his 1933 graduation with abachelor’s degree in electrical engineering, Pur-cell won an exchange fellowship to the Technis-che Hochschule in Karlesruhe, Germany. Onthe ocean voyage to Germany, he met Beth C.Busser, an exchange student from Bryn MawrCollege on her way to Munich to study Germanliterature. They would marry in 1937 and havetwo sons, Dennis and Frank.

In 1934, Purcell returned to the UnitedStates and entered Harvard University, whichbecame his lifelong academic home, for his grad-uate studies. It was there that JOHN HOUSBROOK

VAN VLECK’s course on electric and magneticsusceptibilities influenced the future course ofhis career. He received his Ph.D. in 1938 for anexperimental thesis under Kenneth T. Bain-

bridge on the focusing properties of the electricfield in the space between two concentric metalspheres forming a spherical condenser (what isnow called a capacitor).

Purcell was a physics instructor at Harvardfor two years, before going to work at the Radia-tion Laboratory at the Massachusetts Institute ofTechnology (MIT), which had just been orga-nized for the purpose of radar development. Dur-ing World War II, between 1941 and 1946, hewas the leader of the advanced developmentsgroup, responsible for moving the radar systemsto shorter wavelengths. He was among the fewscientists who stayed on after the MIT facilityclosed in order to publish a series of books pre-serving the technology developed over the fiveyears of its existence. He gained invaluableexperience at MIT, where he knew scientistssuch as ISIDOR ISAAC RABI who were interestedin the study of molecular and nuclear propertiesby radio methods.

By then Rabi had theoretically determinedthat magnetic resonance, associated with groupsof atoms shot through a region of strong mag-netic fields as a beam, was a measurable phe-nomenon. But instruments that were capable ofmeasuring magnetic resonance in liquids orsolids had not yet been designed. Purcell, armedwith the latest information on energy states innuclear particles and on microwave energy, sur-mised that with a strong magnetic field he couldmove the spinning nuclear particles of a speci-men into alignment, then use microwaves tofind their resonant frequency and magnetism. Athree-scientist team, consisting of Purcell; Tor-rey, who had worked in Rabi’s lab; and Pound, acolleague from the MIT lab, improvised anexperiment using inactive Radiation Lab equip-ment, which they moved to the Research Labo-ratory of Physics at Harvard. Working mostlyevenings and weekends, they succeeded indetecting the absorption of radio frequency byprotons in paraffin wax by magnetic resonanceon December 15, 1945. The great advantage of

232 Purcell, Edward Mills

Purcell’s new experimental approach was that itcould be applied to solid, liquid, and gaseous sub-stances. Its extraordinary sensitivity also made itideal as a micromethod in many scientific andtechnical fields. Seven years later, when he wasawarded the Nobel Prize for this work, Purcellcommented that the reward of the discoverer is“to see the world as something rich and strange.”

In 1946, he returned to Harvard as a tenuredassociate professor and began developing thenew field of magnetic resonance of nuclei. Oneof his first graduate students was NICOLAAS

BLOEMBERGEN, who helped him in developingmore sensitive instrumentation for futurenuclear magnetic resonance (NMR) studies.Bloembergen, Purcell, and Pound used the newinstruments for a series of important experi-ments, which explained the thermal relaxationof the nuclear spins and the collision narrowingof NMR lines in liquids, gases, and certain solids.Purcell became full professor at Harvard in 1949.

In the late 1940s, Purcell encouraged a grad-uate student, Harold I. Ewen, to look for an astro-nomical spectral line based on the hyperfinesplitting of the ground state of the interstellaratomic hydrogen in the galaxy. Then, in 1951,Dutch astronomers predicted that in the near-vacuum of space, lonely hydrogen atoms, afterbeing moved to a slightly higher energy level byradiation or collision, would emit a radio wave of21-cm wavelength as they dropped back to thelowest energy level. Ewen and Purcell, working atnight and with borrowed equipment, help from auniversity carpenter, and a $500 grant, built ahorn antenna on the roof of Harvard’s LymanLaboratory. On March 24, 1951, they detectedthe elusive spectral line radio emissions fromclouds of hydrogen in space for the first time.Their observations matched predictions that theemissions would have a wavelength of 21 cm.The same observation was then made by theDutch scientist Jan Oort, who, by observingcloud motions, was able to map the otherwiseinvisible far side of the rotating Milky Way

galaxy. Since hydrogen is the most abundant sub-stance in the universe, its 21-cm wavelengthbecame a fundamental tool in astrophysics. As aprominent landmark in radio astronomy, it hasbeen the focus of efforts to detect signals fromextraterrestrial life.

Purcell continued working in the field ofnuclear magnetism, especially relaxation phe-nomena, molecular structure, measurement ofatomic constants, and nuclear magnetic behav-ior at low temperatures. During the 1960s, as aresult of his contribution to radio astronomy, hebecame involved in astrophysics. The problemof understanding the mechanisms of the interac-tions of interstellar dust and light propagatingthrough the galaxy was a central research focusin his later years. He also did important work onbiophysics; with Howard Berg he developed amachine based on concentric rotating cylindersfor separating molecules in liquid states accord-ing to their masses. He and Berg later shared theBiological Physics Prize of the American Physi-cal Society in 1984 for their work on the hydro-dynamics of Escherichia coli bacteria.

A devoted educator, who wrote a textbookon electricity and magnetism in the early 1960s,Purcell wrote a pedagogical column for theAmerican Journal of Physics between 1983 and1988. Entitled “Back of the Envelope,” it pre-sented thought problems, which he could solvequantitatively in a few lines.

He served on the President’s Science Advi-sory Committee to Presidents Eisenhower,Kennedy, and Johnson. Under Eisenhower, hechaired the subcommittee on space, which wasinfluential in the organization of the NationalAeronautics and Space Administration (NASA)and the development of the space explorationprogram. He resigned from Johnson’s committeein 1965 because of his stance against the Viet-nam War and two years later served as spokes-person for a group of antiwar Harvard professorswho met with Johnson to explain their position.He retired from Harvard in 1977. He died of res-

Purcell, Edward Mills 233

piratory failure on March 7, 1997, in Cambridge,Massachusetts.

Both of Purcell’s major discoveries have hadfar-reaching consequences. NMR has become amajor research tool in material sciences, chem-istry, and medicine, in which magnetic resonanceimaging (MRI) is a fundamental diagnostic tool.Radio spectroscopy of atoms and molecules inspace, whose development resulted from thedetection of the hyperfine transition in hydrogen,

the first element studied, plays an increasinglygreater role in radio astronomy.

Further ReadingMatson, James. The Pioneers of NMR and Magnetic

Resonance in Medicine: The Story of MRI. Jericho,N.Y.: Dean, 1996.

Pound, Robert V. “Edward Mills Purcell,” in Biographi-cal Memoirs. Vol. 78. Washington, D.C.: NationalAcademy Press, 2000, pp. 182–209.

234 Purcell, Edward Mills

R� Rabi, Isidor Isaac

(1898–1988)AmericanTheoretician, Experimentalist, SolidState Physicist

Isidor Isaac Rabi was a major figure in 20th-cen-tury physics, who is best known for his inventionof the technique of atomic and molecular beammagnetic resonance (ABMR). This technique isalso the basis for nuclear magnetic resonance, amethod for determining the magnetic momentsof atoms and nuclei. He won the 1944 NobelPrize in physics for this work. Intimatelyinvolved with the Manhattan Project, whichdeveloped the first atomic bomb, he laterbecame a strong advocate for arms control.

He was born on July 29, 1898, in Galicia,Poland, the son of David Rabi and Janet Teig.The following year his family immigrated to theUnited States, where Isidor grew up on theLower East Side of Manhattan. His father workedin the sweatshops of Manhattan, makingwomen’s blouses, until he had saved enough tomove his family to Brooklyn, where he bought agrocery store. The Rabi family, which had fledthe poverty and anti-Semitism of Eastern Europe,was Yiddish-speaking and practiced a fundamen-talist form of Orthodox Judaism. As a child,Isidor did not know that the Earth revolved

around the Sun until he read it in a library book.His secularizing exposure to modern scientificknowledge in the public schools of Manhattanand Brooklyn quickly transformed his sense ofthe world and led him to a life in science.

In 1919, he received his bachelor’s degree inchemistry from Cornell University in Ithaca,New York. He worked for three years in jobsunrelated to science before beginning his gradu-ate studies at Cornell in 1921, and later atColumbia University. In 1926, he married HelenNewmark, with whom he would have twodaughters. The following year he was awardedhis Ph.D. for a dissertation on the magneticproperties of crystals. He then spent two years inEurope, supported by fellowships, which gavehim the opportunity to work with such giants ofearly-20th-century physics as ARNOLD JOHANNES

WILHELM SOMMERFELD; NIELS HENRIK DAVID

BOHR; OTTO STERN; WOLFGANG PAULI; andWERNER HEISENBERG. When he returned to theUnited States, Rabi became a lecturer in theo-retical physics at Columbia, where he rosesteadily through the ranks, becoming a full pro-fessor in 1937.

Rabi began his work on magnetic phenom-ena in atoms at the outset of his career. In 1930,he began investigating the magnetic propertiesof atomic nuclei, developing Stern’s molecularbeam method to a new level of precision as a

235

tool for measuring these properties. His appara-tus was based on the production of ordinaryelectromagnetic oscillations of the same fre-quency as that of the physical precession, thatis, rotation, of the magnetic moments of atomicsystems in an external magnetic field. By aningenious application of an electromagneticresonance principle, he succeeded in detectingand measuring single states of rotation of atomsand molecules and in determining the mag-netic moments of the nuclei. He had theoreti-

cally determined that magnetic resonance wasa measurable phenomenon. But instrumentscapable of measuring magnetic resonance inliquids or solids had not yet been designed.When FELIX BLOCH and EDWARD MILLS PUR-CELL succeeded in doing so in the late 1940s,the field of nuclear magnetic resonance (NMR),which would give rise to magnetic resonanceimaging (MRI), was launched.

In 1940, Rabi took a leave from Columbia tobecome associate director of the newly opened

236 Rabi, Isidor Isaac

Isidor Rabi is best known for his invention of the atomic and molecular beam magnetic resonance method fordetermining the magnetic moments of atoms and nuclei. (AIP Emilio Segrè Visual Archives)

Radiation Laboratory at the Massachusetts Insti-tute of Technology, created to develop radar tech-nology. When he was invited by J. ROBERT

OPPENHEIMER, director of the Manhattan Projectcharged with development of the atomic bomb,to become associate director of the work at LosAlamos, Rabi refused. For one thing, he believedthat radar was more immediately important to theprogress of the war. More fundamentally, how-ever, as he told Oppenheimer, he was unwilling todevote himself to working full-time “to make theculmination of three centuries of physics” aweapon of mass destruction. Eventually, however,he did participate in the project, as a visiting con-sultant. He was present at Trinity, the first test ofthe atomic bomb in the Nevada desert.

When, at the war’s conclusion, he returnedto Columbia as head of the physics department,he became involved with the BrookhavenNational Laboratory for Atomic Research onLong Island, New York, which was dedicated toresearch into the peaceful uses of atomic energy.

In 1945, Rabi was the first to suggest theidea of using the hyperfine states of an atom asan atomic clock. The hyperfine state of anatom is associated with the quantum mechani-cal interaction of electrons and nuclei inatoms. The atomic clock uses oscillationsoccurring in the electromagnetic field gener-ated by the changes that occur between themagnetic moments of two different hyperfinequantum mechanical states of atoms.

During this period, he made fundamentalinvestigations of the hyperfine structure of theelectron in an external magnetic field. The elec-tron had long been known to have the property ofacting as small magnet whose strength, as mea-sured by its magnetic moment, was determined byPAUL ADRIEN MAURICE DIRAC’s theory of theelectron to be equal to a quantity known as theBohr magneton. However, at the beginning of1947, Rabi and his collaborators found that thehyperfine structure of the electron in externalmagnetic fields did not entirely conform with the

predictions of Dirac’s theory. The physicist Gre-gory Breit hypothesized that this might be due tothe fact that the value of the magnetic moment ofthe electron was larger than the value of one Bohrmagneton as predicted by the Dirac equation.POLYKARP KUSCH, working in Rabi’s laboratory,then did the experiment that confirmed thishypothesis. This result spurred the reformulationof quantum electrodynamics (QED), the theoryof the interaction of electrons and electromag-netic radiation.

Rabi worked toward control of nuclearweapons as a member of the General AdvisoryCommittee to the Arms Control and DisarmamentAgency, and of the United States National Com-mission for the United Nations Educational, Sci-entific, and Cultural Organization (UNESCO). In1955, he served as the U.S. delegate and vice pres-ident of the International Conference on Peace-ful Uses of Atomic Energy, in Geneva. He wasalso a member of the Science Advisory Commit-tee of the International Atomic Energy Agency.

A man of principle, Rabi defended Oppen-heimer, when he was persecuted as a Communistand deprived of his security clearance, in strongterms as

a man who had done greatly for his coun-try. A wonderful representative. . . . Hewas a man of peace and they destroyedhim. He was a man of science and theydestroyed this man. A small, mean group.

In 1970, reflecting on the development ofnuclear weapons, Rabi wrote:

The lesson we should learn from all thisand the frightening thing that we didlearn in the course of the war, was . . .how easy it is to kill people when youturn your mind to it. When you turn theresource of modern science to the prob-lem of killing people, you realize howvulnerable they really are.

Rabi, Isidor Isaac 237

By the time of Rabi’s death in 1988, it wasclear that his experimental technique for deter-mining the magnetic moments of atoms andnuclei, as well as his atomic clock, had lain thefoundations of precision atomic measurementsin modern physics.

Rabi had a deeply emotional commitmentto science and thought that physics was “infi-nite.” He expressed disappointment that youngphysicists, more interested in technique, seemedoblivious of “the mystery of it: how very differentit is from what you can see, and how profoundnature is.”

See also RAMSEY, NORMAN F.

Further ReadingBernstein, Jeremy. “Physicist.” The New Yorker Part I:

Oct 15, 1975; Part II: Oct 20, 1975.Rabi, Isidor Isaac. My Life and Times as a Physicist.

Claremont, Calif.: Clermont College, 1960.———. Science: The Center of Culture. New York:

World Publishing, 1970.———. Oppenheimer. New York: Scribner’s & Sons,

1969.Rigden, John S. Rabi: Scientist and Citizen. New York:

Basic Books, 1987.

� Raman, Sir Chandrasekhara Venkata(1888–1970)IndianExperimentalist (Optics, Acoustics),Spectroscopist

Sir Chandrasekhara Venkata Raman, the fatherof Indian science, was a brilliant experimental-ist, who made fundamental contributions to theunderstanding of the nature of light. He won the1930 Nobel Prize in physics for his discovery ofwhat came to be called the Raman effect: thescattering of monochromatic photons of light asthey pass through a transparent medium inwhich the interaction of the photons with themolecules of the medium causes the scattered

photons to have wavelengths different from thatof the incident photons. Raman scattering spec-tra can be used to determine information on thestructure of molecules.

Raman was born on November 7, 1888, inTrichinopoly, Madras, in southern India, into ahighly educated family. His father was a profes-sor of physics, and his nephew, SUBRAMANYAN

CHANDRASEKHAR, was destined to become aNobel Prize winner in astrophysics. An excep-tional student from the start, Raman passed hismatriculation exam at the age of twelve. In1902, he entered Presidency College, Madras,where he earned his B.A. two years later, alongwith the gold medal in physics. By 1907, at theage of 19, he had completed the requirements forthe M.A., with the highest distinction.

Continuing his scientific studies in thoseyears would have entailed travel to England, astep he could not take because of poor health.Since India offered no opportunity for a scientificcareer, Raman took a job with the financial divi-sion of the civil service. For 10 years, he workedas an accountant in Calcutta; he managed tocontinue to pursue his research during this time,publishing an astonishing 30 papers. Using thelaboratories of the Indian Association for theCultivation of Science in Calcutta, he investi-gated diffraction, vibrations in sound, and thetheory of musical instruments, which remained alifelong interest. The attention he gainedthrough this work generated the offer of a profes-sorship in physics at the University of Calcutta.

In 1917, Raman began a new life inacademia, remaining at Calcutta for the next 16years, the period when he would do his mostimportant work. In 1921, when he was returningby ship from a conference in England, theintense blue color of the sea inspired his work ondiffraction. He was led to question the theory ofLORD RAYLEIGH (JOHN WILLIAM STRUTT) thatthe sea’s color was due to the scattering of lightby particles suspended in the water. Back in Cal-cutta, he showed that it was the scattering of

238 Raman, Sir Chandrasekhara Venkata

light by water molecules that caused the sea tobe blue. In 1922, he published his paper “Molec-ular Diffraction of Light,” in which he describedhis experiments on the diffusion of sunlight in itspassage through water, transparent blocks of ice,and other materials.

In 1923, ARTHUR HOLLY COMPTON discov-ered the Compton effect, which X rays are scat-tered when they pass through matter andemerge with a longer wavelength. He explainedthis phenomenon by proposing that X-ray parti-cles or photons had collided with electrons andlost some energy. In 1925, WERNER HEISENBERG

predicted that the Compton effect should alsobe observed with visible light—a conclusionRaman had already reached two years earlier onthe basis of actual observation. Raman usedmonochromatic light from a mercury arc andthe spectroscope to study the nature of diffusedradiation emerging from the material underexamination. In 1928, after refining his experi-ments for the scattering of monochromatic lightin dust-free air and pure liquids, Ramanannounced the existence of a Compton-likescattering phenomenon for visible light pho-tons, which came to be known as Raman scat-tering. He explained the scattering effect asbeing due to the internal motion of themolecules encountered, which can either trans-fer energy to the light photons or absorb energyfrom them in the resulting collisions. TheRaman scattering effect was then used in whatis now known as Raman spectroscopy, whichgives precise information on the motion andshape of molecules.

A shaping force in the development ofphysics in his native country, he established theIndian Journal of Physics in 1926. In 1928, hesponsored the founding of the Indian Academyof Sciences and became its first president. Healso initiated the Proceedings of that academy,in which most of his own work was published.The British government knighted him in 1929,a year before he became the first Indian to win

a Nobel Prize in physics in 1930. Although henever earned a doctorate, he was awarded sev-eral honorary doctorates and memberships inscientific societies.

In 1934, Raman became head of the physicsdepartment at the Indian Institute of Science.He remained there until 1948, serving a term aspresident from 1933 to 1937. He left in order tobecome the first director of the Raman ResearchInstitute, built for him by the Indian govern-ment in Bangalore. One of his colleagues at theinstitute was HOMI JEHANGIR BHABHA, a leadingparticle physicist and influential figure in India’sscientific development. During this vital periodof his career, Raman made important contribu-

Raman, Sir Chandrasekhara Venkata 239

Chandrasekhara Venkata Raman discovered whatcame to be called the Raman effect, in which theinteraction of the photons with a transparent mediumcauses the scattered photons to have wavelengthsdifferent from those of the incident photons. (AIPEmilio Segrè Visual Archives)

tions to the understanding of many differentkinds of physical phenomena, including theeffects of sound waves on the scattering of light;the vibration of atoms in crystals; the optics ofgemstones, particularly diamonds, and of miner-als; and the physiological mechanisms of humancolor vision. Raman remained head of the insti-tute until his death in Bangalore, on November21, 1970.

The leading Indian scientist of his genera-tion, Raman was also a devoted educator whotrained large numbers of his compatriots, thussignificantly enhancing the standards andstature of Indian physics. His discovery of theRaman scattering effect afforded a method forthe analysis of molecular structure, as well asdemonstrating conclusively that visible lightphotons behave as particles, thereby offeringconfirmation of the quantum theory.

Further ReadingVenkataraman, G. Journey into Light: Life and Science of

C. V. Raman. Bangalore, India: Indian Academyof Sciences, 1989.

� Ramsey, Norman F.(1915– )AmericanExperimentalist, Particle Physicist,Quantum Theorist

Norman F. Ramsey did pioneering work inatomic and molecular physics by extending anddeveloping the atomic beam magnetic reso-nance method developed by ISIDOR ISAAC RABI.He won the 1989 Nobel Prize in physics for theinvention of the separated oscillatory fieldsmethod and its use in the hydrogen maser, amethod of storing and studying atoms, and inthe cesium atomic clock, now used as the mod-ern time standard.

Ramsey was born on August 27, 1915, inWashington, D.C., the descendant of German

and Scottish immigrants. His mother had beena university mathematics instructor; his fatherwas a West Point graduate and officer in theArmy Ordnance Corps. As a military family,the Ramseys traveled a great deal, both in theUnited States and abroad. In the midst of thesefrequent moves, Norman managed to skipgrades and graduated from high school at theage of 15. When the Ramseys moved oncemore, this time to New York City, Normanentered Columbia University in 1931, in themidst of the Great Depression, starting out asan engineering major. Soon, however, findingthat he craved a deeper understanding ofnature, he switched to mathematics, in whichhe excelled.

After graduation in 1935, he received aKellett Fellowship from Columbia, which tookhim to Cambridge University, England, wherehe enrolled as a physics undergraduate. Hethrived at Cambridge’s Cavendish Laboratory,then enjoying a golden age under the director-ship of ERNEST RUTHERFORD. Having becomeinterested in molecular and atomic beams, afterreceiving a bachelor’s degree—his second—from Cambridge, he returned to Columbia towork with Rabi, who was then developing hisfamous atomic beam magnetic resonance(ABMR) method, the basis of nuclear mag-netic resonance (NMR). Thus the noviceexperimentalist, as Rabi’s first graduate student,was able to participate in the new field of mag-netic resonance and to share in the discovery ofthe electric quadrupole moment charge distri-bution on the deuteron (a nuclear particlemade up of the bound state of a proton and aneutron). He was awarded a Ph.D. for this workand went on the Carnegie Institution in Wash-ington, D.C., to study neutron–proton and pro-ton–helium scattering.

Ramsey married Elinor Jameson of Brook-lyn, New York, on June 3, 1940; the couplewould have four daughters. They set out to beginlife together at the University of Illinois. Shortly

240 Ramsey, Norman F.

afterward, however, World War II intervened,and Ramsey became involved in the war effort,working at the Massachusetts Institute of Tech-nology (MIT) Radiation Laboratory in Cam-bridge, Massachusetts, as head of a radardevelopment group. After a period in Washing-ton, D.C., where he served as radar consultant tothe secretary of war, in 1943 the Ramseys movedto Los Alamos, where the Manhattan Project tobuild an atomic bomb was under way. Over thenext two years, he did important work on bombdelivery systems.

With the war’s conclusion Ramsey rejoinedRabi at Columbia and helped him in revivingthe molecular beam laboratory. He and Rabialso collaborated in establishing the BrookhavenNational Laboratory on Long Island, NewYork, where in 1946 Ramsey became the firsthead of the physics department. He remainedin this position for only a year, however, beforejoining the physics department at HarvardUniversity, where he would teach for the next40 years, directing the research dissertations ofno fewer than 86 graduate students. He wouldleave Harvard only briefly, for visiting profes-sorships at Middlebury College, Oxford Uni-versity, Mount Holyoke College, and theUniversity of Virginia.

Soon after arriving at Harvard, Ramseybegan working on improvements to Rabi’sABMR technique, a method of obtaining dataon the quantum energy levels of the atomthrough measuring its optical spectra. InABMR, when a beam of atoms passes through ahomogeneous magnetic field with a superim-posed oscillating electromagnetic field, the lat-ter can induce the atoms to undergo specificquantum transitions if the frequency of theoscillating field is in resonance with the fre-quency of light that is emitted in this transi-tion. The time the atoms spend in theoscillating field determines the width of theresonance line—the longer the time, the nar-rower the line—provided that the magnetic

field is sufficiently homogeneous to allow thismeasurement to be made.

When he set up his molecular beam lab atHarvard, Ramsey had the goal of producingmore accurate measurements by increasing thehomogeneity of the magnetic fields. Inspired byhis initial failures, he invented a new technique:the separated oscillatory field. Ramsey’s modi-fied ABMR method worked by introducing twoseparated magnets, each generating an oscilla-tory magnetic field. This caused a spatial inter-ference pattern in the magnetic fields to appearbetween the two magnets; its sharpness

Ramsey, Norman F. 241

Norman F. Ramsey did pioneering work in atomic andmolecular physics by extending and developing theatomic beam magnetic resonance method developedby Isidor I. Rabi. (AIP Emilio Segrè Visual Archives.Physics Today Collection)

depended only on the distance between themagnets, independent of the degree of homo-geneity of the individual magnetic field gener-ated by each magnet. The interference patternof the magnetic fields thus created an artificialhomogeneity, which greatly increased the accu-racy of measurement. Ramsey and his studentsthen used this method to measure in manymolecules a number of molecular and nuclearproperties, including nuclear spins, nuclear mag-netic dipole and electric quadrupole moments,rotational magnetic moments of molecules,spin-rotational interactions, spin–spin interac-tions, and electron distribution in molecules.

During this period, Ramsey also workedwith groups engaged in the application of theseparated oscillatory field method to atomicclocks. This work produced the cesium clock,in which transitions between two very closelyspaced hyperfine levels in the cesium atom areobserved. The accuracy of such a clock, whichis the present modern time standard, is todayabout one part in 10,000 billion. Since 1967,one second has been defined as the time dur-ing which the cesium atom makes exactly9,192,631,770 oscillations.

Working with his student Daniel Kleppner,Ramsey also used his methods to invent thehydrogen maser, a method of storing and study-ing atoms. Atoms of hydrogen in an excitedstate are fed into a cavity, which can be putinto a state of self-oscillation if properly tuned.The line width is determined by the averagetime the atoms spend in the cavity—about onesecond. The walls of the cavity are coveredwith Teflon to reduce the effect of wall colli-sions. The hydrogen maser was first used tostudy the hyperfine structure of hydrogen withextreme precision. Although it is inherentlymore stable than the cesium clock, its absoluteaccuracy is inferior. It is thus used mainly as asecondary standard and in measurement offrequency shifts when extreme precision isneeded. A dramatic example of this was the ver-

ification of the gravitational red shift, the effectof gravitation on electromagnetic radiationpredicted by ALBERT EINSTEIN’s general theoryof relativity. By comparison of the frequenciesof a hydrogen maser on a rocket to those of oneon the Earth’s surface, the predictions of thegeneral theory of relativity have been verifiedto one part in 10,000.

When Ramsey was at the Institut Laue-Langevin in Grenoble, France, he and his stu-dents accurately measured the magneticmoment of the neutron and set a low limit tothe dipole moment of the neutron (a test oftime-reversal symmetry), as well as discoveringand measuring the parity nonconserving rota-tions of the spins of neutrons passing throughvarious materials. During this same period, hewas director of the Harvard Cyclotron and par-ticipated in proton–proton scattering experi-ments there. He was later chair of the jointHarvard–MIT committee managing construc-tion of the six-giga-electron-volt Cambridgeelectron accelerator, which he used for variousparticle physics experiments. For what he hascalled “sixteen exciting years,” he was on half-time leave from Harvard as president of Uni-versities Research Association. Working withthe laboratory directors, LEON M. LEDERMAN

and Robert W. Wilson, he played a major rolein the construction and operation of the 200-GeV accelerator at the Fermi Laboratory,Batavia, Illinois.

After the death of his wife, Elinor, in 1983,he married Ellie Welch of Brookline, Mas-sachusetts, with whom he has enjoyed a sharedfamily of seven children and six grandchildren.Although retired from Harvard since 1986,Ramsey has remained an engaged physicist,teaching at Williams College and at the Uni-versities of Chicago and Michigan and con-ducting research at the Joint Institute forLaboratory Astrophysics at the University ofColorado, in Grenoble, and in his Harvardoffice. He has published over 300 research

242 Ramsey, Norman F.

papers; his books include Experimental NuclearPhysics, with Emilio Segrè (1953); NuclearMoments (1953); Molecular Beams (1956 and1985); and Quick Calculus (1965 and 1985).

A brilliant experimentalist, Ramsey hasalso published fundamental theoretical physicspapers on parity and time-reversal symmetry,NMR chemical shifts, nuclear interactions inmolecules, and thermodynamics and statisticalmechanics at negative absolute temperatures.His experimental methods have contributed tothe knowledge of magnetic moments, thestructural shape of nuclear particles, the natureof nuclear forces, and the thermodynamics ofenergized populations of atoms and molecules(e.g., those in masers and lasers). Applicationsof Ramsey’s methods have been used in suchfundamental measurements as testing the prin-ciples of quantum electrodynamics and thegeneral theory of relativity.

See also BOHR, NIELS HENRIK DAVID.

Further ReadingItano, Wayne M., and Norman F. Ramsey. “Accurate

Measurement of Time,” Scientific American 269:56–65, 1993.

Ramsey, Norman F. Spectroscopy with Coherent Radia-tion: Selected Papers of Norman F. Ramsey. Singa-pore: World Scientific, 1997.

� Rayleigh, Lord (John William Strutt)(1842–1919)BritishTheorist and Experimentalist(Electrodynamics, Thermodynamics,Statistical Mechanics)

Lord Rayleigh was one of the last great classicalphysicists, who made important contributionsin several fields, including electromagnetic the-ory, thermodynamics, and statistical mechanics.Although his work was influential in the devel-opment of both quantum theory and relativity,

he remained steadfastly opposed to both theo-ries. He is most renowned for discovering,together with William Ramsay, the inert gasargon, for which he was awarded the NobelPrize in physics in 1904. Not least among hisdiscoveries is the phenomenon of Rayleigh scat-tering of sunlight in the atmosphere, on thebasis of which he explained why the sky is blueand the sunset red.

He was born John William Strutt on Novem-ber 12, 1842, in Langford Grove, Essex, the first ofseven children born to John James Strutt, the sec-ond Baron Rayleigh, and Clara Elizabeth LaTouche. The pursuit of science was neither tradi-tional nor highly valued in this family of heredi-tary aristocrats and landowners. A frail child,whose schooling at Eton and Harrow was inter-rupted by bouts of illness, John William showedno early signs of scientific aptitude. He was pri-vately tutored until 1861 and seemed to haveonly average abilities. Not until he entered Trin-ity College, Cambridge University, to study math-ematics did he excel. He studied under EdwardRouth, an applied mathematician, who providedhim with the mathematical skills he would lateruse to good purpose in his scientific career, partic-ularly the ability to identify the appropriate meth-ods for solving individual physical problems.Although he performed no experiments himself,watching his physics professor, GEORGE GABRIEL

STOKES, do so opened up the world of the labora-tory to him. His intellectual powers blossomed inthis atmosphere, and he emerged from his fourthyear exams as “Senior Wrangler,” the top student.When he graduated in 1865, he was elected a fel-low of Trinity College.

Whereas it was standard practice for youngpeople of means to make a “grand tour” ofEurope before settling down, Rayleigh, aftergraduating, headed west, to the United States,instead. When he returned to England in 1868,he set up his own laboratory at the family homeat Terling Place, Witham, in Essex. In this way,he announced his decision to commit his life to

Rayleigh, Lord 243

science, despite the disapproval of his family andsocial class. Rayleigh was an economical man,and, since these were hard times for agriculturein England, his reduced income forced him towork with cheap, unsophisticated equipment inhis home laboratory. Nonetheless, he was able todo his first important work on properties ofwaves in optics and acoustics, extending theresearch of HERMANN LUDWIG FERDINAND VON

HELMHOLTZ on resonance and vibration. Whileinvestigating the nature of light and color in1871, he discovered the physical explanation ofwhy the sky is blue and the sunset red, in termsof the effect of the scattering of light by dust par-ticles. Rayleigh’s reasoning was based on the factthat small particles in the atmosphere interactwith and scatter the sunlight incident on them.By analyzing this process using JAMES CLERK

MAXWELL’s equations for the electromagneticfield, he found that the intensity of scatteredradiation varies inversely with the fourth powerof the wavelength. This meant that the shorterblue wavelengths of sunlight would be scatteredmore efficiently into the atmosphere than thelonger red wavelengths of sunlight: thus, the skyappears blue; the sunset, red.

During this period, he also showed that theresolving power of diffraction gratings is deter-mined by the total number of lines in the grat-ing multiplied by the order of the spectrum, andnot by the closeness of the lines. This discoveryled to improvements in the spectroscope,which in the 1870s was rapidly becoming anessential instrument for investigating solar andchemical spectra.

While he was at Cambridge, Raleigh’s fel-low student, the earl of Balfour, who would laterbecome prime minister, had introduced him tohis sister, Evelyn. In 1871, they married. Theirlong union would produce three sons, the eldestof whom would become a physicist. Shortly afterthe marriage, Rayleigh had rheumatic fever and,at his doctor’s urging, went to Egypt with hisnew wife to recuperate. The trip nurtured both

his health and his scientific career: While sailingdown the Nile, he began writing his classic book,The Theory of Sound, which he would completefive years later.

When his father died in 1873, he becamethe third baron of Rayleigh. The new title didnothing to dampen his passion for scientificresearch. That year he was elected a fellow of theRoyal Society. In 1876, despite his progressivemanagement of his estate, he handed thoseduties over to his younger brother, an arrange-ment that allowed him to devote all his time toscience. In need of additional income, in 1879,he agreed to succeed Maxwell as Cavendish Pro-fessor of Experimental Physics at Cambridge, aposition he held until 1884. There he improvedthe teaching of experimental physics, causing anexplosion of interest in the subject, which led tothe flowering of British physics. In 1884, contin-uing the work of Maxwell, he established theaccurate standardization of the three basic elec-trical units, the ohm, the ampere, and the volt.

His income having improved, in 1884, hereturned to his Terling laboratory, to theresearch life he loved most. His professorship atthe Royal Institution in London, from 1887 to1905, did not require him to leave home often.From then on he conducted most of his experi-mental research in his private laboratory. Hewrote a paper in 1879 on traveling waves that inthe modern era was developed into the theory ofsoliton waves (waves that can travel through anonlinear medium without changing shape). In1885, he published his famous paper on Rayleighwave theory, elucidating his discovery that elas-tic waves can be guided by a surface. Whereas hethought it would have potential value only inseismology; it later led to the explosive growth ofthe field of electronic signal processing.

Rayleigh’s most famous work involved a care-ful study of the measurement of the density of dif-ferent gases. According to the accepted theory ofhis time, known as Prout’s hypothesis, all ele-ments have atomic weights that are multiples of

244 Rayleigh, Lord

hydrogen and have atomic weights in integermultiples of the weight of nitrogen. However,Rayleigh’s results did not support this theory. Heobserved that when he measured the density ofnitrogen in air, it was 0.5% greater than the den-sity of nitrogen from any other source. After rul-ing out all possible explanations for the source ofthe impurity causing the increase, he found him-self devoid of new ideas for solving the mystery.He published a short note in Nature in 1892,inviting suggestions. He and Ramsay studied theproblem for the next three years and jointlyannounced the discovery of a new element, argon,from the Greek word for “inactive.” Chemists hadpreviously failed to detect it, because argon ischemically inert, that is, virtually devoid of theability to make chemical combinations withother elements. In 1904, Rayleigh received theNobel Prize in physics for this work, while Ram-say was awarded the Nobel Prize in chemistry.

In 1900, he published the Rayleigh–Jeansequation, which described the distribution ofwavelengths in blackbody radiation, accountingfor only the longer wavelengths. Later, WIL-HELM (CARL WERNER OTTO FRITZ FRANZ) WIEN

produced an equation to describe the shorter-wavelength radiation. It was MAX ERNEST LUD-WIG PLANCK who would account for thedistribution of all wavelengths by postulatingthe existence of indivisible energy packetscalled quanta, thereby sparking the quantumrevolution. Rayleigh resisted the quantum the-ory, because it overturned classical radiationtheory; for similar reasons he could not acceptNIELS HENRIK DAVID BOHR’s explanation of thehydrogen spectrum, which furthered quantumtheory. He also opposed ALBERT EINSTEIN’s spe-cial theory of relativity, because it rejected theclassical idea of the ether as the medium inwhich light waves moved. Ironically, Rayleigh’sown unsuccessful attempt in 1901 to detect theether inadvertently lent support to relativity.

Lord Rayleigh published 446 papers from1869 to 1920, each a model of clarity and ele-

gance, on a vast range of topics in physics andapplied mathematics. His amazing scope isreflected in the sheer number of terms used inmodern physics that bear his name: Rayleigh dis-tribution (statistics), Rayleigh–Jeans law (black-body radiation), Rayleigh scattering (coloration ofthe sky), Rayleigh damping (damped vibrationalbehavior), Rayleigh quotient (elastodynamics),Rayleigh–Ritz process (elastomechanics),Rayleigh waves (surface waves), Rayleigh fadingand Rayleigh distance (propagation of electro-magnetic waves), Rayleigh criterion (resolvingpower of telescopes), and Rayleigh number (natu-ral convection).

Although he worked at home, he was farfrom isolated and had many connections withthe scientific community. From 1885 to 1896,he served as secretary of the Royal Society; hewas president from 1905 to 1908. Through hiswife, he was connected with the political sceneand held many advisory roles on national com-mittees, including one on aeronautics. In 1908,he was appointed chancellor of Cambridge Uni-versity, a post he retained for the rest of his life.Despite his renown, he maintained humility, asdemonstrated by his comments in 1902, at thecoronation of King Edward VII, when hereceived the Order of Merit:

The only merit of which I personally amconscious was that of having pleasedmyself by my studies, and any resultsthat may be due to my researches wereowing to the fact that it has been a plea-sure for me to become a physicist.

A generous man, he donated the cash awardfor the 1904 Nobel Prize to Cambridge Univer-sity, to build an extension to the Cavendish Lab-oratories. He died at home on June 30, 1919, ofa heart attack.

Opposed to relativity and quantum mechan-ics, Lord Rayleigh made great contributions tothe consolidation and advancement of the

Rayleigh, Lord 245

branches of classical mechanics that remainedvalid. Further, his discovery of argon led to theuncovering of a whole family of elements (thenoble gases) that are of great importance inthemselves and to an understanding of chemicalbonding. Among the applications of argon inmodern industry are its uses in welding, as ashield of the molten metal; in nuclear reactors, asan inert cooling agent; in electric light bulbs; andin lasers, in the manufacture of semiconductorcrystals, in which an inert atmosphere plays animportant part.

See also FRAUNHOFER, JOSEPH VON; KIRCH-OFF, GUSTAV ROBERT; MICHELSON, ALBERT

ABRAHAM.

Further ReadingHumphrey, A. T. “Lord Rayleigh—the Last of the

Great Victorian Polymaths.” GEC Review 7:167–179, 1992.

Lindsay, R. B. Lord Rayleigh, the Man and His Works.London: Oxford University Press, 1970.

� Reines, Frederick(1918–1998)AmericanExperimentalist, Particle Physicist

Frederick Reines shared the Nobel Prize inphysics in 1995 for his historic 1956 experiment,with Clyde Cowan, in which he discovered theelusive neutrino, a particle first predicted byWOLFGANG PAULI in the mid-1930s. Through-out his career, he continued to explore the neu-trino’s properties and interactions, in thecontext of both elementary particle physics andastrophysical processes.

Reines was born on March 16, 1918, theyoungest of the four children of Israel Reines andGussie Cohen, who had immigrated to theUnited States (where they met) from the samesmall town in Russia. Reines’s childhood cen-tered around the general store his father ran in

the town of Hillburn, New York, where hedeveloped his mechanical and musical interestsand first became interested in science when hebecame aware of the phenomenon of lightdiffraction. Because older siblings were studyingmedicine and law, the household was filled withbooks. Although initially attracted to literature,he declared in the yearbook in his senior year inhigh school that his main ambition was “to be aphysicist extraordinaire.”

Reines attended the Stevens Institute ofTechnology in Hoboken, New Jersey, where hestudied engineering, while finding time todevelop his interests in drama, dance, and, mostenduringly, choral music. For a while he consid-ered a career as a professional singer, and,although he abandoned this idea, he would con-tinue singing during his physics career, perform-ing in Gilbert and Sullivan operettas whileworking at Los Alamos. While living in Cleve-land, he performed in the chorus of the ClevelandSymphony Orchestra under George Szell—anexperience that stood out for him as “the peak ofmy musical endeavors.” In between receiving abachelor’s degree in engineering in 1939 and amaster’s degree in mathematical physics in 1941,both from the Stevens Institute, Reines marriedSylvia Samuels. Theirs would be a lasting union,producing two children and six grandchildren.

Reines continued his graduate work at NewYork University, first concentrating on experi-mental cosmic ray physics. However, the thesis hesubmitted in 1944 for his Ph.D. was a theoreticalstudy, directed by R. D. Present, “The LiquidDrop Model for Nuclear Fission.” By this time, hewas already working for RICHARD PHILLIPS FEYN-MAN on the Manhattan Project to develop anatomic bomb in Los Alamos, where he wouldremain for the next 15 years. He soon became agroup leader in the theoretical division and laterwas made director of Operation Greenhouse, aseries of Atomic Energy Commission experimentsat Eniwetok atoll. He analyzed the results of bombtests at Eniwetok, Bikini, and the Nevada testing

246 Reines, Frederick

ground and coauthored a study with John vonNeumann on the effects of nuclear blasts.

In the mid-1930s, physicists studying thenuclear radioactive beta decay process (e.g., theradioactive decay of a neutron into a proton)became aware that the nucleus appears to emitonly an electron when it disintegrates byradioactive beta decay, thereby apparently vio-lating conservation of energy and momentum.This problem led Pauli to postulate the exis-tence of a new elementary particle. In what hetermed his “desperate solution,” he hypothesizedthat another subatomic particle, which lackedelectric charge and hence reacted very weaklywith its environment, was also emitted in thenuclear beta decay process, taking part of theenergy and momentum with it and then disap-pearing again into nothingness. The name neu-trino (“little neutral one”) was bestowed uponPauli’s new particle by ENRICO FERMI, therebydistinguishing it from the neutron. Fermi devel-oped a successful theory of weak nuclear pro-cesses, in which the neutrino played a centralrole. But the neutrino’s extremely weak couplingto matter posed a formidable challenge todetecting it. Most physicists preferred not to try.

Reines, however, had been considering thischallenge for several years, and, during a sabbati-cal from his Los Alamos work in 1951, he madethe decision to take it on. A Los Alamos col-league, Clyde Cowan, joined him in this work.They considered different sources of neutrinos—a nuclear bomb test, the nuclear reactor at Han-ford, Washington—but finally settled on theSavannah River reactor facility in South Car-olina, which was completed in 1955. The follow-ing year they succeeded in detecting the electronneutrino through inverse beta decay in which aneutrino hitting a proton makes it into a neu-tron. The neutrino appeared to have the proper-ties of an uncharged electron; however, at thattime the question of whether the neutrino had anonzero mass was unknown. (Current experi-ments now seem to imply that the electron neu-

trino has a very small but finite mass.) WhenCowan left Los Alamos, their collaborationended, but Reines carried forward their ground-breaking experimental work. After Cowan died,Reines received the Nobel Prize for this work,which was described as “a feat considered to bor-der on the impossible. They had raised the neu-trino from its status as a figure of the imaginationto an existence as a free particle.”

After this, Reines worked on gamma rayastronomy, as well as beginning the first of aseries of experiments at Savannah River to studythe properties of the neutrino. This work ush-ered in the era of “neutrino physics” when neu-trinos, whether accelerator-produced or reactorand cosmic ray neutrinos, could be used to inves-tigate the weak interactions, the structure of

Reines, Frederick 247

Frederick Reines discovered the elusive neutrino, aneutral spinning particle with zero mass first predictedby Wolfgang Pauli in the mid-1930s. (AIP Emilio SegrèVisual Archives and Los Alamos Scientific Laboratory)

protons and neutrons, and the properties of theirinternal constituents, quarks.

Reines ended his long period at Los Alamosby serving, in 1958, as a delegate to the Atomsfor Peace conference in Geneva. The followingyear he joined the Case Institute of Technology,Cleveland, where he was involved in neutrinoexperiments at reactors and in pioneering stud-ies deep underground to search for atmosphericand cosmic particles. His group worked in reac-tor neutrino physics, double beta decay, electronlifetime studies, and searches for nucleon decay.They also conducted bold experiments in a goldmine in South Africa that made the first obser-vation of the neutrinos produced in the atmo-sphere by cosmic rays. The experiments weredesigned to explore the properties of the neu-trino and to probe the limits of fundamentalsymmetry principles and conservation laws, suchas the conservation of charge, baryon number,and lepton number. In carrying out these exper-iments, the group necessarily became expert inthe operation of deep underground laboratories,where, according to Reines, “the projects alsodrew us into developing innovative detectortechniques, including the use of large liquidscintillator and water Cherenkov detectors.”

In 1966, he took his group with him to theUniversity of California, Irvine, where hebecame the founding dean of the School ofPhysical Sciences, a position he held until 1974,when he returned to full-time teaching andresearch. He became distinguished professor ofphysics in 1987 and professor emeritus in 1988.The “neutrino group” still plays a leading role inmajor neutrino experiments, including thefamous “IMB” (Irvine/Michigan/Brookhaven)underground detector and its proton decayexperiment. The IMB detector was the first toobserve double beta decay in the laboratory. Itwas used to study neutrino physics, primarilyemploying neutrinos produced by interactionsof cosmic rays in the atmosphere. The detector’simpressive size and neutrino detection capabil-

ity led to the historic detection of the burst fromthe supernova SN1987A—providing conclu-sive proof that neutrinos play a role in stellarcollapse. The IMB group shared the Bruno RossiPrize of the American Astronomical Society(1989) with the Kamiokande experiment inJapan for their joint observation of this phe-nomenon, which led to the birth of neutrinoastronomy.

This work led Reines to explore many otherintriguing experimental ideas and researchareas, including the search for relic neutrinosfrom the big bang; the “neutrino Mössbauereffect,” in which a photon is replaced by a neu-trino; a neutrino technique to improve theaccuracy of the measurement of the gravita-tional constant G, the most poorly measuredfundamental constant, by several orders of mag-nitude; a spherical neutrino lens space tele-scope; an attempt to set more stringent limits onviolation of the Pauli exclusion principle;exploration of the brain using ultrasound; and avariety of new detector ideas.

When Reines died in August 1998, theneutrino was far less elusive than it had been atthe start of his career. He left a rich legacy ofcontributions, including the first detection ofneutrinos produced in the atmosphere; the firststudy of muons induced by neutrino interac-tions underground; the first observation of thescattering of electron antineutrinos with elec-trons; the detection of the weak neutral currentinteractions of electron antineutrinos withdeuterons; investigations looking for neutrinooscillations (the possibility of neutrino transfor-mation from one type to another); and the firstdetection of a neutrino from a supernova. Cur-rent studies have shown that neutrino oscilla-tions actually do occur; that means that theneutrino must have nonzero mass. This discov-ery will have profound implications for cosmo-logical models in terms of the estimated missingmass of the universe.

See also CHERENKOV, PAVEL ALEKSEYEVICH.

248 Reines, Frederick

Further ReadingFranklin, Allan. Are There Really Neutrinos? An Evi-

dential History. Cambridge, Mass.: Perseus, 2000.Kropp, W., J. Schultz, M. Moe, L. Price, and H. Sobel,

eds. Neutrinos and Other Matters: Selected Worksof Frederick Reines. Singapore: World Scientific,1996.

Solomey, Nickolas. The Elusive Neutrino: A SubatomicDetective Story. New York: W. H. Freeman, 1997.

Sutton, Christine. Spaceship Neutrino. Cambridge:Cambridge University Press, 1992.

� Richter, Burton(1931– )AmericanExperimentalist, Particle Physicist

Burton Richter is an outstanding experimentalparticle physicist, whose career has centeredon high-energy electrons and electron–positroncolliding beams. He shared the 1976 NobelPrize in physics with SAMUEL CHAO CHUNG

TING for his discovery of what is now calledthe J/ψ particle, an excited state of nuclearmatter exhibiting the physical attributes asso-ciated with the existence of charmed quarks,which confirmed the standard quark–leptonmodel of electroweak and nuclear forces.

He was born on March 22, 1931, in Brook-lyn, New York City, the elder child of Abrahamand Fanny Richter. He was a member of thatextraordinary generation of physicists, childrenof European Jewish immigrants, who grew up inNew York in the years of the Great Depressionand World War II, who included MURRAY GELL-MANN, SHELDON LEE GLASHOW, LEON M. LEDER-MAN, and STEVEN WEINBERG. After making anexcellent record for himself in the New Yorkpublic schools, he was accepted in 1948 at thehighly competitive Massachusetts Institute ofTechnology (MIT) in Cambridge. Undecided atfirst whether to major in physics or chemistry, hechose physics as a result of the strong influence

of Francis Friedman, one of his professors, whorevealed to him the inherent beauty of the sub-ject. He was introduced to the electron–positronsystem, which would be important in his futurecareer, during the summer following his junioryear, when he worked with Francis Bitter inMIT’s magnet laboratory. There he assisted Mar-tin Deutsch in his classical positronium experi-ments, using a large magnet. Later, Bitter agreedto direct Richter’s senior thesis on the quadraticZeeman effect in hydrogen.

For his graduate studies, begun in 1952,Richter remained at MIT and continued work-ing with Bitter and his group. Initially, heworked with the group on a measurement of theisotope shift and hyperfine structure of mercuryisotopes. Soon, however, he became more inter-ested in the nuclear and particle physics prob-lems he had studied as an undergraduate. Aftersix months at the Brookhaven National Labora-tory on Long Island, New York, working at thethree-giga-electron-volt proton accelerator, heknew that particle physics research was what hewanted to do. When he returned to MIT, it wasto the synchrotron laboratory. He would laterwrite, “This small machine was a magnificenttraining ground for students, for not only did wehave to design and build the apparatus requiredfor our experiments, but we also had to helpmaintain and operate the accelerator.” Workingunder L. S. Osborne, he completed a doctoralthesis on the photoproduction of pi mesons fromhydrogen in 1956.

From 1956 to 1960, he was a research asso-ciate at the High-Energy Physics Laboratory(HEPL) at Stanford University. He was drawn toHEPL’s 700-MeV electron linear accelerator,which would allow him to pursue his interest inexperimentally testing quantum electrodynam-ics (QED, the quantum field theory describingthe interaction of electrons and electromagneticradiation) and, specifically, to investigate theshort-distance behavior of the electromagneticinteraction. His very first experimental study at

Richter, Burton 249

HEPL, which looked at electron–positron pairsby using gamma rays, established that QED wascorrect to distances as small as about 10–13 cm.

In 1960, Richter became an assistant profes-sor in the physics department at Stanford andmarried Laurose Becker, with whom he wouldhave two children, Elizabeth and Matthew. Forthe next few years, Richter worked with G. K.O’Neill of Princeton, W. C. Barber, and B. Git-telman on the construction of the first collidingbeam device, which became the prototype for allfuture colliding beam storage rings. Using theHEPL linear accelerator as an injector, theirdevice allowed them to study electron–electronscattering at a center-of-mass energy 10 timeslarger than that used in Richter’s earlier pairexperiment. In 1965, they conducted an experi-ment resulting in extension of the validity ofQED down to less than 10–14 cm.

Richter’s next goal was to create a high-energy electron–positron colliding beam machinethat would allow him to study the structure of thehadronic (strongly interacting) particles associ-ated with the excited states of protons, neutrons,and mesons. At the Stanford Linear AcceleratingCenter (SLAC), which he had joined in 1963, heand his group designed the machine andembarked on the long struggle for funding. Whenit finally came through in 1970, they built theStanford Positron Electron Accelerator Ring(SPEAR), including the storage ring and a largemagnetic detector. Experiments began in 1973.

In November 1974, Richter and his teamdetected a new kind of massive hadronic particlestate that had the physical properties of a meson.They gave this excited hadronic state the nameψ. The particle was more than twice as heavy asany comparable hadronic particle and yet athousand times more narrow in its energy spec-trum (which, according to the uncertainty prin-ciple, meant that it was a long-lived particle).They published their results in a 35-author paper(characteristic for high-energy experimentalteams) in Physical Review Letters.

Meanwhile, in August 1974, at theBrookhaven Laboratory, Samuel Ting and histeam had made a startling discovery: the first ofa totally unpredicted new group of extremelyheavy long-lived mesons. In November, afterrechecking his results, Ting announced his dis-covery, which he called the J particle (based onthe symbol for the electromagnetic current). Justbefore publishing his findings, Ting attended aconference at Stanford University with scien-tists working at SLAC, where he learned ofRichter’s almost simultaneous discovery. It wasat this conference that the new particle state wasnamed the J/ψ particle.

The significance of Richter and Ting’s dis-covery was considerable. In 1961, Murray Gell-Mann and YUVAL NE’EMAN had devised theeightfold way, a system for classifying the myriadnewly discovered elementary particles into eightfamilies of elementary building blocks calledquarks, of which, at that time, there were threetypes. The unique feature of the newly discov-ered J/ψ particle was that it did not belongto any of the families, as they were knownbefore 1974. Its detection confirmed SheldonGlashow’s earlier prediction of a fourth quark(i.e., a “charmed quark”), which was needed inorder to make the Gell-Mann SU(3) quark the-ory of the strong interactions consistent withthis observation. Ting and Richter’s discovery ofthe J/ψ particle changed the landscape of parti-cle physics. Two years later, they shared theNobel Prize for their work.

Later in the 1970s, working with physicistsat CERN; Novosibirsk, Russia; and Cornell Uni-versity, Richter developed the ideas that led tothe creation of the SLAC Linear Collider, whichhe describes as “a kind of hybrid machine, withboth electrons and positrons accelerated in thesame linear accelerator, and with an array of mag-nets at the end to separate the two beams andthen bring them back into head-on collisions.”Completed in 1987, it began to be used for exper-iments in 1990. Richter predicted,

250 Richter, Burton

Probably the most lasting contributionthat this facility makes to particlephysics will be the work of acceleratorphysics and beam dynamics that hasbeen done with the machine and whichforms the basis of very active R&D pro-grams aimed at the TeV [trillion elec-tron volt] scale linear colliders for thefuture.

While bringing this major project tofruition, Richter became a scientific administra-tor, serving as technical director of SLAC from1982 to 1984, and then as director from 1984until his retirement in 1999.

Richter, who has over 300 publications inhigh-energy physics, accelerators, and collidingbeam systems, is a fellow of the American Physi-cal Society and served as its president in 1994. Inreviewing his life in physics, Richter has written:

[I] realize what a long love affair I havehad with the electron. Like most loveaffairs, it has had its ups and its downs,but for me the joys have far outweighedthe frustrations.

By experimentally verifying the need for acharmed quark, Burton Richter’s groundbreak-ing experiment opened the door to the furtherelaboration of the fully developed StandardModel of electromagnetic, weak, and nuclearforces, which currently contains six quarks: up,down, strange, charm, top, and bottom.

See also SALAM, ABDUS; SCHWINGER, JULIAN

SEYMOUR; FEYNMAN, RICHARD PHILLIPS; DYSON,FREEMAN.

Further ReadingKane, Gordon. The Particle Garden: Our Universe as

Understood by Particle Physicists. Cambridge,Mass.: Perseus, 1995.

Ne’eman, Yuval, and Murray Gell-Mann. The Eight-fold Way. Cambridge, Mass.: Perseus, 2000.

Ne’eman, Yuval, and Yoram Kirsh. The Particle Hunters.Cambridge: Cambridge University Press, 1996.

� Röntgen, Wilhelm Conrad(1845–1923)GermanExperimental Physicist(Electrodynamics, Optics)

Wilhelm Conrad Röntgen discovered X rays in1895, initiating a new era in physics andmedicine. For this momentous achievement, hebecame the first recipient of the Nobel Prize inphysics in 1901.

Röntgen was born in Lennep, in the LowerRhine region of Germany, on March 27, 1845,the only child of a cloth manufacturer. CharlotteConstanze Frowein, his mother, was from Ams-terdam, and, when Wilhelm was three, the fam-ily moved to Apeldoorn, the Netherlands, wherehe received his early education at a boardingschool. As a boy, he loved to explore the coun-tryside and showed an early aptitude for makingmechanical devices. His boyhood was marred bythe injustice of being expelled from the UtrechtTechnical School for drawing a caricature of oneof the teachers; the prank, in fact, had beencommitted by another student. He overcamethis setback, however, and gained admission tothe Federal Polytechnic Institute in Zurich,Switzerland, in 1866, to study mechanical engi-neering; there he received his diploma in 1868.

In 1869, Röntgen received a Ph.D. from theUniversity of Zurich. While in Zurich, he metAnna Bertha Ludwig, the daughter of a caféowner, and married her in 1872. They would nothave children of their own; in 1887, theyadopted the six-year-old daughter of AnnaRöntgen’s only brother. In his immediate post-doctoral years, while serving as assistant to theGerman experimental physicist August Kundt,Röntgen decided to pursue pure science, special-izing in physics. In order to be near Kundt, he

Röntgen, Wilhelm Conrad 251

held a series of positions, in Würzburg and Stras-bourg; in 1875, he became professor of physicsand mathematics at the Agricultural Academyof Hohenheim. He returned to Strasbourg thefollowing year to teach physics. From 1879 to1888, he was professor of physics at Giessen.Then, in 1888, he became professor of physics atWürzburg, where his colleagues included HER-MANN LUDWIG FERDINAND VON HELMHOLTZ

and HENDRIK ANTOON LORENTZ.During this period, Röntgen carried out

significant research on an impressive number ofquestions. He published his first paper, dealingwith the specific heats of gases, in 1870.Between 1876 and 1895, he made importantstudies of the characteristics of gases and crys-talline substances. These included thermalconductivity of gases, electrical and other char-acteristics of quartz, the influence of pressure onthe refractive indices of various fluids, modifica-tion of the planes of polarized light by electro-magnetic influences, variations in the behaviorof the temperature and compressibility of waterand other fluids, and the phenomena accompa-nying the spreading of oil drops on water.

However, this large body of work would beovershadowed by the great discovery Röntgenmade in November 1895. He was studying theproperties of cathode rays emitted by a partiallyevacuated glass Crookes tube (a glass vacuumtube with electrodes at each end). While exper-imenting with a barium compound, he was sur-prised to observe that it glowed even when thetube was encased in black cardboard. He tookthe chemical into another room; it continued toglow whenever the tube was activated. Röntgenconcluded that these rays, with such high pene-trating power, were entirely different from cath-ode rays. Later, when asked what his thoughtshad been at the moment of his discovery, hesaid: “I didn’t think. I investigated.”

His investigations revealed that this newkind of cathode ray passed unchanged throughcardboard and thin plates of metal, traveled in

straight lines, and was not deflected by electric ormagnetic fields. He called them X rays, since hecould not explain their nature. Later MAX

THEODOR FELIX VON LAUE and his students wouldshow that X rays possess the same electromag-netic nature as light but have a higher frequencyof vibration. Using X rays, Röntgen took his first“X-ray photograph,” of his wife’s hand; it showedthe shadows thrown by the bones of her hand andof the ring she was wearing, surrounded by thepenumbra of the flesh, which threw a faintershadow since it was more permeable to the rays.

In January 1896, after two months of thor-ough investigation the properties of X rays, herevealed his discovery to the general public.Almost immediately Röntgen’s announcementinspired further breakthroughs in both pureand applied science. Before long, developmentof X-ray equipment and photography for use inmedical work was under way in Europe and theUnited States. Röntgen became the first recip-ient of the Nobel Prize in physics in 1901. Hewas showered with prizes, medals, honorarydoctorates, and honorary and correspondingmemberships to learned societies in Germanyand abroad; several cities and streets werenamed after him.

In 1900, Röntgen became professor ofphysics and director of the Physical Institute atMunich, where he remained until he retired in1920. He was a man of great integrity, uninter-ested in amassing personal wealth or honors. Herefused the title von Röntgen, which would havemade him a member of the German nobility, anddonated the money for his Nobel Prize to theUniversity of Würtzburg. He did, however,accept the honorary degree of doctor of medicineoffered to him at Würzburg. Ironically, he nevertook out a patent on X rays and refused to bene-fit financially from the fruits of his discovery,since he believed that the products of scientificresearch should be available to everyone. He wasalmost bankrupt at the end of his life, during aperiod of runaway inflation in Germany that fol-

252 Röntgen, Wilhelm Conrad

lowed World War I. He died in Munich onFebruary 10, 1923, of intestinal cancer.

Röntgen’s discovery of X rays had an enor-mous impact on the development of 20th-cen-tury physics. It led ANTOINE-HENRI BECQUEREL

to discover radioactivity that same year, that dis-covery in turn caused a revolution in ideas aboutthe atom. It would later lead to the discovery ofX-ray diffraction, which yielded methods ofstudying atomic and molecular structure. In con-temporary physics, X rays continue to find newuses in a growing number of fields, includingcondensed matter physics, molecular biophysics,astrophysics, nuclear physics, relativity, plasmaphysics, and cosmology.

See also RUTHERFORD, ERNEST; THOMSON,JOSEPH JOHN (J. J.).

Further ReadingGlasser, Otto. Wilhelm Conrad Roentgen and the Early

History of the Roentgen Rays. Novato, Calif.:Jeremy Norman, 1992.

Physics Today, November 1995 issue commemoratingthe centennial of Röntgen’s discovery of X rays.

� Rubbia, Carlo(1934– )ItalianExperimentalist, Particle Physicist

Carlo Rubbia designed and headed the syn-chrotron experiments at the Center for Euro-pean Nuclear Research (CERN) that led to thediscovery of the intermediate vector boson par-ticles W and Z. At the deepest level of matterthese extremely heavy particles act as carriers ofthe weak interaction between quarks and lep-tons, thereby generating radioactive decay.Their existence was theoretically predicted bythe electroweak quantum field theory devel-oped by SHELDON LEE GLASHOW, ABDUS

SALAM, and STEVEN WEINBERG, which unifiedthe electromagnetic force associated with quan-

tum electrodynamics (QED) and the weak forceassociated with radioactive decay into a singletheory. Rubbia shared the 1984 Nobel Prize inphysics with his collaborator Simon Van derMeer for this work.

Rubbia was born on March 31, 1934, in thesmall town of Gorizia, near Trieste, in Italy. Hisfather worked as an electrical engineer for thelocal telephone company, and his mother was anelementary school teacher. When, at the end ofWorld War II, the province of Gorizia was takenover by Yugoslavia, the Rubbia family fled, firstto Venice and then to Udine. As a boy, Rubbiaearly evinced the qualities that would lead himto experimental physics: he read everything hecould find on the electrical and mechanicalideas that so fascinated him and was drawn to“the hardware and construction aspects” ratherthan to theoretical concerns.

His formal education had been badly dis-rupted by the war, however, and he failed hisentrance examinations to the Scuola Normalein Pisa, where he had hoped to study physics. Hehad resigned himself to studying engineering inMilan when the withdrawal of one of the win-ning contestants allowed him to enter theScuola Normale after all. Overjoyed by thishappy accident, he moved to Pisa, where hestruggled to make up for the shortcomings in hispreparation. Under his thesis adviser MarcelloConversi, he participated in the construction ofnew instruments such as the first pulsed gas par-ticle detector and earned his undergraduatedegree with a thesis on cosmic ray experiments.

Eager to learn about giant particle accelera-tors, Rubbia, in 1958, went to the United States;there he worked at the Nevis Cyclotron Labora-tory at Columbia University. With W. Baker, heperformed the first of a series of experiments onweak interactions, which would be his primaryfocus. The two men measured the angular sym-metry associated with the capture of polarizedmuons, thereby showing that parity violationoccurs in this basic process.

Rubbia, Carlo 253

Rubbia was attracted back to Europe twoyears later by the establishment of CERN inGeneva, Switzerland. Using a cyclotron superiorto that at the Nevis Laboratory, Rubbia and hiscolleagues carried out a number of importantexperiments on the structure of weak interac-tions, notably including the discovery of theradioactive beta decay process of the positivepion and the first observation of the muon cap-ture by free hydrogen.

In the early 1960s, Rubbia began workingon the newly constructed proton synchrotronat CERN, where he determined the parity vio-lation in the beta decay of the lambda hyperon(an excited state of the nucleus). After VAL

LOGSDON FITCH announced the discovery ofcharge-parity symmetry violation (known asCP or T violation) in some particle processes,Rubbia began a long series of CP symmetry—related observations associated with the K0 par-ticle decay and on the KL–KS particle massdifference.

A few years later, in 1973, together withDavid Cline and Alfred Mann, Rubbia proposeda major neutrino experiment at the Fermi Labo-ratory in Batavia, Illinois. After more than a yearof hard work they were able to observe cleanlythe presence of the all-muon events in neutrinointeractions needed to confirm experimentallynew theoretical predictions made at CERNabout the existence of a “charmed quark” andthe ψ particle resonance.

By 1976, it was already clear that the uni-fied electroweak theory of the symmetry typeSU(2)×(1) had a good chance of predicting theexistence and masses of the triplet of extremelymassive intermediate vector bosons W and theneutral Z particle singlet that were required tocarry the electroweak interaction. The problemwas finding a practical way to discover them. Toachieve high enough energies to create thesebosons (roughly 100 times heavier than pro-tons), experimentalists needed a radically newapproach.

At CERN, under the leadership of VictorWeisskopf, a new type of colliding beammachine had been built with intersecting stor-age rings in which counterrotating beams ofprotons collide with one another. Rubbia andhis collaborators transformed this high-energyaccelerator into a colliding beam device inwhich a beam of protons and antiprotons coun-terrotate and collide head-on. For this purpose,they had to develop techniques for creatingantiprotons, confining them in a concentratedbeam, and colliding them with an intense pro-ton beam. Rubbia did this with Van der Meer,Guido Petrucci, and Jacques Gareyte at CERN,where the first collisions were observed in1981.

Hundreds of scientists were involved in theseexperiments in teams throughout the world. In1983, Rubbia and collaborating teams of scien-tists announced the discovery of the W and Z par-ticles on the basis of signals from detectorsspecially designed for this purpose. When the1984 Nobel Prize was awarded for this work, Rub-bia was cited for developing the idea; Van derMeer, the equipment.

Their work was the culmination of 50 yearsof research into the weak interaction, begun in1934 with ENRICO FERMI’s discovery that betadecay radiates into a final state involving anelectron and a neutrino pair. Fermi assumed thatthe electron and the neutrino pair were createddirectly, when neutrons were transformed intoprotons. Rubbia’s work showed that pair cre-ation is a two-step process, in which the particlesW and Z are emitted in the first intermediatestep and then convert into an electron and aneutrino pair in the second and final step. (Thisprocess has an analogy in QED, in which twoelectron bodies interact with each other byexchanging photons.)

For many years Rubbia divided his timebetween Cambridge, Massachusetts, where hetaught for one semester a year at Harvard Uni-versity, where he had been appointed professor in

254 Rubbia, Carlo

1960, and at Geneva, where he conducted exper-iments such as the UA-1 collaboration at theproton–antiproton collider. He served as directorgeneral of CERN from 1989 to 1993. Married toMarisa Rubbia, a high school physics teacher, heis the father of two and a grandfather.

In November 1993, he proposed his EnergyAmplifier project, a search for new sources ofnuclear energy, exploiting knowledge and skillsfrom high-energy physics that suggested thedevelopment of a power plant in which energywould be produced in a subcritical reactor. In1994 he began to explore a route to energy pro-duction through controlled nuclear fission.

Rubbia believes that future experiments willlead to the discovery of an ever-finer definitionof nature’s fundamental building blocks:

I think that an elementary particle issomething much more complex than amathematical point. . . . For a long timewe thought nuclei were elementary par-ticles. Even the word “atom” means“that which cannot be divided.” Later,we thought that protons were elemen-tary particles. Now we know that theproton is made of quarks. In the historyof physics, we have often over-simplifiedthe structure of nature.

The fundamental impact of Carlo Rubbia’sNobel Prize–winning work, in verifyingGlashow, Weinberg, and Salam’s unified elec-troweak SU(2) × U(1) theory, was to open thedoor for physicists to begin searching for a globalunification of the electroweak theory with thequantum chromodynamic SU(3) strong interac-tion theory of MURRAY GELL-MANN. The searchfor a “theory of everything” to complete this uni-fication is one of the leading directions in parti-cle physics today.

See also ANDERSON, CARL DAVID; LEE,TSUNG DAO; WU, CHIEN-SHIUNG; YANG, CHEN

NING; YUKAWA, HIDEKI.

Further ReadingForward, Robert L., and Joel Davis. Mirror Matter:

Pioneering Antimatter Physics. Lincoln, Nebr.:iUniverse.com, 2001.

Taubes, Gary. Nobel Dreams: Power, Deceit, andthe Ultimate Experiment. New York: RandomHouse, 1987.

� Rutherford, Ernest (Lord Rutherfordof Nelson)(1871–1937)New Zealander/BritishTheorist and Experimentalist(Radioactivity), Atomic Physicist,Nuclear Physicist

Ernest Rutherford is famous for discovering thebasic structure of the atom, showing that it con-sists of a central nucleus surrounded by orbitingelectrons. He invented the language to describethe theoretical concepts of the atom and thephenomenon of radioactivity. He won the 1908Nobel Prize in chemistry for his discovery thatradioactivity is produced by the disintegrationof atoms and that alpha particles consist ofhelium nuclei.

Rutherford was born near Nelson, on August30, 1871, in a remote province of New Zealand,the fourth of 12 children. Both his father, awheelwright and flax miller, and his mother, anEnglish schoolteacher, had emigrated fromBritain as children. Despite the family’s limitedmeans, he managed to get a good education, firstin state schools and then at Nelson College,which he entered at age 16. In 1889, he wona scholarship to Canterbury College inChristchurch, part of the University of NewZealand, and went on to earn a string of degrees:a B.A. in 1892, an M.A. in 1893, and a B.Sc. in1894. At Canterbury he became a pioneer indesigning original experiments with high-fre-quency alternating currents. In the same yearthat Guglielmo Marconi began his radio experi-

Rutherford, Ernest 255

ments and six years after HEINRICH RUDOLF

HERTZ discovered radio waves, Rutherford stud-ied the magnetic properties of iron exposed tohigh-frequency electric discharges and con-structed a very sensitive detector of radio waves.

Rutherford left New Zealand for England in1895, on a scholarship enabling him to study atthe Cavendish Laboratory, Cambridge, underJOSEPH JOHN (J. J.) THOMSON, the discoverer ofthe electron. Under Thomson’s influence, heembarked on what would be his life’s work:atomic and nuclear physics. He began by study-ing the effect of X rays on the discharge of elec-tricity in gases, found that X rays form positiveand negative ions in gases, and measured theirmobility. In 1897, he made a similar study of theeffects of ultraviolet light in gases, as well as theradioactivity produced by uranium minerals.Intrigued by radioactivity, he began to investi-gate its nature. In 1898, he discovered two kindsof radioactivity with different penetrating power.He called the less penetrating alpha rays and themore penetrating beta rays. Later these “rays”were found to consist of streams of particles andbecame known as alpha and beta particles.

In 1898, Thomson helped Rutherford obtainhis first academic appointment, at McGill Uni-versity in Montreal, Canada. Working at theuniversity’s superbly equipped MacDonald Lab-oratory, Rutherford and his colleagues wouldmake McGill a focal point for early work in sub-atomic physics. In 1900, he married Mary New-ton, with whom he would have a daughter,Eileen. That same year he discovered a thirdtype of radioactivity with great penetratingpower, which he called gamma rays. These werelater found to be quanta of very high frequencyelectromagnetic fields; today they are still calledgamma rays or gamma radiation.

Rutherford began to use a radioactive ele-ment called thorium as a source of radioactivityinstead of uranium; he found that it produced anintensely radioactive gas, a process he calledemanation. He studied the emanation of tho-

rium and discovered a new noble gas, an isotopeof radon, later known as thoron. To identifythese radioactive products he enlisted the aid ofFrederick Soddy, who arrived at McGill in 1900from Oxford. In 1903, experimental evidenceled Rutherford and Soddy to propose the disinte-gration theory of radioactivity, which viewsradioactive phenomena as nuclear processes,that is, processes that occur in the nucleus of anatom. Together they discovered a number of newradioactive substances and fixed their positionsin the series of radioactive transformations ofthe elements.

Rutherford found that the intensity of theradioactivity produced decreases at a rate gov-erned by the element’s half-life, a term heinvented to designate the time it takes for halfthe nuclei of a sample of radioactive substance todecay. His cogent explanation of the revolution-ary idea that atoms could change their identityled to its immediate acceptance. Next Ruther-ford wanted to identify the alpha rays, which hewas sure consisted of positively charged parti-cles—either hydrogen or helium ions. In 1903,his experiments on deflection of alpha rays inelectric and magnetic fields proved that theywere positive particles, but his apparatus was notsensitive enough to allow him to determine theamount of charge. In 1904, he worked out theseries of transformations that radioactive ele-ments undergo and showed that they end withthe element lead. In 1907, he estimated the ratesof change involved and calculated the ages ofmineral samples, arriving at figures of more thana thousand million years. This was the first accu-rate calculation of the age of rocks, derivedthrough the method of radioactive dating.

In 1907, Rutherford was offered a position atthe University of Manchester and returned toBritain. There he would build a renowned labo-ratory and make his momentous discoveries ofthe nuclear atom and artificial transformation.He continued to explore alpha particles and,with HANS WILHELM GEIGER, developed ioniza-

256 Rutherford, Ernest

tion chambers and scintillation screens to countthe particles produced by a source of radioactiv-ity. They devised a method of detecting a singlealpha particle and counting the number of parti-cles emitted from radium. That same yearRutherford proved that alpha particles arehelium ions: when he performed experiments inwhich he trapped alpha particles in a glass tubeand sparked the gas produced, its spectrumshowed that it was helium.

In 1908, Rutherford won the Nobel Prize inchemistry for “his investigations into the disin-tegration of the elements, and the chemistry ofradioactive substances.” Some said this was amistake; he should have been given the prize forphysics. But, as a presenter would say, the newscience of nuclear physics was “at the same time,both physics and chemistry.”

Rutherford’s next major discovery emergedin 1909 from experiments that involved bom-barding a thin gold foil with alpha particles. Heused a scintillation counter that could be movedaround the foil, which was struck by a beam ofalpha particles from a radon source. He observedthat although all the particles passed throughthe gold foil, one in 8,000 “bounced,” backward,deflected through angles of more than 90degrees by the foil. In Rutherford’s words, it was“as if you fired a 15-inch naval shell at a piece oftissue paper and the shell came right back andhit you.” From this simple observation, he con-cluded that the atom’s mass must be concen-trated in a small positively charged nucleus andthe electrons must inhabit the farthest reachesof the atom. Rutherford was convinced that theexplanation lay in the nature of the gold atomsin the foil, believing that each contained a posi-tively charged nucleus surrounded by orbitingelectrons. Only such nuclei could repulse thepositively charged alpha particles that happenedto strike them to produce such enormous deflec-tions. From this he calculated that the nucleusmust have a diameter of about 10–13 cm—100,000 times smaller than that of the atom—

and calculated the number of particles thatwould be scattered at different angles.

These predictions about the nuclear struc-ture of the atom were confirmed experimen-tally in 1911. In announcing these results,Rutherford said that practically the whole massof the atom and all of its positive charge wereconcentrated in the nucleus—a minute spaceat the center; the much lighter electronsrevolved around it, as planets revolve aroundthe Sun. Most physicists were skeptical that theatom could be almost entirely empty space.Rutherford’s supporters, however, included thefuture father of quantum mechanics, NIELS

Rutherford, Ernest 257

Ernest Rutherford is famous for discovering the basicstructure of the atom, showing that it consists of acentral nucleus surrounded by orbiting electrons.(AIP Emilio Segrè Visual Archives, Otto Hahn, andLawrence Badash)

HENRIK DAVID BOHR. Bohr went to Manchesterin 1912 to work with Rutherford and the nextyear produced his quantum model of the atom.In Bohr’s model a central positive nucleus issurrounded by electrons orbiting at discreteenergy levels. Other experiments, performed in1913, verified the existence of the atomic num-ber, which identifies elements, and showed thatthis number was equal to the number of posi-tive charges on the nucleus, and, since atomsare electrically neutral, also equal to the num-ber of electrons around it. Rutherford’s view ofthe nuclear atom was thereby vindicated anduniversally accepted.

Rutherford would go on to make moreimportant discoveries at Manchester. In 1914,he performed experiments that proved gammarays are electromagnetic waves that can bediffracted with a crystal. The wavelengths ofgamma rays were found to lie beyond X raywavelengths in the electromagnetic spectrum.ANTOINE-HENRI BECQUEREL, in 1900, had iden-tified beta rays with cathode rays, which wereshown to be electrons, thus the nature ofradioactivity was now fully revealed.

In 1919, the year he moved to Cambridgeand became director of the Cavendish Labora-tory, Rutherford made another great discovery.He found that the nuclei of certain light ele-ments, such as nitrogen, could be “disintegrated”by the direct hit of energetic alpha particles froma radioactive source (a process he described as“playing with marbles”). He noted that duringthis process fast protons were emitted. (In 1920,at Rutherford’s suggestion, the name proton wasgiven to the hydrogen nucleus.) Six years later,PATRICK MAYNARD STUART, LORD BLACKETT,who developed the Wilson cloud chamber intoan invaluable tool for studying nuclear reac-tions, would prove that the nitrogen in this pro-cess was actually transformed into an oxygenisotope. What Rutherford had done was to per-form the first artificial transmutation of one ele-ment into another. Blackett also used a cloud

chamber to record the tracks of disintegratednuclei; he showed that the bombarding alphaparticles combine with the nucleus before disin-tegration and do not break the nucleus apart as abullet would.

Bombardment with alpha particles had itslimits, since large nuclei repelled them withoutdisintegrating. Rutherford directed the con-struction of an accelerator to produce particlesof the required energy. The first one was builtby JOHN DOUGLAS COCKCROFT and ErnestWalton and went into operation at theCavendish in 1932. In the same year, anothercolleague, SIR JAMES CHADWICK discovered theneutron, whose existence Rutherford had pre-dicted in 1920.

In 1934, Rutherford made his final impor-tant discovery when, using an isotope of watercalled deuterium, which had recently been dis-covered in the United States, he and MarcusOliphant and Paul Harteck produced the firstnuclear fusion reaction.

Rutherford would remain director of theCavendish for the rest of his life. In addition to150 original papers, he published a numberof books, including Radioactivity (1904), Radio-active Transformations (106), The ElectricalStructure of Matter (1926), The Artificial Trans-mutation of the Elements (1933), and The NewerAlchemy (1937). Not least among his achieve-ments was his work during World War II inopening English academic life to Jewish scien-tists fleeing nazism.

Rutherford died suddenly in Cambridge of astrangulated hernia on October 18, 1937, at age66. His ashes are buried in Westminster Abbey,not far from the remains of SIR ISAAC NEWTON

and LORD KELVIN (WILLIAM THOMSON).One of the great figures in early 20th-cen-

tury physics, Ernest Rutherford was the father ofnuclear physics.

See also BECQUEREL, ANTOINE-HENRI; RÖNT-GEN, WILHELM CONRAD; WILSON, CHARLES

THOMSON REES.

258 Rutherford, Ernest

Further ReadingAsimov, Isaac. Atom: Journey Across the Subatomic

Cosmos. New York: Dutton/Plume, 1992.Oliphant, Mark. Rutherford: Recollections of the Cam-

bridge Days. London: Elsevier, 1972.Von Baeyer, Hans Christian. Taming the Atom: The

Emergence of the Visible Microworld. New York:Dover, 2000.

� Rydberg, Johannes Robert(1854–1919)SwedishMathematical Physicist, AtomicSpectroscopist

Johannes Rydberg discovered a mathematicalformula, containing a constant now known asthe Rydberg constant, that gives the frequenciesof spectral lines for elements.

He was born in Halmstad, a port town insouthwestern Sweden, on November 8, 1954, toSven Rydberg and the former Maria Anderson.His father was a local merchant and small shipowner, who died when Johannes was only four.The boy received his schooling at the local gym-nasium (high school). In 1873 he entered theUniversity of Lund, where he studied mathemat-ics and received his bachelor’s degree two yearslater. He went on to earn his doctorate in math-ematics, for a dissertation on conic sections, in1879.

The University of Lund was to become hispermanent academic home, although his schol-arly involvement there would undergo a majortransformation. While serving as a lecturer inmathematics from 1880 to 1882, he began work-ing on problems in friction electricity and soonbecame a lecturer in physics. In 1886, he marriedLydia Eleonora Matilda Carlsson, with whom hewould have two daughters and a son.

Rydberg’s major work, which was in spec-troscopy, was motivated by the desire to under-stand the periodic table of the elements. By

organizing existing data on spectral lines, heclassified the lines into three categories: princi-pal (strong, persistent lines), sharp (weaker, butwell-defined lines), and diffuse (broader lines).At the time it was known that each spectrum ofan element consists of several series of theselines superimposed on one another. Rydbergwanted to find a mathematical expression todefine the relationship of frequencies in any oneseries of lines. In 1890, he succeeded with a for-mula introducing the concept of the wave num-ber N, which is the reciprocal of the wavelength(i.e., 1 divided by the wavelength) and is a mea-sure of the number of waves per centimeter. Ryd-berg’s formula expressed the wave number interms of a constant common to all series oflines, the so-called Rydberg constant; two addi-tional constants that characterize the particularseries; and an integer. The structure of the linesseries emerged as a result of the changing valueof the integer.

At this point in his investigations, Rydberglearned that a formula for a series of lines of thehydrogen spectrum had already been worked outby the Swiss physicist Johann Balmer; Balmer’sformula proved to be a special case of Rydberg’smore general one. His next goal was to discovera formula capable of expressing the frequency ofevery line in every series of an element. Eventu-ally, he came up with

N = R[1/(n + a)2 – 1/(m + b)2]

where N is the wave number; R is the Rydbergconstant; n and m are integers, m greater than n;and a and b are constants for a particular series.This formula succeeded in expressing five moreseries of hydrogen lines. Rydberg had no theoret-ical explanation for his result, and it wouldremain for NIELS HENRIK DAVID BOHR to showthat Rydberg’s equation described the quantumenergy states required for the theory of atomicstructure that he unveiled in 1913.

In 1879, Rydberg received a temporaryappointment as full professor of physics at

Rydberg, Johannes Robert 259

Lund. That year he presented the idea ofatomic number and its importance in revisingthe periodic table. His views were validated byHenry Moseley’s research into X-ray spectrain 1913.

In 1902, Rydberg’s appointment as fullprofessor at Lund was made permanent.Although his health began to deteriorate in1914, he remained at his post until a few weeksbefore his death in Lund on December 28,1919, of a brain hemorrhage. Earlier that year

he was elected as a member of the Royal Soci-ety of London. Although he never attained hisgoal of determining the structure of the atom,his work formed the basis for others, such asBohr, to do so.

Further ReadingSiegbahn, Manne. “Johannes Robert Rydberg.” In

Swedish Men of Science. Stockholm: Almquist &Wiksell International, 1952, pp. 214–218.

260 Rydberg, Johannes Robert

S

261

� Sakharov, Andrei Dmitriyevich(1921–1989)RussianTheoretical Physicist, Nuclear Physicist

Andrei Sakharov embodied the 20th-centuryphysicist’s recognition of moral responsibilityfor the social consequences of his or her work.The man known as “the father of the Soviethydrogen bomb” became a passionate advocateof nuclear disarmament and defender of humanrights, who received the Nobel Prize in peace in1975. As his political awareness evolved, hetraded the privileged life of a Soviet weaponsscientist for the hardships and internal exile ofa dissident against the Communist system.Released by Premier Mikhail Gorbachev in themid-1980s, he became the spiritual leader ofthe burgeoning democratic movement, only todie prematurely, at 68, at a crucial phase of thatstill ongoing struggle.

Andrey Dmitriyevich Sakharov was born onMay 21, 1921, into a family of Moscow intellec-tuals, whose forebears included military nobilityand Russian Orthodox priests. As a member ofthe first postrevolutionary generation, hebelieved in his country as the harbinger of inter-national justice and social equality. Schooled athome until the seventh grade, he first learnedphysics from his father, Dmitri, a college profes-

sor and author of textbooks and popular sciencebooks. He enrolled as a student of physics atMoscow State University in 1938, at the heightof the Stalinist purges, when the best of thephysics faculty had been picked off. When theGermans invaded in 1941, young Sakharov,found unfit for military service, was evacuated toCentral Asia, along with other remaining stu-dents and professors. After graduating with hon-ors in 1942, he declined graduate school in favorof laboratory work at a munitions factory on theVolga. There he met Klavdia Vikhireva, a tech-nician, and married her in 1943.

As the war was ending in 1945, the couplereturned to Moscow, where Sakharov enrolled asa graduate student at FIAN, the Russianacronym for the renowned P. N. Lebedev Insti-tute of Physics of the USSR Academy of Sci-ences. Under the Soviet system, the nation’sscientific elite carried out research and men-tored the next generation at academy institutes,rather than colleges and universities. The physi-cist who was to shape Sakharov’s career in cru-cial ways was Igor Tamm, head of the theoreticaldepartment, who would become a Nobel laure-ate in physics in 1958. Eager to continue work-ing with Tamm on fundamental science,Sakharov twice refused an invitation to work onthe Soviet atomic bomb project. But afterreceiving his doctorate for work on particle

physics in 1947, he joined Tamm in a specialgroup at FIAN under the leadership of YakovZeldovich, which was studying the feasibility ofa thermonuclear, or hydrogen, bomb. The Zel-dovich team was exploring the Truba (Russianfor “tube”) design, based on data obtained byspies from the Manhattan Project, the LosAlamos–based team engaged in developingatomic and hydrogen bombs. Convinced of theinadequacy of Truba and spurred by a sense ofnational emergency, Sakharov worked feverishlyand within two months came up with an alter-native design. Nicknamed Sloyka (Russian for“layer cake”), it was based on alternating layersof light elements (deuterium, tritium, and theirchemical compounds) and heavy elements (ura-nium 238), which initiated a chain of energy-

releasing events: fission–fusion–fission. Thisstructure would be basic to all future designvariants. Another student of Tamm, VitalyGinzburg, proposed that lithium deuteride,instead of deuterium and tritium, be used inthe fusion layer, thereby maximizing the effi-cacy of the thermonuclear explosive material inSakharov’s design. These conceptual break-throughs made possible the first Soviet H-bomb,which was successfully tested on August 12,1953. Although it yielded four hundred kilotons,15% to 20% from fusion, it did not put the Sovi-ets ahead of the American bomb makers, whoalready had a bigger atomic bomb, as well asmegaton hydrogen bombs.

By then Sakharov had been transferred toArzamas-16, a secret city, whose real name wasSarov, in the central Volga region. Sometimesnicknamed Los Arzamas after its American pro-totype, Los Alamos, the city had a special designbureau that was the nerve center of Sovietnuclear weapons research. While there, Sakharovwould make major contributions to the so-calledCzar-Bomb of 1961, the most powerful deviceever exploded. His work there, however, was notall military-related. In 1950 Sakharov and Tamminvented the TOKOMAK (an acronym of the Rus-sian term for the toroidal chamber with magneticcoil), a controlled thermonuclear fusion reactor.Soviet research on controlled fusion was eventu-ally declassified, and TOKOMAK came to beregarded as a promising direction in the quest forcreating an unlimited source of cheap energy.

In 1964, Sakharov returned to fundamentalscience, after a hiatus of 19 years. He published apaper on cosmology, which attempted to explainthe asymmetry between the amount of matterand amount of antimatter in the universe byproposing that protons, generally assumed to bestable particles, can spontaneously decay. In asecond paper, he took on the highly complexand still unresolved problem of constructing aunified field theory: one that unifies gravitationwith other physical forces.

262 Sakharov, Andrei Dmitriyevich

Andrei Sakharov, “the father of the Soviet hydrogenbomb,” became a passionate advocate of nucleardisarmament and defender of human rights. He wasawarded the Nobel Peace Prize in 1975. (AIP EmilioSegrè Visual Archives and VNIIEF Museum and Archive)

During his years at Arzamas-16, Sakharov wasa highly rewarded member of a scientific commu-nity in which weapons-related research garneredthe lion’s share of prestige and resources. At 32, hebecame the youngest scientist ever to receive fullmembership in the prestigious Soviet Academy ofSciences. He was awarded several Hero of Social-ist Labor Medals, a Stalin Prize, and a dacha (cot-tage) in the elite Moscow suburb of Zhukovka.

Sakharov’s political conscience hadexpressed itself in his younger years through hisaid to victims of repression and opposition to thefaction within the academy supporting Lysenko’scrusade against modern genetics. By the mid-1960s, political activism was becoming the dom-inant force in his life. While still pursuingresearch on new weapons, he became concernedabout the dangers of nuclear testing; that con-cern led him to urge the Soviet leadership toaccept American proposals for a moratorium onantiballistic missile defense. When his attemptsto work within the system failed, he stepped out-side it, publishing in samizdat, the undergrounddissident network, his famous 1968 essay“Reflections on Progress, Peaceful Co-Existenceand Intellectual Freedom.” In it, he proposedinternational cooperation in the interest ofreducing nuclear arms and establishment of civilliberties in the Soviet Union. When the essayfound its way into the Western press, Sakharovwas banished from military-related research.

A year later, his wife, Klavdia, died of can-cer. Left to care for their three children, thenaged 24, 19, and 11, Sakharov accepted an offerto return to FIAN in Moscow, to work on aca-demic topics. There his political activism accel-erated. In 1970, he founded the human rightsmovement with other Soviet dissidents and metanother activist, Yelena Bonner, the womanwho would become his devoted companion andcomrade in arms. They married in 1972. WhenSakharov was refused permission to travelabroad to accept the Nobel Prize in peace in1975, Yelena Bonner accepted it in his stead.

As he became the country’s foremostdefender of human rights, Sakharov was underincreasing pressure from the regime. In 1980,after his strenuous and highly publicized protestsagainst the war in Afghanistan, he was exiled tothe city of Gorky (now renamed Nizhniy Nov-gorod), where, with Bonner, he would remainfor close to seven years. During this ordeal ofconstant surveillance and isolation, he wasbuoyed by support from American physicistswho found ways of getting reprints of theirpapers into his hands and campaigned for hisrelease in the media. His three hunger strikes,protesting his and his family’s persecution, werewidely publicized in the West.

But Sakharov would not regain his freedomuntil the ascendance of Mikhail Gorbachev, who,in December 1986, in the spirit of perestroyka(rebuilding or reform), recalled him to Moscowand allowed him to resume his public role. Heswiftly became the commanding figure in thestruggle for democracy and, in April 1989, waselected to the Soviet Union’s new parliament. Ascoleader of the democratic faction, Sakharovchampioned the adoption of a new constitutionthat would abolish the hegemony of the Commu-nist Party and allow Russia to evolve peacefullytoward a multiparty system. After a day of acrimo-nious debate, on December 14, 1989, Sakharovdied of a sudden heart attack. His funeral,attended by 50,000 people, took place on a day ofnational mourning for the man who was reveredas the “saint” of Russia’s democratic rebirth.

Further ReadingBonner, Yelena. Alone Together. New York: A. A.

Knopf, 1986.Holloway, David. Stalin and the Bomb: The Soviet

Union and Atomic Energy, 1939–1956. NewHaven, Conn.: Yale University Press, 1994.

Kapitsa, S. P., and S. Drell. Sakharov Remembered.New York: American Institute of Physics, 1991.

Rhodes, Richard. Dark Sun: The Making of the Hydro-gen Bomb. New York: Simon & Schuster, 1995.

Sakharov, Andrei Dmitriyevich 263

Sakharov, A. D. Memoirs. New York: A. A. Knopf,1990.

———. Progress, Coexistence, and Intellectual Free-dom. New York: Norton, 1968.

———. Sakharov Speaks. New York: A. A. Knopf,1974.

� Salam, Abdus(1926–1996)PakistaniTheoretician, Particle Physicist,Quantum Field Theorist

Abdus Salam shared the 1979 Nobel Prize inphysics with STEVEN WEINBERG and SHELDON

LEE GLASHOW for his groundbreaking work in

unifying the electromagnetic and weak forces.The first Pakistani and the first Muslim scientistto win this most prestigious of awards, Salam wasa champion in the cause of developing science inthe Third World.

He was born on January 29, 1926, in Jhang,a small town in what is now Pakistan, into aMuslim family with a long tradition of piety andlearning. His father, who worked in an impover-ished farming district as an official in theDepartment of Education, had prayed to Allahfor a son of outstanding intellect. Abdus did notdisappoint him. At the age of 14, he became alegend in his hometown, when he received thehighest marks ever recorded on the matricula-tion examination given at the University ofPanjab. When he bicycled home after the newsgot out, the town’s inhabitants turned out inforce to welcome him.

Awarded a scholarship to Government Col-lege at the University of Panjab, Lahore, heearned his master’s degree in 1946. That year, heleft the country on a scholarship to Saint John’sCollege at Cambridge University, England, wherethe great PAUL ADRIEN MAURICE DIRAC becamehis mentor and hero. Three years later, hereceived his B.A. with honors, with a double firstplace in mathematics and physics. In 1950, hewon Cambridge’s Smith Prize, awarded for themost outstanding predoctoral contribution tophysics. He remained at Cambridge, at theCavendish Laboratory, for his graduate studies,intending to become an experimentalist, but soonjudged himself lacking in what he called “the sub-lime quality of patience—patience in accumulat-ing data, patience with recalcitrant equipment.”He began working under Herbert Kemmer andearned his doctorate in theoretical physics in1952 for a thesis on the question of whether quan-tum electrodynamics (QED) was renormalizable,that is, capable of being altered by a mathematicalprocedure that cancels the unwanted infinities ina quantum field theory by introducing the appro-priate renormalization constants.

264 Salam, Abdus

Abdus Salam shared the 1979 Nobel Prize in physicswith Steven Weinberg and Sheldon Glashow for hisgroundbreaking theoretical work unifying theelectromagnetic and weak forces. (AIP Emilio SegrèVisual Archives, Marshak Collection)

Around this time, he came up with thestartling idea that “all neutrinos are left-handed,” which suggested the possibility that aviolation of parity could occur in the weak inter-actions, before that revolutionary hypothesiswas put forth by TSUNG-DAO LEE and CHEN

NING YANG and experimentally confirmed byCHIEN-SHIUNG WU. When Salam described theidea to WOLFGANG PAULI, he summarily dis-missed it, convincing Salam not to publish it.After this chastening experience, Salam deter-mined never again to listen to “grand old men”and adopted a “publish or perish” policy, whichresulted in the publication of over 300 papers.

As a newly minted Ph.D., who already hadan international reputation, Salam returned toPakistan, with the intention of being a physicistin his own land. He was made head of the math-ematics department of the University of Panjab,where he wanted to establish a school ofresearch. But prevailing conditions persuadedhim there was no way to have the kind ofresearch atmosphere and collegial stimulationhe needed. In 1954, he returned to England as alecturer at Cambridge and, at the invitation ofLORD PATRICK MAYNARD STUART BLACKETT, in1957, moved to Imperial College, London,where he founded the Theoretical PhysicsGroup. Always receptive to strange new ideas,he encouraged the young Israeli physicist YUVAL

NE’EMAN to develop the ideas that resulted inhis independent discovery of the unitary symme-try SU (3), which MURRAY GELL-MANN, makingthe same discovery, would dub the “eightfoldway” of classifying the growing number of ele-mentary particles.

At the same time, Salam was determined toimprove the situation for scientists in develop-ing countries. In 1964, he founded the Interna-tional Center for Theoretical Physics (ICTP) inTrieste, Italy. There he instituted a program ofresearch associateships, which allowed deservingyoung physicists from Third World countries tospend three months a year at the center, inter-

acting with leaders in their fields. He wouldremain director of the ICTP until his death.

At Imperial College, in the 1960s, he did hisNobel Prize–winning work. Salam was influ-enced by the research he did in 1961 withSteven Weinberg on spontaneous symmetrybreaking, that is, asymmetric relations that havespontaneously arisen from the functioning ofsymmetrical laws. (An example of this is theasymmetric crystal structure of ice, which freezesout from the symmetric liquid structure of waterwhen the temperature becomes low enough.) Healso worked extensively with his colleague JohnWard on unsuccessful attempts to unify the elec-tromagnetic and weak forces.

In the early 1960s, Salam, like Weinbergand Glashow, was aware of the groundbreakingwork of Yang and Robert Mills in creating theso-called non-Abelian Yang–Mills gauge theo-ries with internal symmetries. In 1950, they hadshown that the QED formalism developed ear-lier by JULIAN SEYMOUR SCHWINGER, RICHARD

PHILLIPS FEYNMAN, and SIN-ITIRO TOMONAGA

could be generalized to include internaldynamic symmetries that were more generalthan the standard spacetime C (charge), P (par-ity), and T (time-reversal) symmetries. Salam,Weinberg, and Glashow also knew that PeterHiggs had shown that coupling a scalar field toa Yang–Mills gauge theory could cause thespontaneous breaking of these internal symme-tries to occur, thus creating new kinds of force-carrying particles, some of them massive.

Using these ideas and working independentlywith different theoretical approaches, the threephysicists reached the same conclusion: if the vir-tual particles that carry the electromagnetic andweak forces (known collectively as the intermedi-ate vector boson W and Z particles) were relatedby a broken internal symmetry in a Yang–Millsgauge theory, these new theoretical ideas mightmake it possible to estimate their masses in termsof the unified, more symmetrical force fromwhich the two forces were thought to have arisen.

Salam, Abdus 265

However, over the next four years this uni-fied electroweak theory attracted scant atten-tion since, unlike quantum electrodynamics, theelectroweak theory had not yet been shown tobe renormalizable. But in 1971, the Dutch physi-cist GERARD ’T HOOFT used computer algebratechniques to prove that the electroweak theorywas indeed renormalizable.

Although experimental verification of theelectroweak theory would not occur until 1983, ’tHooft’s proof was the final step that led the NobelCommittee to the unusually insightful decision toaward Salam, Glashow, and Weinberg the 1979prize in physics. Salam upstaged his corecipientsby appearing at the ceremonies in Stockholm intraditional clothing (including bejeweled turban,baggy pants, scimitar, and curly shoes), with histwo wives (permitted him by Muslim law).

While pursuing his own theoretical work,Salam remained vitally involved in Pakistan’sscientific development, serving as a member ofthe Pakistan Atomic Energy Commission, amember of the Scientific Commission of Pak-istan, and chief scientific adviser to the presi-dent from 1961 to 1974.

Salam was a prominent and dedicated mem-ber of the international science community, atireless worker who was known to sacrifice restand recreation for his many causes. He served ona number of United Nations committees on theadvancement of science and technology in devel-oping countries. His contributions to peace andinternational scientific collaboration were recog-nized by the Atoms for Peace Award (1968) andmany others. He used his money from both theAtoms for Peace prize and the Nobel Prize toassist physicists in developing countries.

Salam’s books include Supergravities in DiverseDimensions, with Ergin Sezgin (1990); Science andthe Third World (1991); and The Renaissance ofSciences in Islamic Countries (1994).

When Abdus Salam died at age 70, of Parkin-son’s disease, on November 21, 1996, in Oxford,England, he was mourned by the physics commu-

nity, Pakistan, and the world. He was survived bya wife, two sons, and four daughters. He wasrevered as both a brilliant physicist and a tirelessadvocate for the development of science, not onlyin Pakistan, but throughout the Third World. Adevout Muslim, he made no distinction betweenhis religion and his scientific pursuits:

The Holy Quran enjoins us to reflecton the verities of Allah’s created lawsof nature; however, that our genera-tion has been privileged to glimpse apart of His design is a bounty and agrace for which I render thanks with ahumble heart.

See also RUBBIA, CARLO; VELTMAN, MAR-TINUS J. G.

Further ReadingGhani, Abdul. Abdus Salam. Karachi: Ma’aref, 1982.Hassan, Z., and C. H. Lai, (eds.) Ideals and Realities:

Selected Essays of Abdus Salam. Singapore: WorldScientific, 1983.

Salam, Abdus. Science and the Third World. Edin-burgh: Edinburgh University Press, 1991.

� Schawlow, Arthur Leonard(1921–1999)AmericanExperimentalist, Laser Spectroscopist

Arthur Leonard Schawlow was an experimen-talist who, in collaboration with CHARLES

HARD TOWNES, in 1958 invented the laser, anacronym for light amplification by stimulatedemission of radiation. Their landmark discoveryhas led to advances in virtually every field ofmodern technology.

Schawlow was born in Mount Vernon, NewYork, on May 5, 1921, five years after his fatherhad immigrated to the United States from Riga,Latvia. When Arthur was three, at the urging of

266 Schawlow, Arthur Leonard

his mother, who was Canadian, the family movedto Toronto, where he attended public schools. Hispassionate interest in science, particularly elec-tronics, mechanical subjects, and astronomy, wasborn in those early years. His high school yearscoincided with the Great Depression of the 1930sand Schawlow’s father, an insurance agent, was inno position to send him or his sister to college.Fortunately, both won scholarships to the Facultyof Arts at the University of Toronto. Arthur’s wasin physics, which seemed to him “pretty close” tohis original choice of radio engineering. He wouldlater consider this the correct path, since he didnot have “the patience with design details that anengineer must have” and enjoyed the “chance toconcentrate on concepts and methods” thatphysics provided.

When Canada entered World War II in1941, Schawlow spent three years teachingclasses to armed service personnel at the Uni-versity of Toronto, before joining a group work-ing on microwave antenna development at aradar factory. Returning to his graduate studiesafter the war, to an understaffed and under-equipped physics department, he was attractedto an area in which Toronto had a solid tradi-tion: optical spectroscopy. Running an atomicbeam spectroscopy experiment in the basementof a campus laboratory, Schawlow would sere-nade his atomic beam on his jazz clarinet (hewould pursue his love of jazz throughout hiscareer). After a rewarding experience writinghis dissertation under Malcolm F. Crawford, hewas awarded the Ph.D. in 1949.

He then took a postdoctoral fellowship underCharles Townes in the physics department atColumbia University—an exhilarating place tobe in those years, under the leadership of ISIDOR

ISAAC RABI and with no fewer than eight futureNobel laureates in the department. His associa-tion with Townes, the leader of research onmicrowave spectroscopy, opened up Schawlow’slife both professionally and personally; in 1951,he married Townes’s youngest sister, Aurelia, a

musician, mezzo soprano, and choral conductor.The marriage would produce a son and twodaughters; it had the immediate, unfortunateeffect, however, of forcing Schawlow to leaveColumbia, since the university’s antinepotismrules prevented Townes from keeping him on thestaff. He became a physicist at Bell Laboratoriesin New Jersey in 1951, working mainly on super-conductivity, and thus was excluded from theexciting developments surrounding Townes’s1951 invention of the maser, an acronym for“microwave amplification by stimulated emissionof radiation.”

The idea of stimulated emission of radiationhad originated with ALBERT EINSTEIN. Whilestudying the theory of blackbody radiation in1917, Einstein had found that the process oflight absorption must be accompanied by a com-plementary process in which the absorbed radia-tion stimulates the atoms to emit the same kindof radiation. However, in order for amplificationof the radiation by stimulated emission to occurin a physical medium, the stimulated emissionmust be larger than the absorbed radiation.Hence, the physical medium must have moreatoms in a high-energy state than in a lower-energy state (i.e., an inverted population ofexcited atoms). Since energy spontaneouslyflows from a higher to a lower state, such aninverted population of excited atoms is inher-ently unstable. Moreover, to generate beams ofcoherent light from this inverted population ofexcited atoms, that is, intense light waves con-sisting of essentially one frequency and movingin the same direction, it would be necessary tofind the specific atomic systems with the correctinternal storage mechanisms.

Townes selected the simple case of ammo-nia molecules, because they can occupy onlytwo energy levels. The ammonia moleculeshad the property of emitting radiation with a1.25-cm wavelength, which lies within themicrowave range of the electromagnetic spec-trum. He reasoned that when an ammonia

Schawlow, Arthur Leonard 267

molecule in the high-energy state absorbed aphoton of this frequency, the molecule wouldfall to the lower energy level, emitting twocoherent photons of the same frequency, thusproducing a coherent beam of single-frequencyradiation with a 1.25-cm wavelength. By study-ing the behavior of ammonia molecules in aresonant cavity containing electric fields,Townes developed a method that separated therelatively few high-energy molecules from themore numerous low-energy ones and thus cre-ated the population inversion required formaser action. By 1953, he had constructed thefirst working model of the maser. Masers soonfound a range of applications: in the most accu-rate timepieces available to this day, atomicclocks; in shortwave radios, where they serve asextremely sensitive receivers; in radio astron-omy; and in space research, for recording theradio signals from satellites.

Although Schawlow, exiled in New Jersey,was not part of this work, he and Townes hadnot lost touch. On weekends in New York theycontinued working on their book MicrowaveSpectroscopy (1955), and their collaborationsoon took a dramatic turn. Schawlow began toworked with Townes

to see what would be needed to extendthe principles of the maser to muchshorter wavelengths, to make an opticalmaser or . . . laser. Thereupon, I beganwork on optical properties and spectraof solids, which might be relevant tolaser materials and then to lasers.

In 1957, he and Townes began working onthe principle of a device, the laser, light amplifi-cation by stimulated emission of radiation, thatcould operate at shorter wavelengths than themaser. Because the change from microwavesand visible light required a 100,000-foldincrease in frequency, a fundamentally differentoperating structure was required. Schawlow had

the idea of building a chamber, or cavity, con-sisting of a synthetic ruby that would act as akind of echo chamber for light. The atoms ormolecules of a ruby or garnet crystal, or of a gas,liquid, or other substance, were excited by lightin the cavity in which they were contained, sothat more of them were at higher energy levelsthan were at lower ones. In order to achieve thenecessary high radiation density, two mirrors ateach end of the cavity forced the light tobounce back and forth until coherent lightescaped from the cavity. With Schawlow focus-ing on the device and Townes on the theory,they coauthored a paper in the December 1958Physical Review, “Infrared and Optical Masers,”in which they showed theoretically that anoptical maser, or laser, could be produced by acoherent beam of visible light, instead of amicrowave beam. The publication set off aninternational competition to build the firstworking laser, which was won in 1960 byTheodore Maiman, working at the HughesResearch Laboratories in Malibu, California.

In 1961, Schawlow left Bell to become pro-fessor and then chair in 1966 of the departmentof physics at Stanford University, where hisresearch focused on molecular spectroscopy.Both fatherly and inspiring, he gathered abouthim a following of devoted students andrenowned visitors. He was famous for suchaphorisms as “To do successful research, youdon’t need to know everything; you just need toknow of one thing that isn’t known.” and “Any-thing worth doing is worth doing twice, the firsttime quick and dirty, and the second time, thebest way you can.” A serious scientist with anirrepressible sense of humor, he earned the nick-name “Laser Man,” because of his populardemonstrations of the tool he had helped toinvent. In one, designed to show the laser’sselectivity, he used a “ray gun” laser to shootthrough a transparent balloon to pop a darkMickey Mouse balloon inside without damagingthe outer balloon.

268 Schawlow, Arthur Leonard

It was Townes who, in 1964, shared theNobel Prize in physics with the Russian physi-cists Nikolay Basov and Aleksandr Prokhorov,for invention of the laser. Schawlow did notbecome a Nobel laureate until 1981, when heshared the prize in physics with NICOLAAS

BLOEMBERGEN for their “contributions to laserspectroscopy.”

In addition to his physics career,Schawlow’s life in California was focused onthe Peninsula Children’s Center for handi-capped children, attended by his autistic son,Artie. The Schawlows became activists onbehalf of autistic people and played a role inestablishing California Vocations, a nonprofitorganization dedicated to creating group homesfor those afflicted with the disease. In 1991, theyear he retired from teaching and became pro-fessor emeritus, his wife died in an automobileaccident while on her way to visit their son.Schawlow died on April 28, 1999, at the age of77, of congestive heart failure resulting fromleukemia, in a hospital in Palo Alto, California,where he lived.

Schawlow and Townes had not anticipatedthe applications of the laser; nor did either ofthem, as Bell employees, profit from any ofthem. In 1998, a year before he died, Schawlow,with a characteristic lack of self-importance,commented on the avalanche of innovationsthat continues to flow from their great discovery:

The thing that turns me on now, partic-ularly, is that lasers now permit people tostudy single atoms and single photons,and we’re really learning a lot moreabout just how strange the world ofquantum mechanics is and finding newways to test it. . . . And it’s nice thatthere are medical uses. . . . One of thefirst applications of lasers was for surgeryof the retina in the eye to prevent blind-ness. Neither Charlie [Townes] nor I hadever heard of surgery for detached reti-

nas . . . and if we had we probably would-n’t have been fooling around with stim-ulated emissions from atoms. . . . It’sbeen a great 40 years.

See also CHU, STEVEN; KUSCH, POLYKARP.

Further ReadingSchawlow, Arthur L. “Advances in Optical Masers.”

Scientific American, July 1963, pp. 28, 34–45.———. “Optical Masers.” Scientific American June

1961, pp. 41, 52–61.

� Schrieffer, John Robert(1931– )AmericanTheoretician, Solid State Physicist

John Robert Schrieffer is a solid state theoreti-cian, who, as a 26-year-old graduate student,working with JOHN BARDEEN and Leon Cooper,discovered the Bardeen–Cooper–Schrieffer(BCS) theory, a comprehensive explanation ofsuperconductivity, the phenomenon in whichelectricity flows through a substance withoutany loss due to electrical resistance.

He was born in Oak Park, Illinois, on May 31,1931, to John H. Schrieffer and Louise AndersonSchrieffer. The family moved in 1940 to Manhas-set, New York, and again, when John was 16, toEustis, Florida, when his father quit his job as apharmaceutical salesman and began a successfulnew career in the citrus industry. John remem-bers spending much of his time in Florida playingwith gadgets: first home-made rockets, then hamradio, a hobby that sparked his interest in anelectrical engineering career. He graduated fromEustis High School in 1949 and entered theMassachusetts Institute of Technology in Cam-bridge, where he started out as an electrical engi-neering major. In his junior year, he switched hisfield of concentration to physics. Working underJohn C. Slater, he wrote a bachelor’s thesis on the

Schrieffer, John Robert 269

energy level multiplet structure of heavy atoms.By now he knew that he was interested in pursu-ing a career in solid state physics. He entered theUniversity of Illinois for graduate studies andbegan working with Bardeen, who had alreadydiscovered the transistor in 1946. After joiningBardeen’s illustrious group of scientists workingon semiconductor research, Schrieffer beganworking on a problem related to electrical con-duction on semiconductor surfaces; he spent ayear in the laboratory applying theoretical analy-sis to several surface problems. In the third year ofgraduate studies, working with Bardeen andCooper, he developed as his doctoral dissertationthe theory of superconductivity, which wouldlater be known as the Bardeen–Cooper–Schrief-fer (BCS) theory.

While riding the New York subway in Jan-uary 1957, Schrieffer had an insight that wouldsolve the mystery set in motion in 1911, whenHEIKE KAMERLINGH ONNES first observed super-conductivity: zero electrical resistance in somemetals below a critical temperature. Since thenphysicists had been looking for a microscopicinterpretation of this phenomenon. The meth-ods that were successful in explaining the elec-tric properties of normal metals were unable topredict the effect. At very low temperatures,metals were still expected to have a finite resis-tance, which was due to scattering of mobileelectrons by the ions in the crystal lattice. TheBCS solution to this problem was to show that ina crystalline material electrons have the poten-tial to pair up quantum mechanically through anattractive interaction mediated by the crystallattice, and that zero resistivity occurs when thethermal energy available is insufficient to breakapart the pair.

Thus, for electrons embedded in a crystal,the normal Coulomb repulsion can be compen-sated for by this pairing effect when the temper-ature is below the critical value. The ion coresin the crystal lattice respond to the presence ofa nearby electron, and the motion may result in

another electron’s being attracted to the ion.The net effect is an attraction between twoelectrons through the mediating response of theions in the solid. The BCS theory was based onthe idea that the interaction between the elec-trons and the lattice leads to the formation ofbound pairs of electrons, which came to becalled Cooper pairs. The different pairs arestrongly coupled to each other, an arrangementthat leads to a complex collective pattern inwhich a considerable fraction of the total num-ber of conduction electrons are coupled to forma superconducting state. Because of this charac-teristic coupling of all the electrons, one cannotbreak up a single pair of electrons without alsoperturbing all the others, and this breakingrequires an amount of energy that must exceed acritical value. This is the reason for the exis-tence of a critical temperature below whichsuperconductivity occurs. Many of the remark-able qualities of superconductors can be under-stood qualitatively from the structure of thiscorrelated many-electron state.

The comprehensive BCS theory has theability to explain all known properties associatedwith superconductivity. Although applicationsof superconductivity to magnets and motorswere possible without the BCS theory, the the-ory is important for examining strategies toincrease the critical temperature as high as pos-sible, since, if the temperature could be raisedabove liquid nitrogen temperature, the eco-nomics of superconductivity would be trans-formed. In addition, the theory was an essentialprerequisite for the prediction of Josephsonjunction quantum tunneling with its importantapplications in magnetometers, computers, anddetermination of the fundamental constants ofphysics. The BCS theory has had profoundeffects on nearly every field of physics from ele-mentary particle to nuclear physics and heliumfrom liquids to neutron stars. Schrieffer and histwo colleagues shared the Nobel Prize in physicsfor their theory in 1972.

270 Schrieffer, John Robert

Schrieffer continued his research on super-conductivity as a National Science FoundationFellow at the University of Birmingham and theNiels Bohr Institute in Copenhagen during the1957–1958 academic year. He spent the nextyear as an assistant professor at the University ofChicago, before joining the faculty of the Uni-versity of Illinois in 1959. During a summer visitto the Bohr Institute in 1960, he becameengaged to Anne Grete Thomsen, whom hemarried at Christmas of that year. They wouldhave three children.

In 1962, Schrieffer took a position at theUniversity of Pennsylvania in Philadelphia,where, two years later, he became Mary AmandaWood Professor of Physics. He published Theoryof Superconductivity, a book that would become aclassic in its field, in 1964. Five years later, hewas awarded a six-year term as Andrew D.White Professor-at-Large.

In 1980, Schrieffer joined the faculty of theUniversity of California, Santa Barbara, wherehe was appointed Chancellor Professor in 1984.He served as director of the Institute of Theoret-ical Physics in Santa Barbara from 1984 to 1989.In 1992, he was appointed University Professorat Florida State University and Chief Scientistof the National High Magnetic Field Laboratory.

Despite its mathematical complexity, theBCS theory enabled physicists to develop newmaterials that conduct at temperatures that donot need to be supercold, resulting in the pro-duction of whole new classes of superconduct-ing metals. By 1960, physicists had used theBCS theory to solve problems in nuclear physicsconcerning the unusual behavior of neutronsand protons in the atomic nucleus. When pul-sars—small rotating stars that emit regularbursts of radio waves—were discovered in 1963,astrophysicists used BCS theory to interprettheir behavior.

In 1987, however, the theory was challengedby the surprising discovery of a class of so-calledhigh-temperature cuprate superconductors,

which have the property of becoming supercon-ducting at temperatures above 40 K. This vio-lated the BCS theory, which asserted thatsuperconductivity was theoretically impossible atthese temperatures.

In his most recent work, Schrieffer hasjoined the group of physicists attempting tounderstand high-temperature superconductivity;he believes that rather than being negated bythe new phenomenon, the BCS theory may pro-vide its theoretical groundwork. CurrentlySchrieffer is continuing this research at theNational High Magnetic Field Laboratory inFlorida, directing a team of investigators whoseresearch focuses on developing and extendingthe BCS formalism into a theory of high-tem-perature superconductivity, as well as on thedynamics of electrons in strong magnetic fields.

See also JOSEPHSON, BRIAN DAVID.

Further ReadingSchrieffer, J. Robert. Theory of Superconductivity.

Cambridge, Mass.: Perseus, 1999.

� Schrödinger, Erwin(1887–1961)AustrianTheoretical Physicist (QuantumMechanics)

Erwin Schrödinger was one of the great architectsof quantum mechanics. The famous equation thatbears his name, which describes the behavior ofelectrons in atoms, created wave mechanics,thereby setting quantum mechanics on a firmmathematical foundation. Schrödinger’s workgarnered him the 1933 Nobel Prize in physics,which he shared with PAUL ADRIEN MAURICE

DIRAC. However, as were ALBERT EINSTEIN andMAX ERNEST LUDWIG PLANCK, Schrödinger wasphilosophically incapable of accepting the proba-bilistic view of nature to which his ideas led. Hemade his second most famous contribution to

Schrödinger, Erwin 271

20th-century physics, a thought experimentknown as the cat paradox, in order to refute it.

Erwin Schrödinger was born in Vienna onAugust 12, 1887. His father, who ran a smalllinoleum factory inherited from his family, was acultured man who studied chemistry, painted,and wrote papers on botany. His mother, thedaughter of a chemistry professor, was half-English and half-Austrian. Young Erwin, an onlychild, who grew up speaking both English andGerman, was tutored privately until the age of10, when he entered the gymnasium (secondaryschool) in Vienna. He loved mathematics,physics, German poetry, and ancient languagesbut resisted rote memorization, a sign, perhaps ofhis latent originality as a thinker.

Entering the University of Vienna in 1906,Schödinger specialized in physics. The ideas hewas exposed to as a student by Fritz Hasenohr, thesuccessor of LUDWIG BOLTZMANN, who consid-ered phenomena in terms of probability theory,made a strong impression on him and became thesubject of his first published paper. He received adoctorate in 1910 for his theoretical dissertation“On the Conduction of Electricity on the Surfaceof Insulators in Moist Air.” The following year, heaccepted an assistantship in experimental physicswith Max Wien at the University of Vienna’s Sec-ond Physics Institute. He would later say that thisearly experimental work was invaluable to hisfuture theoretical work.

World War I would decelerate his physicscareer without wholly derailing it. While servingas an artillery officer, first on the Italian borderand then in Hungary, Schrödinger managed towrite and submit theoretical papers. Sent backto the Italian front, he saw combat as a batterycommander and received a citation for outstand-ing service. As the war was ending, Schrödingerreturned to an academic post in Vienna, wherehe would remain until 1920, publishing his firstresults on quantum mechanics and doing impor-tant work in color theory. Because of the hard-ships of life in postwar Vienna, he moved to Jenaand then Stuttgart, Germany, in 1920. Thatsame year he married Annemarie Bertel, whowas to remain with him until his death, despitehis series of scandalous affairs.

The young couple would move again, in1921, when Schrödinger was offered a professor-ship at the University of Zurich. There he woulddo his best work and enjoy the friendship of suchillustrious colleagues as Peter Debye and Her-mann Weyl, who was instrumental in develop-ing his mathematical prowess. He wrote paperson a variety of subjects, including the theory ofcolor vision, specific heats of solids, electrody-namics, and atomic spectra.

Schrödinger found himself dissatisfied withthe ad hoc nature of NIELS HENRIK DAVID BOHR’s

272 Schrödinger, Erwin

Erwin Schrödinger, who discovered the famousequation that describes the behavior of electrons inatoms, created wave mechanics and set quantummechanics on a firm mathematical foundation. (AIPEmilio Segré Visual Archives)

model of the atom, in which electrons rotatearound the nucleus in a certain number of dis-crete stable orbits, emitting or absorbing quantaof energy only when they jump from one orbit toanother. There was no physical reason for Bohr’squantized orbits, but they “worked.” They suc-cessfully explained the spectral lines of thehydrogen atom. For Schrödinger, who was famil-iar with LOUIS-VICTOR-PIERRE, PRINCE DE

BROGLIE’s, discovery that an electron or anyother particle has an associated wave, the nextbreakthrough in understanding atomic structurewould require an equation capable of combiningwithin a unified framework Bohr’s quantizedelectron leaps and de Broglie’s wave–particleduality. He began searching for a type of partialdifferential equation—a wave equation, likethose used to describe sound, for example—capable of describing the behavior of electronsand other particles. De Broglie himself wasinvolved in a similar quest: in 1926, he andSchrödinger came up with the same equation inthe attempt to find this synthesis, but it failed topredict the observed spectra. Schrödinger tried adifferent approach later that year, formulatinghis Schrödinger equation in terms of the ener-gies of the electron and the field in which it waslocated. In the new model of atomic structurerevealed by Schrödinger’s wave function, theelectron, although most likely to be found whereBohr expected it to be, did not follow an orbit.Instead, it existed within what he called anorbital, an electron cloud or spatial region, whichwas an extension of Broglie’s model of electronsexisting in standing waves around the nucleus.Schrödinger got rid of Bohr’s disturbing conceptsof quantum jumps and discontinuities byexplaining “so-called electron orbits” as thevibration frequencies of electron “matter waves”around the nucleus of the atom.

Schrödinger’s wave mechanics came on thescene when another mathematical formulationof atomic structure, the matrix mechanics ofWERNER HEISENBERG and MAX BORN, was gen-

erating much excitement. In May 1926,Schrödinger published an article proving thatwave and matrix mechanics were equivalentmathematically, while claiming the superiority ofhis own approach. The physics community atlarge agreed. Matrix mechanics, which was basedon abstract calculation, without an accompany-ing picture of the atom, was far less accessiblethan Schrödinger’s familiar visualization. Planckhailed wave mechanics as “epoch-making;” andEinstein dubbed it a “decisive advance.”

Schrödinger’s subsequent renown generatedthe offer of a professorship at the University ofWisconsin, Madison, where he delivered a bril-liant series of lectures in 1927. He acceptedPlanck’s former position as professor of theoreticalphysics in Berlin, then a hub of scientific debateand discovery. Schrödinger plunged wholeheart-edly into discussions with an array of exceptionalcolleagues who included Einstein himself. Hewould remain there until the rise of the Nazis in1933, when he decided that living in a countrythat persecuted Jews as a matter of national policywas not an option for him.

It was in Oxford, England, where he becamea fellow at Magdalen College in the spring of1934, that he learned he had won the 1933Nobel Prize in physics for discovering wavemechanics. Refusing an offer from Princeton, heremained at Oxford for the next two years. In1935, he published a three-part essay, “The Pre-sent Situation in Quantum Mechanics,” inwhich he presented the cat paradox, his famousattempt to discredit the Copenhagen interpreta-tion of his work, which asserted that nature con-tains a fundamental randomness, an idea hecould never accept. Schrödinger believed thathis wave function represented an actual elec-tron, which was smeared out in the electroncloud. The Copenhagen interpretation, as for-mulated by Max Born, responded, “No, the wavefunction describes the probability of finding theelectron in the cloud.” According to this view, aparticle exists in an indefinite state until it is

Schrödinger, Erwin 273

observed, at which point it becomes a definiteparticle. To illustrate the absurdities to whichthis interpretation leads, Schrödinger deviseda thought experiment in which a cat in aclosed box either lived or died according towhether a quantum event occurred. The para-dox arose from applying the conventionalquantum mechanical view about the micro-scopic world to a macroscopic object (a cat),which is, after all, made of atoms and should,therefore, follow the same laws. Until the cat isobserved and found to be either dead or alive, itmust be viewed as existing in an indeterminatestate—neither dead nor alive. This discomfitingparadox has never been satisfactorily resolved,although attempts to do so have led to differentinterpretations of quantum mechanics.

While wrestling with these complexities,Schrödinger came face to face with his personalparadox: his love for a homeland that had becomeboth repulsive and inimical to him. His tenure atthe University of Graz (soon to be renamed AdolfHitler University), in Austria, lasted only twoyears. He fled with his wife in 1939, via Rome, tothe Institute for Advanced Studies in Dublin,where he remained until 1956. He devoted him-self to the problem of unifying gravitation andelectromagnetism and in 1947 triumphantly pre-sented his solution. When Einstein, with whomhe had been corresponding on the issue, rejectedhis ideas, he was devastated and broke off corre-spondence.

Schrödinger returned to his beloved Viennain 1956. But he had occupied his chair at theUniversity of Vienna for only a year when hebecame seriously ill. He died in Vienna on Jan-uary 4, 1961. In 1993, the International ErwinSchrödinger Institute for Mathematical Physics(ESI) was established in the building where hespent his last years.

In his later years, he turned his intellect tothe task of applying philosophy to physics andthe atom. In Nature and the Greeks (1954), hepresented his vision of Greek science and philos-

ophy. His final book, My View of the World, pub-lished posthumously in 1961, expressed his per-sonal metaphysical outlook.

Schrödinger’s own words best describe hisoriginal genius: “The task is, not so much to seewhat no one has yet seen; but to think whatnobody has yet thought, about that which every-body sees.”

Further ReadingGribben, John. In Search of Schrödinger’s Cat: Quan-

tum Physics and Reality. New York: Bantam Dou-bleday Dell, 1984.

———. Schrodinger’s Kittens and the Search for Reality:Solving the Quantum Mysteries. Boston: Little,Brown, 1996.

Marshall, Ian N., Danah Zohar, and F. David Peat.Who’s Afraid of Schrödinger’s Cat?: An A-To-ZGuide to All the New Science Ideas You Need toKeep Up With the New Thinking. New York:William Morrow, 1998.

Milburn, Gerard J. Schrödinger’s Machines: The Quan-tum Technology Reshaping Everyday Life. NewYork: W. H. Freeman, 1997.

Moore, Walter J. A Life of Erwin Schrödinger. London:Cambridge University Press, 1994.

Schrödinger, Erwin. My View of the World. Wood-bridge, Conn.: Ox Bow Press, 1994.

———. Space-Time Structure. Cambridge, Eng.: PressSyndicate of the University of Cambridge, 1990.

� Schwinger, Julian Seymour(1918–1994)AmericanTheoretician, Quantum Field Theorist

Julian Schwinger, one of the great theoreticalphysicists of his time, won the 1965 Nobel Prize inphysics for his role as a prime architect of quantumelectrodynamics (QED), the study of the interac-tion of electrons and electromagnetic radiation.Working concurrently with RICHARD PHILLIPS

FEYNMAN and SIN-ITIRO TOMONAGA, Schwinger

274 Schwinger, Julian Seymour

laid the foundations of relativistic QED and setthe stage for FREEMAN DYSON’s work, which rec-onciled his mathematical formalism with Feyn-man’s diagrammatic formulation of QED.

Schwinger was born on February 12, 1918,in New York City, into a middle-class Jewishfamily, the younger of two sons. His father, Ben-jamin, who had immigrated to the United Statesin 1880, was a successful designer of women’sclothing. His mother, Belle, had immigrated as achild from Lodz, then in eastern Poland. Thefamily lived in Jewish Harlem, a well-to-doneighborhood, and later in the prosperous envi-rons of Riverside Drive. A prodigy who discov-ered his obsession with physics at an early age,Schwinger attended Townsend Harris HighSchool, a renowned institution affiliated withthe City College of New York (CCNY), whichhe entered in 1934.

At the age of 16, he wrote his first paper(never published), “On the Interaction of Sev-eral Electrons,” an insightful analysis of the elec-tron field within the context of the quantummechanics of the electromagnetic field. He wasfrom the beginning an autodidact, who sat in thecollege’s library teaching himself modern physicsfrom original papers. He read all the papers ofPAUL ADRIEN MAURICE DIRAC, who he later saidwas “by far the overwhelming influence” in histhinking. However, his failure to attend classesled to a mediocre record at CCNY.

Then, through the intervention of ISIDOR

ISAAC RABI, whom he instantly impressed withhis theoretical insights, Schwinger was admittedto Columbia University, where, despite an F in achemistry course, he was elected to Phi BetaKappa. At the age of 19, he published his firstpaper, “The Magnetic Scattering of Neutrons,”which contained the core of his soon-to-be-completed dissertation, in Physical Review in1937. He hid not receive a Ph.D. until two yearslater, however, since, refusing to attend classes,he had trouble fulfilling the formal requirementsfor the degree. For the next two years he was at

the University of California at Berkeley, first as aNational Research Council Fellow and then asan assistant to J. ROBERT OPPENHEIMER.

When World War II began, he was teachingelementary physics to engineering students atPurdue University, where, in 1942, he was madean assistant professor. The following year he wasgiven a leave of absence by Purdue and went towork at the Radiation Laboratory at the Mas-sachusetts Institute of Technology (MIT), Cam-bridge. He was soon sent to the University ofChicago’s Metallurgical Laboratory, which wasinvolved in the atom bomb project. During thatsummer he worked on improving the design ofthe Hanford nuclear reactor. His colleagues atChicago found working with him to be a chal-lenge, since Schwinger had a two-handed black-board technique and when excited would besimultaneously solving two equations. Dissatis-fied with this type of work, Schwinger droveback to Boston and was reinstated at the Radia-tion Lab; he worked in George Uhlenbeck’sgroup, in which he became the prime force inthe development of radar waveguides.

Later, he would say of his work at the Radia-tion Lab, “I first approached radar problems as anuclear physicist, but soon I began to think ofnuclear physics in the language of electrical engi-neering that would eventually emerge as theeffective range formulation of nuclear scattering.”

Having become aware of the large magni-tude of microwave powers available, he began tothink about electron accelerators, which led tothe question of radiation by electrons in mag-netic fields. He was especially impressed by thefact that at the classical level, the reaction of theelectron’s field alters the properties of the parti-cle, including its mass. This property would besignificant in the future development of QED.During this period he also developed variationaltechniques that produced major advances in sev-eral fields of mathematical physics.

In 1945, when the war ended, Schwingerresigned from his position at Purdue to become

Schwinger, Julian Seymour 275

associate professor at Harvard. Two years later hewas promoted to full professor and marriedClarice Carrol of Boston. This was the begin-ning of a legendary period of physics in Cam-bridge. Schwinger’s friendship with the eminenttheorist Victor Weisskopf, who was at MIT,forged the theoretical physicists at Harvard andMIT into a close-knit community. Schwinger’sbrilliant lectures and mentoring of outstandinggraduate students helped Harvard rapidlybecome one of the most important traininggrounds for theoretical physicists. The notes fromone of Schwinger’s courses were compiled byJohn Blatt as “Advanced Theoretical Nuclear

Physics” and had a tremendous influence ongraduate students in the late 1940s and 1950s.

While Schwinger was thriving at Harvard,in 1947, WILLIS EUGENE LAMB, working inRabi’s laboratory at Columbia University,began experimental investigations that wouldhave a profound impact on the formulation ofQED. Applying the art of spectroscopy withunprecedented precision, he shone a beam ofmicrowaves onto a hot wisp of hydrogen gasblowing from an oven. He found that two finestructure levels in the next lowest group, whichshould have coincided with the Dirac theory,were in reality shifted relative to each other bya certain quantity (the Lamb shift). He mea-sured it with great accuracy and later made sim-ilar measurements on heavy hydrogen. Lamb’sannouncement of his news to the participantsof the 1947 Shelter Island (New York) Confer-ence had an electrifying effect. Schwinger, whowas present, commented:

Everybody was highly euphoric. . . .The facts were incredible—to be toldthat the sacred Dirac theory wasbreaking down all over the place.

Another flaw in the Dirac theory was foundthat same year in the same Columbia lab, byPOLYKARP KUSCH, who discovered a tiny dis-crepancy from what the theory predicted whenhe made highly accurate measurements of themagnetic moment of the electron.

Schwinger and other quantum theorists suchas HANS ALBRECHT BETHE, RICHARD PHILLIPS

FEYNMAN, and SIN-ITIRO TOMONAGA began torealize that what was missing from Dirac’s theorywas a proper interpretation of the unwieldy con-cept of the self-interaction of the electron, whichby its very nature contains infinities, thus pre-venting a straightforward physical interpretation.When the electromagnetic field is quantized,according to the rules of quantum mechanics,particles of light called photons are generated. At

276 Schwinger, Julian Seymour

Julian Seymour Schwinger was a prime theoreticalarchitect of relativistic quantum electrodynamics(QED), the study of the interaction of electrons,positrons, and electromagnetic radiation. (AIP EmilioSegrè Visual Archives. Physics Today Collection)

the heart of the quantum electrodynamic processis the quantum exchange force by which differ-ent electrons interact by exchanging photons; inthis context an electron can also exchange aphoton with itself.

How were physicists to deal with this self-interaction? QED, as it was formulated in themid-1940s, was not considered to be a relativis-tically covariant formalism (that is, it was notformally compatible with the rules of special rel-ativity). This lack of relativistic covariance pre-vented a unique mathematical interpretation ofthe physical effects of self-interaction. Schwingerchanged all this when he discovered a relativis-tically covariant form for QED, by introducingthe concept of renormalization, which allowed aconsistent mathematical interpretation of theself-energy infinities.

On the physical level, renormalizationimplied that physical particles are surrounded bya cloud of virtual particles, that is, ghostly parti-cles that exist within the context of the uncer-tainty principle, whose energy, momentum, andcharge modify the physical appearance of thebare original particle. In applying the method ofrenormalization, Schwinger found that the self-energy infinities could be subtracted out. Thisled to a fully consistent relativistic theory ofQED that explained the Lamb shift as due to thevirtual particle modification of the Coulombforce between the electron and the proton in thehydrogen atom. Using his new relativisticallycovariant QED formalism with renormalization,Schwinger was also able to calculate the anoma-lous magnetic moment of the electron.

After his groundbreaking work on QED,Schwinger concentrated on general theoreticalquestions, rather than specific topics of immedi-ate experimental interest. Early in 1957, he antic-ipated the existence of two different neutrinos,associated, respectively, with the electron and themuon. This was later confirmed experimentallyby LEON M. LEDERMAN. A related and somewhatearlier speculation, that all weak interactions are

transmitted by heavy, charged, unit-spin particles,was also later confirmed by decisive experimentaltests. Schwinger’s habit of finding theoreticalvalue in experimentally unknown particles ledhim to a revived concern with the possible exis-tence of magnetically charged particles calledmagnetic monopoles, which later were found tobe involved in the understanding of strong inter-actions.

In his later years, Schwinger backed awayfrom his earlier work on quantum field theory andworked on a phenomenological theory of parti-cles, which he called “source theory,” which dealsuniformly with strong interacting particles, pho-tons, and gravitons, thus providing a generalapproach to all physical phenomena. Hedescribed this work in his two-volume Particles,Sources, and Fields. The theory’s modest scientificgoal was to move from solid knowledge of phe-nomena at accessible energies to that at higherenergies. He perceived it as a sound and simplemathematical description of laboratory practice,without the difficulties that occur in the standardquantum field operator formalism. It incorporatedno infinities and thus needed no renormalization;no new constants would appear, because allparameters were fixed when the class of phenom-ena under examination was fixed.

However, the physics community, which wasevolving into the realm of the unified gauge theo-ries of elementary particles, was less than enthusi-astic about Schwinger’s new development. In1965, Physical Review Letters returned his submis-sions with scathing comments. In protest, heresigned from the American Physical Society.Schwinger grew increasingly isolated as he pur-sued his new theory. Nonetheless, his views influ-enced what is now known as the effective fieldtheory (EFT) approach to particle processes. Therationalizing of EFT has produced a resurgence ofinterest in Schwinger’s legacy, even if its long-termeffects are currently unpredictable.

In 1972, Schwinger left Harvard and fromthen until his death in 1994, he taught at the

Schwinger, Julian Seymour 277

University of California, Los Angeles. Anenormously respected and highly gifted lec-turer, he supervised numerous gifted graduatestudents, including three future Nobel Prizewinners. His books include Discontinuities inWaveguides, with D. Saxon (1968); QuantumKinematics and Dynamics (1970); Einstein’sLegacy: The Unity of Space and Time, (1987) andParticles, Sources, and Fields (1989). He died onJuly 16, 1994, in Los Angeles at the age of 76.

Schwinger’s career spanned an unusual arc—from early recognition for his work on QED topost–Nobel Prize ostracism for his work on thesource theory of elementary particles. Nonethe-less, he was a legendary figure in mid-20th-cen-tury physics, who will be remembered for hisreformulation of QED. His concept of renormal-ization made possible the first relativistically self-consistent framework for the quantization offields from which physical consequences could beextracted and experimentally verified.

See also BOHR, NIELS HENRIK DAVID; HEISEN-BERG, WERNER.

Further ReadingMehra, Jagdish, and Kimball A. Milton. Climbing the

Mountain: The Scientific Biography of JulianSchwinger. Oxford: Oxford University Press, 2000.

Schweber, Silvan S. QED and the Men Who Made It:Dyson, Feynman, Schwinger, and Tomonaga.Princeton, N.J.: Princeton University Press, 1994.

� Segrè, Emilio Gino(1905–1989)Italian/AmericanExperimentalist, Nuclear Physicist,Particle Physicist

Emilio Gino Segrè opened the door to the modernexploration of the world of antimatter with his dis-covery of the antiproton in 1955. He and his col-league Owen Chamberlain were honored for thiswork with the 1959 Nobel Prize in physics. DuringWorld War II, Segrè made a key contribution to

the development of the atomic bomb by his con-firmation that plutonium is fissionable.

He was born on February 1, 1905, in Tivoli,Rome, the son of Guiseppe Segrè, an industrial-ist, and Amelia Treves. The Segrès were awealthy family of intellectuals, professionals,and businesspeople. After completing his sec-ondary education in Rome, Emilio entered theUniversity of Rome in 1922 to study engineer-ing. Fascinated with the new developments inphysics, he changed fields five years later. Segrèreceived a doctoral degree in 1928 as the firstdoctoral student of the great ENRICO FERMI,who remained his friend and collaborator forover three decades. After Fermi’s death, Segrèbecame his biographer.

After being discharged from the Italianarmy, in which he served between 1928 and1929, Segrè became a research assistant at theUniversity of Rome. A Rockefeller FoundationFellowship in 1930 gave him the opportunity towork with OTTO STERN in Hamburg, Germany,and PIETER ZEEMAN in Amsterdam. In 1932, hereturned to Italy, where he was appointed associ-ate professor at the University of Rome andbegan a period of intensive collaboration withFermi and his group. Until 1934, except for ashort period spent in investigating molecularbeams, all his research focused on atomic spec-troscopy. Between 1934 and 1935, he played apioneering role in the discovery of slow neu-trons, which became an important componentin the discovery of nuclear reactors.

Segrè left Rome in 1936 to become director ofthe Physics Laboratory at the University ofPalermo but was forced to leave Italy only twoyears later to escape Mussolini’s anti-Semiticdecrees. He decided to immigrate to the UnitedStates and eventually became a U.S. citizen. HisAmerican career began where it would end manyyears later: at the University of California, Berke-ley. Starting out as a research assistant at the Radi-ation Laboratory, he went on to become a lecturerin the physics department. His prewar period atBerkeley was one of his most productive times in

278 Segrè, Emilio Gino

nuclear physics, when he worked with GlennSeaborg on methods of separating nuclear isomers,that is, pairs of isotopes of the same proton andneutron numbers, but in different quantum states.

When World War II erupted, as were manyscientists of the time, Segrè was concerned aboutGermany’s possible military application of thenew discoveries in nuclear fission. He undertooka study to prove that a bomb based not on sepa-rated isotopes of uranium, but on plutonium, dis-covered in 1943, was feasible. The results of thiswork put him in the center of the uranium pro-ject, which later became the Manhattan Projectto build the first atomic bomb. Moving his fam-ily to the Los Alamos Laboratory, from 1943 to1946, he directed a group whose task was tostudy spontaneous fission of uranium and pluto-nium isotopes. Present at the first test of anatomic bomb at Alamogordo in July 1945, hedescribed it as “an awesome sight, comparable togreat natural phenomena, [which] had a sober-ing impact on the beholders.”

After the war, Segrè had several offers fromuniversities; drawn by the prospect of new accel-erators and the exciting experimental possibili-ties they offered, he chose to return to Berkeleyas a full professor of physics. There, in 1955 heand his colleagues, Owen Chamberlain, ClydeWeigand, and Thomas Ypsilantis, discovered theantiproton. The notion of antiparticles origi-nated with PAUL ADRIEN MAURICE DIRAC, whoin 1931 had predicted the existence of a positron,or positive electron. Dirac’s prediction was moti-vated by his discovery that the mathematicsdescribing the electron contained twice as manystates as were expected. He proposed that thepositive energy states described the electron, andthat the negative energy states could be physi-cally interpreted as describing a particle with amass equal to that of an electron but with anopposite (positive) charge of equal strength, thatis, an antiparticle of the electron. Independentexperiments by CARL DAVID ANDERSON andLORD PATRICK MAYNARD STUART BLACKETT, in1932 and 1933, confirmed that a positron could

be produced by a photon. Dirac’s discovery of thepositron led to the prediction of other antiparti-cles, such as the antiproton.

In 1954, the testing of this prediction couldonly be done by means of a high-energy protonaccelerator, such as the Bevatron at Berkeley,which had reached its planned capacity of 6 bil-lion electron volts (Bevs)—the energy requiredfor the pair formation of protons–antiprotons.This, however, was only a starting point. Segrèwould later recall:

The chief difficulty of the experimentwas the extraction of a reliable antipro-ton signal out of a huge noise produced bythe many reactions occurring in the tar-get. In fact, only about one in 50,000 ofthe negatively charged particles emergingfrom the target was an antiproton. Twolines of attack were possible: a determina-tion of the e/m ratio for the particles pro-duced, or an observation of the terminalevent that was sufficiently detailed toidentify the annihilation process.

Segrè and Chamberlain’s ingenious methodsof detection and analysis used both approachesto establish the existence of the antiproton. Thecolleagues shared the 1959 Nobel Prize inphysics for this work.

Shortly afterward, another group at Berkeleydiscovered the antineutron, the antimatter coun-terpart of the neutron. From this point on, Segrè’smajor focus of research became antinucleons, theantimatter counterpart of the nuclear structure ofmatter. However, he would make no further basicdiscoveries. His group dispersed and Segrè himself,who preferred “to keep apparatus as simple andinexpensive as possible [and] to have a solid theo-retical foundation,” was never at home with theincreasingly more powerful accelerators or withthe larger and larger collaborations that becamenecessary in order to work with them.

Segrè was married, first to Elfriede Spiro,with whom he had a son and two daughters, and

Segrè, Emilio Gino 279

later to Rosa M. Segrè. During the 1960s and1970s, he was editor of The Annual Review ofNuclear Science. After his retirement fromBerkeley in 1972, he devoted much of his timeto studying the history of physics and publishedFrom X-Rays to Quarks: Modern Physicists andTheir Discoveries and Falling Bodies to RadioWaves: Classical Physicists and Their Discoveries.He died on April 29, 1989, of a heart attack.

Speaking of his 1964 text, Nuclei and Parti-cles, which reflects the experience of his genera-tion of physicists, Segrè offered an importanthistorical perspective: “Nuclei and particles werenot yet separated, and indeed, a good fraction ofthe particle physicists came from the ranks ofnuclear physicists or cosmic-ray physicists.”Segrè’s own career both illustrated and furtheredthis progress. As a young physicist he probed thephysics of the nucleus, then thought to consistonly of neutrons and protons. In his mature work,through his experimental detection of theantiproton, he glimpsed the far greater complex-ity of the exotic world of elementary particlesand became one of the first particle physicists.

See also LEON M. LEDERMAN; J. ROBERT

OPPENHEIMER.

Further ReadingSegrè, Claudio G. Atoms, Bombs and Eskimo Kisses: A

Memoir of Father and Son. New York: VikingPenguin, 1995.

Segrè, Emilio. A Mind Always in Motion: The Autobi-ography of Emilio Segrè. Berkeley: University ofCalifornia Press, 1993.

� Shockley, William Bradford(1910–1989)AmericanTheoretical Physicist, Solid StatePhysicist

William Bradford Shockley shared the 1956Nobel Prize in physics with JOHN BARDEEN andWalter Battrain for his part in inventing the

transistor, the basis for the most important tech-nological advances of the 20th century.

He was born on February 13, 1910, in Lon-don, England, to American parents, WilliamHillman Shockley, a mining engineer, and MayBradford Shockley, a federal deputy surveyor ofmineral lands. The family remained in Londonon business until William Jr. was three, whenthey returned to the United States and settled inPalo Alto, California. Shockley’s parentsschooled him at home until he was eight. In addi-tion to his parents’ encouragement of his scien-tific interests, he was stimulated by hisrelationship with a neighbor who taught physicsat Stanford University. He spent two of his highschool years at the Palo Alto Military Academybefore enrolling briefly in the Los AngelesCoaching School to study physics. After round-ing out his idiosyncratic secondary education atHollywood High School, he entered the Univer-sity of California at Los Angeles in 1927. After ayear he transferred to the California Institute ofTechnology in Pasadena, where he studied with anumber of distinguished physicists, includingLinus Pauling. He earned a B.S. in 1932 andwent on to the Massachusetts Institute of Tech-nology (MIT) in Cambridge for his graduatework, on a teaching fellowship. In 1933, he mar-ried Jean Alberta Bailey, with whom he wouldthree children. MIT gave him his grounding insolid state physics and awarded him a Ph.D. in1936 for a dissertation on the energy band struc-ture of sodium chloride.

Shockley then took a job with Bell Labora-tories in Murray Hill, New Jersey, where he firstproved himself by his vacuum tube research,which advanced the company’s goal of usingelectronic switches for telephone exchangesinstead of the mechanical switches that werecurrently in use.

When World War II broke out, Shockleyturned to work on military projects at Bell, par-ticularly the refinement of radar systems. Hethen became research director of the Antisub-

280 Shockley, William Bradford

marine Warfare Operations Research Group, setup by the United States Navy, at Columbia Uni-versity. After the war, he continued to servenational interests as a member of the ScientificAdvisory Panel of the United States Army, theAir Force Scientific Advisory Board, and thePresident’s Scientific Advisory Board.

Returning to Bell Labs in 1945, Shockleywas made head of a research group focusing onthe basic physical nature of semiconductors thatincluded John Bardeen and Walter Brittain.Through the application of quantum theory tosolid state physics in the late 1930s physicistsfirst understood the electrical properties ofsemiconductors: they became aware of the roleof low concentrations of impurities in control-ling the number of mobile charge carriers inmaterials. Current rectification (i.e., the con-version of oscillating current into direct cur-rent) at metal–semiconductor junctions hadlong been known, but the next step requiredwas to produce amplification analogous to thatachieved by vacuum tube technology. Shock-ley’s group began a program to control the num-ber of charge carriers at semiconductor surfacesby varying the electric field.

In the spring of 1947, Shockley asked themto investigate the reason for the failure of anamplifier he had designed, which was based on acrystal of silicon, later replaced by germanium.By observing Brittain’s experiments, Bardeenrealized that the assumption they had been mak-ing—that electrical current traveled through allparts of the germanium in the same way—wasincorrect. On the contrary, electrons behave dif-ferently at the surface of the metal. If they couldcontrol what was happening at the surface, theamplifier should work. On the basis of thisinsight they were able to demonstrate the effectsof amplification by using two metal contacts0.05 mm apart on a germanium surface. Largevariations of the power output through one con-tact were observed in response to tiny changes inthe current through the other.

Using this technique Bardeen and Brittainsucceeded in building the first point-contacttransistor on December 23, 1947; it was the fore-runner of the many complex devices now avail-able through silicon chip technology. Theycalled this first successful amplifying device thetransistor because it combined the notions ofcharge transfer and electrical resistance. Appar-ently stung by the discovery, in which he hadnot directly participated, Shockley hastened tomake improvements to the original transistor in1950, developing the junction transistor, whichmade mass production of transistors possible.

The year 1955 was a time of transition.Shockley divorced his first wife and marriedEmmy Laning. He also resigned as director of theTransistor Physics Department at Bell Labs. In1956, he shared the Nobel Prize in physics forthe invention of the transistor with Bardeen andBattrain. He then served as visiting professorand consultant at various universities and corpo-rations. For a while he directed his own lab fordeveloping transistors and related devices, how-ever, it folded in 1968. In 1963, he wasappointed professor of engineering at StanfordUniversity, where he taught until 1975.

He was the author of numerous scientificarticles, as well as two books on semiconduc-tors, and the holder of more than 90 U.S.patents. His 1950 publication, Electrons andHoles in Semiconductors, became an essentialguide for researchers.

During the latter part of his career he becameincreasingly immersed in a system of raciallynoxious ideas on the relationship betweenintelligence and genetics, which strongly resem-bled the program of the eugenics movement inthe 1910s and 1920s. His argument that thehigher birth rate among those with lower IQsposed a threat to the future of the populationwas couched in racial terms: he claimed thatblacks were genetically inferior to whites. Fur-ther, he advocated that eugenic measures betaken to prevent this outcome. Shockley’s

Shockley, William Bradford 281

stance made him increasingly controversial andan object of widespread hatred. In 1980, hesued the Atlanta Constitution for accusing him ofideas similar to those of the Nazi geneticsexperiments and won a $1 million settlement.Running on the 1982 California Republicanticket for the Senate on the single issue of “dys-genics,” he finished eighth.

Shockley died in Stanford, California, onAugust 11, 1989. His scientific insights eventu-ally led to the mass marketing of silicon chipelectronic devices that enabled computers andother electronic equipment to be produced morecheaply, more rapidly, and more reliably andultimately led to the birth of Silicon Valley.

Further ReadingBernstein, Jeremy. Three Degrees Above Zero: Bell Labs

in the Information Age. New York: Scribner &Sons, 1984.

Riordan, Michael, and Lillian Hoddeson. Crystal Fire:The Invention of the Transistor and the Birth of theInformation Age. New York: W. W. Norton, 1998.

� Snell, Willibrord(1580–1626)DutchExperimentalist (Optics)

Willebrord Snell is best known for discoveringthe law of refraction, also known as Snell’s law,which describes the way light rays are deviatedwhen they pass from one material to another.

He was born, in 1580, in Leiden, theNetherlands, where his father taught mathemat-ics at the university. While pursuing his interestin mathematics, he studied law at the Universityof Leiden. From 1600 to 1604, he traveledthroughout Europe, collaborating with such sci-entific luminaries as the astronomers TychoBrahe and Johannes Keppler. He received hisdegree from Leiden in 1607 and, six years later,assumed his father’s position there.

In 1617, Snell published his method ofdetermining distances by triangulation, using hishouse and the spires of nearby churches as refer-ence points. He used a large quadrant more thantwo meters long to determine angles and, bybuilding up a network of triangles, obtained avalue for the distance between two towns on thesame meridian. In this way he was able to deter-mine accurately the radius of the Earth, thusfounding the science of geodesics.

Snell made his great contribution to optics in1621, when, after exhaustive experimental work,he discovered his law of refraction, which relatesthe angle of incidence of an incoming light ray asit enters a material medium to the angle of refrac-tion of an outgoing light ray as it leaves a materialmedium. The physical process of refraction causesa light ray to change its direction as it passes fromone material medium to another. Snell definedthe index of refraction (n) of a transparentmedium as the speed of light in a vacuum (c)divided by the speed of light in a transparentmaterial (v). Then n = c/v. Since the speed oflight in a transparent material is slower than thespeed of light in a vacuum, Snell found that thisquantity is greater than or equal to 1. Snell didexperiments with two different transparent media(i.e., medium 1 and medium 2 with indices ofrefraction n1 and n2, respectively) separated by aflat surface. In these experiments he defined theangle of incidence as the angle between the per-pendicular to the flat surface and the light rayleaving medium 1 and the angle of refraction ofthe angle between the perpendicular to the flatsurface and the light ray entering medium 2. Onthe basis of these experiments Snell formulatedthe following physical law:

n1 sin(angle of incidence) = n2 sin(angle of refraction)

where the symbol sin represents the trigonomet-ric sine of the angle.

Unfortunately, Snell did not publish thisresult at the time of its discovery and it remained

282 Snell, Willibrord

unpublished for many years after his death inLeiden on October 30, 1626, at the age of 46.Through the work of René Descartes and CHRIS-TIAAN HUYGENS, Snell’s law of refractionbecame an essential element of the modern sci-ence of optics. Its ability to predict how light isbent as it passes from air to glass, for example,makes it an invaluable tool in designing lenses.

Further ReadingJoyce, W. B., and A. Joyce. “Descartes, Newton, and

Snell’s Law.” Journal of the Optical Society ofAmerica 66, no. 1: 1–8, 1976.

� Sommerfeld, Arnold Johannes Wilhelm(1868–1951)PrussianTheoretical Physicist (StatisticalMechanics, Quantum Mechanics),Atomic Physicist

Arnold Sommerfeld was an influential andrevered member of the community of European-born physicists who produced the quantum revo-lution in the first third of the 20th century. As aresearcher, he made the major contribution ofrefining NIELS HENRIK DAVID BOHR’s model ofthe atom, thereby setting that model on firmerground and solidifying the claims of quantumtheory. As a gifted teacher, he introduced thenew physics to generations of students and nur-tured the careers of several of its major architects.

Arnold Johannes Wilhelm Sommerfeld wasborn on December 5, 1868, in Königsberg, Prus-sia (now Kaliningrad, Russia). After completinghis studies at the gymnasium in his native city, heentered Königsberg University, where he choseto specialize in mathematics, despite Königs-berg’s preeminence as a school for theoreticalphysics. After receiving his Ph.D. in 1891, hebecame an assistant at the Mineralogical Insti-tute at Göttingen University. Four years later, he

won the post of lecturer at Göttingen, where hisresearch moved in several directions: the mathe-matical theory of diffraction, propagation of elec-tromagnetic waves in wires, and the study of thefield produced by a moving electron. His nextacademic position took him, in 1897, to the Min-ing Academy in Clausthal, where he taughtmathematics. While there he began workingwith Felix Klein on the 13-year study of gyro-scopes that would result in their four-volumework on the subject. He then moved on to theTechnical Institute in Aachen, in 1900; there heserved as professor of technical mechanics.

Sommerfeld’s years of academic wanderingcame to an end in 1906, when the University ofMunich appointed him director of the Instituteof Theoretical Physics, which had been createdthere for him. His ability to attract brilliant stu-dents and faculty, including the future NobelPrize winners WOLFGANG PAULI, WERNER

HEISENBERG, and HANS ALBRECHT BETHE, madeMunich an internationally respected center. Itwas Sommerfeld who directed MAX THEODOR

FELIX VON LAUE and his colleagues when theymade their famous discovery of X-ray diffractionin 1912.

His own research began to focus on quan-tum theory, which he promoted as a fundamen-tal law of nature. He is credited with inspiringBohr to apply the theory to the structure of theatom. In 1913, Bohr proposed that electrons areconfined to a certain number of stable orbits, inwhich they neither emit nor absorb energy.Only when it jumps from one discrete orbit to alower one does the electron lose energy: it sendsoff an individual photon (particle of light).Since an electron in the innermost orbit has noorbit with less energy to jump to, the atomremains stable. Bohr’s theory explained many ofthe spectral lines for hydrogen. This modelbegan to break down, however, when it failed toaccount for new observations that revealed thefine structure of the spectral lines of hydrogen.In 1916, Sommerfeld, who had been studying

Sommerfeld, Arnold Johannes Wilhelm 283

atomic spectra, suggested a modification of theBohr model, which would permit electrons tomove in elliptical orbits as well as circular ones.The new model required the introduction of asecond quantum number, the orbital quantumnumber, l, which describes the electron’s angularmomentum, in addition to the principal Bohrquantum number, n. Sommerfeld later intro-duced the magnetic quantum number, m, whichdetermines the orientation of the electronorbital in a magnetic field. When spectroscopicstudies confirmed Sommerfeld’s predictions,acceptance of Bohr’s quantum theory of theatom accelerated.

The golden years of Sommerfeld’s instituteended in the early 1930s, when the Nazisgained power. The man who had boldlydefended ALBERT EINSTEIN and other Jewishscientists would see his school closed in 1940,when he was 71. He would return to his postafter World War II and remain in Munich untilhe died on April 26, 1951, after being struck bya car.

In the later part of his career, Sommerfeldcontinued to demonstrate his versatility as aresearcher. He successfully replaced HENDRIK

ANTOON LORENTZ’s 1905 explanation of theelectronic properties of metals, which wasbased on classical physics, with an approachbased on statistical mechanics. Among themany influential books in which he presentedstate-of-the-art knowledge in several fields, themost famous are Atomic Structure and SpectralLines, published in 1919 and reprinted in anumber of editions in the 1920s, and WaveMechanics, 1929.

See also BOLTZMANN, LUDWIG.

Further ReadingSommerfeld, Arnold. Electrodynamics. New York:

Academic Press, 1952.———. Mechanics. New York: Academic Press, 1964.Wheaton, Bruce R. The Tiger and the Shark. Cam-

bridge: Cambridge University Press, 1990.

� Stark, Johannes(1874–1957)BavarianTheoretician and Experimentalist,Atomic Physicist

Johannes Stark is famous for his discovery ofwhat is now known as the Stark effect, thedivision of spectral lines in an electric field,work that was recognized by the 1919 NobelPrize in physics.

Stark was born in Schikenhof, Bavaria, onApril 15, 1874. His father, a landowner, sent theboy to secondary schools in Bayreuth andRegensburg. Stark then went on to the Univer-sity of Munich, where he studied physics, math-ematics, chemistry, and crystallography. Hewrote his dissertation on the phenomenon ofNewton’s rings in a dim medium, and receivedhis Ph.D. in 1897. For the next three years, heworked as a research assistant at the PhysicsInstitute at the University of Munich.

In 1900, Stark moved to the University ofGöttingen to work as an unsalaried lecturer.However, two years later, his fortunes changedwhen he predicted that the high-velocity canalrays (positively charged ions produced in a cath-ode ray tube) should exhibit the Doppler effect(an apparent change in the frequency of a wavemotion, caused by relative motion between thesource and the observer). In 1905, he confirmedthis prediction by demonstrating the frequencyshift in hydrogen canal rays. On the basis of thiswork, he was made a professor at the TechnischeHochschule in Hanover, in 1906 and, threeyears later, obtained a similar position at theTechnische Hochschule in Aachen, where heremained until 1917.

More than a decade earlier, PIETER ZEEMAN

had demonstrated that a division of the spectrallines emitted by atoms can be caused by the influ-ence of a magnetic field, the so-called Zeemaneffect. Stark built on this work by demonstratingthat the same division of spectral lines can be

284 Stark, Johannes

produced by the influence of an electric field. Histechnique was to photograph the spectrum emit-ted by canal rays, consisting of hydrogen andhelium atoms, as they passed through a strongelectric field. The electric field caused the elec-trons in the radiating atoms to change positionrelative to the nucleus and distorted the electronorbital motion. Since light is emitted when anexcited electron moves from a higher- to a lower-energy orbit, distortion of the orbits also distortsthe emitted light, which manifests itself as divi-sion of the spectral lines. Stark announced hisdiscovery of this spectral phenomenon, nowknown as the Stark effect, in 1913.

In that same year, Stark made yet anotherimportant contribution when he generalized thephotoelectric law proposed by ALBERT EINSTEIN

in 1906. This principle, now called theStark–Einstein law, states that each moleculeinvolved in a photochemical reaction absorbsonly one quantum of the radiation that causesthe reaction.

Stark went on to become professor of physicsat the University of Greifswald. His discovery ofthe Stark effect garnered him the 1919 NobelPrize in physics, and he used his prize money toset up his own laboratory. Surprisingly, at thishigh point in his career, he made a detour intothe world of commerce, attempting to set up aporcelain factory in northern Germany. TheGerman economy was depressed, however, andStark was forced to abandon his venture andreturn to the world of science.

Stark married Luise Uepler, with whom hehad five children. The later part of his scientificcareer was marred by his involvement in the rabidanti-Semitism sweeping Germany, which led himto join the Nazi Party in 1930. He became animportant figure in German physics, serving aspresident of both the Reich Physical–TechnicalInstitute and the German Research Association,from 1933 to 1939, when a conflict with govern-ment authorities caused him to resign. AfterWorld War II, he was sentenced, for his Nazi

activities, by a German denazification court, tofour years in a labor camp.

A prolific writer, Stark published more than300 scientific papers, as well as books on elec-tricity, elementary radiation, and electrical spec-troscopic analysis of chemical atoms. Hefounded the Jahrbuch der Radioaktivitat und Elec-tronik (Yearbook of radioactivity and electron-ics), which he edited from 1904 to 1913. In hisfinal years, he worked in his private laboratoryon his country estate near Traunstein, West Ger-many, studying the effect of light deflection inan inhomogeneous electric field. He died onJune 21, 1957, in Traunstein.

The discovery of the Stark effect, togetherwith the Zeeman effect, provided support for thequantum mechanical model of the atom andacted as an experimental template against whichthe development of quantum mechanics in gen-eral, and the evolution of the Bohr model of theatom, could be refined and advanced.

See also BARKLA, CHARLES GLOVER; BOHR,NIELS HENRIK DAVID; LAUE, MAX THEODOR FELIX

VON; LENARD, PHILIPP VON; SCHRÖDINGER,ERWIN.

Further ReadingBorn, Max. Atomic Physics. New York: Dover, 1989.

� Stefan, Josef(1835–1893)AustrianExperimentalist (Electromagnetism,Thermodynamics)

Josef Stefan made a lasting contribution tophysics in 1879 when he empirically determinedthe relationship between the amount of energy ablackbody radiates and its temperature. Fiveyears later, in 1884, Stefan’s brilliant studentLUDWIG BOLTZMANN would formulate the theo-retical basis for the relationship, which becameknown as the Stefan–Boltzmann law. This work

Stefan, Josef 285

on blackbody radiation proved crucial in theevolution of ideas leading up to the formulationof the quantum theory.

Stefan was born on March 24, 1835, inSaint Peter, Austria, and studied at the sec-ondary school there. At the age of 19 he enteredthe University of Vienna, which would remainhis academic home for the rest of his life: in1858, after completing his studies, he became alecturer; in 1863, he was promoted to the rank ofprofessor of higher mathematics and physics. Healso became director of Vienna’s Institute forExperimental Physics in 1866.

Stefan’s inquiries into the laws of radiationarose from a troubling inconsistency in the lawsof cooling derived by SIR ISAAC NEWTON.According to Newton, the rate of cooling of ahot body is proportional to the difference intemperature between the body and its surround-ings; however, researchers had found that New-ton’s formulation greatly underestimated theamount of heat bodies give out at very high tem-peratures. By measuring the heat energy radiatedby a blackbody, that is, a body that absorbs allthe radiant energy that falls on it, Stefan deter-mined that the power emitted per unit area wasproportional to the fourth power of the absolutetemperature in degrees Kelvin. Boltzmannderived this same law from thermodynamic prin-ciples and the kinetic theory developed byJAMES CLERK MAXWELL. It became known as theStefan–Boltzmann law, and the universal pro-portionality constant in the equation was calledthe Stefan–Boltzmann constant. By treating theSun as an approximate blackbody, Stefan wasable to use his equation to determine its surfacetemperature to be about 6000°C.

Later Stefan would help to confirmMaxwell’s kinetic theory by making accuratemeasurements of the conductivity of gases. Healso served as vice president of the ImperialAcademy of Sciences from 1885 until his death,in Vienna, on January 7, 1893.

See also PLANCK, MAX; ERNEST LUDWIG.

Further ReadingKuhn, Thomas S. Black-Body Theory and the Quantum

Discontinuity. Chicago: University of ChicagoPress, 1987.

� Stern, Otto(1888–1969)German/AmericanTheoretician and Experimentalist,Atomic Physicist, Physical Chemist

Otto Stern was a distinguished experimentalistwhose pioneering work with the molecularbeam method, a powerful tool for studying theproperties of molecules, atoms, and atomicnuclei, provided the first evidence that beams ofatoms and molecules have wave properties, anddetermined the magnetic moment of the pro-ton. He won the 1943 Nobel Prize in physics forthese contributions.

He was born in Sohrau, Upper Silesia, Ger-many (now Zory, Poland), on February 17, 1888,the son of a mill owner. When he was four, thefamily moved to Breslau, where Stern enteredthe Johannes Gymnasium in 1897 and obtaineda diploma in 1906. He studied physical chem-istry in universities: in Frieburg im Breisgau,Munich, and Breslau; in Breslau he had anapprenticeship with the eminent physicistARNOLD JOHANNES WILHELM SOMMERFELD andearned a Ph.D. in 1912 for a dissertation onphysical chemistry. He became intrigued withtheoretical physics and managed to become apostdoctoral associate to ALBERT EINSTEIN inPrague. He followed Einstein to Zurich in 1913,taking a job as an unpaid lecturer at the techni-cal high school.

Then, in 1914, Stern moved on to the Uni-versity of Frankfurt am Main as an unpaid lec-turer of theoretical physics. When World War Ibegan, Stern joined the army and was assignedto meteorological work on the Russian front. Hecontinued his theoretical work in his spare time;

286 Stern, Otto

toward the end of the war he was transferred to alaboratory in Berlin. After the war he returnedto Frankfurt, where he remained until 1921.

Between 1912 and 1918, Stern publishedtheoretical work on statistical thermodynamicsand quantum theory. His most significant contri-butions, however, were in experimental physics,through his development of the molecular beammethod, discovered in 1911 by Louis Dunoyer.In Stern’s molecular beam method a tiny open-ing is made in a heated container held inside aregion of high vacuum. The vaporized moleculesinside the heated container flow out, withoutcolliding with one another, to form a straightbeam of moving particles. The molecular beamcould be narrowed still further by the use of slits,and a system of rotating slits could be used toselect only those particles traveling at particularvelocities. In 1919, Stern used this molecularbeam method to verify Maxwell’s law of velocitydistribution in gases.

Stern then used his technique to resolve adilemma that had arisen in physicists’ under-standing of the influence of magnetic fields onthe electric forces within the atom. ANDRÉ-MARIE AMPÈRE had shown that the intrinsicmagnetic fields associated with atoms can gener-ally be ascribed to the presence of electric cur-rents in the atoms. However, the classical theoryand the quantum theory generated very differentpredictions about the behavior of these atomicmagnets in an external magnetic field. The clas-sical theory predicted that the atomic magnetsassume all possible directions with respect to thedirection of the external magnetic field. On theother hand, the quantum theory predicted thatthey can take only two directions: parallel andantiparallel to the external magnetic field. Inparticular, using NIELS HENRIK DAVID BOHR’squantum model of the atom, Sommerfeld hadderived a formula for the magnetic moment ofthe silver atom and predicted that silver atomsin a magnetic field could orient in only twodirections with respect to that field. In 1920, in

collaboration with Walter Gerlach, Sterndesigned an experiment to show which of thesetheories was correct.

In the historic Stern–Gerlach experiment, anarrow beam of silver atoms was passed through astrong magnetic field. According to classical the-ory, this field would cause the beam to broaden.However, the spatial quantization, that is, thesplitting of the beam of atoms in an externalmagnetic field, predicted by the quantum theoryimplied that the beam would split into two dis-tinct beams. The experimental result, showing asplit beam, was the first clear evidence for spacequantization. This experiment also made it possi-ble to obtain a measurement of the silver atom’smagnetic moment, the strength of the magneticfield generated by a current-carrying loop. Themagnetic moment proved to be in close accordwith the universal quantized unit of atomic mag-netic moment, the so-called Bohr’s magneton.

During 1921 and 1922, Stern was associateprofessor of theoretical physics at the Univer-sity of Rostock, and, in 1923, he became profes-sor of physical chemistry at the University ofHamburg and director of the Institute of Physi-cal Chemistry, where he remained until 1933.The 10 years between 1923 and 1933 were thepeak of his career, during which he made impor-tant contributions to quantum theory and builtup a thriving research group. During this periodStern improved his molecular beam techniqueand was able to detect the wave nature of parti-cles in the beams. This was an important confir-mation of the wave–particle duality proposed byLOUIS-VICTOR-PIERRE, PRINCE DE BROGLIE, in1924 for the electron.

In 1933, Stern measured the magneticmoment of the proton and the deuteron. Themagnetic moment of the proton had been pre-dicted by PAUL ADRIEN MAURICE DIRAC to beone nuclear magneton. It was known that theatomic nucleus, as does the electron, possessesan intrinsic rotation of its own, known as spin.However, the intrinsic spin of a charged proton

Stern, Otto 287

creates current loops that can generate anintrinsic magnetic field, which gives the protona magnetic moment. Only indirect, approximatemeasurements of the tiny nuclear magnet—esti-mated to be a couple of thousand times smallerthan that of the electron—could be made.Because the proton, together with the neutron,formed the basic constituents of matter, physi-cists ascribed great importance to determiningthe magnetic properties of the hydrogennucleus, or proton. If the proton and neutronwere to be regarded as true elementary particles,then the proton’s magnetic factor would be asmany times smaller than the electron’s as itsmass is greater than the electron’s. Stern deter-mined that the proton factor was about 2.3 timesgreater than anticipated.

With the rise of the Nazis, Stern, who wasJewish, found himself in increasingly precariouscircumstances. At first he found a measure ofsecurity in his personal wealth and internationalreputation and devoted himself to finding posi-tions abroad for his Jewish coworkers. But condi-tions worsened, and Stern knew it was time toemigrate when he was ordered to remove a por-trait of Einstein from his laboratory. In 1933, heleft Germany for the United States.

Stern was appointed research professor ofphysics at the Carnegie Institute of Physics,Pittsburgh, where he set up a new departmentfor the study of molecular beams. In 1939, hebecame a U.S. citizen and worked as a consul-tant to the United States War Department dur-ing World War II. In 1945, he became professoremeritus at Carnegie and moved to Berkeley,California, where he died of a heart attack onAugust 17, 1969.

Stern’s own words, contained in his NobelPrize acceptance speech, best summarize thenature of his contribution to modern physics:

The most distinctive characteristic prop-erty of the molecular ray method is itssimplicity and directness. It enables us to

make measurements on isolated neutralatoms or molecules with macroscopictools. For this reason, it is especially valu-able for testing and demonstratingdirectly fundamental assumptions of the[quantum] theory.

See also MAXWELL, JAMES CLERK.

Further ReadingCampargue, Roger, ed. Atomic and Molecular Beams:

The State of the Art 2000. New York: Springer-Verlag, 2001.

Estermann, Immanuel, ed. Recent Research on Molecu-lar Beams: A Collection of Papers Dedicated to OttoStern on the Occasion of his 70th Birthday. NewYork: Academic Press, 1959.

� Stokes, George Gabriel(1819–1903)IrishMathematical Physicist(Hydrodynamics, Optics)

George Gabriel Stokes left his mark on modernphysics through his discovery of what is calledStokes’s law, which relates the force acting on abody moving a body through a liquid to thevelocity and size of the body and the viscosity ofthe fluid. In the field of optics, he coined theterm fluorescence and made vital contributions tothe understanding of that phenomenon.

He was born on August 13, 1819, in Skreen,Sligo, in Ireland, the youngest of six children in areligious Protestant family. His father, Gabriel,was rector of the Church of Ireland, and hismother was the daughter of a minister. George’sfour older brothers served the church. The familyvalued education, and George was taught athome, by his father and the clerk of SkreenParish, who noted that the boy “worked out forhimself new ways of doing sums, better than thebook.” He entered school in 1832 in Dublin,

288 Stokes, George Gabriel

where he lived with his uncle. Despite the deathof his father, money was found to continue hiseducation. Three years later, he moved to Eng-land and attended Bristol College for two years,preparing for his entrance into Cambridge Uni-versity. After winning prizes in mathematics, in1837, he entered Pembroke College, the thirdoldest at Cambridge. There he was influenced byWilliam Hopkins, a renowned academic coach,who urged him to use his mathematical prowessfor understanding the material universe. Whenhe graduated four years later with a degree inmathematics, he was “Senior Wrangler,” the topmath student in the whole university, and wasimmediately awarded a fellowship by PembrokeCollege.

Stokes began to work in the field of hydro-dynamics, publishing papers on the motion ofincompressible fluids in 1842 and 1843, and onthe internal friction of fluids in motion in 1845.A report to the British Association for theAdvancement of Science in 1846 on recentresearch in hydrodynamics established his repu-tation as a mathematician. He became knownfor his contribution to the Navier–Stokes equa-tion, which is the primary equation of computa-tional fluid dynamics, relating pressure andexternal forces acting on a fluid to the responseof the fluid flow.

Over the next few years, while engaged inwork on viscous fluids, he would make his great-est discovery. In a seminal 1851 paper on hydro-dynamics, he derived the equation thatdetermines the movement of a small spherethrough viscous fluids of varying density. Theequation, which became later known as Stokes’slaw, was given by

F = 6π r ηv

where F is the force acting on the sphere, r is theradius of the sphere, v is the velocity of thesphere, and ηis the coefficient of viscosity of thefluid. Stokes’s law enables physicists to assess theresistance of fluids to motion and to determine

the terminal velocity of a body. It proved to be ofgreat importance in ROBERT ANDREWS MIL-LIKAN’s oil-drop experiments, performedbetween 1909 and 1913, which determined thecharge on the electron.

In 1848, Stokes was led by his studies of fluiddynamics to look into the question of the ether,the hypothetical fluid permeating the universethrough which light waves were thought topropagate. Stokes showed that the laws of opticsheld if the Earth dragged the ether with it in itsmotion through space; this caused him to pro-pose that the ether was an elastic substance thatflowed with the Earth. Later, in the 1880s, theMichelson–Morley experiments would disprovethe existence of the ether altogether.

In 1849, Stokes was appointed to the presti-gious position of Lucasian Professor of Mathe-matics at Cambridge, previously held by SIR

ISAAC NEWTON, which he would retain for therest of his life. He began giving lecture courseson hydrostatics that he would continue for thenext 53 years. A famous anecdote about himclaimed that he would always answer questionswith a plain yes or no, when something moreelaborate was expected. This habit was said todate from the time he transferred from Irish toEnglish schools, when his brothers warned himthat if he gave long Irish answers, he would belaughed at by his fellow students. To supplementthe professorship’s meager income, Stokes tookan additional position as professor of physics atthe Government School of Mines in London.That same year, he made an important contribu-tion to the field of geodesy when he published astudy of the variation of gravity at the surface ofthe Earth.

In 1852, Stokes offered the first explana-tion of a newly discovered phenomenon inmatter, which he called fluorescence. In thisresearch he had found that when illuminatedby ultraviolet light, a solution of quinine sul-fate that is normally colorless emits fluorescentblue light in certain circumstances. He was

Stokes, George Gabriel 289

able to use fluorescence as a method to studyultraviolet spectra. He based his explanationon the idea that fluorescence results fromabsorption of ultraviolet light and emission ofblue light by the molecules of matter. Ironi-cally, his explanation was based on 19th-cen-tury concepts that incorrectly assumed theexistence of an elastic ether that vibrates as aresult of the illuminated molecules.

In 1854, he realized that the Sun’s spectrumis made up of spectra of the elements it containsand concluded that the dark Fraunhofer lines arethe spectral lines of elements absorbing light inthe Sun’s outer layers. This important ideawould be developed by Robert Bunsen and GUS-TAV ROBERT KIRCHHOFF, who proposed themethod of spectrum analysis in 1860.

In 1857, Stokes moved from his highlyactive theoretical research period to administra-tive and experimental work. This change wasconnected to his marriage that year to MarySusanna Robinson, without whom, he wrote tohis bride-to-be, “I should go to my grave a think-ing machine unenlivened and uncheered andunwarmed by the happiness of domestic affec-tion.” He turned away from his life of intensemathematical research at this point. He had togive up his fellowship at Pembroke College,whose rules required that fellowship holders beunmarried; when the rules changed, he resumedhis fellowship in 1862. The marriage was said tobe a happy one, but it was marred by the deathsof three of their four children, two in infancy.

A gifted mathematician, Stokes helpeddevelop Fourier series. His pure mathematicalresults arose from the needs of the physical prob-lems he studied independently and with others.To a great extent, however, Stokes’s activities asa mathematician were driven by the needs ofindustrial applications in his own time. In addi-

tion to his connection to the School of Mines,he served as consultant to a renowned opticalworks and adviser on lighthouse illuminants andon wind pressure on railway structures.

Stokes was a deeply religious man, who hadalways been interested in the relationshipbetween religion and science. From 1886 to1903, he was president of the Victoria Institute,whose aim was to examine this broad issue.

He served as master of Pembroke Collegefrom 1902 until his death in Cambridge, onFebruary 1, 1903.

Stokes was a brilliant mathematical physi-cist whose broad range of studies in the physicsof fluids exerted an important formative influ-ence on the next Cambridge generation. Mostprominent among them was JAMES CLERK

MAXWELL, who used Stokes’s mathematicaldiscoveries in formulating his theory of elec-tromagnetism, now known as Maxwell’s equa-tions. Stokes was known for his generosity inputting aside his own research to help othersand serving as a sounding board for manyfamous scientists, such as LORD KELVIN

(WILLIAM THOMSON), with whom he carriedon an extensive correspondence. TheNavier–Stokes equation is currently used incomputations for aircraft and ship design,weather prediction, and climate modeling.

See also BECQUEREL, ANTOINE-HENRI;FRAUNHOFER, JOSEPH VON; MICHELSON, ALBERT

ABRAHAM.

Further ReadingWilson, D. B. Kelvin and Stokes: A Comparative Study

in Victorian Physics. Bristol, England: AdamHilger, 1987.

Wood, Alistair. “George Gabriel Stokes 1819–1903:An Irish Mathematical Physicist.” Irish Mathe-matical Society Bulletin 35: 49–58, 1995.

290 Stokes, George Gabriel

T

291

� Taylor, Joseph H., Jr.(1941– )AmericanAstrophysicist, Relativist, RadioAstronomer

Joseph H. Taylor Jr. shared the 1993 Nobel Prizein physics with his graduate student, Russell A.Hulse, for their 1974 discovery of the first binarypulsar, a rapidly spinning neutron star orbitingaround a companion star. Their radio pulse mea-surements of a binary pulsar system provided thefirst experimental confirmation of the existenceof the gravitational waves, the traveling waveripples in the geometric curvature of space andtime, predicted by ALBERT EINSTEIN in 1916 inhis general theory of relativity.

Taylor was born on March 29, 1941, inPhiladelphia, Pennsylvania, the second son ofJoseph Hooton and Sylvia Evans Taylor. Eventu-ally, the family would expand to six children andmove back to the family farm in CinnaminsonTownship, New Jersey. Taylor describes a whole-some, carefree childhood, steeped in his parents’Quaker values of frugal simplicity, tolerance, andconcern for others. When he was not collectingstone arrowheads, he and his brother, Hal, tookpleasure in erecting large rotating ham radioantennas and working with ham radio transmit-ters and receivers. He attended mostly Quaker

schools, including Moorestown Friends School,and Haverford College, where he fell in love withmathematics, was an avid and versatile athlete,and, in spite of the poor quality of his physicsand chemistry courses, began to understand “thedelights of what science is really all about.” For hissenior honors project Taylor built a working radiotelescope, an activity that allowed him to combine“a working knowledge of radio-frequency elec-tronics with an awakening appreciation of scien-tific inquiry.” It also led him to the field of physics,which he would pursue in his graduate studies.

After receiving his B.A. from Haverford in1963, Taylor won admission to Harvard Univer-sity, where, in the departments of astronomy,physics, and applied mathematics, he main-tained a grueling work schedule, especially dur-ing his first year. His doctoral thesis, supervisedby Alan Maxwell, taught him the signal process-ing techniques that later played an importantrole in his discovery of pulsars and earned him aPh. D. in astronomy in 1968. The following yearTaylor joined the physics faculty at the Univer-sity of Massachusetts, Amherst, where, in 1974,he and his graduate student Russell Hulse wouldplan the work that would take them to Arecibo,Puerto Rico, to use the 300-meter radio tele-scope to search systematically for pulsars.

Pulsars were discovered in 1967 by theBritish physicist Antony Hewish, who observed

that certain radio sources in space emitted radiosignals (pulses) that were repeated with great reg-ularity at intervals of about a second. This discov-ery made it possible to establish the existence ofneutron stars, which physicists had been speculat-ing about since the 1930s. A neutron star is theextremely dense remnant of a supernova explo-sion, which occurs when a massive star runs out offuel at the end of its life. The combination of largemass and small size results in an extremely largegravitational field, estimated to be about 100billion times that on Earth. When a supernovaexplodes, a newly formed neutron star can be sentrapidly spinning. Moreover, such a star can have amagnetic field many orders of magnitude largerthan those found on Earth. If a neutron star is alsosurrounded by a plasma environment, such anobject is called a pulsar. If the spin axis of the neu-tron star is properly aligned, it is possible for thespinning highly magnetized neutron star to gen-erate enough electric potential to acceleratecharges in the plasma surrounding the star, result-ing in a beam of nonthermal radio emission thatrotates with the star. To an observer, this radiobeam appears as a series of radio pulses as thebeam sweeps across the line of sight, similarly tothe rotating beacon of a lighthouse.

Using the immense radio telescope atArecibo, Taylor and Hulse picked up an unusualseries of radio pulses that varied in a regular pat-tern. The time between pulses, 59 milliseconds,was not constant: it changed, periodicallydecreasing and increasing over an eight-hourperiod. This signal pattern led them to surmisethat they were observing a pulsar, which must bealternately moving toward and away from theEarth. In accordance with the Doppler effect,when the pulsar moved toward the Earth, theantenna picked up a higher-frequency signal;when it moved away from the Earth, a lower-fre-quency signal was received. This meant that thepulsar must be moving around a companion staras part of a binary system where the companionmust also be a neutron star.

Taylor and Hulse called this binary pulsarsystem by the code name PSR 1913 + 16, toindicate its celestial coordinates. They foundthat the pulsar whirled around its companion ata speed of up to 300 kilometers per second—10times faster than the speed at which the Earthorbits the Sun. More importantly, they realizedthat they had stumbled across an unparalleledopportunity—a cosmic laboratory—to test theprediction of the general theory of relativity thatobjects traveling at extremely high speeds emitgravitational radiation, or gravitational waves:ripples in the curvature of spacetime. With itsenormous interacting gravitational fields, thebinary pulsar should emit gravitational waves,and the resulting energy drain should diminishthe orbital distance between the two stars, asindicated by the change in the electromagneticsignals that the orbiting pulsar emits. This is pre-cisely what Taylor and Hulse observed. In 1978,they announced that the orbiting period of thepulsar around its companion diminishes overtime by a minuscule amount, in agreement withEinstein’s prediction to an accuracy of 0.5%.This finding provided the first experimentalconfirmation of Einstein’s gravitation theory.Taylor and his group went on to repeat the mea-surements of PSR 1913+16 carefully and to dis-cover several other binary pulsars. More than 30years after the discovery of the first pulsar, about750 pulsars have been detected and cataloged.

Taylor joined the faculty of Princeton Uni-versity in 1981 and was named James S. McDon-nell Distinguished University Professor in 1986.

Taylor, who is married to Marietta BissonTaylor, continues to work with the pulsar groupat Princeton, which has pioneered the applica-tion of pulsar studies in a wide range of topics ingravitational physics, stellar evolution, cosmol-ogy, fundamental astrometry, and time-keepingmetrology.

Further ReadingHewish, Antony, et al, eds. Pulsars as Physics Labora-

tories. Oxford: Oxford University Press, 1994.

292 Taylor, Joseph H., Jr.

Lyne, Andrew G., and Francis Graham-Smith. PulsarAstronomy. Cambridge: Cambridge UniversityPress, 1989.

Manchester, Richard N., and Joseph H. Taylor. Pul-sars. San Francisco: W. H. Freeman, 1977.

Piran, Tsvi. “Binary Neutron Stars.” Scientific Ameri-can 272 52, 1995.

� Teller, Edward(1908– )Hungarian/AmericanTheoretical Physicist (QuantumMechanics), Nuclear Physicist

Edward Teller’s vociferous support for the devel-opment of an American hydrogen bomb and hiscrucial role in designing one earned him the titleof “father of the hydrogen bomb.” Hungarian-born and German-educated in the tumultuousfirst third of the 20th century, Teller fled bothcommunism in his native land and Nazi fascismfor U.S. shores. In America he turned his prodi-gious scientific inventiveness toward the cre-ation of weapons of mass destruction, makingsignificant contributions to the development ofthe atomic bomb. A polarizing figure, who laterlobbied for the development of a far deadliernuclear fusion bomb when the majority of hiscolleagues opposed such a weapon, Teller hasconsistently championed the use of advancedtechnology for purposes of national defense.

Edward Teller was born on January 15, 1908,in Budapest, when Hungary was a part of theAustro-Hungarian Empire. His family belongedto the community of affluent Hungarian Jewsthat produced an unusual number of outstandingphysicists, including EUGENE PAUL WIGNER andJohn Von Neumann. Teller relates his childhoodattraction to mathematics to the linguistic con-fusion of the Teller household, where he wastaught both German and Hungarian at the sametime and “did not catch on” at first. He foundthe world of numbers more congenial. When he

was 10, a retired mathematics professor, LeopoldKlug, whom he would call “the man who had thegreatest influence on my life,” gave him a copyof Leonhard Euler’s Algebra, which became hisfavorite book. When he graduated from sec-ondary school he knew he wanted to be a math-ematician. He compromised with his father,however, who insisted that his son have a “prac-tical” career, and agreed to study chemical engi-neering at the Institute of Technology inKarlsruhe, Germany.

While in Karlsruhe Teller changed directionafter he was exposed to the new ideas of quan-tum theory. In 1928, he transferred to the Uni-versity of Munich, where he studied briefly with“the most famous teacher of quantum mechan-ics,” ARNOLD JOHANNES WILHELM SOMMER-FELD. In Munich he suffered a personal tragedy,losing his left foot in a streetcar accident. Whenhe had recovered and learned to walk using aprosthesis, he moved to the University ofLeipzig, to study with WERNER HEISENBERG.After receiving a Ph.D. in physics in 1930, hebecame a research consultant at the Universityof Göttingen and published his first paper on thehydrogen molecular ion, which describes theorbiting of one electron around two nuclei. Itproved to be an early statement of what remainsthe most widely held view of this molecule.

When the Nazis came to power, Teller wasobliged to truncate his promising career in Ger-many. He would later say, “No one could havehad a greater influence on me than Hitler . . .who made it entirely clear to me that one couldnot ignore politics, and very particularly onecould not ignore the worst evils in politics.”

In 1934, Teller left for London and, after abrief stay, emigrated to Denmark. He joinedNIELS HENRIK DAVID BOHR’s Institute for Theo-retical Physics in Copenhagen, where he partic-ipated in the quest to unlock the secrets of theatom, using the radical insights of quantum the-ory. Teller would later say of this period, “Of allthe strange and important things that I have wit-

Teller, Edward 293

nessed in my life, this was the most strange andthe most important.”

It was in Copenhagen, too, that Teller methis future wife, Augusta Harkany, and formed aclose friendship with another political refugee,the Russian physicist GEORGE GAMOW. In 1935,Gamow, who had gone on to George Washing-ton University in Washington, D.C., invitedTeller to join him. When Teller and his wifeeagerly accepted, a period of collaborationbetween the two men, which resulted in theGamow–Teller rules for classifying subatomicparticle behavior in radioactive decay, began.

In 1941, Teller became a U.S. citizen andjoined the illustrious group of physicists workingon the Manhattan Project, which, under theauspices of the United States Army, was coordi-nating British and American efforts to developan atomic bomb. Teller worked in Chicago withENRICO FERMI and Leo Szilard, before moving toJ. ROBERT OPPENHEIMER’s laboratory in LosAlamos, New Mexico. Among Teller’s impor-tant contributions to atomic bomb research wasa calculation that reassured physicists whofeared that an uncontrolled nuclear reactionmight continue indefinitely and devastate theentire planet. Teller’s numbers showed that onlya limited area would be destroyed. The “limitedarea,” as history has recorded, proved to be theJapanese cities of Hiroshima and Nagasaki.Their destruction led to the Japanese surrenderand the end of World War II.

By this time Teller had a new obsession.Since Fermi had suggested the idea to him in1941, he had passionately championed thedevelopment of a thermonuclear explosive, a“superbomb.” At Los Alamos, in 1944, he haddone a theoretical study of the possibility ofusing an atomic bomb to ignite a mass of deu-terium, a weapon he called the “Super,” whichmight explode with a force equivalent not tothousands of tons of trinitrotolvene (TNT) butto millions. Such a bomb would use the intenseheat generated by nuclear fission, the instanta-

neous disintegration of heavy atomic nuclei intolighter ones, that underlies the atomic bomb inorder to provide a catalyst for the generation ofnuclear fusion, the instantaneous merging oflight atomic nuclei into heavier ones.

After the war, Teller urged his superiors atLos Alamos to go forward with work on thehydrogen bomb. Oppenheimer, who had beenmade chairman of the Atomic Energy Commis-sion, and most commission members opposedthe development of such a fusion weapon. But in1949, after it was learned that the Soviets hadexploded their first atomic bomb, PresidentHarry Truman ordered the team at Los Alamosto begin developing the next generation ofnuclear weapons.

A breakthrough occurred in 1951, whenStanislaw Ulam came up with the idea of usingcompression as a way to improve the reactionrates and staging as a way to achieve this. Tellerthen proposed using the photon radiation emit-ted by the primary fission device, rather than theneutron emission, to compress the secondarythermonuclear device. Use of a radiation shockwave instead of a material shock wave toimplode the secondary thermonuclear devicewould cause a faster and longer-sustained com-pression of the fusion fuel to greater density.This Ulam–Teller invention tipped the balancein the argument about building the H-bomb;physicists now knew they could do it. Teller,who was loath to share credit for the break-through, worked to make it his own. Later headded a crucial additional stage: a second fissioncomponent positioned within the thermonu-clear second stage to increase the efficiency ofthermonuclear burning.

But, in 1951, Teller left Los Alamos whenhe was passed over for the job of heading thethermonuclear program, in favor of MarshallHolloway. Because of what had been called his“wild Hungarian temperament,” Teller was notconsidered administrator material. Thus, whenin 1952 Los Alamos scientists held the first suc-

294 Teller, Edward

cessful test of a staged thermonuclear device onEniwotok Atoll in the Pacific Ocean, Teller wasnot there to watch his former colleagues explodeit. He did claim paternity, however, in a tele-gram announcing, “It’s a boy.”

Meanwhile, claiming that Los Alamos scien-tists were unenthusiastic about their new mission,Teller had lobbied for a second weapons labora-tory. In 1952, the Lawrence Livermore Laboratoryin northern California was established. Tellerwould be associated with Livermore from itsfounding until his retirement in 1975, acting asdirector between 1958 and 1960. During theheated debates of those times over whether toweaponize the thermonuclear device (as was lateraccomplished at Livermore), Teller’s was a lead-ing voice urging hydrogen bomb testing; RobertOppenheimer’s was the leading voice against it.

When, at the height of anti-Communisthysteria, in 1954, Oppenheimer was tried beforeMcCarthy’s House Un-American ActivitiesCommittee for disloyalty, Teller was asked to tes-tify. Stopping short of calling his former boss atraitor, he admitted his mind would rest easierknowing that Oppenheimer’s security clearancehad been revoked. Oppenheimer did lose hisclearance and influence on science policy.Rather than any personal antagonism, thesource of Teller’s uneasiness appears to havebeen Oppenheimer’s stance against developing a“usable” hydrogen bomb. His early experienceswith Hungarian communism gave his fear of theSoviet regime a special intensity. Whatever itsmotivation, there were many in the scientificcommunity—and elsewhere—who never for-gave Teller for his damning testimony.

Over the years Teller has been a leadingadvocate of a strong national defense; in the1980s, he was an outspoken proponent of Pres-ident Ronald Reagan’s strategic missile defensesystem (otherwise known as SDI or “StarWars”). He was also a leading advocate ofnuclear energy as a power source for peacefulends. He has authored more than a dozen

books on nuclear energy and defense issues. In1960, he accepted a joint appointment as pro-fessor of physics at the University of Californiaand as associate director of the Lawrence Liv-ermore Laboratory, a post he held until hisretirement in 1975. He then became a seniorfellow at the conservative Hoover Institute forthe Study of War, Revolution and Peace atStanford University. Now in his 90s, he livesin Palo Alto, California.

Looking back, Teller has defended, instraightforward terms, his advocacy of the mostdestructive weapons known to human beings:

What would have happened if Stalingot the hydrogen bomb and we didnot? . . . If I claim credit for anything, Ithink I should not claim credit forknowledge, but for courage. It was noteasy to contradict the great majority ofthe scientists who were my only friendsin a new country.

Further ReadingHerken, George. Brotherhood of The Bomb: The Tan-

gled Lives and Loyalties of Robert Oppenheimer,Ernest Lawrence and Edward Teller. New York:Henry Holt, 2002.

Rhodes, Richard. Dark Sun: The Making of the Hydro-gen Bomb. New York: Simon & Schuster, 1995.

Teller, Edward, with Judith L. Shoolery. Memoirs: ATwentieth-Century Journey in Science and Politics.New York: Perseus Books, 2001.

� Tesla, Nikola(1856–1943)Serbian/AmericanExperimental Physicist (ClassicalElectromagnetism), Electrical Engineer

Nikola Tesla was a great experimentalist andinventor whose work ushered in the age of elec-trical power. One of the pioneers of the use of

Tesla, Nikola 295

alternating currents, he invented the alternatingcurrent induction motor and the high-frequencycoil that bears his name.

He was born at midnight on July 9, 1856, inthe village of Smiljan, Croatia, then part of theAustro-Hungarian Empire, to Serbian parents.Nikola was supposed to follow in the footsteps ofhis father, a Serbian Orthodox priest, but his nat-ural inclinations led him along other paths. Thecombination of poetic imagination and scientificdiscipline that would characterize his amazingcareer manifested itself early in life. A cleverchild, he liked poetry (he would later write hisown poetry and translate Serbian poetry intoEnglish) and scientific experimentation. At theage of five he built a small waterwheel with anunusual design that he would recall years laterwhen designing his bladeless turbine. In sec-ondary school he developed an interest in scienceand, on graduating, entered the Technical Uni-versity in Graz, Austria, where he studied engi-neering. In 1878, after seeing a demonstration ofa direct current electric dynamo and motor, heconceived the idea of improving the machine byremoving the commutator and sparking brushes,which were sources of wear.

Tesla went on to the University of Prague in1880 but was forced to leave without graduatingwhen his father died the following year. Teslathen took a job in Budapest as an engineer for atelephone company. That year, while strolling inthe park with a friend, he visualized the princi-ple of the rotating magnetic field, which is pro-duced by two currents running out of step withone another, or alternating. This was the princi-ple that lay at the heart of his idea of the induc-tion motor: an iron rotor spinning betweenstationary coils that were electrified by two out-of-phase alternating currents producing a rotat-ing magnetic field. Before a working motor hadbeen built, Tesla had conceptualized an array ofpractical applications for it. Years later, he woulddescribe the manner in which an inventionwould come to life in his imagination:

Before I put a sketch on paper, the wholeidea is worked out mentally. In my mind Ichange the construction, make improve-ments, and even operate the device.Without ever having drawn a sketch I cangive the measurements of all parts toworkmen, and when completed all theseparts will fit, just as certainly as though Ihad made the actual drawings.

Tesla would not build an actual workinginduction motor until 1883, when he had movedto Paris and was working for the ContinentalEdison Company. Finding little interest indeveloping it in Europe, however, in 1884, hesailed to the United States. He arrived in NewYork with a few coins in his pocket and a letterof recommendation from a European businessassociate to the eminent inventor Thomas Edi-son at his Menlo Park, New Jersey, research lab-oratory. The letter said, “I know two great menand you are one of them; the other is this youngman.” Edison was impressed with this and gavethe young man a job, but he was a staunch sup-porter of direct current, which moves in onedirection only, rather than alternating current,which regularly reverses its direction. After ayear Tesla and Edison parted ways.

Tesla lost little time in obtaining patents forthe generation, transmission, and use of alter-nating current electricity, which he sold, in May1885, to George Westinghouse, head of theWestinghouse Electric Company in Pittsburgh.He received $60,000 for his patents and a con-tract promising him $2.50 per horsepower ofelectricity sold. But when Westinghouse’s com-pany found itself in financial trouble, Teslaagreed to forgo any royalties, as a gesture offriendship and support, “so that you can developmy inventions.” His selfless act would later pre-vent him from realizing the financial benefits ofmany of his other inventions.

The Westinghouse purchase precipitated anintense power struggle between Edison’s direct

296 Tesla, Nikola

current systems and the Tesla–Westinghousealternating current approach. Because of itshigher efficiency, alternating current, which canbe transmitted over much longer distances thandirect current, eventually won out. Westing-house demonstrated the superiority of alternatingcurrent by using his system for lighting at the1893 World Columbian Exposition in Chicago.In 1896, Westinghouse won the contract toinstall the first power machinery to generateelectricity, at Niagara Falls, using Tesla’s systemto supply and deliver alternating current to Buf-falo, 22 miles away.

Tesla himself had meanwhile becomeinvolved in a number of projects in the personallaboratory and workshop he had set up in 1887.He experimented with shadowgraphs, similar tothose used by WILHELM CONRAD RÖNTGEN, in1895, when he discovered X rays, as well asworking on a carbon button lamp, the power ofelectrical resonance, and various types of light-ing. To show that there was nothing to fear fromalternating currents, he gave exhibitions in hislaboratory in which he lighted lamps withoutwires by allowing electricity to flow through hisbody. As his fame grew, he was in demand forlectures in the U.S. and abroad.

At the time he became an American citi-zen, in 1891, Tesla directed his inventive pow-ers to developing alternating currents at veryhigh frequencies, believing they would be use-ful for lighting and communication. He exper-imented with high-frequency alternatorsbefore designing what came to be called theTesla coil, which produces high-voltage oscil-lations from a low-voltage direct currentsource. The Tesla coil is widely used in radioand television sets and other electronic equip-ment. At the peak of his creative powers, dur-ing this period he also invented fluorescentlighting, the bladeless turbine, and radio.

One of his most fervid interests was radiocommunication. In 1898, he demonstratedremote control of two model boats before large

crowds in Madison Square Garden in New York.He later extended this to remote controlledweapons, in particular, torpedoes.

During an 1899–1900 stay in ColoradoSprings, Colorado, Tesla made what he viewedas his most significant discovery: terrestrial sta-tionary waves, with which he proved that theEarth could be used as a conductor and would beas responsive as a tuning fork to electrical vibra-tions of a certain frequency. Using high-fre-quency alternating currents, he was also able tolight more than 200 lamps over a distance of 25miles without using intervening wires. Becausegas-filled tubes are readily energized by thesehigh-frequency currents, this kind of light couldeasily be operated within the field of a largeTesla coil. Later, he used the Tesla coil to pro-duce artificial lightning: an electric flash 135feet long. However, sometimes his imaginativeleaps seemed excessive to his contemporaries:when he announced that he had received signalsfrom another planet in his Colorado laboratory,he was ridiculed in scientific journals.

In 1900, with support from the financier J.Pierpont Morgan, he began building a wirelessworld broadcast station on Long Island, NewYork. His ambition was to provide worldwidecommunication and to furnish facilities for send-ing pictures, messages, weather warnings, andstock reports. When his backers found the projecttoo expensive, he reluctantly abandoned thisidea, considering it to be his greatest defeat.

Tesla created several other inventions,including electrical clocks and turbines, many ofwhich remained on the drawing board for lack offinancial backers to produce them. One of hismost ambitious ideas was to transmit alternatingcurrent electricity to anywhere in the worldwithout wires, using the Earth itself as an enor-mous oscillator. His scheme for detecting shipsat sea was later developed into what is nowknown as radar.

In 1917, he received the Edison Medal, thehighest honor awarded by the American Insti-

Tesla, Nikola 297

tute of Electrical Engineers. The standard inter-national unit of magnetic flux density wasnamed the tesla in his honor.

Eccentric and withdrawn, he lived his lastyears as a recluse. He was known for his loyaltyto his few close friends, one of whom was MarkTwain. When he died in New York City on Jan-uary 7, 1943, he owned more than 700 patents.His funeral was attended by a large crowd, and aflood of telegrams paid tribute to his genius andcontributions.

It would be difficult to overstate the impactof Tesla’s inventive genius. His discovery thatalternating current can be transmitted overmuch greater distances than direct currentunderlies our capability to power the machineryof the modern world.

Further ReadingCheney, Margaret. Tesla: Man out of Time. New York:

Dell, 1981.Hunt, Inez, and Wanetta W. Draper. Lightning in His

Hand: The Life Story of Nikola Tesla. ThousandOaks, Calif.: Sage Books, 1964.

Tesla, Nikola. My Inventions: The Autobiography ofNikola Tesla. Edited and with an introduction byBen Johnston. Williston, Vt.: Hart Bros., 1944.

� Thomson, Joseph John (J. J.)(1856–1940)BritishExperimentalist (ClassicalElectromagnetism), Atomic Physicist

J. J. Thomson was a brilliant experimentalistwhose exploration of the nature of cathode raysled him to the discovery of the electron. He wasawarded the 1906 Nobel Prize in physics for hisresearch on the conduction of electricitythrough gases.

Born in Manchester, England, on December18, 1856, Thomson became a physicist bydefault. Intending to become an engineer, he

enrolled at Owens College (later to becomeManchester University) at the age of 14. Butwhen his father, a seller of antique books, diedtwo years later, he found himself without themeans to finance an engineering apprenticeship.Instead, he managed to win a scholarship tostudy mathematics, physics, and chemistry and,in 1876, entered Trinity College, Cambridge.

After graduating in mathematics in 1880,he worked at the Cavendish Laboratory underLORD RAYLEIGH (JOHN WILLIAM STRUTT),whom he succeeded as Cavendish Professor ofExperimental Physics in 1884. Over the next 35years he would develop the Cavendish Labora-tory into the world’s leading center for sub-atomic physics. It was at the Cavendish thatThomson, applying his genius for designingapparatus turning to the mysteries of atomicstructure, made his breakthrough discoveries.

His Treatise on the Motion of Vortex Rings,which won him the Adams Prize in 1884,approached the subject from the point of view,espoused by many of Thomson’s peers, thatatoms exist in vortex rings within a hypothetical“ether,” which was thought to permeate all ofspace. From there he turned his attention to thecurrent debate over the nature of cathode rays,that is, the phenomenon that produced a fluo-rescent glow when most of the air was pumpedout of a glass tube with wires embedded at eachend and a high voltage was sent across it. Physi-cists asked whether cathode rays were chargedparticles or some undefined wavelike process inthe ether. When Thomson performed his firstexperiment, prior evidence seemed to favorwaves. The German physicist HEINRICH RUDOLF

HERTZ had apparently shown that cathode rayswere not deflected by an electric field; this indi-cated that they did not possess electric chargeand, therefore, did not have a particle nature. In1897, Thomson invalidated Hertz’s results,showing that they were caused by his use of aninsufficiently evacuated cathode ray tube. WhenThomson used a new technique to try to bend

298 Thomson, Joseph John

cathode rays with an electric field, extractingnearly all the gas from a tube, he succeededwhere Hertz had failed.

He then sought to determine the basic prop-erties of the cathode ray particles. Although helacked the means to measure the mass or electriccharge of such particles, he could measure howmuch the rays were bent by a magnetic field andhow much energy they carried. From these datahe could calculate the ratio of the electric chargeof a particle to its mass. He collected data byusing a variety of tubes as well as different gases.Whatever gas he used, he found that the ratio of

the charge divided by the mass of the cathoderay particles was constant and had a value nearly1000 times larger than that of a charged hydro-gen atom. These results led Thomson to a logicalfork in the road: either the cathode rays carriedan enormous charge, as compared with a chargedatom, or else they were extraordinarily light rel-ative to their charge. The question was settledby PHILIPP VON LENARD in experiments on howcathode rays penetrate gases. He showed that ifcathode rays were particles they had to have amass much smaller than the mass of any atom.Subsequent experiments by ROBERT ANDREWS

Thomson, Joseph John 299

Joseph John (J. J.) Thomson’s exploration of the nature of cathode rays led him to the discovery of the electron. (AIPEmilio Segrè Visual Archives)

MILLIKAN measured the charge directly and con-firmed Lenard’s conclusions.

At a historic meeting of the Royal Institutionin 1897 Thomson announced his results. Havingshown that cathode rays were fundamental, nega-tively charged particles with a mass much lessthan that of the lightest atom known, he went onto suggest that these material particles were thebuilding blocks of the atom, the basic unit of allmatter in the universe that physicists had longbeen seeking. For Thomson, however, this discov-ery only led to another, deeper mystery:

I can see no escape from the conclusionthat [cathode rays] are charges of nega-tive electricity carried by particles ofmatter . . . [but] what are these particles?Are they atoms, or molecules, or matterin a still finer state of subdivision?

What Thomson called “corpuscles” or “par-ticles” would later be given the name electrons,and physicists would devise numerous theoriesto explain how they combined to form atoms.Thomson himself suggested a model for theatom called the “plum pudding” or “raisin cakemodel,” in which thousands of tiny, negativelycharged corpuscles move inside a cloud of posi-tive charge. Later on, using alpha particles (a dif-ferent kind of particle beam), Thomson’s formerstudent ERNEST RUTHERFORD disproved Thom-son’s model, replacing it with his solar systemmodel of the atom: a massive, positively chargedcenter circled by only a few electrons.

After investigating the nature and proper-ties of electrons for several more years, Thomsonbegan researching “canal rays,” streams of posi-tively charged ions (i.e., atoms that have lostone of their negatively charged electrons),which he named positive rays. In the process helearned how to use positive rays for separatingdifferent kinds of atoms and molecules. His tech-nique led to the development of the mass spec-troscope, an instrument that measures thecharge-to-mass ratio. Using magnetic and elec-

tric fields to deflect these rays, Thomson found,in 1912, that ions of neon gas were deflected bydifferent amounts, indicating that they consistof a mixture of ions with different charge-to-mass ratios. He confirmed the existence of iso-topes, earlier proposed by the British chemistFrederick Soddy, when in that same year heidentified the isotope neon 22. Later many moreisotopes would be discovered.

In 1919, Thomson resigned his post at theCavendish Laboratory, after being elected Masterof Trinity College. He would remain at Trinityuntil his death on August 30, 1940, at the age of84. As an educator he devoted much attentionto the problems of teaching science at secondaryand university levels. Many universities used hisprolific writings on electricity, magnetism, andother topics. His profound personal impact onhis students is reflected in the fact that seven ofthem—including his own son, George—wenton to win the Nobel Prize in physics.

Most importantly, however, through his dis-covery of the first known elementary particle,the electron, Thomson initiated a period ofexploration that would lead 20th-century physi-cists to uncover a new universe of the infinitesi-mally small.

Further ReadingBuchwald, Jed Z. Histories of the Electron (Dibner Insti-

tute Studies in the History of Science and Technol-ogy). Cambridge, Mass.: MIT Press, 2001.

Dahl, Per F. Flash of the Cathode Rays: A History of J.J. Thomson’s Electron. Philadelphia: Institute ofPhysics, 1997.

� Ting, Samuel Chao Chung(1936– )Chinese/AmericanExperimentalist, Particle Physicist

Samuel C. C. Ting is a leading experimentalist,best known for his pioneering work in particle

300 Ting, Samuel Chao Chung

physics. His discovery of the J/ψ particle, anexcited state of nuclear matter, confirmed thestandard quark lepton model of electroweak andnuclear forces. For this work, he shared the1976 Nobel Prize in physics with BURTON

RICHTER, who had independently made thesame discovery.

He was born on January 27, 1936, in AnnArbor, Michigan, the first of three children ofKuan Hai Ting and Tsun-Ying Wong, who wereboth foreign graduate students at the Universityof Michigan. The accident of his prematurebirth made Samuel an American citizen. Twomonths later, his family returned to Beijing,China, where his father became a professor ofengineering, and his mother a professor of psy-chology. World War II prevented him fromattending school until he was nine, although hishome was always filled with his parents’ col-leagues, who imbued him with an early desire tobe part of academic life. With both parentsworking, he was raised by his maternal grand-mother, a widow who had struggled to educateherself and her daughter during turbulent yearsin China’s history. Ting writes of his grand-mother and mother, “Both of them were daring,original, and determined people, and they haveleft an indelible impression on me.” After thewar, the family moved to Taiwan, where Tingcontinued his schooling, excelling in mathemat-ics, science, and history.

In quest of a better education, in 1956, Tingreturned to Ann Arbor as an undergraduate athis parents’ alma mater. He had heard thatAmerican students earned their own waythrough college and told his parents he would dolikewise. Knowing little English, he arrived with$100 in his pocket and an invitation to stay withhis father’s former engineering professor. But hemanaged to obtain scholarships and worked veryhard to retain them. Entering as an engineeringstudent, he soon switched his major to physics.Only three years later, in 1959, he received aB.S. in physics and mathematics. He stayed at

Michigan for his graduate studies and received aPh.D. in physics in 1962 for an experimentalthesis supervised by Lawrence Jones and thefuture Nobel laureate Martin Perl.

In 1963, Ting was awarded a Ford Founda-tion Fellowship to work at the European Centerfor Nuclear Research (CERN) in Geneva, wherehe collaborated with Giuseppi Cocconi onexperiments using the 28-billion-volt protonsynchrotron. Cocconi taught him a great dealabout physics and deeply impressed him with his“simple way of viewing a complex problem” andthe care with which he conducted experiments.

Ting returned to the United States in thespring of 1965, to spend an exciting year as aninstructor at Columbia University, where he hadthe chance to observe such eminent physicists asLEON M. LEDERMAN, TSUNG-DAO LEE, ISIDOR

ISAAC RABI, and CHIEN-SHIUNG WU. The fol-lowing year, however, he took leave fromColumbia in order to lead an experimentalgroup at the Deutsches Elektronen Synchrotron(DESY) in Hamburg, Germany. His goal was toreproduce an experiment performed that year atthe Cambridge Electron Accelerator at HarvardUniversity on electron–positron pair productionby photon collision with a nuclear target.(Positrons are the antiparticles of electrons.)The experiment seemed to indicate findingsinconsistent with what Ting knew of quantumelectrodynamics (QED), which describes theproperties of the interaction of matter and elec-tromagnetic radiation. With the new detectorthey built, Ting’s group confirmed the results ofthe Harvard group.

This was a turning point in Ting’s career:from then on he would devote himself to thephysics of electron or muon pairs, studying thequantum electrodynamic production and decayof new photonlike particles, which decay toelectron or muon pairs. He explains, “Thesetypes of experiments are characterized by theneed for a high-intensity incident flux, for highrejection against a large number of unwanted

Ting, Samuel Chao Chung 301

background events, and at the same time theneed for a detector with good mass resolution.”To achieve these conditions, he took his groupback to the United States in 1971, to theBrookhaven National Laboratory in Stony-brook, New York.

In the spring of 1972, Ting’s group modifiedthe detector they had designed in Germany,increasing its sensitivity to the specific energysignal of the electron–positron pairs in order todiscern its specific signal amid the noise of mil-lions of other particle collisions. The NobelPrize committee would later liken this feat tobeing able to “hear a cricket close to a jumbo jettaking off.” With their newly improved detector,Ting’s team bombarded a beryllium target with aproton beam, took measurements, and lookedfor the signature of the electron–positron pairs.In August 1974, they made a startling discovery:the first of a totally unpredicted new group ofextremely heavy long-lived mesons. Afterrechecking his results, in November of that year,Ting announced his discovery, which he calledthe J particle (a name based on the symbol forthe electromagnetic current).

Just before publishing his findings, Tingattended a conference at Stanford Universitywith scientists working at the Stanford LinearAccelerator Center and made another astound-ing discovery: The physicist Burton Richter,using a wholly different experimental approach,had found the same particle, which he called thepsi particle. Two years later, both men shared theNobel Prize for their work in detecting whatcame to be called the J/ψ particle, determined tobe more than twice as heavy as any comparableparticle and yet a thousand times more narrow inits energy spectrum (and that, according to theuncertainty principle, meant that it was a long-lived particle).

In 1961, MURRAY GELL-MANN and YUVAL

NE’EMAN had devised the eightfold way, a systemfor classifying the myriad newly discovered ele-mentary particles into eight families of elemen-

tary building blocks called quarks, of whichthere were three types. The unique feature of thenewly discovered J/ψ particle was that it did notbelong to any of the families as they were knownprior to 1974. Its detection confirmed SHELDON

LEE GLASHOW’s prediction of a fourth quark (i.e.,the charmed quark, which was needed in orderto make the Gell-Mann SU(3) quark theory ofthe strong interactions consistent with thisobservation).

In 1969, Ting was appointed professor ofphysics at the Massachusetts Institute of Tech-nology (MIT) in Cambridge, where, in 1977, hewas selected as the first recipient of the ThomasDudley Cabot Institute Professorship. In 1985,he married Dr. Susan Marks, with whom he hada son, Christopher, the following year. He alsohas two daughters, Jeanne and Amy, from a pre-vious marriage.

Ting continues to spend most of his time atCERN, where he heads the L3 Experiment,launched in 1982, involving more than 500physicists from about 33 universities and institu-tions throughout the world. Another major cur-rent project in which he is involved is theconstruction of a three-ton detector, called theAlpha Magnetic Spectrometer (AMS), designedto search for the existence of antimatter nucleiamong cosmic rays, which will operate in theInternational Space Station. Since antimatter isexpected to be extremely difficult to detect,experimentation in empty space, where “back-ground noise” is considerably less, is essential. InJune 1998, a prototype AMS was tested on theSpace Shuttle Discovery.

The AMS may also play a role in investigat-ing the mysterious dark matter, which, thoughestimated to make up the greater part of the uni-verse, has so far eluded detection. The AMS maybe sensitive to certain properties of weakly inter-acting particles that some physicists believe tobe the essence of dark matter.

Ting and Richter’s discovery of the J/ψ par-ticle changed the landscape of particle physics.

302 Ting, Samuel Chao Chung

By verifying the need for a charmed quark, itopened the door to the further elaboration of thefull Standard Model, which contains six quarks:up, down, strange, charm, top, and bottom.

See also ANDERSON, CARL DAVID; DIRAC,PAUL ADRIEN MAURICE; SALAM, ABDUS; WEIN-BERG, STEVEN.

Further ReadingKane, Gordon. The Particle Garden: Our Universe as

Understood by Particle Physicists. Cambridge,Mass.: Perseus, 1995.

Ne’eman, Yuval, and Murray Gell-Mann. The Eight-fold Way. Cambridge, Mass.: Perseus, 2000.

Ne’eman, Yuval, and Yoram Kirsh. The ParticleHunters. Cambridge: Cambridge UniversityPress, 1996.

� Tomonaga, Sin-Itiro(1906–1979)JapaneseQuantum Field Theorist, ParticlePhysicist

Sin-Itiro Tomonaga was a great Japanese theoreti-cian, who laid the foundations of a relativisticquantum electrodynamics (QED), the study ofthe quantum mechanical interaction of electrons,positrons, and photons. He shared the 1965Nobel Prize in physics with RICHARD PHILLIPS

FEYNMAN and JULIAN SEYMOUR SCHWINGER,who, working concurrently, achieved the sameresult, using different approaches.

He was born in Tokyo, Japan, on March 31,1906, the eldest son of Sanjuro and HideTomonaga. When he was seven, the familymoved to Kyoto, where his father was appointeda professor of philosophy at Kyoto Imperial Uni-versity. He was a sickly boy, who did poorly inathletics and was teased by his peers as a “cry-baby.” He discovered his passion for scienceearly and spent his free time with a friend build-ing simple electric circuits with parts they had

found in junkyards. After graduating from therenowned Third Higher School, he enteredKyoto Imperial University in 1923. After earn-ing their rigakushi (bachelor’s degrees) inphysics in 1929, Tomonaga and his good friend,another future Nobel Prize winner, HIDEKI

YUKAWA, traveled to Tokyo to listen to a seriesof lectures by WERNER HEISENBERG and PAUL

ADRIEN MAURICE DIRAC, which made a strongimpression on them.

He remained at Kyoto for three years ofgraduate studies, after which he was taken on asa research associate by Yoshio Nishina, one ofJapan’s leading physicists at the Institute forPhysical and Chemical Research (known asRiken) in Tokyo. Nishina, who introducedresearch on quantum mechanics to Japan, was arole model and father figure for the youngTomonaga, who later reminisced:

The Nishina laboratory in those dayswas full of freshness. All the memberswere young; even our great chiefNishina was still in his early forties. Weall got together for lunch every day, aneager group of people discussing variousmatters, not only physics, but also suchthings as plans for beer parties, excur-sions and so on.

In this stimulating atmosphere, Tomonagamade his first contribution to QED in a 1933paper, coauthored with Nishina, on photoelec-tric pair creation. With the other members ofthe theoretical group, he studied Dirac’s work,translating his textbook on quantum mechanicsinto Japanese.

In the mid-1930s, Tomonaga’s interestsshifted to nuclear physics. From 1937 to 1939, hewas in Leipzig, Germany, studying nuclearphysics and quantum field theory under Heisen-berg. With Heisenberg’s encouragement, heattacked the problem of the description in theBohr liquid-drop model of the heating of a

Tomonaga, Sin-Itiro 303

nucleus when it absorbs a neutron. He had hopedto continue working with Heisenberg, but whenwar broke out on September 1, 1939, he returnedto Japan. The results of his Leipzig researchformed a large part of his doctoral thesis, whichhe submitted in December 1939 at Tokyo Impe-rial University. The following year, he marriedRyoko Sekiguchi, with whom he would have twosons and a daughter.

With his country at war, Tomonaga, who, in1941, became professor of physics at Tokyo Uni-versity of Education (Bunrika), managed to presson with his fundamental research on QED. Headdressed himself to the problem that, whereasevery physical theory must obey the rules of spe-cial relativity, QED, in its early Dirac formula-tion, was not fully relativistic. Some physicists

believed that the infinities (also called diver-gences) that QED yielded, which were physi-cally nonsensical, could be dealt with morerealistically if the theory could be made relativis-tically covariant, that is, compatible with therules of special relativity. In work done between1941 and 1943, Tomonaga proposed a relativis-tic formulation of quantum field theory, inwhich the concepts of the quantum state vector(the quantum field theoretic equivalent of theSchrödinger wave function) and its equation ofmotion, concepts having relativistic spacetimemeaning, were generalized so as to be relativisti-cally covariant.

In 1943, Tomonaga published this work,developed in isolation from his Western counter-parts, who would not learn of it until four yearslater, just as he was forced to turn away from basicresearch to problems related to military needs.Until the end of the war, he worked on the prop-erties of magnetrons and the behavior ofmicrowaves in waveguides and cavity resonators,developing a unified theory of the systems con-sisting of waveguides and cavity resonators.

In the midst of Japan’s postwar devastation,Tomonaga and his family found themselveshomeless and hungry. Nonetheless, there was asense of communal responsibility for nationalreconstruction among the group of young scien-tists who gathered around Tomonaga in Tokyo.In 1946, he returned to the problems of quantumfield theory, with the goal of summarizing andapplying the covariant field theory to actualphysical systems. He was sure that the diver-gence problems in QED could be overcome byfinding a way to handle the infinite mass andcharge due to field reaction. Elimination of thedivergences was to be accomplished by a renor-malization procedure that first identified thedivergent terms according to their relativisticand gauge transformation properties, thenshowed that these divergent contributions couldbe absorbed in a redefinition of the mass andcharge parameters entering the original formula-

304 Tomonaga, Sin-Itiro

Sin-Itiro Tomonaga shared the 1965 Nobel Prize inphysics with Richard Phillips Feynman and Julian S.Schwinger for his work in quantum electrodynamics(QED), the study of the quantum mechanicalinteraction of electrons, positrons, and photons. (AIPMeggars Gallery of Nobel Laureates)

tion of the theory. If this could be done, then therenormalized formalism could make predictionsabout observable phenomena.

In 1947, Tomonaga learned about the Lambshift and read HANS ALBRECHT BETHE’s article inPhysical Review, presenting his nonrelativisticLamb shift calculation. He recognized its impor-tance and went on to work out his mass renor-malization method, substituting the experimentalmass for the fictive mechanical mass thatappeared in the equations of QED. He performeda similar renormalization of the electric charge.He also deduced a correct formula for the Lambshift, which agreed with measurements. In 1948,he wrote about his work to J. ROBERT OPPEN-HEIMER, who urged him to submit a summary toPhysical Review for publication.

In a scientific community only slowly over-coming the barriers imposed by global war,Tomonaga’s discovery did not influence QEDresearch in the United States. Schwinger inde-pendently made the same advances and Feynmanwas unaware of his Japanese colleague’s work.However, Tomonaga did resume his collaborationwith Western physicists when, in 1949, he wasinvited to the Institute for Advanced Study,Princeton; there he turned his attention tonuclear physics, investigating a one-dimensionalfermion system. In so doing he clarified the natureof collective oscillations of a quantum mechanicalmany-body system and opened a new frontier oftheoretical physics, the modern many-body prob-lem. In 1955, he published an elementary theoryof quantum mechanical collective motions.

Tomonaga was a leader in establishing theInstitute for Nuclear Physics, Tokyo, in 1955.From 1956 to 1962, he was president of theTokyo University of Education. In 1963, hebecame president of the science council of Japanand director of the Institute for OpticalResearch at the Tokyo University of Education.He held many key positions on governmentcommittees dealing with scientific research andpolicy making.

In 1965, Tomonaga shared the Nobel Prizein physics with Schwinger and Feynman but wasprevented by an accident from being present inStockholm.

He published widely in scientific journals onQED, the meson theory, nuclear physics, cosmicrays, and the many-body problem. His bookQuantum Mechanics was published in Japan in1949; an English-language edition appeared in1962. His memoir, Development of QuantumElectrodynamics: Personal Recollections, becameavailable in English translation in 1966.

Tomonaga, who died on July 8, 1979, inTokyo, was a physicist of great intellectual pow-ers, an extraordinary teacher in the Socratic tra-dition whose dictum was that “if you formulatethe problem correctly, that is, if you ask the rightquestion, the answer emerges spontaneously.”He possessed keen aesthetic sensibilities and alove of communing with nature. He will beremembered as a strong advocate of nonprolifer-ation of nuclear weapons and the peaceful usesof atomic energy.

See also EINSTEIN, ALBERT; KUSCH, POLYKARP;LAMB, WILLIS EUGENE.

Further ReadingSchweber, Silvan S. QED and the Men Who Made It:

Dyson, Feynman, Schwinger, and Tomonaga.Princeton, N.J.: Princeton University Press,1994.

Tomonaga, Sin-Itiro. The Story of Spin. Chicago: Uni-versity of Chicago Press, 1998.

� Townes, Charles Hard(1915– )AmericanTheoretician and Experimentalist(Optics), Laser Spectroscopist

Charles Hard Townes is a giant of 20th-centuryphysics, who, together with ARTHUR LEONARD

SCHAWLOW, invented the laser, the revolution-

Townes, Charles Hard 305

ary device that creates and amplifies a narrow,intense beam of coherent light. Townes inde-pendently invented the laser’s forerunner, themaser. He shared the 1964 Nobel Prize inphysics for these accomplishments with the Rus-sian physicists Nikolay Basov and AleksandrProkhorov, who independently made the samediscoveries.

He was born on July 28, 1915, in Greenville,South Carolina, to Henry Keith Townes, anattorney, and Ellen Hard Townes. A child whohad to know how things work, he onceinstructed his older sister to “buy out a hardwarestore” for his Christmas present. After attending

the Greenville public schools, he gained earlyadmission at age 16 to Furman University inGreenville, where he earned both a B.Sc. inphysics and a B.A. in modern languages summacum laude in 1935. In addition to his broad aca-demic interests, he was an “all-around” student,a member of the swimming team, the collegenewspaper, and the football band. From earlychildhood, when he took long walks in thewoods with his father and carried home a collec-tion of pet frogs, caterpillars, lizards, and snakes,he had a strong love of nature; at Furman, heserved as curator of the natural history museumand was collector for the summer biology camp.But it was physics, with its “beautifully logicalstructure,” that most engaged him. Townesdecided to pursue graduate work at Duke Uni-versity and, in 1937, received his master’s degreein physics. From there he went on to the Cali-fornia Institute of Technology, where he wrote adissertation on isotope separation and nuclearspin, earning a Ph.D. in 1939.

Townes then began work for Bell TelephoneLaboratories in New York City and, in 1941,married Francis H. Brown, with whom he wouldhave four daughters. During World War II, hedid important work using microwave techniquesto design radar bombing systems, using theshorter wavelength of microwave radiation,which permitted radar beams to reveal the shapeof a target more accurately. When the warended, sensing in this technology a potentiallyrevolutionary method for studying atomic andmolecular structure, as well as for controllingelectromagnetic waves, he set about findingpeaceful applications in microwave spectroscopyfor his discoveries. When he left Bell Laborato-ries in 1947 to join the physics faculty atColumbia University, he continued his work onmicrowaves; by 1950, he had become a professorof physics and director of the Columbia Radia-tion Laboratory.

At the time, physicists around the world weretrying to find a way to produce extremely short

Charles Hard Townes invented the laser, therevolutionary device that creates and amplifies anarrow, intense beam of coherent light. (AIP EmilioSegrè Visual Archives, and AT&T Bell Labs)

306 Townes, Charles Hard

waves for measuring the properties of matter; thevacuum technology of the time was not capable ofdoing this. In 1951, while sitting on a park benchin Washington, D.C., where he was attending aconference devoted to this problem, Townes sud-denly saw the solution and scribbled it on anenvelope he found in his shirt pocket. He hadconceived the idea of the maser, an acronym formicrowave amplification by stimulated emission ofradiation, and the laser, a similar verbal construc-tion, with the word light substituted for microwave.

The concept of stimulated emission origi-nated with ALBERT EINSTEIN, who, while study-ing the theory of blackbody radiation in 1917,had found that the process of light absorptionmust be accompanied by a complementary pro-cess in which the absorbed radiation stimulatesthe atoms to emit the same kind of radiation.However, in order for amplification of the radia-tion by stimulated emission to occur in a physi-cal medium, the stimulated emission must belarger than the absorbed radiation. For this tohappen, the physical medium must have moreatoms in a high-energy state than in a lower one.Since the law of conservation of energy impliesthat energy spontaneously flows from a higher toa lower state, this physical situation, whichinvolves an inverted population of excitedatoms, is inherently unstable. Moreover, in orderto use this method to generate beams of coher-ent light (i.e., intense light waves consisting ofessentially one frequency and moving in thesame direction), it would be necessary to findthe specific atomic systems with the right inter-nal storage mechanisms.

In order to do this, Townes selected the sim-ple case of ammonia molecules, because they canoccupy only two energy levels. The ammoniamolecules had the property of emitting radiationwith a 1.25-cm wavelength, which lies withinthe microwave range of the electromagneticspectrum. He reasoned that when an ammoniamolecule in the high-energy state absorbed aphoton of this frequency, the molecule would

fall to the lower energy level, emitting twocoherent photons of the same frequency, thusproducing a coherent beam of single-frequencyradiation with a 1.25-cm wavelength.

By studying the behavior of ammoniamolecules in a resonant cavity containing elec-tric fields, Townes developed a method that sep-arated the relatively few high-energy moleculesfrom the more numerous low-energy ones andthus created the required population inversionneeded for maser action to occur. By 1953, hehad constructed the first working model of themaser. Masers soon found a range of applications:in the most accurate timepieces available to thisday—atomic clocks; in short wave radios, wherethey serve as extremely sensitive receivers; inradio astronomy; and in space research, forrecording the radio signals from satellites.

Townes continued his research at Columbia,where he was made chairman of the physicsdepartment in 1952. In December 1958, he andhis former research student (now his brother-in-law) Arthur Schawlow published a landmarkpaper, “Infrared and Optical Masers,” in PhysicalReview, in which they showed theoretically thatan optical maser, or laser, could be produced by acoherent beam of visible light, instead of amicrowave beam. Because the change frommicrowaves and visible light required a 100,000-fold increase in frequency, a fundamentally dif-ferent operating structure was required. Theatoms or molecules of a ruby or garnet crystal orof a gas, liquid, or other substance are excited bylight in the cavity in which they are contained,so that more of them are at higher energy levelsthan are at lower ones. In order to achieve thenecessary high-radiation density, two mirrors,one at each end of the cavity, force the light tobounce back and forth until coherent lightescapes from the cavity. The first working laserwas built in 1960 by Theodore Maiman at theHughes Research Laboratories.

At this high point of his career, Townes tooka leave of absence from Columbia University

Townes, Charles Hard 307

and served as vice-president and director ofresearch at the Institute for Defense Analysis, anonprofit organization in Washington, D.C.,from 1959 to 1961. He was then appointedprovost and professor of physics at the Mas-sachusetts Institute of Technology (MIT),where, in addition to shaping MIT’s overallresearch program, he engaged in research inquantum electronics and astronomy. In 1964, heshared the Nobel Prize in physics with Basov andProkhorov for invention of the laser. Schawlowwas inexplicably excluded from this select groupand would not have his contribution recognizedby the Nobel Committee until 1981.

In 1967, Townes joined the faculty of theUniversity of California, Berkeley, where hisresearch focused on the study of radiation fromspace, using principles of radio and infraredastronomy. He and his colleagues discoveredwater and ammonia in interstellar space, the firstcomplex molecules found outside our solar sys-tem, and showed that water was producingintense natural maser activity there. This dis-covery prompted him to comment:

For billions of years [astronomical masers]have been sending out intense radiation inall directions . . . but we have only recentlygotten their message. . . . The whole field ofmasers and lasers may well have originatedfrom discovery there, and the develop-ment . . . might have had a very differenthistory.

Townes served as chairman of the NASA Sci-ence Advisory Committee for the Lunar Landing.

With a team of researchers, he designed instru-ments used to analyze infrared radiation fromspace. He became professor emeritus in 1986. Heand his wife continue to reside in Berkeley.

The evolution of the early lasers into themultitude of laser devices in the modern worldled Townes to comment:

People said, “It’s a nice idea, but what can itdo?” My view then was that it would touchmany applications because it combinedelectricity and light. But it is amazing howit is used today. . . . I’ve had people come upto me and say “lasers saved my eyesight.”That’s a very emotional experience for me.It’s so personal, this connection.

Lasers are so pervasive in daily life—in thebar-code scanners at supermarket checkout coun-ters, in laser printers, scanners, and compact disctechnology—that the term Laser Age has beencoined to describe the present era. Although it isprobably true, as Townes believes, that lasers arestill in their “adolescence,” they are already pow-erful tools for research in many fields, widely usedin industry for cutting and boring metals andother materials; in medicine for surgery; in com-munication, scientific research, and holography.

Further ReadingChiao, Raymond Y. Amazing Light: A Volume Dedi-

cated to Charles Hard Townes on His 80th Birthday.New York: Springer-Verlag, 1996.

Townes, Charles Hard. How the Laser Happened:Adventures of a Scientist. Oxford: Oxford Univer-sity Press, 1999.

308 Townes, Charles Hard

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309

� Van Allen, James(1914– )AmericanAstrophysicist

James Van Allen is a pioneering astrophysicistwho played a vital role in the early developmentof the U.S. space program. His work in magneto-spheric physics led to the discovery of a zone ofhigh-level radiation around the Earth caused bythe presence of trapped charged particles, knownas the magnetosphere or the Van Allen belt.

He was born in Mount Pleasant, Iowa, onSeptember 7, 1914, the second of four sons ofAlfred Van Allen and Alma Olney Van Allen.Although his father was an attorney in a familyof lawyers, he encouraged the boy to follow hisown path. Van Allen writes:

My boyhood activities were all centeredaround our closely knit family, whichhad a strong resemblance to that ofother pioneer families. The virtues offrugality, hard work, and devotion toeducation were enforced rigorously andon a daily basis by my father. My motherexemplified the pioneer qualities ofaffection and nurture for her husbandand their children and of comprehen-sive self-reliance.

A studious boy, with a consuming interest inscience and mechanical and electrical devices,he was an avid fan of the magazines PopularMechanics and Popular Science. When he gradu-ated from Mount Pleasant High School in 1931,he was class valedictorian.

From there he went on to Iowa WesleyanCollege, where he was drawn to both physicsand chemistry and received a B.S. in 1935. Theopportunity to work in a high-pressure researchlab assisting his professor helped him to decidein favor of physics. He then went on to the Uni-versity of Iowa, where he earned an M.S. in 1936and a Ph.D. in 1939, writing a dissertation onnuclear disintegration. From 1939 to 1942, VanAllen worked as a research fellow at theCarnegie Institute in Washington, D.C., in theDepartment of Terrestrial Magnetism, where hestudied the photodisintegration process. It wasthere that he “crossed the culture gap fromnuclear physics to the department’s traditionalresearch in geomagnetism, cosmic rays, auroraland ionospheric physics,” which he resolved tomake his future fields of research.

During World War II, he “plunged into thewar effort with the patriotic fervor of those days.”In April 1942, he moved to the applied physicsdepartment at Johns Hopkins University, wherehe worked on the creation of a rugged vacuumtube. He helped to develop the proximity fuze, a

device attached to a missile such as an antiaircraftshell that detonated when it neared the target,when the radio waves it emitted were reflectedback to it with sufficient intensity from the target.The proximity fuse allowed the detonation tooccur even if the missile had not been aimed accu-rately enough for a direct hit and greatly increasedthe effectiveness of antiaircraft weapons. By thefall of 1942, Van Allen had been commissioned asan officer in the United States Navy and was sentto the Pacific to field test and complete opera-tional requirements for the proximity fuze.

In 1946, the war now ended, Van Allen mar-ried his lifetime companion, Abigail FithianHalsey, with whom he would have five children.For the next four years he was involved in high-altitude research, as supervisor of the high-alti-tude research group and proximity fuse unit at

Johns Hopkins, working on utilization of theunused German stock of V-2 rockets and of theAerobee rockets for research purposes. The groupdeveloped devices for measuring the levels of cos-mic radiation that were sent to the outer reachesof the atmosphere in these rockets, which radioedthe data back to Earth. Van Allen’s experience inminiaturization of electronic equipment enabledhim to include a maximum of instrumentation inthe limited payload of these rockets, an achieve-ment that was to be crucial in the early stages ofthe U.S. space program.

After a year at the Brookhaven NationalLaboratory on a Guggenheim Fellowship, in1951, he became professor of physics and head ofthe physics department at the University ofIowa. Working with his students, he inventedthe rocket–balloon (rockoon), which went intouse in 1952. It consisted of a small rocket thatwas lifted by means of a balloon into the upperregions of the atmosphere and then fired off,thus reaching heights otherwise attainable onlyby a much larger rocket.

From 1949 to 1957, Van Allen also organizedand led scientific expeditions to Peru (1949), theGulf of Alaska (1950), Greenland (1952 and1957), and Antarctica (1957) to study cosmicradiation. During an Arctic expedition in 1953,rockoons fired by Van Allen and his students werethe first to detect a hint of the radiation belts sur-rounding the Earth.

He became part of the organizing panel ofInternational Geophysical Year (IGY), July1957–December 1958, whose members activelypromoted the adoption of scientific satellites ofthe Earth as an element of the IGY program andlaid the foundations for the scientific program ofthe National Aeronautics and Space Administra-tion, created in 1958. In the mid-1950s, the U.S.government had first seriously considered the pos-sibility of sending a rocket into orbit around theEarth, thereby creating an artificial satellite. In1955, President Eisenhower announced theVanguard Program, designed to put an artificial

310 Van Allen, James

James Van Allen discovered a zone of high-levelradiation around the Earth caused by the presence oftrapped charged particles, known as the magnetosphereor the Van Allen belt. (AIP Emilio Segrè Visual Archives)

satellite into orbit within two years, to coincidewith the scheduled IGY, which was itself timedto coincide with a peak in solar activity. VanAllen was given responsibility for the instru-mentation of the project.

On October 4, 1957, the day that the SovietUnion launched Sputnik 1, the world’s first artifi-cial satellite, Van Allen was on a scientific expe-dition to the Antarctic. On hearing the news, theAmerican team lost no time in launching Explorer1, on January 31, 1958. It was carrying a Geigercounter Van Allen had intended to use to mea-sure the levels of cosmic radiation, but at a heightof about 500 miles the counters registered a radia-tion level of zero. This nonsensical reading ledVan Allen to suspect instrument failure. Whenthe same result was recorded on Explorer 3,launched on March 26, 1958, he realized that thezero reading could have resulted from the coun-ters’ being swamped with very high levels of radi-ation. On July 29, 1958, Explorer 4 was sent upwith a counter shielded with lead in order toallow less radiation to penetrate, and this methodshowed clearly that parts of space containedmuch higher levels of radiation than previouslysuspected. Van Allen studied the size and distri-bution of these high-radiation zones and foundthat they consisted of two toroidal (i.e., donut-shaped) radiation belts around the Earth, whicharise by the trapping of charged particles in theEarth’s magnetic field. The inner belt was madeup of high-energy protons, the outer belt of high-energy electrons and other particles. These radia-tion belts were found to be part of the tear-shapedmagnetic region around the Earth called the mag-netosphere. The radiation belts started at an alti-tude of several hundred miles from the Earth andextended for several thousand miles into space. In1993, other scientists discovered a third belt,enclosed by the inner belt, containing ions ofoxygen, nitrogen, and neon.

Van Allen was elected to the NationalAcademy of Sciences in 1952 and became presi-dent of the American Geographical Union in

1982. In 1959, he was made professor of astron-omy at Iowa and, from 1972 to 1985, was CarverProfessor of Physics; after retirement, he eventu-ally became professor emeritus there. At age 85,he was still mentoring graduate students, doingresearch, and monitoring transmissions from thesystem he invented on Pioneer 10, launched in1972, as the first artificial object to carry soundsand images from Earth into outer space.

As an astrophysicist, James Van Allen playeda vital role in the early development of the U.S.space program. In one capacity or another, hewas involved in the first four Explorer probes, thefirst Pioneers, several Mariner efforts, and theorbiting geophysical observatory. From 1966 to1970, as a member of the Space Science Boardand the Lunar and Planetary Missions Board, hebecame a leading advocate for missions to theouter planets, especially Jupiter. The first fruits ofthese efforts were the National Aeronautics andSpace Administration’s (NASA’s) two missionsto Jupiter, Pioneer 10 and Pioneer 11, launched in1972 and 1973.

Further ReadingGillmor, C. Stewart, and John R. Spreiter. Discovery

of the Magnetosphere. Washington, D.C.: Ameri-can Geographical Union, 1997.

Newton, David E. “James A. Van Allen,” in Emily J.McMurray, ed., Notable Twentieth-Century Scien-tists. New York: Gale Research, 1995, pp.2070–2072.

Van Allen, James. “Autobiography,” Annual Review ofEarth and Planet Sciences, 18: pp. 1–26, 1990.

———. Origins of Magnetospheric Physics. Washing-ton, D.C.: Smithsonian Institution Press, 1983.

� Van de Graaff, Robert Jemison(1901–1967)AmericanExperimentalist, Particle Physicist

Robert Jemison Van de Graaff made a majorcontribution to advances in high-energy physics

Van de Graaff, Robert Jemison 311

through his invention of what came to be calledthe Van de Graaff generator, an electrostatichigh-voltage accelerator capable of acceleratingelectrons to millions of volts of kinetic energy.

He was born on December 20, 1901, inTuscaloosa, Alabama, to Minnie Cherokee Har-grove and Adrian Sebastian Van de Graaff. Hisearly education was in the public schools ofTuscaloosa. Intending to become a mechanicalengineer, he studied at the University ofAlabama, where he received his B.S. degree in1922 and his M.S. the following year. He thentook a job as a research assistant with theAlabama Power Company but left after only ayear to travel to the Sorbonne in Paris to con-tinue his education. The trip was to change thedirection of his life. In Paris he attended the lec-tures of MARIE CURIE, one of the great pioneersof the study of radioactivity, who exposed him tothe ongoing revolution in atomic physics.

He continued his European education as aRhodes Scholar at Oxford University, underJohn Sealy Edward Townsend, a major figure indeveloping the study of the kinetics of electronsand ions in gases. Van de Graaff worked primar-ily on these topics at Oxford, where he wasawarded a B.Sc. in 1926 and a Ph.D. in 1928.During this period, as he became aware of thework of ERNEST RUTHERFORD and others tryingto fathom the mysteries of atomic structure, thepressing need for a high-energy subatomic parti-cle accelerator, capable of disintegrating atomicnuclei, became increasingly clear to him. Herealized that a high potential could be built upby storing electrostatic charge within a hollowsphere and that this could be achieved bydepositing charges on a moving belt that carriesthe charges into the sphere, where a collectortransfers them to the outer surface of the sphere.Van de Graaff’s idea led him to develop a device,now known as a Van de Graaff generator, thatconsisted of a large smooth metal sphere on topof a hollow insulating cylinder within which anendless insulating belt ran between pulleys at

each end of the cylinder. Electric charge wassprayed from metal points connected to a high-voltage source onto the bottom of the belt; itwas then carried up to the top of the belt, whereit was collected by other metal points and accu-mulated on the outside of the sphere, causing itto become highly charged at a high electrostaticpotential difference. Charged particles fallingthrough this large electrostatic potential differ-ence would then be accelerated to very high val-ues of kinetic energy.

While at Oxford, Van de Graaff beganworking on designs for his generator. When hereturned to the United States in 1929 he builthis first working model, operating at 80,000volts, at the Palmer Physics Laboratory atPrinceton University, where he was a NationalResearch Fellow from 1929 to 1931. He demon-strated an improved model, which operated at 1million volts, at the inaugural dinner of theAmerican Institute of Physics in November1931.

That year he moved to Cambridge, Mas-sachusetts, as a research associate at the Mas-sachusetts Institute of Technology (MIT), where,in 1934, he would become an associate professorof physics. In an aircraft hangar in South Dart-mouth, Massachusetts, he constructed his firstlarge generator, able to produce 7 million volts,which was demonstrated on November 28, 1933.He developed the generator so that it could beused to accelerate subatomic particles to veryhigh velocities. The previous year JOHN DOU-GLAS COCKCROFT and Ernest Walton had builtthe first particle accelerator, which produced thefirst nuclear transformations by means of artifi-cially accelerated particles, at the CavendishLaboratory at Cambridge. Van de Graaff’smachine was more compact, simpler in design,and capable of producing higher voltages (and,therefore, higher particle accelerations) than theCockcroft–Walton accelerator.

In 1936, he married Catherine Boyden, withwhom he would have two sons, John and

312 Van de Graaff, Robert Jemison

William. Having obtained the patent for hisgenerator, he began working with John G.Trump, a professor of electrical engineering atMIT, in designing a modified generator capableof producing X rays for treating canceroustumors. It had its first clinical trial at HarvardMedical School in 1937.

During World War II, the U.S. Navy com-missioned the production of five generators witha 2-million-volt capacity for use in the X-rayexamination of munitions. With the experienceof this work behind him, together with Trump,he was able to set up the High Voltage Engineer-ing Company (HVEC), in 1946, for the com-mercial production of generators. The companydeveloped the Van de Graaff generator for thewide variety of scientific, medical, and industrialresearch purposes it has today. Van de Graaff washonored with the Duddel Medal of the PhysicalSociety of Great Britain in 1947.

Numerous improvements of the generatorwere to follow. The tandem principle of particleacceleration, developed by LUIS W. ALVAREZ in1951, was incorporated into a tandem version ofthe Van de Graaff machine, in which the high-voltage terminal is able to accelerate the iontwice. In the late 1950s, Van de Graaff inventeda new insulating core transformer that generatedhigh currents by using magnetic flux rather thanelectrostatic charging. He also developed tech-niques of controlling beams during and afteracceleration, allowing physicists to adapt themfor specific research needs. The improved accel-erators yielded a mass of data on nuclear disinte-grations and reactions, which led directly toadvances in the theory of the atomic nucleus.

In 1960, he resigned from MIT in order todevote all his time to HVEC. He was awardedthe American Physical Society’s Tom W. BonnerAward in 1966 for his generator.

Van de Graaff, who died in Boston on themorning of January 16, 1967, at the age of 65,left a substantial legacy to modern science andtechnology. Since its invention in the early

1930s, the Van de Graaff generator has played avital role in many fields of physics, in astro-physics, and in medicine and industry.

Further ReadingBurrill, E. Alfred. “Van de Graaff, the Man and His

Accelerators,” Physics Today 2, no. 20 (February1967): 49–52.

Livingston, M. Stanley. Particle Accelerators: A BriefHistory. Cambridge, Mass.: Harvard UniversityPress, 1967.

� Van Vleck, John Housbrook(1899–1980)AmericanTheoretician, Solid State Physicist

John Housbrook Van Vleck, who developed thefirst complete quantum mechanical theory ofmagnetism in matter in the early 1930s, isknown as “the father of modern magnetism.” Heshared the 1977 Nobel Prize in physics withPHILIP WARREN ANDERSON and SIR NEVILL

FRANCIS MOTT for his fundamental theoreticalinvestigations of the electronic structure of mag-netism in the solid state of matter.

He was born on March 13, 1899, in Middle-town, Connecticut, into a family of scientists.As a child, John reacted to having a father whowas a professor of mathematics and a grandfatherwho was a professor of astronomy by rebellingagainst the academic tradition and vowing notto continue it. When his father accepted a posi-tion at the University of Wisconsin, the familymoved to Madison, where John attended publicschools.

He did his undergraduate work at the Uni-versity of Wisconsin and his graduate studies atHarvard University, where he took courses withPERCY WILLIAMS BRIDGMAN and Edwin C.Kemble. He wrote his dissertation, on the bind-ing energy of the helium atom, under Kemble,whom he described as “the one person in Amer-

Van Vleck, John Housbrook 313

ica at that time qualified to direct purely theo-retical research in quantum atomic physics,”and earned his doctorate in 1922. He had longbefore outgrown his “childish prejudices,” as hecalled them, and realized that he was best qual-ified for the life of a physicist in an academicenvironment.

For the next year Van Vleck served as aninstructor at Harvard; he then took a position asassistant professor at the University of Min-nesota, where he had the opportunity, rarelygiven to a new faculty member, of teaching onlygraduate courses. In 1927, he was promoted tofull professor and married Abigail Pearson; theirunion would last more than 50 years. The youngcouple then set out on a bit of academic wander-ing: in 1928, they moved to Wisconsin, whereVan Vleck was a professor of physics at his almamater and remained until 1934. During thisperiod, Van Vleck was a Guggenheim Founda-tion Fellow. In 1930, they moved to Harvard,where he did his groundbreaking work on mag-netism and published his classic work The Theoryof Electric and Magnetic Susceptibilities in 1932.

The focus of his long, illustrious career wasmagnetism and its relationship to the quantumtheory of atomic structure. As quantum wavemechanics was being developed in the early1930s, Van Vleck set out to understand its impli-cations for magnetism. As a result, he con-structed a theory, using ERWIN SCHRÖDINGER’swave mechanics, that offered a precise explana-tion of the magnetic properties of individualatoms in a series of chemical elements. He wenton to propose the notion of temperature-inde-pendent susceptibility in paramagnetic materi-als, that is, materials with small susceptibility tothe external magnetic field. This phenomenon,which came to be called Van Vleck paramag-netism, drew attention to the importance ofelectron correlation (the interaction betweenthe wave mechanical motion of electrons) in theappearance of localized magnetic moments (tinyquantum mechanical magnets in metals). His

former student Philip Anderson would furtherdevelop these ideas to explain how local mag-netic moments can occur in metals such as cop-per and silver, which in pure form are notmagnetic at all.

Van Vleck’s most important work was hisformulation of the quantum mechanics of chem-ical bonding in crystals, used for interpreting thepatterns of chemical bonds in complex com-pounds. This theory was able to explain themagnetic, electrical, and optical properties ofmany elements and compounds by consideringthe influences exerted on the electrons in partic-ular atoms by other atoms nearby. It gave the fol-lowing description of how a perturbing (foreign)ion or atom behaves in a crystal: at first the elec-trons of a perturbing ion feel the influence of theelectric field that is generated by the atomicnuclei and the electrons of the host crystal; then,through the action of its electrons, the perturb-ing ion enters into chemical bonding with itsenvironment. In this context he also found thata perturbing atom in a crystal could sometimesreplace a host atom without essential changes inthe surrounding lattice. However, under certaincircumstances the electronic structure of theperturbing atom is so incompatible with thesymmetry of the environment that it leads to alocal distortion of the lattice. This phe-nomenon, which later became known as theJahn–Teller effect, played an important role inthe development of the physics of the solid state.At age 78, Van de Graaff was awarded the NobelPrize in physics for this work.

During World War II, he worked on radar,discovering that water molecules in the atmo-sphere absorb radar waves with a wavelength ofabout 1.25 cm and that oxygen molecules have asimilar effect on 0.5-cm radar waves. This find-ing played an important role in the design ofeffective radar systems and later in microwavecommunication and radio astronomy.

In 1951, Van Vleck became Hollis Professorof Mathematics and Natural Philosophy at Har-

314 Van Vleck, John Housbrook

vard. He also served as Dean of Engineering andApplied Physics from 1951 to 1957. He tooksabbaticals from Harvard to serve as Lorentz Pro-fessor at Leiden University, Holland, in 1960,and as Eastman Professor at Oxford University,in 1962–1963. In 1969, when he retired, hebecame professor emeritus. He died in his sleepat his home in Cambridge, Massachusetts, onOctober 27, 1980, at the age of 81.

Van Vleck’s groundbreaking research on theelectronic structure of magnetism in the solid stateof matter led to the development of the laser, newindustrial uses of glass, and copper spirals used inbirth control devices. The quantum chemicalmethods have now become routine tools, particu-larly in inorganic chemistry, with importantextensions to molecular biology, medicine, andbiology. His research into molecular spectra andthe theoretical problems associated with their finestructure contributed to advances in radio astro-nomical investigations of molecular gases in space.

Further ReadingMailis, Norberto. The Quantum Theory of Magnetism.

Singapore: World Scientific, 2001.

� Veltman, Martinus J. G.(1931– )DutchQuantum Field Theorist, ParticlePhysicist

Martinus J. G. Veltman is a pioneer in the devel-opment of the quantum field theoretic gaugetheories of particle physics. He shared the 1999Nobel Prize in physics with his former student,GERARD ’T HOOFT, for work they did in 1971,which proved that the quantum field theoreticstructure of gauge theories, undergoing sponta-neous symmetry breaking interactions with aHiggs scalar field, was renormalizable. Veltman’sdevelopment of his “Schoonschip” symbolicmanipulation computer program, which alge-

braically simplified the complicated Feynmandiagrammatic equations found in quantum fieldtheories, was the foundation of this work.

Veltman was born on June 27, 1931, in thesmall town of Waalwijjk, in the south of theNetherlands, the fourth of what would becomea six-child family. Veltman considers himselfthe inheritor of both the practicality of hismother’s family of tradespeople and the stu-diousness of his father’s family of pedagogues.Veltman’s father was head of the local primaryschool, a comfortable position that exemptedhis family from the hardships of the Depressionyears. Veltman saw the German army marchingin, as they invaded his country in 1940, andremembers how they requisitioned his father’sschool for the billeting of soldiers. He was fondof playing with the ammunition left carelesslyabout by Allied troops but somehow survivedthis pastime, as well as the bombing of hishometown; the memory of that carnage wouldremain with him. Liberated in the fall of 1944,the southern part of the Netherlands escapedthe brutal winter of 1944–1945, in which manyDutch people died of hunger.

In the midst of the war, in 1943, Veltmanentered high school, where conditions, as heput it, “were marked by irregularities,” such asthe substitution of a horse stable for a more con-ventional classroom. During these years helearned about electronics from the localplumber and became the town radio repairman.But his academic performance declined as aresult of his lack of aptitude for foreign lan-guages. In 1948, at the age of 17, he narrowlypassed his final examinations.

Through the benevolent intervention of hishigh school physics teacher, Veltman’s parentswere persuaded to send him to the University ofUtrecht, a 90-minute commute from his home.He made the round trip regularly for three years,although the teaching of physics there, in the dif-ficult postwar years, when many physicists hadbeen killed or had left the country, was uninspir-

Veltman, Martinus J. G. 315

ing. He then moved to Utrecht, supporting him-self meagerly by typing lectures notes but gener-ally happy in his life of “mainly bummingaround.” He took five years, rather than the usualthree, to pass his candidate’s exam.

At this point, a revelation occurred to himin the form of a popular book on the theory ofrelativity—a subject that had not been touchedupon in his physics courses. He obtained a copyof ALBERT EINSTEIN’s The Meaning of Relativity,and from then on he was “hooked.” While sup-porting himself as a part-time teacher at a lowertechnical school, teaching physics to plumbers,he embarked on graduate studies in physics.

Veltman began studying experimental physicsbut soon realized that this was not his “real des-tiny.” He switched to theoretical work with LeonVan Hove in 1955 but was soon interrupted bytwo years of military service. When he returned tothe university in February 1959, Van Hove tookhim on as his Ph.D. student, despite his “relativelyadvanced age” of 27. Since Van Hove did statisti-cal mechanics and Veltman wanted to do particlephysics, he supplemented his education by attend-ing summer schools in Naples and Edinburgh.

In 1961, he followed Van Hove to the Euro-pean Center for Nuclear Research (CERN), inGeneva. He had married his wife, Anneke, in1960, and she remained in the Netherlands forthe birth of their daughter, Helene (who wouldone day do a thesis on particle physics at Berke-ley), before joining him. In Geneva, Veltmancompleted a dissertation on both unstable parti-cles and Coulomb corrections to the productionof vector bosons produced by neutrinos, whichearned him the Ph.D. from Utrecht in 1963.While at CERN, Veltman became deeplyinvolved with the neutrino experiments beingconducted there and was spokesperson for thegroup at the Brookhaven Conference in 1963.The experience left him with a lasting fascina-tion for experiments.

Veltman’s development of his “Schoonschip”symbolic computer program, while at the Stan-

ford Linear Accelerator (SLAC) in Stanford in1963, was a direct response to the frustration heand colleagues had felt at the work involved indoing error-free algebraic calculations for vectorboson production. He returned to CERN in 1964and remained there until just after the birth of hisson, Hugo, in 1966, after which he spent a shortperiod at the Brookhaven National Laboratory.

Veltman then returned to the University ofUtrecht, where he succeeded Van Hove as pro-fessor of theoretical physics and began buildingup the particle physics group, which thrivedunder his leadership. Hoping to alleviate his rel-ative isolation, he took over as editor of PhysicsLetters but quit after two years, oppressed by thelarge amount of “junk” he received and feltobliged to reject.

In the scholarly quiet of a one-month visitin April 1968 to Rockefeller University, Velt-man began the work he would successfully com-plete back at Utrecht, in 1971, with his doctoralstudent, Gerard ’t Hooft. When “Tini,” as every-one called Veltman, took ’t Hooft on as his stu-dent, the first material he gave him to study wasa 1950 paper by CHEN NING YANG and RobertMills, telling him, “This stuff you must know.”Yang and Mills had shown that the quantumelectrodynamic (QED) formalism developedearlier by JULIAN SEYMOUR SCHWINGER,RICHARD PHILLIPS FEYNMAN, and SIN-ITIRO

TOMONAGA could be generalized to includeinternal dynamic symmetries that were moregeneral than the standard spacetime C (charge),P (parity), and T (time-reversal) symmetries.

In the early 1960s, SHELDON LEE GLASHOW,ABDUS SALAM, and STEVEN WEINBERG used thisnew generalization of QED to unify the elec-troweak forces into one quantum field theoreticformalism. At the heart of their quest was thefascinating phenomenon of so-called brokensymmetries—asymmetric relations that havespontaneously arisen from the functioning ofsymmetrical laws (e.g., the asymmetric crystalstructure of ice that freezes out from the sym-

316 Veltman, Martinus J. G.

metric liquid structure of water when the tem-perature becomes low enough)—that seem topermeate matter.

They were aware that in the early 1960s PeterHiggs had published papers demonstrating thatspontaneous symmetry breaking events associatedwith coupling to a scalar field could create newkinds of force-carrying particles, some of themmassive. This led them to speculate that if the vir-tual particles that carry the electromagnetic andweak forces (known collectively as the intermedi-ate vector boson W and Z particles) were relatedby such a broken symmetry, it might be possible toestimate their masses in terms of the unified, moresymmetrical force from which the two forces werethought to have arisen. Working independently,each constructed a unified quantum field theoryof electromagnetic and weak interactions (i.e., aquantum electroweak theory) that could make averifiable prediction of the approximate masses ofthe triplet W and singlet Z particles needed todescribe the weak interactions. However, at first,physicists ignored the electroweak theory, which,when used to calculate the properties of the Wand Z particles and other physical quantities, pre-dicted nonsensical infinite results.

Meanwhile, in the Netherlands, Veltmanhad not given up hope of renormalizing theorieslike the electroweak theory. Twenty years earlier,Feynman had systematized the calculation prob-lem with his diagrams. Veltman hoped to find away of renormalizing the theory by using“Schoonschip,” which was capable of perform-ing algebraic simplifications of the complicatedexpressions that all quantum field theories resultin when quantitative calculations are made.When ’t Hooft chose a topic for his Ph.D. thesisin 1969, he chose to apply himself to the prob-lem Veltman was working on: renormalization ofthe so-called Yang–Mills non-Abelian gaugefield theories, which at the time were beingapplied to the study of the weak interactions.

In 1971, ’t Hooft succeeded in this task andpublished two articles describing his break-

through. However, it was the second paper, inwhich he renormalized massless Yang–Millsfields for theories by using Higgs spontaneoussymmetry breaking mechanism to generate themasses of the fields, that attracted world atten-tion. After using Veltman’s computer program toverify ’t Hooft’s results, the two men were able towork out a detailed calculation of the renormal-ization method. Using spontaneous symmetrybreaking, the renormalized non-Abelian gaugetheory of electroweak interaction was now afunctioning theoretical machinery capable ofperforming precise calculations. They presentedtheir results at a 1971 international particlephysics conference in Amsterdam.

The impact was enormous. From 1971 on,all theories for the weak interactions that wereproposed were Yang–Mills theories that usedspontaneous symmetry breaking, and over thenext decade it became clear that the Glashow,Weinberg, and Salam’s model was correct. Thedecisive experiments were first made by CARLO

RUBBIA and his team at CERN in 1981. Twoyears later, in 1983, they announced the discov-ery of the triplet W and singlet Z particles,which was based on signals from detectors spe-cially designed for this purpose.

Veltman and ’t Hooft went on to calculatethe mass of the top quark, the heavier of the twoquarks in the third family of the Standard Model.Many years later, in 1995, the top quark wasobserved directly for the first time at the FermiLaboratory in Batavia, Illinois. Another highlyimportant element of the model is the existenceof a massive Higgs particle responsible for thespontaneous symmetry breaking, which has notyet been observed. Physicists hope that the LargeHadron Collider (LHC), to be completed atCERN around 2005, will succeed in finding it.

As Veltman and ’t Hooft both moved on todifferent research interests, their collaborationdissolved. Then, in 1981, after spending a sab-batical at the University of Michigan in AnnArbor, Veltman decided to accept the univer-

Veltman, Martinus J. G. 317

sity’s offer to remain there. From 1981 to 1996,Veltman occupied the John D. and CatherineMacArthur Chair, working on gauge theoriesand their applications to elementary particlephysics. In particular he studied radiative correc-tions in the Standard Model, the Higgs sectorand its relationship to the vacuum structure inquantum field theories, and the implications forphenomenology and for new physics beyond theStandard Model. While in the United States, heserved on experiment-planning committees atthe big laboratories—SLAC, Brookhaven, andthe Fermi Laboratory in Batavia, Illinois.

Upon retiring in 1996, Veltman becameprofessor emeritus at Michigan and retired withhis wife to the town of Bilthoven in the Nether-lands, where they had previously lived.

Veltman’s landmark achievement made itpossible for physicists to use gauge theories tomake specific predictions of particle propertiescapable of experimental verification. Ulti-mately, it was the tool that validated the Wein-berg–Glashow–Salam electroweak theory.

See also BETHE, HANS ALBRECHT; DYSON,FREEMAN; GELL-MANN, MURRAY

Further Reading’T Hooft, Gerard. In Search of the Ultimate Building

Blocks. Cambridge: Cambridge University Press,1997.

Veltman, Martinus J. G. “The Higgs Boson.” ScientificAmerican 259, no. 9 (November 1986): 88–94.

� Volta, Alessandro Guiseppe AntonioAnastasio(1745–1827)ItalianExperimental Physicist (ClassicalElectromagnetism)

Alessandro Volta was the pioneer in the field ofelectricity who built the voltaic pile, the fore-runner of the modern electric battery. In a

famous debate with Luigi Galvani, he success-fully argued that the source of the electric cur-rent generated when metals are brought intocontact with the muscles of a frog are the metalsrather than the frog. An ingenious experi-menter, he also invented the electrophorus, adevice for producing charges of static electricity.

He was born in Como, in Lombardy, Italy,on February 18, 1745, into a noble family. Whenyoung Alessandro failed to develop speech untilthe age of four, his family was sure he was intel-lectually impaired. By age seven, however, whenhis father died, he had caught up to his agegroup. Educated at religious schools, he showedan early aptitude for science, and when he was14, he decided to become a physicist. The theoryof electricity, which he learned about by study-ing the work of Benjamin Franklin, so entrancedhim that he composed an excellent Latin poemon the subject. At the age of 20, he began exper-imenting with static electricity. His renown as ascientist grew rapidly, leading to his appoint-ment in 1774 as principle of the gymnasium inComo, where, the next year, became a professorof experimental physics.

Volta’s work on static electricity culminatedin 1775, with his invention of the electrophorus.His extensive knowledge of the nature andquantity of electrostatic charge generated by dif-ferent materials enabled him to develop a fairlysimple device for the production of charges: itconsisted of one metal plate covered withebonite and a second metal plate with an insu-lated handle. The ebonite-covered plate isrubbed and given a negative electric charge. Ifthe plate with a handle is placed over it, a posi-tive electric charge is attracted to the lower sur-face, a negative charge repelled to the upper.The negative charge is built up in the plate withthe handle. Today’s electrical condensers arebased on this type of charge-accumulatingmachine. Volta also realized from his electro-static experiments that the quantity of chargeproduced is proportional to the product of its

318 Volta, Alessandro Guiseppe Antonio Anastasio

electrostatic potential, which he measured withan electrometer of his own invention, and thecapacity of the conductor.

At this point, Volta’s interests veeredtoward the study of air and gases. By isolatingand examining the properties of marsh gas foundin Lake Maggiore (adjacent to Lake Como), hediscovered methane. In another study, he accu-rately estimated the proportion of oxygen in theair by exploding air with hydrogen to removethe oxygen. Volta would return to these investi-gations 20 years later, making the discovery thatthe vapor pressure of a liquid depends only ontemperature and is independent of atmosphericpressure, a principle that the British chemist andphysicist John Dalton would later enunciate inhis law of partial pressures.

However substantial these achievements,they were only a digression in Volta’s pursuit ofthe mysteries of electricity. In 1778, he trans-ferred his laboratory from Como to Padua, wherehe accepted a position as professor of experimen-tal physics. He would remain in Padua until1819, surviving the conflict between Austriaand France that engulfed the region. His consid-erable political acumen enabled him to hang onto his position no matter who was in charge andcarry on his scientific work.

Volta’s path to his great discovery began in1791, when his friend Luigi Galvani sent him hispapers describing some interesting results: Gal-vani had produced contractions in the musclesof dead frogs by placing two different metals(brass and iron) into contact with the muscleand with each other. Galvani believed that thecontractions had their source in the frogs’ mus-cles. Volta was not so sure. He successfullyrepeated Galvani’s experiments, using differentmetals and different animals, and concludedthat the source of the electricity lay in the junc-tion of the metals. In the ensuing controversybetween the two Italians, the French physicistCHARLES AUGUSTIN COULOMB was a strongadvocate of Volta’s position, which prevailed as

evidence in its favor accumulated. This includedan experiment in which Volta placed the metalson his tongue and produced an unpleasant sen-sation. He attributed this effect to electricity andwent on to compose a list of metals in order oftheir electricity production, based on thestrength of the sensation they made on histongue. In this way, he derived what came to beknown as the electromotive series, the arrange-ment of chemical elements in order of their stan-dard electrode potentials.

From here, it would be but a brief step to hisdiscovery of the voltaic pile. In 1796, attemptingto measure the electricity produced by differentmetals, he tried piling disks of metals on top ofone another and found that they had to be sepa-rated by a moist conductor to produce a current.His work was disrupted by political upheavals,but by 1800 he had created his prototype of themodern electric battery. In that year he wrote tothe president of the Royal Society, Joseph Banks,to describe two arrangements of conductors thatproduced an electric current. One was a pile ofsilver and zinc disks separated by cardboardmoistened with brine, the other was a series ofglasses of salty or alkaline water in whichbimetallic curved electrodes were dipped. Thiswas the first electric battery.

Volta’s breakthrough, which meant thathigh electric currents could now be produced,was greeted with immense excitement. Voltatraveled to Paris in 1801 to demonstrate his dis-coveries to Napoleon, who, duly impressed,made him a count and awarded him a pension.He was the recipient of many honors, includingmembership in England’s Royal Society, whichhonored him with its Copley medal and decora-tion by the Legion of Honor. In 1810, he wasmade a senator of the kingdom of Lombardy andgiven the title of count. Volta retired in 1819.On March 5, 1827, he died in Como.

Volta’s invention of the battery signaled thebeginning of a century of discoveries, whichwould establish the dynamics of electricity and

Volta, Alessandro Guiseppe Antonio Anastasio 319

electromagnetism and harness their power inways that would transform civilization. The unitof electric potential, or electromotive force, isnamed the volt in his honor.

Further ReadingPera, Marcello, and Jonathan Mandelbaum. The Gal-

vani–Volta Controversy on Animal Electricity.Princeton, N.J.: Princeton University Press, 1992.

320 Volta, Alessandro Guiseppe Antonio Anastasio

321

W� Weber, Wilhelm Eduard

(1804–1891)GermanExperimentalist (ClassicalElectromagnetism)

Wilhelm Eduard Weber was an ingenious exper-imentalist who made vital contributions to elec-tromagnetism. With the highly sensitiveapparatus he developed he found new ways tomeasure electricity and magnetism and to defineelectric and magnetic units. He is also remem-bered as the first physicist to propose that elec-tricity consists of charged particles.

He was born in Wittenberg, Saxony (nowGermany), on October 24, 1804, into a distin-guished family. His father was professor of theol-ogy at the University of Wittenberg; his olderbrother, Ernst, would become a seminal figure indeveloping the physiology of perception. WhenWilhelm was 10, the family moved to Halle,where he would enter the university eight yearslater. After receiving his doctorate in 1826, hestayed on at Halle, at first as a lecturer and later,from 1828 to 1831, as an assistant professor. Hethen accepted a position as full professor at theUniversity of Göttingen, where he met themathematician and physicist JOHANN CARL

FRIEDRICH GAUSS. Their collaboration markedthe beginning of Weber’s work on magnetism.

Gauss and Weber created absolute units ofmagnetism, defined in terms of length, mass, andtime. Working on his own, Weber built highlysensitive magnetometers, as well as a 3-km tele-graph to connect his physics laboratory toGauss’s at the astronomical observatory. InGauss’s and Weber’s hands, this first workingtelegraph was used for scientific, rather thancommercial, purposes: to connect a network ofobservation stations in order to correlate mea-surements of terrestrial magnetism made in dif-ferent parts of the world.

Political events disrupted Weber’s academiclife. In 1837, when Queen Victoria came topower, her uncle became the new ruler ofHanover and promptly suspended the constitu-tion. Weber was one of seven professors who for-mally protested the action, all of whom werefired. He stayed in Göttingen, pursuing hisresearch, until he was offered a professorship inLeipzig. Under these circumstances, hebranched out into the measurement of electric-ity, defining an electromagnetic unit for electriccurrent that was applied to measurements of cur-rent made by the deflection of a galvanometer.

Eventually, in 1849, he regained his positionin Göttingen; he would remain there until hisretirement in the 1870s. His later work therefocused on electrodynamics and the electricalstructure of matter.

In 1855, Weber studied the ratio betweenthe electrodynamic and electrostatic units ofcharge. Weber calculated this ratio as 3.1074 ×108 m/s; however, he did not understand thephysical implications of the fact that this ratiowas close to the speed of light. It would fall toJAMES CLERK MAXWELL, in creating his electro-magnetic theory of light, to realize that thisimplied that light waves were time-dependentelectromagnetic fields traveling through space ata speed equal to the ratio Weber had found.

During his later years, Weber focused onresearch in electrodynamics and the electricalstructure of matter. After his death in Göttingenon June 23, 1891, Weber’s name was given to thestandard international unit of magnetic fluxdensity, the weber, in recognition of his pioneer-ing work in electromagnetism.

Further ReadingKoch Torres Assis, André. Fundamental Theories of

Physics. Vol. 66. Weber’s Electrodynamics. Dor-drecht, Netherlands: Kluwer Academic, 1994.

� Weinberg, Steven(1933– )AmericanTheoretical Physicist, Quantum FieldTheorist, Particle Physicist,Astrophysicist

Steven Weinberg is a giant of contemporaryphysics, a theorist with broad research interestswhose most notable work has been in unifiedfield theory. In 1967, he hypothesized that quan-tum electrodynamics can be generalized into aform that allows the electromagnetic and weakforces to be unified into a single electroweakquantum field theory at extremely high energylevels. When his theory was confirmed by parti-cle accelerator experiments in 1983, physicsmoved significantly closer to the goal of finding“the theory of everything,” a single quantum field

theory to describe nature’s basic forces. For thiswork, Weinberg shared the 1979 Nobel Prize inphysics with SHELDON LEE GLASHOW and ABDUS

SALAM, who independently developed similarversions of the same ideas.

Steven was born on May 3, 1933, in theBronx, New York City, to Frederick Weinbergand Eva Weinberg, who had lost much of herfamily in Germany during the Holocaust.Encouraged by his father, who was a courtstenographer, and by his teachers at the BronxHigh School of Science (where SheldonGlashow was his close friend) to follow hisinnate interest in science, he already knew atage 16 that he was heading for a career in theo-retical physics. Far from one-sided, however, hegrew up listening to classical music, a love hewould retain all his life.

Weinberg attended Cornell University,where he met his future wife, Louise, anotherCornell undergraduate, who would eventuallybecome a lawyer. The couple was married in1954, the year Weinberg graduated. He beganhis life as a researcher the following year, atwhat is now the Niels Bohr Institute in Copen-hagen, working with David Frisch. After hisreturn to the United States, he enrolled atPrinceton University to complete his graduatestudies. Working under Sam Treiman, he wrotehis doctoral thesis on the application of renor-malization theory to the effects of strong inter-actions in weak interaction processes andreceived his Ph.D. in 1957.

His first position was at Columbia Univer-sity, where he stayed for only two years beforemoving to the University of California, Berke-ley. In 1963, his daughter, Elizabeth, was born.For the next few years, he worked on a broadspectrum of problems, including high-energybehavior of Feynman graphs, second-class weakinteraction currents, broken symmetries, scat-tering theory, and muon physics. Highly stu-dious and self-disciplined, Weinberg writes that,in many cases, he chose a problem “because I

322 Weinberg, Steven

was trying to teach myself some area of physics.”In the early 1960s, he first became interested inastrophysics; he wrote papers on the cosmicpopulation of neutrinos and began his bookGravitation and Cosmology, which he wouldcomplete in 1971. Late in 1965, he began towork on current algebra and the application tostrong interactions of the idea of spontaneoussymmetry breaking.

The following year, Weinberg left Berkeleyon what was to be a leave of absence but turnedout to be a final break. From 1966 to 1969, hewas Loeb Lecturer at Harvard University andthen visiting professor at the MassachusettsInstitute of Technology (MIT), where, in 1969,he accepted a professorship in the physicsdepartment under the chairman Victor Weis-skopf. In 1967, at MIT, he did his groundbreak-ing work, turning his previous studies of brokensymmetries, current algebra, and renormaliza-tion theory in the direction of the unificationof weak and electromagnetic interactions.

Weinberg’s starting point was the innova-tive work of CHEN NING YANG and Robert Mills.In 1950, they had shown that the quantum elec-trodynamic (QED) formalism developed earlierby JULIAN SEYMOUR SCHWINGER, RICHARD

PHILLIPS FEYNMAN, and SIN-ITIRO TOMONAGA

could be generalized to include internal dynamicsymmetries that were more general than thestandard spacetime C (charge), P (parity), and T(time-reversal) symmetries. In terms of these so-called non-Abelian Yang–Mills gauge theorieswith internal symmetries, Weinberg’s quest wasto find the hidden symmetry of the apparentasymmetries that occurred in particle physics.He would later write:

Nothing in physics seems so hopeful tome as the idea that it is possible for atheory to have a very high degree ofsymmetry, which is hidden from us inordinary life. The physicist’s task is tofind this deeper symmetry.

He was fascinated by the fact that naturewas replete with so-called broken symmetries—asymmetric relations that have spontaneouslyarisen from the functioning of symmetrical laws(e.g., the asymmetric crystal structure of ice thatfreezes out from the symmetric liquid structure ofwater when the temperature becomes lowenough).

Weinberg was aware that in the early 1960sPeter Higgs had published papers demonstratingthat spontaneous symmetry breaking eventscould create new kinds of force-carrying parti-cles, some of them massive. This led Weinbergto speculate that if the virtual particles that carrythe electromagnetic and weak forces (known

Weinberg, Steven 323

Steven Weinberg discovered that quantumelectrodynamics could be generalized into a form thatallowed the electromagnetic and weak forces to beunified in a single electroweak quantum field theory atextremely high energy levels. (AIP Emilio Segrè VisualArchives)

collectively as the intermediate vector boson Wand Z particles) were related by a broken sym-metry, these new theoretical ideas might make itpossible to estimate their masses in terms of theunified, more symmetrical force from which thetwo forces were thought to have arisen.

First Weinberg tried, unsuccessfully, to applythe new theoretical ideas of symmetry breakingto the strong force, but he soon realized that thedescriptions emerging from his equations—oneset massless, the other massive—resemblednothing related to the strong force but fit per-fectly with the particles that carry the weak andelectromagnetic forces. The massless particlewas the photon, carrier of electromagnetism; themassive particles were the W’s and the Z’s, carri-ers of the weak force. By accident, Weinberg hadfound a unified quantum field theory of electro-magnetic and weak interactions (i.e., a quantumelectroweak theory) that could make a verifiableprediction of the approximate masses of therequired triplet W and the singlet Z particlesneeded to describe the weak interactions. Thefollowing year, Salam independently made thesame finding.

However, over the next four years, Wein-berg’s unified theory attracted scant attentionsince, unlike quantum electrodynamics, hiselectroweak theory had not yet been shown tobe renormalizable, that is, capable of beingaltered by a mathematical procedure that can-cels the unwanted infinities in a quantum fieldtheory by introducing the appropriate renor-malization constants. But, in 1971, the Dutchphysicist GERARD ’T HOOFT used computer alge-bra techniques to prove that Weinberg’s elec-troweak theory was indeed renormalizable.After this development, the attention of thephysics community shifted to testing the elec-troweak theory. In 1973, Weinberg acceptedSchwinger’s recently vacated chair as HigginsProfessor of Physics at Harvard, together withan appointment as Senior Scientist at theSmithsonian Astrophysical Observatory. Dur-

ing the 1970s, he worked primarily with theimplications of the unified theory of weak andelectromagnetic interactions, development ofthe related theory of strong interactions knownas quantum chromodynamics, and the unifica-tion of all interactions.

Although decisive experimental confirma-tion would not be found until 1983, Weinberg,Salam, and Glashow shared the 1979 NobelPrize for their theoretical breakthrough. Twoparticle accelerator teams at the EuropeanCenter for Nuclear Research (CERN) and theFermi Laboratory in Batavia, Illinois, raced totest the predictions of the electroweak theory.The CERN team under Paul Musset found theneutral currents associated with the singlet Zparticle, but these results were inconclusive,since other competing theories of the weakinteractions could predict the existence ofthese particles.

Finally, in 1981, CARLO RUBBIA, workingwith Simon Van der Meer, Guido Petrucci, andJacques Gareyte at CERN, did the decisive exper-iment and found the triplet W and singlet Z par-ticles characteristic of Weinberg’s electroweaktheory. His team used a new type of collidingbeam machine built with intersecting storagerings in which a beam of protons and antiprotonscounterrotate and collide head-on. The teamdeveloped techniques for creating antiprotons,confining them in a concentrated beam and col-liding them with an intense proton beam.

Hundreds of scientists were involved inthese experiments in teams throughout theworld. The first collisions were observed in1981. In 1983, Rubbia and collaborating teamsof scientists announced the discovery of thetriplet W and singlet Z particles, which wasbased on signals from detectors speciallydesigned for this purpose.

In 1982, Weinberg moved to the physicsand astronomy departments of the University ofTexas at Austin, where he currently holds theJosey Regental Chair of Science, and founded its

324 Weinberg, Steven

theory group. His wife, Louise Weinberg, alsojoined the university, as a professor of law. Hewas extremely active in the lobbying campaignfor a multibillion-dollar Superconducting Super-collider to be located near Waxahachie, Texas,which Congress killed in 1993.

Weinberg is a prolific author and fine prosestylist, who was recently in 2000 awarded theLewis Thomas Prize, given to the researcher whobest embodies “the scientist as poet.” His booksfor general readers include the prize-winningThe First Three Minutes (1993), which has beentranslated into 22 languages; The Discovery ofSubatomic Particles; Dreams of a Final Theory(1993); and most recently Facing Up: Science andIts Cultural Adversaries (2001). He has also writ-ten many books for specialists, such as TheQuantum Theory of Fields, volume 1, Founda-tions, and volume 2, Modern Applications (2000),and Elementary Particles and the Laws of Physics,with Richard Feynman.

An outspoken atheist, Weinberg wasawarded the 1999 Emperor Has No ClothesAward from the Freedom from Religion Founda-tion and the 2002 Humanist of the Year Awardfrom the American Humanist Foundation. ForWeinberg, a redemption of sorts lies not in reli-gion, but in the scientific endeavor:

The effort to understand the universe isone of the very few things that liftshuman life above the level of farce, andgives it some of the grace of tragedy.

Weinberg’s discovery of the electroweaktheory became the precursor to what is knowntoday as the Standard Model of the strong andelectroweak interactions, which uses a combina-tion of three symmetry principles to unify theelectromagnetic, weak, and nuclear forces intoone renormalizable quantum field theoretic for-malism. Weinberg is today’s foremost proponentof the idea that physicists are moving towardgeneralizing the Standard Model into the formu-

lation of the long-sought “final theory” that willunify all particles and fundamental forces ofnature in the context of a single universal sym-metry principle.

See also GELL-MANN, MURRAY; LEE, TSUNG-DAO; WU, CHIEN-SHIUNG.

Further ReadingWeinberg, Steven. Dreams of a Final Theory: The Sci-

entist’s Search for the Ultimate Laws of Nature.New York: Vintage Books, 1993.

———.Facing Up: Science and Its Cultural Adver-saries. Cambridge, Mass.: Harvard UniversityPress, 2001.

———.The First Three Minutes: A Modern View of theOrigin of the Universe. New York: Basic Books,1977.

� Wheeler, John Archibald(1911– )AmericanQuantum Theorist, Particle Physicist,Relativist, Astrophysicist

John Archibald Wheeler has worked at the cut-ting edge of theoretical physics for more thanfive decades. The scope of his research and con-tributions to the main fields of modern physicshas been amazing. He was directly involved inthe theoretical development of the atomicbomb. With his student RICHARD PHILLIPS

FEYNMAN, he reformulated the theory of elec-tricity and magnetism with insights aboutcharged particles moving backward and for-ward in time. When he turned his attention toALBERT EINSTEIN’s general theory of relativity,he single-handedly reversed the opinion ofmost physicists that general relativity was irrel-evant to all but a few minor features of physicalreality. He coined the term black hole and con-tributed to the understanding of this bizarrecosmic phenomenon. In his later yearsWheeler made a bold attempt to unify the the-

Wheeler, John Archibald 325

ory of relativity with the measurement processin quantum mechanics.

Wheeler was born on July 9, 1911, in Jack-sonville, Florida, the son of two librarians. Notsurprisingly, then, it was the reading of sciencebooks when he was a boy that first aroused hisinterest in science. He attended Baltimore CityCollege and went on to Johns Hopkins Univer-sity, in Baltimore, Maryland, which awarded hima Ph.D. in 1933, when he was only 21. The fol-lowing year he married an old acquaintance,Janette Hegner, after only three dates. He thenserved one-year apprenticeships with GregoryBreit at New York University and with NIELS

HENRIK DAVID BOHR, the father of quantummechanics, at Bohr’s institute in Copenhagen.Then followed three years of teaching physics atthe University of North Carolina. In 1938, hejoined the faculty of Princeton University,where, apart from numerous leaves of absence, hewould spend the greater part of his long career.

In 1939, Bohr visited the United States andasked Wheeler to collaborate with him on aproblem of considerable interest. That year, LISE

MEITNER and Otto Frisch, interpreting puzzlingresults obtained by Otto Hahn and Fritz Strass-mann, had discovered nuclear fission, launchingthe field of fission physics. But a solid theoreticalunderpinning for the phenomenon was stillmissing. Bohr and Wheeler’s highly compatiblebrainstorming resulted in publication of thepaper “The Mechanism of Nuclear Fission”(1939), in which they explained fission in termsof a liquid-drop model. In this theory, a slowneutron entering a uranium-235 nucleus mod-eled in terms of a liquid drop caused it to split asa drop of liquid into two smaller drops represent-ing the nuclei of a tellurium-137 atom and a zir-conium-97 atom, while emitting two neutrons.The energy released by this type of reactionformed the basis of nuclear fission theory.

Wheeler later recalled, “Like most physi-cists, I was interested in nuclear fission for whatit revealed about basic science, not for what it

might have to do with reactors or bombs.” Nev-ertheless, his work with Bohr proved extremelyimportant to the Manhattan Project, singlingout uranium-235 for use in the development ofan atomic bomb. After the Japanese attack onPearl Harbor, Wheeler worked at the Metallur-gical Laboratory at the University of Chicago,where he identified and proposed countermea-sures to the problem of reactor poisoning, and inRichmond, Washington, where he was involvedin the development of the giant nuclear reactorsat nearby Hanford, designed to produce pluto-nium for atomic weapons. Despite these contri-butions, having lost his younger brother, Joe, inthe final year of World War II, he always regret-ted that neither he nor the United States haddone more to accelerate the production of thefirst atomic bomb.

After the war, Wheeler worked with hisgraduate student Richard Feynman and returnedto an earlier research interest on the problem ofrelativistic action at a distance. The conceptstruck him as a simpler, more satisfying descrip-tion of electrodynamics than the standard fieldtheory of electrodynamics, which assigned “sub-stance” to electric and magnetic fields existingin space. The resulting theory published in 1945became known as Wheeler–Feynman electrody-namics. It was based on the amazing idea, sug-gested by Wheeler to Feynman in one of theirmany conversations, that the theory of relativ-ity allowed the possibility that the electrody-namic interaction between charged particlesmight be able to propagate both backward andforward in time.

Later in the early 1950s, while on a sabbati-cal in Paris, Wheeler responded to a call from hisgood friend EDWARD TELLER and joined theeffort to develop the hydrogen bomb at LosAlamos. From 1951 to 1953, he was director ofPrinceton’s Project Matterhorn, which was insti-tuted in order to design thermonuclear weapons.

Returning to academia after the successfulconclusion of the hydrogen bomb project in the

326 Wheeler, John Archibald

late 1950s, Wheeler delved into Einstein’s gen-eral theory of relativity, which was based on theradical idea that the force of gravity was due tothe warping or curvature of the geometry ofspacetime caused by the presence of mass–energy. He was appalled by the prediction, con-tained in the theory’s equations, that a dead starcould collapse into a mass so dense that not evenlight could escape from it, leading it eventuallyto be squeezed out of existence. The final state ofthis collapsed stellar object had the bizarre prop-erty that at its center there existed a singularitywhere spacetime would be infinitely curved. Atthis point, as Wheeler would say, “smoke poursout of the computer.”

In 1956, Wheeler studied articles by SUBRA-MANYAN CHANDRASEKHAR, LEV DAVIDOVICH

LANDAU, J. ROBERT OPPENHEIMER, and GeorgeVolkoff on the collapse of dead stars, hoping tocontinue their investigations. He set himself thetask of comprehending all “cold dead matter,”matter that had completely burned its nuclearfuel, and, with his student B. Kent Harrison,worked out the equation of state for such matter.In the process of doing so, he revived interest ingeneral relativity, which had been neglectedbecause it could not be tested in the lab, and madePrinceton the center of research in the field.

During the same period, in his bookGeometrodynamics (1962), he studied the inter-action of gravitational and electrodynamic fieldsin general relativity, developing the radical con-cept of geons, concentrations of electromagneticradiation energy so intense that they are heldtogether by their own gravity.

In the following years Wheeler continued toresist the idea of a final state of stellar collapse withits inherent spacetime singularity. Nonetheless, heeventually accepted the idea and, in 1967, calledit by the name for which it is now famous, a blackhole. During this period, Wheeler also formulatedthe “no-hair” theorem, which states that blackholes are “bald”: that is, their only known physicalproperties are their mass, charge, and angular

momentum. He derived a harsh lesson from thiswork, noting in his 1998 autobiography that theblack hole “teaches us that space can be crumpledlike a piece of paper into an infinitesimal dot, thattime can be extinguished like a blown-out flame,and that the laws of physics that we regard as‘immutable’ are anything but.”

In analyzing the connection betweenquantum mechanics and general relativityWheeler thought that this kind of breakdownof physics was not limited to dead, distant stars,because even spacetime was subject to theuncertainty principle. Ultimately, it, too, wasdiscontinuous, dissolving into a chaos ofunconnected points and wormholes, whatWheeler called quantum foam.

Wheeler, John Archibald 327

John Archibald Wheeler single-handedly reversed theopinion of most physicists that Albert Einstein’s generaltheory of relativity was irrelevant to all but a few minorfeatures of physical reality. (AIP Emilio Segrè VisualArchives)

In 1976, he took a 10-year leave fromPrinceton, where he was Joseph Henry Professorof Physics, to become director of the Center forTheoretical Physics at the University of Texas,Austin. There he returned to the study of quan-tum theory, which he regarded as a greater chal-lenge than relativity for the 20th century. Oneidea he explored with his Texas colleagues wasthe notion that the universe is a giant computerand that quantum theory can somehow bederived from information theory.

In 1978 Wheeler proposed a “delayedchoice” double-slit experiment, successfullycarried out in 1984, in which a difference inwhat one measures on a photon now makes anirretrievable difference in what one has theright to say the photon already did in the past.Specifically, in a delayed choice double-slitexperiment, in which photons pass throughtwo slits and create an interference pattern, theexperimenter could wait until after the photonhad passed the slits to determine which detec-tor to employ and thus determine whether ithad been a particle or a wave in the past.Wheeler called this process in which the physi-cist observer acting in the present would beparticipating in creating the past of the photonobserver-participancy. On hearing about thesuccess of the experiment he claimed:

The experimental verdict is in: theweirdness of the quantum world is real,whether we like it or not. . . . The verybuilding blocks of the universe are theseacts of observer-participancy. Youwouldn’t have the stuff out of which tobuild the universe otherwise. The par-ticipatory principle takes for its founda-tion the absolutely central point of thequantum: No elementary phenomenonis a phenomenon until it is an observed(or registered) phenomenon.

In 1979, he became the center of a pro-longed controversy, when he called for the

expulsion of the recently admitted parapsychol-ogists from the American Association for theAdvancement of Science. For Wheeler, whobelieved that a phenomenon must be observedto be taken seriously, parapsychology had pro-duced no hard results and was unworthy of mem-bership in a respectable scientific society.

Wheeler was a beloved teacher, character-ized by former students as a physicist who wasnever afraid to think about Really Big Questionsand who “brought the fun back into physics.”He is equally gifted in explaining complex ideasin simple language. His much-praised booksinclude Spacetime Physics with Edwin Taylor(1963 and 1992); Gravitation Theory and Gravi-tational Constants (1965); Einstein’s Vision(1968); Gravitation, with his former students KipThorne and Charles Misner (1973); Frontiers ofTime (1979); Quantum Theory and Measurement(1983); A Journey into Gravity and Spacetime(1990); At Home in the Universe (1993); andExploring Black Holes with Edwin Taylor (2000).

Personally modest, Wheeler is possessed of acontagious enthusiasm and charming informal-ity. He is a scientist–philosopher, whose thoughtshave ranged from the smallest microstructure tothe largest structures in the cosmos. He createdthe phrase “the gates of time,” to express thebeginning of the cosmos (the big bang) and itsending (the big crunch).

Married for more than 67 years, John andJanette Wheeler have three children, eightgrandchildren, and nine great-grandchildren.The establishment of a chair in his name atPrinceton commemorated his 90th birthday.After heart surgery in 1986, Wheeler moved to aretirement home near Princeton. At age 91, hecommuted to his office at Princeton twice aweek; there he dictated to his secretary his stilllively thoughts about the nature of the cosmos.In a 2002 interview he said:

The creation question is so formidablethat I can hardly hope to answer it in

328 Wheeler, John Archibald

the time left to me. But each Tuesdayand Thursday I will put down the bestresponse that I can, imagining that I amunder torture.

Believing that “We will understand howsimple the universe is when we recognize howstrange it is,” Wheeler continues to explore ideasthat would intimidate less adventurous minds.

See also GAMOW, GEORGE; HAWKING,STEPHEN.

Further ReadingAczel, Amir D. Entanglement: The Greatest Mystery in

Physics. New York: Four Walls Eight Windows,2002.

Thorne, Kip S. Black Holes and Time Warps: Einstein’sOutrageous Legacy. New York and London: W.W. Norton, 1994.

Wheeler, John Archibald, with Kenneth Ford. Geons,Black Holes, and Quantum Foam: A Life inPhysics. New York: W. W. Norton, 1998.

� Wien, Wilhelm (Carl Werner OttoFritz Franz)(1864–1928)PrussianTheoretical and Experimental Physicist(Electrodynamics, Thermodynamics)

Wilhelm Wien is most famous for his contribu-tions to the study of blackbody radiation. Hisformulation of a displacement law for radiationemitted by a perfectly efficient blackbody earnedhim the 1911 Nobel Prize in physics and leddirectly to MAX ERNEST LUDWIG PLANCK’s dis-covery of quantum theory.

Wilhelm Wien was born a landowner’s sonat Gaffken, East Prussia (now Poland), on Jan-uary 13, 1864, and seemed destined for the life ofa gentleman farmer. He received his secondaryschooling in Rasternburg and Konigsberg, fol-lowed by university studies, from 1882 to 1886,

mainly at the University of Berlin, where he wasa student of HERMANN LUDWIG FERDINAND VON

HELMHOLTZ; he also studied briefly in Göttingenand Heidelberg. In 1886, he was awarded hisPh.D. for an experimental thesis on the diffrac-tion of light on sections of metals and the influ-ence of materials on the color of refracted light.When his father became ill, he returned home tomanage the family estate. But in 1890, wheneconomic problems led to its sale, Wienreturned to Berlin, where he resumed his scien-tific work as an assistant to Helmholtz.

In Berlin, in 1893, he extended the theoriesof LUDWIG BOLTZMANN, who in 1884 haddeduced a law for the total energy emitted by ablackbody, that is, a surface that absorbs all radi-ant energy impinging on it. Since a perfect black-body does not exist in nature, Wien devised amethod to create a good approximation of oneexperimentally, by using an oven with a tiny pin-hole. Any radiation entering the pinhole wouldbe scattered and reflected from the inner walls ofthe oven so often that nearly all incoming radia-tion would be absorbed and the chance of some ofit finding its way out of the hole again would beextremely small. Thus the radiation emergingfrom this hole would be very close to the equilib-rium blackbody electromagnetic radiation corre-sponding to the oven temperature.

Using this experimental method, Wien dis-covered his law of displacement, which statesthat the frequency at which the maximal energyis radiated is proportional to the absolute tem-perature of the blackbody. The basis of this workwas the assumption that the blackbody con-tained a very large number of electromagneticoscillators having all possible frequencies and inthermal equilibrium. Wien’s law proved applica-ble at high frequencies but had serious limita-tions at low ones. LORD RAYLEIGH (JOHN

WILLIAM STRUTT) found another formula thatsatisfied low frequencies but not high ones. In1900, in the effort to develop a treatment validfor the whole range of frequencies, Planck enun-

Wien, Wilhelm 329

ciated his quantum theory. Wien was awardedthe Nobel Prize in physics for his contributions,in 1911.

In 1896, Wien was appointed professor ofphysics at Aix-la-Chapelle. It was at Aix, twoyears later, that he met his future wife, LuiseMehler, with whom he had four children. Healso found a laboratory equipped for the study ofelectrical charges in vacuo and began to studythe nature of cathode rays, that is, particles thatseemed to emanate from hot filaments of wire.He confirmed an earlier discovery that negativecathode rays are composed of rapidly moving,negatively charged particles (electrons). Almostat the same time as JOSEPH JOHN (J. J.) THOM-SON in Cambridge, England, but with a differentmethod, he measured the relation of the electriccharge on these particles to their mass andfound, as Thomson did, that they are about 2000times lighter than hydrogen atoms. Wien alsopresented valuable ideas on positive cathoderays, by investigating their deflection whilestudying streams of ionized gases in the presenceof electrostatic and magnetic fields. He con-cluded that positive cathode rays are composedof positively charged particles, with a massapproximately equal to that of the hydrogenatom. With this work he laid the foundation ofmass spectroscopy. J. J. Thomson refined Wien’sapparatus and conducted further experiments in1913. After work by ERNEST RUTHERFORD in1919, Wien’s particle was accepted and namedthe proton.

In 1899, Wien became a professor of physicsat Geissen but remained there only a year beforeaccepting a similar position at Würzburg. In1900, he published his Textbook of Hydrodynam-ics and a theoretical paper on the possibility ofan electromagnetic basis for mechanics. Duringhis Würzburg years he continued his work oncathode rays, showing that if the pressure is notextremely weak, these rays lose and regain theirelectric charge as they move along by collisionwith atoms of residual gas. In addition, he mea-

sured the progressive decrease of the luminosityof cathode rays after they leave the cathode.From these experiments he deduced what classi-cal physics calls the decay of luminous vibrationsin atoms.

In 1920, Wien succeeded WILHELM CON-RAD RÖNTGEN as professor of physics inMunich, where he remained until his death onAugust 30, 1928.

Wien’s work on blackbody radiation, whichdemonstrated the inability of classical physics toexplain the phenomenon of radiation, stimu-lated Planck to develop revolutionary new ideas.In the words of MAX THEODOR FELIX VON LAUE,“his immortal glory” was that “he led us to thevery gates of quantum physics.”

Further ReadingKuhn, Thomas S. Black-Body Theory and the Quantum

Discontinuity. Chicago: University of ChicagoPress, 1987.

� Wigner, Eugene Paul(1902–1995)Hungarian/AmericanQuantum Theorist, Nuclear Physicist,Mathematical Physicist

A giant of 20th-century physics, Eugene PaulWigner is most famous for the work that earnedhim the 1963 Nobel Prize in physics: the intro-duction of symmetry theory to quantummechanics and chemistry. Yet he was a scientistof amazing breadth, who also pioneered theapplication of quantum mechanics in the fieldsof chemical kinetics and the theory of solids, for-mulated many of the basic ideas in nuclearphysics and nuclear chemistry, and did seminalwork in quantum chaos.

He was born in Budapest, Hungary, onNovember 17, 1902, with the Hungarian nameJeno Pal Wigner, into an upper-middle-classJewish family. He was the middle of three chil-

330 Wigner, Eugene Paul

dren of Antal Wigner, director of a leather fac-tory, and Erzsebet Wigner, a homemaker, both ofwhom were nonobservant Jews. The conversionof his family to Lutheranism when he was in hislate teens had a minimal effect on Wigner, whowould later refer to himself as “only mildly reli-gious.” Eugene was tutored at home from the ageof five to 10, when he entered an elementaryschool. By the time he went on to the LutheranHigh School in Budapest, he had already devel-oped a deep interest in mathematics. In highschool, where he gained a solid grounding inmathematics, literature, the classics, and reli-gion, he met John von Neumann, the mathe-matical genius who would become a lifelongfriend. His student days were abruptly inter-rupted in March 1919 when his entire family—imperiled members of the managerial class—fledto Austria in the wake of the Communisttakeover in Hungary. When, only a few monthslater, the Communists fell from power, theWigners were able to return. Eugene continuedhis studies, taking two years of stimulatingphysics and mathematics courses with von Neu-mann. When he graduated in 1920, he was oneof the outstanding students in his class.

Although his fervent desire was to become aphysicist, acceding to the wishes of his father,who was determined that Eugene should join thefamily business, he studied for a degree in chem-ical engineering. He dutifully enrolled at theTechnische Hochschule in Berlin, whichawarded him a doctorate in engineering in 1925for a thesis containing the first theory of therates of association and dissociation ofmolecules. At the same time, however, he con-tinued studying physics and mathematics,attending lectures by the University of Berlin’sextraordinary physics faculty, which includedALBERT EINSTEIN, MAX ERNST LUDWIG PLANCK,MAX THEODOR FELIX VON LAUE, and WALTHER

NERNST. There he enjoyed friendships with theHungarian physicists Michael Polyani, Leo Szi-lard, and EDWARD TELLER. After receiving his

doctorate, he returned home and joined hisfather’s tannery firm. He was so clearly unsuitedto this life, however, that after a few months hisfather supported his decision to take a job inBerlin working as a research assistant to a crys-tallographer at the Kaiser Wilhelm Institute. Histask was to determine “why the atoms occupypositions in the crystal lattices which correspondto symmetry axes,” a problem that obliged himto study group theory (the study of the formationand properties of mathematical groups).

By this time both WERNER HEISENBERG’smatrix version of quantum mechanics andERWIN SCHRÖDINGER’s competing wave theoryhad been published. Wigner had the idea ofapplying symmetry theory to quantum mechan-ics and soon realized that such an approachwould open up vast new areas of mathematicalphysics. His first application was to the degener-ate states of symmetrical, atomic, and molecularsystems. In 1926, extending Heisenberg’s workon two-electron atoms, Wigner published apaper on the spectrum of three-electron atoms.This initial work involving the application ofgroup theory to quantum mechanics would havedeep implications for fundamental physics. It ledWigner to the realization that quantummechanics, with its inherent superposition prin-ciple for quantum states, permitted more far-reaching conclusions concerning invariantquantities associated with these states than clas-sical mechanics. He was able to use the tools ofgroup theory to derive new rules concerning thesymmetry of atomic spectra that followed fromthe simple assumption of rotational symmetry ofthe associated quantum states. His famous workin applying group theory to quantum mechanicshad begun.

In 1927, the great mathematician DavidHilbert, who had become interested in quantummechanics and needed to collaborate with aphysicist, invited him to the University of Göt-tingen. Although Hilbert’s serious illness causedtheir collaboration to flounder, the year in Göt-

Wigner, Eugene Paul 331

tingen proved highly productive for Wigner. Inhis 1927 paper “On the Conservation Laws ofQuantum Mechanics,” he formulated his law ofthe conservation of parity, which states that itshould be impossible to distinguish left fromright in the fundamental interactions of elemen-tary particles. Wigner’s conservation of paritylaw became an integral part of quantummechanics. However, in 1956, the physicistsTSUNG-DAO LEE, CHEN NING YANG, and CHIEN-SHIUNG WU showed that conservation of parityis violated in the weak interactions of subatomicparticles by virtue of the fact that the neutrinohas a left-handed spin whereas its antiparticlethe antineutrino has a right-handed spin.

Returning to Berlin, Wigner lectured onquantum mechanics and worked on whatwould become his classic text, Group Theoryand Its Application to the Quantum Mechanics ofAtomic Spectra (1931). In 1930, Wigner andvon Neumann were hired by Princeton Univer-sity, sharing a single position. Between 1930and 1933, Wigner divided his time betweenBerlin and Princeton, but when the Nazis roseto power in 1933, he saw his Berlin positiondissolve. As did others of his generation of bril-liant Hungarian Jewish physicists, includingSzilard, von Neumann, and Teller, he immi-grated to the United States and became a natu-ralized citizen in 1937.

Wigner, who was molded by the standards ofpolite behavior of upper-class European society,had a difficult time adjusting to the UnitedStates and was initially lonely and isolated. Hisformality gave rise to a great body of “Wignerstories,” such as the one about his habit of writ-ing, “Your paper contains some very interestingconclusions!” on research papers in which hehad found many errors. He was joined at Prince-ton by his younger sister, Margit, whom he intro-duced to the great British physicist PAUL ADRIEN

MAURICE DIRAC during his visit to Princeton;they married in 1937. Wigner’s own marriage toAmelia Frank, a member of the physics faculty,whom he met while teaching at the Universityof Wisconsin, from 1936 to 1938, ended intragedy. When they had been married for lessthan a year, she died of cancer in 1937, plunginghim into a deep depression. He managed to doimportant work at this time, formulating thetheory of neutron absorption, which laterproved useful in building nuclear reactors.

Needing to escape the scene of his grief, hereturned to Princeton, where he becameThomas D. Jones Professor of MathematicalPhysics in 1938. Three years later, he marriedMary Annette Wheeler, a physics professor atVassar College, with whom he would have twochildren. During the prewar years, he did major

332 Wigner, Eugene Paul

Eugene Paul Wigner introduced the concept ofsymmetry principles into the theory of quantummechanics and chemistry. (AIP Emilio Segrè VisualArchives, Physics Today Collection)

work in a number of fields. He pioneered theapplication of quantum mechanics to importantaspects of solid state physics, determined thatthe nuclear force that binds neutrons and pro-tons is necessarily short-range and independentof any electric charge, and developed the princi-ples involved in applying group theory to inves-tigate the energy level of atoms.

By 1938, when it was clear that war inEurope was imminent, Wigner persuaded hisparents to immigrate to the United States. Thatyear, Otto Hahn and Fritz Strassmann in Berlinannounced the discovery of nuclear fission,revealing the huge amounts of energy released inthe process. Wigner, Szilard, and ENRICO FERMI

concluded that a fission-induced chain reactioncould be achieved with sufficient materials. In1939, Wigner and Szilard, fearing the conse-quences of the Nazis’ obtaining large quantitiesof uranium, persuaded ALBERT EINSTEIN to jointhem in writing a letter to President Franklin D.Roosevelt that set in motion the race to developan atomic bomb. Wigner worked at the Metal-lurgical Laboratory at the University of Chicagoduring World War II, from 1942 to 1945; therehe helped Fermi build the first atomic pile.Putting to use his experience as a chemical engi-neer, Wigner headed a group that succeeded indesigning large reactors that could produce therequired quantities of plutonium. Althoughproud of his contribution to the release ofnuclear energy, Wigner was loath to use theweapon on civilians and was one of the physi-cists who tried to persuade President Truman notto drop an atomic bomb on Japan.

When the war ended, Wigner began tothink about ways of exploring peaceful uses ofatomic energy. From 1946 to 1947, he was direc-tor of research and development at the ClintonLaboratories, the forerunner of Oak RidgeNational Laboratory in Tennessee, where hetrained young scientists and engineers in theprinciples involved in reactor development andassembled an expert team to design safe and effi-

cient nuclear reactors. As the debate over anational nuclear energy program heated up,Wigner decided he was not the person to directa laboratory in such a complex, politicized envi-ronment and returned to his work at Princeton.

He plunged into a period of intenseresearch, frequently collaborating with associ-ates or graduate students and directing 40 doc-toral theses. He conducted research on quantummechanics, the theory of the rates of chemicalreactions, and nuclear structure and made fun-damental contributions to the quantum theoryof chaos. He also wrote a number of philosophi-cal essays during this period.

In 1963, along with MARIA GERTRUDE

GOEPPERT-MAYER and J. Hans D. Jensen, hereceived the Nobel Prize in physics, for “his con-tributions to the theory of the atomic nucleusand the elementary particles, particularlythrough the discovery and application of funda-mental symmetry principles.”

His books include Nuclear Structure (1958)with L. Eisenbud, The Physical Theory of NeutronChain Reactors (1958) with A. Weinberg, Disper-sion Relations and Their Connection with Causality(1964), and Symmetries and Reflections (1967). Hepublished more than 500 papers, which have beencollected in an eight-volume edition of his work.

When he retired from Princeton in 1971,Wigner continued his intense involvement withphysics, philosophy, and technology and acceptedvisiting professorships at various universities. Heconsulted with Oak Ridge National Laboratoryon means of protecting civilians in the event ofnuclear attack and worked with the FederalEmergency Management Agency (FEMA) onprevention of and provision of emergency aid innational disasters.

In 1977, his wife, Mary, died of cancer. Twoyears later, he married Eileen Hamilton, thewidow of Princeton’s dean of graduate studies,who was his close companion for the rest of hislife. Near the end of his life, after 60 years in theUnited States, he wrote that he still felt more

Wigner, Eugene Paul 333

Hungarian than American and that “much ofAmerican culture escapes me.” When Commu-nist repression began to weaken its hold on Hun-gary, he resumed ties with the country’s culturaland scientific leaders, becoming a spokespersonfor enhanced freedoms. In his eighties he experi-enced serious memory losses in all areas but sci-ence and technology. He died on January 1,1995, in Princeton, New Jersey, at the age of 92.

The extent of Wigner’s scientific legacy tophysics is reflected in the many concepts and phe-nomena that bear his name: the Wigner–Eckarttheorem for the addition of angular momenta,the Wigner effect in nuclear reactors, theWigner correlation energy, as well as the Wignercrystal in solids, the Wigner force, theBreit–Wigner formula in nuclear physics, andthe Wigner distribution in the quantum theoryof chaos. His spiritual legacy is revealed in thephilosophical writings in which he plumbed thenature and scope of the scientific endeavor:

The miracle of the appropriateness ofthe language of mathematics for the for-mulation of the laws of physics is a won-derful gift, which we neither understandnor deserve.

Physics does not even try to give uscomplete information about the worldaround us—it gives information aboutthe correlations of those events.

The promise of future science is tofurnish a unifying goal to mankindrather than merely the means to an easylife, to provide some of what the humansoul needs, in addition to bread alone.

Further ReadingSzanton, Andrew. The Recollections of Eugene P.

Wigner as Told to Andrew Szanton. New York:Perseus Books Group, 1992.

Wigner, Eugene. Symmetries and Reflections. Wood-bridge, Conn.: Ox Bow Press, 1979.

———.“The Unreasonable Effectiveness of Mathe-matics in the Natural Sciences,” in Timothy Fer-ris, ed., The World Treasury of Physics, Astronomy,and Mathematics. Boston: Little, Brown, 1991.

� Wilson, Charles Thomson Rees(1869–1959)ScottishExperimentalist, Atomic Physicist,Particle Physicist

Charles Thomas Rees Wilson is famous for hisinvention of the Wilson cloud chamber, the firstinstrument to detect the tracks of atomic parti-cles. For this work, which initiated the age ofmodern experimental particle physics, he wasawarded the 1927 Nobel Prize in physics.

He was born on February 14, 1869, in theparish of Glencorse, just outside Edinburgh,into a family who had farmed in the south ofScotland for many generations. His father diedwhen he was four and the family moved toManchester, where he received his early educa-tion at a private school. He went on to OwensCollege (now the University of Manchester),where he majored in biology, intending tobecome a physician. After receiving his B.Sc.in 1887, he won a scholarship to CambridgeUniversity’s Sidney Sussex College, where hebecame interested in physics and chemistry andearned a degree in natural sciences. After grad-uation, he taught for four years at BradfordGrammar School, then returned to Cambridge,where he was the Clerk Maxwell scholar from1896 to 1899.

Wilson invented the cloud chamber at theoutset of his career and, like many great discov-eries, Wilson’s was made inadvertently, while hewas looking for something else. While vacation-ing in 1894, he climbed Ben Nevis, Scotland’shighest mountain, where he was intrigued bythe marvelous optical effects of coronas and“glories” (i.e., colored rings cast by surrounding

334 Wilson, Charles Thomson Rees

shadows on mist and clouds). The experiencesparked a desire to study atmospheric cloud for-mation, and when he returned to Cambridge,from 1895 to 1899, he carried out a series ofgroundbreaking experiments designed to pro-duce “artificial clouds” in the laboratory. Hesucceeded in doing this by causing the adiabatic(i.e., with no heat loss) expansion of moist air.At the time, physicists thought that each waterdroplet must form around a dust particle, but inthe supersaturated air of Wilson’s cloud cham-ber microscopic droplets formed in the absenceof dust particles. When Wilson exposed thecloud of water vapor to X rays, which had beendiscovered that same year by WILHELM CONRAD

RÖNTGEN, the process of droplet formationintensified. From this observation, he con-cluded that water vapor condensed around ions,atoms that have become charged by gaining orlosing electrons. Thus, he reasoned that thetrack of a positively charged alpha particle, forexample, would become visible in a line ofwater droplets. Wilson then used illuminationto make the track stand out clearly, enabling thecloud chamber both to detect ions in gases andto record them photographically.

Having achieved this much, Wilson aban-doned the cloud chamber to pursue another pas-sion spurred by the dramatic weather conditionsof Ben Nevis. In 1895, while on the mountain,he heard distant thunder and, suddenly feelinghis hair stand up, fled without waiting for thestorm to break. The experience led to an intenseinterest in atmospheric electricity, which he pur-sued from 1900 to 1910, while working as a lec-turer at Sidney Sussex. He devised the gold-leafelectroscope, a sensitive device for measuringelectric charge, which enabled him to demon-strate that some electrical charge always occursin air and that the conductivity of air inside theelectroscope is the same in daylight as in dark-ness and is independent of the sign of the chargefor leaf potential. Wilson was at a loss to explainhis results; many years later they would be

understood in terms of the existence of cosmicrays: radiation emitted everywhere in the uni-verse.

The year 1911 was a pivotal one for Wil-son: he married Jessie Frasier of Glasgow, withwhom he would have two sons and two daugh-ters, and he developed a working model for amore advanced cloud chamber. Since the trackof a charged particle was detectable becausewater droplets condensed along the particle’spath, he reasoned, on the basis of JAMES CLERK

MAXWELL’s laws of electrodynamics, that if heapplied a magnetic field to the chamber, the trackwould curve and give a measure of the chargeand mass of the particle. He built his newchamber in the form of a short cylinder inwhich saturation was achieved and controlledby the movement of a piston through a fixed dis-tance. The condensation effects were monitoredthrough the other end. The instrument imme-diately became essential to the study of radio-activity; it was used to confirm the classic alphaparticle scattering and transmutation experi-ments first performed by ERNEST RUTHERFORD.However, the immense value of the Wilson cloudchamber and subsequent variations developed byothers only became apparent in the early 1920s,when modifications by LORD PATRICK MAYNARD

STUART BLACKETT and CARL DAVID ANDERSON

led to the discovery of the positron in 1932 andthe pi meson in 1936.

In 1925, Wilson was appointed JacksonianProfessor of Natural Philosophy at Cambridge, apost he held until 1934. Two years later, heretired and moved to the village of Carlops, nearhis birthplace. C. T. R., as his friends called him,continued to meet with friends and colleagues,continued his research, and wrote his last paper,a long-promised manuscript on the theory ofthundercloud electricity, when he was 87. Hedied at Carlops on November 15, 1959, sur-rounded by his family.

Wilson’s cloud chamber, celebrated byRutherford as “the most original and wonderful

Wilson, Charles Thomson Rees 335

instrument in scientific history,” represented thebeginning of experimental particle physics.Although it is not used today, the principleunderlying it was incorporated by DONALD

ARTHUR GLASER in 1952 into the bubble cham-ber, an extremely sensitive detector that usessupersaturated liquid helium and is a componentof today’s giant particle accelerators.

Further ReadingWilson, John Graham. The Principle of Cloud Chamber

Technique. Cambridge: Cambridge UniversityPress, 1951.

� Wu, Chien-Shiung(1912–1997)Chinese/AmericanExperimentalist, Nuclear Physicist

Chien-Shiung Wu, known to her scientific col-leagues simply as “Madame Wu,” was an extraor-dinary experimentalist who provided theevidence for CHEN NING YANG and TSUNG-DAO

LEE’s hypothesis that the law of conservation ofparity, the mirror symmetry between right andleft, previously thought to be universal innature, is violated in the weak interaction betadecay of the atomic nucleus.

Wu was born in Liu-ho, a small town nearShanghai, China, on May 29, 1912. Her father,Wu Zong-yee, was a school principal. He wasunusual in that time, believing that girls wereentitled to the same education as boys. Wu wasalso encouraged to study by a leading Chineselanguage scholar, Hu Shi, who recognized hertalents. Her love of physics began in high schooland was developed at the prestigious NationalCentral University in Nanjing, where she gradu-ated in 1936. She went on to do her graduatework at the University of California in Berkeley,then a mecca for atomic physics, where she stud-ied under J. ROBERT OPPENHEIMER, who wouldlater head the U.S. effort to develop an atomic

bomb, and Ernest Lawrence, the inventor of thecyclotron. Wu received her Ph.D. in 1940 andmade her reputation as a specialist in nuclear fis-sion. She was particularly interested in the pro-cess of beta decay, in which a neutron in thenucleus of a radioactive atom spontaneouslybreaks apart, releasing a beta particle (a fast-moving electron) and a neutrino (a particle withno mass or charge). In this process, a proton isleft behind, automatically converting the atominto an atom of a different element.

In 1942, she married Luke Yuan, anotherBerkeley physicist. In 1945, they had a son, Vin-cent, who would grow up to be a physicist. Shetaught physics for two years at Smith Collegeand then at Princeton University. In 1944, Wumoved to Columbia University and joined theManhattan Project, whose mission was todevelop an atomic bomb. Her assignment was tofind ways to produce more radioactive uranium.She developed the process of separating ura-nium-235 from the more common uranium-238by gaseous diffusion, using ionization chambersand Geiger counters to monitor the process.

After the war, Wu remained at Columbia,becoming an associate professor in 1952 andcontinuing her study of beta decay. Her reputa-tion as a meticulous experimentalist drew twoother Chinese-born physicists, Yang and Lee, toconsult her in 1956. In June of that year, Yangand Lee had submitted to Physical Review apaper, “The Question of Parity Conservation inWeak Interactions,” raising the question ofwhether parity, the assumption that naturemakes no distinction between left and right, isconserved in weak interactions and suggestingseveral experiments to decide the issue. At thetime, physicists universally believed that physi-cal reactions would be the same (i.e., have parityor equality) whether the particles involved inthem had a right-handed or a left-handed spin,or quantized rotation property. This was knownas the law of conservation of parity. In physics,to say that something is invariant is equivalent

336 Wu, Chien-Shiung

to saying it is conserved. If the physical processproceeds in exactly the same way when referredto an inverted coordinate system, then parity issaid to be conserved. If, on the contrary, the pro-cess has definite left- or right-handedness, thenparity is not conserved in that physical process.

In the early 1950s, applying the principleof conservation of parity to individual sub-atomic particles and their interactions hadproved highly successful in accounting for thebehavior of those particles. By the end of 1955,however, a puzzling contradiction between theparity principle and the other principlesemployed to order the subatomic zoo hademerged. In particular, questions were raised byresults beginning to pour forth from the manyhigh-energy accelerators built in the UnitedStates after World War II, indicating that oneform of radioactive decay appeared to violatethe conservation of parity law. Most physiciststhought this result was due to some kind ofexperimental error, but Yang and Lee made therevolutionary suggestion that the universallyaccepted conservation of parity law might nothold true in weak nuclear interactions, whichinclude radioactive decay.

It was Madame Wu who produced the deci-sive evidence, when she tested their hypothesiswith an experiment that used radioactive cobalt,or cobalt-60. A strong electromagnetic fieldcould make the cobalt atoms line up, just as ironfilings do near a magnet, and spin along thesame axis. She could then count the number ofbeta particles thrown from their nuclei in differ-ent directions as the atoms decayed. If the paritylaw held true for weak interactions, the numberof particles thrown off in the direction of thenuclear spin would be the same as the numberthrown in the opposite direction. If the law didnot hold, the numbers would differ. However,since the cobalt atoms, under normal tempera-tures, would move around too much to line upunder the magnet, the experiment had to bedone at almost absolute zero, the temperature at

which all atomic motion becomes vanishinglysmall.

The only place Wu could achieve these con-ditions was at the National Bureau of Standardsin Washington, D.C., which provided a cryogen-ics laboratory. Her method was to place thecobalt in a strong magnetic field to line up thenorth–south magnetic poles of its nuclei, super-cool it to near absolute zero to minimize theatoms’ random thermal motions, and watchwhere the electrons it emitted went. She foundthat the majority of the tens of thousands ofelectrons emitted by the cobalt every secondwere ejected primarily in one direction. Theexperiment, which had to be repeated severaltimes, was arduous, but the results were electrify-

Wu, Chien-Shiung 337

Chien-Shiung Wu provided experimental evidence thatconservation of parity between right and left-handedspinning particles is violated in the weak interactionbeta decay of the atomic nucleus. (AIP Emilio SegrèVisual Archives)

ing: far more beta particles flew off in the direc-tion opposite the nuclei’s spin than in the direc-tion that matched the spin. This was evidencethat the law of conservation of parity did notapply to the weak interactions.

Wu announced this finding on January 16,1957, causing a stir in the physics community.Within days, LEON M. LEDERMAN and RichardGarwin at Columbia confirmed the result, usingthe university’s Nevis Cyclotron, a 385-million-electron-volt (Mev) device for accelerating par-ticles to high energies. Her discovery generated aparadigm revolution, when physicists began torealize that parity nonconservation was the basicproperty of the weak interaction, one of the fourbasic forces of the universe. It is now known thatparity violation exists nearly maximally in allweak interaction processes. Inexplicably, whenthe Nobel Prize in physics was awarded in 1957,it went to only Yang and Lee, excluding Wu.

After this she became full professor ofphysics at Columbia and was elected to theNational Academy of Sciences in 1958. Shewould remain at Columbia until her retirementin 1981, “the reigning queen of nuclear physics,”as a colleague put it. She wrote a book, BetaDecay, that remains a standard reference on low-energy emission of electrons by decaying atoms.Named Woman of the Year by the Associationof University Women in 1962, she continued tomake important discoveries and tests of others’theories. In 1963, she confirmed experimentallythe theory of conservation of vector currents in

beta decay proposed by RICHARD PHILLIPS FEYN-MAN and MURRAY GELL-MANN. She observedthat electromagnetic radiation from the annihi-lation of positrons and electrons is polarized, asPAUL ADRIEN MAURICE DIRAC had predicted inhis theory of the electron. In 1963 she, Lee andL. W. Mo observed the magnetic equivalent ofthe weak nuclear force, thereby confirming thesymmetry between the weak and electromag-netic currents; this was the cornerstone for thelater unification of these two basic forces into asingle one—the electroweak force.

Wu became the first woman president of theAmerican Physical Society in 1975. Wu retiredin 1981. She died in New York on February 16,1997, at the age of 84, after suffering a stroke.An asteroid was named in her honor in 1990.

Madame Wu, the most distinguishedwoman physicist of her time, was one of thegiants in her field. Her elegantly designed exper-iments led to the revolutionary realization thatparity nonconservation is the basic property ofthe weak interaction, one of the four basic forcesof the universe.

See also FERMI, ENRICO; WEINBERG, STEVEN.

Further ReadingLindop, Laurie. Dynamic Modern Women: Scientists

and Doctors. New York: Holt, 1997, pp. 95–105.McGrayne, Sharon Bertsch. Nobel Prize Women in

Science: Their Lives, Struggles, and MomentousDiscoveries. New York: H. W. Wilson, 1959, pp.491–492.

338 Wu, Chien-Shiung

Y

339

� Yang, Chen Ning (Yang Chen-ning)(1922– )Chinese/AmericanTheoretician, Nuclear Physicist,Particle Physicist

Chen Ning Yang, together with TSUNG-DAO

LEE, predicted that conservation of parity, thesymmetry between right and left occurring inphysical phenomena, is violated in the weakinteractions of the atomic nucleus. On the basisof the experiments of CHIEN-SHIUNG WU, whichprovided evidence for this symmetry violation,Yang and Lee were awarded the 1957 NobelPrize in physics. Later in his career, Yang didseminal work on gauge particle field theories,which greatly advanced the search for a unifiedtheory of elementary particles.

Yang was born on September 22, 1922, inHofei, Anwhei, China, the oldest of five chil-dren born to Ke Chuan Yang and Meng Hwa LoYang. After reading a biography of BenjaminFranklin, he adopted the name Frank for him-self. His father was a professor of mathematics atTsinghua University, near Beijing. Yangattended National Southwest Associated Uni-versity in Kunming, China, earning a bachelor’sdegree in 1942 for his thesis “Group Theory andMolecular Structure.” He went on to TsinghuaUniversity, which had moved to Kunming dur-

ing the Sino-Japanese War (1937–1945); therehe wrote his master’s thesis, “Contributions tothe Statistical Theory of Order–Disorder Trans-formations,” in 1944.

At the end of the war, Yang went to theUnited States on a Tsinghua University Fellow-ship and entered the University of Chicago in1946 to work on his doctorate in physics. He hadhoped to work with ENRICO FERMI at ArgonneNational Laboratory, but as a foreigner he wasbarred from working at that facility. Instead, heworked under EDWARD TELLER, writing a thesison nuclear physics, “On the Angular Distribu-tion in Nuclear Reactions and CoincidenceMeasurements.” After being awarded his Ph.D.by the University of Chicago in 1948, he workedbriefly as an instructor there. In 1949, he took apostdoctoral position under J. ROBERT OPPEN-HEIMER at the Institute for Advanced Study,Princeton University. In 1950, he married ChihLi Tu, whom he met while teaching mathemat-ics at her high school in China; they had threechildren. In 1955, he became a professor atPrinceton University and remained there until1966.

Throughout his career in physics, Yang con-centrated on working in the field of the weakinteractions, which were long thought to causeelementary particles to disintegrate. In June1956, Yang collaborated with Lee on a paper

that raised the question of whether parity, theassumption that nature makes no distinctionbetween left and right, is conserved in weakinteractions. At the time physicists universallybelieved that physical reactions would be thesame (i.e., have parity, or equality) whether theparticles involved in them had a right-handed ora left-handed spin, or quantized rotation prop-erty. If the physical process proceeds in exactlythe same way when referred to an inverted coor-dinate system, then parity is said to be con-served. If, on the contrary, the process hasdefinite left- or right-handedness, then parity isnot conserved in that physical process. This lawof conservation of parity was explicitly formu-lated in the early 1930s by the Hungarian-born

physicist EUGENE PAUL WIGNER and became afeature of quantum mechanics.

The strong forces that hold atoms togetherand the electromagnetic forces that are responsi-ble for chemical reactions obey the law of parityconservation. Since these are the dominantforces in most physical processes, physicistsassumed that parity conservation is an inviolablenatural law. In the early 1950s, applying theprinciple of conservation of parity to individualsubatomic particles and their interactions hadproved highly successful in accounting for thebehavior of those particles. By the end of 1955,however, a puzzling contradiction between theparity principle and the other principlesemployed to order the subatomic zoo hademerged. In particular, questions were raised byresults emerging from the many high-energyaccelerators built in the United States afterWorld War II that indicated that one form ofradioactive decay appeared to violate the con-servation of parity law. One of the newly discov-ered mesons—the so-called K meson—seemedto exhibit decay modes into configurations withdiffering parity. Exploring this paradox fromevery conceivable perspective, Yang and Lee dis-covered that contrary to what had beenassumed, there was no experimental evidenceagainst parity nonconservation in the weakinteractions. The experiments that had beendone, it turned out, were not relevant to thequestion. In their landmark 1956 Physical Reviewpaper, “The Question of Parity Conservation inWeak Interactions,” Yang and Lee startled thephysics community with their proposal that theuniversally accepted conservation of parity lawmight not hold true in weak nuclear interac-tions, which include radioactive decay.

Their suggestions for experiments capable ofdeciding the issue were immediately taken up byMadame Wu at the cryogenic laboratory of theNational Bureau of Standards in Washington,D.C. Testing radioactive cobalt atoms at temper-atures approaching absolute zero, Wu found the

340 Yang, Chen Ning

Chen Ning Yang, together with Tsung-Dao Lee,predicted that conservation of parity, the symmetrybetween right and left that occurs in physicalphenomena, is violated in the weak interactions of theatomic nucleus. (AIP Emilio Segrè Visual Archives,Physics Today Collection, SUNY)

evidence Yang and Lee were looking for: the lawof parity did not apply to weak interactions.Shortly after her announcement in January1957, other experimentalists confirmed herresults. In the wake of this paradigm revolutioncreated by the three Chinese American physi-cists, Yang and Lee were awarded the NobelPrize in physics that very year.

In other arenas, Yang, in collaboration withLee and others, did important work in statisticalmechanics, the study of systems with large num-bers of particles, and later investigated the natureof elementary particle reactions at extremely highenergies. In 1954, while Yang and Robert Millswere visiting physicists at Brookhaven NationalLaboratory, they developed the Yang–Mills gaugetheory of elementary particles, which is consid-ered to be the foundation for the current under-standing of the ways subatomic particles interact.Gauge field theories contain a mathematicaltransformation symmetry of the fields that pre-serves the form of the field equations. Maxwell’sequations for the electromagnetic field are of thistype. As Yang explained:

The earliest understanding of theseforces was Newton’s understanding ofgravity. The next to be understood wereMaxwell’s equations for electric andmagnetic forces. What the gauge[Yang–Mills] theory [covers] is the equa-tions that govern the other two types offorces. And, furthermore, it turns outthat once you understand those,Maxwell’s and Newton’s forces also fallinto the same category. So now we real-ize that all fundamental forces are forcesthat obey gauge equations.

The Yang–Mills gauge theory, in conjunctionwith mass symmetry breaking, a violation of thegauge symmetry that occurs when the tempera-ture of the particle field environment cools belowa certain threshold, is currently considered to be

the best candidate to explain the interaction ofthe weak and strong forces, electromagnetism andgravity. For this reason many now consider Yang’swork on gauge theories more important than hiswork on parity violation.

In 1964, Yang became a U.S. citizen, andfrom 1965 on, he was Albert Einstein Professorat the State University of New York (SUNY),Stonybrook, Long Island. During the 1970s, hewas a member of the Rockefeller University andthe American Association for the Advancementof Science. In 1986, he became DistinguishedProfessor-at-Large at the Chinese University ofHong Kong.

Yang, who had long been involved in theadvancement of Chinese science, with theopening of relations between the United Statesand China in 1971 returned to China for thefirst time, to visit his parents. He recalls:

After I came back I thought that, as aperson deeply involved in both Chinaand the U.S. and who understands thecultures of both countries very well, itwas my responsibility to promote under-standing between the two.

His goal for the next 20 years became the pro-motion of Chinese science, because he thought“that would contribute to the well-being of thepeople in China and also to the peace and stabilityof the whole world.” One of his efforts was theestablishment of a visiting scientist program at theSUNY-Stonybrook Institute, where hundreds ofChinese researchers have made one-year stayssince the early 1980s.

Yang’s work has been characterized as anamazing combination of mathematical powerand elegance. His body of research on gauge the-ories of elementary particles continues to beabsolutely central to the development andsearch for a unified formulation of elementaryparticle theories.

See also WEINBERG, STEVEN.

Yang, Chen Ning 341

Further ReadingBernstein, Jeremy. A Comprehensible World: On Mod-

ern Science and Its Origins. New York: RandomHouse, 1967.

Boorse, H. A., and L. Motz, eds. The World of theAtom. New York: Basic Books, 1966.

Yang, Chen Ning. Selected Papers 1945–80 with Com-mentary. New York: W. H. Freeman, 1983.

� Young, Thomas(1773–1829)BritishExperimentalist (Optics, ClassicalMechanics)

Thomas Young devised one of the privotal exper-iments in the history of physics: the double-slitexperiment, which, by demonstrating the princi-ple of interference of light, showed, within theframework of classical physics, that light is awave and not a particle. He is also famous for hisdiscoveries in the physiology of vision and hisinvention of the theory of elasticity of materials.

Young was born on June 13, 1773, in thesmall village of Milverton, Somerset, England,the first of 10 children. A prodigy, he learned toread by age two and at six read the Biblethrough twice. He was tutored privately at first,then attended private school. A brilliant stu-dent of languages, who had a special interest inancient Middle Eastern languages, he hadtaught himself to read Latin, Greek, Italian,Hebrew, Arabic, Persian, Turkish, and Ethi-opian and had mastered mathematics, physics,and chemistry by age 19.

When Young was 19, in 1792, he beganstudying medicine at Saint Bartholomew’s Hos-pital in London, where he was taught by someof the most eminent physicians of the day. Hebecame interested in the physiology of thehuman eye and, in 1793, read a paper to Lon-don’s Royal Society in which he explained thatthe mechanism by which the eye focuses on

objects at different distances involves a changeof shape in the eye’s lens, which is composed ofmuscle fibers. The next year, the society hon-ored him by election to its ranks. After study-ing in Edinburgh and Göttingen, he moved toCambridge, where his intellectual prowessearned him the nickname “PhenomenonYoung” and where he would receive an M.B. in1803 and an M.D. in 1808.

Young’s versatile genius and prodigiousenergy led him to pursue a dual career as medi-cal practitioner and scientific investigator.When an uncle left him a fortune in 1800, hemoved to London and opened a medical prac-tice there. In 1801, he became professor of nat-ural philosophy at the Royal Institution, wherehis public lectures apparently went over theheads of his listeners. His research was moresuccessful. Continuing his earlier work onvision, in 1801, by experimenting with his owneyes, he showed that astigmatism, a conditionfrom which he suffered, is a defect of the lens ofthe eye that prevents light rays from convergingin a single focal point.

That same year, Young hypothesized thatcolor vision is due to the presence of structuresin the retina that respond to the three primarycolors. He explained color blindness as theinability of one or more of these structures torespond to light. Later experiments would con-firm the existence of three types of fibers, nowcalled cones, which are sensitive to light of dif-ferent wavelenghts. In the 1850s HERMANN

LUDWIG FERDINAND VON HELMHOLTZ wouldfurther develop these ideas into what came to becalled the Young–Helmholtz theory or thetrichromatic theory. JAMES CLERK MAXWELL

would later incorporate Young’s insights into afull theory of vision, explaining how all colorsare produced by adding and subtracting the pri-mary colors, establishing the foundations ofmodern color photography and color television.

Young’s landmark studies of vision led himnaturally to consider a leading controversy of

342 Young, Thomas

the day: is light a particle or a wave? Most scien-tists, following the lead of SIR ISAAC NEWTON,favored particles or “corpuscles,” as they werecalled. But Young was attracted to the wave the-ory espoused by CHRISTIAAN HUYGENS, whichwas better able to explain the phenomena ofreflection, refraction, and diffraction. Heassumed that light waves are propagated in asimilar way to sound waves and are longitudinalvibrations, but with a different medium and fre-quency. He also proposed that different colorsconsist of different frequencies.

In 1802, Young announced his discovery ofthe principle of interference. He had arrived atit through his knowledge that if two soundwaves of equal intensity reach the ear 180degrees out of phase, they cancel each other outand no sound is heard. If light beams consistedof waves, he reasoned, it should be possible toobserve a similar interference effect. Hehypothesized that the bright bands of fringes ineffects such as Newton’s rings result from lightwaves that interfere in such a way that theyreinforce each other. Over the next two years,he proved this experimentally in his famousdouble-slit experiment, in which he beamedlight through two narrow openings andobserved the resulting interference patterns.Etienne Malus’s discovery, in 1808, that lightwaves could be polarized led Young to suggest,in 1817, that light waves contain a transversecomponent of vibration. In 1821, AUGUSTIN

JEAN FRESNEL developed the mathematics ofYoung’s theory and proved that the vibration oflight waves is entirely transverse.

Despite his intense interest in the physicalproperties of light, Young ranked the importanceof this research as secondary, at best, in his hier-archy of values. He wrote, “The nature of light isa subject of no material importance to the con-cerns of life or to the practice of the arts, but it isin many other respects extremely interesting.”

Young also invented the theory of elasticitybased on the concept of absolute measurements

by defining the modulus (the proportionalityconstant) as the weight that would double thelength of a rod of unit cross section. Today it isreferred to as Young’s modulus and is formulatedas stress divided by strain in the elastic region ofthe loading of a material.

In 1804, Young married Eliza Maxwell;seven years later, he became a physician at SaintGeorge’s Hospital in London, a post he wouldhold until his death. In his later years, he dedi-cated himself to his first passion, ancient lan-guages, publishing papers on Egyptology, mostlyconcerned with hieroglyphics. Young was amongthe first to interpret the writings on the RosettaStone, which was found at the mouth of the Nilein 1799. In 1829, his health began to fail. Hedied in London, of a cardiac disorder, on May 10of that year, at age 56.

Young’s demonstration of interference asevidence of the wave nature of light was a cru-cial link in the chain of discoveries leading fromthe classical wave–particle controversy of histime to the quantum wave–particle duality iden-tified in the 20th century.

Further ReadingKipnis, Nahum. History of the Principle of Light. Sci-

ence Networks Historical Studies, Vol. 5. NewYork: Springer-Verlag, 1991.

Shamos, M. Great Experiments in Physics. New York:Dover, 1987.

Wood, Alexander, Frank Oldham, and Charles E.Raven. Thomas Young, Natural Philosopher,1773–1829. Cambridge: Cambridge UniversityPress, 1954.

� Yukawa, Hideki(1907–1981)JapaneseTheoretician, Particle Physicist

Hideki Yukawa is famous for his 1935 theoreti-cal work on the forces binding the atomic

Yukawa, Hideki 343

nucleus, which predicted the existence of newelementary particles called pi mesons. TheNobel Prize in physics awarded to him in 1949for this work was the first to be given to aJapanese scientist.

He was born Hideki Ogawa in Tokyo, Japan,on January 23, 1907, the third son of TakujiOgawa, a geologist. The family moved to Kyotowhen Hideki’s father became professor of geol-ogy at the University of Kyoto. In his autobiog-raphy, Hideki describes himself as a lonely,introverted, and silent child. When he was a stu-dent, it was not unusual for him to spend entiredays reading, without talking to anyone. Hewrote, “The window of my little world openedout only to the garden of science, but from thatwindow enough light streamed in.”

While attending the Third Higher School,a renowned senior high school, he became aclose friend of another future Nobel Prize win-ner, the quantum theorist SIN-ITIRO TOMON-AGA. After graduation, both Hideki andTomonaga entered the University of Kyoto, in1923, and majored in physics. After earningtheir rigakushi (bachelor’s degrees) in physics in1929, Hideki and Tomonaga traveled to Tokyoto listen to a series of lectures by WERNER

HEISENBERG and PAUL ADRIEN MAURICE DIRAC,which made a strong impression on them.Another important influence was YoshioNishina, one of Japan’s leading physicists, whohad studied quantum theory in Copenhagenwith NIELS HENRIK DAVID BOHR and pioneeredquantum research in Japan. In 1932, Hidekimarried Sumiko Yukawa, taking her familyname; they had two sons, Harumi and Takaaki.By this time, he had moved to Osaka Univer-sity, where he taught and studied for his doctor-ate, which he received in 1938.

While pursuing his graduate studies, in1935, Yukawa published his paper “On the Inter-action of Elementary Particles,” which proposeda new field theory of nuclear forces and pre-dicted the existence of the pi meson. At the

time, physicists were struggling to understandwhat holds the nucleus together. In 1932, SIR

JAMES CHADWICK had discovered a secondnuclear component, in addition to the positivelycharged proton: the neutron, which had nocharge. Yukawa noted the dilemma this posed:because of the Coulomb forces, the protonsshould repel each other and break the nucleusapart. Seeking the required attractive force toexplain why this does not happen, he postulatedthe existence of an “exchange force” that coun-teracts the mutual repulsion and holds thenucleus together. Such a force came to be knownto physicists as the strong interaction.

Yukawa sought to understand the mecha-nism of the strong force by using the electro-magnetic force as an analogy. Here, thelong-range electromagnetic interaction betweencharged particles is seen as the result of thecontinuous exchange of a quantum or unit ofenergy carried by a virtual particle, that is, onewhose energy and momentum cannot be pre-cisely determined because of the uncertaintyprinciple. The virtual particle in this case is thephoton, which has a zero mass and, therefore,interacts over long ranges. Yukawa postulatedthat just as electrons and protons interact byexchanging photons, so nucleons interact byexchanging an appropriate virtual particle.Yukawa knew that the quantum theory pre-dicted that the range of the force generated bya virtual particle is inversely proportional toits mass. Since the nuclear force has a veryshort range and acts only inside the atomicnucleus, Yukawa concluded that the virtualparticle generating the nuclear force wouldhave to have a nonzero mass. Hence, in con-structing a model of the nuclear force, Yukawarequired that the nuclear exchange forcewould (1) involve the transfer of a massive par-ticle, (2) generate an interaction strongenough to overcome the repulsive Coulombforces between the protons, and, (3) decreasein intensity rapidly enough to have a negligible

344 Yukawa, Hideki

effect on the innermost electrons. Using quan-tum theory, he calculated that his predictednuclear exchange force particle would havea mass about 200 to 300 times that of an elec-tron (but with the same charge as an elec-tron)—about one-ninth the mass of a protonor neutron—and that the particle would beradioactive, with an extremely short half-life.

No particle with these characteristics had yetbeen discovered.

However, in 1936, CARL DAVID ANDERSON

discovered the muon (or mu meson) in cosmicray tracks, which possessed some, but not all, ofthe properties of Yukawa’s predicted particle.Although the muon had the appropriate mass,it interacted with nucleons so infrequently that

Yukawa, Hideki 345

Hideki Yukawa is famous for his theoretical work on the forces binding the atomic nucleus, which predicted theexistence of new elementary particles called pi mesons. (AIP Emilio Segrè Visual Archives, W. F. MeggarsCollection)

it could not possibly be the nuclear “glue”Yukawa had predicted. Meanwhile, in 1936,Yukawa predicted that a nucleus could absorbone of the innermost orbiting electrons andthat this process would be equivalent to emit-ting a positron. These innermost electronsbelong to the 1K electron shell and this processof electron absorption by the nucleus becameknown as K capture.

Finally, in 1947, Yukawa’s predicted particlewas found when Cecil Powell discovered in cos-mic ray tracks the pion (or pi meson), a particlesimilar to Anderson’s muon but fulfilling all therequirements of Yukawa’s exchange particle. Ithad a mass 264 times that of the electron, itsdecay products were muons, and it interactedvery strongly with the nucleons. Two years later,Yukawa traveled to Sweden to accept his NobelPrize for his prescient theoretical work.

The following year, he returned to Kyoto,where, except for various visiting professorships(including one to Princeton’s Institute forAdvanced Study at J. ROBERT OPPENHEIMER’sinvitation, 1948–1949, and one to Columbia,1949–1953), he remained for the rest of hiscareer. He was professor of theoretical physicsfrom 1939 to 1950, when he became professoremeritus. Then, in 1953, he was appointed direc-tor of the university’s new Research Institute forFundamental Physics. He was active in the Pug-wash Conference and a strong advocate for ban-

ning nuclear weapons and developing peacefuluses of nuclear energy. He retired in 1970.

In addition to numerous scientific papers,he published many books, including Introduc-tion to Quantum Mechanics (1946), Introductionto the Theory of Elementary Particles (1948), andTabito (The Traveler), an autobiographicalaccount. He edited an English-language jour-nal, Progress of Theoretical Physics, which hefounded in 1946.

Yukawa died of pneumonia and heart dis-ease in 1981, at the age of 74, in his home inKyoto. He is remembered both for his specificcontribution to the embryonic field of particlephysics and for his important role in the devel-opment and recognition of Japanese science inthe post–World War II years. Yukawa’s ground-breaking insight into the nature of the nuclearforce laid the foundation for future studies,which ultimately led to the currently acceptedquark model of the nuclear force.

See also FEYNMAN, RICHARD PHILLIPS;GELL-MANN, MURRAY; SCHWINGER, JULIUS

SEYMOUR.

Further ReadingYukawa, Hideki. Creativity and Intuition: A Physicist

Looks at East and West. Tokyo and New York:Kodansha International, 1973.

———. Tabito (The traveler). Singapore: World Sci-entific, 1982.

346 Yukawa, Hideki

347

Z� Zeeman, Pieter

(1865–1943)DutchExperimentalist (Electromagnetism,Optics), Atomic Physicist

Pieter Zeeman is famous for discovering whatcame to be known as the Zeeman effect, thesplitting of the spectral lines of atoms by anexternal magnetic field. This effect proved to bean invaluable tool for uncovering the structureof the atom. Zeeman shared the 1902 NobelPrize in physics with his professor, HENDRIK

ANTOON LORENTZ, who had predicted the effecton the basis of his theoretical work on the rela-tionship between light and magnetism.

Zeeman was born in Zonnemaire, a smallvillage in the Isle of Schouwen, Zeeland, theNetherlands, on May 25, 1865, to a local clergy-man and his wife. While still a pupil in a localschool, he produced a description and drawingof the aurora borealis, then visible above theNetherlands, that was deemed good enough forpublication in Nature. Zeeman went on to thegymnasium (secondary school) in Delft, wherehis curriculum included the classical languagesrequired for university entrance. In Delft, heformed a nurturing friendship with the physicistHEIKE KAMERLINGH ONNES, who was a decadeolder than Zeeman and amazed by the boy’s pas-

sion for performing experiments. Zeeman’sextensive reading included works by JAMES

CLERK MAXWELL on electromagnetism. In 1885,he entered the University of Leiden, where hestudied under Kamerlingh Onnes and Lorentz.He earned a Ph.D. in 1893 with a thesis on theKerr effect, the appearance of birefringence incertain isotropic substances when placed in astrong electric field. After a semester in Stras-bourg studying the propagation and absorptionof electric waves in fluids, he returned to Ley-den, where he would be a lecturer from 1895 to1897.

The impetus for Zeeman’s groundbreakingexperiment was the work of his mentor Lorentz,who hypothesized that since light is generatedby oscillating electric currents, the presence of astrong magnetic field would have an effect onthe charged particles that make up the oscillat-ing currents. Specifically, it would result in asplitting of spectral lines by causing the wave-lengths of the lines to vary. In 1896, Zeeman setout to test this hypothesis. He placed a sodiumflare between the poles of a powerful electro-magnet and produced emission spectra by usinga large concave diffraction grating. This experi-mental arrangement enabled him to detect abroadening of the spectral lines when the mag-netic field was activated. He also showed thatthe shape of the flame was not responsible for

this effect, since a similar broadening wasachieved with the sodium absorption spectra.Lorentz’s hypothesis was validated.

In 1897, Zeeman refined his experiment andsuccessfully resolved the broadening of the nar-row blue–green spectral line of cadmium, pro-duced in a vacuum discharge, into threecomponent lines. This experiment showed thatatomic energy levels are affected by externalmagnetic fields, which split atomic levels intodiscrete substates of different angular momen-tum. In addition to confirming Lorentz’s theory,Zeeman demonstrated that oscillating particleshave negative charge, as well as an unexpectedlyhigh charge-to-mass e/m ratio. The followingyear, JOSEPH JOHN (J. J.) THOMPSON discoveredthe existence of free electrons in the form ofcathode rays, which proved to have the samecharge and e/m ratio that Zeeman had found forthe oscillating particles in his experiment. In thisway it became clear that the electrons and oscil-lating particles were identical. This finding con-firmed that the magnetic field was affecting theforces that control the electrons within the atom.

In 1897, in the midst of this research, Zee-man moved to the University of Amsterdam,where he became a lecturer and later, in 1900, aprofessor of physics. He would retain this positionfor the next 35 years. In 1895, he had marriedJohanna Elisabeth Lebret, with whom he wouldhave one son and three daughters. Zeeman,whose interests extended to literature and the-ater, was known as an entertaining host, engaginghis guests in lively intellectual discussion. Hiscompetence and personal kindness were said tohave earned him the devotion of his students.

At Amsterdam, Zeeman developed his pre-vious work in a new direction, suggesting thatthe accepted existence of strong magnetic fieldson the surface of the Sun could be verified, sincethey should cause splitting of the spectral linesderived from light from the Sun’s surface. In1908, the astronomer George Hale, director ofthe Mount Wilson Observatory, confirmed Zee-man’s prediction, which suggested an interrela-tionship between the directions of polarizationand those of the magnetic field. The conclusionreached was that sunspots must be associatedwith intense magnetic fields within the Sun.

In 1923, he became director of the new Zee-man Laboratory, built especially for him. Itincluded a concrete block weighing a quarter ofa million kilograms erected free from the floor, asa suitable platform for vibration-free experi-ments. Eminent scientists from around the worldvisited him there. He died after a short illness, inAmsterdam, on October 9, 1943.

Today the Zeeman effect not only explainsthe mechanism of light radiation and thenature of matter and electricity, but offers animportant means for revealing the internalstructure of the atom. Further study of the Zee-man effect led to important theoreticaladvances in the quantum mechanics of atoms,and later investigators were able to show that aZeeman effect associated with an external mag-netic field interacting with the intrinsic spin ofthe electron also exists.

Further ReadingBorn, Max. Atomic Physics. New York: Dover,

1989.

348 Zeeman, Pieter

ACOUSTICS

Doppler, ChristianHelmholtz, Hermann Ludwig

Ferdinand vonLangevin, PaulMach, ErnstRaman, Sir Chandrasekhara

Venkata

ASTRONOMY

Ångstrom, Anders JonasArchimedesFizeau, Armand-Hippolyte-

LouisFoucault, Jean-Bernard-LéonFraunhofer, Joseph vonGalilei, GalileoGauss, Johann Carl FriedrichHooke, RobertHuygens, ChristiaanNewton, Sir Isaac

ASTROPHYSICS ANDCOSMOLOGY

Alfvén, Hannes Olof GöstaBethe, Hans AlbrechtChandrasekhar, SubramanyanGamow, GeorgeHawking, StephenPenzias, Arno Allan

Purcell, Edward MillsTaylor, Joseph H., Jr.Van Allen, JamesWeinberg, StevenWheeler, John Archibald

ATOMIC PHYSICS

Blackett, Patrick MaynardStuart, Lord

Chu, StevenFranck, JamesLandau, Lev DavidovichLangevin, PaulLenard, Philipp vonMillikan, Robert AndrewsOppenheimer, J. RobertPerrin, Jean-BaptisteRutherford, ErnestSommerfeld, Arnold Johannes

WilhelmStark, JohannesStern, OttoThomson, Joseph John (J. J.)Wilson, Charles Thomson

ReesZeeman, Pieter

BIOPHYSICS

Chu, StevenFranck, James

Glaser, Donald ArthurPurcell, Edward Mills

CLASSICAL ELECTRODYNAMICSAND ELECTROMAGNETISM

Ampère, André-MarieBoltzmann, LudwigCavendish, HenryCompton, Arthur HollyCoulomb, Charles-Augustin deEinstein, AlbertFaraday, MichaelFitzGerald, George FrancisFoucault, Jean-Bernard-LéonGauss, Johann Carl FriedrichHenry, JosephHertz, Heinrich RudolfKelvin, Lord (William

Thomson)Kirchhoff, Gustav RobertLaue, Max Theodor Felix vonLenz, Heinrich Friedrich EmilLorentz, Hendrik AntoonMaxwell, James ClerkOhm, Georg SimonØrsted, Hans ChristianPlanck, Max Ernest LudwigPoynting, John HenryRayleigh, Lord (John William

Strutt)

349

ENTRIES BY FIELD

350 A to Z of Physicists

Röntgen, Wilhelm ConradStefan, JosefTesla, NikolaThomson, Joseph John (J. J.)Volta, Alessandro Guiseppe

Antonio AnastasioWeber, Wilhelm EduardWien, Wilhelm (Carl Werner

Otto Fritz Franz)Zeeman, Pieter

CLASSICAL MECHANICS

ArchimedesCoulomb, Charles-Augustin deFoucault, Jean-Bernard-LéonGalilei, GalileoHooke, RobertHuygens, ChristiaanMach, ErnstNewton, Sir IsaacYoung, Thomas

ELECTRICAL AND ELECTRONICENGINEERING

Alvarez, Luis W.Bardeen, JohnKilby, Jack St. ClairTesla, Nikola

ELECTROSTATICS

Coulomb, Charles-Augustin de

GEOPHYSICS

Lenz, Heinrich Friedrich Emil

GRAVITATION

Cavendish, HenryEinstein, AlbertHooke, RobertNewton, Sir IsaacPoynting, John Henry

HIGH PRESSURE AND HIGHTEMPERATURE PHYSICS

Bridgman, Percy Williams

HOLOGRAPHY

Gabor, Dennis

HYDROSTATICS ANDHYDRODYNAMICS

ArchimedesBernoulli, DanielHelmholtz, Hermann Ludwig

Ferdinand vonLandau, Lev DavidovichStokes, George Gabriel

INFORMATION THEORY

Gabor, Dennis

LASER SPECTROSCOPY

Bloembergen, NicolaasSchawlow, Arthur LeonardTownes, Charles Hard

LOW TEMPERATURE PHYSICSAND SUPERCONDUCTIVITY

Kamerlingh Onnes, HeikeKapitsa, Pyotr LeonidovichLandau, Lev Davidovich

MATHEMATICAL PHYSICS

Ampère, André-MarieArchimedesBernoulli, DanielDyson, FreemanGalilei, GalileoGauss, Johann Carl FriedrichHuygens, ChristiaanLangevin, PaulNewton, Sir IsaacRydberg, Johannes RobertStokes, George GabrielWigner, Eugene Paul

NUCLEAR PHYSICS

Bethe, Hans AlbrechtChadwick, Sir JamesCockcroft, John DouglasFermi, EnricoGamow, GeorgeGeiger, Hans WilhelmGlaser, Donald ArthurGoeppert-Mayer, Maria

GertrudeLandau, Lev DavidovichMeitner, LiseOppenheimer, J. RobertPurcell, Edward MillsRutherford, ErnestSakharov, Andrei

DmitriyevichSegrè, Emilio GinoTeller, EdwardWigner, Eugene PaulWu, Chien-ShiungYang, Chen Ning

OPTICS

Doppler, Christian JohannFizeau, Armand-Hippolyte-

LouisFoucault, Jean Bernard LéonFraunhofer, Joseph vonFresnel, Augustin JeanHelmholtz, Hermann Ludwig

Ferdinand vonHooke, RobertHuygens, ChristiaanLorentz, Hendrik AntoonMach, ErnstMaxwell, James ClerkMichelson, Albert AbrahamNewton, Sir IsaacRaman, Sir Chandrasekhara

VenkataRöntgen, Wilhelm ConradSnell, WillibrordStokes, George Gabriel

Entries by Field 351

Townes, Charles HardYoung, ThomasZeeman, Pieter

PARTICLE PHYSICS

Alvarez, Luis W.Anderson, Carl DavidBhabha, Homi JehangirBlackett, Patrick Maynard

Stuart, LordChadwick, Sir JamesCherenkov, Pavel

AlekseyevichCompton, Arthur HollyDavisson, Clinton JosephDirac, Paul Adrien MauriceFermi, EnricoFeynman, Richard PhillipsFitch, Val LogsdonGell-Mann, MurrayGlaser, Donald ArthurGlashow, Sheldon LeeLederman, Leon M.Lee, Tsung-DaoMössbauer, Rudolf LudwigNe’eman, YuvalPauli, WolfgangRamsey, Norman F.Reines, FrederickRichter, BurtonRubbia, CarloSalam, AbdusSegrè, Emilio GinoTing, Samuel Chao ChungTomonaga, Sin-ItiroVan de Graaff, Robert JemisonVeltman, Martinus J. G.Weinberg, StevenWilson, Charles Thomson

ReesWheeler, John ArchibaldYang, Chen NingYukawa, Hideki

PHILOSOPHY OF SCIENCE

Bohr, Niels Henrik DavidBridgman, Percy WilliamsEinstein, AlbertMach, Ernst

PHYSICAL CHEMISTRY

Cavendish, HenryCurie, MarieFaraday, MichaelFranck, JamesGoeppert-Mayer, Marie

GertrudeHelmholtz, Hermann Ludwig

Ferdinand vonNernst, WaltherØrsted, Hans ChristianPerrin, Jean-BaptisteStern, Otto

PLASMA PHYSICS

Alfvén, Hannes Olof GöstaLandau, Lev Davidovich

QUANTUM ELECTRODYNAMICSAND QUANTUM FIELD THEORY

Dyson, FreemanFeynman, Richard PhillipsGlashow, Sheldon Lee’t Hooft, GerardKusch, PolykarpLamb, Eugene Willis Jr.Landau, Lev DavidovichLenard, Philipp vonRamsey, Norman F.Salam, AbdusSchwinger, Julian SeymourTomanaga, Sin-ItiroVeltman, Martinus J. G.Weinberg, StevenWheeler, John ArchibaldWigner, Eugene Paul

QUANTUM MECHANICS

Barkla, Charles GloverBloch, FelixBohr, Niels Henrik DavidBorn, MaxBroglie, Louis-Victor-Pierre,

prince deDirac, Paul Adrien MauriceEinstein, AlbertFranck, JamesHeisenberg, WernerLandau, Lev DavidovichLandé, AlfredLaue, Max Theodor Felix vonOppenheimer, J. RobertPauli, WolfgangPlanck, Max Ernest LudwigSchrödinger, ErwinSommerfeld, Arnold JohannTeller, Edward

RADIOACTIVITY

Becquerel, Antoine-HenriCurie, MarieMeitner, LiseRutherford, Ernest

RADIO ASTRONOMY

Penzias, Arno AllanTaylor, Joseph H., Jr.

RELATIVITY

Einstein, AlbertHawking, StephenLandau, Lev DavidovichLaue, Max Theodor Felix vonLorentz, Hendrik AntoonTaylor, Joseph H., Jr.Wheeler, John Archibald

SOLID STATE AND CONDENSEDMATTER PHYSICS

Alferov, Zhores IvanovichAnderson, Philip Warren

Bardeen, JohnBarkla, Charles GloverBethe, Hans AlbrechtBloch, FelixBorn, MaxEinstein, AlbertJosephson, Brian DavidKilby, Jack St. ClairKroemer, HerbertLandau, Lev DavidovichLangevin, PaulLaue, Max Theodor Felix vonLenard, Philipp vonMott, Sir Nevill FrancisPurcell, Edward MillsRabi, Isidor IsaacSchrieffer, John RobertSchockley, William BradfordVan Vleck, John Housbrook

SPECTROSCOPY

Ångstrom, Anders Jonas

Fraunhofer, Joseph vonKirchhoff, Gustav RobertRaman, Sir Chandrasekhara

VenkataRydberg, Johannes Robert

STATISTICAL MECHANICS

Bloch, FelixBoltzmann, LudwigEinstein, AlbertRayleigh, Lord (John William

Strutt)Sommerfeld, Arnold Johannes

WilhelmStark, Johannes

TERRESTRIAL MAGNETISM

Gauss, Johann Carl Friedrich

THERMODYNAMICS

Boltzmann, LudwigCarnot, Nicolas Léonard Sadi

Clausius, Rudolf JuliusEmmanuel

Helmholtz, Hermann LudwigFerdinand von

Joule, James PrescottKelvin, Lord (William

Thomson)Kirchhoff, Gustav RobertMaxwell, James ClerkNernst, WaltherRayleigh, Lord (John William

Strutt)Stark, JohannesStefan, JosefWien, Wilhelm (Carl Werner

Warner Fritz Franz)

352 A to Z of Physicists

AUSTRIA

Boltzmann, LudwigDoppler, ChristianMach, ErnstMeitner, LisaPauli, WolfgangSchrödinger, ErwinStefan, Josef

BAVARIA

Ohm, George SimonStark, Johannes

CHINA

Lee, Tsung-DaoTing, Samuel Chao ChungWu, Chien-ShiungYang, Chen Ning

DENMARK

Bohr, Niels Henrik DavidØrsted, Hans Christian

ENGLAND

Barkla, Charles GloverBlackett, Patrick Stuart

Maynard, LordChadwick, Sir JamesCockcroft, John DouglasDirac, Paul Adrien Maurice

Dyson, FreemanFaraday, MichaelHawking, StephenHooke, RobertJoule, James PrescottMott, Sir Nevill FrancisNewton, Sir IsaacPoynting, John HenryRayleigh, Lord (John William

Strutt)Thomson, Joseph John (J. J.)Young, Thomas

ESTONIA

Lenz, Heinrich Friedrich Emil

FRANCE

Ampère, André-MarieBecquerel, Antoine-HenriBroglie, Louis-Victor-Pierre,

prince deCarnot, Nicolas Léonard SadiCavendish, HenryCoulomb, Charles AugustinFizeau, Armand-Hippolyte-

LouisFoucault, Jean-Bernard-LéonFresnel, Augustin JeanLangevin, PaulPerrin, Jean-Baptiste

GERMANY

Bethe, Hans AlbrechtBorn, MaxEinstein, AlbertFranck, JamesFraunhofer, Joseph vonGauss, Johann Carl FriedrichGeiger, Hans WilhelmGoeppert-Mayer, Maria

GertrudeHeisenberg, WernerHelmholtz, Hermann Ludwig

Ferdinand vonHertz, Heinrich RudolfKirchhoff, Gustav RobertKroemer, HerbertKusch, PolykarpLandé, AlfredLaue, Max Theodor Felix vonMössbauer, Rudolf LudwigPenzias, Arno AllanPlanck, Max Ernest LudwigRöntgen, Wilhelm ConradStern, OttoWeber, Wilhelm Eduard

HUNGARY

Gabor, DennisLenard, Philipp vonTeller, Edward

353

ENTRIES BYCOUNTRY OF BIRTH

Wigner, Eugene Paul

INDIA

Bhabha, Homi JehangirChandrasekhar, SubramanyanRaman, Sir Chandrasekhara

Venkata

IRELAND

FitzGerald, George FrancisKelvin, Lord (William

Thomson)Stokes, George Gabriel

ISRAEL

Ne’eman, Yuval

ITALY

Fermi, EnricoGalilei, GalileoRubbia, CarloSegrè, Emilio GinoVolta, Alessandro Giuseppe

Antonio Anastasio

JAPAN

Tomonaga, Sin-ItiroYukawa, Hideki

NETHERLANDS

Bloembergen, NicolaasBernoulli, Daniel’t Hooft, GerardHuygens, ChristianKamerlingh Onnes, HeikeLorentz, Hendrik AntoonSnell, WillibrordVeltman, MartinusZeeman, Pieter

NEW ZEALAND

Rutherford, Ernest

PAKISTAN

Salam, Abdus

POLAND

Curie, MarieRabi, Isidor Isaac

PRUSSIA

Clausius, Rudolf JuliusEmmanuel

Michelson, Albert AbrahamNernst, WaltherSommerfeld, Arnold Johannes

WilhelmWien, Wilhelm (Carl Werner

Otto Fritz Franz)

RUSSIA

Alferov, Zhores IvanovichCherenkov, Pavel

AlekseyevichGamow, GeorgeKapitsa, PyotrLandau, Lev DavidovichSakharov, Andrey

Dmitriyevich

SCOTLAND

Maxwell, James ClerkWilson, Charles Thomson

Rees

SERBIA

Tesla, Nikola

SICILY

Archimedes

SWEDEN

Alfvén, Hannes Olof GöstaÅngstrom, Anders JonasRydberg, Johannes Robert

SWITZERLAND

Bloch, Felix

UNITED STATES

Alvarez, Luis W.Anderson, Carl DavidAnderson, Philip WarrenBardeen, JohnBridgman, Percy WilliamsChu, StevenCompton, Arthur HollyDavisson, Clinton JosephFeynman, Richard PhillipsFitch, Val LogsdonGell-Mann, MurrayGlaser, Donald ArthurGlashow, SheldonHenry, JosephKilby, Jack St. ClairLamb, Willis Eugene Jr.Lederman, Leon M.Millikan, Robert AndrewsOppenheimer, J. RobertPurcell, Edward MillsRamsey, Norman F.Reines, FrederickRichter, BurtonSchawlow, Arthur LeonardSchrieffer, John RobertSchwinger, JulianShockley, WilliamTaylor, Joseph H., Jr.Townes, Charles HardVan Allen, JamesVan de Graaff, Robert JemisonVan Vleck, John HousbrookWeinberg, StevenWheeler, John Archibald

WALES

Josephson, Brian David

354 A to Z of Physicists

AUSTRIA

Boltzmann, LudwigDoppler, ChristianMach, ErnstStefan, Josef

CZECHOSLOVAKIA

Mach, Ernst

DENMARK

Bloch, FelixBohr, Niels Henrik DavidGamow, GeorgeHeisenberg, WernerØrsted, Hans ChristianTeller, Edward

ENGLAND

Barkla, Charles GloverBhabha, Homi JehangirBlackett, Lord Patrick

Maynard BlackettBohr, Niels Henrik DavidBorn, MaxCavendish, HenryChadwick, Sir JamesChandrasekhar, SubramanyanCockcroft, John DouglasDirac, Paul Adrien MauriceFaraday, MichaelFitzGerald, George Francis

Gabor, DennisGamow, GeorgeGeiger, Hans WilhelmHawking, StephenHooke, RobertJosephson, Brian DavidJoule, James PrescottKelvin, Lord (William

Thomson)Maxwell, James ClerkMott, Sir Nevill FrancisNe’eman, YuvalNewton, Sir IsaacPoynting, John HenryRayleigh, Lord (John William

Strutt)Rutherford, ErnestSalam, AbdusStokes, George GabrielThomson, Joseph John (J. J.)Wilson, Charles Thomson

ReesYoung, Thomas

FRANCE

Ampère, André-MarieBecquerel, Antoine-HenriBroglie, Louis-Victor-Pierre,

prince deCarnot, Nicolas Léonard SadiCoulomb, Charles-Augustin de

Curie, MarieFizeau, Armand-Hippolyte-

LouisFoucault, Jean-Bernard-LéonFresnel, Augustin-JeanHuygens, ChristiaanLangevin, PaulPerrin, Jean-Baptiste

GERMANY

Bethe, Hans AlbrechtBloch, FelixBorn, MaxClausius, Rudolf Julius

EmmanuelEinstein, AlbertFranck, JamesFraunhofer, Joseph vonGabor, DennisGamow, GeorgeGauss, Johann Carl FriedrichGeiger, Hans WilhelmGoeppert-Mayer, Maria

GertrudeHeisenberg, WernerHelmholtz, Hermann Ludwig

Ferdinand vonHertz, Heinrich RudolfKirchhoff, Gustav RobertKroemer, HerbertLandé, Alfred

355

ENTRIES BY COUNTRY OFMAJOR SCIENTIFIC ACTIVITY

356 A to Z of Physicists

Laue, Max Theodor Felix vonLenard, Philipp vonMeitner, LiseMichelson, Albert AbrahamMössbauer, Rudolf LudwigNernst, WaltherOhm, George SimonPauli, WolfgangPlanck, Max Ernest LudwigRöntgen, Wilhelm ConradSchrödinger, ErwinSommerfeld, Arnold Johannes

WilhelmStark, JohannesStern, OttoTeller, EdwardTing, Samuel Chao ChangWeber, Wilhelm EduardWien, Wilhelm (Carl Werner

Otto Fritz Franz)Wigner, Eugene Paul

INDIA

Bhabha, Homi JehangirRaman, Sir Chandrasekhara

Venkata

ISRAEL

Ne’eman, Yuval

ITALY

Fermi, EnricoGalilei, GalileoRubbia, CarloSalam, AbdusSegrè, Emilio GinoVolta, Alessandro Giuseppe

Antonio Anastasio

JAPAN

Tomonaga, Sin-ItiroYukawa, Hideki

NETHERLANDS

’t Hooft, GerardHuygens, ChristiaanKamerlingh Onnes, HeikeLorentz, Hendrik AntoonSnell, WillibrordVeltman, MartinusZeeman, Pieter

PAKISTAN

Salam, Abdus

POLAND

Curie, Marie

RUSSIA

Alferov, Zhores IvanovichBernoulli, DanielCherenkov, Pavel

AlekseyevichGamow, GeorgeKapitsa, Pyotr LeonidovichLandau, Lev DavidovichLenz, Heinrich Friedrich EmilSakharov, Andrey

Dmitriyevich

SCOTLAND

Kelvin, Lord (WilliamThomson)

Maxwell, James ClerkWilson, Charles Thomson

Rees

SICILY

Archimedes

SWEDEN

Alfvén, Hannes Olof GöstaÅngstrom, Anders JonasMeitner, LisaRydberg, Johannes Robert

SWITZERLAND

Bernoulli, DanielClausius, Rudolf Julius

EmmanuelEinstein, AlbertLederman, Leon M.Pauli, WolfgangRubbia, CarloSchrödinger, ErwinTing, Samuel Chao Chung

UNITED STATES

Alvarez, Luis W.Anderson, Carl DavidAnderson, Philip WarrenBardeen, JohnBethe, Hans AlbrechtBloch, FelixBloembergen, NicolaasBridgman, Percy WilliamsChandrasekhar, SubramanyanChu, StevenCompton, Arthur HollyDavisson, Clinton JosephDyson, FreemanFermi, EnricoFeynman, Richard PhillipsFitch, Val LogsdonFranck, JamesGamow, GeorgeGell-Mann, MurrayGlaser, Donald ArthurGlashow, SheldonGoeppert-Mayer, Maria

GertrudeHenry, JosephKilby, Jack St. ClairKroemer, HerbertKusch, PolykarpLamb, Willis Eugene Jr.Landé, AlfredLederman, Leon M.

Lee, Tsung-DaoMichelson, Albert AbrahamMillikan, Robert AndrewsMössbauer, Rudolf LudwigNe’eman, YuvalOppenheimer, J. RobertPenzias, Arno AllanPurcell, Edward MillsRabi, Isidor IsaacRamsey, Norman F.Reines, Frederick

Richter, BurtonRubbia, CarloSchawlow, Arthur LeonardSchrieffer, John RobertSchwinger, Julian SeymourSegrè, Emilio GinoShockley, WilliamStern, OttoTaylor, Joseph H., Jr.Tesla, NikolaTeller, Edward

Ting, Samuel Chao ChungTownes, Charles HardVan Allen, JamesVan de Graaff, Robert JemisonVan Vleck, John HousbrookVeltman, Martinus J. G.Weinberg, StevenWheeler, John ArchibaldWigner, Eugene PaulWu, Chien-ShiungYang, Chen Ning

Entries by Country of Major Scientific Activity 357

THIRD CENTURY B.C.–FOURTH CENTURY A.D.Archimedes

1400–1599Galilei, GalileoSnell, Willibrord

1600–1699Hooke, RobertHuygens, ChristiaanNewton, Sir Isaac

1700–1799Ampère, André-MarieBernoulli, DanielCarnot, Nicolas Léonard SadiCavendish, HenryCoulomb, Charles-Augustin deFaraday, MichaelFraunhofer, Joseph vonFresnel, Augustine-JeanGauss, Johann Carl FriedrichHenry, JosephOhm, George SimonØrsted, Hans ChristianVolta, Alessandro Guiseppe

Antonio AnastasioYoung, Thomas

1800–1849Ångstrom, Anders JonasBoltzmann, LudwigClausius, Rudolf Julius

EmmanuelDoppler, ChristianFizeau, Armand-Hippolyte-

LouisFoucault, Jean-Bernard-LéonHelmholtz, Hermann Ludwig

Ferdinand vonJoule, James PrescottKelvin, Lord (William

Thomson)Kirchhoff, Gustav RobertLenz, Heinrich Friedrich EmilMach, ErnstMaxwell, James ClerkRayleigh, Lord (John William

Strutt)Röntgen, Wilhelm ConradStefan, JosefStokes, George GabrielWeber, Wilhelm Eduard

1850–1899Barkla, Charles GroverBecquerel, Antoine-HenriBlackett, Patrick Maynard

Stuart, Lord

Bohr, Niels Henrik DavidBorn, MaxBridgman, Percy WilliamsBroglie, Louis-Victor-Pierre,

prince deChadwick, Sir JamesCockcroft, John DouglasCompton, Arthur HollyCurie, MarieDavisson, Clinton JosephEinstein, AlbertFitzGerald, George FrancisFranck, JamesGeiger, Hans WilhelmHertz, Heinrich RudolfKamerlingh Onnes, HeikeKapitsa, Pyotr LeonidovichLandé, AlfredLangevin, PaulLaue, Max Theodor Felix vonLenard, Philipp vonLorentz, Hendrik AntoonMeitner, LiseMichelson, Albert AbrahamMillikan, Robert AndrewNernst, WaltherPerrin, Jean-BaptistePlanck, Max Ernest LudwigPoynting, John HenryRabi, Isidor Isaac

358

ENTRIES BYYEAR OF BIRTH

Raman, Sir ChandrasekharaVenkata

Rutherford, ErnestRydberg, JohannesSchrödinger, ErwinSommerfeld, Arnold Johannes

WilhelmStark, JohannesStern, OttoTesla, NikolaThomson, Joseph John (J. J.)Van Vleck, John HousbrookWien, WilhelmWilson, Charles Thomson

ReesZeeman, Pieter

1900–1909Alfvén, Hannes Olaf GöstaAnderson, Carl DavidBardeen, JohnBethe, Hans AlbrechtBhabha, Homi JehangirBloch, FelixCherenkov, Pavel

AlekseyevichDirac, Paul Adrien MauriceFermi, EnricoGabor, DennisGamow, GeorgeGoeppert-Mayer, Maria

GertrudeHeisenberg, Werner

Landau, Lev DavidovichMott, Sir Nevill FrancisOppenheimer, J. RobertPauli, WolfgangSegré, Emilio GinoTeller, EdwardTomonaga, Sin-ItiroVan de Graaff, Robert JemisonWigner, Eugene PaulYukawa, Hideki

1910–1919Alvarez, Luis W.Chandrasekhar, SubramanyanFeynman, Richard PhillipsKusch, PolykarpLamb, Eugene Willis Jr.Purcell, Edward MillsRamsey, Norman F.Reines, FrederickSchwinger, Julian SeymourShockley, William BradfordTownes, Charles HardVan Allen, JamesWheeler, John ArchibaldWu, Chien-Shiung

1920–1929Anderson, Philip WarrenBloembergen, NicolaasDyson, FreemanFitch, Val LogsdonGell-Mann, Murray

Glaser, Donald ArthurKilby, JackKroemer, HerbertLederman, Leon M.Lee, Tsung-DaoMössbauer, Rudolf LudwigNe’eman, YuvalSakharov, Andrei

DimitriyevichSalam, AbdusSchawlow, Arthur LeonardYang, Chen Ning

1930–1939Alferov, Zhores IvanovichGlashow, Sheldon LeePenzias, Arno AllenRichter, BurtonRubbia, CarloSchrieffer, John RobertTing, Samuel Chao ChungVeltman, Martinus J. G.Weinberg, Steven

1940–1949Chu, StevenHawking, Stephen’t Hooft, GerardJosephson, Brian DavidTaylor, Joseph H., Jr.

Entries by Year of Birth 359

360

CHRONOLOGY

1550 1575 1600 1625 16751650200250 225275300 17251700 1750 1775 B.C. A.D.

1700 17401720 1760 1800 1820 1840 1860 1880 1900 1920 1940 1960 19801780

Archimedes

Robert HookeSir Isaac Newton

Daniel BernoulliHenry Cavendish

Charles-Augustin de CoulombAlessandro Guiseppe Volta

André-Marie AmpèreThomas Young

Hans Christian ØrstedJohann Carl Friedrich Gauss

Fraunhofer

Galileo Galilei

Christiaan HuygensWillibrord Snell

Georg Simon OhmFresnel

Michael FaradayNicolas Léonard Carnot

Joseph Henry

Wilhelm Eduard Weber

Anders Jonas Ångstrom

James Prescott Joule

Jean-Bernard Foucault

Christian DopplerHeinrich Lenz

Armand-Hippolyte-Louis FizeauGeorge Gabriel Stokes

Herman Ludwig HelmholtzRudolf Clausius

Chronology 361

1780 1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000

James FranckMax Born

Niels Hendrik David Bohr

Otto SternSir Chandrasekhara Venkata Raman

Erwin Schrodinger

Gustav Robert Kirchhoff

James Clerk MaxwellJosef Stefan

Lord Kelvin (William Thomson)

Ernst MachWilliam John Strutt (Lord Rayleigh)

Wilhelm Conrad RöntgenGeorge Francis FitzGerald

Ludwig Boltzmann

Antoine-Henri BecquerelJohn Henry Poynting

Albert Abraham MichelsonHeike Kamerlingh Onnes

Hendrik Antoon LorentzJohannes Rydberg

Joseph John ThomsonNikola Tesla

Heinrich HertzMax PlanckPhilipp Lenard

Wilhelm WienWalther NernstPieter ZeemanMarie Curie

Arnold SommerfeldRobert Andrews MillikanCharles Thomson Rees WilsonJean-Baptiste Perrin

Ernest RutherfordPaul Langevin

Johannes StarkCharles Glover Barkla

Lisa MeitnerAlbert Einstein

Max Theodor Felix von LaueClinton Joseph Davisson

Hans Wilhelm GeigerPercy Williams Bridgman

362 A to Z of Physicists

1780 1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000

Alfred Landé

Arthur Holly Compton Louis-Victor-Pierre de Broglie

Sir James Chadwick

Pyotr Leonidovich KapitsaJohn Douglas Cockcroft

Isidor Isaac RabiJohn Housbrook Van Vleck

Lord Blackett

Wolfgang PauliDennis Gabor

Enrico FermiRobert Jemison Van de Graaff

Werner HeisenbergPaul Adrien Maurice Dirac

Eugene Paul WignerRobert J. Oppenheimer

George GamowPavel Alekseyevich Cherenkov

Felix BlochCarl David Anderson

Emilio Gino SegrèSir Nevill Francis Mott

Marie Goeppert-MayerSin-Itiro Tomonaga

Hans Albrecht BetheHideki Yukawa

Lev Davidovich LandauJohn Bardeen

Hannes Olof GöstaEdward Teller

Homi Jehangir BhabhaWilliam Bradford ShockleySubramanyan Chandrasekhar

Luis W. AlvarezPolykarp Kusch

John Archibald WheelerEdward Mills Purcell

Chien-Shiung WuWillis Eugene Lamb

James Van Allen

Charles Hard TownesRichard Phillips Feynman

Norman F. Ramsey

Chronology 363

1780 1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000

Julian Seymour Schwinger

Nicolaas Bloembergen Andrei Dmitriyevich Sakharov

Frederick Reines

Arthur Leonard SchawlowLeon M. Lederman

Philip Warren AndersonFreeman Dyson

Chen Ning Yang

Val Logsdon FitchJack St. Clair Kilby

Yuval Ne’emanAbdus Salam

Donald Arthur GlaserTsung-Dao LeeHerbert Kroemer

Murray Gell-MannRudolf Ludwig MössbauerZhores Ivanovich Alferov

Burton RichterJohn Robert SchriefferMartinus J.G. VeltmanSheldon Lee Glashow

Arno Allan PenziasSteven Weinberg

Carlo RubbiaSamuel Chao Chung Ting

Brian David Josephson

Joseph H.Taylor, Jr.Stephen Hawking

Gerard ’t HooftSteven Chu

BIBLIOGRAPHY

Abbott, David, ed. The Biographical Dictionary ofScientists: Physicists. New York: PeterBedrick Books, 1984.

Aczel, Amir D. God’s Equation: Einstein, Rela-tivity, and the Expanding Universe. NewYork: Dell, 2000.

———. Entanglement: The Greatest Mystery inPhysics. New York: Four Walls Eight Win-dows, 2002.

Alfvén, Hannes. On the Origin of the Solar Sys-tem. Westport, Conn.: Greenwood Press,1973.

———. Worlds–Antiworlds: Antimatter in Cos-mology. New York: W. H. Freeman, 1966.

Alvarez, Luis W. Adventures of a Physicist. NewYork: Basic Books, 1978.

American Men and Women of Science, 1995–96:A Biographical Directory of Today’s Leaders inPhysical, Biological, and Related Sciences.New York: R. R. Bowker, 1994.

Archimedes. The Works of Archimedes. NewYork: Dover, 2002.

Isaac, Asimov. Asimov’s Biographical Encyclo-pedia of Science and Technology: The Livesand Achievements of 1510 Great Scientistsfrom Ancient Times to the Present Chrono-logically Arranged. New York: Doubleday,1982.

———. Atom: Journey Across the SubatomicCosmos. New York: Dutton/Plume. 1992

Badash, Lawrence. Kapitsa, Rutherford, and theKremlin. New Haven, Conn.: Yale Univer-sity Press, 1985.

Baird, David, Alfred Nordman, and R. I.Hughes, eds. Heinrich Hertz: Classical Physi-cist, Modern Philosopher. Boston: KluwerAcademic, 1997.

Balibar, Francoise. Einstein: Decoding the Uni-verse. New York: Harry N. Abrams, 2001.

Barkan, Diana. Nernst: Architect of Physical Rev-olution. London: Cambridge UniversityPress, 1999.

Beckman, Olof. Ångstrom: Father and Son. ActaUniversitatis Upsaliensis, C. OrganisationOch Historia, No. 60. Philadelphia: Coro-net Books, 1997.

Berlinski, David. Newton’s Gift: How Sir IsaacNewton Unlocked the System of the World.New York: Free Press, 2000.

Bernstein, Jeremy. A Comprehensible World: OnModern Science and Its Origins. New York:Random House, 1967.

———. Albert Einstein and the Frontiers ofPhysics. Oxford: Oxford University Press,1996.

———. Three Degrees Above Zero: Bell Labs inthe Information Age. New York: Scribner &Sons, 1984.

———. Hans Bethe, Prophet of Energy. NewYork: Basic Books, 1980.

364

Bethe, Hans Albrecht. The Road from LosAlamos. Master of Modern Physics. NewYork: Springer-Verlag, 1991.

“Biographical Memoirs,” Washington, D.C. Na-tional Academy Press, 1994, 2000. Availableon-line: URL: http://books.nap.edu/books.

Boag, J. W., P. E. Rubinin, and D. Shoenberg,eds. Kapitsa in Cambridge and Moscow: Lifeand Letters of a Russian Physicist. Amster-dam: Elsevier Science, 1990.

Bodanus, David. E = Mc2: A Biography of theWorld’s Most Famous Equation. New York:Walker, 2000.

Bonner, Yelena. Alone Together. New York: A.A. Knopf, 1986.

Boorse, H. A. and L. Motz, eds. The World of theAtom. New York: Basic Books, 1966.

Born, Max. Atomic Physics. New York: Dover,1989.

———. My Life. New York: Scribner’s, 1978.Brennan, Richard P. Heisenberg Probably Slept

Here: The Lives, Times and Ideas of the GreatPhysicists of the 20th Century. New York:John Wiley & Sons, 1997.

Brian, Denis. Einstein: A Life. New York: JohnWiley & Sons, 1997.

Bridgman, Percy Williams. The Logic of ModernPhysics. New York: Macmillan, 1961.

Brown, Andrew P. The Neutron and the Bomb: ABiography of Sir James Chadwick. Oxford:Oxford University Press, 1997.

Buchwald, Jed Z. The Creation of Scientific Ef-fects: Heinrich Hertz and Electric Waves.Chicago: Chicago University Press, 1994.

———. Histories of the Electron. Dibner Insti-tute Studies in the History of Science andTechnology. Cambridge, Mass.: MIT Press,2001.

———. The Rise of the Wave Theory of Light:Optical Theory and Experiment in the EarlyNineteenth Century. Chicago: University ofChicago Press, 1989.

Bühler, W. K. Gauss: A Biographical Study. NewYork: Springer-Verlag, 1987.

Cahan, David, ed. Hermann Von Helmholtz andthe Foundations of Nineteenth-Century Sci-ence. California Studies in the History ofScience, No. 12. Berkeley: University ofCalifornia Press, 1993.

Calder, Nigel. Einstein’s Universe. New York:Random House, 1990.

Cantor, Geoffrey, David Gooding, and Frank A.James. Michael Faraday. Amherst, N.Y.:Prometheus Books, 1996.

Cardwell, D. S. L. From Watt to Clausius: TheRise of Thermodynamics in the Early Indus-trial Age. Cornell, N.Y.: Cornell UniversityPress, 1971.

Cassidy, David. Uncertainty: The Life and Scienceof Werner Heisenberg. New York: W. H.Freeman, 1992.

Cercignani, Carlo. Ludwig Boltzmann: The ManWho Trusted Atoms. Oxford: Oxford Uni-versity Press, 1998.

Cheney, Margaret. Tesla: Man Out of Time.New York: Dell, 1981.

Cohen, R. S., ed. Boston Studies in the Philosophyof Science. Vol. 6. Ernst Mach: Physicist andPhilosopher. Boston: Kluwer Academic Pub-lishers, 1975.

Compton, Arthur Holly. Atomic Quest—a Per-sonal Narrative. Oxford: Oxford UniversityPress, 1956.

Concise Dictionary of Scientific Biography. NewYork: Scribner’s, 1981.

Cooper, Dan. Enrico Fermi: And the Revolutionsin Modern Physics. Oxford: Oxford Univer-sity Press, 1998.

Coulson, Thomas. Joseph Henry: His Life andWork. Princeton, N.J.: Princeton Univer-sity Press, 1950.

Crease, Robert P., and Charles C. Mann. TheSecond Creation: Makers of the Revolution inTwentieth Century Physics. Revised ed. NewBrunswick, N.J.: Rutgers University Press,1995.

Curie, Eve. Madame Curie. New York: Double-day, 1937.

Bibliography 365

Dahl, Per F. Flash of the Cathode Rays: A Historyof J.J. Thomson’s Electron. Philadelphia: In-stitute of Physics, 1997.

Daintith, John, and John O. E. Clark. The FactsOn File Dictionary of Physics. 3rd ed. NewYork: Facts On File, 1999.

Daintith, John, Sarah Mitchell, ElizabethTootill, and Derek Gjertsen, eds. Biographi-cal Encyclopedia of Scientists. Philadelphia:Institute of Physics, 1994.

Darrigol, Olivier. Electrodynamics from Ampèreto Einstein. Oxford: Oxford UniversityPress, 2000.

Dictionary of Scientific Biography. New York:Scribner’s, 1970–1980.

Drake, Ellen Tan. Restless Genius: Robert Hookeand His Earthly Thoughts. Oxford: OxfordUniversity Press, 1996.

Drake, Stillman. Galileo At Work: His ScientificBiography. Chicago: University of ChicagoPress, 1978.

Dugdale, J. S. Entropy and Its Physical Meaning.London: Taylor & Francis, 1996.

Dyson, Freeman. Disturbing the Universe. Cam-bridge, Mass.: Perseus Books, 2001.

Eden, Alan. The Search for Christian Doppler.New York: Springer-Verlag, 1992.

Einstein, Albert. The Expanded Quotable Ein-stein, Alice Calaprice, ed. Princeton, N.J.:Princeton University Press, 2000.

———. Ideas and Opinions. New York: RandomHouse, 1988.

———. Out of My Later Years. Secaucus, N.J.:Carol, 1972.

Elliott, Clark A. Biographical Dictionary ofAmerican Science: The Seventeenth Throughthe 19th Centuries. Westport, Conn.:Greenwood Press, 1979.

Fauvel, John, ed. Let Newton Be! Oxford: Ox-ford University Press, 1988.

Fermi, Laura. Atoms in the Family: My Life withEnrico Fermi. Chicago: University ofChicago Press, 1994.

Ferris, Timothy. Coming of Age in the MilkyWay. New York: William Morrow, 1988.

———, ed. The World Treasury of Physics, As-tronomy, and Mathematics. Boston: Little,Brown, 1991.

Feynman, Richard. The Meaning of It All:Thoughts of a Citizen Scientist. Reading,MA: Addison Wesley, 1995.

———. QED: The Strange Theory of Light andMatter. Princeton, N.J.: Princeton Univer-sity Press, 1985.

Feynman, Richard, and R. Leighton. SurelyYou’re Joking, Mr. Feynman: Adventures of aCurious Character. New York: W. W. Nor-ton, 1997.

Forward, Robert L. and Joel Davis. Mirror Mat-ter: Pioneering Antimatter Physics. Lincoln,Nebr.: iUniverse. Com, 2001.

Franklin, Allan. Are There Really Neutrinos? AnEvidential History. New York: PerseusBooks, 2000.

Fraser, Gordon. Antimatter: The Ultimate Mirror.London: Cambridge University Press, 2000.

Fraunfelder, H. The Mössbauer Effect. NewYork: W. A. Benjamin, 1963.

Frisch, Otto. What Little I Remember. London:Cambridge University Press, 1991.

Gabor, Dennis. Innovations: Scientific, Techno-logical and Social. Oxford: Oxford Univer-sity Press, 1970.

Galileo. Discoveries and Opinions of Galileo: In-cluding the Starry Messenger (1610), Letter tothe Grand Duchess Christina (1615), and Ex-cerpts from Letters on Sunspots (1613), TheAssayer (1623). Translation by StillmanDrake. Based on Work by Galileo. NewYork: Doubleday, 1989.

Gamow, George. The Great Physicists fromGalileo to Einstein. New York: Dover, 1988.

———. My World Line: An Informal Autobiog-raphy. New York: Viking Penguin, 1970.

———. Thirty Years That Shook Physics: TheStory of Quantum Theory. New York: Dover,1985.

Gell-Mann, Murray. The Quark and the Jaguar:Adventures in the Simple and the Complex.New York: W. H. Freeman, 1994.

366 A to Z of Physicists

Gell-Mann, Murray and Yuval Ne’eman. TheEightfold Way. Cambridge, Mass.: Perseus2000.

Ghani, Abdul. Abdus Salam. Karachi: Ma’aref,1982.

Glashow, Sheldon L. The Charm of Physics.New York: Springer-Verlag, 1991.

———. Interactions: A Journey Through theMind of a Particle Physicist and the Matter ofThis World. New York: Warner Books,1988.

Glasser, Otto. Wilhelm Conrad Roentgen and theEarly History of the Roentgen Rays. Novato,Calif.: Jeremy Norman, 1992.

Gleick, Richard. Genius: The Life and Science ofRichard Feynman. New York: PantheonBooks, 1992.

Goudaroulis, Y. and Gavrolu, K., eds. ThroughMeasurement to Knowledge: The Selected Pa-pers of Heike Kamerlingh Onnes. Dordrecht,Netherlands: Kluwer Academic, 1991.

Greene, Brian. The Elegant Universe: Super-strings, Hidden Dimensions, and the Quest forthe Ultimate Theory. New York: W. W. Nor-ton, 1999.

Gribben, John. Schrödinger’s Kittens and theSearch for Reality: Solving the Quantum Mys-teries. Boston: Little, Brown, 1996.

———. In Search of Schrödinger’s Cat: QuantumPhysics and Reality. New York: BantamDoubleday Dell, 1984.

Harman, Peter M. The Natural Philosophy ofJames Clerk Maxwell. London: CambridgeUniversity Press, 1998.

Hassan, Z. and C. H. Lai, eds. Ideals and Reali-ties: Selected Essays of Abdus Salam. Singa-pore: World Scientific, 1983.

Hawking, Steven. A Brief History of Time: Fromthe Big Bang to Black Holes. New York: Ban-tam Books, 1998.

———. Stephen Hawking’s Universe: The CosmosExplained. New York: Basic Books, 1998.

———. The Future of Spacetime. New York: W.W. Norton, 2002.

Herken, Gregg. Brotherhood of the Bomb: TheTangled Lives and Loyalties of Robert Oppen-heimar, Ernest Lawrence and Edward Teller.New York: Henry Holt, 2002.

———. The Universe in a Nutshell. New York:Bantam Books, 2002.

Heilbron, J. L. The Dilemmas of an Upright Man:Max Planck and the Fortunes of Germany.Cambridge, Mass.: Harvard UniversityPress, 2000.

Helmholtz, Hermann Von and David Cahan,eds. Science and Culture: Popular and Philo-sophical Essays. Chicago: University ofChicago Press, 1995.

Hermann, A. Wolfgang Pauli: Scientific Corre-spondence with Bohr, Einstein, Heisenberg.Vol. 191. New York: Springer-Verlag, 1979.

Hewish, Antony, et al. Pulsars as Physics Laborato-ries. Oxford: Oxford University Press, 1994.

’t Hooft, Gerard. In Search of the Ultimate Build-ing Blocks. London: Cambridge UniversityPress, 1997.

———. Under the Spell of the Gauge Principle.Singapore: World Scientific, 1994.

Hofmann, James R. Andre-Marie Ampère: En-lightenment and Electrodynamics. London:Cambridge University Press, 1966.

Koch Torres Assis, André. Fundamental Theo-ries of Physics. Vol. 66. Weber’s Electrody-namics. Dordrecht, Netherlands: KluwerAcademic, 1994.

Krauss, Lawrence. Atom. Boston: Little, Brown,2002.

Kropp, W., J. Schultz, M. Moe, et al., eds. Neu-trinos and Other Matters: Selected Works ofFrederick Reines. Singapore: World Scien-tific, 1996.

Kuhn, Thomas S. Black-Body Theory and theQuantum Discontinuity. Chicago: Univer-sity of Chicago Press, 1987.

Kursunoglu, Behram N. and Eugene Wigner,eds. Paul Adrien Maurice Dirac: Reminis-cences About a Great Physicist. London:Cambridge University Press, 1987.

Bibliography 367

Lafferty, Peter. Archimedes. New York: Book-wright Press, 1991.

Laurikainen, Kalervo Vihtori. Beyond the Atom:Philosophical Thoughts of Wolfgang Pauli.New York: Springer-Verlag, 1988.

Lederman, Leon M. and David N. Schramm.From Quarks to the Cosmos: Tools of Discov-ery. New York: W. H. Freeman, 1995.

Lederman, Leon M. and Dick Teresi. The GodParticle: If the Universe Is the Answer, WhatIs the Question? New York: Houghton Mif-flin, 1993.

Holloway, David. Stalin and the Bomb: The So-viet Union and Atomic Energy, 1939–1956.New Haven, Conn.: Yale University Press,1994.

Howard, Donald R. and John Stachel, eds. Ein-stein: The Formative Years 1879–1909.Boston: Birkhauser, 1986.

Hunt, Bruce J. The Maxwellians. Ithaca, N.Y.:Cornell University Press, 1995.

Hunt, Inez and Wanetta W. Draper. Lightning inHis Hand: The Life Story of Nikola Tesla.Thousand Oaks, Calif.: Sage Books, 1964.

“Index of Inventors.” Available on-line. URL:http://www.invent.org/book/book-text/in-dexbyname.html.

Ipsen, D. C. Archimedes: Greatest Scientist of theAncient World. Hillside, N.J.: Enslow, 1988.

Jaffe, Bernard. Michelson and the Speed of Light.Garden City, N.Y.: Doubleday, 1960.

Jelved, Karen, ed. Selected Scientific Works ofHans Christian Ørsted. Princeton, N.J.:Princeton University Press, 1998.

Johnson, George. Strange Beauty: Murray Gell-Mann and the Revolution in Twentieth-CenturyPhysics. New York: Alfred A. Knopf, 1999.

Jungnickel, Christa and Russell K. McCor-mach, eds. Cavendish: The ExperimentalLife. Bucknell, Pa.: Bucknell UniversityPress, 1999.

Kane, Gordon. The Particle Garden: Our Uni-verse as Understood by Particle Physicists.Cambridge, Mass.: Perseus Books, 1995.

Kapitsa, S. P. and S. Drell. Sakharov Remem-bered. New York: American Institute ofPhysics, 1991.

Kargon, Robert H. The Rise of Robert Millikan:Portrait of a Life in American Science. Ithaca,N.Y.: Cornell University Press, 1982.

Keithley, Joseph F. The Story of Electrical andMagnetic Measurements: From Early Days tothe Beginnings of the 20th Century. NewYork: Wiley-IEEE Press, 1998.

Kipnis, Nahum. History of the Principle of Light.Science Networks Historical Studies, Vol.5. New York: Springer-Verlag, 1991.

Khalatnikov, I. M., ed. Landau, the Physicist andthe Man: Recollections of L. D. Landau. Ox-ford: Oxford University Press, 1989.

Lindley, David. Boltzmann’s Atom: The GreatDebate That Launched a Revolution inPhysics. New York: Free Press, 2000.

Lindop, Laurie. Dynamic Modern Women: Scien-tists and Doctors. New York: Holt, 1997.

Lindsay, R. B. Lord Rayleigh, the Man and HisWorks. London: Oxford University Press,1970.

Livanova, Anna Mikhailovna. Landau: A GreatPhysicist and Teacher. Oxford: Oxford Uni-versity Press, 1980.

Livingston, Dorothy Michelson. Master of Light:A Biography of Albert A. Michelson. NewYork: Scribner, 1973.

Ludwig, Charles. Michael Faraday: Father ofElectronics. Scottdale, Pa.: Herald Press,1978.

Mailis, Norberto. The Quantum Theory of Mag-netism. Singapore: World Scientific, 2001.

Marshall, Ian N., Danah Zohar, and F. DavidPeat. Who’s Afraid of Schrödinger’s Cat:An A-to-Z Guide to All the New ScienceIdeas You Need to Keep Up With the NewThinking. New York: William Morrow,1998.

Matson, James. The Pioneers of NMR and Mag-netic Resonance in Medicine: The Story ofMRI. Jericho, NY: Dean Book, 1996.

368 A to Z of Physicists

Maxwell, James Clerk, ed. The Electrical Re-searches of the Honourable Henry Cavendish.London: Frank Cass, 1967.

McMurray, Emily J., ed. Notable Twentieth-Cen-tury Scientists. New York: Gale Research,1995.

Mehra, J. and K. Milton. Climbing the Mountain:The Scientific Biography of Julian Schwinger.Oxford: Oxford University Press, 2000.

Mendelssohn, Kurt. The World of WaltherNernst: The Rise and Fall of German Science,1864–1941. Pittsburgh: University of Pitts-burgh Press, 1973.

Milburn, Gerard J. Schrödinger’s Machines: TheQuantum Technology Reshaping EverydayLife. New York: W. H. Freeman, 1997.

Millar, David, Ian Millar, John Millar, and Mar-garet Millar, eds. The Cambridge Dictionaryof Scientists. New York: Cambridge Univer-sity Press, 1996.

Millikan, Robert Andrews and I. BernardCohen. Autobiography of Robert A. Millikan.Manchester, N.H.: Ayer, 1980.

Moore, Walter J. A Life of Erwin Schrödinger.London: Cambridge University Press, 1994.

Mott, Nevill. A Life in Science. London: Taylor& Francis, 1987.

Moyer, Albert E. Joseph Henry: The Rise of anAmerican Scientist. Washington, D.C.:Smithsonian Institution Press, 1997.

“National Inventors Hall of Fame.” Availableon-line. URL: http://www.invent.org/in-venture.html.

Ne’eman, Yuval and Yoram Kirsh. The ParticleHunters. Cambridge: Cambridge UniversityPress, 1996.

Newton, Isaac. The Principia: Mathematical Prin-ciples of Natural Philosophy. Translated byBernard Cohen and Anne Whitman.Berkeley: University of California Press,1999.

The Nobel Foundation. “Nobel Laureates.”Available on-line. URL: http://www.nobel.com.

Oliphant, Mark. Rutherford: Recollections of theCambridge Days. London: Elsevier, 1972.

Overbye, Dennis. Einstein in Love: A ScientificRomance: New York: Viking Penguin, 2000.

Pais, Abraham. Niels Bohr’s Times: In Physics,Philosophy, and Polity. Oxford: Oxford Uni-versity Press, 1991.

———. Subtle Is the Lord . . . the Science and theLife of Albert Einstein. Oxford: Oxford Uni-versity Press, 1982.

Pais, Abraham, et al., eds. Paul Dirac, the Manand His Work. London: Cambridge Univer-sity Press, 1998.

Pasachoff, Naomi. Marie Curie and the Science ofRadioactivity. Oxford: Oxford UniversityPress, 1997.

Pelletier, Paul A. Prominent Scientists: An Indexto Collective Biographies. New York: NealSchuman, 1994.

Penzias, Arno. Digital Harmony: Business, Tech-nology and Life After Paperwork. New York:Harper Business, 1996.

———. Ideas and Information: Managing in aHigh-Tech World. New York: W. W. Norton,1989.

Pera, Marcello and Jonathan Mandelbaum. TheGalvani-Volta Controversy on Animal Elec-tricity. Princeton, N.J.: Princeton Univer-sity Press, 1992.

Perrin, Jean. Atoms. Reprint edition of 1913French original. Woodbridge, Conn.: OxBow Press, 1990.

American Physical Society. “Physics Today.”Available on-line. URL: http://www.aip.org/publications.html/pt.

Porter, Roy, ed. The Biographical Dictionary ofScientists. New York: Oxford UniversityPress, 1994.

Quinn, Susan. Marie Curie: A Life. New York:Simon & Schuster, 1995.

Rabi, Isidor. Science: The Center of Culture.New York: World, 1970

Rabi, Isidor, et al. Oppenheimer. New York:Scriber’s & Sons, 1969.

Bibliography 369

Ramsey, Norman F. Spectroscopy with CoherentRadiation: Selected Papers of Norman F.Ramsey. Singapore: World Scientific, 1997.

Reid, T. R. The Chip: How Two Americans In-vented the Microchip and Launched a Revolu-tion. New York: Simon & Schuster, 1984.

Reston, James. Galileo: A Life. New York:HarperCollins, 1994.

Rhodes, Richard. Dark Sun: The Making of theHydrogen Bomb. New York: Simon &Schuster, 1995.

———. The Making of the Atom Bomb. NewYork: Simon & Schuster, 1986.

Ridgen, John S. Rabi: Scientist and Citizen. NewYork: Basic Books, 1987.

Rife, Patricia. Lisa Meitner and the Dawn of theNuclear Age. Cambridge, Mass.: Birkhauser,1998.

Riordan, Michael and Lillian Hoddeson. CrystalFire: The Invention of the Transistor and theBirth of the Information Age. New York: W.W. Norton, 1998.

Ruhla, Charles. The Physics of Chance: FromBlaise Pascal to Niels Bohr. Oxford: OxfordUniversity Press, 1992.

Sachs, Robert. Maria Goeppert-Mayer,1906–1972, a Biographical Memoir. Wash-ington, D.C., National Academy of Sci-ences, 1979.

“St. Andrews, History of Science.” Availableon-line. URL: http://www-history.mcs.st-andrews.ac.uk/history/.

Sakharov, Andrey Dmitriyevich. Memoirs. NewYork: A. A. Knopf, 1990.

———. Progress, Coexistence, and IntellectualFreedom. New York: Norton, 1968.

———. Sakharov Speaks. New York: A. A.Knopf, 1974.

Salam, Abdus. Science and the Third World.Edinburgh: Edinburgh University Press,1991.

Schlesinger, Bernard S. and June H.Schlesinger. Who’s Who of Nobel Prize Win-ners. Phoenix: Oryx Press, 1991.

Schrieffer, J. Robert. Theory of Superconductiv-ity. New York: Perseus, 1999.

Schrödinger, Erwin. Space-Time Structure. Cam-bridge: Press Syndicate of the University ofCambridge, 1990.

———. My View of the World. Woodbridge,Conn.: Ox Bow Press, 1994.

Schweber, Silvan S. In the Shadow of the Bomb.Princeton, N.J.: Princeton University Press,2000.

———. QED and the Men Who Made It: Dyson,Feynman, Schwinger, and Tomonaga. Prince-ton, N.J.: Princeton University Press, 1994.

“Scientific Biographies.” Available on-line.URL: http://home.achilles.net/~jtalbot/bio/biographies.html.

Segrè, Claudio G. Atoms, Bombs and EskimoKisses: A Memoir of Father and Son. NewYork: Viking Penguin, 1995.

Segrè, Emilio. Enrico Fermi, Physicist. Chicago:University of Chicago Press, 1995.

———. A Mind Always in Motion: The Autobi-ography of Emilio Segrè. Berkeley: Universityof California Press, 1993.

Shamos, M. Great Experiments in Physics. NewYork: Dover, 1987.

Siegbahn, Manne. Swedish Men of Science.Stockholm: Almquist & Wiksell Interna-tional, 1952.

Silk, Joseph. The Big Bang. New York: HenryHolt, 2000.

Silverman, Mark P. Waves and Grains. Prince-ton, N.J.: Princeton University Press, 1998.

Sime, Ruth Lewin. Lise Meitner: A Life inPhysics. Berkeley: University of CaliforniaPress, 1996.

Smith, Alice K. and Charles Weiner, ed., RobertOppenheimer: Letters and Recollections.Cambridge, Mass.: Harvard UniversityPress, 1980.

Smith, Crosbie and M. Norton Wise. Energyand Empire: A Biographical Study of LordKelvin. Cambridge: Cambridge UniversityPress, 1989.

370 A to Z of Physicists

Smolin, Lee. Three Roads to Quantum Gravity.New York: Basic Books, 2001.

Sobel, Dava. Galileo’s Daughter: A HistoricalMemoir of Science, Faith, and Love. NewYork: Walker, 1999.

Solomey, Nickolas. The Elusive Neutrino: ASubatomic Detective Story. New York: W. H.Freeman, 1997.

Spangenburg, Ray and Diane Moser. Niels Bohr:Gentle Genius of Denmark. New York: FactsOn File, 1995.

Speyer, Edward. Six Roads from Newton: GreatDiscoveries in Physics. Wiley Popular Sci-ence. New York: John Wiley, 1996.

Srinivasan, G., ed. Chandrasekhar: The Man Be-hind the Legend—Chandra Remembered.Chicago: University of Chicago Press,2000.

Stewart, C., ed. Coulomb and the Evolution ofPhysics and Engineering in Eighteenth CenturyFrance. Princeton, N.J.: Princeton Univer-sity Press, 1971.

Struik, Dirk Jan. The Land of Stevin and Huy-gens: A Sketch of Science and Technology inthe Dutch Republic During the Golden Cen-tury. Dordrecht, Netherlands: D. Reidel,1982.

Susskind, Charles. Heinrich Hertz: A Short Life.San Francisco: San Francisco Press, 1995.

Sutton, Christine. Spaceship Neutrino. London:Cambridge University Press, 1992.

Szanton, Andrew. The Recollections of Eugene P.Wigner as Told to Andrew Szanton. NewYork: Perseus Books, 1992.

Taubes, Gary. Nobel Dreams: Power, Deceit, andthe Ultimate Experiment. New York: Ran-dom House, 1987.

Teller, Edward with Judith L. Shoolery. Memoirs:A Twentieth-Century Journey in Science andPolitics. New York: Perseus Books, 2001.

Tesla, Nikola. My Inventions: The Autobiographyof Nikola Tesla. Edited and with an intro-duction by Ben Johnston. Williston, Vt.:Hart Bros., 1944.

Thompson, Silvanus P. The Life of Lord Kelvin.New York: Chelsea, 1977.

Thorne, Kip S. Black Holes and Time Warps:Einstein’s Outrageous Legacy. New York: W.W. Norton, 1994.

Tomonaga, Sin-Itiro. The Story of Spin.Chicago: University of Chicago Press,1998.

Townes, Charles Hard. How the Laser Hap-pened: Adventures of a Scientist. Oxford: Ox-ford University Press, 1999.

Trower, W. Peter, ed. Discovering Alvarez.Chicago: University of Chicago Press,1987.

Van Allen, James A. Origins of MagnetosphericPhysics. Washington, D.C.: SmithsonianInstitution Press, 1983.

Venkataraman, G. Bhabha and His MagnificentObsessions. Hyderabad, India: UniversitiesPress, 1994.

———. Journey into Light: Life and Science of C.V. Raman. Bangalore, India: IndianAcademy of Sciences, 1989.

Vidali, Gianfranco. Superconductivity: The NextRevolution? Cambridge: Cambridge Univer-sity Press, 1993.

Von Baeyer, Hans Christian. Taming the Atom:The Emergence of the Visible Microworld.New York: Dover, 2000.

———. Warmth Disperses and Time Passes: AHistory of Heat. New York: Modern Library,1999.

Warshofsky, Fred. The Chip War: the Battle forthe World of Tomorrow. New York: Scribner& Sons, 1984.

Weinberg, Steven. Dreams of a Final Theory:The Scientist’s Search for the Ultimate Laws ofNature. New York: Vintage Books, 1993.

———. Facing Up: Science and Its Cultural Ad-versaries. Cambridge, Mass.: Harvard Uni-versity Press, 2001.

———. The First Three Minutes: A ModernView of the Origin of the Universe. NewYork: Basic Books, 1977.

Bibliography 371

Weiss, Richard J., ed. The Discovery of Anti-Matter: The Autobiography of Carl DavidAnderson, the Youngest Man to Win theNobel Prize. Series in Popular Science, Vol.2. Singapore: World Scientific, 1999.

Westfall, Richard S. Never At Rest: A Biographyof Isaac Newton. London: Cambridge Uni-versity Press, 1983.

Wheaton, Bruce R. The Tiger and the Shark: Em-pirical Roots of Wave–Particle Dualism. Lon-don: Cambridge University Press, 1990.

Wheeler, John Archibald with Kenneth Ford.Geons, Black Holes, and Quantum Foam: ALife in Physics. New York: W. W. Norton,1998.

Whitaker, Andrew. Einstein, Bohr and the Quan-tum Dilemma. London: Cambridge Univer-sity Press, 1996.

Who’s Who in Science and Engineering,1994–1995. New Providence, N.J.: MarquisWho’s Who, 1994.

Who’s Who in Science in Europe. Essex, England:Longman, 1994.

Wigner, Eugene. Symmetries and Reflections.Woodbridge, Conn.: Ox Box Press, 1979.

Williams, Trevor I., ed. A Biographical Dictionaryof Scientists. 4th ed. Glasgow: Harper-Collins, 1994.

Wilson, D. B. Kelvin and Stokes: A ComparativeStudy in Victorian Physics. Bristol: AdamHilger, 1987.

Wilson, E. J. N. An Introduction to Particle Ac-celerators. Oxford: Oxford University Press,2001.

Wilson, Jane, ed. All in Our Time: The Reminis-cences of 12 Nuclear Physicists. Chicago Bul-letin of the Atomic Scientists, 1975.

Wilson, John Graham. The Principle of CloudChamber Technique. London: CambridgeUniversity Press, 1951.

Wolpert, Lewis and Alison Richards. PassionateMinds: The Inner World of Scientists. Ox-ford: Oxford University Press, 1998.

Wood, Alexander, Frank Oldham, and CharlesE. Raven. Thomas Young, Natural Philoso-pher, 1773–1829. London: Cambridge Uni-versity Press, 1954.

Yang, Chen Ning. Selected Papers 1945–80 withCommentary. New York: W. H. Freeman,1983.

Yoder, Joella G. Unrolling Time: Christiaan Huy-gens and the Mathematization of Nature.Cambridge University Press, 1988.

Yount, Lisa. A to Z of Women in Science andMath. New York: Facts On File, 1998.

Yukawa, Hideki. Tabito (The Traveler). Singa-pore: World Scientific, 1982.

———. Creativity and Intuition: A PhysicistLooks at East and West. Tokyo and NewYork: Kodansha International, 1973.

372 A to Z of Physicists

373

INDEX

Aacceleration, law of 213acoustics

Doppler, Christian 75–77Helmholtz, Hermann Ludwig

Ferdinand von 139–141Langevin, Paul 176–178Mach, Ernst 191–192Raman, Sir Chandrasekhara

Venkata 238–240adiabatic process 50aerodynamics 25, 191, 192Alferov, Zhores Ivanovich 1–3,

163, 165, 166Alfvén, Hannes Olof Gösta 3–6Alfvén theory 4Alfvén wave 4alpha decay 53, 115, 120, 256, 257Alpha Magnetic Spectrometer 302alpha particle bombardment 93alternating currents 296–297alternating gradient synchrotron

99, 181Alvarez, Luis W. 6–8, 33, 313ammonia 267–268, 307ampere 244Ampère, André-Marie 8–10, 142,

216, 220, 287Ampère’s law 9, 194Anders, Bill 214Anderson, Carl David 10–11, 11,

31, 279, 335, 345Anderson, Philip Warren 12–14,

204, 206, 313, 314

Anderson localization 13Anderson model 13Ångstrom, Anders Jonas 14–15antiaircraft weapons 310antiferromagnetics 12antimatter 11antineutron 279antiproton 11, 58, 74, 254, 278,

279antiquarks 124Arago, François 90, 102, 103, 108Archimedes 15–17Archimedes’ principle 15, 16Archimedes screw 17argon 243, 245Aristotle 112–113, 213Ashkin, Art 60astigmatism 342astronomy

Ångstrom, Anders Jonas14–15

Archimedes 15–17Fizeau, Armand-Hippolyte-

Louis 101–103Foucault, Jean-Bernard-Léon

103–104Fraunhofer, Joseph von

106–107Galilei, Galileo 112–115Gauss, Johann Carl Friedrich

118–120Hooke, Robert 148–149Huygens, Christiaan 149–151Newton, Sir Isaac 210–214

astrophysics and cosmologyAlfvén, Hannes Olof Gösta

3–6Bethe, Hans Albrecht 25–28Chandrasekhar, Subramanyan

54–56Gamow, George 115–118Hawking, Stephen 133–136Penzias, Arno Allan 224–226Purcell, Edward Mills

231–234Taylor, Joseph H., Jr. 291–292Van Allen, James 309–311Weinberg, Steven 322–325Wheeler, John Archibald

325–329atom(s)

evidence for existence of 226,227–228

hyperfine state of 237model of 37, 38, 41, 175, 185,

186, 223, 258, 273, 283–284,287, 300

number of 84structure of 43, 255, 257

atomic accelerator 125atomic beam magnetic resonance

235, 240, 241atomic bomb 198. See also

Manhattan Projectatomic clock 237, 238, 240, 242atomic fountain clock 60atomic fountain interferometer 59,

60

Note: Boldface page numbers indicate main headings. Italic page numbers indicate illustrations.

atomic number 21, 260atomic physics

Blackett, Patrick MaynardStuart, Lord 31–32

Chu, Steven 58–61Franck, James 104–106Landau, Lev Davidovich

172–174Lenard, Philipp von

185–186Millikan, Robert Andrews

201–203Oppenheimer, J. Robert

217–219Perrin, Jean-Baptiste

226–228Rutherford, Ernest 255–258Sommerfeld, Arnold Johannes

Wilhelm 283–284Stark, Johannes 284–285Stern, Otto 286–288Thomson, Joseph John

298–300Wilson, Charles Thomson

Rees 334–336Zeeman, Pieter 347–348

“atomic pile” 93atomic transmutations 31atomic traps 60atomist-energeticist debate 41,

192, 227Auger electrons 197aurora borealis 14Avogadro number 84, 227

Bbackground radiation, cosmic

microwave 117, 224–226Bainbridge, Kenneth T. 232Baker, W. 253ball lightning 159Balmer, Johann 259Banks, Joseph 319Bardeen, John 12, 18–21, 19, 153,

269, 280, 281Bardeen-Cooper-Schrieffer (BCS)

theory of superconductivity 12,20, 34, 153, 269–271

barium 197Barkla, Charles Glover 21–22

Barrow, Isaac 212Basov, Nikolay 269, 306battery 318, 319Battrain, Walter 280Becker, Herbert 53Becquerel, Antoine-Henri 22–23,

67, 68, 196, 253, 258Bell Laboratories 12, 13, 19, 59,

71, 72, 162, 224–225, 267,280–281

Berg, Howard 233Bernoulli, Daniel 23–25Bernoulli effect 24, 25beryllium 53Besso, Michael 83beta decay 53, 92, 93, 116, 123,

247, 248, 254, 256, 258, 336,338

Bethe, Hans Albrecht 25–28, 27,33, 78, 79, 95, 172, 218, 276,283, 305

Bethe-Bloch formula 33Bevatron 125Bhabha, Homi Jehangir 28–30,

30, 239Bhabha scattering 28big bang theory 5, 115, 117,

134–135, 224–225binary pulsar 291, 292biophysics

Chu, Steven 58–61Franck, James 104–106Glaser, Donald Arthur

124–126Purcell, Edward Mills

231–234Birkeland, Kristian 4Bitter, Francis 249blackbodies 84, 225, 228–229

perfect 163, 165blackbody radiation 41, 84,

228–229, 245, 267, 285–286,307, 329–330

Blackett, Patrick Maynard Stuart,Lord 10, 29, 31–32, 105, 258,265, 279, 335

black holes 54, 55, 56, 133,134–135, 325, 327

Blatt, John 276Bloch, Felix 32–35, 231, 236

Bloch walls 33Bloembergen, Nicolaas 35–37,

233, 269blue shift 77, 102Bohr, Niels Henrik David 26, 33,

37–40, 38, 47, 73, 96, 104, 116,131, 137, 166, 173, 175, 197,205, 218, 222–223, 224, 230,235, 245, 258, 259, 272–273,283, 287, 293, 326, 344

Bohr magneton 168, 175, 237Boltzmann, Ludwig 40–42, 192,

194–195, 196, 227, 229, 285,286, 329

Boltzmann constant 41Bondi, Hermann 225Booth, Eugene T. 181Born, Max 42–44, 44, 92, 104,

105, 130, 137, 138, 175, 179,218, 222, 273

Born approximation method 43boron 54bosons 253, 254Bothe, Walter 53, 65bow wave 57Boyle, Robert 148Boyle’s law 148Boys, Charles 231Bragg, Lawrence 205Brahe, Tycho 114breaking radiation 26Breguet, Louis 102Breit, Gregory 168, 237, 326Breit-Wigner distribution 334Bremsstrahlung 26Bridgman, Percy Williams 44–46,

217, 313Brittain, Walter 19, 281Broglie, Louis-Victor-Pierre-

Raymond, prince de 46–48, 72,87, 138, 273, 287

broken symmetries 146, 316,323–324. See also spontaneoussymmetry breaking

Brown, Robert 84, 227Brownian motion 84, 176–177,

226, 227bubble chamber 124–125, 336Bunsen, Robert 156, 163, 164,

185, 290

374 A to Z of Physicists

Bunsen burner 164Burg, A. 76

Ccadmium 93calculus 210, 211caloric theory of heat 50, 61calorie 154canal rays 284, 285, 300capacitor 232capacitor-discharge bridgewire

detonators 7carbon button lamp 297Carnot, Nicolas Léonardi Sadi

49–51, 160Carnot cycle 50Carnot’s theorem 50, 160–161cathode ray oscillographs 110cathode rays 185–186, 226, 252,

298–300, 330. See also electronscat paradox 44, 272–274Cavendish, Henry 51–52Cavendish experiment 52Cavendish Laboratory 13, 29, 52,

63, 71, 158, 195, 298cavity resonators 304Celsius temperature scale 160centimeter-gram-second (CGS)

unit for magnetic flux density119

centrifugal force 150centrifuge 195Ceres (asteroid) 118CERN. See European Center for

Nuclear Researchcesium 45, 164cesium clock 240, 242Chadwick, Sir James 10, 29,

52–54, 53, 121, 205, 258, 344Challenger explosion 97Chamberlain, Owen 278, 279Chandrasekhar, Subramanyan

54–56, 183, 238, 327Chandrasekhar limit 55, 56Chandra X-Ray Observatory 56Chapman, Sydney 4charge and parity symmetries

99–100, 254, 265, 316, 323charge symmetry 99charge-to-mass ratio 226, 300, 348

charm quarks 124, 126, 128, 129,249, 250, 254, 302

chemical bonds 314Cherenkov, Pavel Alekseyevich

56–58Cherenkov detector 57, 58Cherenkov effect 56–57, 58Cherenkov radiation 56–57, 58Chu, Steven 58–61Cicero 17classical electrodynamics and

electromagnetismAmpère, André-Marie 8–10Boltzmann, Ludwig 40–42Cavendish, Henry 51–52Compton, Arthur Holly

64–65Coulomb, Charles-Augustin de

66–67Einstein, Albert 82–88Faraday, Michael 89–91FitzGerald, George Francis

100–101Foucault, Jean-Bernard-Léon

103–104Gauss, Johann Carl Friedrich

118–120Henry, Joseph 141–143Hertz, Heinrich Rudolf

143–144Kelvin, Lord 160–161Kirchhoff, Gustav Robert

163–165Laue, Max Theodor Felix von

178–180Lenz, Heinrich Friedrich Emil

186–188Lorentz, Hendrik Antoon

188–190Maxwell, James Clerk

193–195Ohm, Georg Simon

215–216Ørsted, Hans Christian

220–221Planck, Max Ernest Ludwig

228–230Poynting, John Henry

230–231Rayleigh, Lord 243–246

Röntgen, Wilhelm Conrad251–253

Stefan, Josef 285–286Tesla, Nikola 295–298Thomson, Joseph John

298–300Volta, Alessandro Guiseppe

Antonio Anastasio318–320

Weber, Wilhelm Eduard321–322

Wien, Wilhelm 329–330Zeeman, Pieter 347–348

classical mechanicsArchimedes 15–17Coulomb, Charles-Augustin de

66–67Hooke, Robert 148–149Huygens, Christiaan

149–151Mach, Ernst 191–192Newton, Sir Isaac 210–214Young, Thomas 342–343

Clausius, Rudolf Julius Emmanuel51, 61–62, 154, 161, 194, 210

Cline, David 254cloud chamber 10, 11, 31, 125,

181, 197, 202, 258, 334–335cobalt 337COBE satellite 226Cocconi, Giuseppe 301Cockcroft, John Douglas 29,

62–63, 116, 258, 312coherent anti-Stokes Raman

scattering 37collapsed stars 55colliding beam machine 254, 324color blindness 193, 342colors 193, 212, 238–239, 244, 342color vision 193, 342comets 213Commins, Eugene 59companion star 291, 292compass 220Compton, Arthur Holly 21,

64–65, 65, 93, 203, 239Compton effect 64, 65, 73, 121,

239Compton Gamma Ray Observatory

65

Index 375

Condon, Edward 105conductivity 216conductors 66, 319cones 342conservation of energy. See energy,

conservation ofconservation of momentum 150,

197, 213conservation of parity. See parity,

law ofconservation of strangeness 208control rods 93Conversi, Marcello 253Cooper, Leon 20, 269Cooper pairs 20, 270Copenhagen school 39Copernicus’ heliocentric theory

113–114, 210correspondence, principle of 39Cosmic Microwave Background

Explorer (COBE) satellite 226cosmic microwave background

radiation 117, 224–226cosmic rays 3–4, 10, 11, 29, 31–32,

64–65, 139, 203Cosmotron 125Coulomb, Charles-Augustin de

66–67, 319Coulomb barrier 115Coulomb force 277, 344Coulomb’s law 67, 194counter-controlled cloud chamber

31covariant tensor calculus 87Cowan, Clyde L. 224, 246, 247Crawford, Malcolm F. 267Cronin, James W. 98Crooke, William 185crystals

absorbing gamma rays 204characteristics of 252fluorescent 23lattice energies of 42light absorption of 22magnetic properties of 235nature of 178, 179X-ray diffraction in 178, 179

Curie, Marie 22, 67–70, 69, 177,196, 312

Curie, Pierre 22, 67–69, 176, 177

cyclotron 54, 254Czar-Bomb 262

DDalton, John 319Davisson, Clinton Joseph 71–72Davy, Sir Humphry 89, 90Descartes, René 150, 283deuterium 26, 225, 258deuteron 26, 240, 287–288deuteron accelerator 7Deutsch, Martin 249Dewar, James 157diamagnetic phenomena in gases

177diamonds, synthesis of 45Dicke, Robert 117, 225dielectrics 66diffraction 108diffraction grating 107dinosaur extinction theory 8dipole moment of neutron 242Dirac, Paul Adrien Maurice 10,

29, 43, 72–75, 74, 96, 138, 168,170–171, 218, 237, 264, 271,275, 279, 287, 303, 332, 338, 344

Dirac equation 72–73, 168, 218,276

direct currents 296–297disintegration theory of

radioactivity 256disordered systems 12–13displacement, law of 329dissociation energy of molecules

105Doppler, Christian 75–77Doppler cooling 60Doppler effect 75–77, 191, 204,

284Doppler shifts 77double beta decay 248double-heterostructure laser 166double-slit experiment 328, 342,

343doublet structure of electron 180,

181doublet structure of muon 180,

181down quarks 124, 128Dunoyer, Louis 287

dynamo 296Dyson, Freeman 77–81, 79, 96,

97, 169, 275Dyson sphere 81

EEarth

as enormous oscillator 297measuring density of 52radius of 282rotation of 103, 156

echolocation 177–178Eddington, Arthur 55, 56, 87Eddington paradox 55Edison, Thomas 296effective field theory (EFT) 277Ehrenfest, Paul 218eightfold way theory 121, 123,

127–128, 207–208, 250, 265, 302Einstein, Albert 82–88, 83, 218

and atomic bomb 88, 333on blackbody radiation 267,

307and Bohr, Niels 39and Broglie, Louis 46on Brownian motion 84,

176–177, 227and Feynman, Richard 95on Galilei 112on general theory of relativity

87, 91, 179, 191, 242, 291,325, 327

gravitational theory of 292on kinetic energy of electron

202and Laue, Max 178–179and Lorentz-FitzGerald

contraction hypothesis 101on Mach principle 192on Michelson, Albert 201on Newton’s theories 83, 84,

85, 87on Pauli, Wolfgang 222on photoelectric effect 64,

84–85, 230, 285and Schrödinger, Erwin 273,

274on special relativity 85–86,

176, 179, 188, 200, 245and Stern, Otto 286

376 A to Z of Physicists

Eisenhower, Dwight D. 233,310–311

elastic collision 150elasticity

Hooke’s law of 148, 149theory of 343

electrical and electronicengineering

Alvarez, Luis W. 6–8Bardeen, John 18–21Kilby, Jack St. Clair 162–163Tesla, Nikola 295–298

electrical attraction and repulsion66, 67

electric battery 318, 319electric currents 215, 220

alternating 296–297direct 296–297source of 318, 319

electric generator 89, 90electricity

heat and 154theory of 215–216

electric motor 89electric quadrupole moments 240,

242electrodynamics. See classical

electrodynamics andelectromagnetism

electrolysis 90electromagnet 154electromagnetic induction 89, 90,

142, 187electromagnetic motor 142electromagnetic plasma wave 4electromagnetic radiation 163,

193, 194electromagnetic resonance 236electromagnetic theory of light

322electromagnetism. See classical

electrodynamics andelectromagnetism

electrometer 232electromotive force 215electromotive series 319electron accelerator 242, 275electron degeneracy 55electron diffraction 26, 47, 72,

232

electron-electron scattering 250electron neutrinos 180, 182, 247electron-positron colliding beams

249, 250electron-positron pairs 301–302electrons. See also cathode rays

arrangement of 131, 257–258,273, 283

Auger 197charge-to-mass ratio of 226Cooper pairs 20, 270determining charge of 201,

202discovery of 298, 300in disordered system 13doublet structure of 180, 181ejection of 84free

collisions of 105in magnetic field 173

high-energy 249, 250hyperfine structure of 237kinetic energy of 202magnetic moment of 79, 167,

168, 277positive. See positronpredicting characteristics of 92relativistic theory of 73–74secondary 176self-interaction of 78, 95–96,

171, 276–277spinning 73–74valence 177wave nature of 47, 71, 72

electron scattering, on positrons28, 29

electron volts 105electrophorus 318electrostatic force 90–91electrostatics 66–67electroweak theory 59, 124,

126–129, 146, 181, 253,264–266, 301, 316, 317, 322, 325

emanation 256energy, conservation of 61, 139,

140, 141, 154, 187, 188, 197,209–210

entropylaw of. See second law of

thermodynamics

zero. See third law ofthermodynamics

Esaki, Leo 152, 153ether 85, 86, 102, 108–109, 188,

195, 199–200, 214, 226, 245,289, 298

Euler, Leonard 24, 25European Center for Nuclear

Research (CERN) 34, 40, 125,135, 147, 181, 253, 254, 301,316, 317, 324

Ewen, Harold I. 233exchange particle 344–346excited hadronic state 250exclusion principle 92, 138Explorer 1 311

Ffalling object

law of 113speed of 112–113

farad 91Faraday, Michael 89–91, 141,

142, 143, 161, 186, 187, 194,231

Faraday constant 91Faraday effect 91Faraday’s law of electrolysis 90,

194Fechner, Gustav 191Feinberg, Gary 126Fermi (unit) 94Fermi, Enrico 4, 7, 26, 33, 54, 65,

74, 91–94, 92, 122, 130,131–132, 197, 218, 223–224,247, 254, 278, 294, 333

Fermi Award 94Fermi-Dirac statistics 75, 92Fermi Laboratory 181, 254, 324Fermi level 94fermions 74, 92, 181fermium 94ferroelectrics 12ferromagnetism 12, 33, 138Feynman, Richard Phillips 77,

79–80, 81, 94–98, 95, 123, 135,146, 169, 172, 208, 246, 265,274, 276, 303, 305, 316, 317,323, 325, 326, 338

Feynman-Dyson method 80

Index 377

fine structure 175Dirac’s theory of 170–172of hydrogen, anomaly in

170–172, 283–284first law of motion 213first law of thermodynamics. See

energy, conservation ofFitch, Val Logsdon 98–100, 254FitzGerald, George Francis 85,

100–101, 188, 200Fizeau, Armand-Hippolyte-Louis

77, 101–103, 103, 104, 109fluid flow, mathematical theory of

24fluorescence 23, 57, 185, 226, 288,

289–290, 298Foucault, Jean-Bernard-Léon 101,

103–104, 109, 156, 164, 199Foucault pendulum 103, 104Fourier series 290Fowler, R. H. 55, 73, 158, 205Franck, James 104–106Franck-Condon principle 105Frank, Il’ya Milhailovich 57Franklin, Benjamin 318Fraunhofer, Joseph von 106–107Fraunhofer lines 14–15, 106, 107,

164, 290Fresnel, Augustin-Jean 9, 102,

107–109, 148, 179, 343Fresnel lens 107, 108Friedman, Francis 249Frisch, Otto 197–198, 326frozen-in-flux theorem 3

GGabor, Dennis 110–112Galilei, Galileo 17, 86, 103,

112–115, 113, 150, 210Galvani, Luigi 318, 319galvanometer 9, 216, 321gamma radiation 10, 26, 29, 53,

204, 256, 258Gamow, George 115–118, 116,

225, 294Gamow-Teller selection rule for

beta decay 116Gareyte, Jacques 254, 324Garwin, Richard 338

gas(es)in Carnot cycle 50characteristics of 252density of 244–245diamagnetic phenomena in

177electricity in 256expanding in vacuum 154,

157, 161kinetic theory of 24, 25, 41,

194, 286noble 246paramagnetic phenomena in

177perfect 92thermal equilibrium in 41thermodynamic theory of 154ultraviolet light in 256

gasket seal 45gauge field theory. See Yang-Mills

gauge theorygauss 119Gauss, Johann Carl Friedrich

118–120, 321Gauss’s law 118, 119GCA radar 7gedanken experiment 83, 86, 87Geiger, Hans Wilhelm 53,

120–121, 256–257Geiger counter 120–121Gell-Mann, Murray 97, 99,

121–124, 122, 127, 128,207–208, 250, 265, 302, 338

general theory of relativity 87, 91,179, 191, 242, 291, 292, 325, 327

generators 159genetic code 117geocentric theory 113–114geodesy 119, 282, 289geometry 211geophysics

Bardeen, John 18–21Lenz, Heinrich Friedrich Emil

186–188Georgi, Howard 129Gerlach, Walter 287germanium 1, 19, 281Germer, Lester 72“g-2” experiment 181g-formula 174, 175

Giaever, Ivar 152, 153Gilbert, William 220Ginzburg, Vitaly 262Glaser, Donald Arthur 7,

124–126, 336Glashow, Sheldon Lee 124,

126–129, 127, 146, 250, 253,264, 265, 266, 302, 316, 322, 324

glass semiconductors 206Goeppert-Mayer, Maria Gertrude

130–132, 131, 333Gold, Thomas 225Goldberg-Ophir, Haim 208gold-leaf electroscope 335Grand Unified Theory 126, 129gravitation

Cavendish, Henry 51–52Einstein, Albert 82–88Hooke, Robert 148–149inverse-square law of 213law of 210, 211, 212Newton, Sir Isaac 210–214Poynting, John Henry

230–231gravitational constant 51, 52, 230,

231gravitational force 210, 213gravitational mass 86gravitational waves 291, 292Grossman, Marcel 86–87ground-controlled approach

(GCA) radar 7group theory 331guiding center approximation 4Gurney, R. W. 205gyroscope 103

Hhadrons 123–124Hahn, Otto 195, 196, 197, 198,

326, 333Hale, George 348half-life 256Halley, Edmond 212Hanford nuclear reactor 275Hansen, W. W. 34Harrison, B. Kent 327Harteck, Paul 258Hartle, Jim 135Hasenohr, Fritz 272

378 A to Z of Physicists

Hawking, Stephen 133–136, 134Hawking radiation 133, 135He3 7hearing, theory of 140heat

and electricity 154mechanical theory of 154,

161heat conductivity 14Heisenberg, Werner 33, 39, 42, 43,

73, 92, 136–139, 137, 222, 224,235, 239, 273, 283, 293,303–304, 331, 344

Heitler, W. 29heliocentric theory 113–114, 210heliotrope 119helium 116. See also liquid heliumhelium three (He3) 7Helmholtz, Hermann Ludwig

Ferdinand von 62, 139–141,144, 185, 188, 193, 199, 209,244, 329, 342

henry 143Henry, Joseph 90, 141–143, 187Herlofson, N. 5hertz 144Hertz, Gustav 104, 105Hertz, Heinrich Rudolf 100, 141,

143–144, 185, 194, 298Hertzsprung-Russell diagram 117Hess, V. F. 203heterostructure bipolar transistor

166, 167heterostructures 1–2, 165,

166–167Hewish, Antony 291Higgs, Peter 128, 146, 265, 317,

323Higgs particle 147, 317high-speed transistors 167high-temperature and high-pressure

physics 44–46high-temperature

superconductivity 271Hilbert, David 175, 331holography 110–112homostructures 2‘t Hooft, Gerard 128, 145–148,

266, 315, 316, 317, 324Hooke, Robert 148–149, 212

Hooke’s law 148, 149Hopkins, William 289Hoyle, Fred 225Hubble, Edwin 77, 117Huggins, William 77Hulse, Russell A. 291, 292Huygens, Christiaan 108, 113,

149–151, 283, 343Huygens’s principle 150hydrogen

discovery of 51emitting radio wave 233fine structure of, anomaly in

170–172, 283–284hyperfine structure of 242

hydrogen bomb 93–94, 117, 219,261, 262, 293, 326

hydrogen bubble chamber 6, 7hydrogen canal rays 284hydrogen maser 240, 242hydrostatic balance 112hydrostatics and hydrodynamics

Archimedes 15–17Bernoulli, Daniel 23–25Helmholtz, Hermann Ludwig

Ferdinand von 139–141Stokes, George Gabriel

288–290hyperfine structure 237, 242

IIliopolos, John 128“IMB” underground detector 248incompressible fluid model 194induction 89, 90, 142, 187induction motor 296inelastic collision 105inertia, law of 213inertial mass 86information theory 110–112infrared radiation from space 308integrated circuit 162–163intelligence, mathematical

modeling of 153interference, principle of 343interference of light 342interference pattern 111interferometer 199, 200, 201International Geophysical Year

310–311

interstellar space 225inverse-square law of gravitation

213Ioffe Institute 1–2, 166ionization chambers 256–257Irvine/Michigan/Brookhaven

(“IMB”) underground detector248

isothermal process 50isotopes 300

JJahn-Teller effect 314Jefferts, Keith 225Jensen, Hans D. 132, 333Joffe, A. F. 158Johannesson, Olaf 5Johnson, Lyndon B. 233Jones, Lawrence 301Jordan, Pascual 42, 137, 138Josephson, Brian David 152–153Josephson effect 12, 152–153Josephson junction tunneling 20,

152–153, 270Joule, James Prescott 50, 61,

153–155, 161, 187Joule-Kelvin effect 154, 157, 161Joule’s law 154, 187J particle 250, 302J/ψ particle 249, 250, 301, 302junction transistor 281

KKamerlingh Onnes, Heike 20,

156–157, 270, 347Kapitsa, Pyotr Leonidovich 63,

157–159, 173–174Kelvin, Lord (William Thomson)

50–51, 153–154, 157, 160–161,290

Kelvin temperature scale 160Kemble, Edwin C. 313Kemmer, Herbert 264Kepler’s laws of planetary motion

213Kerr effect 347Kilby, Jack St. Clair 1, 162–163,

165kinetic energy of electron 202

Index 379

kinetic theoryof gases 24, 25, 41, 194, 286of liquid state 156

Kirchhoff, Gustav Robert106–107, 144, 156, 163–165,228, 290

Kirchhoff’s laws 164Klein, Felix 283Kleitman, Daniel 126Kleppner, Daniel 242Klug, Leopold 293K mesons 98–99, 184, 340Kotzebue, Otto von 187Kroemer, Herbert 1, 2, 163,

165–167krypton 197K series X-ray emissions 22K-shell electron capture process 7Kundt, August 251Kusch, Polykarp 95, 167–169,

168, 170, 237, 276

LLamb, Willis Eugene Jr. 78, 95,

169, 170–172, 171, 276Lamb shift 78, 79, 95, 96, 97, 169,

170, 172, 276, 277, 305Landau, Lev Davidovich 97, 158,

159, 172–174, 173, 327Landé, Alfred 174–176Landé splitting factor 175Lane, Kenneth 147Langevin, Paul 176–178Large Hadron Collider 147, 317large number hypothesis 75Lark-Horovitz, Karl 232lasers 2, 35, 36, 110, 111, 166, 167,

266, 268, 305–306, 307, 308laser spectroscopy

Bloembergen, Nicolaas35–37

of positronium 59Schawlow, Arthur Leonard

266–269Townes, Charles Hard

305–308lattice energies of crystals 42Laue, Max Theodor Felix von

178–180, 252, 283, 330Lauterburg, P. C. 35

Lavoisier, Antoine 89Lawrence, Ernest 6, 336least action, principle of 94Lederman, Leon M. 180–182,

242, 277, 338Lee, Tsung-Dao 99, 182, 183–185,

184, 332, 336, 339–341left hand-right hand

symmetry/asymmetry 99Lenard, Philipp von 185–186,

299Lenard window 185Lenz, Heinrich Friedrich Emil

186–188Lenz’s law 186, 187, 188leptons 128, 180, 181light

absorption of, by crystals 22and colors 238–239, 244as electromagnetic radiation

193, 194, 322gravitation and 86, 87interference of 342monochromatic 239particle theory of 84–85, 102,

108, 150, 342, 343and photographic emulsion

205polarized 108, 151, 343radiation pressure of 144Rayleigh scattering of 243,

244reflection of 100, 108refraction of 100, 108,

282–283study of. See spectroscopysurface 228–229ultraviolet, in gases 256velocity of 85–86, 101, 102,

103–104, 144, 179, 188, 199wave theory of 102, 103, 107,

108, 150, 214, 342, 343white 210, 212

light diffraction 246light-emitting diodes 3, 167light quanta. See photonslinear accelerator 116, 250Lippershey, Hans 113liquid-droplet model of nucleus 40,

116, 326

liquid helium 157, 158superfluidity of 159, 174

liquid oxygen 159liquid state, kinetic theory of 156localization theory 13Lodge, Oliver 21, 200Loomis, F. Wheeler 167Lorentz, Hendrik Antoon 85, 100,

186, 188–190, 284, 347Lorentz-FitzGerald contraction

hypothesis 100, 101, 188, 200Lorentz transformation 188Lorenz, Ludwig 188Lorenz-Lorentz formula 188low-temperature physics

Kamerlingh Onnes, Heike156–157

Kapitsa, Pyotr Leonidovich157–159

Landau, Lev Davidovich172–174

L series X-ray emissions 22luminescence 22–23, 185

MMach, Ernst 41, 83–84, 191–192,

222, 227Mach number 191, 192Mach principle 192magnetic domain structure 33magnetic electron lens 110magnetic flux density 119magnetic moment

of deuteron 287–288of electron 79, 167, 168, 277of neutron 7, 33, 242of proton 287–288of silver atom 287

magnetic monopoles 277magnetic needle 216magnetic resonance 232–233magnetic resonance imaging 35,

236magnetic scattering of neutrons 33magnetism. See also classical

electrodynamics andelectromagnetism

absolute units of 321quantum mechanical theory of

313, 314

380 A to Z of Physicists

magnetohydrodynamics 3, 4magnetometers 321magnetooptical trap 60magnetosphere 309, 311magnetrons 304Maiani, Luciano 128Maiman, Theodore 268, 307Malus, Etienne 343Manhattan Project

Alvarez, Luis W. in 7Bethe, Hans in 26–27Bloch, Felix in 34Bohr, Niels in 40Chadwick, Sir James in 54Compton, Arthur in 64Einstein, Albert in 88Fermi, Enrico in 93Feynman, Richard Phillips in

95Fitch, Val Logsdon in 98Franck, James in 105Oppenheimer, J. Robert in

217–219Rabi, Isidor Isaac in 235, 237Ramsey, Norman in 241Reines, Frederick in 246Segrè, Emilio Gino in 279Teller, Edward in 294Wheeler, John in 326

Mann, Alfred 254Marsden, Ernest 120maser 35, 36, 267, 268, 306, 307Mason, David 135mass

gravitational 86inertial 86invention of concept of 213Mach, Ernst on 192

Massachusetts Institute ofTechnology 7, 232, 249, 323

mass spectroscopy 168, 300mathematical modeling of

intelligence 153mathematical physics

Ampère, André-Marie 8–10Archimedes 15–17Bernoulli, Daniel 23–25Dyson, Freeman 77–81Galilei, Galileo 112–115

Gauss, Johann Carl Friedrich118–120

Huygens, Christiaan 149–151Langevin, Paul 176–178Newton, Sir Isaac 210–214Rydberg, Johannes Robert

259–260Stokes, George Gabriel

288–290Wigner, Eugene Paul

330–334mathematical theory of fluid flow

24matrix mechanics 42, 43, 137–138,

273, 331matter waves 47Maxwell, Alan 291Maxwell, James Clerk 4, 21, 38,

41, 83, 91, 94, 100, 118, 141,143, 144, 161, 188, 193–195,199–200, 231, 286, 290, 322, 342

Maxwell-Boltzmann distribution41, 195

Maxwell’s demon 195Maxwell’s equations 100, 194, 195,

244, 290Mayer, Joseph Edward 130McCarthyism 219, 295McGill University 256mechanical theory of heat 154,

161Meer, Simon Van der 253, 254,

324Meitner, Lise 195–198, 196, 326meitnerium 198Mercator, Nicolas 212mercury 105meson 11, 184, 250, 302metallic-filament lamp 209methane 319mho 216Michelson, Albert Abraham 101,

195, 199–201, 200Michelson-Morley experiment 85,

101, 188, 195, 199–201, 289microchip 162–163microwave 224–225, 304microwave generators for radar

168microwave radio radiation 117

microwave spectroscopy 36, 267Millikan, Robert Andrews 10, 71,

201–203, 289, 299–300Mills, Allen 59Mills, Robert 146, 265, 316, 323Minkowski, Herbert 86Minkowski space or spacetime 86molecular beam epitaxy 167molecular beam method 168, 235,

286, 287molecular individualism 60–61momentum, conservation of 150,

197, 213monochromatic light 239Morel, Pierre 12Morgan, J. Pierpont 297Morley, Edward 101, 195, 199Morse, Samuel F. B. 141, 142–143Moseley, Henry 260Mössbauer, Rudolf Ludwig

203–204Mössbauer effect 203, 204Mössbauer spectroscopy 203, 204motion, laws of 210, 211, 212, 213motion, planetary, Kepler’s laws of

213Mott, Sir Nevill Francis 12, 13,

204–206, 313moving-needle telegraph 119M series X-ray emissions 22Müller, Walther 121mu meson 10, 11muon 10, 11, 180, 181, 301,

345–346muonium 59muon neutrinos 180, 182Musset, Paul 324mutual induction 142

NNASA 97, 226, 233, 310Navier-Stokes equation 289, 290Neddermeyer, Seth 10, 11, 34Ne’eman, Yuval 207–209, 250,

265, 302Nernst, Walther 202, 209–210Nernst heat theorem 209Nernst lamp 209Neumann, John von 95, 247, 331,

332

Index 381

neutrino 93, 181, 197, 222,223–224, 246–248

neutrino beam method 180, 182neutron(s)

antineutron 279arrangement of 130–131dipole moment of 242discovery of 52, 53–54, 258,

344magnetic moment of 7, 33,

242scattering of 7, 33slow 278

neutron stars 28, 291, 292Newton, Sir Isaac 25, 52, 83, 84,

85, 87, 108, 149, 150, 192, 210,210–214, 211, 211, 212, 213,286, 343

Newton’s rings 212, 343nickel 71–72Nishina, Yoshio 303, 344nitrogen 245noble gases 246no-boundary universe 135“no-hair” theorem 327noncrystalline semiconductors 206nonlinear optics 36nonthermal radiation 5Northwest Passage 220Noyce, Robert 162–163nuclear disarmament 26, 28, 40,

63, 81, 159, 237, 261, 263nuclear energy 198nuclear fission 195, 197–198, 326,

333nuclear fusion bomb 293nuclear magnetic resonance

(NMR) 32, 34, 35, 36, 231, 233,235, 236, 240

nuclear magnetic resonancerelaxation times 36

nuclear physicsBethe, Hans Albrecht 25–28Chadwick, Sir James 52–54Cockcroft, John Douglas

62–63Fermi, Enrico 91–94Gamow, George 115–118Geiger, Hans Wilhelm

120–121

Glaser, Donald Arthur124–126

Goeppert-Mayer, MariaGertrude 130–132

Landau, Lev Davidovich172–174

Meitner, Lise 195–198Oppenheimer, J. Robert

217–219Purcell, Edward Mills

231–234Rutherford, Ernest 255–258Sakharov, Andrei

Dmitriyevich 261–263Segrè, Emilio Gino 278–280Teller, Edward 293–295Wigner, Eugene Paul 330–334Wu, Chien-Shiung 336–338Yang, Chen Ning 339–341

nuclear reactor 93, 198, 333Nuclear Test Ban Treaty 28nucleons 40, 344nucleus 40, 116, 257, 326number theory 118

OOcchialini, Guiseppe 31oersted 221ohm 215, 216, 244Ohm, Georg Simon 215–216Ohm’s law 164, 215oil droplet experiment 201, 202,

289Oliphant, Marcus 258Oort, Jan 233operationalism 45Operation Greenhouse 246ophthalmometer 140ophthalmoscope 140Oppenheimer, J. Robert 7, 34, 65,

80, 105, 170, 184, 217,217–219, 237, 275, 294, 295,305, 327, 336, 339, 346

optical molasses 60optics

Doppler, Christian 75–77Fizeau, Armand-Hippolyte-

Louis 101–103Foucault, Jean-Bernard-Léon

103–104

Fraunhofer, Joseph von106–107

Fresnel, Augustin-Jean107–109

Helmholtz, Hermann LudwigFerdinand von 139–141

Hooke, Robert 148–149Huygens, Christiaan 149–151Lorentz, Hendrik Antoon

188–190Mach, Ernst 191–192Maxwell, James Clerk

193–195Michelson, Albert Abraham

199–201Newton, Sir Isaac 210–214Raman, Sir Chandrasekhara

Venkata 238–240Röntgen, Wilhelm Conrad

251–253Snell, Willibrord 282–283Stokes, George Gabriel

288–290Townes, Charles Hard

305–308Young, Thomas 342–343Zeeman, Pieter 347–348

orbital 273Orion Project 81Ørsted, Hans Christian 9, 90, 142,

215, 220–221Osborne, L. S. 249oscillating electromagnetic motor

142oscillator 144oscillographs 110oxygen, liquid 159

PPackard, M. E. 34paddle-wheel experiment 154pair annihiliation 31Pais, Abraham 99paramagnetic phenomena in gases

177parapsychology 328parity, law of 332

violation of 182, 183–184,265, 336–338, 339–341

parity symmetry 99

382 A to Z of Physicists

partial pressures, law of 319particle accelerators 62, 63, 135,

181–182, 249–250, 253, 258,279, 312, 322

particle physicsAlvarez, Luis W. 6–8Anderson, Carl David 10–11Bhabha, Homi Jehangir

28–30Blackett, Patrick Maynard

Stuart, Lord 31–32Chadwick, Sir James 52–54Cherenkov, Pavel

Alekseyevich 56–58Compton, Arthur Holly

64–65Davisson, Clinton Joseph

71–72Dirac, Paul Adrien Maurice

72–75Fermi, Enrico 91–94Feynman, Richard Phillips

94–98Fitch, Val Logsdon 98–100Gell-Mann, Murray 121–124Glaser, Donald Arthur

124–126Glashow, Sheldon Lee

126–129Lederman, Leon M. 180–182Lee, Tsung-Dao 183–185Mössbauer, Rudolf Ludwig

203–204Ne’eman, Yuval 207–209Pauli, Wolfgang 222–224Ramsey, Norman F. 240–243Reines, Frederick 246–248Richter, Burton 249–251Rubbia, Carlo 253–255Salam, Abdus 264–266Segrè, Emilio Gino 278–280Ting, Samuel Chao Chung

300–303Tomonaga, Sin-Itiro

303–305Van de Graaff, Robert Jemison

311–313Veltman, Martinus J. G.

315–318Weinberg, Steven 322–325

Wheeler, John Archibald325–329

Wilson, Charles ThomsonRees 334–336

Yang, Chen Ning 339–341Yukawa, Hideki 343–346

particle theory of light 84–85, 102,108, 150, 342, 343

partons 97Paschen, Louis 175Pauli, Wolfgang 39, 92, 95, 137,

138, 166, 181, 197, 218,222–224, 223, 235, 246, 265, 283

Pauli exclusion principle 74, 92,138, 222, 223

pendulum 103, 104, 112, 156pendulum clock 149, 150Penrose, Roger 134Penzias, Arno Allan 13, 115, 117,

224–226perfect blackbody 163, 165perfect gases 92periodic table of elements 259Perl, Martin 301Perrin, Jean-Baptiste 84, 176,

226–228Petrucci, Guido 254, 324philosophy of science

Bohr, Niels Henrik David37–40

Bridgman, Percy Williams44–46

Einstein, Albert 82–88Mach, Ernst 191–192

phosphorescence 23, 185photoelectric effect 64, 84–85,

185, 186, 202, 230, 285photoelectric pair creation 303photographic emulsion 205photon collision 301photons 46, 57, 64, 78–79, 84, 96,

117, 230, 238, 239, 279, 324,328, 344

physical chemistryCavendish, Henry 51–52Curie, Marie 67–70Faraday, Michael 89–91Franck, James 104–106Goeppert-Mayer, Maria

Gertrude 130–132

Helmholtz, Hermann LudwigFerdinand von 139–141

Nernst, Walther 209–210Ørsted, Hans Christian

220–221Perrin, Jean-Baptiste

226–228Stern, Otto 286–288

pi (π) 15–16piezoelectricity 177pi mesons 11, 27, 335, 344, 346pitchblende 68Planck, Max Ernest Ludwig 38, 43,

84–85, 104, 165, 178, 196, 202,210, 228–230, 229, 245, 329,330

Planck’s constant 73, 84, 105, 201,202, 228, 229

Planck’s quantum hypothesis 105Planck’s radiation law 229planetarium 17planetary motion, Kepler’s laws of

213planets, origin of, Alfvén theory of

4plasma physics

Alfvén, Hannes Olof Gösta3–6

Landau, Lev Davidovich172–174

Plutarch 17plutonium 278, 279, 326, 333polarized light 108, 151, 343polonium 67, 68, 69positive rays 300positron 10, 28, 29, 74, 218, 279,

335, 346positronium, laser spectroscopy of

59Pound, Robert V. 231, 232, 233Powell, Cecil 346Poynting, John Henry 230–231Poynting-Robertson effect 231Poynting vector 230, 231Present, R. D. 246pressure broadening 12Priestley, Joseph 66primary colors 193probability theory 8Project Matterhorn 326

Index 383

Prokhorov, Aleksandr 269, 306protactinium 196proton-antiproton collider 254,

255proton-proton scattering

experiment 242protons 258, 344

arrangement of 130–131magnetic moment of

287–288negative. See antiproton

proton synchrotron 301Prout’s hypothesis 244proximity fuze 309–310ψ particle 250, 254, 302pulsars 271, 291–292pulse-propagation effect 59–60Purcell, Edward Mills 34,

231–234, 236

Qquanta 165, 229, 245quantum chromodynamics (QCD)

124, 147quantum electrodynamic formalism

146quantum electrodynamics and

quantum field theoryBhabha, Homi Jehangir

28–30Dyson, Freeman 77–81Einstein, Albert rejecting 87Feynman, Richard Phillips

94–98Glashow, Sheldon Lee

126–129‘t Hooft, Gerard 145–148Kusch, Polykarp 167–169Lamb, Willis Eugene

170–172Landau, Lev Davidovich

172–174Ramsey, Norman F. 240–243Richter, Burton 249–251Salam, Abdus 264–266Schwinger, Julian Seymour

274–278Tomonaga, Sin-Itiro 303–305Veltman, Martinus J. G.

315–318

Weinberg, Steven 322–325Wheeler, John Archibald

325–329quantum foam 327quantum mechanical theory of

magnetism 313, 314quantum mechanics

Barkla, Charles Glover21–22

Bloch, Felix 32–35Bohr, Niels Henrik David

37–40Born, Max 42–44Broglie, Louis-Victor-Pierre-

Raymond, prince de 46–48Dirac, Paul Adrien Maurice

72–75Einstein, Albert 82–88Franck, James 104–106Heisenberg, Werner 136–139Landau, Lev Davidovich

172–174Landé, Alfred 174–176Oppenheimer, J. Robert

217–219Pauli, Wolfgang 222–224Planck, Max Ernest Ludwig

228–230Schrödinger, Erwin 271–274Sommerfeld, Arnold Johannes

Wilhelm 283–284Teller, Edward 293–295Wigner, Eugene Paul

330–334quantum tunneling 115, 152–153quarks 97, 121, 123–124, 128, 147,

250, 302, 317. See also charmquarks

quartz mercury lamp 110

RRabi, Isidor Isaac 34, 95, 168, 170,

181, 232, 235–238, 236, 240,241, 267–268, 275

radar 7, 168, 170, 237, 241, 267,275, 280, 297, 314

radiation. See specific radiationradiation law, Planck’s 229radio 224–225radioactive dating 256

radioactive decay 57, 97, 181, 182,253. See also alpha decay; betadecay

violating parity law 182, 183,184

radioactivityBecquerel, Antoine-Henri

22–23Curie, Marie 67–70determining quantity of

120–121Fermi, Enrico 91–94Meitner, Lise 195–198Rutherford, Ernest 255–258

radio astronomyPenzias, Arno Allan 224–226Taylor, Joseph H., Jr. 291–292

radio transmission 143radio waves 143, 144, 194, 233,

256radium 67, 68, 69Rainwater, Jim 98Raman, Sir Chandrasekhara

Venkata 29, 238–240, 239Raman effect 238, 239Ramsay, William 243, 245Ramsey, Norman F. 240–243Rayleigh, Lord (John William

Strutt) 229, 238, 243–246, 298,329

Rayleigh-Jeans equation 245Rayleigh scattering 243, 244Rayleigh wave theory 244Reagan, Ronald 295red shift 77, 102, 242reflecting telescope 210, 212reflection of light 100, 108refraction, law of 282–283refraction of light 100, 108,

282–283refractor telescope 212Reines, Frederick 224, 246–248,

247relativistic electron theory 79relativity. See also general theory of

relativity; special relativityEinstein, Albert 82–88Hawking, Stephen 133–136Landau, Lev Davidovich

172–174

384 A to Z of Physicists

Laue, Max Theodor Felix von178–180

Lorentz, Hendrik Antoon188–190

Taylor, Joseph H., Jr. 291–292Wheeler, John Archibald

325–329renormalization 79, 96, 97, 127,

146, 172, 264, 277, 305, 317,322, 324

resistance 215resonance absorption of gamma

radiation 204Richter, Burton 249–251, 301,

302Robertson, Howard 231rocket-balloon 310rock magnetism 32rockoon 310Röntgen, Wilhelm Conrad 23,

186, 251–253, 330Roosevelt, Franklin D. 88, 93, 218Rosetta Stone 77, 343rotating-mirror method 102, 104,

199Routh, Edward 243Royal Institution 89, 90Royal Society 148, 150, 154Rubbia, Carlo 147, 253–255, 317,

324rubidium 164rugged vacuum tube 309Rutherford, Ernest 23, 31, 38, 53,

63, 64, 73, 116, 120–121, 158,176, 186, 192, 205, 218, 240,255–258, 257, 300, 312, 330,335

Rydberg, Johannes Robert259–260

Rydberg constant 259

SSadler, C. A. 22Sakharov, Andrei Dmitriyevich

261–263, 262Salam, Abdus 126, 127, 128, 146,

207, 253, 264, 264–266, 316,322, 324

satellite 310–311Saturn, rings of 193

Sauter, Fritz 166scattering matrix 80, 97Schawlow, Arthur Leonard 36,

266–269, 305, 307, 308“Schoonchip” 146, 315, 316, 317Schrieffer, John Robert 18, 20,

269–271Schrödinger, Erwin 32, 43, 44, 46,

47, 73, 74, 137–138, 230,271–274, 272, 314, 331

Schrödinger equation 271, 273Schrödinger-Heisenberg quantum

theory 73Schwartz, Melvin 180, 181Schwinger, Julian Seymour 12, 77,

79, 80, 81, 94, 95, 96, 97, 126,146, 169, 171, 172, 265,274–278, 276, 303, 305, 316,323

scintillation screens 257Seaborg, Glenn 279secondary electrons 176second law of motion 213second law of thermodynamics 61,

161, 195, 210, 229Segrè, Emilio Gino 11, 74,

278–280Seitz, Frederick 18self-induction 142self-interaction of electron 78,

95–96, 171, 276–277semiconductor lasers 166semiconductors 1–3, 13, 19,

166–167, 206, 281separated oscillatory fields method

240, 241–242shadowgraphs 297shell model theory 130–132Shockley, William Bradford 18, 19,

166, 280–282shock wave 57, 192siemens 216silver atom, magnetic moment of

287singularities in classical

gravitational theory 134Slater, John C. 269–270slow neutrons 278S-matrix 80, 97Smithsonian Institution 143

Snell, Willibrord 282–283Snell’s law 282–283Snow, C. P. 159Soddy, Frederick 256, 300solar spectrum 14–15, 106–107,

164–165, 290solenoid 9solid state and condensed matter

physicsAlferov, Zhores Ivanovich

1–3Anderson, Philip Warren

12–14Bardeen, John 18–21Barkla, Charles Glover

21–22Bethe, Hans Albrecht 25–28Bloch, Felix 32–35Born, Max 42–44Josephson, Brian David

152–153Kilby, Jack St. Clair 162–163Kroemer, Herbert 165–167Landau, Lev Davidovich

172–174Langevin, Paul 176–178Laue, Max Theodor Felix von

178–180Mott, Sir Nevill Francis

204–206Purcell, Edward Mills

231–234Rabi, Isidor Isaac 235–238Schrieffer, John Robert

269–271Shockley, William Bradford

280–282Van Vleck, John Housbrook

313–315soliton waves 244Sommerfeld, Arnold Johannes

Wilhelm 26, 54, 137, 175, 179,222, 235, 283–284, 286, 293

sonar 176, 177–178sound, velocity of 191, 192sound waves 75–76, 191source theory of elementary

particles 277, 278space-time diagrams 79–80, 94,

95, 96, 98

Index 385

special relativity 85–86, 176, 179,188, 200, 245

spectral line radio emissions 233spectral lines 284–285, 290. See

also Zeeman effectspectrometer 232spectroscope 106, 164, 244spectroscopy

Ångstrom, Anders Jonas14–15

Fraunhofer, Joseph von106–107

Kirchhoff, Gustav Robert163–165

Raman, Sir ChandrasekharaVenkata 238–240

Rydberg, Johannes Robert259–260

spherical condenser 232spin 223spinning electrons 73–74spin-orbit coupling 131–132spontaneous symmetry breaking

128, 265, 315, 317, 323–324Sputnik 1 311Stalin, Joseph 158–159, 173–174Standard Model 124, 126, 129,

147, 317, 325Stanford Linear Accelerating

Center 97, 250–251, 316Stanford Positron Electron

Accelerator Ring 250Stark, Johannes 284–285Stark effect 284–285Stark-Einstein law 285stars. See also black holes

collapsed 55energy of 25, 26

static electricity 318statics 15, 16statistical mechanics

Bloch, Felix 32–35Boltzmann, Ludwig 40–42Rayleigh, Lord 243–246Sommerfeld, Arnold Johannes

Wilhelm 283–284steady-state theory 225steam engine 49–50Stefan, Josef 41, 285–286Stefan-Boltzmann constant 286

Stefan-Boltzmann law 41, 285,286

Steinberger, Jack 180, 181stellar collapse 248stellar energy 26Stern, Otto 235, 278, 286–288Stern-Gerlach experiment 287Stokes, George Gabriel 160, 243,

288–290Stokes’s law 288, 289strangeness 99, 121, 123, 208strange quarks 124, 128Strassmann, Fritz 197, 326, 333strong interactions 123, 208, 344Strutt, John William. See Rayleigh,

Lord (John William Strutt)SU(3). See unitary symmetrysunlight 212sunspots 3, 348Sun’s radiation 231superconducting quantum

interference devices 153superconducting quantum

tunneling 152–153Superconducting Supercollider

325superconducting synchrotron 181superconductivity

Bardeen-Cooper-Schrieffertheory of 12, 20, 34, 153,269–271

comprehensive theory of 18discovery of 156, 157high-temperature 271Josephson effect and 12,

152–153superexchange 12superfine structure 175superfluidity

of liquid helium 159, 174theory of 97

superlattice Bloch oscillator 167supernova explosions 28, 292supersonic flight 192surface light 228–229symmetry principles 99, 184synchrocyclotron 93, 181synchrotron radiation 5Szilard, Leo 88, 93, 218, 294, 333

TTamm, Igor Yevgenyevich 57,

261–262Tate, John T. 168Taylor, Joseph H., Jr. 291–292telegraph 119, 142–143, 321telescope 113, 150

reflecting 210, 212refractor 212

Teller, Edward 96, 116, 130, 131,218–219, 293–295, 326, 339

tellurium 326temperature, absolute scale of 160terrestrial magnetism 119terrestrial stationary waves 297tesla 119, 298Tesla, Nikola 295–298Tesla coil 297Texas Instruments 162–163thermal equilibrium in gases 41thermocouple 216thermodynamics

Boltzmann, Ludwig 40–42Carnot, Nicolas Léonardi Sadi

49–51Clausius, Rudolf Julius

Emmanuel 61–62first law of. See energy,

conservation ofHelmholtz, Hermann Ludwig

Ferdinand von 139–141Joule, James Prescott

153–155Kelvin, Lord (William

Thomson) 160–161Kirchhoff, Gustav Robert

163–165Maxwell, James Clerk

193–195Nernst, Walther 209–210Rayleigh, Lord (John William

Strutt) 243–246second law of 61, 161, 195,

210, 229Stefan, Josef 285–286third law of 209, 210Wien, Wilhelm 329–330

thermometer 112–113thermonuclear bomb. See hydrogen

bomb

386 A to Z of Physicists

third law of motion 213third law of thermodynamics 209,

210Thomson, George 71, 72Thomson, Joseph John (J. J.) 21,

38, 71, 176, 185, 205, 226, 256,298–300, 299, 330, 348

Thomson, William. See Kelvin,Lord (William Thomson)

thorium 68, 256Thorne, Kip 134thoron 256three-color theory of vision 1403H. See tritiumtides 213time-reversal symmetry 99–100Ting, Samuel Chao Chung 249,

250, 300–303TOKOMAK 262Tomonaga, Sin-Itiro 77, 94, 95,

96, 97, 146, 172, 265, 274, 276,303–305, 304, 316, 323, 344

torpedoes 297Torrey, Henry C. 231, 232torsion balance 66Townes, Charles Hard 36,

224–225, 266, 267–268, 268,305–308, 306

Townsend, John Sealy Edward 312transformation theory 138transformer 89, 90, 143transistors 1–2, 18, 19, 162, 166,

167, 206, 270, 280, 281Treiman, Sam 322trichromatic theory 342Trinity College 100tritium (3H) 7Truman, Harry S 219, 294, 333Trump, John G. 313

UUlam, Stanislaw 294ultrasonic waves 176, 177–178ultraviolet light 256uncertainty principle 136, 138,

222, 327, 344unified field theory 262, 322. See

also electroweak theoryunitary symmetry [SU(3)] 121,

123, 128, 207–208, 265, 302

universeage of 75no-boundary 135origin of 5, 115, 116–117,

134–135, 224–225University of Chicago 6, 130University of Göttingen 42–43,

105, 130, 166up quarks 124, 128uranium 23, 40, 68, 93, 115, 195,

197–198, 326, 333, 336

Vvacuum tube technology 168, 280valence electrons 177Van Allen, James 309–311, 310Van Allen belt 309, 311Van de Graaff, Robert Jemison

311–313Van de Graaff generator 312–313Van der Waals, Johannes 156Vanguard Program 310–311Van Hove, Leon 316Van Vleck, John Housbrook 12,

204, 232, 313–315Van Vleck paramagnetism 314Varian Associates 166Vavilov, Sergey 57vector currents, conservation of

338Veltman, Martinus J. G. 145–147,

315–318virtual particles 277vision

color 193, 342physiology of 342three-color theory of 140

Vixen 7Volkoff, George 327volt 244Volta, Alessandro Guiseppe

Antonio Anastasio 89,318–320

voltage 215voltage multiplier 63voltaic pile 318, 319

WWalton, Ernest 62, 63, 258, 312Ward, John 127, 265

Watson, Ernest 116wavefront reconstruction 110waveguides 304wave mechanics 43, 137–138, 273,

314wave-particle duality 46, 47, 55,

64, 71, 72, 287wave theory of light 102, 103, 107,

108, 150, 214, 342, 343wave theory of quantum mechanics

331weak force 97, 123, 146, 181, 182,

208, 336–338, 339–341. See alsoelectroweak theory

weber 322Weber, Heinrich 83Weber, Wilhelm Eduard 119, 141,

321–322Weigand, Clyde 279Weinberg, Steven 126, 128, 146,

253, 264, 265, 266, 316,322–325, 323

Weisskopf, Victor 79, 122, 254,276, 323

Westinghouse, George 296–297Wheatstone, Charles 119, 143Wheeler, John Archibald 40, 94,

325–329, 327Wheeler-Feynman electrodynamics

326white dwarfs 55white light 210, 212Wien, Max 272Wien, Wilhelm 229, 245,

329–330Wigner, Eugene Paul 18, 74, 93,

132, 183, 330–334, 332, 340Wigner correlation energy 334Wigner crystal 334Wigner distribution 334Wigner-Eckart theorem 334Wigner effect 334Wigner force 334Wilson, Charles Thomson Rees

31, 64, 125, 334–336Wilson, Robert 115, 117, 224, 225,

226, 242Wilson cloud chamber 181, 197,

258, 334–335

Index 387

W particle 146, 147, 253, 254,317, 324

Wu, Chien-Shiung 99, 184, 332,336–338, 337, 339–341

XXerox Corporation 20X-ray crystallography 178X-ray diffraction 178, 179, 253,

283X-ray emissions 22X rays

discovery of 251, 252and electricity in gases 256medical use of 69

nature of 178, 179produced by fluorescent

crystals 23X-ray scattering 21, 22, 64

YYang, Chen Ning 99, 145–146,

182, 183–184, 265, 316, 323,332, 336, 339–341, 340

Yang-Mills gauge theory 127, 128,146–147, 265, 317, 323, 341

Young, Thomas 102, 140, 193,214, 342–343

Young-Helmholtz theory 342Young’s modulus 343

Ypsilantis, Thomas 279Yukawa, Hideki 11, 303,

343–346, 345

ZZeeman, Pieter 175, 188, 278, 284,

347–348Zeeman effect 137, 175, 188, 249,

284, 347–348Zeldovich, Yakov 134, 262zirconium 326Z particle 146, 147, 253, 254, 317,

324Zrelov, Valentin 58Zweig, George 123, 208

388 A to Z of Physicists