Memories ofFey n manTheodore A. Welton

In this memoir, written in 1983, a contemporary and close friend of RichordFeynman's recalls the blossoming of Feynman's genius with vignettes fromcollege, Los Alamos, ond afterward.

AfJer the adventures he describes here, Ted Welton [ginawelton@multipro.com) moved to Oak Ridge NaUona! Laboratory in ^Tennessee in 1951. He has since retired from his position ifiere os a senior theoretical physicist in the physics division ond nov/ liveswith his wife, Gina, in Crossville, Tennessee. ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ _ _ ^ _ , , ^ ^ ^ ^ ^ ^

Almost 50 years ago, in September 1935, unnoticedamong the as-yet-unditferentiated horde of entering fresh-men at MIT were two ambitious, rather diffident physidsts-to-be. One was Dick Feynman and the other was the authorof these recollections. Initially unknown to one another, weremained so tor thy freshman year, since MIT grouped its stu-dents into classes by majur. I was Course Vlll (physics) fromthebt'ginning, while Feynman briefly vacillated, finding elec-trical engineering too practical after one semester and math-ematics too abstract after another semester. My first hint ofwhat was to come was on the occasion of the annual springopen house in 1936, when I found at one of the mathematicsexhibits a fresh-faced kid (almost precisely my age, actually)who seemed to have a thorough comprehension of the con-cept of the Fourier transform and of the operation of the me-chanical harmonic analyzer. Up to this point, 1 had nourishedthe fond, if secret, belief that I was the only freshman com-petent to handle such esotsiric matters. Thus began my trueeducation!

By the end of the summer of ]93f>, I had passed exams inthe required mathematics courses for sophomore and juniorphysics majors and thus had available some interesting gapsin my schedule, which I promptly filled by signing up for thecourse Introduction to flieoretical Physics, taught from thebook of the same name by John Slater and Nathaniel Frank.Before the first lecture, I had gone to the physics library andtaken out TullioLevi-Ci vita's book 77ft'A/isi)/((f('Di f/•('(?(/«/Oi/-cuhts, which I hoped would reveal some further secrets of dif-ferential geometry not covered in Arthur Eddington's book TlicMathftiititical Theory of Relativit}/, which 1 had read the previousyear. Vicn on to class, where I discovered the mathematicswhiz of the previous spring, apparently also prepared to dobattle with theoretical physics. As 1 sat next to him, he glancedover at my books and immediately announced (in a somewhatraucous Far Rockaway version of standard English) that hehad been trying to get hold of Levi-Qvita and could he see itwhen I had finished. My interest piqued, I noticed that hisstack contained Albert Wills's Vector Annh/^is, ivith mi hitroduc-tioii to Tensor Anahf:i^is, so he must be the reason I had been un-able to find it in the library. Since we were, I think, the onlytwo sophomores in that class, it apparently simultaneously oc-curred to the two of us that cooperation in the struggle againsta crew of aggre.ssive-Iooking seniors and graduate studentsmight be mutually beneficial. Our friendship dated from thatalmost instantaneous recognition, and recollections from thatperiod have enriched (and sometimes complicated) my life

ever since.

Julius Stratton, who would later be chancellor or presi-dent or whatever they have at MIT, was the lecturer in thatcourse, which we will both always remember with the great-est of pleasure. I was apparently easily accepted as a goodstudent, but Dick was quickly recognized as tmly superior.In fact, Stratton, who was certainly an admirable lecturer,would occasionally skimp on his preparation, with the usualconsequence that he would come to an embarrassed halt, alittle red creeping into his complexion. With only a moment'shesitation, he would ask, "Mr. Feynman, how did you han-dle this problem?" and Dick would diffidently proceed to theblackboard and give his solution, always correct and fre-quently ingenious. Stratton never entrusted his lecture to meor to any other student.

The mysteries of quantum mechanicsDick and I quickly found that our interests, aspirations, andgeneral state of physical knowledge were remarkably simi-lar, or overlapped to such an extent that our conversations onsuch matters were enormously profitable to both of us. Lateron, Dick would occasionally claim that I taught him quantummechanics. The truth is that we learned it together, and theprocess was so pleasant that we never thought of it as work.

In our first conversation, on the afternoon of that mem-orable first class with Stratton, Dick announced that hewanted to leam general relativity. 1 already knew a bil and,with proper superiority, announced that I wanted to leamquantum mechanics. Dick promptly said that he had read agood book on the subject by somebody named Dirac and in-timated that I should try my hand at it. Somewhat miffed atnever having heard of Dirac or his book, I secretly resolvedto get it and remedy this defect in my preparation. We talkedfor several hours about Albert Einstein's work on gravitation,of which, of course, neither of us had any deep appreciation.Tiie mathematical manipulations ot the general theory were,however, clear and interesting so that we considered our-selves real professionals. Dick had, by the way, ended his vac-illation between too practical and too abstract and decidedthat theoretical physics was just right. I had previously cometo the same conclusion, so we had no argument there.

Tlie next day 1 got Paul Dirac's book, Princiiile^ ofQiuvi'tum Meclintiics, from the library and rather quickly found my-self in over my head. Shortly thereafter, one of us locatedLinus Pauling and E. Bright Wilson's book Introduction toQuantum Mechanics, with Applictitions to Chemistry, and thiswas the level we diose for our entry into thf mysterious reatmof quantum mechanics. We wandered, without external guid-

46 February 2007 Physics Today © 2007 American Institule of Physics, S-0031-9228-0702'030-3

Philip Morse, a professor of physics of MIT, played an influ-ential role in the education there of Richard Feynman and lheauthor, [Courtesy of AIP Emilio Segre Visual Archives.)

ance (except for the ideas of orthogonal functions and suchthat we were encountering in Stratton's course), throughmuch of quantum mechanics, with naturally some enormousgaps in our understanding. Around Christmastime, one ofour fellow students in Stratton's course announced that hehad found a new book that seemed to have answers for mostof [lie fundamental problem of physics. Its name v fas The Ret-ntivifi/ Theory of Protons and Electrons, and its author was Ed-dington, whom we had already identified as a true prophetof the new physics from The Mathematical Tlieory of Relativity(not a bad book, but actually a bit pretentious). We got thisbook of promised revelation and took turns trying to makesense of it. We were both enormously impressed and far tooimmature to recognize it as garbage. It perhaps reflectsfaintly to our credit that we never fooled ourselves into be-lieving we understood the book, but we did suffer throughseveral agonizing months, tantalized hy Eddington's claimedresults, but convinced that we were somehow too dumb tounderstand his methods.

One amazing (in retrospect) quirk displayed by Dick inStratton's course was his maddening refusal to concede thatJoseph-Louis Lagrange might have something useful to sayabout physics, Tlie rest of us were appropriately impressedwith the compactness, elegance, and utility of Lagrange's for-mulation of mechanics, but Dick stubbornly insisted that realphysics lay in identifj'ing all the forces and prt>perly resolv-ing them into components. Fortunately, that madness ap-pears to have lasted only a few years!

For the sect)nd semester. Introduction to TheoreticalPhysics was taken over by Phil Morse, who had been trainedas a quantum mechanician and had worked extensively inseveral aspects of the field. Morse took proper advantage ofhis opportunity and included a section on elementary wavemechanics to complete the year. Dick and 1 already had ac-quired a fair grasp of the subject at that level, but Morse's sys-tematic presentation did us no harm and further allowedMorse to see from our problem sets and questions that wewere ready for greater things. Consequently, Dick and I wereinvited, with AI Clogston, who was a year ahead of us, tocome to Morse's office for one afternoon a week the next year(our junior year) to be properly exposed to quantum mechan-ics. We accepted with alacrity and Morse thereby can claiman important roie in our training.

"Real research"After we had vuv\ through Dirac's book, Morse suggested wemight be ready for a little real research and suggested somecalculations of atomic properties using a rather convenientformulation of the variational method, whidi Morse hadworked out in a previous paper. Dick and I set to work witha will, first learning how to use the "chug-chug-ding-chug-chug-chug-ding" calculators of those prewar days, Morse'sscheme involved using kinetic and potential energy integralscalculated with hydrogenic radial functions and tabulated forvarious values of the coefficients occurring in the functions.For Dick, they were "hygienic" fimctions, and my efforts toconvert him to "hydrogenic" were totally unavailing.

The result of our work was, of course, a gradual realiza-tion that quantum mechanics was more than a romanticdream and might have something to do with life outside thecollege years. By this time, I had ieamed one lesson well,

namely, that 1 was not going to be able to compete with Dickin his chosen field, Unfortimately, some years would pass be-fore 1 was to leam that life could be lived, perhaps even pleas-antly, without that possihility. Fortunately, the first realiza-tion did not embitter me, and I continued to enjoy Dick'scompany and support, although we began to grow apart ashe matured in his chosen Held and I wandered a bit intellec-tually. Of course, we learned mudi together in addition toquantum mechanics, and I have always recognized elementsin his later work that clearly came directly from some of thewell-organized and well-taught MIT courses, particularly thephysics but also the elementary electrical engineeringcourses we were required to take. Many of the chapters in TheFeynman Lectures on Physics stem directly from material wewere subjected to—rather pleasurably, I should add—duringthose years.

In our senior year, we had a nice experimental physicscourse given by George Harrison and featuring a well-organized lab. Harrison's lectures were a pleasure to attend,with a wealth of ingenious applications of physical princi-ples. The laboratory required each student to select a projectfrom a list, think of a way to execute it, and carry it thrt^ugh.Dick chose to make a mechanism to read out the ratio of twoshaft speeds, He thought of a mechanism consisting of aturntable turned by one shaft, with the second shaft threadedand oriented parallel to a radius of the turntable. Threadedonto the shaft was a wheel whose rim was in contact with theturntable. As the two shafts rotated, the wheel would ad-vance itself along the threads to a distance from the center ofthe tumtahle that was obviously proportional to the desiredratio. We all admired this simple and ingenious principle,and Dick went energetically and skillfully to work with thelathe, (In those days ever)- physicist was supposed to knowsuch things.) Then came the great day of the test, Everythingfitted and rotated, but the accursed little wheel stubbornly re-fused to move to the correct location. The friction between

www.physicstoday.org February 2007 Physics Today 47

the wheel and the turntable was too small in comparison withthat between the wheel and the threaded shaft. I rememberDick's (and our) disappointment vividly Another studentwas attempting to solve the same problem by charging anddischarging condensers with commutators attached to thetwo shafts. His device did not simply fail on test; it blew upwith gratifying electrical fireworks as all the capacitors let goat once. Very educational for all!

We also signed up that year for a nuclear physics semi-nar that was occasioned by the desire of Morse and Nat Frankto absorb the recently printed review articles by Hans Betheand Stanley Livingston. Tliey were a useful introduction tomaterial needed later, but our attention was being largely ab-sorbed by the required senior thesis. Dick did his under thedirection of Slater and made a real contribution (the Feyn-man-Hellman theorem) to the understanding of molecularstructure. My thesis, with Morse, was undistinguished, and1 was left without an offer from a graduate school, while Dickaccepted one from Princeton. We left MIT in 1939 not reallyexpecting to meet again. Fortunately, Morse was able to lo-cate an assistantship for me at the University of Illinois, butthat is another story.

Los Alamos reunionMy Feynman saga resumes in the early spring of 1944. BobSerber, Sidney Dancoff, and Phil Morrison had successivelyleft Illinois (and me) to go to war research laboratories withpurposes supposed by army intelligence to be unknown tous. (Actually, we knew a great deal.) 1 had gotten my degree,was married with a child on the way, and was quietly tryingto retain my civilian status by teaching defense-orientedcourses. This finally wore a bit thin as the draft regulationskept shifting, and the acting department head called me inand informed me that my best chance was to go up toChicago where at a certain time, in a certain hotel room, amysterious stranger would reveal to me a possible nonmili-tary future. Tlie stranger turned out to be Arthur L. Hughes,personnel director of the Los Alamos project, and he, in fact,offered me a spot working on his mysterious project (which1, in fact, already knew of in broad outline). It was the classicoffer impossible to refuse, and I duly embarked in BedroomB, Car 192 of the Santa Fe Chief for a strange-sounding des-tination in Santa Fc. Finally arriving on the mesa, my bus wasmot by a very familiar Dick Feynman set in a wildly unfa-miliar context.

It turned out that he had saved my pitiful civilian life bynoticing my name on a list of available physicists and fillingout a suitable requisition. We went for a long hike thatevening and began again the friendship that had first begunin 1935. Hi.s first question, "Do you know what we're doinghere?" was answered truthfully, "Yes. You're making anatomic bomb." A momentary, slightly thunderstruck expres-sion was followed by a second question, "Well, did you knowwe're going to make it with a new element?" That was an-swered in the negative, and he proceeded with the job ofbringing mo up to date.

Although 1 was 7000 feet above my normal altitude, mybody postponed its demands long enough so that we walkedthe length of Los Alamos mesa, descended into Omegacanyon, walked back the length of the mesa to Omega Site,home of the criticality experiments, and then climbed themore-or-less precipitous canyon wall back to square one. Allthis was done with a steady stream of excited conversation.Feynman was, of course, thorouglily adjusted to the altitude,but 1 could not have done such a feat again for perhaps amonth following.

After giving me a thorough briefing on the work of theproject and of his group—Julius Ashkin, Fred Roines, andDick Ehriich, until the addition of myself-the talk degener-ated to a description of our interests in nonmilitary physics.I quickly perceived that Dick's former distaste for the workof Lagrange had undergone a certain alteration. I was alreadyfamiliar with the Fokker-Tetrode Lagrangian (yielding thehalf-advanced, half-retarded electromagnetic interaction be-tween charged particles), and Dick proceeded to explain insome detail how he and John Wheeler had attempted to gothis route in avoiding the self-action problem. That work im-pressed me at the time as extraordinarily ingenious andhopeful. It was only after much hard work following the warthat I was to realize that it was an untenable formulation.

As an important tool in the attempt to domesticateFokker and Tetrode, Dick had discovered his later-to-be-famous formulation of quantum mechanics in terms of asummation over all possible spacetime trajectories of the sys-tem. He showed me how it worked by a simple illustration,but at that time neither he nor 1 had any idea of the use towhich the method would eventually be put. Another inter-esting lecture was delivered on the iniquity of displacing in-tegration paths for real integrals into the complex plane.Dick's view was that if you are going to do a real integral, youshould do it and not mess around with the complex plane.He told how a fellow student at Princeton had challengedhim to do all the definite integrals in the back of WilliamSmyth's Elements of the Differential and Integral Calculuii with-out setting foot ot'f the real axis, with a 24-hour time limit.Dick didn't get much sleep, but he succeeded. I think this partof his thinking also had to be changed a bit to allow lhe workof 1947-48.

Much had also transpired at the personal level. Dick hadmarried his high-school sweetheart, then discovered that shehad a mysterious malady, finally and very belatedly diag-nosed as tuberculosis. She was hospitalized in Albuquerque,where Dick visited every weekend and where she died, lateinto the project. Tlic news was particularly sad for me to hearsince 1 had met her in the spring of our last year at MIT in thecourse of a well-planned and executed joke by Dick on hisshy friend. My wife was forced to remain in Illinois until afterthe birth of our son, at which time she came to Los Alamosand met Dick also. In this connection, I came in for somegood-natured ribbing from Dick on my new responsibilities.

Dick had established a reputation for energy and inge-nuity that was unmatched on the mesa. The four of us in hisgroup (T~4, under Betlie of the theoretical division) wereworked unmercifully but were proud to carry out our parts.The morale of T-4 was as high as that of any of the groups. Weknew from experience that if an idea was needed, it wouldquickly come with suitable help trom Dick. Some ideas toocomplex or bizarre for us to originate would emerge fullyformed from Dick's fertile imagination. He would carefullydescribe what was to be done; we would skeptically ask howsuch a thing could work; he would patiently reply, "Let's tryit and see!" We would all pitch in and do a prototype calcu-lation with our faithful Work Projects Administration math ta-bles and Marchant mechanical calculators. An essential fea-ture would always bo a prcnaxisting special-case calculationwith which comparison could then be made. We knew that anew method worked and what its error limits were when wewere through with it. This game of innovation, played manytimes over, was perhaps the most stimulating time ot my adultlife. I know that it honed Dick's talents for what was to come.

Many others have detailed recollections of Feynman atLos Alamos, each viewpoint tinged with personal feelings.

48 February 2007 Physics Today www.physicstoday.org

I II

Los Alamos badge photos forRichard Feynmon (left) and theauthor. (Feynman photo courtesyof AlP Emilio Segre VisualArchives]

We all saw him diplomatically, forcefully, usually withhumor (gentle or not, as needed) dissuade a respected col-league from some unwise course. We all saw him forcefullyrebuke a colleague less favored by his respect, frequentlywith definitely ungentle humor. Only a fool would have sub-jected himself twice to such an experience.

PuzzlesDick loved to solve puzzles. Once presented with a clearlyformulated physical paradox, mathematical result, card trick,or whatever, he would not sleep until he had the solution.Shortly after I arrived, I presented him with a problem (laterimmortalized in his Lectures, volume 2, section 17-4). I hadgotten it from a friend at the Naval Research Laboratory andhad immediately solved it. I stated the problem and Dicka.sked if I had solved it. I said yes, but truthfully and a bitstrangely, the answer had slipped away. He promptly set towork on it, with me steadily demolishing his attempted so-lutions but still not remembering my own. We parted to getsome sleep (I thought), but the next morning Dick showedup at the office a bit the worse for wear yet triumphant. Thissort of thing happened over and over again, frequently withimportant matters rather than trivia. Incidentally, part of myeducation consisted of watching the already great of physicsstruggle unsuccessfully with that little problem as it spreadlike a plague through our close-knit community.

I have seen Feynman unsuccessful only once with one ofthese challenges. It was a card trick for which he was warnedin advance that he could see it only once. The trick was dulyperformed with a result much to his surprise. He promptlysaid, "Do it again!" and was reminded that he had had hisone permitted view. Muttering angrily, he went off to attemptto solve the problem. He failed, to his considerable annoy-ance. To make matters worse, the rest of his group solved it.Actually, we cheated, since we compared our separate expe-riences as we remembered the trick and thus effectively hadthe trick performed more than once.

Shortly after the start of the project but considerably be-fore my arrival, the senior people (they actually weren't veryold, being roughly 10 years older than we were) were chew-ing over the problem oi calculating critical masses in a sys-tem with spherical symmetry and monoenergetic, isotropi-cally scattered neutrons. Tlie problem was approximatelythat formulated by Eberhard Hopf (the sun's limb darkening)and so beautifully solved by Norbert Wiener and Hopf, butthe mathematics involved—integral equations—was thor-

oughly unfamiliar to all of us. There was a dear necessity todevise useful and general approximations, Wiener-Hopfbeing of no use except in an idealized situation. Dick, whowas never shy about proposing physical ideas and had longadmired the variational method in quantum mechanics,piped up with the suggestion that the criticality problemmight be usefully approximated by a variational formulation.Bethe (probably among many) considered this to be nonsenseand said so. Dick rose immediately to the challenge and whennext seen had performed a simple, elegant, and convincingcalculation. As an important result, Bethe, who combines acertain fair-mindedness with his talent for physics, correctlydecided that Dick was a man to be trusted with complexphysical problems, and Dick shortly found himself in greatdemand.

As another illustration, the explosion of a fission weaponwould seem to be a matter of great complication, which it cer-tainly is when viewed in detail. There was a clear need for re-liable estimates of the yield of a given configuration, andsome unprofitable attempts to make estimates that took thecomplications into account. Dick shortly produced Feyn-man's Famous Formula (one line, with only a few key pa-rameters) for the efficiency of a fission explosion, therewould be other famous formulae, but this one achieved aunique honor. When atomic spy Klaus Fuchs was passing in-formation to courier Harry Gold, he included FFF. The KGB(or whatever the Soviets had in those days) would passGold's stuff to a group of their own scientists who could thensend back queries by way of Gold to Fuchs. It is known fromFuchs's confession that his opposite numbers in Russia couldnot believe that the efficiency could be given reliably by sucha simple formula, and Fuchs had to give Gold a detailed der-ivation. My understanding is that this query was one ofmaybe two that Fuchs had to answer.

Another type of puzzle had absorbed part of Dick's spareenergy for several years. He had learned to pick Yale locksand had become very proficient. His method, which he will-ingly described, was the standard method of locksmiths andburglars the world over. At Los Alamos a related challengeappeared in the form of the combination safes. Dick quicklyfound that a straightforward testing of all possible combina-tions would consume about 8 hours, so the safes were actu-ally safe since they would be viewed by a guard much morefrequently than that. He did some private research on thesafes in use and found he could quickly open them. He didnot reveal his secret method to anyone at the time (he has

www. physicstoday. org February 2007 Physics Today 49

Young Richord Feynman(center), talking withStanislaw Ulom (left)and John van Neumannin New Mexico's Bande-lier National Monumentaraund 1947. (Courtesyof AIP Emilio SegreVisual Archives.)

since told all in a most interesting interview), but it did be-come widely known that in case of necessity, Dick could bedepended on to open any sate. He developed another skill,namely the ability to dissect a sick Marchant calculator andrestore il to perfect health. Bethe, thinking of all the good the-oretical man-hours going down the drain, finally had the witto get the army to procure enlisted men with the appropriateskills and to forbid Feynman from spending any more of hisvaluable time on such activities. Of course, the new locksmithcouldn't easily open a safe whose combination he didn'tknow, so Feynman was left a portion of his old territory.

The boss does \\ againEdward Teller, in his prime, was a most remarkable theoreti-cal physicist. He produced ingenious ideas at a great rate,many of them potentially very useful. Unfortunately, he wasalso a great salesman and he could sell an ultimately unwork-able idea with great enthusiasm. One of his ideas, aimed at aneventual thermonuclear weapon, was to fabricate the availablefissionable material as the hydride, rather than the metal, Tellerargued that the critical mass would be much reduced and thatthe performance as a weapon would not thereby be fatally de-graded. Bethe accordingly set Feynman and T-4 the task ofevaluating Teller's suggestions with great care.

Up to that time, problems involving slowing of neutronshad also involved relatively large systems so that the slow-ing could be reasonably handled by Enrico Fermi's age ap-proximation. Now we were faced with the necessity of mak-ing a real advance in techniques for cHticality calculations ifa genuine critique of this new proposal were to be made.Group T-2, under Serber, had been charged with bomb criti-cality calculations and had done an excellent job of theWiener-Hopf-typecalculations. Bob Marsbak had come fromMontreal, bringing with bim a generalization of diffusiontheory, the spherical-harmonic method. T-2 had thus carriedthrough a variety of calculations of known accuracy for two-region, infinite spherical systems, witb only elastic isotropicscattering and monoenergetic neutrons.

This available variety of results was not yet enough tosatisfy the clear needs of T-4, so we began a somewhat sneakyinvasion of T-2's territory. This started with one of Feynman's

seemingly mystical insights to the effect that the generalproblem (omitting only inelastic scattering in the outer re-flector region) could be solved very simply and accurately ifonly a table or, preferably, a simple formula were available ofthe eigenvalues defining criticality for the general spherical,infinite, two-region, monoenergetic, isotropic problem.

We displaced our usual incredulity at his bold assertion,following which our usual testing period convinced us allthat the boss had done it again! Unfortunately, the requiredtable or formula did not exist, nor did it seem likely to. Onlya short period of reflection was, however, required beforeFeynman announced that we were going to take tbe accu-mulated computational results from T-2, put them throughthe meat grinder, season them with some further insights (yetto be produced), and extrude this mixture as a handyinterpolation-extrapolation formula. (Its name would beFFF #2,1 suppose.)

We quickly set to it, and after a very hard day's work, wehad the formula, a full rationale, and a thorough checkagainst the available data, We then had the job of persuadingT-2 that our result was (a) correct and (b) u.sefi.il. This took alittle longer, but it is worth noting that when Serber eventu-ally produced an ingenious method of rather directly ap-proximating to the solution of the general integral equation,he took as his test of success the quite good agreement hefound with FFF #2.

We had definitely scored, but not yet quite on Bethe's re-quired target because we could not yet handle a moderatingreflector. Feynman muttered and mumbled, but nothing co-herent came out for awhile. Finally he announced that hethought he had a beautiful general solution building neatlyonto what we had already done. Ashkin and 1 pressed himfor details, but he pled lack of time since he was about to leaveon a vacation trip. We subsided but agreed we would makea concerted effort to steal a march on Dick in his absence. Wedid work at top speed for a week and probably showed a con-siderable excess over our normal ingenuity. On Feynman's re-tum we proudly showed what we had accomplished (a po-tentially useful special class of problem) and in turn askedbim about his new invention. He looked at us in (feigned?)surprise and asked us for further information. We assured

50 February 2007 Physics Today www.physicstoday.org

The Shelter Island Conferenceof 1947 gathered 23 physicsluminaries to discuss the foun-dations of quantum mechanics.Willis Lamb's report there ofthe first measurement of the1058-MHz level splitting in thehydrogen spectrum was alandmark in the developmentof quontum electrodynamics.Shown here from left to rightare Lamb, Abraham Pais, JohnWheeler, Richard Feynman,Herman Feschbach, and JulianSchwinger. (Courtesy of AIPEmilio Segre Visual Archives.)

him that we knew only that hehad promised a general solu-tion to the problem we had at-tempted, ln some (feigned?)astonishment, he assured usthat he would go off and at-tempt to resurrect his sup-posed inspiration. Somewhatskeptically we waited, untilafter a few hours Dick burst in to give us a lecture. This onewas less transparent than any he had thus far delivered, andwe reacted with the usual skepticism. Dick told us how heproposed to test it, and we got to work. Within a couple ofhours we were convinced, but we still did not understandwhy it worked.

Dick had to spend several days in the hospital, and I tookthe opportunity to attempt some alternate, understandable(to me, that is) derivation of this mysterious new result. Tomy gratification, I did get the germ of an idea. To my annoy-ance, when Dick returned and I explained my idea, he tookthe ball and ran very fast with it. Within an hour he had a dif-ferent formalism on the blackboard. At least we all under-stood this one, but we were confused as to how both couldbe correct. It took only a short time to convince ourselves thatboth worked well, although the results were not identical.Much later Dick resolved the problem and showed how eachmethod was a plausible approximation to the exact solution.

Finally, we had sharpened our computational task to thepoint where a reliable judgment could be made on Teller'shydride proposal. The answer was negative, in that the pres-ence of the hydrogen grossly lengthened the generation timeso that the efficiency formula effectively gave zero.

Atabout this time, theglory days of T'-4 were past. Feyn-man was asked to take on a major new responsibility for thegroup doing hydrodynamic calculations, and the rest of ustook on smaller tasks, for which the master's touch was notessential. He continued to support us and was always avail-able for advice, but we had no more of those crash develop-ments that had so enhanced our days.

Postwar diasporaFinally came the test and the two bombs on Japan and thenthe six months' job of winding down the project. I took on themajor task of writing up the many-velocity criticality meth-ods, and the rest of us were similarly occupied, but the warwas now over and urgency had departed. We had time to

begin to think about postwar activities, \iach senior scientist,of course, already had a spot lined up: Bethe back to CornellUniversity (he briefly planned to go to Columbia, I. 1. Rabibeing a major attraction), Victor Weisskopf to MIT, Serber totbe University of Califomia, Berkeley, and Rudy Peierls to theUniversity of Birmingham. Each had been commissioned tobring one or more junior people with him, and a number ofus then had tbe problem of deciding where to go. Keynmanhad it easy, having decided some time before to cast his lotwith Bethe. I was torn Lietween Weisskopf, whose style inphysics seemed to be more of the kind I might reasonably as-pire to, and Bethe, who made a strong case for tbe fact thathe could perhaps teach me to calculate, a skill that was notfully apparent in my work up to that point. I was too unsureof myself to consider Peierls's offer to take me to Englandwith bim, and since a goodly part of my graduate traininghad been with Serber, it was time to seek further experiencewith someone new.

Aside from the clear fact that Bethe's facility with theo-retical calculations tended to frighten me rather than fill myyouthful head with visions of how I might emulate him, therewas a practical fact militating against Cornell (and unfortu-nately, therefore, Bethe also). Feynman would be there, andit was clear that 1 had to strike out on my own or be a paleshadow of my friend for the rest of my life. Dick was under-standing when I explained my feelings after he had entreatedme to go along and teach him field theory. I smiled at thatone! I had learned field theory under Serber's tutelage, and Iassumed that Dick bad learned it with Wheeler and was justbuttering me up a bit. Later on I came to realize that Dick hadsomehow been insulated from quantum electrodynamics (orat least from the more general aspects of quantum field the-ory) at Princeton and that Ibis strange innocence had proba-bly played a crucial role in allowing him the freedom to in-novate as he did a few years later.

So it was to be Weisskopf and MIT for me. I bade farewellto Los Alamos and Feynman, knowing this time, however,

www.physicstoday.org February 2007 Physics Today 51

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that we would meet again. Weisskopf had opted t or MIT be-cause they had made him a fine offer and because JulianSchwinger was to be only a mile or so away at Harvard. Wehad frequent joint theoretical seminars with the Harvard peo-ple, and I quickly acquired a healthy respect for Julian. For atime the burning issues seemed to be quite apart from thequantum electrodynamics that consumed much of lny energywithout yielding any visible fruit. I encountered Feynman atmeetings and was entranced as always by the flow of ideas,but it was clear that his mind was not really where it prop-erly belonged.

After shidying the self-energy problem in about everyway I could imagine, the light briefly dawned, and I obtainedan interesting-looking formula for the level shift in an atom.Weisskopf was interested and wanted to present it at the Shel-ter Island Conference, but I was convinced 1 would have a rel-ativistic result in a few weeks and asked him to desist. On re-turning from vacation, I encountered Bethe at GeneralElectric and asked how things had gone at Shelter Island.Since the atomic level shift had now clearly become a hotitem, I thought it time to fill him in on my ideas. To my con-siderable dismay, he pulled a manuscript from his drawerwith the crucial 1000 megacycles already calculated. So muchfor my idea, but where was Feynman? I was desperatelyworking, hoping to regain some lost ground, but unfortu-nately by this time so was everyone else! Schwinger was de-livering magnificent weekly lectures in which he developeda formalism with beauty and power I could not dream ofmatching. Weisskopf was starting a full-dress relativistic cal-culation of the Lamb shift and traveling each weekend toIthaca to keep Bethe informed of progress (and, presumably,to warn him off from the race). Still no Feynman!

Feynman arrivesFinally—1 think it was at the New York American PhysicalSociety meeting in January 1948—1 had my usual talk withDick, and he told me that Bethe had finally gotten himpointed in the right direction and explained what he was upto. I went back to Cambridge and gave my colleagues theirfirst coherent account of the rumblings then beginning atIthaca. Dick had succeeded in doing a relativistic mass-renormalization using what he would later call a modifiedphoton propagator, but he did not yet actually have the full,beautiful, clearly covariant formalism, which is today learnedand used by everyone. Feynman had finally arrived! Fromthen on for several years, I watched with interest and admi-ration while the Feynman machine built up power and over-took the already highly perfected Schwingerian approach. Iwas, of course, still struggling to get something out of my ownclearly outclassed efforts, and finally came to appreciate thefull beauty of what Dick had done only several years after hehanded me his two cmcial reprints with the quiet advice,"You may find these interesting."

And so the story ends. I have seen Dick a few times sinceleaving MIT and have talked extensively with him a very fewtimes. He has had a profound influence on my life, and I hopeto have reciprocated in some degree. He will smile if he readsthis, but I feel as I imagine Marcel Grossmann must have feltabout Einstein or Christopher Wren about Newton: amazedat having been given the privilege of knowing so interestinga character. After long reflection, 1 would think it apt to com-pare the young Feynman with the young Newton. Of course,Newton had it easy; he had a new science to invent. Feynmancould only perfect something already existing, but the inge-nuity and energy with which he went about the job have beenseen only rarely since the plague years. •

See www.pt.inis.ca/12138-22 52 February 2007 Physics Today