that improves the accuracy of GPS position esti-mates. Commercial aircraft had to resort to in-flight backup systems.

High-energy particles will interfere with air-

could bring down the entire grid. Other indus-trial countries are also vulnerable, but North America faces greater danger because of its prox-imity to the north magnetic pole Because of the

rent (DC). The DC flows up the transformer ground wires and can lead to temperature spikes of 200 degrees Celsius or higher in the trans-former windings causing coolant to vaporize )

The entire East Coast and much of the rest of the country would lose power. This map shows the blacked-out regions expected from a severe storm like that of 1921, which would induce ground fields of about 20 volts per kilometer. Scientists have yet to model the effects of a full-blown 1859-like storm on the power grid.

These currents surge into transformers and

can fry them. It would take weeks or longer for

workers to fix them all.

Pipeline

Electric currents in the ionosphere

Induced current

Induced current

[EFFECTS ON POWER]

Darkness Falls Electric currents in the ionosphere induce electric currents in the ground and in pipelines.

Transformer

CRED

IT

82 SC IENT IF IC AMERIC AN Augu st 20 0 8

The 1859 Superstorm The authors have reconstructed what happened in 1859, based in part on similar (though less intense) events seen by modern satellites. UTC is Coordinated Universal Time—basically, Greenwich Mean Time.

August 26 Large sunspot group

appears near longitude 55 degrees west on the sun; first CME possibly launched.

August 28 CME arrives at Earth with a

glancing blow because of the solar longitude of its

source; its magnetic orien-tation is north ward.

August 28 07:30 UTC Greenwich Magnetic Obser-

vatory detects a distur-bance, signaling compres-

sion of the magneto sphere.

August 28 22:55 UTC Main storm phase begins,

with large magnetic distur-bances, telegraphic disrup-tions and auroral sightings

as far south as magnetic lat-itude 25 degrees north.

August 30 Geomagnetic disturbances

from first CME end.

September 1 11:15 UTC Astronomer Richard C.

Carrington, among others, sights a white-light flare on

the sun; the large sunspot group has rotated to longi-

tude 12 degrees west.

September 2 05:00 UTC Greenwich and Kew magnet-

ic observatories detect dis-turbances followed immedi-

ately by geomagnetic chaos; second CME arrives at Earth within 17.5 hours, traveling at 2,380 kilo meters per sec-

ond with southward mag-netic orientation; auroras appear down to magnetic latitude 18 degrees north.

September 3–4Main phase of geomagnetic

disturbances from second CME ends; scattered auro-ral sightings continue, but with diminishing intensity.

Impact of a Coronal Mass Ejection

Sun

EarthMagnetic field line

Magnetopause

Solar wind

Magnetosphere

Van Allen belts

NORMAL CONDITIONS: Earth’s magnetic field typically deflects the charged particles streaming out from the sun, carving out a teardrop-shaped volume known as the magnetosphere. On the sun-facing side, the boundary, or magnetopause, is about 60,000 kilometers from our planet. The field also traps particles in a doughnut-shaped region known as the Van Allen belts.

FIRST STAGES OF IMPACT: When the sun fires off a coronal mass ejection (CME), this bubble of ionized gas greatly compresses the magnetosphere. In extreme cases such as superstorms, it can push the magnetopause into the Van Allen belts and wipe them out.

Sunspots Coronal mass ejection

CME magnetic field (S)Earth’s magnetic field (N)

MAGNETIC RECONNECTION: The solar gas has its own magnetic field, and as it streams past our planet, it stirs up turbulence in Earth’s magnetic field. If this field points in the opposite direction as Earth’s, the two can link up, or reconnect—releasing magnetic energy that accelerates particles and thereby creates bright auroras and powerful electric currents.

CME plasma

Reconnected region

Reconnected region

Current

Auroras

Turbulent field lines

SUNSPOTS

CORONAL MASS EJECTION

AURORA SIGHTINGS

X-RAY FLARE

AURORA SIGHTINGS

w w w.Sc iAm.com

How to PrepareIf a storm were on its way, we could do the following:

Satellite operators put off critical command sequences. During the storm itself, they monitor their birds and override any spurious commands.

GPS users switch to backup navigation systems.

Astronauts avoid space walks.

Solar particles and radiation puff up the atmosphere, increasing the drag forces on low-orbiting satellites.

High-energy particles degrade solar panels. They also penetrate circuitry and generate

spurious signals that can corrupt data or even cause a satellite to

spiral out of control.

Electrons can collect on satellites and cause static electrical discharges that

physically damage the circuitry ( ).

[EFFECTS ON SATELLITES]

Feeling the Full BruntThe harshness of space takes a toll on satellites even at the best of times. A superstorm would cause years’ worth of damage within a few hours.

[SLICING SPACETIME]

How Time Is Not Like Space Physicists, artists and graph makers of all kinds routinely depict time as another dimension of space, creating a unified spacetime—shown here as a three-dimensional block in which a ball bounces off a wall. Relativity theory holds that spacetime can be sliced up in various ways. But not all are equally sensible.

t

y

y

x

t

x

x

The usual way takes slices of space at successive moments of time, creating a movie of the ball’s motion. Each frame leads to the next, according to the familiar laws of physics.

An alternative considers slices not from past to future but from left to right. Each slice is part space, part time. To the left of the wall, the ball appears in two positions; on the right, it does not appear at all. If this slicing seems strange, it should: it makes the laws of physics very unwieldy.

●1 ●2●3●4

●1 ●2 ●3 ●4

●1 ●2 ●3 ●4

●1

●2●3●4

recently investigated timeless theories [see “A Simple Twist of Fate,” by George Musser, on page 14]. But to convey the basic problem that

[see “A Quantum Threat to Special Relativity,” by David Z. Albert and Rivka Galchen; S����-����� A�������, March 2009].

[A NEW VIEW OF TIME]

Who Needs Time, Anyway?

LIGHT:300,000 kilometers per second

HEART:75 beats per minute

EARTH:1 rotation per day

Thus, some physicists argue that time is a common currency, making the world easier to describe but having no independent existence. Measuring processes in terms of time could be like using money ( ) rather than barter transactions ( ) to buy things.

$2 $2,000

50 cups of coffee per pair of shoes

$100

VS.

VS. 1,000 cups of coffee per used car

. . . but these processes could be related directly to one another without making reference to time.

1 beat

108,000 beats per rotation

Time is a way to describe the pace of motion or change, such as the speed of a light wave, how fast a heart beats, or how frequently a planet spins . . .

1 cup of coffee

240,000 kilometers per beat

[HOW IT WORKS]

Tracking FingersThe most advanced multi-touch screens respond to the motion and pressure of numerous fingers. In the Perceptive Pixel design ( ), projectors send images through an acrylic screen onto the surface facing the viewer. When fingers or other objects (such as a stylus) touch the surface, infrared light shone inside the acrylic sheet by LEDs scatters off the fingers and back to sensors. Software interprets the data as finger move-ments. Tapping the screen brings up command menus when desired.

LED

LED

Projector

Reflection sensor

Internal reflections

Light scattered toward reflection sensor

Image from projector

Acrylic waveguide

Pressure-sensitive polymer

Computer

To create a signal, LEDs bounce light through the acrylic sheet. No light escapes. But if a finger is placed against the face ( ), light will scatter off it toward the sensors. Also, a pressure-sensitive coating flexes when pressed firmly or lightly, making the scattered fingertip signal appear slightly brighter or dimmer, which the computer interprets as more or less pressure.

mundane activity. The great strength of multi-touch is letting multiple people work together on a complex activity. It is hard to remember how liberating the mouse seemed when it freed peo-ple from keyboard arrow keys some 25 years ago. Soon the multi-touch interface could help untether us from the ubiquitous mouse. “It’s very rare that you come upon a really new user interface,” Han says. “We’re just at the begin-ning of this whole thing.”

[INSIDE LOOK]

Touch TableA projector inside Microsoft’s multi-touch table, called Surface, sends imagery up through the acrylic top. An LED shines near-infrared light up as well, which reflects off objects or fingers back to var-ious infrared cameras; a com-puter monitors the reflections to track finger motions.

Projector

Infrared cameras

LED light source

Computer

Sensory thalamus

Thalamus

Mediodorsal thalamus

Globus pallidusinternal segment

Subthalamic nucleus

Nucleusaccumbens

Pedunculopontine nucleus

Subgenualcingulate

Orbitofrontalcortex

Anteriorcingulate cortex

Ventralpallidum

Periventricular gray/periaqueductal gray

Anterior limbof the internal

capsule

Lateral hypothalamus Brain stem

Motor thalamus

HOW

WHATWHERE

ex-bbs ba-

um-tine ver,

Ani-the rive

mak-ckly mar-iven es—

ion, gic. gni-n be n of nan-

BRAIN AREAS that become activated in response to reward or risk include those shown above, among others.

Ventral tegmental area

Ventromedial prefrontal cortex Nucleus accumbens

Amygdala

some of those proteins might be worth consid-ering as drug targets. Analysis of the TB genome also hinted that, contrary to conventional wis-dom, the bacterium is perfectly capable of living in the absence of air—a suggestion now verified. Under such anaerobic conditions, Mtb’s metab-olism slows down, making it intrinsically less sensitive to existing antibiotics. Targeting the metabolic elements that remain active under these circumstances is one of the most promis-i i f h i i

the problem is that bacteria are autonomous life-forms, selected throughout evolution for their ability to adapt and respond to external threats. Like modern aircraft, they have all manner of redundancies, bypasses, fail-safes and emergency backup systems. As Jeff Gold-blum’s character in Jurassic Park puts it, life finds a way. Until we truly appreciate the com-plexities of how TB interacts with humans, new drugs against it will remain elusive. The good

i h ki h

tends to concentrate in the air sacs, or alveoli, of the lungs because it prefers environments rich in oxygen. In

most people, the immune system is able to keep bacterial replication in check, dispatching defensive cells known

as macrophages to the site of infection, where they form a shell around the bacteria. But in 10 percent of infected individuals, breaks down the shell, after which it can begin to multiply.

Tuberculosis, caused by the bacterium , occurs in both latent and active forms. People can become infected by breathing in even just a few bacteria released into the air when those with active TB cough, spit or talk. causes coughing, the most familiar symptom, because it accumulates abundantly in the lungs, but it can harm other organs as well ( ).

[INFECTION BASICS]

AN ILL WINDBrain

Lung

Kidney

Bone Scan highlights infection in lung.

Unfettered by the immune system, the bacteria destroy the tissue of the lungs; some may also make their way into the bloodstream and infect other parts of the body, including the brain, kidneys and bone. Eventually affected organs may sustain so much damage they cease to function, and the host dies.

Alveolus

Macrophage

Mtb

Tuberculosis occurs in virtually every country in the world, although it is most wide-spread in developing nations. The incidence of TB caused by strains of resistant to two or more of the first-line drugs for the disease—so-called multidrug-resistant TB (MDR-TB)—has been rising as a result of improper use of antibiotics. Worse still is exten-sively drug-resistant TB (XDR-TB)—a largely untreatable form identified in 2006; as of June 2008, 49 countries had confirmed cases. Sadly, that figure most likely underesti-mates XDR-TB’s prevalence.

[AFFECTED NATIONS]

WORLDWIDE RESISTANCE

Reported cases oftuberculosis per 100,000 citizensitttttiti

No estimate

0–24

25–4922

50–99

100–299

300 or more

TB

Percent of MDR-TBff f among new TB cases1994-2007

More than 6%

3%–6%33

Less than 3%

No data

Multidrug-resistant TB

Extensively drug-resistant TB

The process by which a pathogen of animals evolves into one exclusive to humans occurs in five stages. Agents can become stuck in any of these stages. Those in early stages may be very deadly (Ebola, for example), but they claim few lives overall because they cannot spread freely among humans. The better able a virus is to propagate in humans, the more likely it is to become a pandemic.

[STAGES TO WATCH]

From Animal Microbe to Human Pathogen

Stage 1: Pathogen is present in animals but has not been detected in humans under natural conditions.

Stage 2: Animal pathogen has been trans-mitted to humans but not between humans.

Stage 3: Animal pathogen that can be trans-mitted between humans causes an outbreak of disease but only for a short period before dying out.

Stage 4: Pathogen exists in animals and undergoes a regular cycle of animal-to-human transmission but also sustains long outbreaks arising from human-to-human transmission.

Stage 5: Pathogen has become exclusive to humans.

Reichenowi malariaDISEASE EXAMPLES: Rabies Ebola Dengue HIV

SOURCE:

Nature,

[PREVENTION PROPOSAL]

Building a Surveillance NetworkBy monitoring microorganisms in wild animals and the people who are frequently exposed to them, scientists may be able spot an emerging infectious disease before it becomes widespread. To that end, the author recently organized the Global Viral Forecasting Initia-tive (GVFI), a network of 100 scientists and public health officials in six countries ( and

) who are working to track potentially dangerous agents as they move from animals into human populations. The GVFI focuses on tropical regions ( ) in particu-lar, because they are home to a wide variety of animal species and because humans there commonly come into contact with them through hunting and other activities. Eventually the GVFI hopes to expand the network to include more countries with high levels of biodi-versity, some of which are shown here ( ).COUNTRY: Cameroon

VIRUSES PREVIOUSLY SPAWNED: HIVSENTINEL POPULATION UNDER STUDY FOR NEW PATHOGENS: People who hunt and butcher wild animals

COUNTRY: ChinaVIRUSES PREVIOUSLY SPAWNED: SARS, H5N1SENTINEL POPULATION: “Wet market” workers

COUNTRY: MalaysiaVIRUSES PREVIOUSLY SPAWNED: NipahSENTINEL POPULATION: Wildlife hunters

COUNTRY: Democratic Republic of the CongoVIRUSES PREVIOUSLY SPAWNED: Marburg, monkeypox, EbolaSENTINEL POPULATION: People who hunt and butcher wild animals

Primary study site (human and animal testing)Secondary study site (animal testing only)

Tentative site for future studyTropical region

[WHAT ASTRONOMERS LOOK FOR]

A circumstellar disk of dust and gas, like the one that gave rise to the planets of our solar system, absorbs starlight and emits infrared radiation. We observe a composite of direct starlight and disk emission.

Light from disk

Starlight

Star

Circumstellar disk

An example is the brown dwarf OTS 44, whose spectrum ( ) initially

falls off at infrared wavelengths but then flattens—indicating that the dwarf,

whose spectrum would be expected to peak at short wavelengths ( ), is surrounded by

cooler material whose spectrum peaks at longer wavelengths ( ).

Glowing in the DarkAstronomers generally detect planets indirectly, by virtue

of their effects on the velocity, position or brightness of their host stars. For most of the cases discussed in the article, astronomers focus on one type of indirect sign: the presence of a disk of dust orbiting the star. A so-called protoplanetary disk occurs around newly born stars and is thought to be the site of planet formation. A so-called debris disk occurs around mature stars and is thought to arise from collisions or evaporation of comets and asteroids, thus signaling the likely presence of planets now or in the past.

Observers identify both types of disk from how they absorb starlight and reradiate the absorbed energy at infra-red wavelengths ( ). NASA’s Spitzer Space Telescope, launched in 2003, has proved to be a veritable disk discovery machine. Its large field-of-view infrared cameras can cap-ture hundreds of stars in a single image and pinpoint those with evidence of disks for further study.

Spitzer builds on the successes of past infrared telescopes, such as the Infrared Astronomical Satellite (IRAS) mission in the 1980s and the European Space Agency’s Infrared Space Observatory (ISO) in the mid-1990s. Unlike IRAS, which was an all-sky survey, Spitzer points at specific celestial bodies for intensive study, and the five-year-plus lifetime of its liquid-helium coolant far exceeds that of any previous mission. The telescope has studied everything from extrasolar planets to galaxies in the early universe.

The coolant is now running out, and the telescope will soon start to warm from nearly absolute zero to 30 kelvins. Even so, it will be able to operate at the short-wavelength end of the infrared band through at least the middle of 2011. Taking up the slack will be the newly launched Herschel Space Observatory and the James Webb Space Telescope (JWST), planned for launch in 2013. —

Infrared Light Reveals Disks and Thus Planets or Their Building Blocks

Brown dwarfDisk

Brown dwarf plus disk

Brig

htne

ss (a

rbit

rary

uni

ts)

Wavelength (microns)1 3 10 30

Even when the system is too far away for telescopes to resolve spatially, the spectrum reveals the blending of light.

remain in the body as “memory” cells—some-times for decades—ready to squelch any at-tempted reinfection by the same organism. Vac-cines replicate this process by introducing a whole pathogen or fragments of it that will be recognized as a foreign invader. Not all vaccines succeed in generating a full immune response, but some pathogens can be stopped by antibod-ies alone, so killer T cells are not needed for protection.

The nature of the pathogen and how it causes ill i d i ’ id

[BASICS]

Vaccines Mimic Infection to Avert ItVaccines deliver a killed or weakened pathogen, or pieces of it, to trigger an immune response that generates “memory” cells primed to recognize the same microorganism quickly in the future. These cells can later block true infections or at least minimize illness.

VACCINE ADMINISTRATIONA small dose of live but weakened virus is one common form of vaccine. Injected into the skin, the virus will infect some cells and reproduce slowly. “Innate” immune system cells, such as macrophages and dendritic cells, engulf and digest foreign material and infected body cells. Dendritic cells also emit signaling chemicals called cytokines to sound an alarm.

DENDRITIC CELL MIGRATION AND INTERACTIONSLoaded with foreign material (antigen), dendritic cells mature and migrate to lymph nodes to interact with T cells and B cells, components of the “adaptive” immune system. Displaying antigen and emitting cytokines, the dendritic cells induce T cells to mature into helper and killer types; the helper T cells also signal to incite the killer T cells to attack infected cells and induce B cells to produce antibodies tailored to the pathogen.

IMMUNE MEMORYSome of the B and T cells become long-lived memory cells, standing guard against a future infection.

Injection site

Virus in vaccine

Infected cells

Infected cell

Macrophage

Dendritic cellVirus fragments

Cytokines

AntigenLymph node

Cytokines

Maturation and migration

to lymph nodes

T cell precursors

B cell

Helper T cells

Killer T cells

Antibodies

Memory T cells and B cells Attempted infectionV

innatling fropha

desc

tcanpe

adthe

k

l

COMMON VACCINE TYPES

ATTENUATED: ■ Live but weakened whole virus or bacterium. Minimal reproduc-tion extends immune cells’ exposure to antigen without causing disease.

INACTIVATED: ■

Whole but “killed” and unable to reproduce or to cause disease.

SUBUNIT: ■ Fragments of the pathogen, such as genetic material or external pro-teins, provide antigen for immune cells to recognize.

lar keys, a group known as the Toll-like recep-tors (TLRs) seemed most important for driving the dendritic cells’ behavior [see “Immunity’s Early-Warning System,” by Luke A. J. O’Neill; S��������� A�������, January 2005].

To date, 10 functional Toll-like receptors have been identified, and each recognizes a dif-ferent basic motif of viruses or bacteria. TLR-4

PATHOGEN RECOGNITIONDendritic cells contain Toll-like receptors (TLR) that each recognize molecules typical of many pathogens, such as bacterial proteins or distinctive viral gene motifs ( ). Adjuvants that trigger one or a combination of TLRs can simulate different natural threats.

DENDRITIC CELL DIRECTIONSDendritic cells’ signaling determines how T and B cells will mature and proliferate. For example, the cytokine interleukin-12 favors development of killer T cells and a helper T subtype needed to defend against intracellular pathogens, whereas IL-6 favors a helper T type that induces B cells to produce antibodies. IL-6, together with IL-23, induces still another helper T subtype that promotes inflamma-tion. Interleukins themselves are also under study as adjuvants.

Adjuvants Add Emphasis Adjuvants enhance immune responses to vaccine antigens by several mechanisms, but their most potent effects are likely to be through activation of microbe-recognition receptors on dendritic cells. Depending on the type of threat they sense, dendritic cells will direct other immune cells to respond in different ways. Vaccine designers can use this knowledge to choose adjuvants that will not only boost immune response but also emphasize the desired responses.

TLR NATURAL TRIGGER●1 ●2 ●6 Bacterial lipoproteins●3 Double-stranded RNA●4 Lipopolysaccharide (LPS), heat-shock proteins, respiratory syncytial virus●5 Bacterial flagellin protein●7 ●8 Single-stranded RNA●9 Bacterial CpG DNA ●10 Unknown●11 Bacterial profilin protein

Killer T cells

Cytokines

Helper T cells

Antibody-inducing helper T cells

Inflammation-inducing helper T cells

IL-12

IL-12

IL-23

IL-6

Toll-like receptor

IL-6

[VACCINE BOOSTERS]

Cosmic ExpansionThe evolution of the universe is driven by the expansion of space. As space stretches like the rubber in an inflating balloon, galaxies move apart and light waves elongate (hence redden).

[PRIMER]

Before the Big BangCosmologists do not yet know how the universe began, but this question has now come within the realm of science, with a number of speculative scenarios being discussed.

[COSMIC TIMELINE]

gg

Quantum emergence B Ordinary space and time develop out of a primeval state described by a quantum theory of gravity

10–43 secondPlanck era: earli-est meaningful time; space and time take shape

Cyclic universe D The big bang is the latest stage in an eternal cycle of expansion, collapse and renewed expansion

Multiverse C Our universe and others bud off from eternal space

No previous era A Matter, energy, space and time begin abruptly with the bang

(from previous cycle)

Formation of Atoms Dark Ages Modern Era

10–35 secondCosmic inflation creates a large, smooth patch of space filled with lumpy quark soup

10–30 sOne potential type of dark matter (axions) is synthesized

10–11 sMatter gains the upper hand over antimatter

10–10 sA second poten-tial type of dark matter (neutralinos) is synthesized

10–5 sProtons and neutrons form from quarks

0.01–300 sHelium, lithium, and heavy hydro-gen nuclei form from protons and neutrons

380,000 yearsAtoms form from nuclei and electrons, releasing the cosmic microwave back-ground radiation

300 million yrFirst stars and galaxies form

1 billion yrLimit of current observations (highest-redshift objects)

3 billion yrClusters of galax-ies form; star formation peaks

9 billion yrSolar system forms

10 billion yrDark energy takes hold and expansion begins to accelerate

13.7 billion yrToday

s Erraa

380,000–300 million yr Gravity continues to amplify density differences in the gas that fills space

Earliest Moments of the Big Bang The cosmic timeline continues with fairly well-established events leading to the present day.

40 SC IENT IF IC AMERIC AN

Nucleosynthesis theory accurthe abundances of elements and sured in the most primeval sampverse—namely, the oldest stars andgas clouds. The abundance of deuis very sensitive to the densitythe universe, plays a special rolevalue implies that ordinary matt

4.5 ± 0.1 percenenergy den

maindeter a

gy.agwp

hafrom

of the

BULK OF UNIVERSE consists of dark energy and dark matter,

neither of which has been identified. Ordinary matter

of the kind that makes up stars, planets and interstellar

gas accounts for only a small fraction.

4.0% Gas0.5% Stars and planets

24% Dark matter71.5% Dark energy

The FuturePredictable events such as galactic collisions dominate the near future. But the ultimate destiny of our universe hinges on whether dark energy will continue to cause cosmic expansion to accelerate. Broadly, four fates are possible.

20 billion yearsMilky Way collides with Andromeda galaxy

Acceleration B continues

Acceleration C intensifies

Acceleration changes D to rapid deceleration and collapse

Acceleration ends A and universe expands eternally

100 trillion yearsLast stars burn out

30 billion yearsCosmic redout: cosmic acceleration pulls all other galaxies out of our view; all evidence of the big bang is lost

30 billion years Big crunch, perhaps followed by a new big bang in an eternal cycle

50 billion yearsBig rip: dark energy tears apart all structures, from superclusters to atoms

(to next cycle)cycclelell

42 SC IENT IF IC AMERIC AN