Discovery Showcase

Nanotechnology

2010-11-16T04:33:00.000-08:00

Technology / Nanotechnology

How it might kill us, how it might save us, and how it was used in the smallest ever marketing stunt

by Rebecca Coffey

iStockphoto

1 Get small. A nanometer is about the width of a strand of DNA; if you design, build, or use functional systems smaller than 100 of these, you’re a nanotechnologist.

2 By that definition, we have been doing nanotech for centuries. For instance, thecolors in medieval stained glass windows result from nanocrystalscreated in the heating and cooling of the glass.

3 Size matters. At the nano scale, materials take on unusual properties. Their color, transparency, and melting point often differ significantly from those of larger clumps of the same stuff.

4 Nanoscale bits of metal oxide, carbon fiber, or metal blends can detoxify hazardous waste: Their extreme solubility and chemical reactivity help them zero in on the nasty stuff.

5 This approach is already being used at sites in a dozen states, mostly to clean groundwater fouled by solvents, metals, and petroleum.

6 Brighter colors! Richer flavors! Less spoilage! Those are some of the reasons why companies are dumping nanoparticles into hundreds of products, including cosmetics, sunscreens, and food.

7 Analysts say the global market for manufactured goods using nanomaterials could hit $1.6 trillion by 2013.

8 Uh-oh. Studies show that nanoparticles can work their way into the bloodstream, penetrate cells, and get past the blood-brain barrier. Research has linked such particles to lung damage; the brain may be affected too.

9 But if those particles don’t kill us, they just might save us. Scientists at U.C. San Diego have designed afluorescent nanoparticle that glows inside the body, making it easier to image tumors and organ damage.

10 Yale researchers have created plastic nanospheres that encapsulate proteins called cytokines, which stimulate the immune system’s killer T-cells. An injection of those spheres could help fight disease and infection.

11 And in a University of Southern California lab, nanotubes have been used to create synthetic neurons (pdf).

12 The USC team is trying to assemble these neurons into functional networks, which would bring us closer to assistive brain implants.

13 In 1989, using an atomic force microscope, IBM engineer Don Eigler became the first person to move and control a single atom.

14 Eigler and his team later used 35 xenon atoms to spell out “IBM,” thus performing the world’s smallest PR stunt.

15 Atoms? Big whoop. Researchers at Princeton and U.C. Santa Barbara can control the spin of a single electron, trapping it in a “corral” created by applying voltage to minuscule electrodes.

16 But they’re not playing cowboy. The breakthrough could lead to powerful quantum computers that store and manipulate data in the spin of individual electrons.

17 Not to be outdone, Stan ford scientists used scanning tunneling microscopy and holograms to write informationwithin the interference patterns formed by electron waves on a copper sheet. The letters are less than a third the size of Eigler’s “IBM.”

18 Government researchers have created arrays of chromium nanodots that can store magnetic data with unprecedented uniformity. One goal: drawing more complex integrated circuits on silicon chips.

19 For the rodent who has everything. Georgia Tech scientists made piezoelectric generators out of nanowires and attached them to tiny hamster jackets. When the critters ran, the generators created electricity.

20 Zhong Lin Wang, co-inventor of the jacket, envisions a shirt that charges your cell phone as you stroll, or an implanted device for measuring blood pressure that’s powered by your own heartbeat.

Physics & Math / Cosmology

2010-09-02T13:03:00.000-07:00

The Real Rules for Time Travelers

Time travel may in fact be possible, but it wouldn't work like in Back to the Future. (For one thing, you don't have worry about your parents failing to create you—you already exist.)

This piece is adapted from Cosmic Variance blogger Sean Carroll’s latest book, From Eternity to Here: The Quest for the Ultimate Theory of Time, which was published last month by Dutton.

The video still of the exploding clock to the right was captured by Biwa Studios in New York City. If you like the photo, the high-def, slow-motion video of the clock exploding is even better.

People all have their own ideas of what a time machine would look like. If you are a fan of the 1960 movie version of H. G. Wells’s classic novel, it would be a steampunk sled with a red velvet chair, flashing lights, and a giant spinning wheel souped-up stainless steel sports car. Details of operation vary from model to model, but they all have one thing in common: When someone actually travels through time, the machine ostentatiously dematerializes, only to reappear many years in the past or future. And most people could tell you that such a time machine would never work, even if it looked like a DeLorean. on the back. For those whose notions of time travel were formed in the 1980s, it would be a

They would be half right: That is not how time travel might work, but time travel in some other form is not necessarily off the table. Since time is kind of like space (the four dimensions go hand in hand), a working time machine would zoom off like a rocket rather than disappearing in a puff of smoke. Einstein described our universe in four dimensions: the three dimensions of space and one of time. So traveling back in time is nothing more or less than the fourth-dimensional version of walking in a circle. All you would have to do is use an extremely strong gravitational field, like that of a black hole, to bend space-time. From this point of view, time travel seems quite difficult but not obviously impossible.

These days, most people feel comfortable with the notion of curved space-time. What they trip up on is actually a more difficult conceptual problem, the time travel paradox. This is the worry that someone could go back in time and change the course of history. What would happen if you traveled into the past, to a time before you were born, and murdered your parents? Put more broadly, how do we avoid changing the past as we think we have already experienced it? At the moment, scientists don’t know enough about the laws of physics to say whether these laws would permit the time equivalent of walking in a circle—or, in the parlance of time travelers, a “closed timelike curve.” If they don’t permit it, there is obviously no need to worry about paradoxes. If physics is not an obstacle, however, the problem could still be constrained by logic. Do closed timelike curves necessarily lead to paradoxes?

If they do, then they cannot exist, simple as that. Logical contradictions cannot occur. More specifically, there is only one correct answer to the question “What happened at the vicinity of this particular event in space-time?” Something happens: You walk through a door, you are all by yourself, you meet someone else, you somehow never showed up, whatever it may be. And that something is whatever it is, and was whatever it was, and will be whatever it will be, once and forever. If, at a certain event, your grandfather and grandmother were getting it on, that’s what happened at that event. There is nothing you can do to change it, because it happened. You can no more change events in your past in a space-time with closed timelike curves than you can change events that already happened in ordinary space-time, with no closed timelike curves.

As we will see, the time travel paradox—the possibility of changing our past—seems intractable only because it conflicts with our notion of ourselves as beings with free will. Consistent stories are possible, even in space-times with closed timelike curves.

To illustrate this point, imagine that you stumble upon a time machine in the form of a gate. When you pass through it in one direction, it takes you exactly one day into the past; if you pass through in the other direction, it takes you exactly one day into the future. You walk up to the gate, where you see an older version of yourself waiting for you. The two of you exchange pleasantries. Then you leave your other self behind as you walk through the gate into yesterday. But instead of obstinately wandering off, you wait around a day to meet up with the younger version of yourself (you have now aged into the older version you saw the day before) with whom you exchange pleasantries before going on your way. Everyone’s version of every event would be completely consistent.

We can have much more dramatic stories that are nevertheless consistent. Imagine that we have been appointed Guardian of the Gate, and our job is to keep vigilant watch over who passes through. One day, as we are standing off to the side, we see a person walk out of the rear side of the gate, emerging from one day in the future. That’s no surprise; it just means that you will see that person enter the front side of the gate tomorrow. But as you keep watch, you notice that he simply loiters around for one day, and when precisely 24 hours have passed, the traveler walks calmly through the front of the gate. Nobody ever approached from elsewhere. That 24-hour period constitutes the entire life span of this time traveler. He experiences the same thing over and over again, although he doesn’t realize it himself, since he does not accumulate new memories along the way. Every trip through the gate is precisely the same to him. That may strike you as weird or unlikely, but there is nothing paradoxical or logically inconsistent about it.

The real question is this: What happens if we try to cause trouble? That is, what if we choose not to go along with the plan? Let’s say you meet a day-older version of yourself just before you cross through the front of the gate and jump backward in time, as if you will hang around for a day to greet yourself in the past. But once you actually do jump backward in time, you still seem to have a choice about what to do next. You can obediently fulfill your apparent destiny, or you can cause trouble by wandering off. What is to stop you from deciding to wander? That seems like it would create a paradox. Your younger self bumped into your older self, but your older self decides not to cooperate, apparently violating the consistency of the story.

We know what the answer is: That cannot happen. If you met up with an older version of yourself, we know with absolute certainty that once you age into that older self, you will be there to meet your younger self. That is because, from your personal point of view, that meet-up happened, and there is no way to make it un-happen, any more than we can change the past without any time travel complications. There may be more than one consistent set of things that could happen at the various events in space-time, but one and only one set of things actually does occur. Consistent stories happen; inconsistent ones do not. The vexing part is understanding what forces us to play along.

The issue that troubles us, when you get down to it, is free will. We have a strong feeling that we cannot be predestined to do something we choose not to do. That becomes a difficult feeling to sustain if we have already seen ourselves doing it.

Of course, there are some kinds of predestination we are willing to accept. If we get thrown out of a window on the top floor of a skyscraper, we expect to hurtle to the ground, no matter how much we would rather fly away and land safely elsewhere. The much more detailed kind of predestination implied by closed timelike curves, where it seems that we simply cannot make certain choices (like walking away after meeting a future version of ourselves), is bothersome.

The nub of the problem is that you cannot have a consistent “arrow of time” in the presence of closed timelike curves. The arrow of time is simply the distinction between the past and the future. We can turn an egg into an omelet, but not an omelet into an egg; we remember yesterday, but not tomorrow; we are born, grow older, and die, never the reverse. Scientists explain all of these manifestations of the arrow of time in terms of entropy—loosely, the “disorderliness” of a system. A neatly stacked collection of papers has a low entropy, while the same collection scattered across a desktop has a high entropy. The entropy of any system left to its own devices will either increase with time or stay constant; that is the celebrated second law of thermodynamics. The arrow of time comes down to the fact that entropy increases toward the future and was lower in the past.

A statement like “We remember the past and not the future” makes perfect sense to us under ordinary circumstances. But in the presence of closed timelike curves, some events are in our past and also in our future. So do we remember such events or not? In general, events along a closed timelike curve cannot be compatible with an uninterrupted increase of entropy along the curve. That’s a puzzle: On a closed curve, the entropy has to finish exactly where it started, but the arrow of time says that entropy tends to increase and never decrease. Something has to give.

To emphasize this point, think about the hypothetical traveler who emerges from the gate, only to enter it from the other side one day later, so that his entire life story is a one-day loop repeated ad infinitum. Take a moment to contemplate the exquisite level of precision required to pull this off, if we think about the loop as “starting” at one point. The traveler would have to ensure that, one day later, every single atom in his body was in precisely the right place to join up smoothly with his past self. He would have to make sure, for example, that his clothes did not accumulate a single extra speck of dust that was not there one day earlier.

This seems incompatible with our experience of how entropy increases. If we merely shook hands with our former selves, rather than joining up with them, the required precision doesn’t seem quite so dramatic. In either case, though, the insistence that we be in the right place at the right time puts a very stringent constraint on our possible future actions.

Our concept of free will is intimately related to the idea that the past may be set in stone, but the future is up for grabs. Even if we believe that the laws of physics in principle determine the evolution of some particular state of the universe with perfect fidelity, we don’t know what that state is, and in the real world the increase of entropy is consistent with any number of possible futures. A closed timelike curve seems to imply predestination: We know what is going to happen to us in the future because we witnessed it in our past.

Closed timelike curves, in other words, make the future resemble the past. It is set in stone, not up for grabs at all. The reason we think the past is fixed once and for all is that there is a boundary condition at the beginning of time. The entropy of the universe started very small (at the time of the Big Bang) and has been growing ever since. Ordinarily we do not imagine that there is any analogous boundary condition in the future—entropy continues to grow, but we cannot use that information to draw any conclusions. If we use a closed timelike curve to observe something about our future actions, those actions become predestined. That’s extra information about the history of the universe, over and above what we normally glean from the laws of physics, and it makes us uncomfortable.

If closed timelike curves exist, ensuring that all events are consistent is just as strange and unnatural to us as a movie played backward, or any other example of evolution that decreases entropy. It’s not impossible; it’s just highly unlikely. So either closed timelike curves cannot exist, or big, macroscopic things cannot travel on truly closed paths through space-time—unless everything we think we know about entropy and the arrow of time is wrong.

Life on a closed timelike curve seems pretty drab. Once you start moving along such a curve, you are required to come back to precisely the point at which you started. An observer standing outside, however, has what is seemingly the opposite problem: What happens along such a curve cannot be uniquely predicted from the prior state of the universe. We have the strong constraint that evolution along a closed timelike curve must be consistent, but there will always be a large number of consistent evolutions that are possible, and the laws of physics seem powerless to predict which one will actually come to pass.

In the usual way of thinking, the laws of physics function like a computer. You give as input the present state, and the laws return as output what the state will be one instant later (or earlier, if we wish). By repeating this process many times, we can build up the entire history of the universe, from start to finish. In that sense, complete knowledge of the present implies complete knowledge of all of history.

Closed timelike curves would make such a program impossible, as a simple thought experiment reveals. Hark back to the stranger who appeared out of the gate into yesterday, then jumped back in the other side a day later to form a closed loop. There would be no way to predict the existence of such a stranger from the state of the universe at an earlier time. Let’s say we start in a universe that, at some particular moment, has no closed timelike curves. The laws of physics purportedly allow us to predict what happens in the future of that moment. This ability vanishes as soon as someone builds a time machine and creates a closed timelike curve. Mysterious strangers and other random objects can then appear out of thin air and disappear just as quickly.

We can insist all we like that what happens in the presence of closed timelike curves be consistent. But that requirement is not enough to make the events predictable, with the future determined by the laws of physics and the state of the universe at one moment in time. Indeed, closed timelike curves can make it

impossible to de-fine “the universe at one moment in time.” Ordinarily we can imagine “slicing” our four-dimensional universe into three-dimensional “moments of time.” In the presence of closed timelike curves, though, we generally will not be able to slice space-time that way. Locally—in the near vicinity of any particular point in space-time—we can always divide events into the “past” and the “future.” But we might not be able to do this throughout the universe. The warping associated with the closed timelike curve could cause our slice to twist back on itself, making it impossible to divide all of space-time into distinct moments.

We would therefore have to abandon the concept of determinism, the idea that the state of the universe at any one time determines the state at all other times. We would also have to abandon free will—because witnessing part of our future history implies some amount of predestination.

Do we value determinism so highly that we should reject the possibility of closed timelike curves entirely? Not necessarily. We could imagine a different way in which the laws of physics could be formulated—not as a computer that calculates the next moment from the present moment but as a set of conditions that are imposed on the history of the universe as a whole. It is not clear what such conditions might be, but we have no way of excluding the idea on the basis of pure thought.

All this may sound like vacillation, but it provides an important lesson. Some of our understanding of time is based on logic and the known laws of physics, but some of it is based purely on convenience and reasonable-sounding assumptions. We think that the ability to uniquely determine the future from knowledge of our present state is important, but the real world might end up having other ideas. If physicists discover that closed timelike curves really can exist, we will have to dramatically rethink the way we understand time. In that case, the universe could not be nicely divided into a series of separate “moments” of time.

The ultimate answer to the puzzles raised by closed timelike curves is probably that they simply cannot exist. If that is true, though, it is because the laws of physics do not let you warp space-time enough to create them—not because they let you kill your grandfather before you are born.

Physics & Math

2010-09-02T12:56:00.000-07:00

What Is This? Whipped Petroleum?

Hint: It makes your hard drive work and also makes pretty colors in the sky.

Image: R. Mark Bessette

This image depicts the magnetic field lines between two bar magnets. Earth has a field of its own that protects us from charged particles from the sun. It channels some of these particles toward the poles, where they can collide with air molecules and release energy in the form of light, producing brightly colored aurora .

Physics & Math / Subatomic Particles

2010-09-02T12:53:00.000-07:00

Ice Fishing For Neutrinos From the Middle of the Galaxy

An intrepid reporter braves Siberia’s frozen Lake Baikal in search of the fundamental particles that could answer some of the deepest questions in physics.

Image: NASA/MODIS

About 25 million years ago, Earth parted in the southeast corner of Siberia. Since then, countless rivers have converged on the gaping continental rift, creating the vast body of water known as Lake Baikal. Surrounded by mountains, this 400-mile-long inland sea has remained isolated from other lakes and oceans, leading to the evolution of unusual flora and fauna, more than three-quarters of which are found nowhere else on the planet. Russians regard it as their own Galápagos. The lake contains 20 percent of the world’s unfrozen freshwater—or just a little less during the severe Siberian winter when, despite its enormous size and depth, Baikal freezes over.

On one such winter’s day, I found myself on the lake near the town of Listvyanka, which is nestled in a crook of the shoreline. I was in an old van that was trying to head west, not along a coastal road—for there was none—but over the ice. The path, however, was blocked by a ridge. It looked like a tectonic fault: Two sections of the lake’s solid surface had slammed together and splintered, throwing up jagged chunks of ice. The driver, a Russian with a weather-beaten face, peered from underneath his peaked cap, looking for a break in the ridge.

When he spied a few feet of smooth ice, he got out and prodded it with a metal rod, only to shake his head as it crumbled: not thick enough to support the van. We kept driving south, farther and farther from shore, in what I was convinced was the wrong direction. The van shuddered and lurched, its tires crunching on patches of fresh snow and occasionally slithering on ice. The ridge continued as far as the eye could see. Suddenly we stopped. In front of us was a dangerous-looking expanse littered with enormous pieces of ice that rose from the lake’s frozen surface like giant shards of broken glass.

The driver seemed to be contemplating going around them to look for thick ice that would let us reach our destination, an underwater observatory operating in one of the deepest parts of the lake. But if he did that, we’d get even farther from the shore, and it would take just one punctured tire to strand us. The sun was little more than an hour from setting, and the temperature was falling. I couldn’t ask the driver if he had a radio or a phone to call for help, since he did not speak a word of English and the only Russian phrase I knew was do svidaniya. The last thing I wanted to say to him at this point was “Good-bye.”

Thankfully, he decided to turn around. We drove along until we came upon vehicle tracks that went over some ice covering the ridge. The driver swung the van westward and cleared the ridge, and soon we were racing across the lake at a speed that turned every frozen lump into a speed bump. The van’s front rose and fell sickeningly, rattling the tools strewn around on the front seat. I worried that the ice would give way and we would plunge into the frigid waters below. But it remained solid, and the van, despite its appearance, was in fine mechanical fettle, its shock absorbers holding firm. In the distance I spied a dark spot on the otherwise white expanse. As we approached, the spot grew to its full size, revealing itself as a three-foot-high Christmas tree. We still had 20 miles to cover, and the sun would soon disappear below the icy horizon. But now that we had found the Christmas tree, I knew we were fine.

I had first seen the tree two days earlier, with Nikolai (Kolja) Budnev, a physicist from Irkutsk State University, and Bertram Heinze, a German geologist. We were headed to the site of the Lake Baikal neutrino observatory, which lay deep beneath the ice. We had just driven onto the lake from the shore near Listvyanka when Heinze asked, “When does the ice start breaking?”

“Sometime in early March,” Budnev answered. My heart skipped a beat. It was already late March, and we were on the ice in an old, olive-green military jeep. “Sorry, sometime in early April,” Budnev corrected himself. Phew.

For more than two decades now, Russian and German physicists have camped on the frozen surface of Lake Baikal from February to April, installing and maintaining instruments to search for the elusive subatomic particles called neutrinos. Artificial eyes deep below the surface of the lake look for dim flashes of blue light caused by a rare collision between a neutrino and a molecule of water. I was told that human eyes would be able to see these flashes too—if our eyes were the size of watermelons. Indeed, each artificial eye is more than a foot in diameter, and the Baikal neutrino telescope, the first instrument of its kind in the world, has 228 eyes patiently watching for these messengers from outer space.

The telescope, which is located a few miles offshore, operates underwater all year round. Cables run from it to a shore station where data are collected and analyzed. It is a project on a shoestring budget. Without the luxury of expensive ships and remote-controlled submersibles, scientists wait for the winter ice to provide a stable platform for their cranes and winches. Each year they set up an ice camp, haul the telescope up from a depth of 0.7 mile, carry out routine maintenance, and lower it back into the water. And each year they race against time to complete their work before the sprigs of spring begin to brush away the Siberian winter and the lake’s frozen surface starts to crack.

What is it about the neutrino that makes scientists brave such conditions? Neutrinos—some of them dating back to right after the Big Bang—go through matter, traveling unscathed from the time they are created and carrying information in a way no other particle can. The universe is opaque to ultraenergetic photons, or gamma rays, which are absorbed by the matter and radiation that lie between their source and Earth. But neutrinos, produced by the same astrophysical processes that generate high-energy photons, barely interact with anything along the way. For instance, neutrinos stream out from the center of the sun as soon as they are produced, whereas a photon needs thousands of years to work its way out from the core to the sun’s brilliant surface.

Neutrinos therefore represent a unique window into an otherwise invisible universe, even offering clues about the missing mass called dark matter, whose presence can be inferred only by its gravitational influence on stars and galaxies. Theory suggests that over time the gravity wells created by Earth, the sun, and the Milky Way would have sucked in an enormous number of dark-matter particles. Wherever they gather in great concentrations, these particles should collide with one another, spewing out (among other things) neutrinos. It is as if a giant particle accelerator at our galaxy’s center were smashing dark-matter particles together, generating neutrinos and beaming them outward, some toward us.

That neutrinos play such a key role in advancing physics would have surprised scientists of a few generations ago. For them the neutrino was a figment of imagination, a theoretical necessity, but one that seemed impossible to detect because of its ethereal nature—a ghost of a particle. The story of the neutrino begins in the late 1920s. Physicists had been puzzling over something called radioactive beta decay, in which one kind of atom changes into another. For instance, carbon-14 has eight neutrons and six protons. During beta decay, one of these neutrons decays into a proton and emits an electron. The new nucleus, now with seven protons and seven neutrons, is transformed into nitrogen-14. But during this process, some energy seemed to go missing. It was the Austrian-born physicist and Nobel laureate Wolfgang Pauli who theorized that beta decay must emit an as yet undiscovered neutral particle. A few years later, the physicist Enrico Fermi jokingly named the particle a neutrino, Italian for “little neutral one,” and the name stuck.

For decades the neutrino remained a theoretical construct, a useful particle that helped physicists save their theories from embarrassment. Nobody had seen one. Nobody even knew how to find one—until Frederick Reines, a researcher working at Los Alamos during the 1950s, realized that a nuclear bomb would be a significant source of neutrinos. Reines and his colleague Clyde L. Cowan Jr. thought a nuclear power plant would also be a source.

They calculated that a detector near a nuclear reactor would encounter nearly 10¹³ neutrinos per square centimeter per second. There was just one small problem: Since neutrinos are electrically neutral, they could be detected only if they directly hit the nucleus of an atom. Reines and Cowan would have to look for the signature of such a collision. And they found it.

By the 1960s, physicists following up on Reines’s work had started building neutrino detectors inside mines, using the ground as a natural shield from cosmic rays, which can swamp the signal from neutrinos. (Neutrinos can pass through the thick walls of the mines, but cosmic rays cannot.) In 1968 Raymond Davis and his colleagues from Brookhaven National Laboratory completed an experiment inside the Homestake Gold Mine in Lead, South Dakota. They used a tank containing 100,000 gallons of tetrachloroethylene, a common dry-cleaning agent. When a neutrino smashed into an atom of chlorine, the atom was transformed into one of radioactive argon. By counting the number of argon atoms that were produced, the physicists could calculate the flux of neutrinos coming from the sun. Then in the early 1980s, researchers around the world built detectors using thousands of tons of water in underground tanks lined with photomultiplier tubes (PMTs). The PMTs look for light emitted when a neutrino smashes into water. Normally the neutrino will pass right through water without any interaction. But on the rare occasions when one does hit a nucleus of hydrogen or oxygen, the collision can spit out another subatomic particle, a muon. The charged muon interacts with the water electromagnetically, and because it is moving faster than the speed of light in water, it leaves in its wake a cone of blue light. This is called a Cherenkov cone, after the Russian physicist who first described the phenomenon. It is analogous to the sonic boom caused by an aircraft traveling faster than the speed of sound.

It was another Russian researcher, Moisey Alexandrovich Markov, a “poet” of astroparticle physics, who suggested using natural bodies of water as neutrino detectors. Instead of building tanks of water inside mines, why not use lakes or even oceans? Just submerge long strings of photomultiplier tubes into the water and watch for the Cherenkov light left behind by neutrino-generated muons. The idea was enticing, but there were huge practical difficulties. For one thing, without rock above to protect it, a detector would be exposed to cosmic rays that could drown out signals from neutrinos. More to the point, sunlight (not a problem inside mines) would blot out the Cherenkov emission.

The solution was to go deep, where the sun’s rays could not reach. The physicists realized that they could use the Earth itself as a shield. While many muons can make it through a mile of water, a similar stretch of rock will stop them cold. So a neutrino detector can sit deep underwater, near the lake bed, looking downward for muons created by neutrinos that come from below. None of the muons created by cosmic rays in the atmosphere on the other side of the Earth can penetrate the planet. Neutrinos, however, zip right through, and occasionally one will hit a nucleus in the water or in the lake bed itself. Such a collision generates a muon, which then shoots up toward the surface. Catch an upward-moving muon and you have essentially detected a neutrino that came from the other side of the Earth. All that was needed was a suitable body of water. By the mid-1980s, the Russians realized that they had a massive tank of pure water in their own backyard: Lake Baikal.

On my first morning in Siberia, we drove across the lake toward the telescope. The frozen white lake spread for miles around us in every direction except to the northwest, where we were relatively close to shore. When we stopped to rest, men milled around the vehicles. The subzero temperature seemed to affect everyone differently. Some stood bareheaded; others had woolen caps rolled down to the tips of their ears. And then there was Ralf Wischnewski, in his enormous Russian fur cap that looked like a fluffed-up rabbit. A German neutrino physicist who had been working with the Russians at Lake Baikal for 20 years, Wischnewski was the reason I was here. I had met this ruddy-faced man six months earlier in London, outside the Tate Modern museum on the south bank of the Thames. We walked over to a Greek pub and discussed the Baikal expedition over chilled lager. It was he who had alerted me to the tradition of bringing spirits to share with the Russians during the winter evenings.

And here we were, except that it was still morning. The Russians had planned a welcome drink for Heinze. Kolja Budnev bounded out of our jeep with a bottle of vodka. Someone sliced a sausage into circular pieces. Bright yellow, blue, and red plastic cups were set up on the jeep’s expansive hood, and soon everyone had a vodka-filled cup in hand. Budnev dipped a finger into his and flicked a few drops onto the ice—an offering to the great spirit of Lake Baikal.

Soon we got back into our vehicles and headed toward the neutrino telescope, a contraption made of 11 strings of photomultiplier tubes, each with a large buoy at the top and a counterweight at the bottom. Smaller buoys attached to the strings float about 30 feet below the surface. All year round, a total of 228 PMTs watch for the Cherenkov cones. Each winter the team has to locate the telescope, the upper part of which drifts slightly over the course of the year. The team has two months to carry out any routine maintenance, put the strings back in the water, and get out before the ice cracks.

The term “experimental physics” took on new meaning in this biting cold, which at times dropped to –4 degrees Fahrenheit. Most of the physicists lived in 10-by-20-foot cabins, two to a cabin. Others slept in bunk beds at the shore station, amid workbenches cluttered with computers, electronics, wires, and cables. They worked long hours, from early in the morning to sometimes well past midnight. There was no running water, which meant no showers for two months. Toilets were wooden cabins with pits in the ground. The extreme cold helped control the stench, but it still wafted up when warm urine hit the pit. There was one luxury: the banya, a traditional Russian sauna. Naked men sat in an outbuilding, chucked water on hot stones to raise steam, and beat one another with leafy twigs and branches of birch.

A wicked wind kicked up one evening. It was time for everyone to leave the open ice and head back to the shore station. Once there, I gratefully sat down for a cup of tea, and a can of sweet, syrupy condensed milk materialized. One scientist looked at the can wistfully. Condensed milk had been his dream as a child growing up in the Siberian city of Tomsk. “They had this in Moscow,” he said, “but not in Tomsk.”

"Each year they set up an ice camp, racing against time to finish their work before the lake’s frozen surface starts to crack."

Later that evening, I had to head back out and traverse part of the icy lake to reach the canteen for dinner. It wasn’t going to be easy. I had turned up on a frozen lake in the depths of a Siberian winter in “European summer shoes,” as Wischnewski put it, disbelief in his voice. On the lake I found walking nearly impossible, my smooth-soled shoes slipping the entire way. After a few days, I learned to find fresh snow for my shoes to grip, but that night, fear nearly paralyzed me. Fortunately, a jeep pulled up beside me, and Wischnewski, having noticed my plight, asked the driver—Igor Belolaptikov, a tall, mustached physicist from the Joint Institute of Nuclear Research in Dubna, near Moscow—to take me to the canteen. I sat with Belolaptikov at dinner and happily accepted a ride back to his small cabin for a chat about neutrinos.

“My business is the reconstruction of muons and neutrinos,” Belolaptikov said, laughing with a childlike joy as he made this disclosure. That reconstruction is tricky business. Hundreds of photomultiplier tubes watch for the flashes of Cherenkov light at the bottom of Lake Baikal. As a neutrino-induced muon races through the water, the light from its Cherenkov cone reaches different tubes at slightly different times. The skill lies in collecting all the information and sifting through it to reconstruct the path of the upward-moving muon. This can then be used to calculate the path of the original neutrino. It is this ability to figure out where a neutrino comes from that differentiates a neutrino telescope from a mere neutrino detector. A telescope must identify the source of neutrinos in the sky, and the Lake Baikal instrument can do so with an angular resolution of about 2.5 degrees, meaning that it can distinguish neutrinos coming from points in the sky separated by a distance of five full moons. So far the Baikal telescope has seen only atmospheric neutrinos, secondary particles created by cosmic rays crashing into atoms in the air. Everyone here is waiting for the day when a high-energy neutrino from outer space makes its presence felt in their little corner of the lake.

Belolaptikov recalled his first neutrino—indeed, the Baikal detector’s first—from 1993. “It was great,” he said. “Here, you can see.” He leaned over his bunk bed and removed a piece of paper pinned to the wall above. It was a printout of the path of an upward muon, reconstructed from the detection of its Cherenkov cone: the first-ever neutrino seen by humans using a natural body of water as a detector. Belolaptikov and colleagues had done the reconstruction and put the Lake Baikal detector on the map.

The next two days slid by, but even in this short time a rhythm was established. A trip down to the lake in the mornings to get a bucketful of drinking water from a hole in the ice. Then back to the cabin for coffee with condensed milk and honey, making sure to plug the hole in the can of milk with paper to prevent “little animals” (as Wischnewski calls insects) from getting in. From my cabin I could see clear across the lake, and I had to remind myself that it had more water than America’s five Great Lakes put together and a surface area larger than Belgium. Eighty percent of Russia’s freshwater was here. Even at great depths, the lake is well oxygenated, making it one of the most hospitable waters for life. Because of the voracious crustaceans that live at all depths, nothing dead or dying lasts more than a few days in this lake. If fishermen leave their catch in the nets too long, the crustaceans invade the fish through their mouths and gills, eating them from the inside out. These critters keep the lake free of dead matter, leaving it unimaginably clear, especially deep down. Murky waters would make watching for muons nearly impossible. “It is a very, very kind water,” Budnev said.

When the Russians turned on the Lake Baikal telescope in 1993, it was the only game in town. That has since changed. European physicists have started building similar detectors in the Mediterranean. And an American-European team went to the South Pole in the mid-1990s to construct the Antarctic Muon and Neutrino Detector Array (AMANDA) while laying the groundwork for IceCube, the largest-ever neutrino detector. Several German physicists who had worked at Lake Baikal joined the South Pole team. For a few years Wischnewski, too, split his time between Antarctica and Baikal before committing fully to Baikal. The South Pole detectors are looking for Cherenkov light emitted when muons hit the ice, and IceCube will be watching a cubic kilometer of ice for these ephemeral flashes.

"Budnev flicked a few drops of vodka onto the ice—an offering to the great spirit of lake baikal"

he innovations at Baikal—including Belolaptikov’s work on reconstructing muons—inspired the early efforts in Antarctica. Although Antarctic ice is clearer than the waters of Lake Baikal, for now the water has a unique advantage. Light can travel more than 10 times as far in the lake as it can in the ice before it is scattered. Catch the photons before they scatter and you can tell exactly where they are coming from. Catch them after they have been scattered a few times and it gets hard to work out their original direction. This means that more PMTs are needed in the Antarctic ice to achieve the same end.

Grigory Domogatsky, spokesman for the Baikal project, made this point emphatically one evening while we were sitting at a table in his cabin next to a roaring fire. Despite a rasping smoker’s cough that could stop him in midsentence, he passionately argued that the world’s biggest neutrino detector should be built right here in Lake Baikal. The Americans and their European partners were spending $270 million on IceCube, and Domogatsky thought that a tenth of that would be enough to build a comparable detector in Siberia. Besides the advantage of needing far fewer photomultiplier tubes to detect high-energy neutrinos, Domogatsky pointed out that only a detector in the Northern Hemisphere could see neutrinos from the center of our galaxy.

“But you can see the center of the Milky Way from the South Pole,” I said, somewhat puzzled.

“Yes, but not neutrinos,” Domogatsky replied, with the gentle yet triumphant note of a teacher who has just made a telling point. Of course: Neutrino detectors that use natural bodies of water or ice can see only those neutrinos that come through the Earth, so they have to look upside down—and from that vantage, the center of the Milky Way never comes into view at the South Pole. Domogatsky further argued that Lake Baikal was the best body of water in which to build such a detector, for there are no deepwater currents, as there are in the Mediterranean. “Lake Baikal is like an aquarium,” he said. Besides, scientists in the Mediterranean need ships to lower their strings into the sea and remote-controlled submersibles to wire them up, making the operation expensive. Here, winter ice makes retrieving and working on the detectors comparatively simple. But, Domogatsky sighed, convincing people to work in Siberia during the winter, when the alternative was the sun-soaked Mediterranean, was going to be hard.

omogatsky’s heavily furrowed face showed the effects of 40 years of physics, many of them spent in this hostile place. Now he was looking to pass the baton. His team had just figured out that the telescope they had built so far could form a cell of a much, much larger telescope. Put next to each other, such cells could cover a cubic kilometer of water. All he needed was about $25 million, an order of magnitude less than the money being spent on the Mediterranean neutrino projects or at the South Pole.

The fire died. Outdoors the sun was setting. “I hope to help start this project,” Domogatsky said. “But the work should be performed by younger physicists.” We stepped outside. I took a picture of this grand old man of contemporary Russian physics against the backdrop of his beloved lake, then started walking back to the shore station. There was just one thing left to do. Wischnewski had suggested that my visit would be incomplete without my spending a night in one of the cabins at the ice camp. I had agreed. But then he casually mentioned that the ice heaves. Despite the lake’s thickly frozen surface, the water beneath is alive and kicking. Sometimes the entire sheet of ice below the camp can jerk and lurch.

That night we drove to the ice camp and a graduate student named Alexey Kochanov ushered me into his cabin. He told me not to worry; he found the sound of ice creaking beneath him relaxing. Obviously he had been here way too long—but then he explained. The creaking means that the ice cover is solid. It is the sound of ice moving in response to the motion of the water beneath. It is only when you don’t hear the creaking that you should worry. That’s when the cracks are so big that there is plenty of give in the ice and you should not be on the lake.

Suddenly the ice’s protestations were music to my ears.All night it groaned. When sounds came from far away, they were like muffled gunshots; when they were close, more like the crack of a whip. At five in the morning, the ice heaved. It was the only significant movement I had felt all night. I couldn’t go back to sleep, so I went outside. It was still dark. The ice did not open to swallow me. Thin cracks crisscrossed the surface. You could tell that the new fissures had formed in the night because they had not yet been covered by snow. Scorpio’s tail was visible next to the moon, and overhead was Ursa Minor. On the far shore, embers of a forest fire glowed on the slopes of the Khamar-Daban range.

Somewhere deep below, a cone of bluish light raced upward through the cold water. A neutrino had traveled from some distant part of the universe, escaped collision with every bit of matter across trillions of miles, and gone through the center of the Earth, only to collide with a molecule of water in Lake Baikal and disappear in a flash of light.

Excerpted from The Edge of Physics by Anil Ananthaswamy, copyright © 2010. Reprinted by permission of Houghton Mifflin Harcourt Publishing Co. All rights reserved.

Ultimate particle

Soon after verifying the existence of neutrinos, physicist Frederick Reines called these particles “the most tiny quantity of reality ever imagined by a human being.” Indeed, neutrinos have the smallest mass of any known particle—and yet they are incredibly important for understanding the world around us. Most neutrinos originated just fractions of a second after the Big Bang and so carry unique information about the infant universe. Others started their journey in the sun’s core or in powerful supernova explosions, revealing secrets about how stars shine and how they die.

Today astronomers rely primarily on visible light or other forms of electromagnetic radiation (like radio or X-rays) to study the distant universe; that is how the Hubble Space Telescope creates its beautiful images of galaxies and nebulas. In many ways, though, neutrinos make better cosmic messengers. Unlike light, which is easily absorbed as it moves through space, neutrinos rarely interact with anything. And unlike many other subatomic particles, neutrinos have no charge, so they travel in a straight line from their source without being deflected by the magnetic fields around stars.

Unfortunately, the inertness that makes neutrinos such a valuable source of information also makes them difficult to detect. Sixty billion solar neutrinos hit your thumbnail each second, and nearly every one of them passes through unscathed. As a result, neutrino observatories must scan vast quantities of water or some other good target to detect the exceedingly rare interaction between a neutrino and another particle.

With its 228 optical sensors, the observatory at Lake Baikal (diagrammed at left) looks for the debris created when a neutrino collides with a hydrogen or oxygen nucleus in the water: a shower of new particles that triggers a cone of bluish light. To exclude other particles that can produce a similar signal, scientists limit their search to showers cascading upward from below. This ensures that the original particle has passed through the Earth’s crust, a feat that only a neutrino can accomplish. andrew grant

Neutrino Spotting

Lake Baikal is not the only place where physicists are using elaborate detectors to study the most evasive particles in the universe. Here are other sites around the globe where the work goes on:

IceCube, Antarctica The latest and greatest neutrino observatory can be found in one of the most inhospitable locales on Earth. Scientists have buried beads of optical sensors under almost a mile of ice, where it is dark and clear enough to detect the blue light of a neutrino-induced particle shower even from hundreds of feet away.

Super-Kamiokande, Japan Within a mine more than half a mile underground, 13,000 detectors probe 50,000 tons of purified water for the blue-flash signature of neutrinos. In 1998 scientists at Super-Kamiokande found the first evidence that neutrinos have mass.

Sudbury Neutrino Observatory (SNO), Canada An engineering marvel, SNO is a transparent spherical chamber filled with liquid, ringed with sensitive light detectors and submerged in a water-filled mine. To improve sensitivity, researchers removed the heavy water that initially filled the chamber so that a petroleum-like liquid could be injected instead.

Main Injector

Neutrino Oscillation Search (MINOS), U.S. This underground observatory in Minnesota detects neutrinos beamed from Fermilab, 450 miles away near Chicago. Scientists at MINOS hope to learn more about the three neutrino “flavors”: electron, muon, and tau.

Oscillation Project with Emulsion-Tracking Apparatus (OPERA), Italy Here, a man-made beam of neutrinos (created near Geneva) hits 150,000 lead bricks separated by photosensitive plastic. a. g.

Physics & Math / Cosmology

2010-08-13T03:47:00.000-07:00

What triggered the Big Bang? According to a new theory, our universe crashed into another three-dimensional world hidden in higher dimensions. "The model suggests a radically different view of cosmic history in which the key events shaping the structure of the universe occurred before the Big Bang," says cosmologist Paul Steinhardt.

Before the Big Bang

Maverick cosmologists contend that what we think of as the moment of creation was simply part of an infinite cycle of titanic collisions between our universe and a parallel world

The Catholic Church, which put Galileo under house arrest for daring to say that Earth orbits the sun, isn't known for easily accepting new scientific ideas. So it came as a surprise when Pope Pius XII declared his approval in 1951 of a brand new cosmological theory—the Big Bang. What entranced the pope was the very thing that initially made scientists wary: The theory says the universe had a beginning, and that both time and space leaped out of nothingness. It seemed to confirm the first few sentences of Genesis.

Eventually, astrophysicists followed the pope's lead, as evidence for the Big Bang became too powerful to ignore. They accepted the notion that the entire observable universe—100 billion galaxies, each stuffed with 100 billion stars, stretching out more than 10 billion light-years in all directions—was once squashed into a space far smaller than a single electron. They bought the idea that the cosmos burst into existence precisely 13.7 billion years ago and has been expanding ever since. But even now, many astrophysicists are still uncomfortable with the implication that the Big Bang marked the beginning of time itself. And the theory has yet to yield a satisfactory answer to a key question: What made the Big Bang go bang?

Cosmologists Paul Steinhardt and Neil Turok have a radical idea that could wipe away these mysteries. They theorize that the cosmos was never compacted into a single point and did not spring forth in a violent instant. Instead, the universe as we know it is a small cross section of a much grander universe whose true magnitude is hidden in dimensions we cannot perceive. What we think of as the Big Bang, they contend, was the result of a collision between our three-dimensional world and another three-dimensional world less than the width of a proton away from ours—right next to us, and yet displaced in a way that renders it invisible. Moreover, they say the Big Bang is just the latest in a cycle of cosmic collisions stretching infinitely into the past and into the future. Each collision creates the universe anew. The 13.7-billion-year history of our cosmos is just a moment in this endless expanse of time.

The hidden dimensions and colliding worlds in the new model are an outgrowth of superstring theory, an increasingly popular concept in fundamental physics. Scientists currently rely on two mutually incompatible theories—relativity and quantum mechanics—to describe the most massive objects in the universe on the one hand and subatomic particles on the other. For nearly a century, theorists have attempted to come up with a single model and a single set of equations that melds the two views of physics. Superstring theory is an evolving attempt to do just that: explain matter, energy, space-time, and the basic forces of nature in one framework.

String theory is hellishly complex. In order to make it work, theorists have to assume that space isn't merely three-dimensional, the way it appears to our puny human senses, but rather that it has up to 10 spatial dimensions. Just as a bedsheet hanging on a clothesline appears to be a two-dimensional object hanging in a three-dimensional world, all of space-time would be suspended in a higher-order space. In keeping with this two-dimensional analogy, string theorists describe our observable universe as a membrane—"brane" for short—flapping in the breezes of the actual 10-dimensional cosmos.

Physicists are just beginning to poke and prod at the big implications of superstring theory. That's what Burt Ovrut of the University of Pennsylvania was doing during a 1998 cosmology conference at the Newton Institute of Mathematical Sciences in Cambridge, England. He asked: If we live on a brane that's wafting through multidimensional space, why shouldn't there be other such branes floating around out there? Nothing in the theory ruled out this possibility. And if other branes exist, they could interact. It would be fascinating, Ovrut proposed during his talk, to consider what might happen if they did.

The idea intrigued Steinhardt, a professor at Princeton University who was sitting in the audience. If the interaction between branes was a collision, it would trigger a fantastically powerful reaction, Steinhardt guessed, given the immense amounts of matter and energy in each one. The crash would release so much energy, in fact, that it might be comparable to another energy release he was already quite familiar with: the Big Bang.

Meanwhile, Turok, a professor at Cambridge University, was sitting in the same audience having similar thoughts. After the lecture both men approached Ovrut to discuss their ideas. "It was clear that a collision of branes would be a dramatic event," Turok says. "People had talked about it in a mathematical way before, but nobody had thought of it as a real, physical process."

Steinhardt, Turok, and Ovrut, along with Steinhardt's graduate student Justin Khoury, decided to see what implications colliding branes might have for cosmology. They weren't driven by idle curiosity alone. Steinhardt, in particular, had been growing increasingly disenchanted with the conventional Big Bang model. The problem wasn't just that the theory required that time and space have a beginning but also that the more cosmologists tried to refine their model, the messier it seemed.

The original Big Bang model was simple: a hot dense knot of energy burst outward, congealed into matter, and kept expanding. But by the 1980s, astrophysicists had embraced a more complex elaboration of the Big Bang known as inflation. Ironically, one of the theorists who developed this idea was Steinhardt. Inflation theory postulates that in the first hundred-millionth of a billionth of a billionth of a billionth of a second of its life, the universe expanded as though it were turbocharged, swelling much faster than the speed of light, before settling down to a more sedate rate of growth. The only way that could have happened is if there had been some incredible energy source pervading the newborn cosmos and blowing it apart. We don't see anything like that in the universe today, however, so cosmologists had to assume the potent energy field existed for only a fraction of a second after the Big Bang and then vanished.

Conjuring up new, unknown energy fields goes against both common sense and one of the most cherished scientific doctrines. A principle known as Occam's razor says the simplest possible explanation for natural phenomena is usually right. Perhaps the best-known example is the Earth-centered cosmology of Ptolemy, which dominated Western science for 1,000 years. When Ptolemaic theorists discovered that the planets did not appear to be moving in a simple pattern around Earth, they added epicycles—tiny circular movements on top of the grand orbital circles. Closer examination showed that this didn't quite explain observations either, so the theorists added epicycles on top of epicycles until the model did work. The final result was also very complex. Then Copernicus came along with the idea of a sun-centered cosmology, and Johannes Kepler realized that planets actually move in ellipses. Suddenly, planetary motions made sense without the complexity of epicycles, and the old theory was dropped.

IN THE BEGINNING . . .

Is the universe infinite or finite? Is it eternal or will there be an end of time? Did it arise from something else, or did it simply pop out of nothingness—creation ex nihilo? Cosmologists have wrestled with these questions since Edwin Hubble first uncovered evidence of cosmic expansion in 1929. For more than half a century, the standard answer has been that our universe began as a single burst of energy—the Big Bang. Recent elaborations have answered some questions but not the biggest ones. A radical new cosmology proposes that our universe is just a tiny fraction of a vast, higher-dimensional realm and that the Big Bang is one step in an endless cycle of creation.

—Alex Stone

STANDARD MODEL

According to the reigning Big Bang theory, the universe began as an infinitely hot, dense dot. Within a tiny fraction of a second, the cosmos underwent a period of runaway expansion, called inflation. Over billions of years, the universe cooled, giving rise to galaxies, stars, and planets. Today, 13.7 billion years after the Big Bang, the universe continues to expand and

in fact is speeding up under the influence of a mysterious energy force. If things keep going this way, the future of the universe looks bleak: Stars will burn out, galaxies will disintegrate, and the universe will end eternally dark and lifeless. This theory leaves many unknowns hanging. It does not explain why the Big Bang happened and what, if anything, existed before. It also does not explain the nature of the unidentified energy field that is causing our universe to accelerate.

CYCLIC MODEL

To address some of the limitations and paradoxes of the Big Bang model, cosmologists Paul Steinhardt and Neil Turok have developed a new cosmology that views the visible universe as one small part of a much larger reality, most of which exists in other dimensions that we cannot perceive. Our universe exists on a three-dimensional membrane (represented by the flat panels at right) that lies right next to another membrane. Every trillion years or so, the two membranes collide, unleashing a firestorm of energy analogous to the Big Bang. As in the earlier model, the universe cools, gives rise to galaxies, and eventually expands to near emptiness. In this version, however, another collision between membranes then restarts the whole cycle of creation. Thus, time and space are both infinite.

Inflation seemed like a necessary complexity. Without it, the universe would look very different—for instance, galaxies on one side of the universe would be distributed differently from galaxies on the other side, which they don't appear to be. As inflation caught on, however, some cosmologists grumbled about epicycles. Then the Big Bang got even more complicated. Starting about five years ago, astronomers measuring the expansion rate of the universe discovered that billions of years after the Big Bang—long after inflation had died out—cosmic expansion started speeding up again.

Step One: EMPTY UNIVERSE
Each panel represents a three-dimensional membrane. The observable universe exists within the panel on the right; the other membrane is invisible to us. At the end of one cosmic cycle—after about a trillion years of accelerating expansion—matter is so spread out that space is essentially empty. This stage corresponds to the distant future of our universe. All is not static, however: The membranes still contain energy, and a force of attraction gradually draws them together again.

Theorists invoked another unknown energy field, called dark energy, to account for that cosmic acceleration. "This wasn't really predicted at all," says Steinhardt. "We can fit it into the model, but we don't know what this so-called dark energy is. The standard model is definitely becoming more encumbered with time. It may still be valid, but the fact that we have to keep adding things is a bad sign."

Astronomical evidence clearly indicates that the observable universe has been expanding for the past 13.7 billion years. In the inflationary Big Bang model, the universe was hot and dense at the outset, and then immediately went through a period of hyperexpansion. Steinhardt and his colleagues considered a very different possibility: What if the universe actually started out cool and vacuous?

If that were the case, the idea of branes colliding in a hidden dimension might provide a simpler explanation for the ongoing expansion. To find out whether the idea made sense, the pair took on the daunting task of mastering the equations of superstring theory and applying them to their theory. For simplicity, the researchers assumed that the branes were flat and parallel to each other. They also assumed that the branes contained no matter.

That didn't mean the branes were voids: Quantum theory asserts that even the total vacuum of empty space is seething with "virtual" subatomic particles that constantly wink in and out of existence. In aggregate, these virtual particles add up to a huge amount of latent energy—which, according to Einstein's theory of special relativity, is equivalent to an astounding amount of mass. So a crash between two empty branes would still be a collision of gigantic proportions.

Step Two: FIERY COLLISION

As the two membranes draw nearer to each other, they ripple and distort so that the surfaces come together in different places and at different times. As the membrane surfaces crash into each other, vast amounts of energy are released (white zone). Called ekpyrosis—the Greek word for conflagration—the colossal collision gives birth to a baby universe in our membrane (right). The force of the impact causes space to expand rapidly and also pushes the two membranes apart.

That's exactly what the universe looked like before the first stars ignited and the first galaxies formed. We know that because the Wilkinson Microwave Anisotropy Probe (WMAP), launched in 2001, recently revealed the pattern of hot and cold spots in the heat left over from the earliest days of the universe (see the January 2004 issue of Discover, page 37). In the Big Bang/inflation model, the hot spots are generated by quantum noise that is magnified by the inflationary energy field. "Much to our surprise, after doing these enormous, intricate calculations, we found out colliding branes would produce exactly the same pattern of temperature fluctuations," says Turok.

Step Three: GALAXY-FILLED UNIVERSE

After the two membranes collide, they move apart. The initial fireball expands and cools, with the ripples of the membrane leading to the small temperature fluctuations in microwave background radiation observed in our universe. The subsequent sequence of events echoes the Big Bang model: Lumps of gas give rise to galaxies and other cosmic structures, and space continues to expand. This roughly corresponds to the current state of our universe.

"It seemed almost miraculous to us that it turned out this way," says Steinhardt. The new idea was dubbed the ekpyrotic universe. Ekpyrosis means conflagration in Greek and refers to an ancient Stoic cosmological model in which the universe is caught in an eternal cycle of fiery birth, cooling, and rebirth.

The research team subsequently turned its attention to what would happen in the branes after a collision. Calculations suggested that the crash would generate a universe-wide fireball of pure energy within each brane. That blast would drive the two branes apart again. Then, as the fireball suffusing our brane began to cool, its underlying energy would undergo a phase transition, like water freezing into ice. This transition would unleash a force that would make the universe start to expand. The hot spots of the fireball would congeal into clumps of matter that would eventually become clusters of galaxies. The cold spots would become the empty voids that lie between thclusters.

This theorizing agrees with what we can see in our universe now. The ekpyrotic model leads to a scenario a lot like the fireball of the Big Bang, but there is no episode of inflation. From the outset, the cosmos experienced just one force that accelerated the expansion. That force is still at work today, which means that instead of coasting to a stop, the universe is expanding faster today than it was a billion years ago and will be expanding faster a billion years from now. In short, that one force would also explain the enigmatic force that astronomers have recently named dark energy. Further calculations by Steinhardt and Turok suggest we're at the beginning of a very long process that will eventually result in what appears to be an empty universe. Trillions of years from now, matter will be so widely spread out that its average density will be much less than a single electron per quadrillion cubic light-years of space. That's so close to zero density that there's no meaningful difference.

Again, this scenario echoes the predictions of conventional Big Bang cosmology, except that in the model proposed by Steinhardt and Turok, the story does not end there. In the far future, another three-dimensional world still lurks nearby, similarly emptied out after its encounter with ours, invisible and imperceptible to us. Although they bounced apart after the collision, the two branes will exert a force on each other that's analogous to gravity, and they will ultimately meet in another crash, triggering another Big Bang. The cycle of such collisions would be eternal.

"Cyclic-universe models were popular in the 1920s and '30s," Steinhardt says. "But they were based on the idea of a Big Bang followed by a Big Crunch followed by another Big Bang." In these models, the same matter is endlessly recycled, so the entropy of the universe—its tendency toward disorder over time—increases from one cycle to the next. "The result is that each subsequent cycle gets longer," Steinhardt says. "And if you go back into the past, each cycle gets shorter. Ultimately, you still have to have a beginning." In principle, scientists shouldn't care. In practice, most have a very human tendency to abhor the idea of a beginning to time. And most find the prospect of a universe that will end someday to be rather grim. In this new cyclic model, the universe starts essentially empty each time. That means virtually no matter gets recycled. So entropy doesn't increase, and there is no beginning or end to time.

Step Four: OLD UNIVERSE
Toward the end of one cosmic era, space has expanded to such an extent that galaxies have drifted very far apart. After about a trillion years, most of the stars have burned out, and our universe is nearly empty. But this is not the end of the story. The continued attraction between the neighboring membranes draws them together again, setting the stage for another colossal collision and an ekpyrotic rebirth of our universe. The cycle of collisions between membranes continues into eternity.

The model works so well that one might expect cosmologists to embrace it wholeheartedly. Actually, the reception has been lukewarm. One reason is that at the moment of collision, the extra dimension separating the two branes goes from vanishingly small to literally zero. That creates what physicists call a singularity, a point at which the laws of physics break down. Although superstring theory might help explain what happens in a singularity, it hasn't done so yet. "The problem is very difficult," Turok admits.

That, say some physicists, is an understatement. "I don't think Paul and Neil come close to proving their case," says Alan Guth, a cosmologist at MIT who is a founding father of inflation theory. "But their ideas are certainly worth looking at." Nathan Seiberg, a string theorist at the Institute for Advanced Study in Princeton, is also cautious. "I don't know whether their model is right or wrong," he says.

Joel Primack, a physicist and cosmologist at the University of California at Santa Cruz, isn't even all that interested in whether it's right or wrong. "I think it's silly to make much of a production about this stuff," he says. "I'd much rather spend my time working on the really important questions observational cosmology has been handing us about dark matter and dark energy. The ideas in these papers are essentially untestable."

Steinhardt and Turok respond that their theory could gain credence from LISA, a proposed space probe that would look for gravity waves from the early universe. Gravity waves are ripples in the fabric of space-time that were predicted by Albert Einstein. So far, they are theoretical. But by 2020, the LISA experiment—pairs of free-flying satellites that would move apart and together with each passing wave—could either find confirming evidence of inflation or find nothing and thus tip the scales toward ekpyrosis. Inflation theory posits that the entire mass of the universe accelerated to many times the speed of light in a fraction of a second and should have set the entire cosmos ringing with gravity waves. Ekpyrosis, by contrast, which involves a very slow collision between universes, wouldn't generate observable waves. "If we're right," says Steinhardt, "it will be terrifically exciting. If we turn out to be wrong, that'll be disappointing, of course, but it's still important to challenge inflation with alternate theories so we can see how robust it really is."

David Spergel, a Princeton astrophysicist and a member of the WMAP satellite research team, agrees. "Cosmology has to be tied in with superstring theory sooner or later," he says. "There are several ideas out there competing with inflation, and they may all turn out to be wrong. But I'd say this one has the best chance of being right." If it is, we need to rethink our place in the universe—in fact, we need to rethink the universe itself. In the ekpyrotic view of reality, everything that astronomers have ever observed is just a speck within the higher dimensions, and all of history since the Big Bang is but an instant in the infinity of time. This view of creation is far grander than the universe of traditional cosmology or the universe of the Bible.

So far, the pope hasn't weighed in.

Physics & Math / Materials Science

2010-08-11T11:32:00.000-07:00

Programmable Matter Moves From Sci-Fi to Sci-Real

Quantum dots can change the very properties of matter by controlling electrons.

The idea of programmable matter occurred to me in 1998. I was working on a short story that later evolved into a novel called The Collapsium and eventually into a series of books collectively known as The Queendom of Sol, a future history of the solar system (and some parts beyond). As Arthur C. Clarke famously said, “Any sufficiently advanced technology is indistinguishable from magic,” so in my books I sought to include technologies that felt like magic but had a basis in real science. Programmable matter certainly fit the “magic” part. This marvelous substance could be used to build anything from a chair to a spaceship and could transform itself almost instantly. A table could behave as if it were made out of gold one moment, out of diamond the next.

The “real science” part came from tiny semiconductor objects known as quantum dots, which confine electrons to a small space. Here’s the cool part: As far as the electrons are concerned, this environment is almost the same as the one they experience while bound in an orbit around an atomic nucleus. So the electrons behave as if they were part of an atom—exactly which type of atom depends on the size and shape of the dot, as well as the number of electrons pumped in or out of it. Change the number of electrons and you can switch from one atomlike electron structure into another.

I realized that if scientists could make quantum dots behave like synthetic atoms at room temperature in bulk, it would be possible to create materials whose properties could be adjusted in real time. In other words, we could really make programmable matter, or “wellstone,” as I called it in the book.

After The Collapsium hit the shelves, I started getting letters from skeptics, and I found myself writing complex articles to defend the concept. I visited labs and spoke with scientists all over the world about the actual state of the art. Columbia, Harvard, Stanford, and more have teams working on quantum dots. There are thousands of researchers working on materials that exploit quantum effects to yield surprising properties, such as bending light around an object to make it invisible. My research culminated in a nonfiction book titled Hacking Matter. Because I’m an engineer, it also led to two patents and a start-up company, the Programmable Matter Corporation.

Today the technology is in the hands of a building-materials company called RavenBrick LLC, whose “thermoreflective” windows and walls bring to life my fictional scenes in which buildings adapt to changes in the environment. Still, we’ve barely scratched the surface of what programmable materials may be capable of doing. I think science fiction has been, and will continue to be, instrumental in pointing the way. What follows is an edited excerpt from the last book in the Queendom of Sol series, To Crush the Moon. In the far future, the novel’s protagonists find themselves picking up the pieces centuries after a series of technological disasters.

Click on the red dots to read more about matter that can be mutated in To Crush the Moon.

2010-08-11T11:30:00.000-07:00

Microscopy Approaches Fundamental Limits

If God can’t pin down tiny atoms, what hope do mere mortals have?

Platinum* atoms measuring
four-billionths of an inch across

Image courtesy of S.J. Pennycook,
A.R. Lupini, G.M.Veith,
Oak Ridge National Laboratory

The worst primary-school scolding I ever received was for ridiculing a classmate who asked, “What’s an atom?” To my third grader’s mind, the question betrayed a level of ignorance more befitting a preschooler, but the teacher disagreed and banned me from recess for a week. I had forgotten the incident until a few years ago, while sitting in on a quantum mechanics class taught by a Nobel Prize–winning physicist. Midway through a brutally abstract lecture on the hydrogen atom, a plucky sophomore raised his hand and asked the very same question. To the astonishment of all, our speaker fell silent. He stared out the window for what seemed like an eternity before answering, “I don’t know.”

He was half joking—but only half. He knew the answer was freighted with uncertainty. What is an atom, really, or the particles (electrons, quarks) that compose it? Two and a half millennia ago, the ancient Greek philosopher Democritus imagined slicing bread into ever-smaller pieces, down to irreducible specks, and the concept of the atom was born. Today the fact that atoms are the building blocks of matter—there are 10⁸⁰ in the universe, 10²⁸ of which are inside you right now—is as fundamental to physics as DNA is to biology. No less an authority than Richard Feynman, the modern demigod of quantum theory, defends the primacy of this view in his Lectures on Physics. By way of introduction he wrote:

If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is . . . that all things are made of atoms—little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied.

Feynman was trying not to scare off his freshmen. In truth, it takes a spectacular amount of imagination and thinking to grasp the sublime elasticity of the atomic domain. Ultimately, as Feynman and his colleagues famously noted, no one ever completely does grasp it.

That is because, on some basic level, atoms and all subatomic things are invisible—not just in the trivial sense that they are too small to see but also in that, according to quantum physics, they do not have a well-defined position. Worse still, the very act of observing atoms disturbs their state, blurring the image. When physicists speak of uncertainty, it is not flaws in our equipment to which they are referring but to an innate ambiguity that our best efforts cannot eliminate, even in principle. It is impossible to measure, say, the angular momentum of an atom in more than one direction, not because of any experimental challenges involved but because, as Reed College physicist David Griffiths is fond of saying, “God doesn’t know.” If God can’t get a fix on atoms, then what hope do mere mortals have?

Well, physicists are a stubborn bunch. In the late 1960s, after about half a century of trying, they finally got their first real look at atoms. Researchers used a new tool—scanning transmission electron microscopy, or STEM, in which a beam of electrons plays the role that a beam of light normally does. By beaming high-voltage electrons through a sample and recording how the electrons scatter off the nuclei, STEM builds up a picture point by point.

The first person to see an atom was Joe Wall, a graduate student at the University of Chicago in 1969. He worked in the physics lab of Albert Crewe, who developed the earliest STEM with truly atomic-scale resolution. Crewe’s team was trying to image an atom of uranium, a large element with 238 protons and neutrons, number 92 on the periodic table. When they succeeded, it was cause for celebration. “Crewe had a couple of bottles of champagne in the fridge, and he pulled them out,” Wall remembers.

Since then, STEM imaging technology has advanced at a rate not seen since the 1930s, when the resolution of optical microscopes doubled almost every year. Breakthroughs in microfabrication, electromagnetic optics, as well as in high-speed computers that can adjust for aberrations and analyze images, have so improved accuracy that STEM imaging is now approaching the fundamental limits of vision set by quantum mechanics.

The current world record is held by the Electron Microscopy Group at Oak Ridge National Laboratory, where STEM images have been produced with a resolution in the range of 0.6 angstrom—less than one-millionth the width of a human hair. A typical atom is about one angstrom wide, and Crewe’s lab had managed to see only down to a little under three angstroms. “We can now see all these atomic details with a clarity we’ve never had before,” says the Oak Ridge group’s leader, Stephen Pennycook. “It’s like being blind and putting on your glasses and being able to see.”

Being able to see how atoms and bonds are organized in different types of matter is allowing scientists to design better materials. “The Titanic didn’t sink because it hit an iceberg; it sank because the steel was brittle and it cracked,” Pennycook says. “If you know the structure of a material, you can figure out how to improve it.” The understanding gleaned from STEM images has led to major improvements in the design and fabrication of computer chips.

Currently, the smallest atom scientists can see is lithium, number 3 on the periodic table. The next milestone is to push the resolution below the Bohr radius, about half an angstrom. At that level, even the tiniest atoms—hydrogen and helium—come into view. “That may take a couple of years,” Pennycook says. The ultimate dream is to take STEM into three dimensions with confocal electron microscopy, which images a material in slices by changing the focus of the beam. Pennycook and others have made major strides in this direction, and 3-D pictures of individual atoms are already becoming available. “This is a historic time,” says Pennycook. “Only once do we pass that threshold of being able to see atoms.”

Yet physicists know they are also approaching a wall. “We’re getting close to the fundamental limit due to quantum zero energy,” Pennycook notes. In quantum mechanics, every particle is a little blurry because it always carries a minimum iota of energy—the so-called ground state energy. Cooling the sample to ultralow temperatures helps slow the atoms down, but they will never sit perfectly still for the camera. “You can cool the atom, but you’ll never stop it entirely,” Pennycook says. Physicists expect STEM to bottom out at around one-tenth of an angstrom. No matter how much our technology improves, on some level atoms will always remain invisible.

Beyond the STEM image lies only the imagination. In poet Muriel Rukeyser’s words, “The universe is made of stories, not of atoms.” Physicists have laid bare the atomic domain, and what we will never see is as meaningful—and beautiful—as what we can.

Physics & Math / Subatomic Particles

2010-08-11T11:25:00.000-07:00

How to Build a $1000 Fusion Reactor in Your Basement

Admittedly, the project is a little dangerous—not because of a few little fusion reactions but because of the the very flammable gas and voltages high enough to instantly kill you.

Most college freshmen fill their dorm rooms with clothes, books, and electronics. Thiago Olson also brought his fusion reactor. But Vanderbilt University drew the line: No do-it-yourself reactors in the dorm! Instead, his device was housed in a nearby laboratory.

Olson’s project was motivated by the challenge of doing fusion—and by the same promise that has inspired thousands of physicists over the past half century. Nuclear fusion is the energy source that powers the sun; if channeled correctly, it could become a major source of clean energy here on Earth. Fusion occurs when the nuclei of two atoms are forced so close to each other that they bind together, releasing a great deal of energy in the process. Because positively charged nuclei forcefully repel each other, though, high temperatures are needed to bring about a union. Most fusion reactors are therefore enormous machines, like the $3.5 billion National Ignition Facility that recently opened in California.

Olson and a small cadre of other amateur nuclear engineers have found a simpler way. They are creating home-grown reactors, welding and wiring the devices in their backyards, garages, and basements (much to the alarm of neighbors). The hazards to the community are slim, the main ones being heavy use of electricity and short-range radiation that can be of risk to the “fusioneers” themselves. You can find out more about building a fusion reactor at www.fusor.net, an online community of fusioneers who help each other find parts, assemble, and problem solve. Also, check out a pair of books, Radiation Detection and Measurement by Glenn F. Knoll and Building Scientific Apparatus by John H. Moore.

If you decide to proceed, though, a few cautions: Beware of high-voltage electricity, which can skyrocket to more than 50,000 volts—enough that contact with a loose wire will kill you instantly. Pressurized flammable gas can also be fatal. And electrons hitting the stainless steel chamber produce X-rays, so do not look at the little window directly. Instead use a camera or leaded glass filter.

Contact your state’s department of health for regulations. Your reactor will use a lot more energy than it produces. It is barely capable of achieving a detectable nuclear reaction, so fusion is one of the least hazardous parts of this project.
For those who would like to join in on the fusion fun, DISCOVER offers this guide to the essentials. With a lot of scrounging for cheap parts online or at scrapyards, plus a lot of elbow grease, it is possible to put together a fusion reactor for as little as $1,000. If you need fusion right now, though, you can pay retail and get what you need for about $20,000.

RADIATION DETECTION EQUIPMENT Prove that you really achieved fusion by using a bubble dosimeter, which provides instant visual verification and measurement of neutrons produced by fusion reactions. If you get bubbles, you did it! Price: $120

VACUUM CHAMBER Get a stainless steel chamber to seal your fusion particles in and to keep air out. Olson’s vacuum is made from an old mass spectrometer he found on eBay. You will probably need a lot of bolts to get the chamber closed tightly, and possibly a large flange for patching up a gaping hole, which can cost $500. If you are a student, try asking the manufacturer for a discount. Price: $300–$4,000

DEUTERIUM The atomic nuclei in the hydrogen plasma are what collide to create fusion inside the chamber. Deuterium, or heavy hydrogen, is found in seawater, but it is hard to separate from its far more common, lighter cousin. Its distribution is also tightly regulated due to its close ties to nuclear technology. Unless you have special connections, a business or university will need to request it on your behalf. Price: around $250 for 50 liters of gas in a lecture bottle

HIGH-VOLTAGE POWER You will need at least 20,000 volts* and a 10-milliamp current to create enough heat to crush those hydrogen nuclei together. Remember that because you are trying to attract positive deuterium ions, you want negative output, so you must ground the positive charge. Olson uses an X-ray transformer salvaged from an old mammogram machine. A commercial power supply by Spellman or Glassman is another option, or the intrepid electrician can make one from scratch. Price: $400–$10,000

VACUUM PUMP Suck all the unwanted particles out of the chamber. A two-stage roughing pump will get you to a near vacuum. Then use a turbo or oil diffusion pump to reach a high vacuum. Price: $350–$4,000

GAS REGULATOR Use this to inject tiny amounts of deuterium into the chamber and to regulate pressure inside your reactor. Needle valves can fine-tune the amount going in; capillary tubing (with an inner diameter as narrow as a pin) will really slow it down. If you can afford to, forget those and instead use a mass flow controller, which allows you to delegate the job to your computer. Price: $100–$200

Physics & Math / String Theory

2010-08-11T11:22:00.000-07:00

Discover Interview The Man Who Plucks All the Strings

Brian Greene says string theory is still scientific even if it's not falsifiable.

In the 1960s, Italian physicist Gabriele Veneziano developed a theory to explain the inner workings of the atom and failed—at first. Now many scientists believe an improved version of his conjecture, known as string theory, may do more than merely explain the atom. It could be the elusive theory of everything, a set of universal laws governing everything from the smallest quark within the atom to the largest cluster of galaxies, from the Big Bang to this moment.

String theory explains what you might see if you zoomed in without limit, past the cells that constitute your body, past the atoms that make up those cells, past even the electrons and gluons that those atoms are made of, all the way to the scale of a billionth of a trillionth of a trillionth of a centimeter. At that level, according to the theory, lies the foundation of all the particles and forces in the universe: one-dimensional strands of energy, or “strings,” vibrating in nine dimensions. That may seem wildly counterintuitive, but many scientists agree it is the most promising approach to explain the laws of physics

Columbia University physicist Brian Greene has become the public face of string theory. He has provided insight into the topology of those additional dimensions, and in 1999 he introduced the theory to nonscientists in a best-selling book, The Elegant Universe. In 2008 he cofounded the World Science Festival, an annual event that brings together scientists, artists, and ordinary people who are simply interested in the great questions of the universe. Greene talked to DISCOVER about how string theory has evolved, the attempts to find supporting evidence through new experiments, and the challenges of making science exciting to the general public.

What is the major problem string theory attempts to solve?
Our current theory of gravity—Einstein’s general theory of relativity—and our current theory of the behavior of atoms and subatomic particles—quantum mechanics—both work fantastically well in their respective domains: general relativity for big things, quantum mechanics for small things. But when you try to meld the two, there is an incompatibility, a hostility. It’s uncomfortable to have two laws of physics, each claiming that the other somehow doesn’t work. In reality, both sets of laws are meant to work everywhere.

How does string theory create a single worldview that applies everywhere—and what exactly is a string, anyway?
The fundamental idea is that the elementary constituents of matter—electrons, quarks, and so forth—might not be dots of no size, which is the traditional image, but rather little filaments. They could exist in either little loops of filament—tiny loops of energy—or little snippets of energy, open strings as we call them. When people stared at the mathematics governing the motion of these little filaments, they found, remarkably, that the math didn’t work in a universe that has only three dimensions of space. It required nine dimensions, and when you add in time it gives you 10 dimensions, which is an astoundingly bizarre idea. Nevertheless, it’s an idea that string theorists take seriously, because that’s where the math leads, and math has proved itself to be a very sure-footed guide to how the universe works.

How can we envision these extra dimensions, and how would they manifest themselves in our seemingly three-dimensional world?
The shape and size of the extra dimensions would affect the properties of particles. So if you asked me, “Why does the electron have its charge or its particular mass?” the answer in string theory would be because the extra dimensions have the shape that they do. An electron weighs what it does because it has a certain internal energy, and that energy, according to Einstein, equals mc². The energy depends on how its little string can vibrate, and the string vibrates in a manner that depends on its environment, so it depends on the shape of the extra dimensions. The dream in the 1990s was to find the shape of the extra dimensions and then calculate the values of all those properties that experimenters have found.

What is the current status of string theory research?
We have a range of possibilities for the shape of the extra dimensions. We have, in fact, catalogs of shapes. Literally, I could write out a book and turn page by page and show you different shapes for the extra dimensions that people have mathematically determined as being possible. The problem is we don’t know which page is the right one, and the number of pages has grown fantastically in the last few years. There are on the order of at least 10⁵⁰⁰ different pages now [a number that dwarfs the number of particles in the universe], and when you’re faced with a book of that many pages, some people throw up their hands in disgust. Others say that maybe all those shapes are out there in different universes. That’s the most recent and controversial approach that people have been following.

So there could be a multitude of other universes, each corresponding to a different solution or “page” of string theory?
As scientists we track down all promising leads, and there’s reason to suspect that our universe may be one of many—a single bubble in a huge bubble bath of other universes. And you can then imagine that maybe these different bubbles all have different shapes for their extra dimensions. This suggests a landscape of different universes with different forms of extra dimensions and therefore different properties within those universes. If that is true, our universe would be one of many, and then the question becomes why are we in this one and not in some other one.

One of your findings is helping scientists make sense of those extra dimensions and other universes, right?
We found that classical geometry, the kind you learn in elementary school, breaks down at extremely small scales. Instead, quantum geometry takes over, in which, for example, there can be two very different shapes in the extra dimensions that nevertheless yield exactly the same physics. In other words, there can be two different shapes from the perspective of a classical mathematician, but when dressed up with their quantum properties they become identical. What got us really excited was that horrendously complicated calculations framed in the language relevant to one shape became simple when reframed using the other shape. People like to talk about the Eskimos’ having 20 terms for snow and ice.

It might take us a paragraph or a book to try to describe those distinctions, because our language is not set up to describe them. Similarly, with these shapes we’re basically rephrasing things from one language to another, and suddenly some very clunky and cumbersome descriptions become sleek, elegant, and completely solvable.

Critics of string theory have called it unscientific because it is not falsifiable. How can we evaluate string theory?
Falsifiability for a theory is great, but a theory can still be respectable even if it is not falsifiable, as long as it is verifiable. There are aspects of a theory that you can go out and look for and confirm, and that’s another way to gain confidence in it. For instance, it’s really hard to falsify the statement that there is life on another planet, but you can verify it by finding one example. We’re hoping that certain features of string theory are confirmable.

What kind of things are you looking for?
At the Large Hadron Collider in Geneva, there are features of string theory that may result in data that have no other natural explanation. For instance, string theory suggests that there should be a class of particles called supersymmetric particles [that every particle should have a partner particle], and we’ve never seen them before. If we see them, it won’t prove string theory right, but it would be a strong piece of circumstantial evidence, because their most natural home is in string theory. There’s also a long-shot chance that scientists will find evidence for extra dimensions at the LHC. String theory is not the only theory that can accommodate extra dimensions, but it certainly is the one that really demands and requires it.

How are physicists trying to find extra dimensions?
When two protons collide, as they will be doing quite frequently in the LHC, some of the debris created from the collision might be ejected out of our familiar dimensions and crammed into the others. We could notice that by detecting missing energy in our dimensions. The energy would seemingly disappear, but in reality it would just go to a place that our detectors don’t have direct access to.

If today you somehow found out that string theory is wrong, how would you feel about all your work of the past 25 years?
If it was false by virtue of an actual error that we all overlooked for 25 years, I’d feel pretty bad. But that’s so unlikely—nearly impossible, I’d say. The more likely thing is that we’ll learn that the theory is perhaps incapable of describing physics as we know it. The bottom line is progress, and if we can understand why it is that string theory failed, that will be progress. It won’t be the progress that we had hoped for, but it will be progress nevertheless, and that’s how science works.

How confident are you that string theory is correct?
One time I was listening to a radio program and I was described as a believer in string theory. I almost hit the roof because I don’t “believe” in string theory. I don’t believe in anything until it’s experimentally proven. I do feel strongly that string theory is our best hope for making progress at unifying gravity and quantum mechanics. Moreover, I’ve been spectacularly impressed over the past 20 years with the progress that string theory has made. But that’s not proof, and therefore I don’t believe it. There are a lot of very interesting ideas that are worthy of attention, and sometimes worthy of decades of attention, because they have such capacity to make progress on deep, unsolved questions. But that doesn’t mean that you believe the ideas are right. If you want to use the word belief, I simply believe that this is the best approach that we have.

You are the author of a best-selling book and the cofounder of a popular science festival. How do you go about getting people interested in something as esoteric as string theory?
I think many people had experiences in school where science was about learning details or completing rigorous calculations that may not have aligned with their personality. What gets missed is that those details are ultimately used by science to address big questions that we all care about: Where did the universe come from? Where did life come from? Will it all eventually come to an end? I think students often, by virtue of the way we teach, miss the big story and are led through the gritty details, leaving a bad taste in the mouth. Tracy Day and I created the World Science Festival to go around existing structures and create a place where people, led by real scientists, could immerse themselves in science’s great stories and big ideas. Don’t get me wrong, the details are important, but people will never want to know the details unless they can focus on the big ideas.

Physics & Math / Subatomic Particles

2010-08-11T11:17:00.000-07:00

The Hottest Science Experiment on the Planet

In a Long Island lab, gold particles collide to form a subatomic stew far hotter than the sun.

Brookhaven National Laboratory

Rocking the thermometer at 4 trillion degrees Celsius, a subatomic soup that might reflect the state of matter shortly after the Big Bang has set a new world record: It's the hottest substance ever created in a lab. The previous record, recorded at Sandia National Lab in 2006, was a balmy 2 billion degrees Celsius. The core of the sun burns at a chill 15 million degrees.

The uber-hot brew is created at Brookhaven National Laboratory on Long Island. The lab's Relativistic Heavy Ion Collider, RHIC, accelerates gold particles to nearly the speed of light before slamming them together to see what they're made of. When the energy of the colliding gold particles is transferred into heat, the temperature soars.

Scientists with the Pioneering High Energy Nuclear Interaction eXperiment, PHENIX, who took the temperature measurement, announced a value of 4 trillion, but that's only an average over the lifetime of the substance. At its hottest stage, the infusion may reach 7 trillion degrees Celsius.

"Matter as we know it shouldn't exist at that temperature," says PHENIX Spokesperson Barbara Jacak. And from what they can tell, it doesn't really. The protons and neutrons making up the gold nuclei appear to melt in the intense heat, and leave behind porridge made of the subatomic particles quarks and gluons. Jacak describes the resulting substance as "a liquid-like plasma."

But those words can't really describe the nature of the soupy mess. Nothing can, yet. Particle physicists, cosmologists, and even string theorists are all trying to understand why quarks and gluons, the building blocks of protons and neutrons (which in turn build atoms), behave this way at such high temperatures. Why doesn't the mixture turn into a gas, like water turns to steam at 100 degrees Celsius? How hot would it have to be to vaporize? And if the universe was filled with this liquid goop shortly after the Big Bang, how did it eventually turn into stars, planets, and people?

"We get giant discussions and even some vociferous arguments," says Jacak. "The big question for us is what is going on inside [this substance] and how does it work. On the experimental side we're trying to measure its properties, and one of the first properties you could measure is its temperature."

It sounds simple enough, but PHENIX scientists have been working on this task since the construction of the experiment ten years ago. Taking the temperature of a subatomic plasma that lives in the wreckage of a gold particle collision turns out to be extremely difficult (which is why Jacak says it's possible that other experiments have created even hotter substances, but might have no way to measure them).

Potters know that in the belly of a kiln, a piece of clay will change color as it heats up: First it's a warm red, then a brilliant yellow, and finally a blinding white. It's the photons coming off the clay that reveal the temperature, and PHENIX scientists relied on the same principle to measure the temperature of the plasma. The problem is, those photons (which are too high-energy to be seen by human eyes) are lost in the shower of photons created by the gold particle collision. The task was not so much like pulling a needle out of a haystack as it is like finding a single non-descript piece of hay in the entire barn. PHENIX's breakthrough analysis not only represents a new world record, but new possibilities for understanding the universe.

Long Island residents might be wondering how PHENIX doesn't burn a hole in the Earth with their flaming concoction, or if the group could harness the heat to run a generator. But the substance only exists for one trillionth of a trillionth of a second, and is smaller than a single atom. Nonetheless, trying to conceive of just how hot that tiny drizzle of particle goulash gets is enough to fry your brain.

2010-08-11T11:14:00.000-07:00

Two More Steps Toward Quantum Computing

The first solid state quantum processor, developed at Yale
University, can perform simple algorithms.

Blake Johnson/Yale University

Quantum computing—using individual atoms as information carriers—could transform the way we study the world, solving problems that would take many human lifetimes for today’s supercomputers in a matter of days. Unlike conventional computers, which store each piece of data as a single value (either zero or one), quantum processors can take on multiple values simultaneously, which is why they are so efficient. Or rather why they would be, if we could figure out how to build them. So engineers in the field are abuzz about two major advances toward the creation of a practical quantum computer.

Researchers at the National Institute of Standards and Technology (NIST) in Colorado unveiled a device that meets the basic criteria for a scaled-up quantum computer. It can store and display data, shuttle information around the processor, and perform repeated logic operations with a consistently low error rate. “We’ve pulled all the components together for the first time,” says Jonathan Home, a physicist at NIST who leads the project. His team accomplished the feat by pairing quantum bits—in this case, super-cold beryllium atoms used to store data—with magnesium atoms that act as refrigerants. (Even a little heat makes it difficult to control the atoms.) Lasers allowed the scientists to direct the computations performed by the atoms.

Meanwhile, a separate group headed by physicist Robert Schoelkopf at Yale University has built the first solid-state quantum processor. Unlike most quantum computing systems, the structure of this device resembles that of the integrated circuits in current computers, which could help bridge the gap between today’s technology and tomorrow’s.

Physics & Math / Telescopes

2010-08-11T11:11:00.000-07:00

The Mystery of the Rocketing Particles That Shouldn't Exist

From deep space, cosmic rays come fast and pack a heck of a punch. They may also carry clues to the most vexing mysteries in the universe.

The Advanced Thin Ionization Calorimeter, shown here in Antarctica
before a 2005 launch, detected cosmic rays in the upper atmosphere.

Image Courtesy of T, Gregory Guzik, ATIC

Nothing on the tree-less plains of western Argentina seems to expend much energy. Cattle stand nearly motionless as they graze on the thin grass, which grows slowly in the dry heat and high altitude. A cylindrical water tank with a small solar panel and a skyward-facing antenna sits unobtrusively in the nearly motionless landscape. But hidden within this scene is plenty of drama. At any given moment, millions of projectiles from deep space are raining down, penetrating every object in their path. Each particle then vanishes without a trace—unless it happens to pass through the water tank, where it causes a minute spark visible to scientists thousands of miles away.

The tank is one of 1,600 spaced out at one-mile intervals over 1,100 square miles of land, an area bigger than Rhode Island. Collectively they make up the Pierre Auger Cosmic Ray Observatory, a $50 million physics experiment to study bits of atomic shrapnel that blast out from some of the most violent places in the universe. These energetic particles, called (somewhat misleadingly) cosmic rays, tell revealing tales about the exploding stars and black holes that have shaped galaxies and seeded the cosmos with the essential elements of life...

Physics & Math / Cosmology

2010-08-11T11:09:00.000-07:00

Inside the World of Stephen Hawking

The world's most famous theoretical physicist will make you think—and laugh.

Stephen Hawking amyotrophic lateral sclerosis arrived for his DISCOVER photo shoot bearing a familiar look: corduroy jacket, dark blue shirt, and a wisp of a sly smile. Even though he is mostly paralyzed due to (ALS), he has no trouble making himself understood. In part he relies on an infrared switch attached to his wheelchair, which enables him to write and to talk through a voice synthesizer. But even with his restricted body motions, Hawking’s thoughts come across clearly. Every arch of his eyebrows and roll of the eyes carries as much meaning as another person’s torrent of words.

One thing Hawking cannot do is jot notes on a blackboard, which left DISCOVER’s executive editor, Corey S. Powell, scrambling to illustrate the renowned physicist’s ideas for the photographer. Fortunately Hawking has written a number of remarkably accessible popular books, including A Brief History of Time. Spend a little time in Hawking’s world and you, too, will be able to sketch the effects of a black hole on the structure of subatomic space.

Hawking has made critical contributions to cosmology and quantum gravity, but his work on black holes remains his most famous. Black holes were once regarded as one-way paths to oblivion because of their tremendous gravitational fields that, the theory went, allowed nothing—not even light—to escape. Hawking realized that the universe is not so tidy. Black holes can also send stuff back out, emitting radiation that is, in a sense, plucked from empty space. That process, now known as Hawking radiation, explains why we do not have to fear any mini black holes created by the Large Hadron Collider; they would “evaporate” into radiation almost instantly.

The Lucasian Professor of Mathematics at the University of Cambridge, Hawking is far less stuffy than that august title might suggest. He has played himself in cartoon form in several episodes of The Simpsons. In 2009 he plans to take a daredevil flight on Virgin Galactic’s new space-tourism service. And even his serious statements have an air of sardonic wit. Last April, in a lecture honoring NASA’s 50th anniversary, he addressed the possibility of extraterrestrial life. “Primitive life is relatively common,” he said, “but intelligent life is very rare.”

An appreciation of Hawking by Michio Kaku, professor of theoretical physics, City College of New York, and author of Physics of the Impossible:

Perhaps the greatest problem in all of physics is to unify the quantum theory with Einstein’s theory of gravity, thereby creating a “theory of everything” that would allow us to “read the mind of God,” as Einstein once wrote. Such a theory would answer some of our deepest questions, such as: What happened before the Big Bang? Are there parallel universes? Is time travel possible? What lies inside a black hole? Stephen has made some of the biggest breakthroughs in this area, showing that quantum effects can allow black holes to emit radiation, so black holes are actually gray.

I once spoke at Cambridge University at a conference organized by Stephen and had the chance to visit his house. I noticed various contraptions in the living room to help him cope with his illness. There was, for example, an automatic page turner. You put a physics journal in it, and it grabs a page and turns it for you. And then a thought passed through my head that made me shudder. What kind of ferocious mental power can enable him to be so active in research while losing the power of practically every muscle in his body? I asked myself: Would I trade places with him? I could become instantly famous, but I would pay the price of losing control of my own body.

I thought not.

Physics & Math / Cosmology

2010-08-11T11:05:00.000-07:00

Discover Interview Space Is Getting Bigger, and It's Getting Bigger Faster

Saul Perlmutter changing our understanding of the entire universe by discovering that its expansion is accelerating.

This article is a sample from DISCOVER's special Extreme Universe issue, available only on newsstands through March 22.

Also see the video from DISCOVER's Mysteries of the Cosmos event, in which Perlmutter was a panelist.

Few scientists can say their work forever changed how we see the universe. Saul Perlmutter is one of them, for his central role in the 1998 discovery of dark energy. That invisible energy, which accounts for a whopping 73 percent of everything in the cosmos, is stretching the fabric of space and could cause a runaway expansion of the universe. Through his groundbreaking research, the then 38-year-old physicist at Lawrence Berkeley National Laboratory in California basically turned our model of the universe on its head.

Scientists had long assumed that atoms—the constituent parts of stars, planets, and people—dominated the universe. Now it is generally accepted that matter makes up merely 5 percent, its share dwarfed by the mysterious antigravity energy that is propelling space apart. (The remaining 22 percent of the cosmos is so-called dark matter, unrelated to dark energy except in its ability to defy all current methods of detection.) Scientists had also long assumed that the universe would either slow infinitely or eventually stop expanding and collapse in on itself. Perlmutter’s findings have forced them to consider that it might instead expand away into nothingness or, worse, end in a “big rip” as the ingredients of stars and galaxies are literally pulled apart.

Since 1998 Perlmutter has worked to refine his measurements of the accelerating universe and the dark energy causing it. Theories abound about the nature of this elusive energy, and Perlmutter is hotly pursuing observational evidence to help find the answer. He spoke to DISCOVER about his strange discovery, the latest ideas about dark energy, and the projects that have the best shot at making sense of this cosmic mystery.

What was the underlying motivation behind the research that led to your discovering dark energy in 1998?
In the 1920s, Edwin Hubble showed that the universe is expanding. But the very next thing out of people’s mouths was more questions: Will it keep expanding? Could it stop expanding? Maybe it could turn around and collapse. How do we know the universe will last forever? These are the obvious things you want to know when you say we live in a changing, expanding universe. And the way you answer questions about the future is by looking at the past.

How do you approach such a complex problem as the history of the universe’s expansion?
The basic idea is that when you look at farther and farther distances, you’re looking further and further back in time. There were some very early papers in the 1930s that proposed using supernovas—really, really bright exploding stars—to measure the universe’s expansion because it appeared there was consistency in how bright they got. If every supernova had almost exactly the same brightness, then you could use how bright it appeared from Earth to measure its distance. But it turned out that the more you looked at supernovas, the wider the variety you saw, and that consistency disappeared. It wasn’t until the 1980s that scientists realized there are subgroups of supernovas, and that one of them, called Type Ia, is very consistent in its brightness. Fortunately, it’s also the brightest of the group, so it’s the one you could follow farthest away.

How did those supernovas reveal the way the universe is expanding?
We used these Type Ia supernovas as our distance indicators. Then you want to know how much the universe has expanded since each explosion occurred. There’s a really convenient way of getting that. The supernova sends out almost all its light in a specific wavelength of blue. But as that blue light travels, it gets stretched exactly as the universe stretches, so it looks red [with a longer wavelength] by the time it reaches us. How red the light looks tells you exactly how much the universe has expanded since the explosion of that supernova.

Looking at different supernovas, you should be able to figure out how much the universe has expanded since, for example, 5 billion, 3 billion, then 1 billion years ago, and you would see how that expansion has changed over time. The expectation was that over time the universe’s expansion would be slowing down due to the gravitational attraction of all the mass of all the stuff in the universe. As it turned out, we found that the universe’s expansion was actually speeding up.

Why is it so significant that the universe is expanding faster and faster?
It suggests that the universe is not just a single-parameter story. It can’t just be mass that is causing the change in expansion; the only thing mass can do is slow everything down. So we immediately knew that there was something else in the story. It turns out that most of the stuff in the universe is in the form of some energy in the vacuum that has an odd repulsive property. It makes space reproduce faster, accelerating the expansion of the universe. We don’t know what it actually is, but for now people use the term dark energy as a placeholder to describe the attributes of this mystery.

Was there a moment when the enormous implications of your research really hit you?
Well, it’s funny. This had to be the slowest aha in history, an aha spread out over several months. And the reason is that these are really complex data analysis jobs and there are many steps you have to calibrate and get all straightened out before you get those nice, final data points. On the other hand, there was the very first time I went out to give a talk and present the data. After the talk a famous cosmologist, Joel Primack, stood up and said he just wanted to point out to the physicists in the audience that this is an amazing, absolutely flabbergasting result. I think at that moment I felt the extra sense of ah, that’s right, this is really shocking.

How are scientists now attempting to explain dark energy?
Einstein originally put a term called lambda into his equation for general relativity that was meant to counteract the effects of gravity and create a static universe. Edwin Hubble’s discovery of an expanding universe convinced Einstein that lambda was unnecessary. But later, people realized that in quantum mechanics lambda could easily be identified with the effects of particles that spontaneously appear and disappear in all empty space. They’re called virtual particles, and the energy associated with the background hum of their constant appearance and disappearance became the way in which we understand the source of repulsive vacuum energy.

Unfortunately, if you do the basic calculations for how much of that energy you expect, you get numbers that are way off—10¹²⁰ (1 followed by 120 zeros) times too large. You have a big problem when your answer is that far off. So it has been assumed that there must be a perfect cancellation that makes that discrepancy go right to zero. But now we see that the answer isn’t exactly zero. I think most of the particle theorists believe that we need new explanations.

What are some of the explanations?
One explanation is that dark energy is a scalar field whose properties at every point in space “roll” from one value to another. While it is rolling, the effect of its energy is high enough to make the universe accelerate. Or perhaps the general relativity equations that Einstein gave us are not completely perfect, and we’re going to need to modify them a little bit. Another fun explanation is the possibility that there are extra dimensions and that gravity can leak away into those other dimensions that aren’t visible. For the last 10 years there have been two or three papers a week on dark energy explanations. But if you ask these theorists if they believe their particular model is the answer, I think almost every one of them would say, “No, I’m just trying out different ideas and hoping we can get some clues.” Then they turn back to us, the experimentalists, for more data.

How are we going to find out more about what dark energy really is?
A good example is the Nearby Supernova Factory, an experiment that has turned up more than 500 Type Ia supernovas to help explore the nature of dark energy. I’m also involved in the Joint Dark Energy Mission, which is being funded by NASA and the U.S. Department of Energy. The plan is to send up a satellite that will search for supernovas and also pursue other techniques for exploring dark energy’s influence. I’m optimistic that if we can just do a really good project, then the theorists can have the other aha moment that we’re looking for within a half-dozen years. All we need to do is start getting some hints that will point people in the right direction. I think theorists are very creative and will be able to get the job done, but right now there’s simply too wide a scope. Dark energy could be anything

How has the universe’s expansion, and hence the influence of dark energy, changed since the Big Bang?
For cosmologists there’s this interesting moment in the very, very early universe—10^–35 seconds or so after the Big Bang—called the inflationary period. Inflation was another period of acceleration, and we don’t know what caused that acceleration, either. It’s possible that there was another kind of dark energy back then. After inflation there was so much mass so close together that gravity dominated and the expansion slowed. That lasted until about halfway through the life of the universe. It was some 7 billion years before the universe expanded to the point where matter was too scattered to keep the expansion slowing. At that point, dark energy’s power started to be felt and the universe started to accelerate again.

What does this discovery mean for the fate of the universe? Will dark energy ever let up?
Well, you can just take the naive approach of saying that the universe is accelerating now, so that means it will accelerate forever and lead to a very dark, empty, cold end, and that’s all we have to look forward to. However, we should remember that we don’t know what’s causing the current acceleration, and we don’t know what caused that acceleration during inflation at the very beginning of the universe.

That inflation turned around—it stopped and the universe started to decelerate. Who knows whether we’re seeing something now that might also decay away, and then the universe could collapse. So I would say that the fate of the universe has to remain in the category of unknown until we have any clue as to why it is currently accelerating.

Physics & Math / Math

2010-08-11T10:58:00.000-07:00

Discover Interview The Math Behind the Physics Behind the Universe

Shing-Tung Yau explains how he discovered the hidden dimensions of string theory.

Shing-Tung Yau is a force of nature. He is best known for conceiving the math behind string theory—which holds that, at the deepest level of reality, our universe is built out of 10-dimensional, subatomic vibrating strings. But Yau’s genius runs much deeper and wider: He has also spawned the modern synergy between geometry and physics, championed unprecedented teamwork in mathematics, and helped foster an intellectual rebirth in China.

Despite growing up in grinding poverty on a Hong Kong farm, Yau made his way to the University of California at Berkeley, where he studied with Chinese geometer Shiing-Shen Chern and the master of nonlinear equations, Charles Morrey. Then at age 29 Yau proved the Calabi conjecture, which posits that six-dimensional spaces lie hidden beneath the reality we perceive. These unseen dimensions lend rigor to string theory by supplementing the four dimensions—three of space and one of time—described in Einstein’s general relativity.

Since then Yau has held positions at the Institute for Advanced Study, Stanford University, and Harvard (where he currently chairs the math department), training two generations of grad students and embarking on far-flung collaborations that address topics ranging from the nature of dark matter to the formation of black holes. He has won the Fields Medal, a MacArthur Fellowship, and the Wolf Prize.

Through it all, Yau has remained bluntly outspoken. In China he has called for the resignation of academia’s old guard so new talent can rise. In the United States he has critiqued what he sees as rampant errors in mathematical proofs by young academics. Yau has also strived to speak directly to the public; his book The Shape of Inner Space, coauthored with Steve Nadis, is scheduled for publication this fall. He reflected on his life and work with DISCOVER senior editor Pamela Weintraub at his Harvard office over four days in February.

You’ve described your father as an enormous intellectual influence on you. Can you tell me about him?
He went to Japan to study economics, but he came back to help the Chinese defend themselves before the Japanese invaded in 1937. By the end of the war he was distributing food and clothes to the poor for the U.N. After the revolution in 1949, he worried about getting in trouble with the Communists, so he brought the whole family to Hong Kong. We were very poor—at first we were almost starving—but my father had a large group of students constantly at home to talk about philosophy and literature. I was 10, 11, 12 years old, and I grew accustomed to abstract reasoning. My father made us memorize long essays and poems. At the time I didn’t understand what they meant, but I remembered them and later made use of it.

Did part of you ever rebel?
I read most of the Kung Fu novels in secret. I quit school for more than half a year. I’d wake up and say I was going, but I’d spend the whole day exploring the mountains and then come back—but I did the homework that my father assigned to me at home.

I heard you led a gang at one point.
I had a group of friends under me. I’d go around, and sometimes we ended up in fistfights with some other groups. So?

How did you go from that rough-and-tumble young man to the focused person you are now?
In the early 1960s my father was chairman of the department of literature and philosophy at Hong Kong College. The college president wanted to make a deal with the Taiwanese government to send in spies. My father refused to go along and resigned. That created a big money problem because he had eight children by then. My father had to run around among different, distant colleges to support the family. Back in China he’d lent a friend some money, and after the Communists took over, the friend moved to Macau, a city near Hong Kong, and ran his own schools.

So he told my father, “I cannot return your money, but your daughter can come to my school, and I’ll give her free room and board and free tuition.” So my older sister went to Macau to study and got some flu, some funny disease, we never knew exactly what. She came back and she was treated, but she died in 1962. Then my elder brother got a brain disease; at the time we didn’t know what it was. My father had all kinds of burdens on his shoulders and then he got a disease, which I believe was cancer, but we didn’t know much in those days. My mother was running around trying to get funding to help my father. Finally we raised some money, but it was too late. He died after two months in the hospital in 1963, in the middle of my studies in the ninth grade. We could no longer afford our apartment, so we were kicked out. That’s when I realized I would have to make decisions for myself.

What did you do then?
After a while the government leased us some land, and we built a small house thanks to money from friends, but it was in a village far from school. The other kids looked down on us for being poor, and I had to ask the school president to allow me to pay tuition at the end of the year, when my government fellowship came through. It was humiliating. But I studied hard and did very well, especially in math. Then a former student of my father started a primary school in a town closer to school. He said I could help teach math and stay there at night. I had to take care of myself, I had to wash things and all of that, but I learned how to survive.

What happened once you made your way to college?
I had fallen in love with math early on, but at the Chinese University of Hong Kong I realized that mathematics was built on standard actions and logic. Soon I had arranged to take tests for the required math courses without actually attending while sitting in on more advanced classes, and no one seemed to mind.

In my second year, Stephen Salaff, a young mathematician from U.C. Berkeley, came to teach in Hong Kong. He liked to talk to the students in the American way: He gave lectures and then he asked students questions. In many cases it turned out I could help him more than he helped me, because there were problems he couldn’t solve during class. Salaff suggested I apply to graduate school early. I was admitted to Berkeley and even got a fellowship. I borrowed some money from friends and flew to San Francisco in September 1969.

What did you think of California when you arrived?
The first thing that impressed me was the air. In Hong Kong it’s humid, hot, but in California it was cool and clear. I thought it was like heaven. A friend of Salaff’s came to the airport to pick me up and took me to the YMCA, where I shared a big room with four or five people. I noticed that everybody was watching baseball on TV. We didn’t have a TV at home. My neighbor who was sleeping there was a huge black man. He was talking in a language I had never heard before.

He said, “Man, where the hell you come from?” It was fun, but I had to look for an apartment. I was walking around the street when I met another Chinese student from Hong Kong and we decided to share, but we couldn’t afford a place. We looked around and found another Chinese student, from Taiwan, so there’s three of us and it’s still not enough. Then we found an Alaskan also studying math, also on the street. So four of us went in together and the rent for each was $60 a month. My fellowship gave me $300 a month, and I sent half of it home.

What about your math studies?
There were many holes in my knowledge so I’d wake up early and start class at 8 a.m. I took three classes for credit, and the rest I audited. I brought my own lunch so even at lunchtime I was in class. I was especially excited about topology because I thought it could help reveal the structure of space. Einstein used geometry in his equation to give us the local picture: how space curved around our solar system or a galaxy. But the Einstein equation didn’t give the overall picture, the global structure of the whole universe. That’s where topology came in.

What is topology? Is it like geometry?
Geometry is specific and topology is general. Topologists study larger patterns and categories of shapes. For example, in geometry, a cube and a sphere are distinct. But in topology they are the same because you can deform one into the other without cutting through the surface. The torus, a sphere with a hole in the middle, is a different form. It is clearly distinct from the sphere because you cannot deform a torus into a sphere no matter how you twist it.

Does that mean geometry and topology are really two perspectives on the same thing?
Yes. It is like Chinese literature. A poem might describe a farewell between lovers. But in the language of the poem, instead of a man and woman, there is a willow tree, where the leaves are soft and hanging down. The way the branch is hanging down is like the feeling of the man and the woman wanting to be together. Geometry gives us a structure of that willow tree that is solid and extensive. Topology describes the overall shape of the tree without the details—but without the tree to start with, we would have nothing.

It has always amazed me to observe how different groups of people look at the same subject. My friends in physics look at space-time purely from the perspective of real physics, yet the general theory of relativity describes space-time in terms of geometry, because that’s how Einstein looked at the problem.

When you looked at the world through the lens of geometry and topology, what did you learn?
That nonlinear equations were fundamental because in nature, curves abound. Climate isn’t linear. If the wind blows stronger that way, it may cause more trouble over there; it may even depend on the geometry of the earth. Usually you see the stock market described by linear equations and straight lines, but that is not really correct. The stock market fluctuates up and down in a nonlinear way.

The Einstein equation described the curvature of the universe, and it was nonlinear. I ended up learning nonlinear equations from a master, although I didn’t know he was a master at the time. His name was Charles Morrey, and he was a classical gentleman. He always dressed in suits in class. He was a very nice man. Even if I was the only one there, he would lecture to me, just as if he were lecturing to the whole class.

Wait—you were sometimes the only one in his class?
Why should people care about ancient days? Morrey didn’t use modern notations. His book was hard to read. Kent State had just happened. The students and the faculty were all on strike, but Morrey still gave lectures. Soon everyone had dropped the class but me.

What happened next in your mathematical explorations?
It was Christmas break and I couldn’t go home, so I spent my time at the library reading all the journals and looking at rare books. That was the first time I met my wife, although only much later were we formally introduced. Through all this reading about topology I came across a theorem that talked about loops where curvature is everywhere negative—where the curve goes in like a saddle.

The theorem says that when we have two such loops with vertices at the same point, they can’t deform into each other by bending or twisting unless they are equal to or multiples of each other. I came up with a related theorem: If the curvature is either negative or zero and if the loops conform, then there must be a lower-dimensional surface—specifically a torus—sitting somewhere inside.

How can a lower dimension sit inside a higher one?
Imagine attaching a rubber band to the handle of a coffee cup. The cup has three dimensions, but the rubber band, which is just a curved line, effectively has only one.

Why should anyone other than a mathematician care about a torus or a string hidden within higher dimensions?
Because topology can affect and constrain geometry in the physical world. If water flows around a sphere, for example, there must be two points where the water is totally still. On a planet covered with an ocean, the water can’t all flow in the same direction, say east to west, everywhere, without hitting a snag. In the case of another topology, the torus, water can flow around and around and there’s no point at which the flow stops because the hole eliminates the impasse. For each fixed topology, the geometry follows different laws.

In other words, you realized that topology sets the basic rules for geometry, which in turn affects the world around us. But then you went further, asking whether the underlying structure of space might explain the laws of physics. How so?
I started to look into complex manifolds. A manifold is just a space, with each point immediately around you looking like Euclidean space—the familiar kind of space that we see around us. Imagine the earth is covered with a checkerboard or a grid, like latitude and longitude. This is the kind of coordinate system that Descartes introduced to geometry in the 17th century. At each point on the grid the space appears flat and finite, but it’s actually curved, a sphere. Instead of being measured with real numbers, though, we measure complex manifolds with complex numbers, in which one of the coordinates includes a real number multiplied by the square root of negative 1—an imaginary number that we call i. [Since the product of two negative numbers is positive, ordinary math suggests the square root of negative 1 cannot exist—hence the moniker “imaginary.”]

How can complex manifolds and complex numbers help us understand the structure of space?
Space is not necessarily something you see in day-to-day life. You can define geometry locally, but globally you cannot visualize the big picture, you can only imagine it and represent it through coordinates. We draw lines of latitude and longitude in a coordinate system for the continents. But that system doesn’t work well at the north or south poles, where all the lines converge. In order to get a more complete picture in those regions, we need another, more localized coordinate system for more detail. In the end, we need several such coordinate systems patched together to get a detailed picture of the entire globe.

More generally, in describing any space, we are not restricted to the three dimensions we experience in our lives. Mathematically, we can suggest any number of dimensions: two, three, four, five, ten, just by drawing additional coordinates on a grid. In complex space, every number in a coordinate system describes not just one dimension but two. Most important, complex numbers make it simpler to move from one coordinate system to another, a necessary step when working in the higher dimensions necessary for string theory.

You are best known for your work on the Calabi conjecture, which at the time was a major unsolved problem in higher-dimensional mathematics. What attracted you to it?
I was drawn to important problems that gave insight into geometry and space-time. Sometimes solving a problem creates a new kind of thinking, sometimes the math itself is beautiful. The problem I went with, the Calabi conjecture, is a very elegant statement about the curvature of complex manifolds.

What does “curvature” mean in this context, since you aren’t talking about the kind of curves we normally experience?
Curvature is second-order information—for instance, suppose I am driving a car around a curved freeway. The car’s velocity will change as you go, so you can measure the curve in terms of changes in velocity along that one-dimensional line. Then there is Gauss curvature, which gives you the curvature of a two-dimensional surface by multiplying the largest and smallest curvature of the family of all curves tangential to the surface at a given point.

For higher-dimensional space, such as the three-dimensional space around us, we calculate the curvature of all the two-dimensional surfaces passing through the point where curvature is in question. Finally there is Ricci curvature, which we measure by averaging the curvature of all two-dimensional surfaces tangential to each other along a common direction. In essence, Ricci curvature is an average of part of the total curvature of a space. It is an abstract geometric concept, but it is fundamental.

Why is Ricci curvature fundamental?
In physics, Ricci curvature is analogous to matter. Space with zero Ricci curvature is space without matter—a vacuum.

And how does all this relate to the Calabi conjecture?
Calabi said that certain topological conditions call for the existence of nonflat, closed, complex spaces without Ricci curvature anywhere. Such spaces would enjoy many beautiful properties. You might find the sub-dimensional loops or the torus I described in that very first paper I wrote—or you might find intersecting branes [short for “membrane,” another topological shape]. I was 100 percent sure that the spaces Calabi called for could not exist. No mathematician or physicist had ever found an example of one, and most geometers considered them too good to be true.

So what did you do next?
I spent a lot of time thinking about how to disprove Calabi. By 1973 I was teaching at SUNY–Stony Brook and planning to move to Stanford. That May I put my belongings into this little Volkswagen and drove across the country on Highway 80. I thought America was a country where everyone traveled around, but to my amazement, a lot of the people I met told me they had never driven more than 10 miles from their town. I crossed the Rocky Mountains. The car broke down at one point. By the time I was at Stanford for a few months, I thought I had finally proven Calabi wrong.

Disproving the Calabi conjecture would have been a major achievement; how did you announce it?
In August there was a big conference at Stanford with the top geometers in the world, including Calabi. I talked to Calabi and told him my idea. He said, “That sounds great. Why don’t you give a discussion about it to me?” It was scheduled for 7 p.m. Calabi brought a few colleagues from the University of Pennsylvania, and then a few others heard about it, and a few others.

There was a little crowd. I talked for about an hour, and Calabi was excited. “I’ve been waiting for this for a long time, and I hope it’s right,” he said. All the other people said, “Great, finally we can stop the wishful thinking that Calabi is true.” Then Calabi wrote to me in October. He said, “I’m trying to reconstruct your argument, and I’m having some difficulty. Could you explain the detail?” I started to reconstruct it and I found a problem too. I got totally embarrassed. I did not respond to Calabi at that moment and instead tried extremely hard to patch up the proof. I couldn’t, so I looked around to find other examples where Calabi was wrong.

I didn’t sleep for two weeks. But every time I found an example that was close, the proof fell apart at the last minute. Finally I said, gee, this cannot be such a delicate matter. Now I had much deeper insight into the issue and felt there must be some truth to the whole thing. I determined that it had to be right.

So after all that work trying to prove that Calabi’s conjecture was wrong, you decided it was correct after all?
I began developing the tools to understand it, and by 1975, only one part of the proof was left. That year my wife got a job in Los Angeles. I moved to UCLA. All in a short time, we got married, bought a car, bought a house in the Valley, and had to look for furniture. My mother came from Hong Kong for the wedding, and then her parents came—they all stayed under one roof and got into fights; it was complicated and crazy. I was fed up, so I locked myself in the study and thought about Calabi instead of the family problems, and I solved the whole thing. I went over the proof three times in detail, and I went to see Calabi in Pennsylvania. On a snowy Christmas Day, he came with me to visit mathematician Louis Nirenberg at New York University. We spent all day Christmas going over it, and I spent the next month writing up the proof for publication.

The implications were enormous. You were instantly famous.
It solved some major problems in algebraic geometry—about a dozen of them. A lot of people offered me jobs.

Some of the higher-dimensional spaces now called Calabi-Yau spaces proved fundamental to string theory. What is the connection?
When Einstein published his general theory of relativity in 1915, there was an immediate urge to unify the force of gravity with the other forces known at the time, with electricity and magnetism. Mathematicians thought they could do this with five dimensions, four of space and one of time. But then physicists found new particles and needed extra dimensions for the strong force and the weak force. When they worked it all out, they determined they could explain the universe with something they called string theory, which replaces the pointlike particles in particle physics with tiny, elongated vibrating strings.

To be consistent with quantum theory, the strings needed 10 dimensions in which to vibrate: three of space, one of time, and six dimensions of “compact space.” Dimensions in compact space are so small you can’t detect them through any conceivable experiment. They amount to pure structure. It so happens that Calabi-Yau spaces with six dimensions also have specific topological traits corresponding to the requirements of string theory. If these spaces truly modeled the six-dimensional space called for in string theory, they would help us deduce the geometry and, by extension, the physical laws of the universe.

Some cosmology theories imply the existence of other universes. Could each Calabi-Yau space describe a different set of laws in each of those universes?
Yes, each isolated universe can be modeled by a different Calabi-Yau space. But some of my colleagues have also studied a beautiful concept called mirror symmetry, in which each space has a mirror image with the same quantum field theory and the same physics.

How many Calabi-Yau spaces are there?
Using a computer program, Philip Candelas at the University of Texas at Austin found up to 10,000 Calabi-Yau spaces, with almost half of them mirror partners of each other. Each member of a pair is topologically distinct but still conforms to the other algebraically and gives rise to the same forces, the same particles, the same rules. The resulting geometric structure can be used to determine physical quantities associated with each space, like particle mass.

String theory is often described as a mathematically elegant way to explain all of physics. But how can we know that it describes the real universe?
We cannot know for sure, but the mathematics inspired by string theory solves some old, longtime questions. That part is rigorous and its truth cannot be challenged. If the structure of the math is deep, it will solve something in nature one way or another; it is difficult to imagine that such deep structure corresponds to nothing. Everything fundamental in math has ultimately had a meaning in the physical world.

If these spaces modeled the six-dimensional space called for in string theory, they would help us deduce the geometry and the physical laws of the universe.

You’ve long promoted mathematics in China. How have academic conditions changed there over the years?
I first went back in 1979, right after China opened up to outsiders. People were poor. Times were difficult. It was bedlam. I saw lots of people who were uneducated, and I felt I needed to help. By 1985 I’d taught about 15 Chinese grad students accepted to programs in the States. At first it was my adviser and mentor, Shiing-Shen Chern, who went to China and founded a mathematical institute there. I didn’t want to interfere with his work, but he was getting old and I started to go visit more often. In 1994 I was asked to give a speech. I said it’s great that China has an open policy; now we must start moving forward step by step, training young people to establish an intellectual base.

Eventually you founded four math institutes in China. How did that happen?
I met with Jiang Zemin, the future president, who wanted me to help build up math in China. After that, with the help of a donor, I built the Institute of Mathematical Sciences at the Chinese University of Hong Kong followed by three more institutes on the mainland—but China has always been run in a collaborative way, and other universities began demanding part of the funds. Still, the institutes have been able to carve out some independence, and today I go to China five or six times a year.

In the past decade, you’ve been critical of science and math in China. Why?
The university system is beset by academic politics, and it’s difficult for young people to move ahead. When China opened up, the people running things were in their fifties and sixties. The same people are still running things. Most do not follow modern developments because of their age. There are some brilliant young people, but it is a struggle for them to be recognized. Often that happens in China only after they are recognized by the outside world. I said, “Give some freedom to the young guys,” and people got upset.

You’ve commented that at the highest levels of accomplishment, Chinese mathematicians have far to go, and that the best of them have left the country. What are the prospects for math and science in China today?
The economy has been getting better and the government wants to invest more in science, so in the long run, I think the future is bright. Many more Chinese graduate students who come to study in the United States will be willing to return to China.

How does China’s relationship with the United States come into play?
I see a constructive relationship for academia. The U.S. gets human resources in the form of bright, young Chinese kids. The students learn well here, because the U.S. provides them with the freedom to research in their own way, and some of them will bring their knowledge back to China. But my goal is to train many more young mathematicians within China by providing an environment that allows them to focus on research and be recognized for their work.

You have criticized the academic system in the United States as well.
Young people are under too much pressure here. As a result, some of the proofs they publish are factually wrong. Before I published my proof of the Calabi conjecture, I checked it three times. Many young mathematicians don’t do that.

Most people don’t realize how political math can be: In 2006 The New Yorker accused you of taking credit from the Russian mathematician Grigory Perelman after he proved the famed Poincaré conjecture. What happened there?
In a process as intricate and daunting as proving the Poincaré conjecture, it is understandable that Perelman released his manuscript with several key steps merely sketched or outlined. One of my students tried to fill in some of the details, and I supported that. I also said that my friend Richard Hamilton, a geometer at Columbia University, laid much of the groundwork that Perelman ultimately relied on to construct his proof. For these things The New Yorker tried to accuse me of stealing credit, but that is ridiculous. What I think of as the Hamilton-Perelman proof of the Poincaré conjecture is a great triumph for mathematics, and I fully support the award of the Fields Medal to Perelman. Hamilton deserved the Fields Medal too, but he was ineligible because of the age restriction [you must be under 40]. To suggest that my position has ever been any different is completely untrue.

Physicists often talk about the beauty of math. What does that mean to you?
The first time I saw my wife, I thought she was charming—more than charming, shocking to me. I had great motivation to know her more. When I look at the Calabi conjecture, it shocks me too. It’s an elegant, simple construct and explains a great deal. It’s exciting when you go deeper and deeper into a complicated structure that you can spend most of a lifetime working on. It was shocking when it showed up in physics, and it’s beautiful whether it’s true or not.

Physics & Math / Subatomic Particles

2010-08-11T10:48:00.000-07:00

Back From the Future

A series of quantum experiments shows that measurements performed in the future can influence the present. Does that mean the universe has a destiny—and the laws of physics pull us inexorably toward our prewritten fate?

Jeff Tollaksen may well believe he was destined to be here at this point in time. We’re on a boat in the Atlantic, and it’s not a pleasant trip. The torrential rain obscures the otherwise majestic backdrop of the volcanic Azorean islands, and the choppy waters are causing the boat to lurch. The rough sea has little effect on Tollaksen, barely bringing color to his Nordic complexion. This is second nature to him; he grew up around boats. Everyone would agree that events in his past have prepared him for today’s excursion. But Tollaksen and his colleagues are investigating a far stranger possibility: It may be not only his past that has led him here today, but his future as well.

Tollaksen’s group is looking into the notion that time might flow backward, allowing the future to influence the past. By extension, the universe might have a destiny that reaches back and conspires with the past to bring the present into view. On a cosmic scale, this idea could help explain how life arose in the universe against tremendous odds. On a personal scale, it may make us question whether fate is pulling us forward and whether we have free will.

The boat trip has been organized as part of a conference sponsored by the Foundational Questions Institute to highlight some of the most controversial areas in physics. Tollaksen’s idea certainly meets that criterion. And yet, as crazy as it sounds, this notion of reverse causality is gaining ground. A succession of quantum experiments confirm its predictions—showing, bafflingly, that measurements performed in the future can influence results that happened before those measurements were ever made.

As the waves pound, it’s tough to decide what is more unsettling: the boat’s incessant rocking or the mounting evidence that the arrow of time—the flow that defines the essential narrative of our lives—may be not just an illusion but a lie...

Physics & Math / String Theory

2010-08-11T10:43:00.000-07:00

Is the Search for Immutable Laws of Nature a Wild-Goose Chase?

Four iconoclastic thinkers are challenging the assumption of scientists from Newton to Einstein: That there is one set of laws that perfectly describe the universe for all time.

The Coma cluster is about 320 million light years away and stretches 20 million light-years across. Many of its galaxies are featureless ellipticals. ("fuzz balls")

Image: NASA/ESA/Hubble Heritage Team(STSCI/AURA)

Also see the other articles in this issue's special Beyond Einstein section: Back From the Future and The Mystery of the Rocketing Particles That Shouldn't Exist.

If you want to build a star, start with the rules. That is the advice I give to my Ph.D. students at the University of Rochester. Using advanced supercomputers and programming, we simulate the complex interplay of gravity, radiation, and magnetic fields that constitutes the life of stars like the sun. Our goal is to better understand how stars are born, grow old, and die. Fundamentally, we start with the known laws of physics and take them wherever they lead us. The implicit understanding is that nature’s rules are eternal, unbreakable, and all-controlling. As Albert Einstein once said, learning to read the laws of physics is like reading the mind of God.

Such thinking has animated much of the enterprise of physics ever since Isaac Newton formulated his laws of universal gravitation in 1687: one set of laws for both the heavens and the earth. The idea took full root a century ago, when Einstein developed his general theory of relativity. If we work hard enough, he suggested, we will eventually find the elegant and simple rules that undergird the entire universe. Physicists have taken it as an article of faith that the bedrock laws are there to be discovered, if only we are clever enough in looking for them. The dogged pursuit of that ultimate truth has led to many great discoveries, but recently it has begun to seem like a promise unkept.

THE MAN WHO KILLED TIME

Andreas Albrecht did not start out trying to buck the system. His father had been a chemist, and Andreas first became fascinated with physics at the breakfast table. He remembers reading a high school textbook about atoms and stumbling upon an appendix on quantum theory. “I just loved the idea that there were deeper laws behind what we see,” he says. He went on to study physics at Cornell University and the University of Pennsylvania, with a particular interest in the early universe. He had no problem with physics as a quest for the immutable laws of nature—until he ran into a paradox that he calls the clock ambiguity.

In our ordinary experience, we tend to take the passage of time for granted. If we want to know how long we have been procrastinating at work, we glance up at the clock and realize an hour has gone by. In the brief succession of moments immediately following the Big Bang, however, there were no walls and no clocks to hang on them: The universe was anything but ordinary. Albrecht, now a professor of physics at the University of California at Davis, was trying to understand what was going on in the infant universe when it had existed for only a million-billion-billion-billionth of a second. To get a handle on what was happening, he needed a clock or something that could serve as one—some regularly occurring phenomenon, like water dripping from a faucet, the swinging of a pendulum, or the oscillations of a quartz crystal.

Albrecht was not doing a real experiment, of course. It would take a collider 1,200 light-years around to reproduce the conditions of these first moments of creation. Rather, what he was attempting was an extrapolation of what my students and I do when we calculate the motion of a star. We plug time into the equation and let the forces acting on the star unfold in whatever way the laws of physics say they should. Because Albrecht was interested in a time when the entire universe was compressed into a space the size of a grapefruit, he was forced to rely heavily on the equations of quantum mechanics, which rule in matters of the very small.

Those equations, though, become confusing when you are trying to tell a story that unfolds in a linear way, as Albrecht was attempting to do. The equations he had written out on paper described all possible futures of the early universe in terms of the probability that any one would actually happen. Without a clock, he realized, there was no unambiguous way to come up with a single, ticktock version of how events unfolded.

To get around this problem, Albrecht tried to manipulate the equations of quantum cosmology to isolate the dimension of time. That put him in the awkward position of having to undo the unification of time and space, a key achievement of Einstein’s general relativity. Peeling time from the equations appeared to make everything else unwind, and Albrecht found his model falling apart in his hands. Each time he tried to jury-rig a clock, the equations led him to a completely different kind of universe. In one universe, protons did not exist. In others, an action on one particle would have weird effects on neighboring particles. For instance, dropping a marble on the floor might cause an explosion on the scale of a supernova.

“I called it the clock ambiguity,” Albrecht says. “Basically, different choices of a clock lead to different kinds of physics. I got entirely different kinds of universes depending on the clock I chose.”

If we really want to understand the basic laws of the universe, we must look for explanations that do not dismiss the near-at-hand.

“I called it the clock ambiguity,” Albrecht says. “Basically, different choices of a clock lead to different kinds of physics. I got entirely different kinds of universes depending on the clock I chose.

This is not what Albrecht was expecting or hoping for. He had expected quantum cosmology to tell him exactly why the universe we live in looks the way it does. The discovery of the clock ambiguity seemed to block that path. It looked to him as if quantum cosmology would never predict the course of history through the universe because the laws determining that history could never be specified beforehand. A few physicists have challenged this radical idea, but many share their colleague’s befuddlement. “What I was finding seemed crazy,” he says. “It meant that the fundamental physical laws were not fundamental.”

Albrecht’s frustration was understandable. The clock ambiguity goes against not just the Newtonian belief in universal law, but the even more deeply held faith in law itself—in the idea that nature is guided by timeless rules that can be described in mathematical terms. “All is number,” said Pythagoras (he of the famous triangle theorem) 2,500 years ago. Plato believed in a realm of “ideal forms.” When Newton wrote a single equation that described the fall of apples and the motion of planets, he was already tapping into an ancient tradition.
That tradition was threatened early in the 20th century when physicists realized that general relativity and quantum mechanics—the two leading ways of describing the world—were in key ways incompatible with each another. The theories break down most spectacularly in the early universe, when everything was compressed into a small space. Suddenly the domains of the very small (quantum mechanics) and the very large (relativity) overlap. You need to use quantum mechanics to describe the physics, but those equations do not encompass gravity.

The quest to reconcile the quantum and relativistic worldviews has occupied physics for decades. At the moment, string theory seems to be the most promising way forward. In this vision, matter is made up of incredibly minuscule vibrating strings that exist in an 11-dimensional space-time.

With this formulation, many string theorists say, it may be possible to come up with one set of laws that describe the universe from the Big Bang onward. So far, though, no single version of string theory has yielded a consistent or complete answer.

With no established map, researchers must explore the terrain in bits and pieces. It was in exploring those interstitial domains that Albrecht stumbled on his clock ambiguity, which may have uncovered a fatal flaw: Even if string theory works, it is not clear how to use it to predict the kind of universe that would unfold from its rules. And that is far from the only objection being leveled against physicists’ leading effort to craft a master theory of reality.

THE SLAYERS OF STRING THEORY

Like Albrecht, and like just about every other physicist, Lee Smolin of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, started as a true believer in timeless law. In the 1980s he did some work on string theory. He also developed his own version of a multiverse in which every black hole spawns a new universe at its center. This introduced Darwinian natural selection to his idea of the cosmos: Whether or not a particular kind of universe proliferates depends on its fitness. The universes that are good at creating black holes thrive; it is no coincidence, he concluded, that we live in just such a universe.

As Smolin was developing this notion, he began to have misgivings about string theory, which has come to dominate the orthodoxy of theoretical physics. His 2006 book, The Trouble With Physics, was a withering attack on this orthodoxy. His big complaint about string theory is that it could lead almost anywhere. Rather than converging on a single set of laws—namely, the ones we can observe—it opens up a vast new array of untestable possibilities. This struck Smolin as a dangerous departure from experimentally falsifiable physics. If we really want to understand the basic laws of the universe, he argues, we must look for deeper explanations that do not dismiss the near-at-hand. And to do that, we might have to abandon our attachment to the idea of timeless laws.

Smolin takes particular issue with two tenets of present-day physics: the claim that time as we know it emerges from some deeper set of laws, like the quantum cosmological equations Albrecht works with, and the belief that our universe is just one of many.

The so-called multiverse theory of the universe arose, like string theory, as a way to explain away some uncomfortable mysteries in cosmology. The troubles began when scientists began to accept inflation, a theory developed by American physicist Alan Guth and his Soviet counterpart, Andrei Linde, in the early 1980s. Inflation holds that shortly after the Big Bang, a small shard of space-time underwent extremely rapid expansion, ultimately to become what we see around us: a universe of galaxies receding from one another. That theory opened up the possibility that other chunks of space-time went through their own inflation, creating a tremendous number of “pocket universes.”

Eventually this idea grew into what is now known as the multiverse theory, the notion that our observable universe is just one of perhaps an infinite number of cosmic domains, each with its own version of the laws of physics. In this view there is no need to explain why our universe has a particular set of physical laws, since somewhere out there exists a pocket universe for each possible set.
Smolin does not like some of the metaphysical overtones of today’s physics and cosmology, but he primarily rejects hidden dimensions in physics and multiverse approaches in cosmology for technical reasons. He sees problems, for example, in the details of quantum cosmology—the type of problems Albrecht has also encountered. These technical objections have given Smolin the uneasy feeling that there is something rotten at the core of physics.

That feeling began to take on more concrete form when he met Roberto Mangabeira Unger, a professor at Harvard Law School. Smolin had been invited to a conference (on art and critical theory) and was trying to decide whether to go when he saw Unger’s name on the guest list. Smolin had known of Unger’s work, and he was intrigued. A mutual friend put them in touch, and during several phone conversations about multiverses and the nature of time, they realized that they were soul mates in skepticism. A few years later, at Unger’s suggestion, Smolin organized a workshop at the Perimeter Institute called Evolving Laws and invited Unger to come and talk things over with the group. Now the two scholars are collaborating on a book, The Reality of Time and the Nature of Cosmological Laws.

As a nonscientist, Unger approaches the problem from the standpoint of philosophy. The problem with theories that include hidden dimensions and alternate universes, he says, is that they are not theories at all but allegories. There is no way to test them with any experiments or observations. String theory cannot be made to work in a world of only four dimensions. In response, string theorists posited the existence of seven extra dimensions that are hidden from us. Of course, no one has observed these extra dimensions of space, and worse, it is not clear that such an observation is possible. The equations of string theory predict that there are an unimaginable number of different possibilities for how those dimensions are configured—on the order of 10 to the 500th power. It would take more time than has so far elapsed since the Big Bang just to count them all.
The experimental basis for a multiverse theory is equally shaky. None of the other universes that crop up could ever be seen because the space between us and them would be expanding at faster-than-light speed.

Neither string theory nor the multiverse theory explain nature’s mysteries so much as explain them away, Unger concludes. “When we imagine our universe to be just one out of a multitude of possible worlds, we devalue this world, the one we see, the one we should be trying to explain,” he says. “The scientist should treasure the riddles he can’t solve, not explain them away at the outset.”
Unger and Smolin want to shift the emphasis in physics away from these possible worlds and back to the one real world—our world, which is saturated with time. They urge their colleagues to abandon the search for timeless truths like string theory.

More broadly, they argue that physics should refrain from spinning any theories that require the existence of things that could never be disproved, such as multiverses. And it should recognize that there is no ideal realm of perfect, timeless mathematical forms that embody the laws of physics. Time is inherent in the universe, and nothing exists outside of time. Smolin thinks that Albrecht’s clock ambiguity is a symptom of the larger problem with the current approach to physics.

Developing equations for a new kind of physics can come later, in Smolin and Unger’s view. For now they want to open a frank conversation about the rationale for looking at those equations in the first place. With only one time-saturated universe, physicists will have to revise the way they think about nature’s laws. If time is real, then everything in the universe is part of time and subject to it. The essence of time is change. What we call the laws of physics may also change with time. History will have to matter, even in this hardest of all sciences.

THE AGENT OF CHANGE

Theoretical biologist Stuart Kauffman has the advantage of never having been indoctrinated in the physicist’s way of looking at the world. As a theoretician, though, he is used to tackling big ideas. Kauffman, a MacArthur “genius award” winner, pioneered the application of complexity theory to the life sciences. He honed those ideas during a 10-year residency at the famed Santa Fe Institute in New Mexico and most recently as a professor of biochemistry and mathematics at the University of Vermont. In the last couple of years Kauffman has turned his attention to physics, and like Smolin he has come to believe that the laws that underpin the cosmos are far from the immutable things we thought they were. But he plunges in where even Smolin does not dare to tread.

Kauffman has no qualms about abandoning an idea that has dominated the sciences since the days of Galileo: that a set of physical laws is all that is needed to predict the unfolding of reality. The name for this idea is reductionism—the belief that the whole can be understood by the predictable behavior of the parts. It is the philosophical underpinning of the physicist’s conviction that timeless, eternal laws rule the universe from the bottom up. Understand quarks, the thinking goes, and everything else follows.

“The dream of reductionism,” Kauffman says, “is that when all is said and done, science will provide us with a linked set of laws that begin with particle physics and take us through life all the way to social systems.” Albrecht’s clock ambiguity and Smolin’s critiques of string theory expose chinks in the armor of reductionism. Kauffman has come to believe that reductionism can take us just so far. Only by moving beyond it will we be able to see the universe’s hidden creativity.

Physicists should not spin any theories that require the existence of things, such as multiverses, that cannot be disproved.

That creativity is essentially Darwinian. Biological evolution, in Kauffman’s view, offers a powerful model for how novelty, rather than timeless laws, could play an expanded role in cosmology and physics. If the laws of the biosphere have evolved over time, why can’t the laws of the universe? Just as evolution in biology favors change from the simple to the more complex, perhaps evolution has taken the universe from the relative simplicity of its early moments to the full glory of our modern universe in all its dazzling complexity.

The game of chess is another useful metaphor for understanding how physical laws might have changed. Chess has its rules, and the way most people play, those rules are fixed, much like the laws of physics are assumed to be. But chess was a different kind of game when it was first played in India in the sixth century. When Europeans adopted the game in the 15th century, they renamed the pieces and modified the rules to suit themselves. Eventually chess settled on the intricate and complex game that we know now. In a similar way, the laws of space-time may have started off one way and changed over time, until the universe settled on what we know now.

We do not see change happening now—perhaps because the universe’s laws have reached a point of stasis, or perhaps because they are changing very slowly. But the idea should, in theory, be testable. It should be possible to look back into the early universe and measure changes in physical laws. We may already have glimmers of such evidence. From measurements of the radiation given off by distant quasars, scientists have surmised that “alpha,” the physical constant that defines how tightly electrons are held to an atom’s nucleus, may have been slightly different in the early universe. The observations are tentative, partly because scientists have not been looking for signs of changing laws. At the very least, Kauffman suggests, we should be examining this possibility much more closely.

Extending evolutionary models to physics would mean exploring the notion that physical laws may have evolved for a time and then became fixed. Or they could still be evolving now. In biology there are constraints and rules that guide the behavior of the biosphere, rules that emerge in time and in the process set the stage for the next step in evolution. “In this way the biosphere builds the way it builds itself,” Kauffman says. “Perhaps the universe acts in a similar way, sorting through all different kinds of laws to give us what we see today.”

Physicists tend to recoil from Kauffman’s notion of a universe that emerges from countless arbitrary laws because the universe we see seems to be remarkably regular in structure and behavior. But the laws we see now may simply be the ones that allowed us to be here looking, Kauffman notes. “Remember, in evolution we only see the winners,” he says. “Everything else disappears.” His idea has a kinship with Smolin’s notion that universes can be spawned within other universes and evolve, with certain types of physical laws coming to dominate because they are more successful in producing a complex universe.
Kauffman’s reasoning may sound like the anthropic principle—a controversial idea in cosmology that the only possible laws of physics are the ones that allow us to be here to observe them—but the two ideas differ in a fundamental way.

The anthropic principle assumes a multitude of universes, each with its own immutable laws, and states that we lucked out by being in the one fine-tuned for life. Kauffman believes there is one universe, whose laws have evolved toward the complexity that allows for life. Rather than reasoning our way back to the beginning, we have to plumb the history of our universe to figure out how it evolved, step by step, into its present form.

From Kauffman’s perspective, everyone from Newton to Einstein to the latest practitioners of string theory may have all been barking up the wrong tree, and the long-sought theory of everything may be nothing more than wishful thinking. “The whole point,” he says, “is that there might not be eternal laws to reason backward to.”

Physics & Math / Light

2010-08-11T10:32:00.000-07:00

20 Things You Didn't Know About... Light

The first light in the universe, the light used to push spacecraft, and the light produced by kicking the head of a walrus.

iStockPhoto

1 God commanded, “Let there be light,” but it didn’t happen for nearly half a million years. That’s how long after the Big Bang the universe took to expand enough to allow photons (light particles) to travel freely.

2 Those photons are still running loose, detectable as the cosmic microwave background, a microwave glow from all parts of the sky.

3 Light moves along at full “light speed”—186,282.4 miles per second—only in a vacuum. In the dense matrix of a diamond, it slows to just 77,500 miles per second.

4 Diamonds are the Afghanistan of gemstones: Any entering photon quickly gets bogged down. It takes a lot of pinging back and forth in a thicket of carbon atoms to find an exit. This action is what gives diamonds their dazzling sparkle.

5 Eyeglasses can correct vision because light changes speed when it passes from air to a glass or plastic lens; this causes the rays to bend.

6 Plato fancied that we see by shooting light rays from our eyes.

7 The Greek philosopher was not completely wrong. Like all living things, humans are bioluminescent: We glow. We are brightest during the afternoon, around our lips and cheeks. The cause may be chemical reactions involving molecular fragments known as free radicals.

8 Bioluminescence is the largest source of light in the oceans; 90 percent of all creatures who live below about 1,500 feet are luminous.

9 World War II aviators used to spot ships by the bioluminescence in their wakes. In 1954 Jim Lovell (later the pilot of Apollo 13) used this trick to find his darkened aircraft carrier.

10 Incandescent bulbs convert only 10 percent of the energy they draw into light, which is why Europe will outlaw them by 2012. Most of the electricity turns into unwanted heat.

11 In the confined space of an Easy-Bake oven, a 100-watt bulb can create a temperature of 325 degrees Fahrenheit.

12 Light has no mass, but it does have momentum. Later this year the Planetary Society will launch LightSail-1, attempting to capture the pressure of sunlight the way a boat’s sail gathers the wind.

13 Laser beams bounced off mirrors left behind by Apollo astronauts show that the moon is moving 1.5 inches farther from Earth each year.

14 Visible light makes up less than one ten-billionth of the electromagnetic spectrum, which stretches from radio waves to gamma rays.

15 Goldfish can see infrared radiation that is invisible to us. Bees, birds, and lizards have eyes that pick up ultraviolet.

16 Photography means “writing with light.” English astronomer John Herschel, whose father discovered infrared, coined the term.

17 Shoot now: The “golden hour,” just after sunrise and before sunset, produces the prettiest shadows and colors for photographs.

18 Day and night are everywhere the same length on the vernal equinox, which occurs this year on March 20.

19 Auroras light up the night sky when solar wind particles excite atoms in the upper atmosphere. Oxygen mostly shines green; nitrogen contributes blue and red.

20 But to the Inuits, auroras are spirits of the dead kicking around the head of a walrus.

Physics & Math / Light

2010-08-11T08:35:00.000-07:00

4-D Microscopy Captures the Movements of Individual Atoms

New technique shows hearbeat-like "drumming" in atoms in graphite and may one day let us see reactions in living cells

Electron microscopes have given scientists unprecedented views of atomic and molecular structures. Now those vistas are evolving from still photographs into motion pictures. Physicist Ahmed Zewail of Caltech, who won the 1999 Nobel Prize in Chemistry for his use of lasers to study chemical reactions, is pioneering 4-D electron microscopy, which allows direct observation of atomic-scale changes in real time. His filmmaking technique relies on applying a short laser pulse to the subject, followed by an ultrafast pulse of electrons, which scatter off the material to produce an image for the microscope. A series of these images can be collected in rapid succession and viewed as a movie. The extremely brief electron pulses ensure that the image remains sharp, much like a short-exposure photograph of a speeding object.

In late 2008 Zewail and his colleagues announced that they had observed atomic motion in gold and in graphite (a sheet of carbon atoms). They discovered that atoms in heated graphite began to pulse in an unexpected synchronized “drumming” action, much like a heartbeat. Last summer the lab reported capturing changes in the pattern of bonding among graphite’s carbon atoms following intense compression of the sample. And in December they described watching nanotubes briefly glow after being hit with laser light. “You can see things evolve over time in a way that you never could with a snapshot,” says physicist and collaborator Brett Barwick. Eventually the group hopes to study chemical reactions in living cells.

Physics & Math / Subatomic Particles

2010-08-11T08:33:00.000-07:00

Ice Fishing For Neutrinos From the Middle of the Galaxy

An intrepid reporter braves Siberia’s frozen Lake Baikal in search of the fundamental particles that could answer some of the deepest questions in physics.

NASA

On one such winter’s day, I found myself on the lake near the town of Listvyanka, which is nestled in a crook of the shoreline. I was in an old van that was trying to head west, not along a coastal road—for there was none—but over the ice. The path, however, was blocked by a ridge. It looked like a tectonic fault: Two sections of the lake’s solid surface had slammed together and splintered, throwing up jagged chunks of ice.

The driver, a Russian with a weather-beaten face, peered from underneath his peaked cap, looking for a break in the ridge. When he spied a few feet of smooth ice, he got out and prodded it with a metal rod, only to shake his head as it crumbled: not thick enough to support the van. We kept driving south, farther and farther from shore, in what I was convinced was the wrong direction. The van shuddered and lurched, its tires crunching on patches of fresh snow and occasionally slithering on ice. The ridge continued as far as the eye could see. Suddenly we stopped. In front of us was a dangerous-looking expanse littered with enormous pieces of ice that rose from the lake’s frozen surface like giant shards of broken glass.

The driver seemed to be contemplating going around them to look for thick ice that would let us reach our destination, an underwater observatory operating in one of the deepest parts of the lake. But if he did that, we’d get even farther from the shore, and it would take just one punctured tire to strand us. The sun was little more than an hour from setting, and the temperature was falling. I couldn’t ask the driver if he had a radio or a phone to call for help, since he did not speak a word of English and the only Russian phrase I knew was do svidaniya. The last thing I wanted to say to him at this point was “Good-bye.”

Thankfully, he decided to turn around. We drove along until we came upon vehicle tracks that went over some ice covering the ridge. The driver swung the van westward and cleared the ridge, and soon we were racing across the lake at a speed that turned every frozen lump into a speed bump. The van’s front rose and fell sickeningly, rattling the tools strewn around on the front seat. I worried that the ice would give way and we would plunge into the frigid waters below. But it remained solid, and the van, despite its appearance, was in fine mechanical fettle, its shock absorbers holding firm. In the distance I spied a dark spot on the otherwise white expanse. As we approached, the spot grew to its full size, revealing itself as a three-foot-high Christmas tree. We still had 20 miles to cover, and the sun would soon disappear below the icy horizon. But now that we had found the Christmas tree, I knew we were fine.

I had first seen the tree two days earlier, with Nikolai (Kolja) Budnev, a physicist from Irkutsk State University, and Bertram Heinze, a German geologist. We were headed to the site of the Lake Baikal neutrino observatory, which lay deep beneath the ice. We had just driven onto the lake from the shore near Listvyanka when Heinze asked, “When does the ice start breaking?”

“Sometime in early March,” Budnev answered. My heart skipped a beat. It was already late March, and we were on the ice in an old, olive-green military jeep. “Sorry, sometime in early April,” Budnev corrected himself. Phew.

For more than two decades now, Russian and German physicists have camped on the frozen surface of Lake Baikal from February to April, installing and maintaining instruments to search for the elusive subatomic particles called neutrinos. Artificial eyes deep below the surface of the lake look for dim flashes of blue light caused by a rare collision between a neutrino and a molecule of water. I was told that human eyes would be able to see these flashes too—if our eyes were the size of watermelons. Indeed, each artificial eye is more than a foot in diameter, and the Baikal neutrino telescope, the first instrument of its kind in the world, has 228 eyes patiently watching for these messengers from outer space.

The telescope, which is located a few miles offshore, operates underwater all year round. Cables run from it to a shore station where data are collected and analyzed. It is a project on a shoestring budget. Without the luxury of expensive ships and remote-controlled submersibles, scientists wait for the winter ice to provide a stable platform for their cranes and winches. Each year they set up an ice camp, haul the telescope up from a depth of 0.7 mile, carry out routine maintenance, and lower it back into the water. And each year they race against time to complete their work before the sprigs of spring begin to brush away the Siberian winter and the lake’s frozen surface starts to crack.

What is it about the neutrino that makes scientists brave such conditions? Neutrinos—some of them dating back to right after the Big Bang—go through matter, traveling unscathed from the time they are created and carrying information in a way no other particle can. The universe is opaque to ultraenergetic photons, or gamma rays, which are absorbed by the matter and radiation that lie between their source and Earth. But neutrinos, produced by the same astrophysical processes that generate high-energy photons, barely interact with anything along the way. For instance, neutrinos stream out from the center of the sun as soon as they are produced, whereas a photon needs thousands of years to work its way out from the core to the sun’s brilliant surface.

Neutrinos therefore represent a unique window into an otherwise invisible universe, even offering clues about the missing mass called dark matter, whose presence can be inferred only by its gravitational influence on stars and galaxies. Theory suggests that over time the gravity wells created by Earth, the sun, and the Milky Way would have sucked in an enormous number of dark-matter particles. Wherever they gather in great concentrations, these particles should collide with one another, spewing out (among other things) neutrinos. It is as if a giant particle accelerator at our galaxy’s center were smashing dark-matter particles together, generating neutrinos and beaming them outward, some toward us.

That neutrinos play such a key role in advancing physics would have surprised scientists of a few generations ago. For them the neutrino was a figment of imagination, a theoretical necessity, but one that seemed impossible to detect because of its ethereal nature—a ghost of a particle. The story of the neutrino begins in the late 1920s. Physicists had been puzzling over something called radioactive beta decay, in which one kind of atom changes into another. For instance, carbon-14 has eight neutrons and six protons. During beta decay, one of these neutrons decays into a proton and emits an electron. The new nucleus, now with seven protons and seven neutrons, is transformed into nitrogen-14. But during this process, some energy seemed to go missing. It was the Austrian-born physicist and Nobel laureate Wolfgang Pauli who theorized that beta decay must emit an as yet undiscovered neutral particle. A few years later, the physicist Enrico Fermi jokingly named the particle a neutrino, Italian for “little neutral one,” and the name stuck.

For decades the neutrino remained a theoretical construct, a useful particle that helped physicists save their theories from embarrassment. Nobody had seen one. Nobody even knew how to find one—until Frederick Reines, a researcher working at Los Alamos during the 1950s, realized that a nuclear bomb would be a significant source of neutrinos. Reines and his colleague Clyde L. Cowan Jr. thought a nuclear power plant would also be a source. They calculated that a detector near a nuclear reactor would encounter nearly 10¹³ neutrinos per square centimeter per second. There was just one small problem: Since neutrinos are electrically neutral, they could be detected only if they directly hit the nucleus of an atom. Reines and Cowan would have to look for the signature of such a collision. And they found it.

By the 1960s, physicists following up on Reines’s work had started building neutrino detectors inside mines, using the ground as a natural shield from cosmic rays, which can swamp the signal from neutrinos. (Neutrinos can pass through the thick walls of the mines, but cosmic rays cannot.) In 1968 Raymond Davis and his colleagues from Brookhaven National Laboratory completed an experiment inside the Homestake Gold Mine in Lead, South Dakota. They used a tank containing 100,000 gallons of tetrachloroethylene, a common dry-cleaning agent. When a neutrino smashed into an atom of chlorine, the atom was transformed into one of radioactive argon. By counting the number of argon atoms that were produced, the physicists could calculate the flux of neutrinos coming from the sun.

Then in the early 1980s, researchers around the world built detectors using thousands of tons of water in underground tanks lined with photomultiplier tubes (PMTs). The PMTs look for light emitted when a neutrino smashes into water. Normally the neutrino will pass right through water without any interaction. But on the rare occasions when one does hit a nucleus of hydrogen or oxygen, the collision can spit out another subatomic particle, a muon. The charged muon interacts with the water electromagnetically, and because it is moving faster than the speed of light in water, it leaves in its wake a cone of blue light. This is called a Cherenkov cone, after the Russian physicist who first described the phenomenon.

It is analogous to the sonic boom caused by an aircraft traveling faster than the speed of sound.

It was another Russian researcher, Moisey Alexandrovich Markov, a “poet” of astroparticle physics, who suggested using natural bodies of water as neutrino detectors. Instead of building tanks of water inside mines, why not use lakes or even oceans? Just submerge long strings of photomultiplier tubes into the water and watch for the Cherenkov light left behind by neutrino-generated muons. The idea was enticing, but there were huge practical difficulties.

For one thing, without rock above to protect it, a detector would be exposed to cosmic rays that could drown out signals from neutrinos. More to the point, sunlight (not a problem inside mines) would blot out the Cherenkov emission.

The solution was to go deep, where the sun’s rays could not reach. The physicists realized that they could use the Earth itself as a shield. While many muons can make it through a mile of water, a similar stretch of rock will stop them cold. So a neutrino detector can sit deep underwater, near the lake bed, looking downward for muons created by neutrinos that come from below. None of the muons created by cosmic rays in the atmosphere on the other side of the Earth can penetrate the planet. Neutrinos, however, zip right through, and occasionally one will hit a nucleus in the water or in the lake bed itself.

Such a collision generates a muon, which then shoots up toward the surface. Catch an upward-moving muon and you have essentially detected a neutrino that came from the other side of the Earth. All that was needed was a suitable body of water. By the mid-1980s, the Russians realized that they had a massive tank of pure water in their own backyard: Lake Baikal.

On my first morning in Siberia, we drove across the lake toward the telescope. The frozen white lake spread for miles around us in every direction except to the northwest, where we were relatively close to shore. When we stopped to rest, men milled around the vehicles. The subzero temperature seemed to affect everyone differently. Some stood bareheaded; others had woolen caps rolled down to the tips of their ears. And then there was Ralf Wischnewski, in his enormous Russian fur cap that looked like a fluffed-up rabbit. A German neutrino physicist who had been working with the Russians at Lake Baikal for 20 years, Wischnewski was the reason I was here. I had met this ruddy-faced man six months earlier in London, outside the Tate Modern museum on the south bank of the Thames. We walked over to a Greek pub and discussed the Baikal expedition over chilled lager. It was he who had alerted me to the tradition of bringing spirits to share with the Russians during the winter evenings.

And here we were, except that it was still morning. The Russians had planned a welcome drink for Heinze. Kolja Budnev bounded out of our jeep with a bottle of vodka. Someone sliced a sausage into circular pieces. Bright yellow, blue, and red plastic cups were set up on the jeep’s expansive hood, and soon everyone had a vodka-filled cup in hand. Budnev dipped a finger into his and flicked a few drops onto the ice—an offering to the great spirit of Lake Baikal.

Soon we got back into our vehicles and headed toward the neutrino telescope, a contraption made of 11 strings of photomultiplier tubes, each with a large buoy at the top and a counterweight at the bottom. Smaller buoys attached to the strings float about 30 feet below the surface. All year round, a total of 228 PMTs watch for the Cherenkov cones. Each winter the team has to locate the telescope, the upper part of which drifts slightly over the course of the year. The team has two months to carry out any routine maintenance, put the strings back in the water, and get out before the ice cracks.

The term “experimental physics” took on new meaning in this biting cold, which at times dropped to –4 degrees Fahrenheit. Most of the physicists lived in 10-by-20-foot cabins, two to a cabin. Others slept in bunk beds at the shore station, amid workbenches cluttered with computers, electronics, wires, and cables. They worked long hours, from early in the morning to sometimes well past midnight. There was no running water, which meant no showers for two months. Toilets were wooden cabins with pits in the ground. The extreme cold helped control the stench, but it still wafted up when warm urine hit the pit. There was one luxury: the banya, a traditional Russian sauna. Naked men sat in an outbuilding, chucked water on hot stones to raise steam, and beat one another with leafy twigs and branches of birch.

A wicked wind kicked up one evening. It was time for everyone to leave the open ice and head back to the shore station. Once there, I gratefully sat down for a cup of tea, and a can of sweet, syrupy condensed milk materialized. One scientist looked at the can wistfully. Condensed milk had been his dream as a child growing up in the Siberian city of Tomsk. “They had this in Moscow,” he said, “but not in Tomsk."

Later that evening, I had to head back out and traverse part of the icy lake to reach the canteen for dinner. It wasn’t going to be easy. I had turned up on a frozen lake in the depths of a Siberian winter in “European summer shoes,” as Wischnewski put it, disbelief in his voice. On the lake I found walking nearly impossible, my smooth-soled shoes slipping the entire way. After a few days, I learned to find fresh snow for my shoes to grip, but that night, fear nearly paralyzed me. Fortunately, a jeep pulled up beside me, and Wischnewski, having noticed my plight, asked the driver—Igor Belolaptikov, a tall, mustached physicist from the Joint Institute of Nuclear Research in Dubna, near Moscow—to take me to the canteen. I sat with Belolaptikov at dinner and happily accepted a ride back to his small cabin for a chat about neutrinos.

“My business is the reconstruction of muons and neutrinos,” Belolaptikov said, laughing with a childlike joy as he made this disclosure. That reconstruction is tricky business. Hundreds of photomultiplier tubes watch for the flashes of Cherenkov light at the bottom of Lake Baikal. As a neutrino-induced muon races through the water, the light from its Cherenkov cone reaches different tubes at slightly different times. The skill lies in collecting all the information and sifting through it to reconstruct the path of the upward-moving muon. This can then be used to calculate the path of the original neutrino.

It is this ability to figure out where a neutrino comes from that differentiates a neutrino telescope from a mere neutrino detector. A telescope must identify the source of neutrinos in the sky, and the Lake Baikal instrument can do so with an angular resolution of about 2.5 degrees, meaning that it can distinguish neutrinos coming from points in the sky separated by a distance of five full moons. So far the Baikal telescope has seen only atmospheric neutrinos, secondary particles created by cosmic rays crashing into atoms in the air. Everyone here is waiting for the day when a high-energy neutrino from outer space makes its presence felt in their little corner of the lake.

Belolaptikov recalled his first neutrino—indeed, the Baikal detector’s first—from 1993. “It was great,” he said. “Here, you can see.” He leaned over his bunk bed and removed a piece of paper pinned to the wall above. It was a printout of the path of an upward muon, reconstructed from the detection of its Cherenkov cone: the first-ever neutrino seen by humans using a natural body of water as a detector. Belolaptikov and colleagues had done the reconstruction and put the Lake Baikal detector on the map.

The next two days slid by, but even in this short time a rhythm was established. A trip down to the lake in the mornings to get a bucketful of drinking water from a hole in the ice. Then back to the cabin for coffee with condensed milk and honey, making sure to plug the hole in the can of milk with paper to prevent “little animals” (as Wischnewski calls insects) from getting in. From my cabin I could see clear across the lake, and I had to remind myself that it had more water than America’s five Great Lakes put together and a surface area larger than Belgium. Eighty percent of Russia’s freshwater was here.

Even at great depths, the lake is well oxygenated, making it one of the most hospitable waters for life. Because of the voracious crustaceans that live at all depths, nothing dead or dying lasts more than a few days in this lake. If fishermen leave their catch in the nets too long, the crustaceans invade the fish through their mouths and gills, eating them from the inside out. These critters keep the lake free of dead matter, leaving it unimaginably clear, especially deep down. Murky waters would make watching for muons nearly impossible. “It is a very, very kind water,” Budnev said.

When the Russians turned on the Lake Baikal telescope in 1993, it was the only game in town. That has since changed. European physicists have started building similar detectors in the Mediterranean. And an American-European team went to the South Pole in the mid-1990s to construct the Antarctic Muon and Neutrino Detector Array (AMANDA) while laying the groundwork for IceCube, the largest-ever neutrino detector. Several German physicists who had worked at Lake Baikal joined the South Pole team. For a few years Wischnewski, too, split his time between Antarctica and Baikal before committing fully to Baikal. The South Pole detectors are looking for Cherenkov light emitted when muons hit the ice, and IceCube will be watching a cubic kilometer of ice for these ephemeral flashes.

Budnev flicked a few drops of vodka onto the ice—an offering to the great spirit of lake baikal.

The innovations at Baikal—including Belolaptikov’s work on reconstructing muons—inspired the early efforts in Antarctica. Although Antarctic ice is clearer than the waters of Lake Baikal, for now the water has a unique advantage. Light can travel more than 10 times as far in the lake as it can in the ice before it is scattered. Catch the photons before they scatter and you can tell exactly where they are coming from. Catch them after they have been scattered a few times and it gets hard to work out their original direction. This means that more PMTs are needed in the Antarctic ice to achieve the same end.

Grigory Domogatsky, spokesman for the Baikal project, made this point emphatically one evening while we were sitting at a table in his cabin next to a roaring fire. Despite a rasping smoker’s cough that could stop him in midsentence, he passionately argued that the world’s biggest neutrino detector should be built right here in Lake Baikal. The Americans and their European partners were spending $270 million on IceCube, and Domogatsky thought that a tenth of that would be enough to build a comparable detector in Siberia. Besides the advantage of needing far fewer photomultiplier tubes to detect high-energy neutrinos, Domogatsky pointed out that only a detector in the Northern Hemisphere could see neutrinos from the center of our galaxy.

“But you can see the center of the Milky Way from the South Pole,” I said, somewhat puzzled.

“Yes, but not neutrinos,” Domogatsky replied, with the gentle yet triumphant note of a teacher who has just made a telling point. Of course: Neutrino detectors that use natural bodies of water or ice can see only those neutrinos that come through the Earth, so they have to look upside down—and from that vantage, the center of the Milky Way never comes into view at the South Pole. Domogatsky further argued that Lake Baikal was the best body of water in which to build such a detector, for there are no deepwater currents, as there are in the Mediterranean. “Lake Baikal is like an aquarium,” he said.

Besides, scientists in the Mediterranean need ships to lower their strings into the sea and remote-controlled submersibles to wire them up, making the operation expensive. Here, winter ice makes retrieving and working on the detectors comparatively simple. But, Domogatsky sighed, convincing people to work in Siberia during the winter, when the alternative was the sun-soaked Mediterranean, was going to be hard.

Domogatsky’s heavily furrowed face showed the effects of 40 years of physics, many of them spent in this hostile place. Now he was looking to pass the baton. His team had just figured out that the telescope they had built so far could form a cell of a much, much larger telescope. Put next to each other, such cells could cover a cubic kilometer of water. All he needed was about $25 million, an order of magnitude less than the money being spent on the Mediterranean neutrino projects or at the South Pole.

The fire died. Outdoors the sun was setting. “I hope to help start this project,” Domogatsky said. “But the work should be performed by younger physicists.” We stepped outside. I took a picture of this grand old man of contemporary Russian physics against the backdrop of his beloved lake, then started walking back to the shore station. There was just one thing left to do. Wischnewski had suggested that my visit would be incomplete without my spending a night in one of the cabins at the ice camp. I had agreed. But then he casually mentioned that the ice heaves. Despite the lake’s thickly frozen surface, the water beneath is alive and kicking. Sometimes the entire sheet of ice below the camp can jerk and lurch. That night we drove to the ice camp and a graduate student named Alexey Kochanov ushered me into his cabin.

He told me not to worry; he found the sound of ice creaking beneath him relaxing. Obviously he had been here way too long—but then he explained. The creaking means that the ice cover is solid. It is the sound of ice moving in response to the motion of the water beneath. It is only when you don’t hear the creaking that you should worry. That’s when the cracks are so big that there is plenty of give in the ice and you should not be on the lake.

Suddenly the ice’s protestations were music to my ears. All night it groaned. When sounds came from far away, they were like muffled gunshots; when they were close, more like the crack of a whip. At five in the morning, the ice heaved. It was the only significant movement I had felt all night. I couldn’t go back to sleep, so I went outside.

It was still dark.The ice did not open to swallow me. Thin cracks crisscrossed the surface. You could tell that the new fissures had formed in the night because they had not yet been covered by snow. Scorpio’s tail was visible next to the moon, and overhead was Ursa Minor. On the far shore, embers of a forest fire glowed on the slopes of the Khamar-Daban range.

Somewhere deep below, a cone of bluish light raced upward through the cold water. A neutrino had traveled from some distant part of the universe, escaped collision with every bit of matter across trillions of miles, and gone through the center of the Earth, only to collide with a molecule of water in Lake Baikal and disappear in a flash of light.

Ultimate particle

Soon after verifying the existence of neutrinos, physicist Frederick Reines called these particles “the most tiny quantity of reality ever imagined by a human being.” Indeed, neutrinos have the smallest mass of any known particle—and yet they are incredibly important for understanding the world around us. Most neutrinos originated just fractions of a second after the Big Bang and so carry unique information about the infant universe. Others started their journey in the sun’s core or in powerful supernova explosions, revealing secrets about how stars shine and how they die.

Today astronomers rely primarily on visible light or other forms of electromagnetic radiation (like radio or X-rays) to study the distant universe; that is how the Hubble Space Telescope creates its beautiful images of galaxies and nebulas. In many ways, though, neutrinos make better cosmic messengers. Unlike light, which is easily absorbed as it moves through space, neutrinos rarely interact with anything. And unlike many other subatomic particles, neutrinos have no charge, so they travel in a straight line from their source without being deflected by the magnetic fields around stars.

Unfortunately, the inertness that makes neutrinos such a valuable source of information also makes them difficult to detect. Sixty billion solar neutrinos hit your thumbnail each second, and nearly every one of them passes through unscathed. As a result, neutrino observatories must scan vast quantities of water or some other good target to detect the exceedingly rare interaction between a neutrino and another particle.

With its 228 optical sensors, the observatory at Lake Baikal (diagrammed at left) looks for the debris created when a neutrino collides with a hydrogen or oxygen nucleus in the water: a shower of new particles that triggers a cone of bluish light. To exclude other particles that can produce a similar signal, scientists limit their search to showers cascading upward from below. This ensures that the original particle has passed through the Earth’s crust, a feat that only a neutrino can accomplish. andrew grant

Neutrino Spotting

Lake Baikal is not the only place where physicists are using elaborate detectors to study the most evasive particles in the universe. Here are other sites around the globe where the work goes on:

IceCube, Antarctica The latest and greatest neutrino observatory can be found in one of the most inhospitable locales on Earth. Scientists have buried beads of optical sensors under almost a mile of ice, where it is dark and clear enough to detect the blue light of a neutrino-induced particle shower even from hundreds of feet away.

Super-Kamiokande, Japan Within a mine more than half a mile underground, 13,000 detectors probe 50,000 tons of purified water for the blue-flash signature of neutrinos. In 1998 scientists at Super-Kamiokande found the first evidence that neutrinos have mass.

Sudbury Neutrino Observatory (SNO), Canada An engineering marvel, SNO is a transparent spherical chamber filled with liquid, ringed with sensitive light detectors and submerged in a water-filled mine. To improve sensitivity, researchers removed the heavy water that initially filled the chamber so that a petroleum-like liquid could be injected instead.

Main Injector

Neutrino Oscillation Search (MINOS), U.S. This underground observatory in Minnesota detects neutrinos beamed from Fermilab, 450 miles away near Chicago. Scientists at MINOS hope to learn more about the three neutrino “flavors”: electron, muon, and tau.

Oscillation Project with Emulsion-Tracking Apparatus (OPERA), Italy Here, a man-made beam of neutrinos (created near Geneva) hits 150,000 lead bricks separated by photosensitive plastic. a. g.

Mind & Brain / Memory, Emotions, & Decisions

2010-08-02T23:13:00.000-07:00

The 4 Stages of Fear, Attacked-by-a-Mountain-Lion Edition

Fight and flight are part of the brain's automatic system for dealing with life-threatening situations—but there's more to the story.

This excerpt is a sample from DISCOVER's special Brain issue, available only on newsstands through June 28.

In the throes of intense fear, we suddenly find ourselves operating in a different and unexpected way. The psychological tools that we normally use to navigate the world—reasoning and planning before we act—get progressively shut down. In the grip of the brain’s subconscious fear centers, we behave in ways that to our rational mind seem nonsensical or worse. We might respond automatically, with preprogrammed motor routines, or simply melt down. We lose control.

In this unfamiliar realm, it can seem like we’re in the grip of utter chaos. But although the preconscious fear centers of the brain are not capable of deliberation and reason, they do have their own logic, a simplified suite of responses keyed to the nature of the threat at hand. There is a structure to panic.

When the danger is far away, or at least not immediately imminent, the instinct is to freeze. When danger is approaching, the impulse is to run away. When escape is impossible, the response is to fight back. And when struggling is futile, the animal will become immobilized in the grip of fright. Although it doesn’t slide quite as smoothly off the tongue, a more accurate description than “fight or flight” would be “fight, freeze, flight, or fright”—or, for short, “the four fs.”

On a winter morning a few years back, a young woman named Sue Yellowtail went through them all in about 10 minutes.

FREEZE
The Mancos River rises in southwestern Colorado and flows through the Ute Mountains on its way to New Mexico, where it empties into the San Juan River three miles shy of the Four Corners intersection. Over millions of years, the river and its tributaries have carved a fanlike rill of dramatic canyons out of the ancient sediments of the Mesa Verde tablelands, a maze of vertiginous stone walls. The rugged, arid landscape of juniper forest proves a rich habitat for wildlife.

At 25, Sue Yellowtail was just a few years out of college, working for the Ute Indian tribe as a water quality specialist. Her job was to travel through remote areas of the Ute reservation, collecting samples from streams, creeks, and rivers. She spent her days crisscrossing remote backcountry, territory closed to visitors and rarely traveled even by locals. It’s the kind of place where, if you got in trouble, you were on your own.

On a clear, cold morning in late December, Yellowtail pulled her pickup over to the side of a little-used dirt double-track, a few yards from a simple truss bridge that spanned a creek. As she collected her gear, she heard a high-pitched scream. Probably a coyote killing a rabbit, she thought. She clambered down two steep embankments to the water’s edge. Wading to the far side of the creek, she stooped to stretch her tape measure the width of the flow. Just then she heard a rustling and looked up. At the top of the bank, not 30 feet away, stood a mountain lion. Tawny against the brown leaves of the riverbank brush, the animal was almost perfectly camouflaged. It stared down at her, motionless.

She stood stock-still.

Yellowtail had entered the first instinctual fear-response state, the condition of freezing known as attentive immobility. Even before she was aware of danger, subconscious regions of her brain were assessing the threat. Cued to the presence of a novel stimulus, the brain deployed the orienting reflex, a cousin of the startle reflex. Within milliseconds Yellowtail’s heart rate and breathing slowed. A brain region called the superior colliculus turned her head and slewed her eyes so that the densest part of the retina, the fovea, formed a detailed image of the cat. The visual information then flowed via the thalamus to the visual cortex and the amygdala, the key brain center for evaluating threat. Her pattern-recognition system found a match in the flow of sensory information. It recognized a pair of eyes, then the outline of a feline head. In less than half a second, before her cortex even had time to complete the match and recognize what she was seeing, her emotional circuitry had already assessed the situation: It was bad. Subconsciously, her brain also determined that the threat was not immediately pressing, and so a region called the ventral column of the periaqueductal gray (PAG) triggered attentive immobility. This is generally considered the first stage of the fear response, because it tends to occur when the threat is far away or not yet aware of the subject’s presence. The goal is to keep it that way.

When a person is frozen with fear, she is motionless but far from passive. With cortisol and adrenaline coursing through her body, she is primed for physical action, alert and intensely focused. The heart rate slows and blood pressure shoots up. Muscles tense and the pupils dilate. The body may tremble and the eyes bulge. If the fear is intense, the mind might be plunged into a state called hypervigilance, in which a person scans the environment rapidly and randomly, unable to think through the available options clearly.

Freezing is a posture of an animal that, while in danger, is primarily concerned with not getting in worse danger. Its plan is to do nothing, hope to avoid being detected, and see what happens. In the natural environment, it often proves an effective strategy. Young antelope can spend the better part of the day lying crouched and motionless in tall grass, their ears tucked and heads pressed against the ground. When accidentally disturbed by a passing lion or hyena, they bolt so unexpectedly that the predator may be too startled to chase after them.

Yellowtail’s was just the kind of situation that the behavior had evolved for: eluding a nearby predator. But freezing is essentially a temporary measure, a stopgap until the danger either goes away or becomes more pressing. It is a posture that asks the question: What next?

In the morning light of Mancos Canyon, human and animal stood confronting each other. Yellowtail had never seen a mountain lion in the wild before. Even as she fought to contain her fear, she marveled at the beauty of it. Its dark eyes looked back at her. Who knew what it was thinking behind that gaze. Was it curious, or hungry?

FLIGHT
As she locked eyes with it, the mountain lion moved forward, descending the shrubby bank and heading straight toward her.

Yellowtail waded back across the three-foot-deep stream, back toward her truck. To be prudent, she thought, she had better keep the width of the icy stream between herself and the animal. As she made it to the far side, the big cat quietly slipped into the water.

A former biology major, Yellowtail had studied predator behavior. She knew that if she began climbing the steep bank up toward her truck, she would expose her back, and she guessed that the moment of vulnerability might spur the mountain lion to attack. Instead she moved quickly down the edge of the stream and crossed again, feeling her way over the slick cobbles underfoot. Looking behind her, she expected to see the animal climb the far bank and disappear. But no: It followed her path along the water’s edge and again started swimming after her.

“I’m in trouble,” Yellowtail thought. “This is serious.” There was no doubting the mountain lion’s intention now. Trapped between the stream’s steep narrow banks, she couldn’t think of any way to keep the animal away. She was holding a microcassette recorder that she kept for taking notes, and she threw it at the cat. It just kept coming.

Yellowtail retreated down the riverbank, shouting and throwing rocks and chunks of ice. Somehow she managed to keep herself from running. She crossed the stream, worked farther down the bank, and crossed again. The cat followed, relentlessly closing the distance. Even as she felt panic building, Yellowtail had enough presence of mind to understand that what she was seeing was a classic example of predator behavior. Running would only stoke the animal’s attack instinct. She had to fight the urge.

The mountain lion was close now, near enough to pounce. As she splashed once more across the stream, the need to run surged over her like a shiver. She bolted, splashing madly through the shallow water, her legs churning over the rough, slippery cobbles of the streambed.

She ran with everything she had.

Yellowtail was now in the grip of the second phase of the fear response, flight. The sudden movement of the mountain lion had broken the spell of her attentive immobility and gotten her moving, but while the animal was still a fair distance off she had managed to keep her wits and suppress her fear centers’ automatic panic reaction. But as the cat drew closer, reason and willpower wavered as the fear grew stronger. At last they gave way altogether.

This process has been witnessed in the laboratory using brain-scan technology. Subjects inside an fMRI scanner were asked to play a Pacman-like game in which they were chased by a predator. When they were “caught,” they were given a series of mild electric shocks. While not exactly a realistic scenario, the game did elicit brain activity that paralleled Yellowtail’s. When the “predator” was far away, the subjects’ brains showed activity mostly in the prefrontal cortex. As it drew nearer, the area of greatest metabolism shifted to the periaqueductal gray, the region that codes for the behavioral patterns of the four fs.

Yellowtail made it only halfway across the creek before her rubber boot caught on a large rock. She stumbled, twisting, and went down hard into the water. At that instant the mountain lion pounced. Instinctively it lunged for Yellowtail’s neck, but as she fell it misjudged and dragged its teeth across her scalp. Under the weight of the big cat, Yellowtail slipped below the surface.

FRIGHT
Looking back on the moment from years after the fact, Yellowtail can still recall every detail with perfect clarity. She remembers feeling the warmth of the animal’s mouth on her head. She remembers looking up toward the surface through her sunglasses and thinking, with a perplexing degree of calm: “When your time’s up, your time’s up.”

Yellowtail had entered a third phase of the fear response, a state known as tonic immobility, or quiescence—in lay terms, playing possum. When an animal is seized by an attacker, the caudal ventrolateral region of the PAG generates a response that from the outside looks like total collapse. In the teeth of a full-blown sympathetic response, the parasympathetic system now swings into overdrive. The body, insensitive to pain, goes completely limp, often falling to the ground as awkwardly as rag doll, limbs splayed, head thrown back. Eyes closed, it trembles, defecates, and lies still. It looks, in a word, dead.

This is the position of utter despair, a final, last-ditch Hail Mary pass of a strategy. The one hope of quiescence is that the attacker, thinking its quarry has expired, will stop attacking. In Yellowtail’s case, the mountain lion appeared to react to her quiescence. Momentarily it released its grip. That was enough. In an instant she snapped out of her dissociative dream state and was sputtering back up to the air. Without reason, without thought, she started running again, flailing so hard that she ran right out of one of her hip boots.

And then—nothing. Whatever happened next, Yellowtail has no idea, because for the next 10 or 15 seconds she was overcome by a panic so blind that she blacked out. She had entered a realm of fear strong enough to shut down the memory-forming hippocampus and perhaps even consciousness itself.

The science behind that kind of amnesia remains murky, because such intense fear is a state as yet inaccessible to science. It is known that amnesia often accompanies extremely terrifying experiences. Chances are, an overdose of cortisol or a related substance, corticosterone, disrupts the hippocampus and inhibits the formation of new memories. This could be beneficial if it prevents later traumatic recollections.

Yellowtail will never know what terror her amnesia cloaked. At any rate, it did not last long. The next thing she remembers, she was on the riverbank on the far side of the stream. She had emerged from her blind panic oddly collected and remembers that time seemed to be moving in slow motion. She found herself lying on top of the mountain lion’s shoulders, her right arm thrust down its throat. She looked down and saw that the animal’s jaws were so huge that its canines were overlapped on either side of her arm.

FIGHT
“I’ve got to kill this animal or it’s going to kill me,” she thought. She happened to be wearing her fly fishing vest, from which hung a surgical-steel hemostat on a retractable string. In the strange clarity of total fear, she reasoned through a course of action. First she tried to wrap the string around the cat’s throat to strangle it but abandoned that plan when the cat thrashed, slashing its teeth dangerously close to her fingers. Before moving on to a new strategy, she paused and carefully inspected her left hand to make sure her fingers were all there. “Because if they weren’t, I was going to pick them up and put them in my pocket,” she says today. “It’s just crazy, the stuff that you think about.”

Her next thought was to stab it in the eye with the hemostat. “It just dawned on me: ‘I’ve got to get to the brain,’ so the eye was the best bet.” Without thinking twice, she clutched the hemostat and stabbed it over and over again into the cat’s left eye. The beast screamed a horrifying yowl.

She kept stabbing.Yellowtail had worked her way through to the last of the four fs, the fight, or aggressive defense, response. Like quiescence, aggressive defense is a tactic of last resort. People in the throes of full sympathetic overdrive are capable of totally uninhibited, blind violence. They will use any weapon and inflict any injury they can.

On the battlefield this impulse may be useful in the heat of fighting, but it can also lead to reckless, even mindless, behavior. And it is very difficult to shut off. Once the cortex has yielded control to the PAG, there is no getting it back until the shouting is over. The annals of military history are filled with tales of soldiers who kept slaughtering well after the battle was over.

In Yellowtail’s case, there was no need to restrain her impulse to violence. After a while, though, she sensed that the mountain lion had had enough. She kicked off her other hip boot and got ready to stand up. The cat let go of her arm. As soon as Yellowtail’s weight was off it, the cat stood up too. Yellowtail lunged at it, swearing and shouting, “Come on, you want some more?” The cat didn’t move. Yellowtail lunged again, to see if it seemed ready to attack her again. It just stood there, looking dazed. Yellowtail backed up about 20 feet, then turned and ran down the bank until she found a cattle path through the brush leading back up the embankment to the road, and then to her truck. “The whole time, I was worried that she was going to come through the brush and get me,” Yellowtail says, “but she never did.”

Yellowtail got into her truck and drove for help. Not until she was in an ambulance did her multiple cuts and bruises begin to throb with pain. Trackers returned to the site of the attack, located the mountain lion, and shot it. It turned out to be an aged female, underweight and weak from starvation. Yellowtail figures that if the cat had been a full-size male, she would be dead now. As it was, she came very close.

“It’s amazing what you can do when you’re under that kind of stress, in a life-or-death situation,” she says. “You do whatever it takes to keep yourself alive.”

This excerpt is a sample from DISCOVER's special Brain issue, available only on newsstands through June 28.

Mind & Brain / Senses

2010-08-02T23:03:00.000-07:00

The Brain The First Yardstick for Measuring Smells

Smell is a powerful and evocative sense yet also a deeply enigmatic one. So scientists have invented a more concrete way to pin down what our noses are telling us.

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Your nose is a paradox. In some ways the human sense of smell is astonishingly precise. For example, natural gas companies add a smelly molecule called n-butyl mercaptan to natural gas, which is odorless by itself, so that people can sniff gas leaks. All it takes is one n-butyl mercaptan molecule for every 10 billion molecules of methane to do the trick. To put this precision in perspective, imagine you are standing in front of two Olympic-size swimming pools. One of them contains a grand total of three drops of n-butyl mercaptan, and the other has none. Your nose could tell the difference.

But don’t get too smug, because in other ways your sense of smell is practically useless. To judge for yourself, find someone to help you run a simple experiment. Close your eyes while your partner raids your refrigerator and then holds different foods under your nose. Try to name each scent. If you’re like most people, you’ll bomb. In a number of studies, scientists have found that people tested on items in their own kitchens and garages give the wrong answer at least half the time. And as bad as we normally are at identifying smells, we can easily be fooled into doing worse.

If orange food coloring is added to cherry-flavored soda, for example, people are more likely to say that it smells like oranges.

Noam Sobel of the Weizmann Institute of Science in Israel and his colleagues have been puzzling over this paradox for the past several years. What has been missing in the science of smell, they argue, is a meaningful way to measure it—an olfactory yardstick. Now they have built one.

That it has taken so long for someone to come up with a yardstick for smell is something of a scandal. Scientists who study vision, for example, know that light with a wavelength of 620 nanometers will appear a particular shade of orange. They know with perfect certainty that orange is closer in wavelength (and perceived color) to yellow than it is to green. And they have used such objective measures about light and vision to learn a great deal about the biology that allows us to see. Scientists who study smell have had no equivalently objective way to judge, for example, whether the smell of roses is closer to spearmint or vanilla.

Part of the reason for this lack of an odor yardstick may have been the common belief that the human sense of smell is crude. Dogs and other mammals have a better sense of smell than we do, but their prowess doesn’t mean our noses are useless. In fact, as Sobel and his colleagues demonstrated in a 2007 experiment, humans can do a pretty good impression of a bloodhound.

Sobel and company went into an open field and set down 30 yards of twine scented with chocolate.

Then they brought together 32 people and gave them a mission: Follow the trail using nothing but your nose. The scientists put blindfolds on their subjects so they could not see the twine. Earmuffs blocked out sounds. Elbow pads, knee pads, and work gloves shielded them from tactile clues. Only their noses could provide them with information. The subjects got down on all fours about 10 feet from the start of the scent trail. Then they started to sniff.

Remarkably, most of the volunteers were able to find the twine. Even more remarkably, 21 of them were able to follow its scent from start to finish. Whenever they veered off course, they sniffed their way back. Not only did they track the scent impressively well, but they also improved with practice. The scientists arranged for some of the subjects to run the course for 45 minutes a day for three days; they cut their times and improved their accuracy.

When Sobel’s human bloodhounds put their noses to the ground, they drew in a gaseous cocktail of many different kinds of molecules—from the dirt, the grass, and anything else riding along in the air. Those molecules then latched onto olfactory receptors located on nerve endings in their nostrils. Only certain molecules, one theory holds, have the right shape to latch onto certain receptors. A given receptor can snag a number of different odor molecules, and a given odor molecule can latch onto several different receptors. Each nerve in a person’s nose builds all its receptors using just a single gene.

The olfactory neurons are the only ones in the central nervous system that are directly exposed to the air. When a receptor grabs a molecule, it causes an electric signal to travel the length of the neuron from the nasal lining to the smell-processing regions of the brain. There, the neuron converges with thousands of other neurons delivering their own signals. The brain does not just passively accept all these signals. If we learn how to tell two odors apart through one nostril, for example, we are able to tell them apart with the other nostril as well. The learning happens in the brain, not in the nose.

All this complex signal processing means that we can distinguish among thousands of different odor molecules. Sobel and his colleagues recently set out to pin down how that process works by determining the relationship between the structure of a molecule and the way it smells. The scientists began by building a database of 1,500 odor-producing molecules, cataloging 1,664 different traits—their size, the strength of the chemical bonds between their atoms, and so on.

Next, Sobel and his team looked for patterns in this dizzying cloud of data using a statistical technique known as principal component analysis, a method commonly employed to analyze large sets of data and tease out patterns. They searched for traits that consistently varied in lockstep with one another from molecule to molecule. A few key traits account for a lot of the variation in structure from one molecule to the next. For instance, the size of a molecule varies along with how tightly its atoms are packed. Sobel used these patterns to give each molecule in his database a single, simple score, like notches on a yardstick.

This yardstick, Sobel soon determined, is not just a statistical abstraction. It has a deep connection to how we smell the world. The researchers selected molecules from different intervals along the yardstick and had people sniff them. The farther apart the molecules were on the yardstick, the easier it was for people to tell them apart by their odor.

Sobel also got a striking result when he asked people to report how pleasant or unpleasant they judged various smells to be. Molecules ranked at one end of the yardstick stank to high heaven. At the other end, they were delightfully fragrant. The yardstick did such a good job of measuring the quality of odors that the scientists could use it to predict just how pleasant (or unpleasant) people would rate a new molecule.

To see whether this yardstick is universal, neurobiologist Nathalie Mandairon and her colleagues at the University of Lyon in France decided in 2008 to test Sobel’s odor-ranking system on mice. The researchers picked a set of odors and observed how long the animals sniffed them. The closer an odor was to the pleasant end of Sobel’s yardstick, the longer the mice spent smelling it. Sobel’s odor yardstick seems to have uncovered a fundamental truth about the nature of smell. When the noses of our distant ancestors evolved into sophisticated molecular detectors, he suggests, they started to process key traits to come up with a simple measurement—an internal yardstick. Our ancestors felt pleasure when they sensed smells that signified desirable things (a mother’s teat, a ripe piece of fruit) and moved toward them. They felt disgust or fear at odors that signified danger (rotting corpses or a predator’s feces) and moved away.

Our sense of smell is not a purely automatic system, however. An odor, Sobel argues, is more than the physical properties of a molecule; it is also the emotions these properties summon up. This is where learning comes in. We can learn to fear certain smells that signal danger, just as we learn to make associations with dangerous sights or sounds.

At a deeper level, our brains can revalue the same smell for different conditions. The smell of bacon may be alluring if you are hungry, but after a fourth helping, the same smell can start to get sickening. Scientists can see this revaluing take place within the brain as emotion-regulating regions change their activity. As a result, we can use pleasure and disgust as a guide not just for finding the right kinds of food but also for eating the right amount. These links to emotion and learning also help explain why a single whiff can summon up powerful memories.

Using Sobel’s yardstick, scientists may be able to start untangling the paradox of smell: why we are so good at distinguishing odors and so bad at naming them. Our brains appear to have evolved an elegant way to reduce the dizzying variety of molecules in our environment into a simple scale based on what matters most about scents—whether they smell good or bad. By giving different odor molecules a place on the yardstick, we can distinguish fine gradations among them. Although this method may be helpful and efficient, it doesn’t give us much information that we can use in putting a name to different smells. Imagine that someone showed you pictures of different types of fruit and had you name each one. Now imagine that the pictures zoom in on a single patch of color on each piece of fruit. You might be easily able to tell the difference between two shades of red without being able to say which belonged to a strawberry and which to a raspberry.

This analogy, Sobel argues, actually understates the difficulty we have in naming smells. He draws a distinction between odor molecules and “odor objects.” There is a visual object we call “banana” that encompasses our experience of seeing a banana. There is also an odor object version of “banana,” a combination of the inherent pleasantness of the molecules released by the fruit (as measured by Sobel’s yardstick) and our subjective mental state when we encounter them. Emotions are notoriously hard to put into words, and the emotions wrapped up in odors make the problem of identification even harder.

Supreme Court judge Potter Stewart famously wrote in 1964 that pornography was hard to define but that he knew it when he saw it. In the same way, we may not be able to put a name to an odor, but we sure know when something stinks.

Mind & Brain / Memory, Emotions, & Decisions

2010-08-02T22:58:00.000-07:00

The 4 Stages of Fear, Attacked-by-a-Mountain-Lion Edition

Fight and flight are part of the brain's automatic system for dealing with life-threatening situations—but there's more to the story.

This excerpt is a sample from DISCOVER's special Brain issue, available only on newsstands through June 28.

In the grip of the brain’s subconscious fear centers, we behave in ways that to our rational mind seem nonsensical or worse. We might respond automatically, with preprogrammed motor routines, or simply melt down. We lose control.

On a winter morning a few years back, a young woman named Sue Yellowtail went through them all in about 10 minutes.

She stood stock-still.

Who knew what it was thinking behind that gaze. Was it curious, or hungry ?

FLIGHT
As she locked eyes with it, the mountain lion moved forward, descending the shrubby bank and heading straight toward her.

She ran with everything she had.

This process has been witnessed in the laboratory using brain-scan technology.

Subjects inside an fMRI scanner were asked to play a Pacman-like game in which they were chased by a predator. When they were “caught,” they were given a series of mild electric shocks. While not exactly a realistic scenario, the game did elicit brain activity that paralleled Yellowtail’s. When the “predator” was far away, the subjects’ brains showed activity mostly in the prefrontal cortex. As it drew nearer, the area of greatest metabolism shifted to the periaqueductal gray, the region that codes for the behavioral patterns of the four fs.

FIGHT

“I’ve got to kill this animal or it’s going to kill me,” she thought. She happened to be wearing her fly fishing vest, from which hung a surgical-steel hemostat on a retractable string. In the strange clarity of total fear, she reasoned through a course of action. First she tried to wrap the string around the cat’s throat to strangle it but abandoned that plan when the cat thrashed, slashing its teeth dangerously close to her fingers. Before moving on to a new strategy, she paused and carefully inspected her left hand to make sure her fingers were all there. “Because if they weren’t, I was going to pick them up and put them in my pocket,” she says today. “It’s just crazy, the stuff that you think about.”

Yellowtail had worked her way through to the last of the four fs, the fight, or aggressive defense, response. Like quiescence, aggressive defense is a tactic of last resort. People in the throes of full sympathetic overdrive are capable of totally uninhibited, blind violence. They will use any weapon and inflict any injury they can. On the battlefield this impulse may be useful in the heat of fighting, but it can also lead to reckless, even mindless, behavior. And it is very difficult to shut off. Once the cortex has yielded control to the PAG, there is no getting it back until the shouting is over. The annals of military history are filled with tales of soldiers who kept slaughtering well after the battle was over.

“It’s amazing what you can do when you’re under that kind of stress, in a life-or-death situation,” she says. “You do whatever it takes to keep yourself alive.”

This excerpt is a sample from DISCOVER's special Brain issue, available only on newsstands through June 28.

Mind & Brain / Depression & Happiness

2010-08-02T22:47:00.000-07:00

Psychologist Says Antidepressants Are Just Fancy Placebos

Irving Kirsh aims to "explode the myth" of Prozac and its ilk, arguing that there's little evidence that they actually work for most patients.

his article is a sample from DISCOVER's special Brain issue, available only on newsstands through June 28.

Depression is a chemical imbalance, most people think. Researchers, drug manufacturers, and even the Food and Drug Administration assert that antidepressants work by “normalizing” levels of brain neurotransmitters—chemical messengers such as serotonin.

And yet hard science supporting this idea is quite poor, says Irving Kirsch, professor of psychology at the University of Hull in the U.K. An expert on the placebo effect, Kirsch has unearthed evidence that antidepressants do not correct brain chemistry gone awry. More important, the drugs are not much more effective against depression than are sugar pills, he says.

To support these controversial claims, Kirsch conducted a meta-analysis, digging up data from unpublished clinical trials. When all the evidence is weighed together, Prozac, Paxil, and other such popular pills seem to be at best weakly effective against depression—an argument Kirsch presses in his new book, The Emperor’s New Drugs. Some other research backs up his claims. A study Journal of the American Medical Association found that psychoactive drugs are no better than placebos for people suffering from mild to moderate depression. published this winter in the

Where did the idea of depression as a chemical imbalance come from? 
The initial two drugs, imipramine and iproniazid, that were discovered and promoted as effective antidepressants both seemed to increase the amount of serotonin in the brain. It was discovered afterward that one of them seemed to block the reabsorption of serotonin, leaving it to linger longer at cell receptors, and the other blocked the destruction of the serotonin neurotransmitters in the synapses in the brain.

Then there was an observational finding that a drug called reserpine produced depression. Reserpine decreased the available serotonin, so that seemed to fit together nicely with the other discovery. But there was only one clinical trial to compare reserpine to a placebo with depressed patients. In that trial the scientists were actually testing reserpine for antidepressant effects, and they found it to decrease depression. So this drug, which decreases serotonin, also decreased depression.

The theory thrived over the years because of the apparent success of antidepressants: If altering brain chemistry cures depression, the reasoning went, depression must be caused by faulty brain chemistry.

The current antidepressant drugs have a variety of chemical structures, but they all work equally well. What does that tell you? 
These different antidepressants do things that, in some cases, are incompatible. Selective serotonin reuptake inhibitors (SSRIs) such as Prozac increase the amount of serotonin that’s available to be used by the brain. Then you have the norepinephrine-dopamine reuptake inhibitors (NDRIs) such as Wellbutrin that are not supposed to affect serotonin at all. And most recently you have the selective serotonin reuptake enhancers (SSREs) such as Stablon, which enhance the reuptake of serotonin rather than inhibit it.

These drugs all have different and in some cases opposite effects on brain chemistry, and yet they all show exactly the same response rate. It’s uncanny! That suggests it’s really the placebo effect that is helping the patients. In practice, all the different antidepressants have the same response rate. In a population of depressed people, they all work equally well. If they were actually correcting chemical imbalances, it would mean that the exact same number of people who are depressed have each kind of chemical imbalance: The proportion of people who have too much serotonin is exactly the same as the fraction who don’t have enough norepinephrine. The odds against that are astronomical.

Nevertheless, many studies suggest that  antidepressant drugs do have an edge over  placebos. How do you account for that? 
When you do a clinical trial, you tell people that they might get a placebo. When researchers give placebos, what they are trying to control for is the expectancy of improvement, which can produce a sense of hope. You also tell them that the active drug causes side effects and what those side effects are. If I were a patient in one of these trials, I’d be wondering, well, what am I getting? And if I’ve started noticing side effects, and especially the side effects that had been described to me, I would no longer be “blind.” I would think, “Oh, my mouth is dry, that’s great—that means I got the active drug.” That would further increase my expectation that the drug was going to help. In the few studies where that has been assessed, about  80 percent of patients do figure out what group they are in. So it’s actually the side effects, the undesirable chemical effects of these drugs, that cause subjects on antidepressants to do a little better than those on the placebo.

How could hope alone—the hope you get from taking a pill—alleviate depression? 
One of the most popular theories of emotion in psychology is the cognitive theory pioneered by Aaron Beck, the University of Pennsylvania professor emeritus who created cognitive therapy for depression. What he liked to talk about—and he had nice research to back it up—is that the emotions that people feel depend in part on what they’re thinking about the future. If you’re feeling hope—“Things are not good now, but I know they’re going to get better because I’ve been given something that people say will reverse the problem”—that in itself will induce a more positive mood.

Doesn’t that suggest that it is actually a good  idea to treat depression with placebos? 
No, because you’d have to lie to people, and I don’t think patients should be lied to. You destroy the placebo effect if you destroy people’s faith and trust in their doctors. It’s unethical and ultimately self-defeating. Also, there are alternatives that are better than placebos and not deceptive at all. Those alternatives, first and foremost, include psychotherapy, and especially cognitive-behavioral therapy, which has a large research base showing it to be not only more effective than placebos, but also in the long run much more effective than any of the antidepressant drugs.

Doesn’t the chemical imbalance theory  take away some of the debilitating social  stigma of depression?
“You’re sick; you have this diseased brain”—that seems stigmatizing to me. “You’re in a lousy situation” seems less stigmatizing. In treatment, many depressed people talk about economic problems. Sometimes depression might be a normal response to an abnormal situation.

What advice do you have for someone who is taking antidepressants now? 
Don’t just stop on your own. If you quit antidepressants cold turkey, the withdrawal symptoms can be quite severe. If you’re taking an antidepressant, it’s working for you, you’re not unhappy with the side effects, and you’re being monitored regularly by a doctor, keep taking them. As a patient, you’re not concerned with why something works, but whether it works. On the other hand, if you’re on antidepressants and they’re not working, or if the side effects are making you feel bad, then discuss with your physician the possibility of tapering off and going into psychotherapy, especially short-term cognitive-behavioral therapy. Or explore physical exercise programs, because they’ve also been found to be effective in combating depression.

This article is a sample from DISCOVER's special Brain issue, available only on newsstands through June 28.

Mind & Brain / Senses

2010-08-02T22:39:00.000-07:00

Your Hidden Sense of Touch

Nerve cells in our sweat glands and blood vessels may constitute an important, previously unrecognized source of sensory info.

You are more sensitive than you realize, neuroscientist Frank Rice of Albany Medical College has discovered. His study of patients whose skin lacks normal nerve fibers has revealed a previously unknown source of perception that contributes to the familiar ability to feel texture, temperature, pressure, and pain: the nerve endings surrounding blood vessels and sweat glands in human skin.
Rice, neurologist David Bowsher of the University of Liverpool, and their colleagues were studying two patients who were unable to feel pain, yet somehow retained a rudimentary ability to distinguish hot from cold and rough from smooth. On examining skin samples and other biopsies, the researchers found that all of the usual nerve endings associated with skin sensation were missing. The only possible sources of feeling were the nerves of the blood vessels and glands.
Scientists knew that such nerves existed but thought they simply regulated blood flow and perspiration. The evidence from the patients examined by Rice and Bowsher suggests that the nerve cells also act as an additional sensory system. “It is very likely that these nerve endings contribute to conscious perception in all of us,” Rice says. If he is correct, problems with this previously unknown system could contribute to poorly understood pain conditions, such as migraines and fibromyalgia. Rice and a group of collaborators are gearing up to investigate this potential link by searching for malformations of the blood-vessel nerves that could affect their function.