The Nobel Prize may be the most prestigious award in science, but the new Fundamental Physics Prize is by far the world's most lucrative scientific award, instantly making its first winners this August multimillionaires. But the size of the payout isn’t the only difference between the two prizes: Unlike the Nobel, the Fundamental Physics Prize can be awarded for research that has not yet been verified by experiment. Is it foolhardy to extol work later findings might prove wrong?
The Fundamental Physics Prize is the brainchild of Russian tycoon Yuri Milner, a one-time physics graduate student turned billionaire investor in internet companies such as Facebook, Twitter, Groupon and Zynga. Milner personally selected the inaugural class of nine winners, each of whom received $3 million, roughly three times as much as a Nobel grant.
Although some of the work recognized by this year’s awards has been experimentally verified (for example, the principles of quantum computers are firmly grounded in experiment), others, like string theory, which compares elementary particles to loops of vibrating string, and the holographic principle, which suggests that our three-dimensional reality is a projection of information stored on a far-off two-dimensional surface, live further out on a theoretical limb.
Ideas like these may not get experimental verification any time soon, either. Take string theory. As Fundamental Physics Prize winner Ashoke Sen, a string theorist at the Harish-Chandra Research Institute in India, explains, "Unfortunately the strings are so small that the energy required for seeing these structures is huge, much larger that what we have achieved in the present day accelerators.”
Yet many physicists (including, unsurprisingly, some Milner honorees) argue that unverified ideas, and even ideas that are unverifiable with today’s technology, are prizeworthy—even if future tests should prove them wrong.
"Many of the most important developments in physics involve subjects for which there is little hope of experimental verification anytime soon," argued cosmologist Alan Guth at the Massachusetts Institute of Technology, one of the winners of the Milner prize. Guth invented the theory of cosmological inflation, which suggests our universe expanded staggeringly just a sliver of a second after it was born. This rapid expansion that would help explain, among other things, why the cosmos is so extraordinarily uniform on large scales, with only very tiny variations in the distribution of matter and energy.
In fact, two of the greatest theoretical breakthroughs of the 20th century—Albert Einstein's theories of special and general relativity—were never honored by a Nobel Prize, said Stanford cosmologist Andrei Linde, another winner of the Fundamental Physics Prize. These ideas changed the world by showing that mass and energy are equivalent and that gravity is a result of mass curving the fabric of space and time. Although Einstein was awarded the Nobel Prize in 1921, he was given the prize not for relativity but for describing how light was composed of discrete packets of energy now called photons, because the Nobel committee felt that relativity had not at the time been verified.
"More recently, we have the case of the Higgs particle, with almost 50 years between the theoretical advance and the experimental verification," Guth added. "If this kind of theoretical work is not respected, then progress in fundamental physics would suffer tremendously."
Even if theoretical research does lead to a dead end, it can help inform what ultimately prove to be successful ideas, said theoretical physicist Nima Arkani-Hamed at the Institute for Advanced Study in Princeton, New Jersey, a winner of the new prize who has investigated ideas such as extra dimensions of reality and new theories regarding the Higgs particle.
"One of the great developments in physics in the 20th century was the Standard Model of particle physics, which explains particles such as electrons and quarks and gluons," Arkani-Hamed said. "But before the Standard Model was known to work, there were people exploring lots of other theoretical possibilities that might be consistent with our world. Even if they didn't pan out, collecting ideas that have a chance of working may help lead to developments like the Standard Model."
“Wrong” ideas can advance science in other ways, too. "We should keep in mind that Newtonian mechanics was ultimately found to be incorrect, but it nonetheless was a momentous force in driving science forward," Guth said. "Today there are many developments in physics that are recognized by the community as being important, even though we cannot prove that they are correct."
As to how the prize-winners might spend their gains, other than paying taxes and mortgages, they often said they were still in shock over the award. "I continue to remind my students that they should not go into physics for the money," Guth said.
Editor's picks for further reading
Fundamental Physics Prize
The official web site of the Fundamental Physics Prize Foundation.
Nature: Theoretical physicists win massive awards
Geoff Brumfield talks with winners—and critics—of the new prize.
New York Times: 9 Scientists Receive a New Physics Prize
Kenneth Chang reports on the announcement of the Fundamental Physics Prize winners.
Did the universe have a beginning? What, if anything, came before the Big Bang?
Today, we see galaxies rushing away from us in every direction, suggesting that, if you could press the rewind button on the entire universe, the whole thing would screech to a halt at a moment about 13.7 billion years in the past, when the entire cosmos was apparently compressed into a singularity—an infinitely small, dense point.
“How does the universe begin from such a state?” asks Alexander Vilenkin, a theoretical physicist at Tufts University. Indeed, the laws of physics as we know them break down around singularities, so physicists have devised a number of ways to sidestep the singularity problem.
One possibility is that the universe is cyclic: Every Big Bang expansion is followed by a contraction, ending in a “Big Crunch” from which a new Big Bang emerges, and so on and so on in an infinite series that extends eternally into the past and future. The idea was first proposed centuries ago, but received a fresh take from the physicists Paul Steinhardt and Neil Turok in 2002. There is a problem with this elegant idea, though: the second law of thermodynamics, which states that the total amount of disorder or entropy in a system increases over time—the party-pooper law that prevents the existence of perpetual motion machines. A universe that experienced repeated cycles of expansion and contraction would have get more and more disordered over time until it began completely disordered, something we do not see in our universe. One way to avoid such increasing entropy would be for the volume of the cosmos to increase with each cycle. However, if one ran this scenario backward in time, one would still be forced to conclude the universe began with a singularity.
If our Big Bang wasn't preceded by a Big Crunch, perhaps our universe instead existed as kind of dormant seed—“like a cosmic egg,” says Vilenkin—before suddenly breaking open in the Big Bang. But here, too, there is a problem: In the uncertain world of quantum physics, the “egg” couldn’t stay stable forever. It would have expanded and contracted and could have even collapsed into nothingness. "This means it couldn't have existed forever in the past," Vilenkin said, findings he and his student Audrey Mithani detailed in the January issue of the Journal of Cosmology and Astroparticle Physics.
But the same quantum fluctuations that could have cracked the cosmic egg could be birthing new universes as you read this, says Vilenkin. This idea, called eternal inflation, suggests that our universe is just one bubble within a larger multiverse which is perpetually popping out new bubble universes. Although inflation may have stopped in bubbles such as ours, new instances of inflation occur in the multiverse forever into the future, keeping the idea of eternal inflation true to its name. But what about the past? If one assumes that the multiverse is expanding and not contracting, then it had to have expanded from a certain point in time, Vilenkin explains. Even eternal inflation must have a beginning.
Even if the universe did have a beginning, it likely occurred so very far in the past that the cosmos might as well appear as if began an eternity ago, says theoretical physicist Leonard Susskind at Stanford University in California."We're talking about the beginning potentially occurring at time scales vastly, vastly larger than the age of our universe, longer than any time that you can name," Susskind explains. "Statistically, given this extremely long amount of time, we probably occurred very, very late in history, making us very far from the beginning, so most of the information about the beginning would be lost to us. I think we're really in the dark about what it would've been like."
Still, Vilenkin is hopeful that it might be possible to observe evidence of the beginning. In some versions of the eternal inflation model, bubbles occasionally collide, which we might detect as distortions in the cosmic microwave background radiation that pervades all of space. If there are a number of collisions between bubbles that are clumped together in one direction more than another, "that might be linked with the beginning of the universe," he said.
Vilenkin has no problem with the universe having a beginning. "I think it's possible for the universe to spontaneously appear from nothing in a natural way," he said. The key there lies again in quantum physics—even nothingness fluctuates, a fact seen with so-called virtual particles that scientists have seen pop in and out of existence, and the birth of the universe may have occurred in a similar manner.
"Of course, maybe someone will come up with another model of an eternal universe, and we'll have to start thinking about it all over again," Vilenkin said.
Editor's picks for further reading
arXiv: Eternal Inflation and Its Implications
Alan Guth, the physicist who originated the inflation hypothesis, summarizes the arguments for eternal inflation.
Edge: The Cyclic Universe
Neil Turok on the past and present of the cyclic universe model.
FQXi: Did the Universe Have a Beginning?
In this podcast, Alexander Vilenkin asks whether the universe could have existed forever into the past.
Last week, we asked whether astronomers could be wrong about dark matter, the invisible stuff that seems to help hold galaxies together. Is it possible that dark matter doesn’t really exist?
This week, we’ll investigate whether there are viable alternatives to the idea of dark energy, the mysterious stuff that astrophysicists believe is pushing our universe apart.
In every direction we look, galaxies are hurtling away from us. That isn’t surprising in itself—after all, the Big Bang sent space and everything in it flying apart. One would expect that the gravitational pull of all the “stuff” in the cosmos would gradually slow down this expansion, bringing it to a dead stop or even collapsing everything back together in a "Big Crunch." Yet instead, astronomers see that the galaxies in our universe are rushing apart faster and faster.
What could be causing this acceleration? Physicists call it dark energy, and it could make up more than 70 percent of the cosmos. But so much remains unknown about dark energy that some scientists are asking whether it exists at all.
What if, instead of a mysterious unseen energy, "there is something wrong with gravity?" asks Sean Carroll, a theoretical physicist at the California Institute of Technology.
Einstein's theory of general relativity represents gravity as the curvature of space and time. Perhaps this idea "is still right, but we're not solving the equations correctly," suggests Carroll. "We're used to thinking of the universe expanding perfectly smoothly, and we know it isn't, and maybe these deviations are important." If we accounted for how the universe is clumpy instead of smooth, it might turn out that the gravitational pull of clusters of galaxies and other large agglomerations of matter alter spacetime more than previously appreciated. Distant objects would thus appear to be farther away than they actually are, leading to the false conclusion that the universe's expansion is accelerating.
The problem with this kind of model, Carroll says, is that while it suggests that these clumped-up astronomical bodies might distort our view of the universe more than suspected, gravity still remains the weakest of the known fundamental forces of nature. Also, these astronomical clumps would evolve in size and gravitational strength over time. In contrast, the mysteries that dark energy was invoked to solve require something with a lot of energy that changes less over time.
Another approach is to modify the laws of gravity to do away with dark energy. This tack suggests that "the laws of gravity as we know them work better on relatively small scales such as our solar system,” says Carroll, but perhaps they need “tweaks” to work on cosmic scales. Carroll and other theorists have developed alternative descriptions of gravity that could explain why the universe evolved as it did. One set of scenarios suggests that the strength of gravity increases over time and has different values depending on the distances involved. But critics argue that, to avoid contradicting well-established features of general relativity, these models are unacceptably contrived.
Another family of alternative gravity models analyzes how gravity behaves if there are extra dimensions of reality, as suggested by string theory. But this approach has problems of its own: It leads to empty space "decaying" into particles in potentially detectable ways, Carroll says.
To avoid modifying gravity, some theorists have suggested that our galaxy and its neighborhood might lie within a giant void, an emptier-than-average region of space roughly 8 billion light years across. With so little matter to slow down its expansion, the void would expand faster than the rest of the universe. If we lived near the heart of this void, our observations of accelerating cosmic expansion would be an illusion.
"The advantage of giant void models is that they don't require any new physics to explain the apparent acceleration of the universe, like the existence of some weird dark energy or a modified theory of gravity," says theoretical cosmologist Phil Bull at the University of Oxford.
Still, "there are lots and lots of problems with void scenarios," says theoretical physicist Malcolm Fairbairn at King's College London. "It's very difficult to get them to fit existing data—for instance, the cosmic microwave background (CMB) radiation usually gets distorted in these models compared to what we actually see." For the void model to match observations of CMB radiation, we would need to be very close to the center of the void, to within one part in 100 million. That "seems like an unacceptable 'fine-tuning' to some people,” says Bull. “Why should we find ourselves so close to the center?"
In addition, astronomers using NASA's Hubble Space Telescope recently found evidence against the existence of such a void. After refining their measurements of the rate at which the universe is expanding, they all but ruled out the possibility that the accelerating expansion is an illusion created by a void. In addition, if we are living inside a void, Bull and his colleagues argue, we should see very strong fluctuations of cosmic microwave background radiation reflected off hot gas in the clusters of galaxies surrounding the void. Yet we do not see any reflections that strong. "This was pretty much the final nail in the coffin for void models," Bull says.
To support the existence of dark energy—or vindicate one of these alternatives—we need giant sky surveys which will clock the speeds of even more galaxies, Fairbairn says. The colorful scenarios that theorists are dreaming up "ultimately show what an interesting and weird universe we live in," Carroll says. "It's one where we must keep an open mind as to what the answers may be."
Editor's picks for further reading
COSMOS: Doubts Over Dark Energy
Reexamining the evidence for dark energy.
New York Times Magazine: Out There
In this article, Richard Panek explores the evidence for dark energy.
NPR’s 13.7: Dark Energy and the Joy of Being Wrong
In this blog post, Adam Frank recounts the history of the discovery of dark energy.
What is dark matter?
An invisible substance thought to make up a quarter of all the “stuff” in the universe, dark matter leaves its gravitational fingerprints all over the cosmos. But despite decades of trying, scientists have failed to capture a single speck of dark matter, in part because they don't have a clear idea of what it actually is.
But what if the solution to the mystery of dark matter is that dark matter doesn't actually exist? What if this ghostly stuff is just a phantom of astronomers’ imaginations? Could there be another answer to the puzzles dark matter was invoked to solve?
Since the 1930s, astronomers have suspected that galaxies contain more mass that we can account for. That’s because, when astronomers clock the speed of stars circling around the center of the Milky Way and of galaxies moving in distant clusters, they all seem to be going too fast. They are going so fast that they should overtake the force of gravity tugging them inward and fly out into the void beyond. Yet something holds them back.
That “something,” most astronomers believe, is dark matter: matter we can’t see yet which has enough mass to keep those speeding stars in stable galactic orbits. But what is dark matter? Scientists have largely ruled out all known materials. The consensus is that dark matter must be a new species of particle, one that interacts only very weakly with all the known forces of the universe except gravity, with which it interacts as strongly as ordinary matter does. Dark matter is invisible and intangible, its presence detectable only via the gravitational pull it exerts.
But not every astronomer is satisfied with this interpretation. Some, like Stacy McGaugh at the University of Maryland, College Park, believe that the definition of dark matter is so slippery that it is impossible to prove or disprove. Researchers might be able rule out the existence of any specific conjectured form of dark matter particles, but "we cannot falsify the concept, so if one fails, we are free to make up another," says McGaugh. "This cycle can be endless — as long as we're convinced as a community that it has to be dark matter, we won't take alternatives seriously, but we can never be disabused of the concept of dark matter."
Instead of relying on mystery particles, a small community of researchers suggests an intriguing alternative: What if the answer lies in changing what we know about the laws of gravity? The leading alternative to dark matter is known as Modified Newtonian Dynamics (MOND). The assumption is that at large scales, the laws of gravity are different from Einstein's theory of general relativity. "MOND merely tweaks the way a known force, gravity, works—we don't have to accept that the universe is filled with invisible mass," McGaugh said.
In general, by tweaking Newton's laws of gravity when it comes to orbits at large scales, MOND predicts the velocities of stars within galaxies even better than dark matter does. "It works so well it seems there must be something to it," McGaugh said. MOND works especially well on a class of galaxies known as low surface brightness galaxies, very faint galaxies without bright centers, explains theoretical cosmologist Priyamvada Natarajan at Yale University. "It's better than dark matter at explaining the rotation curves of these galaxies, the speeds at which stars in a galaxy orbit the center."
However, critics point out that dark matter beats out MOND on other astronomical puzzles. "The biggest problem is perhaps clusters of galaxies—though MOND works well in individual galaxies, it doesn't fit clusters terribly well," McGaugh said.
In fact, even with MOND, there is still a need for dark matter. "The need for dark matter in such a theory is horrible," McGaugh said. "On the other hand, it is a fairly limited problem in scope—we believe there is more than enough ordinary matter in the universe that is yet undetected that would easily suffice to make up the difference."
Skeptics of MOND, however, point at the Bullet Cluster, two colliding clusters of galaxies. There is a clear separation of luminous and unseen matter seen there exactly matches what one would expect with the dark matter model—dark matter, being largely intangible even to itself, would "feel" the forces of the collision very differently than ordinary matter. MOND advocates say that although unseen matter could be involved, it might again be unseen forms of ordinary matter.
Maps of the cosmic microwave background—radiation left over from the Big Bang—also provide strong support for dark matter. Temperature aberrations seen in the cosmic microwave background seem to reflect the presence of both ordinary matter, which interacts with both matter and radiation, and dark matter, which influences matter but is essentially invisible to radiation.
So MOND advocates have a difficult task: Their theory must explain all the puzzles that dark matter has already solved, and it must present a new way of accounting for everything Einstein's theory of general relativity currently explains. For instance, general relativity proposes that matter and energy curve spacetime, creating the effect we know of as gravity. Massive bodies curve spacetime enough to visibly bend light, an effect known as gravitational lensing that astronomers have witnessed for decades. "We cannot explain the phenomenon of gravitational lensing without general relativity, and this is where MOND spectacularly fails," Natarajan said.
"It has proven hard to construct a relativistic version of MOND,” acknowledges McGaugh. “If one is going to introduce a new theory, it has to encompass existing, successful theories."
Meanwhile, physicists continue the quest to directly detect dark matter particles. "There are no significant results yet, but I am optimistic," says Natarajan. "In any case, I'm quite comfortable as it is with the evidence for the existence of dark matter."
But until physicists actually “see” a dark matter particle, researchers will continue to investigate alternatives to the dark matter model. "It could be wrong," McGaugh says. "We do not understand all there is to understand yet—there do remain fundamental mysteries to explore."
This is the first part of a two-part series on critics of dark matter and dark energy. Return next week for a look at alternatives to dark energy.
Editor's picks for further reading
FQXi: Out of the Darkness
Physicist Glenn Starkman is evaluating alternatives to general relativity.
NOVA scienceNOW: The Dark Matter Mystery
In this video, explore the evidence for dark matter.
Scientific American: What if There is no Dark Matter?
Could modifications to the theory of gravity eliminate the need for dark matter?
Are we living in someone else’s fantasy?
The Chinese philosopher Zhuangzi posed this question more than two thousand years ago when he recalled waking from a dream unsure whether he was a man who dreamed he was a butterfly or a butterfly dreaming that he was a man. Today, with the advent of computers that can simulate cells, cities, and even solar systems, philosophers and scientists are asking this ancient question in a new way: Are we living in a computer simulation?
This question is more than just the premise of "The Matrix." It's a conjecture that lives at the intersection of humanity and technology—and though it might seem like philosophy, it spurs ambitious new questions about what computers are capable of and about the nature of reality itself. As theorists begin to think of our universe as nothing more than a vast collection of information, can we ever truly know whether our reality is as “real” as we think it is?
The philosopher Nick Bostrom, director of the Future of Humanity Institute at the University of Oxford, posed the latest iteration of this ancient question in a 2003 paper. His "simulation argument" begins with the observation that modern computers have improved at an exponential rate since their invention. If computing power continues to grow at this pace, advanced civilizations will one day be able to build titanic, densely-packed supercomputers capable of doing everything from beating the stock market to predicting the weather months or years in advance. “Post-human” programmers might even use these machines to simulate entire civilizations, vast electronic worlds that would put today’s computer games to shame.
What would it take to create this kind of simulation?
When it comes to simulating a person, scientists estimate it might take 1017 operations per second—that's one followed by 17 zeroes—to simulate a human brain, based on the number of neurons in the brain and rate of which those neurons “talk” to each other. Assuming that simulating the sensory events a person experiences—every taste, sound, smell, touch and sight that is coded in our neurons—takes about 100 million bits per second, and that approximately 100 billion humans have lived on Earth to date, Bostrom estimates it might take 1036 calculations in total to create a simulation of the whole of human history that is indistinguishable from reality.
That’s just to simulate the parts of the universe that humans can sense. What about the microscopic structure of the Earth's interior or the subtle features of distant stars? These little details could be safely omitted until a simulated person needed to observe them. In addition, to save computing power, maybe not every person in a simulation would be fully simulated. Perhaps some of the characters in the simulation would be "zombies or 'shadow-people'—humans simulated at a level sufficient for the fully simulated people to not notice anything suspicious," Bostrom writes in his paper.
So how close are we to achieving this dream (or nightmare)? Today’s most powerful supercomputers are capable of operating at roughly 10 petaflops per second—that is, 1016 calculations per second. A planet-sized computer based on current electronics might carry out 1042 operations per second. Bostrom also notes that quantum physicist Seth Lloyd of MIT has calculated that a 1-kilogram "ultimate laptop" that operates at the known limits of physics might be capable of 5 × 1050 operations per second. So, the planet-sized computer might be able to simulate all of human history in a millionth of a second; the ultimate laptop, a hundredth of a billionth of a second.
Given that fully simulating every person who has ever lived might only take a tiny fraction of an advanced civilization's resources, Bostrom reasons that the number of computer-generated minds buzzing away inside simulations could vastly outnumber the total sum of real minds that have ever lived. If that is true, the odds are that we are simulated, not real. It may even be possible that our simulators are themselves simulated, and their simulators are simulated, and so on. "Reality may thus contain many levels," Bostrom says.
This does not prove that we live in a simulation, Bostrom emphasizes. There are a number of caveats that could stop this bizarre future before it starts. One glum possibility is that civilizations might very well go extinct or collapse—say, by annihilating themselves in a nuclear war—before they can develop supercomputers of such immense power. Another thought is that civilizations simply have no desire to commit the vast resources needed to create supercomputers. Or perhaps advanced civilizations might not indulge in such simulations—maybe they would be ethically opposed to simulating minds and their suffering, or they might prefer to entertain themselves with machines that directly stimulate their brain's pleasure centers. "Personally, I assign less than 50 percent probability to the simulation hypothesis—rather something like in the 20 percent region, perhaps, maybe," Bostrom writes, although he describes this as a gut feeling rather than part of his logical argument.
Unless the simulators decide to make themselves known, there may be no way to prove or disprove the simulation argument. Some have suggested looking for "glitches" in the simulation, but such glitches would be more plausibly explained as hallucinations, visual illusions, fraud or self-deception. Even if errors did pop up, a smart simulator could simply wipe any memory of the anomaly from our simulated brains.
If we are living in a computer simulation, how should we live our lives? "The simulation hypothesis currently does not seem to have any radical implications for how one should live," Bostrom said. Still, "it helps to shed light on, among other things, the prospects of our species."
Also, thinking of the universe as a computer may actually be a helpful approach in science. "You can start thinking about what kind of computer it is, what kind of operations can it do, what kinds of problems can it solve," said theoretical computer scientist Scott Aaronson at MIT. "That's an extraordinarily fruitful way of thinking about the universe that has led to the whole field of quantum computers—devices based on the quantum physics that explains how the fundamental building blocks of the universe behave."
We may never know whether we are living in someone else's fantasy; whether we’re the man or the butterfly. But if we do one day develop supercomputers capable of simulating minds and universes, perhaps our creations will be able to answer the question for us.
Why are qubits like cats?
They’re strange and contradictory—and they don’t like to be herded.
Qubits are the essential elements of quantum computers. Conventional computers symbolize data as a series of ones and zeroes—binary digits known as bits. Quantum computers use quantum bits, or “qubits,” that don’t just toggle on or off like the transistors in conventional computers, but can be both on and off simultaneously. In principle, quantum computers can vastly outperform traditional computers. But actually building such a machine is a challenge akin to—you guessed it—herding cats.
To understand how quantum computers work, you can start by opening your eyes. If you see something, you pretty much know it's there, right? However, if you can't see something—if it's hidden in a box, for instance, or it's too small to see—you might very well imagine that it might be anywhere, or nowhere. This realm of uncertainty is more than just a fanciful idea; it is the backbone of quantum physics, and it is exactly the odd life that the elementary building blocks of the universe live if you aren't looking. Atoms and subatomic particles live in states of flux known as "superpositions" where they can, for instance, exist in two or more places at once, or spin in two opposite ways simultaneously. However, once a particle gets disturbed by its surroundings, its superposition "collapses" so that it is in just one of the many possible states represented by the superposition.
Quantum computers are based on objects in superposition—those qubits that can read both “zero” and “one” simultaneously. The more qubits you "entangle," or link together so that they operate in perfect unison, the more potential on/off combinations your quantum computer can run at the same time. A quantum computer with just 300 such qubits could run more calculations in an instant than there are atoms in the universe.
Superpositions are extraordinarily fragile, though. The easiest chunks of matter to coax into superpositions are usually very small, because their activity is easier to control, or very cold, because their low energy makes it unlikely they will interact with their environment—for instance, super-cooled rubidium or ytterbium atoms.
So far quantum computers are only capable of fairly rudimentary behavior, such as figuring out what numbers multiply together to get 15. But these are just toy versions of the powerhouses that quantum computers could one day become. Today, militaries, intelligence agencies, corporations and universities worldwide are competing to develop quantum computers that live up to that promise.
Conventional computers symbolize data as a series of ones and zeroes, binary digits known as bits. This code is conveyed via transistors, which are electronic switches that are flicked either on or off to represent a one or a zero, and is the basis for all the calculations associated with traditional computers. In contrast, quantum computers are based on objects in superpositions—quantum bits or "qubits" that don't just work on or off, but both on and off simultaneously. The more qubits are "entangled" or linked together in a way where they operate in perfect unison, the more potential on-off combinations they can run at the same time. A quantum computer with just 300 such qubits could run more calculations in an instant than there are atoms in the universe.
"A quantum computer will allow humankind to perform tasks that are far beyond what the best classical supercomputer can do," said physicist Matteo Mariantoni at the University of California at Santa Barbara.
Certain tasks thought impossible for regular computers could be accomplished quickly by quantum computers. For instance, a quantum computer could easily factor a number hundreds of digits long. This is a math problem that’s too difficult for even the best computers today, which is why online encryption of credit card numbers and passwords depends on it. The National Security Agency (NSA) and others in the intelligence community are therefore racing to build a quantum computer that’s up to the task before someone gets there first. "My bet is the first quantum computer will appear in a lab related to the NSA," said Raymond Laflamme, executive director of the Institute for Quantum Computing at the University of Waterloo in Canada.
Quantum computers could be good for more than just hacking. Since they are quantum systems, they can be used to simulate other quantum systems, helping scientists investigate how complex molecules behave. Such work "could revolutionize the pharmaceutical industry," Mariantoni said. Quantum simulations could also help "solve mysteries of physics," such as superconductivity, the phenomenon where electrons zip without resistance through objects, said Markus Greiner, a physicist at Harvard University. In the process, such research could also help develop novel materials with fantastic, unforeseen new properties, he added.
Research teams across the world are pursuing a wide variety of different methods to create quantum computers. Qubits are being made from electrically charged atoms held in place by electrical fields, from photons of light, and from superconducting circuits, among many other architectures. An intriguing development in quantum computing are qubits that don't need super-cold temperatures, but rather can exist at room temperature. For instance, impurities within diamond can stay in superposition because their placement within such a pure crystal insulates them from outside disturbances.
Although scientists have created basic working quantum computers with a few qubits for nearly 20 years now, more advanced versions with hundreds of qubits that can outperform classical computers will likely take decades to materialize. Superpositions are delicate and easily broken, and the problem of keeping them isolated gets harder with each additional qubit. Moreover, it's not certain which architecture is optimal. "It's not even clear there will be a winner. Maybe we'll see hybrid devices that take advantage of several architectures, or a different approach altogether," said Jeremy O'Brien, director of the Center for Quantum Photonics at the University of Bristol in England. "However, personally, I'm very confident that an all-optical approach with single photons is the leading one."
Although it might seem as if development of quantum computers is slow, "Charles Babbage conceptualized and designed the first programmable computer in the 1830s," Awschalom said. "Nevertheless, it took until the second half of the 20th century for a recognizable electronic computer to arrive."
Still, benefits from spinoff technologies should appear long before a quantum computer more powerful than a conventional supercomputer does. For instance, research into quantum computers is now pioneering ways to resist hacking. When qubits are entangled, they stay in sync instantaneously as if they were one, even if they are at separate ends of the universe, a seemingly impossible connection Einstein dubbed "spooky action at a distance." If anyone tried to eavesdrop on communications involving qubits, the disturbance would immediately be obvious. Such research is now helping develop a new kind of extraordinarily secure cryptography. "Those applications may outpace the development of a quantum computer that will break current cryptographic schemes, which is a good thing for information security," Awschalom said.
The first quantum computers will probably live in labs or server farms. However, according to experimental physicist Ian Walmsley at the University of Oxford in England "As they get easier to build and designs get more sophisticated, I think we'll see them in the office—maybe in the home."
If you find it hard to imagine a quantum computer sitting on your desk, Laflamme suggests looking to history: “If you went back to the 1950s and asked if you really needed a computer in the house, I think you'd get a similar answer."