Decoding the brain
The neural code is the most important scientific problem you have (probably) never heard of.
Analogous to the software of a computer, the neural code is the set of rules or the syntax that transforms the electrical pulses emitted by brain cells into perceptions, memories and decisions. 
Knowledge of the neural code could give us almost unlimited power over our psyches, because we could monitor and manipulate brain cells with exquisite precision by speaking to them in their own private language. The neural code could also solve one of philosophy's oldest conundrums, the mind-body problem. We may finally understand how this wrinkled lump of jelly in our skulls generates a unique self with a sense of personal identity and autonomy, a self that perceives, emotes, remembers, imagines, chooses, acts, creates.
Until recently, a complete decoding of the brain seemed impossibly remote, because researchers had limited means of probing the microcircuitry of living brains. Trying to glean the neural code with external scanning methods such as magnetic resonance imaging or electroencephalography is like trying to learn English by standing outside a baseball stadium and listening to the roar of the crowd. But over the past decade researchers have begun crafting arrays of microelectrodes that can eavesdrop on hundreds and even thousands of separate neurons simultaneously. These advances "have really transformed the field," says Terry Sejnowski, of the University of California at San Diego, a leading neural-code theorist.
The immediate goal of many researchers is producing "neural prostheses" for the disabled. By far the most successful neural prosthesis is the artificial cochlea, which restores hearing by feeding signals from an external microphone to an implanted chip that stimulates the auditory nerve. Work is proceeding slowly but surely on prostheses that can restore vision to the blind and enable the paralyzed to control computers and other devices. The Pentagon, which funds research on neural prostheses, has openly broached the possibility of implanting chips in healthy soldiers to enhance their perceptions and memories.
Neuroscientists are still far from converging on a solution to the neural code. They are embroiled in debates over whether information is represented primarily by signals from individual neurons, by many neurons firing in lockstep, by even higher-level waves of chaotic electrical activity sweeping through the brain, or all of those schemes and more. These disputes have led some theorists to warn that the neural code may never be fully deciphered. But 60 years ago, many biologists feared the genetic code was too complex to crack. Then in 1953 Francis Crick and James Watson unraveled the structure of DNA, and researchers quickly established that the double helix mediates an astonishingly simple genetic code governing the heredity of all organisms.
Science's success in deciphering the genetic code, which has culminated in the Human Genome Project, has been widely acclaimed -- and with good reason, because knowledge of our genetic makeup could enable us to reshape our fundamental nature. A solution to the neural code could, in principle, give us much greater and more direct control over ourselves than mere genetic manipulation. It is not too soon to start pondering the potential consequences of this achievement, especially given the Pentagon's interest. How will knowledge of the neural code be used, and by whom? Who will be liberated, and who enslaved?
Physics: New dimensions
Albert Einstein once said that his chief mission as a scientist was to determine whether God had any choice in creating the universe. In other words, was our cosmos in some sense probable or even inevitable, or is it just an arbitrary, brute fact that we must accept and can never explain? Modern physicists share Einstein's obsession with this riddle. They have constructed an extraordinarily detailed account of physical reality, embodied in the standard model of particle physics, which accounts for electromagnetism and the nuclear forces; and general relativity, Einstein's description of gravity. But physicists still have no idea why we find ourselves in this particular universe ruled by these particular laws.
Physicists such as Lisa Randall, of Harvard, hope to solve the conundrum by finding a theory that combines the standard model and general relativity -- which offer disparate mathematical and conceptual approaches to reality, one quantum mechanical and probabilistic and the other deterministic -- into a single, tidy, consistent package. Randall is a leading proponent of string theory, which for some 20 years now has been the leading candidate for this so-called unified theory. String theory holds that reality boils down to infinitessimal strings, or loops, or membranes vibrating in a hyperspace of 10 or more dimensions. Viewing reality from higher dimensions makes certain problems that have stymied unification efforts much more mathematically tractable.
String theory has suffered from various problems. One is that it offers few predictions that can be tested by any current accelerators. Moreover, far from making our cosmos seem less arbitrary, string theory allows for more than a googol (1 followed by 100 zeros) possible universes with dimensions, particles, forces and other properties radically unlike our own. But Randall has proposed a version of string theory that she believes may solve these problems. In most versions, the extra dimensions are "compactified," wrapped up into balls so small that they cannot be detected. In Randall's variant, which she describes in her acclaimed new book "Warped Passages," some extra dimensions -- or passages, as she calls them -- stretch to infinity and may be experimentally discernible.
Together with Andreas Karch, of the University of Washington, Randall has also shown that a universe like ours emerges quite naturally from the physics she postulates, whereas in other universes gravity would be too stringy or too weak to allow for the emergence of stars, planets and life. Randall hopes that the Large Hadron Collider, a powerful accelerator being built in Switzerland, may provide evidence for her theory within the next decade.
Then we may discover that God had little choice after all.
Robots with common sense
In the mid-1960s, Marvin Minsky, a founding father of the field of artificial intelligence, predicted that computers would be as smart as humans in less than a decade. Since then, computers have become exponentially more powerful and clever; they can now translate languages, recognize voices, judge loan applications, interpret cardiograms, play championship chess, help us navigate our cars. But while computers excel at performing tasks that can be precisely defined, they still lack the flexible, all-purpose intelligence -- the ordinary common sense -- that most humans acquire in childhood.
Some artificial-intelligence researchers now doubt that computers will ever display the complex, humanoid intelligence of HAL, the silicon star of Stanley Kubrick's film "2001." In the essay collection "HAL's Legacy," the computer scientist Roger Shank declares that HAL "is an unrealistic conception of an intelligent machine" and "could never exist." Computer scientists can only create machines that "know a great deal about what they are supposed to know about and miserably little about anything else." Minsky rejects that pessimism, pointing out that computers have failed to acquire common sense because scientists have failed to give it to them. "There's been only large project to do something about that," Minsky remarked recently, "that's the famous Cyc project."
The gigantic software program called Cyc is the brainchild of Douglas Lenat. Since 1984, he and a small team of co-workers have painstakingly embedded millions of common-sense rules, or assertions, into Cyc. As a result, Lenat says, Cyc "knows that trees are usually outdoors, that once people die they stay dead, and that a glass filled with milk will be right side up, not upside down." Those are the sorts of assumptions that supposedly smart computers often fail to make. Lenat calls Cyc "the world's first true artificial intelligence, having both common sense and the ability to reason with it." He believes Cyc has already achieved something akin to consciousness. "If you ask it what it is, it knows that it is a computer," he says. "If you ask who we are, it knows that we are users."
In 1994 Lenat founded Cycorp in Austin, Texas, to market commercial applications for Cyc. In an effort to tap into funds flowing from the Department of Homeland Security, Lenat has trained Cyc to be an expert in identifying security loopholes in communication networks. But Cyc's most impressive talent is gleaning the contextual rather than just literal meaning of language. As a result, Cyc can supplement speech-recognition and language-translation programs; it can also boost the power of search engines by responding to the spirit and not just the letter of requests for information.
Lenat hopes that Cyc will eventually become more or less autonomous, capable of acquiring new knowledge by prowling the Web and absorbing information on its own. After that phase transition, Lenat predicts, Cyc will begin evolving in ways that may be difficult to predict. Cyc will become a "full-fledged creative member of a group that comes up with new discoveries," Lenat says. "Surprising discoveries. Way out of boxes."
Lenat has given versions of Cyc to other computer scientists, who are free to tinker with it as they choose -- creating, in effect, children of the original Cyc, which will no doubt develop in their own idiosyncratic ways.
Perhaps Cyc and its offspring will help us solve the neural code or other problems -- that is, if they do not turn on us, like the psychopathic killer HAL.
122 years young
In 1997, a French woman named Jeanne Calment died at the age of 122, making her the longest-lived human on record. Soon, some anti-aging enthusiasts suggest, we may pity Madame Calment for dying so young. In a recent issue of the journal Gerontology, Aubrey de Grey, a computer scientist turned biogerontologist at Cambridge University, predicts that some people now in their 60s will still be alive in the year 3000.
De Grey is merely one of the more flamboyant members of a growing corps of scientists who believe we are on the verge of solving that quintessential aspect of the human condition, mortality. As the journalist Steve Hall documents in "Merchants of Immortality," the National Institutes of Health and venture capital firms such as Kleiner Perkins have poured money into research aimed at slowing down, stopping and even reversing senescence. The White House Council on Bioethics takes the prospect of immortality seriously enough to deplore it in position papers.
Over the past decade, researchers have identified myriad biological processes that contribute to aging as well as ways to extend the lifespan of simple organisms.
Early on, investigators focused on telomeres, bundles of DNA that cap the ends of chromosomes. Every time cells divide, telomeres get a little shorter, until finally cells stop dividing altogether after 50 or so divisions. Some researchers speculate that if they can prevent telomeres from shortening, they might make individual cells and even entire organisms immortal. Scientists have also discovered genes that, when manipulated, can boost the lifespan of yeast, worms and fruitflies. Genes with similar structures have been identified in humans, inspiring hopes that genetic tinkering might greatly extend human life.
Scientists have boosted the lifespan of mice and other animals by more than 50 percent simply by curtailing their diets, a method called caloric restriction. Recent investigations suggest that caloric restriction works by altering activity within mitochondria, cellular structures essential to metabolism. As mitochondria consume nutrients, they produce oxygen ions called free radicals, which in abundance wreak havoc on DNA and other crucial biological components. Free radicals are thought to cause the wear and tear of senescence as well as genetic mutations that trigger cancer and other diseases.
Some gerontologists advocate a low-calorie diet -- especially one rich in antioxidants, substances that counter the effects of free radicals -- as a way to extend life by reducing the risk of cancer, heart disease and other afflictions of age. Others have proposed countering free radicals with more exotic interventions involving modified versions of antioxidant enzymes found in bacteria. De Grey advocates an approach he calls Strategies for Engineered Negligible Senescence, or SENS, which involves attacking aging on every possible front: with genetic engineering, stem cells, telomere intervention, cloning, antioxidants and caloric restriction.
Aging, he says in a recent issue of Technology Review, "is something we need to fix," and at 42 de Grey is confident that he will live long enough to reap the benefits.
Desktop fusion reactor
For more than half a century, physicists have been trying to harness fusion -- the nuclear reaction that makes the sun and other stars shine and hydrogen bombs explode -- to create a cheap, clean, boundless source of energy. Unlike fission, which involves splitting the nuclei of heavy elements such as uranium and underpins the nuclear-power industry, fusion occurs when the nuclei of two light elements such as hydrogen fuse to form a heavier element such as helium. Unfortunately, the experimental fusion reactors built to date are gigantic, expensive, Rube Goldberg contraptions, which attempt to mimic the stupendous heat and pressure of the sun but so far consume more energy than they produce.
Physicists have long dreamed of finding a way to generate fusion with small, simple devices at or near room temperature. A method dubbed cold fusion briefly galvanized researchers more than a decade ago but turned out to be bogus. The fusion-research community is therefore thrilled by the news that physicists at the University of California at Los Angeles have built a desktop fusion reactor the size of a lunch bucket. The reactor consists of a so-called pyroelectric crystal in a chamber filled with gaseous deuterium, a variant of hydrogen containing an extra neutron. When heated, the crystal acquires an electric charge, ripping electrons off the surrounding deuterium atoms and propelling them toward a target of solid deuterium. When the gaseous and solid deuterium atoms collide they fuse -- creating helium atoms and spewing high-energy neutrons.
The remarkably low-tech UCLA device has no moving parts and does not even have to be plugged in to work. Dunking it into warm water can heat the pyroelectric crystal enough to yield some fusion.
With some refinements, the gadget could serve as a compact neutron source, which could be incorporated into implantable devices for irradiating tumors, handheld medical imagers, baggage and cargo scanners, radioactive-material detectors, propulsion systems for spacecraft, and particle accelerators for further research on fusion.
The UCLA team emphasizes that the device probably cannot produce more energy than it consumes and hence cannot serve as an energy source. But at the very least, the gadget should energize the moribund fusion-research community --which for years has been losing prestige and funding -- to seek other simple, low-cost fusion techniques that can be scaled up for large-scale energy generation.
Decades ago, fusion researchers justified their enormous budgets by promising that one day fusion would give us an energy source "too cheap to meter," freeing us of our dependence on fossil fuels and fission reactors, which require fuels that can also be used to make nuclear bombs. Obviously, we need such a breakthrough now more than ever.
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