A comfortable chaos reigns in Ed Witten’s sunny corner office at the Institute for Advanced Study in Princeton. It’s not cluttered; it’s just that entropy has run its course. Stacks of papers—articles, mathematical journals, Witten’s own calculations—sprawl across his desk and cover a nearby coffee table, hanging off the corners in seeming defiance of gravity.
Discerning order within systems much more complicated than these ziggurats of paper is, in essence, what Witten does. It’s going to be hard to understand exactly what that is, even with Witten himself to guide us.
“Part of what I do is apply physics to math,” he says. Now, if you thought physics was pretty mathematical to begin with, you have plenty of company. Only a handful of people on the cutting edge of those two disciplines understand the way Witten—a physicist by training—uses math to explore particle physics (and physics to open up new areas of math). Last spring he was working on black holes. “The quantum behavior of black holes is a little bit mysterious,” he says. “It would be nice to have a mathematical model of them.”
He might be the guy to break the code—to decipher, in other words, the fundamental language in which all creation is written. In 1990, Witten became the first and, to date, the only physicist to win the Fields Medal, the math world’s equivalent of a Nobel Prize, awarded only once every four years. He is best known as the leading proponent of string theory, an approach to particle physics that argues that the irreducible building blocks of the universe are not the atomic or even subatomic particles most of us learned about in high school, but something exponentially smaller: infinitesimal strands of vibrating energy.
As the institute’s background material puts it, Witten, 56, “is largely responsible for the modern interest in superstrings as a candidate theory for unification of all known physical interactions.”
To understand that last bit—about “unification”—one needs a quick refresher. The twentieth century saw two great revolutions in physics. The first began in 1905, when Albert Einstein published his Special Theory of Relativity, which explained that matter and energy are ultimately the same thing. This revolution progressed with his 1916 General Theory of Relativity, which argued that gravity is the result of the warping of space and time by huge objects on the scale of planets and stars. Though Einstein’s work overturned much of classical Newtonian physics, it postulated a world that at least was mathematically reliable. Absolutely, positively, E = MC2.
The second revolution was quantum mechanics, which developed over the first quarter of the century and applied to subatomic particles. According to quantum mechanics’ best-known formulation, the Heisenberg Uncertainty Principle, it is impossible to simultaneously determine a subatomic particle’s momentum and its position. One or the other, but not both at once. Instead of certainty (the proverbial apple falling on Newton’s head), one has to speak of probability.
Quantum theory described the interaction of the tiniest particles in the universe as brilliantly as Newton had described the motion of things in our everyday world and Einstein had described the fabric of what came to be known as space-time. The quantum universe, though, was a very different place from the one Einstein was describing. No one was more troubled by its implications than Einstein himself, who famously protested, referring to God, “He does not play dice.”
Einstein spent the rest of his life—most of those years at the Institute for Advanced Study—trying to find a unified theory that would reconcile the apparent contradictions of quantum mechanics and relativity. By the time he died in 1955 without having succeeded, a unified “theory of everything” had become the Holy Grail for the world’s top theoretical physicists.
For more than 30 years, the best candidate for a unified explanation has been string theory. Stephen Hawking put it forward as such in his best-selling A Brief History of Time. It first grabbed Witten’s attention in the early 1970s, when he was a graduate student at Princeton studying particle physics. String theorists were so imaginative and diligent that, by the early 1990s, not only had they come up with five different formulations of string theory, but they had also added six dimensions to the four we already knew about.
For scientists, the multitude of theories was a “source of quiet discomfort,” as Brian Greene, the Columbia University professor who is string theory’s great explainer, wrote in his 2004 book, The Fabric of the Cosmos.
Twelve years ago, Witten gave string theory a vital boost. At Strings ’95, the annual gathering of string theorists, he was able to show that the five theories were really just parts of a single, grander unifying theory. “What turns out to be the case is that different equations describe the same thing,” he says. “For one question, one equation offers the best description; for another question, another equation. But they’re both correct.”
Oh, and one more thing: To the ten dimensions already proposed by string theorists, Witten added an eleventh. He called his theory M-Theory, adding that the “M” might stand for magic, mystery, or matrix. Does this mean that Einstein was wrong? Does God play dice with the universe after all? At least in the sense that Einstein meant—that there is a degree of randomness at the root of things—well, yes.
Most string theorists resort to analogies. Greene compares those five early theories to translations of a single undiscovered original text. Witten uses a metaphor that even children can relate to: “We know the dinosaurs existed because we see fossils,” he says. “If we really had a live dinosaur, we’d know a thousand times more than we do from just fossils. Real M-Theory is the equivalent of the live dinosaur. What we have at present are a few fossils.”
Witten’s breakthrough became known as the second superstring revolution. It breathed new life into string theory and turned Witten into an unlikely celebrity. When Life compiled a list of the “50 Most Influential Baby Boomers” in 1996, Witten, whom the magazine hailed as “our Einstein,” was ranked sixth, between Oprah Winfrey and Bill Gates.
Where Einstein was sociable, hosting musical soirées at his Princeton home, Witten is less gregarious. He speaks in a small, somewhat high-pitched voice, and he sometimes takes so long to answer a question that it seems he’s waiting for the next one. Growing up in Baltimore, Witten was an avid Orioles fan. He went to Brandeis University as an undergraduate, where he majored in neither math nor science, but in history. At Brandeis the Vietnam War politicized him, and the Israeli-Palestinian conflict has remained one of his central concerns. He has served on the board of Americans for Peace Now since 1992.
Witten and his wife, Chiara Nappi, a Princeton University physics professor, have two daughters, ages 27 and 23, and a son, Rafi, 17, with whom Witten enjoys playing tennis and chess. Witten is just serious enough about his tennis skills to wince at the memory of playing poorly when a CNN film crew happened to be visiting. “I was down 5–0 when they left,” he says. He lost that set, then won the next two.
Unfailingly modest, Witten points out that he is only one string theorist among many, proud to be contributing to this important work. “To a large extent, [string theory] is still murky,” he acknowledges. “I have made the picture a little clearer. But whatever it is, it’s startlingly deep because it has wide-ranging manifestations in many aspects of particle physics. But we’re far from understanding it.”
Witten’s forthrightness aside, there is in certain corners of the scientific world a growing impatience with string theory. Doubters have dismissed Witten and his fellow theorists as “pluckers,” and the title of a recent book, Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law, by Columbia mathematician Peter Woit, exemplifies the opposing attitude. The problem: Science requires that theories be tested, but strings are so small and esoteric that no one has yet designed an experiment to confirm or rule out their existence. Critics want proof, arguing that they’ve been patient, but it’s time for the pluckers to put up or shut up.
This exasperates Witten, but he’s decided not to engage his critics in the public arena, where few are knowledgeable enough to evaluate the scientific claims and counterclaims. He hopes that when the Large Hadron Collider at CERN, near Geneva, comes online next May, dramatically enhancing our ability to study particle physics, it will shed light on whether string theorists are on the right track. The math tells him they are. “I just don’t believe,” he says, “that physicists would describe a theory that was wrong about nature but had so much deep mathematical truth.”