Brian Greene first heard about string theory on a bitter, blustery day in 1985. Walking by Blackwell's, a famous bookstore near the Oxford campus, he spotted a flyer for a lecture on "The Theory of Everything." He went. He saw. He was immediately conquered, though he has a hard time articulating why. The best he can do is invoke an even earlier memory of a subway ride he took when he was a teenager.

"I was feeling that way that adolescents sometimes get," he recalls. "You know -- 'What does it all mean? What is life all about?' The usual questions. And I remember thinking, 'Well, people have thought about these issues for ages, and it's not likely that I'm going to have any answers.' But it did occur to me that if I was able to get a thorough familiarity of what the questions actually were -- how is it that there are stars and galaxies and planets and people? -- I would get a certain kind of satisfaction."

String theory reconciles two previously incompatible tenets of twentieth-century physics: the theory of general relativity (which describes the behavior of very large things, like the steady outward streaming of the galaxies) and quantum mechanics (which describes very small things, like the flighty path of an electron). The former supposes that space is gently curving; the latter implies that space is jittery and unpredictable. String theory modifies Einstein's theory in just such a way that these two conceptions of space are brought into alignment.

During the past five years, string theorists have made exhilarating strides. They posit some pretty wild notions, including the existence of eleven dimensions, a concept that Greene very clearly and engagingly explains in The Elegant Universe. Even as far back as the seventies, physicists knew that string theory predicted gravity -- without relying on the theories of Einstein or Newton -- proving, to some skeptics, that string theory was at least on the right track.

Greene made his first major contribution eight years ago, when he discovered with Ronen Plesser, now a physicist at Duke, that for every possible shape of the cosmos, there is a "mirror shape" that generates an alternate universe with exactly the same properties. Then, in 1993, while he was working at the Institute for Advanced Study, he and colleagues Paul Aspinwall and David Morrison made another breakthrough. After months of handwritten calculations, they realized that the fabric of space can tear, meaning the universe can change shape by ripping itself apart and coming back together again in a completely different form -- a far more exotic contortion of space than Einstein had ever dreamed. When their computer spit out the final result they were hoping for, Greene shot out of his chair and started running around the room. "You know, like the guys who score a touchdown," he says. "They spike the ball, they flip over backwards, they do a little victory dance."

At the moment, Greene is working with several colleagues on a notion that not only overthrows conventional wisdom but plays pixie tricks with your head. They are postulating that space and time, concepts we take for granted as irrefutable aspects of everyday life, are in fact only vague approximations. Space, they think, only seems like space to us. And time, they think, only feels like time to us. But if human beings were smaller, they'd see that space and time were merely the perceivable facets of a much more nuanced series of organizing principles -- the same way that crude patterns are the only thing one sees, at first, when thumbing through the pages of a Magic Eye book. "So if we were born not 20 inches long, but 10-to-the-minus-33 inches long -- that's a billionth of a trillionth of a trillionth of an inch -- then we would know what those organizing principles were," says Greene. "They would be of second nature to us, just like time and space."