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She has talked of ending her program in the next year or two and moving on to other projects, but her charismatic appeal is unlikely to diminish. "Oprah is probably the greatest media influence on the adult population," says writer Fran Lebowitz. "She is almost a religion." Amen.

EDWARD WITTEN Physicist

Physicists half jokingly call it the TOE--Theory of Everything. The idea is to describe all matter, all energy, all the fundamental forces of nature in one tidy, elegant set of equations. But it's so devilishly difficult that Einstein spent his last years in frustration trying to concoct just a partial solution to the problem.

Yet physicists now think they're finally on the right track with something known as superstring theory; young theorists are flocking to study its abstruse mathematics, convinced that therein lies the path to ultimate truth. And that's largely owing to Edward Witten, 44, a professor at the Institute for Advanced Study in Princeton.

Witten didn't invent superstring theory, which posits that the basic building blocks of nature are not tiny particles but unimaginably small loops and snippets of what loosely resembles string--except that the string exists in a bizarre, 10-dimensional universe. The current version of the theory took shape in the late 1960s, when the tall, thin, shy, wispy-voiced scientist was still an undergraduate at Brandeis.

By the mid-1980s, though, when Witten turned his attention to superstrings, he was widely regarded as the most gifted physicist in the world, and perhaps the most brilliant who has ever lived. And simply by choosing to work in the field, he utterly transformed it. Says Michio Kaku, a theoretical physicist at New York University: "I remember fondly that back in the '70s, superstring theory was like a cottage industry. Only a handful of us diehards worked on it. But when Ed Witten declared that the theory would dominate the next 50 years of physics, it was like a tidal wave hit." Superstrings were suddenly hot.

That doesn't necessarily mean the theory is correct, of course. As Einstein's example makes clear, very smart people sometimes tilt at windmills. And even in the case of his greatest success, the General Theory of Relativity, Einstein had to wait patiently for experimentalists to go out and verify its predictions. Until they did, the theory was simply a set of clever equations. The same holds true today for superstring theory; unfortunately, it would take an atom smasher thousands of times as powerful as any on Earth to test it directly--at least in its current version.

But with Witten on the case, superstring theory may well be refined to the point where it can be tested in real-world experiments. Already his work on a related idea known as topological quantum field theory, which allows physicists to find connections between seemingly unrelated equations, has earned Witten the Fields Medal, the mathematical equivalent of the Nobel Prize. That's no small feat, considering that mathematicians usually look down on the dabblings of mere physicists.