Reinvigorated nonetheless, string theorists have gone on to take string theory out from the microworld of subatomic particles to the vast reaches of the cosmos. The branes might describe the three-dimensional world we know as being embedded in a larger, multidimensional universe. They might also help explain black holes. And the strings might account for the “wormholes” within black holes—or possibly even some other unusual formation, Peskin says, “like a neck or a knot.” Since black holes contain singularities—points of infinite density—in space, might there not be an equivalent in space-time? That would take us back in time to that other singularity, the Big Bang. Perhaps string theory explains that? “It’s so hot, so dense, and so compact that the usual application of gravity without quantum mechanics would not work,” MIT’s Zwiebach says of the beginning of the universe. Because string theory incorporates gravity, however, it would. “So you can really ask the question of what happened at the very earliest times,” Zwiebach says. “We could see the origin of the universe, and the very deep meaning of how space and time are born and what they are.” And even, Peskin adds intriguingly, possibly back through the Big Bang, to discover a universe that might have existed before time as we know it began. “But there is a big debate as to whether this idea makes any sense.”

While string theorists view their work as a cathedral in the making, to Woit it is a far less promising, far more rickety affair—a vast, teetering Tinkertoy assemblage of only tangentially related theorems, propositions, and wan hopes that have left the simple clarity of those quivering strings a long way behind. Smolin likewise complains of the endless “maneuvering” of string theorists to account for the fresh problems that arise from each new theoretical development. “As long as no one quite knows exactly what string theory is,” Woit writes, “its proponents are able to hold very optimistic theories about it.” And there remains that nagging problem of evidence. “It has become the dominant paradigm in the field without any experimental basis,” Woit complains. “And there’s no conceivable experiment we have now which can ever show that it’s wrong or show that it’s right. And I haven’t really ever seen that happen before in the history of physics.” Smolin is more judicious in his summary. “I’ve gone back and forth on it,” he tells me, before giving a finely calibrated answer: “Basically I think that it is a very interesting set of ideas and examples and approximate calculations. But—and there are several buts—other approaches to quantum gravity are more promising. String theory has simply not worked out as well as we expected.”

Both sides of the argument are hoping for some resolution from the Large Hadron Collider, which CERN scientists will turn on next year. With a track nearly 20 miles around, it is capable of detecting particles about a 10th the size of the ones that show up now. That would take researchers down to 10 to the negative 16th centimeter, no small accomplishment. But the strings, if they exist, are flyspecks, down nearly to Planck length: 10-33 centimeters, or 10,000 trillion times smaller. At that scale, scientists will detect the strings only by inference—most likely by finding evidence of at least one of the “partner” particles posited by supersymmetry (to find the strings themselves, Woit claims, the track would have to swing not 20 miles but around the galaxy). But even if the new collider does discover evidence of supersymmetry, Woit adds, it still won’t prove the validity of string theory, since many other competing theories involve supersymmetry as well. Greene conceded as much in the Times op-ed: “No one successful experiment would establish that string theory is right, but neither would the failure of all such experiments prove the theory wrong.” So string theory remains: vast promise, little hard evidence.

Unlike most of the string theorists, Woit came of age in the late ’60s. He was a young boy in Paris during the student uprising of 1968, which passed by his window. That left him with a distrust of authority, and the ever-expanding social structure of string theory makes him highly suspicious. But he can see that it is safer to play along with the existing hierarchy than to question it. And the complexity of string theory only increases the obligation; it is a field that can require total commitment. Just to grasp the quantum mechanics on which the field is built requires several years of study, and string theory infinitely more, as its many offshoots evolve into thickening branches of increasingly abstruse theory. Once you get a handle on it, in short, it has a handle on you.

Harvard physics professor Nima Arkani-Hamed scoffs at the idea that there is any kind of “string theory cabal,” and says he believes that physicists can “vote with their feet” like any other professionals. But there does seem to be a dangerous insularity to the field. Even the ever-politic Greene became slightly testy when I asked if he was inclined to dismiss Woit because of a lack of standing. He replied that the question was “a touch awkward to respond to. So I’d rather not go there.” Still, he insisted that he had no particular stake in the outcome of the theory. “I have only one investment, and that’s in finding truth.” While Greene avoided taking Woit on personally, others either dismiss his criticisms as “not very interesting” or dispute his book without having read it. As a longtime practitioner in the field. Smolin has been taken more seriously, but he has changed no minds. In string theory, it appears, one is either pro or con.

Woit himself has backed off from some of the more extreme attitudes in his book, and he bears the look of someone who has been kicked once too often. “I’m continually getting grief from people who say, ‘Oh, you’re saying string theory is completely useless.’” He now shades it a little differently, acknowledging that string theory has made important contributions to the understanding of how certain subatomic particles behave and has led to some “very interesting” mathematics. Lee Smolin may be closer to the mark when he calls string theory an “overinvestment.” Although they overlap in the same math department, Woit and Greene rarely see each other, and when they do, they never discuss their disagreement in any detail. Indeed, they occupy such different spheres that it is almost as if each is tucked away in a divergent alternative universe. The difference is situational, but stylistic too. Harvard physics professor Lisa Randall went to Stuyvesant High School in New York with Greene, who won citywide math championships all four years; she observes that the showman in Greene sometimes wins out over the scientist. “He gives a more polished, more finished view,” she says. “And it comes out more established and more confident than it is in reality.” But then she pauses, perhaps afraid of going too far. “The fact is, science is messy, and in any intermediate stage we don’t know what is going on.” This causes a skeptic like Woit to be skeptical, and a promoter like Greene to promote. Ultimately, the debate will be resolved by the facts, but in a realm of physics as audacious as string theory, that may take a while. Or forever.

Eager actually to lay eyes on Brian Greene, after Woit and I had lunch at a French place a few blocks from his office, I took a short walk across the campus to the physics department to see if I could scare him up. When I asked the department secretary if Greene was around, she shrugged. “We never know where he is.” But she did show me his Institute for Strings, Cosmology and Astroparticle Physics, which was down the hall. I was expecting something as impressive as its title, but when she swung the door open, I encountered a large, mostly empty space with three graduate students peering into standard-issue computer screens. On the walls, there was only a blurry photograph of some stars. No picture of a superstring? I joked. “Oh, God, no,” said one of the grad students with a laugh. “If you had one of those, you’d be famous.”

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John Sedgwick is the author of In My Blood: Six Generations of Madness and Desire in an American Family, due out in January from HarperCollins.

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