Alarmed, Woit says, he complained to the Harvard physics chairman, who silenced Motl on the subject of string theory critics. By e-mail, Motl declined a request for an interview: “I don’t enjoy elementary human rights right now.” Needless to say, this created a buzz in the string theory blogosphere. A science consultant summarized the clash by saying that Motl had done to the image of string theory “what the movie Deliverance did for canoeing holidays.”

Perhaps it is the alluring beauty of what Greene has called the “Aeolian” harmonies of these invisible strings; perhaps it’s because any theory that touts itself as the Theory of Everything is bound to attract the ambitious; or perhaps because, in a winner-take-all world, the leading theory in physics, too, is destined to crowd out all the others. For whatever reason, string theory is It, and has been It for well over 20 years. No one can even say for sure what’s in second place. Motl’s Harvard colleague, professor Cumrun Vafa, calls string theory “the major leagues” in the field of quantum gravity. As for other theoretical pursuits, he derides them as “little efforts here and there.” And critics like Woit? “My question to them is: ‘Why are you wasting your time challenging these guys?’ Do your job! Write your own paper. It would revolutionize the field.”

Solidly as it is entrenched now, string theory began fairly humbly, when some researchers in Europe and the United States were trying to puzzle out how a fairly esoteric 200-year-old mathematical formula almost perfectly described some effects of the “strong force” involving interactions between quarks and gluons within the nucleus of an atom. An Italian physicist named Gabriele Veneziano had made the claim in a paper he published in 1968. String theory grew out of one answer and has continued to grow ever since. The math made sense, it turned out, only if some of the particles involved did not behave like particles at all but like something “stringy,” as theorists like to say of a single extendable dimension, in which these new particles could vibrate at particular frequencies by stretching and contracting like rubber bands.

In 1974, Joel Scherk and John Schwarz, entranced by the simple beauty of this image, used the idea to analyze a mysterious particle with two units of spin that showed up when they were doing their own calculations on the strong force. To their amazement, the properties of the so-called “spin-two” particle matched the properties of the graviton, a massless particle that conveys the force of gravity. Before then, gravity had simply not fit the conception, it was so subtle at the quantum level. And it was so different, too. In quantum mechanics, particles career wildly about, crashing into each other or, sometimes, passing right through. Gravity is far more stately and smooth as it arcs through space. But there the graviton was in the equation, yet another pitch in the harmony of all the vibrating strings. Says Steven Gubser of Princeton: “It was a syllogism—if strings and quantum mechanics, then gravity.” Because of some lingering inconsistencies between string theory and quantum mechanics, other physicists remained skeptical until 1984, when Schwarz and another collaborator worked them out. And once they did, “everything broke open,” Schwarz told me. “There was a big reaction.” The rebels had stormed the palace gates.

The theory led rapidly to other implications—“not things that were added,” insists Michael Peskin of the Stanford Linear Accelerator Center, “but all properties of the original mathematical framework.” To explain the commonality of force and matter in this new unified theory, theorists imported the notion of supersymmetry that had been incorporated into the Standard Model, by which each elementary particle, the fermions that make up matter and the bosons that account for force, had a heretofore unknown partner of the other class. To work out the math, 10 space-time dimensions would be necessary. “You can imagine them, it just takes a little practice,” Peskin says, only half-joking. A group of physicists including Harvard’s Andy Strominger gave one possible explanation: six-dimensional Calabi-Yau spaces, theoretical configurations that might look like crumpled-up Mobius strips, with all the extra dimensions folded in. In theory, Calabi-Yau spaces are hiding everywhere, tucked inside the three-dimensional space we know—plus time makes 10—each one possibly housing strings that vibrate through them.

To Smolin, the string revolution that provoked this flurry of theories came about too quickly. He watched in some distress as “there developed an almost cultlike atmosphere. . . . Nothing else was important or worth thinking about.” Woit steered clear entirely, distrustful of so much theory being constructed on so little evidence. In particular, he recoiled at the massive readjustments to the Standard Model required by string theory’s brand of supersymmetry. He cites the no-nonsense physicist Richard Feynman, who likewise disdained the string theorists: “I don’t like that they’re not calculating anything. I don’t like that they don’t check their ideas. I don’t like that for anything that disagrees with an experiment, they cook up an explanation—a fix-up to say, ‘Well, it still might be true.’”

Indeed, the Calabi-Yau spaces raised more questions. They come in a nearly infinite variety, each one representing a different physical make-up of the universe. Yet so far, none of these alternate universes has matched the characteristics of our own—a significant liability to a theory that was supposed to do just that. “The closest are caricatures of our world,” admits Barton Zwiebach, a leading string theorist at MIT. “That’s a disappointment.”

And how was supersymmetry, with all its new “partner” particles, to fit in? Five different versions of string theory were advanced to try to explain that. All seemed plausible, but none was compatible with the others. Physicists longed for a “metatheory” that would somehow make each, as Peskin puts it, a “facet” of one ultimate solution.

It was a new search for the Theory of Everything, and Ed Witten rose to the challenge. He was a professor at Princeton’s Institute for Advanced Study, where Einstein famously hung his hat. In a world that ranks itself by the smart, the really smart, and the really smart, Witten was indisputably the class act of the field. “He’s a god,” Woit says.

In 1995, Witten produced the metatheory so many had hoped for, posing, among other things, the new idea of a membrane, or “brane,” which extended the one-dimensional string into higher dimensions—raising the question of whether the branes themselves weren’t the fundaments of nature. Although the theory touched on the five theories, it left a lot to be filled in. It was less a theory, in fact, than a proclamation that a theory exists. “Nobody really knows what it is,” admits Peskin. Witten himself was rather cavalier about it. He called it M-theory, noting blithely that the M stood for “magic, mystery or membrane, according to taste.”

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