Wednesday, November 29, 2006

String Theory Unraveling?

Once so promising as the latest “theory of everything”, it may be unraveling.

The Rise of String Theory, the Fall of a Science, and What Comes ­Next

Until just over two decades ago, string theory was an esoteric branch of mathematical physics that held the attention of only a handful of maverick researchers. For their efforts, these pioneers endured a mixture of puzzlement and derision from their colleagues, and had trouble finding positions at academic institutions where they could pursue their quirky endeavors. But nowadays, it’s hard to land a job in a ­high-­powered department of theoretical physics if you don’t do string ­theory.

Aficionados claim that string theory provides the foundation for a “theory of everything”—a harmonious unification of all of fundamental physics. To the contrary, declare Lee Smolin, a physicist at Canada’s Perimeter Institute, and Peter Woit, a mathematician at Columbia University, string theory has thus far explained exactly nothing. But Smolin and Woit offer conflicting recommendations on how to restore sanity to theoretical physics, suggesting that string theory’s dominance does not yet face a wholly persuasive ­challenge.

The essence of string theory is a literal assertion: Elementary ­particles—­electrons, photons, quarks, and their numerous ­cousins—­are not ­point­like objects but “strings” of energy forming tiny, wiggly loops. If a stringy loop vibrates one way, it manifests itself as an electron. If it shimmies some other way, it looks like a quark. Wacky as this idea may sound, there are good reasons why physicists so fervently embraced it. Smolin, the more elegant writer, is far better at conveying the conceptual import of physical theorizing with a minimum of technical detail. Neither book, though, is easy reading for the ­uninitiated.

To put it very briefly, what turned interest in string theory from an oddball enthusiasm to a mainstream occupation was a twofold realization that came in 1984. That’s when two of the early string pioneers, John Schwarz of Caltech and Michael Green, who was based in London, published a paper showing that just a handful of possible string theories were free of mathematical inconsistencies that plagued tradi­tional ­particle-­based models, and also had sufficient capacity (the number and variety of internal vibrations, roughly speaking) to accom­modate all the known elementary particles and their interactions. There was one little difficulty: The systems these theories described existed only in 10 ­dimensions.

Since we live in a world that has but three dimensions of space and one of time, that last point might seem to be a ­deal ­breaker, but so appealing were the other virtues of string theory that physicists found a solution. The “extra” dimensions, they proposed, could be wrapped up so tight that we couldn’t see them. In effect, what we thought of as points in our world were tiny ­six-­dimensional structures. A little bizarre, to be sure, but not ­impossible.