Is it just our imagination, or are we hearing more rumbles of dissatisfaction from physicists over superstring theory, which has been touted as the much-sought Theory of Everything?
This theory has been all the rage among theoretical physicists for several years now, though it is untestable in principle and bizarre to describe. Its strength, its proponents say, is its beautiful mathematics, which unifies diverse phenomena. The key question is whether it is anything more than that. In short: Do the superstrings describe reality?
Superstring theory alleges that space is made up of nine dimensions, not just three, six of which are curled up into a tiny ball too small to see--whatever that means. The reason nine dimensions are needed is that otherwise the theory doesn't come out right.
Further, the theory says, the subatomic particles that experimental physicists discover in their atom smashers are not really points but are tiny loops of string. How each little string moves in the nine dimensions of space determines what kind of particle it is.
The fact that this sounds weird is not enough to disqualify it. On first hearing, quantum mechanics sounds weird, too. But there are six decades of experimental evidence in support of quantum mechanics. It is a law of nature well grounded in fact. Superstrings, however, have no such support. While the mathematics behind it may be elegant (we take their word for it), at least some physicists are crying foul.
"Superstring physicists have not yet shown that their theory really works," Sheldon Glashow, a Nobel laureate physicist at Harvard, wrote in a recent issue of The Sciences. "They have not yet made even one teeny-tiny experimental prediction."
Worse, he says, the all-but-complete rupture between theory and experiment raises questions about whether superstring theory qualifies as science. "Until the string people can interpret perceived properties of the real world, they simply are not doing physics," Glashow says. "Should they be paid by universities and be permitted to pervert impressionable students? Will young Ph.D.s whose expertise is limited to superstring theory be employable if and when the string snaps? Are string thoughts more appropriate to departments of mathematics or even to schools of divinity than to physics departments? How many angels can dance on the head of a pin?"
Tough questions, but worth asking. No doubt the string theorists will argue that distinguished colleagues sometimes lose touch with the cutting edge of new work, just as Einstein did. But until superstrings are more than just pretty mathematics, the burden of proof is on the theorists. They have much to prove.