Even Without Evidence, String Theory Gains Influence “String theorists keep saying that
they’re succeeding. The rest of us can wonder whether they are walking along the road to
triumph or whether in 20 years they’ll realize that they were
walking into this enormous, beautiful, mathematically elegant cul-de-sac.”

String theory has constantly changed since it first emerged several decades
ago, and even its ardent adherents concede that they still do not understand
more than what Dr. Gross called “the tail of the tiger,” or a few suggestive
parts of what is believed to be a complete theory. Until recently the physical
crux of the theory was thought to be vibrating, 10-dimensional loops of string
roughly a billion trillion times smaller than a proton. Different modes of
vibration of the strings (made of what, no one is sure) represented different
particles in nature.

Now physicists believe the ultimate objects are 11-dimensional membranes.
Either way, the extra dimensions beyond the usual four would be curled up so
as to be nearly imperceptible. And because the vibrations would include the
graviton, the particle thought to transmit gravity, as well as particles involved
in the strong and weak nuclear forces and electromagnetism, string theory
offered the prospect of unifying physics.

But with that aesthetic attraction came deep problems. First, in the 1980’s, it
seemed that the strings had a basic inability to cope with known differences
between particles and their mirror images, and other such broad facts of
nature. But closer study showed that, contrary to all expectation, various
terms in the theory canceled each other, fixing the problem. New York Times