The most celebrated theory in modern physics faces increasing attacks from skeptics who fear it has lured a generation of researchers down an intellectual dead end.
In its original, simplified form, circa the mid-1980s, string theory held that reality consists of infinitesimally small, wiggling objects called strings, which vibrate in ways that yield the different subatomic particles that comprise the cosmos. An analogy is the vibrations on a violin string, which yield different musical notes.
Advocates claimed that string theory would smooth out the conflicts between Einsteinian relativity and quantum mechanics. The result, they said, would be a grand unifying "theory of everything," which could explain everything from the nature of matter to the Big Bang to the fate of the cosmos.
Over the years, string theory has simultaneously become more frustrating and fabulous. On the one hand, the original theory has become mind-bogglingly complex, one that posits an 11-dimensional universe (far more than the four- dimensional universe of Einstein).