Science: Hanging the Universe on Strings

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Although even physicists still have difficulty understanding the theory, superstrings may be thought of as one-dimensional bits of energy measuring a billionth of a trillionth of a trillionth of a centimeter in length. Depending on different versions of the theories, these strings may be either open, or closed into a loop, and they interact in two ways: either two strings coalesce into one, or one string splits into two. Depending on how the strings are vibrating and rotating, they can represent any of the known particles of matter, from quarks to electrons. The nature of the interacting particles, in turn, determines which of the four forces is manifested.

The problems have not been entirely ironed out. For one thing, superstrings require ten dimensions in order to work, although scientists know of only four in the real world: three dimensions of space, and one of time. Admits Schwarz: "We don't live in ten dimensions." He and his colleagues offer an explanation for the discrepancy by assuming that after the Big Bang, four dimensions were liberated onto the large scale of the universe, while the remaining six remained rolled up into a little ball at every point in space-time. "What's pretty sure," says Schwarz, "is that today we have to have six of the dimensions disappear. How things got to be this way is a little less clear."

There is an even bigger stumbling block: a complete lack of experimental evidence. No particle accelerator has ever detected anything that suggests the existence of strings. Still, string theorists believe that the immediate goal is not necessarily to search for new particles but simply to reconcile the mathematics of the theory. Says Schwarz: "Experimentalists would love for me to say such and such is an unambiguous consequence of string theory, and if you find it, it's right, and if not, it's dead. But I can't say that yet. They'll just have to be patient."

Witten is optimistic that superstrings hold the key to the long-sought TOE, though he and other theorists hesitate to predict whether the remaining problems of the new theory will be solved in five years or 50. "String theory has a very rich and complicated structure that we don't understand much about," says Witten. "But enough beautiful things have been discovered that we're pretty sure we've just found the tip of the iceberg." --By Natalie Angier.