There is an ill-concealed skeleton in the closet of physics: "As they are currently formulated, general relativity and quantum mechanics cannot both be right." Each is exceedingly accurate in its field: general relativity explains the behavior of the univrse at large scales, while quantum mechanics describes the behavior of subatomic particles. Yet the theories collide horribly under extreme conditions such as black holes or times close to the big bang. Brian Greene, a specialist in quantum field theory, elieves that the two pillars of physics can be reconciled in superstring theory, a theory of everything. Superstring theory has been called "a part of 21st-century physics that fell by chance into the 20th century." In other words, it isn"t all wored out yet. Despite the uncertainties--"string theorists work to find approximate solutions to approximate equations"--Greene gives a tour of string theory solid enough to satisfy the scientifically literate. Though Ed Witten...