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 universe 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, believes 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 worked 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 of the Institute for Advanced Study is in many ways the human hero of The Elegant Universe, it is not a human-side-of-physics story. Greene's focus throughout is the science, and he gives the nonspecialist at least an illusion of understanding - or the sense of knowing what it is that you don't know. And that is traditionally the first step on the road to knowledge.