Many physicists charge that TOEs, as they are sometimes abbreviated, are mathematical abstractions without any basis in physical reality. But Greene demonstrates that the TOE represents one of the most promising pursuits in science today.

As it stands now, each major physics theory describes only part of the universe. For example, Einstein's General Theory of Relativity describes gravity, the force that holds galaxies together and makes apples fall. Quantum theory predicts the behavior of very small particles such as electrons. Electrons, in turn, are mainly governed by electromagnetism the force that holds magnets to your refrigerator and causes lightning bolts to strike the earth.

"The Elegant Universe," by Brian Greene

As Greene points out in "The Elegant Universe," these theories clash when applied to the same phenomena. For instance, when equations from quantum theory and general relativity are combined to describe the behavior of a black hole, they provide answers that turn out to be meaningless. Greene thinks this means one or both theories must have something wrong.

So Greene and other physicists are devoting their careers to building a single theory that can accommodate all forces and particles and anticipate their behavior together. They want a single theory that not only predicts all the possible particles but correctly describes the four different forces -- gravity, electromagnetism, and their two lesser-known siblings: the weak force, best known for causing radioactive atoms to decay, and the strong force, which binds the cores of atoms.

Although several ideas for the TOE exist, few have aroused the passion of physicists the way superstring theory has. Greene explains the theory in remarkably simple language. Granted, it's sometimes difficult to endure his brimming confidence that physics may soon give us the deepest possible description of nature. Yet to his credit, Greene persuasively argues that superstring theory is the most revolutionary idea in physics since Einstein's time.

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