Physicists believe in a unified description of the world. The complex structures and phenomena we observe today, in every physical system, have at their heart one set of conceptually simple rules, although the mathematical formalism can be staggeringly complex. Cosmology is the study of the structure and evolution of one such system, the Universe, and the same set of rules must apply; there are no "special systems." And these basic rules, which seem to work so extraordinarily well for every other system, are quantum-mechanical in nature.

The gist of quantum cosmology, the description of the entire Universe in terms of quantum theory, is simply this: every system, including the system we call "the Universe" must be described by a quantum-mechanical state function which encapsulates all the "knowledge" of that system. At the heart of the quantum cosmological program lie two goals. The first is the elucidation...