In 1957, in his Princeton doctoral dissertation, Hugh Everett, 111, pro- posed a new interpretation of quantum mechanics that denies the exist- ence of a separate classical realm and asserts that it makes sense to talk about a state vector for the whole universe. This state vector never col- I lapses, and hence reality as a whole is rigorously deterministic. This reality, which is described jointly by the dynamical variables and the state vector, is not the reality we customarily think of, but is a reality composed of many worlds. By virtue of the temporal development of the dynamical variables the state vector decomposes naturally into orthogonal vectors, reflecting a continual splitting of the universe into a multitude of mutually unobservable but equally real worlds, in each of which every good measurement has yielded a definite result and in most of which the familiar statistical quantum laws hold.