The view of the natural world held by physicists today is the result of a profound revolution in human thought that began about the turn of this century. One of the most intriguing characteristics of that revolution has been the overthrow of some fundamental, "obvious," "common-sensical" views of natural events.

For example, a cornerstone of classical physics for nearly three centuries had been the belief in cause-and-effect determinism. Physicists assumed that if they knew the state of a particle and the forces acting on that particle at any one moment in time, they could then predict the future of that particle with certainty. Werner Heisenberg 's development of the uncertainty principle showed that this view was untenable and that scientists could do no more than talk about the probability that various events would or would not occur.

Perhaps the most profound of all revolutionary concepts to develop at...