In the world about us, the past is distinctly different from the future. More precisely, we say that the processes going on in the world about us are asymmetric in time, or display an arrow of time. Yet this manifest fact of our experience is particularly difficult to explain in terms of the fundamental laws of physics. Newton's laws, quantum mechanics, electro-magnetism, Einstein's theory of gravity, etc., make no distinction between past and future -- they are time-symmetric.

Reconciliation of these profoundly conflicting facts is the topic of this volume. It is an interdisciplinary...