Introduction

Abstract

The asymmetry of nature under a ‘reversal of time’ (that is, a reversal of motion and change) appears only too obvious, as it deeply affects our own form of existence. If physics is to justify the hypothesis that its laws control everything that happens in nature, it should be able to explain (or consistently describe) this fundamental asymmetry which defines what may be called a direction in time or even — as will have to be discussed — a direction of time. Surprisingly, the very laws of nature are in pronounced contrast to this fundamental asymmetry: they are essentially symmetric under time reversal. It is this discrepancy that defines the enigma of the direction of time, while there is no lack of asymmetric formalisms or pictures that go beyond the empirical dynamical laws.