The Direction of Time

A law is postulated which describes the asymmetry of probability distributions under time reversal. Briefly, it states that influences coming from infinity in different directions are statistically independent; a precise statement of the law is provided. This irreversible statistical law supplements the reversible dynamical laws of classical relativistic fields and particles, and from it the time direction of irreversible physical processes can be derived. This is illustrated by deriving the time direction of (i) electromagnetic waves radiated from a dipole, (ii) the scattering of beams of particles, and (iii) recording processes. A restricted law of increasing entropy is also obtained, and some cosmological implications of the theory are indicated. No attempt is made to derive detailed kinetic equations for the irreversible processes in many-particle systems. To ensure that all temporal asymmetries in the theory derive from the postulated law, a symmetric definition of probability is provided.