Entropy in an oscillating universe

Abstract

Irreversible processes in a model universe containing gas and radiation are studied. By making simplified but plausible hypotheses regarding the ex­change of energy between the two components, the effects of these pro­cesses are traced, as manifested in the dynamical behaviour of the model and in the evolution of a suitably defined entropy. The dynamical be­haviour is found to change systematically from cycle to cycle, coming to resemble more and more closely that of a system that is just barely bound (i. e. just contracting). The entropy increases continuously, and so provides an arrow of time even in the contracting phase. These conclu­sions are illustrated with numerical computations.