Some reflections on the nature of entropy, irreversibility and the second law of thermodynamics

Abstract

We discuss the conceptual problem of understanding irreversibility and the arrow of time. We point out that by generalizing the concepts of system and state, and the mechanics which governs them, it is possible to create the conceptual framework in which the occurrence of irreversibility can be understood naturally. The destruction of correlations is the principal mechanism which, in the generalized evolution given by a stochastic dynamics, leads to the increase of entropy and all the consequences of the second law. In the Appendix, we treat the case of two interacting spin systems and show that the destruction of correlations and the appropriate stochastic dynamics lead to irreversibility.