Classical typicality of the canonical distribution

Abstract

We consider the typicality of the canonical ensemble’s probability distribution from a classical perspective, resuming recent discussions on quantum-mechanical aspects of canonical typicality. In the conventional derivation of the classical canonical distribution for a system S that is weakly coupled to a heat bath B, it is assumed that the composite S +B is epresented by the microcanonical ensemble i.e., by a uniform probability distribution on an energy shell of the composite S +B. Here we show that for a very large heat bath almost all probability distributions defined on this energy shell behave according to the microcanonical ensemble, yielding a marginal probability distribution for S of the canonical form. Consequently, the classical canonical distribution can be regarded as much more “typical” than suggested by the standard derivation.