Einstein and Boltzmann: Determinism and Probability or The Virial Expansion Revisited

Boltzmann's Principle S = k ln W was repeatedly criticized by Einstein since it lacked a proper dynamical foundation in view of the thermal motion of the particles, out of which a physical system consists. This suggests, in particular, that the statistical mechanics of a system in thermal equilibrium should be based on dynamics. As an example, a dynamical derivation of the density expansions of the two-particle distribution function, as well as of the thermodynamic properties of a moderately dense gas in thermal equilibrium, is outlined here. This is a different derivation than the usual one based on Gibbs' probabilistic canonical ensemble, where dynamics is eliminated at the beginning and equilibrium statistical mechanics is reduced to statics. It is argued that the present derivation in this paper could, in principle, also be applied to other equilibrium properties and perhaps also to other fields.