Microscopic expression of the second law of thermodynamics

Abstract

The microscopic derivation of the second law for macroscopic system is given under the phenomenological assumption that both the initial and final states are described by mutually different canonical ensembles. In particular, it is also shown that the entropy difference between the initial and final states is composed of two positive components. One of the components is expressed as the relative entropy between the initial and final states, while the other is positive due to a dynamical stability called passivity of the canonical ensemble.