The Definition of States in Quantum Statistical Mechanics

Abstract

The controversy relative to the use of normal states in quantum physics is discussed in the light of ergodic theory. The nature of the spectrum of the Hamiltonian is shown to play a central role in the decision to enlarge the ordinary frame provided by the traditional density‐matrix formalism. The connection of these considerations with the infinite‐time, infinite‐volume limits in nonequilibrium statistical mechanics is pointed out.