Positive Commutator Method in Nonequilibrium Statistical Mechanics

We extend the method of positive commutators, which was very successfully applied to zero temperature problems, to positive temperatures, i.e. to nonequilibrium quantum statistical mechanics. Using this technique, we give another proof of a fundamental property of large quantum systems, called Return to Equilibrium. This property says that if a system is slightly perturbed from its equilibrium state, then it converges back to it as time goes to infinity.