We study the time evolution of correlation functions in closed quantum systems for nonequilibrium ensembles of initial conditions. For a scalar quantum field theory we show that generic time-reversal invariant evolutions approach equilibrium at large times. The calculation provides a first principles justification of Boltzmann's conjecture that the large-time behavior of isolated macroscopic systems can be described by thermal ensemble averages.
Categories: hep-ph cond-mat hep-lat