  Equilibrium statistical mechanics provides powerful tools to understand
physics at the macroscale. Yet, the question remains how this can be justified
based on a microscopic quantum description. Here, we extend the ideas of pure
state quantum statistical mechanics, which focus on single time statistics, to
show the equilibration of isolated quantum processes. Namely, we show that most
multitime observables for sufficiently large times cannot distinguish a
nonequilibrium process from an equilibrium one, unless the system is probed for
an extremely large number of times or the observable is particularly
fine-grained. A corollary of our results is that the size of non-Markovianity
and other multitime characteristics of a nonequilibrium process also
equilibrate.
