  A fundamental question in many-body physics is how closed quantum systems
reach equilibrium. We address this question experimentally and theoretically in
an ultracold large-spin Fermi gas where we find a complex interplay between
internal and motional degrees of freedom. The fermions are initially prepared
far from equilibrium with only a few spin states occupied. The subsequent
dynamics leading to redistribution among all spin states is observed
experimentally and simulated theoretically using a kinetic Boltzmann equation
with full spin coherence. The latter is derived microscopically and provides
good agreement with experimental data without any free parameters. We identify
several collisional processes, which occur on different time scales. By varying
density and magnetic field, we control the relaxation dynamics and are able to
continuously tune the character of a subset of spin states from an open to a
closed system.
