  Using symmetric boundary conditions at separated times, I show analytically
that both the time ordering of (macroscopic) causality and the direction of
entropy increase follow from these boundary conditions. In particular, when the
endpoints have low entropy, these arrows of time point away from the ends and
toward the middle. Causality in this context means that when perturbations are
applied, the effect of the perturbation---the macroscopic change in the
system's behavior---is confined to one temporal side of the perturbations.
These results hold for both mixing and integrable systems, although relaxation
for integrable systems is incomplete. Simulations are presented for purposes of
illustration.
