Vacuum Structure and the Arrow of Time
  We find ourselves in an extended era of entropy production. Unlike most other
observations, the arrow of time is usually regarded as a constraint on initial
conditions. I argue, however, that it primarily constrains the vacuum structure
of the theory. I exhibit simple scalar field potentials in which low-entropy
initial conditions are not necessary, or not sufficient, for an arrow of time
to arise. I argue that the string theory landscape gives rise to an arrow of
time independently of the initial entropy, assuming a plausible condition on
the lifetime of its metastable vacua. The dynamical resolution of the arrow of
time problem arises from the same structural properties of the string landscape
that allow it to solve the cosmological constant problem without producing an
empty universe, particularly its high dimensionality and the large difference
in vacuum energy between neighboring vacua.
