Vacuum structure and the arrow of time
We nd ourselves in an extended era of entropy production. Unlike most other observations, the arrow of time is usually regarded as a constraint on initial con- ditions. I argue, however, that it primarily constrains the vacuum structure of the theory. I exhibit simple scalar eld potentials in which low-entropy initial conditions are not necessary, or not sucient, 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 pro- ducing an empty universe, particularly its high dimensionality and the large dierence in vacuum energy between neighboring vacua.