- qc / 0 50 50 37 v 1 9 M ay 2 00 5 Does Inflation Provide Natural Initial Conditions for the Universe ? 1

If our universe underwent inflation, its entropy during the inflationary phase was substantially lower than it is today. Because a low-entropy state is less likely to be chosen randomly than a high-entropy one, inflation is unlikely to arise through randomlychosen initial conditions. To resolve this puzzle, we examine the notion of a natural state for the universe, and argue that it is a nearly-empty spacetime. If empty space has a small vacuum energy, however, inflation can begin spontaneously in this background. This scenario explains why a universe like ours is likely to have begun via a period of inflation, and also provides an origin for the cosmological arrow of time. Submitted for consideration in the Gravity Research Foundation Essay Competition. Based on hep-th/0410270. This work was supported in part by the U.S. Dept. of Energy, the National Science Foundation, the NDSEG Fellowship, and the David and Lucile Packard Foundation.