Inflationary Models and Connections to Particle Physics †

The basic workings of inflationary models are summarized, along with the arguments that strongly suggest that our universe is the product of inflation. The mechanisms that lead to eternal inflation in both new and chaotic models are described. Although the infinity of pocket universes produced by eternal inflation are unobservable, it is argued that eternal inflation has real consequences in terms of the way that predictions are extracted from theoretical models. The ambiguities in defining probabilities in eternally inflating spacetimes are reviewed, with emphasis on the youngness paradox that results from a synchronous gauge regularization technique. To clarify (but not resolve) this ambiguity, a toy model of an eternally inflating universe is introduced. Vilenkin’s proposal for avoiding these problems is also discussed, as is the question of whether it is meaningful to discuss probabilities for unrepeatable measurements. Talk given at the Pritzker Symposium on the Status of Inflationary Cosmology, Chicago, Illinois, January 29 – 31, 1999. To appear in the proceedings. This work is supported in part by funds provided by the U.S. Department of Energy (D.O.E.) under cooperative research agreement #DF-FC02-94ER40818, and in part by funds provided by NM Rothschild & Sons Ltd and by the EPSRC. Present address.