Inflation and the Beginning of the Universe

The question of whether there was a Beginning of the Universe is a truly challenging puzzle for physics and for philosophy. Classical general relativity implies that our observable universe originated in a singularity fifteen billion years ago, but this may be merely a reflection of the incompleteness of the theory. Inflationary theory and quantum cosmology provide our best current attempt to describe these early moments. It has been claimed that the inflationary mechanism renders moot the question of exactly how the universe began. I argue that, on the contrary, if one asks the question of what was in the past, we find ourselves staring directly back at a putative Beginning after all.

Constraining isocurvature perturbations with cosmic microwave background polarization

The role of cosmic microwave background polarization data in constraining the presence of primordial isocurvature modes is examined. While MAP will be unable to simultaneously constrain isocurvature modes and cosmological parameters, PLANCK will set strong limits on isocurvature modes. If one allows isocurvature modes, the recently obtained BOOMERANG measurement of the curvature of the Universe fails. However, a comparably sensitive polarization measurement on the same angular scales will permit a determination of the curvature without the prior assumption of adiabaticity.

Cosmology in the Laboratory: Defect Dynamics in Liquid Crystals

Liquid crystals are remarkably useful for laboratory exploration of the dynamics of cosmologically relevant defects. They are convenient to work with, they allow the direct study of the "scaling solution" for a network of strings, and they provide a model for the evolution of monopoles and texture. Experiments described here support the simple "one-scale" model for cosmic string evolution, as well as some qualitative predictions of string statistical mechanics. The structure of monopoles and their apparent cylindrical but not spherical symmetry is discussed. A particular kind of defect known as texture is described and is shown to have a dynamical instability-it can decay into a monopole-antimonopole pair. This decay process has been observed occurring in the liquid crystal, and studied with numerical simulations.