Inflation and Eternal Inflation

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. Vilenkin's proposal for avoiding these problems is also discussed.Comment: 27 pages, including 5 figures, LaTeX (elsart macros for Physics Reports, included). To be published in the David Schramm Memorial Volume of Physics Report

Volumes of balls in Riemannian manifolds and Uryson width

If $(M^n, g)$ is a closed Riemannian manifold where every unit ball has volume at most $\epsilon_n$ (a sufficiently small constant), then the $(n-1)$-dimensional Uryson width of $(M^n, g)$ is at most 1.Comment: 26 page

A short proof of the multilinear Kakeya inequality

We give a short proof of a slightly weaker version of the multilinear Kakeya inequality proven by Bennett, Carbery, and Tao.Comment: 7 pages, minor revision, accepted for publication in the Mathematical Proceedings of the Cambridge Philosophical Societ