Cosmological inflation is the leading candidate theory for the physics of the early universe, and is in beautiful agreement with current cosmological data such as the WMAP Cosmic Microwave Background measurement. I consider alternatives to inflation with a critical eye, and present a simple argument showing that any model which matches the observed universe must have one of three properties: (1) accelerated expansion, (2) speed of sound faster than the speed of light, or (3) super-Planckian energy density. Download the slides