I will begin by reviewing how inflation works, emphasizing how inflation can account for the observed uniformity of the universe, its near-critical mass density, and the spectrum of primordial density perturbations. These density perturbations can be seen today in the cosmic microwave background radiation, and measurements by the Planck satellite and many earlier projects have found beautiful agreement with the predictions of inflation. I will describe how the density perturbations arise from microscopic quantum fluctuations in the early universe, stretched by inflation to astronomical length scales. At the end I will discuss briefly how the density perturbations with wavelengths much larger than the observed universe might give rise to eternal inflation --- inflation that goes on forever producing an infinite number of "pocket universes".
Refreshments in CW 119 at 4:15 p.m.