The results of ESA’s Planck satellite confirm the basic predictions of inflationary cosmology as well as differentiate between theoretical models, leaving natural inflation as the best fit to the data. Inflationary cosmology was proposed by Alan Guth in 1980 to explain the large-scale smoothness, isotropy, and flatness of the Universe, as well as to dilute an excess of magnetic monopoles. At very early times, a small causally connected region grows exponentially to encompass the portion that will become our observable Universe today, thereby smoothing out any inhomogeneities. An important byproduct of this rapid expansion phase is the density perturbations that are the seeds of galaxies and other large structures today. Both the density perturbations and gravity waves produced by inflation provide sensitive tests of individual inflationary models. In 1990 my collaborators and I proposed natural inflation, in which shift symmetries explain the required properties of the potential. While many models are ruled out by the new data, the original natural inflation as well as modern variants remain viable. The successes of inflation will be reviewed in this talk and the important contributions made by the Planck satellite emphasized.
