Observational tests of inflation

Abstract

We are on the verge of the first precision testing of the inflationary cosmology as a model for the origin of structure in the Universe. I review the key predictions of inflation which can be used as observational tests, in the sense of allowing inflation to be falsified. The most important prediction of this type is that the perturbations will cross inside the Hubble radius entirely in their growing mode, though nongaussianity can also provide critical tests. Spatial flatness and tensor perturbations may offer strong support to inflation, but cannot be used to exclude it. Finally, I discuss the extent to which observations will distinguish between inflation models, should the paradigm survive these key tests, in particular describing a technique for reconstruction of the inflaton potential which does not require the slow-roll approximation.