Is inflation testable?
Yes and no. Inflation makes quite strong predictions, including a geometrically flat universe (already verified by measurements of the cosmic microwave background) and a particular set of primordial perturbations, both fluctuations in the matter density and in gravitational waves. The fluctuations in the matter density seem consistent with the predictions of inflation, while looking for gravitational waves from inflation is a major goal of experimenters. However, there are two caveats. First, there are many different models of inflation, and they give somewhat different predictions, so it’s possible to wriggle out of almost any definitive statement. And second, the predictions of inflation may also be predictions of some alternative model which has not yet been thought of. We will never prove inflation beyond any possible doubt; we will only gain increasing (or decreasing) confidence in the inflationary paradigm, as developments in both theory and experiment either remain consistent wi
