The Cosmic Microwave Background and Inflation

Inflation in the early universe, there's still quantum fluctuations. This gives rise to density perturbations we see in the cosmic microwave background. It doesn't just lead to densities; it also leads to fluctuations in the gravitational field as well. Those have a unique signature that is called the B mode. The E mode is predicted to be there whether or not there are gravitational waves and it has already been observed. There are other things that can give rise to B modes in later universe that don't give us evidence for inflation or against it.