Observing alternatives to inflation

TL;DR

This paper explores alternative cosmological models to inflation, especially bouncing cosmologies, emphasizing the need for future observations to distinguish between competing theories despite inflation's current success.

Contribution

It highlights the importance of considering and testing alternatives to inflation, such as bouncing models, to strengthen the empirical foundation of cosmological theories.

Findings

Inflation has passed many tests but remains indirectly verified.

Bouncing cosmologies are viable contenders to explain current data.

Future observations could differentiate between inflation and its alternatives.

Abstract

We discuss the possibility that the inflationary paradigm, undoubtfully today's best framework to understand all the present cosmological data, may still have some viable challengers. The underlying idea for such discussions is that although inflation already passed quite a large number of tests, indeed enough to make it part of the so-called ``standard model'' of cosmology, it has always been through indirect measurements: there is not a chance that we may ever directly check its validity, and therefore, in order to assert its factuality with increasing level of confidence, it is required that we compare its predictions not only to observations, but also to as many contenders as possible. Among other categories of possible models, we wish to put the emphasis in particular on bouncing cosmologies that, however not as complete as the inflation paradigm might be, could still represent a reasonnable way of explaining the current data. Hopefully, future data will be able to discriminate between these various sets of theories.