Patrick Peter
Institut d'Astrophysique de Paris, IAP

Abstract
Bouncing alternatives to inflationary cosmology permit to avoid the Big-Bang singularity that plagues most other models. As the singularity is a consequence of the classical theory of gravitation (general relativity), it is expected to be naturally avoided upon quantisation, as is indeed often seen to be the case in practice.

Quantising general relativity is notoriously difficult (and yet undone!), but there are ways to at least get an idea of what to expect. I will describe the canonical quantisation procedure and show how to apply it in the simplest case relevant for cosmology: the so-called Friedmann minisuperspace. I’ll explain how this permits to obtain regular, bouncing, semiclassical approximations.

To compare with observational data as those provided by the CMB, one then needs to calculate the predicted spectrum of primordial perturbations. I will then show that there exists some ambiguities, directly related with the quantisation process: a given classical theory has precisely two different sets of predictions, and observations are required to raise the degeneracy, as if also the case in all quantum mechanical systems.

2021 November 30, 15:30

IA/U.Porto
Centro de Astrofísica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto