Dr. Flavio Mercati, Through the Big Bang

by Dr Flavio Mercati (Dipartimento di Fisica, Sapienza Universit`a di Roma)

Wednesday 22 May 2019, 11:00 → 12:00 Europe/Rome

2N22 (Monte S.Angelo)

I will discuss a recent result in classical General Relativity in collaboration with T. Koslowski and D. Sloan. We considered homogeneous but not isotropic cosmological models (Bianchi IX universes) in presence of stiff matter. Homogeneity implies that Einstein's equations reduce to ordinary differential equations, while the stiff equation of state of matter makes the dynamics "quiescent", i.e. the billiard-ball-like behaviour (Misner's "mixmaster" dynamics) near the Big Bang singularity end after a finite number of bounces. Our contribution was to prove the existence of a set of variables that allow to completely describe the dynamics, and for which the existence and uniqueness theorem for ordinary differential equations apply, even at the singularity. This implies that each solution can be continued in a unique way past the Big Bang, at which point the universe changes its spatial orientation. I will then discuss the extension of this result to more realistic cosmological models, in particular I will show that the result still holds in inflationary models. A way towards the extension of the result to non-homogeneous models, relying on recent results on the BKL conjecture, will also be sketched.