Bounce versus long squeeze: on two different outcomes of quantum gravitational collapse (Zoom), Michal Bobula (University of Wroclaw)

I will discuss aspects of two models of dust collapse in effective quantum gravity. The first is the Husain-Kelly-Santacruz-(Wilson-Ewing) dust collapse model in effective loop quantum gravity. The model of consideration is a special case of the Giesel-Liu-Singh-Weigl framework for polymerized Lemaitre-Tolman-Bondi spacetimes. I will focus on rigorous causal structure analysis, in particular, I will present numerically computed Penrose-Carter diagrams for both homogeneous Oppenheimer-Snyder collapse scenario and nonhomogeneous one with a Gaussian initial dust profile.  In the nonhomogeneous variant, the results for a considerable portion of spacetime will no longer be reliable due to the presence of so-called shell-crossing singularities, however, the problem of (non)-existence of the timelike singularity known from the homogeneous scenario will remain open. In the second part of my talk, I will discuss a modified model of a homogeneous Oppenheimer-Snyder collapse scenario where the exterior of the collapsing dust ball is a Hayward black hole spacetime and the interior is a dust Friedmann-Robertson-Walker cosmology. This interior cosmology will be entirely determined by the junction conditions with the exterior black hole. It turns out to be non-singular, displaying a power-law contraction which precedes a de Sitter phase (long squeeze) or, reversely, a power-law expansion followed by a de Sitter era. We will learn that cosmic inflation, in the time-reversed setting, is a (quantum) mechanism that decelerates the collapsing matter and prevents it from singularity formation.