Loop Quantum Gravity: from Computation to Phenomenology

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At the frontier of fundamental physics there is the problem of combining quantum theory and Einstein's General Relativity. Today we have tentative theories that try to achieve this goal or theories of quantum gravity but none of these theories is yet tested by experiments or observations support. The goal of my Discovery program is to develop theoretical tools that could lead us to test these theories. There are two domains where quantum gravity is expected to play a significant role in describe nature: black hole physics and the Big Bang. Einstein's General Relativity disregards quantum theory and is not reliable for predicting what happens at the center of a black hole, or what happens to the black hole in the distant future. A quantum gravity theory currently under study, Loop Quantum Gravity, suggests that quantum effects in these regions determine a transition (a tunnelling effect) that transforms a black hole into a white hole, which can subsequently emit matter. My program of research will develop recently produced computer programs that compute transition probabilities in Loop Quantum Gravity, with the aim of applying them to determine the parameters of this black hole to white hole transition. It will then use these results to compare the predictions of the theory with astrophysical observations, such as high-energy cosmic rays or extra-galactic radio signals, to study if these observations, or other astrophysical phenomena such as dark matter, could be connected to the black-hole to white-hole transition. The same computer codes can also be developed and used to study the behaviour of the primordial universe. Loop Quantum Gravity indicates that the observed cosmic explosion that has generated the universe we observe could be the result of a bounce following a previous contraction phase. This project aims at studying the strong quantum gravitational phenomena expected at the bounce. In particular, it aims at studying the quantum fluctuations of the spacetime geometry generated at that time, and the effect that these might have had on the formation of the large structures of the universe, such as galaxies and galaxy clusters. The objective is to be able to get more elements of knowledge concerting the early life of our Universe, and, hopefully, find some observables traces of primordial quantum gravitational phenomena in observable cosmological phenomena such as the Cosmic Background Radiation.