What to measure in non-perturbative quantum gravity

by Marcus Reitz (Radboud University Nijmegen)

Tuesday 17 Mar 2020, 16:15 → 18:15 Europe/Berlin

Abbeanum SR 102

An open question in quantum gravity is if and how small scale fluctuations and inhomogeneities behave in such a way, that at some larger scale they can be well approximated by a (semi-)classical geometry. Causal Dynamical Triangulation (CDT) is a non-perturbative approach to quantum gravity, based on a lattice regularisation of space-time, in which these kind of questions possibly can be asked. To address these questions it is necessary to find a suitable set of scale dependent observables with a clear relation to curvature, which is a highly non-trivial task in a framework without a background metric. After introducing the framework and its phase diagram, I will present two new candidate observables and discuss their advantages and disadvantages. One is based on Wilson loops and one on discrete approximate Killing vectors. Especially the discrete approximate Killing vectors show promise as a tool for quantum gravity to study the appearance of a (semi-)classical geometry under coarse-graining. As a proof of concept, I will present preliminary results on a quantum ensemble of two-dimensional toroidal geometries in CDT.