Wolfgang Wieland, "Quantum Geometry of the Light Cone"

Wednesday 6 Nov 2024, 16:00 → 17:00 Europe/Rome

0M04

In relativity, the light cone, which emanates from a given event, separates causally connected from causally disconnected events in spacetime. Under the influence of gravity, the light cones bend. A previously expanding light cone can fall back into itself. In this way, the causal structure of spacetime becomes itself dynamical. In my talk, I will explain how to understand this link between gravity, geometry and causality at the quantum level. This is, in fact, an exciting problem common to different approaches to quantum gravity, from holography, to the perturbative S-matrix approach and loop quantum gravity. I will report on three new results on this frontier. First, I provide a non-perturbative characterization of the gravitational phase space on a light cone. Second, the description is taken to the quantum level. Third, an immediate physical implication is found: in the model, the Planck luminosity separates the eigenvalues of the radiated gravitational wave power. Below the Planck power, the spectrum of the radiated power is discrete. Above the Planck power, the spectrum is continuous and the resulting physical states contain caustics that can spoil the semi-classical limit.  The talk is based on arXiv:2402.12578, arXiv:2401.17491, arXiv:2104.05803.