General Relativity & Quantum Cosmology

Many aspects of classical AdS/CFT can be understood from the point of view of group theory. In this talk, I will argue that applying the same philosophy can provide us with some powerful insights regarding the construction of its flat counterpart, dubbed flat holography. The basic setup will be a massless gauge field of arbitrary (integer) spin propagating on Minkowski spacetime of any dimensions. An asymptotic analysis will reveal the data composing the solution space, as well as the asymptotic symmetries acting on the latter. I will show how part of this solution space can be understood in terms of unitary irreducible representations of the Lorentz group, seen as the group of conformal transformations of the celestial sphere. This interpretation allows us to capture some universal aspects of field theories in Minkowski space-time within the framework of celestial holography, while we will see that the other parts of the solution space have a more natural Carrollian interpretation.

In this talk, we will explore what low-energy experiments on gravitationally mediated entanglement (GME) can reveal about the quantum nature of gravity. We will analyze the key assumptions necessary to interpret GME experiments as evidence for quantum aspects of the gravitational interaction and examine how these assumptions influence our conclusions. Additionally, we will discuss possible modifications to experimental designs aimed at minimizing dependence on assumptions. Then we will discuss what these experiments in different regimes can and cannot probe about gravity’s quantum nature.

I plan to review several ways of testing if the gravitational field has quantum aspects in the low energy regime.  I explain why the hybrid (half quantum/half classical) models are inadequate and how they could be ruled out. Furthermore, I maintain that there is no prima facie reason to expect problems when quantizing gravity in the linear regime; I summarise the main perceived difficulties only to dismiss them as irrelevant. Going beyond the linear regime is challenging in the lab, and one might have to look towards astrophysics and cosmology of the early universe instead.  Finally, many interesting features of quantum field theory could be explored in the low-energy regime that may not necessarily be specific to gravity.