**Collection Number**C20031

**Collection Date**

**Collection Type**Conference/School

## Reflections on quantum gravity in 2020

Ted Jacobson
University of Maryland

## Random tensors, melonic theories and quantum gravity

Sylvain Carrozza
Perimeter Institute for Theoretical Physics

I will present a brief review of large-N tensor models and their applications in quantum gravity. On the one hand, they provide a general platform to investigate random geometry in an arbitrary number of dimensions, in analogy with the matrix models approach to two-dimensional quantum gravity. Previously known universality classes of random geometries have been identified in this context, with continuous random trees acting as strong attractors. On the other hand, the same combinatorial structure supports a generic family of large-N quantum theories, collectively known as melonic theories.

## Dark Matter meets Quantum Gravity

Manuel Reichert
University of Southern Denmark

## Sprinklings in Causal Set Theory and Local Structures to Discretize Field Propagators

Christoph Minz
University of York

## Virasoro hair and entropy for axisymmetric Killing horizons

Linqing Chen
Okinawa Institute of Science and Technology (OIST)

## Black hole information, spacetime wormholes, and baby universes

Henry Maxfield
University of California

Recent discoveries suggest that semiclassical gravity is more consistent with unitarity than previously believed. I will argue that it makes predictions for the measurements of asymptotic observers that are in complete accord with the idea that black holes are ordinary quantum systems, with states counted by the Bekenstein-Hawking formula. The argument uses the semiclassical gravitational path integral, incorporating newly discovered `spacetime wormhole' topologies. These new ideas revive an old paradigm, relating the information problem to the physics of baby universes.

## Soft modes in quantum gravity

Monica Pate
Harvard University

I will review advances for gravity in asymptotically flat spacetimes arising from investigations into their structure in the infrared. The recently-discovered infinite-dimensional symmetries of the scattering problem is the central result underlying much of the progress. Key examples include symmetry-based explanations for the previously-observed universal nature of infrared phenomena including soft theorems and memory effects.

## Free Energy from Replica Wormholes

Netta Engelhardt
Massachusetts Institute of Technology (MIT)

## Quantum gravity signals in cosmology and gravitational waves

Mairi Sakellariadou
King's College London - Department of Mathematics

I will highlight cosmological consequences of models inspired from string theory or non-perturbative approaches to QG. In particular, I will address the initial singularity, inflation and the late-time accelerated expansion. I will then briefly discuss how recent gravitational waves data can provide a test for some QG models.

## Parallel Discussion Session: Observations at the interface of strong gravity and QG

Thomas Sotiriou
University of Nottingham