Conference

An alternative interpretation of the EHT observations of M87, involving a strongly magnetized ergomagnetosphere, that expels essentially of the gas supplied at large radius as a jet-collimating MHD wind is described. In this case, the emitting regions are approximated as rapidly evolving flares or sparks. Six generic consequences, that can be sought in existing data, are described.

In this talk I will review my work on relational observables in perturbative quantum gravity and put it in context of quantizing coordinates in gravity. I will then discuss more recent work on quantum reference frames and give some outlook on how these two strands could fit together.

Causal set theory is an approach to quantum gravity where the underlying spacetime is a locally finite poset. Glaser gave a formula for the causal set theory analogue of the d'Alembertian in general dimension (growing out of previous work of Sorkin, Benincasa and Dowker, and Dowker and Glaser). The formula contains rational coefficients. Who can resist trying to find something that these coefficients count -- not me! -- so I will tell you about such a something.

Within the AdS/CFT correspondence, two manifestations of the black hole information paradox are given by the nonisometric nature of the bulk-boundary map and by the factorisation puzzle. By considering timeshifted microstates of the eternal black hole, we demonstrate that both these puzzles may be simultaneously resolved by taking into account non-local quantum corrections that correspond to wormholes arising from state averaging. This is achieved by showing, using a resolvent technique, that the resulting Hilbert space for an eternal black hole in Anti-de Sitter space is finite-dimensional with a discrete energy spectrum. The latter gives rise to a transition to a type I von Neumann algebra. Talk based on 2411.09616.

The swampland is the space of those effective field theories that cannot be ultraviolet completed in quantum gravity. Understanding the swampland is relevant for phenomenological model-building and for observational tests of quantum gravity. This talk will have three parts: First, I will introduce the notion relative swamplands, to distinguish the swamplands of different quantum-gravity approaches. Their intersection forms the absolute swampland. Second, I will discuss a subset of swampland conjectures in the light of asymptotically safe gravity. Third, I will explain how asymptotic safety can provide a mechanism to generate universality, when it is realized within an intermediate regime between a non-quantum-field-theoretic quantum regime of gravity and the standard effective field theory regime below the Planck scale.

Gravitational waves are generally a classical GR phenomenon, carrying the imprint of compact merger sources with strong curvature and dynamic interactions. I will give an overview of current and future gravitational-wave observations, and discuss some areas where gravitational waves astronomy makes contact with the quantum regime.

Observers in a typical gravitational or cosmological setting only have access to part of the spacetime and the degrees of freedom in it. The observer sees an open quantum system, and the complete dynamics of all degrees of freedom can be reconstructed by gluing together the (possibly overlapping) open systems associated with each observer. I will discuss what can be learned from treating familiar laboratory closed systems as ensembles of open systems, and how we can begin to extrapolate from there to systems relevant for cosmology.