Extremal black holes, Holography & Coarse graining

TL;DR

This paper explores the intersection of gravitational thermodynamics, holography, and quantum mechanics, focusing on black hole microstates, extremal black holes, and the holographic encoding of gravity, highlighting recent theoretical advances and unresolved puzzles.

Contribution

It synthesizes recent developments in understanding black hole microstates, extremal black holes, and holography, proposing new perspectives on the emergence of effective theories near horizons.

Findings

Black hole microstates can be modeled using the LLM description in supergravity.

Extremal black holes exhibit a dual CFT description via the AdS${}_3$/CFT${}_2$ correspondence.

Holographic screens act as diathermic walls, encoding non-local gravity features.

Abstract

I review some of the concepts at the crossroads of gravitational thermodynamics, holography and quantum mechanics. First, the origin of gravitational thermodynamics due to coarse graining of quantum information is exemplified using the half-BPS sector of ${\cal N}=4$ SYM and its LLM description in type IIB supergravity. The notion of black holes as effective geometries, its relation to the fuzzball programme and some of the puzzles raising for large black holes are discussed. Second, I review recent progress for extremal black holes, both microscopically, discussing a constituent model for stationary extremal non-bps black holes, and semiclassically, discussing the extremal black hole/CFT conjecture. The latter is examined from the AdS${}_3$/CFT${}_2$ perspective. Third, I review the importance of the holographic principle to encode non-local gravity features allowing us to relate the gravitational physics of local observers with thermodynamics and the role causality plays in these arguments by identifying horizons (screens) as diathermic walls. I speculate with the emergence of an approximate CFT in the deep IR close to any horizon and its relation with an effective dynamical description of the degrees of freedom living on these holographic screens.