Editorial: Coarse graining in quantum gravity -- Bridging the gap between microscopic models and spacetime physics

TL;DR

This paper discusses how the Renormalization Group can connect microscopic quantum gravity models to observable spacetime physics, highlighting its potential to unify approaches and explain emergent symmetries despite traditional challenges.

Contribution

It reviews recent developments in applying the Renormalization Group to quantum gravity, emphasizing reconciliation with background independence and the emergence of spacetime symmetries.

Findings

Renormalization Group links microscopic models to observable physics

Universality classes may unify diverse quantum gravity approaches

Emergence of spacetime symmetries at fixed points

Abstract

The Renormalization Group encodes three concepts that could be key to accelerate progress in quantum gravity. First, it provides a micro-macro connection that could connect microscopic spacetime physics to phenomenology at observationally accessible scales. Second, it enables a search for universality classes that could link diverse quantum-gravity approaches and allow us to discover that distinct approaches could encode the same physics in mathematically distinct structures. Third, it enables the emergence of symmetries at fixed points of the Renormalization Group flow, providing a way for spacetime symmetries to emerge from settings in which these are broken at intermediate steps of the construction. These three concepts make the Renormalization Group an attractive method and conceptual underpinning of quantum gravity. Yet, in its traditional setup as a local coarse-graining, it could appear at odds with concepts like background independence that are expected of quantum gravity. Within the last years, several approaches to quantum gravity have found ways how these seeming contradictions could be reconciled and the power of the Renormalization Group approach unleashed in quantum gravity. This special issue brings together research papers and reviews from a broad range of quantum gravity approaches, providing a partial snapshot of this evolving field.