Bulk supertranslation memories: a concept reshaping the vacua and black holes of general relativity

TL;DR

This paper explores how extending supertranslation symmetries into the bulk spacetime reveals new geometrical features of vacua and predicts significant memory effects during black hole mergers, altering the final stationary metrics.

Contribution

It introduces a consistent extension of supertranslation diffeomorphisms into the bulk, linking memory effects to black hole dynamics and vacuum structure in general relativity.

Findings

Finite supertranslation diffeomorphisms extend into the bulk.

Black hole mergers induce measurable memory effects.

Final stationary metrics deviate from Schwarzschild solutions.

Abstract

The memory effect is a prediction of general relativity on the same footing as the existence of gravitational waves. The memory effect is understood at future null infinity as a transition induced by null radiation from a Poincar\'e vacuum to another vacuum. Those are related by a supertranslation, which is a fundamental symmetry of asymptotically flat spacetimes. In this essay, I argue that finite supertranslation diffeomorphisms should be extended into the bulk spacetime consistently with canonical charge conservation. It then leads to fascinating geometrical features of gravitational Poincar\'e vacua. I then argue that in the process of black hole merger or gravitational collapse, dramatic but computable memory effects occur. They lead to a final stationary metric which qualitatively deviates from the Schwarzschild metric.