Testing Quantum Black Holes with Gravitational Waves

TL;DR

This paper discusses how gravitational wave observations from black hole mergers can test the hypothesis that black hole horizon areas are quantized, potentially confirming or ruling out specific quantum gravity proposals.

Contribution

It proposes a method to test black hole area quantization using gravitational wave data, offering a way to confirm or refute theoretical models of quantum black holes.

Findings

Detection of ring down signals can test horizon area quantization.

Multiple events with different spins can rule out specific quantization proposals.

Echoes in gravitational waves could indicate near-horizon quantum effects.

Abstract

We argue that near-future detections of gravitational waves from merging black hole binaries can test a long-standing proposal, originally due Bekenstein and Mukhanov, that the areas of black hole horizons are quantized in integer multiples of the Planck area times an $\mathcal O(1)$ dimensionless constant $\alpha$. This condition quantizes the frequency of radiation that can be absorbed or emitted by a black hole. If this quantization applies to the "ring down" gravitational radiation emitted immediately after a black hole merger, a single measurement consistent with the predictions of classical general relativity would rule out most or all (depending on the spin of the hole) of the extant proposals in the literature for the value of $\alpha$. A measurement of two such events for final black holes with substantially different spins would rule out the proposal for any $\alpha$. If the modification of general relativity is confined to the near-horizon region within the hole's light ring and does not affect the initial ring down signal, a detection of "echoes" with characteristic properties could still confirm the proposal.