Are there echoes of gravitational waves?

Abstract

In several approaches to evading the information paradox, the semiclassical black hole is replaced by an Exotic Compact Object (ECO). It has been conjectured that gravitational waves emitted by the merger of ECOs can reflect off the ECOs and produce a detectable `echo'. We argue that while a part of the wave can indeed reflect off the surface of an ECO, this reflected wave will get trapped by a new closed trapped surface produced by its own backreaction. Thus no detectable signal of the echo will emerge to infinity. The only assumption in this analysis is that causality is maintained to leading order in gently curved spacetime. Thus if echoes are actually detected, then we would face a profound change in our understanding of physics.

13 pages, 2 figures, Essay awarded an Honorable Mention in the Gravity Research Foundation 2022 Awards for Essays on Gravitation

References in corpus (7)

• The information paradox: A pedagogical introduction
• Testing the nature of dark compact objects: a status report
• Echoes from the Abyss: Tentative evidence for Planck-scale structure at black hole horizons
• The flaw in the firewall argument
• Can we observe fuzzballs or firewalls?
• Modave Lectures on Fuzzballs and Emission from the D1-D5 System
• Electromagnetic Albedo of Quantum Black Holes

Cited by in corpus (5)

• Towards a Non-singular Paradigm of Black Hole Physics
• Reflecting boundary conditions in numerical relativity as a model for black hole echoes
• Black hole spectroscopy and nonlinear echoes in Einstein-Maxwell-scalar theory
• Resonant interactions from dynamical perturbers on generic orbits around an extreme mass ratio inspiral
• Firewall black holes and echoes from an action principle