Ten years of extreme gravity tests of general theory of relativity with gravitational-wave observations

TL;DR

Over the past decade, gravitational-wave observations have opened a new frontier for testing general relativity in the extreme gravity regime. The paper inventories a suite of null GR tests—spanning consistency, generation, propagation, polarization, and Kerr-nature checks—applied to BBH and NS binaries, using Bayesian and hierarchical methods to combine information across events. Across GWTC-3, no credible deviations from GR are detected, with progressively tighter constraints on post-Newtonian deviations, graviton mass, and ringdown QNM properties. The work highlights current limitations, such as waveform-systematics and detector networks, while outlining a path forward toward more stringent tests through higher-SNR events, advanced waveform models, and multi-messenger observations.

Abstract

Ten years ago, the first direct detection of gravitational waves (GWs) from the merger of two black holes, GW150914, provided the very first opportunity to test Einstein's general theory of relativity (GR) in the extreme gravity regime, where the gravitational field is strong, characteristic speeds are highly relativistic, and spacetime is dynamical. Such a regime is currently accessible only through coalescing compact binaries. In this review, we summarize the status of testing GR with GW observations and discuss the lessons learned. We also touch upon the challenges we currently have in testing GR and the potential path forward to detect a credible violation of GR, should one exist in the data.