Bounding the speed of gravity with gravitational wave observations

TL;DR

This paper uses gravitational wave observations from LIGO to set bounds on the speed of gravity, finding it is consistent with the speed of light within certain confidence intervals, and projecting improvements with more detections.

Contribution

It introduces a Bayesian method to constrain the gravitational wave speed using multiple detections, providing the first bounds from LIGO data and forecasts future constraints.

Findings

Current bounds: 0.55c < c_gw < 1.42c at 90% credible interval.

Approximately 20 detections could constrain c_gw within 20% of c.

Five detections by LIGO-Virgo-Kagra could constrain c_gw within 1% of c.

Abstract

The time delay between gravitational wave signals arriving at widely separated detectors can be used to place upper and lower bounds on the speed of gravitational wave propagation. Using a Bayesian approach that combines the first three gravitational wave detections reported by the LIGO collaboration we constrain the gravitational waves propagation speed c_gw to the 90% credible interval 0.55 c < c_gw < 1.42 c, where c is the speed of light in vacuum. These bounds will improve as more detections are made and as more detectors join the worldwide network. Of order twenty detections by the two LIGO detectors will constrain the speed of gravity to within 20% of the speed of light, while just five detections by the LIGO-Virgo-Kagra network will constrain the speed of gravity to within 1% of the speed of light.