Does Gravity Fall Down? Evidence for Gravitational Wave Deflection Along the Line of Sight to GW 170817

Understand

We present a novel test of general relativity (GR): measuring the geometric component of the time delay due to gravitational lensing.

• GR predicts that photons and gravitational waves follow the same geodesic paths and thus experience the same geometric time delay.
• We show that for typical systems, the time delays are tens of seconds, and thus can dominate over astrophysical delays in the timing of photon emission.
• For the case of GW 170817, we use a multi-plane lensing code to evaluate the time delay due to four massive halos along the line of sight.