Does Gravity Fall Down? Evidence for Gravitational Wave Deflection Along
  the Line of Sight to GW 170817
  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. From literature mass and distance measurements of
these halos, we establish at high confidence (significantly greater than 5
sigma) that the gravitational waves of GW 170817 underwent gravitational
deflection to arrive within 1.7 seconds of the photons.
