The detection of the neutron star inspiral GW170817 in 2017, detected through both gravitational waves and gamma rays, provides the so far by far best limit on the difference between the speed of light and that of gravity. Photons were detected 1.7 seconds after peak gravitational wave emission; assuming a delay of zero to ten seconds, the difference between the speeds of gravitational and electromagnetic waves, vGW − vEM, is constrained to between −3×10−15 and +7×10−16 times the speed of light.
One YEC casualty of the confirmation that the speed of gravitational wave and light waves were both finite and equal to c, was Dr. Jason Lisle’s Asymmetrical Speed of Light explanation of distance starlight.