That (some, not all) gravitational waves travel at the speed of light was Eddington's 1922 fabrication (nothing to do with Einstein's general relativity): http://rspa.royalsocietypublishing.o...6/268.full.pdf

Also, the simultaneous arrival of optical signals and gravitational waves (if the latter exist; actually they don't) in LIGO's GW170817 experiment can only be discussed if the gravitational waves experience Shapiro delay, which is nonsense of course. (Does Einstein's relativity predict Shapiro delay for gravitational waves?)

Conclusion: LIGO conspirators obviously FAKED the simultaneous arrival of optical signals and gravitational waves in the GW170817 (neutron-star-collision) experiment.

Pentcho Valev