From LIGO website re how gravity waves are measured: "The arrival times change because when the arms of the interferometer change lengths, so too do the distances the light waves travel before exiting the interferometer. What gravitational waves do not change, however, is the speed of light. This means that a wave of light that happens to be in a longer arm during a gravitational wave has to travel farther before exiting, so it takes longer to leave than the beam that was in the shorter arm." So does this not mean that the light speed is actually NOT constant? Will you be not measuring different speed of light when there is a gravity wave and different when there isnt?