Science

that produces visible and invisible light. For one thing, we know it's not so much a space-time continuum, it's a gravity-time continuum.

I weigh a few nanograms less here at 6000 feet than I did at sea level, for instance, and I'm aging slightly faster than I would have back there. Neither is perceptible on a human scale, but they are measurable. GPS only works because the even larger time differential is constantly being adjusted.

LIGO has detected gravity waves, but they don't seem to be simultaneous with observable phenomena. The waves might be either faster or slower than the speed of light, we just don't know as yet.