The effect of these gravitational waves is to squeeze and stretch space. If you were floating near these black holes, you would literally be squeezed and stretched. If you were close enough, you would feel the difference between the squeezing and stretching on your face or your feet. We’ve even conjectured that your eardrum could ring in response, like a resonant membrane, so that you would literally hear the wave, hear it even in the absence of a medium like air. Even though we think that empty space is silent, in these circumstances you would hear the black holes collide but you wouldn’t see them; it would happen in complete darkness. The two black holes would be completely dark, and your only evidence of their collision would be to hear the spacetime ringing.
JANNA LEVIN is a professor of physics and astronomy at Barnard College of Columbia University. She is the author of How the Universe Got Its Spots; A Madman Dreams of Turing Machines; and most recently, Black Hole Blues and Other Songs from Outer Space. Janna Levin's Edge Bio Page