There were headlines this year about the discovery of gravitational waves. Gravitational waves are ripples in the curvature of spacetime. They propagate as waves, in the way we are used to seeing the rings propagate from the stone thrown into the water traveling outward from their source.
In the old physics of Isaac Newton, gravitational waves cannot exist – something to do with physical interactions propagating at infinite speed. But then in 1916, Mr. Einstein’s theory of general relativity said that gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation.
In the book Black Hole Blues and Other Songs from Outer Space, Janna Levin writes about them and the quest to record the soundtrack of our universe.
I like Levin’s scientific writing that a non-scientist can enjoy and understand. She is a theoretical astrophysicist and professor of physics and astronomy at Barnard College of Columbia University. I have read two of her earlier books, How the Universe Got Its Spots and, one of my favorites, A Madman Dreams of Turing Machines.
She writes about those dark black holes that science-fiction loves to use. These holes – so odd to think of nothing as something – sometimes collide. Those unilluminated collisions produce energy more powerful than any since the origin of the universe. The energy emanates as waves.
We can’t see these events. No telescope will ever record a collision. The evidence would be the sound of spacetime ringing.
Einstein predicted gravitational waves as part of his theory of curved spacetime. It has taken us a century to begin recording the first sounds of it from space.
I think this unseen aspect is rather wonderful, as in full of wonder. How strange to think that telescopes cannot see events earlier than about 380,000 years after the Big Bang, when the universe became transparent.
There are other theories. One is that it the gravitational influences of other universes.
Levin writes about 50 years of searching for these spacetime waves. The original searchers, Rai Weiss, Kip Thorne, and Ron Drever – have added hundreds of others and new massive instruments sensitive enough to detect a bit of sound from space.
In a conversation on edge.org, she says that:
“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.”
Can you imagine two black holes colliding, curving space and time around them? They are orbiting each other, moving curves, moving black holes, maxing out that cosmic speed limit of light and sucking in time, space, even information. I can imagine it, and yet not imagine it.