Gravitational waves are curves in the shape of space-time that propagate and carry energy.
One way to think about space-time is the curves that things fall along around an object. So I could in some sense paint the shape of space-time by dropping things around the Earth and watching them fall.
Now if the Earth were to move around and collide with the sun those curves have to change with them, and it creates like a wave, like a wave in water. And that's what a gravitation wave is.
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So let's say you have two black holes colliding. They're like mallets on a drum: the shape of the drum begins to rumble in response to the motion of those mallets.
If you were to record the shape of a ringing drum you would play that back as sound.
And that ringing of the shape of space-time travels through the universe at the speed of light, basically unimpeded until it washes over the Earth.
And so when it's played back to us it will be played back as different sounds. So let's say two black holes collide. It has a very characteristic, what we call a chirp. It gets louder and higher in frequency as the black holes collide and you literally hear this sort of chirping up sound.
The big ambition with these experiments is to record the shape of space-time ringing, and to reconstruct the motion of the mallets and the shape of the mallets. And what was going on when that sound was emitted, however long ago, a billion years ago, or however long ago.
—Janna Levin