On August 14, 2017, did you feel taller?
For a brief moment, you were. By about a millionth of the diameter of a proton. You were shorter by that amount, too, a few nanoseconds later. That’s because at 10:30:43 UTC on that day, the gravitational waves from a merging pair of black holes 1.8 billion light years away passed through you, oscillating your height a few times.
I’m guessing you probably didn’t feel it. But LIGO did. And a bigger deal is that Virgo did, too.
LIGO is the Laser Interferometry Gravitational-wave Observatory. It’s actually two detectors, one in Washington State and the other in Louisiana. In 2016 LIGO detected the first ever gravitational waves in human history, one of the last predictions of Einstein’s theory of General Relativity that had yet to be shown directly.
I suggest you read the link above to get all the info, but this bit is the important one:
One of the outcomes of Einstein’s General Relativity theory is that space and time are two facets of the same thing, which we call spacetime. There are lots of analogies for it, but you can think of it as the fabric of space, a four-dimensional tapestry (three of space and one of time) in which we are all embedded. Remember, it’s not literally like this; we’re using an analogy. But it’ll help you picture it.
We think of gravity as a force, pulling us toward an object. But Einstein revisualized it, seeing it as an outcome of the warping of spacetime. A massive object distorts the shape of space, and another object moving through that warped space gets accelerated. We see that as gravity. In other words, matter tells space how to bend, and space tells matter how to move.
Another outcome of the mathematics of GR is that if a massive object is accelerated, it will cause ripples, waves, to move away from itself as it moves. These are actually ripples in the fabric of spacetime itself! Spacetime expands and contracts in complicated ways as a wave passes, a bit like…