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Einstein predicted their existence 101 years ago, and now it's official: we've detected gravitational waves directly for the first time ever!

The Theory of Everything, A Little Bit Closer:
The Amazing Cosmic Discovery That Almost Was:
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NSF/LIGO press conference in Washington, DC


[SciShow intro plays]

Caitlin: If you’ve been around the more science-y corners of the internet lately, you’ve probably seen a lot of people talking about a big announcement that was made today. There were simultaneous press conferences all over the world, and what they announced was, indeed, a huge deal. For the first time ever, we’ve detected gravitational waves!

The idea that gravitational waves should exist comes from Einstein’s Theory of General Relativity, which he published in 1915. He proposed that any kind of mass distorts the shape of the universe, as well as time, aka spacetime. And when a mass moves through the universe, it creates what are basically ripples in spacetime, which he called gravitational waves. We can predict what those gravitational waves would look like, using Einstein’s equations and supercomputers. Problem is, the simulations show that the ripples are almost always ridiculously tiny, which has made them incredibly difficult to detect. And it’s been a bumpy road, with some major setbacks. But now, we have found them.

The signal was detected on September 14, 2015, by the LIGO observatories in both Washington State and Louisiana. The observatories are set up to detect ripples in spacetime, based on the positions of mirrors, with beams of laser-generated light bouncing off of them, to measure their distance. And in September, the mirrors appeared to move a tiny bit. But in fact, the mirrors themselves didn’t move -- the space between them, and all around them, moved! It was a sign that spacetime was being compressed and stretched by gravitational waves.

For the last five months, researchers around the world have been checking and re-checking the data, to make sure that what we’re seeing really is the result of gravitational waves -- as opposed to some kind of glitch, or a misread signal. And now, they’re as sure as they’ll ever be: the signal came from gravitational waves. Specifically, it came from two black holes, 1.3 billion light-years from Earth. These black holes -- each about 150 kilometers in diameter, and about 30 times the mass of our sun -- crashed into each other.

Black holes tend to do everything in extremes, and in this case, their collision created ripples in spacetime so strong that we were able to detect them here on Earth. Even those ripples were tiny -- we’re talking a scale about a thousandth the size of a proton. But the LIGO observatories are precise enough to detect that change. So, we’ve officially discovered gravitational waves, which not only helps prove that another aspect of general relativity is right -- it’s also going to open up a whole new field of discoveries.

Because once we get good at detecting gravitational waves, we can use them to work backwards, and figure out what sort of events out there in the universe would have created any particular set of ripples. In fact, some of the scientists at the press conference in DC were comparing this discovery to the invention of the telescope, in terms of how much more we’re going to be able to learn about the universe.

There’s a lot more we want to talk about with this discovery, and Hank is going to go into those things in a special, in-depth video on Thursday next week. But in the meantime, scientists -- and science enthusiasts -- everywhere are cracking open the champagne. The really nice bottles that they’ve had sitting in a cabinet waiting for the right moment. This is that moment. In the words of David Reitze, the executive director of LIGO: “We did it!”

Thanks for watching this breaking-news episode of SciShow Space, and thanks especially to our patrons on Patreon who help make this show possible.