00:00What is dark matter? Dark matter should be called invisible matter. It's matter
00:08that doesn't interact with light or with any other charged particles. It's matter
00:14that has nothing to do with light. That's the point. I'm Paul Sutter and this is
00:20Paul Explains, the show where I, you know, explain. How do we know that dark matter
00:27exists? Well, we don't see it in Earth or the solar system. You have to look at big
00:35scales before dark matter really starts to reveal itself. And we saw it first in
00:41the 1930s with the motions of galaxies inside of galaxy clusters. The galaxies
00:47were just moving way too fast. The galaxy cluster should have ripped itself apart
00:52billions of years ago, but there was still existing. So something had to
00:57be gluing all those galaxies. Even our own galaxy, the Milky Way, just shouldn't be
01:03here. Then in the 1970s, we discovered that stars are, again, moving way too fast.
01:13There has to be an extra source of gravity to hold the stars in. And the source of
01:20gravity can't come from something we see like stars or nebula or anything else that
01:25glows. Otherwise, we would have seen it. We would have accounted for it. There is
01:30something inside of galaxies. There is something inside of galaxy clusters that
01:34has mass, that has gravity, but isn't emitting any light. Since the 1970s, we've
01:42gone even further to solidify our understanding of dark matter or that we
01:48know it exists. From the earliest moments of the universe, we have the cosmic
01:53microwave background. This is leftover light from when the universe was just
01:57three hundred eighty thousand years old. And by studying tiny little variations in
02:02that light, we can get a picture, a map of what the universe was like back then. And
02:06guess what? There was a lot of matter back then that didn't interact with light. So
02:11we have all these different pieces of evidence that all fit together and all point
02:17to dark matter. Very likely, dark matter or invisible matter is streaming through the
02:24room you're in right now. But it doesn't interact with light, doesn't interact with
02:29charged particles, it doesn't interact with normal matter. So you just don't see it.
02:33You just don't care about it. It's invisible to you. But at the very largest
02:36scales, it affects how things move. What we do know for sure is that the dark matter does exist.
02:45things can also be applied.
02:46human
02:47and
02:47the life of
02:51human
02:52human
02:53and
02:53human
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