WEBVTT - What Happens When Galaxies Collide? 0:00:07.640 --> 0:00:10.000 Hey, Daniel, what keeps you up at night? Oh? I 0:00:10.039 --> 0:00:14.240 worry about a lot of things. Financial crises, my kids 0:00:14.280 --> 0:00:16.760 growing up to be just like me, all sorts of stuff. 0:00:16.880 --> 0:00:20.480 I worry about that too for them. You worry about 0:00:20.480 --> 0:00:22.240 my kids growing up to be just like me. We 0:00:22.320 --> 0:00:26.040 can't have more of him in the world, Okay, But 0:00:26.200 --> 0:00:29.319 like on a galactic scale, on a universe scale, what's 0:00:29.360 --> 0:00:31.520 something we should be concerned about. Well, we do have 0:00:31.600 --> 0:00:33.239 a lot of things look forward to in terms of 0:00:33.240 --> 0:00:35.920 our galaxy. If we survived the Sun exploding and the 0:00:35.920 --> 0:00:38.640 waters the Earth boiling off, then we have something pretty 0:00:38.720 --> 0:00:41.120 dramatic to look forward to, which is that our galaxy, 0:00:41.159 --> 0:00:44.040 the Milky Way, is going to collide with their nearest 0:00:44.080 --> 0:00:47.560 neighbor and Dromeda. Meaning right now, there's an entire galaxy 0:00:47.880 --> 0:00:51.440 Drameda heading towards us at this very moment. That's right. 0:00:51.640 --> 0:00:53.960 It's like somebody shot it at us with a slingshot 0:00:54.000 --> 0:00:56.440 and it's zooming right towards us, and it's going to 0:00:56.560 --> 0:01:17.440 hit us smack on him. And I'm Daniel, and this 0:01:17.480 --> 0:01:21.280 is our podcast. Daniel and Jorge explained the universe on 0:01:21.319 --> 0:01:27.840 the episode. Today, we're going to talk about what will 0:01:27.880 --> 0:01:31.160 happen when galaxies collide. Is this something we should all 0:01:31.200 --> 0:01:34.120 be worrying about our packing our bags, about building our 0:01:34.200 --> 0:01:36.880 underground shelters or are we all screwed? Or is it 0:01:36.880 --> 0:01:39.200 just going to be like a big nothing? How much 0:01:39.200 --> 0:01:43.080 should I pack? You should definitely be stalking lentils no 0:01:43.120 --> 0:01:45.400 matter what. Lentils are a good investment for any of 0:01:45.480 --> 0:01:49.000 these end of the world. Not just beans, no, no, lentils. 0:01:49.680 --> 0:01:52.480 I mean lentils are kind of lego for a galactic emergency. 0:01:53.600 --> 0:01:56.040 That's the that's the one to go with. Yeah, absolutely, 0:01:56.040 --> 0:01:58.120 I would. I would invest in lentils heavily. And it's 0:01:58.120 --> 0:02:00.760 not just because I happened to purchase lentils just before 0:02:00.840 --> 0:02:03.240 we recorded this podcast and I'm trying to drum up 0:02:03.240 --> 0:02:07.000 the lentil futures, you know. I'm I'm sincerely worried about 0:02:07.000 --> 0:02:09.160 our listeners, and I encourage you all to go out 0:02:09.200 --> 0:02:11.679 there in stockpi lentils. Well that's a whole hill of 0:02:11.720 --> 0:02:15.440 beans worth of advice right there, that's right. And so 0:02:15.480 --> 0:02:18.320 this is the question and today's podcast, what will happen 0:02:18.360 --> 0:02:21.720 when our galaxy, the Milky Way, collides with the neighboring galaxy? 0:02:21.880 --> 0:02:24.200 And this question I love not just because it's huge 0:02:24.240 --> 0:02:26.519 and dramatic and galactic and all this sort of stuff, 0:02:26.680 --> 0:02:29.680 but because it was suggested by one of our listeners. 0:02:29.720 --> 0:02:33.280 That's right. It's Blake from Australia who listens to this 0:02:33.320 --> 0:02:36.320 podcast on her commute to work every day. That's right. 0:02:36.360 --> 0:02:38.520 And she didn't tell us what she uses to commute. 0:02:38.560 --> 0:02:41.119 Maybe she rides in a beautiful pickup truck, maybe she's 0:02:41.160 --> 0:02:45.200 in the back of a limo, maybe rides kangaroo who knows, 0:02:45.360 --> 0:02:48.960 that's right, with a really nice sound system. Yeah, but 0:02:49.040 --> 0:02:51.960 she has some interesting feedback for us about our podcast. Right, 0:02:52.000 --> 0:02:54.560 what did she say? Yeah, she said that she likes 0:02:54.639 --> 0:02:57.000 listening to me explain things, but she also likes when 0:02:57.040 --> 0:03:00.720 you interrupted me. She said that often you interrupt me 0:03:00.960 --> 0:03:03.200 just the same moment when she has a question and 0:03:03.240 --> 0:03:05.480 you pose the same question that was bouncing around in 0:03:05.520 --> 0:03:08.560 her head that she was shouting at her limo sound 0:03:08.560 --> 0:03:10.880 system or kangaroo speakers or whatever it is she us 0:03:10.919 --> 0:03:13.720 going to listen to. And so I was glad for that, 0:03:13.840 --> 0:03:15.760 because you know, I like when you interrupt me. Also 0:03:15.800 --> 0:03:18.160 it breaks the flow and it keeps me from just 0:03:18.280 --> 0:03:20.560 droning on and on and on. So Thank you Blake 0:03:20.600 --> 0:03:24.640 for suggesting this topic, and thank you Orge for occasionally interrupting. Yeah, no, 0:03:24.680 --> 0:03:31.720 I'm happy to be rude. It seems to come naturally. Yeah, yeah, 0:03:31.720 --> 0:03:34.640 And so that's the topic of today's podcast, And we 0:03:34.760 --> 0:03:37.360 thought first before we dove into it, we would walk 0:03:37.360 --> 0:03:39.480 around like we usually do and ask people, are you 0:03:39.520 --> 0:03:41.839 worried about a galactic collision? What do you think will 0:03:41.880 --> 0:03:45.800 happen when our galaxy collides with a neighboring galaxy? So 0:03:45.960 --> 0:03:49.680 put that image in your mind to giant galaxies, full 0:03:49.760 --> 0:03:52.880 stars running into each other. What do you think is 0:03:52.880 --> 0:03:57.000 going to happen? Here's what people had to say, big explosion. 0:03:57.200 --> 0:04:01.120 We'd probably all die. It is going to be mostly 0:04:01.160 --> 0:04:04.080 nothing because of all the empty space around the world, 0:04:04.400 --> 0:04:07.080 although there will be some crushes and so on in 0:04:07.080 --> 0:04:10.760 the way. Okay, probably somewhere between a glacial, slow event 0:04:10.800 --> 0:04:13.720 that we won't even notice and nothing at all. Maybe 0:04:13.760 --> 0:04:17.080 leaning towards nothing at all. I think it would probably 0:04:17.120 --> 0:04:21.640 be a big explosion with something pretty crazy happening. All right, 0:04:21.720 --> 0:04:23.919 That was a little anti climatic. People seem to have 0:04:24.040 --> 0:04:26.440 very low expectations of this event. What do you mean 0:04:26.480 --> 0:04:27.960 It seems like half of the people are like it's 0:04:27.960 --> 0:04:30.800 gonna be nothing, and the other half of like big explosions, 0:04:30.839 --> 0:04:36.320 we're all gonna die. Well, why do you why do 0:04:36.360 --> 0:04:38.159 you think Blake asked this question? Do you think there's 0:04:38.160 --> 0:04:40.679 something she's concerned about or is something she's curious about? 0:04:40.720 --> 0:04:42.960 You know? I think Blake is probably deciding whether or 0:04:42.960 --> 0:04:46.479 not to stock up on lentils. You know, Um, she's 0:04:46.480 --> 0:04:50.880 probably right now, story she asked. I think it's part 0:04:50.960 --> 0:04:53.160 of just trying to be a sort of a citizen 0:04:53.200 --> 0:04:56.080 of the larger universe, you know, wondering where we stand 0:04:56.520 --> 0:04:58.719 and trying to think bigger than just our planet, you know, 0:04:58.720 --> 0:05:01.160 because there's so much going on out there, it's so 0:05:01.160 --> 0:05:03.640 easy to just walk around on the surfaces planet never 0:05:03.680 --> 0:05:06.000 really look up and remember that there is an enormous 0:05:06.040 --> 0:05:09.719 amount of stuff happening out there, And then you wonder like, well, 0:05:09.800 --> 0:05:11.640 how is that relevant to me? And is he going 0:05:11.720 --> 0:05:14.680 to ruin my life? Or can I go on ignoring it? Um? So, 0:05:14.720 --> 0:05:16.599 I think maybe she was just sort of thinking into 0:05:16.640 --> 0:05:18.840 the deep future and wondering like, how long can this 0:05:18.880 --> 0:05:23.080 whole ridiculous, beautiful thing we call life on Earth go on? Right? 0:05:23.240 --> 0:05:25.919 Is it going to change from how it is now, right, Yeah, 0:05:25.960 --> 0:05:28.360 exactly do I need to change the way I live? 0:05:28.520 --> 0:05:30.839 Does it affect any decision making? On the other hand, 0:05:30.880 --> 0:05:33.520 it could be that Blake, like many people, is just 0:05:33.560 --> 0:05:35.800 a thinker and likes to think about these scenarios, and 0:05:35.960 --> 0:05:38.240 she probably heard that the Milky Way will collide with 0:05:38.240 --> 0:05:40.360 Andromeda and wonder like, what's that going to be? Like? 0:05:40.920 --> 0:05:42.520 You know this this this is the other side of 0:05:42.560 --> 0:05:45.000 me that likes to smash stuff together. I mean, I'm 0:05:45.040 --> 0:05:47.599 a particle physicist, but then we have the whole universe 0:05:47.600 --> 0:05:49.279 to play with, right, and so you might wonder, like 0:05:49.440 --> 0:05:52.400 what happens when planets collide, what happens when solarcisms? Like 0:05:52.720 --> 0:05:55.000 oh my gosh, what if we could build a galaxy 0:05:55.040 --> 0:05:57.280 collider and shoot them against each other and smash them 0:05:57.279 --> 0:05:59.280 into each other? Right, So it just comes out of 0:05:59.320 --> 0:06:03.880 like a curiosity to see stuff break by smashing it together. Yeah, well, 0:06:03.920 --> 0:06:05.760 let's let's take it step back and just kind of 0:06:05.800 --> 0:06:09.480 think about why even galaxies would collect, Like is this 0:06:09.520 --> 0:06:12.040 a relevant question that is something that happens a lot 0:06:12.120 --> 0:06:15.680 galaxies colliding, or is it something that's incredibly rare. It 0:06:15.720 --> 0:06:18.680 turns out galaxies colliding happens all the time. It's like 0:06:18.720 --> 0:06:22.360 a totally natural thing. And our galaxy. Yeah, not only 0:06:22.400 --> 0:06:24.800 will our galaxy collide with and John Day in a 0:06:24.880 --> 0:06:28.760 few billion years, it's currently colliding with other smaller galaxies. 0:06:28.800 --> 0:06:33.039 That what Yeah, we're in a collision right now. Yeah, 0:06:33.080 --> 0:06:36.599 that's right. And remember that the galactic time scales are 0:06:36.720 --> 0:06:39.720 very different. You know, the galaxy takes about two hundred 0:06:39.960 --> 0:06:44.360 million years just to rotate once, to go around once. Yeah, 0:06:44.400 --> 0:06:48.880 so one galactic year is two hundred million earth years. 0:06:49.880 --> 0:06:52.640 But it looks so swirly. It looks you know, you 0:06:52.680 --> 0:06:54.480 know what I mean, Like it looks like it's in motion, 0:06:54.960 --> 0:06:57.200 but it's actually it is. It is in motion, it's 0:06:57.240 --> 0:07:00.240 just very slow, right, And so all these things are 0:07:00.360 --> 0:07:03.920 dancing around each other and sometimes they bump into each other. 0:07:03.960 --> 0:07:05.800 And the thing I think is amazing is that, you know, 0:07:05.920 --> 0:07:08.880 until like a hundred years ago, we didn't even know 0:07:08.960 --> 0:07:11.240 there were other galaxies. Like we looked up at the 0:07:11.320 --> 0:07:13.760 night sky and we saw stars, and we thought, oh, 0:07:13.840 --> 0:07:16.160 there's just stars that go on forever. At the universe 0:07:16.200 --> 0:07:18.480 is just filled with stars. The universe is just like 0:07:18.520 --> 0:07:22.560 a giant MESSI pinpoints, right, just stars. Yeah, yeah, like 0:07:22.600 --> 0:07:26.560 somebody had scattered stars across the cosmos, right, And it 0:07:26.680 --> 0:07:29.960 was Hubble, the guy for whom the telescope and the 0:07:30.000 --> 0:07:32.240 constant are named. He's the guy who figured out, oh, 0:07:32.280 --> 0:07:33.760 some of those things that are really far out there 0:07:33.760 --> 0:07:36.800 are not stars. There are other galaxies. Right, So there's 0:07:37.000 --> 0:07:39.160 the universe is filled with other galaxies. And of course 0:07:39.360 --> 0:07:42.800 there are more galaxies than stars, and and then each galaxy, 0:07:42.840 --> 0:07:45.800 of course, contains hundreds of billions of stars, and so 0:07:46.080 --> 0:07:48.880 the numbers pretty quickly blow your head up before you 0:07:48.920 --> 0:07:51.440 can understand them. But the point I wanted to make 0:07:51.520 --> 0:07:54.280 was that we didn't realize there were galaxies until recently, 0:07:54.600 --> 0:07:57.800 and now we're realizing that galaxies are in motion relative 0:07:57.840 --> 0:08:00.600 to each other, and they're moving. Like the these galaxies 0:08:00.640 --> 0:08:02.000 that we see out there in the sky, they're not 0:08:02.040 --> 0:08:05.360 just like hanging there in space never to change, right, 0:08:05.720 --> 0:08:09.080 They are moving their dynamic things, and they're constantly in motion, 0:08:09.120 --> 0:08:12.000 and they have huge gravitational attraction. Well, let's break it down. 0:08:12.040 --> 0:08:14.920 What exactly is a galaxy? I mean, I know it's 0:08:14.920 --> 0:08:17.400 like kind of like a collection of stars, but you 0:08:17.440 --> 0:08:21.000 know what, why do stars clump together like that? First 0:08:21.000 --> 0:08:24.720 of all? And what makes a galaxy special? Like, why 0:08:24.760 --> 0:08:27.400 is it more than just a clump of stars. Well, 0:08:27.440 --> 0:08:29.640 what makes our galaxy special is that you're in it. Horse. 0:08:29.920 --> 0:08:33.680 There's no other galaxy that features such a good looking, 0:08:33.760 --> 0:08:37.920 funny cartoonists, meet me and lentils. We make it, make 0:08:37.960 --> 0:08:42.480 it habitable, right, Okay, so what's the recipe for a galaxy? Right? Well, 0:08:42.880 --> 0:08:45.360 the thing that the galaxies have the most of, remember, 0:08:45.440 --> 0:08:49.040 is dark matter. In general, there's about five times as 0:08:49.120 --> 0:08:52.280 much dark matter as there is any other kind of matter, 0:08:52.320 --> 0:08:54.160 you know, the stuff that makes up gas and dustin 0:08:54.240 --> 0:08:57.240 stars and people and cartoonists and and and ice cream. 0:08:57.480 --> 0:09:00.120 So it's mostly dark matter. So that's the stuff we 0:09:00.200 --> 0:09:02.440 can't see your touch. I mean, we did a whole 0:09:02.440 --> 0:09:05.080 podcast episode on dark matter, but it just in case 0:09:05.240 --> 0:09:08.640 somebody didn't listen to it. Um, it's like this weird 0:09:08.920 --> 0:09:14.760 invisible dark gravity thing that's hanging out every galaxy has, 0:09:15.000 --> 0:09:17.880 that's right. Yeah, we call it dark and matter because 0:09:17.960 --> 0:09:19.600 we can't see it. So it's dark and we know 0:09:19.679 --> 0:09:23.520 it gives gravity, so therefore it's matter and the crazy 0:09:23.559 --> 0:09:25.400 things that until you know, a few decades ago, we 0:09:25.400 --> 0:09:27.320 didn't even know it existed. And now we know that 0:09:27.520 --> 0:09:30.800 galaxies are mostly made up of this stuff. Right. So 0:09:31.000 --> 0:09:32.920 number one ingredient when you want to make a galaxy 0:09:33.040 --> 0:09:34.959 is you have to have dark matter. It's like five 0:09:35.040 --> 0:09:37.840 times more than the stars, right, yeah, exactly, Like a 0:09:37.880 --> 0:09:40.640 galaxy is basically a clump of dark matter with a 0:09:40.679 --> 0:09:42.880 few sprinkles of stars in it. That's right. Yeah. If 0:09:42.880 --> 0:09:45.840 a galaxy was a cupcake, right, the dark matter would 0:09:45.880 --> 0:09:48.719 be the chocolate cake, and you know there everything else 0:09:48.760 --> 0:09:51.199 would be the frosting and the sprinkles. The gas and 0:09:51.240 --> 0:09:53.000 the dust would be the frosting. The stars would be 0:09:53.000 --> 0:09:55.880 the sprinkles on top. Oh I see, Okay, that's kind 0:09:55.880 --> 0:09:59.440 of the right proportions. Yeah, something like that. Um, So 0:09:59.480 --> 0:10:02.280 you start with big blob of dark matter and that's 0:10:02.360 --> 0:10:04.720 most of it, and then after that you have huge 0:10:04.720 --> 0:10:07.160 amounts of gas and dust, right, And that's the stuff 0:10:07.200 --> 0:10:09.679 that's left over from the Big Bang or left over 0:10:09.720 --> 0:10:12.720 from stars exploding, and those the ingredients you need to 0:10:12.760 --> 0:10:15.480 make planets and stars and all sorts of stuff that 0:10:15.480 --> 0:10:18.480 you're familiar with, right. And so you have dark matter, 0:10:18.600 --> 0:10:22.560 you have gas, you have dust, you have planets and 0:10:22.760 --> 0:10:26.320 stars and black holes right, Like there's just a little 0:10:26.320 --> 0:10:29.880 black hole sprinkled throughout throughout probably, But there's a huge 0:10:30.280 --> 0:10:33.440 giant black hole at the center of every galaxy. That's right. 0:10:33.679 --> 0:10:35.520 I can't believe I forgot the black hole. The black 0:10:35.559 --> 0:10:38.080 hole at the center of almost every galaxy is huge. 0:10:38.120 --> 0:10:40.959 It's like, you know, millions of solar masses and it's 0:10:40.960 --> 0:10:42.360 sitting there at the center of the black hole, and 0:10:42.360 --> 0:10:44.600 it's it's got a lot of stuff to it also, right, 0:10:44.600 --> 0:10:46.800 it carries a lot of mass and so it contributes. 0:10:47.160 --> 0:10:48.959 So that's what a galaxy is. And you know, a 0:10:49.040 --> 0:10:51.680 galaxy couldn't really form without all those elements, Like you 0:10:51.679 --> 0:10:54.400 couldn't really have a galaxy without dark matter because dark 0:10:54.400 --> 0:10:58.040 matter provides the gravitational attraction to suck all this stuff together. 0:10:58.400 --> 0:11:00.920 You know, they do these simulations of the universe. They say, 0:11:00.960 --> 0:11:02.800 what would the universe look like if you never had 0:11:02.880 --> 0:11:04.840 dark matter in it? And it would take a lot 0:11:04.880 --> 0:11:08.160 longer for galaxies to form because dark matter has pulled 0:11:08.160 --> 0:11:10.240 all this stuff together. It's like it's made a you know, 0:11:10.320 --> 0:11:12.600 like a well in the rubber sheet of the universe, 0:11:12.600 --> 0:11:20.040 so everything rolls together more closely. Okay, so that's a 0:11:20.240 --> 0:11:23.320 that's a galaxy. It's a black hole surrounded by dark 0:11:23.360 --> 0:11:26.600 matter and sprinkles of stars and gas and dust and 0:11:26.679 --> 0:11:31.120 lintels and lintels exactly yes, And so they're not just 0:11:31.240 --> 0:11:34.439 hanging out in space. They're moving around. That's right there. 0:11:34.480 --> 0:11:36.720 Each one is spinning, right, which is why you see 0:11:36.760 --> 0:11:39.280 a lot of them having these these spiral features. Each 0:11:39.280 --> 0:11:42.600 one is spinning, and then they're also moving around each other. 0:11:42.640 --> 0:11:45.720 They have gravity and they're moving around each other, and 0:11:45.760 --> 0:11:47.920 they have these Each galaxy is a member of a 0:11:47.960 --> 0:11:50.560 cluster of galaxies, and so these guys are orbiting the 0:11:50.600 --> 0:11:53.320 center of the cluster. And then the clusters are members 0:11:53.320 --> 0:11:56.960 of superclusters. So these things have a lot of gravitational 0:11:57.000 --> 0:12:00.600 interactions everywhere. It's like a system of galaxy. They all 0:12:01.080 --> 0:12:04.480 interact with each other, and they all spin around their 0:12:04.600 --> 0:12:07.280 common center of mass exactly right, And they're all spinning 0:12:07.280 --> 0:12:09.280 around that center. So it's sort of like a big 0:12:09.320 --> 0:12:12.120 slow motion tornado. Right you looked at it. If you 0:12:12.120 --> 0:12:14.240 looked at it really really slow, you're like, oh, nothing's 0:12:14.280 --> 0:12:16.480 really moving. I mean, I guess a little bit, but 0:12:16.679 --> 0:12:19.080 you you you watch it at natural speed of tornado, 0:12:19.120 --> 0:12:21.240 and obviously it's going really fast, and so a galaxy 0:12:21.280 --> 0:12:23.720 is that's sort of that same way. The gather system 0:12:23.760 --> 0:12:26.120 of galaxies is sort of that same way, but they're 0:12:26.120 --> 0:12:28.280 all moving around each other and then occasionally, you know, 0:12:28.360 --> 0:12:30.559 they bump into each other. Wow, that's so weird to 0:12:30.600 --> 0:12:33.680 think that gravity works the way like we are, you know, 0:12:33.800 --> 0:12:36.160 moving around the center of the Earth. The Earth is 0:12:36.200 --> 0:12:39.439 moving around our solar system, around the center of gravity, 0:12:39.440 --> 0:12:41.400 which is mostly the Sun, but the Sun is also 0:12:41.480 --> 0:12:43.880 we were moving around the center of gravity of the galaxy, 0:12:43.880 --> 0:12:46.760 and the galaxy is also moving around the center of 0:12:46.760 --> 0:12:49.840 gravity of its cluster of galaxies. That's right, Yeah, and 0:12:50.000 --> 0:12:52.040 on and on and on like a bunch of nested 0:12:52.080 --> 0:12:55.120 Russian dolls, you know, until you get to the biggest 0:12:55.120 --> 0:12:57.600 structures in the universe, you know, which are the superclusters, 0:12:57.600 --> 0:13:00.600 and then the filaments of superclusters, and beyond that, we 0:13:00.640 --> 0:13:03.120 don't know anything about whether there are bigger and bigger structures. 0:13:03.120 --> 0:13:05.839 That's as far as we've seen. So we're moving around 0:13:05.880 --> 0:13:09.160 and sometimes these two two galaxies can just run into 0:13:09.160 --> 0:13:12.160 each other. In the giant, vastness of space, all these 0:13:12.200 --> 0:13:16.760 moving galaxies can sometimes cross pass right. Yeah. And there's 0:13:16.760 --> 0:13:18.280 another thing I want to say about that before we 0:13:18.280 --> 0:13:20.520 talk about what actually happens, which is that it's incredible 0:13:20.520 --> 0:13:23.800 to me that gravity is the force that's dominant on 0:13:23.840 --> 0:13:27.000 these scales, right, Like, that's the thing that's controlling how 0:13:27.000 --> 0:13:29.360 galaxies form and how they dance around each other, and 0:13:29.360 --> 0:13:31.480 that's pulling them all the way through the universe and 0:13:31.800 --> 0:13:35.240 forming these crazy structures. It's all gravity, right. But gravity 0:13:35.320 --> 0:13:38.920 is the weakest force of nature. It's weaker than electromagnetism, 0:13:38.960 --> 0:13:42.120 it's weaker than any of the nuclear forces. It's pathetically weak, 0:13:42.520 --> 0:13:45.480 but it's the only one that operates on these huge scales, 0:13:45.679 --> 0:13:48.719 and it can't be balanced out. And so because it's 0:13:48.760 --> 0:13:51.600 only an attractive force, there's no repulsive version of it. 0:13:52.000 --> 0:13:55.200 And so that's why, like on these huge scales, gravity 0:13:55.240 --> 0:13:57.800 is the thing that dominates. Gravity determines the structure the 0:13:57.880 --> 0:14:00.720 Solar system, the structure the galaxy, the structure of the clusters. 0:14:01.080 --> 0:14:03.280 Gravity sort of winds in the end. It's like, you know, 0:14:03.400 --> 0:14:06.360 revenge of the nerd forces, Right, It's the weakest force 0:14:06.400 --> 0:14:09.400 in the end controls the universe. It's like slow and 0:14:09.440 --> 0:14:14.400 steady wins the race. It's the turtle of forces. Yeah, Anyway, 0:14:14.440 --> 0:14:16.199 we need to do a whole other podcast on why 0:14:16.280 --> 0:14:18.439 gravity is so weird and weak and whatever, and we're 0:14:18.520 --> 0:14:21.760 into that. Okay, so we have a cult clusters and 0:14:21.800 --> 0:14:24.920 galaxies are moving around space and sometimes they collide. So yeah, 0:14:25.040 --> 0:14:27.160 let's talk about what actually happens when two of these 0:14:27.200 --> 0:14:42.880 things collide. But first let's take a quick break. All right. 0:14:42.960 --> 0:14:46.320 So we're sitting in a galaxy and we are moving 0:14:46.360 --> 0:14:49.040 inside of this galaxy, and this galaxy is moving in space. 0:14:49.440 --> 0:14:52.880 But there's another galaxy nearby called the Andromeda galaxy, and 0:14:52.960 --> 0:14:56.040 it's kind of an interset course with us, right, like 0:14:56.080 --> 0:14:58.240 we're going to run into it in about four and 0:14:58.280 --> 0:15:01.480 a half billion years. Yeah, not kind of. They've measured it. 0:15:01.760 --> 0:15:04.200 They can measure the velocity of Andromeda relative to us, 0:15:04.240 --> 0:15:06.120 and they can see that it's getting closer and closer 0:15:06.120 --> 0:15:09.080 every year, and they can also measure the lateral velocity, 0:15:09.160 --> 0:15:11.160 like is it going to shoot by us or just 0:15:11.400 --> 0:15:14.200 or come right at us? And after for a while 0:15:14.240 --> 0:15:16.080 they weren't sure. They were like, oh, it's heading our way, 0:15:16.080 --> 0:15:18.280 but it could miss, you know, like every time they 0:15:18.280 --> 0:15:21.000 say there's an asteroid coming within, you know, a certain 0:15:21.000 --> 0:15:23.400 thousands of miles of the Earth, and usually it misses. 0:15:24.280 --> 0:15:26.480 For a while, they weren't sure, but now they're pretty 0:15:26.480 --> 0:15:29.040 certain they've taken enough measurements, they've seen it move, and 0:15:29.200 --> 0:15:31.800 they can project confidently that these two things are going 0:15:31.840 --> 0:15:34.480 to collide. Also, Andromeda and Milky, we have a lot 0:15:34.480 --> 0:15:37.560 of gravity, and so you don't have to aim perfectly 0:15:37.600 --> 0:15:40.480 to get a collision, right, They're gonna um pull each 0:15:40.480 --> 0:15:44.320 other closer and closer. They want to collide, you know, 0:15:44.480 --> 0:15:45.760 you know what I mean, Like, it's not like a 0:15:45.840 --> 0:15:49.560 random asteroid. It's like we're we're pulling towards each other. Yeah, well, 0:15:49.600 --> 0:15:51.480 I don't know if you can really say they want Like, 0:15:51.840 --> 0:15:53.760 do you understand the psychology of the galaxy? Do you you 0:15:53.840 --> 0:15:56.640 know what galaxy wants in life? You know, Hey, galaxy 0:15:56.760 --> 0:16:01.720 have feelings, right, I think I read that science fiction 0:16:01.760 --> 0:16:04.160 novel right where every galaxy is actually a living thing 0:16:04.200 --> 0:16:06.640 and we're just like the tiny moats on the on 0:16:06.680 --> 0:16:09.480 an island of red blood cells instead of galaxy. Anyway, Yeah, 0:16:09.520 --> 0:16:11.920 so you don't have to shoot perfectly, and they're gonna collide. 0:16:12.240 --> 0:16:14.040 So to think about what happens in the collision, you 0:16:14.080 --> 0:16:16.880 probably think about each individual piece separately, Like we're a 0:16:16.920 --> 0:16:19.680 cluster of things. Like a galaxy is not a solid object. 0:16:19.760 --> 0:16:21.680 It's like a word almost like a cloud of things, 0:16:21.800 --> 0:16:24.680 right is that kind of way? Mean? Yeah, yeah, exactly. 0:16:24.960 --> 0:16:28.320 And you know, imagine two crowds right passing into each other, 0:16:28.360 --> 0:16:30.520 and like one gets off the train and one's coming 0:16:30.560 --> 0:16:32.480 down the stairs and they pass each other in the platform. 0:16:32.520 --> 0:16:35.600 What's going to happen, Well, it depends on how they interact, right, 0:16:35.680 --> 0:16:38.360 and how dense they are. So we can start with 0:16:38.440 --> 0:16:41.080 something and the obvious parts, like the stars. Okay, so 0:16:41.120 --> 0:16:43.720 you might think, oh my gosh, there's a hundred billion 0:16:43.840 --> 0:16:46.360 stars coming right at us. That's going to be a 0:16:46.400 --> 0:16:48.360 big deal. Is that the right size? Like it isn't 0:16:48.400 --> 0:16:51.240 drama about the same size as the Milky Way. Actually 0:16:51.240 --> 0:16:53.120 I think it's bigger than the Milky Way. But you know, 0:16:53.560 --> 0:16:56.520 factors of ten here are not important. Um, so it's 0:16:56.600 --> 0:16:58.760 hundreds of billions of stars, and each star, of course 0:16:58.840 --> 0:17:00.520 is really big. And you might think, while they're heading 0:17:00.560 --> 0:17:01.920 right at us, you know, this is gonna be a 0:17:02.000 --> 0:17:05.520 big deal, But remember that the stars are really far apart. Also, like, 0:17:05.600 --> 0:17:08.480 galaxies are huge, not just in terms of the number 0:17:08.520 --> 0:17:11.080 of stars, in terms of the amount of space they 0:17:11.119 --> 0:17:14.000 take up. And you know, you look around you in 0:17:14.280 --> 0:17:17.080 our galaxy, there aren't that many stars nearby, right, and 0:17:17.160 --> 0:17:20.520 the closest stars are light years away. I like this 0:17:20.640 --> 0:17:23.760 crowd analogy that's pretty interesting. Like we're a crowd of 0:17:23.800 --> 0:17:26.440 people getting off the subway. There's a crowd of people 0:17:26.760 --> 0:17:29.760 coming down the stairs to get on the subway. It's 0:17:29.760 --> 0:17:32.959 going to be a disaster potentially. Potentially, But if it's 0:17:33.000 --> 0:17:35.199 not rush hour and the crowds are pretty light, you know, 0:17:35.200 --> 0:17:37.600 there's like enough space the two crowds can just pass 0:17:37.720 --> 0:17:39.840 right through each other. Like if the stairways and the 0:17:39.880 --> 0:17:42.760 hallways are huge and people are pretty spread out, it 0:17:42.800 --> 0:17:44.400 may not be like a riot, you know, it may 0:17:44.480 --> 0:17:46.960 just be like a busy intersection. Right, It's like two 0:17:47.000 --> 0:17:50.240 people leaving Yankee Stadium at the same time as as 0:17:50.320 --> 0:17:53.320 somebody else's trying to come in. Like there's plenty of exits, 0:17:53.359 --> 0:17:56.360 nobody's gonna bump into each other, right, And that's sort 0:17:56.359 --> 0:17:58.800 of the case with stars. I read this one comparison 0:17:58.840 --> 0:18:01.119 where if you imagine the stars the size of a 0:18:01.160 --> 0:18:06.080 ping pong ball on average, the nearest stars three kilometers away, right, 0:18:06.119 --> 0:18:08.720 So like if you were going to throw a ping 0:18:08.760 --> 0:18:11.760 pong ball into a cloud of ping pong balls, where 0:18:11.760 --> 0:18:13.879 the spaces between them were three kilometers away. You'd be 0:18:13.920 --> 0:18:16.240 lucky if you hit anything, right, even if you were trying. 0:18:16.760 --> 0:18:21.840 Oh I see, Okay, So our galaxy is actually pretty sparse, 0:18:22.280 --> 0:18:24.680 meaning the stars are pretty far apart from each other. 0:18:24.800 --> 0:18:28.280 We're not sort of clumped together. Yeah, exactly, and astronomically speaking, 0:18:28.320 --> 0:18:31.200 astronomically speaking, and so there's gonna be very few or 0:18:31.240 --> 0:18:34.280 probably zero direct collisions. You know, where one star like 0:18:34.440 --> 0:18:38.320 actually slams into another one, you get stellar explosions. I mean, 0:18:38.359 --> 0:18:40.480 that would be pretty awesome. I would pay for front 0:18:40.520 --> 0:18:43.879 road seat, but I think it's pretty unlikely that's going 0:18:43.960 --> 0:18:46.879 to happen. But you know, there's a hundred billion stars 0:18:46.960 --> 0:18:49.600 running into a hundred billion other stars. Surely some of 0:18:49.640 --> 0:18:52.000 them are going to hit head on, isn't it. Aren't they? 0:18:52.200 --> 0:18:54.320 I mean, there's always a non zero probability, and you 0:18:54.320 --> 0:18:57.719 could get lucky you're unlucky, depending on which which outcome 0:18:57.800 --> 0:19:00.600 you're rooting for. But if they're diffuse enough, right, they're 0:19:00.800 --> 0:19:03.160 they're far enough apart, then then all of them could 0:19:03.160 --> 0:19:05.240 pass through without hitting. I mean, I think probably the 0:19:05.240 --> 0:19:08.000 most likely scenarios that maybe you get one. The stars 0:19:08.040 --> 0:19:10.719 also don't have to hit directly to affect each other. Right. 0:19:10.760 --> 0:19:13.119 Each one is a big blob of mass, which means 0:19:13.160 --> 0:19:15.640 it has gravity, and so they can jostle each other. 0:19:15.720 --> 0:19:18.160 I mean, if another star came by and near our 0:19:18.160 --> 0:19:21.439 Solar System and pass nearby, it could affect the orbits 0:19:21.440 --> 0:19:24.600 of all the planets, like nudge a planet out of orbit. 0:19:24.680 --> 0:19:27.240 Didn't have to hit the star directly head on or 0:19:27.280 --> 0:19:29.800 to affect our lives. It could maybe pull us out 0:19:29.800 --> 0:19:34.320 of orbit or sunk us into that other star. That's right, Um, 0:19:34.359 --> 0:19:38.000 it could it could steal planets right exactly. Or um, 0:19:38.000 --> 0:19:39.720 one of our planets could get ejected out of the 0:19:39.760 --> 0:19:43.240 Solar System right, or it could even kick our star 0:19:43.320 --> 0:19:46.040 out of the galaxy. Our star is in orbit around 0:19:46.080 --> 0:19:48.840 the center of the galaxy, right, and if it comes, 0:19:48.880 --> 0:19:51.640 if another star comes near enough, it could get pulled 0:19:51.720 --> 0:19:54.800 and so that it gets you out of that orbit, right. 0:19:54.800 --> 0:19:56.280 And orbit is sort of a delicate thing. You have 0:19:56.359 --> 0:19:58.359 to be the right radius and the right velocity for 0:19:58.440 --> 0:20:00.760 it all to work and start going to fast and 0:20:00.800 --> 0:20:03.600