WEBVTT - Will our supercluster be torn apart? 0:00:08.760 --> 0:00:11.799 Hey or hey, I have a physics version of would 0:00:11.800 --> 0:00:12.280 you rather? 0:00:12.640 --> 0:00:14.960 Well, oh, I'd rather not play? 0:00:16.120 --> 0:00:20.079 Not an option today? So would you rather be blown 0:00:20.160 --> 0:00:22.919 up in a supernova or crushed in a black hole? 0:00:23.160 --> 0:00:25.560 Well, if I fell into a black hole, there would 0:00:25.560 --> 0:00:28.560 be time dilation, so it sounds like it would take forever. 0:00:29.280 --> 0:00:32.360 So maybe I'll go with a supernova, nice and quick. 0:00:33.479 --> 0:00:36.760 All right? Next one, would you rather be eaten by 0:00:36.840 --> 0:00:41.320 aliens or live your life never knowing if aliens exist? 0:00:41.600 --> 0:00:43.920 I would pick live my life over and being eaten 0:00:44.040 --> 0:00:47.120 by anything, aliens or otherwise. 0:00:47.600 --> 0:00:51.600 Wrong answer, wrong answer. Next one, would you rather keep 0:00:51.640 --> 0:00:53.840 playing this game or start the podcast? 0:00:54.000 --> 0:00:59.360 I'll pick the supernova again. Please, I'm crushed just trying 0:00:59.360 --> 0:01:00.000 to blow this up. 0:01:15.280 --> 0:01:15.360 Hi. 0:01:15.440 --> 0:01:18.240 I'm hoorhamy cartoonist and the creator of PhD comics. 0:01:18.360 --> 0:01:21.399 Hi I'm Daniel. I'm a particle physicist and a professor 0:01:21.440 --> 0:01:24.039 at UC Irvine, and I would rather be eaten by 0:01:24.040 --> 0:01:26.920 aliens than never know if they exist for real. 0:01:27.480 --> 0:01:28.840 Well, I guess if you get do you get to 0:01:28.920 --> 0:01:31.920 choose when you get eaten by aliens? You know, if 0:01:31.920 --> 0:01:34.959 you can choose to get it done right before you're 0:01:34.959 --> 0:01:38.120 gonna die of natural causes. Maybe that's okay, but like 0:01:38.240 --> 0:01:40.200 right now, you would make that choice right now. 0:01:40.920 --> 0:01:43.000 I think this game is all about those loopholes, like 0:01:43.040 --> 0:01:44.640 when people are planning for end of life, like do 0:01:44.640 --> 0:01:46.240 you want to get buried or do you want to 0:01:46.240 --> 0:01:48.240 get cremated. I'm going to fill out a box that 0:01:48.280 --> 0:01:50.720 says I want to get eaten by aliens. But yeah, 0:01:50.760 --> 0:01:52.600 it'd be nice if they waited till after I already 0:01:52.600 --> 0:01:54.960 died of natural causes. Then you know, hey, barbecue me 0:01:55.000 --> 0:01:56.400 for the alien pot luck. That's fine. 0:01:56.520 --> 0:01:59.240 You gotta be careful, though, do you mean like extraterrestrial 0:01:59.320 --> 0:02:04.240 aliens or people who are you know, alien alien to 0:02:04.280 --> 0:02:06.160 your life or to your city? 0:02:07.520 --> 0:02:09.080 You know what, I'm not gonna be around, so I 0:02:09.080 --> 0:02:10.240 guess it doesn't really matter. 0:02:10.320 --> 0:02:11.960 Oh you're gonna be around as you're getting in. 0:02:13.440 --> 0:02:15.640 As long as I get to learn about the aliens 0:02:15.639 --> 0:02:18.320 while I'm still alive, nothing else really matters. 0:02:19.000 --> 0:02:23.560 Oh boy. Anyways, Welcome to our podcast Daniel and Jorge 0:02:23.680 --> 0:02:26.920 Explain the Universe, a production of iHeartRadio in which. 0:02:26.760 --> 0:02:30.000 We take great pains and great sacrifices to try to 0:02:30.080 --> 0:02:33.760 explain the nature of the universe to you. We cast 0:02:33.800 --> 0:02:37.280 our minds out into that dark cosmic mystery and wonder 0:02:37.320 --> 0:02:40.800 what's out there, who's out there, what's going on out there, 0:02:41.160 --> 0:02:43.640 how big is it? Is it still sloshing around, and 0:02:43.680 --> 0:02:47.160 what will be its final fate. We want to understand 0:02:47.240 --> 0:02:50.760 the cosmic context of our very existence because it drives 0:02:50.800 --> 0:02:53.600 the choices we make every day about whether or not 0:02:53.840 --> 0:02:56.600 we sign ourselves up to be part of an alien barbecue. 0:02:56.800 --> 0:02:59.760 That's right. It is a humongous universe full of amazing 0:03:00.080 --> 0:03:03.840 and awesome things out there that may kill you or 0:03:03.919 --> 0:03:06.960 eat you, and or inspire you to learn more about 0:03:06.960 --> 0:03:09.840 the universe and the cosmos and how everything works in it. 0:03:09.880 --> 0:03:12.920 And it's part of this sort of incredible mental history, 0:03:13.240 --> 0:03:16.960 the trajectory of our sort of mental map of the cosmos. 0:03:17.240 --> 0:03:20.120 You know, it started out pretty small, your little village, 0:03:20.120 --> 0:03:23.880 your neighborhood, eventually expanded to be a larger and larger region. 0:03:24.320 --> 0:03:27.840 Finally people started incorporating the cosmos into it, this mental 0:03:27.840 --> 0:03:29.960 picture of the whole universe that we were in. But 0:03:30.040 --> 0:03:33.120 it just gets bigger and bigger as we understand where 0:03:33.160 --> 0:03:35.840 our solar system sits and where our galaxy sits, and 0:03:35.880 --> 0:03:38.240 as our telescopes get more and more powerful, we can 0:03:38.280 --> 0:03:42.520 now understand even further the context of our cosmic neighborhood. 0:03:42.680 --> 0:03:45.080 Yeah, it used to be there. Our context was pretty 0:03:45.120 --> 0:03:48.240 much like the Earth, and people thought that the Sun 0:03:48.360 --> 0:03:51.960 and the moon and the stars all revolved around the Earth. 0:03:52.480 --> 0:03:54.839 People thought that the entire universe was just us. 0:03:55.000 --> 0:03:58.080 Yeah. I was reading about ancient Chinese astronomy and they 0:03:58.120 --> 0:04:01.040 even calculated like how far away the stars were. They 0:04:01.040 --> 0:04:04.000 thought it was something like twenty seven thousand miles above 0:04:04.040 --> 0:04:04.440 the Earth. 0:04:04.560 --> 0:04:05.480 Oh, that's pretty close. 0:04:07.560 --> 0:04:10.160 And the Greeks thought that everything moved in like literal 0:04:10.320 --> 0:04:14.240 crystal spheres around the Earth. That was the original ether. 0:04:14.640 --> 0:04:17.679 Interesting, now, Daniel, do we know for sure that's not true? 0:04:18.279 --> 0:04:20.520 Do you know for sure that's not true. 0:04:20.880 --> 0:04:23.640 I mean, we've sent probes out there to visit these things, 0:04:23.680 --> 0:04:26.480 so we're pretty sure there are no crystal spheres out 0:04:26.520 --> 0:04:28.520 there moving the planets. 0:04:28.600 --> 0:04:31.440 By we mean the perverurial we but have you gone 0:04:31.480 --> 0:04:33.400 up there and touched these that made sure there's no 0:04:33.480 --> 0:04:34.200 crystal spheres. 0:04:34.279 --> 0:04:36.080 I'm going to take NASA's word for it, you know, 0:04:36.400 --> 0:04:38.919 for sure. I'm not part of the conspiracy community that 0:04:38.960 --> 0:04:41.440 thinks NASA's been lying to us all these years. 0:04:41.640 --> 0:04:43.680 You know, part of the crystal sphere conspiracy. 0:04:45.520 --> 0:04:48.360 I'm sure there's a group of crystal truthists out there. 0:04:49.200 --> 0:04:51.360 You know, part of the China was right theory. 0:04:53.640 --> 0:04:55.559 No, but the Chinese did make a lot of really 0:04:55.600 --> 0:04:59.120 amazing observations. You know, we have like records of eclipses 0:04:59.200 --> 0:05:02.480 dating back foulands of years from China and observations is 0:05:02.560 --> 0:05:05.560 like super nova from almost a thousand years ago. So 0:05:05.600 --> 0:05:09.159 it's a really rich history of astronomical observations, some of 0:05:09.200 --> 0:05:12.640 which are still relevant to our studies today. Is incredible. 0:05:12.760 --> 0:05:14.799 Oh, it's pretty cool. Yeah, because, as you were saying, 0:05:15.320 --> 0:05:18.479 our understanding of where or and how we fit in 0:05:18.520 --> 0:05:21.200 this universe keeps growing and growing, and it seems like 0:05:21.200 --> 0:05:24.480 each time we just get more and more insignificant with 0:05:24.560 --> 0:05:25.320 each step. 0:05:25.080 --> 0:05:28.400 But we become more and more aware of that significance, 0:05:28.440 --> 0:05:32.240 which makes us sort of like philosophically more important. Right, 0:05:32.320 --> 0:05:35.640 We're like incorporating more of the universe into our minds. 0:05:35.920 --> 0:05:40.080 No, that makes no sense. We're insignificant specs in this 0:05:40.160 --> 0:05:41.000 giant universe. 0:05:41.160 --> 0:05:44.320 But it's better to know about your insignificance because then 0:05:44.360 --> 0:05:46.600 you've gained some philosophical stature. 0:05:46.480 --> 0:05:48.480 Like being know where you're being in by aliens doesn't help. 0:05:48.480 --> 0:05:49.640 The fact that you're being eaten by. 0:05:49.560 --> 0:05:53.040 Eight still makes it worth. It still makes it worth. 0:05:54.040 --> 0:05:57.880 In fact, that makes it worse. But it does seem 0:05:57.920 --> 0:05:59.960 like we are getting smaller and smaller in the sumer 0:06:00.160 --> 0:06:03.640 And literally that's true, right because every year, every second 0:06:03.680 --> 0:06:06.920 of the day, the universe, or our understanding of how 0:06:06.920 --> 0:06:08.279 big it is, keeps getting bigger. 0:06:08.440 --> 0:06:11.440 Right, it does. And even though we cannot explore the 0:06:11.480 --> 0:06:14.599 far flung edges of the observable universe, we can build 0:06:14.600 --> 0:06:17.200 this mental model, this sort of map of our neighborhood 0:06:17.240 --> 0:06:20.560 that tells us where we are in this glittering cosmos. 0:06:20.600 --> 0:06:23.479 And so even though no human will probably visit those 0:06:23.520 --> 0:06:26.520 planets or visit those stars, we can still tell you 0:06:26.520 --> 0:06:28.839 something about what's going on out there. And to me 0:06:28.920 --> 0:06:31.839 that's incredible. Yes, we are probably trapped on this rock 0:06:32.000 --> 0:06:34.840 or our neighboring rocks, but still we can build this 0:06:34.960 --> 0:06:38.080 map of the cosmos, we can understand something about it. 0:06:38.360 --> 0:06:41.039 And to me, that's a great achievement sort of intellectually 0:06:41.080 --> 0:06:43.560 and scientifically, and what I'm pretty proud of. 0:06:43.800 --> 0:06:46.240 Yeah, again, I think you're using the proverbial we there, 0:06:48.480 --> 0:06:51.000 you're proud of the work of others. Let's be honest here. 0:06:51.120 --> 0:06:53.760 No, I'm standing on the shoulders of many, many giants, 0:06:53.760 --> 0:06:56.800 and I'm proud of their work. Absolutely, I'm not personally 0:06:56.800 --> 0:07:00.279 taking credit for our understanding of the universe in case 0:07:00.279 --> 0:07:01.599 anybody misunderstood, But. 0:07:01.600 --> 0:07:03.719 At least we're helping, I guess talk about what they've 0:07:03.760 --> 0:07:07.160 done and disseminate this information out to others. And it's 0:07:07.200 --> 0:07:09.600 interesting when you say like that we might never reach 0:07:09.680 --> 0:07:11.640 those places that we're seeing far far away. I'm wonder 0:07:11.680 --> 0:07:14.400 if that's really true. I guess that's true because our 0:07:14.480 --> 0:07:16.640 view of the universe expanding at the speed of light, 0:07:17.320 --> 0:07:20.280 and there's no way that humans could outpacete that. Right. 0:07:20.360 --> 0:07:22.880 Yeah, it's amazing we can see things that are moving 0:07:22.920 --> 0:07:25.440 away from us faster than the speed of light. A 0:07:25.440 --> 0:07:27.800 bunch of listeners wrote in and asked, like, how does 0:07:27.840 --> 0:07:31.040 that work? We have a whole episode covering it, but briefly, 0:07:31.200 --> 0:07:33.840 the thing to understand when you're looking at an object 0:07:33.880 --> 0:07:35.960 and they tell you, oh, this thing is thirty billion 0:07:36.280 --> 0:07:38.400 years away and it's moving away from us faster than 0:07:38.440 --> 0:07:40.360 the speed of light, is that you're not seeing it 0:07:40.400 --> 0:07:43.120 where it is now. They're telling you where it is now. 0:07:43.160 --> 0:07:45.520 But you're seeing the light that was emitted from it 0:07:45.600 --> 0:07:47.840 when it was much much closer. So it used to 0:07:47.880 --> 0:07:50.080 be much closer, and it's sent a photon our way. 0:07:50.240 --> 0:07:53.040 In the meantime, it's moved really really far away. When 0:07:53.040 --> 0:07:55.120 they say here, we're looking at a galaxy that's really 0:07:55.200 --> 0:07:57.440 really far away, we're not seeing light that came to 0:07:57.520 --> 0:07:59.920 us from it when it was that far away. Were 0:08:00.040 --> 0:08:02.120 seeing light that came to us when it was much 0:08:02.200 --> 0:08:05.360 much closer. Light that leaves it now we will never see, 0:08:05.400 --> 0:08:07.800 which means also we will never visit it. 0:08:07.960 --> 0:08:11.280 Mmm. Yeah, Because the universe is expanding faster and faster 0:08:11.440 --> 0:08:14.160 every time, every second of the day. Although we don't 0:08:14.200 --> 0:08:15.680 know what's going to happen in the future right, it 0:08:15.720 --> 0:08:18.320 could be that in the far distant future or maybe tomorrow, 0:08:18.400 --> 0:08:20.720 the universe might decide, Hey, I think I'm going to 0:08:20.760 --> 0:08:23.080 stop growing and I'm going to collapse back on myself, 0:08:23.160 --> 0:08:26.200 and in which case, we're going to basically visit every 0:08:26.240 --> 0:08:27.679 place in the universe at some point. 0:08:28.080 --> 0:08:29.840 Yeah, or they're going to come visit us and they're 0:08:29.840 --> 0:08:31.880 going to bring with them all their aliens, with all 0:08:31.920 --> 0:08:33.120 their barbecue. 0:08:32.640 --> 0:08:35.840 Tools, all their appetites. Well, maybe the big joke is 0:08:35.840 --> 0:08:37.560 that in the end, the universe eats us. 0:08:37.559 --> 0:08:37.760 All. 0:08:38.800 --> 0:08:40.880 Well, we are the universe, so I guess the universe 0:08:40.880 --> 0:08:42.520 eats itself. I'm not sure how that works. 0:08:42.640 --> 0:08:44.640 Whoa dude. 0:08:45.559 --> 0:08:47.720 And even though we are learning that we are a 0:08:47.760 --> 0:08:50.679 tiny speck in a vast, vast cosmos, I think it 0:08:50.679 --> 0:08:54.240 does make us sort of like philosophically or intellectually more 0:08:54.360 --> 0:08:57.400 powerful to have grappled with that vast cosmos. It's better 0:08:57.440 --> 0:09:00.640 at least than being ignorant of what's going on right right? 0:09:00.840 --> 0:09:03.120 But don't they say ignorance is bliss Sometimes? 0:09:03.280 --> 0:09:08.000 Who's looking for bliss? Man, I'm looking for knowledge. 0:09:09.080 --> 0:09:11.240 Maybe that's the difference between you and me and Daniel. 0:09:11.240 --> 0:09:12.480 I'll go for bliss any day. 0:09:12.679 --> 0:09:15.880 Okay, Well, I'm glad we can split the tasks. But 0:09:15.960 --> 0:09:18.320 it's also fun to think about that far future you 0:09:18.320 --> 0:09:21.360 were talking about and wondering, like, what does the future hold? 0:09:21.480 --> 0:09:24.079 Will our solar system survive for our billion years? Will 0:09:24.120 --> 0:09:27.360 our galaxy survive for ten billion years? What exactly is 0:09:27.440 --> 0:09:31.680 going to happen to our cosmic neighborhood over cosmic deep time? Yeah? 0:09:31.720 --> 0:09:34.160 Because, as we mentioned, the universe is expanding faster and 0:09:34.160 --> 0:09:37.559 faster and faster and that has some pretty dramatic consequences 0:09:37.559 --> 0:09:40.520 for some of the bigger structures in the universe. And 0:09:40.559 --> 0:09:42.679 so today on the podcast we'll be tackling the question 0:09:47.880 --> 0:09:53.079 will our super cluster be torn apart? Sounds kind of sad. 0:09:53.760 --> 0:09:55.600 Like a chunk of juicy barbecue. 0:09:56.280 --> 0:10:01.040 Well, wow, who would eat a giant supercluster galaxies. 0:10:00.720 --> 0:10:05.400 Some giant super space crab? I suppose, Oh boy? 0:10:05.559 --> 0:10:09.000 And how big does the barbecue sauce bottle need to be? Well, 0:10:09.000 --> 0:10:11.080 this is an interesting question and so we'll dig into 0:10:11.120 --> 0:10:14.360 it of what a supercluster is, what does it mean 0:10:14.400 --> 0:10:16.080 for it to be torn apart? And what could be 0:10:16.160 --> 0:10:18.320 causing it to be torn apart? But as usual, we 0:10:18.320 --> 0:10:21.000 were wondering how many people had considered these words together 0:10:21.120 --> 0:10:23.600 as a question out there in the internet. 0:10:23.640 --> 0:10:26.319 So thanks very much to everybody who participates in this 0:10:26.480 --> 0:10:29.360 segment of our podcast. It's super fun for us to 0:10:29.400 --> 0:10:31.960 hear what you're thinking about the topic of the day. 0:10:32.120 --> 0:10:34.680 Please don't be shy. If you'd like to participate in 0:10:34.679 --> 0:10:38.400 the future, just write to me to Questions at Danielandjorge 0:10:38.600 --> 0:10:39.240 dot com. 0:10:39.240 --> 0:10:40.959 So think about it for a second. Do you think 0:10:41.160 --> 0:10:44.719 our supercluster will be torn apart. Here's what people have 0:10:44.800 --> 0:10:47.880 to say. I say no, I believe that dark matter 0:10:47.920 --> 0:10:51.760 and dark energy will keep it together, just like it 0:10:51.880 --> 0:10:54.400 build the supercluster that we see today. 0:10:54.559 --> 0:10:59.280 Well, our supercluster, if I believe right, is a collection 0:10:59.360 --> 0:11:03.320 of galaxy that we're in kind of grouped up. So 0:11:03.400 --> 0:11:06.000 if anything, I feel like it would get larger just 0:11:06.040 --> 0:11:10.360 by gravitationally attracting other galaxies that are just floating out there. 0:11:10.720 --> 0:11:13.600 If I get it right, the galaxies of our supercluster 0:11:13.800 --> 0:11:19.080 won't drift apart due to the expansion of the universe, 0:11:20.000 --> 0:11:21.840 but they might dive into each other. 0:11:22.440 --> 0:11:27.120 A supercluster is a group of galaxy dark energy. Obviously 0:11:27.120 --> 0:11:30.400 he's moving things apart. But I think the galaxy would 0:11:30.400 --> 0:11:36.280 stay together, but that galaxies would separate from each other. 0:11:36.880 --> 0:11:40.720 So I reckon our supercluster will be torn apart. 0:11:40.920 --> 0:11:44.640 All right, Some people are feeling optimistic about our supercluster. 0:11:44.800 --> 0:11:48.440 It looks like three to one for our superclusters sticking together. 0:11:48.640 --> 0:11:50.040 We got some optimists out there. 0:11:50.160 --> 0:11:53.400 Yeah. Yeah, everyone wants to remain I guess in the cluster. 0:11:54.400 --> 0:11:56.360 They want to stay cozy. No one wants to blow 0:11:56.440 --> 0:11:56.959 up our spot. 0:11:57.080 --> 0:12:00.720 Yeah, but I guess some people mentioned gravity us together 0:12:00.800 --> 0:12:03.840 instead of letting the supercluster get torn apart, and some 0:12:03.880 --> 0:12:06.319 people mention dark matter as a way to keep things together. 0:12:06.480 --> 0:12:09.320 Yeah, and the overall theme here is pretty much spot 0:12:09.360 --> 0:12:11.840 on that the universe is in a tug of war 0:12:12.320 --> 0:12:16.000 between gravity and dark energy and those things play out 0:12:16.160 --> 0:12:19.840 very differently on different distances and different scales. And so 0:12:19.920 --> 0:12:22.320 the fascinating question is like, at what point does dark 0:12:22.400 --> 0:12:24.520 energy win? And where will gravity win? 0:12:25.320 --> 0:12:28.240 Who will eat who? Gravity versus dark energy. 0:12:29.360 --> 0:12:31.839 That's like Godzilla versus King Kong. 0:12:32.160 --> 0:12:36.440 That's like slow roasted ribs versus grilled chicken. 0:12:37.440 --> 0:12:38.400 I'll just eat them both. 0:12:38.440 --> 0:12:46.760 Mane sounds good. Well, let's dive into this tasty topic here, 0:12:46.880 --> 0:12:50.000 step us through Daniel. What is a supercluster of galaxies? 0:12:50.040 --> 0:12:53.320 So a supercluster is the biggest thing in the universe. 0:12:53.800 --> 0:12:58.280 It's the largest structure we think can exist in the universe. 0:12:58.559 --> 0:13:01.000 And this episode is going to hinge closely on what 0:13:01.080 --> 0:13:04.640 we mean by a structure. What is a thing in 0:13:04.679 --> 0:13:07.240 the universe? Because you could just look out in space 0:13:07.280 --> 0:13:09.240 and say I'm going to group all this stuff together 0:13:09.280 --> 0:13:10.880 and call it a thing and give it a name, 0:13:11.120 --> 0:13:13.640 the way we sort of do for constellations, But astronomers 0:13:13.679 --> 0:13:16.360 like to think about things in the universe structures as 0:13:16.440 --> 0:13:19.400 things that sort of hold themselves together, that have enough 0:13:19.440 --> 0:13:23.200 gravity to be tied together to be an equilibrium. So 0:13:23.240 --> 0:13:25.960 in our immediate neighborhood, for example, we think of the 0:13:26.000 --> 0:13:28.680 Solar System as a thing. The Earth is going around 0:13:28.720 --> 0:13:30.920 the Sun and it's going to keep doing that. Gravity 0:13:31.000 --> 0:13:33.200 is holding the Earth around the Sun and all the 0:13:33.240 --> 0:13:35.800 other planets, So we think of the Solar System as 0:13:35.800 --> 0:13:39.360 a structure, as this gravitationally bound kind of object. 0:13:39.520 --> 0:13:41.160 Yeah, because I guess if you think about just the 0:13:41.200 --> 0:13:43.839 word structure and what it means in our everyday lives, 0:13:43.920 --> 0:13:47.880 it basically just means like things that are clumped together, right, 0:13:47.960 --> 0:13:50.360 or that move together, or that can be separated from 0:13:50.400 --> 0:13:52.920 each other. And you sort of drill down into it, 0:13:53.040 --> 0:13:55.520 like even the house you're sitting on, or the building 0:13:55.559 --> 0:13:58.240 you're sitting on, or maybe even the car you're sitting on, 0:13:58.400 --> 0:14:02.000 it's just a collection of loose parts being held together 0:14:02.040 --> 0:14:04.480 by a force in the universe. Like they're not part 0:14:04.480 --> 0:14:07.280 of the same thing. They're individual particles, but there's just 0:14:07.320 --> 0:14:09.760 some force that keeps them all moving together. 0:14:09.960 --> 0:14:11.840 Yeah, and it feels like a really natural thing. Right 0:14:11.880 --> 0:14:14.800 to say I'm held together, I'm a thing. You're held together, 0:14:14.920 --> 0:14:17.480 you're another thing. Even if we're standing next to each other, 0:14:17.640 --> 0:14:19.560 it's easy to draw the line between us and say, 0:14:19.600 --> 0:14:22.600 like where I end and you begin. That's sort of philosophically, 0:14:22.680 --> 0:14:25.440 very straightforward, and so we imagine maybe that's possible to 0:14:25.440 --> 0:14:27.560 do for other stuff too, Right to say, well, here's 0:14:27.600 --> 0:14:30.120 one planet and there's another planet, to draw these lines 0:14:30.160 --> 0:14:32.640 and say this thing holds itself together, and that thing 0:14:32.640 --> 0:14:34.840 holds itself together. So that's sort of the idea of 0:14:34.880 --> 0:14:37.200 a structure, But it can also get kind of fuzzy, 0:14:37.320 --> 0:14:38.920 Like when you look up at the sky and you 0:14:38.920 --> 0:14:42.640 see a cloud. It's this big blob of vapor. It's 0:14:42.640 --> 0:14:44.920 not really holding itself together. I mean, it looks like 0:14:44.960 --> 0:14:48.160 a thing sort of localized and clumped, but it's definitely 0:14:48.200 --> 0:14:51.000 not gravitationally holding itself together. It just sort of happens 0:14:51.040 --> 0:14:53.440 to be all in the same place at the same time, 0:14:54.000 --> 0:14:56.080 or like a crowd in a park at lunchtime. Right, 0:14:56.200 --> 0:14:58.200 they all happen to be near each other. They're clumped, 0:14:58.240 --> 0:15:01.040 but they're not holding themselves together. So there can be 0:15:01.120 --> 0:15:03.120 sometimes things that are like near each other. There are 0:15:03.120 --> 0:15:04.560 clumps but not structures. 0:15:05.440 --> 0:15:08.360 Interesting, Yeah, crowd is a good example, right, because it 0:15:08.440 --> 0:15:10.960 may look like a cluster, or like from a farm, 0:15:11.040 --> 0:15:13.160 might look like a clump of things, but really there's 0:15:13.200 --> 0:15:16.680 nothing keeping those individual people or structures together. 0:15:16.800 --> 0:15:16.960 Right. 0:15:17.040 --> 0:15:19.320 They could at any moment just leave the group. 0:15:19.400 --> 0:15:21.680 Yeah. Every kindergarten teacher knows that when you try to 0:15:21.720 --> 0:15:23.560 take them out on a field trip, right, they can 0:15:23.600 --> 0:15:26.080 all just suddenly run in any random direction. 0:15:26.480 --> 0:15:29.640 Yeah, Whereas maybe like for the planet Earth, all the 0:15:29.760 --> 0:15:33.160 rocks on planet Earth are being kept from flying away 0:15:33.280 --> 0:15:34.520 by gravity, by a force. 0:15:34.680 --> 0:15:36.640 And it's really fascinating to think about the sort of 0:15:36.720 --> 0:15:39.080 levels of structure, right, Like a rock is a structure, 0:15:39.080 --> 0:15:42.320 but it's also part of a larger structure the Earth, 0:15:42.560 --> 0:15:44.880 and the Earth of course is a structure, but again 0:15:44.920 --> 0:15:47.640 it's part of a larger structure. So we have this 0:15:47.720 --> 0:15:52.600 incredible nested hierarchy of structures, which is really fascinating to 0:15:52.640 --> 0:15:54.960 think about, like the scale of those things, right, Like 0:15:55.000 --> 0:15:57.760 an atom is a structure, You're made of so many 0:15:57.800 --> 0:16:00.960 structures on so many levels. Incredible to think about, like 0:16:01.360 --> 0:16:04.320 how organized the universe is, and as a whole group 0:16:04.320 --> 0:16:06.600 of philosophers who study this kind of thing and wonder like, 0:16:06.960 --> 0:16:09.160 why do we have structure of these distances and not 0:16:09.280 --> 0:16:11.920 other distances? And does it bubble up from the fundamental 0:16:11.960 --> 0:16:14.800 laws of the universe and all sorts of fascinating philosophical 0:16:14.880 --> 0:16:17.280 rabbit holes. But it's also just kind of fun to 0:16:17.280 --> 0:16:19.600 figure out, like what is the structure? What is our 0:16:19.680 --> 0:16:22.920 cosmic neighborhood, and so we can like zoom out step 0:16:22.960 --> 0:16:26.000 by step and understand how we fit in to this 0:16:26.080 --> 0:16:28.960 sort of larger cosmic set of like Russian nesting dolls. 0:16:29.240 --> 0:16:31.280 Yeah, because I guess you know, sort of like you 0:16:31.320 --> 0:16:34.840 were saying, the atoms in my body make up my structure, 0:16:35.040 --> 0:16:38.560 but they're all also kind of being pulled by the 0:16:38.600 --> 0:16:41.600 gravity of the earth, right, so like is it more 0:16:41.800 --> 0:16:44.240 part of my structure or are all the atoms in 0:16:44.280 --> 0:16:47.280 my body more part of the earth structure? And even 0:16:47.320 --> 0:16:49.320 like the atoms in my body are being pulled by 0:16:49.320 --> 0:16:51.640 the gravity of the sun. But we wouldn't say, like, hey, 0:16:51.680 --> 0:16:54.320 I'm just me and the sun are one, even though 0:16:54.400 --> 0:16:57.360 if you sort of follow the chain of forces that 0:16:57.480 --> 0:16:59.640 we are sort of in the same structure as the Sun. 0:16:59.760 --> 0:17:01.920 Yeah, And so you're part of many structures or you 0:17:01.920 --> 0:17:04.200 could say that there's substructure, right, You could just look 0:17:04.200 --> 0:17:06.240 at the whole galaxy and say the galaxy is a blob, 0:17:06.320 --> 0:17:09.600 but obviously it has substructure. It's not just a smooth 0:17:09.680 --> 0:17:13.520 distribution of atoms. There are stars and solar systems and 0:17:13.560 --> 0:17:16.760 even clumps to those stars. They are like these groups 0:17:16.800 --> 0:17:19.959 of stars are all formed together that are still moving together, 0:17:20.119 --> 0:17:22.240 like that Kindergarten group. So there's sort of lots of 0:17:22.359 --> 0:17:26.160 layers of structure, and it's fascinating to ask, like how 0:17:26.160 --> 0:17:29.520 many layers are there? How many layers can we zoom 0:17:29.560 --> 0:17:32.560 out and still see things that seem to be holding 0:17:32.640 --> 0:17:35.879 themselves together. So we start with ourselves, and then of 0:17:35.920 --> 0:17:38.840 course we have the Earth, and then there's the solar system, 0:17:39.520 --> 0:17:41.560 and then we zoom out. The next sort of big 0:17:41.640 --> 0:17:44.639 layer of structure would either be like a group of 0:17:44.760 --> 0:17:47.640 stars that we all form together with or you would 0:17:47.680 --> 0:17:50.000 zoom all the way out to the galaxy. Because those 0:17:50.040 --> 0:17:52.400 groups of stars that form together, they don't really hold 0:17:52.440 --> 0:17:55.800 themselves together for very long. They tend to disperse into 0:17:55.840 --> 0:17:56.480 the galaxy. 0:17:56.800 --> 0:17:59.399 M do we know that's for sure? Or I mean, like, 0:17:59.440 --> 0:18:02.120 do we know which stars are near us? And would 0:18:02.119 --> 0:18:04.639 you say maybe they're too far away for their gravity 0:18:04.680 --> 0:18:05.679 to really affect us. 0:18:05.880 --> 0:18:08.040 Yeah, other stars are too far away for the gravity 0:18:08.040 --> 0:18:10.320 to really affect us. And we all have velocity through 0:18:10.320 --> 0:18:12.560 the galaxy, and so we know a lot about actually 0:18:12.600 --> 0:18:16.160 how stars dissipate from their original cluster. It can take 0:18:16.240 --> 0:18:18.719 tens or hundreds of millions of years, but we definitely 0:18:18.720 --> 0:18:20.679 see evidence of that when we look out at the 0:18:20.720 --> 0:18:24.200 pattern of the stars in our galaxy. It also helps 0:18:24.280 --> 0:18:27.439 us understand how the stars are moving. For example, like 0:18:27.480 --> 0:18:30.000 the Big Dipper is a group of stars that were 0:18:30.040 --> 0:18:33.000 all formed together, and they're moving together, but they're also 0:18:33.080 --> 0:18:35.680 moving really fast and they're kind of close by, which 0:18:35.720 --> 0:18:38.080 means that the Big Dipper is changing. You don't think 0:18:38.080 --> 0:18:40.639 about the constellations as changing very much, but they actually 0:18:40.720 --> 0:18:42.720 are all moving. We're not all moving at the same 0:18:42.840 --> 0:18:45.760 relative velocity. So like the galaxy is a big, slashing 0:18:45.840 --> 0:18:48.680 bathtub of stars. So the Big Dipper changes, and over 0:18:48.760 --> 0:18:51.399 like one hundred thousand years or a few hundred thousand years, 0:18:51.600 --> 0:18:54.080 the Big Dipper will no longer look like the Big Dipper. 0:18:54.200 --> 0:18:56.480 Now are they would you say they're a structure or 0:18:56.520 --> 0:18:59.480 are they just moving together like a crowd, or like 0:18:59.520 --> 0:19:00.760 a wisp of clouds. 0:19:00.840 --> 0:19:02.520 They are not a structure because they're not going to 0:19:02.560 --> 0:19:05.720 hold themselves together. They're not like tight enough to be 0:19:05.800 --> 0:19:08.399 a structure. They're definitely going to dissolve into the larger 0:19:08.440 --> 0:19:13.040 sort of bathtub of the galaxy. There are sometimes substructures 0:19:13.040 --> 0:19:14.920 to the galaxy, but those tend to be like little 0:19:15.000 --> 0:19:18.560 dwarf galaxies that orbit the Milky Way and that have 0:19:18.640 --> 0:19:22.280 their own gravitational hold on themselves that haven't gotten pulled 0:19:22.320 --> 0:19:24.720 apart by the Milky Way. But within the Milky Way, 0:19:24.720 --> 0:19:26.440 there aren't really those kinds of structures. 0:19:26.600 --> 0:19:29.400 So you would say, like after our solar system, the 0:19:29.440 --> 0:19:32.639 next structure is a galaxy. You wouldn't maybe call the 0:19:32.800 --> 0:19:34.280