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Remember they're real people with loved 0:01:30.560 --> 0:01:32.760 ones who need them to get home safely. Protect our 0:01:32.760 --> 0:01:34.880 cyclists and pedestrians because they're people too. 0:01:35.120 --> 0:01:35.679 Go safely. 0:01:35.760 --> 0:01:38.600 California from the California Office of Traffic Safety in Caltrans. 0:01:38.720 --> 0:01:41.160 When you pull up to game night, Ay, all new Camri, 0:01:41.920 --> 0:01:44.119 but it's actually Bingo. 0:01:43.760 --> 0:01:50.120 Night Minigolf anyone, It's a Camri five, the all new 0:01:50.280 --> 0:02:02.160 all hybrid Camri Toyota. Let's go places. Hey, Orge, are 0:02:02.200 --> 0:02:05.680 you preparing your kids for when the end times come? 0:02:06.280 --> 0:02:06.480 Oh? 0:02:06.680 --> 0:02:10.480 You mean when bananas go extinct? Or do you mean 0:02:10.520 --> 0:02:11.240 when I retire? 0:02:11.639 --> 0:02:14.160 Yeah? I mean the fall of civilization when we're all 0:02:14.280 --> 0:02:16.639 listening to podcast in our caves. 0:02:17.520 --> 0:02:19.280 I feel like I've been preparing my whole life. If 0:02:19.280 --> 0:02:21.840 there's a post apocalyptic movie out there, I. 0:02:21.960 --> 0:02:24.680 Probably see it. Well, then I hope you're teaching your 0:02:24.760 --> 0:02:28.639 kids some useful skills, you know, blacksmithing, martial arts, cartooning. 0:02:28.919 --> 0:02:32.200 Oh yeah, cartooning for sure, that's going to come in handy. 0:02:33.040 --> 0:02:35.160 But you don't think they should learn a particle physics. 0:02:36.080 --> 0:02:38.520 I don't know that anybody's going to be building colliders 0:02:38.560 --> 0:02:40.080 out of sticks and rocks. 0:02:40.480 --> 0:02:43.079 Isn't it fire? Doesn't it fire evolve particles colliding? 0:02:43.320 --> 0:02:45.880 A fire is kind of a chemical accelerator. I suppose 0:02:45.880 --> 0:02:47.880 there must be some collisions. 0:02:47.840 --> 0:02:49.960 Or are you going to be like, you know, freezing 0:02:50.000 --> 0:02:52.000 out there, and you're going to be like, oh no, no, sorry, 0:02:52.360 --> 0:02:54.160 the fire is just not fundamental enough for me. 0:02:57.360 --> 0:02:59.320 I think I would be hiding in my cave eating 0:02:59.360 --> 0:03:01.120 the last of the world world's chocolate reserves. 0:03:01.800 --> 0:03:04.320 Would that be a useful skill? You could be it 0:03:04.440 --> 0:03:07.880 the world's only chocolate tear. Hopefully the zombies like chocolate. 0:03:09.560 --> 0:03:18.919 Dark chocolate is the world's final currency. 0:03:27.400 --> 0:03:29.919 I am Jorge make carctoonist and the author of Oliver's 0:03:29.919 --> 0:03:30.760 Great Big Universe. 0:03:30.880 --> 0:03:33.639 Hi, I'm Daniel. I'm a particle physicist and a professor 0:03:33.680 --> 0:03:37.200 at uc Irvine, and I purposely got into particle physics 0:03:37.240 --> 0:03:38.840 because it was useless. 0:03:39.040 --> 0:03:41.040 You're like, how can I make my time here on 0:03:41.120 --> 0:03:42.440 Earth less useful? 0:03:44.400 --> 0:03:47.440 I wasn't so much worried about the positive practical benefits 0:03:47.480 --> 0:03:50.000 as the negative. You know, my parents worked in the 0:03:50.000 --> 0:03:52.600 weapons programs, and I really really didn't want to do 0:03:52.680 --> 0:03:55.040 anything that could be used as the basis of a 0:03:55.080 --> 0:03:55.600 death ray. 0:03:55.920 --> 0:03:58.760 I see, but you could have picked something positively useful, 0:04:01.480 --> 0:04:04.440 like making a chocolate Yeah, there you go, making people happy. 0:04:05.400 --> 0:04:07.360 Well, you know, my dad did retire from the lab 0:04:07.400 --> 0:04:10.400 and then became a blacksmith, so he's definitely got useful 0:04:10.400 --> 0:04:11.600 skills for the end times. 0:04:11.720 --> 0:04:15.640 He became a blacksmith. Wow, was he forging like swords 0:04:15.800 --> 0:04:18.760 or internal combustion engines in your garage? 0:04:19.000 --> 0:04:22.400 Or what swords? Spears? All kinds of stuff? 0:04:22.480 --> 0:04:26.320 Yes, he's like, I want to eat more weapons. 0:04:28.960 --> 0:04:31.040 I wish I were joking more and. 0:04:30.960 --> 0:04:35.600 More direct, but anyways, Welcome to our podcast, Daniel and 0:04:35.680 --> 0:04:39.400 Jorge Explain the Universe, a production of iHeartRadio. 0:04:38.800 --> 0:04:41.680 In which our only weapon is our minds. As we 0:04:41.760 --> 0:04:45.520 tackle the quest of understanding the universe, we go forging 0:04:45.560 --> 0:04:48.080 through all of the craziness that's out there and try 0:04:48.120 --> 0:04:50.760 to weave it all together into an explanation that makes sense. 0:04:51.160 --> 0:04:53.440 We hope that whatever the universe is made out of 0:04:53.440 --> 0:04:56.440 its tiny little basic bits, that somehow they're danced together 0:04:56.520 --> 0:05:00.080 can explain everything that we experience in the universe. We 0:05:00.120 --> 0:05:02.799 can somehow find fundamental laws, and then we can also 0:05:03.160 --> 0:05:04.359 make sense of it all. 0:05:04.720 --> 0:05:07.440 That's right. We try to hone our knowledge of signs 0:05:07.440 --> 0:05:10.800 here and try to prepare you for the end times 0:05:11.040 --> 0:05:13.159 when we'll all be looking up at the stars wondering 0:05:13.200 --> 0:05:15.080 how do we all get here and how do we 0:05:15.120 --> 0:05:16.560 avoid those pesky zombies. 0:05:18.440 --> 0:05:20.480 I guess we should all try to sharpen our minds 0:05:20.480 --> 0:05:22.440 so we can slice our way through these problems. 0:05:22.600 --> 0:05:25.960 Yeah, I'm sure having physics knowledge will be helpful only 0:05:26.120 --> 0:05:30.839 in the apocalypse, right, you can, I guess, try to 0:05:30.880 --> 0:05:33.040 build a laser gun to fight the zombies. 0:05:34.000 --> 0:05:36.200 If the zombies assigned a lot of homework problems, then 0:05:36.200 --> 0:05:37.360 I'm definitely there to help. 0:05:38.920 --> 0:05:40.719 Oh, that could be another way to defeat them. You know, 0:05:40.800 --> 0:05:43.880 you give them physics problems that are so tricky that 0:05:43.920 --> 0:05:46.760 their brains explode, and that everyone knows that's how you 0:05:46.800 --> 0:05:47.560 kill zombies. 0:05:47.720 --> 0:05:54.440 Wow, Yes, exactly too many into girls. 0:05:55.040 --> 0:05:55.680 Coculus. 0:05:55.760 --> 0:06:02.920 No, you know, Newton definitely believed in zombies. Really, Newton 0:06:02.920 --> 0:06:05.720 definitely believed in some weird stuff. I don't know about zombies, 0:06:06.160 --> 0:06:09.039 but you know, he was an alchemist and he definitely 0:06:09.120 --> 0:06:10.320 was a fan of the arcane. 0:06:11.200 --> 0:06:13.560 Wasn't he really into currencies too. 0:06:13.760 --> 0:06:15.520 Mm hmmm, yeah, exactly. 0:06:15.560 --> 0:06:17.679 At some point became like a coin master or something. 0:06:17.760 --> 0:06:19.320 He was definitely a weird dude. 0:06:19.480 --> 0:06:23.839 Yes, by word, do you mean a genius who basically 0:06:23.839 --> 0:06:24.760 invented science? 0:06:26.160 --> 0:06:28.039 I think that's actually giving him a little bit too 0:06:28.120 --> 0:06:31.000 much credit. But yeah, he invented lots of physics and 0:06:31.400 --> 0:06:33.800 big chunks of math, and I think he would be 0:06:33.880 --> 0:06:37.080 pretty tickled if we could use calculus against the zombies. 0:06:37.440 --> 0:06:39.160 Oh well, I'm sure a lot of people will be 0:06:39.360 --> 0:06:42.400 relieved to learn it's useful for something after all that 0:06:42.440 --> 0:06:43.279 work in high school. 0:06:43.640 --> 0:06:45.480 Yeah, they can integrate it into their lives. 0:06:46.040 --> 0:06:50.200 Oh boy, that was very ridico. But anyways, we do 0:06:50.360 --> 0:06:51.800 like to think about the universe and we try to 0:06:51.839 --> 0:06:54.760 explain it here on the podcast, and sometimes that involves 0:06:54.839 --> 0:06:56.000 answering questions. 0:06:56.560 --> 0:06:58.800 That's right, it's not just Isaac Newton who's thinking about 0:06:58.800 --> 0:07:01.719 the nature of the universe. It's everybody. The goal of 0:07:01.760 --> 0:07:04.160 science is to understand the universe, and that means for 0:07:04.240 --> 0:07:07.320 everybody to figure it out, and that, of course means 0:07:07.320 --> 0:07:09.640 everybody's got to be out there thinking about the universe, 0:07:09.720 --> 0:07:12.960 asking questions, wondering how it all works, and we want 0:07:13.120 --> 0:07:15.400 you to be doing that. We hope that this podcast 0:07:15.600 --> 0:07:19.000 stimulates your curiosity. You hear on the podcast about the 0:07:19.040 --> 0:07:21.000 questions we are asking, but we want to hear about 0:07:21.000 --> 0:07:23.840 the questions you are asking, and then we want to 0:07:23.880 --> 0:07:26.520 answer them. So if you have questions about the nature 0:07:26.520 --> 0:07:28.200 of the universe or something you heard about on the 0:07:28.240 --> 0:07:31.640 podcast or something you heard about on gas another podcast, 0:07:31.800 --> 0:07:35.600 please write to me to questions at Danielanjorge dot com. 0:07:35.760 --> 0:07:36.760 We'll clear it up for you. 0:07:36.920 --> 0:07:39.760 Yeah, because it's part of human nature to be asking questions, 0:07:39.840 --> 0:07:42.760 and it's totally fun to ask questions as well, and 0:07:42.800 --> 0:07:44.760 so here in the podcast we sometimes like to answer 0:07:44.920 --> 0:07:47.200 questions that listeners send us, and so to be on 0:07:47.240 --> 0:07:56.280 the podcast, we'll be tackling listener questions number sixty six. 0:07:56.640 --> 0:07:58.720 You have a sixty six related snide. 0:07:58.360 --> 0:08:02.520 Comment warning, Daniel. If we keep going, we're gonna hit 0:08:02.720 --> 0:08:04.200 listener questions six sixty six. 0:08:05.480 --> 0:08:06.720 Oh, I thought you were going to warn you about 0:08:06.720 --> 0:08:09.680 listener question sixty nine, where we turned everything upside down. 0:08:11.520 --> 0:08:16.840 I have warned you repeatedly about that milestone, and you 0:08:16.920 --> 0:08:17.960 don't seem very concerned. 0:08:18.080 --> 0:08:20.080 I'm mindlessly barreling towards it. 0:08:21.120 --> 0:08:24.000 We'll just maybe we'll record it, but then we'll censor it. 0:08:25.920 --> 0:08:28.040 Maybe we'll just skip it. We'll go straight to seventy. 0:08:28.320 --> 0:08:30.240 Yeah, seventy isn't sixty nine. 0:08:30.760 --> 0:08:34.360 Nobody says that. Don't make that a thing. 0:08:35.280 --> 0:08:37.280 I don't care if other people say, oh, I see, 0:08:37.559 --> 0:08:39.360 but yeah. We do like to answer questions here on 0:08:39.400 --> 0:08:41.760 the podcast that listeners said this, and so today we 0:08:41.840 --> 0:08:46.199 have three awesome questions. They are about galaxies colliding but 0:08:46.360 --> 0:08:50.720 extreme forces, and about the air we breathe. So let's 0:08:50.760 --> 0:08:53.640 jump right in. Our first question comes from Pedra, who 0:08:53.720 --> 0:08:54.920 hails from Boston. 0:08:55.600 --> 0:08:56.400 Hi, Daniel, and Jor. 0:08:57.160 --> 0:09:00.000 I'm routinely here not to worry about the impending collision 0:09:00.120 --> 0:09:03.920 between our galaxy and the Andromeda galaxy, since the space 0:09:03.960 --> 0:09:07.280 between the stars within each galaxy is so great there 0:09:07.280 --> 0:09:10.600 won't be any direct collisions. However, on some of the 0:09:10.600 --> 0:09:14.360 podcast episodes, it seems as though the orbital stability of 0:09:14.400 --> 0:09:17.559 the planets in our solar system isn't all that great? 0:09:18.240 --> 0:09:21.800 For example, some planets may have traded places, while other 0:09:21.840 --> 0:09:26.120 planets could have been captured or ejected. So really, which 0:09:26.240 --> 0:09:29.000 argument wins? Do I need to tell my descendants to 0:09:29.040 --> 0:09:31.920 start worrying about it? In four point five billion years, 0:09:32.600 --> 0:09:34.560 I really want them to see the Sun become a 0:09:34.559 --> 0:09:36.679 red giant. Thanks for the great podcast. 0:09:37.160 --> 0:09:42.160 All right, interesting question. Basically, should we be worried four 0:09:42.200 --> 0:09:43.400 and a half billion years from now? 0:09:43.840 --> 0:09:48.240 Yeah? Exactly if we're all alive? Or should the zombies 0:09:48.320 --> 0:09:51.360 that have succeeded us, should they be worried about. 0:09:51.120 --> 0:09:54.520 What's going to happen? I think that's the best part 0:09:54.520 --> 0:09:56.800 of being a zombies. You don't have to worry about anything. 0:09:57.360 --> 0:09:59.040 As long as you've killed off all the people who 0:09:59.120 --> 0:10:00.840 might assign you homework problems, you're. 0:10:00.640 --> 0:10:02.679 Fine, man. I think the best part of being a 0:10:02.760 --> 0:10:04.280 zombie is you can just turn your brain off. 0:10:04.360 --> 0:10:06.000 Don't you need to protect it from exploding? 0:10:06.080 --> 0:10:06.240 Right? 0:10:06.360 --> 0:10:08.040 Isn't that the kryptonite of zombies? 0:10:08.360 --> 0:10:10.319 Well? I think fire also kills zombies. 0:10:10.360 --> 0:10:13.200 Oh boy, wow, yeah, I'm so glad you've been doing 0:10:13.200 --> 0:10:13.720 this research. 0:10:13.840 --> 0:10:15.400 I'm glad the people I'll be hanging out with know 0:10:15.440 --> 0:10:16.600 how to make a fire. 0:10:19.880 --> 0:10:22.520 But I think Petra's question is really touching on two 0:10:22.600 --> 0:10:25.560 things we hear about a lot in science, One that 0:10:25.600 --> 0:10:29.080 our galaxy is colliding with another galaxy, and the other 0:10:29.200 --> 0:10:31.520 that our solar system is kind of fragile, that the 0:10:31.679 --> 0:10:35.120 orbits are not really that stable, and so he's worried 0:10:35.440 --> 0:10:37.840 that even if stars are pretty dilute in the galaxy, 0:10:38.480 --> 0:10:40.160 would our solar system get upset? 0:10:41.440 --> 0:10:45.040 Basically, what's going to happen when our galaxy collides with Andromeda? 0:10:45.160 --> 0:10:45.240 Like? 0:10:45.600 --> 0:10:47.520 Be safe? Like, is nothing going to happen to us? 0:10:47.960 --> 0:10:51.520 Or should we be concerned that maybe our plant might 0:10:51.559 --> 0:10:53.440 get disrupted and thrown out into space. 0:10:53.679 --> 0:10:56.560 Yeah, it's definitely a valid concern, and it touches on 0:10:56.600 --> 0:10:58.880 a lot of really interesting physics. And first thing I 0:10:58.880 --> 0:11:02.120 want to talk about is why Andrama is going to 0:11:02.160 --> 0:11:03.760 collide with the Milky Way, because I get a lot 0:11:03.760 --> 0:11:07.080 of questions about exactly this. People hear us talking about 0:11:07.080 --> 0:11:09.920 how the universe is expanding and space is being created 0:11:10.320 --> 0:11:13.080 between galaxies, and then they hear us talking about how 0:11:13.120 --> 0:11:15.480 Andromeda is coming towards us and say, how does that 0:11:15.520 --> 0:11:18.600 make any sense? Why isn't space expanding between us and 0:11:18.600 --> 0:11:22.040 Andromeda and pushing it further and further away. And so 0:11:22.080 --> 0:11:24.679 first we should try to reconcile that apparent contradiction. 0:11:25.040 --> 0:11:30.120 Mm. Yeah, because we talked about like, how because dark 0:11:30.200 --> 0:11:33.280 energy is expanding the universe, the galaxies out there getting 0:11:33.320 --> 0:11:35.640 further and further away from us. But we've also talked 0:11:35.640 --> 0:11:38.560 about how Drama is in a collision course with our galaxy. 0:11:38.800 --> 0:11:41.840 Yeah, And the answer comes down to distances, and dark 0:11:41.960 --> 0:11:45.120 energy is something that gets more powerful for distant objects. 0:11:45.240 --> 0:11:48.559 It's basically like a chunk of space grows a little bit, 0:11:48.600 --> 0:11:51.480 and so more chunks of space are growing more. So 0:11:51.520 --> 0:11:53.960 a little tiny chunk of space is hardly growing, but 0:11:54.040 --> 0:11:58.199 a vast distance between our galaxy cluster and a really 0:11:58.240 --> 0:12:01.720 distant other galaxy cluster that's kind of growing a lot. 0:12:02.120 --> 0:12:05.000 And gravity is the opposite. Gravity gets weaker with distance. 0:12:05.000 --> 0:12:08.480 As things get further apart, gravity fades away. So for 0:12:08.480 --> 0:12:10.880 stuff that's really close together, like the Earth and the Sun, 0:12:11.320 --> 0:12:15.280 or even our galaxy in the neighboring galaxy, gravity wins 0:12:15.320 --> 0:12:18.439 over dark energy. Things that are really really far apart, 0:12:18.480 --> 0:12:23.120 like clusters of galaxies, not individual galaxies, dark energy is winning. 0:12:23.520 --> 0:12:25.400 And most of the universe is far apart from most 0:12:25.440 --> 0:12:28.800 of the universe, so mostly things are expanding away from 0:12:28.800 --> 0:12:32.000 each other, but in little neighborhoods, like our cluster of galaxy, 0:12:32.160 --> 0:12:35.360 stuff is still getting pulled together by gravity. So gravity 0:12:35.440 --> 0:12:37.800 is the reason the Milky Way and Andromeda will collide 0:12:38.120 --> 0:12:39.199 in a few billion years? 0:12:39.679 --> 0:12:41.520 Is it gravity? Or is it just that we just 0:12:41.600 --> 0:12:44.720 happen to be in a course that intercepts the course 0:12:44.720 --> 0:12:48.920 of Andromeda, Like, is Indrameda really being attracted to our galaxy? 0:12:49.320 --> 0:12:51.760 I mean, obviously it is, but is it really significant 0:12:52.160 --> 0:12:54.079 to call it the main reason it's we're going to 0:12:54.120 --> 0:12:54.839 collide with it? 0:12:54.840 --> 0:12:56.920 It definitely is. I mean, the Milky Way Andromeda are 0:12:56.960 --> 0:13:00.000 part of a cluster of galaxies, and that cluster exhibits 0:13:00.280 --> 0:13:03.160 because of gravity, so it's holding it together, and the 0:13:03.160 --> 0:13:05.760 galaxies are sort of sloshing around. It's not guaranteed at 0:13:05.800 --> 0:13:08.360 any moment that they're going to hit each other, but 0:13:08.480 --> 0:13:11.160 it's gravity that holds them together, that's pulling them together. 0:13:11.480 --> 0:13:14.400 It's sort of like asking if a comet falls towards 0:13:14.400 --> 0:13:16.760 the Sun and it collides to the Sun, why is 0:13:16.760 --> 0:13:19.120 that Well, it's definitely because of the gravity. That doesn't 0:13:19.120 --> 0:13:21.600 mean that every comet does collide with the Sun. Gravity 0:13:21.640 --> 0:13:23.800 is not omnipotent. Sometimes comets go around the back of 0:13:23.840 --> 0:13:26.000 the Sun in the same way in the local cluster. 0:13:26.320 --> 0:13:28.920 Not every galaxy is gonna collide with every other galaxy 0:13:28.920 --> 0:13:32.120 as soon as possible. Sometimes they pass around each other. 0:13:32.480 --> 0:13:34.560 But it is gravity that's pulling these two together. 0:13:35.120 --> 0:13:36.600 Well, I guess what I mean is like if you 0:13:36.640 --> 0:13:39.559 have to asteroids, for example, in the Solar System, and 0:13:39.600 --> 0:13:41.959 they're gonna collide with each other. I mean, sure, they're 0:13:42.000 --> 0:13:44.560 in the Solar System together because of the gravity well 0:13:44.559 --> 0:13:46.520 of the Sun, but the fact that they're colliding with 0:13:46.559 --> 0:13:49.240 each other as opposed to not colliding, it's mostly just 0:13:49.320 --> 0:13:51.520 kind of look right, Yeah. 0:13:51.320 --> 0:13:54.280 It's gravity plus chance. It's possible to have a cluster 0:13:54.520 --> 0:13:58.160 where galaxies like ours and Andromeda don't collide until later on. 0:13:58.960 --> 0:14:01.480 Eventually everything is going to collide and it's all going 0:14:01.559 --> 0:14:04.400 to collapse into one super massive black hole. So it's 0:14:04.440 --> 0:14:05.560 really just a waiting game. 0:14:05.840 --> 0:14:07.520 But the collision that's going to happen in four and 0:14:07.559 --> 0:14:11.760 a half billion years, that's basically luck, right, It's not 0:14:11.800 --> 0:14:14.160 like it's inevitable, like if our galaxy was moving a 0:14:14.160 --> 0:14:16.680 few degrees in another direction, or to the right or 0:14:16.679 --> 0:14:19.120 to the left, we wouldn't be colliding with Andromeda, would we. 0:14:19.400 --> 0:14:21.520 Yeah, that's right. If you changed the initial conditions, that 0:14:21.520 --> 0:14:24.360 collision might happen later. It also might happen earlier. Right, 0:14:24.680 --> 0:14:26.440 It could be that we're lucky we got this far 0:14:26.640 --> 0:14:28.960 now colliding with Andromeda. So yeah, the whole system is 0:14:29.080 --> 0:14:31.640 very chaotic, but it is gravity. But gravity is really 0:14:31.680 --> 0:14:32.920 the only force at play here. 0:14:33.200 --> 0:14:36.240 M and So the reason we're worried about Andromeda and 0:14:36.280 --> 0:14:39.640 not other galaxies is because the other galaxies are further away, 0:14:39.920 --> 0:14:42.720 and those are definitely moving away from us because of 0:14:42.800 --> 0:14:46.080 dark energy, or are some of them potentially getting closer 0:14:46.120 --> 0:14:46.400 to us. 0:14:46.680 --> 0:14:50.320 Everything in our galaxy cluster is gravitationally bound, which means 0:14:50.320 --> 0:14:52.920 it has enough gravity to hold itself together and resist 0:14:53.000 --> 0:14:56.640 the pull of dark energy. Galaxy clusters are like the 0:14:56.680 --> 0:15:00.240 biggest thing that have that property. Anything that's larger than that, 0:15:00.400 --> 0:15:03.560 what we call a supercluster, is probably too big and 0:15:03.640 --> 0:15:06.080 too spread out for gravity to hold itself together, and 0:15:06.160 --> 0:15:08.040 dark energy is going to win. So that's sort of 0:15:08.040 --> 0:15:11.200 the tipping point. So anything that's in our galaxy cluster 0:15:11.720 --> 0:15:14.480 is eventually going to collapse. Into one big super massive 0:15:14.480 --> 0:15:17.000 black hole, and we're talking very very far in the. 0:15:16.960 --> 0:15:21.320 Future unless dark energy changes, right, Yes, like if it accelerates, 0:15:21.360 --> 0:15:23.960 then it's going to get a little more crowded, but 0:15:24.200 --> 0:15:26.800 it or if it like weekends, things might get a 0:15:26.800 --> 0:15:27.400 little room hear. 0:15:27.480 --> 0:15:29.920 Yeah, I think it's the opposite. If dark energy accelerates, 0:15:30.240 --> 0:15:32.400 then even our galaxy cluster is going to get torn 0:15:32.400 --> 0:15:35.480 apart because it becomes more powerful than gravity. We talked 0:15:35.480 --> 0:15:37.680 about that once on the podcast. There's even a theory 0:15:37.720 --> 0:15:40.400 of like phantom dark energy, where dark energy gets so 0:15:40.480 --> 0:15:43.960 powerful that it tears apart atoms and even protons. And 0:15:44.000 --> 0:15:47.680 if dark energy weakens, then gravity wins over larger distances 0:15:47.720 --> 0:15:49.960 and it might gather together even superclusters. 0:15:50.240 --> 0:15:51.840 Right, that's what I meant. I meant the opposite of 0:15:51.840 --> 0:15:52.320 what I said. 0:15:52.840 --> 0:15:55.200 But you're definitely right on the conceptual part, which is 0:15:55.400 --> 0:15:57.520 that we don't know what dark energy is or what 0:15:57.560 --> 0:15:59.400 it's going to do, and we can't really predict it. 0:15:59.440 --> 0:16:02.760 So this is assuming a naive extrapolation of dark energy, 0:16:03.000 --> 0:16:04.720 which is basically all we can do at this point. 0:16:04.840 --> 0:16:07.040 All Right, so we're in a collision course with Andromeda. 0:16:07.720 --> 0:16:09.280 What's going to happen when we collide. 0:16:09.680 --> 0:16:11.920 So when we collide with Andromeda, there's a bunch of 0:16:11.960 --> 0:16:14.520 different components of the galaxy, and you really need to 0:16:14.560 --> 0:16:17.240 think about each of them individually because they all have 0:16:17.320 --> 0:16:20.360 different behavior. So, for example, the gas and the dust 0:16:20.720 --> 0:16:22.520 that are in the two galaxies, those are going to 0:16:22.560 --> 0:16:24.520 collide and you're going to get all sorts of dramatic stuff. 0:16:24.640 --> 0:16:27.080 It's going to see the creation of lots of new stars, 0:16:27.360 --> 0:16:30.080 which would be really exciting. But the stars themselves are 0:16:30.120 --> 0:16:31.960 very different from the gas and the dust. Right, the 0:16:32.000 --> 0:16:34.280 gas in the dust is very spread out. It's definitely 0:16:34.280 --> 0:16:36.600 going to smash into the other stuff. But stars are 0:16:36.640 --> 0:16:39.080 very different from gas and dust. They're not as spread out. 0:16:39.120 --> 0:16:41.800 They're tiny, and they're clumpy, and they're really really dilute. 0:16:42.400 --> 0:16:45.640 So when stars approach other stars, it's very hard for 0:16:45.680 --> 0:16:49.080 them to actually collide because space is really really big 0:16:49.120 --> 0:16:51.040 and the stars are really really far apart. 0:16:52.200 --> 0:16:54.240 I guess how far apart are they? Like how far 0:16:54.320 --> 0:16:55.480 is there are year's neighbor? 0:16:55.680 --> 0:16:58.920 So our nearest neighbor is light years away, right, the 0:16:59.000 --> 0:17:02.280 closest star to us almost four light years away, and 0:17:02.320 --> 0:17:05.320 the Sun is the tiny fraction of a light year wide. 0:17:05.640 --> 0:17:07.760 I mean, if you shrink, for example, the Sun down 0:17:07.800 --> 0:17:09.160 to the size of a tennis ball that you could 0:17:09.160 --> 0:17:12.160 hold in your hand, then the nearest neighbor star would 0:17:12.200 --> 0:17:14.359 be four or five thousand miles away. 0:17:14.880 --> 0:17:18.399 WHOA, that's like on the other side of the Atlantic kind. 0:17:18.280 --> 0:17:21.800 Of yeah, exactly. So imagine you're throwing a tennis ball 0:17:21.840 --> 0:17:24.080 and somebody on the other side of the ocean is 0:17:24.119 --> 0:17:26.520 throwing a tennis ball. What are the chances that they're 0:17:26.520 --> 0:17:30.240 going to hit each other over the ocean? Like basically zero? 0:17:31.240 --> 0:17:35.520 But I guess how wide is the sphere of influence 0:17:35.560 --> 0:17:37.960 of something like the Sun, Like how close do you 0:17:37.960 --> 0:17:40.040 need to get to it before you feel it's gravity? 0:17:40.280 --> 0:17:43.360 Yeah? Exactly, good point, because we're not actually just interested 0:17:43.400 --> 0:17:46.600 in like a collision where like the two stars really 0:17:46.640 --> 0:17:49.520 touch each other and merge and become one. Stars can 0:17:49.560 --> 0:17:52.080 pull in each other if they're even near each other, right, 0:17:52.320 --> 0:17:55.080 And that's really what Petra's question is about, is how 0:17:55.119 --> 0:17:57.479 close does the star need to get to distort our 0:17:57.520 --> 0:17:59.960 star or distort the orbit of stuff around the star? 0:18:00.040 --> 0:18:04.040 Are right? Because near misses can destabilize things, and we 0:18:04.119 --> 0:18:06.760 know that already in our galaxy because other stars are 0:18:06.920 --> 0:18:09.639 moving relative to the Sun. Sometimes they come closer, sometimes 0:18:09.640 --> 0:18:12.639 they come further away, and that can distort the orbits 0:18:12.640 --> 0:18:15.560 of stuff in our Solar system. So it's not a clear, 0:18:15.640 --> 0:18:18.919 crisp answer. It's not like there's a certain distance within 0:18:19.040 --> 0:18:22.720 which something happens and out of which nothing happens. It's gradual, right. 0:18:22.720 --> 0:18:25.200 The closer it comes, the greater the gravitational distortion. 0:18:26.400 --> 0:18:29.800 But I guess maybe it depends on how unstable our 0:18:29.920 --> 0:18:34.399 orbit is or how fragile our orbit is. Do you 0:18:34.400 --> 0:18:38.280 have a sense of how precarious are a path around 0:18:38.280 --> 0:18:41.040 the Sun is? Like if I bring in another Sun, 0:18:41.800 --> 0:18:45.240 I don't know, a few million miles away, is it 0:18:45.280 --> 0:18:46.960 going to affect us and kick us out of the 0:18:47.000 --> 0:18:49.600 Solar System or maybe cause us to fall into the Sun, 0:18:49.720 --> 0:18:50.720 or are we going to be okay? 0:18:51.040 --> 0:18:54.280 Yeah, it's a good question. The Earth is pretty stable, 0:18:54.760 --> 0:18:56.840 like just the Earth in the Solar System is a 0:18:56.840 --> 0:18:59.359 pretty stable orbit. There's a lot of stuff going on 0:18:59.440 --> 0:19:02.240 that's going to end fluence the Earth's orbit that makes 0:19:02.280 --> 0:19:05.440 its orbit change. For example, like the Sun is losing mass, 0:19:05.480 --> 0:19:08.800 so it's gravity shrinks. The Sun is also pushing on 0:19:08.880 --> 0:19:10.840 the Earth, not just pulling on it with gravity but 0:19:10.920 --> 0:19:14.160 its wind pushes on the Earth. There's effects of Jupiter, 0:19:14.800 --> 0:19:18.679 there's gravitational radiation. But you're right, the biggest wild card 0:19:18.760 --> 0:19:21.679 are like things from outside the Solar system. And this 0:19:21.760 --> 0:19:24.000 is something we've thought about, not just in the case 0:19:24.040 --> 0:19:27.439 of another galaxy, but again just stuff in our Solar system. So, 0:19:27.440 --> 0:19:30.560 for example, there is a star it's called Glease seven 0:19:30.560 --> 0:19:33.520 to ten that we've been tracking, and we predict that 0:19:33.600 --> 0:19:37.040