WEBVTT - Do we live in a super bubble? 0:00:07.840 --> 0:00:11.880 Think about where you are right now. Maybe you're in 0:00:11.920 --> 0:00:14.800 your car commuting, or you're out walking the dogs or 0:00:14.920 --> 0:00:19.120 at home doing the dishes. But where are you relative 0:00:19.239 --> 0:00:22.319 to everyone else? How do you define it? Probably you 0:00:22.520 --> 0:00:25.880 zoom out and put yourself in a wider context, your town, 0:00:26.040 --> 0:00:29.920 your region, your whole country. Listeners to this pod will 0:00:30.000 --> 0:00:33.280 likely be inclined to zoom out even further to all 0:00:33.320 --> 0:00:36.959 of Earth and then the whole Solar System. From there, 0:00:37.000 --> 0:00:39.880 it's very tempting to skip forward and put our solar 0:00:39.880 --> 0:00:43.120 system into its place in the galaxy, than the galaxy 0:00:43.280 --> 0:00:47.800 into its cluster, and then that cluster within the supercluster foam. 0:00:48.800 --> 0:00:52.040 But have we been too hasty? Is our galaxy so simple, 0:00:52.200 --> 0:00:55.520 just a collection of stars floating around a central black hole? 0:00:56.240 --> 0:01:00.480 Or is there more nuance to our galactic context? We 0:01:00.520 --> 0:01:03.480 think of the galaxy as mostly stars, but they're formed, 0:01:03.640 --> 0:01:06.959 they burn, and they die. There's a constant slashing of 0:01:07.120 --> 0:01:11.360 energy back and forth between those stars and vast clouds 0:01:11.360 --> 0:01:15.360 of raw material. Where is our Solar system relative to 0:01:15.440 --> 0:01:18.839 those clouds? Are we in the midst of a galactic fog? 0:01:19.240 --> 0:01:22.319 Or are we floating through an open bubble? Today on 0:01:22.360 --> 0:01:25.399 the pod will zoom out to this fascinating scene, understand 0:01:25.440 --> 0:01:28.440 the dynamics of star formation and destruction, and let you 0:01:28.600 --> 0:01:33.840 know exactly where you we all of us stand galactically speaking. 0:01:34.720 --> 0:01:38.000 Welcome to Daniel and Kelly's Extraordinary Galaxy. 0:01:51.280 --> 0:01:54.240 Hello, I'm Kelly Winer Smith. I study parasites and space 0:01:54.280 --> 0:01:55.440 and I love bubbles. 0:02:04.920 --> 0:02:09.120 Well, Hi, I'm Daniel. I'm a particle physicist. I love bubbles, 0:02:09.120 --> 0:02:10.880 and I have all of my organs. 0:02:11.240 --> 0:02:13.800 Okay, yeah, right, So that I was gonna ask you 0:02:14.360 --> 0:02:17.520 about the most painful thing you ever experienced in your 0:02:17.560 --> 0:02:19.600 life as a lead into why my laugh is going 0:02:19.639 --> 0:02:23.040 to be a little off today, folks. 0:02:23.120 --> 0:02:25.640 I'm going to try to restrain myself from being funny 0:02:25.680 --> 0:02:28.320 today because if I make a joke that makes Kelly 0:02:28.360 --> 0:02:30.240 crack up, she could literally crack up. 0:02:30.840 --> 0:02:36.239 Oh I could, Yes, I could split a stitch. So 0:02:36.919 --> 0:02:40.720 what aside from labor, The most painful thing that ever 0:02:40.720 --> 0:02:45.320 happens to me was the gallstones that tried to pass 0:02:45.400 --> 0:02:48.200 their way out of my body on Friday, but ended 0:02:48.240 --> 0:02:51.600 up getting removed surgically. The whole thing, the whole gallbladder 0:02:51.639 --> 0:02:55.520 was removed, and so I am still working on resolving 0:02:55.560 --> 0:02:58.520 my stitches. And so it hurts to laugh. So I 0:02:58.560 --> 0:02:59.880 think I've come up with the way to laugh that 0:03:00.000 --> 0:03:02.240 it hurts less, and so my my laugh will sound 0:03:02.320 --> 0:03:04.440 a little I don't know, maybe even less annoying. I 0:03:04.480 --> 0:03:06.800 have seen there's a couple complaints about the way I laugh. 0:03:07.200 --> 0:03:10.120 You'all can just kiss my rear ends. But anyway, Daniel, 0:03:10.160 --> 0:03:11.960 what is the most painful thing that's ever happened to you? 0:03:13.520 --> 0:03:16.480 Oh? Most painful thing that's ever happened to me? I 0:03:16.560 --> 0:03:19.280 broken my wrist, but weirdly that didn't hurt that much. 0:03:20.400 --> 0:03:22.720 I think maybe the most painful thing is when I 0:03:22.720 --> 0:03:27.360 broke my little toe. I like massively stubbed it on 0:03:27.440 --> 0:03:31.720 a little concrete outpost and cracked it and wow, yeah, 0:03:31.760 --> 0:03:32.920 I thought I was gonna die. 0:03:33.400 --> 0:03:35.520 Ouch. Yeah, And how long did it take to heal? 0:03:35.920 --> 0:03:37.600 What do you do? Just put like a nothing. 0:03:37.600 --> 0:03:39.880 You just tape it to the next toe, and like 0:03:40.400 --> 0:03:43.920 whatever happens inside of it happens. Like there's no surgery 0:03:44.000 --> 0:03:46.280 to correct, like the little bones inside your little toe, 0:03:46.320 --> 0:03:48.960 nobody needs it. I was like, just cut that bugger off, 0:03:49.000 --> 0:03:51.000 but I was like, no, you just tape it to 0:03:51.000 --> 0:03:53.920 the next one. That's it. 0:03:55.120 --> 0:03:57.200 Well, you know, Daniel, it sounds like if you lived 0:03:57.200 --> 0:03:59.119 in a bubble, you would have been safe. But if 0:03:59.160 --> 0:04:01.520 I lived in a bubble, well, that wouldn't have saved me. 0:04:02.560 --> 0:04:04.640 And so well, you know, maybe if the whole universe 0:04:04.680 --> 0:04:06.360 was in a bubble, that would save us from some 0:04:06.400 --> 0:04:09.760 of the bumps and bruises of existence. But do we 0:04:09.840 --> 0:04:11.000 live in a bubble? Daniel? 0:04:13.440 --> 0:04:15.760 Well, we are trying to pop the bubble of ignorance 0:04:15.800 --> 0:04:20.240 out there and help everybody understand their cosmic context, where 0:04:20.279 --> 0:04:22.840 we are situated in our solar system, where our solar 0:04:22.839 --> 0:04:25.960 system is situated in the galaxy, and the whole context 0:04:26.240 --> 0:04:29.680 for our existence. I love filling in all those details 0:04:29.680 --> 0:04:33.000 and helping people understand really where they live. And today 0:04:33.000 --> 0:04:35.920 we're going to dive into that topic essentially, where our 0:04:36.040 --> 0:04:39.240 sun is in the galaxy? Is there structure out there? 0:04:39.240 --> 0:04:40.080 How does it all work? 0:04:40.200 --> 0:04:42.480 And I think all of our inner kids are excited 0:04:42.520 --> 0:04:45.240 today to find out whether or not we live in 0:04:45.279 --> 0:04:46.040 a super bubble. 0:04:47.520 --> 0:04:49.719 So before we dive into it, I was wondering what 0:04:49.800 --> 0:04:52.400 people out there knew on the topic. So I went 0:04:52.440 --> 0:04:55.040 to our group of volunteers, I asked them, do we 0:04:55.120 --> 0:04:59.920 live in a super bubble? Here's what folks had to say, 0:05:00.080 --> 0:05:02.080 I don't even really know what a super bubble is, 0:05:02.839 --> 0:05:06.520 so maybe what do you think, Glen. I have no 0:05:06.600 --> 0:05:08.800 idea what a super bubble is. I have not heard 0:05:08.800 --> 0:05:11.720 the term super bubble. It makes me think about some 0:05:11.760 --> 0:05:15.000 conceptualizations of fourth dimensionality. 0:05:14.640 --> 0:05:17.280 Considering I couldn't tell you what a super bubble is. 0:05:18.200 --> 0:05:20.919 I can't really say if we live in one, but 0:05:21.320 --> 0:05:26.360 it sounds like one of these really exciting astrophysical maybe 0:05:26.400 --> 0:05:29.960 who knows cool universe things, so I'm eager to learn 0:05:29.960 --> 0:05:32.839 about it. I have never heard of the term super bubble, 0:05:33.360 --> 0:05:35.200 but we probably live in one. 0:05:35.640 --> 0:05:37.839 I like the I've never heard of it, so yes, 0:05:41.080 --> 0:05:41.400 this is. 0:05:41.360 --> 0:05:42.919 Really exciting to me that nobody had heard of it, 0:05:42.960 --> 0:05:45.240 because it means we get to share this really cool 0:05:45.279 --> 0:05:48.679 thing about the universe with everybody. Yay. 0:05:49.080 --> 0:05:49.919 We love doing that. 0:05:51.320 --> 0:05:53.960 You know that great XKCD comic. I mean they're all great, 0:05:54.200 --> 0:05:57.440 but the one about the moment you discover somebody doesn't 0:05:57.480 --> 0:05:59.919 know something really cool about the universe and how you 0:06:00.000 --> 0:06:02.279 should treat that with reverence and respect because it's a 0:06:02.320 --> 0:06:05.560 wonderful teaching moment. That's where we are today about super bubbles. 0:06:06.279 --> 0:06:07.799 I mean, I think we can all agree that Randall 0:06:07.839 --> 0:06:10.159 Monroe is the greatest web cartoonist to have ever lived. 0:06:10.200 --> 0:06:25.719 Right, Wow, that's instant karma right there. Wow. I hope 0:06:25.800 --> 0:06:27.280 Zach is listening and laughing at that. 0:06:31.440 --> 0:06:32.840 All right, all right, bubbles, all. 0:06:32.839 --> 0:06:35.200 Right, bubbles. So we're talking about the Sun and the 0:06:35.200 --> 0:06:38.840 Solar System's context in the galaxy. But before we get there, 0:06:38.920 --> 0:06:42.040 let's do like an overview of like what's out there 0:06:42.080 --> 0:06:45.760 in space? How empty is it? Anyway? So to get oriented, 0:06:45.800 --> 0:06:49.039 remember that our situation here on Earth is very unusual. 0:06:49.760 --> 0:06:52.839 Like the density of stuff around you is very rare 0:06:52.920 --> 0:06:56.200 in the universe. The universe is mostly very very low density, 0:06:56.200 --> 0:06:58.839 and we live in a very very high density situation. 0:06:59.240 --> 0:07:02.920 The Earth, of course, is wonderful and cozy, and in 0:07:03.000 --> 0:07:06.680 like a normal atmosphere, you'll find a huge number of 0:07:06.720 --> 0:07:09.159 molecules per cubic meter, like ten to the twenty five 0:07:09.200 --> 0:07:12.440 molecules per cubic meter. It's a big number. And that's 0:07:12.480 --> 0:07:15.680 just because like Avagadro's number is pretty big, and gravity 0:07:15.720 --> 0:07:18.000 has gathered the Earth and the stars and all that 0:07:18.000 --> 0:07:20.240 stuff together into little dense clumps. 0:07:20.360 --> 0:07:23.360 I thought Avagadro's number was ten to the twenty three. 0:07:23.160 --> 0:07:24.640 It is, yeah, exactly. 0:07:24.800 --> 0:07:26.679 Oh but this is ten to the twenty fifth. 0:07:26.840 --> 0:07:29.160 Yeah, because a mole is less than a cubic meter. 0:07:29.400 --> 0:07:31.560 Got it, got it. I'm with you now, Okay, these 0:07:31.560 --> 0:07:33.320 are big numbers, Daniel, big numbers. 0:07:33.400 --> 0:07:36.119 These are big numbers. And you know, sometimes on Earth 0:07:36.120 --> 0:07:39.480 we want to do experiments in low density situations, like 0:07:39.520 --> 0:07:41.920 when we collide particles together, we don't want a whole 0:07:41.920 --> 0:07:44.400 bunch of other particles around, Or when you build a 0:07:44.440 --> 0:07:48.840 plasma inside eater to diffusion, you want mostly a vacuum 0:07:48.880 --> 0:07:51.560 before you start. And so we have all these vacuums 0:07:51.560 --> 0:07:54.240 in labs. We've created these situations you pump out all 0:07:54.280 --> 0:07:56.880 the air, and you might be surprised to learn that 0:07:56.960 --> 0:08:00.560 even in those highly specialized vacuums on Earth, we still 0:08:00.560 --> 0:08:02.920 have something like ten to the twelve or ten to 0:08:02.960 --> 0:08:06.760 the fifteen molecules per cubic meter. Like that's down ten 0:08:07.080 --> 0:08:11.120 or thirteen orders of magnitude from your general atmosphere. So like, 0:08:11.360 --> 0:08:14.160 really good work, and this is not easy, but still 0:08:14.200 --> 0:08:15.560 it's a lot of molecules. 0:08:15.760 --> 0:08:18.880 When somebody says the vacuum of space, are we doing 0:08:19.040 --> 0:08:21.920 better than the vacuum of space? When we make a 0:08:22.000 --> 0:08:24.440 vacuum in the lab or are we doing about the 0:08:24.480 --> 0:08:27.240 same as the quote unquote vacuum of space. 0:08:27.680 --> 0:08:31.000 Neither. We're not doing anywhere close to the vacuum of space. 0:08:31.360 --> 0:08:34.520 The density of vacuums in labs here on Earth is 0:08:35.000 --> 0:08:38.240 much higher, is much much more stuff in our lab 0:08:38.320 --> 0:08:41.840 quote unquote vacuums than there is out there in space. Okay, 0:08:41.960 --> 0:08:44.840 but let's stick into that and zoom our mental picture 0:08:44.960 --> 0:08:48.000 out from the surface of the Earth. Obviously, the atmosphere 0:08:48.080 --> 0:08:51.880 drops gradually, right, There's no like huge wall or gait 0:08:52.000 --> 0:08:54.319 or anything. This is not space balls, where atmosphere is 0:08:54.320 --> 0:08:57.640 that contained by a huge bubble right where the code 0:08:57.640 --> 0:09:00.200 is one two three four. But in a funny way, 0:09:00.240 --> 0:09:02.880 there is because space officially starts at like one hundred 0:09:02.920 --> 0:09:05.760 kilometers above the surface of the Earth, which I always 0:09:05.760 --> 0:09:06.400 thought was weird. 0:09:06.760 --> 0:09:08.880 There's some debate about that though, isn't there. 0:09:09.000 --> 0:09:11.240 Yes, absolutely there is, and like you can be an 0:09:11.280 --> 0:09:15.679 astronaut if you've gone eighty kilometers above. There's definitely a debate. 0:09:15.720 --> 0:09:18.120 It's something about astronomy, so it's not just it depends. 0:09:18.200 --> 0:09:19.839 It's a bunch of nerds arguing about it. 0:09:20.000 --> 0:09:23.560 I thought one hundred kilometers was something like at that point, 0:09:23.640 --> 0:09:27.119 there aren't enough molecules to hold up your airplane anymore, 0:09:27.240 --> 0:09:28.880 and so that's where space starts. 0:09:29.200 --> 0:09:30.680 Oh that's cool, isn't it. 0:09:30.679 --> 0:09:31.640 The Von Carmon line. 0:09:31.960 --> 0:09:35.320 That's the Von Carmen line. Yeah, And the ISS is 0:09:35.440 --> 0:09:37.760 like three hundred or four hundred kilometers above the surface 0:09:37.800 --> 0:09:40.720 of the Earth, so definitely in space. And so if 0:09:40.720 --> 0:09:44.439 you're inside our Solar system but outside Earth and its atmosphere, 0:09:44.840 --> 0:09:47.640 then there's still stuff out there. The vacuum of space 0:09:47.720 --> 0:09:51.000 inside the Solar System is not a perfect vacuum. There's 0:09:51.000 --> 0:09:53.120 a bunch of particles. Most of it comes from the 0:09:53.160 --> 0:09:55.520 Sun because the Sun, as we say often is producing 0:09:55.559 --> 0:09:58.360 a lot of stuff, not just photons but also matter. 0:09:58.640 --> 0:10:01.800 The solar wind is electronic and protons and alpha particles. 0:10:02.280 --> 0:10:04.280 These things are zooming around with a lot of energy. 0:10:04.720 --> 0:10:08.520 And so there's something like ten million protons per cubic 0:10:08.640 --> 0:10:12.680 meter between planets. So remember on Earth it's ten to 0:10:12.679 --> 0:10:16.400 the twenty five molecules per cubic meter, labs on Earth 0:10:16.480 --> 0:10:18.280 is ten to the twelve. Now we're down to like 0:10:18.320 --> 0:10:21.760 ten to the seven protons per cubic meter, so that's 0:10:21.800 --> 0:10:24.760 down like five or six orders of magnitude compared to 0:10:24.800 --> 0:10:25.640 vacuums on Earth. 0:10:26.080 --> 0:10:29.959 Wow, you wouldn't want to go out there, people, but. 0:10:29.920 --> 0:10:32.200 It would be a good place to do vacuum based experiments. 0:10:32.559 --> 0:10:33.000 Sure. 0:10:33.200 --> 0:10:36.800 Yeah, but it's still not that empty, right, Like millions 0:10:36.840 --> 0:10:39.160 and millions of protons are out there. It's not something 0:10:39.200 --> 0:10:40.679 you could say is empty. And when we talk about 0:10:40.760 --> 0:10:45.280 vacuum in physics and theoretical physics, we mean space with 0:10:45.480 --> 0:10:48.439 no extra energy, and it's a minimum energy state of space. 0:10:48.480 --> 0:10:52.480 And so this interplanetary space is not approaching the theoretical 0:10:52.520 --> 0:10:55.839 physics vacuum at all. Okay, And then take your mental 0:10:55.840 --> 0:10:58.319 picture and zoom out from the Solar System and now 0:10:58.320 --> 0:11:02.120 we're between stars. Were between our star and Alpha Centauri 0:11:02.200 --> 0:11:05.760 for example. Now we're in what we call the interstellar medium, 0:11:05.800 --> 0:11:08.840 the stuff between the stars. And even this is not 0:11:09.080 --> 0:11:11.720 that empty, right. It turns out there's a big range 0:11:11.720 --> 0:11:14.960 of densities of stuff from ten to the six molecule 0:11:15.040 --> 0:11:18.920 percubic meter, which is like the density in our Solar system, 0:11:19.120 --> 0:11:21.280 all the way down to ten to the four molecules 0:11:21.280 --> 0:11:22.000 per cubic meter. 0:11:22.240 --> 0:11:24.080 Isn't this where we thought the Ork cloud would be? 0:11:24.200 --> 0:11:26.160 Or this is like when we get past the Ork Cloud. 0:11:26.320 --> 0:11:28.680 Yeah, so there's a couple of different boundaries here. You 0:11:28.720 --> 0:11:30.640 go out past the planets, you get to like the 0:11:30.720 --> 0:11:34.320 dwarf planets, and then the Kuiper Belt objects. Beyond that, 0:11:34.800 --> 0:11:38.719 there's the boundary of the heliosphere where the Sun dominates 0:11:38.760 --> 0:11:42.880 and it meets the interstellar wind, the galactic wind. That's 0:11:42.920 --> 0:11:45.480 a region where you're exiting the Solar System. But you're 0:11:45.559 --> 0:11:49.520 right beyond that is more stuff. So the Orc Cloud 0:11:49.600 --> 0:11:53.360 technically is part of the interstellar medium because it's past 0:11:53.440 --> 0:11:56.880 that boundary. It's in a region where the interstellar wind 0:11:57.040 --> 0:12:01.640 dominates over the Sun's wind, but it is gravitationally bound 0:12:01.640 --> 0:12:03.840 to the Sun, so it's sort of like playing both 0:12:03.880 --> 0:12:04.880 sides of the equation off. 0:12:04.880 --> 0:12:10.439 That makes sense, it does, but it's still so overwhelmed 0:12:10.480 --> 0:12:12.920 by the gas in that area that the interstellar medium 0:12:12.960 --> 0:12:15.000 is ninety nine percent gas and all the rocks out 0:12:15.000 --> 0:12:17.880 there are just make up one percent dust. Would that 0:12:17.880 --> 0:12:18.520 be fair to say? 0:12:18.720 --> 0:12:20.360 Yes, that's right, and we're going to come back to 0:12:20.400 --> 0:12:22.440 the interstellar medium and do a deep dive into it. 0:12:22.440 --> 0:12:25.800 Has a lot of really interesting structure, but yeah, most 0:12:25.800 --> 0:12:28.600 of it is gas. It's ninety nine percent gas, and 0:12:28.640 --> 0:12:31.520 then a little bit of it is rocks or comets, 0:12:31.559 --> 0:12:34.160 like in the oricloud and dust. There's a few cosmic 0:12:34.240 --> 0:12:37.840 rays out there, but mostly it's just gas and has 0:12:37.880 --> 0:12:40.400 all sorts of interesting turbulence and structure that we're going 0:12:40.480 --> 0:12:43.320 to talk about and don't forget out there. Also in 0:12:43.360 --> 0:12:46.720 the galaxy is dark matter. We're only talking right now 0:12:46.760 --> 0:12:49.000 about the luminous matter, the kind of stuff that's made 0:12:49.040 --> 0:12:52.120 up of atoms, but we know that the universe is 0:12:52.160 --> 0:12:55.080 dominated by dark matter. We know that it's spread out 0:12:55.120 --> 0:12:57.760 throughout the galaxy, but it there's five times as much 0:12:57.800 --> 0:13:00.959 of it as there is luminous matter, so you can't 0:13:01.000 --> 0:13:03.120 interact with it, but it is there. And so if 0:13:03.160 --> 0:13:05.960 you're just thinking about like the density of matter overall, 0:13:06.200 --> 0:13:08.079 you have to also account for that dark matter. 0:13:08.520 --> 0:13:12.080 Okay, so in the interstellar space mostly gas, little bit 0:13:12.120 --> 0:13:15.400 of dust, you're not likely to stub your toe. But 0:13:15.559 --> 0:13:18.880 so now we're talking about what's between the stars, But 0:13:18.920 --> 0:13:22.680 what about what's between the galaxies and the intergalactic space. 0:13:23.120 --> 0:13:26.000 Yeah, so now we're leaving the region we've ever probed directly, 0:13:26.080 --> 0:13:28.600 Like we've sent probes that have left the Solar System 0:13:28.880 --> 0:13:32.120 just barely like Voyager one reached the interstellar medium in 0:13:32.160 --> 0:13:35.960 twenty twelve, Voyager two and twenty eighteen. But now we're 0:13:36.040 --> 0:13:39.000 going well beyond where we've ever probed directly, and we're 0:13:39.040 --> 0:13:42.480 relying just on observations and theory and stimulation. So now 0:13:42.520 --> 0:13:45.400 between the galaxies, what is there, Well, this is something 0:13:45.400 --> 0:13:49.200 we call very creatively the intergalactic medium, and this is 0:13:49.320 --> 0:13:53.800 mostly rarefied plasma, so that means essentially ionized hydrogen is 0:13:53.880 --> 0:13:57.560 just protons and out there. On average it's like one 0:13:57.640 --> 0:14:01.400 to ten atoms per cubic meter, so a pretty small number, 0:14:01.600 --> 0:14:05.200 but still not that small. I mean, intergalactic space is 0:14:05.559 --> 0:14:09.560 unimaginably vast. There's just so much of it. Even if 0:14:09.600 --> 0:14:12.240 you think about space between the planets as being big, 0:14:12.520 --> 0:14:14.760 and most of the space and the Solar System is 0:14:14.800 --> 0:14:17.920 the space between the planets, right, planets and the Sun 0:14:18.040 --> 0:14:21.040 are rare, like you're randomly sampled inside the Solar System. 0:14:21.080 --> 0:14:22.960 You would very rarely touch a planet or a star 0:14:23.640 --> 0:14:27.080 inside the galaxy. Right structure is also very rare. But 0:14:27.120 --> 0:14:29.960 between the galaxies, it's even hard to comprehend because we 0:14:30.000 --> 0:14:33.360 have like millions of light years between these galaxies, and 0:14:33.480 --> 0:14:36.280 yet it's still filled with stuff. There's one to ten 0:14:36.320 --> 0:14:40.760 atoms out there, and actually these tendrils of plasma there's 0:14:40.800 --> 0:14:43.800 also structure to it. It's not just randomly distributed. All 0:14:43.840 --> 0:14:47.360 the galaxies are connected by these tendrils of plasma, these filaments, 0:14:47.920 --> 0:14:50.480 and something like half of all the atoms in the 0:14:50.560 --> 0:14:54.720 universe are outside of galaxies and are inside these tendrils 0:14:54.800 --> 0:14:55.960 between galaxies. 0:14:56.000 --> 0:14:58.120 It's incredible, wow, And how do they get there? Do 0:14:58.320 --> 0:15:00.400 they get like shot out by suns? They were just 0:15:00.440 --> 0:15:02.800 there from the beginning of the creation of the universe 0:15:02.840 --> 0:15:03.840 and they just stayed. 0:15:03.520 --> 0:15:07.080 There both and all of those like there's a feedback 0:15:07.120 --> 0:15:12.040 loop where galaxies are emitting particles right, supernovas and shockwaves 0:15:12.080 --> 0:15:15.640 and all sorts of stuff. But mostly this structure represents 0:15:15.840 --> 0:15:19.480 the dark matter structure of the universe. Galaxies form in 0:15:19.480 --> 0:15:22.000 the deepest wells and then there are tendrils of dark 0:15:22.040 --> 0:15:24.960 matter between these wells, and that's where you find these 0:15:24.960 --> 0:15:27.760 tendrils of plasma. So the plasma is like a tracer 0:15:27.800 --> 0:15:30.760 that tells you where the dark matter is. And also 0:15:30.880 --> 0:15:33.440 between these galaxies, of course, is a significant amount of 0:15:33.520 --> 0:15:36.200 dark energy. Dark energy is everywhere in space. It's just 0:15:36.240 --> 0:15:39.640 a really, really tiny amount, but because it doesn't get diluted, 0:15:39.640 --> 0:15:43.320 as the universe expands over vast spaces, it really starts 0:15:43.320 --> 0:15:45.840 to add up. Between the galaxies, you have to start 0:15:45.880 --> 0:15:48.840 accounting for the dark energy. And then as you zoom out, 0:15:48.960 --> 0:15:53.160 galaxies form clusters, and between those clusters most of the 0:15:53.280 --> 0:15:56.120 energy density between those clusters. It's not matter at all. 0:15:56.360 --> 0:15:59.440 It's dark energy, all right. 0:15:59.560 --> 0:16:02.920 So at the big scale, we're mostly thinking about dark energy, 0:16:03.080 --> 0:16:06.200 and as we zoom in, we're starting to think about gas. 0:16:07.920 --> 0:16:10.200 Let's take a break, and when we come back, I 0:16:10.240 --> 0:16:13.600 want to go back to the interstellar medium and go 0:16:13.640 --> 0:16:36.320 into more detail about what's there. Yeah, and we're back, 0:16:36.360 --> 0:16:38.440 and Daniel is going to be telling us more about 0:16:38.440 --> 0:16:40.800 what is in the interstellar medium. 0:16:40.840 --> 0:16:43.200 That's right. Today we're talking about the context of our 0:16:43.240 --> 0:16:45.320 solar system where it is and how much stuff there 0:16:45.400 --> 0:16:48.800 is around us, and whether our solar system is jumping 0:16:48.920 --> 0:16:52.840 into a huge bubble in the galaxy. Sounds fun, and 0:16:52.880 --> 0:16:55.320 so the important thing is to understand this bit between 0:16:55.400 --> 0:16:57.680 the stars. And the thing I love doing is going 0:16:57.720 --> 0:17:01.080 back in history and understanding when we understood something and 0:17:01.080 --> 0:17:04.680 what our early silly ideas were, you know, because it's 0:17:04.680 --> 0:17:07.000 easy to just like, download all of human knowledge into 0:17:07.040 --> 0:17:10.320 your brain right now. But remember that people like struggled 0:17:10.359 --> 0:17:12.439 and puzzled to figure this out, and there were many 0:17:12.520 --> 0:17:16.320 wrong paths and silly ideas entertained for hundreds of years 0:17:16.359 --> 0:17:17.120 along the way. 0:17:17.480 --> 0:17:19.639 It's kind of cute to imagine that nobody in like 0:17:19.680 --> 0:17:21.320 fifty years is going to look back at us and 0:17:21.359 --> 0:17:24.639 be like, oh, remember that cute thing that the physicists 0:17:24.640 --> 0:17:28.320 thought in twenty twenty six about anyway, they could be 0:17:28.400 --> 0:17:30.840 laughing at us eventually, but let's go ahead and laugh 0:17:30.880 --> 0:17:31.200 at them. 0:17:33.040 --> 0:17:37.160 So first, remember, in the broader context, we didn't know 0:17:37.240 --> 0:17:41.199 that our galaxy was one of many galaxies until like 0:17:41.240 --> 0:17:44.200 the early nineteen hundreds, right, we thought we had a galaxy. 0:17:44.400 --> 0:17:46.359 It was a bunch of stars and that was it. 0:17:46.359 --> 0:17:48.800 It was just our galaxy, and that was everything. The 0:17:48.840 --> 0:17:52.280 galaxy was basically the universe and everything that was out 0:17:52.320 --> 0:17:54.840 there that wasn't actually in our galaxy, but we didn't 0:17:54.840 --> 0:17:56.760 know it yet. We called like a nebula because it 0:17:56.840 --> 0:17:59.440 was like a smeary blob in the sky we couldn't resolve. 0:18:00.160 --> 0:18:02.160 So that's sort of like the bigger picture. But then 0:18:02.200 --> 0:18:04.560 what about inside the galaxy, Well, people try to make 0:18:04.640 --> 0:18:07.119 like maps of the galaxy early on to try to 0:18:07.200 --> 0:18:10.240 understand the structure. But we're interested in like the bit 0:18:10.359 --> 0:18:13.280 between the stars. And it was like the late seventeen 0:18:13.320 --> 0:18:16.280 hundreds people started to wonder, like, hmm, is the space 0:18:16.359 --> 0:18:20.440 between the stars really a vacuum or is there something there? 0:18:21.119 --> 0:18:24.200 You know? And how would we know? And this coincides 0:18:24.200 --> 0:18:27.960 a little bit later with Maxwell's development of electromagnetism, the 0:18:28.040 --> 0:18:32.200 idea that light is a balance between electricity and magnetism. 0:18:32.400 --> 0:18:35.160 The energy slashes back and forth between the two fields, 0:18:35.400 --> 0:18:38.440 but then it moves as a wave in these fields 0:18:38.800 --> 0:18:41.080 at the speed of light. And this is Maxwell's great 0:18:41.080 --> 0:18:44.280 discovery that light is a wave, which of course begged 0:18:44.280 --> 0:18:47.879 the question of a wave in what right, And so 0:18:48.119 --> 0:18:52.040 we saw the rise of the theory of the luminiferous ether. Right. 0:18:52.160 --> 0:18:55.000 This is a famous theory which was invented to explain 0:18:55.800 --> 0:18:59.080 what light is wiggling? Right, Maybe there's something out there, 0:18:59.119 --> 0:19:02.600 like if waves are wiggles and water, and sounds wiggles 0:19:02.600 --> 0:19:05.200 and air, maybe light is a wiggle in this luminiferous 0:19:05.200 --> 0:19:08.560 ether that we hadn't ever discovered before it fills the universe. 0:19:09.040 --> 0:19:12.879 So this would be an early theory of the interstellar medium. 0:19:12.920 --> 0:19:15.240 What is out there between the stars, what allows the 0:19:15.320 --> 0:19:18.080 light to go from Alpha Centauri to us here? 0:19:18.600 --> 0:19:21.600 And so the luminiferous ether. I thought I was going 0:19:21.680 --> 0:19:24.320 to get it on the first shot. Totally did I 0:19:24.400 --> 0:19:28.320 stumbled a little. Would you find that between like Earth 0:19:28.520 --> 0:19:31.800 and Mars or that was just between the end of 0:19:31.840 --> 0:19:34.640 our solar system and the start of the next solar system? 0:19:35.000 --> 0:19:37.760 Great question. No, is should be everywhere. If it exists, 0:19:37.800 --> 0:19:40.720 it should be everywhere. And that was key because people 0:19:40.760 --> 0:19:42.159 looked for it and they said, well, let's try to 0:19:42.200 --> 0:19:46.160 measure our velocity through this ether. If it's out there 0:19:46.200 --> 0:19:48.680 and it's a medium for light, light is wiggling through 0:19:48.680 --> 0:19:52.080 this ether, then Earth moving around the Sun should be 0:19:52.200 --> 0:19:56.000 moving zigzagging basically back and forth through this ether. And 0:19:56.080 --> 0:19:58.720 if light has a constant velocity relative to the ether, 0:19:59.240 --> 0:20:01.200 then we should be able to measure light moving in 0:20:01.280 --> 0:20:05.080 different velocities as we move in different velocities through the ether. Okay, right, 0:20:05.119 --> 0:20:07.399 the same way that like you can catch up to 0:20:07.520 --> 0:20:10.040 sound waves and air because they have a constant velocity 0:20:10.119 --> 0:20:12.399 relative to the air, so you can catch up to 0:20:12.440 --> 0:20:14.800 them and even pass them. Right, just like when you're 0:20:14.800 --> 0:20:16.840 on a boat in a lake, you're making ripples. If 0:20:16.880 --> 0:20:18.719 you go fast enough, you can catch up to them, 0:20:18.760 --> 0:20:22.320 which it gives you awake, right, And so if light 0:20:22.400 --> 0:20:24.160 is moving through this ether, and then as the Earth 0:20:24.200 --> 0:20:26.320 moves around the Sun, we should see a change in 0:20:26.359 --> 0:20:29.520 the velocity of light famous Michaelson. More the experiment of 0:20:29.520 --> 0:20:32.639 course proved that light is the same speed year round, 0:20:32.720 --> 0:20:36.119 regardless of the direction, and so apparently there is no 0:20:36.280 --> 0:20:39.320 luminiferous ether. So then people are like, oh, wow, maybe 0:20:39.440 --> 0:20:41.880 there really is a vacuum in between the stars. 0:20:42.119 --> 0:20:44.240 And you all didn't find another use for the word 0:20:44.480 --> 0:20:47.440 luminiferous ether. That's a total bummer because it just sounds 0:20:47.520 --> 0:20:49.920 so nice. 0:20:50.400 --> 0:20:53.760 Well, these days is actually a proliferation of ether theories, 0:20:54.000 --> 0:20:57.280 which is very confusing because ether most generally just refers 0:20:57.320 --> 0:21:00.520 to like a theory of the substrate of space, and 0:21:00.600 --> 0:21:03.480 our current theory that quantum field theory, where space is 0:21:03.480 --> 0:21:07.080 filled with these fields and these fields exist in space. 0:21:07.400 --> 0:21:10.560 Then that's sort of the modern ether, and that's totally 0:21:10.600 --> 0:21:13.560 cool and nobody objects to that. But that's an ether 0:21:13.640 --> 0:21:17.399 where you can't measure your velocity relative to it, like 0:21:17.520 --> 0:21:20.320