WEBVTT - Winter solstice listener questions 0:00:07.520 --> 0:00:10.640 So, Daniel, you do a lot of cooking. What is 0:00:10.680 --> 0:00:13.560 the biggest kitchen implement that you have? 0:00:15.320 --> 0:00:18.759 Do We measure kitchen implements by size. Now is the 0:00:18.800 --> 0:00:20.320 biggest one? The most important? 0:00:21.160 --> 0:00:24.000 It is to me, I got one giant ladle and 0:00:24.040 --> 0:00:27.720 that is the most important. What is let's talk about 0:00:27.760 --> 0:00:30.639 sheer volume? What takes up the most space for you? 0:00:31.280 --> 0:00:34.680 Well, actually, we went out and bought a huge soup pot. 0:00:34.960 --> 0:00:37.160 Last time, we made soup for about one hundred people. 0:00:37.840 --> 0:00:40.840 One hundred people for dinner. That's a lot. 0:00:41.720 --> 0:00:44.320 Yeah. Well, you know, we were out celebrating solstice and 0:00:44.360 --> 0:00:46.480 you got to go a little crazy on the solstice. 0:00:46.680 --> 0:00:48.559 So we had one hundred people over for sit down 0:00:48.600 --> 0:00:50.160 dinner and we made a lot of soup. 0:00:50.560 --> 0:00:54.279 I would rather burn my kitchen down in a ritualistic 0:00:54.440 --> 0:01:00.240 bonfire than do one hundred sets of dishes after that. 0:01:00.240 --> 0:01:02.800 That sounds like a great way to celebrate the solstice. Actually, 0:01:02.920 --> 0:01:04.440 kitchen bonfire. 0:01:04.080 --> 0:01:07.600 Kitchen effigy. There we go, No more washing dishes. 0:01:07.680 --> 0:01:10.400 Hooray, it's the solstice magic. 0:01:27.120 --> 0:01:27.320 Hi. 0:01:27.400 --> 0:01:29.920 I'm Daniel. I'm a particle physicist and a professor a 0:01:30.080 --> 0:01:33.000 uc irvine and I'm not into astrology, but I do 0:01:33.080 --> 0:01:34.200 love the Solstice. 0:01:34.560 --> 0:01:38.920 I am Katie Golden. I host podcast on animal behavior 0:01:39.040 --> 0:01:45.640 called Creature Feature, and I am super duper into Solstice 0:01:46.000 --> 0:01:53.960 magics such as logs in the house and putting stones 0:01:54.080 --> 0:01:58.880 up such that they make interesting shapes and the light 0:01:59.440 --> 0:02:02.160 hits them in just such a way. M. 0:02:02.400 --> 0:02:04.040 I see you're building Katie hinge. 0:02:04.280 --> 0:02:07.920 Katie hinge. You know, Okay for the summer Solstice one, 0:02:07.960 --> 0:02:11.280 I actually did talk about Britta Boyne, but I also 0:02:11.360 --> 0:02:15.119 want to talk about how there's a wood hinge as 0:02:15.200 --> 0:02:19.200 well as the stone hinge. And the word hinge it 0:02:19.480 --> 0:02:23.960 actually comes from the idea of a thing hanging like 0:02:24.000 --> 0:02:28.200 a hinge hanging. So stone hinge is like hanging rocks, 0:02:28.919 --> 0:02:34.000 and wood hinge is another ancient people's way of creating 0:02:34.320 --> 0:02:39.240 basically a annual sun dial, and that was made out 0:02:39.280 --> 0:02:40.600 of wooden timber. 0:02:41.120 --> 0:02:43.000 M I just always thought they were trying to hinge 0:02:43.040 --> 0:02:46.320 their bets. I was thinking about starting a hinge. 0:02:46.040 --> 0:02:49.519 Fund, you know, Oh my god, Well we do need 0:02:49.560 --> 0:02:52.359 to teach Daniel about the difference between a hinge and 0:02:52.400 --> 0:02:55.079 a hedge. 0:02:56.160 --> 0:02:57.560 Well could you have a hedge hinge? 0:02:57.960 --> 0:03:01.120 Uh? You know what, It's never been done as far 0:03:01.160 --> 0:03:04.120 as I know in gardening science, but that never doesn't 0:03:04.160 --> 0:03:04.640 mean never. 0:03:05.200 --> 0:03:07.160 Well, okay, how about a biology one that a hedgehog 0:03:07.240 --> 0:03:09.000 hinge hedgehog hinge. 0:03:09.240 --> 0:03:12.880 Well, you know, maybe there's a hedgehog hinge for hedgehogs 0:03:12.880 --> 0:03:13.640 looking for love. 0:03:15.000 --> 0:03:16.799 All right, we'll hedge our bets until we get there. 0:03:16.800 --> 0:03:20.080 But anyway, welcome to the podcast Daniel and Jorge Explain 0:03:20.120 --> 0:03:23.200 the Universe, a production of iHeartRadio in which we do 0:03:23.240 --> 0:03:25.799 not hedge our bets. We go all in on trying 0:03:25.840 --> 0:03:29.040 to understand how the universe works and explain it all 0:03:29.080 --> 0:03:31.520 to you. We tackle the biggest questions, from the very 0:03:31.600 --> 0:03:34.560 nature of the universe to the smallest questions about quantum 0:03:34.560 --> 0:03:37.920 particles and the fundamental nature of space and time and 0:03:38.240 --> 0:03:41.360 everything in between, including how to get your hedgehogs out 0:03:41.400 --> 0:03:42.160 of your hinge. 0:03:42.840 --> 0:03:46.280 So there is a question I always get about hedgehogs, 0:03:46.320 --> 0:03:49.560 and it is how do they reproduce? And my answer 0:03:49.720 --> 0:03:54.120 is very carefully, that's a. 0:03:54.160 --> 0:03:59.600 Very pointed answer, Katie. And people have questions about the universe. 0:03:59.600 --> 0:04:02.080 They want about hedgehogs, they want about quantum particles, they 0:04:02.080 --> 0:04:05.080 wonder about quantum hedgehogs, they wonder about hinges, and what 0:04:05.160 --> 0:04:08.200 ancient people saw on them. They wonder what the solstice means, 0:04:08.280 --> 0:04:12.000 and they wonder what's going on between us and distant stars. 0:04:12.440 --> 0:04:14.840 And that's all part of doing physics. You don't have 0:04:14.920 --> 0:04:17.200 to be a professional academic to be a physicist. You 0:04:17.240 --> 0:04:19.880 just have to wonder about the nature of the universe 0:04:20.080 --> 0:04:23.280 and then share that curiosity with everybody else, and we 0:04:23.360 --> 0:04:26.120 hope you share it with us. If you have a 0:04:26.200 --> 0:04:28.640 question about how the universe works, and you can find 0:04:28.640 --> 0:04:31.560 an answer on Google or chat, GPT or your friendly 0:04:31.600 --> 0:04:35.000 neighborhood physicists, please write to me to questions at Daniel 0:04:35.040 --> 0:04:38.279 Andjorge dot com. We will answer it. Everybody gets an 0:04:38.320 --> 0:04:41.000 answer in their inbox, and sometimes we take an answer 0:04:41.040 --> 0:04:44.080 and put it right here on the podcast, also because 0:04:44.120 --> 0:04:45.920 we've been missing you and we wanted to hear from 0:04:45.960 --> 0:04:46.359 you again. 0:04:47.320 --> 0:04:51.320 So ninety nine percent of a part of coul physicist's 0:04:51.400 --> 0:04:55.880 job is asking the right questions, and one percent is 0:04:55.920 --> 0:04:57.120 you know, math or whatever. 0:04:58.560 --> 0:05:00.000 And there's also got to be rooting there for now. 0:05:00.279 --> 0:05:03.160 Napping is crucial, right right, And like a little bit 0:05:03.200 --> 0:05:03.839 of grant. 0:05:03.560 --> 0:05:08.960 Writing occasionally, and so on today's episode, we'll be answering 0:05:14.240 --> 0:05:19.680 listener questions. Winter Solstice Edition Happy holidays and New Year 0:05:19.720 --> 0:05:22.760 and Solstice to everybody out there who celebrates whatever it 0:05:22.839 --> 0:05:25.560 is you celebrate. Today, we're going to be celebrating my 0:05:25.720 --> 0:05:29.000 answering a really fun question from a listener, a question 0:05:29.120 --> 0:05:32.080 he thought of while he was in his backyard shed, 0:05:32.400 --> 0:05:37.040 maybe building his own hinge. Here's the question from Alex. 0:05:37.880 --> 0:05:41.880 Hi, guys, I was working in my backyard on my shed, 0:05:42.480 --> 0:05:45.880 and I was using a metal crowbar to help out 0:05:46.240 --> 0:05:49.080 one day when I just realized holding it how strong 0:05:49.080 --> 0:05:52.720 it was. So my question that came to me was, 0:05:53.440 --> 0:05:57.720 what is actually the longest physical possible crowbar made of 0:05:57.760 --> 0:06:05.600 metal that that could exist in space? Is it possible 0:06:05.640 --> 0:06:09.320 that you could build one? One could exist that's long 0:06:09.400 --> 0:06:12.880 enough to stretch between stars, especially if you didn't have 0:06:12.880 --> 0:06:15.600 to worry about adding to its length with unlimited supplies, 0:06:17.320 --> 0:06:19.720 and if it was nowhere near any other gravitational objects. 0:06:20.440 --> 0:06:23.440 What would the ramifications be of having it like a 0:06:23.480 --> 0:06:26.000 crowbar where one end was light hours away from the other, 0:06:26.160 --> 0:06:29.120 or even light years away from the other. It seems 0:06:29.120 --> 0:06:32.839 a bit weird to travel light speed and not get 0:06:32.839 --> 0:06:35.320 from one end to the other on one particular object. 0:06:36.480 --> 0:06:40.719 Thank you, So you know I have a similar question. 0:06:40.839 --> 0:06:44.080 But once I just saw a crow bar on the ground, 0:06:44.440 --> 0:06:47.560 I think there were some people working on something like 0:06:47.600 --> 0:06:51.240 a manhole or something sort of nearby. But also I 0:06:51.320 --> 0:06:54.840 wondered if the world operates by video game rules, which is, 0:06:55.000 --> 0:06:57.599 if you find a crowbar, is that yours now? Do 0:06:57.680 --> 0:06:59.560 you pick it up and put it in your inventory? 0:06:59.680 --> 0:07:01.039 Or is that that's still stealing? 0:07:02.040 --> 0:07:04.479 I don't know. Maybe the world operates by checkof rules. 0:07:04.520 --> 0:07:06.920 If you find a crowbar in act one, then you're 0:07:06.920 --> 0:07:08.839 gonna have about to break into something with it in 0:07:08.880 --> 0:07:09.520 Act three. 0:07:10.000 --> 0:07:11.960 I mean that is just video game rules. 0:07:12.000 --> 0:07:16.680 Also exactly exactly. I used to play like King's Quest 0:07:16.760 --> 0:07:18.680 back in the day, and every time you found like 0:07:18.720 --> 0:07:20.400 a weird magic rap mushroom, you put it in your 0:07:20.400 --> 0:07:22.200 back pocket because you knew you were gonna need it 0:07:22.240 --> 0:07:24.000 to solve some puzzle later on. 0:07:24.520 --> 0:07:27.240 Get ye bucket. You're gonna need that bucket for the 0:07:27.360 --> 0:07:29.280 dragon at the end of the game. 0:07:29.480 --> 0:07:31.920 Exactly, and you can't go back, so get the bucket now. 0:07:32.480 --> 0:07:35.080 And Alex is wondering about like the practical limits of 0:07:35.160 --> 0:07:38.160 how big we could build something like, could you build 0:07:38.160 --> 0:07:40.600 a crowbar that's long enough that you can use it 0:07:40.680 --> 0:07:44.119 to like poke people on other planets that that's pretty crazy, 0:07:44.160 --> 0:07:44.760 thought Alex. 0:07:45.720 --> 0:07:49.160 It's interesting, right, because sure you could have like a 0:07:49.280 --> 0:07:52.520 large object, but the bigger it gets. Like, there's a 0:07:52.520 --> 0:07:55.120 lot of questions here, right, we need to know about 0:07:55.800 --> 0:07:59.400 a what are crowbars made out of? Steel? Iron? 0:08:00.040 --> 0:08:00.320 Feeling? 0:08:00.960 --> 0:08:04.000 Steal? And so it's like, I guess a lot of 0:08:04.040 --> 0:08:08.800 it is basically the strength, like the steal, you know, 0:08:08.840 --> 0:08:11.720 the the what steals made out of? How that would work? 0:08:12.680 --> 0:08:16.760 But also you know how even if it's made out 0:08:16.800 --> 0:08:19.720 of any material, right, Like let's say crowbar made out 0:08:19.760 --> 0:08:24.400 of whatever material, the strongest, hardest material you could get, Like, 0:08:24.640 --> 0:08:28.080 is there a limit to the size of physical objects 0:08:28.080 --> 0:08:30.960 in the universe before some wacky starts happening? 0:08:31.800 --> 0:08:34.600 Yeah, this is really fun, And there's a really important 0:08:34.679 --> 0:08:38.560 lesson here about how we do physics anyway, because an 0:08:38.559 --> 0:08:41.839 important sort of often implicit step that we don't talk 0:08:41.880 --> 0:08:45.520 about when we do physics is building a simplified model 0:08:45.760 --> 0:08:48.760 of the universe. Like you want to answer a physics question, 0:08:48.920 --> 0:08:51.720 you know, like a piano is falling from a window. 0:08:52.160 --> 0:08:53.920 Is it going to squish that little doggie? 0:08:54.360 --> 0:08:55.520 No? 0:08:55.559 --> 0:08:58.280 Oh no, hopefully answer is no. But to answer that 0:08:58.320 --> 0:09:01.720 physics question, which you have to do is simplify at first. 0:09:01.760 --> 0:09:03.440 Because you don't care about a lot of the details. 0:09:03.440 --> 0:09:05.360 You don't care about the color of the piano, you 0:09:05.400 --> 0:09:08.679 can probably ignore the crosswinds. You build a simplified model 0:09:08.679 --> 0:09:11.079 that just contains the information necessary to. 0:09:11.040 --> 0:09:13.839 Answer the question, like the breed of the dog for. 0:09:13.840 --> 0:09:16.360 Example, Yeah we don't care, I mean we care, but 0:09:16.440 --> 0:09:19.320 doesn't change the answer. And so the trick there is 0:09:19.360 --> 0:09:21.240 to make a model that's simple enough that you can 0:09:21.280 --> 0:09:23.560 actually answer it because you've included all the details of 0:09:23.559 --> 0:09:27.800 all the quantum particles and be intractable, but is sophisticated 0:09:27.920 --> 0:09:30.920 enough that it still provides a realistic answer. That's the 0:09:30.960 --> 0:09:34.280 sweet spot for doing physics. And the interesting thing is 0:09:34.320 --> 0:09:36.959 that that's a different model in every scenario. You can 0:09:37.040 --> 0:09:39.360 ignore the winds in this case, but if you're solving 0:09:39.400 --> 0:09:41.360 a different problem like what's going to happen to this 0:09:41.440 --> 0:09:44.280 leaf and a tornado, you can't ignore the winds. So 0:09:44.320 --> 0:09:46.079 every time you solve a physics problem, you need to 0:09:46.120 --> 0:09:49.640 ask yourself, am I including the right assumptions or the 0:09:49.640 --> 0:09:52.480 assumptions I'm making going to ruin it? And so I 0:09:52.600 --> 0:09:55.079 run into this all the time with these very long 0:09:55.200 --> 0:09:57.439 space rods. Al It turns out Alex is not the 0:09:57.520 --> 0:10:00.199 only person to think about really long rods. It comes 0:10:00.280 --> 0:10:02.720 up a lot because people have this idea that a 0:10:02.880 --> 0:10:06.240 rod is sort of like infinitely rigid. Like if I'm 0:10:06.320 --> 0:10:08.520 across the room from you and I have a dowel 0:10:08.600 --> 0:10:11.280 like a wooden stick, if I push it, then you're 0:10:11.320 --> 0:10:13.240 gonna feel me pushing it. You're holding the other end, 0:10:13.240 --> 0:10:15.520 you're gonna feel it. And people imagine that sort of 0:10:15.520 --> 0:10:18.200 happens instantaneously, that if I push on the stick on 0:10:18.200 --> 0:10:21.240 one side, you feel it instantly. And that's mostly true, 0:10:21.280 --> 0:10:23.280 and for basically every problem you're going to solve here 0:10:23.320 --> 0:10:26.959 on Earth, that's basically the case, because the information travels 0:10:27.080 --> 0:10:29.760 very very fast. But then people wonder, all right, what 0:10:29.800 --> 0:10:31.640 if I take a rod and I build it so 0:10:31.679 --> 0:10:34.960 it's like four light years long, and I stretch it 0:10:35.000 --> 0:10:37.880 from here to Alpha Centauri and some alien is holding 0:10:37.880 --> 0:10:41.040 the other side. Can I tap on my side and 0:10:41.200 --> 0:10:43.520 use that to communicate faster than the speed of light. 0:10:43.600 --> 0:10:46.680 That's a very common question I get, And the answer 0:10:46.720 --> 0:10:50.120 is obviously no. You can't break special relativity with a 0:10:50.360 --> 0:10:52.160 dowel that's four light years long. 0:10:52.520 --> 0:10:54.160 Even dowels have their limits. 0:10:54.160 --> 0:10:57.040 I guess, yeah, and the reason is that you've broken 0:10:57.080 --> 0:11:00.800 the assumptions. Down here on Earth, it works to a boom. Yeah, 0:11:00.840 --> 0:11:03.480 the information travels instantly. That when you push one side 0:11:03.480 --> 0:11:06.320 of the dowel, the other side moves instantly. But that 0:11:06.360 --> 0:11:09.880 doesn't work anymore when the dowel's really really long, because 0:11:09.920 --> 0:11:13.000 the time it takes now matters, because a dowel, even 0:11:13.040 --> 0:11:16.720 here on Earth, doesn't transmit information instantly. What happens when 0:11:16.760 --> 0:11:19.200 you push on one side of the dowel is that 0:11:19.240 --> 0:11:21.840 you don't immediately move the other side. You push on 0:11:21.840 --> 0:11:24.760 one side, and it moves the layer of molecules that 0:11:24.800 --> 0:11:27.160 are next to the edge, which you mean the next layer, 0:11:27.200 --> 0:11:29.320 which moved the next layer, which moved the next layer. 0:11:29.679 --> 0:11:32.280 Because a dowel is not infinitely rigid, it's like a 0:11:32.360 --> 0:11:34.840 very stiff version of a tube of water or like 0:11:34.880 --> 0:11:37.480 a string. You're pushing on it and there's a wave 0:11:37.600 --> 0:11:41.160 of information that travels down the dowel. So here on Earth, 0:11:41.200 --> 0:11:42.679 you push on one side of the dowel, the other 0:11:42.760 --> 0:11:46.520 side moves very shortly afterwards, but not instantly. It takes 0:11:46.559 --> 0:11:50.160 time for that information and move down the dowel. Now, 0:11:50.120 --> 0:11:52.280 when your Dowel is four light years long. That time 0:11:52.360 --> 0:11:54.880 is no longer something you can ignore. It plays a 0:11:54.880 --> 0:11:57.920 big part in how long it takes for the information 0:11:57.960 --> 0:12:00.600 to get there. And if you ignore that, you're violating 0:12:00.600 --> 0:12:03.600 special relativity. And it seems like you could send information 0:12:03.640 --> 0:12:05.600 to the stars faster than the speed of light, which 0:12:05.640 --> 0:12:06.600 of course you can't. 0:12:06.960 --> 0:12:10.160 This is actually the same problem from a biological perspective 0:12:10.160 --> 0:12:13.720 of having like a giant brain, right, could you have 0:12:14.360 --> 0:12:20.480 an enormous brain that could like communicate instantly, right, like 0:12:20.559 --> 0:12:24.720 some galaxy sized brain. And the problem is that the 0:12:24.760 --> 0:12:26.880 way our brains work in the same way that you 0:12:26.920 --> 0:12:29.560 talked about, how like the molecules have to push on 0:12:29.600 --> 0:12:32.400 the other molecules, Like our brain is all physics based. 0:12:32.480 --> 0:12:35.640 Our whole bodies are basically a big rub Goldberg machine 0:12:35.880 --> 0:12:41.240 of molecules bonking into other molecules, which creates things like thought. 0:12:41.840 --> 0:12:45.000 And so if you have a say, a giant enough brain, 0:12:45.440 --> 0:12:48.520 the time it would take to like have a single 0:12:48.600 --> 0:12:53.400 thought would be incredibly slow. So the bigger the brain, 0:12:53.880 --> 0:12:57.080 the more galaxy size the brain, actually the slower it 0:12:57.120 --> 0:12:58.280 would take to have it. 0:12:58.400 --> 0:13:01.800 Not yeah, exactly. And so if you're ignoring that, when 0:13:01.800 --> 0:13:03.560 you're just thinking about a small brain. You can no 0:13:03.640 --> 0:13:06.520 longer ignore that in a large brain. So the lesson is, 0:13:06.559 --> 0:13:08.600 when you're doing physics, you have to always think about 0:13:08.679 --> 0:13:11.760 what are the assumptions we're making and are those assumptions 0:13:11.800 --> 0:13:14.640 still valid for this scenario. In the case of the 0:13:14.760 --> 0:13:18.959 like five light year long rod, if you assume instantaneous 0:13:19.000 --> 0:13:21.240 motion from one side to the other, then you're assuming 0:13:21.280 --> 0:13:24.320 special relativity is broken. So you can't then go and say, oh, look, 0:13:24.360 --> 0:13:26.599 this rod breaks special relativity. Well, you assume to it 0:13:26.760 --> 0:13:29.400 is broken, and that's why you broke it. And so 0:13:29.640 --> 0:13:32.520 there's a lot of unpacking of those assumptions in these questions. 0:13:33.080 --> 0:13:35.000 But Alex's question is a little bit different. He's not 0:13:35.040 --> 0:13:37.360 trying to communicate with aliens. He's just trying to build 0:13:37.360 --> 0:13:39.760 a really long rod, and he's wondering, like how big 0:13:39.840 --> 0:13:42.400 could you make it? Anyway? And I think that's exactly 0:13:42.440 --> 0:13:44.920 what he's digging into, like what would break down? What 0:13:45.000 --> 0:13:48.400 assumptions we make about building long rods would break down 0:13:48.400 --> 0:13:50.200 if we try to make one that's like a light 0:13:50.280 --> 0:13:52.480 year long, Which is a really cool question. 0:13:52.400 --> 0:13:55.200 Yeah, because I mean there's a lot of things that 0:13:55.520 --> 0:13:57.800 we could say, like on Earth, right, Like, we could 0:13:57.880 --> 0:14:00.200 try to build a really long crow bar and at 0:14:00.200 --> 0:14:03.319 a certain point it could collapse under its own weight. 0:14:03.600 --> 0:14:07.600 But if something's in space, we'd have to figure out 0:14:07.640 --> 0:14:11.640 what kinds of forces or how gravity would be acting 0:14:11.800 --> 0:14:15.440 on something in a way that's different from Earth, right, Like, yes, 0:14:15.720 --> 0:14:18.280 you can. You know, it's like have you ever you 0:14:18.280 --> 0:14:21.920 know whiteboard pins? Like you create a big old lightsaber 0:14:21.960 --> 0:14:25.240 out of whiteboard pins and at a certain point there's 0:14:25.320 --> 0:14:29.840 too many and it collapses. But that's all using Earth physics. 0:14:29.880 --> 0:14:35.120 So you could make a much longer whiteboard pin lightsaber 0:14:35.520 --> 0:14:39.280 out in space because gravity is not impacting it in 0:14:39.320 --> 0:14:41.040 the same way that it is on Earth. But then 0:14:41.080 --> 0:14:44.920 once you get big enough, right with this pin dowel 0:14:45.080 --> 0:14:49.440 or iron crowbar or whatever it is, something's happening. And 0:14:49.480 --> 0:14:52.040 this is where I would like you to talk. 0:14:52.680 --> 0:14:56.800 Yeah, exactly. So let's take this question out into deep space. 0:14:57.280 --> 0:14:59.160 And the first thing the wonder is like, well, what's 0:14:59.200 --> 0:15:02.080 the biggest thing we built in space so far? And 0:15:02.120 --> 0:15:04.560 that's the International Space Station. It's not that impressively long, 0:15:04.600 --> 0:15:07.600 it's about thirty six meters long, but you know, it's 0:15:07.600 --> 0:15:10.120 not very far out in space, and they're not trying 0:15:10.120 --> 0:15:13.040 to build something super duper long. I think the longest 0:15:13.080 --> 0:15:15.120 thing that's ever actually been in space, it's more like 0:15:15.120 --> 0:15:18.160 a kilometer. They build a space tether, which is like 0:15:18.200 --> 0:15:21.560 a really long wire that you dangle from a spaceship 0:15:21.600 --> 0:15:24.560 to try to like generate electrical current or to learn 0:15:24.600 --> 0:15:28.640 to steer using mechnetic fields. So like a kilometer long, 0:15:28.640 --> 0:15:31.240 it's the biggest thing that we've ever put into space. 0:15:31.760 --> 0:15:34.120 But again that's also just the near Earth orbit. So 0:15:34.360 --> 0:15:37.040 let's go deeper out into space and try to build 0:15:37.040 --> 0:15:40.640 something that's really long and think about the forces involved. 0:15:40.680 --> 0:15:43.520 Like when you build a rod at a steel or 0:15:43.560 --> 0:15:46.160 even a dowel out of wood or whatever, how are 0:15:46.160 --> 0:15:48.680 you actually building that thing. Usually we ignore it and 0:15:48.720 --> 0:15:51.280 just say, oh, it's some smooth, continuous substance. But if 0:15:51.280 --> 0:15:54.800 you zoom in, the reason it takes time to propagate 0:15:54.800 --> 0:15:57.720 information along it is the same thing that's holding it together, 0:15:57.760 --> 0:16:00.720 which is the forces between those molecules. All of these 0:16:00.760 --> 0:16:03.200 objects in the end are like a mesh of modules. 0:16:03.280 --> 0:16:05.360 Yet you have these little bits of matter tied together 0:16:05.480 --> 0:16:09.280 by forces to build something larger, and it's those forces 0:16:09.320 --> 0:16:12.760 that transmit the information also limit how big something can 0:16:12.880 --> 0:16:16.120 get right and so out into deep space. What is 0:16:16.160 --> 0:16:19.000 the thing that's limiting us. Well, those forces can work. 0:16:19.000 --> 0:16:22.720 They can tie something together basically infinitely. There's no limitation there. 0:16:22.720 --> 0:16:25.040 You can just keep adding layers and layers and layers 0:16:25.040 --> 0:16:27.160 to your rod. The thing that's going to keep you 0:16:27.160 --> 0:16:30.480 from building that rod light years long or infinitely long 0:16:30.560 --> 0:16:33.920 in the end, are going to be the gravitational effects, 0:16:33.960 --> 0:16:37.160 residual as they are, and the nature of space and 0:16:37.200 --> 0:16:40.720 time itself. But let's first talk about the gravitational effects. 0:16:40.920 --> 0:16:44.440 So one effect are tidal forces. So you say, well, 0:16:44.480 --> 0:16:47.640 let's be out between the stars. AX is actually talking 0:16:47.640 --> 0:16:49.760 about something which stretches between the stars. You have like 0:16:49.840 --> 0:16:51.840 one end at one star and the other end at 0:16:51.880 --> 0:16:54.440 another star. And if you have something that's like five 0:16:54.520 --> 0:16:56.800 light years long, you can't have it that far away 0:16:56.800 --> 0:16:59.160 from stars because it's going to be big enough. There's 0:16:59.160 --> 0:17:02.440 always going to be some star nearby. And remember that 0:17:02.520 --> 0:17:04.679 gravity does more than just pull on things. It can 0:17:04.720 --> 0:17:07.919 actually pull things apart. These are called tidal forces. And 0:17:07.960 --> 0:17:11.160 for example, if you're near a black hole, then your 0:17:11.280 --> 0:17:14.000 head can have a different gravitational tug on it than 0:17:14.040 --> 0:17:17.000 your feet, and that can effectively tear you apart. Like, 0:17:17.040 --> 0:17:19.080 if the black hole is pulling on your feet harder 0:17:19.119 --> 0:17:21.080 than it's pulling on your head because your feet are 0:17:21.119 --> 0:17:23.520 a little bit closer, then it's going to pull you 0:17:23.560 --> 0:17:26.560 apart because its gravity is really really strong. But if 0:17:26.560 --> 0:17:30.160 you're really really long, then you don't need strong gravity 0:17:30.200 --> 0:17:32.200 to have tidal forces. Because if one end of this 0:17:32.320 --> 0:17:34.960 rod is closer to the star then the other end, 0:17:35.240 --> 0:17:37.680 and the rod is really really long, it's going to 0:17:37.720 --> 0:17:40.960 be a very large difference in the gravitational force from 0:17:40.960 --> 0:17:42.320 one end of the rod to the other, and that 0:17:42.400 --> 0:17:44.679 star is going to tear it apart. Even if the 0:17:44.680 --> 0:17:47.959 star doesn't have really powerful gravity like black holes, the 0:17:47.960 --> 0:17:51.600 sheer length of the rod makes the title forces very significant. 0:17:51.720 --> 0:17:56.320 I see. So you can't span a dell from one 0:17:56.359 --> 0:17:59.160 start to the other because of the same title forces 0:17:59.240 --> 0:18:04.640 that spaghettifies you in a black hole. But what if 0:18:04.680 --> 0:18:08.720 you took away the stars? Right? Like, could you get 0:18:08.760 --> 0:18:14.040 a like infinity rod if you took away stars and 0:18:14.200 --> 0:18:18.160 just had it existing on its own in space without 0:18:18.280 --> 0:18:19.040 hitting anything? 0:18:19.520 --> 0:18:21.680 Yeah? Right, So get rid of the other gravity, and 0:18:21.800 --> 0:18:23.800 you still have the issue of the gravity of the 0:18:23.920 --> 0:18:28.000 rod itself. Right, You can't build an infinitely massive rod, 0:18:28.040 --> 0:18:30.120 because eventually that thing is going to have its own 0:18:30.240 --> 0:18:34.199 self gravity, that it's going to collapse into a black hole. Like, 0:18:34.240 --> 0:18:36.720 you can't just make a blob of metal and keep 0:18:36.760 --> 0:18:38.800 adding blobs of metal to it and make it as 0:18:38.840 --> 0:18:41.440 big as you want, because it's going to start collapsing. 0:18:41.640 --> 0:18:44.240 This already happens for things like planets, like the Earth 0:18:44.320 --> 0:18:47.280 is about the largest rocky planet you can make. You 0:18:47.320 --> 0:18:49.159 can add more rock to it, but that's going to 0:18:49.200 --> 0:18:51.560 mean more gravity, and it's just going to compress the 0:18:51.640 --> 0:18:54.560 Earth further. So as you add more mass to the Earth, 0:18:54.600 --> 0:18:57.600 it doesn't get any bigger, it just gets denser. And 0:18:57.680 --> 0:19:00.239 eventually you keep adding mass, you're going to end up 0:19:00.240 --> 0:19:02.800 with a black hole. And so there is a limit 0:19:02.880 --> 0:19:05.760 to how large and how massive you can make something 0:19:06.040 --> 0:19:09.000 before it collapses into a black hole. So something self 0:19:09.040 --> 0:19:12.280 gravity will also limit how large you can make an 0:19:12.320 --> 0:19:15.160 object out of practical stuff like steel or wood. 0:19:15.359 --> 0:19:19.119 Okay, so what about a really thin rod. Now stay 0:19:19.160 --> 0:19:22.320 with me. What if you have a rod that is 0:19:22.440 --> 0:19:26.840 like one atom per unit, right, is like one atom thick, 0:19:27.080 --> 0:19:30.880 and then you just stack a bunch of atoms into 0:19:30.920 --> 0:19:37.160 this very long rod, would that still be something that 0:19:37.359 --> 0:19:40.840 would at a certain point start to collapse in on 0:19:40.920 --> 0:19:44.560 itself because of gravity, or am I already breaking some 0:19:44.680 --> 0:19:47.600 laws of physics by trying to create a one atom 0:19:49.040 --> 0:19:50.160 diameter rod. 0:19:50.760 --> 0:19:53.520 Now you could probably make a carbon nanofiber. Eventually it's 0:19:53.560 --> 0:19:55.920 like one atom thick and super duper long. I don't 0:19:55.920 --> 0:19:58.239 think it's a technical problem there, But what you're going 0:19:58.280 --> 0:20:00.199 to run into is a problem with a knee. You're 0:20:00.240 --> 0:20:02.879 a space and time, and if you can get rid 0:20:02.880 --> 0:20:05.439 of gravity then nearby stars and effectively get rid of 0:20:05.440 --> 0:20:08.200 the self gravity by making this thing really really lightweight, 0:20:08.720 --> 0:20:12.320 you're going to run into dark energy. So in short distances, 0:20:12.880 --> 0:20:14.560 like the size of our Solar system of the size 0:20:14.560 --> 0:20:17.800 of our galaxy, the dominant force is gravity. It holds 0:20:17.800 --> 0:20:20.520 things together, it shapes things, it determines the nature of 0:20:20.560 --> 0:20:24.399 our universe. But over very large distances, gravity gets weaker. Right, 0:20:24.480 --> 0:20:26.960 the further you are away from something, the weaker it's 0:20:26.960 --> 0:20:30.480 gravity is. And at those distances something else takes over, 0:20:30.520 --> 0:20:34.280 which is dark energy, meaning the expansion of the universe itself. 0:20:34.840 --> 0:20:38.440 Remember that everywhere in the universe is expanding. Take any 0:20:38.600 --> 0:20:41.639 arbitrary chunk of space as time goes on, that space 0:20:41.720 --> 0:20:45.119 is getting larger. It's making new space. So between the 0:20:45.160 --> 0:20:48.080 Earth and the Sun, for example, new space is being made, 0:20:48.240 --> 0:20:50.719 but the gravity of the Earth and the Sun overpowers it. 0:20:51.040 --> 0:20:54.720 Between our galaxy and the neighboring galaxy, new space is 0:20:54.760 --> 0:20:58.199 being made, but again the gravity overpowers it. But eventually, 0:20:58.480 --> 0:21:02.920 between clusters of galonyes, dark energy becomes more powerful because 0:21:02.960 --> 0:21:05.480