WEBVTT - Winter soltice listener questions 0:00:07.480 --> 0:00:10.559 So, Daniel, you do a lot of cooking. What is 0:00:10.640 --> 0:00:13.480 the biggest kitchen implement that you have? 0:00:15.240 --> 0:00:18.680 Do We measure kitchen implements by size. Now is the 0:00:18.720 --> 0:00:20.279 biggest one? The most important? 0:00:21.120 --> 0:00:23.960 It is to me, I got one giant ladle and 0:00:24.000 --> 0:00:27.640 that is the most important. What is let's talk about 0:00:27.680 --> 0:00:30.680 sheer volume? What takes up the most space for you? 0:00:31.200 --> 0:00:34.599 Well, actually, we went out and bought a huge soup pot. 0:00:34.880 --> 0:00:37.080 Last time, we made soup for about one hundred people. 0:00:37.760 --> 0:00:40.760 One hundred people for dinner. That's a lot. 0:00:41.680 --> 0:00:44.240 Yeah. Well, you know, we were out celebrating solstice and 0:00:44.280 --> 0:00:46.520 you got to go a little crazy on the solstice. 0:00:46.640 --> 0:00:48.520 So we had one hundred people over for sit down 0:00:48.520 --> 0:00:50.080 dinner and we made a lot of soup. 0:00:50.479 --> 0:00:54.240 I would rather burn my kitchen down in a ritualistic 0:00:54.360 --> 0:01:00.160 bonfire than do one hundred sets of dishes after that. 0:01:00.160 --> 0:01:02.760 That sounds like a great way to celebrate the solstice. Actually, 0:01:02.840 --> 0:01:04.360 kitchen bonfire. 0:01:04.000 --> 0:01:07.520 Kitchen effigy. There we go, No more washing dishes. 0:01:07.600 --> 0:01:28.240 Hooray, it's the solstice magic. Hi. I'm Daniel. I'm a 0:01:28.240 --> 0:01:31.280 particle physicist and a professor a uc irvine and I'm 0:01:31.319 --> 0:01:34.160 not into astrology, but I do love the Solstice. 0:01:34.520 --> 0:01:38.840 I am Katie Golden. I host podcast on animal behavior 0:01:38.959 --> 0:01:45.600 called Creature Feature, and I am super duper into Solstice 0:01:45.920 --> 0:01:53.919 magics such as logs in the house and putting stones 0:01:54.000 --> 0:01:58.800 up such that they make interesting shapes and the light 0:01:59.360 --> 0:02:01.280 hits them in just such a way. 0:02:02.040 --> 0:02:03.960 M I see you're building Katie hinge. 0:02:04.240 --> 0:02:07.840 Katie hinge. You know, Okay for the summer Solstice one, 0:02:07.880 --> 0:02:11.280 I actually did talk about Britta Boyne, but I also 0:02:11.280 --> 0:02:15.040 want to talk about how there's a wood hinge as 0:02:15.120 --> 0:02:19.120 well as the stone hinge. And the word hinge it 0:02:19.400 --> 0:02:23.880 actually comes from the idea of a thing hanging like 0:02:23.919 --> 0:02:28.840 a hinge hanging. So stone hinge is like hanging rocks, 0:02:28.880 --> 0:02:33.920 and wood hinge is another ancient people's way of creating 0:02:34.240 --> 0:02:39.160 basically a annual sun dial, and that was made out 0:02:39.200 --> 0:02:40.520 of wooden timber. 0:02:41.480 --> 0:02:43.440 I just always thought they were trying to hinge their bets. 0:02:44.639 --> 0:02:46.280 I was thinking about starting a hinge. 0:02:46.000 --> 0:02:49.440 Fund, you know, Oh my god, Well we do need 0:02:49.480 --> 0:02:52.320 to teach Daniel about the difference between a hinge and 0:02:52.360 --> 0:02:55.040 a hedge. 0:02:56.120 --> 0:02:57.520 Well could you have a hedge hinge? 0:02:57.919 --> 0:03:01.040 Uh? You know what, It's never been done as far 0:03:01.080 --> 0:03:04.079 as I know in gardening science, but that never doesn't 0:03:04.080 --> 0:03:04.560 mean never. 0:03:05.120 --> 0:03:07.120 Well, okay, how about a biology one that a hedgehog 0:03:07.160 --> 0:03:08.920 hinge hedgehog hinge. 0:03:09.160 --> 0:03:12.800 Well, you know, maybe there's a hedgehog hinge for hedgehogs 0:03:12.840 --> 0:03:13.560 looking for love. 0:03:14.919 --> 0:03:16.720 All right, we'll hedge our bets until we get there. 0:03:16.760 --> 0:03:20.000 But anyway, welcome to the podcast Daniel and Jorge Explain 0:03:20.080 --> 0:03:23.160 the Universe, a production of iHeartRadio in which we do 0:03:23.200 --> 0:03:25.720 not hedge our bets. We go all in on trying 0:03:25.760 --> 0:03:28.960 to understand how the universe works and explain it all 0:03:29.000 --> 0:03:31.440 to you. We tackle the biggest questions, from the very 0:03:31.520 --> 0:03:34.480 nature of the universe to the smallest questions about quantum 0:03:34.520 --> 0:03:37.840 particles and the fundamental nature of space and time and 0:03:38.200 --> 0:03:41.280 everything in between, including how to get your hedgehogs out 0:03:41.320 --> 0:03:42.080 of your hinge. 0:03:42.760 --> 0:03:46.200 So there is a question I always get about hedgehogs, 0:03:46.240 --> 0:03:49.520 and it is how do they reproduce? And my answer 0:03:49.680 --> 0:03:54.040 is very carefully, that's a. 0:03:54.080 --> 0:03:59.520 Very pointed answer, Katie. And people have questions about the universe. 0:03:59.560 --> 0:04:02.240 They about hedgehogs, They want about quantum particles, they wonder 0:04:02.240 --> 0:04:05.440 about quantum hedgehogs, they wonder about hinges and what ancient 0:04:05.440 --> 0:04:08.160 people saw in them. They wonder what the solstice means, 0:04:08.200 --> 0:04:11.920 and they wonder what's going on between us and distant stars. 0:04:12.400 --> 0:04:14.800 And that's all part of doing physics. You don't have 0:04:14.840 --> 0:04:17.120 to be a professional academic to be a physicist. You 0:04:17.200 --> 0:04:19.800 just have to wonder about the nature of the universe 0:04:20.000 --> 0:04:23.240 and then share that curiosity with everybody else, and we 0:04:23.279 --> 0:04:26.040 hope you share it with us. If you have a 0:04:26.120 --> 0:04:28.560 question about how the universe works, and you can find 0:04:28.600 --> 0:04:31.479 an answer on Google or chat, GPT or your friendly 0:04:31.520 --> 0:04:34.960 neighborhood physicists, please write to me to questions at Daniel 0:04:34.960 --> 0:04:38.120 and Jorge dot com. We will answer it. Everybody gets 0:04:38.120 --> 0:04:40.680 an answer in their inbox, and sometimes we take an 0:04:40.680 --> 0:04:43.559 answer and put it right here on the podcast, also 0:04:43.680 --> 0:04:45.680 because we've been missing you and we wanted to hear 0:04:45.680 --> 0:04:46.279 from you again. 0:04:47.279 --> 0:04:51.200 So ninety nine percent of a part of cul physicists 0:04:51.320 --> 0:04:55.800 job is asking the right questions and one percent is 0:04:55.839 --> 0:04:57.080 you know, math or whatever. 0:04:58.480 --> 0:04:59.920 And this is also got to be rooting there for NAT. 0:05:00.240 --> 0:05:03.080 Napping is crucial, right right, And like a little bit 0:05:03.120 --> 0:05:04.200 of grant writing. 0:05:05.440 --> 0:05:15.320 Occasionally, and so on today's episode, we'll be answering listener questions. 0:05:15.480 --> 0:05:20.440 Winter Solstice Edition, Happy holidays and New Year and Solstice. 0:05:20.480 --> 0:05:24.480 To everybody out there who celebrates whatever it is you celebrate. Today, 0:05:24.480 --> 0:05:26.880 we're going to be celebrating my answering a really fun 0:05:27.000 --> 0:05:29.920 question from a listener, A question he thought of while 0:05:29.960 --> 0:05:34.360 he was in his backyard shed, maybe building his own hinge. 0:05:34.760 --> 0:05:36.600 Here's the question from Alex. 0:05:37.839 --> 0:05:41.800 Hi, guys, I was working in my backhout on my shed, 0:05:42.440 --> 0:05:45.800 and I was using a metal crowbar to help out 0:05:46.160 --> 0:05:49.000 one day when I just realized holding it how strong 0:05:49.040 --> 0:05:52.640 it was. So my question that came to me was, 0:05:53.360 --> 0:05:57.640 what is actually the longest physical possible crowbar made of 0:05:57.720 --> 0:06:05.760 metal that could exist in space? Is it possible that 0:06:06.000 --> 0:06:09.560 you could build one? One could exist that's long enough 0:06:09.560 --> 0:06:12.840 to stretch between stars, especially if you didn't have to 0:06:12.880 --> 0:06:17.359 worry about adding to its length with unlimited supplies, and 0:06:17.400 --> 0:06:20.440 if it was nowhere near any other gravitational objects. What 0:06:20.480 --> 0:06:23.839 would the ramifications be of having it like a crowbar 0:06:23.839 --> 0:06:25.920 where one end was light hours away from the other 0:06:26.080 --> 0:06:29.039 or even light years away from the other. It seems 0:06:29.080 --> 0:06:32.760 a bit weird to travel light speed and not get 0:06:32.760 --> 0:06:35.239 from one end to the other on one particular object. 0:06:36.400 --> 0:06:40.679 Thank you, So you know I have a similar question 0:06:40.760 --> 0:06:44.000 but once I just saw a crow bar on the ground, 0:06:44.360 --> 0:06:47.520 I think there were some people working on something like 0:06:47.520 --> 0:06:51.200 a manhole or something sort of nearby. But also I 0:06:51.279 --> 0:06:54.760 wondered if the world operates by video game rules, which is, 0:06:54.920 --> 0:06:57.520 if you find a crowbar, is that yours? Now? Do 0:06:57.600 --> 0:06:59.520 you pick it up and put it in your inventory? 0:06:59.640 --> 0:07:00.960 Or is that still stealing? 0:07:01.960 --> 0:07:04.440 I don't know. Maybe the world operates by checkof rules. 0:07:04.440 --> 0:07:06.880 If you find a crowbar in act one, then you're 0:07:06.880 --> 0:07:08.760 gonna have about to break into something with it in 0:07:08.800 --> 0:07:09.280 Act three. 0:07:09.960 --> 0:07:11.920 I mean that is just video game rules. 0:07:11.920 --> 0:07:16.640 Also exactly exactly. I used to play like King's Quest 0:07:16.720 --> 0:07:18.640 back in the day, and every time you found like 0:07:18.640 --> 0:07:20.320 a weird magic rap mushroom, you put it in your 0:07:20.320 --> 0:07:22.040 back pocket because you knew you were going to need 0:07:22.040 --> 0:07:23.920 it to solve some puzzle later on. 0:07:24.440 --> 0:07:27.160 Get ye bucket. You're gonna need that bucket for the 0:07:27.280 --> 0:07:28.640 dragon at the end of the. 0:07:28.640 --> 0:07:31.280 Game, exactly, and you can't go back, So get the 0:07:31.280 --> 0:07:34.440 bucket now. And Alex is wondering about like the practical 0:07:34.480 --> 0:07:37.600 limits of how big we could build something like, could 0:07:37.680 --> 0:07:40.240 you build a crowbar that's long enough that you can 0:07:40.320 --> 0:07:43.160 use it to like poke people on other planets. That 0:07:43.280 --> 0:07:44.680 that's pretty crazy, thought, Alex. 0:07:45.640 --> 0:07:49.120 It's interesting, right, because sure you could have like a 0:07:49.200 --> 0:07:52.440 large object, but the bigger it gets. Like, there's a 0:07:52.480 --> 0:07:55.400 lot of questions here, right, we need to know about 0:07:55.720 --> 0:08:01.200 a what are crowbars made out of? Steel? Iron? Steal? 0:08:01.960 --> 0:08:04.160 And so it's like, I guess a lot of it 0:08:04.240 --> 0:08:08.840 is basically the strength, like the steal, you know, the 0:08:09.000 --> 0:08:11.640 the what steals made out of? How that would work? 0:08:12.640 --> 0:08:16.680 But also you know how even if it's made out 0:08:16.720 --> 0:08:19.680 of any material, right, Like let's say crobar made out 0:08:19.680 --> 0:08:24.320 of whatever material, the strongest, hardest material you could get, Like, 0:08:24.560 --> 0:08:28.000 is there a limit to the size of physical objects 0:08:28.040 --> 0:08:30.920 in the universe before some wacky starts happening? 0:08:31.720 --> 0:08:34.560 Yeah, this is really fun And there's a really important 0:08:34.600 --> 0:08:38.480 lesson here about how we do physics anyway, because an 0:08:38.520 --> 0:08:41.800 important sort of often implicit step that we don't talk 0:08:41.800 --> 0:08:45.480 about when we do physics is building a simplified model 0:08:45.679 --> 0:08:48.720 of the universe. Like you want to answer a physics question, 0:08:48.880 --> 0:08:51.679 you know, like a piano is falling from a window. 0:08:52.120 --> 0:08:53.960 Is you going to squish that little doggie? 0:08:54.280 --> 0:08:54.559 No? 0:08:55.520 --> 0:08:57.800 Oh no, I hope the answer is no. But to 0:08:57.840 --> 0:09:00.440 answer that physics question, what you have to do is 0:09:00.720 --> 0:09:02.760 simplify at first. Because you don't care about a lot 0:09:02.800 --> 0:09:04.439 of the details. You don't care about the color of 0:09:04.480 --> 0:09:07.640 the piano, you can probably ignore the crosswinds. You build 0:09:07.679 --> 0:09:11.000 a simplified model that just contains the information necessary to. 0:09:10.960 --> 0:09:14.160 Answer the question, like the breed of the dog for example. 0:09:14.280 --> 0:09:16.360 Yeah we don't care, I mean we care, but it 0:09:16.400 --> 0:09:19.240 doesn't change the answer. And so the trick there is 0:09:19.280 --> 0:09:21.160 to make a model that's simple enough that you can 0:09:21.200 --> 0:09:23.480 actually answer it because you've included all the details of 0:09:23.480 --> 0:09:27.719 all the quantum particles and be intractable, but is sophisticated 0:09:27.840 --> 0:09:30.880 enough that it still provides a realistic answer. That's the 0:09:30.920 --> 0:09:34.200 sweet spot for doing physics. And the interesting thing is 0:09:34.240 --> 0:09:36.880 that that's a different model in every scenario. You can 0:09:36.960 --> 0:09:39.319 ignore the winds in this case, but if you're solving 0:09:39.360 --> 0:09:41.280 a different problem like what's going to happen to this 0:09:41.400 --> 0:09:44.200 leaf and a tornado, you can't ignore the winds. So 0:09:44.280 --> 0:09:46.000 every time you solve a physics problem, you need to 0:09:46.040 --> 0:09:49.559 ask yourself, am I including the right assumptions or the 0:09:49.559 --> 0:09:52.440 assumptions I'm making going to ruin it? And so I 0:09:52.520 --> 0:09:55.040 run into this all the time with these very long 0:09:55.160 --> 0:09:56.000 space rods. 0:09:56.160 --> 0:09:56.319 Aly. 0:09:56.320 --> 0:09:58.040 It turns out Alex is not the only person to 0:09:58.080 --> 0:10:01.520 think about really long rods up a lot, because people 0:10:01.559 --> 0:10:04.080 have this idea that a rod is sort of like 0:10:04.120 --> 0:10:07.480 infinitely rigid. Like if I'm across the room from you 0:10:07.640 --> 0:10:10.200 and have a dowel like a wooden stick, if I 0:10:10.280 --> 0:10:12.400 push it, then you're gonna feel me pushing it. You're 0:10:12.440 --> 0:10:14.640 holding the other end, you're gonna feel it. And people 0:10:14.679 --> 0:10:17.559 imagine that sort of happens instantaneously, that if I push 0:10:17.559 --> 0:10:19.920 on the stick on one side, you feel it instantly. 0:10:20.160 --> 0:10:22.560 And that's mostly true, and for basically every problem you're 0:10:22.559 --> 0:10:25.160 going to solve here on Earth, that's basically the case, 0:10:25.640 --> 0:10:29.160 because the information travels very, very fast. But then people wonder, 0:10:29.240 --> 0:10:31.040 all right, what if I take a rod and I 0:10:31.080 --> 0:10:34.160 build it so it's like four light years long, and 0:10:34.320 --> 0:10:36.880 I stretch it from here to Alpha Centauri and some 0:10:36.960 --> 0:10:39.840 alien is holding the other side. Can I tap on 0:10:39.960 --> 0:10:42.880 my side and use that to communicate faster than the 0:10:42.880 --> 0:10:45.840 speed of light. That's a very common question I get, 0:10:46.080 --> 0:10:48.840 And the answer is obviously no. You can't break special 0:10:48.880 --> 0:10:52.080 relativity with a dowel that's four light years long. 0:10:52.440 --> 0:10:54.079 Even dowels have their limits. 0:10:54.120 --> 0:10:57.000 I guess yeah, And the reason is that you've broken 0:10:57.000 --> 0:10:59.960 the assumptions. Down here on Earth, it works to assume 0:11:00.000 --> 0:11:03.000 whom Yeah, The information travels instantly. That when you push 0:11:03.040 --> 0:11:05.520 one side of the dowel, the other side moves instantly. 0:11:05.960 --> 0:11:09.000 But that doesn't work anymore when the dowel's really really long, 0:11:09.480 --> 0:11:12.640 because the time it takes now matters, because a dowel, 0:11:12.720 --> 0:11:16.520 even here on Earth, doesn't transmit information instantly. What happens 0:11:16.520 --> 0:11:19.000 when you push on one side of the dowel is 0:11:19.080 --> 0:11:21.600 that you don't immediately move the other side. You push 0:11:21.640 --> 0:11:24.599 on one side and it moves the layer of molecules 0:11:24.640 --> 0:11:26.600 that are next to the edge, which you meant the 0:11:26.600 --> 0:11:28.599 next layer, which moved the next layer, which moved the 0:11:28.640 --> 0:11:32.000 next layer. Because a dowel is not infinitely rigid, it's 0:11:32.040 --> 0:11:34.440 like a very stiff version of a tube of water 0:11:34.559 --> 0:11:36.800 or like a string. You're pushing on it and there's 0:11:36.840 --> 0:11:40.440 a wave of information that travels down the dowel. So 0:11:40.559 --> 0:11:42.319 here on Earth, you push on one side of the dowel, 0:11:42.360 --> 0:11:46.000 the other side moves very shortly afterwards, but not instantly. 0:11:46.040 --> 0:11:50.079 It takes time for that information and move down the dowel. Now, 0:11:50.080 --> 0:11:52.200 when your Dowel is four light years long. That time 0:11:52.280 --> 0:11:54.800 is no longer something you can ignore. It plays a 0:11:54.840 --> 0:11:57.840 big part in how long it takes for the information 0:11:57.920 --> 0:11:59.960 to get there. And if you ignore that, then you 0:12:00.160 --> 0:12:03.080 violating special relativity. And it seems like you could send 0:12:03.080 --> 0:12:05.280 information to the stars faster than the speed of light, 0:12:05.320 --> 0:12:06.520 which of course you can't. 0:12:06.920 --> 0:12:10.079 This is actually the same problem from a biological perspective 0:12:10.080 --> 0:12:13.640 of having like a giant brain, right, could you have 0:12:14.280 --> 0:12:20.400 an enormous brain that could like communicate instantly, right, like 0:12:20.520 --> 0:12:24.640 some galaxy sized brain. And the problem is that the 0:12:24.679 --> 0:12:26.800 way our brains work in the same way that you 0:12:26.840 --> 0:12:29.480 talked about, how like the molecules have to push on 0:12:29.520 --> 0:12:32.360 the other molecules, like our brain is all physics based. 0:12:32.400 --> 0:12:35.800 Our whole bodies are basically a big Rubok Goldberg machine 0:12:35.840 --> 0:12:41.160 of molecules bonking into other molecules, which creates things like thought. 0:12:41.760 --> 0:12:44.960 And so if you have a say, a giant enough brain, 0:12:45.360 --> 0:12:48.480 the time it would take to like have a single 0:12:48.559 --> 0:12:53.320 thought would be incredibly slow. So the bigger the brain, 0:12:53.840 --> 0:12:57.040 the more galaxy size the brain, actually the slower it 0:12:57.040 --> 0:12:58.319 would take to have a. 0:12:58.320 --> 0:13:01.720 Thought, Yeah, exactly. And so if you're ignoring that when 0:13:01.760 --> 0:13:03.520 you're just thinking about a small brain. You can no 0:13:03.600 --> 0:13:06.480 longer ignore that in a large brain. So the lesson is, 0:13:06.480 --> 0:13:08.559 when you're doing physics, you have to always think about 0:13:08.600 --> 0:13:11.679 what are the assumptions we're making and are those assumptions 0:13:11.720 --> 0:13:14.560 still valid for this scenario. In the case of the 0:13:14.720 --> 0:13:18.920 like five light year long rod, if you assume instantaneous 0:13:18.920 --> 0:13:21.160 motion from one side to the other, then you're assuming 0:13:21.200 --> 0:13:24.280 special relativity is broken. So you can't then go and say, oh, look, 0:13:24.280 --> 0:13:26.760 this rod breaks special relativity. Well, you assume to is 0:13:26.800 --> 0:13:29.760 broken and that's why you broke it. And so there's 0:13:29.800 --> 0:13:32.440 a lot of unpacking of those assumptions in these questions. 0:13:33.000 --> 0:13:34.960 But Alex's question is a little bit different. He's not 0:13:35.000 --> 0:13:37.280 trying to communicate with aliens. He's just trying to build 0:13:37.320 --> 0:13:39.720 a really long rod, and he's wondering, like how big 0:13:39.760 --> 0:13:42.320 could you make it? Anyway? And I think that's exactly 0:13:42.400 --> 0:13:44.880 what he's digging into, Like what would break down? What 0:13:44.920 --> 0:13:48.320 assumptions we make about building long rods would break down 0:13:48.320 --> 0:13:50.120 if we try to make one that's like a light 0:13:50.200 --> 0:13:51.559 year long, Which is a really. 0:13:51.440 --> 0:13:54.360 Cool question, yeah, because I mean there's a lot of 0:13:54.360 --> 0:13:57.320 things that we could say, like on Earth, right, Like, 0:13:57.360 --> 0:13:59.640 we could try to build a really long crow bar 0:13:59.720 --> 0:14:02.720 and at a certain point it could collapse under its 0:14:02.760 --> 0:14:07.000 own weight. But if something's in space, we'd have to 0:14:07.000 --> 0:14:10.920 figure out what kinds of forces or how gravity would 0:14:10.960 --> 0:14:15.360 be acting on something in a way that's different from Earth, right, Like, yes, 0:14:15.640 --> 0:14:18.200 you can. You know, it's like have you ever you 0:14:18.240 --> 0:14:21.840 know whiteboard pins? Like you create a big old lightsaber 0:14:21.920 --> 0:14:25.200 out of whiteboard pins and at a certain point there's 0:14:25.240 --> 0:14:29.760 too many and it collapses. But that's all using Earth physics. 0:14:29.840 --> 0:14:35.080 So you could make a much longer whiteboard pin lightsaber 0:14:35.440 --> 0:14:39.240 out in space because gravity is not impacting it in 0:14:39.240 --> 0:14:40.960 the same way that it is on Earth. But then 0:14:41.000 --> 0:14:44.840 once you get big enough, right with this pin dowel 0:14:45.000 --> 0:14:49.360 or iron crowbar or whatever it is, something's happening. And 0:14:49.400 --> 0:14:52.000 this is where I would like you to talk. 0:14:52.600 --> 0:14:56.720 Yeah, exactly. So let's take this question out into deep space. 0:14:57.200 --> 0:14:59.120 And the first thing the wonder is like, well, what's 0:14:59.120 --> 0:15:01.200 the biggest thing that we'd built in space so far? 0:15:01.800 --> 0:15:04.520 And that's the International Space Station. It's not that impressively long, 0:15:04.520 --> 0:15:07.520 it's about thirty six meters long, but you know, it's 0:15:07.560 --> 0:15:10.040 not very far out in space, and they're not trying 0:15:10.040 --> 0:15:13.000 to build something super duper long. I think the longest 0:15:13.000 --> 0:15:15.040 thing that's ever actually been in space, it's more like 0:15:15.080 --> 0:15:18.120 a kilometer. They build a space tether, which is like 0:15:18.120 --> 0:15:21.520 a really long wire that you dangle from a spaceship 0:15:21.560 --> 0:15:24.440 to try to like generate electrical current or to learn 0:15:24.560 --> 0:15:28.720 to steer using mechnetic fields. So, like a kilometer long's 0:15:28.760 --> 0:15:31.760 the biggest thing that we've ever put into space. But 0:15:31.800 --> 0:15:34.520 again that's also just the near Earth orbit. So let's 0:15:34.560 --> 0:15:37.240 go deeper out into space and try to build something 0:15:37.240 --> 0:15:40.720 that's really long and think about the forces involved. Like 0:15:40.920 --> 0:15:43.720 when you build a rod at a steel or even 0:15:43.760 --> 0:15:46.160 a dowel out of wood or whatever, how are you 0:15:46.200 --> 0:15:49.040 actually building that thing. Usually we ignore it and just say, oh, 0:15:49.120 --> 0:15:52.000 it's some smooth, continuous substance. But if you zoom in, 0:15:52.440 --> 0:15:56.080 the reason it takes time to propagate information along it 0:15:56.120 --> 0:15:57.960 is the same thing that's holding it together, which is 0:15:58.000 --> 0:16:01.240 the forces between those molecules. All of these objects in 0:16:01.280 --> 0:16:03.440 the end are like a mesh of modules. Yet you 0:16:03.480 --> 0:16:06.360 have these little bits of matter tied together by forces 0:16:06.640 --> 0:16:09.880 to build something larger, and it's those forces that transmit 0:16:09.920 --> 0:16:13.480 the information also limit how big something can get right 0:16:14.000 --> 0:16:16.400 and so out into deep space. What is the thing 0:16:16.480 --> 0:16:19.200 that's limiting us. Well, those forces can work. They can 0:16:19.240 --> 0:16:22.720 tie something together basically infinitely, there's no limitation there. You 0:16:22.760 --> 0:16:25.080 can just keep adding layers and layers and layers to 0:16:25.120 --> 0:16:27.240 your rod. The thing that's going to keep you from 0:16:27.240 --> 0:16:30.560 building that rod light years long or infinitely long in 0:16:30.640 --> 0:16:34.440 the end, are going to be the gravitational effects, residual 0:16:34.520 --> 0:16:38.000 as they are, and the nature of space and time itself. 0:16:38.360 --> 0:16:41.320 But let's first talk about the gravitational effects. So one 0:16:41.360 --> 0:16:44.720 effect are tidal forces. So you say, well, let's be 0:16:44.920 --> 0:16:48.000 out between the stars. AX is actually talking about something 0:16:48.000 --> 0:16:50.240 which stretches between the stars. You have like one end 0:16:50.280 --> 0:16:52.520 at one star and the other end at another star. 0:16:53.000 --> 0:16:55.200 And if you have something that's like five light years long, 0:16:55.440 --> 0:16:57.760 you can't have it that far away from stars because 0:16:57.800 --> 0:16:59.600 it's going to be big enough. There's always going to 0:16:59.600 --> 0:17:03.400 be some nearby. And remember that gravity does more than 0:17:03.480 --> 0:17:06.080 just pull on things. It can actually pull things apart. 0:17:06.440 --> 0:17:08.639 These are called tidal forces. And for example, if you're 0:17:08.760 --> 0:17:12.199 near a black hole, then your head can have a 0:17:12.200 --> 0:17:14.919 different gravitational tug on it than your feet, and that 0:17:14.920 --> 0:17:17.640 can effectively tear you apart. Like, if the black hole 0:17:17.680 --> 0:17:19.719 is pulling on your feet harder than it's pulling on 0:17:19.760 --> 0:17:22.160 your head because your feet are a little bit closer, 0:17:22.520 --> 0:17:24.520 then it's going to pull you apart because its gravity 0:17:24.600 --> 0:17:28.080 is really really strong. But if you're really really long, 0:17:28.600 --> 0:17:31.120 then you don't need strong gravity to have tidal forces. 0:17:31.280 --> 0:17:33.080 Because if one end of this rod is closer to 0:17:33.119 --> 0:17:36.240 the star then the other end, and the rod is 0:17:36.280 --> 0:17:38.600 really really long, that's going to be a very large 0:17:38.600 --> 0:17:41.359 difference in the gravitational force from one end of the 0:17:41.400 --> 0:17:42.920 rod to the other, and that star is going to 0:17:42.960 --> 0:17:45.760 tear it apart. Even if the star doesn't have really 0:17:45.800 --> 0:17:48.920 powerful gravity like black holes, the sheer length of the 0:17:49.040 --> 0:17:51.520 rod makes the tidle forces very significant. 0:17:51.640 --> 0:17:56.240 I see. So you can't span a doll from one 0:17:56.280 --> 0:17:59.080 start to the other because of the same title forces 0:17:59.160 --> 0:18:04.560 that spaghetifies you in a black hole. But what if 0:18:04.600 --> 0:18:08.639 you took away the stars? Right? Like, could you get 0:18:08.680 --> 0:18:14.000 a like infinity rod if you took away stars and 0:18:14.119 --> 0:18:18.119 just had it existing on its own in space without 0:18:18.200 --> 0:18:18.960 hitting anything? 0:18:19.480 --> 0:18:21.600 Yeah? Right, so's get rid of the other gravity, and 0:18:21.720 --> 0:18:23.760 you still have the issue of the gravity of the 0:18:23.840 --> 0:18:27.920 rod itself. Right, You can't build an infinitely massive rod, 0:18:27.960 --> 0:18:30.040 because eventually that thing is going to have its own 0:18:30.200 --> 0:18:34.119 self gravity. It's going to collapse into a black hole. Like, 0:18:34.160 --> 0:18:36.640 you can't just make a blob of metal and keep 0:18:36.680 --> 0:18:38.760 adding blobs of metal to it and make it as 0:18:38.800 --> 0:18:41.359 big as you want, because it's going to start collapsing. 0:18:41.560 --> 0:18:44.200 This already happens for things like planets, like the Earth 0:18:44.240 --> 0:18:47.240 is about the largest rocky planet you can make. You 0:18:47.240 --> 0:18:49.080 can add more rock to it, but that's going to 0:18:49.160 --> 0:18:51.520 mean more gravity, and it's just going to compress the 0:18:51.560 --> 0:18:54.520 Earth further. So as you add more mass to the Earth, 0:18:54.560 --> 0:18:57.520 it doesn't get any bigger, it just gets denser. And 0:18:57.600 --> 0:19:00.200 eventually you keep adding mass, you're going to end up 0:19:00.080 --> 0:19:02.359 up with a black hole. And so there is a 0:19:02.440 --> 0:19:05.280 limit to how large and how massive you can make 0:19:05.320 --> 0:19:08.480 something before it collapses into a black hole. So something 0:19:08.600 --> 0:19:11.880 self gravity will also limit how large you can make 0:19:12.040 --> 0:19:15.080 an object out of practical stuff like steel or wood. 0:19:15.280 --> 0:19:19.040 Okay, so what about a really thin rod? Now stay 0:19:19.080 --> 0:19:22.280 with me. What if you have a rod that is 0:19:22.359 --> 0:19:25.920 like one atom per unit, right, it is like one 0:19:25.960 --> 0:19:29.000 atom thick, and then you just stack a bunch of 0:19:29.160 --> 0:19:35.600 atoms into this very long rod. Would that still be 0:19:35.800 --> 0:19:40.440 something that would at a certain point start to collapse 0:19:40.440 --> 0:19:43.360 in on itself because of gravity, Or am I already 0:19:43.400 --> 0:19:46.480 breaking some laws of physics by trying to create a 0:19:46.920 --> 0:19:50.119 one atom diameter rod. 0:19:50.680 --> 0:19:53.480 Now you could probably make a carbon nanofiber eventually that's 0:19:53.480 --> 0:19:55.880 like one atom thick and super duper long. I don't 0:19:55.880 --> 0:19:58.240 think it's a technical problem there. But what you're going to 0:19:58.320 --> 0:20:01.200 run into is a problem with a nature space and time. 0:20:01.920 --> 0:20:03.719 And if you can get rid of gravity the nearby 0:20:03.720 --> 0:20:06.439 stars and effectively get rid of the self gravity by 0:20:06.480 --> 0:20:09.359 making this thing really really lightweight, you're going to run 0:20:09.359 --> 0:20:13.280 into dark energy. So in short distances, like the size 0:20:13.280 --> 0:20:15.400 of our Solar system of the size of our galaxy, 0:20:15.640 --> 0:20:18.359 the dominant force is gravity. It holds things together, it 0:20:18.400 --> 0:20:21.679 shapes things, it determines the nature of our universe. But 0:20:21.760 --> 0:20:24.800 over very large distances, gravity gets weaker. Right, the further 0:20:24.880 --> 0:20:27.680 you are away from something, the weaker it's gravity is. 0:20:28.160 --> 0:20:30.840 And at those distances something else takes over, which is 0:20:30.960 --> 0:20:35.119 dark energy, meaning the expansion of the universe itself. Remember 0:20:35.160 --> 0:20:38.960 that everywhere in the universe is expanding. Take any arbitrary 0:20:39.080 --> 0:20:41.720 chunk of space as time goes on, That space is 0:20:41.720 --> 0:20:45.359 getting larger. It's making new space. So between the Earth 0:20:45.400 --> 0:20:48.000 and the Sun, for example, new space is being made, 0:20:48.160 --> 0:20:50.639 but the gravity of the Earth and the Sun overpowers it. 0:20:51.000 --> 0:20:54.679 Between our galaxy and the neighboring galaxy, new space is 0:20:54.720 --> 0:20:58.119 being made, but again the gravity overpowers it. But eventually, 0:20:58.400 --> 0:21:02.879 between clusters of galaxy, dark energy becomes more powerful because 0:21:02.880 --> 0:21:05.400 you have more of these cubes of space and each 0:21:05.480 --> 0:21:08.600 one is expanding, so that adds up and gravity gets 0:21:08.680 --> 0:21:12.679