WEBVTT - How does gravity escape a black hole? 0:00:08.640 --> 0:00:11.760 Hey, Katie, have you ever been to Las Vegas? I 0:00:12.160 --> 0:00:16.400 have once, and so what did you think about America's 0:00:16.480 --> 0:00:17.880 favorite adult playground? 0:00:18.200 --> 0:00:20.880 Well, I can't really tell you. 0:00:21.600 --> 0:00:24.280 Is that because it was so much fun you remember nothing? 0:00:24.560 --> 0:00:27.880 I mean, it is a bit of an information black hole. 0:00:28.120 --> 0:00:29.640 You mean, like you don't want to talk about it. 0:00:29.680 --> 0:00:31.960 Like what happens in Vegas stays in Vegas. 0:00:32.320 --> 0:00:36.120 It is a singular experience for sure. 0:00:36.520 --> 0:00:39.480 All right, we'll leave that past. The Katie event arrived. 0:00:41.760 --> 0:00:43.599 Like they're just handing out margarite? 0:00:43.720 --> 0:00:55.480 Is there? What am I supposed to say? 0:01:00.840 --> 0:01:00.960 Hi? 0:01:01.200 --> 0:01:04.560 I'm Daniel. I'm a particle physicist and a professor at 0:01:04.760 --> 0:01:08.680 UC Irvine, and I have definitely been to Vegas. 0:01:08.920 --> 0:01:12.840 I am Katie Golden, I am made out of particles. 0:01:13.319 --> 0:01:19.319 I host a podcast about animals, and I mostly liked 0:01:19.360 --> 0:01:23.640 the food from Las Vegas, not so much the casinos. 0:01:23.800 --> 0:01:27.080 I recently went to Vegas with my thirteen year old daughter, 0:01:27.160 --> 0:01:30.760 which was quite an experience to see it through her eyes. 0:01:30.959 --> 0:01:33.400 Definitely a place to go at least once. 0:01:33.800 --> 0:01:37.959 It is a fascinating city. I regret that I have 0:01:38.040 --> 0:01:40.920 not been there since they have put the giant orban. 0:01:41.480 --> 0:01:43.600 Yeah, the orb is cool. There's definitely a lot of 0:01:43.600 --> 0:01:46.000 stuff you can do even if you're not eighteen or 0:01:46.040 --> 0:01:49.080 twenty one plus, though some of the stuff she wanted 0:01:49.080 --> 0:01:52.160 to do, like drive tanks through the desert and shoot 0:01:52.200 --> 0:01:55.360 automatic weapons were definitely age restricted. 0:01:55.560 --> 0:01:59.000 Yeah, I have a friend who I think shot guns 0:01:59.040 --> 0:02:02.120 from a helicopter in Vegas. There's a lot of things 0:02:02.160 --> 0:02:02.640 you can do. 0:02:02.880 --> 0:02:06.240 There's all sorts of crazy stuff you can do in Vegas, 0:02:06.440 --> 0:02:08.920 stuff that helps you understand who you are and who 0:02:09.040 --> 0:02:12.760 you aren't. And Welcome to the podcast Daniel and Jorge 0:02:12.840 --> 0:02:15.120 Explain the Universe, in which we try to explain to 0:02:15.160 --> 0:02:18.320 you what the universe is and what the universe isn't. 0:02:18.600 --> 0:02:21.000 We try to pull back the curtain and help you 0:02:21.240 --> 0:02:24.840 understand what's going on out there in the deepest, darkest 0:02:24.960 --> 0:02:25.720 regions of. 0:02:25.680 --> 0:02:27.880 Space, such as Las Vegas. 0:02:30.240 --> 0:02:33.000 There is no Vegas casino yet called the black Hole, 0:02:33.160 --> 0:02:35.760 but I am assuming one it will eventually open up. 0:02:35.840 --> 0:02:39.840 That is a missed opportunity, or like a mini golf 0:02:39.840 --> 0:02:41.239 course called the black. 0:02:40.919 --> 0:02:43.880 Holes that just sucks in all the balls. Well, on 0:02:43.919 --> 0:02:46.680 this podcast, we do try to explain to you black 0:02:46.680 --> 0:02:49.959 holes and also how everything works on the smallest scales 0:02:50.000 --> 0:02:52.800 because we don't just want to describe the universe to you. 0:02:52.919 --> 0:02:55.359 We want to explain it. We want you to get 0:02:55.360 --> 0:02:59.400 an understanding, a microscopic picture of how everything around you 0:02:59.520 --> 0:03:02.120 actually works. We want to dive deep into the very 0:03:02.200 --> 0:03:05.480 nature of reality and come out with a bottom up 0:03:05.639 --> 0:03:09.520 understanding of how the universe actually works. My friend Jorge 0:03:09.560 --> 0:03:11.440 can't be here today, but I'm very glad to be 0:03:11.560 --> 0:03:14.840 joined by one of our regular co hosts. Thanks Katie 0:03:14.880 --> 0:03:17.320 for joining us on this black Hole of an episode. 0:03:17.520 --> 0:03:20.680 I am excited because no matter how many times you 0:03:20.720 --> 0:03:24.200 explain to me what a black hole is, I still 0:03:24.280 --> 0:03:28.200 feel like I cannot wrap my head around it. So surely, 0:03:28.480 --> 0:03:32.000 surely this will be the episode where I understand black holes. 0:03:32.240 --> 0:03:34.600 Well, I would say there's probably nobody out there who 0:03:34.680 --> 0:03:39.760 fully deeply understands black holes, because to fully deeply understand something, 0:03:39.800 --> 0:03:43.280 I think we need a particle level explanation for it. 0:03:43.400 --> 0:03:45.160 You know, we need to be able to moot up 0:03:45.160 --> 0:03:47.760 from the tiniest little bits and say, here's what's really 0:03:47.800 --> 0:03:50.240 happening at the smallest scales when you get sucked into 0:03:50.280 --> 0:03:53.320 a black hole or when photons try to escape. And 0:03:53.360 --> 0:03:55.960 the reason I say that nobody understands them is that 0:03:56.000 --> 0:03:59.800 we do not have a particle level understanding of black 0:03:59.840 --> 0:04:02.160 hole holes. The way, for example, we can understand what 0:04:02.240 --> 0:04:05.520 happens when photons go through glass, They interact with the atoms, 0:04:05.520 --> 0:04:07.480 the electrons and all that stuff in there, and it 0:04:07.560 --> 0:04:09.920 bends their path, and we have some way to tell 0:04:09.960 --> 0:04:13.320 a story microscopically if what's happening to those photons and 0:04:13.600 --> 0:04:17.440 related to what we see actually macroscopically, we can't do 0:04:17.560 --> 0:04:21.120 that for black holes because we don't understand particles and gravity. 0:04:21.400 --> 0:04:24.040 We have no theory of quantum gravity that tells us 0:04:24.320 --> 0:04:27.960 what happens to particles when they feel gravity, and that's 0:04:27.960 --> 0:04:31.279 what black holes are all about. Gravity. So we don't 0:04:31.320 --> 0:04:35.360 have this sort of deep down, microscopic understanding of black holes. 0:04:35.400 --> 0:04:38.680 So probably nobody understands, but that doesn't stop us from 0:04:38.720 --> 0:04:41.000 asking questions and from trying to grapple with what we 0:04:41.200 --> 0:04:44.599 have learned about black holes. Then, on this podcast, we 0:04:44.720 --> 0:04:47.359 encourage everybody to think deeply about the universe and to 0:04:47.400 --> 0:04:49.920 try to fit these ideas into their heads, to ask 0:04:49.960 --> 0:04:53.080 themselves questions to see does this make sense to you? 0:04:53.320 --> 0:04:55.240 Is it possible for you to grapple with what we 0:04:55.320 --> 0:04:57.680 do and do not know about black holes. 0:04:58.040 --> 0:05:02.760 The problem, Daniel is I have a finite number of neurons, 0:05:03.600 --> 0:05:08.200 a finite sort of number of synaptic pathways in my brain, 0:05:08.680 --> 0:05:11.320 and it is very difficult for those little guys to 0:05:12.560 --> 0:05:16.280 understand all we know about black holes and what we 0:05:16.360 --> 0:05:19.560 don't know about black holes. If we were somehow able 0:05:19.680 --> 0:05:22.800 to measure everything about a black hole, do you think 0:05:22.839 --> 0:05:25.599 we could even fully understand it? As humans? 0:05:25.920 --> 0:05:28.839 It's a deep question in philosophy, like are we even 0:05:29.040 --> 0:05:33.080 capable of describing the universe in our minds? Can we 0:05:33.200 --> 0:05:35.839 understand the universe? And not a question I know the 0:05:35.920 --> 0:05:39.840 answer to or I think anybody knows the answer to. Amazingly, 0:05:40.120 --> 0:05:42.880 so far we have been able to do it, to 0:05:43.320 --> 0:05:46.880 write these little mathematical models, tell ourselves these little stories 0:05:46.880 --> 0:05:49.520 in our minds, and use them to explain everything that 0:05:49.560 --> 0:05:53.920 we see and everything we experience, everything our experiments tell us. 0:05:54.680 --> 0:05:57.320 Is it possible for us to understand them? The smartest 0:05:57.400 --> 0:05:59.920 human I don't know. I think there probably is a 0:06:00.360 --> 0:06:03.359 limit to how smart the smartest human is, and so 0:06:03.400 --> 0:06:05.680 it might be that the universe it's just more complex 0:06:05.720 --> 0:06:08.320 than that, and that no human, regardless of how smart 0:06:08.360 --> 0:06:11.000 they are, could ever understand it. But you know, we've 0:06:11.000 --> 0:06:13.719 been making a lot of progress in recent years asking 0:06:13.800 --> 0:06:16.680 and answering questions about the deepest nature of the universe 0:06:16.760 --> 0:06:19.560 and about black holes. So I'm kind of bullish on 0:06:19.640 --> 0:06:23.800 the possibility for some humans someday to understand it. And 0:06:24.040 --> 0:06:26.839 that's not just limited to like the Albert Einsteins of 0:06:26.920 --> 0:06:29.760 the world. I think it's possible for basically everybody out 0:06:29.800 --> 0:06:33.080 there to get some kind of intuitive grasp or how 0:06:33.240 --> 0:06:36.320 black holes work. One thing I love about hearing from 0:06:36.360 --> 0:06:39.400 listeners to the podcast is that it's been teaching them 0:06:39.440 --> 0:06:42.440 to think like a physicist, you know, like, what does 0:06:42.480 --> 0:06:45.440 that mean? To think like a physicist? It means to 0:06:45.600 --> 0:06:48.480 try to understand the world around you, to tell yourself stories, 0:06:48.480 --> 0:06:51.960 to ask yourself questions, to say, do I understand how 0:06:52.000 --> 0:06:54.880 this works? To put these models in your head and 0:06:54.960 --> 0:06:56.920 like turn them around and say, well, if that's true, 0:06:57.040 --> 0:06:58.839 doesn't it mean this or how does this connect with 0:06:58.880 --> 0:07:02.520 this other thing I do understand? And that's especially important 0:07:02.560 --> 0:07:05.640 for weird things like black holes. So we get lots 0:07:05.680 --> 0:07:08.600 of questions from listeners who're doing just that. Wh we're 0:07:08.640 --> 0:07:11.480 trying to think like a physicist about black holes? To 0:07:11.520 --> 0:07:15.480 try to incorporate it into the mathematical stories in their minds. 0:07:15.840 --> 0:07:20.480 This podcast is Daniel's secret weapon of trying to convert 0:07:20.640 --> 0:07:25.360 everyone into physicists. We are onto you, Daniel. You are 0:07:25.400 --> 0:07:28.960 trying to create an army of physicists. There are so 0:07:29.120 --> 0:07:33.160 many questions that I have about black holes. It's hard 0:07:33.160 --> 0:07:36.000 for me to even think about how to phrase my 0:07:36.160 --> 0:07:40.440 confusion about black holes into a question. So just being 0:07:40.520 --> 0:07:46.200 able to ask a distinct, coherent question about black holes, 0:07:46.240 --> 0:07:47.240 I think is impressive. 0:07:48.400 --> 0:07:50.680 I mean, your question about black holes is like black holes, 0:07:50.880 --> 0:07:51.920 what's the deal with that? 0:07:52.440 --> 0:07:56.760 Yeah? My question is like, huh what. 0:07:57.400 --> 0:07:59.560 That's the first step, right, is to be confused, and 0:07:59.560 --> 0:08:01.880 then the second second step is to try to weave 0:08:01.920 --> 0:08:04.560 together a few bits of information and say, like, what 0:08:04.720 --> 0:08:07.320 parts specifically of the story don't make sense to me? 0:08:07.360 --> 0:08:09.400 Which parts do I need to understand better in order 0:08:09.400 --> 0:08:11.920 to have something in my mind that does work where 0:08:11.920 --> 0:08:14.560 the understanding does click. Because what I'd love is for 0:08:14.600 --> 0:08:16.680 people to have that moment where they're like, oh, I 0:08:16.760 --> 0:08:19.200 get it. This connects with that thing, and now it 0:08:19.360 --> 0:08:21.920 kind of makes sense to me, even though it's pretty 0:08:21.920 --> 0:08:23.640 weird and a lot of people out there are trying 0:08:23.640 --> 0:08:26.040 to do that, and many of them have run into 0:08:26.080 --> 0:08:29.280 the same stumbling block. And so today on the podcast, 0:08:29.320 --> 0:08:32.040 I want to answer a very common question that we 0:08:32.160 --> 0:08:41.800 get about black holes. Can gravity escape a black hole? 0:08:42.360 --> 0:08:44.960 I feel like I'm going crossside just trying to think 0:08:44.960 --> 0:08:45.840 about this question. 0:08:46.000 --> 0:08:48.520 I love this question because it reveals that people are 0:08:48.520 --> 0:08:51.880 being physicists. They're thinking about what a black hole is, 0:08:51.960 --> 0:08:54.840 how everything gets sucked into it, how nothing can escape. 0:08:55.200 --> 0:08:57.280 But they're also thinking, hold on a second, we feel 0:08:57.320 --> 0:09:00.840 gravity from a black hole. How's that possible? How can 0:09:00.880 --> 0:09:04.120 the gravity get out of the black hole? And right there, 0:09:04.360 --> 0:09:07.240 that's being a physicist, that's saying I was told this, 0:09:07.520 --> 0:09:09.760 But there's also that how do I make this and 0:09:09.800 --> 0:09:12.080 that work together? How do I put it together in 0:09:12.200 --> 0:09:14.480 my head to tell a story that makes sense. 0:09:15.080 --> 0:09:18.280 So what you're asking us to do is to listen 0:09:18.320 --> 0:09:21.240 to what you're saying and then go hold on, Daniel, 0:09:21.679 --> 0:09:24.640 you just said this. Are you lying to us? 0:09:27.120 --> 0:09:30.960 Everybody's doing their best, nobody's lying to anybody. But in 0:09:31.000 --> 0:09:33.560 the end, learning is a very personal experience, and an 0:09:33.559 --> 0:09:35.920 explanation that makes sense to one person doesn't work for 0:09:36.160 --> 0:09:38.440 somebody else. So that's why in this podcast, we often 0:09:38.480 --> 0:09:41.839 try two or three different analogies or explanations or ways 0:09:41.880 --> 0:09:44.920 to communicate an idea, and that's what you're here for, Katie, 0:09:44.960 --> 0:09:47.760 also to make sure that what I'm saying makes sense 0:09:47.920 --> 0:09:48.280 to you. 0:09:48.480 --> 0:09:51.719 My method of learning is definitely food based metaphors. I'm 0:09:51.800 --> 0:09:52.840 very food motivated. 0:09:53.120 --> 0:09:54.760 Is your appetite something like a black hole? 0:09:55.000 --> 0:09:57.480 It's something like that. Yeah, one could say I'm a 0:09:57.480 --> 0:10:00.439 bit of a black hole, but yeah, I mean, it's 0:10:00.480 --> 0:10:04.200 a very interesting question because it's hard for me to 0:10:04.280 --> 0:10:07.520 think of gravity as like a thing, right, like a 0:10:07.559 --> 0:10:12.920 thing that can escape something. Gravity to me is like, well, 0:10:13.040 --> 0:10:17.280 I don't even know exactly what gravity is. I remember 0:10:17.360 --> 0:10:21.960 from previous podcasts the things that you've taught me about gravity, 0:10:22.000 --> 0:10:26.120 but it is so hard for me to conceptualize gravity 0:10:26.200 --> 0:10:28.360 because it feels like it is like a kind of 0:10:28.440 --> 0:10:33.760 thing woven into like the universe, that is not necessarily like, 0:10:34.360 --> 0:10:37.920 you know, a physical matter thing, but it has everything 0:10:37.960 --> 0:10:41.000 to do with physics. So it's it's a very confusing 0:10:41.600 --> 0:10:45.240 kind of concept. And then you add to that the 0:10:45.320 --> 0:10:49.600 black hole, which itself is quite confusing, and so this 0:10:49.760 --> 0:10:52.800 question feels no pun intended, but very heavy. 0:10:52.960 --> 0:10:55.200 Exactly well, you put your finger on. Really the concepts 0:10:55.200 --> 0:10:57.560 here that are entertangled. You know, what do we know 0:10:57.640 --> 0:11:02.319 about gravity? How is gravitation information communicated? Like? How is 0:11:02.360 --> 0:11:05.439 it that you are feeling gravity from the sun even 0:11:05.480 --> 0:11:07.840 though the Sun is super dup far away and not 0:11:08.080 --> 0:11:12.040 touching you. Does that count as information you're getting from 0:11:12.040 --> 0:11:14.920 the sun? What kind of stuff is captured by a 0:11:14.960 --> 0:11:17.600 black hole? And what isn't captured by a black hole? 0:11:17.720 --> 0:11:20.679 Is that information? How does that all work? You know? 0:11:20.720 --> 0:11:23.160 Do you need to pass little particles back and forth 0:11:23.200 --> 0:11:25.679 in order to feel gravity or what. So. One of 0:11:25.720 --> 0:11:27.920 the reasons I love this question is that it combines 0:11:28.040 --> 0:11:32.240 all of these fun, interesting, fascinating and difficult questions together, 0:11:32.320 --> 0:11:34.040 and going through it I think is really helpful to 0:11:34.080 --> 0:11:36.400 clarify for people what a black hole is and what 0:11:36.440 --> 0:11:39.520 a black hole isn't and how physicists think about it. 0:11:39.559 --> 0:11:42.079 But before we hear about how physicists think about it, 0:11:42.120 --> 0:11:44.679 I wanted to hear what everybody else out there was 0:11:44.720 --> 0:11:46.960 thinking about it. So we have a nice little team 0:11:46.960 --> 0:11:50.360 of volunteers who answer questions for the podcast before we 0:11:50.400 --> 0:11:53.560 dig into them. Helps me understand what people are thinking 0:11:53.800 --> 0:11:57.199 and helps you calibrate your thoughts against the other listeners. 0:11:57.520 --> 0:12:00.560 So thanks very much to everybody who participates. You want 0:12:00.559 --> 0:12:03.160 to jump in for a future episode, we would love, love, 0:12:03.600 --> 0:12:06.600 love to have your voice on the team. Right to me. 0:12:06.679 --> 0:12:11.160 Two questions at Danielandjorge dot com, So think about it 0:12:11.160 --> 0:12:13.720 for a moment before you hear these answers. Do you 0:12:13.760 --> 0:12:17.800 think gravity can escape a black hole? Here's what people 0:12:17.840 --> 0:12:18.400 had to say. 0:12:18.720 --> 0:12:21.840 I feel like, since it kind of depends on the 0:12:21.840 --> 0:12:26.120 mass of an object, it just moves with that object, 0:12:26.480 --> 0:12:29.880 so it would be dependent on the object being able 0:12:29.880 --> 0:12:30.920 to escape the black hole. 0:12:31.280 --> 0:12:34.000 It really matters what we think of as gravity. If 0:12:34.000 --> 0:12:38.000 you think it's gravito gravitons, like with the quantum theories, 0:12:38.760 --> 0:12:41.760 then I guess it escapes. I think, yeah, gravity can 0:12:41.960 --> 0:12:45.280 escape black holes, otherwise I wouldn't be stucking everything in. 0:12:45.559 --> 0:12:50.640 Gravity is a distortion in space time, So I would 0:12:50.720 --> 0:12:56.400 say that gravity itself cannot escape. Actually it's being created 0:12:56.440 --> 0:12:59.600 by the black hole itself. But if we are talking 0:12:59.600 --> 0:13:03.640 about gravitational waves, I believe it can escape a black 0:13:03.640 --> 0:13:07.559 hole if it is outside the event horizon. I even 0:13:07.640 --> 0:13:12.760 think that gravitational waves were discovered by watching collisions of 0:13:12.880 --> 0:13:16.839 black holes and stuff like that. So my guess is yes, 0:13:17.360 --> 0:13:21.360 under the right circumstances, gravitational waves should be able to 0:13:21.440 --> 0:13:22.280 escape a black hole. 0:13:22.880 --> 0:13:24.800 I can't even wrap my head around the question. 0:13:25.200 --> 0:13:27.160 I didn't even know those words could go together. 0:13:27.880 --> 0:13:31.040 I guess it can escape, because isn't that kind of 0:13:31.040 --> 0:13:32.560 what gravitational waves are. 0:13:33.160 --> 0:13:38.679 I love all of the references to gravitational waves because 0:13:38.800 --> 0:13:40.560 we did an episode on that recently. 0:13:40.880 --> 0:13:44.040 We did absolutely an episode on gravitational waves, and that's 0:13:44.080 --> 0:13:47.120 going to turn out to be crucial in understanding what 0:13:47.280 --> 0:13:51.559 is gravitational information and what is not, what is trapped 0:13:51.600 --> 0:13:54.400 within the black hole, and what is not trapped within 0:13:54.440 --> 0:13:57.840 the black hole. Absolutely, so, gravitational waves are a really 0:13:57.840 --> 0:13:59.400 helpful way to think about that. 0:13:59.559 --> 0:14:05.640 I get the root of this question. Is this seeming paradox, right, 0:14:05.880 --> 0:14:08.520 the idea that nothing can escape from a black hole, 0:14:09.000 --> 0:14:12.600 and yet we do know about black holes, We get 0:14:12.720 --> 0:14:16.959 information about black holes, But how can we receive any 0:14:17.000 --> 0:14:20.960 information about a black hole if it is something that 0:14:21.080 --> 0:14:24.480 is all consuming and nothing can escape it? 0:14:24.840 --> 0:14:28.720 Boom Exactly, Adie, you were officially a physicist because you 0:14:28.800 --> 0:14:32.520 are putting together those two ideas that you understand and saying, 0:14:32.560 --> 0:14:34.760 how can these two things be compatible. How can we 0:14:34.760 --> 0:14:39.280 weave them together into a singular understanding of black holes? 0:14:39.320 --> 0:14:40.760 And what it's going to take is a little bit 0:14:40.800 --> 0:14:43.080 of a refinement of the idea of what a black 0:14:43.080 --> 0:14:45.800 hole is and what a black hole isn't to make 0:14:45.840 --> 0:14:47.440 this all work together in your head. 0:14:47.520 --> 0:14:49.680 Well, now that you have proclaimed I am a physicist, 0:14:49.760 --> 0:14:52.120 I am just gonna waltz into like the hard drung 0:14:52.240 --> 0:14:56.880 collider and be like physicists coming through. Let's smash some particles. 0:14:56.960 --> 0:14:57.320 Guys. 0:14:57.680 --> 0:15:00.440 That's right, you have officially a PhD in podcast physics 0:15:00.800 --> 0:15:03.360 from the Daniel and Jorge University. 0:15:04.080 --> 0:15:07.080 Worth its weight in gold. So yes, I would love 0:15:07.200 --> 0:15:12.160 some clarification on what a black hole is. You know, 0:15:12.320 --> 0:15:17.000 I know it's a big, sucky thing. I understand that 0:15:17.400 --> 0:15:23.320 it has something to do with just an incredible density 0:15:24.120 --> 0:15:30.760 of matter, and furthermore that gravity is very much a 0:15:30.800 --> 0:15:33.560 defining characteristic of a black hole. 0:15:33.760 --> 0:15:35.400 Then let's make sure we know what it is we're 0:15:35.440 --> 0:15:39.080 talking about. So a black hole is a region of 0:15:39.240 --> 0:15:43.920 space where the curvature of space is so powerful that 0:15:44.000 --> 0:15:48.800 nothing that's inside that region can escape to outside, and 0:15:48.840 --> 0:15:51.480 that region is defined by this threshold, not really like 0:15:51.520 --> 0:15:54.200 a barrier, not like a physical wall. There's not got 0:15:54.200 --> 0:15:57.360 a dotted line somebody draws in space that says beyond 0:15:57.400 --> 0:16:00.680 this point, if you pass, then you will ever escape. 0:16:00.720 --> 0:16:03.200 You'll be trapped within that region forever. 0:16:03.440 --> 0:16:06.600 Someone's got to put a sign up, a warning, you know, warning, 0:16:06.680 --> 0:16:10.360 do not pass this region. You will be spaghettified into 0:16:10.400 --> 0:16:13.160 a black hole. But I mean, when you say space 0:16:13.280 --> 0:16:16.240 is curved, you know, this is definitely a concept I've 0:16:16.280 --> 0:16:19.760 been introduced to before, but it's still something that I 0:16:19.840 --> 0:16:24.160 struggle to understand because when I think of curvature, right, 0:16:24.200 --> 0:16:27.160 I think of like a physical object that is warped, 0:16:27.800 --> 0:16:30.160 or like say, I think of fabric and I feel like, 0:16:30.480 --> 0:16:33.000 you know, I think of pulling down on the fabric 0:16:33.040 --> 0:16:35.160 and then they're being sort of a curvature and things 0:16:35.200 --> 0:16:39.000 falling into it, and then that's how I think about gravity. 0:16:39.520 --> 0:16:43.520 But I believe that is not really exactly the correct 0:16:44.040 --> 0:16:46.800 understanding of it. Space is not like a piece of 0:16:46.800 --> 0:16:50.040 fabric that you pull on and things fall into that 0:16:50.080 --> 0:16:54.080 sort of like dip. But what exactly does curvature mean 0:16:54.280 --> 0:16:55.320 in terms of space? 0:16:55.760 --> 0:16:58.040 Yeah? Good, It's important to think about in terms of 0:16:58.080 --> 0:17:00.840 curvature because I think a lot of people think about 0:17:00.840 --> 0:17:03.440 black holes in sort of a Newtonian way, where gravity 0:17:03.520 --> 0:17:06.040 is a force and the force of gravity is so 0:17:06.040 --> 0:17:09.120 strong that it's sucking stuff up right, And that cartoon 0:17:09.160 --> 0:17:11.680 model of a black hole breaks down very quickly because 0:17:11.680 --> 0:17:14.160 it can't explain to you, like, well, why does light 0:17:14.240 --> 0:17:16.520 get trapped by a black hole? Why can't a photon 0:17:16.920 --> 0:17:20.879 not leave a black hole? Because the Newtonian picture of gravity, 0:17:21.160 --> 0:17:24.159 gravity is a force between objects with mass, and photons 0:17:24.200 --> 0:17:26.480 have no mass, so they should feel no gravity, and 0:17:26.520 --> 0:17:28.919 so they should be able to escape. In order to 0:17:28.960 --> 0:17:31.760 have an understanding of what black holes are, you really 0:17:31.800 --> 0:17:35.600 have to move your thinking of gravity is from this 0:17:35.760 --> 0:17:40.760 idea of forces between objects with mass to an apparent 0:17:40.880 --> 0:17:43.399 force something that actually results from, as you say, the 0:17:43.480 --> 0:17:46.679 curvature of space itself. So what do we mean by 0:17:46.720 --> 0:17:49.560 the curvature of space itself? Means that space has a 0:17:49.720 --> 0:17:53.400 characteristic to it that's invisible, something you can't see when 0:17:53.480 --> 0:17:55.639 you look at it. You look at some chunk of 0:17:55.680 --> 0:17:58.800 space and you can't tell whether or not it's curved. 0:17:59.000 --> 0:18:01.919 But if you shine a laser beam through it, it 0:18:01.960 --> 0:18:04.320 will either go in a straight line or it will not. 0:18:04.520 --> 0:18:06.440 It will curve, it will bend. This way, or will 0:18:06.480 --> 0:18:10.320 bend that way, because space has this additional, weird property 0:18:10.359 --> 0:18:13.119 that Newton never imagined. And on the smaller scale, what 0:18:13.200 --> 0:18:16.880 it means is that the relative distances between two points 0:18:16.960 --> 0:18:19.800 can get changed. So when we say that like space 0:18:19.880 --> 0:18:22.439 is curved or space is bent, it means that you 0:18:22.440 --> 0:18:25.440 can take two locations in space, you can effectively make 0:18:25.440 --> 0:18:28.160 them closer together, or you can make them further apart. 0:18:28.359 --> 0:18:30.879 And what that does is it changes the path that 0:18:30.960 --> 0:18:33.400 light will take through that space, because light always takes 0:18:33.400 --> 0:18:37.199 the shortest path between two points. Now you're changing what 0:18:37.280 --> 0:18:40.240 the relative distances are between two points, and so you're 0:18:40.320 --> 0:18:43.280 changing the path that light will take. But I think 0:18:43.320 --> 0:18:45.119 the most intuitive way to think about it is that 0:18:45.160 --> 0:18:47.840 like space has this additional bit to it, this characteristic 0:18:48.280 --> 0:18:50.679 so when a photon is passing through it, basically the 0:18:50.720 --> 0:18:54.160 space tells the photon where to go, doesn't just pass 0:18:54.240 --> 0:18:54.960 through blindly. 0:18:55.200 --> 0:18:58.800 It's so interesting because I think the reason it's such 0:18:58.800 --> 0:19:03.719 a difficult concept is that as humans we deal with 0:19:03.720 --> 0:19:09.520 physics all the time, but we can observe Newtonian physics. 0:19:09.560 --> 0:19:13.040 We can observe that type of physics, So it's I 0:19:13.040 --> 0:19:16.400 think easier to think of particles when even like particles 0:19:16.400 --> 0:19:19.239 that you can't observe with the naked eye when they 0:19:19.240 --> 0:19:22.879 are behaving according to forces, because we can on the 0:19:22.920 --> 0:19:26.280 more macro level observe forces. You can see a ball 0:19:26.359 --> 0:19:29.160 knocking into a ball, you can see something fall down 0:19:29.200 --> 0:19:32.399 a hole. But with gravity, even though yes, it's true, 0:19:32.480 --> 0:19:35.080 we can observe gravity. We see it all the time, 0:19:35.240 --> 0:19:37.280 right because you know, you jump up, you fall down. 0:19:37.760 --> 0:19:40.280 It's one of the main problems that we have to 0:19:40.400 --> 0:19:44.119 encounter as a physical being in the world, and yet 0:19:44.200 --> 0:19:49.720 we can't actually see or kind of experience this like 0:19:50.119 --> 0:19:55.200 secret framework behind gravity, which is that what you described, 0:19:55.280 --> 0:19:58.959 like the relative distance between two things like becoming shorter 0:19:59.520 --> 0:20:04.119 and like the actual like you know, space like reality 0:20:04.240 --> 0:20:07.439 sort of warping in a way. It's like so easy 0:20:07.480 --> 0:20:10.359 to fall into that trap of thinking of it in 0:20:10.480 --> 0:20:13.280 terms of the type of physics that we see and 0:20:13.320 --> 0:20:13.920 we observe. 0:20:14.160 --> 0:20:18.280 It's confusing precisely because it's invisible. You can't see this 0:20:18.359 --> 0:20:21.199 curvature of space. You can only see its effect, and 0:20:21.240 --> 0:20:24.159 the effect of the curvature of space looks in almost 0:20:24.240 --> 0:20:27.280 every case as if there was a force there. It 0:20:27.359 --> 0:20:30.760 looks like there is this force we call gravity that's 0:20:30.800 --> 0:20:34.119 pulling on things, when really things are just following the 0:20:34.160 --> 0:20:37.720 curvature of space. The shape of space itself is changing 0:20:37.760 --> 0:20:41.200 the direction in which things move. And if you can't 0:20:41.280 --> 0:20:43.600 see space doing it, it's like a bunch of stage 0:20:43.600 --> 0:20:47.000 hands wearing black nudging stuff. Then you imagine that there's 0:20:47.000 --> 0:20:49.240 a force there. And so that's why we call gravity 0:20:49.320 --> 0:20:51.639 and a parent force. It's not an actual force the 0:20:51.680 --> 0:20:54.800 way like electromagnetism is, or the weak force or the 0:20:54.840 --> 0:20:58.240 strong force. It's just the effect of the invisible curvature 0:20:58.400 --> 0:20:59.080 of space. 0:20:59.480 --> 0:21:02.840 So I hop down from let's say a safe height 0:21:03.440 --> 0:21:07.119 and land on the ground. I am not really getting 0:21:07.480 --> 0:21:11.400 sucked into the ground, because this is an effect of gravity, right, 0:21:11.440 --> 0:21:15.840 The gravity of Earth is affecting me, and so I'm 0:21:15.880 --> 0:21:18.920 not really getting sucked to the ground, but I am 0:21:19.520 --> 0:21:23.640 like sort of just following where space is curving. 0:21:24.000 --> 0:21:27.000 Yeah, that's a great example. Let's walk through it in 0:21:27.040 --> 0:21:30.240 the sort of Newtonian intuitive picture, and then let's move 0:21:30.280 --> 0:21:33.360 over to the Einstein space curvature picture. You'll find that 0:21:33.440 --> 0:21:36.320 it's a very different story about exactly the same thing. 0:21:36.920 --> 0:21:39.199 So in the Newtonian way of thinking, where gravity is 0:21:39.200 --> 0:21:42.040 a force, you are standing on a chair, and you 0:21:42.119 --> 0:21:44.240 imagine that there's a force of gravity pulling you down, 0:21:44.440 --> 0:21:46.120 and there's a force of the chair pulling you up, 0:21:46.160 --> 0:21:48.480 and when you stand on the chair, all forces are balanced, 0:21:48.480 --> 0:21:51.000 so you're not going anywhere. You jump off the chair 0:21:51.080 --> 0:21:52.960