WEBVTT - Daniel Whiteson on Space Itself 0:00:03.040 --> 0:00:05.360 Welcome to Scoot to Blow Your Mind production of My 0:00:05.480 --> 0:00:14.600 Heart Radio. Hey you welcome to Stuff to Blow Your Mind. 0:00:14.640 --> 0:00:17.400 My name is Robert Lamb and I'm Joe McCormick. And 0:00:17.480 --> 0:00:20.280 today we have got a special treat for you. Returning 0:00:20.360 --> 0:00:24.360 champion previous guests to the show, Daniel Whiteson of Daniel 0:00:24.400 --> 0:00:27.600 and Jorge Explain the Universe. We are so privileged to 0:00:27.640 --> 0:00:30.400 have Daniel join us again today. Daniel, say hi and 0:00:30.560 --> 0:00:33.960 introduce yourself. For anybody who wasn't around last time, Hi guys, 0:00:34.000 --> 0:00:37.519 thanks so much for having me on. Great to be back. Um. 0:00:37.520 --> 0:00:41.320 I'm Daniel Whitson. I'm a professor of particle physics at 0:00:41.520 --> 0:00:44.839 u c Irvine down here in southern California, and I'm 0:00:44.840 --> 0:00:47.879 also the co host of the podcast Daniel and Jorge 0:00:47.920 --> 0:00:51.120 Explain the Universe, a podcast with my good friend and 0:00:51.159 --> 0:00:54.440 collaborator Jorge cham in which we talk all about the 0:00:54.560 --> 0:00:57.400 craziness of the universe. We try to answer questions, We 0:00:57.440 --> 0:00:59.760 try to share the wonder and the mystery of the 0:00:59.800 --> 0:01:02.480 uni verse in a way that makes it accessible and 0:01:02.520 --> 0:01:05.080 hopefully a little bit fun. Well, we really appreciate you 0:01:05.160 --> 0:01:08.280 joining us today, Daniel. So I wanted to invite you 0:01:08.319 --> 0:01:11.800 onto stuff to blow your mind today to talk about space. 0:01:11.959 --> 0:01:14.880 This is actually a subject I've I've wanted to tackle 0:01:14.920 --> 0:01:18.200 on the show for a while with uh, the unifying 0:01:18.280 --> 0:01:21.840 question of what is space? Why is there such a 0:01:21.920 --> 0:01:25.000 thing as the distance between the Earth and the Sun, 0:01:25.280 --> 0:01:28.800 or between an atomic nucleus and the electron that orbits it. 0:01:29.480 --> 0:01:31.720 Because I think a lot of the time when we 0:01:31.840 --> 0:01:36.240 think about physical reality, we just immediately look past space 0:01:36.720 --> 0:01:39.560 to the things that occupy it. We we assume space 0:01:39.600 --> 0:01:42.480 as a kind of given, a de facto canvas on 0:01:42.520 --> 0:01:45.160 which physics can be realized. But I wanted to think 0:01:45.160 --> 0:01:48.400 about space itself. What is it? How does it exist? 0:01:48.480 --> 0:01:50.920 Do we know anything about where it comes from and 0:01:51.320 --> 0:01:54.040 where it's going? So maybe the easiest way to start 0:01:54.080 --> 0:01:56.600 off today would be to to get as simple as 0:01:56.640 --> 0:01:59.840 we can so in simplest terms in a sentence, if 0:01:59.840 --> 0:02:03.680 you could do it, how would a physicist define space? 0:02:05.360 --> 0:02:08.079 While all of space in one sentence? That is a 0:02:08.120 --> 0:02:11.360 pretty tall order, you know, I have to say, to 0:02:11.400 --> 0:02:13.240 be honest, I'd have to say, we really have no 0:02:13.400 --> 0:02:16.760 idea what space is. I mean, I think it's wonderful 0:02:17.120 --> 0:02:20.480 that you're asking this question. It's the kind of question 0:02:20.560 --> 0:02:23.400 that it takes like a sort of maturity of science 0:02:23.400 --> 0:02:27.400 and philosophy to even understand why the question is interesting 0:02:27.600 --> 0:02:31.000 and important. You know. It's like it's like we're have 0:02:31.120 --> 0:02:35.120 been fish scientists for a thousand years swimming through this fluid, 0:02:35.520 --> 0:02:40.160 and then only recently have realized that it's it's something fascinating, 0:02:40.200 --> 0:02:42.960 something to study, something that has property, something can do 0:02:43.120 --> 0:02:46.120 weird things. And so it's a it's a deep and 0:02:46.160 --> 0:02:48.720 important question, you know. And and just to digress a 0:02:48.760 --> 0:02:51.640 tiny bit more like it makes me wonder how many 0:02:51.760 --> 0:02:55.560 other crazy basic questions we aren't even asking because we 0:02:55.600 --> 0:02:58.560 don't realize how rich the topic is, you know. So 0:02:58.600 --> 0:03:00.680 I feel sort of privilege that we're at this moment 0:03:00.720 --> 0:03:03.800 in science when we can ask this question what is 0:03:03.880 --> 0:03:07.919 space and understand that it is an important question? Alright, 0:03:07.960 --> 0:03:11.959 So I totally dodged your question there, But I could 0:03:11.960 --> 0:03:15.240 try to give a one sentence answer if if you'd like, sure, 0:03:15.280 --> 0:03:17.600 we'll start simple and then and then we'll get more 0:03:17.639 --> 0:03:20.800 into the nuances here. All right, Well, a simple answer 0:03:20.840 --> 0:03:25.480 to what is space? Is that? Oh man? I mean 0:03:25.520 --> 0:03:29.000 I could try to maybe impossible, um, I'd say the 0:03:29.040 --> 0:03:33.079 simplest description I could give for what space is is 0:03:33.680 --> 0:03:38.840 something which has various properties. We've discovered it can contain 0:03:38.960 --> 0:03:43.640 quantum fields, it can expand, and it has relationships to 0:03:43.760 --> 0:03:46.560 other parts of space. And so that's more a description 0:03:46.600 --> 0:03:50.200 of like what we've what we've observed about space. It's 0:03:50.240 --> 0:03:53.080 not really an inherent understanding of what it is because 0:03:53.120 --> 0:03:56.240 we don't have that understanding. Well, maybe this brings me 0:03:56.360 --> 0:03:58.880 to a question I wanted to ask later on. But 0:04:00.080 --> 0:04:02.320 if there is no good answer to this, it can 0:04:02.360 --> 0:04:04.280 help ground us as we go forward. So I wanted 0:04:04.280 --> 0:04:06.960 to ask, is there such a thing as even a 0:04:07.080 --> 0:04:13.520 hypothetical physics without space? Does all physics assume space? And 0:04:13.600 --> 0:04:17.520 can we imagine, say a possible world that exists but 0:04:17.720 --> 0:04:21.520 does not contain space, or is that just inconceivable? Now? 0:04:21.640 --> 0:04:24.280 I think that all physics that we do assume space, 0:04:24.360 --> 0:04:26.760 Like all of our modern theories, the standard model and 0:04:26.839 --> 0:04:30.719 quantum field theory, they all operate in some space. And 0:04:30.760 --> 0:04:33.120 there are different kinds of theories that we have, and 0:04:33.200 --> 0:04:36.040 some of those make different assumptions for what that space is. 0:04:36.520 --> 0:04:39.600 Like quantum field theory, you write down with the spaces 0:04:39.600 --> 0:04:42.919 in advance. You say I'm gonna assume space. You know 0:04:43.080 --> 0:04:45.920 is three dimensions and extents in all in all these directions, 0:04:46.120 --> 0:04:47.840 and then I'm going to talk about the fields that 0:04:47.880 --> 0:04:52.040 are in that space. Other theories like general relativity. Space 0:04:52.120 --> 0:04:54.039 is a part of what you're sort of trying to 0:04:54.080 --> 0:04:56.960 get at. It's not like the backdrop. It's the thing 0:04:57.000 --> 0:04:59.960 you solve for. You say, if I have this configuration, 0:05:00.040 --> 0:05:03.000 then what does the space look like? But they all 0:05:03.040 --> 0:05:07.840 assume space. I mean space gives you a relationship between stuff, right, 0:05:07.960 --> 0:05:10.039 tells you this is here and this is not here. 0:05:10.680 --> 0:05:12.440 And in the end, all of our theories are trying 0:05:12.440 --> 0:05:14.520 to understand the world we live in, and everything we 0:05:14.560 --> 0:05:17.599 live in has space. So it's pretty hard to grapple 0:05:17.680 --> 0:05:22.680 with a non spatial theories or non spatial physics. So yeah, 0:05:22.720 --> 0:05:25.560 I would say that we need space, okay, But so 0:05:25.600 --> 0:05:27.520 if we could come at it from the exact opposite 0:05:27.520 --> 0:05:30.320 angle you think, you you couldn't really have a physics 0:05:30.400 --> 0:05:34.600 without space. Could you have a universe full of space 0:05:34.760 --> 0:05:38.480 with no matter of energy in it? Could space exist 0:05:38.600 --> 0:05:43.080 without any contents? Could space exists without any contents in it? Yeah? 0:05:43.080 --> 0:05:46.520 That is an awesome question, and it's fascinating because we 0:05:46.600 --> 0:05:50.080 have two theories of physics right now, quantum mechanics and 0:05:50.200 --> 0:05:55.080 general relativity, and they're both awesome achievements, staggering insights into 0:05:55.120 --> 0:05:57.600 the way the universe works, and they give different answers 0:05:57.640 --> 0:06:02.520 to this question. Right, So general activity um is Einstein's theory. 0:06:02.839 --> 0:06:04.680 And he has a bunch of equations. Let's say, what 0:06:04.720 --> 0:06:06.920 the universe look like depending what you put in it, 0:06:07.240 --> 0:06:09.279 and he has and one of the and it's really 0:06:09.320 --> 0:06:11.640 hard to solve, like, there's very few ways you can 0:06:11.680 --> 0:06:14.520 actually solve these equations. One of the very few ways 0:06:14.520 --> 0:06:16.760 you actually can get an answer out is what they 0:06:16.800 --> 0:06:19.839 call the vacuum solution, like to say, assume there's nothing, 0:06:20.400 --> 0:06:22.279 then what does the universe look like? If there's nothing 0:06:22.320 --> 0:06:25.880 in it? All? Right? Einstein can solve that problem quantum 0:06:25.920 --> 0:06:28.799 field theory. Though, quantum field theory says, hold on a second, 0:06:29.279 --> 0:06:32.279 um space is filled with all these quantum fields and 0:06:32.400 --> 0:06:34.680 particles and matter and all the stuff that you make 0:06:34.720 --> 0:06:38.200 me and you are just like excited states of these fields. 0:06:38.320 --> 0:06:41.360 So when you look at an electron, it's not a particle, 0:06:41.400 --> 0:06:44.160 it's not a wave. It's a little ripple in some 0:06:44.320 --> 0:06:47.760 field which is not in space. It's part of space. 0:06:48.320 --> 0:06:50.680 So if all these fields. You have the electron field, 0:06:50.720 --> 0:06:53.760 the electromagnetic field, all the fields associated with each of 0:06:53.800 --> 0:06:55.880 the forces. As lots of them. We can talk about 0:06:55.920 --> 0:06:59.400 them later if you'd like. But some of them never 0:06:59.520 --> 0:07:03.640 relax completely. Some of them are always have some energy 0:07:03.680 --> 0:07:06.760 in them, for example, the Higgs field. The Higgs field 0:07:06.839 --> 0:07:09.240 is in every part of space, and it's always got 0:07:09.279 --> 0:07:12.760 some built intention to it, and that means that there's 0:07:12.840 --> 0:07:16.040 energy in every part of space. So quantum field theory says, no, 0:07:16.160 --> 0:07:18.840 you can't have space without some energy in it. There's 0:07:18.840 --> 0:07:22.720 some inherent energy to space, where the general relativity says, 0:07:23.040 --> 0:07:25.920 I could totally imagine it. And we don't know which 0:07:26.000 --> 0:07:29.160 theory is the fundamental, true theory of the universe. If 0:07:29.200 --> 0:07:31.840 either one, we can't seem to make them play together 0:07:31.960 --> 0:07:34.680 very well. And so this question really goes to the 0:07:34.720 --> 0:07:37.880 heart of the nature of reality itself. It's fascinating. It's 0:07:37.880 --> 0:07:40.760 the kind of thing that in five years physicists will 0:07:40.760 --> 0:07:42.760 know the answer to and look back at us and 0:07:42.760 --> 0:07:46.080 be like, oh, man, those people didn't understand anything about 0:07:46.120 --> 0:07:48.000 the nature of the universe they were living in, right, 0:07:48.120 --> 0:07:50.440 What a bunch of cave men and cave women like 0:07:50.680 --> 0:07:53.280 they were subjignary misses. So I love that idea about 0:07:53.360 --> 0:07:55.840 quantum field theory. And if I understand this right, you're 0:07:55.840 --> 0:07:59.600 saying that under the assumptions of quantum field theory, you 0:07:59.600 --> 0:08:01.560 could have a big block of space, and even if 0:08:01.560 --> 0:08:04.040 you were able to clear everything out of it, clear 0:08:04.040 --> 0:08:06.600 out all the hydrogen particles, clear out all the dust, 0:08:06.680 --> 0:08:10.560 so there's no matter left in it, you'd still you 0:08:10.640 --> 0:08:14.400 still really wouldn't have an empty void. Is that correct? 0:08:14.800 --> 0:08:18.360 That's right. Every unit of space comes with energy built 0:08:18.400 --> 0:08:21.600 in it comes from the factory with energy already in it, 0:08:22.200 --> 0:08:26.240 and um and and lots of those fields cannot cannot relax. 0:08:26.240 --> 0:08:28.440 The Higgs field is one example, but many of these 0:08:28.480 --> 0:08:31.480 fields cannot relax all the way down to zero. And 0:08:31.520 --> 0:08:34.600 so it's impossible, according to these quantum theories, to have 0:08:34.720 --> 0:08:37.760 space with no energy density in it at all. And 0:08:37.800 --> 0:08:40.000 that means and that's stuff, right, All stuff is is 0:08:40.040 --> 0:08:42.120 some kind of energy, like the matter that makes it 0:08:42.200 --> 0:08:45.080 me and you. That's just a form of energy. So 0:08:45.160 --> 0:08:47.360 to say that this space has energy in it really 0:08:47.400 --> 0:08:50.600 means it's not empty. So what you're describing space as 0:08:51.120 --> 0:08:53.840 really goes against a lot of our intuitions, where you know, 0:08:54.080 --> 0:08:56.719 I think the standard understanding of empty space what's out 0:08:56.760 --> 0:08:58.800 there beyond Earth, you know, even if you could clear 0:08:58.800 --> 0:09:01.800 all the hydrogen and dust and everything out of it, 0:09:01.840 --> 0:09:05.440 is that it's just this empty relationship between two points. 0:09:05.480 --> 0:09:08.600 But you mentioned, of course, the the idea that there, 0:09:08.600 --> 0:09:11.679 you know, quantum fields that can be excited and can 0:09:11.679 --> 0:09:14.360 give birth to particles and stuff. Well, I might be 0:09:14.360 --> 0:09:17.520 putting words in your mouth. There is that correct though. Yeah, okay, 0:09:18.120 --> 0:09:21.160 but earlier you mentioned also that it has other properties, 0:09:21.200 --> 0:09:23.920 So it sounds like you're saying space really is a thing. 0:09:24.120 --> 0:09:28.199 It's almost like a substance of a kind. Yes, space 0:09:28.320 --> 0:09:32.160 is a goo. Right. We first imagine space sort of 0:09:32.200 --> 0:09:34.480 as a place to hold our ideas, right where like 0:09:34.920 --> 0:09:37.880 maybe when you think space and you think a deep space, 0:09:37.920 --> 0:09:41.360 you imagine some like glowing x y z axes that 0:09:41.480 --> 0:09:44.080 used to like the backdrop on which maybe your calculations 0:09:44.120 --> 0:09:47.400 take place or your spaceship flies through or whatever sort of. 0:09:47.840 --> 0:09:51.920 But they're like mental metrics we use to understand where 0:09:51.960 --> 0:09:54.720 things are. That sort of the initial idea of space. 0:09:55.040 --> 0:09:57.120 But then it turns out the space can do things 0:09:57.360 --> 0:10:01.080 that are inconsistent with that, right, Like space can ripple 0:10:01.679 --> 0:10:05.280 we've seen gravitational waves. When black holes orbit each other 0:10:05.320 --> 0:10:08.400 and eventually collide or other things happen, they create these 0:10:08.480 --> 0:10:13.040 ripples in space itself. These ripples, they're space getting stretched 0:10:13.240 --> 0:10:17.520 and space getting contracted, right, squeezing and shrinking and then 0:10:17.559 --> 0:10:20.200 expanding again, and very very very small, which is why 0:10:20.240 --> 0:10:22.719 they were hard to discover. But yes, we've discovered that 0:10:22.760 --> 0:10:27.120 space can do things. So it can ripple, it can expand, right, 0:10:27.160 --> 0:10:30.480 We've talked about the expansion of the universe, the universe 0:10:30.640 --> 0:10:34.640 expanding its first moments, and it's continuing to expand. In addition, 0:10:34.720 --> 0:10:38.000 space can bend. Maybe the most familiar example is understanding 0:10:38.040 --> 0:10:43.240 gravity as distortions in space by having mass nearby and 0:10:43.240 --> 0:10:46.520 and so space can do all these things that nothingness 0:10:46.559 --> 0:10:49.360 cannot do, that a backdrop cannot do. You can't just 0:10:49.400 --> 0:10:52.400 think of spaces like the theater of the universe. It's 0:10:52.440 --> 0:10:55.760 a weird dynamical thing in itself. Yeah, I think in 0:10:55.800 --> 0:10:58.240 general our listeners are going to be more familiar with 0:10:58.240 --> 0:11:01.120 the idea that space can can bend in accordance with 0:11:01.160 --> 0:11:03.640 general relativity. There's a big object, you know, and that 0:11:03.800 --> 0:11:07.600 creates curvature, and in spacetime it's a little bit harder 0:11:07.600 --> 0:11:09.960 to picture exactly what's happening with the first thing you 0:11:10.000 --> 0:11:12.720 mentioned with the ripples through spacetime. So that's something that 0:11:12.720 --> 0:11:16.520 would be like, that's like how we detected gravitational waves, right, 0:11:16.679 --> 0:11:20.320 is that correct? Um? So what what exactly is happening 0:11:20.360 --> 0:11:23.880 when a ripple goes through space? Like? How do how 0:11:23.880 --> 0:11:27.439 do you measure that? What? What is that in the moment? Right? Well, 0:11:27.840 --> 0:11:31.040 you know, a ripple through space is information propagating through 0:11:31.040 --> 0:11:34.040 the gravitational field. Something that's very important that came out 0:11:34.080 --> 0:11:36.840 of general relativity that we didn't have with Newton's gravity 0:11:37.160 --> 0:11:41.160 is the concept that information takes time to move gravitationally. 0:11:41.520 --> 0:11:45.120 Like if the Sun disappeared, would we feel the Sun's 0:11:45.200 --> 0:11:49.320 gravity instantly disappear or would it take a moment? Turns 0:11:49.320 --> 0:11:52.720 out Newton says it would go away instantly. Einstein says, no, 0:11:52.920 --> 0:11:55.720 you wouldn't even notice for eight minutes because the gravity 0:11:55.800 --> 0:11:58.840 from the Sun would take The information about the Sun 0:11:58.880 --> 0:12:01.840 being gone would take eight minutes to get here gravitationally, 0:12:02.679 --> 0:12:06.839 And so that's propagation of information. And so gravitational wave 0:12:07.200 --> 0:12:10.400 is a special form of that. Say you're familiar with 0:12:10.720 --> 0:12:14.079 the concept of like putting a mass and that deforms space. 0:12:14.200 --> 0:12:16.160 We'll imagine you put a mass in space, and then 0:12:16.200 --> 0:12:17.680 you take it away, and you put it in space, 0:12:17.720 --> 0:12:19.240 and you take it away, and you put in space 0:12:19.280 --> 0:12:21.480 and you take it away. What's going to happen, Well, 0:12:21.520 --> 0:12:23.040 you know it's not gonna be very pleasant for the 0:12:23.040 --> 0:12:25.800 occupants of your space. They're gonna get jerked around, right, 0:12:25.840 --> 0:12:28.360 It's back and forth and back and forth. And that's 0:12:28.360 --> 0:12:31.079 sort of a more dramatic version of what happens when 0:12:31.120 --> 0:12:35.520 two black holes orbit each other. Is they're creating ripples 0:12:35.600 --> 0:12:39.840 in this gravitational field, and you feel those as stretching 0:12:39.840 --> 0:12:42.680 and squeezing of space itself. And we measured that here 0:12:42.679 --> 0:12:47.040 on Earth by having really long rods essentially and watching 0:12:47.080 --> 0:12:50.760 them shrink and expand shrink and expand. With those north 0:12:50.880 --> 0:12:52.800 there would be like lasers that you would use to 0:12:52.960 --> 0:12:56.320 measure that. Yeah, the practical way you measure a very 0:12:56.400 --> 0:12:59.079 small change in the length of a long rod is 0:12:59.120 --> 0:13:01.199 that you don't actually of the physical rods. That was 0:13:01.240 --> 0:13:03.320 the first thing they tried, actually did that here, you see, 0:13:03.320 --> 0:13:05.960 I Jo Webber did that, and it's because he had 0:13:06.000 --> 0:13:08.200 no idea like maybe this is easy to spot right, 0:13:08.320 --> 0:13:10.240 let's just build a big block of metal and see 0:13:10.240 --> 0:13:12.520 if its shrinks and expands. I was gonna say, what 0:13:12.600 --> 0:13:14.679 was it made out of? Yeah, it's just a big 0:13:14.800 --> 0:13:18.480 cylinder of metal. Um. But nowadays they're miles long and 0:13:18.600 --> 0:13:21.199 their laser and they use lasers to measure the length 0:13:21.280 --> 0:13:25.400 between two isolated mirrors. And I think that the biggest 0:13:25.440 --> 0:13:30.280 misconception people have about space being bent by mass is 0:13:30.280 --> 0:13:32.960 that they're used to this rubber sheet analogy where you 0:13:33.000 --> 0:13:34.800 have like a big rubber sheet and you put a 0:13:34.840 --> 0:13:37.439 bowling ball in it and it bends space. And the 0:13:37.440 --> 0:13:39.959 bowling ball is supposed to represent the sun and the 0:13:40.040 --> 0:13:43.439 rubber sheet is supposed to represent space. And that's helpful 0:13:43.520 --> 0:13:45.400 up to a point because it gets you to think 0:13:45.440 --> 0:13:48.880 about space being bent instead of flat. But it's also 0:13:48.920 --> 0:13:52.240 I think confusing. And the way it's confusing is that 0:13:52.400 --> 0:13:54.880 it's bending in some sort of third dimension, right, and 0:13:54.920 --> 0:13:58.360 that analogy space the universe is two D and you 0:13:58.440 --> 0:14:00.840 put some object in it and it bends in some 0:14:01.000 --> 0:14:04.680 third dimension. But our space it's three D. First of all, 0:14:05.040 --> 0:14:06.840 when you put a mass in it, it doesn't bend 0:14:06.920 --> 0:14:10.280 in some fourth dimension. It's not like our space is 0:14:10.320 --> 0:14:12.960 embedded in some higher dimensional space and then it gets 0:14:13.000 --> 0:14:16.600 bent in fourth dimension. It's an intrinsic bending, not an 0:14:16.640 --> 0:14:19.440 extrinsic It's not like there's somebody out there with a 0:14:19.520 --> 0:14:22.200 true set of rulers in four D space and they're 0:14:22.280 --> 0:14:26.640 noticing our space being bent. It's an intrinsic bending, which 0:14:26.680 --> 0:14:30.640 means it just changes the relationship between points in space. 0:14:31.240 --> 0:14:33.960 Right it says, Okay, now that space, that bit of 0:14:34.000 --> 0:14:36.000 space is closer and this bit of a space is 0:14:36.040 --> 0:14:39.000 further away. Wow. So I've never thought of it that way. So, 0:14:39.160 --> 0:14:41.600 so you're saying that the gravitational influence of a large 0:14:41.640 --> 0:14:45.840 object like a star is in some literal sense shortening 0:14:45.920 --> 0:14:49.160 the distance between points of space as you get closer 0:14:49.200 --> 0:14:54.000 to it. Absolutely. You know, massless particles like photons travel 0:14:54.360 --> 0:14:58.440 not in straight lines. They travel along geodesics, which means 0:14:58.480 --> 0:15:01.840 the shortest path through curved space. Now out in the 0:15:01.840 --> 0:15:04.640 middle of nowhere, there's no mass anywhere that happens to 0:15:04.640 --> 0:15:06.560 be a straight line. That's why it seems like photons 0:15:06.600 --> 0:15:10.080 travel straight. But photons can also be bent by the sun. 0:15:10.160 --> 0:15:13.000 How does that happen? Photons have no mass, right, Well, 0:15:13.040 --> 0:15:15.840 the the Sun is changing the shape of space, so 0:15:15.920 --> 0:15:18.400 that the shortest path from A to B is no 0:15:18.520 --> 0:15:22.000 longer what we would consider a straight line. It's a geodesic. 0:15:22.040 --> 0:15:25.960 It's the shortest path. And so general relativity and mass 0:15:26.080 --> 0:15:30.680 changes the relationship between space between here and there, and um, 0:15:30.720 --> 0:15:32.800 that's what we maybe you hear people talk about like 0:15:32.840 --> 0:15:36.040 the spacetime metric that relates like how bits of space 0:15:36.080 --> 0:15:39.280 are connected. So this is sort of the biggest conceptual 0:15:39.320 --> 0:15:41.880 leap to make from the rubber sheet analogy to our 0:15:41.920 --> 0:15:45.840 actual three D space, which is that it's an intrinsic bending. 0:15:45.840 --> 0:15:48.800 It's a relationship between points in space, and that's what 0:15:48.840 --> 0:15:51.840 a gravitational wave is doing. Also, it's a ripple in 0:15:51.880 --> 0:15:54.840 this metric as it passes through space, and it's saying, oh, 0:15:54.880 --> 0:15:57.400 these things are now closer together, now the further apart. 0:15:57.960 --> 0:16:01.120 Like you can change the distance, but weeen two things 0:16:01.160 --> 0:16:05.640 without those things moving relative to each other, right, because 0:16:05.680 --> 0:16:09.000 you change the relative distances. Well, it almost makes me 0:16:09.040 --> 0:16:12.560 think in terms of how this is communicated to non experts, 0:16:12.560 --> 0:16:15.160 that would maybe be better to not use terms like 0:16:15.240 --> 0:16:18.320 bending of space and maybe more like compressing or squeezing 0:16:18.320 --> 0:16:21.800 of space. Yeah, but space can also be expanded, right, 0:16:21.880 --> 0:16:24.160 like what we're seeing in the universe right now is 0:16:24.200 --> 0:16:27.200 that space is expanding, which is crazy. It's like something 0:16:27.200 --> 0:16:31.320 out there is manufacturing new units of space all the time. 0:16:31.320 --> 0:16:35.040 It's filling the universe with new space. Like that's that's 0:16:35.040 --> 0:16:36.720 the hardest thing for me to get my mind around. 0:16:36.760 --> 0:16:38.760 It's like where this new space is coming from, what 0:16:38.840 --> 0:16:41.000 it means to make new space? And are you making 0:16:41.160 --> 0:16:44.520 units of new space? There's space continuous and smooth and like, man, 0:16:44.560 --> 0:16:46.800 there's so many questions. Oh well, I want to talk 0:16:46.800 --> 0:16:48.440 about that. Maybe we should take a quick break and 0:16:48.440 --> 0:16:50.920 then when we come back we can explore the expansion 0:16:50.920 --> 0:16:56.840 of space. Sounds good than all? Right, we're back. We're 0:16:56.840 --> 0:17:01.000 talking with Daniel Whitson about space, the nature of space. 0:17:01.400 --> 0:17:03.720 That's right. So before we went to the break, Daniel, 0:17:03.800 --> 0:17:06.399 you just introduced the idea of the expansion of space. 0:17:06.400 --> 0:17:08.760 As we've we've been talking about the properties of space 0:17:08.800 --> 0:17:12.199 as a as a thing and not just an emptiness. Uh. 0:17:12.240 --> 0:17:14.200 And so of course we know one of the things 0:17:14.240 --> 0:17:18.159 that space is doing is that it's expanding. Uh. I 0:17:18.200 --> 0:17:20.480 think we all know now that the universe as a 0:17:20.520 --> 0:17:24.080 whole is expanding and maybe expanding at an accelerating rate. 0:17:24.119 --> 0:17:26.199 If I've got that writing, comment on that in a second. 0:17:26.760 --> 0:17:31.040 What exactly does it mean for space to expand? Because 0:17:31.520 --> 0:17:34.360 I think from an intuitive level, people might think, well, 0:17:34.800 --> 0:17:38.320 I don't notice space expanding, Like I don't notice it 0:17:38.359 --> 0:17:42.320 doesn't seem like the space in between the molecules in 0:17:42.359 --> 0:17:46.000 my body is expanding. So so is space in general 0:17:46.080 --> 0:17:50.320 expanding or is it just say, the distance between galaxies 0:17:50.400 --> 0:17:53.600 is expanding. What form does that expansion take? Yeah, it's 0:17:53.600 --> 0:17:56.040 a great question. I love the intuition there. You know. 0:17:56.119 --> 0:17:58.280 The idea is like this thing is supposed to be 0:17:58.359 --> 0:18:01.160 happening everywhere in the universe. Kind of sort of reconcile 0:18:01.280 --> 0:18:03.960 that with my experience. Can I see that happening around me? 0:18:04.240 --> 0:18:06.240 And you know, like a few hundred years ago, that 0:18:06.280 --> 0:18:08.800 was a big conceptual leap to say like the rules 0:18:08.800 --> 0:18:11.320 of the universe should also being applied here. Um. So 0:18:11.520 --> 0:18:14.200 it's a great question. And and the short answer is 0:18:14.240 --> 0:18:17.479 that space is expanding everywhere, Like every unit of space 0:18:17.680 --> 0:18:20.120 is the same. It's homogeneous as far as we understand. 0:18:20.280 --> 0:18:22.760 There's no difference to this chunk of space and a 0:18:22.840 --> 0:18:26.520 chunk of space out there in the deepest voids between galaxies. 0:18:26.560 --> 0:18:28.040 They're all the same from the point of view of 0:18:28.080 --> 0:18:30.880 the universe, and they're all expanding, which means they're all 0:18:30.920 --> 0:18:34.600 creating new space. But that's not the only thing happening, right. 0:18:35.119 --> 0:18:38.280 You are made of a mesh of atoms that are 0:18:38.320 --> 0:18:41.879 held together with pretty strong bonds, and this expansion of 0:18:41.920 --> 0:18:45.959 space is dramatic, but per unit of space, it's pretty small. 0:18:46.320 --> 0:18:48.200 Like there's not a whole lot of space being made 0:18:48.240 --> 0:18:52.280 between me and this microphone, for example. It adds up 0:18:52.400 --> 0:18:54.800 when you get to like cosmic scales between me and 0:18:54.800 --> 0:18:57.240 the galaxy, because there's a lot of space between us, 0:18:57.800 --> 0:19:00.320 but here on the small scale, it's not very powerful, 0:19:00.400 --> 0:19:02.840 so the bonds in my body are strong enough to 0:19:02.880 --> 0:19:05.879 hold me together. The same thing said for you know 0:19:05.920 --> 0:19:08.320 the reason why you're staying on Earth. You know, Earth 0:19:08.440 --> 0:19:10.880 is holding you down because if it's gravity, that's enough 0:19:10.920 --> 0:19:14.200 to overcome this expansion of space, and Earth is bound 0:19:14.200 --> 0:19:17.520 gravitationally to the Sun for the same reason. The space 0:19:17.560 --> 0:19:21.040 between us and the Sun is expanding, but the gravity 0:19:21.119 --> 0:19:23.840 the Sun holds us there. It's like if you were 0:19:24.160 --> 0:19:26.840 sliding away from somebody on an ice sheet, but they 0:19:26.840 --> 0:19:28.920 had a rope around you, and so they were keeping 0:19:28.920 --> 0:19:31.800 you at a fixed distance. Okay, so there are forces 0:19:31.880 --> 0:19:35.160 within our bodies, holding our bodies together that are counteracting 0:19:35.200 --> 0:19:39.000 that expansive force. But I'm trying to imagine what exact 0:19:39.080 --> 0:19:42.480 form does that take. So does that mean that the say, 0:19:42.520 --> 0:19:45.360 the bonds between the molecules and our body holding them 0:19:45.359 --> 0:19:49.359 together actually prevent the space from expanding there so it 0:19:49.400 --> 0:19:52.040 doesn't expand, or does the space somehow kind of roll 0:19:52.160 --> 0:19:56.240 out beyond us without affecting our you know, our bodies 0:19:56.280 --> 0:19:59.240 as it does. So you can't stop the expansion of space, 0:19:59.440 --> 0:20:02.200 but you can't and keep your constant distance. If those 0:20:02.240 --> 0:20:04.800 bonds were deleted, then all the items would sort of 0:20:04.880 --> 0:20:07.479 drift further and further apart, but instead you have these 0:20:07.520 --> 0:20:09.720 bonds holding them together. And so it's more of that 0:20:09.840 --> 0:20:12.359 the answers the latter, that space sort of rolls out 0:20:12.400 --> 0:20:16.960 past you. So space is emanating from us at all times. Yeah, 0:20:17.000 --> 0:20:19.480 it's sort of like we're in a pool of space 0:20:19.520 --> 0:20:22.240 that's expanding larger and larger, and we're a smaller and 0:20:22.240 --> 0:20:25.119 smaller dot inside of it. So as a result, you know, 0:20:25.119 --> 0:20:27.800 the universe is getting getting more and more dilute, like 0:20:27.920 --> 0:20:32.000 the matter energy density of the universe decreases with time 0:20:32.080 --> 0:20:34.480 because there's no more stuff being created, but there is 0:20:34.520 --> 0:20:38.440 more space being created all the time. And so that's 0:20:38.440 --> 0:20:41.200 really like the way to think about the whole expansion 0:20:41.200 --> 0:20:43.560 of the universe since the Big Bangs, that the universe 0:20:43.560 --> 0:20:46.520 didn't start out small. It started out dense. It was 0:20:46.560 --> 0:20:49.720 like compressed and hot and nasty and wet, and then 0:20:49.840 --> 0:20:52.760 the Big Bang is just this rapid dilution of space 0:20:52.880 --> 0:20:56.440 into something much more sparse, and then that's just continued. 0:20:56.640 --> 0:20:58.919 The universe has just gotten more and more cold and 0:20:58.960 --> 0:21:01.960 dilute and spread out as new spaces being created and 0:21:02.000 --> 0:21:05.480 these little chunks of matter desperately clinging to each other 0:21:05.720 --> 0:21:09.000 to avoid being totally isolated. And I think there's another 0:21:09.000 --> 0:21:10.760 part of your question which I think is fascinating, is 0:21:10.800 --> 0:21:13.520 like at what scale does that take over? Like you 0:21:13.560 --> 0:21:16.639