WEBVTT - Is Energy Actually Conserved? 0:00:08.600 --> 0:00:12.079 Hey, Daniel, I noticed something about physicists. I'm afraid to 0:00:12.119 --> 0:00:13.800 hear this. I feel like all of you like to 0:00:13.880 --> 0:00:16.119 blow things up. We do. Actually, that's what makes us 0:00:16.160 --> 0:00:18.760 so much fun at parties. I guess. I mean you'd 0:00:18.760 --> 0:00:21.599 like to blow up ideas. You know, you like to 0:00:21.640 --> 0:00:24.480 think things that people think are true and then prove 0:00:24.560 --> 0:00:27.560 that they're actually false. That's true. Actually you mean like 0:00:27.920 --> 0:00:30.200 the Earth being the center of the universe. Yeah, I 0:00:30.240 --> 0:00:32.159 like that. I like that idea, but it turns out 0:00:32.440 --> 0:00:34.479 it's false. Or you know that people thought that the 0:00:34.479 --> 0:00:37.240 world was nice and smooth, but actually it's quantized into 0:00:37.360 --> 0:00:40.320 little pixels called quantum physics. Al Right, So what do 0:00:40.320 --> 0:00:42.640 you think that means about physicists. I think it probably 0:00:42.680 --> 0:00:45.320 means that you like to disagree with the stabich ideas. 0:00:45.400 --> 0:00:48.960 You're basically just contrarians. No, we're not. See do you 0:00:49.040 --> 0:01:07.039 know fun at parties? Hi am or handmade cartoonists and 0:01:07.040 --> 0:01:10.040 the creator of PhD Comics. Hi. I'm Daniel. I'm a 0:01:10.080 --> 0:01:13.920 particle physicist, and I'm very positive about new ideas. Welcome 0:01:13.959 --> 0:01:16.480 to our podcast Daniel and Jorge Explain the Universe, a 0:01:16.560 --> 0:01:19.120 production of Our Heart Radio in which we consider all 0:01:19.160 --> 0:01:22.320 the crazy new ideas out there and all the old ideas. 0:01:22.520 --> 0:01:24.800 Which ones are real, which ones are made up, which 0:01:24.880 --> 0:01:27.480 ones are we still clueless about. We take you on 0:01:27.480 --> 0:01:30.240 a tour of all of them and explain them to you. Yeah, 0:01:30.280 --> 0:01:33.280 we like to explore the universe and talk about all 0:01:33.319 --> 0:01:35.360 of the things that are out there and this beautiful 0:01:35.400 --> 0:01:38.520 cosmos of ours, all the things that are true, and 0:01:38.640 --> 0:01:40.959 all the things that might be true. And part of 0:01:41.000 --> 0:01:44.920 the journey of physics and science in general is understanding 0:01:44.920 --> 0:01:48.320 the universe and questioning the things we thought were true, 0:01:48.640 --> 0:01:51.680 getting a deeper, more fundamental view of the way things 0:01:51.840 --> 0:01:55.600 actually work, which sometimes is really in contrast with the 0:01:55.640 --> 0:01:57.920 way we thought things work. Because there are a lot 0:01:57.960 --> 0:02:01.120 of ideas out there, right, Daniel. I mean they're ideas 0:02:01.160 --> 0:02:03.440 about how the world works, about why things are the 0:02:03.440 --> 0:02:06.680 way they are, and how people think that it all 0:02:06.720 --> 0:02:09.320 comes together. Yeah, And sometimes the first idea you have 0:02:09.440 --> 0:02:12.840 seems reasonable and sticks around for a long time, and 0:02:12.880 --> 0:02:16.000 then you notice small little problems with it, and when 0:02:16.040 --> 0:02:19.120 you pull on that thread, you reveal something really fascinating 0:02:19.360 --> 0:02:22.320 about the whole universe. Like people used to think, hey, there, 0:02:22.360 --> 0:02:25.480 Earth is flat. It certainly looks flat from here. But 0:02:25.520 --> 0:02:28.760 then it's sort of a mind exploding discovery to realize, Wow, 0:02:28.800 --> 0:02:32.400 we're actually living on the surface of a huge sphere. Yeah. 0:02:32.440 --> 0:02:34.560 So there are a lot of ideas out there, and 0:02:34.760 --> 0:02:37.120 I feel like you physicists like to reserve the right 0:02:37.200 --> 0:02:40.840 to change your mind. That's an important part of science, right, 0:02:41.120 --> 0:02:43.960 challenging the orthodoxy. It's one of the best things about 0:02:44.000 --> 0:02:47.480 science that sometimes we look at the very foundations of 0:02:47.480 --> 0:02:49.720 the ideas and we say, wait a second, is that 0:02:49.840 --> 0:02:52.360 really true? How do we actually know that? We've been 0:02:52.400 --> 0:02:55.720 thinking that for a long time, but is it possible 0:02:56.080 --> 0:02:58.160 that we were wrong. I think it's one of the 0:02:58.200 --> 0:03:00.720 deepest virtues of science. Yeah. And if like that's maybe 0:03:00.720 --> 0:03:04.560 your favorite part of science is proving your appears wrong 0:03:05.720 --> 0:03:08.639 on a personal level, yes, And for me it's actually 0:03:08.639 --> 0:03:11.560 the reason I got into science, because I'm really excited 0:03:11.600 --> 0:03:16.119 about those moments of intellectual revolution. I feel like, when 0:03:16.160 --> 0:03:18.480 you discover that the world is really different from the 0:03:18.520 --> 0:03:21.240 way we thought it was, we've pulled the wolf from 0:03:21.240 --> 0:03:24.079 our eyes. We've like peeled back a layer of reality. 0:03:24.120 --> 0:03:27.040 We've discovered some truth that was hidden to us. And 0:03:27.120 --> 0:03:30.640 what's more exciting in science than to have a moment 0:03:30.720 --> 0:03:33.560 of discovery like that a deep revelation, you know, not 0:03:33.639 --> 0:03:37.720 like slowly iterately building up increments of knowledge until you 0:03:37.720 --> 0:03:40.960 get there, like almost like a moment of revelation where 0:03:40.960 --> 0:03:43.760 you understand the universe differently somehow and you can never 0:03:43.840 --> 0:03:46.400 go back to seeing it the old way. Some people 0:03:46.440 --> 0:03:48.440 go for the Eureka moment. You like to go for 0:03:48.520 --> 0:03:52.840 the moment. That's what I'm in for. I'm in it 0:03:52.960 --> 0:03:55.760 for the scientific revolutions, for the Hans. You're in for 0:03:55.800 --> 0:03:58.280 the Hans I am. And there have been lots of 0:03:58.320 --> 0:04:00.840 moments in history where people have made to discoveries like this. 0:04:01.080 --> 0:04:03.680 They've pulled on one little string and then they've unraveled 0:04:03.840 --> 0:04:07.120 that very foundations of science, and so it's exciting to 0:04:07.160 --> 0:04:09.040 think that there might be more of those ahead of us. 0:04:09.320 --> 0:04:11.240 So it's exciting when a bunch of smart people's go, 0:04:11.760 --> 0:04:14.880 never mind, I thought there was flat, but actually it's 0:04:15.120 --> 0:04:18.400 a giant ball. Yeah, because it changes sometimes your whole 0:04:18.440 --> 0:04:21.560 relationship with the universe, you know, thinking that we live 0:04:21.600 --> 0:04:23.920 at the center of the universe everything revolves around us, 0:04:24.320 --> 0:04:27.599 to thinking we're just a tiny little speck of dust 0:04:27.640 --> 0:04:31.200 in an insignificant corner of the universe that really changes 0:04:31.240 --> 0:04:33.679 the way you feel about the universe and life itself 0:04:33.720 --> 0:04:36.360 and how you should live it. So, hey, this stuff 0:04:36.440 --> 0:04:39.240 is actually irrelevant for how people feel about themselves and 0:04:39.279 --> 0:04:42.640 their lives. Yeah. So science is all about challenging ideas, 0:04:42.680 --> 0:04:45.360 and so today on the program will be challenging a 0:04:45.480 --> 0:04:48.359 very core and fundamental idea and physics. I feel like 0:04:48.400 --> 0:04:50.760 this is a very important idea that a lot of 0:04:50.760 --> 0:04:53.440 people have kind of internalized about the universe, but that 0:04:53.680 --> 0:04:57.039 actually might not be so true. That's right. This is 0:04:57.080 --> 0:04:59.640 something pretty basic that if you ask folks on the street, 0:05:00.000 --> 0:05:02.520 it would be pretty confident was true. But it turns 0:05:02.520 --> 0:05:04.279 out we've learned a lot about the nature of the 0:05:04.360 --> 0:05:07.600 universe and it might actually not be quite so fundamental. 0:05:07.680 --> 0:05:15.039 So on the program will be asking the question is 0:05:15.200 --> 0:05:22.000 energy actually conserved? Now, Daniel, this sort of blew my mind. 0:05:22.080 --> 0:05:24.160 How can we even ask this question? What do you mean? 0:05:24.200 --> 0:05:27.960 Is energy always actually conserved? Yeah? That's why it's such 0:05:27.960 --> 0:05:30.840 a wonderful question because it makes you think, like, well, 0:05:31.120 --> 0:05:33.600 why would it be conserved? How do we actually know 0:05:33.720 --> 0:05:36.039 it's conserved? What would it be like to live in 0:05:36.080 --> 0:05:39.440 a universe where it's not conserved? That solve all of 0:05:39.440 --> 0:05:41.479 our energy problems. I feel like you just told me 0:05:41.520 --> 0:05:43.560 the world is not actually a ball. It's like a 0:05:43.600 --> 0:05:46.920 cube or something. We live on a donut and it's 0:05:47.000 --> 0:05:51.400 filled with energy. It's filled with sugar, energy and sprinkles. 0:05:51.800 --> 0:05:54.720 That's right. Just eat the glaze, man, eat the glaze. 0:05:55.839 --> 0:05:59.120 Then then my energy will not be conserved, just an 0:05:59.120 --> 0:06:02.120 increase or be turned into mass. Probably. I know. It's 0:06:02.160 --> 0:06:04.480 a bit mind blowing, and that's why I was especially 0:06:04.520 --> 0:06:06.840 eager to hear what folks on the internet had to 0:06:06.880 --> 0:06:09.160 say about this question. Yes, so it's usual Daniel went 0:06:09.200 --> 0:06:11.840 out there into the wilds of the web and ask 0:06:11.880 --> 0:06:16.240 people the question is energy always conserved? So thank you 0:06:16.279 --> 0:06:18.840 to these folks in advance who participated. And if you 0:06:18.880 --> 0:06:22.400 would like to answer tough physics questions with no preparation 0:06:22.520 --> 0:06:26.120 and have your answers broadcast thousands of people, please write 0:06:26.160 --> 0:06:28.800 to us two questions at Daniel and Jorge dot com. 0:06:28.960 --> 0:06:30.800 Think about it for a second. If someone ask you 0:06:31.040 --> 0:06:35.120 if energy is actually always conserved, what would you answer. 0:06:35.880 --> 0:06:37.919 Here's what people had to say. I always thought that 0:06:38.080 --> 0:06:41.679 was one of the fundamental laws, that energy and matter 0:06:41.839 --> 0:06:44.279 can't be created or destroyed, But the fact that you're 0:06:44.320 --> 0:06:47.919 asking me this question makes me think I'm wrong. Yes, 0:06:48.320 --> 0:06:51.119 I don't know about the energy that goes in into 0:06:51.160 --> 0:06:56.520 a black hole, but it's somewhere there. Yes, is one 0:06:56.560 --> 0:07:00.800 of the fundamental principles of the universe that energy is conserved. 0:07:01.480 --> 0:07:03.840 I know that it gets a little dicey when you're 0:07:03.839 --> 0:07:06.320 talking about black holes. Yes, it is, but I don't 0:07:06.480 --> 0:07:09.159 know if there's any special cases where it's not. Yes, 0:07:09.360 --> 0:07:13.360 energy always is conserved in some form, right, I think 0:07:13.520 --> 0:07:18.520 ultimately everything becomes heat. But if energy does not get conserved, 0:07:19.080 --> 0:07:21.440 where does it go? All right, not a lot of 0:07:21.480 --> 0:07:26.120 doubters here. Everyone just said yes, no confusion. I feel 0:07:26.160 --> 0:07:29.000 like nobody was confused about this. No, nobody was confused. 0:07:29.080 --> 0:07:31.400 I love the person who said the fact you're asking 0:07:31.440 --> 0:07:37.120 me this question makes me think I'm wrong, which is wonderful. Man, 0:07:37.240 --> 0:07:41.160 you totally make that person. You need a doubt because 0:07:41.200 --> 0:07:44.119 that's the process of science. We're like, we're sure that's true. 0:07:44.280 --> 0:07:47.280 Hold on a second, how are we sure? All of 0:07:47.320 --> 0:07:50.000 a sudden, I'm wondering, And then you've got to explore 0:07:50.040 --> 0:07:53.040 your own intellectual framework and wonder like, do you really 0:07:53.080 --> 0:07:56.480 know this or is it just something you've been assuming yeah. 0:07:56.600 --> 0:07:59.200 Especially I guess if a physicist approaches you on the 0:07:59.240 --> 0:08:01.640 street with my acrophone and says, do you think energy 0:08:01.720 --> 0:08:04.040 is always conserved? I feel like, you know that automatically 0:08:04.160 --> 0:08:06.840 makes you a little suspicious. Yeah. Actually, default answer to 0:08:06.880 --> 0:08:10.000 a random physicist asking you a question should be no, 0:08:10.120 --> 0:08:12.520 it should be I don't know, what do you think? 0:08:12.920 --> 0:08:15.120 And then you flipped do you want to participate in 0:08:15.120 --> 0:08:18.840 my experiment? Uh? No? Do you want to know the 0:08:18.840 --> 0:08:22.800 deep secrets of the universe? Not? Really? So this is 0:08:22.920 --> 0:08:24.760 I feel like this is a pretty mind blown question, 0:08:24.840 --> 0:08:26.960 just the idea of asking this question. I feel like 0:08:26.960 --> 0:08:30.960 the idea that energy is always conserved seems very basic 0:08:31.040 --> 0:08:34.800 to physics, and it seems pretty internalized by most of 0:08:34.840 --> 0:08:36.600 the public. Like I feel like, you know, it's like 0:08:36.679 --> 0:08:40.080 asking which way does gravity point? Or you know, it's 0:08:40.080 --> 0:08:42.840 space big people say yes. But there's a bit of 0:08:42.840 --> 0:08:45.280 a history here, right. It used to be that we 0:08:45.360 --> 0:08:48.880 thought energy was conserved and that mass was conserved. We 0:08:48.920 --> 0:08:51.720 would watch chemical reactions and we would notice that it 0:08:51.800 --> 0:08:55.240 was mostly a rearrangement of the atoms, like puzzle pieces 0:08:55.240 --> 0:08:58.400 moving from one place to another, and that no actual 0:08:58.480 --> 0:09:01.960 matter was destroyed or created, and so we had two principles, 0:09:02.000 --> 0:09:06.040 conservation of energy and conservation of mass. But then we 0:09:06.120 --> 0:09:09.840 learned conservation of mass not actually a thing, right, You 0:09:09.880 --> 0:09:13.120 can turn mass into other kinds of energy, and energy 0:09:13.160 --> 0:09:16.439 into mass. So then we generalized into a larger principle, 0:09:16.760 --> 0:09:20.160 conservation of energy, which includes mass as one of its forms. 0:09:20.360 --> 0:09:22.360 But that's a hint, right, that's a hint. That's something 0:09:22.360 --> 0:09:26.360 which seems fundamental, like the existence of matter doesn't necessarily 0:09:26.400 --> 0:09:29.160 have to be concerned. Now, this isn't just a sort 0:09:29.200 --> 0:09:31.600 of like a semantic thing, right, Like we're not saying 0:09:31.640 --> 0:09:35.480 that energy just transforms into mass and so it's not concerned. 0:09:35.480 --> 0:09:38.040 We're asking kind of the bigger question, like is mass 0:09:38.080 --> 0:09:40.800 and energy conserved? That's right now, we're asking the deep 0:09:40.840 --> 0:09:45.559 fundamental question. Is total energy concerned? When you include all forms, 0:09:45.600 --> 0:09:47.960 not just does it slip away into some other kind 0:09:47.960 --> 0:09:51.560 of energy, but energy itself summed up over everything, is 0:09:51.559 --> 0:09:55.560 it actually conserved? Yeah? And it turns out that the 0:09:55.640 --> 0:10:01.320 answer is no. How can it be? No, Daniel, The 0:10:01.400 --> 0:10:04.840 answer is no. He's just during my world, I feel 0:10:04.840 --> 0:10:09.000 like democracy died last night. And now physics, well, that's 0:10:09.000 --> 0:10:11.160 what we're here for. We are here to blow people's 0:10:11.200 --> 0:10:14.160 minds and pull back the veil and help them understand 0:10:14.240 --> 0:10:17.199 the way the world actually works. And so this is 0:10:17.280 --> 0:10:19.880 kind of mind boggling. But the lesson we're gonna learn 0:10:20.080 --> 0:10:23.880 is what's actually important about the universe, what's really fundamental? 0:10:23.960 --> 0:10:26.600 What do we actually know? What really should we be 0:10:26.679 --> 0:10:30.320 paying attention to? All Right, so I guess the short 0:10:30.360 --> 0:10:33.400 answer is no. Energy is not always conserved. That's right, 0:10:33.440 --> 0:10:36.160 And that's even in a closed system. Right, we talked 0:10:36.160 --> 0:10:39.080 about energy conservation. We're usually referring to a closed system 0:10:39.120 --> 0:10:41.560 because you know, if you have a single thing inside 0:10:41.559 --> 0:10:44.160 a larger system, sure it doesn't have to conserve energy, 0:10:44.240 --> 0:10:48.200 Like a battery inside your toy is losing energy, but 0:10:48.280 --> 0:10:50.080 you know that energy is going to other parts of 0:10:50.080 --> 0:10:52.599 the system. But we're talking about a closed system, or 0:10:52.679 --> 0:10:55.559 energy doesn't escape or doesn't enter, we're talking about the 0:10:55.559 --> 0:10:59.200 whole universe. Is energy conserved for the whole universe? And 0:10:59.320 --> 0:11:03.400 even for that, the answer, it turns out is no, Man, Daniel, 0:11:03.920 --> 0:11:06.240 not even for a closed system. I feel like one 0:11:06.240 --> 0:11:09.040 of those celebrities. I'm ready to throw down my microphone 0:11:09.080 --> 0:11:12.400 and walk away. Don't mic drop just yet. There are 0:11:12.480 --> 0:11:16.000 bigger revelations to come, I see their twists. All right, 0:11:16.040 --> 0:11:18.400 we'll step us through first, why do we think that 0:11:18.559 --> 0:11:21.480 energy was conserved? And then maybe we'll get into why 0:11:21.480 --> 0:11:24.120 it wasn't it's not conserved. Yeah, that's a great question. 0:11:24.160 --> 0:11:27.560 And essentially we thought that energy was conserved because mostly 0:11:27.640 --> 0:11:30.800 it is, and so we never noticed we never saw 0:11:30.840 --> 0:11:33.960 a counter example. And a lot of physics works this way. 0:11:34.000 --> 0:11:36.320 We see things happening in the world and we see 0:11:36.360 --> 0:11:39.000 them seeming to follow a rule, and so we just 0:11:39.040 --> 0:11:41.559 sort of like we positive, well, maybe this rule is true. 0:11:41.640 --> 0:11:45.600 Maybe this is fundamental. You know, electric charge is conserved, 0:11:45.720 --> 0:11:48.360 or you know F equals m A. We don't always 0:11:48.440 --> 0:11:50.800 have a reason for it. We don't always have like 0:11:50.840 --> 0:11:54.280 a first principles derivation for it, which is something we observe, 0:11:54.840 --> 0:11:58.240 we categorize, and then we elevate it to a status 0:11:58.320 --> 0:12:00.600 and if nobody ever sees it broken, we think, well 0:12:00.840 --> 0:12:03.200 that must be true. For some reason. We elevated to 0:12:03.240 --> 0:12:05.199 that like a law status. We think it's a law 0:12:05.240 --> 0:12:07.960 of the universe. Yeah, And this is the way science works, 0:12:08.040 --> 0:12:10.000 is that we come up with a rule, we test it, 0:12:10.040 --> 0:12:12.880 we check it, we explore it and lots of different ways, 0:12:12.920 --> 0:12:16.160 and if it survives experimental tests over and over and 0:12:16.200 --> 0:12:18.240 over again. We think, oh, it's probably true, and then 0:12:18.280 --> 0:12:21.880 we can sometimes dig deeper and figure out the reason why. 0:12:22.080 --> 0:12:26.760 We can sometimes later derive that law from deeper truths. 0:12:26.800 --> 0:12:29.480 But sometimes we can reveal that it was only ever 0:12:29.559 --> 0:12:34.679 approximately true. We haven't checked every possible scenario. That's impossible, right, 0:12:35.000 --> 0:12:37.559 and so people will find a place where, look, it 0:12:37.640 --> 0:12:40.640 turns out it's broken over here, it doesn't quite work 0:12:40.679 --> 0:12:43.760 over there. It was the same story with conservation of mass. 0:12:43.840 --> 0:12:47.040 If you're just doing basic chemistry, mass is mostly conserved. 0:12:47.320 --> 0:12:49.319 It's only when you get to like higher energies where 0:12:49.360 --> 0:12:53.640 you're destroying particles or colliding particles that you notice that 0:12:53.720 --> 0:12:57.120 it's broken. So a lot of these conservation rules are 0:12:57.240 --> 0:13:01.319 not exact. They're not like really true. They're almost true, 0:13:01.400 --> 0:13:04.080 or they're true and lots of circumstances and so we 0:13:04.160 --> 0:13:06.559 never notice. It's kind of like F equals m A. 0:13:06.679 --> 0:13:10.360 I feel like that feels really fundamental and intuitive because 0:13:10.360 --> 0:13:13.959 that's what dominates our everyday experience. But like if you 0:13:14.040 --> 0:13:17.520 push the physics of it to extreme situations, it doesn't work. 0:13:17.559 --> 0:13:20.200 It breaks, yeah, exactly. And the same is true for 0:13:20.280 --> 0:13:23.319 things about like time. You know, we've learned that not 0:13:23.440 --> 0:13:26.240 everybody has to agree on the order of events. We 0:13:26.240 --> 0:13:28.480 had a whole podcast about what happens when people are 0:13:28.559 --> 0:13:30.960 running a race and you look at it from different speeds, 0:13:31.360 --> 0:13:32.880 and these are the kind of things you don't notice 0:13:32.880 --> 0:13:35.680 in your everyday life. You don't approach the speed of light. 0:13:36.000 --> 0:13:38.320 And so we never tested things in those sort of 0:13:38.400 --> 0:13:41.880 high speed extremes until recently, and we noticed, whoops. Those 0:13:42.040 --> 0:13:44.640 rules we thought were deep and fundamental and true turned 0:13:44.640 --> 0:13:46.880 out to be a special case that are only valided 0:13:46.960 --> 0:13:51.240 certain situations, not fundamental truths about the universe. And physics 0:13:51.280 --> 0:13:54.760 is all about uncovering the fundamental truths about the universe, 0:13:55.200 --> 0:13:58.200 not just the special cases. And so that's why we 0:13:58.240 --> 0:14:01.360 thought energy was conserved because we've always seen it conserved 0:14:01.400 --> 0:14:04.680 and sort of made sense. Yeah, it's conserved in most 0:14:04.720 --> 0:14:07.280 situations that we're familiar with, right, Like, if you have 0:14:07.320 --> 0:14:10.400 a canister of gas or something, the energy in it 0:14:10.440 --> 0:14:14.480 is going to be mostly conserved, mostly conserved, are totally conserved, 0:14:14.480 --> 0:14:17.679 the energy is going to be almost exactly conserved. And 0:14:17.800 --> 0:14:20.720 thinking about when it's conserved and noticing when those rules 0:14:20.720 --> 0:14:23.440 are broken, it's going to teach us really something fundamental 0:14:23.480 --> 0:14:27.000 about the nature of space and symmetries and conservation laws 0:14:27.040 --> 0:14:31.600 in general. But fuel, for example, is mostly conserved. All right, 0:14:31.680 --> 0:14:35.560 let's get into some examples of when energy is not conserved, 0:14:35.720 --> 0:14:39.280 and let's get into why it's not being the good 0:14:39.280 --> 0:14:42.280 conservative we thought it was. But first let's take a 0:14:42.360 --> 0:14:57.600 quick break. All right, Daniel, we are blowing up people's 0:14:57.640 --> 0:15:01.720 brains here. Apparently energy is not concerned in this universe. 0:15:01.960 --> 0:15:04.160 That's right. It's not always the same, that's right. It's 0:15:04.200 --> 0:15:06.640 not always the same. The amount of energy in the 0:15:06.720 --> 0:15:09.680 universe can change. And this is the kind of thing 0:15:09.720 --> 0:15:12.600 I get email questions from listeners about all the time, 0:15:12.680 --> 0:15:14.880 because people who have been thinking to themselves about dark 0:15:15.000 --> 0:15:17.600 energy have come in their minds to what seems like 0:15:17.640 --> 0:15:22.160 a contradiction. Remember, dark energy is the expansion of the universe. 0:15:22.200 --> 0:15:25.080 It's not something we understand. It's not a law physics. 0:15:25.120 --> 0:15:27.840 It's just sort of the observation that the expansion of 0:15:27.880 --> 0:15:31.560 the universe is continuing and that it's speeding up, and 0:15:31.600 --> 0:15:33.880 we don't understand the mechanism of it. But there is 0:15:33.920 --> 0:15:36.720 something about dark energy that we do know, which is 0:15:36.760 --> 0:15:40.360 that it's constant in space. So it makes more space, 0:15:40.440 --> 0:15:43.760 and then that space has new dark energy. So every 0:15:43.840 --> 0:15:47.280 cubic meter of space, for example, has its own dark energy. 0:15:47.440 --> 0:15:50.160 And as the universe expands, you get more universe, you 0:15:50.240 --> 0:15:53.080 get more dark energy. So these listeners right in and 0:15:53.120 --> 0:15:55.720 they say, hold on a second, where does that energy 0:15:55.880 --> 0:15:59.960 come from? Does that mean that dark energy doesn't concern 0:16:00.040 --> 0:16:02.560 of energy? Right? Yeah, it's it's kind of very puzzling, 0:16:02.640 --> 0:16:04.960 right because you're telling me that the universe is expanding 0:16:05.080 --> 0:16:08.440 with more energy and acceleration, so it has to you know, 0:16:08.560 --> 0:16:12.040 be drawing energy from somewhere, but it's sort of coming 0:16:12.040 --> 0:16:14.880 out of nothingness, this dark energy. And so the answer 0:16:14.960 --> 0:16:17.560 to those listeners is that no, it doesn't have to 0:16:17.640 --> 0:16:21.880 come from somewhere. It violates the conservation of energy. As 0:16:21.920 --> 0:16:24.960 the universe expands, you get more space, and that space 0:16:25.040 --> 0:16:29.040 has new energy, and the energy in the universe increases. 0:16:29.480 --> 0:16:33.960 So as spacetime expands, the energy can go up. And 0:16:34.120 --> 0:16:36.560 where does that energy come from? It doesn't have to 0:16:36.680 --> 0:16:39.960 come from anywhere, because energy conservation is not actually a 0:16:40.000 --> 0:16:43.680 fundamental law of the universe. It's just something we never 0:16:43.720 --> 0:16:47.920 saw broken before. I feel like that throws everything to question. Now, Daniel, 0:16:47.960 --> 0:16:51.720 what do you mean, yes, right, Welcome to physics, questioning everything, 0:16:52.440 --> 0:16:54.320 even even the idea of asking questions. Why are you 0:16:54.320 --> 0:16:59.240 asking questions, Daniel, don't ask questions about that. That's a 0:16:59.360 --> 0:17:02.680 zone of a wild So is that the primary example 0:17:02.720 --> 0:17:05.840 of energy not being conserved is in space and in 0:17:05.880 --> 0:17:08.760 this idea of the universe expanding or is it more 0:17:09.600 --> 0:17:13.720 you know, kind of seeped into our everyday physics. It's 0:17:13.760 --> 0:17:16.920 not really steeped into our everyday physics. And the cases 0:17:16.960 --> 0:17:19.640 where energy is not conserved are really going to give 0:17:19.680 --> 0:17:22.520 us a clue as to why it's not conserved. And 0:17:22.600 --> 0:17:25.439 I can give you another example, which is also related 0:17:25.480 --> 0:17:29.680 to the expansion of space. As space expands, it turns 0:17:29.680 --> 0:17:32.560 out there's a way to lose energy. For example, a 0:17:32.560 --> 0:17:35.560 photon photon is flying through space, and we know that 0:17:35.600 --> 0:17:38.199 if a photon comes to you from far away, but 0:17:38.280 --> 0:17:41.080 that the space between you and the source expands in 0:17:41.119 --> 0:17:45.760 the meantime, that photon red shifts are red shifts associated 0:17:45.800 --> 0:17:48.840 with that source having a velocity. Like a police siren 0:17:48.880 --> 0:17:52.440 that's moving away from you, the wavelength of the sound 0:17:52.520 --> 0:17:55.080 is stretched, and the same is true for light from 0:17:55.200 --> 0:17:57.959 stars that are moving away from us. But there's another 0:17:58.080 --> 0:18:00.359 kind of red shift, which is just the expand engine 0:18:00.440 --> 0:18:03.120 of space between you and that light source. It will 0:18:03.200 --> 0:18:06.560 also stretch the photon and make it redder. Won't slow 0:18:06.560 --> 0:18:09.879 it down, it'll just shift its frequency. That will stretch it. 0:18:09.960 --> 0:18:12.639 That's right. Photons always move with the same speed, the 0:18:12.640 --> 0:18:15.000 speed of light, but they have different levels of energy 0:18:15.320 --> 0:18:18.240 which correspond to their wavelength, which is equivalent to their 0:18:18.280 --> 0:18:20.959 color or their frequency. It's all the same thing. And 0:18:21.040 --> 0:18:24.679 so when you make a photon redder, effectively you're taking 0:18:24.680 --> 0:18:27.800 away its energy. It's losing energy. So in that case, 0:18:27.920 --> 0:18:33.119 the expansion of space disappears energy from a photon. What 0:18:33.720 --> 0:18:35.880 could it all be the same energy, Daniel? Could dark 0:18:35.960 --> 0:18:40.080 energy be the energy of photons getting redder. That wouldn't 0:18:40.080 --> 0:18:41.760 add up to like a factor of tend to one. 0:18:42.400 --> 0:18:45.560 There's so much more dark energy than the energy that's 0:18:45.600 --> 0:18:48.959 being lost by photons being red shifted. But we see this. 0:18:49.000 --> 0:18:50.639 It's a real thing. It's just kind of like a 0:18:50.720 --> 0:18:55.359 dark red energy. I like that phrase, dark red energy. 0:18:55.400 --> 0:18:57.399 That should be a thing. There should be a physics. 0:18:57.440 --> 0:19:00.600 Should be the title your other sci fi novel, dark 0:19:00.720 --> 0:19:03.560 red energy. All right, I'll do it just starting from 0:19:03.560 --> 0:19:05.280 the title. I can just write the novel from there. 0:19:05.840 --> 0:19:09.280 But yeah, So here are two examples, space expanding meaning 0:19:09.520 --> 0:19:14.240 extra energy is created, or space expanding meaning energy is 0:19:14.280 --> 0:19:17.280 lost by photons. And the thing that those two examples 0:19:17.280 --> 0:19:20.680 have in common, of course, is that space is not static. 0:19:20.720 --> 0:19:24.280 In those cases, space is expanding its dynamic and that's 0:19:24.320 --> 0:19:26.720 the clue. I see. Yeah, that's kind of um, it's 0:19:26.760 --> 0:19:29.720 like breaking a law by breaking another law, kind of 0:19:29.960 --> 0:19:32.359 because I feel like, you know, we thought space didn't 0:19:32.440 --> 0:19:35.399 expand we thought space was fixed before, but then we 0:19:35.480 --> 0:19:38.720 learned that space is like malleble and bends and stretches. Yeah, 0:19:38.800 --> 0:19:42.600 and just like thinking that Galilean transformations Newtonian physics always 0:19:42.600 --> 0:19:44.920 worked because we had always seen it work because we'd 0:19:44.920 --> 0:19:48.000 only ever checked low speeds and then discovering that they 0:19:48.040 --> 0:19:50.360 break when you get too high speeds. This is an 0:19:50.359 --> 0:19:53.880 example of something we never thought was possible, expanding space, 0:19:54.400 --> 0:19:57.800 and when it happens, it challenges some pretty basic stuff 0:19:57.840 --> 0:20:00.560 that we thought was true, but turns out only have 0:20:00.680 --> 0:20:04.000 been true in the special scenario we ever tested it in, 0:20:04.320 --> 0:20:07.439 which is fundamentally static space. Right, Well, then step us 0:20:07.480 --> 0:20:12.439 three here, Daniel, why is an energy conserved when space expands? Well, 0:20:12.480 --> 0:20:13.919 I think the best way to tackle that is to 0:20:13.920 --> 0:20:17.040 think about, like, well, why should we expect it to 0:20:17.080 --> 0:20:19.600 be conserved? Did we have a reason to think it 0:20:19.600 --> 0:20:23.399 should be conserved. Is there some fundamental theoretical idea that 0:20:23.440 --> 0:20:25.639 tells us it should be conserved, or is it just 0:20:25.720 --> 0:20:28.960 something we observed and thought was true. And for that, 0:20:29.040 --> 0:20:30.679 I think it's good to think about, like, what do 0:20:30.720 --> 0:20:34.280 we mean exactly about conserved? Right to be kind of 0:20:34.280 --> 0:20:37.600 specific about it, And by that we mean like, here's 0:20:37.640 --> 0:20:40.520 something we calculate, Like you can measure the amount of 0:20:40.600 --> 0:20:42.879 energy and something and then you can let it do 0:20:42.960 --> 0:20:45.080 its thing. You know, maybe you turn on the engine 0:20:45.080 --> 0:20:47.800 of your car or whatever, and then you calculate it again, 0:20:48.080 --> 0:20:50.199 and you notice you get the same answer. So as 0:20:50.200 --> 0:20:53.080 you said before, like you burn the fuel in your car, 0:20:53.400 --> 0:20:55.800 but now you've added speed to your car, so energy 0:20:55.880 --> 0:20:58.159 is moved from one part of the system to another. 0:20:58.520 --> 0:21:00.840 And we've noticed so far that if you add up 0:21:00.840 --> 0:21:03.000 all the energy before and you add of the energy after, 0:21:03.280 --> 0:21:06.359 you get the same thing. And so we call that conserved, 0:21:06.480 --> 0:21:09.080 right that there's a symmetry there that says it hasn't 0:21:09.160 --> 0:21:11.920 changed the accounty. You can account for every cent of 0:21:11.960 --> 0:21:14.760 that energy. That's right, And so people have long wondered, like, 0:21:15.040 --> 0:21:18.040 why are things conserved at all? What does it mean 0:21:18.119 --> 0:21:20.359 about the universe? Because it's the kind of thing that 0:21:20.400 --> 0:21:23.680 makes a physicist scratch his or her head. It's like, well, 0:21:23.720 --> 0:21:25.920 if this thing is concerned, does that mean that it's 0:21:25.960 --> 0:21:28.640 a deep truth in the universe, that it's an important quantity. 0:21:28.680 --> 0:21:32.000