WEBVTT - Does quantum mechanics conserve energy? 0:00:08.560 --> 0:00:12.200 Hey, Jorge, are you worried about energy conservation? 0:00:12.880 --> 0:00:13.080 Uh? 0:00:13.200 --> 0:00:15.040 Not worried, but I try to do as much of 0:00:15.080 --> 0:00:15.880 it as possible. 0:00:16.000 --> 0:00:16.160 Oh. 0:00:16.280 --> 0:00:18.960 Is that because you're very environmentally responsible? 0:00:19.360 --> 0:00:22.120 Nuts? Because I try to do this little exercise as possible. 0:00:23.960 --> 0:00:24.919 You're such an adult. 0:00:25.079 --> 0:00:27.000 Hey, I'm doing it for the planet, not just for me. 0:00:28.160 --> 0:00:30.760 Well on behalf of planet Earth. We're all very grateful 0:00:30.920 --> 0:00:32.159 for your lazy attitude. 0:00:32.280 --> 0:00:36.320 Oh thanks. My body is also very grateful, although maybe 0:00:36.320 --> 0:00:53.920 not in the long term. Hi am Jorgem, a cartoonist 0:00:53.920 --> 0:00:56.600 and the author of Oliver's Great Big Universe. 0:00:56.880 --> 0:01:00.320 Hi. I'm Daniel. I'm a high energy particle physicist, but 0:01:00.360 --> 0:01:06.000 I don't often feel very high energy or high. There 0:01:06.000 --> 0:01:08.000 were times in my life when that was more true. 0:01:07.800 --> 0:01:12.360 Than Yeah, I seem to remember those times. Yeah. But 0:01:12.600 --> 0:01:15.360 isn't it high a relative term at least in physics? 0:01:15.480 --> 0:01:17.560 Like how high is high energy? Can't you always go 0:01:17.760 --> 0:01:18.679 higher in energy? 0:01:18.760 --> 0:01:21.480 You can always go higher in energy? And what people 0:01:21.560 --> 0:01:25.280 called high energy fifty years ago we now call nuclear physics. 0:01:25.480 --> 0:01:29.480 So it doesn't even qualify what it's not low energy, 0:01:29.560 --> 0:01:31.800 It doesn't even qualify as low energy physics. 0:01:32.040 --> 0:01:34.520 I guess nobody wants to be called a low energy physicist. 0:01:36.959 --> 0:01:39.319 Yeah, would you want to be called a low energy cartoonist? 0:01:40.600 --> 0:01:43.000 Well, I am, and if you call me that it 0:01:43.000 --> 0:01:47.440 would be accurate. But I guess you can call me that, 0:01:47.480 --> 0:01:47.800 why not? 0:01:47.960 --> 0:01:51.680 Yeah? Sure? Well, high energy really means highest energy. And 0:01:51.760 --> 0:01:54.560 as we keep pushing the boundaries of what we can achieve, 0:01:55.040 --> 0:01:58.840 then yesterday's high energy collider is today's nuclear physics. 0:01:59.000 --> 0:02:02.040 Mm sounds like a good slogan for the LGC. Yesterday's 0:02:02.080 --> 0:02:05.760 high energies now today's nuclear energy. But anyways, welcome to 0:02:05.800 --> 0:02:08.840 our podcast Daniel and Jorge Explain the Universe, a production 0:02:09.040 --> 0:02:10.560 of iHeartRadio. 0:02:10.160 --> 0:02:12.520 In which we use all of our energy to help 0:02:12.560 --> 0:02:16.840 you understand the nature of the universe. We tear things apart, 0:02:17.000 --> 0:02:20.720 we peer inside. We try to understand at a microscopic level, 0:02:20.840 --> 0:02:23.800 how does everything work? Is there a story we can 0:02:23.840 --> 0:02:27.040 tell about what's happening to the littlest bits in the 0:02:27.120 --> 0:02:30.600 universe and how it comes together to explain our reality? 0:02:30.800 --> 0:02:33.000 That's right. We like to explore the high energies, the 0:02:33.000 --> 0:02:35.639 low energies, and all the energies in between that there 0:02:35.639 --> 0:02:38.519 are in this universe to discover, to explore, to learn about, 0:02:38.720 --> 0:02:40.280 and to blow your mind with. 0:02:40.480 --> 0:02:43.480 And energy is a really central concept in physics and 0:02:43.520 --> 0:02:47.040 in people's understanding of physics. We'd like to think about 0:02:47.040 --> 0:02:51.359 things in terms of energy, little quantum fields vibrating with energy, 0:02:51.520 --> 0:02:55.639 energy being passed between particles, energy used to create particles. 0:02:55.919 --> 0:02:58.560 In some sense, physics is a study. 0:02:58.200 --> 0:03:00.880 Of energy, and one that requires some amount of energy 0:03:00.919 --> 0:03:03.720 to explore, right, I mean, you can't just do physics 0:03:03.720 --> 0:03:04.640 from your couch. 0:03:04.520 --> 0:03:04.799 Can you. 0:03:06.160 --> 0:03:07.720 I don't know if it takes more energy to do 0:03:07.760 --> 0:03:10.480 physics or cartooning, but you can sort of lie in 0:03:10.520 --> 0:03:13.080 your couch and just think about the universe, you know, 0:03:13.160 --> 0:03:15.440 the way the great theorists and the Greeks have done. 0:03:15.680 --> 0:03:19.640 But absolutely to do experiments to explore the universe, to 0:03:20.000 --> 0:03:22.639 investigate it deeply, you need to poke it, you need 0:03:22.639 --> 0:03:24.520 to probe it, you need to interact with it, and 0:03:24.520 --> 0:03:26.040 that does take some energy. 0:03:27.000 --> 0:03:29.040 Well, I feel like energy is kind of a topic, 0:03:29.120 --> 0:03:31.680 that it's a word you learn as a kid, and 0:03:31.720 --> 0:03:34.160 that everybody has heard of this word and we all 0:03:34.240 --> 0:03:36.080 use it every day in our everyday lies. But to 0:03:36.160 --> 0:03:39.960 actually define energy is kind of tricky, isn't it, Not 0:03:40.000 --> 0:03:42.560 just from a physics point of view, but also if 0:03:42.600 --> 0:03:45.560 you ask somebody what energy is, You don't get an 0:03:45.560 --> 0:03:46.120 easy answer. 0:03:46.320 --> 0:03:48.880 Yeah, energy is a very loaded term, right. We have 0:03:48.880 --> 0:03:51.000 a sense of like feeling like you have low energy 0:03:51.040 --> 0:03:53.920 in the morning, or running out of energy to do 0:03:54.000 --> 0:03:56.600 some chores or something. But it's one of these words 0:03:56.600 --> 0:04:00.240 that physics has redefined to have a specific meaning, a 0:04:00.320 --> 0:04:03.200 very crisp idea for what energy means. The way we 0:04:03.240 --> 0:04:06.880 also have like meanings for force and work and other 0:04:06.920 --> 0:04:09.560 words that we also use in everyday English without as 0:04:09.560 --> 0:04:10.640 precise definitions. 0:04:11.000 --> 0:04:13.800 Right, But even those the simple terms have been changing 0:04:13.840 --> 0:04:15.880 in physics over time, right, Like the word the idea 0:04:15.960 --> 0:04:19.120 for force has changed with quantum mechanics. Isn't it Like 0:04:19.160 --> 0:04:21.000 it used to be an invisible force that we feel 0:04:21.080 --> 0:04:23.560 towards the Earth or the sun, But now they're talking 0:04:23.720 --> 0:04:26.000 that maybe it's like a particle or something, it's an 0:04:26.000 --> 0:04:27.040 exchange of particles. 0:04:27.279 --> 0:04:30.000 Yeah, the mechanism that explains it is definitely different. I 0:04:30.000 --> 0:04:33.040 think the concept of force is a change in momentum 0:04:33.120 --> 0:04:36.480 of something. Something in exchange of momentum essentially has been 0:04:36.520 --> 0:04:40.680 pretty constant since Newton. Yeah, these things definitely can change. 0:04:40.880 --> 0:04:43.120 And you know, for example, we've redefined gravity to not 0:04:43.200 --> 0:04:45.840 even be a force, So what gets counted as a 0:04:45.880 --> 0:04:49.000 force and what doesn't and how that all works definitely changes. 0:04:49.279 --> 0:04:51.680 And we like to dig into these basic principles and say, like, 0:04:51.720 --> 0:04:53.680 what does this really mean? Where does it come from? 0:04:53.720 --> 0:04:56.440 Did the universe have to me this way? Is energy 0:04:56.560 --> 0:04:58.760 essential to the universe? And one of the ways that 0:04:58.800 --> 0:05:01.520 we do that is by noticing what the universe respects, 0:05:01.800 --> 0:05:05.680 like what doesn't change in the universe, what's constant, what's conserved. 0:05:05.960 --> 0:05:08.479 That gives you a clue about sort of what's important 0:05:08.640 --> 0:05:10.880 to the underlying machinery of the universe. 0:05:11.120 --> 0:05:12.680 Right, you kind of want to know what the rules 0:05:12.760 --> 0:05:14.760 of the universe are, or what the principles of the 0:05:14.880 --> 0:05:18.840 universe are by which it lets things happen in it, 0:05:19.040 --> 0:05:20.040 right exactly. 0:05:20.400 --> 0:05:23.240 And one of the deepest rules that people imagine in 0:05:23.279 --> 0:05:28.120 the universe follows is conservation of energy. That energy is 0:05:28.160 --> 0:05:31.080 somehow immutable, that it can slosh between different kinds of 0:05:31.200 --> 0:05:34.919 energy kinetic to potential, to mass, to velocity to whatever. 0:05:35.400 --> 0:05:37.800 But the energy has to go somewhere and has to 0:05:37.880 --> 0:05:41.599 come from somewhere. That it's a basic component of the 0:05:41.720 --> 0:05:42.760 universe itself. 0:05:43.120 --> 0:05:45.880 Yeah, it's a very fundamental rule that people seem to 0:05:46.040 --> 0:05:48.920 learn about even in high school physics. But is it 0:05:49.000 --> 0:05:52.880 actually true? Does it always happen in this universe or 0:05:52.920 --> 0:05:57.160 does it get broken at some levels, like the quantum levels. 0:05:57.400 --> 0:05:59.279 And so to the end the podcast, we'll be asking 0:05:59.320 --> 0:06:09.359 the question does quantum mechanics conserve energy? Now, when you 0:06:09.360 --> 0:06:13.360 say quantum mechanics, do you mean like the field or 0:06:13.440 --> 0:06:15.520 the people who study quantum mechanics. 0:06:16.120 --> 0:06:18.120 The mechanics of quantum physics. 0:06:18.839 --> 0:06:21.960 Can you be a quantum mechanic like a car mechanic, 0:06:22.120 --> 0:06:23.160 but at the quantum level. 0:06:23.240 --> 0:06:25.080 Yeah, bring your fields in. They need some new parts. 0:06:25.320 --> 0:06:26.000 We'll order them. 0:06:26.040 --> 0:06:31.920 That's right, Your quantum carburetor needs to be swapped out, exactly. 0:06:31.960 --> 0:06:34.279 No, in this case, we're talking about the rules of 0:06:34.400 --> 0:06:37.720 the smallest bits in the universe, the tiniest little things, 0:06:37.800 --> 0:06:40.719 the electrons, the positrons of photons, all the smallest stuff 0:06:40.720 --> 0:06:44.040 in the universe seems to operate on different rules than 0:06:44.080 --> 0:06:47.600 the bigger stuff in the universe baseballs and basketballs and 0:06:47.680 --> 0:06:49.960 rocks and stuff that we're familiar with. And so while 0:06:49.960 --> 0:06:53.680 we're taught that energy is concerned very generally, we're interested 0:06:53.680 --> 0:06:56.080 in whether that's always true, and whether it's true at 0:06:56.120 --> 0:06:57.440 the smallest scale. 0:06:57.680 --> 0:07:00.000 Yeah, so this is a big question. Does quantum mechanics 0:07:00.400 --> 0:07:03.080 conserve energy? And so, as usually, we were wondering how 0:07:03.120 --> 0:07:05.359 many people out there had thought about this question, whether 0:07:05.400 --> 0:07:07.320 this is a rule that can be broken at the 0:07:07.360 --> 0:07:10.760 quantum level, or whether the whole universe follows it. 0:07:10.800 --> 0:07:13.800 Thanks very much to everybody who answers these questions. If 0:07:13.840 --> 0:07:16.920 you would like to receive a regular dose of tough 0:07:16.920 --> 0:07:20.160 physics questions in your inbox, right to me too, questions 0:07:20.200 --> 0:07:23.280 at Danielandhorge dot com, and I will send them to you. 0:07:23.640 --> 0:07:27.120 Well, regular dose. Now do these doses make you high 0:07:27.760 --> 0:07:28.600 in physics? 0:07:29.000 --> 0:07:31.200 These are microdoses, so yeah. 0:07:30.960 --> 0:07:33.520 Oh, I see right, it's more of a low key high. 0:07:34.000 --> 0:07:36.360 They're not supposed to blow your mind. They're just supposed 0:07:36.360 --> 0:07:39.680 to color your experience of the universe a little bit. 0:07:39.960 --> 0:07:42.080 I see. It's more of a nuclear. 0:07:41.800 --> 0:07:46.320 Hit exactly, It's not a high energy dose. 0:07:46.440 --> 0:07:48.000 Well, think about it for a second. Do you think 0:07:48.120 --> 0:07:52.360 quantum mechanics conserves energy? Here's what people have to say. 0:07:53.000 --> 0:07:56.480 I think so, or at least the rate of decay 0:07:56.720 --> 0:08:00.440 is so minute that we are not currently able to 0:08:02.000 --> 0:08:06.000 detect it on a cosmological scale. 0:08:06.080 --> 0:08:09.080 I think quantum mechanics conserves energy. I feel like it 0:08:09.080 --> 0:08:10.840 would be big news if we found the law of 0:08:10.920 --> 0:08:14.200 conservation of energies to be violated, though maybe it has 0:08:14.240 --> 0:08:16.800 been and I just haven't seen that news. But the 0:08:16.840 --> 0:08:19.920 notion of quantum fluctuations seems like it would violate that law. 0:08:20.040 --> 0:08:22.520 Though I don't really understand quantum fluctuations. 0:08:22.880 --> 0:08:25.080 I'm assuming it doesn't just because I remember listening to 0:08:25.120 --> 0:08:29.160 your podcast on how energy actually isn't conserved in the universe. 0:08:29.240 --> 0:08:32.280 So I'm assuming that quantum mechanics follows that as well, 0:08:32.320 --> 0:08:33.680 But I don't actually know. 0:08:33.960 --> 0:08:38.240 I'm not sure about this question. And like conserve in 0:08:38.360 --> 0:08:42.840 what like in your book frequently asked questions about the universe, 0:08:43.440 --> 0:08:46.320 you did say like there was like a quantum foam, 0:08:47.520 --> 0:08:50.760 and like when the universe is expanding, it's just connecting 0:08:50.800 --> 0:08:57.920 to more quantum particles, I guess. So I'm going to say, 0:08:58.000 --> 0:09:01.479 I don't know, because if you mean in the universe, 0:09:02.360 --> 0:09:07.600 like not the growing section, then no. But if we 0:09:07.679 --> 0:09:11.840 even include all the other disconnected quantum phone then I'm 0:09:11.840 --> 0:09:12.520 not sure. 0:09:13.040 --> 0:09:14.880 All right. People are on the fence about this. Some 0:09:14.920 --> 0:09:18.560 people say it does, some people say they don't think so. Well, 0:09:18.600 --> 0:09:19.280 they're not sure. 0:09:19.480 --> 0:09:22.200 Yeah, I was really surprised by this. I was expecting 0:09:22.200 --> 0:09:24.959 people to rush to the defense of conservation of energy 0:09:24.960 --> 0:09:27.440 and say it's a fundamental law of the universe. 0:09:27.679 --> 0:09:30.320 Maybe it's because we've had whole episodes where we say 0:09:30.320 --> 0:09:33.680 that the energy is not conserving the universe that maybe 0:09:34.360 --> 0:09:35.880 influence the answers here. 0:09:36.640 --> 0:09:39.840 Oh my gosh, people actually listening and absorbing the content. 0:09:40.000 --> 0:09:43.200 Amazing, amazing, they're learning. Well, it's great that they are 0:09:43.760 --> 0:09:46.320 listening to us. And because we have talked about this 0:09:46.400 --> 0:09:49.040 idea of conservation of energy in the universe, and we've 0:09:49.040 --> 0:09:51.800 talked about how it's not actually conserved in the universe 0:09:51.840 --> 0:09:52.360 as a whole. 0:09:52.480 --> 0:09:54.320 Right, that's right, And that was in the context of 0:09:54.360 --> 0:09:57.680 sort of general relativity, thinking about the universe as it 0:09:57.760 --> 0:10:02.080 expands and as space is changing, how we define energy 0:10:02.120 --> 0:10:04.160 in that context, and that sort of blows a lot 0:10:04.160 --> 0:10:07.360 of people's minds to understand that energy might not be 0:10:07.480 --> 0:10:10.520 conserved in the universe at the biggest scales, you know, 0:10:10.520 --> 0:10:12.760 when you zoom all the way out and think about 0:10:12.880 --> 0:10:15.400 how the universe is expanding and what happens to stuff 0:10:15.400 --> 0:10:16.080 inside of it. 0:10:16.320 --> 0:10:18.360 Right, Because in the other episode we talked about how 0:10:18.360 --> 0:10:22.000 the universe is expanding due to dark energy, and basically 0:10:22.160 --> 0:10:25.280 like there's more space being created all the time out 0:10:25.320 --> 0:10:28.120 of nothing, which means that energy sort of being added 0:10:28.160 --> 0:10:30.959 to the universe, created in the universe out of nothing. 0:10:31.040 --> 0:10:33.400 Right, Yeah, that's right, and you're coming out of nothing, 0:10:33.440 --> 0:10:35.800 I think says a lot. You know, it implies that 0:10:35.960 --> 0:10:38.040 energy needs to come from somewhere, and so when you 0:10:38.080 --> 0:10:40.800 say energy is created, you have to give some explanation 0:10:40.920 --> 0:10:43.120 for where it comes from, even if you're saying out 0:10:43.160 --> 0:10:46.520 of nothing. But this tells us that energy isn't something 0:10:46.520 --> 0:10:48.800 fundamental to the universe. That it can go up and 0:10:48.800 --> 0:10:51.040 it can go down, like lots of things in the universe, 0:10:51.120 --> 0:10:53.440 like the number of people in swimming pools is not 0:10:53.520 --> 0:10:55.600 a constant number of the universe. It can go up 0:10:55.640 --> 0:10:56.480 and it can go down. 0:10:56.600 --> 0:10:59.959 How do you know? Are you sure the. 0:11:00.040 --> 0:11:03.960 Middle of an extensive worldwide experiment to measure the number 0:11:03.960 --> 0:11:04.520 of people. 0:11:04.880 --> 0:11:07.280 At any moment? Yes, Oh, you thought you were going to. 0:11:07.280 --> 0:11:09.240 Challenge me on that and call me out, But actually 0:11:09.480 --> 0:11:11.880 I've been doing this in preparation for five years just 0:11:11.920 --> 0:11:13.160 to make that casual comment. 0:11:13.920 --> 0:11:15.640 You know, somehow I don't believe you any. 0:11:16.559 --> 0:11:18.960 Away from my paper in nature. Okay, it's coming out soon, 0:11:19.040 --> 0:11:19.520 I promise. 0:11:20.280 --> 0:11:23.120 Sure. Let's see the draft. Read me a poll paragraph 0:11:23.160 --> 0:11:24.199 from the draft right now. 0:11:25.800 --> 0:11:28.160 Oh, I can't disembargo it because it's too high profile. 0:11:29.920 --> 0:11:30.360 I see. 0:11:30.400 --> 0:11:32.640 I signed an NBA. What am I gonna do? No, 0:11:32.760 --> 0:11:34.800 obviously I have not done that experiment. 0:11:34.400 --> 0:11:37.880 A nuclear disclosure agreement, which means it's really low. 0:11:38.600 --> 0:11:41.920 But clearly there are things in the universe that do change, 0:11:42.080 --> 0:11:44.920 things that are not fundamental to the universe, while there 0:11:44.920 --> 0:11:47.160 are other things that are fundamental, like momentum. We think 0:11:47.200 --> 0:11:50.560 momentum is conserved in the universe, and that comes from 0:11:50.640 --> 0:11:54.080 a really deep symmetry about space and time that the 0:11:54.120 --> 0:11:56.280 experiments you do anywhere in the universe should give you 0:11:56.320 --> 0:11:58.600 the same answer. That doesn't matter where you put your 0:11:58.640 --> 0:12:02.439 origin in space. Rules of physics don't care, and that 0:12:02.520 --> 0:12:06.560 gives you directly as a consequence of Nuther's theorem, momentum conservation. 0:12:07.040 --> 0:12:10.160 But energy is not in that same category, and energy 0:12:10.200 --> 0:12:12.160 can go down and it can go up, like when 0:12:12.200 --> 0:12:14.280 the universe expands, you get in new space, and that 0:12:14.320 --> 0:12:17.640 space comes with energy, but also energy gets decreased because 0:12:17.640 --> 0:12:20.600 as space expands, it reddens the wavelengths of all the 0:12:20.600 --> 0:12:23.960 photons inside of it. Take for example, the cosmic microwave 0:12:23.960 --> 0:12:27.240 background radiation from the early universe. When it was created, 0:12:27.240 --> 0:12:30.200 it was very high energy. That plasma was super dup 0:12:30.240 --> 0:12:32.920 or hot. It was thousands of degrees kelvin. But it's 0:12:32.960 --> 0:12:35.400 been stretched out by the expansion of the universe to 0:12:35.559 --> 0:12:38.640 very long wavelengths, and now it's at like three degrees kelvin. 0:12:39.120 --> 0:12:42.000 Where do that energy go? Didn't go anywhere, it's just gone. 0:12:42.120 --> 0:12:44.720 Well, it's not gone, it's just gonna spread out, is it. 0:12:44.960 --> 0:12:47.840 No, there's less energy in those photons. Those photons have 0:12:47.880 --> 0:12:50.080 gone from high energy to low. 0:12:49.960 --> 0:12:51.719 Energy because they got stretched out. 0:12:51.920 --> 0:12:54.000 But the total energy is also different. It's not just 0:12:54.040 --> 0:12:54.959 the energy density. 0:12:55.320 --> 0:12:59.400 But they're longer now, that's what those are longer. Yeah, 0:12:59.760 --> 0:13:00.920 isn't where the energy went. 0:13:01.040 --> 0:13:03.960 The energy of those photons is less. They're also longer, 0:13:04.440 --> 0:13:06.640 but the energy of those photons is less. If you 0:13:06.640 --> 0:13:08.760 stretch space, the photons get redder, which means they have 0:13:08.880 --> 0:13:09.440 less energy. 0:13:09.480 --> 0:13:11.120 Well, I guess this is what I mean. Because the 0:13:11.880 --> 0:13:14.959 idea of energy, the concept of energy can really vary 0:13:15.000 --> 0:13:17.440 into a lot of these arguments about whether it can 0:13:17.559 --> 0:13:19.839 can be conserved or not. I feel like maybe they 0:13:19.880 --> 0:13:22.480 depend on a good definition of energy, and so maybe 0:13:22.520 --> 0:13:25.440 for folks we should talk about what energy actually is, 0:13:25.440 --> 0:13:26.840 how to physicists define it. 0:13:26.960 --> 0:13:28.840 Yeah, I wish I knew what energy was. 0:13:29.360 --> 0:13:30.040 Wait, what. 0:13:32.040 --> 0:13:34.560 Energy is a really slippery topic. It's something we've been 0:13:34.600 --> 0:13:37.960 struggling with over the last few decades to really define. 0:13:38.000 --> 0:13:41.600 We have some very crisp but unsatisfying definitions of energy. 0:13:41.960 --> 0:13:44.520 You know, in some cases you can say energy is 0:13:44.679 --> 0:13:47.680 the thing that's conserved over time, you know, so you 0:13:47.720 --> 0:13:50.040 can define it to be something that's conserved. Really, I 0:13:50.040 --> 0:13:51.959 think a better way to define energy is to talk 0:13:51.960 --> 0:13:54.160 about like the forms it can take. You know, like 0:13:54.200 --> 0:13:57.400 there's kinetic energy, which means energy of motion. Something is 0:13:57.440 --> 0:14:01.520 moving that has energy. There's potential energy, this energy of configuration. 0:14:01.720 --> 0:14:04.160 Like a book is sitting on the shelf, there's energy 0:14:04.240 --> 0:14:06.400 stored in that. You know, it takes energy to put 0:14:06.400 --> 0:14:09.080 the book on the shelf. Mass, for example, is a 0:14:09.120 --> 0:14:13.160 representation of internal stored energy. Put a bunch of photons 0:14:13.200 --> 0:14:16.080 into a box, they have energy. That box now has 0:14:16.200 --> 0:14:19.440 more mass. All these are different ways you can calculate energy, 0:14:19.840 --> 0:14:21.320 and if you add them all up, you get the 0:14:21.440 --> 0:14:24.720 total energy. And so that's sort of how we define energy, 0:14:24.720 --> 0:14:26.040 but you know it's a little hand wavy. 0:14:26.280 --> 0:14:28.160 Wait wait, wait, So I was right earlier when I 0:14:28.200 --> 0:14:30.680 said that I don't really know what energy kind of is, 0:14:30.760 --> 0:14:32.120 but you made it seem like we did know. 0:14:32.320 --> 0:14:34.440 We don't really know what energy is in the broadest sense, 0:14:34.560 --> 0:14:37.080 but we can define something and say this is what 0:14:37.120 --> 0:14:39.920 we call energy. I don't know if it really captures 0:14:39.960 --> 0:14:42.560 our full experience of energy, but yeah, we can write 0:14:42.560 --> 0:14:44.320 down a formula for what energy is. 0:14:45.440 --> 0:14:47.680 But I guess the question is what did those things 0:14:47.720 --> 0:14:49.760 have in common? And why do you use the same 0:14:49.800 --> 0:14:52.640 word for all of them? The kinetic energy, potential energy, 0:14:53.280 --> 0:14:55.280 you know, energy of mass. Why do you use the 0:14:55.280 --> 0:14:56.760 same word for all of those things? 0:14:57.120 --> 0:14:59.640 Yeah, great question, And the reason is that in classical 0:14:59.720 --> 0:15:02.800 mechare at least, you know, things moving around at our 0:15:02.840 --> 0:15:05.400 scale at or fairly low speeds. We notice that they 0:15:05.400 --> 0:15:07.160 can turn back and forth into each other. Like you 0:15:07.200 --> 0:15:09.200 take that book on the shelf. It has potential energy 0:15:09.200 --> 0:15:11.560 and no kinetic energy. You push it off the shelf. 0:15:11.960 --> 0:15:14.520 Now it's speeding up towards the ground. It's losing potential 0:15:14.600 --> 0:15:17.640 energy and gaining kinetic energy. So we notice that these 0:15:17.640 --> 0:15:20.520 things can turn into each other, and therefore we group 0:15:20.560 --> 0:15:23.160 them together into one big category. And we notice that, 0:15:23.200 --> 0:15:26.160 at least in classical mechanics, the total the sum of 0:15:26.200 --> 0:15:29.080 them all does stay constant. So like if you're add 0:15:29.120 --> 0:15:31.280 of all the potential energy and all the kinetic energy 0:15:31.280 --> 0:15:33.400 at one moment, and you do it again later, you 0:15:33.440 --> 0:15:34.760 find you get the same answer. 0:15:36.000 --> 0:15:38.080 And how does that relate to the energy of a 0:15:38.080 --> 0:15:40.200 photocon which you mentioned earlier. 0:15:40.240 --> 0:15:42.640 So now we're departing classical mechanics a little bit. We're 0:15:42.640 --> 0:15:45.280 talking about a quantum object, but we can still think 0:15:45.320 --> 0:15:48.040 about the energy of a photon. A photon has kinetic 0:15:48.120 --> 0:15:51.200 energy because it's in motion, it's always in motion. It 0:15:51.240 --> 0:15:54.640 has only kinetic energy. So photons definitely have energy. 0:15:55.200 --> 0:15:57.640 Well, it seems like maybe the common factor is the 0:15:57.640 --> 0:16:01.320 idea of motion, like things moving have energy to them, 0:16:01.480 --> 0:16:04.160 and things that can move in the future or can 0:16:04.240 --> 0:16:06.800 cost things to move, or like the potential to cost 0:16:06.800 --> 0:16:09.360 something to move, is what maybe you would call energy. 0:16:09.480 --> 0:16:11.800 Maybe I think that puts kinetic energy in a more 0:16:11.800 --> 0:16:15.560 primary position than potential energy, which I'm not sure is justified. 0:16:15.560 --> 0:16:18.000 I think there really are at its core two different 0:16:18.120 --> 0:16:21.680 kinds of energy. There stored energy potential energy and kinetic energy. 0:16:21.720 --> 0:16:23.760 I'm not sure which one would be more fundamental. 0:16:24.240 --> 0:16:26.440 And so are those the only two kinds of energy? 0:16:26.480 --> 0:16:30.360 So you have in classical physics kinetic and potential. 0:16:30.440 --> 0:16:32.560 Yeah, those are the two forms. People might think, what 0:16:32.680 --> 0:16:35.480 about mass? What is mass? Is that kinetic energy or 0:16:35.480 --> 0:16:37.760 potential energy? It's sort of a special case. It's just 0:16:37.800 --> 0:16:40.280 sort of a label we give some kinds of energy 0:16:40.600 --> 0:16:44.720 if they're stored internally, Like if you have gluons inside 0:16:44.720 --> 0:16:47.200 of proton, they have a bunch of kinetic energy they're 0:16:47.280 --> 0:16:49.680 zooming around. They also have potential energy of their bonds. 0:16:49.960 --> 0:16:52.240 All that energy is inside the proton, so we call 0:16:52.360 --> 0:16:54.400 that mass. So mass is sort of a label we 0:16:54.480 --> 0:16:57.000 give to some energy, but it's not on the same 0:16:57.080 --> 0:16:59.520 level as like kinetic and potential it's not its own 0:16:59.600 --> 0:17:00.440 kind of energy. 0:17:01.080 --> 0:17:04.000 So then if an eight year old asked you, hey, 0:17:04.080 --> 0:17:07.720 doctor Whitson, what is energy? What would you answer? 0:17:07.760 --> 0:17:10.399 I would say, I've had this nightmare scenario many times 0:17:10.400 --> 0:17:11.920 and I have no idea how to respond. 0:17:12.800 --> 0:17:18.280 You would spring in their face, Ah, run away, No, seriously, like, 0:17:18.359 --> 0:17:21.560 what would you say, you have to say something? What 0:17:21.560 --> 0:17:23.960 would you say, I'll get you started. It's a quantity that. 0:17:27.280 --> 0:17:29.720 I'd say, energy is something that makes things move, but 0:17:29.760 --> 0:17:32.600 it's also something you can store. That's my best shot. 0:17:34.040 --> 0:17:35.959 It's almost like a liquid or something. 0:17:36.160 --> 0:17:38.359 You know, for a long time people did imagine that 0:17:38.600 --> 0:17:40.600 energy in the form of heat was a liquid that 0:17:40.720 --> 0:17:45.080 flowed between things. But it's not a physical quantity in itself. 0:17:45.200 --> 0:17:48.439 It's a description of the physical state of other quantities. 0:17:48.720 --> 0:17:51.400 Like a liquid can have energy, but so can solids. 0:17:51.960 --> 0:17:54.359 It's not like when energy flows from one thing to another, 0:17:54.560 --> 0:17:58.480 there's some physical substance that moves between it. It changes 0:17:58.560 --> 0:18:00.000 the state of those objects. 0:18:00.480 --> 0:18:02.439 Well, I guess I'm a little surprised you're having so 0:18:02.520 --> 0:18:06.120 much trouble just defining energy, which is pretty interesting. But 0:18:06.240 --> 0:18:07.919 as you said, I think one thing that we do 0:18:08.000 --> 0:18:09.760 sort of know about it is that in some cases 0:18:09.800 --> 0:18:13.119 it's conserved and maybe in some cases it's not. 0:18:13.520 --> 0:18:13.600 So. 0:18:13.680 --> 0:18:15.840 Well, let's dig into the question and when it's conserved, 0:18:15.880 --> 0:18:18.399 is it conserved at the quantum level or is it not. 0:18:19.000 --> 0:18:21.360 So let's dig into that, But first let's take a 0:18:21.400 --> 0:18:36.680 quick break. All right, we are mustering up the energy 0:18:37.359 --> 0:18:41.480 to talk about something that apparently physicists can't define energy, 0:18:41.760 --> 0:18:44.919 such a basic word that even little kids use, everyone 0:18:45.040 --> 0:18:49.080 uses their in their daily lives. But it seems Daniel, 0:18:49.119 --> 0:18:53.040 that it's something physicists can't really define very well. Maybe 0:18:53.040 --> 0:18:55.720 only mathematically you can define it. Is that kind of 0:18:55.720 --> 0:18:56.160 the case. 0:18:56.480 --> 0:18:58.560 Yeah, And as you'll see, when we get into the 0:18:58.600 --> 0:19:01.359 quantum system, this is going to be even trickier. And 0:19:01.440 --> 0:19:05.080 physicists disagree about how to define energy and whether we 0:19:05.240 --> 0:19:07.960 can even define it in terms of quantum systems. 0:19:08.119 --> 0:19:09.560 Well, it seems like we don't even need to get 0:19:09.560 --> 0:19:12.720 through you already don't know how to define it exactly. 0:19:12.760 --> 0:19:15.000 And that's why I want to be upfront about how 0:19:15.160 --> 0:19:18.600 complicated and confusing this topic is, even in the easy case, 0:19:18.760 --> 0:19:21.000 because when we get to the hard case, it's going 0:19:21.080 --> 0:19:23.000 to get even trickier. So I did my best to 0:19:23.000 --> 0:19:25.560 give you like my understanding of energy, but if you 0:19:25.560 --> 0:19:27.760 look at the official definition of energy, I find it's 0:19:27.800 --> 0:19:31.439 even less satisfying. Like if you just google energy and 0:19:31.480 --> 0:19:34.439 you ask Wikipedia or chat GPT, like, what is energy? 0:19:34.680 --> 0:19:36.679 Well, it's you know, legit sources. 0:19:36.760 --> 0:19:39.960 Legit sources. They say energy is the quantitative property that 0:19:40.080 --> 0:19:42.720 is transferred to a body, and that doesn't really even 0:19:42.720 --> 0:19:44.359 tell you what it is. It's like Okay, well, it 0:19:44.400 --> 0:19:47.399 can move from one thing to another, but what is it? Man, 0:19:47.840 --> 0:19:49.720 it doesn't really answer that question. 0:19:50.200 --> 0:19:51.879 Well, that's kind of what I meant before, is that 0:19:51.960 --> 0:19:55.240 it's a quantity. Is basically kind of the only way 0:19:55.280 --> 0:19:57.680 you physicists know how to define it, right, it's a 0:19:57.760 --> 0:20:01.240 it's a quantity. It's something that can measure, that can 0:20:01.280 --> 0:20:04.359 be a lot or a little, which you seem to 0:20:04.359 --> 0:20:08.280 be able to measure about things, and that sometimes seems 0:20:08.320 --> 0:20:09.119 to be conserved. 0:20:09.320 --> 0:20:12.159 So mathematically, we can write down a formula that defines it, 0:20:12.200 --> 0:20:14.240 and then it's defined in terms of things we can 0:20:14.359 --> 0:20:18.080 measure like velocity and position and stuff like this. And 0:20:18.160 --> 0:20:20.440 it turns out that if you write it in certain ways, 0:20:20.720 --> 0:20:24.119 then that number doesn't change. The internal values can slash 0:20:24.160 --> 0:20:27.040 back and forth, but the total doesn't change. That's sort 0:20:27.040 --> 0:20:30.240 of like the crispest most mathematical definition. But I think 0:20:30.280 --> 0:20:33.040 what we're proving forward is like what does it mean philosophically? 0:20:33.160 --> 0:20:35.800 Like what are the implications of that? And that's much trickier. 0:20:36.080 --> 0:20:38.200 Well, you seem to not want to give primacy to 0:20:38.280 --> 0:20:40.960 kinetic energy, but in a way, that's kind of like 0:20:41.200 --> 0:20:45.920 our most direct experience of energy, which is motion, right, 0:20:45.960 --> 0:20:47.560 Like if something has a lot of energy to either 0:20:47.680 --> 0:20:51.159 moving fast, or it's hot or it's exploding. For us, 0:20:51.240 --> 0:20:54.840 in our experience of the universe, energy is basically things 0:20:54.880 --> 0:20:57.200 moving fast or things that can make things move fast. 0:20:57.320 --> 0:20:59.520 Yeah, if you're talking about the experience of it, then 0:20:59.800 --> 0:21:04.960 you more directly experience motion than stored energy. It's energy 0:21:05.000 --> 0:21:06.879 you don't really experience when it's stored because it's just 0:21:07.000 --> 0:21:10.439 being stored. It's when it's transformed into kinetic energy that 0:21:10.480 --> 0:21:13.200 you're experiencing it. Like if you zap yourself on a battery, 0:21:13.560 --> 0:21:16.399 it's the motion of those electrons being transformed from the 0:21:16.440 --> 0:21:19.359 potential into their kinetic energy that's zapping you. 0:21:19.600 --> 0:21:22.879 All right. So then you said that sometimes it's conserved 0:21:22.920 --> 0:21:26.399 and sometimes it's not. So when is energy conserved in 0:21:26.440 --> 0:21:27.200 a classical way? 0:21:27.359 --> 0:21:31.240 In classical sense, energy is only conserved when space time 0:21:31.400 --> 0:21:34.320 is not curved and when space time is not changing. 0:21:34.960 --> 0:21:37.119 So if space time is fixed, like you have flat 0:21:37.160 --> 0:21:40.040 space time, meaning you shoot two photons and they stay 0:21:40.080 --> 0:21:43.000 parallel to each other, then you can expect energy to 0:21:43.080 --> 0:21:45.920 be conserved. But if that space is changing, like it's 0:21:45.960 --> 0:21:48.960 expanding the way our universe is, then the general relativity, 0:21:49.080 --> 0:21:52.479 energy is not conserved. Even more generally, anytime you have 0:21:52.680 --> 0:21:56.439 curved space in general relativity, you do not have conservation 0:21:56.520 --> 0:21:59.800 of energy. So, for example, black holes colliding do not 0:22:00.119 --> 0:22:01.080 conserve energy. 0:22:01.240 --> 0:22:02.520 Wait, what what do you mean. 0:22:02.400 --> 0:22:04.439 When two black holes collide? You have the collision of 0:22:04.480 --> 0:22:06.879 two curved bits of space, and what comes out of 0:22:06.920 --> 0:22:08.960 that is not the sum of what goes into that. 0:22:09.000 --> 0:22:11.320 You're not guaranteed that in general relativity. 0:22:11.520 --> 0:22:15.359 But is in space always curved like uncurving space around me, 0:22:16.359 --> 0:22:18.320 and yet I don't seem to have infinite energy. 0:22:18.560 --> 0:22:20.560 That's right, you do not have infinite energy and you 0:22:20.560 --> 0:22:23.320 are curving space around you. But the total amount of 0:22:23.440 --> 0:22:27.199 energy in the system changes in time in general relativity, 0:22:27.480 --> 0:22:30.000 and it gets really fuzzy and weird because general relativity 0:22:30.040 --> 0:22:32.320 is really hard to think about in some reference frames. 0:22:32.359 --> 0:22:35.439 According to generalativity, energy is conserved in others, it's not. 0:22:35.880 --> 0:22:37.719 Depends sort of on how you're looking at things. 0:22:37.960 --> 0:22:40.160 Okay, it sort of sounds like you're saying like, if 0:22:40.160 --> 0:22:43.359 you don't think about general relativity, then you can assume 0:22:43.359 --> 0:22:46.320 that energy is being conserved. If you assume that there's 0:22:46.359 --> 0:22:49.280 general relativity and things are being space is being bent 0:22:49.960 --> 0:22:52.200 like around black holes or the expansion of the universe. 0:22:52.240 --> 0:22:55.040 Then you can't assume that energy is being conserved. 0:22:54.640 --> 0:22:56.359 As long as we're above the quantum level. 0:22:56.480 --> 0:22:58.920 Right, So it's mostly like whether or not you ignore 0:22:59.119 --> 0:23:00.560 the bunding of space exactly. 0:23:00.600 --> 0:23:03.240 If you can ignore the bending or expansion of space time, 0:23:03.400 --> 0:23:06.160 then classically you can think of energy as conserved. 0:23:06.280 --> 0:23:08.000 Right. And so we talked about that the universe is 0:23:08.040 --> 0:23:11.199 expanding and so therefore energy is not being concernedd and 0:23:11.200 --> 0:23:14.359 we talked about two black holes colliding. Energy is not 0:23:14.400 --> 0:23:16.720 being conserved there So now the question of the episode 0:23:16.800 --> 0:23:19.040 is when you get down to the quantum level, is 0:23:19.320 --> 0:23:23.800 energy still conserved even though maybe there's no space time 0:23:23.840 --> 0:23:25.960 bending at the quantum level. If you assume there's no 0:23:26.040 --> 0:23:30.159 bending at the quantum level, does energy get conserved. 0:23:30.280 --> 0:23:32.280 Yeah, And we have to assume there's no space time 0:23:32.320 --> 0:23:34.199 bending at the quantum level because we don't know how 0:23:34.200 --> 0:23:36.600 to do quantum mechanics when space is curved and you 0:23:36.600 --> 0:23:40.040 have gravity, and gravity for particles is something we don't understand. 0:23:40.400 --> 0:23:43.520 So let's assume space is totally flat and we have objects, 0:23:43.560 --> 0:23:46.800 you know, like baseballs and rocks for which we think 0:23:47.000 --> 0:23:49.760 energy is conserved and then zoomed down to the quantum 0:23:49.840 --> 0:23:52.320 level and try to understand when you have photons and 0:23:52.359 --> 0:23:56.280 electrons instead of rocks and baseballs, is energy still conserved? 0:23:56.480 --> 0:23:59.000 And really the deep question is like, is energy conservation 0:23:59.119 --> 0:24:01.960 something that's through in through the universe at every scale 0:24:02.119 --> 0:24:04.720 or is this something that emerges only at the scale 0:24:04.760 --> 0:24:07.760 we experience it out of something that operates totally differently, 0:24:07.920 --> 0:24:11.200 because remember, quantum mechanics breaks all the rules of classical physics. 0:24:11.440 --> 0:24:14.480 It says things don't actually have well defined positions and locations, 0:24:14.480 --> 0:24:16.720 and lots of the things that emerge at our level 0:24:16.720 --> 0:24:18.560 are not true at the quantum level. So it's not 0:24:18.600 --> 0:24:22.440 guaranteed that everything about our experience will be translated down 0:24:22.440 --> 0:24:23.320 to the quantum level. 0:24:23.359 --> 0:24:25.560 All right, So then let's answer the question, does quantum 0:24:25.560 --> 0:24:27.240 mechanics can serve energy or not? 0:24:27.440 --> 0:24:29.359 So the short answer is we don't know. 0:24:29.600 --> 0:24:32.160 Surprise, surprise, But let's talk about it anyways. 0:24:32.359 --> 0:24:35.200 The slightly less short answer is it depends on what 0:24:35.240 --> 0:24:38.200 you think is happening at the quantum level, mostly about 0:24:38.200 --> 0:24:40.320 what happens when you try to measure energy. 0:24:40.640 --> 0:24:44.240 What do you mean? So I guess, because it's quantum mechanics, 0:24:44.320 --> 0:24:47.159 you have to measure things. That's very importing quantum mechanics. 0:24:47.160 --> 0:24:49.480 So you're saying, we have to answer this question with 0:24:49.720 --> 0:24:50.600 this idea in mind. 0:24:50.680 --> 0:24:53.440 Yeah, exactly. So let's start off the easy case without 0:24:53.480 --> 0:24:56.280 measurements and have a picture in our minds or what's happening. 0:24:56.359 --> 0:24:59.400 You know, quantum mechanics tells us that there are probabilities 0:24:59.440 --> 0:25:01.960 for various things to happen, and we can calculate those 0:25:02.000 --> 0:25:06.480 probabilities using the rules of quantum mechanics, and those probabilities propagate. 0:25:06.800 --> 0:25:09.560 You have two electrons heading towards each other, they might 0:25:09.600 --> 0:25:11.720 scatter off each other and go that way, they might 0:25:11.760 --> 0:25:15.040 pass right through each other. All those probabilities are sort 0:25:15.040 --> 0:25:18.600 of live until somebody actually asks the question and makes 0:25:18.640 --> 0:25:21.680 a measurement using a classical object and you know, tries 0:25:21.720 --> 0:25:23.879 to take a picture of it. Until then sort of 0:25:24.000 --> 0:25:28.240 have all the possibilities live. So that's quantum mechanics without measurement. 0:25:28.359 --> 0:25:30.720 You know, that's what we're imagining is happening when we're 0:25:30.760 --> 0:25:33.879 not looking. And in that scenario we can ask, well, 0:25:34.080 --> 0:25:38.040 is energy conserved? Like when all those probabilities are slashing around, 0:25:38.160 --> 0:25:41.080 the electrons are maybe bouncing off each other and maybe 0:25:41.119 --> 0:25:44.840 not is energy conserved there? And already we kind of 0:25:44.920 --> 0:25:47.560 run into trouble because we don't really know how to 0:25:47.720 --> 0:25:51.600 define energy here. Like, what if you have a quantum 0:25:51.680 --> 0:25:54.560 system and has a few different possible states, a low 0:25:54.680 --> 0:25:56.919 energy state and a high energy state. How do you 0:25:57.000 --> 0:25:59.920 define the energy of it? Is it like the way 0:26:00.280 --> 0:26:03.919 average of the probabilities of the various states? Is it 0:26:04.080 --> 0:26:06.840 something else. I've had conversations with a bunch of physicists 0:26:06.840 --> 0:26:09.040 this week to try to sort out what people think 0:26:09.160 --> 0:26:11.760 energy is, and some people say, you can't define energy 0:26:11.760 --> 0:26:14.280 in that context, and other people say, no, it's definitely 0:26:14.280 --> 0:26:17.320 the weighted average of the various probabilities. 0:26:16.720 --> 0:26:18.639 Right, I think, meaning maybe for people who are not 0:26:18.760 --> 0:26:22.119 super familiar with quantum mechanics. So in quantum mechanics, particles 0:26:22.119 --> 0:26:24.520 and things like that aren't just in one state, like 0:26:24.520 --> 0:26:27.280 a baseball sitting on your table. It's like it's doing 0:26:27.359 --> 0:26:29.240 multiple things at the same time. It's here, it's a 0:26:29.240 --> 0:26:31.879 little bit there, it's moving in this direction a little bit, 0:26:31.880 --> 0:26:34.000 but it's also has the probability to be moving in 0:26:34.040 --> 0:26:37.240 this other direction. And so you're saying that maybe one 0:26:37.280 --> 0:26:39.840 way to measure its energy, or to think about its 0:26:39.960 --> 0:26:42.520 energy is like, if it has a fifty percent probability 0:26:42.520 --> 0:26:45.600 of going this way, then you take that energy and 0:26:45.680 --> 0:26:48.560 multiply by a half. And if it has a certain 0:26:48.600 --> 0:26:51.240 probility that it's moving this way with that velocity, like 0:26:51.280 --> 0:26:54.560 a twenty five percent probability, then you maybe multiply that 0:26:54.720 --> 0:26:56.760 energy by a quarter, and then you would add it 0:26:56.760 --> 0:26:58.480 all up and maybe that would kind of give you 0:26:58.520 --> 0:27:00.679 an average of it energy. 0:27:00.800 --> 0:27:03.120 Yeah, exactly, Like if it has a fifty percent chance 0:27:03.119 --> 0:27:05.639 of having twenty five jewels of energy and a fifty 0:27:05.640 --> 0:27:08.159 percent chance of having seventy five jewels, then you say, well, 0:27:08.200 --> 0:27:10.080 I'm going to average those two. I'm gonna say its 0:27:10.200 --> 0:27:13.720 energy is fifty jewels because on average that's what it has. 0:27:13.840 --> 0:27:16.600 And here allowing the particle to still have both probabilities 0:27:16.600 --> 0:27:18.840 to say, oh, maybe it's in the lower energy state, 0:27:18.920 --> 0:27:20.359 maybe it's in the higher energy state. 0:27:20.600 --> 0:27:23.240 Right, it's in a superposition, it's with a life and dead. 0:27:23.760 --> 0:27:25.560 Then you said, some of your physicist friends said, you 0:27:25.600 --> 0:27:27.800 can't do that, like that's not even that doesn't make sense. 0:27:27.920 --> 0:27:30.040 Yeah, And they say, you can't do that because you 0:27:30.080 --> 0:27:32.800 can't measure that, right, you never measure the fifty Like 0:27:32.840 --> 0:27:35.040 if you went and asked the question, all right, we 0:27:35.119 --> 0:27:37.159 have the particle in this state, go measure the energy. 0:27:37.240 --> 0:27:39.920 You're gonna get twenty five or you're gonna get seventy five. 0:27:39.960 --> 0:27:42.200 You're never going to get the average. It's like saying 0:27:42.359 --> 0:27:44.800 the average number of children in the US is two 0:27:44.880 --> 0:27:48.080 point four, but nobody actually has two point four children, right, 0:27:48.600 --> 0:27:50.320 and so in the same way, you'll never see this 0:27:50.440 --> 0:27:52.840 particle have that energy. So in what sense is that 0:27:52.880 --> 0:27:55.600 the energy of the particle? That's sort of the complaint. 0:27:55.680 --> 0:27:58.000 That's kind of a fundamental problem with quantum mechanics. Like 0:27:58.080 --> 0:28:00.399 it's you know, the cat is alive and dead. Obviously 0:28:00.480 --> 0:28:03.080 the cat can't be alive if you see the cat. 0:28:03.160 --> 0:28:05.919 It can't be both. But in a quantum sense, it 0:28:06.000 --> 0:28:06.359 is both. 0:28:06.520 --> 0:28:08.760 In a quantum sense, it is both. In quantum sense, 0:28:08.760 --> 0:28:10.920 we need a new idea for what these things mean, 0:28:11.400 --> 0:28:14.320 Like what does position mean in a quantum sense, Well, 0:28:14.359 --> 0:28:16.560 you know, for a particle that you haven't measured, it's 0:28:16.600 --> 0:28:19.760 not really well defined. There's only a probability where is 0:28:19.800 --> 0:28:23.720 the particle Actually, well, it's not anywhere. Actually, So these 0:28:23.800 --> 0:28:26.640 concepts that are so important to us at the macroscopic 0:28:26.720 --> 0:28:28.960 scale have to take different meanings. We have to do 0:28:29.040 --> 0:28:33.040 this like philosophical extrapolation, and this is a problem with energy. 0:28:33.080 --> 0:28:35.320 For example, say we have the particle and has two 0:28:35.359 --> 0:28:38.200 different possibilities, the twenty five jewel and the seventy five jewel. 0:28:38.280 --> 0:28:39.760 Then you go and you measure and it turns out 0:28:39.760 --> 0:28:42.320 it has seventy five jewels. Well, if a minute ago 0:28:42.400 --> 0:28:44.560 you said it had fifty jewels because that was the average. 0:28:44.720 --> 0:28:46.320 Now you've measured it and you said you have seventy 0:28:46.320 --> 0:28:49.120 five jewels. Where did that twenty five jewels come from? 0:28:49.280 --> 0:28:49.440 Right? 0:28:49.480 --> 0:28:52.240 And so boom right there, you have a violation of 0:28:52.240 --> 0:28:56.040 conservation of energy. If that's how you define energy before 0:28:56.080 --> 0:28:56.640 you measure it. 0:28:56.960 --> 0:28:59.080 Wait, say it again. It is energy suddenly appear. 0:28:59.280 --> 0:29:00.840 So if you start out the particle we were just 0:29:00.880 --> 0:29:03.080 talking about, it has a fifty percent chance of having 0:29:03.080 --> 0:29:05.360 twenty five jewels and a fifty percent chance of having 0:29:05.360 --> 0:29:08.120 seventy five jewels. So we say, okay, we define the 0:29:08.240 --> 0:29:10.840 energy of it to be fifty jewels because that's the average. 0:29:10.920 --> 0:29:12.800 Now you go and you measure it, and you measure 0:29:12.800 --> 0:29:15.120 it to have seventy five jewels for example, Then according 0:29:15.160 --> 0:29:17.760 to our definition of energy, it's gone from having fifty 0:29:17.880 --> 0:29:20.920 jewels to having seventy five jewels, and so where did 0:29:20.920 --> 0:29:22.000 that energy come from? 0:29:22.080 --> 0:29:24.440 It didn't come from anywhere, it just said before it 0:29:24.480 --> 0:29:26.680 was a guess about what its energy was. It was 0:29:26.800 --> 0:29:29.520 kind of like the expectations of it or the average 0:29:29.560 --> 0:29:31.840 of what we think its energy was. But then in 0:29:31.960 --> 0:29:35.120 the second instance, is what we measured its energy. So 0:29:35.160 --> 0:29:37.080 they shouldn't be a surprise if it's more or less, 0:29:37.160 --> 0:29:37.640 should it? 0:29:37.760 --> 0:29:40.040 So you're saying, those are really two different things. One 0:29:40.120 --> 0:29:42.400 is an actual energy because you've measured it. The other 0:29:42.520 --> 0:29:45.480 is just some estimation of what we might measure, but 0:29:45.560 --> 0:29:46.680 not really the energy. 0:29:46.880 --> 0:29:49.880 Well, and it is in the quantum sense right like 0:29:49.960 --> 0:29:52.520 it's alive and it's dead before I look at the 0:29:52.520 --> 0:29:54.520 cat in the box and then I wanted to open 0:29:54.520 --> 0:29:56.240 the box. It's alive with it. It's not like the 0:29:57.240 --> 0:29:59.040 cat suddenly came back to life. 0:29:59.160 --> 0:30:00.920 And I think this comes down to a question of 0:30:01.000 --> 0:30:04.080 like interpretation, You know, what is really happening there? It 0:30:04.120 --> 0:30:07.400 does the particle secretly already have seventy five jewels and 0:30:07.440 --> 0:30:09.800 now we're measuring it and discovering it. You know, is 0:30:09.840 --> 0:30:12.760 the uncertainty there or reflection of our lack of knowledge 0:30:13.080 --> 0:30:16.000 about something that's actually already determined or something that really 0:30:16.080 --> 0:30:20.080 isn't determined until we measure it. The particle really is 0:30:20.120 --> 0:30:22.320 in a superposition of those two states. If it really 0:30:22.440 --> 0:30:24.880 isn't determined until we measure it, then we do have 0:30:24.920 --> 0:30:26.800 to kind of ask, like, where does the energy come 0:30:26.800 --> 0:30:29.480 from when the universe decides to make that seventy five 0:30:29.560 --> 0:30:31.960 jewel particle instead of the twenty five jewel particle. 0:30:32.160 --> 0:30:33.800 Well, I guess in the same way that you can 0:30:33.840 --> 0:30:36.560 ask if you find that the cat is alive, how 0:30:36.560 --> 0:30:38.440 did the cat come alive? It was if it was 0:30:38.480 --> 0:30:40.520 alive and dead before you open the box. 0:30:40.360 --> 0:30:42.200 Right, But the difference between the two states of the 0:30:42.200 --> 0:30:45.280 cat doesn't violate the conservation of energy, which we thought 0:30:45.400 --> 0:30:48.120 was maybe a fundamental rule in the universe. That violates 0:30:48.120 --> 0:30:50.760 the conservation of the number of dead cats, which nobody 0:30:50.760 --> 0:30:52.120 really thinks it's a. 0:30:52.040 --> 0:30:55.880 Conservation I hope not well or well, And this says 0:30:55.920 --> 0:30:57.880 that we think that it's impossible for a cat to 0:30:57.880 --> 0:30:59.320 go from being dead to being alive. 0:30:59.480 --> 0:31:01.160 Right, I think if we're going to make the analogy 0:31:01.200 --> 0:31:03.400 to the shorten your cat experiment, and then you want 0:31:03.400 --> 0:31:06.440 to ask the question, is the cat alive before it's measured, 0:31:06.480 --> 0:31:07.880 And the answer I think a lot of people would 0:31:07.880 --> 0:31:09.760 give is it's neither alive nor dead. It has the 0:31:09.800 --> 0:31:13.640 probability of being both. And then to extrapolate that philosophically 0:31:13.680 --> 0:31:16.560 back to our particle, you'd say, well, the particle doesn't 0:31:16.600 --> 0:31:18.720 really have twenty five or seventy five jewels, It just 0:31:18.800 --> 0:31:21.040 has a probability of being both. And energy is not 0:31:21.320 --> 0:31:24.120 really well defined. So I think one answer there is 0:31:24.160 --> 0:31:27.120 to say, well, energy is not really defined without measurements, 0:31:27.400 --> 0:31:29.920 so you can't answer this question, and the others to say, no, 0:31:30.040 --> 0:31:32.600 that's the definition of energy, and there is violation of 0:31:32.640 --> 0:31:34.880 conservation of energy, So you either have to give up 0:31:35.040 --> 0:31:38.479 an understanding of what energy means for quantum particles or 0:31:38.520 --> 0:31:40.520 you have to give up energy conservation. 0:31:40.920 --> 0:31:43.719 All right, So it seems like the moment you measure 0:31:43.720 --> 0:31:47.280 a quantum particle is super important because it's so fuzzy 0:31:47.320 --> 0:31:49.920 before you measure it, and it's so crisp after you 0:31:50.000 --> 0:31:52.240 measure it, and so you kind of fall into a 0:31:52.280 --> 0:31:54.640 trap to try to compare the energy before that moment 0:31:54.720 --> 0:31:57.720 and after that moment, you know, you could interpret it 0:31:57.760 --> 0:32:00.600 as saying that energy is not conserved or could interpret 0:32:00.640 --> 0:32:04.680 it saying, well, you know, there's no definition of energy 0:32:04.680 --> 0:32:07.160 before you measure it, and so therefore don't even worry 0:32:07.160 --> 0:32:10.080 about energy classivation exactly. 0:32:10.200 --> 0:32:13.640 But there's really important loophole that we're overlooking here, and 0:32:13.680 --> 0:32:17.960 that's the measurement itself. Some people argue that energy isn't conserved, 0:32:18.160 --> 0:32:21.720 that this extra energy must come from the measurement, that 0:32:21.760 --> 0:32:24.520 we're only violating conservation of energy because we're not including 0:32:24.520 --> 0:32:27.480 the full system. Right. Energy is only conserved inside a 0:32:27.480 --> 0:32:30.520 closed system where you don't have energy transfer anyway. Right, 0:32:30.600 --> 0:32:33.400 Like energy is not conserved for a battery. As you 0:32:33.560 --> 0:32:35.840 use it, it's energy is decreasing, but if you include 0:32:35.840 --> 0:32:38.680 where that energy is going, usually it is concerned. So 0:32:38.880 --> 0:32:41.840 some people argue, ah, what about the measurement. In order 0:32:41.880 --> 0:32:43.640 to measure something, you have to like poke it, you 0:32:43.640 --> 0:32:46.240 have to interact with it. Maybe you're adding that energy 0:32:46.360 --> 0:32:49.400 when you're making that measurement and things do balance out 0:32:49.440 --> 0:32:50.000 in the end. 0:32:50.360 --> 0:32:53.240 Wait what that was very confusing? Can you give me 0:32:53.280 --> 0:32:53.840 an example. 0:32:54.040 --> 0:32:56.000 So let's say you want to measure this particle and 0:32:56.040 --> 0:32:57.960 you want to say it doesn't have seventy five jewels 0:32:58.040 --> 0:33:00.200 or twenty five jewels, How do you measure things about 0:33:00.200 --> 0:33:02.880 a quantum particle, you have to bounce another quantum particle 0:33:02.880 --> 0:33:05.840 off of them. So shoot this electron with a photon, 0:33:06.320 --> 0:33:08.400 then measure where that photon goes and use that to 0:33:08.440 --> 0:33:11.400 detect what the energy of your particle was. Well, now 0:33:11.440 --> 0:33:13.760 you're shooting your electron with a photon, which is going 0:33:13.840 --> 0:33:17.080 to change its energy. And so people argue, when you're 0:33:17.120 --> 0:33:20.280 doing this, the energy that gives that electron seventy five 0:33:20.360 --> 0:33:22.640 jewels comes from that photon somehow. 0:33:22.760 --> 0:33:26.040 But then wouldn't you measure that the overall energy went 0:33:26.120 --> 0:33:28.440 down because you would measure the photon after it hits 0:33:28.440 --> 0:33:30.920 the electron, and you would see that it was had 0:33:30.960 --> 0:33:32.160 less energy exactly. 0:33:32.200 --> 0:33:33.959 So this is the game people try to play in 0:33:34.080 --> 0:33:37.120 order to recover conservation of energy for quantum mechanics. They say, 0:33:37.120 --> 0:33:39.719 this argument is flawed because you're not taking into account 0:33:39.800 --> 0:33:42.640 the energy of the measurement. So there's a whole cottage 0:33:42.680 --> 0:33:45.000 industry and a bunch of paper. It's recently about whether 0:33:45.040 --> 0:33:47.760 it's possible to recover it using the measurement or whether 0:33:47.800 --> 0:33:48.600 that's a red herring. 0:33:48.720 --> 0:33:50.400 Well, the whole thing could be a red herring, right, 0:33:50.440 --> 0:33:52.320 Like it could be that it just doesn't make sense 0:33:52.320 --> 0:33:54.080 to talk about energy before the measurement. 0:33:54.160 --> 0:33:56.560 It could be and that actually depends also on your 0:33:56.560 --> 0:34:00.040 interpretation of quantum mechanics. We're talking right now in the 0:34:00.040 --> 0:34:03.200 Copenhagen interpretation, which has this whole idea that there's a 0:34:03.240 --> 0:34:05.920 superposition and when you make a measurement it collapses to 0:34:05.960 --> 0:34:09.320 one of those options. That's just one view of quantum mechanics, 0:34:09.800 --> 0:34:13.799 and our argument about the energy non conservation depends on 0:34:13.880 --> 0:34:15.840 that view. It turns out in other views of quantum 0:34:15.840 --> 0:34:17.640 mechanics they tell a whole different story. 0:34:18.360 --> 0:34:20.719 All right, well, let's get into what these other views 0:34:20.719 --> 0:34:24.799 of quantum mechanics are and what they say about the 0:34:24.840 --> 0:34:27.920 conservation of cat energy or not. So let's dig into that. 0:34:27.960 --> 0:34:43.319 But first let's take another quick break. All Right, we're 0:34:43.360 --> 0:34:47.319 talking about energy, whether it's conserved in the universe, is 0:34:47.320 --> 0:34:49.680 it conserved at the quantum level? And I think we've 0:34:49.800 --> 0:34:55.400 established that it's a minefield of confusion for everybody. Some 0:34:55.480 --> 0:34:57.439 people might say, does it even make sense to talk 0:34:57.480 --> 0:35:01.799 about energy before you measure something? And you know, it 0:35:01.800 --> 0:35:03.640 doesn't make sense to talk about whether the cat is 0:35:03.680 --> 0:35:07.160 alive or dead before you open the box. And some 0:35:07.239 --> 0:35:09.879 people might say that it does kind of matter, right, 0:35:10.000 --> 0:35:12.320 or that if you discovered the cat to be aliver 0:35:12.880 --> 0:35:14.800 before or after, maybe you killed the cat when you 0:35:14.840 --> 0:35:17.040 open the box. That's kind of what you're saying exactly. 0:35:17.440 --> 0:35:19.480 And it's amazing to me that this is a topic 0:35:19.560 --> 0:35:22.520 of recent discussion. This is not like something that Bore 0:35:22.600 --> 0:35:25.520 and Heisenberg argued about and figured it out in nineteen 0:35:25.560 --> 0:35:29.040 thirty seven their papers about this. Like last year, you know, 0:35:29.160 --> 0:35:33.400 people are still debating what energy even means in quantum mechanics. Like, 0:35:33.480 --> 0:35:35.640 sort this out, folks. You had it for one hundred years. 0:35:35.680 --> 0:35:37.719 You think that would be enough time to figure out 0:35:37.760 --> 0:35:39.280 basic stuff about quantum mechanics. 0:35:39.400 --> 0:35:41.759 Yeah, can't you just run an experiment to figure this out? 0:35:41.800 --> 0:35:46.120 Like if measuring an electron somehow adds energy to it 0:35:46.239 --> 0:35:48.960 or creates energy, can't you just measure that cad you 0:35:49.000 --> 0:35:51.160 just design an experiment where you should a photon at 0:35:51.160 --> 0:35:51.800 an electron. 0:35:52.080 --> 0:35:54.600 So people are trying to design experiments, and the crucial 0:35:54.640 --> 0:35:58.200 thing is designing an experiment where you think the measurement 0:35:58.320 --> 0:36:01.800 will not influence the energy of the system. That's the goal, 0:36:02.360 --> 0:36:04.400 because then you can have an internal system and an 0:36:04.400 --> 0:36:06.719 external system, and you can isolate it and say this 0:36:06.840 --> 0:36:08.360 is the whole system. So you want to try to 0:36:08.400 --> 0:36:11.120 separate your measuring device from the energy of the system. 0:36:11.280 --> 0:36:12.600 Wait, wait, do you mean like they're trying to come 0:36:12.640 --> 0:36:14.560 up with how to measure something without measuring it. 0:36:14.640 --> 0:36:17.480 Well, they want to measure it without changing its energy, 0:36:17.600 --> 0:36:20.960 so they want a energy independent measuring system. 0:36:21.080 --> 0:36:23.400 But I guess, if you shoot a photon at an electron, 0:36:23.520 --> 0:36:25.879 don't you know how much energy the photon had when 0:36:25.880 --> 0:36:28.640 you shot it so that you can take it into 0:36:28.680 --> 0:36:31.000 account later when it comes out? Like, why is this 0:36:31.040 --> 0:36:31.920 problem so hard? 0:36:32.080 --> 0:36:34.680 Well, every quantum object has an uncertainty to it, and 0:36:34.719 --> 0:36:36.680 so you shoot a photon at it. You try to 0:36:36.719 --> 0:36:39.480 generate photons with a specific energy, but those photons will 0:36:39.520 --> 0:36:42.080 also have an uncertainty to them, and that uncertainty propagates 0:36:42.080 --> 0:36:44.080 through your whole experiment. So what you want to try 0:36:44.080 --> 0:36:46.520 to do is set up a scenario where the uncertainty 0:36:46.680 --> 0:36:50.720 you're adding by your measurement is smaller than the difference 0:36:50.719 --> 0:36:52.640 in the energy between the two states of the thing 0:36:52.719 --> 0:36:54.920 that you're measuring. So you want to try to use 0:36:55.160 --> 0:36:58.040 something really low energy to measure a really big difference. 0:36:58.320 --> 0:36:59.879 I guess it's kind of like you know, you're trying 0:36:59.880 --> 0:37:01.640 to figure out if the cat is alive or dead 0:37:01.640 --> 0:37:03.719 in the box, and you're sending it in a cat 0:37:03.800 --> 0:37:05.680 to do it. But it turns out that the scientist 0:37:05.760 --> 0:37:08.120 cat is also a quantum object, so it could also 0:37:08.160 --> 0:37:10.439 be a live or dead, in which case you don't 0:37:10.440 --> 0:37:13.480 really know the scientist cat is killing the other cat exactly. 0:37:13.520 --> 0:37:14.879 So what you want to do is try to send 0:37:14.920 --> 0:37:18.280 in like a tiny miniature kitten that you can argue 0:37:18.400 --> 0:37:20.840 is going to not influence whether your cat is alive 0:37:20.960 --> 0:37:21.680 or dead as much. 0:37:21.600 --> 0:37:24.120 As possible, or that you know for sure if it's 0:37:24.160 --> 0:37:25.000 alive or dead. 0:37:25.040 --> 0:37:27.600 Or the uncertainty on it is smaller than the uncertainty 0:37:27.640 --> 0:37:29.759 on the thing you're trying to measure. So people come 0:37:29.800 --> 0:37:32.560 up with these crazy clever experiments where you try to 0:37:32.640 --> 0:37:35.919 use really low energy device to measure a very high 0:37:36.080 --> 0:37:39.359 energy difference in the possible states of the object. So 0:37:39.440 --> 0:37:42.520 the thing you're measuring is not influencing the state enough 0:37:42.560 --> 0:37:43.560 to change the answer. 0:37:44.120 --> 0:37:45.879 Oh I see, yeah, Like you said, like you want 0:37:45.920 --> 0:37:49.840 to send in a scientist kitty whose state whether the 0:37:49.880 --> 0:37:51.400 kitty is a live or dead is not really going 0:37:51.480 --> 0:37:54.080 to influence whether the big cat is a live or 0:37:54.080 --> 0:37:56.279 dead exactly. 0:37:56.960 --> 0:37:58.839 And so there's these folks that come up with its 0:37:58.880 --> 0:38:01.759 really clever experience where you take a box and you 0:38:01.800 --> 0:38:04.920 put low energy photons inside of it, and under some 0:38:05.160 --> 0:38:09.520 almost magic like wave mechanics mathematics, there's a place in 0:38:09.520 --> 0:38:11.840 the box where the photon wavelengths add up in a 0:38:11.880 --> 0:38:14.640 special way to wiggle at a really high energy. So 0:38:14.719 --> 0:38:16.920 waves can add up and they can cancel each other out. 0:38:17.000 --> 0:38:20.319 This is constructive and destructive interference, where it turns out 0:38:20.320 --> 0:38:22.799 if you put a bunch of low energy photons into 0:38:22.800 --> 0:38:25.200 a box, there's one portion of the box where they're 0:38:25.239 --> 0:38:28.680 wiggling really really fast where all those photons added up 0:38:29.000 --> 0:38:31.920 kind of make a higher energy photon than the sum 0:38:31.960 --> 0:38:34.440 of all the energy of the photons you put in. 0:38:35.000 --> 0:38:36.520 And they came up with this way to try to 0:38:36.560 --> 0:38:39.400 reflect that one part of the photon out of the 0:38:39.400 --> 0:38:42.160 box by slipping a mirror in really quick. And so 0:38:42.160 --> 0:38:44.560 it's sort of like putting a few low energy photons 0:38:44.560 --> 0:38:46.640 in a box and then getting out a really high 0:38:46.760 --> 0:38:49.919 energy photon. So this is the experiment they propose would 0:38:50.000 --> 0:38:53.480 prove violation or conservation of energy and quantum mechanics. But 0:38:53.520 --> 0:38:56.080 there's a lot of controversy about what this experiment might 0:38:56.160 --> 0:38:57.799 mean and whether you could actually do it. 0:38:58.160 --> 0:39:01.080 Oh, I see, because if you measure a really big 0:39:01.120 --> 0:39:03.480 photon coming out of this corner of the box, you 0:39:03.520 --> 0:39:05.080 have to wonder where that energy came from. 0:39:05.160 --> 0:39:07.960 Yeah, how did the universe make this high energy photon 0:39:08.239 --> 0:39:10.719 out of just a few very low energy photons? Where 0:39:10.760 --> 0:39:12.520 did it come from? Just like the example we were 0:39:12.520 --> 0:39:15.520 talking about before, how did the particle get seventy five 0:39:15.600 --> 0:39:18.160 GeV when the expected value of the energy was fifty 0:39:18.200 --> 0:39:20.600 Where did that energy come from? And you can only 0:39:20.600 --> 0:39:23.000 really ask that question where did it come from if 0:39:23.040 --> 0:39:25.719 you believe it should come from somewhere, which implies that 0:39:25.760 --> 0:39:27.960 it's conserved, that it has to come from somewhere, that 0:39:28.000 --> 0:39:30.799 it's like flows around in it's a limited amount. But 0:39:30.800 --> 0:39:32.719 if energy is not conserved, it can just like go 0:39:32.800 --> 0:39:34.480 up or down, like the number of dead cats in 0:39:34.520 --> 0:39:36.360 the universe. Then that's not really a problem. 0:39:36.400 --> 0:39:38.040 But couldn't you just say that the energy of that 0:39:38.200 --> 0:39:40.719 right photon in the corner came from the little photons 0:39:41.120 --> 0:39:43.320 or would it come out with a much bigger energy 0:39:43.360 --> 0:39:46.520 than the if you add up the little smaller photons. 0:39:46.600 --> 0:39:49.040 Yeah, in this case, the energy is much bigger than 0:39:49.080 --> 0:39:51.200 the sum of the energies of all the photons you 0:39:51.239 --> 0:39:53.520 put in, So you can't explain it by just like 0:39:53.560 --> 0:39:56.720 having added up those photons. It's a really cool experiment. 0:39:56.760 --> 0:39:59.520 It's called super oscillation if you want to check out 0:39:59.520 --> 0:40:00.520 more details about it. 0:40:00.680 --> 0:40:02.680 Well, but then you said that this is all just 0:40:02.960 --> 0:40:06.200 base on one interpretation of quantum mechanics. What did the 0:40:06.239 --> 0:40:08.560 other interpretations say or how can they help us? 0:40:08.719 --> 0:40:10.480 Yeah, because a big part of the issue is what 0:40:10.560 --> 0:40:12.799 happens when you make a measurement. Right if you go 0:40:12.880 --> 0:40:15.680 from a state that has on average fifty jewels of energy, 0:40:15.880 --> 0:40:17.560 then you make a measurement, how do you end up 0:40:17.560 --> 0:40:19.680 in one of those states? And where does that energy 0:40:19.719 --> 0:40:22.360 come from? And other interpretations of quantum mechanics tell a 0:40:22.520 --> 0:40:25.319 very different story about what's happening there. For example, the 0:40:25.360 --> 0:40:28.560 Many Worlds or ever Ready in quantum mechanics says that 0:40:28.600 --> 0:40:31.359 there is no collapse of the wave function. That if 0:40:31.360 --> 0:40:34.440 you have a superposition of two possibilities that has alive 0:40:34.560 --> 0:40:37.319 or dead, the particle has twenty five or seventy five 0:40:37.400 --> 0:40:40.000 jewels of energy, that when you make a measurement, the 0:40:40.120 --> 0:40:42.440 universe just branches and now there's one branch that has 0:40:42.480 --> 0:40:44.600 one option and another branch that has the other option. 0:40:44.840 --> 0:40:47.279 And so in that sense, if you're like averaging over 0:40:47.320 --> 0:40:50.640 the branches, nothing has really changed. You know, the total 0:40:50.760 --> 0:40:53.839 energy in the universe hasn't changed. One individual branch might 0:40:53.880 --> 0:40:56.880 see seventy five jewels, so they might think they're seeing 0:40:57.000 --> 0:41:00.480 violation of conservation of energy. But averaged over all the branches, 0:41:00.520 --> 0:41:03.080 including the ones that don't see, nothing has really changed. 0:41:03.120 --> 0:41:05.440 There's still just a distribution of different energies. 0:41:05.719 --> 0:41:09.000 I feel like you just skipped over a humongas concept 0:41:09.160 --> 0:41:11.040 which is just throwing the multiverse. 0:41:11.200 --> 0:41:13.359 Yes, exactly, in the multiverse. 0:41:12.800 --> 0:41:16.520 Quantum multiverse. So you're saying, like, one way to interpret 0:41:16.600 --> 0:41:19.480 quantum mechanics is that things don't collapse. You know, if 0:41:19.480 --> 0:41:21.319 something if the cat is alive and dead, it means 0:41:21.320 --> 0:41:23.560 that there's a universe where the cat is alive and 0:41:23.640 --> 0:41:27.200 there's a universe where it's dead, and so overall energy 0:41:27.239 --> 0:41:28.719 is still conserved. That's kind of the idea. 0:41:28.960 --> 0:41:33.960 Yeah, energy is just unevenly distributed among those quantum multiverses. 0:41:34.320 --> 0:41:37.000 One of them gets more, another one gets less. Overall 0:41:37.080 --> 0:41:40.200 it all balances out across the multiverse. But in an 0:41:40.239 --> 0:41:44.040 individual universe, an observer does see a violation of energy. 0:41:44.320 --> 0:41:46.719 So that's a pretty different story than what's being told 0:41:46.719 --> 0:41:47.719 by the Copenhagen group. 0:41:47.800 --> 0:41:49.360 Let me see if I get this, so, like, I 0:41:49.400 --> 0:41:51.520 have the cat in the box, and I open the 0:41:51.560 --> 0:41:53.799 box and I find that the cat is alive, and 0:41:53.840 --> 0:41:55.680 I think, oh my god, this is a violation of 0:41:55.840 --> 0:41:59.200 cat aliveness in the universe because before the cat was 0:41:59.239 --> 0:42:01.520 only fifty percent and now it's fully alive. 0:42:01.680 --> 0:42:02.080 Sure. 0:42:02.880 --> 0:42:06.240 Yeah, And you're saying, if you think that the actually 0:42:06.280 --> 0:42:09.680 there's a multiverse, is a quantum multiverse, then there's no 0:42:09.760 --> 0:42:12.640 real violation because if you consider my universe where the 0:42:12.680 --> 0:42:15.279 cat is alive and your universe where the cat is dead, 0:42:15.840 --> 0:42:18.000 then it makes sense for me to see that the 0:42:18.040 --> 0:42:19.640 cat is alive, and it makes sense for you to 0:42:19.680 --> 0:42:21.960 see that the cat is dead. There's no violation here. 0:42:21.840 --> 0:42:24.840 Yeah, because across the quantum multiverse it's still fifty percent 0:42:24.880 --> 0:42:26.360 alive and fifty percent dead. 0:42:26.480 --> 0:42:30.200 But in the single universe version of quantum mechanics, the 0:42:30.440 --> 0:42:33.520 cat aliveness went up from one half to one if 0:42:33.560 --> 0:42:34.520 I see that the cat. 0:42:34.360 --> 0:42:38.360 Is alive exactly. So in the collapse theory where measuring 0:42:38.400 --> 0:42:41.160 it forces the universe to choose one of these branches 0:42:41.200 --> 0:42:44.480 instead of maintaining all of them, then somehow the number 0:42:44.520 --> 0:42:46.600 of live cats in the universe goes up from half 0:42:46.640 --> 0:42:49.840 to one, violating the well known principle of the number 0:42:49.840 --> 0:42:51.360 of living cats in the universe. 0:42:51.800 --> 0:42:54.680 Yeah, or people in swimming pools, which I'm going to 0:42:54.840 --> 0:43:00.000 wait for that paper from me. Okay, hold your breas, yeah, 0:43:00.120 --> 0:43:02.560 to under the pool. Yes, Okay. So then I feel 0:43:02.600 --> 0:43:06.920 like maybe I wonder, like you're saying, if we require 0:43:07.480 --> 0:43:10.400 energy to be conserved in the universe for real, for sure, 0:43:11.280 --> 0:43:14.960 then maybe I wonder if that's proof that the multiverse exists, 0:43:15.239 --> 0:43:17.040 because that's the only way that this is going to work. 0:43:17.120 --> 0:43:19.799 Right, That's a cool perspective I hadn't thought of. Yeah, 0:43:19.840 --> 0:43:23.640 I suppose if you define energy that way as across 0:43:23.640 --> 0:43:29.000 the multiverse and you insist that it's conserved, then Copenhagen 0:43:29.040 --> 0:43:31.680 interpretation of quantum mechanics does violate that. But that's not 0:43:31.719 --> 0:43:34.319 something you can test, right. You can never access these 0:43:34.320 --> 0:43:37.439 other branches of the multiverse. You can never know if 0:43:37.440 --> 0:43:40.320 they exist, and if other people are measuring other things, 0:43:40.360 --> 0:43:42.680 then you can only ever access our branch. 0:43:42.920 --> 0:43:46.319 We think, maybe, right, maybe you can this. I think 0:43:46.320 --> 0:43:48.920 we've talked about this before and in our books, like 0:43:49.239 --> 0:43:52.040 you could maybe discover something about the mathematics of our 0:43:52.120 --> 0:43:55.520 universe that maybe points to the necessity of other universes. 0:43:55.560 --> 0:43:58.359 No, we definitely argue in our book that it might 0:43:58.400 --> 0:44:01.840 be that the only consistent explanation of the universe is 0:44:01.880 --> 0:44:05.680 the multiverse. So you can prove the multiverse exists without 0:44:05.800 --> 0:44:08.480 ever experimentally verifying it, though that takes a lot of 0:44:08.520 --> 0:44:11.399 confidence to say that there's no other explanation out there. 0:44:11.480 --> 0:44:13.960 That would take a high amount of confidence, not a 0:44:14.040 --> 0:44:15.200 nuclear amount of confidence. 0:44:15.239 --> 0:44:18.279 So extrapolining that argument, if you can somehow prove that 0:44:18.360 --> 0:44:21.560 a complete theory of the universe has to satisfy conservation 0:44:21.600 --> 0:44:24.120 of energy at the quantum level, then yeah, that might 0:44:24.200 --> 0:44:26.960 require the existence of the multiverse. But I don't know 0:44:26.960 --> 0:44:30.320 how you would prove that requirement because energy is not 0:44:30.440 --> 0:44:32.920 even necessarily well defined at the quantum level. 0:44:33.160 --> 0:44:34.960 I wonder if that means that some of the other 0:44:35.080 --> 0:44:38.080 places that we've seen energy conservation being violated, like the 0:44:38.120 --> 0:44:40.560 expansion of the universe. I wonder if that can mean that, 0:44:41.080 --> 0:44:43.959 you know, as our universe expands and gains energy, maybe 0:44:43.960 --> 0:44:48.160 there's another universe out there losing energy and being compressed. 0:44:48.239 --> 0:44:49.680 It's a great question and one of the reasons I 0:44:49.760 --> 0:44:52.840 really like this question zooming down to the microscopic scale 0:44:52.880 --> 0:44:55.880 and trying to understand what is conservation of energy there 0:44:56.160 --> 0:44:58.160 is because we're really interested in what it means at 0:44:58.160 --> 0:45:00.560 our scale, Like where does energy come from? Why is 0:45:00.560 --> 0:45:03.040 it conserved for us? Is it because it's required at 0:45:03.040 --> 0:45:05.920 the quantum level, or is it because it emerges somehow? 0:45:06.320 --> 0:45:10.560 And so yeah, maybe energy non conservation in general relativity 0:45:10.880 --> 0:45:15.080 could eventually be derived from some deep quantum gravity, some 0:45:15.239 --> 0:45:17.680 explanation of the nature of space time at the quantum 0:45:17.840 --> 0:45:21.160 level that has these consequences at our scale or at 0:45:21.160 --> 0:45:23.400 the scale of the whole universe. So that would be 0:45:23.440 --> 0:45:24.279 really fascinating. 0:45:24.560 --> 0:45:26.759 Yeah, or maybe vice versa, right, Like, if you prove 0:45:26.880 --> 0:45:30.239 energy conservation at the grand level, it must might have 0:45:30.320 --> 0:45:33.080 some consequences about you know, what we think is happening 0:45:33.160 --> 0:45:34.040 at the quantum level. 0:45:34.080 --> 0:45:37.360 It could be although sometimes conservation laws cannot be exact. 0:45:37.440 --> 0:45:39.800 They can just emerge, so they don't have to always 0:45:39.840 --> 0:45:42.480 hold true at the quantum level to hold true at 0:45:42.520 --> 0:45:44.440 the classical level. But there are some things that are 0:45:44.480 --> 0:45:47.160 truet the quantum level, Like we think conservation momentum is 0:45:47.280 --> 0:45:49.640 rock solid at the quantum level, and the reason we 0:45:49.719 --> 0:45:52.520 have it at our level is because everything is made 0:45:52.560 --> 0:45:55.840 out of these quantum bits which follow these rules. So 0:45:55.880 --> 0:45:58.400 we don't know basically whether conservation of energy is exact 0:45:58.600 --> 0:46:01.520 the way conservation momentum is because it comes out of 0:46:01.520 --> 0:46:04.360 the quantum level, or if it's something that emerges somehow 0:46:04.400 --> 0:46:06.080 when you get classical physics. 0:46:06.400 --> 0:46:08.640 I guess maybe your people in a pool experiment is 0:46:08.640 --> 0:46:10.160 going to conclusively prove that. 0:46:10.200 --> 0:46:13.480 Then give me one hundred years. It's going to take 0:46:13.520 --> 0:46:15.240 a lot of data. 0:46:15.400 --> 0:46:17.120 What do you Why do you need five years to 0:46:17.160 --> 0:46:17.480 do this? 0:46:19.800 --> 0:46:22.200 Oh man, because the I RB you know, you're doing 0:46:22.239 --> 0:46:25.319 experiments on people. You got to sign the papers. It's 0:46:25.360 --> 0:46:25.839 the whole thing. 0:46:27.120 --> 0:46:29.120 I see. Yeah, And then there's a pool, so the 0:46:29.160 --> 0:46:32.080 forms get wet. It's all a big mess. What does 0:46:32.120 --> 0:46:35.239 this have more implications for our understanding of quantum mechanics 0:46:35.360 --> 0:46:38.160 or understanding of energy conservation in the universe. 0:46:38.400 --> 0:46:41.000 I think it has consequences for our understanding of what 0:46:41.160 --> 0:46:43.960 energy is. As we drill down to see what the 0:46:44.040 --> 0:46:47.319 universe really is like at the microscopic scale, we learn 0:46:47.360 --> 0:46:50.600 about things that turn out to just be features of 0:46:50.640 --> 0:46:53.520 our existence. They're not generally true at every level of 0:46:53.520 --> 0:46:56.439 the universe, you know, like there's no equivalent to ice 0:46:56.440 --> 0:46:59.000 cream at the quantum level, for example, there's no equivalent 0:46:59.040 --> 0:47:02.279 to cats. Those things only exist at our level. And 0:47:02.360 --> 0:47:04.480 so I love that as we keep looking deeper into 0:47:04.480 --> 0:47:07.520 the universe, we discover things about our experience that turn 0:47:07.560 --> 0:47:09.360 out to just be part of our experience. They're not 0:47:09.480 --> 0:47:13.480 generally true about the universe, Like our sun is unusual, 0:47:13.520 --> 0:47:16.400 and maybe our planet is weird, maybe our way of 0:47:16.440 --> 0:47:19.319 life is weird. And the same way, we discover that 0:47:19.400 --> 0:47:21.600 the way we experience the universe and the things we 0:47:21.640 --> 0:47:24.399 think are fundamental about it actually aren't. To me, that's 0:47:24.440 --> 0:47:27.440 really cool and opens up questions about like other conservation 0:47:27.560 --> 0:47:30.440 laws are other things that we thought were hard and 0:47:30.480 --> 0:47:32.719 fast and true about the universe actually just sort of 0:47:32.760 --> 0:47:35.960 like emergent approximate things, and at a quantum level they're 0:47:36.000 --> 0:47:38.400 not preserved. That would be kind of scary. 0:47:38.600 --> 0:47:40.480 Well for me, I'm getting the sense that maybe, like 0:47:40.600 --> 0:47:43.360 even if we do discover that energy is conserved or 0:47:43.400 --> 0:47:47.239 not in our universe, that wouldn't maybe really tells what 0:47:47.280 --> 0:47:49.799 the real truth is because we wouldn't have access to 0:47:49.840 --> 0:47:54.200 maybe the multiverse in other universes, which would maybe cancel 0:47:54.280 --> 0:47:56.560 out what we think is the rule of the universe. 0:47:56.800 --> 0:47:58.520 Yeah, that's right. We could see what we think is 0:47:58.640 --> 0:48:01.759 energy non conservation and bigger picture, it all balances out, 0:48:02.360 --> 0:48:04.480 and so we might never really know these answers. 0:48:04.719 --> 0:48:06.480 Well, I'll just take comfort in the fact that even 0:48:06.520 --> 0:48:09.920 if I don't exercise today, maybe there's a quantum Woorge 0:48:10.080 --> 0:48:14.040 in another universe who is doing double the exercise for 0:48:14.080 --> 0:48:16.560 the tour that both us and in some way you 0:48:16.600 --> 0:48:18.120 can say that I exercised today. 0:48:18.280 --> 0:48:21.240 Yeah, that's true, and that quantum Hohoge will live longer 0:48:21.239 --> 0:48:24.879 than you and on average, you know, some fractionales across 0:48:24.880 --> 0:48:26.200 the teams, this will be alive or not. 0:48:27.160 --> 0:48:29.560 Yeah, there you go. There you go, playing with some 0:48:29.680 --> 0:48:33.960 kittens and counting people in a swimming pool. All right, Well, 0:48:33.960 --> 0:48:37.080 we hope you enjoyed that. Thanks for joining us. See 0:48:37.120 --> 0:48:37.640 you next time. 0:48:42.800 --> 0:48:45.680 For more science and curiosity, come find us on social 0:48:45.719 --> 0:48:49.640 media where we answer questions and post videos. We're on Twitter, 0:48:49.760 --> 0:48:53.080 this word instant and now TikTok. And remember that Daniel 0:48:53.120 --> 0:48:56.560 and Jorge explain the universe is a production of iHeartRadio. 0:48:56.840 --> 0:49:00.400 For more podcast from iHeart Radio, visit the iHeart Radio 0:49:00.440 --> 0:49:04.480 Apple Apple Podcasts, or wherever you listen to your favorite shows.