WEBVTT - Where does energy come from? 0:00:06.080 --> 0:00:08.240 One of my favorite things about physics is that it 0:00:08.320 --> 0:00:11.800 lets us think concretely and carefully about the basic nature 0:00:11.920 --> 0:00:14.960 of our experience. What is space? What is matter? What 0:00:15.080 --> 0:00:18.680 is time? What's a particle? Why are there waves everywhere? 0:00:18.880 --> 0:00:22.720 Physics helps us convert these squishy conversations on rooftops over 0:00:22.760 --> 0:00:27.400 smoke banana peels into robust mathematics. The math doesn't require 0:00:27.520 --> 0:00:30.480 persuasion or a clever choice of words. It's either right 0:00:30.680 --> 0:00:33.320 or it's wrong. So instead of answering a question about 0:00:33.320 --> 0:00:35.480 the nature of the squish universe, we get to poke 0:00:35.560 --> 0:00:39.480 and prod our mathematical description of it. Sometimes that gives 0:00:39.520 --> 0:00:42.600 us real insight, like when relativity tells us that distance 0:00:42.600 --> 0:00:46.280 and velocity have to be relative rather than absolute, because 0:00:46.320 --> 0:00:50.960 that's the only mathematical model that describes the universe we see. 0:00:51.080 --> 0:00:54.320 Other times it surprises us by telling us that we 0:00:54.440 --> 0:00:57.960 might just be asking the wrong question. Maybe the things 0:00:58.000 --> 0:01:02.240 we thought were important just reveal our fundamental misunderstandings of 0:01:02.400 --> 0:01:05.520 the universe and how it works. Today we'll be asking 0:01:05.520 --> 0:01:08.600 what physics can tell us about energy, What is it? 0:01:08.720 --> 0:01:12.480 And more importantly, where does it come from? Welcome to 0:01:12.600 --> 0:01:15.959 Daniel and Kelly's Extraordinary energetic Universe. 0:01:29.959 --> 0:01:31.479 Hello. I'm Kelly Wiener Smith. 0:01:31.560 --> 0:01:34.959 I study space and parasites and I just got over 0:01:35.000 --> 0:01:36.880 having the flu for a week and I really could 0:01:36.920 --> 0:01:37.560 have used energy. 0:01:39.240 --> 0:01:41.760 Hi. I'm Daniel. I'm a particle physicist and I love 0:01:41.800 --> 0:01:45.199 how Kelly opens the podcast with so much energy every time. 0:01:46.240 --> 0:01:48.320 Okay, well we both have a lot of energy. 0:01:48.840 --> 0:01:52.000 Speaking of energy, do you rely on caffeine? What is 0:01:52.040 --> 0:01:53.680 your favorite form of liquid energy? 0:01:54.040 --> 0:01:57.160 I do rely on caffeine. I'm drinking coffee right now here. 0:01:57.200 --> 0:02:05.360 You go, Oh oh for you asmr. Folks. Yeah, yes, 0:02:05.400 --> 0:02:07.320 I have caffeine in the mornings, but I can't have 0:02:07.440 --> 0:02:10.080 any really after lunch or interference with my sleep. I'm 0:02:10.120 --> 0:02:13.519 at that age where sleep is not necessarily a given. 0:02:13.919 --> 0:02:14.440 Yeah. Same. 0:02:14.480 --> 0:02:16.720 I used to drink coffee all day long. I like 0:02:16.760 --> 0:02:18.320 didn't drink water in college. 0:02:19.200 --> 0:02:21.600 That doesn't sound like a good idea. 0:02:21.800 --> 0:02:23.560 You know, I got a lot done, I got a 0:02:23.560 --> 0:02:25.640 whole lot done, but I could still fall asleep. But 0:02:25.680 --> 0:02:27.920 now I also if it's after lunch, forget it. I 0:02:27.960 --> 0:02:29.280 can't have coffee anymore either. 0:02:29.480 --> 0:02:32.040 Remember, folks, this is not a health podcast. Do not 0:02:32.080 --> 0:02:32.880 take our advice. 0:02:34.000 --> 0:02:37.200 Noah, no, please don't don't follow our lead. When you 0:02:37.200 --> 0:02:39.680 were a kid, did you ever try jolts? 0:02:39.840 --> 0:02:42.600 Jolt was the kind of thing that was so forbidden 0:02:42.720 --> 0:02:45.800 in my family. Like my mom was very controlling about 0:02:45.800 --> 0:02:47.520 the kind of food we could eat, you know, she 0:02:47.600 --> 0:02:50.160 like counted potato chips, this kind of thing, So junk 0:02:50.200 --> 0:02:52.840 food definitely off of this jolt. She saw that as 0:02:52.880 --> 0:02:55.080 like battery acid, Like there was no way she would 0:02:55.080 --> 0:02:57.040 allow us. Did you try jolts? 0:02:57.880 --> 0:02:59.960 Yeah? Do you remember pixie stick? 0:03:00.360 --> 0:03:01.160 Yeah? 0:03:01.200 --> 0:03:03.680 So there used to be like a megapixie stick. It 0:03:03.680 --> 0:03:06.120 was like a giant plastic tube like the thickness of 0:03:06.120 --> 0:03:07.919 my thumb, and it was just filled with. 0:03:07.800 --> 0:03:09.280 Sugar and food coloring. 0:03:09.840 --> 0:03:12.040 And we had like a party once where we just 0:03:12.080 --> 0:03:14.400 like had those pixie sticks with jolts. 0:03:16.120 --> 0:03:17.880 And I got pretty sick. 0:03:18.200 --> 0:03:21.240 And jolts made me feel horrible the way too much 0:03:21.240 --> 0:03:22.360 caffeine makes me feel now. 0:03:22.400 --> 0:03:23.760 But I tried it once, and it was one thing 0:03:23.800 --> 0:03:24.400 as a kid. 0:03:24.240 --> 0:03:27.160 Where I was like, I shouldn't do that again. Anyway, 0:03:27.200 --> 0:03:27.919 I had a lot more fun. 0:03:27.919 --> 0:03:30.200 It sounds like it does sound like you had more fun, 0:03:30.240 --> 0:03:32.359 but you also got sick. But I have a basic 0:03:32.400 --> 0:03:35.320 biology question for you about caffeine. I mean, I understand 0:03:35.400 --> 0:03:38.640 if you eat a pixie stick, it's sugar. Sugar has energy. 0:03:38.840 --> 0:03:41.480 You could potentially get high and a rush and feel 0:03:41.600 --> 0:03:44.800 energetic from that. But caffeine, how does that give me 0:03:44.920 --> 0:03:47.720 energy or make me alert? Is it really energy from 0:03:47.720 --> 0:03:50.280 the caffeine that my body's using. Is it releasing some 0:03:50.480 --> 0:03:53.000 energy stores in my body? Or is it some much 0:03:53.040 --> 0:03:57.000 more complicated neuro answer, dot dot dot. It depends. 0:03:57.440 --> 0:03:59.640 Probably, it depends. I don't actually know. 0:03:59.680 --> 0:04:01.760 I didn't prepare the answer for that coming in here. 0:04:01.840 --> 0:04:04.240 I believe it binds to certain receptors in your brain. 0:04:04.680 --> 0:04:06.760 My job in college was barista. I worked at like 0:04:06.800 --> 0:04:09.000 four different coffee shops, and so I've had like shirts 0:04:09.000 --> 0:04:11.800 with the caffeine molecule on the front. So yeah, I 0:04:11.800 --> 0:04:13.920 think it binds with some receptors in your brain. And 0:04:13.960 --> 0:04:15.920 I don't know how that results in you feeling awake, 0:04:16.000 --> 0:04:17.080 but it works. 0:04:17.240 --> 0:04:19.000 It pulls on some levers and ropes of the Rube 0:04:19.000 --> 0:04:20.559 Goldberg machine that is my mind. 0:04:21.480 --> 0:04:23.560 That's right, that's right, and thank God for it. I 0:04:23.600 --> 0:04:25.520 don't know how I would have gotten through college without it. 0:04:25.760 --> 0:04:27.800 At some point I was working at a coffee shop 0:04:27.800 --> 0:04:31.240 because I couldn't afford all the coffee I wanted to drink, 0:04:31.240 --> 0:04:32.760 but if I worked at the coffee shop, I could 0:04:32.760 --> 0:04:35.400 afford it and pay my rent. So anyway, I had 0:04:35.400 --> 0:04:37.280 a problem maybe, but I also had fun. 0:04:37.480 --> 0:04:40.279 Well. Energy is a really fun topic because it's something 0:04:40.320 --> 0:04:42.160 that is colloquial and we talk about it in our 0:04:42.200 --> 0:04:44.520 lives and whether you feel energetic and whether you drink 0:04:44.520 --> 0:04:47.600 caffeine whatever, And it's also something deeply important to physics 0:04:47.640 --> 0:04:50.200 and the universe. So it's one of these topics that 0:04:50.240 --> 0:04:53.839 people have like a personal feeling about, like where energy is, 0:04:53.880 --> 0:04:56.280 where it comes from, and what it means. And it's 0:04:56.279 --> 0:04:59.880 also really pervasive in popular science. You know, equals MC squared, 0:05:00.320 --> 0:05:02.400 energy is mass. People tell us there's a lot of 0:05:02.440 --> 0:05:05.520 nonsense out there about energy. So I thought it'd be 0:05:05.560 --> 0:05:07.560 good to have an episode where we dig into some 0:05:07.640 --> 0:05:10.440 details about what energy is and where it comes from 0:05:10.480 --> 0:05:12.680 and what we know and don't know about it. 0:05:12.960 --> 0:05:14.880 Yes, and you always do a great job of getting 0:05:14.920 --> 0:05:17.280 us back on tracks. That was fantastic, and the other 0:05:17.400 --> 0:05:20.240 people who keep us on track are our amazing audience, 0:05:20.600 --> 0:05:23.800 and so we asked them where does energy come from? 0:05:23.800 --> 0:05:25.479 And if you want to answer questions for us, you 0:05:25.480 --> 0:05:28.200 can write us at questions at Daniel and Kelly dot org. 0:05:28.400 --> 0:05:30.760 But let's go ahead and here from our audience, where 0:05:30.960 --> 0:05:32.400 does energy come from? 0:05:32.760 --> 0:05:36.839 Energy comes from heat, which comes from photon. I have 0:05:36.960 --> 0:05:37.720 no idea. 0:05:37.880 --> 0:05:41.960 Is it a mathematical trick, is it just an accounting system? 0:05:42.680 --> 0:05:46.760 Who else? Nobody knows where energy comes from, and nobody's 0:05:46.760 --> 0:05:50.040 ever gonna know. It is the magic of the universe. 0:05:50.600 --> 0:05:54.200 I don't think energy comes from anyway, because you can't 0:05:54.960 --> 0:05:56.200 have not energy. 0:05:56.839 --> 0:05:59.279 Well, it comes from fields that permeate the entire universe. 0:06:00.680 --> 0:06:04.120 Energy comes from hydrogen fusion caused by gravity, So I'd 0:06:04.120 --> 0:06:05.120 have to say gravity. 0:06:05.480 --> 0:06:07.720 Yes, it comes from the Big Bang and has just 0:06:07.800 --> 0:06:12.760 been circulating in different forms ever since. Or powered Now, 0:06:12.760 --> 0:06:15.320 if you're talking about the energy that powered the Big Bang, 0:06:15.440 --> 0:06:18.320 or energy required to keep all the quantum fuels fluctuating 0:06:18.360 --> 0:06:21.440 and alive, I imagine a physicist is better suited to 0:06:21.520 --> 0:06:22.280 provide insight. 0:06:22.680 --> 0:06:26.800 Hint, hint, So I guess that MLGS comes from symmetries 0:06:26.920 --> 0:06:30.520 in nature. Obviously the Big Bang has a big role 0:06:30.560 --> 0:06:33.359 in it, but it might not be the whole thought. 0:06:34.040 --> 0:06:40.159 Since you can't create energy, I assume it originates from 0:06:40.160 --> 0:06:44.440 the Big Bang, and before then who knows. 0:06:44.600 --> 0:06:45.960 I guess it's always better around. 0:06:46.000 --> 0:06:48.159 It just changes form after form. 0:06:48.600 --> 0:06:53.200 Perhaps what we're calling space time is actually energy. Oh well, 0:06:53.240 --> 0:06:59.120 I really am stumped by this one. I really don't know. 0:07:00.279 --> 0:07:03.320 All the energy in the universe today came from the 0:07:03.360 --> 0:07:06.000 storehouse of energy released in the Big Bang. 0:07:06.400 --> 0:07:09.640 Some energy comes from the Big Bang, and some comes 0:07:09.640 --> 0:07:13.960 from dark energy, but most energy in this universe comes 0:07:14.000 --> 0:07:15.720 from eating your waities. 0:07:16.280 --> 0:07:19.400 Have we not always had the same amount of energy? 0:07:19.760 --> 0:07:22.640 I would say all energy originated from the Big Bang 0:07:22.720 --> 0:07:26.400 and everything since then it's just been conversions of different forms. 0:07:26.840 --> 0:07:29.240 But then you can ask where did that come from? 0:07:29.320 --> 0:07:31.040 And where does dark energy come from? 0:07:31.080 --> 0:07:36.360 And I don't know. There's some really philosophical answers in here, 0:07:36.400 --> 0:07:37.840 and I loved listening to these. 0:07:38.240 --> 0:07:39.760 Well, I mean, that's what I've come to expect from 0:07:39.760 --> 0:07:40.160 the audience. 0:07:40.200 --> 0:07:43.640 It's like always a nice combination of like philosophical some 0:07:43.680 --> 0:07:45.840 people who get like exactly the right answer or get 0:07:45.880 --> 0:07:48.320 really close, and then some people who know they don't 0:07:48.320 --> 0:07:48.920 know and so they. 0:07:48.920 --> 0:07:50.520 Just go all in on being hilarious. 0:07:50.760 --> 0:07:52.640 I always love listening to the answers. 0:07:53.040 --> 0:07:56.080 This comment that you can't have not energy, I had 0:07:56.080 --> 0:07:57.680 to pause that and think about it for a while. 0:07:57.680 --> 0:07:59.720 I was like, Wow, that sounds really profound, but I'm 0:07:59.760 --> 0:08:01.360 not even share what it means. 0:08:01.880 --> 0:08:05.600 Like a lot of philosophy, I thought that they were 0:08:05.600 --> 0:08:08.960 trying to say, if there wasn't energy, none of us 0:08:08.960 --> 0:08:12.000 would be here, which doesn't really the answer the question 0:08:12.040 --> 0:08:14.200 where it comes from, but just something had to have 0:08:14.240 --> 0:08:14.960 made it exist. 0:08:15.280 --> 0:08:16.160 I don't know, what do you think? 0:08:16.560 --> 0:08:19.760 I didn't know? Yeah, what is not energy? Is that 0:08:20.000 --> 0:08:23.240 energy equals zero. It's true, you can't have zero energy 0:08:23.280 --> 0:08:27.400 in the universe because of quantum mechanics. Yeah, fascinating, Yeah, 0:08:27.440 --> 0:08:30.200 really fun answers here and a lot of assumptions. You 0:08:30.280 --> 0:08:34.560 hear that energy doesn't come from anywhere because we've had 0:08:34.559 --> 0:08:37.720 the same amount the whole time. Because people have this 0:08:37.800 --> 0:08:40.319 conception which we're going to take apart and debunk a 0:08:40.360 --> 0:08:43.600 little bit, that energy is conserved. The energy has to 0:08:43.640 --> 0:08:47.400 come from somewhere because you can either create nor destroy it, 0:08:47.440 --> 0:08:49.040 and therefore it can only flow. 0:08:49.600 --> 0:08:51.440 So yeah, when I was looking through your outline and 0:08:51.480 --> 0:08:53.720 I saw energy is not conserved, I was like, what, 0:08:55.280 --> 0:08:57.880 I'm sure I've heard that a lot of times, and so, 0:08:58.200 --> 0:08:59.600 you know, I think a lot of us are looking 0:08:59.640 --> 0:09:03.959 forward to having our preconceptions about energy sort of cleared up. 0:09:04.280 --> 0:09:08.679 Yeah, exactly. But before we get into the mind blowing 0:09:08.760 --> 0:09:11.480 revelations about the nature of energy, we have to be 0:09:11.559 --> 0:09:15.360 clear and careful about what is it we're talking about anyway. 0:09:15.960 --> 0:09:18.240 Are we talking about how the earth keeps warm? Are 0:09:18.240 --> 0:09:20.600 we talking about what happens when you eat your wheaties? 0:09:20.920 --> 0:09:24.160 Are we talking about philosophical revelations about the fundamental nature 0:09:24.200 --> 0:09:26.480 of the universe. So the first thing we have to do, 0:09:26.520 --> 0:09:29.320 of course, is define what do we mean when we 0:09:29.400 --> 0:09:30.320 say energy. 0:09:30.800 --> 0:09:34.360 Yeah, so as a biologist, I'm thinking ATP, I'm thinking 0:09:34.400 --> 0:09:37.000 at it at a chemistry level. We're as a physicist. 0:09:37.480 --> 0:09:39.880 Do you think about it like that as well? Or 0:09:39.920 --> 0:09:41.760 this is just a totally different topic. 0:09:42.640 --> 0:09:45.439 Now ATP is like a chemical store of energy, so 0:09:45.480 --> 0:09:49.160 it's completely related to the topic at hand. But it's 0:09:49.160 --> 0:09:52.680 an example, right. It's like if somebody says to you, hey, 0:09:52.720 --> 0:09:55.040 what is a vegetable and you're like, an implant is 0:09:55.040 --> 0:09:57.280 a vegetable, And you're like, yeah, that's true, but what 0:09:57.400 --> 0:09:59.280 makes it vegetable? Why do we have them? Where do 0:09:59.400 --> 0:10:02.520 vegetables come from? Right? Showing you an a plant doesn't 0:10:02.520 --> 0:10:03.360 answer that question. 0:10:03.720 --> 0:10:05.240 Right, and then I'll go on a long rant about 0:10:05.280 --> 0:10:08.240 how vegetables not a phylogenetic category and it's something humans 0:10:08.280 --> 0:10:10.320 made up, and so anyway, go ahead. 0:10:10.360 --> 0:10:13.640 Oh my gosh, wow, oh I love when we accidentally 0:10:13.720 --> 0:10:16.760 stumble up upon a hidden Kelly rant. Love that. Wow. 0:10:16.880 --> 0:10:21.560 Okay, let's go deeper, hurt, but not on vegetables. So 0:10:21.600 --> 0:10:23.680 what is energy? How does a physicist start to answer 0:10:23.720 --> 0:10:24.200 this question? 0:10:24.559 --> 0:10:26.720 I like to answer this question by pointing out that 0:10:26.800 --> 0:10:29.360 we can invent any kind of concept. I mean, you 0:10:29.400 --> 0:10:31.720 can just make up a word called it, you know, 0:10:32.200 --> 0:10:36.560 bliblyon or whatever, and then define it and it could 0:10:36.600 --> 0:10:39.080 be a thing. And the question is like, does that 0:10:39.120 --> 0:10:41.760 reveal anything about the universe? Is it related to the 0:10:41.760 --> 0:10:44.920 physical universe in some insightful way, or is it just 0:10:45.000 --> 0:10:47.440 some nonsense that you made up? And so, from that 0:10:47.480 --> 0:10:50.040 point of view, like everything in physics is something we 0:10:50.160 --> 0:10:51.920 made up, and a lot of it is just nonsense 0:10:51.960 --> 0:10:54.160 we then ignore because it wasn't useful. And some of 0:10:54.200 --> 0:10:56.960 it actually seems to reflect something that's happening in the 0:10:57.080 --> 0:10:59.840 universe and is therefore useful, and we think maybe in 0:11:00.000 --> 0:11:03.880 delightful about the fundamental nature of reality. Right, And so 0:11:04.200 --> 0:11:06.679 energy is that way. It is something we invented. It's 0:11:06.720 --> 0:11:09.320 just like a concept we came up with. We talked 0:11:09.400 --> 0:11:12.080 recently on the podcast about entropy and the history of 0:11:12.200 --> 0:11:17.040 energy is similar predates entropy because entropy was defined as 0:11:17.240 --> 0:11:21.160 moving of energy the een and entropy comes from energy. 0:11:21.559 --> 0:11:23.240 But this is something people have been wondering about it 0:11:23.280 --> 0:11:24.560 for a long time, like how do you get a 0:11:24.559 --> 0:11:26.840 machine to work? And what's going on with heat a temperature? 0:11:27.480 --> 0:11:30.560 And so people came up with this concept of energy 0:11:30.880 --> 0:11:33.440 one hundreds of years ago. It was actually leading It's 0:11:33.520 --> 0:11:38.760 first identified energy of motion, like things in motion have energy, 0:11:39.240 --> 0:11:42.679 and he called it this visviva, this living force, just 0:11:43.040 --> 0:11:45.000 energy of motion. He recognized that. 0:11:44.880 --> 0:11:48.240 That was like a thing, but like an asteroid hurtling 0:11:48.280 --> 0:11:50.800 towards the Earth would have energy. But in what way 0:11:50.840 --> 0:11:53.640 is that a living force? Was he like specifically thinking 0:11:53.640 --> 0:11:54.640 about living organism. 0:11:54.880 --> 0:11:57.920 No, he was just thinking about animation, not necessarily like 0:11:58.200 --> 0:12:01.600 something is alive, but in motion. And so I think 0:12:01.600 --> 0:12:03.640 he was thinking more about the motion than the actual 0:12:03.920 --> 0:12:06.480 life force or the definition of life in some sort 0:12:06.480 --> 0:12:10.080 of biological way. But that's something we still recognize, right. 0:12:10.080 --> 0:12:13.320 We call that kinetic energy today and kinetic energy is 0:12:13.320 --> 0:12:16.679 definitely a form of energy, like photons have energy, right, 0:12:16.720 --> 0:12:19.400 they zoom around the universe. They're moving really really fast, 0:12:19.800 --> 0:12:22.240 So it's a type of energy. But again, this is 0:12:22.320 --> 0:12:24.680 like quoting the eggplant, right, it's not a definition of 0:12:24.720 --> 0:12:26.920 the concept. It's an example of the kind of thing, 0:12:26.920 --> 0:12:30.679 and it comes from history. And something that's especially fascinating 0:12:30.720 --> 0:12:34.360 and revealing about kinetic energy is that it's not conserved. Right. 0:12:34.679 --> 0:12:37.520 For example, you throw a ball up into the air, 0:12:38.240 --> 0:12:40.800 it slows down, right because of gravity. If you throw 0:12:40.800 --> 0:12:43.400 it straight up, it slows down, and eventually, when it 0:12:43.440 --> 0:12:46.480 reaches the top of its arc, its stopped. So kinetic 0:12:46.600 --> 0:12:49.160 energy on its own is not something that's conserved in 0:12:49.200 --> 0:12:51.880 the universe, Like the universe doesn't seem to have a 0:12:51.880 --> 0:12:55.320 special relationship with kinetic energy. It's the way you could 0:12:55.360 --> 0:12:58.000 make up any other thing, like, hey, how many ice 0:12:58.000 --> 0:13:01.319 cream cones are there currently in the universe. That's a 0:13:01.400 --> 0:13:04.400 number that we don't expect to stay constant. Right, I 0:13:04.480 --> 0:13:07.200 eat one, it's gone. I've decreased the number. I make one, 0:13:07.360 --> 0:13:10.320 it goes up. Kelly makes five thousand ice cream cones, 0:13:10.360 --> 0:13:12.920 it goes up a lot. Right, It's not anything meaningful 0:13:13.200 --> 0:13:16.320 or specific and kinetic energy is sort of the same way. 0:13:16.400 --> 0:13:19.079 Like when the ball gets thrown up into the air, 0:13:19.160 --> 0:13:24.040 it loses that kinetic energy. Where does the kinetic energy go. Well, 0:13:24.679 --> 0:13:27.280 energy can just go up and down. In this case, 0:13:27.320 --> 0:13:30.520 we know it actually transforms into another kind of energy 0:13:30.520 --> 0:13:34.880 we call potential energy, because now that ball has gained altitude, 0:13:34.960 --> 0:13:37.920 which means it's moved up in the gravitational field, and 0:13:37.960 --> 0:13:41.240 so it's imbued now with something we call potential energy. 0:13:41.880 --> 0:13:44.640 And so now we have two kinds of energy kinetic energy, 0:13:44.760 --> 0:13:47.960 energy of motion, and potential energy, which is energy of 0:13:48.040 --> 0:13:49.600 position or arrangement. 0:13:50.080 --> 0:13:53.959 Okay, do all different kinds of energy have the same units? 0:13:54.360 --> 0:13:54.600 Yes? 0:13:54.800 --> 0:13:57.760 Units, help me think about scientific phenomena. 0:13:58.240 --> 0:14:00.440 Yes, all energy has the same unit. So you can 0:14:00.559 --> 0:14:03.480 use jewels, for example, as a unit of energy, and 0:14:03.600 --> 0:14:06.280 kinetic energy can be calculated in jewels, and potential energy 0:14:06.320 --> 0:14:09.280 also calculated in jewels, and you can go back and forth. Right, 0:14:09.280 --> 0:14:11.600 if you're standing on the top of a building, you 0:14:11.600 --> 0:14:13.640 have a lot of potential energy because you're high up, 0:14:13.679 --> 0:14:16.200 you have a lot of altitude, and you jump off 0:14:16.200 --> 0:14:19.440 that building. You turn that potential energy into kinetic energy 0:14:19.480 --> 0:14:20.960 because by the time you get to the bottom of 0:14:20.960 --> 0:14:23.360 the building. You no longer have the altitude, so you 0:14:23.360 --> 0:14:26.320 have no potential energy, and you have a lot of velocity. Right, 0:14:26.560 --> 0:14:30.040 So you've turned potential energy into kinetic energy. And you 0:14:30.120 --> 0:14:31.520 roll a ball up a hill, or you throw a 0:14:31.520 --> 0:14:34.800 ball up in the air, kinetic energy turns into potential energy. 0:14:35.320 --> 0:14:37.760 And the same thing is true for example, like a spring. 0:14:38.160 --> 0:14:41.120 A spring is a way to store potential energy. And 0:14:41.240 --> 0:14:42.960 if you push on a spring and then you let 0:14:42.960 --> 0:14:45.160 it go, it will oscillate back and forth and back 0:14:45.200 --> 0:14:48.000 and forth. And what's happening there is it's slashing kinetic 0:14:48.160 --> 0:14:51.840 energy into potential energy, back into kinetic energy, back into 0:14:51.880 --> 0:14:54.920 potential energy. So you know, like a simple model of 0:14:55.040 --> 0:14:58.360 you have a block of stone on a spring, it'll 0:14:58.360 --> 0:15:00.840 just sit there oscillating back and forth if there's no friction, 0:15:01.320 --> 0:15:04.040 turning kinetic and potential energy back and forth into each other. 0:15:04.400 --> 0:15:06.680 Which is also a really helpful way of thinking about 0:15:06.760 --> 0:15:10.600 waves in general. Like whenever we're talking about fields oscillating, 0:15:10.640 --> 0:15:13.560 even quantum fields, that's what's happening is that they're sloshing 0:15:13.600 --> 0:15:17.240 back and forth between different kinds of energy. And so 0:15:18.000 --> 0:15:20.760 now we go from having just kinetic energy energy of 0:15:20.760 --> 0:15:22.760 motion to having two kinds of energy, which, if there's 0:15:22.800 --> 0:15:26.640 no friction, do appear to conserve the total energy. So 0:15:26.720 --> 0:15:30.400 kinetic energy not conserved, potential energy not conserved, but their 0:15:30.440 --> 0:15:34.200 combination in simple systems with no friction or irresistance or 0:15:34.200 --> 0:15:37.600 anything does seem to be conserved, which suggests that it's 0:15:37.640 --> 0:15:40.400 like something may be more important to the universe. 0:15:40.960 --> 0:15:42.960 Okay, all right, So for the examples that we've talked 0:15:43.000 --> 0:15:46.080 about so far, you've got like a ball rolling down 0:15:46.120 --> 0:15:48.320 a hill, or a ball being thrown up in the 0:15:48.360 --> 0:15:51.000 air or something that it seems like the energy for 0:15:51.120 --> 0:15:53.920 those activities came from the energy of the person who's 0:15:54.640 --> 0:15:58.120 making it happen. Is that an okay way to think 0:15:58.160 --> 0:16:00.600 about it? Both of those examples seem the energy is 0:16:00.640 --> 0:16:02.560 coming from the person who set the ball in motion. 0:16:03.200 --> 0:16:04.920 Or carried it originally to the top of the building 0:16:04.920 --> 0:16:05.360 and dropped it. 0:16:05.440 --> 0:16:07.560 Yeah, right, right, Okay, so we haven't really gotten to 0:16:07.560 --> 0:16:10.520 where energy came from because energy seems like it's coming 0:16:10.560 --> 0:16:11.720 from the person who started it. 0:16:11.880 --> 0:16:13.200 Is that a fair way to think about it? 0:16:13.440 --> 0:16:15.840 Yeah? I think that's fair. And there's something cool you 0:16:15.840 --> 0:16:17.680 can do there, which is sort of trace the path 0:16:17.720 --> 0:16:21.280 of the energy. Right, Like say the person threw the 0:16:21.280 --> 0:16:24.120 ball into the air, So you're right, it has potential 0:16:24.200 --> 0:16:27.000 energy which came from its kinetic energy, which came from 0:16:27.000 --> 0:16:31.080 the energy stored in that person's muscles, right, which converted 0:16:31.080 --> 0:16:34.000 some sort of chemical energy storage into the contraction of 0:16:34.040 --> 0:16:37.400 those muscle cells, which accelerated the ball. And that chemical 0:16:37.480 --> 0:16:41.320 energy storage came from something that person ate, right. And 0:16:41.360 --> 0:16:44.040 that thing the person ate probably grew and maybe it 0:16:44.040 --> 0:16:46.040 was an animal and ate plants, or maybe it was 0:16:46.080 --> 0:16:50.360 a plant directly and that grew somehow by drinking light 0:16:50.480 --> 0:16:52.520 from the sun. Right. And so you can play this 0:16:52.560 --> 0:16:54.560 game where you trace the energy back, and one of 0:16:54.560 --> 0:16:57.160 our listeners commented that a lot of the energy on 0:16:57.200 --> 0:17:00.200 Earth seems to come from the sun, which is true, right, 0:17:00.240 --> 0:17:02.440 There's like a little bit of a source of energy 0:17:02.440 --> 0:17:05.359 from inside the Earth, but most of the energy does 0:17:05.440 --> 0:17:08.919 come from the Sun. And playing this game tracing the 0:17:09.040 --> 0:17:11.840 energy back has inside of it an implicit assumption that 0:17:11.920 --> 0:17:14.240 you can trace energy because again, it has to come 0:17:14.280 --> 0:17:17.919 from somewhere because it's conserved. It doesn't just disappear and 0:17:17.960 --> 0:17:20.919 it doesn't appear. And again I'm not saying that energy 0:17:21.040 --> 0:17:23.679 is conserved. I'm saying that if energy were conserved, then 0:17:23.720 --> 0:17:26.400 you can play this game, which is really fascinating because 0:17:26.400 --> 0:17:28.400 it allows you to like, you know, sort of rewind 0:17:28.400 --> 0:17:31.000 the accounting of the universe, and it is kind of 0:17:31.000 --> 0:17:33.600 mind blowing to realize that, like, wow, almost all the 0:17:33.720 --> 0:17:37.040 energy that we use here on Earth was originally created 0:17:37.160 --> 0:17:40.720 in the sun by fusion and then gobbled up by plants. 0:17:42.119 --> 0:17:43.879 All right, let's take a break, and when we come back, 0:17:44.040 --> 0:17:46.399 we are going to dig into whether or not mass 0:17:46.440 --> 0:18:00.960 could be considered a kind of energy. 0:18:04.880 --> 0:18:05.720 All right, we're back. 0:18:05.760 --> 0:18:07.919 So before the break, we were talking about how a 0:18:07.960 --> 0:18:10.359 lot of energy on Earth comes from the Sun, and 0:18:10.440 --> 0:18:13.359 so I'm thinking about you know, plants growing, putting on 0:18:13.520 --> 0:18:16.760 mass as you know, their chloroplasts, or turning energy from 0:18:16.760 --> 0:18:18.680 the Sun into energy for them, and then I eat 0:18:18.720 --> 0:18:21.000 them and put on a little bit of mass, just 0:18:21.080 --> 0:18:23.720 a little and use that energy to make a lot 0:18:23.760 --> 0:18:27.480 of ice cream cones, which makes people very happy. Should 0:18:27.480 --> 0:18:29.520 I think about mass as a third kind of energy. 0:18:29.880 --> 0:18:32.520 It's tempting, right to think about mass and another kind 0:18:32.520 --> 0:18:35.399 of energy, because we talked about stored energy, chemical energy, 0:18:35.440 --> 0:18:40.320 and atp energy stored in protons as they get fused 0:18:40.359 --> 0:18:43.160 together in the sun. And you hear a lot that 0:18:43.320 --> 0:18:47.000 mass is another kind of energy. People say equals mc squared, right, 0:18:47.040 --> 0:18:50.480 and so therefore mass is energy and energy is mass. Yeah, 0:18:50.520 --> 0:18:54.280 so that's not really true, and the deeper answer is 0:18:54.320 --> 0:18:58.959 that mass is just an indicator of internal stored energy. 0:19:00.040 --> 0:19:03.159 Think about some object and you can categorize all of 0:19:03.160 --> 0:19:06.960 its energy into two different boxes. One is the motion 0:19:07.080 --> 0:19:09.760 of that object, like, is the whole thing moving? If so, 0:19:10.280 --> 0:19:13.919 it's got some kinetic energy, right. Cool. The other kind 0:19:13.960 --> 0:19:17.560 of energy you can have is internal energy, like maybe 0:19:17.600 --> 0:19:19.800 there's a bunch of particles and they have bonds, or 0:19:19.840 --> 0:19:23.480 there's chemistry or something. All that internal stored energy is 0:19:23.520 --> 0:19:27.720 what we call mass. Mass is not a new form 0:19:27.840 --> 0:19:29.840 of energy. It's not a special kind of energy on 0:19:29.920 --> 0:19:33.520 its own. It's an indicator of how much energy is 0:19:33.600 --> 0:19:35.199 stored inside something. 0:19:36.560 --> 0:19:40.600 Okay, So like if you've got a big truck and 0:19:40.680 --> 0:19:44.080 a little truck and you set both of them going 0:19:44.119 --> 0:19:46.520