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Where does energy come from? · Daniel and Kelly’s Extraordinary Universe

• 0:06
  Speaker 1: One of my favorite things about physics is that it
• 0:08
  Speaker 1: lets us think concretely and carefully about the basic nature
• 0:11
  Speaker 1: of our experience. What is space? What is matter? What
• 0:15
  Speaker 1: is time? What's a particle? Why are there waves everywhere?
• 0:18
  Speaker 1: Physics helps us convert these squishy conversations on rooftops over
• 0:22
  Speaker 1: smoke banana peels into robust mathematics. The math doesn't require
• 0:27
  Speaker 1: persuasion or a clever choice of words. It's either right
• 0:30
  Speaker 1: or it's wrong. So instead of answering a question about
• 0:33
  Speaker 1: the nature of the squish universe, we get to poke
• 0:35
  Speaker 1: and prod our mathematical description of it. Sometimes that gives
• 0:39
  Speaker 1: us real insight, like when relativity tells us that distance
• 0:42
  Speaker 1: and velocity have to be relative rather than absolute, because
• 0:46
  Speaker 1: that's the only mathematical model that describes the universe we see.
• 0:51
  Speaker 1: Other times it surprises us by telling us that we
• 0:54
  Speaker 1: might just be asking the wrong question. Maybe the things
• 0:58
  Speaker 1: we thought were important just reveal our fundamental misunderstandings of
• 1:02
  Speaker 1: the universe and how it works. Today we'll be asking
• 1:05
  Speaker 1: what physics can tell us about energy, What is it?
• 1:08
  Speaker 1: And more importantly, where does it come from? Welcome to
• 1:12
  Speaker 1: Daniel and Kelly's Extraordinary energetic Universe.
• 1:29
  Speaker 2: Hello. I'm Kelly Wiener Smith.
• 1:31
  Speaker 3: I study space and parasites and I just got over
• 1:35
  Speaker 3: having the flu for a week and I really could
• 1:36
  Speaker 3: have used energy.
• 1:39
  Speaker 1: Hi. I'm Daniel. I'm a particle physicist and I love
• 1:41
  Speaker 1: how Kelly opens the podcast with so much energy every time.
• 1:46
  Speaker 2: Okay, well we both have a lot of energy.
• 1:48
  Speaker 3: Speaking of energy, do you rely on caffeine? What is
• 1:52
  Speaker 3: your favorite form of liquid energy?
• 1:54
  Speaker 1: I do rely on caffeine. I'm drinking coffee right now here.
• 1:57
  Speaker 1: You go, Oh oh for you asmr. Folks. Yeah, yes,
• 2:05
  Speaker 1: I have caffeine in the mornings, but I can't have
• 2:07
  Speaker 1: any really after lunch or interference with my sleep. I'm
• 2:10
  Speaker 1: at that age where sleep is not necessarily a given.
• 2:13
  Speaker 2: Yeah. Same.
• 2:14
  Speaker 3: I used to drink coffee all day long. I like
• 2:16
  Speaker 3: didn't drink water in college.
• 2:19
  Speaker 1: That doesn't sound like a good idea.
• 2:21
  Speaker 3: You know, I got a lot done, I got a
• 2:23
  Speaker 3: whole lot done, but I could still fall asleep. But
• 2:25
  Speaker 3: now I also if it's after lunch, forget it. I
• 2:27
  Speaker 3: can't have coffee anymore either.
• 2:29
  Speaker 1: Remember, folks, this is not a health podcast. Do not
• 2:32
  Speaker 1: take our advice.
• 2:34
  Speaker 3: Noah, no, please don't don't follow our lead. When you
• 2:37
  Speaker 3: were a kid, did you ever try jolts?
• 2:39
  Speaker 1: Jolt was the kind of thing that was so forbidden
• 2:42
  Speaker 1: in my family. Like my mom was very controlling about
• 2:45
  Speaker 1: the kind of food we could eat, you know, she
• 2:47
  Speaker 1: like counted potato chips, this kind of thing, So junk
• 2:50
  Speaker 1: food definitely off of this jolt. She saw that as
• 2:52
  Speaker 1: like battery acid, Like there was no way she would
• 2:55
  Speaker 1: allow us. Did you try jolts?
• 2:57
  Speaker 2: Yeah? Do you remember pixie stick?
• 3:00
  Speaker 1: Yeah?
• 3:01
  Speaker 3: So there used to be like a megapixie stick. It
• 3:03
  Speaker 3: was like a giant plastic tube like the thickness of
• 3:06
  Speaker 3: my thumb, and it was just filled with.
• 3:07
  Speaker 2: Sugar and food coloring.
• 3:09
  Speaker 3: And we had like a party once where we just
• 3:12
  Speaker 3: like had those pixie sticks with jolts.
• 3:16
  Speaker 2: And I got pretty sick.
• 3:18
  Speaker 3: And jolts made me feel horrible the way too much
• 3:21
  Speaker 3: caffeine makes me feel now.
• 3:22
  Speaker 2: But I tried it once, and it was one thing
• 3:23
  Speaker 2: as a kid.
• 3:24
  Speaker 3: Where I was like, I shouldn't do that again. Anyway,
• 3:27
  Speaker 3: I had a lot more fun.
• 3:27
  Speaker 1: It sounds like it does sound like you had more fun,
• 3:30
  Speaker 1: but you also got sick. But I have a basic
• 3:32
  Speaker 1: biology question for you about caffeine. I mean, I understand
• 3:35
  Speaker 1: if you eat a pixie stick, it's sugar. Sugar has energy.
• 3:38
  Speaker 1: You could potentially get high and a rush and feel
• 3:41
  Speaker 1: energetic from that. But caffeine, how does that give me
• 3:44
  Speaker 1: energy or make me alert? Is it really energy from
• 3:47
  Speaker 1: the caffeine that my body's using. Is it releasing some
• 3:50
  Speaker 1: energy stores in my body? Or is it some much
• 3:53
  Speaker 1: more complicated neuro answer, dot dot dot. It depends.
• 3:57
  Speaker 2: Probably, it depends. I don't actually know.
• 3:59
  Speaker 3: I didn't prepare the answer for that coming in here.
• 4:01
  Speaker 3: I believe it binds to certain receptors in your brain.
• 4:04
  Speaker 3: My job in college was barista. I worked at like
• 4:06
  Speaker 3: four different coffee shops, and so I've had like shirts
• 4:09
  Speaker 3: with the caffeine molecule on the front. So yeah, I
• 4:11
  Speaker 3: think it binds with some receptors in your brain. And
• 4:13
  Speaker 3: I don't know how that results in you feeling awake,
• 4:16
  Speaker 3: but it works.
• 4:17
  Speaker 1: It pulls on some levers and ropes of the Rube
• 4:19
  Speaker 1: Goldberg machine that is my mind.
• 4:21
  Speaker 3: That's right, that's right, and thank God for it. I
• 4:23
  Speaker 3: don't know how I would have gotten through college without it.
• 4:25
  Speaker 3: At some point I was working at a coffee shop
• 4:27
  Speaker 3: because I couldn't afford all the coffee I wanted to drink,
• 4:31
  Speaker 3: but if I worked at the coffee shop, I could
• 4:32
  Speaker 3: afford it and pay my rent. So anyway, I had
• 4:35
  Speaker 3: a problem maybe, but I also had fun.
• 4:37
  Speaker 1: Well. Energy is a really fun topic because it's something
• 4:40
  Speaker 1: that is colloquial and we talk about it in our
• 4:42
  Speaker 1: lives and whether you feel energetic and whether you drink
• 4:44
  Speaker 1: caffeine whatever, And it's also something deeply important to physics
• 4:47
  Speaker 1: and the universe. So it's one of these topics that
• 4:50
  Speaker 1: people have like a personal feeling about, like where energy is,
• 4:53
  Speaker 1: where it comes from, and what it means. And it's
• 4:56
  Speaker 1: also really pervasive in popular science. You know, equals MC squared,
• 5:00
  Speaker 1: energy is mass. People tell us there's a lot of
• 5:02
  Speaker 1: nonsense out there about energy. So I thought it'd be
• 5:05
  Speaker 1: good to have an episode where we dig into some
• 5:07
  Speaker 1: details about what energy is and where it comes from
• 5:10
  Speaker 1: and what we know and don't know about it.
• 5:12
  Speaker 3: Yes, and you always do a great job of getting
• 5:14
  Speaker 3: us back on tracks. That was fantastic, and the other
• 5:17
  Speaker 3: people who keep us on track are our amazing audience,
• 5:20
  Speaker 3: and so we asked them where does energy come from?
• 5:23
  Speaker 3: And if you want to answer questions for us, you
• 5:25
  Speaker 3: can write us at questions at Daniel and Kelly dot org.
• 5:28
  Speaker 3: But let's go ahead and here from our audience, where
• 5:30
  Speaker 3: does energy come from?
• 5:32
  Speaker 1: Energy comes from heat, which comes from photon. I have
• 5:36
  Speaker 1: no idea.
• 5:37
  Speaker 4: Is it a mathematical trick, is it just an accounting system?
• 5:42
  Speaker 1: Who else? Nobody knows where energy comes from, and nobody's
• 5:46
  Speaker 1: ever gonna know. It is the magic of the universe.
• 5:50
  Speaker 5: I don't think energy comes from anyway, because you can't
• 5:54
  Speaker 5: have not energy.
• 5:56
  Speaker 1: Well, it comes from fields that permeate the entire universe.
• 6:00
  Speaker 1: Energy comes from hydrogen fusion caused by gravity, So I'd
• 6:04
  Speaker 1: have to say gravity.
• 6:05
  Speaker 4: Yes, it comes from the Big Bang and has just
• 6:07
  Speaker 4: been circulating in different forms ever since. Or powered Now,
• 6:12
  Speaker 4: if you're talking about the energy that powered the Big Bang,
• 6:15
  Speaker 4: or energy required to keep all the quantum fuels fluctuating
• 6:18
  Speaker 4: and alive, I imagine a physicist is better suited to
• 6:21
  Speaker 4: provide insight.
• 6:22
  Speaker 1: Hint, hint, So I guess that MLGS comes from symmetries
• 6:26
  Speaker 1: in nature. Obviously the Big Bang has a big role
• 6:30
  Speaker 1: in it, but it might not be the whole thought.
• 6:34
  Speaker 6: Since you can't create energy, I assume it originates from
• 6:40
  Speaker 6: the Big Bang, and before then who knows.
• 6:44
  Speaker 1: I guess it's always better around.
• 6:46
  Speaker 6: It just changes form after form.
• 6:48
  Speaker 1: Perhaps what we're calling space time is actually energy. Oh well,
• 6:53
  Speaker 1: I really am stumped by this one. I really don't know.
• 7:00
  Speaker 1: All the energy in the universe today came from the
• 7:03
  Speaker 1: storehouse of energy released in the Big Bang.
• 7:06
  Speaker 5: Some energy comes from the Big Bang, and some comes
• 7:09
  Speaker 5: from dark energy, but most energy in this universe comes
• 7:14
  Speaker 5: from eating your waities.
• 7:16
  Speaker 6: Have we not always had the same amount of energy?
• 7:19
  Speaker 5: I would say all energy originated from the Big Bang
• 7:22
  Speaker 5: and everything since then it's just been conversions of different forms.
• 7:26
  Speaker 5: But then you can ask where did that come from?
• 7:29
  Speaker 5: And where does dark energy come from?
• 7:31
  Speaker 1: And I don't know. There's some really philosophical answers in here,
• 7:36
  Speaker 1: and I loved listening to these.
• 7:38
  Speaker 2: Well, I mean, that's what I've come to expect from
• 7:39
  Speaker 2: the audience.
• 7:40
  Speaker 3: It's like always a nice combination of like philosophical some
• 7:43
  Speaker 3: people who get like exactly the right answer or get
• 7:45
  Speaker 3: really close, and then some people who know they don't
• 7:48
  Speaker 3: know and so they.
• 7:48
  Speaker 2: Just go all in on being hilarious.
• 7:50
  Speaker 3: I always love listening to the answers.
• 7:53
  Speaker 1: This comment that you can't have not energy, I had
• 7:56
  Speaker 1: to pause that and think about it for a while.
• 7:57
  Speaker 1: I was like, Wow, that sounds really profound, but I'm
• 7:59
  Speaker 1: not even share what it means.
• 8:01
  Speaker 3: Like a lot of philosophy, I thought that they were
• 8:05
  Speaker 3: trying to say, if there wasn't energy, none of us
• 8:08
  Speaker 3: would be here, which doesn't really the answer the question
• 8:12
  Speaker 3: where it comes from, but just something had to have
• 8:14
  Speaker 3: made it exist.
• 8:15
  Speaker 2: I don't know, what do you think?
• 8:16
  Speaker 1: I didn't know? Yeah, what is not energy? Is that
• 8:20
  Speaker 1: energy equals zero. It's true, you can't have zero energy
• 8:23
  Speaker 1: in the universe because of quantum mechanics. Yeah, fascinating, Yeah,
• 8:27
  Speaker 1: really fun answers here and a lot of assumptions. You
• 8:30
  Speaker 1: hear that energy doesn't come from anywhere because we've had
• 8:34
  Speaker 1: the same amount the whole time. Because people have this
• 8:37
  Speaker 1: conception which we're going to take apart and debunk a
• 8:40
  Speaker 1: little bit, that energy is conserved. The energy has to
• 8:43
  Speaker 1: come from somewhere because you can either create nor destroy it,
• 8:47
  Speaker 1: and therefore it can only flow.
• 8:49
  Speaker 3: So yeah, when I was looking through your outline and
• 8:51
  Speaker 3: I saw energy is not conserved, I was like, what,
• 8:55
  Speaker 3: I'm sure I've heard that a lot of times, and so,
• 8:58
  Speaker 3: you know, I think a lot of us are looking
• 8:59
  Speaker 3: forward to having our preconceptions about energy sort of cleared up.
• 9:04
  Speaker 1: Yeah, exactly. But before we get into the mind blowing
• 9:08
  Speaker 1: revelations about the nature of energy, we have to be
• 9:11
  Speaker 1: clear and careful about what is it we're talking about anyway.
• 9:15
  Speaker 1: Are we talking about how the earth keeps warm? Are
• 9:18
  Speaker 1: we talking about what happens when you eat your wheaties?
• 9:20
  Speaker 1: Are we talking about philosophical revelations about the fundamental nature
• 9:24
  Speaker 1: of the universe. So the first thing we have to do,
• 9:26
  Speaker 1: of course, is define what do we mean when we
• 9:29
  Speaker 1: say energy.
• 9:30
  Speaker 3: Yeah, so as a biologist, I'm thinking ATP, I'm thinking
• 9:34
  Speaker 3: at it at a chemistry level. We're as a physicist.
• 9:37
  Speaker 3: Do you think about it like that as well? Or
• 9:39
  Speaker 3: this is just a totally different topic.
• 9:42
  Speaker 1: Now ATP is like a chemical store of energy, so
• 9:45
  Speaker 1: it's completely related to the topic at hand. But it's
• 9:49
  Speaker 1: an example, right. It's like if somebody says to you, hey,
• 9:52
  Speaker 1: what is a vegetable and you're like, an implant is
• 9:55
  Speaker 1: a vegetable, And you're like, yeah, that's true, but what
• 9:57
  Speaker 1: makes it vegetable? Why do we have them? Where do
• 9:59
  Speaker 1: vegetables come from? Right? Showing you an a plant doesn't
• 10:02
  Speaker 1: answer that question.
• 10:03
  Speaker 3: Right, and then I'll go on a long rant about
• 10:05
  Speaker 3: how vegetables not a phylogenetic category and it's something humans
• 10:08
  Speaker 3: made up, and so anyway, go ahead.
• 10:10
  Speaker 1: Oh my gosh, wow, oh I love when we accidentally
• 10:13
  Speaker 1: stumble up upon a hidden Kelly rant. Love that. Wow.
• 10:16
  Speaker 3: Okay, let's go deeper, hurt, but not on vegetables. So
• 10:21
  Speaker 3: what is energy? How does a physicist start to answer
• 10:23
  Speaker 3: this question?
• 10:24
  Speaker 1: I like to answer this question by pointing out that
• 10:26
  Speaker 1: we can invent any kind of concept. I mean, you
• 10:29
  Speaker 1: can just make up a word called it, you know,
• 10:32
  Speaker 1: bliblyon or whatever, and then define it and it could
• 10:36
  Speaker 1: be a thing. And the question is like, does that
• 10:39
  Speaker 1: reveal anything about the universe? Is it related to the
• 10:41
  Speaker 1: physical universe in some insightful way, or is it just
• 10:45
  Speaker 1: some nonsense that you made up? And so, from that
• 10:47
  Speaker 1: point of view, like everything in physics is something we
• 10:50
  Speaker 1: made up, and a lot of it is just nonsense
• 10:51
  Speaker 1: we then ignore because it wasn't useful. And some of
• 10:54
  Speaker 1: it actually seems to reflect something that's happening in the
• 10:57
  Speaker 1: universe and is therefore useful, and we think maybe in
• 11:00
  Speaker 1: delightful about the fundamental nature of reality. Right, And so
• 11:04
  Speaker 1: energy is that way. It is something we invented. It's
• 11:06
  Speaker 1: just like a concept we came up with. We talked
• 11:09
  Speaker 1: recently on the podcast about entropy and the history of
• 11:12
  Speaker 1: energy is similar predates entropy because entropy was defined as
• 11:17
  Speaker 1: moving of energy the een and entropy comes from energy.
• 11:21
  Speaker 1: But this is something people have been wondering about it
• 11:23
  Speaker 1: for a long time, like how do you get a
• 11:24
  Speaker 1: machine to work? And what's going on with heat a temperature?
• 11:27
  Speaker 1: And so people came up with this concept of energy
• 11:30
  Speaker 1: one hundreds of years ago. It was actually leading It's
• 11:33
  Speaker 1: first identified energy of motion, like things in motion have energy,
• 11:39
  Speaker 1: and he called it this visviva, this living force, just
• 11:43
  Speaker 1: energy of motion. He recognized that.
• 11:44
  Speaker 3: That was like a thing, but like an asteroid hurtling
• 11:48
  Speaker 3: towards the Earth would have energy. But in what way
• 11:50
  Speaker 3: is that a living force? Was he like specifically thinking
• 11:53
  Speaker 3: about living organism.
• 11:54
  Speaker 1: No, he was just thinking about animation, not necessarily like
• 11:58
  Speaker 1: something is alive, but in motion. And so I think
• 12:01
  Speaker 1: he was thinking more about the motion than the actual
• 12:03
  Speaker 1: life force or the definition of life in some sort
• 12:06
  Speaker 1: of biological way. But that's something we still recognize, right.
• 12:10
  Speaker 1: We call that kinetic energy today and kinetic energy is
• 12:13
  Speaker 1: definitely a form of energy, like photons have energy, right,
• 12:16
  Speaker 1: they zoom around the universe. They're moving really really fast,
• 12:19
  Speaker 1: So it's a type of energy. But again, this is
• 12:22
  Speaker 1: like quoting the eggplant, right, it's not a definition of
• 12:24
  Speaker 1: the concept. It's an example of the kind of thing,
• 12:26
  Speaker 1: and it comes from history. And something that's especially fascinating
• 12:30
  Speaker 1: and revealing about kinetic energy is that it's not conserved. Right.
• 12:34
  Speaker 1: For example, you throw a ball up into the air,
• 12:38
  Speaker 1: it slows down, right because of gravity. If you throw
• 12:40
  Speaker 1: it straight up, it slows down, and eventually, when it
• 12:43
  Speaker 1: reaches the top of its arc, its stopped. So kinetic
• 12:46
  Speaker 1: energy on its own is not something that's conserved in
• 12:49
  Speaker 1: the universe, Like the universe doesn't seem to have a
• 12:51
  Speaker 1: special relationship with kinetic energy. It's the way you could
• 12:55
  Speaker 1: make up any other thing, like, hey, how many ice
• 12:58
  Speaker 1: cream cones are there currently in the universe. That's a
• 13:01
  Speaker 1: number that we don't expect to stay constant. Right, I
• 13:04
  Speaker 1: eat one, it's gone. I've decreased the number. I make one,
• 13:07
  Speaker 1: it goes up. Kelly makes five thousand ice cream cones,
• 13:10
  Speaker 1: it goes up a lot. Right, It's not anything meaningful
• 13:13
  Speaker 1: or specific and kinetic energy is sort of the same way.
• 13:16
  Speaker 1: Like when the ball gets thrown up into the air,
• 13:19
  Speaker 1: it loses that kinetic energy. Where does the kinetic energy go. Well,
• 13:24
  Speaker 1: energy can just go up and down. In this case,
• 13:27
  Speaker 1: we know it actually transforms into another kind of energy
• 13:30
  Speaker 1: we call potential energy, because now that ball has gained altitude,
• 13:34
  Speaker 1: which means it's moved up in the gravitational field, and
• 13:37
  Speaker 1: so it's imbued now with something we call potential energy.
• 13:41
  Speaker 1: And so now we have two kinds of energy kinetic energy,
• 13:44
  Speaker 1: energy of motion, and potential energy, which is energy of
• 13:48
  Speaker 1: position or arrangement.
• 13:50
  Speaker 3: Okay, do all different kinds of energy have the same units?
• 13:54
  Speaker 1: Yes?
• 13:54
  Speaker 2: Units, help me think about scientific phenomena.
• 13:58
  Speaker 1: Yes, all energy has the same unit. So you can
• 14:00
  Speaker 1: use jewels, for example, as a unit of energy, and
• 14:03
  Speaker 1: kinetic energy can be calculated in jewels, and potential energy
• 14:06
  Speaker 1: also calculated in jewels, and you can go back and forth. Right,
• 14:09
  Speaker 1: if you're standing on the top of a building, you
• 14:11
  Speaker 1: have a lot of potential energy because you're high up,
• 14:13
  Speaker 1: you have a lot of altitude, and you jump off
• 14:16
  Speaker 1: that building. You turn that potential energy into kinetic energy
• 14:19
  Speaker 1: because by the time you get to the bottom of
• 14:20
  Speaker 1: the building. You no longer have the altitude, so you
• 14:23
  Speaker 1: have no potential energy, and you have a lot of velocity. Right,
• 14:26
  Speaker 1: So you've turned potential energy into kinetic energy. And you
• 14:30
  Speaker 1: roll a ball up a hill, or you throw a
• 14:31
  Speaker 1: ball up in the air, kinetic energy turns into potential energy.
• 14:35
  Speaker 1: And the same thing is true for example, like a spring.
• 14:38
  Speaker 1: A spring is a way to store potential energy. And
• 14:41
  Speaker 1: if you push on a spring and then you let
• 14:42
  Speaker 1: it go, it will oscillate back and forth and back
• 14:45
  Speaker 1: and forth. And what's happening there is it's slashing kinetic
• 14:48
  Speaker 1: energy into potential energy, back into kinetic energy, back into
• 14:51
  Speaker 1: potential energy. So you know, like a simple model of
• 14:55
  Speaker 1: you have a block of stone on a spring, it'll
• 14:58
  Speaker 1: just sit there oscillating back and forth if there's no friction,
• 15:01
  Speaker 1: turning kinetic and potential energy back and forth into each other.
• 15:04
  Speaker 1: Which is also a really helpful way of thinking about
• 15:06
  Speaker 1: waves in general. Like whenever we're talking about fields oscillating,
• 15:10
  Speaker 1: even quantum fields, that's what's happening is that they're sloshing
• 15:13
  Speaker 1: back and forth between different kinds of energy. And so
• 15:18
  Speaker 1: now we go from having just kinetic energy energy of
• 15:20
  Speaker 1: motion to having two kinds of energy, which, if there's
• 15:22
  Speaker 1: no friction, do appear to conserve the total energy. So
• 15:26
  Speaker 1: kinetic energy not conserved, potential energy not conserved, but their
• 15:30
  Speaker 1: combination in simple systems with no friction or irresistance or
• 15:34
  Speaker 1: anything does seem to be conserved, which suggests that it's
• 15:37
  Speaker 1: like something may be more important to the universe.
• 15:40
  Speaker 3: Okay, all right, So for the examples that we've talked
• 15:43
  Speaker 3: about so far, you've got like a ball rolling down
• 15:46
  Speaker 3: a hill, or a ball being thrown up in the
• 15:48
  Speaker 3: air or something that it seems like the energy for
• 15:51
  Speaker 3: those activities came from the energy of the person who's
• 15:54
  Speaker 3: making it happen. Is that an okay way to think
• 15:58
  Speaker 3: about it? Both of those examples seem the energy is
• 16:00
  Speaker 3: coming from the person who set the ball in motion.
• 16:03
  Speaker 1: Or carried it originally to the top of the building
• 16:04
  Speaker 1: and dropped it.
• 16:05
  Speaker 3: Yeah, right, right, Okay, so we haven't really gotten to
• 16:07
  Speaker 3: where energy came from because energy seems like it's coming
• 16:10
  Speaker 3: from the person who started it.
• 16:11
  Speaker 2: Is that a fair way to think about it?
• 16:13
  Speaker 1: Yeah? I think that's fair. And there's something cool you
• 16:15
  Speaker 1: can do there, which is sort of trace the path
• 16:17
  Speaker 1: of the energy. Right, Like say the person threw the
• 16:21
  Speaker 1: ball into the air, So you're right, it has potential
• 16:24
  Speaker 1: energy which came from its kinetic energy, which came from
• 16:27
  Speaker 1: the energy stored in that person's muscles, right, which converted
• 16:31
  Speaker 1: some sort of chemical energy storage into the contraction of
• 16:34
  Speaker 1: those muscle cells, which accelerated the ball. And that chemical
• 16:37
  Speaker 1: energy storage came from something that person ate, right. And
• 16:41
  Speaker 1: that thing the person ate probably grew and maybe it
• 16:44
  Speaker 1: was an animal and ate plants, or maybe it was
• 16:46
  Speaker 1: a plant directly and that grew somehow by drinking light
• 16:50
  Speaker 1: from the sun. Right. And so you can play this
• 16:52
  Speaker 1: game where you trace the energy back, and one of
• 16:54
  Speaker 1: our listeners commented that a lot of the energy on
• 16:57
  Speaker 1: Earth seems to come from the sun, which is true, right,
• 17:00
  Speaker 1: There's like a little bit of a source of energy
• 17:02
  Speaker 1: from inside the Earth, but most of the energy does
• 17:05
  Speaker 1: come from the Sun. And playing this game tracing the
• 17:09
  Speaker 1: energy back has inside of it an implicit assumption that
• 17:11
  Speaker 1: you can trace energy because again, it has to come
• 17:14
  Speaker 1: from somewhere because it's conserved. It doesn't just disappear and
• 17:17
  Speaker 1: it doesn't appear. And again I'm not saying that energy
• 17:21
  Speaker 1: is conserved. I'm saying that if energy were conserved, then
• 17:23
  Speaker 1: you can play this game, which is really fascinating because
• 17:26
  Speaker 1: it allows you to like, you know, sort of rewind
• 17:28
  Speaker 1: the accounting of the universe, and it is kind of
• 17:31
  Speaker 1: mind blowing to realize that, like, wow, almost all the
• 17:33
  Speaker 1: energy that we use here on Earth was originally created
• 17:37
  Speaker 1: in the sun by fusion and then gobbled up by plants.
• 17:42
  Speaker 3: All right, let's take a break, and when we come back,
• 17:44
  Speaker 3: we are going to dig into whether or not mass
• 17:46
  Speaker 3: could be considered a kind of energy.
• 18:04
  Speaker 2: All right, we're back.
• 18:05
  Speaker 3: So before the break, we were talking about how a
• 18:07
  Speaker 3: lot of energy on Earth comes from the Sun, and
• 18:10
  Speaker 3: so I'm thinking about you know, plants growing, putting on
• 18:13
  Speaker 3: mass as you know, their chloroplasts, or turning energy from
• 18:16
  Speaker 3: the Sun into energy for them, and then I eat
• 18:18
  Speaker 3: them and put on a little bit of mass, just
• 18:21
  Speaker 3: a little and use that energy to make a lot
• 18:23
  Speaker 3: of ice cream cones, which makes people very happy. Should
• 18:27
  Speaker 3: I think about mass as a third kind of energy.
• 18:29
  Speaker 1: It's tempting, right to think about mass and another kind
• 18:32
  Speaker 1: of energy, because we talked about stored energy, chemical energy,
• 18:35
  Speaker 1: and atp energy stored in protons as they get fused
• 18:40
  Speaker 1: together in the sun. And you hear a lot that
• 18:43
  Speaker 1: mass is another kind of energy. People say equals mc squared, right,
• 18:47
  Speaker 1: and so therefore mass is energy and energy is mass. Yeah,
• 18:50
  Speaker 1: so that's not really true, and the deeper answer is
• 18:54
  Speaker 1: that mass is just an indicator of internal stored energy.
• 19:00
  Speaker 1: Think about some object and you can categorize all of
• 19:03
  Speaker 1: its energy into two different boxes. One is the motion
• 19:07
  Speaker 1: of that object, like, is the whole thing moving? If so,
• 19:10
  Speaker 1: it's got some kinetic energy, right. Cool. The other kind
• 19:13
  Speaker 1: of energy you can have is internal energy, like maybe
• 19:17
  Speaker 1: there's a bunch of particles and they have bonds, or
• 19:19
  Speaker 1: there's chemistry or something. All that internal stored energy is
• 19:23
  Speaker 1: what we call mass. Mass is not a new form
• 19:27
  Speaker 1: of energy. It's not a special kind of energy on
• 19:29
  Speaker 1: its own. It's an indicator of how much energy is
• 19:33
  Speaker 1: stored inside something.
• 19:36
  Speaker 3: Okay, So like if you've got a big truck and
• 19:40
  Speaker 3: a little truck and you set both of them going
• 19:44
  Speaker 3: down the hill, the big truck is going to have
• 19:46
  Speaker 3: more energy because it has more mass, and it's an
• 19:51
  Speaker 3: indicator that it has more energy.
• 19:53
  Speaker 1: But it's yeah, exactly, if you measure the inertia of
• 19:55
  Speaker 1: something right by giving it a push, you give something
• 19:59
  Speaker 1: a certain amount of and then you measure its acceleration.
• 20:02
  Speaker 1: That tells you it's inertia because F equalsma. Then what
• 20:05
  Speaker 1: you're really measuring is how much energy is stored inside something.
• 20:08
  Speaker 1: And you can make this very concrete, like take a
• 20:10
  Speaker 1: rock that has a certain mass, shoot a photon at it.
• 20:13
  Speaker 1: What happens. The photon is absorbed by the rock, and
• 20:17
  Speaker 1: where's that energy go It like goes into the bond somehow,
• 20:20
  Speaker 1: it makes some rock molecule vibrate more, or if it's
• 20:24
  Speaker 1: a gas that you're hitting that it makes those particles
• 20:26
  Speaker 1: move faster. It's some sort of internal energy, right, it
• 20:28
  Speaker 1: doesn't matter. The mass of that rock goes up when
• 20:32
  Speaker 1: it eats that photon, which means like you lie in
• 20:35
  Speaker 1: the sun absorbing photons, your mass goes up. Or you know,
• 20:39
  Speaker 1: you have an electric car parked in your garage and
• 20:41
  Speaker 1: you've plugged it in and now you're adding energy to
• 20:44
  Speaker 1: the battery. Its mass is going up, right, because that
• 20:47
  Speaker 1: mass is an indicator of how much energy is stored
• 20:50
  Speaker 1: inside of whatever kind. As long as it's internal stored energy,
• 20:54
  Speaker 1: it contributes to the mass. So the mass is not
• 20:56
  Speaker 1: on its own. A new kind of energy it's just
• 20:59
  Speaker 1: an d cater of how much energy is stored inside
• 21:02
  Speaker 1: and that's what equals MC squared means. E. There doesn't
• 21:06
  Speaker 1: mean total energy. It's not saying that all mass is
• 21:08
  Speaker 1: energy and all energy is mass. E really means just
• 21:11
  Speaker 1: internal stored energy, and there's a fuller equation that captures
• 21:15
  Speaker 1: the full energy of the object as a term for
• 21:18
  Speaker 1: momentum as well. So it really tells you that energy
• 21:21
  Speaker 1: is internal stored energy as revealed by mass and another
• 21:26
  Speaker 1: term for energy of motion energy of momentum.
• 21:29
  Speaker 3: All right, so mass is just a reflection of kineticum potential.
• 21:32
  Speaker 1: Energy, internal stored energy, which could be kinetic or potential. Yes, absolutely.
• 21:37
  Speaker 3: Okay, are there other forms of energy or are they
• 21:40
  Speaker 3: all essentially just different versions of kinneticum potential energy?
• 21:44
  Speaker 1: Period It's a great question and the answer is yes.
• 21:46
  Speaker 1: Kineticum potential energy are the two categories of energy, and
• 21:50
  Speaker 1: there's nothing else. Right, So everything can be either kinetic
• 21:53
  Speaker 1: or potential energy. And if it's internal stored energy, it
• 21:57
  Speaker 1: could be kinetic or potential then we call it mass.
• 22:00
  Speaker 1: And if it's just motion of the whole object, then
• 22:02
  Speaker 1: that's kinetic energy of the whole shebang. And this helps
• 22:06
  Speaker 1: you understand things like, well, how can photons have energy
• 22:09
  Speaker 1: if they don't have mass. People write to me a
• 22:10
  Speaker 1: lot and say, like, photons have energy, right, Well, equals
• 22:13
  Speaker 1: empc square, therefore photons have mass, right, Not true, photons
• 22:17
  Speaker 1: don't have mass because again that equation equals empc squared.
• 22:21
  Speaker 1: That e is just internal stored energy. Photons have no
• 22:24
  Speaker 1: internal stored energy because they have no mass. But the
• 22:27
  Speaker 1: full equation has a term for momentum in it, and
• 22:30
  Speaker 1: photons definitely do have momentum, which is why photons also
• 22:34
  Speaker 1: have energy. So you can have energy without having any mass, right,
• 22:38
  Speaker 1: because photons again are pure motion energy. And then you
• 22:42
  Speaker 1: can play all sorts of fun games to confuse yourself
• 22:45
  Speaker 1: by what this means. Like, you know, take a box,
• 22:48
  Speaker 1: for example, and shoot a photon in it, and don't
• 22:51
  Speaker 1: let the photon get absorbed, put back mirrors inside the box,
• 22:54
  Speaker 1: the photon just bounces around. You still just have a
• 22:56
  Speaker 1: photon in the box. Then what you've done is you've
• 22:58
  Speaker 1: added to the mass of the by adding a massless photon.
• 23:02
  Speaker 1: People have this intuition that mass is like the amount
• 23:05
  Speaker 1: of stuff in something, but it really isn't. It really
• 23:08
  Speaker 1: just captures the internal store energy. Even if you add
• 23:11
  Speaker 1: massless things to your box, then you're increasing the mass
• 23:15
  Speaker 1: of the box. It's really kind of mind bending. It
• 23:17
  Speaker 1: really makes you change your understanding of what mass is.
• 23:21
  Speaker 3: I need more coffee, Yeah, but I'm following you. Okay,
• 23:25
  Speaker 3: So let's dig in more to this question about you know, when,
• 23:29
  Speaker 3: if ever, is energy conserved.
• 23:32
  Speaker 2: So you were.
• 23:33
  Speaker 3: Talking about throwing a ball in the air and it
• 23:35
  Speaker 3: goes from kinetic energy to potential energy, but it doesn't
• 23:39
  Speaker 3: always get conserved. Can we talk about the history of
• 23:42
  Speaker 3: why we used to think energy was conserved.
• 23:45
  Speaker 1: It's a really fascinating story. And you know, for a
• 23:47
  Speaker 1: long time we just sort of noticed that energy seemed
• 23:50
  Speaker 1: to be conserved. Like if you created a new quantity
• 23:53
  Speaker 1: number of ice cream sandwiches or something, and then you
• 23:56
  Speaker 1: notice that, weirdly, no matter what you did, the number
• 23:59
  Speaker 1: didn't change, Like every time Kelly ate an ice cream sandwich,
• 24:02
  Speaker 1: Daniel made one, there was this weird cosmic connection or
• 24:06
  Speaker 1: vice versa. Then you'd be like, something is going on here, right,
• 24:10
  Speaker 1: Like the universe respects ice cream sandwiches or something.
• 24:14
  Speaker 2: I want to live in that use.
• 24:17
  Speaker 1: And that's sort of the case for energy. That In
• 24:20
  Speaker 1: lots of situations that we studied, energy seems to be conserved,
• 24:24
  Speaker 1: and so we assumed that it was same was also
• 24:26
  Speaker 1: true for mass. For a long time, people assumed that
• 24:29
  Speaker 1: you couldn't create or destroy mass. A lot of people
• 24:31
  Speaker 1: still out there repeat that, even though now we know
• 24:34
  Speaker 1: that it's not true. We know that you can convert
• 24:36
  Speaker 1: mass into energy of motion or into potential energy that's
• 24:40
  Speaker 1: not internal. I do that all the time at my
• 24:43
  Speaker 1: day job. Right when we smash protons together, we are
• 24:45
  Speaker 1: turning their mass into new forms of energy. We're turning
• 24:48
  Speaker 1: their energy into mass all the time, back and forth,
• 24:52
  Speaker 1: and every time you absorb photons from the Sun, you're
• 24:54
  Speaker 1: turning their energy into mass. But that's a hard thing
• 24:57
  Speaker 1: to notice unless you have control a tiny part of
• 25:00
  Speaker 1: goals and you can see these things happen. Which is
• 25:01
  Speaker 1: why chemists for a long time reasonably believed that mass
• 25:05
  Speaker 1: was conserved, because they would measure the stuff going into
• 25:08
  Speaker 1: a reaction and the stuff coming out of a reaction,
• 25:10
  Speaker 1: and they never saw a change to within their measuring uncertainties. Now,
• 25:14
  Speaker 1: of course, we know that if they had measured more accurately,
• 25:17
  Speaker 1: they would have noticed very tiny changes in mass because
• 25:20
  Speaker 1: mass is very very dense stuff. Right. The C square
• 25:22
  Speaker 1: there tells you that a big change in energy is
• 25:24
  Speaker 1: required to make even a small change in the mass. Anyway,
• 25:28
  Speaker 1: the same thing was long true for energy. People are like, okay,
• 25:31
  Speaker 1: well mass is not conserved, we're going to give that up.
• 25:34
  Speaker 1: But energy still, Energy definitely has got to be a
• 25:36
  Speaker 1: conserved right, because people made all these measurements, and it
• 25:39
  Speaker 1: seemed like the more accurately you measured it, the more
• 25:41
  Speaker 1: you discovered energy had to go somewhere. So in realistic studies,
• 25:45
  Speaker 1: for example, say you throw that ball up into the air,
• 25:47
  Speaker 1: what's going to happen. Well, it's not going to convert
• 25:50
  Speaker 1: all of its kinetic energy into potential because some of
• 25:53
  Speaker 1: it's going to get lost to air resistance. Or if
• 25:55
  Speaker 1: you roll a ball down a hill, right, some of
• 25:57
  Speaker 1: it's going to get lost to friction. That energy seemed
• 25:59
  Speaker 1: to creep out of those systems. But as long as
• 26:02
  Speaker 1: you define the system to include those things, you account
• 26:04
  Speaker 1: for friction and you account for air resistance, you're able
• 26:07
  Speaker 1: to account for all of that energy. The balls flying
• 26:11
  Speaker 1: up into the air and it loses energy to air resistance,
• 26:14
  Speaker 1: but that energy then just goes into heating the air,
• 26:17
  Speaker 1: or if you're sliding down a hill and you feel
• 26:19
  Speaker 1: friction between your pants and the grass, then you're heating
• 26:22
  Speaker 1: up the grass and your pants. That energy is still there.
• 26:26
  Speaker 1: And so for a long time people just noticed, even
• 26:28
  Speaker 1: with more and more careful accounting, that energy did seem
• 26:31
  Speaker 1: to be conserved.
• 26:32
  Speaker 3: So I remember that we were talking about Emmy notors on.
• 26:36
  Speaker 3: I worked so hard to not say her name during
• 26:38
  Speaker 3: the episode because I knew I'd get it wrong, But
• 26:40
  Speaker 3: here I went and put myself in that position.
• 26:42
  Speaker 2: But anyway, that she had come up with a.
• 26:44
  Speaker 3: Really great law or theory that explained when things are
• 26:49
  Speaker 3: symmetrical and when they're not. And so it sounds to
• 26:52
  Speaker 3: me like we're going to determine here that energy is
• 26:54
  Speaker 3: not symmetrical, and that Emmy would tell us that if
• 26:56
  Speaker 3: she were here.
• 26:57
  Speaker 1: Yeah, it's really cool that we can do more than
• 27:00
  Speaker 1: just measure the number of ice cream sandwiches and notice
• 27:04
  Speaker 1: that they do or do not change and then conclude something.
• 27:07
  Speaker 1: It's not just empirical. We actually now have theoretical ways
• 27:11
  Speaker 1: to argue whether something should be conserved or not. And
• 27:14
  Speaker 1: as you say, that's due to Emmy Nuther whose name
• 27:17
  Speaker 1: I'm sure I'm also mispronouncing, and the number of mispronunciations
• 27:21
  Speaker 1: is not conserved. Like it just seems to grow, go
• 27:23
  Speaker 1: up and up and up every time I hear this name,
• 27:26
  Speaker 1: different pronunciations of it. So German listeners, please don't be
• 27:30
  Speaker 1: shy right in and correct our pronunciations. We want to
• 27:32
  Speaker 1: get this stuff right anyway. I mean, other told us
• 27:35
  Speaker 1: that every time we have a conservation law in the universe.
• 27:38
  Speaker 1: You're right, it's connected to some symmetry of the universe.
• 27:41
  Speaker 1: And symmetry has a sort of special meaning there. It
• 27:43
  Speaker 1: says that you can transform your experiment, you can move
• 27:48
  Speaker 1: it or rotate it in some way, and you should
• 27:50
  Speaker 1: get the same answer. And so a famous and powerful
• 27:54
  Speaker 1: example is momentum conservation. You know, alongside energy, we have
• 27:58
  Speaker 1: this concept of moment momentum, which is similar to energy. Right,
• 28:02
  Speaker 1: Momentum contributes to your energy. We said, there's internal storat
• 28:05
  Speaker 1: energy and then this energy of momentum which come together
• 28:08
  Speaker 1: to make your total energy. And the famous and important
• 28:10
  Speaker 1: example of that is momentum, which is something that is
• 28:13
  Speaker 1: actually conserved in our universe. And when we say symmetry there,
• 28:17
  Speaker 1: what we mean is that you can do an experiment
• 28:20
  Speaker 1: and then transform the experiment according to some symmetry and
• 28:24
  Speaker 1: do the experiment again, you should get the same answer.
• 28:27
  Speaker 1: So if you build a physics experiment and you do
• 28:29
  Speaker 1: it in space, you know, you collide billiard balls or whatever,
• 28:32
  Speaker 1: and then you do it ten meters to the left
• 28:35
  Speaker 1: or one hundred meters to the right, or forward one
• 28:37
  Speaker 1: thousand meters, you should get the same answer. So that's
• 28:40
  Speaker 1: a symmetry of the universe. The universe doesn't care where
• 28:43
  Speaker 1: you do your experiment. As long as you set up
• 28:45
  Speaker 1: the conditions the same way nearby masses or whatever, you
• 28:49
  Speaker 1: should get the same answer. That's a fundamental symmetry of
• 28:52
  Speaker 1: the universe. And that symmetry gives you conservation of momentum.
• 28:56
  Speaker 1: So Emmy Nuther has this amazing conceptual bridge which you
• 28:59
  Speaker 1: tell you what symmetry generates a conservation law. So conservation
• 29:04
  Speaker 1: momentum comes from this symmetry of translation, where you don't
• 29:07
  Speaker 1: care about where you are in space, where space is relative.
• 29:11
  Speaker 1: There's no like official zero, there's no like golden numbers
• 29:14
  Speaker 1: glowing in the universe. It doesn't matter where you do
• 29:16
  Speaker 1: your experiment. And so now more than just saying hey,
• 29:20
  Speaker 1: look I noticed, momentum is conserved. You can say why
• 29:23
  Speaker 1: it's conserved, and you can inspect that reason, say does
• 29:26
  Speaker 1: that make sense? You know, we can say momentum is
• 29:28
  Speaker 1: conserved because the universe has no preferred location. You can
• 29:32
  Speaker 1: do your experiment anywhere, and we're like, all right, that
• 29:34
  Speaker 1: makes sense and that's a good reason for momentum to
• 29:36
  Speaker 1: be conserved. Okay, So what about energy? I mean, not
• 29:40
  Speaker 1: there tells us that energy is conserved in the universe
• 29:44
  Speaker 1: if the universe's laws don't change with time. Right, So,
• 29:49
  Speaker 1: momentum is conserved if the universe's laws don't depend on location,
• 29:53
  Speaker 1: if you don't have like different laws of physics in
• 29:54
  Speaker 1: different places, Energy is conserved if the laws don't change
• 29:58
  Speaker 1: with time. If like this, the same rules of electromagnetism
• 30:01
  Speaker 1: applied today and tomorrow and in a thousand years.
• 30:05
  Speaker 3: It feels like I want that to be there. But
• 30:07
  Speaker 3: I think we've decided that energy is not concerved. Can
• 30:10
  Speaker 3: you give me an example of how it's not conserved.
• 30:12
  Speaker 1: Yeah, it's fascinating because we assume that the laws of
• 30:15
  Speaker 1: physics are constant all the time. Think about just how
• 30:18
  Speaker 1: simple it is to read about an experiment in a
• 30:20
  Speaker 1: journal and say I'm going to reproduce that experiment and
• 30:23
  Speaker 1: see if it's true, and I'm going to do the
• 30:25
  Speaker 1: same thing and see if I get the same answer,
• 30:26
  Speaker 1: and reproducing it later, and assuming you get the same answer,
• 30:30
  Speaker 1: assumes the laws of physics shouldn't change, right, And it's
• 30:33
  Speaker 1: really important to our whole process of science that the
• 30:37
  Speaker 1: laws of physics were uncovering now are the same as
• 30:39
  Speaker 1: they were a thousand years ago or even a billion
• 30:42
  Speaker 1: years ago. Like when we look at galaxies deep out
• 30:44
  Speaker 1: into space in early times, we assume we know what
• 30:47
  Speaker 1: the speed of light was back then, and how mass
• 30:50
  Speaker 1: worked and all this kind of stuff. So the universe
• 30:52
  Speaker 1: without any constant laws is very difficult the universe to
• 30:55
  Speaker 1: do science in, right. And so it's not true that
• 30:59
  Speaker 1: the laws of physics are just wially nearly changing with time.
• 31:01
  Speaker 1: That's not something we've seen. But there are a couple
• 31:04
  Speaker 1: aspects of the laws of physics which do seem to
• 31:07
  Speaker 1: be changing with time, and one of them is that
• 31:10
  Speaker 1: the universe is expanding, so space itself, the frame in
• 31:15
  Speaker 1: which we're doing all of this stuff, is not static.
• 31:18
  Speaker 1: And when Emmy Nuther says the universe laws have to
• 31:21
  Speaker 1: be constant in time that includes space, right, it means
• 31:24
  Speaker 1: space itself needs to be constant the way like conservation
• 31:28
  Speaker 1: momentum requires you to be the same location in space,
• 31:31
  Speaker 1: it's put in the context of the space in that
• 31:34
  Speaker 1: same way, energy conservation requires you to have basically the
• 31:37
  Speaker 1: same amount of space. It's not changing the laws of
• 31:41
  Speaker 1: electromagnetism or you know, the speed of light or anything.
• 31:44
  Speaker 1: It's just saying, hey, the conditions of your experiment are
• 31:47
  Speaker 1: not constant because your universe is expanding. And we've known
• 31:51
  Speaker 1: for like twenty or so years that the universe is expanding,
• 31:54
  Speaker 1: and not just expanding, but accelerating in its expansion, Like
• 31:58
  Speaker 1: every year we are making more space between galaxy clusters
• 32:02
  Speaker 1: and between ice cream sandwiches and everywhere in the universe.
• 32:04
  Speaker 1: Space is expanding. And we actually have a not so
• 32:08
  Speaker 1: terrible explanation for why space expanding would mean that energy
• 32:12
  Speaker 1: isn't conserved.
• 32:14
  Speaker 3: Oh, I want to hear about that after the break.
• 32:33
  Speaker 2: All right, we're back.
• 32:34
  Speaker 3: So you blew our minds a second ago by explaining
• 32:36
  Speaker 3: that the expanding universe is why energy can't be concerned.
• 32:39
  Speaker 3: It's crazy to me that something that's happening so far
• 32:41
  Speaker 3: away but I guess also happening everywhere is impacting my
• 32:45
  Speaker 3: day to day experience of energy.
• 32:47
  Speaker 2: But go ahead and tell us the crazy thing you.
• 32:49
  Speaker 1: Replaying, William, I think, well, that sounds kind of abstract, right,
• 32:52
  Speaker 1: Like you're telling me the universe is expanding, and so
• 32:55
  Speaker 1: in some sense the context of our experiments is changing.
• 32:59
  Speaker 1: But why does that mean that energy is not conserved?
• 33:01
  Speaker 1: Like is energy being created somewhere or destroyed somewhere. So
• 33:05
  Speaker 1: let's tack into the details there, Like energy actually is
• 33:08
  Speaker 1: being created by the expansion of the universe. We talk
• 33:11
  Speaker 1: about the expansion of space as creating more space, right,
• 33:15
  Speaker 1: Like the distance between us and some cluster galaxy is growing,
• 33:19
  Speaker 1: and not because we're applying some force to accelerate away
• 33:21
  Speaker 1: from them. This is just like general relativity. Space is expanding, right,
• 33:26
  Speaker 1: We're not measuring any acceleration. They're not measuring any acceleration
• 33:29
  Speaker 1: with their accelerometers. But the distance between our galaxies is
• 33:33
  Speaker 1: increasing and faster and faster every year. So new space
• 33:36
  Speaker 1: is being made. Well, what does that mean? For new
• 33:39
  Speaker 1: space to be made? Space is filled with quantum fields, right,
• 33:43
  Speaker 1: There's the electron field, there's electromagnetic field, there's fields for
• 33:46
  Speaker 1: all the quarks, all these fields in space, and all
• 33:49
  Speaker 1: those fields have non zero energy, like these are quantum fields,
• 33:53
  Speaker 1: which means they can never go down to total zero.
• 33:56
  Speaker 1: They always have some energy in them. So you pop
• 34:00
  Speaker 1: a new cube of space, boom, it comes with quantum
• 34:04
  Speaker 1: fields that have energy in them. Right, So new space
• 34:07
  Speaker 1: means new energy. So right there, making more space means
• 34:12
  Speaker 1: you're creating energy, that doesn't It just.
• 34:14
  Speaker 3: Mean the energy gets spread more thin across this new space.
• 34:17
  Speaker 1: Because every chunk of space is the same and the
• 34:20
  Speaker 1: rules of quantum mechanics have a minimum requirement of that energy.
• 34:24
  Speaker 1: It's not something we deeply understand, but it's something that's
• 34:27
  Speaker 1: required for the accelerated expansion of the universe. We know
• 34:31
  Speaker 1: that dark energy behaves this way. We see, for example,
• 34:34
  Speaker 1: as the universe expands, the density of dark energy doesn't
• 34:38
  Speaker 1: change in the universe like the density of protons goes down.
• 34:42
  Speaker 1: You have a certain number of protons, you know, some
• 34:44
  Speaker 1: huge number of protons in the universe. As the volume
• 34:48
  Speaker 1: of the universe increases, the density of those protons drops
• 34:51
  Speaker 1: exactly the way you would expect. Right you double the volume,
• 34:54
  Speaker 1: that density goes down by a factor too. But dark energies.
• 34:57
  Speaker 1: Density does not decrease. You double the volume, the density
• 35:01
  Speaker 1: stays the same. Right, So dark energy behaves in this
• 35:04
  Speaker 1: weird way that when you create more space, you also
• 35:06
  Speaker 1: create more dark energy.
• 35:08
  Speaker 2: Where does it come from?
• 35:09
  Speaker 1: Where does it come from? Yeah?
• 35:10
  Speaker 2: How does that keep happening?
• 35:11
  Speaker 1: You ask where it comes from? And that's a question
• 35:13
  Speaker 1: that only makes sense if it's conserved, if it has
• 35:16
  Speaker 1: to come from somewhere, right, Like if I make an
• 35:18
  Speaker 1: ice cream sandwich, do you say, hey, where did that
• 35:21
  Speaker 1: ice cream sandwich come from? That seems to violate the
• 35:22
  Speaker 1: loss of physics.
• 35:23
  Speaker 3: You're like, no, I wouldn't ask questions about a new
• 35:26
  Speaker 3: ice cream sandwich, Dane, I would just enjoy it.
• 35:28
  Speaker 1: Right, go on. You know it's true you have to
• 35:30
  Speaker 1: assemble it out of bits, But like the assembly itself
• 35:32
  Speaker 1: didn't violate some law physics. You didn't have to destroy
• 35:35
  Speaker 1: an ice cream sandwich somewhere else to make this one. Right,
• 35:38
  Speaker 1: there's no limit on the number of ice cream sandwiches.
• 35:40
  Speaker 2: Thank the Lord, hallelujah.
• 35:42
  Speaker 1: Yeah, I know, we're all relieved. And so that question
• 35:45
  Speaker 1: where does the energy come from? Only make sense if
• 35:47
  Speaker 1: things have to flow. If you can just change the
• 35:50
  Speaker 1: total energy in the universe or change under ice cream sandwiches.
• 35:53
  Speaker 1: Then the question itself isn't actually as meaningful.
• 35:57
  Speaker 3: Right, So energy comes from nowhere. Energy can just like poop,
• 36:01
  Speaker 3: pop up.
• 36:01
  Speaker 1: Energy can just pop up. Yeah, absolutely, and you can
• 36:05
  Speaker 1: also disappear.
• 36:06
  Speaker 6: Right.
• 36:07
  Speaker 1: We talked about how the density of protons changes as
• 36:10
  Speaker 1: the universe expands and the density of dark energy. So
• 36:13
  Speaker 1: protons dilute in a way that makes a lot of sense, right,
• 36:15
  Speaker 1: Like you double the volume, the density goes down by
• 36:18
  Speaker 1: a factor of two. Interestingly, side note, same thing is
• 36:22
  Speaker 1: true of dark matter dark matter. As you double the
• 36:25
  Speaker 1: volume of the universe, dark matter density drops by two,
• 36:28
  Speaker 1: which is one reason why we think of dark matter
• 36:30
  Speaker 1: as matter, because it dilutes the way it matter does,
• 36:33
  Speaker 1: because radiation doesn't photons, As you double the volume of
• 36:37
  Speaker 1: the universe, their energy density drops by more than two.
• 36:41
  Speaker 1: Like you have a certain number of photons in the universe.
• 36:44
  Speaker 1: Now you increase the volume of the universe, you have
• 36:46
  Speaker 1: the same number of photons and more volumes. You might think, oh,
• 36:48
  Speaker 1: the energy density just decreases because you've increase the volume.
• 36:51
  Speaker 1: Not true, because the expansion of space also red shifts
• 36:56
  Speaker 1: those photons. It stretches their wavelength to rhetoric or longer wavelengths.
• 37:02
  Speaker 1: Longer wavelength means lower energy. So you have a universe
• 37:05
  Speaker 1: filled with photons, you expand that universe, their energy density
• 37:09
  Speaker 1: drops faster than the energy density of matter or dark matter.
• 37:13
  Speaker 1: Where does that energy go? It doesn't have to go anywhere.
• 37:17
  Speaker 3: It just goes moves into the space that was just created.
• 37:21
  Speaker 2: I've solved it. Where's my Nobel price?
• 37:24
  Speaker 1: I love that idea. People are right to be about
• 37:26
  Speaker 1: that a lot. They're like, Okay, energy is creative when
• 37:29
  Speaker 1: you expand space and also destroyed. Do these two numbers
• 37:32
  Speaker 1: add up, And it would be amazing if they did, right,
• 37:34
  Speaker 1: And that would be a beautiful explanation, you know, plus
• 37:36
  Speaker 1: seven thousand minus seven thousand boom. I think we figured
• 37:39
  Speaker 1: it out. These two numbers are vastly different scales. Like
• 37:42
  Speaker 1: the energy and photons in the universe is tiny, like
• 37:46
  Speaker 1: much less than one percent of all the energy and
• 37:48
  Speaker 1: universe is in photons, but the dark energy of the
• 37:51
  Speaker 1: universe is like two thirds of all the energy. So
• 37:54
  Speaker 1: energy is increasing in dark energy much much more rapidly
• 37:58
  Speaker 1: than energy is decreasing by redshift of photons. So we
• 38:02
  Speaker 1: don't think that photons are like getting turned into dark
• 38:04
  Speaker 1: energy or anything.
• 38:05
  Speaker 3: Okay, So bottom line here, we don't know where energy
• 38:09
  Speaker 3: comes from. We know it's not conserved. Physicists have job security.
• 38:16
  Speaker 1: Yeah, we don't even really still have an answer to
• 38:18
  Speaker 1: the original question of like what is energy? Right, still
• 38:23
  Speaker 1: a description of something we've seen, and we have a
• 38:26
  Speaker 1: little bit more theoretical footing now because we could, in
• 38:29
  Speaker 1: principle define energy as the thing that would be conserved
• 38:32
  Speaker 1: if the laws of physics were perfectly symmetric in time. Right,
• 38:36
  Speaker 1: you can use Nuther's theorem as a definition of energy
• 38:39
  Speaker 1: and say, oh, energy is that thing which would be conserved.
• 38:42
  Speaker 1: And that's kind of cool. I like that. It is
• 38:45
  Speaker 1: very theoretically grounded, but it doesn't give you like a
• 38:47
  Speaker 1: conceptual sense for like what is this thing? But unfortunately
• 38:51
  Speaker 1: that sort of turns you back to the philosophy of it, like, well,
• 38:53
  Speaker 1: what do you mean what is this thing? What kind
• 38:55
  Speaker 1: of answer are you looking for when you ask what
• 38:58
  Speaker 1: is energy? Part of the question is not satisfied by like, well,
• 39:02
  Speaker 1: here's the description of the kinds of energy, here are
• 39:04
  Speaker 1: the rules that it follows. Here's how it's created, here's
• 39:07
  Speaker 1: how it's destroyed. Here's how it's not concerned. But part
• 39:10
  Speaker 1: of the question is not answered by that description.
• 39:13
  Speaker 2: Do you think I have no idea?
• 39:16
  Speaker 1: Yeah, I feel like there's something about it that's still unsatisfied,
• 39:19
  Speaker 1: that's still like yeah, but what is it? You know, like,
• 39:22
  Speaker 1: why do we have it? Where does it come from?
• 39:24
  Speaker 1: It's a deep human question, but like the human questions
• 39:26
  Speaker 1: we ask, aren't always the appropriate questions, aren't always the
• 39:30
  Speaker 1: ones that answer the question. Sometimes we discover that something
• 39:34
  Speaker 1: is different from how we expected it to behave and
• 39:36
  Speaker 1: that means the kind of questions we should ask about
• 39:38
  Speaker 1: it are changing. Because energy isn't something that comes from somewhere.
• 39:43
  Speaker 1: It's a feature of the universe, and it does seem
• 39:46
  Speaker 1: to be important because under lots of context it is conserved,
• 39:50
  Speaker 1: but it's not fundamental in that way, and so it
• 39:52
  Speaker 1: could just be something that humans notice, something the humans
• 39:56
  Speaker 1: like to calculate, something that connects with our everyday experience
• 39:59
  Speaker 1: in a way that it's important to us, but isn't
• 40:02
  Speaker 1: Like alien physicists, for example.
• 40:04
  Speaker 3: It only appears to be conserved on human scales because
• 40:08
  Speaker 3: it's being lost at such low numbers it's hard to measure,
• 40:11
  Speaker 3: but it's not even conserved on small scales.
• 40:14
  Speaker 2: It just looks that way.
• 40:14
  Speaker 1: Yeah, that's exactly right. And I think it's useful to
• 40:17
  Speaker 1: think about this because it impacts other questions we have.
• 40:20
  Speaker 1: Like a lot of listeners who wrote in Thought about
• 40:23
  Speaker 1: the conservation of energy, and it talked about how the
• 40:26
  Speaker 1: Big Bang had energy, and maybe all the energy in
• 40:29
  Speaker 1: the universe just came from the Big Bang, right, And
• 40:32
  Speaker 1: so I hope the answer today reveals that, like, no,
• 40:35
  Speaker 1: there's some energy in the universe which was created after
• 40:38
  Speaker 1: the Big Bang. Right, This expansion of the universe is
• 40:40
  Speaker 1: making energy, and that's post Big Bang energy. And also
• 40:43
  Speaker 1: some of the energy of the Big Bang is gone now.
• 40:46
  Speaker 1: Like you have the Big Bang, you have matter and
• 40:48
  Speaker 1: anti matter created, they annihilate. You have a universe mostly
• 40:51
  Speaker 1: filled briefly with photons. So photons did dominate the universe
• 40:55
  Speaker 1: energy budget initially, but a lot of those photons are
• 40:58
  Speaker 1: now red shifted and their energy is gone. Like we
• 41:02
  Speaker 1: talk on the podcast a lot about the cosmic microwave
• 41:04
  Speaker 1: background radiation, this energy from the early universe that reveals
• 41:08
  Speaker 1: so much about how the universe came together and what
• 41:10
  Speaker 1: it means and how it rippled. But those photons are
• 41:13
  Speaker 1: very very red. They're at a temperature of like two
• 41:16
  Speaker 1: point seven calvin, very very cold. The plasma that made
• 41:20
  Speaker 1: them was like three hundred thousand degrees calvin. Right, they
• 41:24
  Speaker 1: were a glow of them, a very very hot plasma,
• 41:26
  Speaker 1: very energetic photons. Originally that energy is just gone now right,
• 41:31
  Speaker 1: It didn't go anywhere. So a lot of the energy
• 41:34
  Speaker 1: in the universe didn't come from the Big Bang, and
• 41:36
  Speaker 1: a lot of the energy of the Big Bang is
• 41:38
  Speaker 1: now gone, it's fizzled out.
• 41:40
  Speaker 3: Do we have less energy over time, more energy over time,
• 41:43
  Speaker 3: or do we not know how this balance is working out.
• 41:45
  Speaker 1: We definitely have more energy over time because dark energy
• 41:47
  Speaker 1: is much more dramatic, and so all the energy created
• 41:51
  Speaker 1: by dark energy, the expansion of the universe vastly outweighs
• 41:56
  Speaker 1: the energy loss due to red shifts of photons.
• 42:00
  Speaker 2: You would said that earlier.
• 42:00
  Speaker 3: But is that the only way that energy is lost
• 42:04
  Speaker 3: or is energy lost while humans are doing all of
• 42:06
  Speaker 3: these reactions down here, and is that impacting the like
• 42:09
  Speaker 3: mass balance equation.
• 42:10
  Speaker 2: For the universe?
• 42:12
  Speaker 1: To my knowledge, the expansion of the universe is the
• 42:15
  Speaker 1: only source of energy gain or loss. Right, You noticed
• 42:18
  Speaker 1: that it's an underlying mechanism for both of these things,
• 42:20
  Speaker 1: because it's the place that Norther's theorem is violated, right,
• 42:24
  Speaker 1: It's the thing that doesn't respect the time symmetry. So
• 42:26
  Speaker 1: the expansion of the universe redshifts those photons, breaking conservation
• 42:30
  Speaker 1: of energy and creates news space breaking conservation of energy.
• 42:34
  Speaker 1: So anything that's sensitive to the expansion of the universe
• 42:37
  Speaker 1: can be a source of the violation of conservation of energy.
• 42:42
  Speaker 1: And I want to make another comment about the Big Bang,
• 42:44
  Speaker 1: which is it seems like a little bit of a
• 42:46
  Speaker 1: loss of power to explain and explore, Like if energy
• 42:50
  Speaker 1: was conserved, then we could do this cool thing of
• 42:52
  Speaker 1: tracing it back into the Sun and then where that
• 42:55
  Speaker 1: came from, where that came from, all the way back
• 42:56
  Speaker 1: to the Big Bang. It's like we have a ledger,
• 42:59
  Speaker 1: you know, the tell us how energy slashes around, and
• 43:02
  Speaker 1: maybe by tracing that we could learn something. And that
• 43:05
  Speaker 1: seems really cool, and it feels like, oh, oh, maybe
• 43:07
  Speaker 1: we've lost that. Maybe we can no longer learn about
• 43:09
  Speaker 1: the Big Bang by studying energy. Well, just now we
• 43:13
  Speaker 1: can ask different questions, you know, we can ask how
• 43:16
  Speaker 1: the energy for the Big Bang came about, Like we
• 43:18
  Speaker 1: know that the universe was filled with hot, frothing energy
• 43:22
  Speaker 1: early on. Where did that come from? We no longer
• 43:25
  Speaker 1: have to just answer that by saying, oh, it came
• 43:27
  Speaker 1: from this other thing with equal energy. Now we have
• 43:30
  Speaker 1: more ideas about how you can create all that energy
• 43:33
  Speaker 1: from some earlier denser states. So, if anything, it opens
• 43:36
  Speaker 1: up the examination to think differently about the origin of
• 43:39
  Speaker 1: the universe. And you know, that's what we want. We
• 43:41
  Speaker 1: want our understanding of physics to evolve and to give
• 43:44
  Speaker 1: us new ways to think about the whole context of
• 43:47
  Speaker 1: reality and where it all came from. And so to me,
• 43:50
  Speaker 1: that's exciting. It like removes blinders a little bit and
• 43:54
  Speaker 1: gives us a broader sense for how the universe works
• 43:57
  Speaker 1: and maybe how it all started.
• 43:59
  Speaker 3: I bet you are great at writing grants. Okay, we
• 44:02
  Speaker 3: were wrong about that, but that's okay, because it's the
• 44:04
  Speaker 3: fascinating thing is actually revealed now.
• 44:08
  Speaker 1: So please send me a million dollars to make a
• 44:09
  Speaker 1: lot of ice cream sandwiches, because I have a lot
• 44:11
  Speaker 1: to learn.
• 44:12
  Speaker 3: You know, please share those ice cream sandwiches. Daniel, Yes,
• 44:15
  Speaker 3: Daniel needs this money.
• 44:16
  Speaker 1: It's important, everybody exactly. My cookies and cream project really
• 44:21
  Speaker 1: top priority for national security.
• 44:24
  Speaker 2: That's right, that's right, all right.
• 44:27
  Speaker 3: Well, I learned a ton today actually, and I can't
• 44:31
  Speaker 3: wait to tell my daughter actually about some of this
• 44:33
  Speaker 3: stuff and blow her mind somehow.
• 44:34
  Speaker 2: I feel like she's going to find this really interesting.
• 44:36
  Speaker 1: Yeah. So energy is not conserved, which means it doesn't
• 44:39
  Speaker 1: have to con from anywhere. But our understanding does seem
• 44:43
  Speaker 1: to be growing, and it seems to em and a
• 44:45
  Speaker 1: from these deep studies of how the universe works. So
• 44:48
  Speaker 1: let's keep doing that.
• 44:49
  Speaker 3: Let's hope our understanding is expanding faster than the information
• 44:53
  Speaker 3: we're losing.
• 44:55
  Speaker 1: All right, go off and enjoy ice cream sandwich. Everyone
• 44:57
  Speaker 1: on us?
• 44:58
  Speaker 2: Oh, not on us, Not on us, Daniel.
• 45:00
  Speaker 1: Virtually on us, spiritually on us.
• 45:03
  Speaker 2: Don't send us three sets.
• 45:04
  Speaker 1: That's all right, emotionally on us.
• 45:06
  Speaker 2: There you go, Okay.
• 45:15
  Speaker 3: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio.
• 45:19
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• 45:21
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• 45:24
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• 45:26
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• 45:33
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