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Is Energy Actually Conserved? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, I noticed something about physicists. I'm afraid to
• 0:12
  Speaker 1: hear this. I feel like all of you like to
• 0:13
  Speaker 1: blow things up. We do. Actually, that's what makes us
• 0:16
  Speaker 1: so much fun at parties. I guess. I mean you'd
• 0:18
  Speaker 1: like to blow up ideas. You know, you like to
• 0:21
  Speaker 1: think things that people think are true and then prove
• 0:24
  Speaker 1: that they're actually false. That's true. Actually you mean like
• 0:27
  Speaker 1: the Earth being the center of the universe. Yeah, I
• 0:30
  Speaker 1: like that. I like that idea, but it turns out
• 0:32
  Speaker 1: it's false. Or you know that people thought that the
• 0:34
  Speaker 1: world was nice and smooth, but actually it's quantized into
• 0:37
  Speaker 1: little pixels called quantum physics. Al Right, So what do
• 0:40
  Speaker 1: you think that means about physicists. I think it probably
• 0:42
  Speaker 1: means that you like to disagree with the stabich ideas.
• 0:45
  Speaker 1: You're basically just contrarians. No, we're not. See do you
• 0:49
  Speaker 1: know fun at parties? Hi am or handmade cartoonists and
• 1:07
  Speaker 1: the creator of PhD Comics. Hi. I'm Daniel. I'm a
• 1:10
  Speaker 1: particle physicist, and I'm very positive about new ideas. Welcome
• 1:13
  Speaker 1: to our podcast Daniel and Jorge Explain the Universe, a
• 1:16
  Speaker 1: production of Our Heart Radio in which we consider all
• 1:19
  Speaker 1: the crazy new ideas out there and all the old ideas.
• 1:22
  Speaker 1: Which ones are real, which ones are made up, which
• 1:24
  Speaker 1: ones are we still clueless about. We take you on
• 1:27
  Speaker 1: a tour of all of them and explain them to you. Yeah,
• 1:30
  Speaker 1: we like to explore the universe and talk about all
• 1:33
  Speaker 1: of the things that are out there and this beautiful
• 1:35
  Speaker 1: cosmos of ours, all the things that are true, and
• 1:38
  Speaker 1: all the things that might be true. And part of
• 1:41
  Speaker 1: the journey of physics and science in general is understanding
• 1:44
  Speaker 1: the universe and questioning the things we thought were true,
• 1:48
  Speaker 1: getting a deeper, more fundamental view of the way things
• 1:51
  Speaker 1: actually work, which sometimes is really in contrast with the
• 1:55
  Speaker 1: way we thought things work. Because there are a lot
• 1:57
  Speaker 1: of ideas out there, right, Daniel. I mean they're ideas
• 2:01
  Speaker 1: about how the world works, about why things are the
• 2:03
  Speaker 1: way they are, and how people think that it all
• 2:06
  Speaker 1: comes together. Yeah, And sometimes the first idea you have
• 2:09
  Speaker 1: seems reasonable and sticks around for a long time, and
• 2:12
  Speaker 1: then you notice small little problems with it, and when
• 2:16
  Speaker 1: you pull on that thread, you reveal something really fascinating
• 2:19
  Speaker 1: about the whole universe. Like people used to think, hey, there,
• 2:22
  Speaker 1: Earth is flat. It certainly looks flat from here. But
• 2:25
  Speaker 1: then it's sort of a mind exploding discovery to realize, Wow,
• 2:28
  Speaker 1: we're actually living on the surface of a huge sphere. Yeah.
• 2:32
  Speaker 1: So there are a lot of ideas out there, and
• 2:34
  Speaker 1: I feel like you physicists like to reserve the right
• 2:37
  Speaker 1: to change your mind. That's an important part of science, right,
• 2:41
  Speaker 1: challenging the orthodoxy. It's one of the best things about
• 2:44
  Speaker 1: science that sometimes we look at the very foundations of
• 2:47
  Speaker 1: the ideas and we say, wait a second, is that
• 2:49
  Speaker 1: really true? How do we actually know that? We've been
• 2:52
  Speaker 1: thinking that for a long time, but is it possible
• 2:56
  Speaker 1: that we were wrong. I think it's one of the
• 2:58
  Speaker 1: deepest virtues of science. Yeah. And if like that's maybe
• 3:00
  Speaker 1: your favorite part of science is proving your appears wrong
• 3:05
  Speaker 1: on a personal level, yes, And for me it's actually
• 3:08
  Speaker 1: the reason I got into science, because I'm really excited
• 3:11
  Speaker 1: about those moments of intellectual revolution. I feel like, when
• 3:16
  Speaker 1: you discover that the world is really different from the
• 3:18
  Speaker 1: way we thought it was, we've pulled the wolf from
• 3:21
  Speaker 1: our eyes. We've like peeled back a layer of reality.
• 3:24
  Speaker 1: We've discovered some truth that was hidden to us. And
• 3:27
  Speaker 1: what's more exciting in science than to have a moment
• 3:30
  Speaker 1: of discovery like that a deep revelation, you know, not
• 3:33
  Speaker 1: like slowly iterately building up increments of knowledge until you
• 3:37
  Speaker 1: get there, like almost like a moment of revelation where
• 3:40
  Speaker 1: you understand the universe differently somehow and you can never
• 3:43
  Speaker 1: go back to seeing it the old way. Some people
• 3:46
  Speaker 1: go for the Eureka moment. You like to go for
• 3:48
  Speaker 1: the moment. That's what I'm in for. I'm in it
• 3:52
  Speaker 1: for the scientific revolutions, for the Hans. You're in for
• 3:55
  Speaker 1: the Hans I am. And there have been lots of
• 3:58
  Speaker 1: moments in history where people have made to discoveries like this.
• 4:01
  Speaker 1: They've pulled on one little string and then they've unraveled
• 4:03
  Speaker 1: that very foundations of science, and so it's exciting to
• 4:07
  Speaker 1: think that there might be more of those ahead of us.
• 4:09
  Speaker 1: So it's exciting when a bunch of smart people's go,
• 4:11
  Speaker 1: never mind, I thought there was flat, but actually it's
• 4:15
  Speaker 1: a giant ball. Yeah, because it changes sometimes your whole
• 4:18
  Speaker 1: relationship with the universe, you know, thinking that we live
• 4:21
  Speaker 1: at the center of the universe everything revolves around us,
• 4:24
  Speaker 1: to thinking we're just a tiny little speck of dust
• 4:27
  Speaker 1: in an insignificant corner of the universe that really changes
• 4:31
  Speaker 1: the way you feel about the universe and life itself
• 4:33
  Speaker 1: and how you should live it. So, hey, this stuff
• 4:36
  Speaker 1: is actually irrelevant for how people feel about themselves and
• 4:39
  Speaker 1: their lives. Yeah. So science is all about challenging ideas,
• 4:42
  Speaker 1: and so today on the program will be challenging a
• 4:45
  Speaker 1: very core and fundamental idea and physics. I feel like
• 4:48
  Speaker 1: this is a very important idea that a lot of
• 4:50
  Speaker 1: people have kind of internalized about the universe, but that
• 4:53
  Speaker 1: actually might not be so true. That's right. This is
• 4:57
  Speaker 1: something pretty basic that if you ask folks on the street,
• 5:00
  Speaker 1: it would be pretty confident was true. But it turns
• 5:02
  Speaker 1: out we've learned a lot about the nature of the
• 5:04
  Speaker 1: universe and it might actually not be quite so fundamental.
• 5:07
  Speaker 1: So on the program will be asking the question is
• 5:15
  Speaker 1: energy actually conserved? Now, Daniel, this sort of blew my mind.
• 5:22
  Speaker 1: How can we even ask this question? What do you mean?
• 5:24
  Speaker 1: Is energy always actually conserved? Yeah? That's why it's such
• 5:27
  Speaker 1: a wonderful question because it makes you think, like, well,
• 5:31
  Speaker 1: why would it be conserved? How do we actually know
• 5:33
  Speaker 1: it's conserved? What would it be like to live in
• 5:36
  Speaker 1: a universe where it's not conserved? That solve all of
• 5:39
  Speaker 1: our energy problems. I feel like you just told me
• 5:41
  Speaker 1: the world is not actually a ball. It's like a
• 5:43
  Speaker 1: cube or something. We live on a donut and it's
• 5:47
  Speaker 1: filled with energy. It's filled with sugar, energy and sprinkles.
• 5:51
  Speaker 1: That's right. Just eat the glaze, man, eat the glaze.
• 5:55
  Speaker 1: Then then my energy will not be conserved, just an
• 5:59
  Speaker 1: increase or be turned into mass. Probably. I know. It's
• 6:02
  Speaker 1: a bit mind blowing, and that's why I was especially
• 6:04
  Speaker 1: eager to hear what folks on the internet had to
• 6:06
  Speaker 1: say about this question. Yes, so it's usual Daniel went
• 6:09
  Speaker 1: out there into the wilds of the web and ask
• 6:11
  Speaker 1: people the question is energy always conserved? So thank you
• 6:16
  Speaker 1: to these folks in advance who participated. And if you
• 6:18
  Speaker 1: would like to answer tough physics questions with no preparation
• 6:22
  Speaker 1: and have your answers broadcast thousands of people, please write
• 6:26
  Speaker 1: to us two questions at Daniel and Jorge dot com.
• 6:28
  Speaker 1: Think about it for a second. If someone ask you
• 6:31
  Speaker 1: if energy is actually always conserved, what would you answer.
• 6:35
  Speaker 1: Here's what people had to say. I always thought that
• 6:38
  Speaker 1: was one of the fundamental laws, that energy and matter
• 6:41
  Speaker 1: can't be created or destroyed, But the fact that you're
• 6:44
  Speaker 1: asking me this question makes me think I'm wrong. Yes,
• 6:48
  Speaker 1: I don't know about the energy that goes in into
• 6:51
  Speaker 1: a black hole, but it's somewhere there. Yes, is one
• 6:56
  Speaker 1: of the fundamental principles of the universe that energy is conserved.
• 7:01
  Speaker 1: I know that it gets a little dicey when you're
• 7:03
  Speaker 1: talking about black holes. Yes, it is, but I don't
• 7:06
  Speaker 1: know if there's any special cases where it's not. Yes,
• 7:09
  Speaker 1: energy always is conserved in some form, right, I think
• 7:13
  Speaker 1: ultimately everything becomes heat. But if energy does not get conserved,
• 7:19
  Speaker 1: where does it go? All right, not a lot of
• 7:21
  Speaker 1: doubters here. Everyone just said yes, no confusion. I feel
• 7:26
  Speaker 1: like nobody was confused about this. No, nobody was confused.
• 7:29
  Speaker 1: I love the person who said the fact you're asking
• 7:31
  Speaker 1: me this question makes me think I'm wrong, which is wonderful. Man,
• 7:37
  Speaker 1: you totally make that person. You need a doubt because
• 7:41
  Speaker 1: that's the process of science. We're like, we're sure that's true.
• 7:44
  Speaker 1: Hold on a second, how are we sure? All of
• 7:47
  Speaker 1: a sudden, I'm wondering, And then you've got to explore
• 7:50
  Speaker 1: your own intellectual framework and wonder like, do you really
• 7:53
  Speaker 1: know this or is it just something you've been assuming yeah.
• 7:56
  Speaker 1: Especially I guess if a physicist approaches you on the
• 7:59
  Speaker 1: street with my acrophone and says, do you think energy
• 8:01
  Speaker 1: is always conserved? I feel like, you know that automatically
• 8:04
  Speaker 1: makes you a little suspicious. Yeah. Actually, default answer to
• 8:06
  Speaker 1: a random physicist asking you a question should be no,
• 8:10
  Speaker 1: it should be I don't know, what do you think?
• 8:12
  Speaker 1: And then you flipped do you want to participate in
• 8:15
  Speaker 1: my experiment? Uh? No? Do you want to know the
• 8:18
  Speaker 1: deep secrets of the universe? Not? Really? So this is
• 8:22
  Speaker 1: I feel like this is a pretty mind blown question,
• 8:24
  Speaker 1: just the idea of asking this question. I feel like
• 8:26
  Speaker 1: the idea that energy is always conserved seems very basic
• 8:31
  Speaker 1: to physics, and it seems pretty internalized by most of
• 8:34
  Speaker 1: the public. Like I feel like, you know, it's like
• 8:36
  Speaker 1: asking which way does gravity point? Or you know, it's
• 8:40
  Speaker 1: space big people say yes. But there's a bit of
• 8:42
  Speaker 1: a history here, right. It used to be that we
• 8:45
  Speaker 1: thought energy was conserved and that mass was conserved. We
• 8:48
  Speaker 1: would watch chemical reactions and we would notice that it
• 8:51
  Speaker 1: was mostly a rearrangement of the atoms, like puzzle pieces
• 8:55
  Speaker 1: moving from one place to another, and that no actual
• 8:58
  Speaker 1: matter was destroyed or created, and so we had two principles,
• 9:02
  Speaker 1: conservation of energy and conservation of mass. But then we
• 9:06
  Speaker 1: learned conservation of mass not actually a thing, right, You
• 9:09
  Speaker 1: can turn mass into other kinds of energy, and energy
• 9:13
  Speaker 1: into mass. So then we generalized into a larger principle,
• 9:16
  Speaker 1: conservation of energy, which includes mass as one of its forms.
• 9:20
  Speaker 1: But that's a hint, right, that's a hint. That's something
• 9:22
  Speaker 1: which seems fundamental, like the existence of matter doesn't necessarily
• 9:26
  Speaker 1: have to be concerned. Now, this isn't just a sort
• 9:29
  Speaker 1: of like a semantic thing, right, Like we're not saying
• 9:31
  Speaker 1: that energy just transforms into mass and so it's not concerned.
• 9:35
  Speaker 1: We're asking kind of the bigger question, like is mass
• 9:38
  Speaker 1: and energy conserved? That's right now, we're asking the deep
• 9:40
  Speaker 1: fundamental question. Is total energy concerned? When you include all forms,
• 9:45
  Speaker 1: not just does it slip away into some other kind
• 9:47
  Speaker 1: of energy, but energy itself summed up over everything, is
• 9:51
  Speaker 1: it actually conserved? Yeah? And it turns out that the
• 9:55
  Speaker 1: answer is no. How can it be? No, Daniel, The
• 10:01
  Speaker 1: answer is no. He's just during my world, I feel
• 10:04
  Speaker 1: like democracy died last night. And now physics, well, that's
• 10:09
  Speaker 1: what we're here for. We are here to blow people's
• 10:11
  Speaker 1: minds and pull back the veil and help them understand
• 10:14
  Speaker 1: the way the world actually works. And so this is
• 10:17
  Speaker 1: kind of mind boggling. But the lesson we're gonna learn
• 10:20
  Speaker 1: is what's actually important about the universe, what's really fundamental?
• 10:23
  Speaker 1: What do we actually know? What really should we be
• 10:26
  Speaker 1: paying attention to? All Right, so I guess the short
• 10:30
  Speaker 1: answer is no. Energy is not always conserved. That's right,
• 10:33
  Speaker 1: And that's even in a closed system. Right, we talked
• 10:36
  Speaker 1: about energy conservation. We're usually referring to a closed system
• 10:39
  Speaker 1: because you know, if you have a single thing inside
• 10:41
  Speaker 1: a larger system, sure it doesn't have to conserve energy,
• 10:44
  Speaker 1: Like a battery inside your toy is losing energy, but
• 10:48
  Speaker 1: you know that energy is going to other parts of
• 10:50
  Speaker 1: the system. But we're talking about a closed system, or
• 10:52
  Speaker 1: energy doesn't escape or doesn't enter, we're talking about the
• 10:55
  Speaker 1: whole universe. Is energy conserved for the whole universe? And
• 10:59
  Speaker 1: even for that, the answer, it turns out is no, Man, Daniel,
• 11:03
  Speaker 1: not even for a closed system. I feel like one
• 11:06
  Speaker 1: of those celebrities. I'm ready to throw down my microphone
• 11:09
  Speaker 1: and walk away. Don't mic drop just yet. There are
• 11:12
  Speaker 1: bigger revelations to come, I see their twists. All right,
• 11:16
  Speaker 1: we'll step us through first, why do we think that
• 11:18
  Speaker 1: energy was conserved? And then maybe we'll get into why
• 11:21
  Speaker 1: it wasn't it's not conserved. Yeah, that's a great question.
• 11:24
  Speaker 1: And essentially we thought that energy was conserved because mostly
• 11:27
  Speaker 1: it is, and so we never noticed we never saw
• 11:30
  Speaker 1: a counter example. And a lot of physics works this way.
• 11:34
  Speaker 1: We see things happening in the world and we see
• 11:36
  Speaker 1: them seeming to follow a rule, and so we just
• 11:39
  Speaker 1: sort of like we positive, well, maybe this rule is true.
• 11:41
  Speaker 1: Maybe this is fundamental. You know, electric charge is conserved,
• 11:45
  Speaker 1: or you know F equals m A. We don't always
• 11:48
  Speaker 1: have a reason for it. We don't always have like
• 11:50
  Speaker 1: a first principles derivation for it, which is something we observe,
• 11:54
  Speaker 1: we categorize, and then we elevate it to a status
• 11:58
  Speaker 1: and if nobody ever sees it broken, we think, well
• 12:00
  Speaker 1: that must be true. For some reason. We elevated to
• 12:03
  Speaker 1: that like a law status. We think it's a law
• 12:05
  Speaker 1: of the universe. Yeah, And this is the way science works,
• 12:08
  Speaker 1: is that we come up with a rule, we test it,
• 12:10
  Speaker 1: we check it, we explore it and lots of different ways,
• 12:12
  Speaker 1: and if it survives experimental tests over and over and
• 12:16
  Speaker 1: over again. We think, oh, it's probably true, and then
• 12:18
  Speaker 1: we can sometimes dig deeper and figure out the reason why.
• 12:22
  Speaker 1: We can sometimes later derive that law from deeper truths.
• 12:26
  Speaker 1: But sometimes we can reveal that it was only ever
• 12:29
  Speaker 1: approximately true. We haven't checked every possible scenario. That's impossible, right,
• 12:35
  Speaker 1: and so people will find a place where, look, it
• 12:37
  Speaker 1: turns out it's broken over here, it doesn't quite work
• 12:40
  Speaker 1: over there. It was the same story with conservation of mass.
• 12:43
  Speaker 1: If you're just doing basic chemistry, mass is mostly conserved.
• 12:47
  Speaker 1: It's only when you get to like higher energies where
• 12:49
  Speaker 1: you're destroying particles or colliding particles that you notice that
• 12:53
  Speaker 1: it's broken. So a lot of these conservation rules are
• 12:57
  Speaker 1: not exact. They're not like really true. They're almost true,
• 13:01
  Speaker 1: or they're true and lots of circumstances and so we
• 13:04
  Speaker 1: never notice. It's kind of like F equals m A.
• 13:06
  Speaker 1: I feel like that feels really fundamental and intuitive because
• 13:10
  Speaker 1: that's what dominates our everyday experience. But like if you
• 13:14
  Speaker 1: push the physics of it to extreme situations, it doesn't work.
• 13:17
  Speaker 1: It breaks, yeah, exactly. And the same is true for
• 13:20
  Speaker 1: things about like time. You know, we've learned that not
• 13:23
  Speaker 1: everybody has to agree on the order of events. We
• 13:26
  Speaker 1: had a whole podcast about what happens when people are
• 13:28
  Speaker 1: running a race and you look at it from different speeds,
• 13:31
  Speaker 1: and these are the kind of things you don't notice
• 13:32
  Speaker 1: in your everyday life. You don't approach the speed of light.
• 13:36
  Speaker 1: And so we never tested things in those sort of
• 13:38
  Speaker 1: high speed extremes until recently, and we noticed, whoops. Those
• 13:42
  Speaker 1: rules we thought were deep and fundamental and true turned
• 13:44
  Speaker 1: out to be a special case that are only valided
• 13:46
  Speaker 1: certain situations, not fundamental truths about the universe. And physics
• 13:51
  Speaker 1: is all about uncovering the fundamental truths about the universe,
• 13:55
  Speaker 1: not just the special cases. And so that's why we
• 13:58
  Speaker 1: thought energy was conserved because we've always seen it conserved
• 14:01
  Speaker 1: and sort of made sense. Yeah, it's conserved in most
• 14:04
  Speaker 1: situations that we're familiar with, right, Like, if you have
• 14:07
  Speaker 1: a canister of gas or something, the energy in it
• 14:10
  Speaker 1: is going to be mostly conserved, mostly conserved, are totally conserved,
• 14:14
  Speaker 1: the energy is going to be almost exactly conserved. And
• 14:17
  Speaker 1: thinking about when it's conserved and noticing when those rules
• 14:20
  Speaker 1: are broken, it's going to teach us really something fundamental
• 14:23
  Speaker 1: about the nature of space and symmetries and conservation laws
• 14:27
  Speaker 1: in general. But fuel, for example, is mostly conserved. All right,
• 14:31
  Speaker 1: let's get into some examples of when energy is not conserved,
• 14:35
  Speaker 1: and let's get into why it's not being the good
• 14:39
  Speaker 1: conservative we thought it was. But first let's take a
• 14:42
  Speaker 1: quick break. All right, Daniel, we are blowing up people's
• 14:57
  Speaker 1: brains here. Apparently energy is not concerned in this universe.
• 15:01
  Speaker 1: That's right. It's not always the same, that's right. It's
• 15:04
  Speaker 1: not always the same. The amount of energy in the
• 15:06
  Speaker 1: universe can change. And this is the kind of thing
• 15:09
  Speaker 1: I get email questions from listeners about all the time,
• 15:12
  Speaker 1: because people who have been thinking to themselves about dark
• 15:15
  Speaker 1: energy have come in their minds to what seems like
• 15:17
  Speaker 1: a contradiction. Remember, dark energy is the expansion of the universe.
• 15:22
  Speaker 1: It's not something we understand. It's not a law physics.
• 15:25
  Speaker 1: It's just sort of the observation that the expansion of
• 15:27
  Speaker 1: the universe is continuing and that it's speeding up, and
• 15:31
  Speaker 1: we don't understand the mechanism of it. But there is
• 15:33
  Speaker 1: something about dark energy that we do know, which is
• 15:36
  Speaker 1: that it's constant in space. So it makes more space,
• 15:40
  Speaker 1: and then that space has new dark energy. So every
• 15:43
  Speaker 1: cubic meter of space, for example, has its own dark energy.
• 15:47
  Speaker 1: And as the universe expands, you get more universe, you
• 15:50
  Speaker 1: get more dark energy. So these listeners right in and
• 15:53
  Speaker 1: they say, hold on a second, where does that energy
• 15:55
  Speaker 1: come from? Does that mean that dark energy doesn't concern
• 16:00
  Speaker 1: of energy? Right? Yeah, it's it's kind of very puzzling,
• 16:02
  Speaker 1: right because you're telling me that the universe is expanding
• 16:05
  Speaker 1: with more energy and acceleration, so it has to you know,
• 16:08
  Speaker 1: be drawing energy from somewhere, but it's sort of coming
• 16:12
  Speaker 1: out of nothingness, this dark energy. And so the answer
• 16:14
  Speaker 1: to those listeners is that no, it doesn't have to
• 16:17
  Speaker 1: come from somewhere. It violates the conservation of energy. As
• 16:21
  Speaker 1: the universe expands, you get more space, and that space
• 16:25
  Speaker 1: has new energy, and the energy in the universe increases.
• 16:29
  Speaker 1: So as spacetime expands, the energy can go up. And
• 16:34
  Speaker 1: where does that energy come from? It doesn't have to
• 16:36
  Speaker 1: come from anywhere, because energy conservation is not actually a
• 16:40
  Speaker 1: fundamental law of the universe. It's just something we never
• 16:43
  Speaker 1: saw broken before. I feel like that throws everything to question. Now, Daniel,
• 16:47
  Speaker 1: what do you mean, yes, right, Welcome to physics, questioning everything,
• 16:52
  Speaker 1: even even the idea of asking questions. Why are you
• 16:54
  Speaker 1: asking questions, Daniel, don't ask questions about that. That's a
• 16:59
  Speaker 1: zone of a wild So is that the primary example
• 17:02
  Speaker 1: of energy not being conserved is in space and in
• 17:05
  Speaker 1: this idea of the universe expanding or is it more
• 17:09
  Speaker 1: you know, kind of seeped into our everyday physics. It's
• 17:13
  Speaker 1: not really steeped into our everyday physics. And the cases
• 17:16
  Speaker 1: where energy is not conserved are really going to give
• 17:19
  Speaker 1: us a clue as to why it's not conserved. And
• 17:22
  Speaker 1: I can give you another example, which is also related
• 17:25
  Speaker 1: to the expansion of space. As space expands, it turns
• 17:29
  Speaker 1: out there's a way to lose energy. For example, a
• 17:32
  Speaker 1: photon photon is flying through space, and we know that
• 17:35
  Speaker 1: if a photon comes to you from far away, but
• 17:38
  Speaker 1: that the space between you and the source expands in
• 17:41
  Speaker 1: the meantime, that photon red shifts are red shifts associated
• 17:45
  Speaker 1: with that source having a velocity. Like a police siren
• 17:48
  Speaker 1: that's moving away from you, the wavelength of the sound
• 17:52
  Speaker 1: is stretched, and the same is true for light from
• 17:55
  Speaker 1: stars that are moving away from us. But there's another
• 17:58
  Speaker 1: kind of red shift, which is just the expand engine
• 18:00
  Speaker 1: of space between you and that light source. It will
• 18:03
  Speaker 1: also stretch the photon and make it redder. Won't slow
• 18:06
  Speaker 1: it down, it'll just shift its frequency. That will stretch it.
• 18:09
  Speaker 1: That's right. Photons always move with the same speed, the
• 18:12
  Speaker 1: speed of light, but they have different levels of energy
• 18:15
  Speaker 1: which correspond to their wavelength, which is equivalent to their
• 18:18
  Speaker 1: color or their frequency. It's all the same thing. And
• 18:21
  Speaker 1: so when you make a photon redder, effectively you're taking
• 18:24
  Speaker 1: away its energy. It's losing energy. So in that case,
• 18:27
  Speaker 1: the expansion of space disappears energy from a photon. What
• 18:33
  Speaker 1: could it all be the same energy, Daniel? Could dark
• 18:35
  Speaker 1: energy be the energy of photons getting redder. That wouldn't
• 18:40
  Speaker 1: add up to like a factor of tend to one.
• 18:42
  Speaker 1: There's so much more dark energy than the energy that's
• 18:45
  Speaker 1: being lost by photons being red shifted. But we see this.
• 18:49
  Speaker 1: It's a real thing. It's just kind of like a
• 18:50
  Speaker 1: dark red energy. I like that phrase, dark red energy.
• 18:55
  Speaker 1: That should be a thing. There should be a physics.
• 18:57
  Speaker 1: Should be the title your other sci fi novel, dark
• 19:00
  Speaker 1: red energy. All right, I'll do it just starting from
• 19:03
  Speaker 1: the title. I can just write the novel from there.
• 19:05
  Speaker 1: But yeah, So here are two examples, space expanding meaning
• 19:09
  Speaker 1: extra energy is created, or space expanding meaning energy is
• 19:14
  Speaker 1: lost by photons. And the thing that those two examples
• 19:17
  Speaker 1: have in common, of course, is that space is not static.
• 19:20
  Speaker 1: In those cases, space is expanding its dynamic and that's
• 19:24
  Speaker 1: the clue. I see. Yeah, that's kind of um, it's
• 19:26
  Speaker 1: like breaking a law by breaking another law, kind of
• 19:29
  Speaker 1: because I feel like, you know, we thought space didn't
• 19:32
  Speaker 1: expand we thought space was fixed before, but then we
• 19:35
  Speaker 1: learned that space is like malleble and bends and stretches. Yeah,
• 19:38
  Speaker 1: and just like thinking that Galilean transformations Newtonian physics always
• 19:42
  Speaker 1: worked because we had always seen it work because we'd
• 19:44
  Speaker 1: only ever checked low speeds and then discovering that they
• 19:48
  Speaker 1: break when you get too high speeds. This is an
• 19:50
  Speaker 1: example of something we never thought was possible, expanding space,
• 19:54
  Speaker 1: and when it happens, it challenges some pretty basic stuff
• 19:57
  Speaker 1: that we thought was true, but turns out only have
• 20:00
  Speaker 1: been true in the special scenario we ever tested it in,
• 20:04
  Speaker 1: which is fundamentally static space. Right, Well, then step us
• 20:07
  Speaker 1: three here, Daniel, why is an energy conserved when space expands? Well,
• 20:12
  Speaker 1: I think the best way to tackle that is to
• 20:13
  Speaker 1: think about, like, well, why should we expect it to
• 20:17
  Speaker 1: be conserved? Did we have a reason to think it
• 20:19
  Speaker 1: should be conserved. Is there some fundamental theoretical idea that
• 20:23
  Speaker 1: tells us it should be conserved, or is it just
• 20:25
  Speaker 1: something we observed and thought was true. And for that,
• 20:29
  Speaker 1: I think it's good to think about, like, what do
• 20:30
  Speaker 1: we mean exactly about conserved? Right to be kind of
• 20:34
  Speaker 1: specific about it, And by that we mean like, here's
• 20:37
  Speaker 1: something we calculate, Like you can measure the amount of
• 20:40
  Speaker 1: energy and something and then you can let it do
• 20:42
  Speaker 1: its thing. You know, maybe you turn on the engine
• 20:45
  Speaker 1: of your car or whatever, and then you calculate it again,
• 20:48
  Speaker 1: and you notice you get the same answer. So as
• 20:50
  Speaker 1: you said before, like you burn the fuel in your car,
• 20:53
  Speaker 1: but now you've added speed to your car, so energy
• 20:55
  Speaker 1: is moved from one part of the system to another.
• 20:58
  Speaker 1: And we've noticed so far that if you add up
• 21:00
  Speaker 1: all the energy before and you add of the energy after,
• 21:03
  Speaker 1: you get the same thing. And so we call that conserved,
• 21:06
  Speaker 1: right that there's a symmetry there that says it hasn't
• 21:09
  Speaker 1: changed the accounty. You can account for every cent of
• 21:11
  Speaker 1: that energy. That's right, And so people have long wondered, like,
• 21:15
  Speaker 1: why are things conserved at all? What does it mean
• 21:18
  Speaker 1: about the universe? Because it's the kind of thing that
• 21:20
  Speaker 1: makes a physicist scratch his or her head. It's like, well,
• 21:23
  Speaker 1: if this thing is concerned, does that mean that it's
• 21:25
  Speaker 1: a deep truth in the universe, that it's an important quantity.
• 21:28
  Speaker 1: It's like a clue about how the universe works. If
• 21:32
  Speaker 1: this thing doesn't change, right, it's like a constraint or
• 21:35
  Speaker 1: a law. And if you're on the hunt for figuring
• 21:37
  Speaker 1: out the fundamental rules of the universe, that seems like
• 21:39
  Speaker 1: an important clue, right, Yeah, well, I guess maybe it's
• 21:42
  Speaker 1: it's it feels fundamental because it's kind of it feels
• 21:46
  Speaker 1: logical for it to be conserved. I know we're trying
• 21:48
  Speaker 1: to question it here, but it's like, you know, if
• 21:50
  Speaker 1: you have some money, it has to go somewhere. Can't
• 21:52
  Speaker 1: just like disappear, and it can't just pop out of
• 21:55
  Speaker 1: the nothingness. I think that's just your intuition. You're just
• 21:58
  Speaker 1: used to having a conserved and actually money is a
• 22:00
  Speaker 1: great example because money is also not conserved. You know,
• 22:04
  Speaker 1: if I take a painting by Picasso and I just
• 22:07
  Speaker 1: set it on fire. Where does the value of that
• 22:10
  Speaker 1: painting go nowhere? Or if I am Picasso, when I
• 22:13
  Speaker 1: make a new painting, right I've created a hundred million dollars,
• 22:17
  Speaker 1: Where does that come from? Right? I wasn't worth a
• 22:20
  Speaker 1: hundred million dollars. It didn't seep out of me. Or
• 22:22
  Speaker 1: one day people decide that some kind of rock is
• 22:26
  Speaker 1: now the most valuable thing in the world, and we
• 22:28
  Speaker 1: will all pay five d dollars an ounce for this
• 22:31
  Speaker 1: kind of rock. Then we've created value. So money is
• 22:35
  Speaker 1: not conserved at all. It's a great example, right, But
• 22:37
  Speaker 1: I feel like money is kind of it's like a
• 22:39
  Speaker 1: psychological concept, money and value. But we're talking about like physics, right, yeah, exactly,
• 22:45
  Speaker 1: Like you know, if if I have something here, it
• 22:47
  Speaker 1: can't just disappear, or I can't just suddenly appear another
• 22:51
  Speaker 1: whore in front of me, although it would be cool
• 22:54
  Speaker 1: because then I could go to sleep. Well, there are
• 22:59
  Speaker 1: actually really interesting fundamental insights about why some things are
• 23:02
  Speaker 1: conserved and some things are not conserved. And this comes
• 23:06
  Speaker 1: from a law from a real genius of physics who
• 23:09
  Speaker 1: have been long overlooked and only recently been appreciated a
• 23:12
  Speaker 1: mathematical physicist from the early part of this century, I
• 23:15
  Speaker 1: mean Utah, and she wrote down a really interesting law,
• 23:18
  Speaker 1: and she says that there's a conservation. There's something that's conserved,
• 23:22
  Speaker 1: like energy or momentum, every time the universe has a symmetry.
• 23:27
  Speaker 1: But there's this deep connection between something being conserved and
• 23:30
  Speaker 1: the universe having some sort of balance or symmetry to it.
• 23:34
  Speaker 1: From a language point of view, that makes sense. If
• 23:36
  Speaker 1: there's a symmetry means there's like an equation, which means
• 23:39
  Speaker 1: things are balanced and conserved. But I'm guessing you mean
• 23:42
  Speaker 1: more like the mathematical idea of symmetry. And there's lots
• 23:45
  Speaker 1: of really fascinating examples before we get to energy. And
• 23:48
  Speaker 1: one of my favorites is momentum. So why is momentum
• 23:52
  Speaker 1: conservad at all? You might ask that, Well, it turns
• 23:54
  Speaker 1: out that momentum is conserved because the universe has no
• 23:58
  Speaker 1: preferred location called this translation symmetry, Like something that happens
• 24:03
  Speaker 1: here in space could equally well happen ten ms to
• 24:06
  Speaker 1: the right or a hundred up or whatever. The laws
• 24:10
  Speaker 1: of physics don't change based on where you are in
• 24:12
  Speaker 1: the universe. That's we call a translation symmetry, and that
• 24:16
  Speaker 1: translation symmetry directly implies conservation of momentum. Like if you
• 24:21
  Speaker 1: didn't know momentum was conserved, but you knew that, you
• 24:24
  Speaker 1: didn't matter where you were in the universe, you could
• 24:27
  Speaker 1: derive conservation of momentum mathematically, How would you, I guess,
• 24:31
  Speaker 1: derive it? Can you give us like an in twitter sense,
• 24:33
  Speaker 1: like you know, the equations can be reduced to like
• 24:37
  Speaker 1: you know, momentum and equals momentum out. Yeah, there actually
• 24:40
  Speaker 1: is a mathematical procedure. That's what Newtis theorem does. It
• 24:44
  Speaker 1: tells you what conservation law comes out of a specific symmetry.
• 24:49
  Speaker 1: If the universe is symmetric to changes in some quantity X,
• 24:53
  Speaker 1: then you can derive the quantity why that is conserved.
• 24:57
  Speaker 1: For those listeners who want a little bit more gory
• 24:59
  Speaker 1: Dta hills, you take the quantity that's conserved, and then
• 25:03
  Speaker 1: you have to take the derivative of the lagrange in
• 25:06
  Speaker 1: of the universe with respect to the derivative of that
• 25:09
  Speaker 1: thing that's conserved, and so it gets a little bit
• 25:11
  Speaker 1: hairy mathematically, but there is a relationship between the quantity
• 25:15
  Speaker 1: that has symmetry. In this case, position in space and
• 25:18
  Speaker 1: the thing that's being conserved in this case mass times
• 25:22
  Speaker 1: the velocity, which is the derivative of your position in space.
• 25:25
  Speaker 1: And so that's the nuts and bolts of the mathematical
• 25:28
  Speaker 1: genius of Emily Nuther. But the idea is that there's
• 25:31
  Speaker 1: a symmetry here, and I think you can understand it intuitively. Like,
• 25:35
  Speaker 1: think about, for example, just a single rock floating in space,
• 25:38
  Speaker 1: and that could be anywhere. Right, you push on that rock,
• 25:42
  Speaker 1: you've given it momentum. It flies off with a certain momentum.
• 25:45
  Speaker 1: It makes sense for momentum to be conserved, your momentum
• 25:48
  Speaker 1: flowing to the momentum of the rock. If nothing pushes
• 25:51
  Speaker 1: on you, you're going to keep coasting at the same speed. Yeah, exactly.
• 25:54
  Speaker 1: And that's true here, or it's true to the left,
• 25:57
  Speaker 1: or it's true to the right, or it's true somewhere else.
• 25:59
  Speaker 1: As law is, space is the same everywhere, The same
• 26:02
  Speaker 1: results come from the same experiment. But what is space
• 26:05
  Speaker 1: isn't the same everywhere? What if, like, you're near a
• 26:08
  Speaker 1: really massive planet and so space is curved, for example,
• 26:12
  Speaker 1: and so it kind of does matter how close you
• 26:14
  Speaker 1: are to that planet, because if you get a push
• 26:17
  Speaker 1: when you're close to the planet, or you get a
• 26:18
  Speaker 1: push when you're far from the planet, you get very
• 26:20
  Speaker 1: different outcomes, right, And so in that scenario, the momentum
• 26:25
  Speaker 1: of the rock is not conserved because space is not
• 26:29
  Speaker 1: the same everywhere. The answer you get depends on where
• 26:31
  Speaker 1: you are in space. But in that case, now you're
• 26:34
  Speaker 1: sort of expanding your system. Now your system is the
• 26:37
  Speaker 1: rock and the planet, and momentum is conserved between them,
• 26:39
  Speaker 1: isn't it exactly? If you include the planet in the system,
• 26:43
  Speaker 1: then momentum is conserved anywhere because you can move the
• 26:46
  Speaker 1: rock plus planet system to anywhere in space. And the
• 26:49
  Speaker 1: reason momentum is conserved is that now the whole system
• 26:52
  Speaker 1: can be shifted anywhere in space, and it as an ensemble,
• 26:55
  Speaker 1: does the same thing. And so the key is that
• 26:58
  Speaker 1: your system can be translated anywhere in space, and then
• 27:01
  Speaker 1: momentum is conserved if it matters where in space your
• 27:04
  Speaker 1: system is. If your system is just the rock, then
• 27:06
  Speaker 1: momentum is no longer conserved. All right. It's something to
• 27:09
  Speaker 1: do with this idea of symmetry and the equations of
• 27:13
  Speaker 1: physics and symmetry. I feel it's a tricky concept because
• 27:18
  Speaker 1: you know, I think we're all familiar with the idea
• 27:20
  Speaker 1: of symmetry, like if something looks the same in front
• 27:22
  Speaker 1: of a mirror, or you know, if I take a
• 27:24
  Speaker 1: piece of paper and folded the ink kind of like
• 27:27
  Speaker 1: copies from on both sides of the paper, and it
• 27:29
  Speaker 1: looks symmetric. But in the equations, it's it's a little
• 27:32
  Speaker 1: bit different, right. It sort of means kind of what
• 27:34
  Speaker 1: you said in me is, which means it's more about
• 27:36
  Speaker 1: conserving or having the laws be the same in different situations. Yeah,
• 27:42
  Speaker 1: exactly if you made a change, would you get the
• 27:45
  Speaker 1: same outcomes? Right? Do the same laws apply here and there?
• 27:50
  Speaker 1: And so for the example of the rock in space,
• 27:52
  Speaker 1: you know, the rules of the universe shouldn't depend on
• 27:56
  Speaker 1: where you are, right, So then it kind of seems
• 27:58
  Speaker 1: to sort of make sense that if you have a symmetry,
• 28:01
  Speaker 1: then that thing is conserved, right, Like that sort of
• 28:05
  Speaker 1: makes intuitive sense. That's kind of interesting. Yeah, there's a
• 28:07
  Speaker 1: connection between the symmetry and the thing that's conserved. In
• 28:10
  Speaker 1: this case, space is the symmetry, and momentum motion through
• 28:14
  Speaker 1: space is a thing that's conserved, right, So momentum is conserved,
• 28:18
  Speaker 1: but then for energy it's different. It has a different symmetry.
• 28:21
  Speaker 1: That's right. The idea of the conservation of energy comes
• 28:24
  Speaker 1: from symmetry in time. If the universe is the same
• 28:28
  Speaker 1: going forwards and backwards, if there's a symmetry in time,
• 28:33
  Speaker 1: then you get conservation of energy. And here's a little
• 28:37
  Speaker 1: bit trickier to understand the connection between energy and time,
• 28:41
  Speaker 1: but it's there, and quantum mechanically, I think it's actually
• 28:43
  Speaker 1: the clearest. We have the Shorting Air equation, which is
• 28:47
  Speaker 1: what tells us how like a quantum mechanical system changes.
• 28:50
  Speaker 1: It says, if you have this quantum wave function, now
• 28:54
  Speaker 1: what quantum wave function will you have in the future.
• 28:56
  Speaker 1: That's the Shorting Air equation and solutions to the Shorting
• 29:00
  Speaker 1: equation are things that work in the universe, but it
• 29:03
  Speaker 1: tells us how things move forwards in time. Well, turns
• 29:06
  Speaker 1: out the Shorting Your equation is just an expression for
• 29:08
  Speaker 1: the energy of the system. Like if you actually look
• 29:11
  Speaker 1: at the mathematics of it, it's kinetic energy plus potential energy.
• 29:15
  Speaker 1: That's just a total energy of the system. And so
• 29:18
  Speaker 1: if the universe is symmetric in time, then energy is
• 29:21
  Speaker 1: conserved in your system for served in time. Kind of
• 29:25
  Speaker 1: like I feel like you're telling me that there's a
• 29:27
  Speaker 1: symmetry in time means that what I have now she's
• 29:30
  Speaker 1: gonna be equal to the things that I have later.
• 29:33
  Speaker 1: So in a way, that sort of translates into you
• 29:35
  Speaker 1: don't lose or gain energy. It has to kind of
• 29:38
  Speaker 1: be the same here and after. Yeah, exactly. This is
• 29:41
  Speaker 1: sort of a conservation there, this conservation of probability. Also
• 29:44
  Speaker 1: in quantum mechanics, it says that things are transformed and
• 29:47
  Speaker 1: they slash around, but they don't disappear. And what is
• 29:51
  Speaker 1: the thing that doesn't disappear. Well, it's the solution to
• 29:54
  Speaker 1: the Shortinger equation, which is really just the sum of
• 29:56
  Speaker 1: all the energies in the system. And so in some sense,
• 30:00
  Speaker 1: it's sort of like asking what is energy. Well, energy
• 30:03
  Speaker 1: is the thing that's conserved if you have time symmetry
• 30:07
  Speaker 1: in your system. And it's something we just sort of noticed.
• 30:11
  Speaker 1: We're like, well, you add all these things up kinetic
• 30:14
  Speaker 1: energy and potential energy here, and you add it up later,
• 30:16
  Speaker 1: we notice we get the same answer. And that's something
• 30:19
  Speaker 1: we've noticed because we've mostly been doing experiments in systems
• 30:22
  Speaker 1: where time doesn't matter. Where if you do the experiment
• 30:25
  Speaker 1: now or a hundred days or in a thousand years,
• 30:28
  Speaker 1: you get the same answer. So whenever time is symmetric,
• 30:31
  Speaker 1: and it has basically always been for our experiments, then
• 30:34
  Speaker 1: energy is conserved. So I feel like you're saying that
• 30:37
  Speaker 1: energy is just an illusion of times, and yes, exactly,
• 30:40
  Speaker 1: that's the message, is that energy is connected to time.
• 30:43
  Speaker 1: And we know that already from quantum mechanics. Right. We
• 30:46
  Speaker 1: know quantum mechanics tells us you can't measure the position
• 30:48
  Speaker 1: and momentum of a particle at the same time. Those
• 30:51
  Speaker 1: two concepts are connected, right, And it also connects energy
• 30:55
  Speaker 1: and time, and it's for the same fundamental reason that
• 30:58
  Speaker 1: there's a connection between those two basic quantities. They're really
• 31:01
  Speaker 1: two sides of the same thing. One symmetry leads to
• 31:05
  Speaker 1: a conservation law. All right, I feel like we're set
• 31:07
  Speaker 1: up now to break the conservation of energy and talk
• 31:10
  Speaker 1: about why that's really true and what it means. But
• 31:14
  Speaker 1: now it's time for us to take another quick break.
• 31:29
  Speaker 1: All right, Dan, we're talking about the conservation of energy,
• 31:31
  Speaker 1: and it turns out that energy is not always conserved,
• 31:34
  Speaker 1: which blows my mind. You're telling me it has something
• 31:37
  Speaker 1: to do with the symmetry of times. If time is symmetric,
• 31:40
  Speaker 1: then energy is conserved. And so I'm guessing what you're
• 31:43
  Speaker 1: gonna say now is that time is not always symmetric,
• 31:46
  Speaker 1: and it's actually a little bit larger than that. It's spacetime.
• 31:50
  Speaker 1: If the universe in which you're doing your experiment is fixed,
• 31:53
  Speaker 1: if spacetime is fixed, it's not changing, then yes, energy
• 31:56
  Speaker 1: is conserved. And so if spacetime is flat and it's
• 31:59
  Speaker 1: not changed, you can do your experiments. You can fuel
• 32:01
  Speaker 1: your car, you can drain your battery, you can collide particles,
• 32:04
  Speaker 1: you can do chemistry, and energy will be conserved. But
• 32:08
  Speaker 1: as soon as you break the symmetry of spacetime, as
• 32:11
  Speaker 1: soon as spacetime is changing, right, the shape of space
• 32:15
  Speaker 1: and the shape of the universe. As soon as that
• 32:17
  Speaker 1: is changing, energy is no longer guaranteed to be conserved
• 32:20
  Speaker 1: because it only was conserved because space time was not changing.
• 32:24
  Speaker 1: Oh I see, So maybe to match up our intuitions
• 32:28
  Speaker 1: to this new idea, we have to maybe expand our
• 32:31
  Speaker 1: idea of conservation of energy. Like maybe it's not a
• 32:33
  Speaker 1: conservation of energy for a closed system. It's like we
• 32:36
  Speaker 1: have to think about conservation of energy being true for
• 32:40
  Speaker 1: like the same spacetime or a static spacetime. But if
• 32:44
  Speaker 1: you change that, if you change spacetime, then you can't
• 32:48
  Speaker 1: say that energy is conserved anymore. Exactly. We have to
• 32:50
  Speaker 1: add a qualifier. We say energy is only conserved when
• 32:54
  Speaker 1: time symmetry is respected, which happens when space time is
• 32:58
  Speaker 1: not changing. But you know, we live in a universe
• 33:01
  Speaker 1: where spacetime is changing. The expansion of the universe is
• 33:05
  Speaker 1: not just things moving through space. It's the stretching of
• 33:08
  Speaker 1: space itself. It's the creation of new space. So we
• 33:12
  Speaker 1: live in dynamic space time, which means energy fundamentally is
• 33:16
  Speaker 1: not conserved. It means that energy is not the deep,
• 33:19
  Speaker 1: true quantity that we thought it was. It means it's
• 33:22
  Speaker 1: not the important thing to be thinking about. So it's
• 33:25
  Speaker 1: expansion of space that destroys the conservation of energy. Or
• 33:29
  Speaker 1: is it the expansion of space time? Are you do?
• 33:31
  Speaker 1: You use it as the same shorthand? Yeah, Well we're
• 33:32
  Speaker 1: talking about the expansion of space time, right, or the
• 33:36
  Speaker 1: expansion of space through time. You can think about it
• 33:38
  Speaker 1: like that because the space in which we're doing our
• 33:42
  Speaker 1: experiments is changing as a function of time. And remember,
• 33:45
  Speaker 1: to have conservation of energy, you need to have symmetry
• 33:48
  Speaker 1: and time. But the universe is not the same today
• 33:50
  Speaker 1: as it was a thousand or a billion years ago.
• 33:53
  Speaker 1: It's a different universe. It's expanded. The space in which
• 33:56
  Speaker 1: we're doing our experiments is different, and so it changes
• 34:00
  Speaker 1: the results of the experiments. And it means energy is
• 34:03
  Speaker 1: not conserved from one moment of space to another moment
• 34:06
  Speaker 1: of space. And that would also work here at the
• 34:09
  Speaker 1: local level too, right Like, if I had a canister
• 34:12
  Speaker 1: of gas and I expanded the space time it was in,
• 34:17
  Speaker 1: I would see energy not conserved. That's true. You would
• 34:20
  Speaker 1: create more dark energy because you've expanded space and every
• 34:24
  Speaker 1: new unit of space has dark energy in it. So yeah,
• 34:27
  Speaker 1: you would have created more energy whether or not there
• 34:29
  Speaker 1: was a canister of gas there. And the thing for
• 34:32
  Speaker 1: people to understand is remember the expansion of the universe
• 34:35
  Speaker 1: seems dramatic. The universe is big, it's expanding super fast,
• 34:38
  Speaker 1: but locally it's not very quick, Like the expansion of
• 34:41
  Speaker 1: space is not something you notice day to day, and
• 34:44
  Speaker 1: it's actually pretty weak. It's pretty small quantity in a
• 34:48
  Speaker 1: small piece of space. It only adds up to be
• 34:50
  Speaker 1: most of the universe because the universe is already so big.
• 34:53
  Speaker 1: There's so much empty space out there that if you
• 34:55
  Speaker 1: add up all the dark energy becomes a huge number.
• 34:58
  Speaker 1: So this violation of energy something that's very, very small.
• 35:02
  Speaker 1: It's very hard to notice because the expansion of space
• 35:05
  Speaker 1: is a very gradual, tiny effect. I see, it's conserved mostly,
• 35:09
  Speaker 1: but if you think about the whole universe, it's not
• 35:12
  Speaker 1: actually insignificant. Yeah, exactly, it's a small violation, and an
• 35:16
  Speaker 1: individual unit of space added up over the whole universe
• 35:19
  Speaker 1: becomes kind of a big deal. But for me, it's
• 35:21
  Speaker 1: not as much about like the size and the number
• 35:24
  Speaker 1: as the fact of it, Like, whoa this thing we
• 35:26
  Speaker 1: thought was a deep truth in the universe turns out
• 35:29
  Speaker 1: to be a coincidence or just a product of where
• 35:31
  Speaker 1: we happen to be. You know. It's like if you
• 35:34
  Speaker 1: grow up eating toast for breakfast and they butter it
• 35:36
  Speaker 1: on the top side, you think, well, toast has to
• 35:38
  Speaker 1: be buttered on the top side, and then you go
• 35:40
  Speaker 1: visit your friend you discover what they eat butter on
• 35:42
  Speaker 1: the bottom side of their toast. That's even possible. It
• 35:45
  Speaker 1: opens your mind a whole new way of thinking about
• 35:48
  Speaker 1: the universe. And that's what this does. It says energy
• 35:50
  Speaker 1: is not the important thing. Right. Energy is something we
• 35:53
  Speaker 1: thought was deep and fundamental, but it's actually important to
• 35:56
  Speaker 1: cosmologists are things like curvature and expansion. Those are the
• 36:00
  Speaker 1: fundamentally interesting things about the universe, not the energy. I
• 36:04
  Speaker 1: guess maybe what would trip people up is thinking about
• 36:07
  Speaker 1: where that energy comes from, right, I mean that's sort
• 36:10
  Speaker 1: of the origin of the original question. If the universe
• 36:12
  Speaker 1: is expanding and there's more energy being created, where does
• 36:16
  Speaker 1: it come from? Are you saying that energy can just
• 36:19
  Speaker 1: be created out of the blue. Yes, that's exactly what
• 36:22
  Speaker 1: we're saying, is that we've discovered that it doesn't have
• 36:24
  Speaker 1: to come from anywhere. That's sort of the wrong question.
• 36:27
  Speaker 1: It's like asking where does the value come from when
• 36:30
  Speaker 1: Picasso paints a new painting, Right, it didn't come from anywhere.
• 36:33
  Speaker 1: It wasn't and now it is. It only has to
• 36:36
  Speaker 1: come from somewhere if it's conserved, and there are things
• 36:40
  Speaker 1: that are universe that are conserved, like electric charge. Right,
• 36:43
  Speaker 1: you can't just create an electron because it's charged, has
• 36:47
  Speaker 1: to come from somewhere, has to come from previously charged particles.
• 36:51
  Speaker 1: Or you can start with a photon and create an
• 36:53
  Speaker 1: electron but then you have to create an anti electron also,
• 36:57
  Speaker 1: so you have balance of charge. There are things that
• 36:59
  Speaker 1: are fundamental that have to be conserved to have to
• 37:01
  Speaker 1: come from somewhere, but energy is not one of them.
• 37:04
  Speaker 1: It should be like demoted from that list of like
• 37:07
  Speaker 1: super important fundamental conserved quantities because it's just sort of
• 37:11
  Speaker 1: like an accident of where we live that we never
• 37:13
  Speaker 1: noticed that's not actually conserved. Man, first you demote pluto,
• 37:17
  Speaker 1: and now you're demoting energy. Who's the next matter? That's right,
• 37:22
  Speaker 1: We are pulling back the veil. Man. We are discovering
• 37:25
  Speaker 1: new deep truths. Matter that was like a hundred years
• 37:27
  Speaker 1: ago demoted matter the same matter doesn't matter. Matter, it
• 37:30
  Speaker 1: doesn't matter. And you know, I think it must have
• 37:32
  Speaker 1: been equally bewildering a hundred years ago to think what
• 37:35
  Speaker 1: you can create matter? Do you think you're some sort
• 37:38
  Speaker 1: of divine being? Right? Matter is you can't where did
• 37:41
  Speaker 1: it come from? When you make new matter, and it
• 37:43
  Speaker 1: doesn't have to come from anywhere. It's transformed from energy.
• 37:47
  Speaker 1: But the matter itself didn't exist, and matter can disappear,
• 37:50
  Speaker 1: It can exist and then just not exist anymore. It
• 37:53
  Speaker 1: doesn't have to be conserved all right, Well, it sort
• 37:56
  Speaker 1: of blows my mind. But it turns out that this
• 37:58
  Speaker 1: is actually a little bit controversial in physics, Like not
• 38:00
  Speaker 1: everyone agrees with this conclusion that energy is not conserved.
• 38:05
  Speaker 1: Is that right? Yeah, that's right. There are some folks
• 38:07
  Speaker 1: who find this very uncomfortable and they don't like this idea,
• 38:10
  Speaker 1: so they try to patch up energy and say, well,
• 38:13
  Speaker 1: let's think about energy in a slightly different way so
• 38:16
  Speaker 1: that it is concerned, and that's totally valid. It's like, well,
• 38:19
  Speaker 1: let's find a different symmetry or a different thing, you know,
• 38:22
  Speaker 1: energy prime or energy two point oh, so that it
• 38:25
  Speaker 1: actually is conserved, because maybe that will give you some
• 38:27
  Speaker 1: deep insight into the universe. And the way they do
• 38:30
  Speaker 1: this is a little bit controversial. I would say like
• 38:32
  Speaker 1: three out of four cosmologists and dentists I asked would
• 38:35
  Speaker 1: say that energy is not conserved. But there's some people
• 38:38
  Speaker 1: out there that try to patch it up by folding
• 38:41
  Speaker 1: this energy back into the gravitational field. Meaning like maybe
• 38:44
  Speaker 1: they think that maybe you're just doing the accounting wrong.
• 38:47
  Speaker 1: They might say that a costs of paintings are conserved
• 38:51
  Speaker 1: in value, is just that you know, you're accounting for
• 38:54
  Speaker 1: people's happiness when they purchase a costs or something like that,
• 38:58
  Speaker 1: right exactly. And they say, there's another category of energy
• 39:03
  Speaker 1: that we're not accounting for, and that's the gravitational energy,
• 39:06
  Speaker 1: and that as the universe expands, it actually gets more
• 39:08
  Speaker 1: and more negative gravitational energy. That the expansion of the
• 39:12
  Speaker 1: universe creates negative energy in the gravitational field that offsets
• 39:17
  Speaker 1: the positive energy from dark matter. And they do some
• 39:20
  Speaker 1: calculations and show that boom, it all adds up to zero,
• 39:23
  Speaker 1: and so energy is actually conserved. According to these folks,
• 39:27
  Speaker 1: is it kind of like the photon that loses energy
• 39:30
  Speaker 1: Like when you grow space you're pulling things apart, which
• 39:33
  Speaker 1: means you're losing gravitational energy, right, or you're gaining you're
• 39:37
  Speaker 1: losing you're gaining when when you're pulling things apart, it
• 39:41
  Speaker 1: takes energy to separate objects, right, So that's negative work
• 39:45
  Speaker 1: and so you're losing energy. You're creating a negative energy
• 39:48
  Speaker 1: situation in the gravitational field. But there's a problem with
• 39:52
  Speaker 1: this and the other folks on the other side of
• 39:55
  Speaker 1: the divide that say the energy is not conserved, they
• 39:57
  Speaker 1: quibble with the way this calculation is done, and they
• 40:00
  Speaker 1: think it's not actually technically correct that you can't actually
• 40:03
  Speaker 1: just measure the energy of a gravitational field, because gravity
• 40:07
  Speaker 1: is a really complicated thing. It's not just like, here's
• 40:10
  Speaker 1: a fixed gravitational potential and you can measure the energy. Remember,
• 40:13
  Speaker 1: gravity is dynamical, it's responding to space, it's shifting, it's changing.
• 40:18
  Speaker 1: And so, for reasons that I think are a little
• 40:20
  Speaker 1: too technical to dive into, there's not really a good,
• 40:22
  Speaker 1: well defined way to calculate the gravitational energy of the
• 40:26
  Speaker 1: whole universe, or even the gravitational energy more importantly of
• 40:29
  Speaker 1: a part of the universe, the gravitational density. So they
• 40:33
  Speaker 1: say that doesn't really count. You can't include it in
• 40:35
  Speaker 1: the calculation. Energy is not concerned. So it's still in progress.
• 40:39
  Speaker 1: People are still talking about it. People are still talking
• 40:41
  Speaker 1: about it, but I think the consensus is energy is
• 40:44
  Speaker 1: not conserved, despite these efforts to try to patch it
• 40:47
  Speaker 1: up and fix it and to say that there's a
• 40:49
  Speaker 1: way to look at energy such that it is concerned.
• 40:52
  Speaker 1: And then what do the dentist thing that if you
• 40:54
  Speaker 1: maybe do a root canal, you consider bypass s base.
• 40:58
  Speaker 1: They think we shouldn't eating fruit loops late at night
• 41:01
  Speaker 1: you should be flossing more often. You'd be flossing your
• 41:05
  Speaker 1: theory is more often because you know you can get
• 41:07
  Speaker 1: gun accumulating. But to me, I think it's fascinating. It's
• 41:10
  Speaker 1: a great investigation into like what's real about the universe,
• 41:13
  Speaker 1: what's deep, what's true. The reason that we try to
• 41:16
  Speaker 1: identify conservation laws is not just because we need a
• 41:19
  Speaker 1: better energy policy, but because we're trying to understand the
• 41:22
  Speaker 1: way the universe works, and finding these things that are
• 41:25
  Speaker 1: conserved or turns out to be not conserved are ways
• 41:28
  Speaker 1: that we get clues as to the way the whole
• 41:30
  Speaker 1: machinery works deep down. Yeah, I think what I'm getting
• 41:33
  Speaker 1: is that physics is maybe as fickle and sensical as
• 41:36
  Speaker 1: the art world. I think is what you're saying, and dentistry.
• 41:40
  Speaker 1: Your theory is genius, it's fundamental. Actually, no, it turns
• 41:43
  Speaker 1: out it's worth nothing. It's like cubism itself, makes no sense.
• 41:49
  Speaker 1: That's right, But there's a real beauty here to this inside,
• 41:53
  Speaker 1: this connection between symmetries and conservation laws, and it tells
• 41:57
  Speaker 1: you that every time you find something symmetric about the universe,
• 42:00
  Speaker 1: there's something out there being conserved. And that's really cool
• 42:04
  Speaker 1: and beautiful to me. Well, I think the takeaway is
• 42:07
  Speaker 1: that we can say that energy is conserved in space time,
• 42:10
  Speaker 1: but that spacetime itself is not always conserved. Yeah, if
• 42:13
  Speaker 1: spacetime is fixed, then energy is definitely conserved. In a
• 42:17
  Speaker 1: situation any universe like ours, where spacetime is expanding, then
• 42:20
  Speaker 1: there's no guarantee of energy conservation. Energy actually increases as
• 42:25
  Speaker 1: space time increases, and it doesn't come from anywhere, which
• 42:28
  Speaker 1: is hard to grapple with, but it is our reality.
• 42:31
  Speaker 1: And that's the job of physics is confronting us with
• 42:34
  Speaker 1: hard to understand truths, things that don't make sense to
• 42:37
  Speaker 1: our intuition, but that we figured out through science. Right,
• 42:40
  Speaker 1: that's why we have science and not just intuition, to
• 42:43
  Speaker 1: confront us with these things which are in conflict with
• 42:46
  Speaker 1: what we thought but turned out to be actually true.
• 42:49
  Speaker 1: All right, done, I won't walk away from the interview.
• 42:52
  Speaker 1: I'm staying. I'm staying for the rest of it, which
• 42:54
  Speaker 1: is about ten seconds. All right, Well, I conserved some
• 42:59
  Speaker 1: energy for this last bit. Well, we hope everyone enjoyed. Dad,
• 43:01
  Speaker 1: Thanks for joining us, and think a little bit more
• 43:04
  Speaker 1: about what do you think is true about the universe
• 43:06
  Speaker 1: and what might be an idea that Daniel and his
• 43:10
  Speaker 1: dentists wrong in the future, hopefully everything. Thanks for joining us,
• 43:14
  Speaker 1: see you next time. Thanks for listening, and remember that
• 43:25
  Speaker 1: Daniel and Jorge explain the universe is a production of
• 43:27
  Speaker 1: I Heart Radio. Or more podcast from my heart Radio
• 43:31
  Speaker 1: visit the I heart Radio app, Apple Podcasts, or wherever
• 43:35
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