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