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