Daniel and Jorge Explain the UniverseDaniel and Jorge tackle some of one of the simplest but trickiest concepts in physics.
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Hey Orge, did you have a good snack before you just hit record?
I did? I just finished the banana?
Actually, and is that banana enough energy to power you for a whole hour?
M depends on what I'm doing that hour. You know, procrastination doesn't take much energy.
Well, it's amazing to me that you can turn bananas into physics podcasts.
That amazes use a physicists is in all energy conserves tuning it be possible from a physics point of view.
Yeah, it might even be possible to do the opposite, right, to turn physics podcasts back into bananas.
Why wouldn't that violate the laws I don't know of physics because imagine all those thousands of people out there with this podcast turning this into a banana.
There must be some loss, though, I think they would end up with a smaller banana than the one you started with.
Or overly rite banana. Maybe that's a good way to describe for a podcasts.
Maybe you can think of iHeart meat is basically amplifying your original banana.
That's bananas, Daniel. At least you're feeding your mind as well as your body. Hi am poor handmade cartoonist and the creator of PhD comics.
Hi, I'm Daniel. I'm a particle of physicists and a professor at UC Irvine, and I am sending you all physics energy.
Physics vies or knowledge is knowledge energy Daniel.
Ooh, there's a question about whether information has mass. So if it does, then information would have energy and knowledge is information, so in some weird theories of the universe, maybe it does.
Wait, what information might have mass? So all those people listening to this, we're increasing their mass.
Only if we actually put some information into this podcast. So far, it's just one hundred percent bana.
It's like cholesterol. You know, there's good information and there's bad information.
Which one is healthier for you. Scientists are still debating it.
Hey, yeah, stay tuned as they gather more information to answer this question. But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we try to sift through all the information humanity has gathered about the crazy universe that's out there. We try to systematize, we try to organize, We try to educate you on what we do know and what we don't know about this crazy universe, how it works, how things slash and flow around, how it comes together to make this incredible, beautiful and dangerous universe that we all love.
Wait, are you saying that our job here is to take everything that's beautiful in the universe, chew it up, eat it, and then regurgitate it back to people as information edible information.
I'm not sure which side it comes out, but yeah, we consume it and then produce it.
It's not a pretty picture either way, is it.
I like to think of it as all part of the information food web. You know, don't think so much about who is eating who as much as you know information is flowing from person to person.
We're all just star dust and predigested information.
Yeah, although maybe you are the information super predator. You're the apex information consumer.
Oh what I really uh and nobody has ever called me the apex anything.
Well, think about it. You talked to lots of scientists, and you distill from all of them little bits of crucial science knowledge.
Wow, maybe that's why I'm so full all the time. It's a lot of bananas to keep.
Yeah. That or you're just consuming all those scientists' brains effectively. That makes you like a science zombie. I'm not sure.
Now I'm a zombie too. Oh my goodness. First I was regurgitating. Now I'm stumbling around half dead. Actually that that is pretty these days.
At this time in the morning. You do a good zombie impression. Now, you told me zombies don't always stumble. Sometimes zombies are fast moving and even articulate.
Yeah, yeah, it's getting to zombies. Yeah, then the new kinds of zombies are now fast and furious.
We've got a lot of response from the Zombie Star episode, people writing in recommending zombie movies that they thought I might enjoy.
Oh good, are you gonna watch them?
Do you need an honest answer to that question?
Well, why not?
There's too many things out there to watch. So they're on my list, but I might not make it.
I see, that's the political answer, got it, got.
It, But thank you everyone for your suggestions. I will get to them eventually.
Well I'm curious you know what's on that list. But today we're talking about something a little bit different than Zombie Stars.
That's right. We are venturing into the border between physics and philosophy. We are not just trying to understand how the universe work. We're trying to understand what it means, because physics is more than just a list of laws. It's an attempt to get some deep, intuitive understanding into how the universe works, to reach those aha moments where you feel like I get it, I understand Dan something now about how the universe is doing it that I didn't understand before.
Wait wait, wait, we're going into philosophical territory here. Can we go back to the zombies?
Well, we can talk about philosophical zombies if you like. That's one of my favorite topics, or.
The philosophy of zombies, Like is a zombie still a person or not?
No, that's philosophy by zombies. You know, they have whole journals that only zombies rite.
For Oh no, it is kind of a half to discipline. Anyways.
Now, the overlap between physics and philosophy is very healthy, very vibrant, really fascinating, and for me, one of the motivating aspects of physics. One reason we do physics is to help answer questions, which, in the end are philosophical. What does it mean to be alive? Why are we here? What should we do with our lives? How do we make sense of this cosmos? Those aren't science questions, but the answers to science questions can help us understand how to tackle those other more difficult philosophical questions.
Yeah, because I guess it is a pretty incredible universe and even though we may one day understand how it all works, there's still sort of the questions that you can ask beyond that, beyond physics, right, like what does it mean? Or why are we here?
And some of those questions are really simple. Sign the questions are the kind of questions you often ask me when I start talking about something complicated and you're like, hold on, back up, what are we even talking about? Can you give me a definition of space or mass? What are these things we're talking about? Do we really understand them?
Yeah, because I guess, you know, you grow up in this universe and maybe you become a physicist or not, but you still kind of study it, and you, you know, you start to take things a little bit for granted, you know, in a way, you know, think about the fact that we walk around on this planet, but why are we stuck to this planet at all and not floating out there in space.
Yeah, it's a really important exercise to take a step back and say, what is this thing we're talking about, What does it really mean? What do we know about it? What can we learn about the nature of the universe from what we know about how these physical processes happen.
Yeah, it always amazes me that there are basic concepts in physics that physics says don't really have a good definition for or a good explanation for. You know, we covered a lot of them in our book We have no idea a guy to the unknown Universe. But it's still amazing that there are things that even we didn't cover in that book that physicists still struggle to define.
You don't have to know what you're talking about to sometimes accomplish something in physics. The most famous example is quantum mechanics. Nobody really understands what it means, but we can do really complicated, really accurate calculations and predictions using quantum mechanics, even if we don't quite grasp what exactly is going on.
Yeah, and maybe out of all those basic concepts about the universe, there are maybe non more basic than the idea of energy. That seems like a super duper basic concept in physics.
It is, in fact, and it's something a lot of listeners over the years have written in to ask us.
To talk about totally. On the podcast will be tackling the question.
What is energy and where can we get some more of it?
Yeah, that's not coming from a coffee cup maybe.
Or dead plants underground.
But it is kind of sort of an interesting question, I think because it's so short, right, Like, this is one of the shortest questions we've tackled in a long time on this podcast. It's just three words, What is energy? Maybe we should add a fourth one man? What is energy? Man?
What is energy? Anyway?
Maybe what? But I guess we could go deeper, we go what.
Is Eventually we'll just be asking the question what. Maybe that's all physics and philosophy is just responding to the universe and going what.
Yeah, but then we will, you know, like a Marvel movie, We'll find another sequel.
We'll go with whoo where.
Or Speechless the new sequel.
But it is a really simple sounding question with a lot of subtle nuances, which is why it took us a little while to figure out how to attack it. It's a short question without an easy, simple answer.
Yeah, I was thinking about this word, and it's kind of interesting because I think everyone you know knows the word obviously energy and has something, you know, some intuitive sense attached to it. But you know, if you sort of think about what is it, it's kind of hard to define.
Yeah, you're used to talking about it, you think about it in your life. You pay for it, you use it. But if you sit on your couch late at night and wonder, like, what is it? It seems to have so many form they can transform back and forth into each other. It's a vital part of the universe. It feels like it should be something fundamental. But is a physical thing? Is it just a calculation that we do? Is it a philosophical question? It's a really hard thing to grapple with.
Yeah, And even physicists in their textbooks have a sort of a hard time pinning this down, right. I mean, there is sort of an official definition of it, right as the capacity to do work.
Yeah, there is that definition. But then you look up the official definition of work and its energy transfer.
No a lot. It moves the bag on itself like inception.
Yeah, exactly definition see definition. So energy is defined in terms of work, and work is defined in terms of energy. So like, what is this thing we're talking about?
Wow? Interesting? Yeah, because I guess that's the only way we know how to define it.
Kind of maybe sort of, And you have to grapple with the subtlety between physics definitions, like what we technically mean by work and are intuitive understanding of these concepts, because physics often repurposes a word that everybody uses in normal language to mean something very specific and technical. For physics, that's true for example, for work interesting.
Well, let's start to dig into this, but first, as usually, we were wondering how many people out there had thought about this very basic question and how many people out there think they know the answer to this.
So thanks very much to everybody who volunteered to answer difficult, random questions from an internet physicist. I really appreciate your work, and if you're out there and have been listening to the podcast and want to put your voice to these questions, please don't be shy. Send me an email to questions at Daniel and hy dot com.
Think about it for a second. What do you think energy is or how would you explain it? Here's what'd be glad to say.
I remember learning in maybe high school physics that energy is the ability for something to do work. I think that that's probably not nuanced enough of a definition. A more nuanced way to look at it might be it's something's ability to affect change, which doesn't necessarily have to be work. In sort of like the classic physics definition.
I think energy is truly just a vibration, and the energy potential is dictated by the field the vibration.
Or string sits with them.
I've asked this question to someone who knew a lot about physics before, and their answer was not useful to me. What I came away with is like, energy is potential for things to happen, and concentrations of that potential, and it's expressed in a lot of ways.
This feels like it should be one of those like really easy questions to answer. Fifth creators should know this or something, but I'm having trouble explaining it. It is a force, like but needed to create force. I mean, I think of going down to like the atomic level, energy is like the movement of electrons.
Intuitively, when I think of energy, I think about vibrating particles, and faster they're vibrating, the faster more energy they have. But I guess at a more fundamental level, energy is about probably fields, and like how much energy is in a certain field, dictating what kind of particle is and what that particle is doing.
I think energy is just like tiny movement of particles that gets passed along from particle to.
Particle energy is the opposite side of the coin is mass. But my guess as you're referring to the fundamental building blocks of energy, and I'm not sure what those could be.
All Right, interesting answers, pretty deep ones too. A lot of people are like, it's a vibe, man, it's a mood.
Yeah, and some people giving examples of what energy is and some people talking about the different forms of it. It's a really interesting answers here. Thanks everyone.
Yeah, and some people even sort of went with the official definition, which is that it's related to your ability to do work or to make work or change work. But did you follow up with them?
Then?
What does work mean?
No?
I don't actually have live conversations with these folks. It's just via email. When I do interviews on campus, then I can ask fun follow up questions like does that scare you? Are you worried about that? But here I just give them the one shot.
Oh I see, I see, I see you try and still fear in them.
No, I try to be friendly and not instilled fear in them over email. In person, yeah, absolutely, I'll put them on the spot.
All right. Well, it's a tricky subject, and I think as we'll find out it's something that has some deep mysteries about it. Right, It's not an easy answer, not an easy answer, all right, Well, Daniel's step us through. What are some of the first things that physicists think of when they think of energy?
So right off the bat, we should just admit that we don't fundamentally know what energy is.
Wait, what we're done with the podcast?
Boom, that's it.
Nobody knows that's it.
We know some things about it, we figured some things out. We can use those to piece together a picture of what it might be and what that means, But fundamentally it remains a philosophical mystery what energy is. First, maybe I should put the question back on you and ask, like, what kind of answer do people expect? Like what kind of answer would be satisfying? What is this sort of nature of the question we're even asking? You want to know if energy is like a thing that flows, or if it's made out of little energy ons or just like a concise definition of what this thing is.
Well, I mean you sort of give it away, you kind of spoil the answer for me here and maket t thing me not want to try. I mean, if you guys don't know what it is? Would I know? But it's kind of an interesting question, I think, you know, at the base of it, I think most people think of energy as like the opposite of not moving, you know what I mean, Like it's the opposite of standing still and not doing anything. Like if you have energy, then you're doing something, You're doing work, I.
Guess, yeah. And I think that a lot of the concepts about energy start from examples. Think some of the difficulty comes from the fact that you can put lots of different kinds of examples together and then wonder like what do they all have in common? You know, if mass is energy or this is energy, then what do they all have in common? And so maybe we should start with sort of like the history of the idea of the development of energy, how people discover different forms of energy and then talk about the common thread between them.
Yeah, yeah, sure, well I was thinking kind it's kind of like maybe the opposite of the phrase nothing happens, Like if nothing happens, ever, then there's no energy, but if things happen, then there's energy. It's like maybe related to the word happening.
That's possibly true, but there are subtle wrinkles there, Like you could have a universe with a lot of energy but no free energy, like the heat death of the universe, nothing can really happen. But there is a lot of energy in the universe, there's just none available to do work because there's no energy gradients.
So there are different kinds of energy.
There are different kinds of energy, And fundamentally, the game we're playing here is that we're looking around in the universe and we're coming up with ways to do calculations, and we're wondering do those mean anything? And energy in that sense isn't like something physical. It's an observation we make about the universe. Like I can look at a physical system, you know, the Earth moving around the Sun, and I can do a calculation that could say, well, I'm going to define some quantity. I call it energy, and here's how I calculate it. I take the velocity i' multiplied by the mass I add this. I add that that's the something I invented. Call it energy. And most of the time, if you just invent a quantity, it's not interesting or useful. It doesn't reveal anything about the universe. But sometimes it does, and it does especially when it seems like it might be and served when you've constructed this quantity which seems to like not change as time goes on through the universe.
Mmmm. Well, that's an interesting concept to think about. How they came up how humans came up with the word, right, Like, did we come up with that a word for energy before science even you know what I mean? Like, I wonder if Caveman had a phrase or a word for this idea of things happening or energy.
I think Caveman had teenagers, and teenagers didn't get out of the cave very early in the morning, and people wondered if they needed more energy. I'm sure that you know the intuitive concept of feeling like you have energy or you're tired. That's an age old idea for sure.
Mmm.
So we probably had a word for it, and then people started to use it in physics.
Yeah, and scientifically, one of the first concepts that was developed was kinetic energy. So you got to go back to people like Leibnitz. It was Newton's contemporary and you know, also developed calculus, and like Newton, he also did a bit of physics, right, and so Leibnitz noticed that things moved that there's motion. And he came up with this quantity mass times velocity times velocity again, so MV squared. And he said, this thing seems to be conserved. He called this thing vis visa like a living force, and so he essentially stumbled across the definition of kinetic energy and said, hey, here's a quantity which is interesting because it seems to be conserved. It seems like as time passes and you recalculate this quantity, it doesn't change, right.
But I guess maybe a question is how did he notice that it was conserved? Like why did he pick MV squared? As the quantity that was conserved was just something specific he was studying.
He didn't know why. He was just sort of like playing around, you know, sort of like a discovery in mathematics.
But what do you mean it play around with what?
You know? By that time, people didn't understand motion. Newton hadn't developed his laws yet, so people were just like multiplying random stuff together and seeing what it could do. You know, there's not that many ways to combine basic quantities mass and velocity in these things, and so it's not that hard to study them, you know. The English channel Newton was studying momentum mass times velocity. So lifness has just multiplied it by velocity one more time. I'm sure he studied other quantities like mass squared times velocity. Now that didn't have any interesting properties.
You make it sound like a bunch of monkeys in an infinite room piping out a typewriter.
It's a bunch of grad students in an infinite room, and they all come with one quantity and they're like, Oh, this one's not interesting. Oh look at this one. This one seems to be conserved. I wonder what that means.
But I guess. I mean, like, what did he see it conserved in? Do you know what I mean? Like he calculated in for one thing and then for another, and then he saw that it was the same. I guess, But what was that thing?
Yes, So, for example, physicists of this age like to do calculations about billiard balls. Right now, billiards is a very very old game. So you can take the kinetic energy at the first ball and then it hits another one, maybe it has a different mass, but you notice that the kinetic energy is conserved, and so you can do simple calculations there and see that kinetic energy is conserved in these systems.
Mmmm, so like after a collision. Then they know it is said that this quantity seems to stay the same, like you added up at the beginning for the two balls, and then you add it up at the end for the two balls, and it seemed to be the same. Is that what happened? Because if you look at the velocities, the velocities don't stay the same.
That's right, the velocities do not stay the same unless the two masses are the same. But like the really slow moving massive ball bumps into a very light ball, a low mass ball, that low mass ball will fly off at higher speeds, and so you're right, velocity isn't conserved. But this weird combination of mass and velocity squared did seem to be conserved. So that was sort of like an experimental discovery that lightning it's made. And you know, this idea of conservation means it might be something important, it might be something like fundamental to the universe. It's like, there's the philosophy aspect to it. Right, just because something is conserved, why do we care? Because it reveals something about the inner workings of the universe. I think about this sometimes an analogy to other systems, like economics, or like the water system. You know, like water goes through lots of different forms. It rains into the ocean and evaporates back up in the clouds, it flows down rivers, but in the end, the water is the water, right. It's changing, it's transforming, but it's flowing through the system. The amount of water isn't changing. So that tells you that, like water is deeply important to this whole cycle. Right, if you identify a quantity which is conserved in physical processes, you get the sense that maybe it's important.
Right.
I think what you're saying is that sometimes we notice that there are things that sort of don't disappear, like you're saying water. In the water cycle, water, it changes shape and it changes forms and it changes states, but it's still sort of like you know, the water, the molecules don't disappear. And maybe in the case of the billiard balls, that you notice that this quantity, like if you compute it, it's there in the beginning and it's there at the end, and somehow it got like transform. So maybe it's like a thing itself.
Yeah, because It's easy to think of counterexamples, like the number of bananas. Right, the number of bananas is not constant in the universe. You can make more bananas, you can eat bananas, right, They can disappear, they can be destroyed, they can be created. Right. The number of bananas is not fundamentally interesting to the universe, even if it might be personally interesting to various people.
Well that you know, right, Daniel, Like maybe they're you haven't surted the whole universe. Maybe every time someone eats a banana here, a banana is born in another planet somewhere in the universe.
Right, you don't know exactly. And if you discovered that to be true, that would mean something deep about bananas and the relationship to the universe. That would be a huge discovery.
That would be crazy, wouldn't it, Like somehow the universe likes to keep the same number of bananas all the time. That would be weird, Right, And if you eat a banana here or destroy it or make a banana smoothie, another bananas born somewhere, that would be really strange.
That would be very strange, and it would be a big clue. It would say the universe is kind of banana e or bananas are fundamental to the universe. So when you discover conserved quantity something the universe maintains, then you're seeing something about the inner workings of the universe. It's revealing to you what's important. It's like how water is important in the water cycle, whereas clouds are not. So if kinetic energy is conserved life and it's thought, well, this must be an important.
Thing, you know. I think if you tell anyone these days, like hey, energy is concern or waterson serve, nobody would blink and I But if you tell them like, hey, did you know the universe conserves bananas, that would be a big revelation about the universe, just like how we should look at energy and water as being kind of a big deal. Right.
Yeah, And just in case anybody's being misled, As far as we know, the universe does not conserve bananas, as far as we know. Yes, as far as we know. For example, I'm pretty sure there were billions of years in which they were exactly zero bananas in the universe that you know of that I know of. Yes, But maybe all the bananas that are appearing on Earth mean that their anti bananas being created on alien worlds somewhere else to balance.
That, or I think you're saying what happened before the Earth was for maybe there were other planets with bananas. I'm just saying, keep an open mind.
You're saying bananas could predate the Earth.
Yeah, that's my theory of bananas.
Well, I think your philosophy is bananas. Yeah.
But anyways, I think obviously trying to make the point that you know, we should be sort of amaze in awe at the fact that energy seems to be considered in that water and for example, the water cycle is conserved because it doesn't have to, right. I think that's what you're saying too.
Yeah, you can come up with all sorts of quantities, you can define them, and most of them are not conserved. So when you find one that is that tells you you're onto something, it's a really interesting clue.
All right. So then I guess at Leipnez called this energy? Did he coin the phrase or was he the first one to use it on Envy Square? Did he call it kinetic energy? Also?
No, he called it vis visa, which is I think Latin for like a living force. And you know, now we know that kinetic energy on its own isn't actually conserved. I mean, under certain assumptions. It is. In elastic collisions where you don't break things up, kinetic energy is conserved. But on its own, kinetic energy more generally isn't conserved.
Of course, And I think Newton was mostly looking at momentum, right, because that one is conserved in most collisions.
Yeah, momentum is actually conserved. So Newton's combination of kinematic variables mass, time's velocity, momentum, this thing actually is conserved. But again, at the time, nobody knew why it wasn't until we had a great mathematical genius a couple hundred years later who told us about the connections between conservation laws and symmetries. How these conservation laws reveal deep symmetries of the universe.
Well, I mean that's what they thought, was that the fundamental law of the universe, right, that momentum is conserved.
Yeah, momentum conservation was discovered before we understood what it meant and why we have it, what symmetry of the universe creates it. We just did a whole podcast episode about why momentum is conserved. It's really fun and deep topic.
Okay, so that's one kind of energy. What were some of the other kinds of energy we've discovered.
So there's a second kind of energy, potential energy, which is a different kind of energy from kinetic energy and something I've never really been comfortable with.
Wait, what potential energy makes you uncomfortable? You don't like the idea of potential I don't want any surprises. Just give me straight up energy.
Yeah, potential energy is weird and confusing. It's definitely a different kind of energy than kinetic energy, but it's also closely related to kinetic energy because while kinetic energy by itself isn't conserved, some kinetic lust potential that is conserved in the universe.
Mmmm.
Interesting. Well, okay, let's get into the details of that, and I want to know why it makes you uncomfortable. But first, let's take a quick break.
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All Right, we're talking about energy, and it's been a very energetic discussion here, Daniel. We talked about how you know, humans when we start to try to understand the world. We came up with this idea of energy because it seems to be conserved in some circumstances, and that was kinetic energy. But there's also potential energy, which is kind of a weird concept in physics, Right, it makes you uncomfortable.
Yeah, it is a weird concept in physics, but it's also something sort of intuitive. Like let's say you have a banana on the top of a bookshelf and it's just sitting there right, not doing anything, and you bump it and it falls off before it hits the ground. It's going pretty fast, so it has kinetic energy. Where did that kinetic energy come from? Right? It came from its height, It came from the fact that it was sitting high up above the ground, and it turned that height in the gravitational field into energy. So that's the potential energy of the banana getting turned into kinetic energy of the banana. So it's definitely energy because you can transform it into kinetic energy into motion. But it's sort of weird because it's energy of its location. It's energy of its configuration.
Right right. I think that's where the name potential comes from. Like, it doesn't really have energy right now. It's just sitting on the table. It doesn't really it's not really moving, but it has the potential to move a lot.
Yeah, I think that's tempting to describe it that way, but it really is energy. Potential. Energy is not just like the potential to have energy. It comes from energy of a potential. Potential is the way we describe how I field impacts a force on an object, Like an electron moving through a potential you know, feels.
A force, right. But I think you're getting mixed up, you know, kind of tripped up here because you're saying it's in a potential because it has the potential to move, to cause it to move, you know what I mean, It's like a circular definition.
Yeah, it has the potential to move exactly. So we don't really know what this stuff is. Potential energy. I always found it really strange. Mostly it makes me uncomfortable because it doesn't really have a value in itself. It's relational, Like the banana. How much potential energy does it have at the top of the bookshelf. We don't know. There's no number, but it has more potential energy than at the bottom of the bookshelf. So potential energy is only important in differences. You could add an arbitrary number to the potential energy of the banana at the bookshelf. Doesn't matter. The only thing that matters is how much more potential energy it has at the top and the.
Bottom, right, Like it's a relative quantity kind of like it depends on where you measure it. If you measure it from the floor, it's one thing. If you're measured from the table, it's zero.
Yeah. It's sort of like velocity in that sense. It's no meaning to say you're moving at a certain speed. You're only moving at a certain speed relative to something else. The banana has potential energy relative to the floor. And something that's fascinating is that it's very easy to see kinetic energy and potential energy sloshing back and forth into each other. If you have, for example, a ball and you drop it, then its potential energy is getting turned into kinetic energy, and then it gets turned around when it hits the floor, and it's kinetic energy then gets turned back into potential energy as it climbs back up to your hand. And if there wasn't friction or air resistance, then it would just go on forever, smoothly sliding back between the two different forms of energy.
Right like if it was jumping on an infinite trampoline, kind of like a perfect trampoline, this energy would, like the kinetic energy would appear and appear and disappear, and the potential energy would also appear and disappear, but it would always add up to the same thing.
It would always add up to the same thing. And a trampoline is a great example because it's basically like a spring. Springs have potential energy in them also, right you squeeze a spring that takes energy, and now the energy you put into squeezing it is somehow stored in the spring. In the arrangement of the spring, the compactification of those bonds that would prefer to be relaxed, and so that's the same kind of energy. You can put it into a gravitational field, you can put it into a spring, you can put it into a squeezing of a ball, which is basically another spring, And so all these things are potential energy.
Right, And in that sense, you can sort of think of it as a thing. Right, it's just the thing that changes from being kinetic to being potential. Like it's somehow there and it's always conserved.
But is it a thing? When you say thing, I think something physical, you know, like water is flowing. And for a long time people were wondering, like is energy a thing to like flow from one thing to another? Is it made of little energy particles? But here, because potential energy is a kind of energy, and it's just an arrangement of other things, then is it itself a thing or is it just the arrangement of other things. It's complicated.
Hmmm, you mean, like does it have a physical embodiment or is it just I don't know, like a label we put on other things.
Yeah, that's a deep question. I'm not sure the answer to the same question can be asked, like, you know, what makes you you? You were made of the same particles as I am, you just arranged a different way. So the units is in the arrangement of the particles the same way. Potential energy comes from configuration of particles together, not the particles themselves. The potential energy isn't stored in the particle, It's in the relationship between the particles.
Right, right, unless you're a zombie, in which case your body is arrangement is decay. Well, I guess what about mass? You know, Like, we know that mass is the same as energy kind of in a way, right, according to equals empty squared is mass energy.
Then I'm going to take probably surprising and weird philosophical position here, which is that mass is not its own kind of energy. Mass is just a representation of how much energy is stored inside something, how much kinetic and potential energy is in something.
What do you mean, Like things don't have inherent mass, like don't particle from the fundamental particles and they have you know, mass, Like the electron has mass, right.
Yeah, so let's break it down, Like the electron fundamentally doesn't have mass on its own. Its mass comes from its interactions with the Higgs field. So that's the kinetic and potential energy of the Higgs field, which changes how the electron moves through the universe as if it did have mass. But if you listen to our episode on like what is renormalization, where is the electron's true mass in charge? Discover that fundamentally, truly, the electron and the other particles have no mass on their own. It's all in their energy.
Right, because I guess even the electron, it's not like it has a little bit of stuff in the middle. It just has the potential to interact with the Higgs field, and that's what we call its mass.
That's what we call its mass.
I act to tchuck because we're doing this podcast, but really I do because we wrote a chapter on it for our second book frequently asked questions about the universe.
Yeah, and if you think about composite particles like a proton, a proton is made out of quarks. Those quarks have almost no mass, but the proton has a good bit of mass. Where does that come from? It comes from the energy that binds those quarks together. So the proton's mass isn't some other weird kind of mass in the universe, not like you're converting kinetic energy into some sort of substance. It just comes from its internal stored energy. So the way I think about mass is sort of like an indicator. It tells you how much energy is internally stored inside this thing. In the end, it's all just energy. Mass isn't its own form of energy. It just reflects how much energy is inside something.
You're basically saying all mass is just potential.
Energy, potential and kinetic energy. Right. Some of the proton's mass comes from the kinetic energy of those gluon and quarks slashing around, So not just potential energy, but also kinetic all right.
So I think what you're saying is that we're trying to define energy. One way to do it is to look at its different kinds, and there are really, to a physic is only two kinds of energy, kinetic energy and potential energy. There are no other other kinds, right, are there? I mean there's dark energy.
Wow, wait to skewer us with our own terrible names. You're totally right, but we don't know what dark energy is. One theory is that it's like the fundamental quantum potential energy of all of these fields, in which case it would be a kind of potential energy. But we really just don't know what dark energy is.
It's a big mystery, all right, So ignore the sixty seven percent of the universe that is dark energy for this discussion, and let's just focus on the small bit of it that we like to talk about.
No, it's a great point, but when we do figure out what dark energy is, either it'll be kinetic energy, or it'll be potential energy, or it will be some new kind of bonkers energy and I'll be wrong, in which case I'll be the first to celebrate.
Well. Yeah, basically, like I said, let's just ignore the sixty of the universe that is dark energy. And you know, for what impacts is there's really only two kinds of energy. You're saying, kinetic energy and potential energy, and that's it, right, And that's kind of what goes into your basic equations of the universe, right, Like, that's basically the definition of the equations of the universe.
That's right. The Schrotener equation has kinetic energy plus potential energy in it. Hamiltonian mechanics is built on that principle. You know, Classical mechanics is based on the principle of least action, and action in the end is defined in terms of these two quantities, kinetic and potential energy. And the deep mystery really is if these two things independently are not conserved potential and kinetic energy, but together they are, what does that mean about what they have in common? And what is that commonality? I think that in the end is the question what is energies? What do these two things together? What larger picture do they make up?
Right? Because I think maybe that's something that maybe a lot of people don't know, is that when you know, when physics say, oh, the laws of the universe or the equations that define the universe, really what you're talking about is basically the idea that kinetic energy and potential energy is conserved, because that's what you assume when you formulate the laws of physics. Right, you start with, hey, let's assume that kinetic and potential energy is conserve, you know, and then let's see what kind of rules that gives us.
I think it actually goes the opposite direction. You can make up laws to a universe that don't have conservation of energy. If those laws, for example, are changing in time, then they don't conserve energy. And one of the greatest insights into this relationship between conservation laws and symmetries came when people were asking about general relativity. They're like, hold on a second, does general relativity conserve energy? That seems like it should be important. So we actually derive the laws from other places and then ask like, hold on a second, is energy conserved? What does that mean about these things?
I guess I mean, like, you know, like the Hamiltonian. That's basically you saying, hey, the sum of kinetic and potential energy should always stay the same, and then from that you derive some of these other equations.
Right, Well, there's very non satisfactory physics definition. The answer to that, which is that once you define the Hamiltonian, then energy is defined to be the thing that's conserved if these rules don't change in time. So you sort of start from the Hamiltonian and then you figure out what is the energy of the system from that.
I guess what I'm saying is that it's a very fundamental concept in how theoretical physics works. Right. It's not like you assume, like, hey, let's assume it's changing. What does that give us? It's like you assume that it's not changing kind of.
I think there are different ways to formulate the theories of the universe, and you can either start from the assumption that energy is conserved figure out what rules are allowed, or you can just start building laws and figuring out what the consequences are and which ones actually describe our universe, and then noticing that in the ones that describe our universe, this quantity we call energy seems to be conserved. There's some different orders you could use there, All.
Right, well, I guess for our discussion, the basic idea is that, you know, physicists sort of describe or define energy as the sum of kinetic energy plus potential energy. But what you're saying is that that's kind of a weird thing to do, because, like, how do you know kinetic energy and potential energy have to be related.
To each other exactly? They seem like very different things, right, What does it mean that these two very different things are closely related? Like if you discovered, well, the number of bananas in the universe isn't conserved, but bananas plus apples that's conserved. That would be really interesting connection between bananas and apples. You're like hm turns out to have more in common than I thought.
Right, don't they have a kid song together? Apples and bananas?
I think we need to hear a snippet of it.
Go ahead, all right, can you play it for us?
I don't have my kazoo here, otherwise I would.
Well, I think. I think what you're saying is that it's kind of weird to put them together. But if you put them together, then it seems to be constant in the universe, and it seems to give us these equations that seem to work and seem to like predict where particles are going to go and what's going to happen to them, and what kinds there are even exactly.
And what that means is that they really do have something in common. They're part of the same thing. They're not the same thing. They're like two halves of a puzzle that click together perfectly to make something new. And then we have to ask the question, what does that mean? What do they have in common? What is this larger thing that they're a part of?
All right, So then are they conserved? Because I know sometimes they're not conserved.
So they are conserved in the case where the laws of physics do not change. So if the laws of physics you're using are the same now and the same in ten minutes and the same in a thousand years, then kinetic energy plus potential energy is conserved. That's absolutely true. Now in our universe, the laws of physics are almost the same from moment to moment. They're usually the same. You can do the experiment of large hadron collider today and tomorrow and next year and get the same measurements. But there is one way in which those laws are changing, which is that space itself is expanding. As you mentioned, dark energy is accelerating the expansion of the uni verse, making it bigger and bigger and changing the distances between things, And that technically is a change in the laws of physics as a function of time, meaning that energy is not technically conserved. That's not really relevant for balls rolling down planes, or bananas falling off of bookshelves, or any experiment we are going to do. But do you want the deepest understanding of energy. Then turns out, in our universe it's not technically conserved but almost.
Right right, Well, I feel like you're maybe cheating a little bit here. I feel like you're saying that we have these laws that we think describe the universe, and in them energy is conserved unless our laws are wrong, in which case they don't and doesn't Does that make sense? I feel like maybe what's really happening is that we don't have the right laws of the universe, Like we only have laws that seem to work for you know, moment to moment, or that doesn't take into account the sixty seven percent of the universe that's making it expand. Really we just kind of maybe don't have the right laws.
It might also be that the laws, really we are a function of time, right, that the way things work changes as the universe goes on. That's just the way the universe is.
Wait, what you mean like it's a function of something, but it's not a function of anything.
There could be a function of time, right, But based on what law, the laws themselves could just be a function of time, you know why. For example, are constant's constant. If the gravitational constant changed as a function of time, then you could get free energy. If gravity disappeared every Tuesday morning for an hour, then I could, with no energy, take a big box of bananas and put it on a bookshelf, and then when gravity came back, I could knock it off and extract the energy from it, So I'd have an infinite energy machine if the gravitational constant wasn't constant. So if these constants are changing, then energy is not concerned.
Right, right. But isn't that I mean, that idea that you're saying, like, hey, let's just give up and stop asking questions. Isn't that sort of a lot of what you talk against about? Right? Like you know, if you discovered that the laws of the universe are changing for some unknown reason, would and you want to know what that reason was?
Oh? Absolutely yes, And doesn't mean you can't find an explanation. Right. The laws can be changing, and those laws can be changing for a good reason. It could be like only one consistent way for the universe to be, and it requires these constants to change. Right. It's still following some system which is governing how those constants change. But the constants themselves, the ones that describe the motion of things and how you get equations of motion, if those are changing, then this quantity we call energy is not conserved.
Right, right. But I guess I'm saying if there's a system that is determining how the laws of the universe are changing, then maybe that system is the real, true, you know, set of equations that govern the universe.
Sure, absolutely, and they could be like the true system that governs these laws. But the ones that determine how things move, right, that determine motion of things through the universe. If those laws are a function of time because they're controlled by some super deep meta laws. Right. If those laws that determine how things move through the universe, if those are changing, then energy is not served.
Well, I think we're getting a little bit lost because we're talking about energy. I think what you're saying is that energy is conserved if you look at it locally, like our little you know, what we've see of the universe and what loss we've coupled together. But if you look at the big, big picture, energy is not conserved, which kind of makes you wonder, like what it is right exactly? It throws into question even more are ideas of it and points of the fact that we don't really know what it is because it's not even conserved like we thought it was exactly.
And it also questions like how important is it one of the reasons we thought it was important because it's because we thought it was conserved and we thought it was a deep truth in the universe. It revealed something fundamental. If it's not actually conserved, you means it's maybe not as important as we thought.
Mmmm, right right, It points like maybe it's just the pawn in the you know, meta law of the universe that we have no idea about so far.
Exactly, it's just like a lowly fruit like a cherry, instead of the legal banana.
Instead of the legal banana, exactly, the all important binna. Yes, all right, Well, let's get into a little bit more about what we don't know about the definition of energy and what it could all mean.
Man.
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All right.
Welcome back to Daniel and Jorge argue about energy when one of us is a physicist and the other one is not clearly, but I've guess I'm getting the picture that you know, we kind of thought we knew what energy was. We thought it was this fundamental thing that always seems to be conserved. But it turns out that it's not always conserved. So now maybe it's not only do we not know what it is, but maybe it's not even fundamental.
Yeah, that's right, and it's sort of disappointing because even a small amount of non conservation means it's just not conserved. You know, there's like two things, things are conserved and things that are not. There's a whole bunch of categories of things that are not concerned, and being almost conserved means I guess you're important but not really truly fundamental.
All right, Well, then what would you say energy is?
Then I would say I wish I knew, and it's something definitely deep and interesting in the universe. Right, It's something that is almost conserved, and it can slosh back and forth between these two different kinds of things that feel very, very different. What is energy? The philosophical question really is what do kinetic and potential energy have in common? What are they part of? When you put them together in the same way that you can put electricity and magnetism together into a holistic thing and get an understanding of electromagnetism, you're like, oh, that explains this and that and brings all these ideas together. You have a feeling of having an answer. If we understood how kinetic energy and potential energy fit together into one holistic thing. We'll be able to grapple better with this question.
I feel like you're saying, like, maybe even the word energy is a little distracting from the real question, which is like why is there a relationship between you know, motion and potential in a way, or or even like why does potential exist at all?
Exactly? And you can try to tease it apart by looking at the equations of motion and saying, like, what is it that defines how things move? And why can this weird quantity slash back and forth? And one way to get a little bit of insight into it is to understand that potential really is also about motion, Like potential energy is what causes forces. Right, the reason that the banana falls off the bookshelf and accelerates towards the floor is because there's a gravitational force there. There's a force there because there's a difference in the potential. So you can think about it in terms of kinetic energy and potential energy. You can also think about it in terms of like motion and forces. Like a particle just flying through the universe, it just has kinetic energy. Now add other particles interacting with it putting forces on it. Those are creating potential energy for that particle. So in some sense, it's not kinetic energy and potential energy, it's kinetic energy and other forces changing its kinetic energy.
I think what you're saying is that maybe there's really only motion and potential motion, Like there's only motion in the universe. And then there's what happens when two things that have motion kind of bump into each other somehow, for some reason, they interact in a way that creates potential But really you're just talking about motion and what happens in that interaction exactly.
And this is the philosophical process of sort of stumbling towards a deeper concept. They're trying to understand what these things have in common and generalize it into an idea that really fits together, that can hold as a bucket all these different concepts that we consider energy in its properties, and it's connected to this other question we talked about, like our fields.
Real Well, it sort of sounds like you're saying that maybe there's only really kinetic energy, right Like, there's only kinetic energy, and there's also what happens when two things that have kinetic energy interact with each other, right Like, it sounds like maybe potential energy is really just about motion and interactions, and so you've got to ask, like why does the universe have motion and why does it have interactions? Like right, right, if it didn't have interactions, everyone would just fly around by themselves. There would just be kinetic energy and that would never change. But it changes because we have these interactions in the universe.
And that goes to like an even more abstract question, which is like why do you consider things as interacting? That assumes that there's different things that you can say, like there's this one thing and that other thing, Well, how do you draw the line between them? Right, it's like one half of the Earth interacting with the other half of the Earth. How do you slice that? Why do you call the Earth one thing and not two things? And anytime your ideas are based on totally arbitrary designations like that like this is a thing, but that's not a thing, or this is two things, then you know that you're looking at it the wrong way. I think the work that's left to be done is to understand this as one holistic thing.
You know, what is it.
Really that's flowing between two objects where one is in motion and then another one is in motion. How is that flowing? Is it really changing into a different kind of energy or is there one holistic, super kind of idea there that you can understand connects these two things.
Right, right, Like, maybe there aren't humans and zombiests. Maybe maybe we're all just human and the z obviously just have the potential to eat humans.
Exactly. Maybe before you eat the banana, the banana is already kind of part of you, you know, or hey, plus banana is already the thing before you eat the banana.
I think what you're saying is that, you know, we talk about kinetic energy and potential energy, but really maybe there's just part of the same thing, like motion plus interactions.
Right, If I zoom in on a particle like a proton and say, oh, look, those quarks have kinetic energy inside of them. But if I zoom out and just look at the proton, I'm like, oh no, the protons at rest, it has no kinetic energy. So how much kinetic energy there is depends on what I'm defining to be a thing or not. It seems sort of arbitrary, and I think that's the biggest clue that will lead us to a deeper understanding of energy, but I don't have that understanding today.
Well, let's touch a little bit into the scenario that you mentioned earlier in the episode, which is the end of the universe, and that maybe one potential end of the universe is the heat death of the universe, where you know, everything has energy, but nothing can happen everything. You know, particles are moving like a gas, and so there's definitely energy there, but no potential energy. Is that what you're saying that there's it's a scenario where there's no potential energy left in the universe.
Yeah, there's useful energy, and then there's sort of useless energy. Useful energy is energy you can use to do work, to like move something up a potential for example. And you know if you have energy in a battery, you can take that energy and use it to power an engine and that can like push your banana up off the floor back to the top of the bookshelf. That's useful energy, and that only happens when you have energy localized somewhere right when you have low entropy, when there's organization of stuff. Opposite of that is useless energy energy like heat if everything is just hot and everything is the same temperature. There's no temperature difference, there's no energy ingredients. You can't use that to power an engine. Like if you have an engine and you're in a universe where everything is smooth but hot, there's no way to take that energy. There's motion of the particles and turn that into something useful. So the key idea there is entropy.
Entropy, right, Yeah, there's like everything's a hot mess, what you're saying, a bland hot mess. But wouldn't I guess even in that in an area, wouldn't gravity eventually kind of brings stuff together, creating potential energy, or like, how does gravity disappear in this scenario?
Gravity doesn't disappear, but it can't do anything in that scenario because everything is smooth and homogeneous. Gravity requires some clump to get things started. Like in the early universe, we didn't have a smooth and homogeneous blob of stuff in the very beginning. We had little quantum fluctuations, little bits of over density and under density that gravity grabbed onto and exaggerated. But if you have the true heat death of the universe, where everything is spread out equally, then every particle feels the same gravitational pull in every direction, so it basically cancels out.
What does this idea of entropy, How does that impact our definition of energy, like, maybe it's not real or something.
Well, folks who love and understand thermyonnemics have different definitions of energy. There's energy in general, and then there's free energy, which is sort of like an energy available to do useful work.
And then there's also discounted energy and energy on sale.
And then there's free lunch, which apparently doesn't even.
Exist that we know of. But as you said, the universe is changing, Daniel. Maybe they'll be free lunch in the future for everyone.
That's right, And these topics always make me uncomfortable. Thermodynamics is the topic of physics that I avoided as much as possible when I was taking classes.
Right, that and zombie movies, or maybe they're about the same thing, right, and zombies are about decay and things I'm breaking down. Maybe this is all turned out to be a deep psychological journey into daniel psyche.
That's right, we're understanding the conservation of Daniel's decisions.
Zombies and entropy make you uncomfortable, Maybe we should dig deeper into that. Daniel does something happen in your childhood?
Yes, zombie came an entrepeaed my bedroom when I was a kid, and I'm scared now.
No.
Thermidonamics to me is complicated because you're just so many particles. That's all about statistical statements of large systems of particles. For me, it's easier to grapple with one particle bouncing off another particle, because I would like to get down to the microscopic picture of what's really happening. And thereodynamics is about like zooming out and trying to make like broad statements about systems.
It's not the same as philosophy though.
Yeah, but philosophy nobody has any wrong answers.
That's right, it's not verifiable. How convenient. Well, I think the overall picture I'm getting is that to answer the question what is energy, it's tough. You know, we have different labels for it. There's kinetic energies, it's potential energy. That seems to be all about there is to it, but that's not the full picture. Like it seems to be conserved, but it's not really conserved in the universe, and so maybe it's not even an important thing, or maybe it's not even a thing like maybe in the future aliens will be like, why do you guys were thinking about energy? That's like thinking about the ether or thinking about you know, the soul or something like. That's that's a thing that doesn't make sense.
Yeah, it definitely is driven from an intwo experience for the world and then try to extrapolate that to physics and understand if it makes sense. And it sort of kind of seems like it does, but maybe it doesn't quite. We definitely still have work to do. And you know, if you look into a physics book or google this question, you might find some confusing answers. Some of them are things like energy is the quantity that's conserved if the laws of physics don't change, so they're like defining it to be the conserved thing, which doesn't really tell you like what it is. It just tells you how Nuther's theorem impacts these laws of physics. It doesn't really tell you like what it is. I think we're still struggling to figure out exactly what energy is.
Right, it might need to be redefined now that we sort of know and this is the only reason that we know that the universe is changing and the laws of physics are not constant.
Yeah, so the history of this scene over a few hundred years is like discovery of kinetic energy that seems to be conserved. Oops, no, it's not only kinetic energy, plus potential energy is conserved. And then Einstein's general relativity is a whole new system for the universe and not otherther says, hold on a second, that doesn't guarantee conservation of energy. So people are like, oop, better patch that up, make sure conserve energy. And then we discover actually, it doesn't conserve energy. The universe disagrees with that whole idea. So it's been a lot of back and forth.
Yeah, I'm amazed you guys still have the energy to keep at it.
Well, somebody keeps eating bananas, and so we keep asking.
Questions, Right, maybe bananas are concern Well it seems like maybe we won't define it anytime soon. But I think it sort of points to the idea that there are these deep relationships in the universe between motion and potential and fields, and we're still trying to figure out what those relationships are, because that kind of tells what's going to tell us what the true nature of the universe.
Is, Yeah, and one of the deepest goals in physics is to come up with a concise, mathematical story about how the universe works in a way that makes sense to us. And that's what we're struggling with here, is connecting these mathematical concepts with intuitive ideas that gel with us, that tell us something about the nature of the universe more than just looking at the black and white equations on a page.
Yeah, that's what it's all about, gelling with the universe. And eat a banana and gel and chill out.
Exactly, But don't eat the last banana because there's a fixed number of them in the universe and if you eat the last one, Jorge can't and then we won't have any more podcast.
Oh no, it's an evergreen quantity, right, that's why I thought that was what we concluded.
Now, Oh, I see, eat all the bananas you want, right, because somewhere, some unknown process.
Is recreating that.
That's a nice universe to live in.
Yeah, yeah, pretty bananas. All right. Well, we hope you enjoyed that discussion. Thanks for joining us, see you next time.
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