Speaker 1: Hey, Jorge, are you worried about energy conservation?
Speaker 2: Uh?
Speaker 3: Not worried, but I try to do as much of
Speaker 3: it as possible.
Speaker 4: Oh.
Speaker 1: Is that because you're very environmentally responsible?
Speaker 3: Nuts? Because I try to do this little exercise as possible.
Speaker 1: You're such an adult.
Speaker 3: Hey, I'm doing it for the planet, not just for me.
Speaker 1: Well on behalf of planet Earth. We're all very grateful
Speaker 1: for your lazy attitude.
Speaker 3: Oh thanks. My body is also very grateful, although maybe
Speaker 3: not in the long term. Hi am Jorgem, a cartoonist
Speaker 3: and the author of Oliver's Great Big Universe.
Speaker 1: Hi. I'm Daniel. I'm a high energy particle physicist, but
Speaker 1: I don't often feel very high energy or high. There
Speaker 1: were times in my life when that was more true.
Speaker 3: Than Yeah, I seem to remember those times. Yeah. But
Speaker 3: isn't it high a relative term at least in physics?
Speaker 3: Like how high is high energy? Can't you always go
Speaker 3: higher in energy?
Speaker 1: You can always go higher in energy? And what people
Speaker 1: called high energy fifty years ago we now call nuclear physics.
Speaker 1: So it doesn't even qualify what it's not low energy,
Speaker 1: It doesn't even qualify as low energy physics.
Speaker 3: I guess nobody wants to be called a low energy physicist.
Speaker 1: Yeah, would you want to be called a low energy cartoonist?
Speaker 3: Well, I am, and if you call me that it
Speaker 3: would be accurate. But I guess you can call me that,
Speaker 3: why not?
Speaker 1: Yeah? Sure? Well, high energy really means highest energy. And
Speaker 1: as we keep pushing the boundaries of what we can achieve,
Speaker 1: then yesterday's high energy collider is today's nuclear physics.
Speaker 3: Mm sounds like a good slogan for the LGC. Yesterday's
Speaker 3: high energies now today's nuclear energy. But anyways, welcome to
Speaker 3: our podcast Daniel and Jorge Explain the Universe, a production
Speaker 3: of iHeartRadio.
Speaker 1: In which we use all of our energy to help
Speaker 1: you understand the nature of the universe. We tear things apart,
Speaker 1: we peer inside. We try to understand at a microscopic level,
Speaker 1: how does everything work? Is there a story we can
Speaker 1: tell about what's happening to the littlest bits in the
Speaker 1: universe and how it comes together to explain our reality?
Speaker 3: That's right. We like to explore the high energies, the
Speaker 3: low energies, and all the energies in between that there
Speaker 3: are in this universe to discover, to explore, to learn about,
Speaker 3: and to blow your mind with.
Speaker 1: And energy is a really central concept in physics and
Speaker 1: in people's understanding of physics. We'd like to think about
Speaker 1: things in terms of energy, little quantum fields vibrating with energy,
Speaker 1: energy being passed between particles, energy used to create particles.
Speaker 1: In some sense, physics is a study.
Speaker 3: Of energy, and one that requires some amount of energy
Speaker 3: to explore, right, I mean, you can't just do physics
Speaker 3: from your couch.
Speaker 5: Can you.
Speaker 1: I don't know if it takes more energy to do
Speaker 1: physics or cartooning, but you can sort of lie in
Speaker 1: your couch and just think about the universe, you know,
Speaker 1: the way the great theorists and the Greeks have done.
Speaker 1: But absolutely to do experiments to explore the universe, to
Speaker 1: investigate it deeply, you need to poke it, you need
Speaker 1: to probe it, you need to interact with it, and
Speaker 1: that does take some energy.
Speaker 3: Well, I feel like energy is kind of a topic,
Speaker 3: that it's a word you learn as a kid, and
Speaker 3: that everybody has heard of this word and we all
Speaker 3: use it every day in our everyday lies. But to
Speaker 3: actually define energy is kind of tricky, isn't it, Not
Speaker 3: just from a physics point of view, but also if
Speaker 3: you ask somebody what energy is, You don't get an
Speaker 3: easy answer.
Speaker 1: Yeah, energy is a very loaded term, right. We have
Speaker 1: a sense of like feeling like you have low energy
Speaker 1: in the morning, or running out of energy to do
Speaker 1: some chores or something. But it's one of these words
Speaker 1: that physics has redefined to have a specific meaning, a
Speaker 1: very crisp idea for what energy means. The way we
Speaker 1: also have like meanings for force and work and other
Speaker 1: words that we also use in everyday English without as
Speaker 1: precise definitions.
Speaker 3: Right, But even those the simple terms have been changing
Speaker 3: in physics over time, right, Like the word the idea
Speaker 3: for force has changed with quantum mechanics. Isn't it Like
Speaker 3: it used to be an invisible force that we feel
Speaker 3: towards the Earth or the sun, But now they're talking
Speaker 3: that maybe it's like a particle or something, it's an
Speaker 3: exchange of particles.
Speaker 1: Yeah, the mechanism that explains it is definitely different. I
Speaker 1: think the concept of force is a change in momentum
Speaker 1: of something. Something in exchange of momentum essentially has been
Speaker 1: pretty constant since Newton. Yeah, these things definitely can change.
Speaker 1: And you know, for example, we've redefined gravity to not
Speaker 1: even be a force, So what gets counted as a
Speaker 1: force and what doesn't and how that all works definitely changes.
Speaker 1: And we like to dig into these basic principles and say, like,
Speaker 1: what does this really mean? Where does it come from?
Speaker 1: Did the universe have to me this way? Is energy
Speaker 1: essential to the universe? And one of the ways that
Speaker 1: we do that is by noticing what the universe respects,
Speaker 1: like what doesn't change in the universe, what's constant, what's conserved.
Speaker 1: That gives you a clue about sort of what's important
Speaker 1: to the underlying machinery of the universe.
Speaker 3: Right, you kind of want to know what the rules
Speaker 3: of the universe are, or what the principles of the
Speaker 3: universe are by which it lets things happen in it,
Speaker 3: right exactly.
Speaker 1: And one of the deepest rules that people imagine in
Speaker 1: the universe follows is conservation of energy. That energy is
Speaker 1: somehow immutable, that it can slosh between different kinds of
Speaker 1: energy kinetic to potential, to mass, to velocity to whatever.
Speaker 1: But the energy has to go somewhere and has to
Speaker 1: come from somewhere. That it's a basic component of the
Speaker 1: universe itself.
Speaker 3: Yeah, it's a very fundamental rule that people seem to
Speaker 3: learn about even in high school physics. But is it
Speaker 3: actually true? Does it always happen in this universe or
Speaker 3: does it get broken at some levels, like the quantum levels.
Speaker 3: And so to the end the podcast, we'll be asking
Speaker 3: the question does quantum mechanics conserve energy? Now, when you
Speaker 3: say quantum mechanics, do you mean like the field or
Speaker 3: the people who study quantum mechanics.
Speaker 1: The mechanics of quantum physics.
Speaker 3: Can you be a quantum mechanic like a car mechanic,
Speaker 3: but at the quantum level.
Speaker 1: Yeah, bring your fields in. They need some new parts.
Speaker 1: We'll order them.
Speaker 3: That's right, Your quantum carburetor needs to be swapped out, exactly.
Speaker 1: No, in this case, we're talking about the rules of
Speaker 1: the smallest bits in the universe, the tiniest little things,
Speaker 1: the electrons, the positrons of photons, all the smallest stuff
Speaker 1: in the universe seems to operate on different rules than
Speaker 1: the bigger stuff in the universe baseballs and basketballs and
Speaker 1: rocks and stuff that we're familiar with. And so while
Speaker 1: we're taught that energy is concerned very generally, we're interested
Speaker 1: in whether that's always true, and whether it's true at
Speaker 1: the smallest scale.
Speaker 3: Yeah, so this is a big question. Does quantum mechanics
Speaker 3: conserve energy? And so, as usually, we were wondering how
Speaker 3: many people out there had thought about this question, whether
Speaker 3: this is a rule that can be broken at the
Speaker 3: quantum level, or whether the whole universe follows it.
Speaker 1: Thanks very much to everybody who answers these questions. If
Speaker 1: you would like to receive a regular dose of tough
Speaker 1: physics questions in your inbox, right to me too, questions
Speaker 1: at Danielandhorge dot com, and I will send them to you.
Speaker 3: Well, regular dose. Now do these doses make you high
Speaker 3: in physics?
Speaker 1: These are microdoses, so yeah.
Speaker 3: Oh, I see right, it's more of a low key high.
Speaker 1: They're not supposed to blow your mind. They're just supposed
Speaker 1: to color your experience of the universe a little bit.
Speaker 3: I see. It's more of a nuclear.
Speaker 1: Hit exactly, It's not a high energy dose.
Speaker 3: Well, think about it for a second. Do you think
Speaker 3: quantum mechanics conserves energy? Here's what people have to say.
Speaker 5: I think so, or at least the rate of decay
Speaker 5: is so minute that we are not currently able to
Speaker 5: detect it on a cosmological scale.
Speaker 6: I think quantum mechanics conserves energy. I feel like it
Speaker 6: would be big news if we found the law of
Speaker 6: conservation of energies to be violated, though maybe it has
Speaker 6: been and I just haven't seen that news. But the
Speaker 6: notion of quantum fluctuations seems like it would violate that law.
Speaker 6: Though I don't really understand quantum fluctuations.
Speaker 2: I'm assuming it doesn't just because I remember listening to
Speaker 2: your podcast on how energy actually isn't conserved in the universe.
Speaker 2: So I'm assuming that quantum mechanics follows that as well,
Speaker 2: But I don't actually know.
Speaker 4: I'm not sure about this question. And like conserve in
Speaker 4: what like in your book frequently asked questions about the universe,
Speaker 4: you did say like there was like a quantum foam,
Speaker 4: and like when the universe is expanding, it's just connecting
Speaker 4: to more quantum particles, I guess. So I'm going to say,
Speaker 4: I don't know, because if you mean in the universe,
Speaker 4: like not the growing section, then no. But if we
Speaker 4: even include all the other disconnected quantum phone then I'm
Speaker 4: not sure.
Speaker 3: All right. People are on the fence about this. Some
Speaker 3: people say it does, some people say they don't think so. Well,
Speaker 3: they're not sure.
Speaker 1: Yeah, I was really surprised by this. I was expecting
Speaker 1: people to rush to the defense of conservation of energy
Speaker 1: and say it's a fundamental law of the universe.
Speaker 3: Maybe it's because we've had whole episodes where we say
Speaker 3: that the energy is not conserving the universe that maybe
Speaker 3: influence the answers here.
Speaker 1: Oh my gosh, people actually listening and absorbing the content.
Speaker 3: Amazing, amazing, they're learning. Well, it's great that they are
Speaker 3: listening to us. And because we have talked about this
Speaker 3: idea of conservation of energy in the universe, and we've
Speaker 3: talked about how it's not actually conserved in the universe
Speaker 3: as a whole.
Speaker 1: Right, that's right, And that was in the context of
Speaker 1: sort of general relativity, thinking about the universe as it
Speaker 1: expands and as space is changing, how we define energy
Speaker 1: in that context, and that sort of blows a lot
Speaker 1: of people's minds to understand that energy might not be
Speaker 1: conserved in the universe at the biggest scales, you know,
Speaker 1: when you zoom all the way out and think about
Speaker 1: how the universe is expanding and what happens to stuff
Speaker 1: inside of it.
Speaker 3: Right, Because in the other episode we talked about how
Speaker 3: the universe is expanding due to dark energy, and basically
Speaker 3: like there's more space being created all the time out
Speaker 3: of nothing, which means that energy sort of being added
Speaker 3: to the universe, created in the universe out of nothing.
Speaker 1: Right, Yeah, that's right, and you're coming out of nothing,
Speaker 1: I think says a lot. You know, it implies that
Speaker 1: energy needs to come from somewhere, and so when you
Speaker 1: say energy is created, you have to give some explanation
Speaker 1: for where it comes from, even if you're saying out
Speaker 1: of nothing. But this tells us that energy isn't something
Speaker 1: fundamental to the universe. That it can go up and
Speaker 1: it can go down, like lots of things in the universe,
Speaker 1: like the number of people in swimming pools is not
Speaker 1: a constant number of the universe. It can go up
Speaker 1: and it can go down.
Speaker 3: How do you know? Are you sure the.
Speaker 1: Middle of an extensive worldwide experiment to measure the number
Speaker 1: of people.
Speaker 3: At any moment? Yes, Oh, you thought you were going to.
Speaker 1: Challenge me on that and call me out, But actually
Speaker 1: I've been doing this in preparation for five years just
Speaker 1: to make that casual comment.
Speaker 3: You know, somehow I don't believe you any.
Speaker 1: Away from my paper in nature. Okay, it's coming out soon,
Speaker 1: I promise.
Speaker 3: Sure. Let's see the draft. Read me a poll paragraph
Speaker 3: from the draft right now.
Speaker 1: Oh, I can't disembargo it because it's too high profile.
Speaker 3: I see.
Speaker 1: I signed an NBA. What am I gonna do? No,
Speaker 1: obviously I have not done that experiment.
Speaker 3: A nuclear disclosure agreement, which means it's really low.
Speaker 1: But clearly there are things in the universe that do change,
Speaker 1: things that are not fundamental to the universe, while there
Speaker 1: are other things that are fundamental, like momentum. We think
Speaker 1: momentum is conserved in the universe, and that comes from
Speaker 1: a really deep symmetry about space and time that the
Speaker 1: experiments you do anywhere in the universe should give you
Speaker 1: the same answer. That doesn't matter where you put your
Speaker 1: origin in space. Rules of physics don't care, and that
Speaker 1: gives you directly as a consequence of Nuther's theorem, momentum conservation.
Speaker 1: But energy is not in that same category, and energy
Speaker 1: can go down and it can go up, like when
Speaker 1: the universe expands, you get in new space, and that
Speaker 1: space comes with energy, but also energy gets decreased because
Speaker 1: as space expands, it reddens the wavelengths of all the
Speaker 1: photons inside of it. Take for example, the cosmic microwave
Speaker 1: background radiation from the early universe. When it was created,
Speaker 1: it was very high energy. That plasma was super dup
Speaker 1: or hot. It was thousands of degrees kelvin. But it's
Speaker 1: been stretched out by the expansion of the universe to
Speaker 1: very long wavelengths, and now it's at like three degrees kelvin.
Speaker 1: Where do that energy go? Didn't go anywhere, it's just gone.
Speaker 3: Well, it's not gone, it's just gonna spread out, is it.
Speaker 1: No, there's less energy in those photons. Those photons have
Speaker 1: gone from high energy to low.
Speaker 3: Energy because they got stretched out.
Speaker 1: But the total energy is also different. It's not just
Speaker 1: the energy density.
Speaker 3: But they're longer now, that's what those are longer. Yeah,
Speaker 3: isn't where the energy went.
Speaker 1: The energy of those photons is less. They're also longer,
Speaker 1: but the energy of those photons is less. If you
Speaker 1: stretch space, the photons get redder, which means they have
Speaker 1: less energy.
Speaker 3: Well, I guess this is what I mean. Because the
Speaker 3: idea of energy, the concept of energy can really vary
Speaker 3: into a lot of these arguments about whether it can
Speaker 3: can be conserved or not. I feel like maybe they
Speaker 3: depend on a good definition of energy, and so maybe
Speaker 3: for folks we should talk about what energy actually is,
Speaker 3: how to physicists define it.
Speaker 1: Yeah, I wish I knew what energy was.
Speaker 3: Wait, what.
Speaker 1: Energy is a really slippery topic. It's something we've been
Speaker 1: struggling with over the last few decades to really define.
Speaker 1: We have some very crisp but unsatisfying definitions of energy.
Speaker 1: You know, in some cases you can say energy is
Speaker 1: the thing that's conserved over time, you know, so you
Speaker 1: can define it to be something that's conserved. Really, I
Speaker 1: think a better way to define energy is to talk
Speaker 1: about like the forms it can take. You know, like
Speaker 1: there's kinetic energy, which means energy of motion. Something is
Speaker 1: moving that has energy. There's potential energy, this energy of configuration.
Speaker 1: Like a book is sitting on the shelf, there's energy
Speaker 1: stored in that. You know, it takes energy to put
Speaker 1: the book on the shelf. Mass, for example, is a
Speaker 1: representation of internal stored energy. Put a bunch of photons
Speaker 1: into a box, they have energy. That box now has
Speaker 1: more mass. All these are different ways you can calculate energy,
Speaker 1: and if you add them all up, you get the
Speaker 1: total energy. And so that's sort of how we define energy,
Speaker 1: but you know it's a little hand wavy.
Speaker 3: Wait wait, wait, So I was right earlier when I
Speaker 3: said that I don't really know what energy kind of is,
Speaker 3: but you made it seem like we did know.
Speaker 1: We don't really know what energy is in the broadest sense,
Speaker 1: but we can define something and say this is what
Speaker 1: we call energy. I don't know if it really captures
Speaker 1: our full experience of energy, but yeah, we can write
Speaker 1: down a formula for what energy is.
Speaker 3: But I guess the question is what did those things
Speaker 3: have in common? And why do you use the same
Speaker 3: word for all of them? The kinetic energy, potential energy,
Speaker 3: you know, energy of mass. Why do you use the
Speaker 3: same word for all of those things?
Speaker 1: Yeah, great question, And the reason is that in classical
Speaker 1: mechare at least, you know, things moving around at our
Speaker 1: scale at or fairly low speeds. We notice that they
Speaker 1: can turn back and forth into each other. Like you
Speaker 1: take that book on the shelf. It has potential energy
Speaker 1: and no kinetic energy. You push it off the shelf.
Speaker 1: Now it's speeding up towards the ground. It's losing potential
Speaker 1: energy and gaining kinetic energy. So we notice that these
Speaker 1: things can turn into each other, and therefore we group
Speaker 1: them together into one big category. And we notice that,
Speaker 1: at least in classical mechanics, the total the sum of
Speaker 1: them all does stay constant. So like if you're add
Speaker 1: of all the potential energy and all the kinetic energy
Speaker 1: at one moment, and you do it again later, you
Speaker 1: find you get the same answer.
Speaker 3: And how does that relate to the energy of a
Speaker 3: photocon which you mentioned earlier.
Speaker 1: So now we're departing classical mechanics a little bit. We're
Speaker 1: talking about a quantum object, but we can still think
Speaker 1: about the energy of a photon. A photon has kinetic
Speaker 1: energy because it's in motion, it's always in motion. It
Speaker 1: has only kinetic energy. So photons definitely have energy.
Speaker 3: Well, it seems like maybe the common factor is the
Speaker 3: idea of motion, like things moving have energy to them,
Speaker 3: and things that can move in the future or can
Speaker 3: cost things to move, or like the potential to cost
Speaker 3: something to move, is what maybe you would call energy.
Speaker 1: Maybe I think that puts kinetic energy in a more
Speaker 1: primary position than potential energy, which I'm not sure is justified.
Speaker 1: I think there really are at its core two different
Speaker 1: kinds of energy. There stored energy potential energy and kinetic energy.
Speaker 1: I'm not sure which one would be more fundamental.
Speaker 3: And so are those the only two kinds of energy?
Speaker 3: So you have in classical physics kinetic and potential.
Speaker 1: Yeah, those are the two forms. People might think, what
Speaker 1: about mass? What is mass? Is that kinetic energy or
Speaker 1: potential energy? It's sort of a special case. It's just
Speaker 1: sort of a label we give some kinds of energy
Speaker 1: if they're stored internally, Like if you have gluons inside
Speaker 1: of proton, they have a bunch of kinetic energy they're
Speaker 1: zooming around. They also have potential energy of their bonds.
Speaker 1: All that energy is inside the proton, so we call
Speaker 1: that mass. So mass is sort of a label we
Speaker 1: give to some energy, but it's not on the same
Speaker 1: level as like kinetic and potential it's not its own
Speaker 1: kind of energy.
Speaker 3: So then if an eight year old asked you, hey,
Speaker 3: doctor Whitson, what is energy? What would you answer?
Speaker 1: I would say, I've had this nightmare scenario many times
Speaker 1: and I have no idea how to respond.
Speaker 3: You would spring in their face, Ah, run away, No, seriously, like,
Speaker 3: what would you say, you have to say something? What
Speaker 3: would you say, I'll get you started. It's a quantity that.
Speaker 1: I'd say, energy is something that makes things move, but
Speaker 1: it's also something you can store. That's my best shot.
Speaker 3: It's almost like a liquid or something.
Speaker 1: You know, for a long time people did imagine that
Speaker 1: energy in the form of heat was a liquid that
Speaker 1: flowed between things. But it's not a physical quantity in itself.
Speaker 1: It's a description of the physical state of other quantities.
Speaker 1: Like a liquid can have energy, but so can solids.
Speaker 1: It's not like when energy flows from one thing to another,
Speaker 1: there's some physical substance that moves between it. It changes
Speaker 1: the state of those objects.
Speaker 3: Well, I guess I'm a little surprised you're having so
Speaker 3: much trouble just defining energy, which is pretty interesting. But
Speaker 3: as you said, I think one thing that we do
Speaker 3: sort of know about it is that in some cases
Speaker 3: it's conserved and maybe in some cases it's not.
Speaker 1: So.
Speaker 3: Well, let's dig into the question and when it's conserved,
Speaker 3: is it conserved at the quantum level or is it not.
Speaker 3: So let's dig into that, But first let's take a
Speaker 3: quick break. All right, we are mustering up the energy
Speaker 3: to talk about something that apparently physicists can't define energy,
Speaker 3: such a basic word that even little kids use, everyone
Speaker 3: uses their in their daily lives. But it seems Daniel,
Speaker 3: that it's something physicists can't really define very well. Maybe
Speaker 3: only mathematically you can define it. Is that kind of
Speaker 3: the case.
Speaker 1: Yeah, And as you'll see, when we get into the
Speaker 1: quantum system, this is going to be even trickier. And
Speaker 1: physicists disagree about how to define energy and whether we
Speaker 1: can even define it in terms of quantum systems.
Speaker 3: Well, it seems like we don't even need to get
Speaker 3: through you already don't know how to define it exactly.
Speaker 1: And that's why I want to be upfront about how
Speaker 1: complicated and confusing this topic is, even in the easy case,
Speaker 1: because when we get to the hard case, it's going
Speaker 1: to get even trickier. So I did my best to
Speaker 1: give you like my understanding of energy, but if you
Speaker 1: look at the official definition of energy, I find it's
Speaker 1: even less satisfying. Like if you just google energy and
Speaker 1: you ask Wikipedia or chat GPT, like, what is energy?
Speaker 3: Well, it's you know, legit sources.
Speaker 1: Legit sources. They say energy is the quantitative property that
Speaker 1: is transferred to a body, and that doesn't really even
Speaker 1: tell you what it is. It's like Okay, well, it
Speaker 1: can move from one thing to another, but what is it? Man,
Speaker 1: it doesn't really answer that question.
Speaker 3: Well, that's kind of what I meant before, is that
Speaker 3: it's a quantity. Is basically kind of the only way
Speaker 3: you physicists know how to define it, right, it's a
Speaker 3: it's a quantity. It's something that can measure, that can
Speaker 3: be a lot or a little, which you seem to
Speaker 3: be able to measure about things, and that sometimes seems
Speaker 3: to be conserved.
Speaker 1: So mathematically, we can write down a formula that defines it,
Speaker 1: and then it's defined in terms of things we can
Speaker 1: measure like velocity and position and stuff like this. And
Speaker 1: it turns out that if you write it in certain ways,
Speaker 1: then that number doesn't change. The internal values can slash
Speaker 1: back and forth, but the total doesn't change. That's sort
Speaker 1: of like the crispest most mathematical definition. But I think
Speaker 1: what we're proving forward is like what does it mean philosophically?
Speaker 1: Like what are the implications of that? And that's much trickier.
Speaker 3: Well, you seem to not want to give primacy to
Speaker 3: kinetic energy, but in a way, that's kind of like
Speaker 3: our most direct experience of energy, which is motion, right,
Speaker 3: Like if something has a lot of energy to either
Speaker 3: moving fast, or it's hot or it's exploding. For us,
Speaker 3: in our experience of the universe, energy is basically things
Speaker 3: moving fast or things that can make things move fast.
Speaker 1: Yeah, if you're talking about the experience of it, then
Speaker 1: you more directly experience motion than stored energy. It's energy
Speaker 1: you don't really experience when it's stored because it's just
Speaker 1: being stored. It's when it's transformed into kinetic energy that
Speaker 1: you're experiencing it. Like if you zap yourself on a battery,
Speaker 1: it's the motion of those electrons being transformed from the
Speaker 1: potential into their kinetic energy that's zapping you.
Speaker 3: All right. So then you said that sometimes it's conserved
Speaker 3: and sometimes it's not. So when is energy conserved in
Speaker 3: a classical way?
Speaker 1: In classical sense, energy is only conserved when space time
Speaker 1: is not curved and when space time is not changing.
Speaker 1: So if space time is fixed, like you have flat
Speaker 1: space time, meaning you shoot two photons and they stay
Speaker 1: parallel to each other, then you can expect energy to
Speaker 1: be conserved. But if that space is changing, like it's
Speaker 1: expanding the way our universe is, then the general relativity,
Speaker 1: energy is not conserved. Even more generally, anytime you have
Speaker 1: curved space in general relativity, you do not have conservation
Speaker 1: of energy. So, for example, black holes colliding do not
Speaker 1: conserve energy.
Speaker 3: Wait, what what do you mean.
Speaker 1: When two black holes collide? You have the collision of
Speaker 1: two curved bits of space, and what comes out of
Speaker 1: that is not the sum of what goes into that.
Speaker 1: You're not guaranteed that in general relativity.
Speaker 3: But is in space always curved like uncurving space around me,
Speaker 3: and yet I don't seem to have infinite energy.
Speaker 1: That's right, you do not have infinite energy and you
Speaker 1: are curving space around you. But the total amount of
Speaker 1: energy in the system changes in time in general relativity,
Speaker 1: and it gets really fuzzy and weird because general relativity
Speaker 1: is really hard to think about in some reference frames.
Speaker 1: According to generalativity, energy is conserved in others, it's not.
Speaker 1: Depends sort of on how you're looking at things.
Speaker 3: Okay, it sort of sounds like you're saying like, if
Speaker 3: you don't think about general relativity, then you can assume
Speaker 3: that energy is being conserved. If you assume that there's
Speaker 3: general relativity and things are being space is being bent
Speaker 3: like around black holes or the expansion of the universe.
Speaker 3: Then you can't assume that energy is being conserved.
Speaker 1: As long as we're above the quantum level.
Speaker 3: Right, So it's mostly like whether or not you ignore
Speaker 3: the bunding of space exactly.
Speaker 1: If you can ignore the bending or expansion of space time,
Speaker 1: then classically you can think of energy as conserved.
Speaker 3: Right. And so we talked about that the universe is
Speaker 3: expanding and so therefore energy is not being concernedd and
Speaker 3: we talked about two black holes colliding. Energy is not
Speaker 3: being conserved there So now the question of the episode
Speaker 3: is when you get down to the quantum level, is
Speaker 3: energy still conserved even though maybe there's no space time
Speaker 3: bending at the quantum level. If you assume there's no
Speaker 3: bending at the quantum level, does energy get conserved.
Speaker 1: Yeah, And we have to assume there's no space time
Speaker 1: bending at the quantum level because we don't know how
Speaker 1: to do quantum mechanics when space is curved and you
Speaker 1: have gravity, and gravity for particles is something we don't understand.
Speaker 1: So let's assume space is totally flat and we have objects,
Speaker 1: you know, like baseballs and rocks for which we think
Speaker 1: energy is conserved and then zoomed down to the quantum
Speaker 1: level and try to understand when you have photons and
Speaker 1: electrons instead of rocks and baseballs, is energy still conserved?
Speaker 1: And really the deep question is like, is energy conservation
Speaker 1: something that's through in through the universe at every scale
Speaker 1: or is this something that emerges only at the scale
Speaker 1: we experience it out of something that operates totally differently,
Speaker 1: because remember, quantum mechanics breaks all the rules of classical physics.
Speaker 1: It says things don't actually have well defined positions and locations,
Speaker 1: and lots of the things that emerge at our level
Speaker 1: are not true at the quantum level. So it's not
Speaker 1: guaranteed that everything about our experience will be translated down
Speaker 1: to the quantum level.
Speaker 3: All right, So then let's answer the question, does quantum
Speaker 3: mechanics can serve energy or not?
Speaker 1: So the short answer is we don't know.
Speaker 3: Surprise, surprise, But let's talk about it anyways.
Speaker 1: The slightly less short answer is it depends on what
Speaker 1: you think is happening at the quantum level, mostly about
Speaker 1: what happens when you try to measure energy.
Speaker 3: What do you mean? So I guess, because it's quantum mechanics,
Speaker 3: you have to measure things. That's very importing quantum mechanics.
Speaker 3: So you're saying, we have to answer this question with
Speaker 3: this idea in mind.
Speaker 1: Yeah, exactly. So let's start off the easy case without
Speaker 1: measurements and have a picture in our minds or what's happening.
Speaker 1: You know, quantum mechanics tells us that there are probabilities
Speaker 1: for various things to happen, and we can calculate those
Speaker 1: probabilities using the rules of quantum mechanics, and those probabilities propagate.
Speaker 1: You have two electrons heading towards each other, they might
Speaker 1: scatter off each other and go that way, they might
Speaker 1: pass right through each other. All those probabilities are sort
Speaker 1: of live until somebody actually asks the question and makes
Speaker 1: a measurement using a classical object and you know, tries
Speaker 1: to take a picture of it. Until then sort of
Speaker 1: have all the possibilities live. So that's quantum mechanics without measurement.
Speaker 1: You know, that's what we're imagining is happening when we're
Speaker 1: not looking. And in that scenario we can ask, well,
Speaker 1: is energy conserved? Like when all those probabilities are slashing around,
Speaker 1: the electrons are maybe bouncing off each other and maybe
Speaker 1: not is energy conserved there? And already we kind of
Speaker 1: run into trouble because we don't really know how to
Speaker 1: define energy here. Like, what if you have a quantum
Speaker 1: system and has a few different possible states, a low
Speaker 1: energy state and a high energy state. How do you
Speaker 1: define the energy of it? Is it like the way
Speaker 1: average of the probabilities of the various states? Is it
Speaker 1: something else. I've had conversations with a bunch of physicists
Speaker 1: this week to try to sort out what people think
Speaker 1: energy is, and some people say, you can't define energy
Speaker 1: in that context, and other people say, no, it's definitely
Speaker 1: the weighted average of the various probabilities.
Speaker 3: Right, I think, meaning maybe for people who are not
Speaker 3: super familiar with quantum mechanics. So in quantum mechanics, particles
Speaker 3: and things like that aren't just in one state, like
Speaker 3: a baseball sitting on your table. It's like it's doing
Speaker 3: multiple things at the same time. It's here, it's a
Speaker 3: little bit there, it's moving in this direction a little bit,
Speaker 3: but it's also has the probability to be moving in
Speaker 3: this other direction. And so you're saying that maybe one
Speaker 3: way to measure its energy, or to think about its
Speaker 3: energy is like, if it has a fifty percent probability
Speaker 3: of going this way, then you take that energy and
Speaker 3: multiply by a half. And if it has a certain
Speaker 3: probility that it's moving this way with that velocity, like
Speaker 3: a twenty five percent probability, then you maybe multiply that
Speaker 3: energy by a quarter, and then you would add it
Speaker 3: all up and maybe that would kind of give you
Speaker 3: an average of it energy.
Speaker 1: Yeah, exactly, Like if it has a fifty percent chance
Speaker 1: of having twenty five jewels of energy and a fifty
Speaker 1: percent chance of having seventy five jewels, then you say, well,
Speaker 1: I'm going to average those two. I'm gonna say its
Speaker 1: energy is fifty jewels because on average that's what it has.
Speaker 1: And here allowing the particle to still have both probabilities
Speaker 1: to say, oh, maybe it's in the lower energy state,
Speaker 1: maybe it's in the higher energy state.
Speaker 3: Right, it's in a superposition, it's with a life and dead.
Speaker 3: Then you said, some of your physicist friends said, you
Speaker 3: can't do that, like that's not even that doesn't make sense.
Speaker 1: Yeah, And they say, you can't do that because you
Speaker 1: can't measure that, right, you never measure the fifty Like
Speaker 1: if you went and asked the question, all right, we
Speaker 1: have the particle in this state, go measure the energy.
Speaker 1: You're gonna get twenty five or you're gonna get seventy five.
Speaker 1: You're never going to get the average. It's like saying
Speaker 1: the average number of children in the US is two
Speaker 1: point four, but nobody actually has two point four children, right,
Speaker 1: and so in the same way, you'll never see this
Speaker 1: particle have that energy. So in what sense is that
Speaker 1: the energy of the particle? That's sort of the complaint.
Speaker 3: That's kind of a fundamental problem with quantum mechanics. Like
Speaker 3: it's you know, the cat is alive and dead. Obviously
Speaker 3: the cat can't be alive if you see the cat.
Speaker 3: It can't be both. But in a quantum sense, it
Speaker 3: is both.
Speaker 1: In a quantum sense, it is both. In quantum sense,
Speaker 1: we need a new idea for what these things mean,
Speaker 1: Like what does position mean in a quantum sense, Well,
Speaker 1: you know, for a particle that you haven't measured, it's
Speaker 1: not really well defined. There's only a probability where is
Speaker 1: the particle Actually, well, it's not anywhere. Actually, So these
Speaker 1: concepts that are so important to us at the macroscopic
Speaker 1: scale have to take different meanings. We have to do
Speaker 1: this like philosophical extrapolation, and this is a problem with energy.
Speaker 1: For example, say we have the particle and has two
Speaker 1: different possibilities, the twenty five jewel and the seventy five jewel.
Speaker 1: Then you go and you measure and it turns out
Speaker 1: it has seventy five jewels. Well, if a minute ago
Speaker 1: you said it had fifty jewels because that was the average.
Speaker 1: Now you've measured it and you said you have seventy
Speaker 1: five jewels. Where did that twenty five jewels come from?
Speaker 3: Right?
Speaker 1: And so boom right there, you have a violation of
Speaker 1: conservation of energy. If that's how you define energy before
Speaker 1: you measure it.
Speaker 3: Wait, say it again. It is energy suddenly appear.
Speaker 1: So if you start out the particle we were just
Speaker 1: talking about, it has a fifty percent chance of having
Speaker 1: twenty five jewels and a fifty percent chance of having
Speaker 1: seventy five jewels. So we say, okay, we define the
Speaker 1: energy of it to be fifty jewels because that's the average.
Speaker 1: Now you go and you measure it, and you measure
Speaker 1: it to have seventy five jewels for example, Then according
Speaker 1: to our definition of energy, it's gone from having fifty
Speaker 1: jewels to having seventy five jewels, and so where did
Speaker 1: that energy come from?
Speaker 3: It didn't come from anywhere, it just said before it
Speaker 3: was a guess about what its energy was. It was
Speaker 3: kind of like the expectations of it or the average
Speaker 3: of what we think its energy was. But then in
Speaker 3: the second instance, is what we measured its energy. So
Speaker 3: they shouldn't be a surprise if it's more or less,
Speaker 3: should it?
Speaker 1: So you're saying, those are really two different things. One
Speaker 1: is an actual energy because you've measured it. The other
Speaker 1: is just some estimation of what we might measure, but
Speaker 1: not really the energy.
Speaker 3: Well, and it is in the quantum sense right like
Speaker 3: it's alive and it's dead before I look at the
Speaker 3: cat in the box and then I wanted to open
Speaker 3: the box. It's alive with it. It's not like the
Speaker 3: cat suddenly came back to life.
Speaker 1: And I think this comes down to a question of
Speaker 1: like interpretation, You know, what is really happening there? It
Speaker 1: does the particle secretly already have seventy five jewels and
Speaker 1: now we're measuring it and discovering it. You know, is
Speaker 1: the uncertainty there or reflection of our lack of knowledge
Speaker 1: about something that's actually already determined or something that really
Speaker 1: isn't determined until we measure it. The particle really is
Speaker 1: in a superposition of those two states. If it really
Speaker 1: isn't determined until we measure it, then we do have
Speaker 1: to kind of ask, like, where does the energy come
Speaker 1: from when the universe decides to make that seventy five
Speaker 1: jewel particle instead of the twenty five jewel particle.
Speaker 3: Well, I guess in the same way that you can
Speaker 3: ask if you find that the cat is alive, how
Speaker 3: did the cat come alive? It was if it was
Speaker 3: alive and dead before you open the box.
Speaker 1: Right, But the difference between the two states of the
Speaker 1: cat doesn't violate the conservation of energy, which we thought
Speaker 1: was maybe a fundamental rule in the universe. That violates
Speaker 1: the conservation of the number of dead cats, which nobody
Speaker 1: really thinks it's a.
Speaker 3: Conservation I hope not well or well, And this says
Speaker 3: that we think that it's impossible for a cat to
Speaker 3: go from being dead to being alive.
Speaker 1: Right, I think if we're going to make the analogy
Speaker 1: to the shorten your cat experiment, and then you want
Speaker 1: to ask the question, is the cat alive before it's measured,
Speaker 1: And the answer I think a lot of people would
Speaker 1: give is it's neither alive nor dead. It has the
Speaker 1: probability of being both. And then to extrapolate that philosophically
Speaker 1: back to our particle, you'd say, well, the particle doesn't
Speaker 1: really have twenty five or seventy five jewels, It just
Speaker 1: has a probability of being both. And energy is not
Speaker 1: really well defined. So I think one answer there is
Speaker 1: to say, well, energy is not really defined without measurements,
Speaker 1: so you can't answer this question, and the others to say, no,
Speaker 1: that's the definition of energy, and there is violation of
Speaker 1: conservation of energy, So you either have to give up
Speaker 1: an understanding of what energy means for quantum particles or
Speaker 1: you have to give up energy conservation.
Speaker 3: All right, So it seems like the moment you measure
Speaker 3: a quantum particle is super important because it's so fuzzy
Speaker 3: before you measure it, and it's so crisp after you
Speaker 3: measure it, and so you kind of fall into a
Speaker 3: trap to try to compare the energy before that moment
Speaker 3: and after that moment, you know, you could interpret it
Speaker 3: as saying that energy is not conserved or could interpret
Speaker 3: it saying, well, you know, there's no definition of energy
Speaker 3: before you measure it, and so therefore don't even worry
Speaker 3: about energy classivation exactly.
Speaker 1: But there's really important loophole that we're overlooking here, and
Speaker 1: that's the measurement itself. Some people argue that energy isn't conserved,
Speaker 1: that this extra energy must come from the measurement, that
Speaker 1: we're only violating conservation of energy because we're not including
Speaker 1: the full system. Right. Energy is only conserved inside a
Speaker 1: closed system where you don't have energy transfer anyway. Right,
Speaker 1: Like energy is not conserved for a battery. As you
Speaker 1: use it, it's energy is decreasing, but if you include
Speaker 1: where that energy is going, usually it is concerned. So
Speaker 1: some people argue, ah, what about the measurement. In order
Speaker 1: to measure something, you have to like poke it, you
Speaker 1: have to interact with it. Maybe you're adding that energy
Speaker 1: when you're making that measurement and things do balance out
Speaker 1: in the end.
Speaker 3: Wait what that was very confusing? Can you give me
Speaker 3: an example.
Speaker 1: So let's say you want to measure this particle and
Speaker 1: you want to say it doesn't have seventy five jewels
Speaker 1: or twenty five jewels, How do you measure things about
Speaker 1: a quantum particle, you have to bounce another quantum particle
Speaker 1: off of them. So shoot this electron with a photon,
Speaker 1: then measure where that photon goes and use that to
Speaker 1: detect what the energy of your particle was. Well, now
Speaker 1: you're shooting your electron with a photon, which is going
Speaker 1: to change its energy. And so people argue, when you're
Speaker 1: doing this, the energy that gives that electron seventy five
Speaker 1: jewels comes from that photon somehow.
Speaker 3: But then wouldn't you measure that the overall energy went
Speaker 3: down because you would measure the photon after it hits
Speaker 3: the electron, and you would see that it was had
Speaker 3: less energy exactly.
Speaker 1: So this is the game people try to play in
Speaker 1: order to recover conservation of energy for quantum mechanics. They say,
Speaker 1: this argument is flawed because you're not taking into account
Speaker 1: the energy of the measurement. So there's a whole cottage
Speaker 1: industry and a bunch of paper. It's recently about whether
Speaker 1: it's possible to recover it using the measurement or whether
Speaker 1: that's a red herring.
Speaker 3: Well, the whole thing could be a red herring, right,
Speaker 3: Like it could be that it just doesn't make sense
Speaker 3: to talk about energy before the measurement.
Speaker 1: It could be and that actually depends also on your
Speaker 1: interpretation of quantum mechanics. We're talking right now in the
Speaker 1: Copenhagen interpretation, which has this whole idea that there's a
Speaker 1: superposition and when you make a measurement it collapses to
Speaker 1: one of those options. That's just one view of quantum mechanics,
Speaker 1: and our argument about the energy non conservation depends on
Speaker 1: that view. It turns out in other views of quantum
Speaker 1: mechanics they tell a whole different story.
Speaker 3: All right, well, let's get into what these other views
Speaker 3: of quantum mechanics are and what they say about the
Speaker 3: conservation of cat energy or not. So let's dig into that.
Speaker 3: But first let's take another quick break. All Right, we're
Speaker 3: talking about energy, whether it's conserved in the universe, is
Speaker 3: it conserved at the quantum level? And I think we've
Speaker 3: established that it's a minefield of confusion for everybody. Some
Speaker 3: people might say, does it even make sense to talk
Speaker 3: about energy before you measure something? And you know, it
Speaker 3: doesn't make sense to talk about whether the cat is
Speaker 3: alive or dead before you open the box. And some
Speaker 3: people might say that it does kind of matter, right,
Speaker 3: or that if you discovered the cat to be aliver
Speaker 3: before or after, maybe you killed the cat when you
Speaker 3: open the box. That's kind of what you're saying exactly.
Speaker 1: And it's amazing to me that this is a topic
Speaker 1: of recent discussion. This is not like something that Bore
Speaker 1: and Heisenberg argued about and figured it out in nineteen
Speaker 1: thirty seven their papers about this. Like last year, you know,
Speaker 1: people are still debating what energy even means in quantum mechanics. Like,
Speaker 1: sort this out, folks. You had it for one hundred years.
Speaker 1: You think that would be enough time to figure out
Speaker 1: basic stuff about quantum mechanics.
Speaker 3: Yeah, can't you just run an experiment to figure this out?
Speaker 3: Like if measuring an electron somehow adds energy to it
Speaker 3: or creates energy, can't you just measure that cad you
Speaker 3: just design an experiment where you should a photon at
Speaker 3: an electron.
Speaker 1: So people are trying to design experiments, and the crucial
Speaker 1: thing is designing an experiment where you think the measurement
Speaker 1: will not influence the energy of the system. That's the goal,
Speaker 1: because then you can have an internal system and an
Speaker 1: external system, and you can isolate it and say this
Speaker 1: is the whole system. So you want to try to
Speaker 1: separate your measuring device from the energy of the system.
Speaker 3: Wait, wait, do you mean like they're trying to come
Speaker 3: up with how to measure something without measuring it.
Speaker 1: Well, they want to measure it without changing its energy,
Speaker 1: so they want a energy independent measuring system.
Speaker 3: But I guess, if you shoot a photon at an electron,
Speaker 3: don't you know how much energy the photon had when
Speaker 3: you shot it so that you can take it into
Speaker 3: account later when it comes out? Like, why is this
Speaker 3: problem so hard?
Speaker 1: Well, every quantum object has an uncertainty to it, and
Speaker 1: so you shoot a photon at it. You try to
Speaker 1: generate photons with a specific energy, but those photons will
Speaker 1: also have an uncertainty to them, and that uncertainty propagates
Speaker 1: through your whole experiment. So what you want to try
Speaker 1: to do is set up a scenario where the uncertainty
Speaker 1: you're adding by your measurement is smaller than the difference
Speaker 1: in the energy between the two states of the thing
Speaker 1: that you're measuring. So you want to try to use
Speaker 1: something really low energy to measure a really big difference.
Speaker 3: I guess it's kind of like you know, you're trying
Speaker 3: to figure out if the cat is alive or dead
Speaker 3: in the box, and you're sending it in a cat
Speaker 3: to do it. But it turns out that the scientist
Speaker 3: cat is also a quantum object, so it could also
Speaker 3: be a live or dead, in which case you don't
Speaker 3: really know the scientist cat is killing the other cat exactly.
Speaker 1: So what you want to do is try to send
Speaker 1: in like a tiny miniature kitten that you can argue
Speaker 1: is going to not influence whether your cat is alive
Speaker 1: or dead as much.
Speaker 3: As possible, or that you know for sure if it's
Speaker 3: alive or dead.
Speaker 1: Or the uncertainty on it is smaller than the uncertainty
Speaker 1: on the thing you're trying to measure. So people come
Speaker 1: up with these crazy clever experiments where you try to
Speaker 1: use really low energy device to measure a very high
Speaker 1: energy difference in the possible states of the object. So
Speaker 1: the thing you're measuring is not influencing the state enough
Speaker 1: to change the answer.
Speaker 3: Oh I see, yeah, Like you said, like you want
Speaker 3: to send in a scientist kitty whose state whether the
Speaker 3: kitty is a live or dead is not really going
Speaker 3: to influence whether the big cat is a live or
Speaker 3: dead exactly.
Speaker 1: And so there's these folks that come up with its
Speaker 1: really clever experience where you take a box and you
Speaker 1: put low energy photons inside of it, and under some
Speaker 1: almost magic like wave mechanics mathematics, there's a place in
Speaker 1: the box where the photon wavelengths add up in a
Speaker 1: special way to wiggle at a really high energy. So
Speaker 1: waves can add up and they can cancel each other out.
Speaker 1: This is constructive and destructive interference, where it turns out
Speaker 1: if you put a bunch of low energy photons into
Speaker 1: a box, there's one portion of the box where they're
Speaker 1: wiggling really really fast where all those photons added up
Speaker 1: kind of make a higher energy photon than the sum
Speaker 1: of all the energy of the photons you put in.
Speaker 1: And they came up with this way to try to
Speaker 1: reflect that one part of the photon out of the
Speaker 1: box by slipping a mirror in really quick. And so
Speaker 1: it's sort of like putting a few low energy photons
Speaker 1: in a box and then getting out a really high
Speaker 1: energy photon. So this is the experiment they propose would
Speaker 1: prove violation or conservation of energy and quantum mechanics. But
Speaker 1: there's a lot of controversy about what this experiment might
Speaker 1: mean and whether you could actually do it.
Speaker 3: Oh, I see, because if you measure a really big
Speaker 3: photon coming out of this corner of the box, you
Speaker 3: have to wonder where that energy came from.
Speaker 1: Yeah, how did the universe make this high energy photon
Speaker 1: out of just a few very low energy photons? Where
Speaker 1: did it come from? Just like the example we were
Speaker 1: talking about before, how did the particle get seventy five
Speaker 1: GeV when the expected value of the energy was fifty
Speaker 1: Where did that energy come from? And you can only
Speaker 1: really ask that question where did it come from if
Speaker 1: you believe it should come from somewhere, which implies that
Speaker 1: it's conserved, that it has to come from somewhere, that
Speaker 1: it's like flows around in it's a limited amount. But
Speaker 1: if energy is not conserved, it can just like go
Speaker 1: up or down, like the number of dead cats in
Speaker 1: the universe. Then that's not really a problem.
Speaker 3: But couldn't you just say that the energy of that
Speaker 3: right photon in the corner came from the little photons
Speaker 3: or would it come out with a much bigger energy
Speaker 3: than the if you add up the little smaller photons.
Speaker 1: Yeah, in this case, the energy is much bigger than
Speaker 1: the sum of the energies of all the photons you
Speaker 1: put in, So you can't explain it by just like
Speaker 1: having added up those photons. It's a really cool experiment.
Speaker 1: It's called super oscillation if you want to check out
Speaker 1: more details about it.
Speaker 3: Well, but then you said that this is all just
Speaker 3: base on one interpretation of quantum mechanics. What did the
Speaker 3: other interpretations say or how can they help us?
Speaker 1: Yeah, because a big part of the issue is what
Speaker 1: happens when you make a measurement. Right if you go
Speaker 1: from a state that has on average fifty jewels of energy,
Speaker 1: then you make a measurement, how do you end up
Speaker 1: in one of those states? And where does that energy
Speaker 1: come from? And other interpretations of quantum mechanics tell a
Speaker 1: very different story about what's happening there. For example, the
Speaker 1: Many Worlds or ever Ready in quantum mechanics says that
Speaker 1: there is no collapse of the wave function. That if
Speaker 1: you have a superposition of two possibilities that has alive
Speaker 1: or dead, the particle has twenty five or seventy five
Speaker 1: jewels of energy, that when you make a measurement, the
Speaker 1: universe just branches and now there's one branch that has
Speaker 1: one option and another branch that has the other option.
Speaker 1: And so in that sense, if you're like averaging over
Speaker 1: the branches, nothing has really changed. You know, the total
Speaker 1: energy in the universe hasn't changed. One individual branch might
Speaker 1: see seventy five jewels, so they might think they're seeing
Speaker 1: violation of conservation of energy. But averaged over all the branches,
Speaker 1: including the ones that don't see, nothing has really changed.
Speaker 1: There's still just a distribution of different energies.
Speaker 3: I feel like you just skipped over a humongas concept
Speaker 3: which is just throwing the multiverse.
Speaker 1: Yes, exactly, in the multiverse.
Speaker 3: Quantum multiverse. So you're saying, like, one way to interpret
Speaker 3: quantum mechanics is that things don't collapse. You know, if
Speaker 3: something if the cat is alive and dead, it means
Speaker 3: that there's a universe where the cat is alive and
Speaker 3: there's a universe where it's dead, and so overall energy
Speaker 3: is still conserved. That's kind of the idea.
Speaker 1: Yeah, energy is just unevenly distributed among those quantum multiverses.
Speaker 1: One of them gets more, another one gets less. Overall
Speaker 1: it all balances out across the multiverse. But in an
Speaker 1: individual universe, an observer does see a violation of energy.
Speaker 1: So that's a pretty different story than what's being told
Speaker 1: by the Copenhagen group.
Speaker 3: Let me see if I get this, so, like, I
Speaker 3: have the cat in the box, and I open the
Speaker 3: box and I find that the cat is alive, and
Speaker 3: I think, oh my god, this is a violation of
Speaker 3: cat aliveness in the universe because before the cat was
Speaker 3: only fifty percent and now it's fully alive.
Speaker 1: Sure.
Speaker 3: Yeah, And you're saying, if you think that the actually
Speaker 3: there's a multiverse, is a quantum multiverse, then there's no
Speaker 3: real violation because if you consider my universe where the
Speaker 3: cat is alive and your universe where the cat is dead,
Speaker 3: then it makes sense for me to see that the
Speaker 3: cat is alive, and it makes sense for you to
Speaker 3: see that the cat is dead. There's no violation here.
Speaker 1: Yeah, because across the quantum multiverse it's still fifty percent
Speaker 1: alive and fifty percent dead.
Speaker 3: But in the single universe version of quantum mechanics, the
Speaker 3: cat aliveness went up from one half to one if
Speaker 3: I see that the cat.
Speaker 1: Is alive exactly. So in the collapse theory where measuring
Speaker 1: it forces the universe to choose one of these branches
Speaker 1: instead of maintaining all of them, then somehow the number
Speaker 1: of live cats in the universe goes up from half
Speaker 1: to one, violating the well known principle of the number
Speaker 1: of living cats in the universe.
Speaker 3: Yeah, or people in swimming pools, which I'm going to
Speaker 3: wait for that paper from me. Okay, hold your breas, yeah,
Speaker 3: to under the pool. Yes, Okay. So then I feel
Speaker 3: like maybe I wonder, like you're saying, if we require
Speaker 3: energy to be conserved in the universe for real, for sure,
Speaker 3: then maybe I wonder if that's proof that the multiverse exists,
Speaker 3: because that's the only way that this is going to work.
Speaker 1: Right, That's a cool perspective I hadn't thought of. Yeah,
Speaker 1: I suppose if you define energy that way as across
Speaker 1: the multiverse and you insist that it's conserved, then Copenhagen
Speaker 1: interpretation of quantum mechanics does violate that. But that's not
Speaker 1: something you can test, right. You can never access these
Speaker 1: other branches of the multiverse. You can never know if
Speaker 1: they exist, and if other people are measuring other things,
Speaker 1: then you can only ever access our branch.
Speaker 3: We think, maybe, right, maybe you can this. I think
Speaker 3: we've talked about this before and in our books, like
Speaker 3: you could maybe discover something about the mathematics of our
Speaker 3: universe that maybe points to the necessity of other universes.
Speaker 1: No, we definitely argue in our book that it might
Speaker 1: be that the only consistent explanation of the universe is
Speaker 1: the multiverse. So you can prove the multiverse exists without
Speaker 1: ever experimentally verifying it, though that takes a lot of
Speaker 1: confidence to say that there's no other explanation out there.
Speaker 3: That would take a high amount of confidence, not a
Speaker 3: nuclear amount of confidence.
Speaker 1: So extrapolining that argument, if you can somehow prove that
Speaker 1: a complete theory of the universe has to satisfy conservation
Speaker 1: of energy at the quantum level, then yeah, that might
Speaker 1: require the existence of the multiverse. But I don't know
Speaker 1: how you would prove that requirement because energy is not
Speaker 1: even necessarily well defined at the quantum level.
Speaker 3: I wonder if that means that some of the other
Speaker 3: places that we've seen energy conservation being violated, like the
Speaker 3: expansion of the universe. I wonder if that can mean that,
Speaker 3: you know, as our universe expands and gains energy, maybe
Speaker 3: there's another universe out there losing energy and being compressed.
Speaker 1: It's a great question and one of the reasons I
Speaker 1: really like this question zooming down to the microscopic scale
Speaker 1: and trying to understand what is conservation of energy there
Speaker 1: is because we're really interested in what it means at
Speaker 1: our scale, Like where does energy come from? Why is
Speaker 1: it conserved for us? Is it because it's required at
Speaker 1: the quantum level, or is it because it emerges somehow?
Speaker 1: And so yeah, maybe energy non conservation in general relativity
Speaker 1: could eventually be derived from some deep quantum gravity, some
Speaker 1: explanation of the nature of space time at the quantum
Speaker 1: level that has these consequences at our scale or at
Speaker 1: the scale of the whole universe. So that would be
Speaker 1: really fascinating.
Speaker 3: Yeah, or maybe vice versa, right, Like, if you prove
Speaker 3: energy conservation at the grand level, it must might have
Speaker 3: some consequences about you know, what we think is happening
Speaker 3: at the quantum level.
Speaker 1: It could be although sometimes conservation laws cannot be exact.
Speaker 1: They can just emerge, so they don't have to always
Speaker 1: hold true at the quantum level to hold true at
Speaker 1: the classical level. But there are some things that are
Speaker 1: truet the quantum level, Like we think conservation momentum is
Speaker 1: rock solid at the quantum level, and the reason we
Speaker 1: have it at our level is because everything is made
Speaker 1: out of these quantum bits which follow these rules. So
Speaker 1: we don't know basically whether conservation of energy is exact
Speaker 1: the way conservation momentum is because it comes out of
Speaker 1: the quantum level, or if it's something that emerges somehow
Speaker 1: when you get classical physics.
Speaker 3: I guess maybe your people in a pool experiment is
Speaker 3: going to conclusively prove that.
Speaker 1: Then give me one hundred years. It's going to take
Speaker 1: a lot of data.
Speaker 3: What do you Why do you need five years to
Speaker 3: do this?
Speaker 1: Oh man, because the I RB you know, you're doing
Speaker 1: experiments on people. You got to sign the papers. It's
Speaker 1: the whole thing.
Speaker 3: I see. Yeah, And then there's a pool, so the
Speaker 3: forms get wet. It's all a big mess. What does
Speaker 3: this have more implications for our understanding of quantum mechanics
Speaker 3: or understanding of energy conservation in the universe.
Speaker 1: I think it has consequences for our understanding of what
Speaker 1: energy is. As we drill down to see what the
Speaker 1: universe really is like at the microscopic scale, we learn
Speaker 1: about things that turn out to just be features of
Speaker 1: our existence. They're not generally true at every level of
Speaker 1: the universe, you know, like there's no equivalent to ice
Speaker 1: cream at the quantum level, for example, there's no equivalent
Speaker 1: to cats. Those things only exist at our level. And
Speaker 1: so I love that as we keep looking deeper into
Speaker 1: the universe, we discover things about our experience that turn
Speaker 1: out to just be part of our experience. They're not
Speaker 1: generally true about the universe, Like our sun is unusual,
Speaker 1: and maybe our planet is weird, maybe our way of
Speaker 1: life is weird. And the same way, we discover that
Speaker 1: the way we experience the universe and the things we
Speaker 1: think are fundamental about it actually aren't. To me, that's
Speaker 1: really cool and opens up questions about like other conservation
Speaker 1: laws are other things that we thought were hard and
Speaker 1: fast and true about the universe actually just sort of
Speaker 1: like emergent approximate things, and at a quantum level they're
Speaker 1: not preserved. That would be kind of scary.
Speaker 3: Well for me, I'm getting the sense that maybe, like
Speaker 3: even if we do discover that energy is conserved or
Speaker 3: not in our universe, that wouldn't maybe really tells what
Speaker 3: the real truth is because we wouldn't have access to
Speaker 3: maybe the multiverse in other universes, which would maybe cancel
Speaker 3: out what we think is the rule of the universe.
Speaker 1: Yeah, that's right. We could see what we think is
Speaker 1: energy non conservation and bigger picture, it all balances out,
Speaker 1: and so we might never really know these answers.
Speaker 3: Well, I'll just take comfort in the fact that even
Speaker 3: if I don't exercise today, maybe there's a quantum Woorge
Speaker 3: in another universe who is doing double the exercise for
Speaker 3: the tour that both us and in some way you
Speaker 3: can say that I exercised today.
Speaker 1: Yeah, that's true, and that quantum Hohoge will live longer
Speaker 1: than you and on average, you know, some fractionales across
Speaker 1: the teams, this will be alive or not.
Speaker 3: Yeah, there you go. There you go, playing with some
Speaker 3: kittens and counting people in a swimming pool. All right, Well,
Speaker 3: we hope you enjoyed that. Thanks for joining us. See
Speaker 3: you next time.
Speaker 1: For more science and curiosity, come find us on social
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