Speaker 1: The big picture task.
Speaker 2: The ultimate quest of physics is to make sense of
Speaker 2: the universe, to sort through our amazing and bonkers experience
Speaker 2: and find as compact and simple an explanation as possible
Speaker 2: for why what happens happens. We've made a lot of progress,
Speaker 2: but we've also struggled together. Do quantum particles really collapse
Speaker 2: together across space time? Why is gravity so difficult to
Speaker 2: unify with quantum theory? Why does time flow forward? Sometimes?
Speaker 2: I wonder if the reason we feel stuck is that
Speaker 2: we started from the wrong place. What if there's a simple,
Speaker 2: basic assumption that we're making that has led us down
Speaker 2: the wrong path. It's happened to us before, like when
Speaker 2: we assumed that time flows the same way across the universe,
Speaker 2: or that we were at the center of the Solar system,
Speaker 2: or that light needed medium to propagate. When we removed
Speaker 2: the mistaken assumption, the veil was pulled from our eyes
Speaker 2: in a simpler, clear if weirder explanation emerged, Could that
Speaker 2: be the cause of our current head scratching? Is there
Speaker 2: some requirement we've imposed on physics that's keeping us from
Speaker 2: seeing the simple explanation staring us in the face. Today
Speaker 2: on the podcast, will knock on the doors the most
Speaker 2: basic intuitive foundational concepts in physics and ask do we
Speaker 2: really need them? We'll question locality, do things have to
Speaker 2: be in the same place in order to interact? And
Speaker 2: its cousin causality, do causes have to come before effects?
Speaker 2: Welcome to Daniel and Kelly's extraordinary counterintuitive Universe.
Speaker 3: Hello. I'm Kelly Readersmith. I study parasites and and after
Speaker 3: today's conversation, I feel really lucky that locality and causality
Speaker 3: just make a lot more sense in biology.
Speaker 1: Hi, I'm Daniel.
Speaker 2: I'm a particle physicist, and I like to pretend sometimes
Speaker 2: to be a philosopher.
Speaker 3: Ooh yeah, I enjoy philosophy too.
Speaker 4: Well.
Speaker 2: One of the things I love about physics is that
Speaker 2: it butts right up against philosophical questions. We're asking about
Speaker 2: the deep, fundamental nature of the universe, and so the
Speaker 2: philosophical questions are like immediate and obvious. I hear a
Speaker 2: little bit less about like the philosophy of biology. You know,
Speaker 2: what does it mean to be a parasite?
Speaker 1: This sort of stuff?
Speaker 3: Well, I mean, we have plenty of arguments about that
Speaker 3: at the conference as we go to. But I feel
Speaker 3: like for us philosophy, Well, what's the difference between philosophy
Speaker 3: and ethics? Is ethics a subset of philosophy? Because we
Speaker 3: talk a lot about ethics associated with the biology stuff
Speaker 3: that we're working on. So I'm more used to tackling
Speaker 3: ethical questions than like, you know, what does causality even mean?
Speaker 2: Well, I think you can your finger on it, because
Speaker 2: anytime you get bogged down in a conversation by defining
Speaker 2: your terms, that's when you know you're doing philosophy.
Speaker 3: Ah, there we go. All right, Well, we spend a
Speaker 3: glorious amount of time talking about how to define terms today,
Speaker 3: and we've got Sean Carroll to help us do that,
Speaker 3: and I love all of the stories that he tells.
Speaker 3: But before we jump into our interview with Sean, we
Speaker 3: should hear what our audience thinks about what it means
Speaker 3: to be local and causal.
Speaker 2: That's right, as usual, I went out there to our
Speaker 2: group of volunteers to see what they thought about these
Speaker 2: fundamental concepts in physics and philosophy. So think about it
Speaker 2: for a moment before you hear these answers. Do you
Speaker 2: think physics has to be local and causal. Here's what
Speaker 2: our listeners had to say.
Speaker 5: Physics used to be local to me years ago when
Speaker 5: I dated a woman whose father was a physicist. Splash, Yes,
Speaker 5: chemist at Bell Labs. But it's not anymore.
Speaker 2: Observations and experiments at much larger scale, much smaller scales
Speaker 2: seem to show that both of those concepts break down
Speaker 2: in the right circumstances.
Speaker 1: Most physicists assume causality.
Speaker 6: I don't think physics have to be local, but I
Speaker 6: think they have to be caucal to have causality.
Speaker 7: I think classical physics is local and causal, but I
Speaker 7: think quantum mechanics, with its spontaneous random activity and its
Speaker 7: ability to have spooky action at a distance, breaks that.
Speaker 4: A little bit.
Speaker 6: Physics has to be local in causal, at least in
Speaker 6: our quarter of the universe. Otherwise Einstein's spooky action would
Speaker 6: have your lamp turned on before you hit the switch,
Speaker 6: Newton would drop his apple in reverse, and all hell
Speaker 6: would have broken loose yesterday.
Speaker 4: I would think physics has to be local in order
Speaker 4: to be testimal, so that the results are always predictable.
Speaker 4: But I'm not sure what causal means. Maybe cause and effect.
Speaker 7: I think It's really interesting to think of physics as
Speaker 7: not being local, because the implications would kind of crazy,
Speaker 7: and maybe it would explain some of the stuff that
Speaker 7: we don't really understand yet.
Speaker 6: How about it has to be at least as local
Speaker 6: as gravity and at least as causal as quantum decay.
Speaker 8: What an interesting question? Does physics have to be local
Speaker 8: and or casual? Well, if it's a dating app I
Speaker 8: was supposed to be local, and because I had a
Speaker 8: casual relationship with physics in high school, I really don't
Speaker 8: get the question. But I would say, isn't physics universal
Speaker 8: and cosmological?
Speaker 6: Maybe things change based on locality and conditions.
Speaker 7: I say, yes, physics has to be local and clusal.
Speaker 2: Love these answers both insightful and hilarious, especially the person
Speaker 2: who misinterpreted causal to be casual.
Speaker 3: Are you sure you spelled it right in your email, Daniel.
Speaker 1: I am not sure. Maybe that was the cause.
Speaker 3: Of Oh yeah, See most things in my world there's
Speaker 3: a cause and effect relationship and there's no going back
Speaker 3: in time.
Speaker 2: Well, you know, this really is a fundamental issue in philosophy.
Speaker 2: We are just discussing on the discord this morning, Like
Speaker 2: does the universe have to make sense? Does there have
Speaker 2: to be an explanation for everything? I think as humans,
Speaker 2: we are curious and we want to know answers to
Speaker 2: questions about the universe because we assume that there are
Speaker 2: answers right, that there is a thing that is happening
Speaker 2: and we can figure it out somehow. And sometimes these
Speaker 2: discussions of like locality and causality tell me that the
Speaker 2: universe could be very, very different from the way that
Speaker 2: we assume that it is, and in a way that
Speaker 2: might never make sense to us.
Speaker 3: And you know, the more we learn about quantum mechanics,
Speaker 3: the more the more it breaks my brain, to be honest,
Speaker 3: but the more yeah interesting questions, I realize that there
Speaker 3: are left to ask like questions about locality and causality
Speaker 3: at the quantum mechanic level. That is what I will
Speaker 3: be thinking about tonight when I'm trying to fall asleep
Speaker 3: and I'm not sure if it's going to keep me
Speaker 3: up or make me fall asleep more quickly. So we'll see.
Speaker 2: And to dig deep into these topics, we invited an
Speaker 2: expert in physics and philosophy on the show and a
Speaker 2: friend of the podcast, Sean Carroll, who's not afraid to
Speaker 2: get bogged down defining terms.
Speaker 3: Yeah, things got heated between you two at a couple points,
Speaker 3: so let's jump in.
Speaker 1: All right, it's my pleasure to welcome to the podcast.
Speaker 1: Shawn Carroll Sean is a.
Speaker 2: Theoretical physicist who's done impouring work on the foundations of
Speaker 2: quantum mechanics, cosmology, and the arrow of time. He holds
Speaker 2: a joint appointment between physics and philosophy at Johns Hopkins.
Speaker 2: He's also a prolific science communicator, the host of the
Speaker 2: mind ski podcast, which I hardly recommend for its impressively
Speaker 2: deep dives, and author several books such as The Biggest
Speaker 2: Ideas in the Universe. Shawn, Welcome to the podcast.
Speaker 4: Thanks very much for having me.
Speaker 9: This is the first time I have been on a
Speaker 9: podcast hosted by two previous guests of my podcast, So
Speaker 9: I like how we are closing the triangle.
Speaker 3: This is exciting.
Speaker 2: We are accelerating towards the podcast singularity. Well, speaking of Singularity,
Speaker 2: today we're going to die really deep on something that
Speaker 2: I've always wanted to understand better in physics, and I
Speaker 2: can't imagine a better person to ask hard questions about
Speaker 2: issues on the boundary of philosophy in physics. I mean,
Speaker 2: I know a lot of people who are physicists to
Speaker 2: interest in philosophy. I know a lot of philosophers who
Speaker 2: do some physics as well, But I don't think I
Speaker 2: know anybody else who literally has an appointment in physics
Speaker 2: and in philosophy. So congratulations on straddling that barrier.
Speaker 4: Thanks.
Speaker 9: So it's not easy to make it happen, you know,
Speaker 9: as you know academia, we love our little silos, and
Speaker 9: I mean there's plenty of people in universities who are
Speaker 9: cross appointed between departments, but a humanities and a science
Speaker 9: thing getting together is really hard to pull off.
Speaker 3: Yeah, and really awesome.
Speaker 9: I think it's awesome. I'm having a good time, so
Speaker 9: you know, it makes me feel special.
Speaker 2: Well, I don't have a joint appointment philosophy. I do
Speaker 2: have a courtesy appointment in the philosophy department, which is
Speaker 2: just because I showed up to enough philosophy seminars to
Speaker 2: ask awkward questions that they were like.
Speaker 9: Who are you?
Speaker 1: And then they're like, oh, do you want to courtesy appointment?
Speaker 1: It gives you nothing. That's very yeah, exactly.
Speaker 3: It's like they're encouraging you to keep coming back though.
Speaker 2: That's nice, Yeah, exactly, yeah, yeah, although I did learn
Speaker 2: there's a big difference between the two fields. And physics seminars,
Speaker 2: it's totally normal to interrupt with questions. You don't understand something,
Speaker 2: raise your hands, speak up, start a discussion. If I
Speaker 2: give a physics seminar, I feel like it's a failure
Speaker 2: if nobody's interrupted to discuss something. First time I asked
Speaker 2: a question in the middle of a philosophy seminar, everybody
Speaker 2: in the room turned to me with horror. So it's
Speaker 2: like objecting in the middle of a wedding or something.
Speaker 1: You know, like hold your question to the end, sir.
Speaker 9: But then also at a philosophy colloquium, you know, often
Speaker 9: they will let the speaker talk for an hour, take
Speaker 9: a five minute break, and then come back for an
Speaker 9: hour of questions, which physicists would never do. Physicists be like,
Speaker 9: what you expected us to listen to? What was happening
Speaker 9: into the seminar? What's going on here?
Speaker 2: All right, Well, let's dive into the topic for today.
Speaker 2: We're talking about locality and causality, and these of course
Speaker 2: are intermingled, but we're going to take them one at
Speaker 2: a time if we can. So let's start with locality, Sean,
Speaker 2: how do you interpret the concept of locality? What does
Speaker 2: locality mean in physics? It doesn't mean like, get your
Speaker 2: donuts from the store around the corner.
Speaker 9: It kind of does. I mean, it's pretty close to that.
Speaker 9: It's the idea that the donuts aren't that far away,
Speaker 9: the donuts that you're actually going to want. You know,
Speaker 9: when I get donuts, I'm more likely to go to
Speaker 9: the place a couple blocks away than to the place
Speaker 9: three thousand miles away. And fundamentally that's because of locality.
Speaker 4: You know.
Speaker 9: Locality comes in different ways in different stretches of physics.
Speaker 9: But the basic idea is that there's this thing called space,
Speaker 9: and indeed we can promote it to space time and
Speaker 9: we can talk about that too. But there are places
Speaker 9: where we're located in the universe. And that kind of sounds,
Speaker 9: you know, obvious. So yes, there are places where we're
Speaker 9: located in the universe, but it's not so obvious. It's
Speaker 9: a very strong claim that what the universe is made
Speaker 9: out of is space and things inside of space. Right,
Speaker 9: Like I have a location, you have a location. This
Speaker 9: electron has a location, et cetera. And then furthermore that
Speaker 9: when these things bump into each other. This sort of
Speaker 9: the basic ideal locality is there is space and things
Speaker 9: in it. The next level ideal locality is that when
Speaker 9: different things interact, they do so at the same point
Speaker 9: in space time, or at least at neighboring points. And
Speaker 9: you might say, well, wait a minute, Like the Sun
Speaker 9: exerts a gravitational field on the Earth, even though it's
Speaker 9: very far away, but there is a field in between
Speaker 9: the Sun and the Earth. And it's more like the
Speaker 9: Sun effects it's gravitational field right at the Sun, and
Speaker 9: that affects the gravitational field right next to that. And
Speaker 9: you work your way up to what's going on here
Speaker 9: on Earth.
Speaker 2: But let me back you up because you said something
Speaker 2: which already blew my mind, Yeah, which is that it's
Speaker 2: a strong claim essentially to say that locations exist before
Speaker 2: we get to locality requirements, that things have to interact
Speaker 2: at the same location. You're saying, it's a big idea
Speaker 2: that there is space and there are locations, right, And
Speaker 2: if that's a strong claim, like, what's the opposite, Like,
Speaker 2: are you suggesting it's possible to have a universe without
Speaker 2: locations or.
Speaker 3: A physicists just making things complicated.
Speaker 7: No.
Speaker 9: In fact, what I was just about to say is
Speaker 9: the thing about that version of locality I just said
Speaker 9: that the world is made of things located in space,
Speaker 9: is that it's false. It is clearly not true, because
Speaker 9: there's this thing called quantum mechanics, and quantum mechanics says
Speaker 9: that's not what the world is made out of. In
Speaker 9: again various different levels of precision. Even if you just
Speaker 9: have one electron, there's a wave function for the electron,
Speaker 9: and that wave function has some profile throughout space, so
Speaker 9: there's no such thing as the point at which the
Speaker 9: electron is located. But you might say, like, okay, but fine,
Speaker 9: there is something called the value of the electrons wave
Speaker 9: function at every point in space. It's kind of like
Speaker 9: the value of the electric field or the gravitational field.
Speaker 9: Is still a kind of locality, which is fine until
Speaker 9: you have two electrons. When you have two electrons, now
Speaker 9: there's not the wave function of electron one and the
Speaker 9: wave function of electron two. There's the wave function quantum
Speaker 9: mechanically for the system of both electrons at once, and
Speaker 9: that's what the world is. And that's not things located
Speaker 9: in space. It's something much weirder than that. And so
Speaker 9: quantum mechanics, and I'm sure we'll get into it, but
Speaker 9: quantum mechanics just makes the world look really not local
Speaker 9: at all. And then the question I would argue is
Speaker 9: why does it kind of look local?
Speaker 4: Right?
Speaker 9: You know, why do we get along so well thinking
Speaker 9: that the world looks local if quantum mechanics is trying
Speaker 9: to tell us something different?
Speaker 3: Does this question about what local means? You know, does
Speaker 3: it not make sense at the quantum level, but when
Speaker 3: you go past the quantum level, it totally makes sense.
Speaker 1: Yes.
Speaker 9: But I will just like be I got to be
Speaker 9: a stickler in this whole conversation, right because where this
Speaker 9: is one of those things where we think we know
Speaker 9: what the words mean, and we're digging deeply into what
Speaker 9: they mean, and so we can't be beholden to our
Speaker 9: folk wisdom about what these words mean. So when you say,
Speaker 9: like the quantum level and not the quantum level, I
Speaker 9: just want to remind everyone everything is the quantum level.
Speaker 9: There's no non quantum level. The world is quantum. It's
Speaker 9: not like you get quantum when you look at things
Speaker 9: that are very small it's the eppisode way around. You
Speaker 9: get classical when you look at things that are very big,
Speaker 9: So classical mechanics, allah, Isaac Newton, et cetera becomes a
Speaker 9: good approximation when things are big and ponderous and macroscopic
Speaker 9: and so forth. And that's the world in which, yes,
Speaker 9: you're completely right. The world looks in the classical limit
Speaker 9: as if it's made of objects with locations bumping into
Speaker 9: other objects when they are at the same location.
Speaker 2: Okay, and before we get quantum, like Isaac Newton's theory
Speaker 2: of gravity's already non local right, like.
Speaker 9: We already got quantum, Daniel, it is too late. You've
Speaker 9: been quantum this whole time. Why are you listening?
Speaker 2: Yes, and I acknowledge that Newton is made of quantum objects. Yeah,
Speaker 2: in that sense, he is quantum, but he didn't know
Speaker 2: about quantum. And when he was developing his theory of gravity,
Speaker 2: he invented a concept which had instantaneous communication across space
Speaker 2: and time. And so if people think about non localities,
Speaker 2: this new fangled thing that emerge from quantum mechanics, isn't
Speaker 2: it sort of the old fangle thing that we sort
Speaker 2: of accepted for a while and then gave up.
Speaker 9: And now we're returning to we had to be very
Speaker 9: very careful. Once again, Sorry for being so careful, but
Speaker 9: please be careful. There are once again two different levels
Speaker 9: of locality that we have to distinguish between. One is
Speaker 9: just what I said, like, the equations of physics are local.
Speaker 9: Means that you write down the things the world is
Speaker 9: made of, and the whole equation is a function of position. Right,
Speaker 9: so in Newtonian gravity, you're right, that's not quite true.
Speaker 9: Like when Isaac Newton literally wrote down the inverse square
Speaker 9: law for gravity, the rule that says that the gravitational
Speaker 9: force is weaker when you're further away, stronger when you're
Speaker 9: close by a factor of one over the distance squared.
Speaker 9: And he worried that this seemed non local, that here's
Speaker 9: the Earth. The Earth is being pulled on by the
Speaker 9: Sun and the Moon and everything in the universe instantaneously.
Speaker 9: Because he's Isac Newton, he doesn't know about relativity. It
Speaker 9: doesn't know about special relativity anyway. So there is absolute space,
Speaker 9: absolute time. And Newton in the principia said like, yeah,
Speaker 9: this bothers me, the fact that somehow the information about
Speaker 9: the gravitational field of everything in the universe is conveyed
Speaker 9: to the Earth immediately, and he literally said, I'm going
Speaker 9: to leave this for future generations to sort out. I
Speaker 9: don't like it. It bugs me. I'm not smart enough.
Speaker 9: I'mder Isaac Newton. You know, eventually we will figure it out. Now,
Speaker 9: there's a sort of little known thing that happened, but
Speaker 9: I think is really crucial. In a circa eighteen hundred,
Speaker 9: Pierre Simone Laplace solved that problem. And no one ever
Speaker 9: gives them credit for this, but Laplace pointed out that
Speaker 9: you can write down Newtonian gravity as a field theory.
Speaker 9: He invented the idea of the gravitational potential. And by
Speaker 9: a field theory, we just mean rather than just saying
Speaker 9: there's a force acting on the Earth, and to know
Speaker 9: what the force is, you have to know what everything
Speaker 9: in the universe is doing. He says, there is something
Speaker 9: called the gravitational potential field, and it's a field, so
Speaker 9: it has a value at every point in space, and
Speaker 9: the equation that that field obeys is entirely local. What
Speaker 9: is happening through the field right here at some point
Speaker 9: only depends on what's happening at right next door points.
Speaker 9: And it's exactly like we said at the beginning, that
Speaker 9: the Sun creates a dimple in the gravitational field at
Speaker 9: where thus is, and that pulls on the field next
Speaker 9: to it, and that pulls on the field next to it,
Speaker 9: and it works its way out to the Earth. So,
Speaker 9: in that sense, because there is a local field theory
Speaker 9: description of Newtonian gravity, Lutonian gravity is entirely local.
Speaker 1: But is it still instantaneous?
Speaker 9: Well, you've skipped ahead to the world of relativity, where
Speaker 9: there's a speed limit. So when relativity comes along, which
Speaker 9: is long after either Newton or laplace, now we have
Speaker 9: an idea that even if the laws of physics are
Speaker 9: local in space time, which they are, like Einstein's equations
Speaker 9: and Maxwell's equations and whatever, still, if something happens at
Speaker 9: a particular point in space time, the effects of that
Speaker 9: thing only ripple out slower than or at the speed
Speaker 9: of light. Right, You do not affect things instantaneously far away.
Speaker 9: And what that means is that we can have a better, stronger,
Speaker 9: more satisfying version of locality, which is that not only
Speaker 9: do the equations simply exist at every point in space
Speaker 9: or every point in space time, but that you're not
Speaker 9: being affected by things infinitely far away instantaneously. So we
Speaker 9: have ex post facto retrofitted our notion of locality to
Speaker 9: demand not instantaneous communication between two different points of space.
Speaker 9: For Newton, that would have been fine. For in the
Speaker 9: post Einstein world, that's no longer okay, because the speed
Speaker 9: of light is a fundamental limit.
Speaker 3: Okay, So the biologist who lives in the world where
Speaker 3: locality works, fine, thank you very much. Is so if
Speaker 3: I can sort of summarize what's happening. So locality is
Speaker 3: a problem because at the quantum level it doesn't really
Speaker 3: work and you scale up. But it sounds like you
Speaker 3: were just saying that locality is fine when you're talking
Speaker 3: about things like the Sun impacting the Earth because you've
Speaker 3: got a field and you're connected every point along the way,
Speaker 3: And so is our conversation then mostly about the quantum level.
Speaker 9: Now am I following, Well, there's lots of conversations. Okay,
Speaker 9: you know, there's definitely that. The distinction we were just
Speaker 9: drawing is between pre relativity classical physics and post relativity
Speaker 9: classical physics, where we have glommed onto the notion of locality.
Speaker 9: The idea that signals don't travel faster than light, so
Speaker 9: there cannot be any instantaneous communication across distances. You know,
Speaker 9: in Isaac Newton's world, I could send a signal to
Speaker 9: the Andromeda Galaxy instantaneously by taking a planet and shaking
Speaker 9: it a little bit right. Its gravitational force in principle,
Speaker 9: although not in practice, would change instantaneously in the Andromeda Galaxy.
Speaker 9: And so is it local, You know, kind of it's
Speaker 9: fading away, but still strictly speaking, it's hard to wrap
Speaker 9: your brain around. But now, in Einstein's universe, if you
Speaker 9: shake a planet, it's going to take you a million
Speaker 9: light years for that signal to get to the Andromeda Galaxy.
Speaker 9: But still that's all within the limit that we called
Speaker 9: the classical limit of quantum mechanics. And so one place
Speaker 9: where our notions of locality are challenged and need to
Speaker 9: be updated is in the quantum realm. But by the way,
Speaker 9: another place that their challenge need to be updated is
Speaker 9: in things like biology. Oh no, yes, because you know
Speaker 9: in biology what happens is most of the biological organisms
Speaker 9: that you and I know and love are moving very
Speaker 9: slow compared to the speed of light. Yeap so even
Speaker 9: though they're big and they're in the classical world and
Speaker 9: they bump into each other, when things do happen, they
Speaker 9: happen essentially instantaneously, right. The signals can get to, you know,
Speaker 9: across the organism very very fast, and so it can
Speaker 9: often be useful at that higher emergent level of biology
Speaker 9: to have both local things like here's a little cell
Speaker 9: or there's a little bacterium or whatever, but also global things, right,
Speaker 9: global variables. What is the pH of your solution that
Speaker 9: you're in, or you know, what is the gradient of nutrients?
Speaker 9: Or is the human being happy or sad? Like, that's
Speaker 9: not a local thing. Where's the happiness, where's the sadness?
Speaker 4: Right?
Speaker 9: So, both at the microscopic quantum level and at the
Speaker 9: emergent non physics y higher levels, the strict notions of
Speaker 9: locality that we have in classical relativistic physics become a
Speaker 9: little shaky.
Speaker 2: All right, So let's trace it historically. We start with
Speaker 2: these concepts where you can have instantaneous interaction across space
Speaker 2: and time. Then we get special relativity, which gives us
Speaker 2: a cool concept of locality. You can only be influenced
Speaker 2: by things in your past like cone and influence things
Speaker 2: in your future like cone, because signals take time to propagate,
Speaker 2: which is still a cool concept of locality. It means that,
Speaker 2: like very much, something interacts with something else, which interacts
Speaker 2: with something else, so you have to have like a
Speaker 2: chain of interactions or you know, wiggle or propagation of
Speaker 2: this interaction. But what about general relativity? Is general relativity
Speaker 2: local in the same way that special relativity is.
Speaker 9: General relativity is almost as local as special relativity is,
Speaker 9: so special relativity came along in nineteen oh five. This
Speaker 9: is Einstein's idea that you can reconcile the non existence
Speaker 9: of any preferred frame of reference in the universe. There's
Speaker 9: no ether or anything like that, with the fact that
Speaker 9: everyone thinks that the speed of light is the same.
Speaker 9: All you have to do, says Einstein, is give up
Speaker 9: your conventional notions of what space is and what time
Speaker 9: is and marry them together. Yeah, that's why he's Einstein,
Speaker 9: you know, marry them together to make space time. And
Speaker 9: then ten years later in general relativity he says, you
Speaker 9: know what I forgot to tell you, but space time.
Speaker 9: This arena in which the game of physics is played
Speaker 9: has a life of its own, it's dynamical, it has
Speaker 9: a geometry, it can be curved, it can respond to
Speaker 9: matter and energy and their motion in the universe. They're
Speaker 9: a player, They're not just the arena in which the
Speaker 9: game is played. So that makes things much trickier when
Speaker 9: it comes to saying, you know, what depends on what,
Speaker 9: like the future of the universe, the future of the
Speaker 9: curvature of the universe, et cetera. In general relativity, in principle,
Speaker 9: this is a deterministic consequence of what's happening in the
Speaker 9: universe right now. But there can be limitations on that.
Speaker 9: There can be weird global structures in the universe. You know,
Speaker 9: there can be closed time like curves where the timelike
Speaker 9: trajectories that a person can travel on in a rocket
Speaker 9: ship can loop back on themselves. Space can be curled
Speaker 9: up on itself. Space can be a tourist. There can
Speaker 9: be extra dimensions of space that are very tiny, and
Speaker 9: things like that. So the fundamental equations of general relativity
Speaker 9: are still one hundred percent local, but there are global
Speaker 9: consequences of those equations that get things a little more subtle.
Speaker 2: Well, what about concepts like work? I mean, if we're
Speaker 2: talking about locality. General relativity gives us more flexibility and
Speaker 2: what locality means because it changes which points of space
Speaker 2: are near each other. Right, So in principle, you open
Speaker 2: a wormhole between our galaxy and Drameda. Now some part
Speaker 2: of Andrameda is local. Is that concept of locality so
Speaker 2: to preserved through the wormhole.
Speaker 9: There is absolutely a concept of locality that is preserved
Speaker 9: even in the presence of wormholes. Like if you say,
Speaker 9: if I take a limit where I look at creatures
Speaker 9: or points of light or particles or whatever that are
Speaker 9: small compared to the curvature and the topology of space time,
Speaker 9: everything is local. All of the equations are local, all
Speaker 9: the dynamics are local. But you're right, you can imagine.
Speaker 9: General relativity gives you this freedom to imagine. Okay, I'm
Speaker 9: going to make a shortcut in space time. I'm going
Speaker 9: to construct a wormhole that attaches two different parts of
Speaker 9: space that I thought were far away. But if I
Speaker 9: go from point A to point B three the wormhole,
Speaker 9: I'm going to say, it doesn't take that long at all.
Speaker 9: They're actually much closer. And this was an idea that
Speaker 9: has been around a long time. Einstein, as usual was
Speaker 9: one of the first people to talk about wormholes. John
Speaker 9: Wheeler gave them the name. We have enough time to
Speaker 9: tell this one, very very amusing story here. It was
Speaker 9: when Carl Sagan wrote this novel Contact that wormholes became
Speaker 9: important in physics because Sagan wrote his book and he
Speaker 9: wanted to get his hero Ellie across the galaxy very
Speaker 9: very quickly. And Sagan, you know, was a great scientist,
Speaker 9: but he was a planetary scientist. He was not a
Speaker 9: fundamental theoretical physicist. He knows general relativity very well, so
Speaker 9: he had her fall into a black hole in the
Speaker 9: original draft of the novel. The good news is that
Speaker 9: Carl Sagan was close friends with Kip Thorne, who does
Speaker 9: know his general relativity very well, and had him read
Speaker 9: the draft and Kip said, you can't have her fall
Speaker 9: into a black hole. She'll get spaghettified and smushed, and
Speaker 9: that's not what you want. What you want is for
Speaker 9: her to fall into a wormhole and that will get
Speaker 9: her across the galaxy in a very short period of time.
Speaker 9: And so that's what happens in the novel and in
Speaker 9: the movie. But then Kip was thinking about it, and
Speaker 9: you know, he thought about it, and he said, look,
Speaker 9: you know, usually we say it's bad if you can
Speaker 9: travel faster than the speed of light, because just change
Speaker 9: your reference frame and now it looks like you're traveling
Speaker 9: backward in time. That's one of the reasons why conventional
Speaker 9: physics we say you probably can't travel faster than the
Speaker 9: speed of light. It enables time travel. And he thought
Speaker 9: about it and his students and post talks and they
Speaker 9: chatted about it, and they realized that's because you can
Speaker 9: travel backward in time if you have a wormhole. And
Speaker 9: he wrote a series of papers with his collaborators on
Speaker 9: building time machines using wormholes. So it's a perfect example
Speaker 9: of how locally everything looks local in a small north
Speaker 9: region of space time everything looks local, but globally in
Speaker 9: the presence of that wormhole, your conventional notions of locality
Speaker 9: or all.
Speaker 2: That stuff, Joe relativity is mine.
Speaker 1: Benning.
Speaker 3: Well, I hope we are acting on you at a
Speaker 3: distance in your head, having fun at whatever location you
Speaker 3: find yourself in, and when we get back we will
Speaker 3: dig more into locality.
Speaker 1: All right.
Speaker 2: We are talking to Sean Carroll by the concepts of
Speaker 2: locality and causality, and I think it's time to dig
Speaker 2: into the thing we've been dancing around, which is locality
Speaker 2: in quantum mechanics. So we've been talking about how you
Speaker 2: have to be the same location to have interactions. But
Speaker 2: now we have this concept in quantum mechanics of extended states.
Speaker 2: You can have particles that interact and that are entangled
Speaker 2: with each other, so their fates are connected, and yet
Speaker 2: they're moving apart from each other. And we know from
Speaker 2: Bell's experiments that if you interact with one, it can
Speaker 2: collapse the wave function of the other. How do we
Speaker 2: need gel locality and quantum mechanics or does quantum mechanics
Speaker 2: require us to give up on locality? Is the universe
Speaker 2: fundamentally non local?
Speaker 9: So the answer you're going to get to this question
Speaker 9: is the universe fundamentally non local because the quantum mechanics
Speaker 9: will be completely different. If you ask a philosopher and
Speaker 9: a physicist and they don't even they don't even disagree
Speaker 9: with each other, they're just caring about different things.
Speaker 4: Okay.
Speaker 9: So, and this is the fundamental weirdness of quantum mechanics
Speaker 9: is that when we tell you the rules for quantum mechanics,
Speaker 9: it's kind of cludgy and awkward.
Speaker 4: Right.
Speaker 9: In classical mechanics, we say, here's a thing like a
Speaker 9: planet or an electric field or something like that, and
Speaker 9: here are the equations that govern how that thing behaves
Speaker 9: at equals M for Newton's laws or Maxwell's equations or whatever.
Speaker 4: That's it.
Speaker 9: That's your theory, that's all you need. In quantum mechanics,
Speaker 9: we say, here's a thing. We call the thing the
Speaker 9: wave function of an electron or of a field or whatever.
Speaker 9: Wave functions are the things. Here's an equation. Just like
Speaker 9: classical mechanics, the equation of this case is the Shroding equation,
Speaker 9: but you can rewrite it in different forms finement path
Speaker 9: integrales or another way of doing it, et cetera. But
Speaker 9: then we don't stop there. Right, Like classically we would
Speaker 9: have stopped. In quantum mechanics, we say, oh, but there's
Speaker 9: more rules. And the rules have to do with what
Speaker 9: happens when you measure or observe the system. Right, you
Speaker 9: can measure certain quantities and you can't predict the outcome
Speaker 9: you're going to get. You can predict the probability of
Speaker 9: getting certain outcomes, and there are rules for how that happens.
Speaker 9: And when you make the measurement. The state the wave
Speaker 9: function changes dramatically in something we call the collapse of
Speaker 9: the wave function. So there's basically two sets of rules
Speaker 9: that apply inner different circumstances. The set of rules, which,
Speaker 9: if you want to be technical and impress your friends
Speaker 9: at parties, are called unitary evolution. That's the part where
Speaker 9: you're just obeying the Shortener equation and not being observed.
Speaker 9: And then there's the measurement process, where you actually measure something.
Speaker 9: And so the measurement process in quantum mechanics, well, let
Speaker 9: me get it exactly right. The state of things in
Speaker 9: quantum mechanics, the wave function is just manifestly nonlocal. It
Speaker 9: just isn't local. It's not a thing with a value
Speaker 9: at every point in space and time. That's not what
Speaker 9: it is, and everyone knows that's not what it is.
Speaker 9: But what is the importance of that. Well, on the
Speaker 9: unitary evolution side, the laws of physics, the Shortener equation
Speaker 9: or what have you still look perfectly local as far
Speaker 9: as we can tell. Indeed, the whole discipline of quantum
Speaker 9: field theory is based on the idea that the thing
Speaker 9: that you're quantizing to make your theory are fields. That
Speaker 9: have values in space and time and only interact with
Speaker 9: each other at the points in space and time where
Speaker 9: they overlap with each other. So the particle physicists, bless
Speaker 9: their hearts, Daniel, that's what they care about. They care
Speaker 9: about that unitary evolution part and they know that at
Speaker 9: the end of the day they're going to measure and
Speaker 9: the wave functions going to collapse. But who cares. They
Speaker 9: have a lot of work to do with Fieman diagrams
Speaker 9: and things like that, just calculating the unitary.
Speaker 2: Evolution, and we spend a lot of money getting those
Speaker 2: particles to the same location in space so that they
Speaker 2: do interact with each other.
Speaker 9: There's a picture right behind you on your zoom background
Speaker 9: of exactly that happening. Yes, getting them to the same
Speaker 9: point really matters. So the physicists are like, locality is
Speaker 9: crucially important. What are you talking about? It's like the
Speaker 9: most important thing. It's what makes quantum field theory go.
Speaker 9: And the philosophers will say, like, who cares about all
Speaker 9: your integrals and your Fineman diagrams and whatever. I care
Speaker 9: about what the measurement process is about and what the
Speaker 9: implications of that are, because that's the part of quantum
Speaker 9: mechanics that is not very well understood and needs deeper explication.
Speaker 9: And guess what, it's wildly non local. That is the
Speaker 9: implication of the EPR thought experiment from Einstein, Podolski, and Rosen,
Speaker 9: who say that particles can be entangled and the measurement
Speaker 9: outcome you get on one particle can instantaneously affect the
Speaker 9: allowed measurement outcomes on another particle. And then John Bell
Speaker 9: comes along and makes that very rigorous. And again, if
Speaker 9: I have a couple of minutes to tell an amusing
Speaker 9: story here, it was David Boehm, who was a young
Speaker 9: assistant professor at Princeton the nineteen fifties, who wrote a
Speaker 9: textbook on quantum mechanics, and he says in the textbook
Speaker 9: he quotes a theorem on John von Neumann, famous physicist
Speaker 9: who says you can't reproduce the predictions of quantum mechanics
Speaker 9: used in what are called hidden variables, saying that there's
Speaker 9: a wave function but also extra variables that are being
Speaker 9: pushed around. And Einstein reads Boehm's book and calls Boem
Speaker 9: into his office right because he's also at the Instruhravan
Speaker 9: study right there in Princeton and says this is wrong.
Speaker 9: Like I speak German. Von Neuman's book was only in German,
Speaker 9: and so like then, the Americans knew what was in
Speaker 9: his book. They just quoted it because they thought he
Speaker 9: was a genius. And Einstein said this, he made a mistake.
Speaker 9: He doesn't cover a lot of the important possibilities that
Speaker 9: you might want to consider here. So you have not shown,
Speaker 9: or you're not even given a good argument that you
Speaker 9: can't have hidden variable theories. So he was inspired by
Speaker 9: this and he goes off and invents a hidden variable theory.
Speaker 9: The only way to make it work, though, is to
Speaker 9: make it non local, so the dynamics of that theory
Speaker 9: are explicitly non local. And then everyone ignores him, because
Speaker 9: everyone ignores the foundations of quantum mechanics. By this point
Speaker 9: in time, it's the fifties, and then in the sixties
Speaker 9: it's discovered by John Bell, who reads Boehm's papers, notices
Speaker 9: that it's non local and wonders to himself, like, is
Speaker 9: there a way of doing this hidden variable thing without
Speaker 9: being non local? And he basically proves that the answer
Speaker 9: is no. You cannot reproduce the predictions of quantum mechanics
Speaker 9: without being non local, and he hid that from his friends.
Speaker 9: He was working at CERN at the time. He didn't
Speaker 9: tell anybody because it was considered disreputable. But a couple
Speaker 9: of years ago people won the Nobel Prize for testing
Speaker 9: his predictions and showing that they're correct.
Speaker 3: So it's non local. But we discussed earlier that these
Speaker 3: interactions can't happen faster than the speed of light, which
Speaker 3: Daniel has also we've talked about on the show right,
Speaker 3: that they can't communicate or whatever it is that they're
Speaker 3: doing faster than the speed of light. So what is
Speaker 3: happening then if it's not local and it's not traveling
Speaker 3: faster than the speed of.
Speaker 9: Light, Daniel, do you know what's happening? Does anyone know
Speaker 9: what's happening? Like, if you know what's happening, you win,
Speaker 9: You save quantum mechanics. Quantachanics has been around for one
Speaker 9: hundred years. Just a couple of weeks ago, Nature the
Speaker 9: Journal came out with a poll that they did of
Speaker 9: working physicists who care about quantum mechanics, showing there's no
Speaker 9: consensus whatsoever about what's going on at the deep levels. So, Kelly,
Speaker 9: you're just you're right, Like, I mean, you didn't. You're
Speaker 9: not right because you asked a question. But you're you know,
Speaker 9: charmingly adorable about thinking that we have the answer to
Speaker 9: that question, because this is exactly what we don't have
Speaker 9: the answer to. And and most working physicists, by the way,
Speaker 9: just you know, use the strategy called denial to deal
Speaker 9: with this, like they just say, just it works, okay, Like,
Speaker 9: don't bug me about this. I can make the predictions,
Speaker 9: the predictions come true. But above Einstein, that's why he
Speaker 9: wrote the CPR paper back in nineteen thirty five. You know,
Speaker 9: he basically it's very unfair to Einstein when I'm about
Speaker 9: to say because he had a much more sophisticated argument.
Speaker 9: But basically he points this out. He says, I can
Speaker 9: get two particles. They're entangled. They're very very far away.
Speaker 9: I observe one, and apparently the formalism is telling me
Speaker 9: that instantly changes the state of the other particle very
Speaker 9: far away. I'm Einstein, I know that's not possible. You
Speaker 9: can't change things instantaneously very far away. What's up with that?
Speaker 9: And we still know what's up with that?
Speaker 2: And I read that bell, you know, he interpreted his
Speaker 2: thought experiments in the later actual experiments to mean, as
Speaker 2: you say that there is no local hidden variable, right,
Speaker 2: the particles are not carrying with them some details created
Speaker 2: at the moment of their entanglement which actually determined the outcome,
Speaker 2: But that there is this loophole that you could have
Speaker 2: global hidden variables. So I think it's widely misunderstood that
Speaker 2: Bell's mus tell you there's no hidden variables. It just
Speaker 2: tells you there's no local hidden variables. And as you say,
Speaker 2: a global theory is possible. But tell me about the
Speaker 2: different interpretations of quantum mechanics. I mean, Kelly asks like
Speaker 2: the question what is real? What is happening? And now
Speaker 2: essentially we feel like there is no local realism. But
Speaker 2: do the different interpretations of quantum mechanics tell different stories
Speaker 2: about how to accommodate this? And I know we have
Speaker 2: like Boemian mechanics where you have a pilot wave which
Speaker 2: is explicitly non locally. You have a global theory, as
Speaker 2: you say, But with the Copenhagen interpretation, is that a
Speaker 2: non local theory or does Copenhagen essentially shrug away this
Speaker 2: question the way it does most of the important.
Speaker 9: Issues yeah, I mean, look, it really is fascinating. I
Speaker 9: do encourage anyone with a little bit of quantum mechanics
Speaker 9: knowledge to actually read the original EPR paper Einstein, Podolski,
Speaker 9: and Rosen, because you know, Daniel can back me up
Speaker 9: on this. But we physicist don't read the original papers
Speaker 9: like that's you know, we have a textbook and that
Speaker 9: tells us what's going on. But the original papers are
Speaker 9: fascinating because they don't know the answer, right, They're struggling
Speaker 9: with figuring out what's going on. So Einstein and Podolski
Speaker 9: and Rosen, but I get the impression that the ideas
Speaker 9: were mostly from Einstein. They didn't just say, look, there
Speaker 9: is this spooky action at a distance that bugs us.
Speaker 9: They were much more careful than that. They tried their
Speaker 9: best to construct an argument that says there should be
Speaker 9: what they called local elements of reality. And I think
Speaker 9: that it was Bell who later called these things be
Speaker 9: a bles be ables in the sense of things that be,
Speaker 9: things that are things that exist.
Speaker 2: Right, philosophers, and they're creating phrases for.
Speaker 9: John Bell is a car carrying physicist. I gotta say.
Speaker 1: He's doing philosophy. Though when he invents a new meaning
Speaker 1: for the word b.
Speaker 9: He's doing philosophy, so he invents this word beable, and
Speaker 9: it's exactly what Einstein wanted to be the case. Einstein
Speaker 9: wanted it to be the fact that at every point
Speaker 9: in space time there's a fact of the matter about
Speaker 9: what is physical going on in the universe. And as
Speaker 9: we said, quantum mechanics doesn't say that. Bell wanted, you know,
Speaker 9: to really understand this locality issue. And so the way
Speaker 9: that Boem solves the problem is there are local beables,
Speaker 9: like in Boehm's theory, there are particles. When you see
Speaker 9: at the LHC the track of a particle, what Boem
Speaker 9: would say is you're not seeing the wave function. You're
Speaker 9: seeing the particle. The particles there in addition to the
Speaker 9: wave function. But the equation that the particle follows is
Speaker 9: non local. It depends on what all the other particles
Speaker 9: everywhere else are doing, which is which is really weird.
Speaker 9: And so Bell asked this question, can you come up
Speaker 9: with any theory where everything is one hundred percent local
Speaker 9: and none of the dynamics are local, none of the
Speaker 9: things are non local or non local issues. I hope
Speaker 9: I said that correctly both times and he proves the
Speaker 9: answer is no. So the different strategies for solving this
Speaker 9: just take very different points of view. In Bomi mechanics,
Speaker 9: despite the bullet there's a non local evolution rule. There
Speaker 9: are what are called objective collapse models of quantum mechanics,
Speaker 9: where the wave function just suddenly changes all over space,
Speaker 9: all at once. That's very non local in its own
Speaker 9: in everready, in quantum mechanics, in the many worlds theory,
Speaker 9: you kind of sidestep the question. One of the axioms,
Speaker 9: one of the assumptions of premises of Bell's theorem is
Speaker 9: that measurements have definite outcomes. When you measure the spin
Speaker 9: of a particle, it will either be spin up or
Speaker 9: spin down, And whatever it says is well, it's spinned
Speaker 9: up in one universe and spin down in another universe.
Speaker 9: So that's not quite what Bell had in mind. So
Speaker 9: people have huge arguments over whether or not many worlds
Speaker 9: is local or not. The answer, of courses depends on
Speaker 9: your definitions, but that is one of the reasons to
Speaker 9: preserve that kind of dynamical locality that you might like
Speaker 9: many worlds Copenhagen. I'm just I'm going to like boycott
Speaker 9: any question about the Copenhagen interpretation from now on, because
Speaker 9: it's giving it too much credit. It's not well defined,
Speaker 9: it's not a theory like many worlds. Bomian mechanics, spontaneous
Speaker 9: collapse models, these are theories. They have equations and they
Speaker 9: make predictions. Copenhagen just won't answer certain questions, which I
Speaker 9: don't think we should reward it by taking it seriously.
Speaker 3: Can we give a little more information about what the
Speaker 3: Copenhagen stuff means for the biologists in the room.
Speaker 9: Yes, yes, Copenhagen is a city in Denmark and I
Speaker 9: got that sean full of people doing quantum mechanics and
Speaker 9: it was a great time. You know, is again fascinating
Speaker 9: to read the original papers. We're here in twenty twenty five.
Speaker 9: It's the it's been dubbed the Year of Quantum because
Speaker 9: the International Year of Quantum, because exactly one hundred years
Speaker 9: ago the first papers came out by Heisenberg and Schrodinger
Speaker 9: et cetera setting up quantum mechanics, and we still understand it.
Speaker 9: But into like the ten years after nineteen ten twenty
Speaker 9: five Nils Borr and Werner, Heisenberg and Wolfgang Powley, who
Speaker 9: all were sort of either affiliated with or spent a
Speaker 9: lot of time at Bor's Institute in Copenhagen, promulgated this
Speaker 9: way of thinking about quantum mechanics. And it's exactly what
Speaker 9: I already said. It said that you have a wave
Speaker 9: function and it solves the Schortener equation when you're not
Speaker 9: looking at it, and then when you do look at it,
Speaker 9: it collapses and you get a probability. But the philosophical
Speaker 9: side of the Copenhagen interpretation is the claim that there's
Speaker 9: no such thing as what is happening when you are
Speaker 9: not looking at the quantum system. And this is very
Speaker 9: explicit in Heisenberg's papers from nineteen twenty five, and it's
Speaker 9: one of the reasons why it's very hard to understand
Speaker 9: these papers. Stephen Weinberg, who is one of the most
Speaker 9: brilliant physicists of the twentieth century, said like he tried
Speaker 9: very hard to read Heisenberg's papers and he has no
Speaker 9: idea what was going on there. But the big philosophical
Speaker 9: move was stop asking about where the electron is. There
Speaker 9: is no such thing as where the electron is. There
Speaker 9: is only where you will see it when you measure it.
Speaker 9: And that's really the fundamental ethos of the Copenhagen interpretation.
Speaker 9: And by that, by itself, that's fine, but it leaves
Speaker 9: a whole bunch of questions unanswered. That's the bad part.
Speaker 9: Number one, What is a measurement? What counts as doing
Speaker 9: a measurement? Can a video camera do a measurement? Do
Speaker 9: you have to be a conscious observer to do a measurement?
Speaker 9: What if you don't have good eyesight, does that count
Speaker 9: as a measurement? Number two, The Copenhagen interpretation says, the
Speaker 9: classical world exists and is real. You and I are
Speaker 9: not quantum things. You know, Daniel made the joke earlier
Speaker 9: about Isaac Newton being made of quantum mechanical things. Werner
Speaker 9: Heisenberg didn't think that. He thought that Isaac Newton was classical,
Speaker 9: and that the things that you look at in a
Speaker 9: microscope or quantum And there's literally an idea called the
Speaker 9: Heisenberg cut. And this is somehow in the space of
Speaker 9: all things happening in the world, there's one side of
Speaker 9: the cut where there's the quantum stuff, and the other
Speaker 9: side of the cut where it's the classical stuff. And
Speaker 9: like who invented that where does that go? Like, no
Speaker 9: one knows what is going on with any of this,
Speaker 9: and so the Copenhagen interpretation is kind of just what
Speaker 9: we teach students in our quantum mechanics courses. But it's
Speaker 9: hilariously ill defined and as a as a starting point
Speaker 9: as the kind of conjectural hypothesis that we throw out
Speaker 9: to do physics. It's great, it's amazing, it makes perfect sense.
Speaker 9: The weird thing is we've been pretending for one hundred
Speaker 9: years that it's somehow a satisfactory final answer.
Speaker 2: I think you've been slightly unfair to the Copenhagen interpretation, and.
Speaker 9: I would be much more unfair if you wanted me to,
Speaker 9: I would be much harder.
Speaker 2: And I can't believe I'm in the situation of defending it.
Speaker 2: I mean, I agree that there's a fundamental issue at
Speaker 2: the heart of it, which is that they don't define
Speaker 2: the distinction between you know, what causes a collapse and
Speaker 2: what doesn't, what's a classical object and what's a quantum object. Absolutely,
Speaker 2: and that's a fatal error. But you know, there's these
Speaker 2: other issues of like are you conscious or you know,
Speaker 2: does a human do it? Or an eyeball do it
Speaker 2: or a video camera do it. I think those are
Speaker 2: maybe side issues, but I agree at the core of it,
Speaker 2: Copenhagen is ill defined.
Speaker 3: Things are heating up, things are eating up.
Speaker 9: So I gotta wait, I gotta I gotta bump in here.
Speaker 9: You gotta interrupt, because I just gave a talk at
Speaker 9: the American Association of Physics Teachers where I was talking
Speaker 9: about the foundations of quantum mechanics, and for that talk,
Speaker 9: I made a slide in which I appealed to a
Speaker 9: th arty. So I'm going to quote some people who
Speaker 9: are much smarter than me talking about the Copenhagen interpretation.
Speaker 9: Albert Einstein says the theory is apt to beguile us
Speaker 9: into error in our search for a uniform basis for physics,
Speaker 9: because in my belief, it is an incomplete representation of
Speaker 9: real things. Erwin Schrodinger says, I don't like it, and
Speaker 9: I'm sorry I ever had anything to do with it.
Speaker 9: Hugh Everett says this is a philosophical monstrosity. And then
Speaker 9: Carl Popper, who invented false fae as the demarketse mean
Speaker 9: science and nonscience, says the Copenhagen interpretation is a mistaken
Speaker 9: and even vicious doctrine.
Speaker 1: Okay, So if you think.
Speaker 9: I'm being unfair, like the people who care about this
Speaker 9: a lot, I think are are pretty hardcore that this
Speaker 9: is not acceptable.
Speaker 1: Well, I'm glad you didn't hold back.
Speaker 2: My own personal anecdote about Copenhagen is I got to
Speaker 2: spend a year at the Boer Institute, and when I
Speaker 2: got there, they gave me an office, and I noticed
Speaker 2: that the office next door to mine was quite different
Speaker 2: in that it had a bathtub in it, and I thought,
Speaker 2: why is there a bathtub.
Speaker 1: In this office?
Speaker 9: And then that can't be good, Nothing good can happen.
Speaker 2: I learned the story that in the old days, when
Speaker 2: you had an institute, you lived at the institute the
Speaker 2: way like the president lives at the White House. And
Speaker 2: so there was an apartment. And then later, after Boor
Speaker 2: was no longer there, they're like, well, let's just turn
Speaker 2: these into offices. And so somebody got the office with
Speaker 2: the bathtub in it.
Speaker 4: Why didn't they?
Speaker 2: He had important thoughts in that tub. You know, you
Speaker 2: can't just get rid of it.
Speaker 3: Are you're gonna crawl in when you need to solve
Speaker 3: your next big NB?
Speaker 2: All right, So on that note, let's solve the next
Speaker 2: big problem. I want to talk about quantum gravity and
Speaker 2: the implications, but first let's detour two causality. We've talked
Speaker 2: about locality a lot, but let's take a break, and
Speaker 2: when we come back, we're going to talk about causality. Okay,
Speaker 2: we're back, and we're talking to physicists and philosophers. Sometimes
Speaker 2: when you measure him, he collapses into one state or
Speaker 2: the other. About causality and locality in physics, So we
Speaker 2: started the conversation about locality with the definition, and we've
Speaker 2: already touched on some of the concepts of causality, But
Speaker 2: could you give us a crisp definition for what we
Speaker 2: mean by causality in physics.
Speaker 9: I'm glad you said it in physics, because just like locality,
Speaker 9: the causality is a notion that physicists and philosophers both
Speaker 9: talk about, but they mean entirely different things. So let's
Speaker 9: first just mention like what someone who is neither would mean. Right,
Speaker 9: You know, we talk about causes and effects. If you say, like,
Speaker 9: why were you late for work? Someone might say, well,
Speaker 9: because the traffic was unusually bad, there was an accident, right,
Speaker 9: and that's a meaningful statement. There's a cause there's an accident,
Speaker 9: there is an effect that there was traffic, and that
Speaker 9: there's another cause there was traffic, and there's another fact
Speaker 9: you're late for work, And there's a chain of causes
Speaker 9: and effects that ripples throughout all of our existence. And
Speaker 9: this goes back to you know, Aristotle thinking about this
Speaker 9: kind of thing. So it's very, very common that we
Speaker 9: take that kind of word that we use in everyday
Speaker 9: language and repurpose it for some rigorous idea in physics
Speaker 9: or philosophy, et cetera. So what the physicists have done
Speaker 9: post Einstein is to notice this feature of relativity that
Speaker 9: we've already talked about that when you do something at
Speaker 9: some location, some event in space and time, the implications
Speaker 9: the effects of that doing something can only ripple forward
Speaker 9: in time, and they can only ripple forward in time
Speaker 9: slower than the speed of light. So, really physicists, by
Speaker 9: the word causality, what they usually mean is that signals
Speaker 9: travel slower than the speed of light, or at the
Speaker 9: speed of light, certainly no faster than the speed of light.
Speaker 2: So an alien shoots their death ray at us from
Speaker 2: Andromeda if they can't kill us today or tomorrow or yesterday.
Speaker 2: They can only kill us in a million years.
Speaker 9: Or so unless they shot at a million years ago, right, yes,
Speaker 9: which is not well defined in relativity. So yeah, I'm
Speaker 9: not gonna I'm worried about the aliens. So, but there's
Speaker 9: already a tension there in that physicist's way of thinking,
Speaker 9: because there's a super important feature of the everyday notion
Speaker 9: of causality, which is that the cause always happens before
Speaker 9: the effect. Right, You would not convince anyone by saying
Speaker 9: there was an accident this morning because I was going
Speaker 9: to be late for work, Right, That's just not how
Speaker 9: causes and effects work. You're late for work as there
Speaker 9: was an accident, not the other way around. But the
Speaker 9: fundamental laws of physics, whether it's relativity or quantum mechanics
Speaker 9: or anything, are time reversal invariant. Are invariant going forward
Speaker 9: and backward in time. So really, when the physicists talk
Speaker 9: about causality, they kind of mean signals propagate to the
Speaker 9: future at or slower than the speed of light. But
Speaker 9: also they get to us from the past at or
Speaker 9: slower than the speed of light. Both are equally good
Speaker 9: features of what physicists call causality and philosophers want to know. Okay,
Speaker 9: but if that's true, why in the macroscopic world of
Speaker 9: our everyday existence do we have this strong feeling that
Speaker 9: causes precede effects. And probably that has something to do
Speaker 9: with entropy in the hour of time. And it's a
Speaker 9: whole long story, all right.
Speaker 2: So in physics we have this concept that the past
Speaker 2: determines the future. Essentially, it's a statement on top of
Speaker 2: the existing laws of physics, which, as you say, are
Speaker 2: mostly invariant with respect to time, that there's a directionality
Speaker 2: to time. Is that a compact way to understand causality
Speaker 2: in physics?
Speaker 9: It might be a little bit too compact, So let
Speaker 9: me be let's just expand it out a little bit.
Speaker 9: You know, back in circa eighteen hundred, again our hero
Speaker 9: Piersimone Laplace points out this existing feature of classical mechanics.
Speaker 9: You know, Newton invented classical mechanics more or less in
Speaker 9: its modern form in the sixteen hundreds. It took a
Speaker 9: while for Laplace to realize the implication of Newton's laws,
Speaker 9: which is that information about what is happening in the
Speaker 9: universe is conserved over time. So if you live in
Speaker 9: a purely Newtonian universe, purely classical, if you know what
Speaker 9: happens at any one moment of time, if you know
Speaker 9: that perfectly, you know the position and the velocity of
Speaker 9: every single atom in the universe. Okay, then according to Laplace,
Speaker 9: the laws of physics determine everything that will happen in
Speaker 9: the future one hundred percent reliability. And it also determines
Speaker 9: everything that happens in the past, because there is no
Speaker 9: distinction between past and future in Newtonian mechanics. So that's
Speaker 9: what we mean by information being conserved from moment to
Speaker 9: moment in time. So this is already kind of different
Speaker 9: than our conventional notion of causality, that the knowledge of
Speaker 9: what is happening in the present determines equally well the
Speaker 9: future and the past. And so to recover from that
Speaker 9: description our folk wisdom about causes preceding effects, the fundamental
Speaker 9: laws of physics are not enough. You also need to
Speaker 9: put in some boundary conditions. And usually what we do
Speaker 9: is we say the early universe, the Big Bang fourteen
Speaker 9: billion years ago, had very very special conditions. They were
Speaker 9: low entropy, they were a very very tiny kind of
Speaker 9: configuration in the space of all possibilities. And because we
Speaker 9: know that, because we know the conditions that were there
Speaker 9: in the early universe, we have a better handle on
Speaker 9: what things were like in the past than we do
Speaker 9: in the future. We say the past is fixed, right,
Speaker 9: We informally think that the past is just in the books.
Speaker 9: There's no decision I can make now that will change
Speaker 9: the past. But we think there's a decision I can
Speaker 9: make now that will change the future. How to reconcile
Speaker 9: that with laplace? The answer is, you know, I don't
Speaker 9: know the position and velocity of every atom in the universe.
Speaker 9: I have some incomplete macroscopic information, and that might be
Speaker 9: enough to really fix what happened in the past, like
Speaker 9: I have a photograph or a video record of it.
Speaker 9: It is never enough to completely fix what happens in
Speaker 9: the future.
Speaker 2: I think that's a really subtle and underappreciated point, that
Speaker 2: the present determines the past in the way you say
Speaker 2: it in some sense. Another way to think about it
Speaker 2: is that from the pre you can recover the past
Speaker 2: because there's a unique moment, like the details of the
Speaker 2: universe now can only have come from a certain history
Speaker 2: of the past, and so in that sense you can recover.
Speaker 2: It's not like if I change the present, the past changes,
Speaker 2: but there's a unique path which I can recover from
Speaker 2: knowing enough about the present. I don't know if you
Speaker 2: saw that not great show Devs where they had this
Speaker 2: whole concept that try to see an image of the Crucifixion,
Speaker 2: for example, by measuring the motion of air particles over
Speaker 2: Malaysia or whatever.
Speaker 9: Well, yes, So one of the reasons why that is
Speaker 9: a TV show and not reality is because again one
Speaker 9: cannot emphasize enough that you don't have information about position
Speaker 9: and velocity of every particle in the universe. If you
Speaker 9: wanted to just to drive it home, if you wanted
Speaker 9: to recover something that was happening in an event two
Speaker 9: thousand years ago, even in principle, you would need to
Speaker 9: know everything that is going on in the universe now
Speaker 9: to within a two thousand light year radius, because there
Speaker 9: were photons emitted from the Earth back two thousand years
Speaker 9: ago and they've been moving away from you to speed
Speaker 9: of light. So if you don't have those photons, you
Speaker 9: cannot recover what was going on back there in the past.
Speaker 9: But at the same time, in principle you could, except
Speaker 9: there's quantum mechanics that gets in the way of this,
Speaker 9: But classically you could absolutely do this. So it's an
Speaker 9: interesting back and forth about the rigidity of the laws
Speaker 9: of physics. What's amazing to me is that we can
Speaker 9: make as much progress as we can talking about both
Speaker 9: the past and the future given such amazingly limited information
Speaker 9: about the state of the universe.
Speaker 2: So let's dig into the quantum mechanics of it. I mean,
Speaker 2: you describe something like a clockwork universe where things are deterministic,
Speaker 2: and in principle, if you knew all the information, you
Speaker 2: could predict the future, et cetera. But we know that's
Speaker 2: not our universe. We know there is fuzziness, and we
Speaker 2: talk a lot in physics, especially in popular science, about
Speaker 2: quantum fluctuations, which are treated as if they have no cause.
Speaker 2: You know, why does there a guy lexi here? Oh
Speaker 2: there was a fluctuation in the early universe. Why is
Speaker 2: there no galaxy there? Oh, there was a fluctuation. Do
Speaker 2: those fluctuations in quantum mechanics do they really have no cause?
Speaker 2: Is there nothing that determines them?
Speaker 9: Well, I, at the risk of yet again being careful
Speaker 9: and pedantic. We have to distinguish between not having a
Speaker 9: cause and not being determined. Those are slightly two different things.
Speaker 9: Of course, you're right. In the macroscopic world, when you
Speaker 9: make a quantum measurement, the outcomes are not determined by
Speaker 9: the quantum state of the universe. As far as we know,
Speaker 9: there is no hidden information that would determine them. In
Speaker 9: theories like Bomian mechanics, there literally is hidden information that
Speaker 9: does determine them. So Boei mechanics is one hundred percent deterministic,
Speaker 9: but we literally have no access to that information. So
Speaker 9: you know, what good is it to think that this
Speaker 9: is a determined event even though we don't know, we
Speaker 9: cannot know what is the thing determining it. But also,
Speaker 9: you know, we're cheating a little bit because we're taking,
Speaker 9: we're borrowing this notion of causality that has kind of
Speaker 9: been handed down since Aristotle, the idea that you know,
Speaker 9: for every event we can assign a cause, which was
Speaker 9: never really very fundamentally rigorous, like, Okay, I'm late for work,
Speaker 9: and I assigned the cause to that that there was
Speaker 9: traffic that morning, But what about assigning the cause to
Speaker 9: that that space time is four dimensional? Like if it weren't,
Speaker 9: I wouldn't have been late for work, or you know,
Speaker 9: I mean like there's a whole bunch of facts about
Speaker 9: the universe on which this result depends. And this is
Speaker 9: full employment for philosophers to figure out exactly what you
Speaker 9: mean by the cause. But in physics we've sidestepped that
Speaker 9: question by replacing the ideas of cause and effect with
Speaker 9: a much more clear, rigorous framework, which is patterns, essentially
Speaker 9: differential equations that tell you from one thing another thing
Speaker 9: is going to follow. Or maybe you have some discrete
Speaker 9: version of physics or whatever it is. But an if
Speaker 9: then statement, you know, if this happens and that happens,
Speaker 9: it's not quite cause and effect, even though we speak
Speaker 9: that way sometimes, Like the example I like to use
Speaker 9: is the real numbers, right, zero, one, two, three minus
Speaker 9: one minus two minus three. There's a pattern there. If
Speaker 9: I tell you the number n, you can figure out
Speaker 9: what the number N plus one is. If I tell
Speaker 9: you five, you can figure out six. But five is
Speaker 9: not the cause of six, right, it's just the previous
Speaker 9: thing in the pattern. That's how the laws of physics work.
Speaker 9: It's one damn thing after another, and it's okay. If
Speaker 9: some of those laws are stochastic, right, Like, maybe they are,
Speaker 9: since we don't understand the foundations of quantum mechanics perfectly well.
Speaker 9: Classical mechanics was deterministic, but maybe quantum mechanics just isn't
Speaker 9: even at the most fundamental level. Or maybe it is,
Speaker 9: as I said, Bomi mechanics many worlds. These are deterministic theories,
Speaker 9: but we don't know which one, if either one of
Speaker 9: those is right. So I wouldn't say that quantum events
Speaker 9: don't have a cause. Events follow the patterns given to
Speaker 9: us by the laws of physics. As to whether those
Speaker 9: patterns are deterministic or stochastic, we just don't know at
Speaker 9: the fundamental level. We do know that as observers in
Speaker 9: the universe, they seem stochastic to.
Speaker 2: Us, right, And I didn't mean to imply that like
Speaker 2: anything goes in quantum mechanics, you do an experiment and
Speaker 2: like anything can happen. Obviously, we construct conditions and quantum
Speaker 2: mechanics gives us predictions for probability distributions. In that sense,
Speaker 2: it determines those distributions, but not the individual experiment. That's
Speaker 2: an important distinction, thank you.
Speaker 9: No, it's actually super important because a lot of people,
Speaker 9: when you tell them that the way that fundamental physics
Speaker 9: works isn't exactly in line with our informal, twenty five
Speaker 9: hundred year old notion of cause and effect, they instantly
Speaker 9: leap to, oh, then anything goes. But that's really not
Speaker 9: what it is. There's still laws, there are still patterns.
Speaker 9: Maybe there's a stochastic element to them. We're just not sure.
Speaker 2: So then let me ask you to speculate why, Because
Speaker 2: we're peering into the future where maybe folks smarter than
Speaker 2: us are going to unravel the nature of space time
Speaker 2: and gives us their quantum gravity that lets us understand
Speaker 2: all of this stuff. Do you think that theory is
Speaker 2: going to be non local and causal only in the
Speaker 2: way the quantum mechanics is. Or do we have no
Speaker 2: idea about what's going to happen with quantum gravity?
Speaker 9: So your second guess is probably more accurate, more more fair,
Speaker 9: more legitimate, more honest to say we have no idea
Speaker 9: what's going to happen. I have my favorite ideas, and
Speaker 9: my favorite idea is just taking quantum mechanics really super
Speaker 9: duper seriously. So what do I mean by that? I
Speaker 9: already said that when it comes to locality, the way
Speaker 9: that we represent the state of a physical system in
Speaker 9: quantum mechanics with a wave function or whatever is non local. Right,
Speaker 9: you have a wave function that depends on all the
Speaker 9: particles in all the fields, not on just one local
Speaker 9: in space. You know, that's a sort of particular specific
Speaker 9: version of a more general abstract statement that quantum states are,
Speaker 9: you know, elements of some abstract mathematical space. And space,
Speaker 9: good old space, good old three dimensional x, y z
Speaker 9: space is not there in the fundamental description of quantum mechanics.
Speaker 9: Time is, which is weird because the Shortinger equation has
Speaker 9: a T in it, but the general form of the
Speaker 9: Shortinger equation does not have an x in it. And
Speaker 9: that's intension with the spirit of relativity. And that's just true,
Speaker 9: and okay, we're gona have to deal with that, et cetera.
Speaker 9: But to me, the real deep question is not how
Speaker 9: do we reconcile ourselves to the apparent non locality of
Speaker 9: quantum measurement, the apparent spooky action at a distance and
Speaker 9: we measure one particle and we see an instantaneous effect
Speaker 9: on its quantum state. That's not the question. The question
Speaker 9: is because remember, there's this two sides of quantum mechanics.
Speaker 9: What happens when you're not looking at it, where everything
Speaker 9: looks local, and what happens when you look at it
Speaker 9: when there are these non local correlations. I'm interested in
Speaker 9: why things ever look local at all? You know, if
Speaker 9: you just think that your starting point is this abstract
Speaker 9: quantum mechanical state vector of the universe, Hilbert space is
Speaker 9: the mathematical space in which these quantum states live, why
Speaker 9: does it look like we live in space and have
Speaker 9: approximately local interactions at all? And in fact, so I've
Speaker 9: written papers about this, like you can actually be a
Speaker 9: working physicist and try to ask this question. It's a
Speaker 9: little bit hard to make too much progress because the
Speaker 9: question is so grandiose. So we don't know a lot
Speaker 9: about it. But I think that it's a different angle
Speaker 9: on quantum gravity than the traditional ones. You know, Traditionally,
Speaker 9: in all of physics, what we do is we invent
Speaker 9: a classical theory of something like electromagnetism or this in
Speaker 9: barmonic osclator or a propagating string and ten dimensions and
Speaker 9: all these are classical descriptions, and then we quantize them.
Speaker 9: We have some rules for turning that quantum theory into
Speaker 9: a classical theory, and we keep bumping into problems when
Speaker 9: applying these rules to the questions of quantum gravity. But
Speaker 9: nature doesn't work that way. Nature doesn't start with the
Speaker 9: classical theory and quantize it. Nature is just quantum from
Speaker 9: the start. So maybe the obstacle defining the right theory
Speaker 9: of quantum gravity is that we keep wanting to start
Speaker 9: with a classical theory and quantizing it. Maybe you should
Speaker 9: start with a quantum theory of nothing at all and
Speaker 9: asking under what conditions might it look like the classical
Speaker 9: three spatial dimensional universe with certain particles and fields and
Speaker 9: stuff like that. So I think that thinking about locality
Speaker 9: in this way might very well turn out to be
Speaker 9: absolutely crucial to making progress in quantum gravity.
Speaker 2: So I think the description you're suggesting here is some
Speaker 2: concept in which space it'sself is not fundamental.
Speaker 9: It's emergent absolutely, And that's actually remarkably common among people
Speaker 9: who think about quantum gravity, that space itself is not fundamental.
Speaker 9: What's not really well understood is what that means. Like
Speaker 9: there's only one way to be fundamental, and there's many
Speaker 9: ways to not be fundamental. So okay, space is emergent,
Speaker 9: it's not fundamental. What does that mean?
Speaker 4: What is it?
Speaker 9: Where did it come from? And different people have different
Speaker 9: opinions about that.
Speaker 2: And it's a real struggle because we think geometrically. I mean,
Speaker 2: if you tell me the universe is a bunch of
Speaker 2: wave functions and they're entangled together, I try to think
Speaker 2: where are they? I imagine them in my head. Yeah,
Speaker 2: because I think about where do I put it? And
Speaker 2: in my head I have a space and that space
Speaker 2: is three dimensional because I have lived in three dimensional space,
Speaker 2: so I think in three D. So it's a real
Speaker 2: struggle to counter our intuitions and to try to come
Speaker 2: up with a conception of the universe that doesn't make
Speaker 2: these assumptions.
Speaker 9: So one question I have that is well beyond my
Speaker 9: pay grade, But could you model a virtual reac environment
Speaker 9: in which space is four dimensional? Could you retrain your
Speaker 9: brain to move and live and perceive things in four
Speaker 9: dimensional space? Or is there something in the structure of
Speaker 9: our brain itself that only makes sense in three dimensions?
Speaker 9: You know, people like a manual cont to the philosopher
Speaker 9: you know, had an argument that three dimensional space was
Speaker 9: kind of necessary. People argue about exactly how necessary he
Speaker 9: thought it was. But it was almost an anthropic argument,
Speaker 9: you know, you tried to argue that this is the
Speaker 9: only way to make sense of the world is if
Speaker 9: you have this spatial arena in which things have locations
Speaker 9: and things like that. It's a what is it? A
Speaker 9: cautionary tale because philosophers should be careful that their ideas
Speaker 9: won't be overthrown by later advances in physics. But I
Speaker 9: don't know, and I have ideas that are very vague
Speaker 9: in hand wavy about why space should have emerged in
Speaker 9: the first place. Maybe not really anthropic, but maybe something
Speaker 9: about locality is very helpful if you just want complexity
Speaker 9: at all, Like if literally every particle in the universe
Speaker 9: could instantaneously affect every other particle, Like how do you
Speaker 9: get through the day? Like how do you make a
Speaker 9: living in a world like that? I don't know. So
Speaker 9: I do think that these questions are very deep and
Speaker 9: certainly not understood, but maybe understandable.
Speaker 2: I have a suspicion about whether we could have four
Speaker 2: dimensional VR. I mean, I remember trying to play video
Speaker 2: games with my teenager, and I played a lot of
Speaker 2: video games as a kid, But you know, the controller
Speaker 2: was simple. There was ab you know, there was a
Speaker 2: little directional thing you could jump on whatever. So then
Speaker 2: I'm trying to play Halo with my teenager and there's
Speaker 2: like a knob for the direction of your gun, is
Speaker 2: a knob for the direction you move, and a knob
Speaker 2: for the direction.
Speaker 1: Your head goes.
Speaker 2: And this kid is moving through essentially six dimensional space,
Speaker 2: you know, and he's controlling it and it's totally intuitive
Speaker 2: to him. And I'm like, I have to put this
Speaker 2: finger on this joystick and that thing on that joystick,
Speaker 2: And of course he know, headshotted me instantaneously every single time.
Speaker 2: So I think the human brain is probably plastic enough
Speaker 2: to be able to adapt to those kind of environments,
Speaker 2: but not yours mine.
Speaker 9: That's funny. You don't look that old Daniels. It's kind
Speaker 9: of weird, but I guess sorry, we're learning.
Speaker 2: That's the zoom filter. But I want to take our
Speaker 2: brains out universal and think, of course, about how aliens
Speaker 2: experience the universe. Do you think if we get to
Speaker 2: talk to aliens that they will have gone through a
Speaker 2: similar trajectory, you know, where they imagine the universe is
Speaker 2: local and causal and then they discover, oh, actually, at
Speaker 2: its foundations, these are just intuitive assumptions we're making in
Speaker 2: the universe doesn't respect them. Or do you think it's
Speaker 2: possible that they grew up natively to imagine a non
Speaker 2: local universe.
Speaker 9: I think that it's. Uh, there's a tension there, because
Speaker 9: I do think that everything is possible when you ask
Speaker 9: these possibility questions, but some things are easier to imagine
Speaker 9: than others. I do think the embodiedness of we beings
Speaker 9: in three dimensional space is pretty natural to imagine as
Speaker 9: a universal feature, even of alien life, because cause, you know,
Speaker 9: the classical world is really helpful to you know, making
Speaker 9: predictions about what's going to happen, and it's a very
Speaker 9: good approximation to the world. So I suspect that whatever
Speaker 9: trajectory of scientific understanding the aliens take, it will start
Speaker 9: with classical three dimensional physics and and move on from there.
Speaker 9: But you know, if the aliens get really good at
Speaker 9: either VR or uploading into the matrix or whatever, maybe
Speaker 9: they're very used to thinking and perceiving things in different
Speaker 9: numbers of dimensions. Maybe that's just a switch they flip
Speaker 9: when they when they go in there. I remember one
Speaker 9: more completely amusing but irrelevant story. I was a science
Speaker 9: consultant for the movie Tron Legacy.
Speaker 3: Fun.
Speaker 9: And you might remember Tron, those of us who are
Speaker 9: old enough. I remember Tron when it came out. It was,
Speaker 9: you know, one of the first early eighties Disney movies
Speaker 9: that had a lot of computer graphics in it, right,
Speaker 9: Jeff Bridges was in it, and it was you know,
Speaker 9: it was not greats and by any stretch, but it was.
Speaker 1: Fun, deeply influential.
Speaker 9: I well, it was great ish. It is a certain
Speaker 9: kind of great.
Speaker 1: Yeah.
Speaker 9: But the sequel that they had later in the two thousands,
Speaker 9: Tron Legacy, and I think they've had another one, right,
Speaker 9: but or they're making it. But so Tron Legacy was
Speaker 9: not as successful cinematically, And part of it was when
Speaker 9: you made Tron, computer graphics were terrible, right, Like it was,
Speaker 9: it was amazing you could do it at all, and
Speaker 9: you were like, oh my god, this is so mind
Speaker 9: blowing that you were in this thing that was obviously
Speaker 9: a bunch of people on scooters with neon taped to them, right,
Speaker 9: but you know they had some computer graphics going on.
Speaker 9: But by you know, twenty ten or whatever, you can
Speaker 9: just make everything look perfectly realistic, and so they did
Speaker 9: so it looked perfectly realistic, like inside the video game,
Speaker 9: things look like the real world. But my attitude was like,
Speaker 9: but we live in the real world, wants to see that.
Speaker 9: What we want to see is something that doesn't look
Speaker 9: anything like the real world, because you can make any
Speaker 9: world you want. And they did not go down that road.
Speaker 9: But I think that that movie still remains to be
Speaker 9: seen where people like are literally living in six dimensional
Speaker 9: space and fighting their motorcycle battles.
Speaker 3: Accordingly, trum Legacy would have done so much better if
Speaker 3: they took your advice.
Speaker 9: So many things in life. Yeah that could be said about.
Speaker 2: Yeah, all right, Well, thank you for joining us today
Speaker 2: on this element of our struggle to understand the real
Speaker 2: world and what is real about the world.
Speaker 1: I appreciate your thoughts and comments. Sean, thanks very much
Speaker 1: for having me.
Speaker 3: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We
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