Speaker 1: Hey, Katie, are you a fan of Italian food?
Speaker 2: Well? I live in Italy, so here we just call
Speaker 2: it food.
Speaker 1: But yeah, all right, Well what about Italian American food?
Speaker 1: You know, the version made by Italian immigrants to America.
Speaker 2: Yeah, no, I like it.
Speaker 3: It's more meatballs and more garlic, but that's still really good.
Speaker 1: Well what about the opposite, what about American Italian food?
Speaker 3: So is that cuisine made by American immigrants who are
Speaker 3: in Italy?
Speaker 2: Yeah?
Speaker 1: Basically you.
Speaker 3: Well, I mean I mostly just have coffee and toast,
Speaker 3: which would be a really short cookbook.
Speaker 1: Maybe you should try innovating. Have you ever tried putting
Speaker 1: a meatball in your coffee?
Speaker 2: I know I have not tried to do that, Daniel.
Speaker 1: Could be a cultural revolution.
Speaker 3: Well, it would indeed be revolting.
Speaker 2: Hi.
Speaker 1: I'm Daniel. I'm a particle physicist and a professor at
Speaker 1: uc Ervine, and I don't like anything in my coffee,
Speaker 1: definitely not meatballs.
Speaker 2: Hi. I am Katie.
Speaker 3: I host a podcast called Creature feature on evolutionary biology,
Speaker 3: and I like a huge amount of sugar in my coffee.
Speaker 3: So we could see how that is with meatballs as well. Well.
Speaker 1: That makes me wonder since you're a biologist, tell me
Speaker 1: who are the natural consumers of coffee? Like, who out
Speaker 1: there in the animal world is eating coffee beans off
Speaker 1: the tree.
Speaker 3: That's the thing is that coffee caffeine in coffee plants
Speaker 3: is meant to be slightly toxic to insects that want
Speaker 3: to eat it. And it's the same story for spicy foods.
Speaker 3: It's actually defense mechanism, and so the insects that will
Speaker 3: try to eat these plants will not farewell. But when
Speaker 3: we have it, it's actually delicious and good. Now, there
Speaker 3: are palm civets who will eat types of coffee plants.
Speaker 3: They eat the berries, and there's actually a coffee drink
Speaker 3: made out of the beans collected from the palm civet hoop.
Speaker 2: And it's very expensive.
Speaker 3: Wow.
Speaker 1: I don't know what blows my mind more there the
Speaker 1: fact that we are sipping insect poison, or the fact
Speaker 1: that that whole strategy has backfired on the coffee tree
Speaker 1: because it attracts us, or how quickly a biologist will
Speaker 1: turn the conversation towards poop.
Speaker 2: The latter is the least surprising.
Speaker 1: That is, in the end, where we overlap the darkest
Speaker 1: matters in the Universe and Welcome the podcast Daniel and
Speaker 1: Jorge Explain the Universe the production of iHeartRadio, in which
Speaker 1: we try to do just that. Explore everything that's out
Speaker 1: there in the universe, ask our deepest, darkest questions about
Speaker 1: who is sipping which bits of the universe and why
Speaker 1: they exist in that way? What are the tiniest particles
Speaker 1: that everything is made out of, What are the rules
Speaker 1: by which they play? How do they come together to
Speaker 1: make civets and cats and poops and coffee and biologists
Speaker 1: who wonder about all those things combined? Is it possible
Speaker 1: to understand and explain the universe? We're going to try.
Speaker 3: That is the first thing I think of when I
Speaker 3: think about civt kat poop is the tiniest of particles
Speaker 3: that make up that coffee. But yeah, I mean, I guess,
Speaker 3: I guess when you can go down really really tiny,
Speaker 3: and that makes things like poop less gross because now
Speaker 3: you're just on the atomic level and these are just atoms.
Speaker 2: They don't smell. Atoms don't smell bad.
Speaker 1: I don't think, well, does it make poop less gross
Speaker 1: to think that it's made of the same basic building
Speaker 1: blocks as everything else, or does it make everything else
Speaker 1: more gross to know that ice cream and lava and
Speaker 1: kittens are made out of the same stuff as poop.
Speaker 2: Interesting question, ice cream, lava.
Speaker 1: Let's put a pin in that. But let's dive deep
Speaker 1: into what the universe is made out of. One of
Speaker 1: our deepest questions in physics, and a question that humans
Speaker 1: have been asking basically since humans have been asking questions,
Speaker 1: is how do things work at the smallest scale? Is
Speaker 1: it possible to zoom down on what's around us and
Speaker 1: explain things in simpler and simpler terms, Because you know,
Speaker 1: you start out with a huge number of things out
Speaker 1: there in the universe blueberries and cats and ice cream
Speaker 1: and coffee and biologists and physicists and everything in between.
Speaker 1: It's an incredible variety. But when you dig down a
Speaker 1: little bit, you discover, oh, everything out there is made
Speaker 1: out of about one hundred basic building blocks the elements
Speaker 1: periodic table. Combined in different ways, you can make essentially everything.
Speaker 1: And even that set of one hundred building blocks is
Speaker 1: made out of an even smaller set of stuff. Right,
Speaker 1: Protons and neutrons and electrons make up all of those atoms,
Speaker 1: which means that the same stuff can be used to
Speaker 1: make lava or kittens, or ice cream or poops, or
Speaker 1: biologists or stars. All that stuff is made out of
Speaker 1: the same thing.
Speaker 3: It's interesting because I do know that one of the
Speaker 3: things that unites kittens and lava and poop is that
Speaker 3: it all obeys the laws of physics. If you throw
Speaker 3: a kitten in some lava, you're going to have a
Speaker 3: predictable result because of the laws of physics. Both the
Speaker 3: kitten and the lava are constrained by the laws of physics.
Speaker 3: But the thing that's interesting to me, and that hurts
Speaker 3: my brain a little bit, is that when you look
Speaker 3: at say like a very tiny quantum part of it
Speaker 3: does not necessarily obey the same laws of physics as
Speaker 3: say a marble. So you know, I think of like
Speaker 3: a marble bonking into another marble. I can somewhat understand
Speaker 3: how that works. But then you go down small enough
Speaker 3: and it's not just tiny atomic marbles bonking into each other.
Speaker 3: Weird stuff happens that blows my mind.
Speaker 1: It is incredible that the laws of physics seem to
Speaker 1: be different at different scales, like at different distances or
Speaker 1: different energies. It seems like different rules apply, like to
Speaker 1: baseballs and to electrons. The rules are fundamentally different. There
Speaker 1: are different kinds of stuff and the rules that apply
Speaker 1: to them are different, and that does feel weird, and
Speaker 1: it's one of the most incredible things about the universe.
Speaker 1: But a helpful way to think about it is in
Speaker 1: terms of phases, Like think about water. Water has a
Speaker 1: liquid phase and a solid phase and a gas phase.
Speaker 1: Right in the end, we think it's all made out
Speaker 1: of the same basic stuff water molecules, but they act
Speaker 1: very differently under different circumstances. And you wouldn't expect the
Speaker 1: laws of an ideal gas to describe what happens when
Speaker 1: water crystallizes, or fluid dynamics to explain how a gas
Speaker 1: would expand different rules apply in different scenarios, different phases,
Speaker 1: And so we imagine that the universe is organized the
Speaker 1: same way you can think of You can think of
Speaker 1: it as sort of different phases where different rules apply.
Speaker 1: What we don't know is if there is an underlying
Speaker 1: theory behind all of it, the sort of physics version
Speaker 1: of the water molecule, the tiniest little bits who's dancing
Speaker 1: and tuing and froing and interacting is somehow making all
Speaker 1: this other stuff emerge, even the quantum particles, even the baseballs,
Speaker 1: even the galaxies. Is there something at the lowest level
Speaker 1: which is determining everything from which all of our experience emerges.
Speaker 3: So this is an interesting and confusing question to me,
Speaker 3: because from my understanding, if we're all in the same universe,
Speaker 3: we would all regardless of whether we're a human or
Speaker 3: a quark or a kitten, we'd have to play by
Speaker 3: the same rules.
Speaker 2: But if the rules are.
Speaker 3: Different somehow, right, like for a quark versus a kitten
Speaker 3: in terms of physics, even though the kitten is also
Speaker 3: made out of quarks or atoms molecules, it's hard for
Speaker 3: me to wrap my head around there not being a
Speaker 3: unifying set of rules that applies to everything, given that
Speaker 3: not only do we live in the same universe, but
Speaker 3: we're made out of all the same stuff.
Speaker 1: Yeah, it's a great question, and a basic assumption about
Speaker 1: a lot of physics is that that's possible that if
Speaker 1: you zoom down to the smallest scale, you can find
Speaker 1: the most basic set of rules, and that then you
Speaker 1: could somehow zoom back out with the fundamental theory of
Speaker 1: the universe in hand, you could explain everything it might
Speaker 1: require you to calculate, like how ten to the twenty
Speaker 1: nine particles come together to make a baseball. But the
Speaker 1: idea is, in principle, it's all determined by what's happening
Speaker 1: at the smaller scale, and when you zoom out, that's
Speaker 1: just what those laws look like. And it might be
Speaker 1: the case, right It might be that even though we
Speaker 1: have trouble explaining how a zillion water droplets interacting in
Speaker 1: the atmosphere make a hurricane, we can't even do it
Speaker 1: with our fastest supercomputers. We think that probably it is
Speaker 1: determined by that, but that's actually a philosophical assumption, and
Speaker 1: some philosophers of science disagree with that. It's called strong
Speaker 1: emergence at some point to lots of things that we
Speaker 1: can't explain using underlying details. A great example is like
Speaker 1: why you are here your consciousness. We have completely failed
Speaker 1: so far to explain the experience of human consciousness in
Speaker 1: terms of like the zapping of the little neurons inside
Speaker 1: of our brains. It might be that somehow all that
Speaker 1: stuff comes together to explain why you are experiencing this
Speaker 1: podcast right now. But it might also be that there
Speaker 1: are just different rules at different levels of the universe
Speaker 1: that aren't actually determined by the lower levels, that somehow
Speaker 1: there are independent layers of the universe and different rules
Speaker 1: apply at each one. It's a weird philosophy of the universe,
Speaker 1: but it might also be our universe.
Speaker 3: That's very hard for my conscious brain to wrap itself around.
Speaker 3: It is very interesting, this philosophical question of consciousness because
Speaker 3: if we apply sort of the rules of like, well,
Speaker 3: a brain works right because you have a communication between
Speaker 3: many parts, you have neurons that are all communicating with
Speaker 3: each other and forming these networks. Well, there's a lot
Speaker 3: of things that do that, from computers to ant colonies,
Speaker 3: and so the question is, well, are those things conscious
Speaker 3: as well? And we can't really quantify that, and we
Speaker 3: can't know whether even though it seems like there's this
Speaker 3: underlying rule of you know, you require these sort of
Speaker 3: individual units that are all communicating together and forming patterns,
Speaker 3: and that's what you need for consciousness. If you see
Speaker 3: that repeated in other systems, whether that actually applies to say,
Speaker 3: can you recreate a consciousness with an electronic version of
Speaker 3: neurons or or is something like a very complex ant
Speaker 3: colony with thousands of ants?
Speaker 2: Does that recreate consciousness. So I guess in a way.
Speaker 3: I could see how there could be different rules applying
Speaker 3: to different layers, but it's just so strange and so like. Currently,
Speaker 3: when we look at like quantum mechanics, it does not
Speaker 3: do a good job of explaining physics on a larger scale.
Speaker 1: Mostly we cannot connect the layers that we have. Even
Speaker 1: though that's basically the motivation for the project to understand
Speaker 1: everything at the smallest scale and use that to explain
Speaker 1: everything else that's bigger, we have very rarely succeeded in
Speaker 1: using a zoomed in microscopic approach to explain anything bigger.
Speaker 4: You know.
Speaker 1: One famous success story is ideal gases. Is say, okay,
Speaker 1: we have this picture of atoms moving in a gas
Speaker 1: as tiny little balls. Can we zoom out and think
Speaker 1: about what happens to ten to the twenty nine balls,
Speaker 1: and can we write equations that tell mathematical stories about
Speaker 1: things that emerge from ten to the twenty nine tiny
Speaker 1: little gas molecules like pressure and temperature and volume, and
Speaker 1: we can you can actually derive, like the ideal gas
Speaker 1: law from statistical mechanics explanations about the velocities of those
Speaker 1: tiny little particles. That's a famous example because it's one
Speaker 1: of the rare successes. Mostly we have failed because the
Speaker 1: universe is kind of chaotic. It's really sensitive often to
Speaker 1: these tiny little details. What happens to this quantum particle
Speaker 1: affects another quantum particle, which affects another quantum particle. We
Speaker 1: don't understand how to do that calculation. Most of the time,
Speaker 1: we don't have the computing power, and we can't avoid
Speaker 1: this chaos problem. So mostly we don't know how to
Speaker 1: do that. It might be that it is determined and
Speaker 1: it's possible to do those calculations, is just sort of
Speaker 1: beyond our ability right now. Or it might be that
Speaker 1: it's just not that different rules apply in different regimes,
Speaker 1: as weird as that is.
Speaker 3: So, I guess I'm not so familiar with quantum mechanics
Speaker 3: and general relativity. Can we kind of just hammer down,
Speaker 3: like what are those two things? How Like what do
Speaker 3: they apply to and what don't they apply to?
Speaker 1: So at the forefront of our understanding of the most
Speaker 1: microscopic picture of how the universe works, we have two
Speaker 1: basic theories. We have quantum mechanics, which tells us about
Speaker 1: really tiny stuff, and general relativity, which tells us about
Speaker 1: really big, heavy stuff, basically quantum mechanics for particles and
Speaker 1: general relativity for gravity. One of the biggest frustrations in
Speaker 1: physics in the last one hundred years has been our
Speaker 1: inability to bring them together into a single story, to
Speaker 1: weave them into a unified picture of how the universe works.
Speaker 1: You know, this whole project of like, let's explain everything
Speaker 1: from the tiniest particles and then zoom out. Well, we
Speaker 1: haven't even succeeded in explaining the tinese particles yet, but
Speaker 1: there's a vigorous program of people working on this stuff.
Speaker 1: And in today's episode, we're going to dig into one
Speaker 1: of the most recent and weirdest ideas about how to
Speaker 1: bring quantum mechanics and relativity together. So on today's episode,
Speaker 1: we're going to be answering the question, what is quantum relativity?
Speaker 3: Hmmm, quantum relativity. So it's like quantum mechanics and general
Speaker 3: relativity had a baby.
Speaker 1: It also sounds like the buzzword name for a startup
Speaker 1: where you're like, I don't even really know what it
Speaker 1: they do, but it sounds pretty good. So before we
Speaker 1: dig into the details of this, I checked in with
Speaker 1: our listeners to see if they had any idea about
Speaker 1: the theory of quantum relativity, if they had heard this before,
Speaker 1: if they had thoughts about it. Thanks very much to
Speaker 1: everybody who participates in this audience feedback segment of the podcast.
Speaker 1: We really love hearing your voice and hearing your thoughts
Speaker 1: on the question of the day. If you would like
Speaker 1: to participate, please don't be shy. Just write to me
Speaker 1: to Questions at Danielandjorge dot com and I'll hook you up.
Speaker 1: So before you hear these answers, think to yourself, have
Speaker 1: you heard of quantum relativity? What do you think that
Speaker 1: might mean. Here's what some listeners have to say.
Speaker 2: Quantum relativity.
Speaker 4: I'm guessing that is the theory that brings quantum mechanics
Speaker 4: and general relativity together. So something that the theory that
Speaker 4: figures out how you work gravity and quantum mechanics together.
Speaker 4: Since gravity, we're not quite sure how that works on
Speaker 4: the smallest scales.
Speaker 1: That is really really tiny relativity.
Speaker 5: To me, that sounds like a parallel to general relativity.
Speaker 5: So I bet that it has to do with how
Speaker 5: particles interact with each other when in proximity to each
Speaker 5: other on a quantum scale.
Speaker 3: I love the answer really tiny relativity because it makes
Speaker 3: me think of some ants or some mites or tartar
Speaker 3: grades in the lab coats drawing on tiny chalkboards.
Speaker 1: Exactly. Also, quantum just sometimes means like fancy or stinazzi,
Speaker 1: or we're going to charge an extra ten bucks for it,
Speaker 1: So like expensive relativity.
Speaker 3: This is a quantum salad for twelve dollars, exactly.
Speaker 1: I'd like to upgrade my salad, actually do a quantum salad.
Speaker 1: Or I ordered quantum on my salad and I didn't
Speaker 1: get enough.
Speaker 2: Could mean anything thanks in.
Speaker 1: A complaint anything. Well, we're going to see today. The
Speaker 1: quantum relativity is the name of a new effort to
Speaker 1: unify quantum mechanics and general relativity, and they really do
Speaker 1: give it that name for a reason. But before that's
Speaker 1: going to make any sense to us, we really have
Speaker 1: to understand the basics of like what is quantum mechanics
Speaker 1: in general relativity, why do we want to unify them,
Speaker 1: and why is it so hard?
Speaker 2: Right?
Speaker 3: Yes, because, like you were kind of saying earlier, general
Speaker 3: relativity is for big stuff.
Speaker 2: Quantum mechanics is for tiny stuff.
Speaker 3: But it's got to be a little more detailed than
Speaker 3: that I would imagine.
Speaker 1: No, that's basically it take quantu mechanics, generativity. It's like
Speaker 1: all done in fifteen minutes. But listeners of the podcast
Speaker 1: will remember that general relativity based describes space and time.
Speaker 1: Special relativity is a theory that tells us about how
Speaker 1: light moves and how observers always see light moving at
Speaker 1: the same speed, and general relativity is what explains gravity.
Speaker 1: Remember Newton had the idea that gravity was a force
Speaker 1: that things with mass pulled on each other and that's
Speaker 1: why the Earth goes around the Sun and you feel
Speaker 1: like you're falling towards the Earth because he described gravity
Speaker 1: as this force. But Einstein tells us that gravity is
Speaker 1: not a force. A gravity is not capable of accelerating anything,
Speaker 1: and that things are actually moving according to the invisible
Speaker 1: curvature of space and time.
Speaker 3: This is the thing that is so hard for me
Speaker 3: to really visualize or hold in my head because every
Speaker 3: kind of analogy I try to make is based in physics,
Speaker 3: like a ball rolling down a hill or something, or
Speaker 3: you know, I think of the fabric of space being
Speaker 3: sort of pulled in a certain direction, and it's like
Speaker 3: that's still physics. In the sun and so of like
Speaker 3: you know, a fabric being pulled and something falling into it.
Speaker 3: Whereas like the idea of gravity being sort of the
Speaker 3: shape of the universe in a way that like makes
Speaker 3: sense in my head is very hard to grasp. I
Speaker 3: understand it in a certain way, but to visualize it
Speaker 3: is so difficult.
Speaker 1: It is very tricky because it changes your entire concept
Speaker 1: of what space is.
Speaker 3: Right.
Speaker 1: We used to thinking of space as like nothingness and
Speaker 1: stuff is there and it can move through space. But
Speaker 1: it turns out that there is something to space, like
Speaker 1: between two points, there's information information about how that space
Speaker 1: is curved or bent, and that affects how stuff moves
Speaker 1: through that space. And yeah, there's a lot of examples
Speaker 1: out there in popular science literature. I think most of
Speaker 1: which are very confusing. You know, the idea of like
Speaker 1: a rubber sheet and you have a ball on the sheet,
Speaker 1: and the rubber sheet is bent and that makes things curved.
Speaker 1: That's very confusing because you still have to have gravity
Speaker 1: in that example in the vertical direction. You have this
Speaker 1: like external third dimension of gravity in your two D world.
Speaker 1: I think that's very very misleading. I prefer to think
Speaker 1: about it in three D. And remember that this curvature
Speaker 1: is intrinsic. It's not external. It's not like there's somebody
Speaker 1: else out there with a ruler in real space who's
Speaker 1: telling us our space is bent relative to their space.
Speaker 1: The curvature is intrinsic. There's no external ruler. It just
Speaker 1: means that the relative distances between two points change, which
Speaker 1: means like the shortest path from A to B might
Speaker 1: not be a straight line that you would draw if
Speaker 1: you ignore the curvature. Once you know what the curvature is,
Speaker 1: there might be a shorter path between A and B,
Speaker 1: and that's the path that light will take. Light always
Speaker 1: takes the shortest path between two points.
Speaker 3: So if I'm standing on my bed and I'm going
Speaker 3: to jump off the bed, as I do every morning,
Speaker 3: so I am subject to the gravity of Earth, and
Speaker 3: it's not so much that it's pulling me down, but
Speaker 3: just that I am traveling along the short this path
Speaker 3: from point A, which is my bed, to point B,
Speaker 3: which is the other point of space. But it's more
Speaker 3: or less just interrupted by the floor.
Speaker 1: Yeah, that's a great example. Let's think about it first
Speaker 1: from the Newtonian point of view, and then let's reboot
Speaker 1: and think about it from an Einsteinian point of view.
Speaker 1: So Newton would say, you're standing on your bed. There's
Speaker 1: the force of gravity pulling down on you from the Earth,
Speaker 1: and there's the force of your bed pushing up, and
Speaker 1: those two things are balanced, so you're not going anywhere.
Speaker 1: Then you jump off your bed. No longer is the
Speaker 1: bed pushing you up, and so now you're falling because
Speaker 1: it's just the force of gravity, and that's accelerating you
Speaker 1: down towards the center of the Earth. That's the way
Speaker 1: people mostly learn about gravity. That's how Newton described it.
Speaker 1: That's where we start. Einstein says something different. Einstein says, well,
Speaker 1: when you're standing on your bed, you actually are being accelerated.
Speaker 1: There's only one force there. There's the force of your bed.
Speaker 1: What's it pushing you against. It's pushing you against your
Speaker 1: natural motion, which is to fall towards the center of
Speaker 1: the earth. So Newton says, you're accelerating when after you
Speaker 1: jump off the bed and you're falling towards the center.
Speaker 1: Einstein says, no, you were accelerating when you were on
Speaker 1: your bed. It's when you jump off your bed that
Speaker 1: you're now following the natural curvature of space. You're no
Speaker 1: longer accelerating. The only force in this scenario is the
Speaker 1: force of the bed on you, and that's keeping you
Speaker 1: from naturally moving towards the center of the Earth. When
Speaker 1: you're standing on the bed. Once you jump off, you're
Speaker 1: the one in free fall. And you can actually measure
Speaker 1: this because you can take an accelerometer, something which measures
Speaker 1: your acceleration. I mean, the scale is basically a gravitometer,
Speaker 1: and you can measure when are you feeling an acceleration.
Speaker 1: If you jump off your bed and you're holding a scale,
Speaker 1: you put it under your feet, what are you going
Speaker 1: to weigh? You're going to weigh nothing because there's no
Speaker 1: force between you and the scale. But if the scale's
Speaker 1: on your bed and you're standing on it, then you're
Speaker 1: going to see your weight. And that's because that's where
Speaker 1: you're accelerating. It's when you're on your bed.
Speaker 3: That's so interesting. Yeah, I can totally visualize that. Also,
Speaker 3: I knew that when I sleep in, I wasn't lazy
Speaker 3: because I've been accelerating the whole time.
Speaker 1: So this is Einstein's picture of gravity, and it's massively successful.
Speaker 3: Right.
Speaker 1: It describes the motion of everything in the universe, the
Speaker 1: expansion of the universe, incredibly high precision black holes oscillating
Speaker 1: around each other, neutron stars getting gobbled by black holes,
Speaker 1: gravitational waves. It's been tested in and out and up
Speaker 1: the wazoo for decades and decades, and it's this beautiful
Speaker 1: geometric picture of the universe that tells us gravity is
Speaker 1: not a force. It's just the way things are flowing
Speaker 1: through the geometry of space and time. And the things
Speaker 1: to take away from this discussion are that it's one
Speaker 1: deterministic right. It says that things move in a certain
Speaker 1: way because of geometry. It's no randomness, there's no probability.
Speaker 1: It's not like when you jump off your bed you
Speaker 1: have a chance of landing here or there. It's determined
Speaker 1: by exactly where you are in the shape of space.
Speaker 1: And the other is that it mostly affects really really
Speaker 1: big stuff because gravity is super weak. Whether it's a
Speaker 1: force or it's the curvature of space time, it takes
Speaker 1: a lot of mass to have any effect. You can
Speaker 1: overcome all the gravity of the Earth or the curvature
Speaker 1: of space and time caused by the Earth using a
Speaker 1: simple kitchen magnet right, or your legs can overcome it.
Speaker 1: You can leap off the surface of the Earth, which
Speaker 1: means it applies mostly to really massive objects. So it's
Speaker 1: deterministic and it applies to really massive stuff. That's the
Speaker 1: important things to remember when we're going to talk about
Speaker 1: trying to integrate it with quantum mechanics.
Speaker 3: Because that's in the opposite direction where it is extremely
Speaker 3: extremely tiny stuff like as a human being, gravity is
Speaker 3: something where it's hard to you know, really visualize like
Speaker 3: the scope of say like the size of the Sun
Speaker 3: or this even the size of the planet. Sure you
Speaker 3: can go on a plane and kind of see part
Speaker 3: of it, but it's it's still hard to visualize how
Speaker 3: big these things are, how massive it is, and then similarly,
Speaker 3: going into quantum mechanics visualizing how tiny these things can be.
Speaker 3: So there really as opposite as you can can get
Speaker 3: in terms of size and scope.
Speaker 1: They are like the ying and ying of physics. But
Speaker 1: we hope they click together to make a holistic picture.
Speaker 1: But let's dig into how quant mechanics explains the tiniest
Speaker 1: stuff in the universe. But first let's take a quick break.
Speaker 3: All right, I'm going to try to start thinking small
Speaker 3: all right, I'm trying to think inside a very tiny box,
Speaker 3: and hopefully that will help me.
Speaker 1: As you mentioned already, the rules seem to be different
Speaker 1: for things like baseball and planets than things like electrons
Speaker 1: and photons and tiny little particles, which is really the
Speaker 1: source of one of the biggest mysteries in modern physics,
Speaker 1: how that all works and whether we can bring it.
Speaker 3: Together right, Because I think I had some concept before
Speaker 3: ever coming on this show, which is that like with
Speaker 3: the small stuff, the really tiny quantum level stuff, there
Speaker 3: was some sort.
Speaker 2: Of like average you could take.
Speaker 3: Of its behavior, and then that would be well integrated into, say,
Speaker 3: other types of physics like general relativity, where it's like, well,
Speaker 3: you know, you just scale up averages of the small
Speaker 3: stuff's activity and then that would fit in some perfect
Speaker 3: formula and represent general relativity.
Speaker 2: But turns out it's not so simple.
Speaker 5: No.
Speaker 1: It turns out the rules of these two concepts are
Speaker 1: fundamentally different and tell really different stories about the nature
Speaker 1: of the universe we live in. About one hundred years ago,
Speaker 1: people did experiments which showed us that when you zoom
Speaker 1: into the tiniest level, the rules really do seem to
Speaker 1: be different. Amazingly, it was Einstein who played a role
Speaker 1: in both of these revolutions. He of course came up
Speaker 1: with relativity, but he also had the idea of how
Speaker 1: to interpret the photoelectric effect, which kicked off the entire
Speaker 1: quantum revolution as well, So that dude was pretty central.
Speaker 2: What's the photo reflective effect?
Speaker 1: This is the experiment where you shine bright light at
Speaker 1: a piece of metal and you see a bunch of
Speaker 1: electrons boil off. And the idea is, Okay, the electrons
Speaker 1: are absorbing the light, they're getting energy, they're boiling off.
Speaker 1: The weird thing about the experiment was as you turn
Speaker 1: up the brightness of the light, like the intensity of
Speaker 1: the light, you expected to get electrons with more energy
Speaker 1: because you're shining brighter light at it. But instead what
Speaker 1: you got were more electrons. And this really puzzled people.
Speaker 1: They're like, why can't the electrons get more energy? And
Speaker 1: the answer in the end is that light is made
Speaker 1: of these tiny little packets. It's not a continuous beam.
Speaker 1: It's a bunch of little packets of energy, and each
Speaker 1: electron can basically only absorb one. It's like one interaction
Speaker 1: between a photon and n electron. So when you turn
Speaker 1: up the brightness of the beam, which you get are
Speaker 1: more electrons absorbing photons, not one electron absorbing more photons.
Speaker 1: And so that was the clue that told people, oh, look,
Speaker 1: maybe light is made of these little packets, and that
Speaker 1: kicked off the whole quantum revolution that showed us that
Speaker 1: everything out there is actually made of these little discrete
Speaker 1: bits that follow very different rules.
Speaker 3: It's like these electrons are flying ryanair and they can
Speaker 3: only have one packet per electron.
Speaker 1: That's right. Otherwise you get some quantum fees carry ons.
Speaker 3: Is that a very small fee or a very big fee?
Speaker 1: Small fees that add up to a lot because of
Speaker 1: interference with your pocketbook?
Speaker 2: I think? Ain't that how it is?
Speaker 1: Anybody out there who works for the airlines, do not
Speaker 1: take this as a creative idea for how to add fees. Okay,
Speaker 1: I don't want to see quantum fees on my quantum fees.
Speaker 2: That's going to be the next thing.
Speaker 1: And what emerged from the next twenty or thirty years
Speaker 1: of studying experiments and shining lights on things and looking
Speaker 1: inside the atom, or a new set of rules for
Speaker 1: how tiny stuff worked. This tiny stuff didn't follow the
Speaker 1: rules of planets and baseballs. You couldn't make a picture
Speaker 1: of the atom that literally had electrons orbiting the center
Speaker 1: of the atom. That just didn't work. The physics of
Speaker 1: it didn't make sense. Those electrons in an orbit would
Speaker 1: radiate away all their energy and collapse into the nucleus
Speaker 1: because anything that's moving in a circle is accelerating, and
Speaker 1: things that accelerate have to give off radiation in order
Speaker 1: to keep bending. But we don't see electrons collapsing into
Speaker 1: the center of the atom and tend to the negative
Speaker 1: thirteen seconds. I told us that the rules were fundamentally different,
Speaker 1: and we came up with a completely new kind of mathematics,
Speaker 1: quantum mechanics, Schrodinger's equation that described the rules of the
Speaker 1: quantum realm, which were totally different from the rules of
Speaker 1: baseballs and electrons. Base Balls move through space. They have
Speaker 1: a path, like they're here and then they are there,
Speaker 1: and so you know they went from here to there.
Speaker 1: They have a location at every moment, and you can
Speaker 1: string those locations together to make a smooth and continuous path.
Speaker 1: Just sort of makes sense to you that everything has
Speaker 1: to be somewhere at all times. But electrons don't follow
Speaker 1: those rules. That's an intuition you developed from your experi
Speaker 1: of baseballs and rocks and other kinds of stuff. Electrons
Speaker 1: can be here and then they can be there, and
Speaker 1: they don't have to go from here to there. They
Speaker 1: don't always have to have a determined location. They can
Speaker 1: exist in probabilistic form where they can say, well, I
Speaker 1: might be here and I might be there. It's not
Speaker 1: determined much more than just being not known. It's actually
Speaker 1: not determined by the universe.
Speaker 3: Right, Because it's hard to understand this sometimes where you
Speaker 3: think in these kinds of thought experiments of like an
Speaker 3: electron not knowing sort of the location of electron or
Speaker 3: the spin of something. It's like I think sometimes I
Speaker 3: have this concept of like, well, this is just sort
Speaker 3: of some kind of weird math. It's not actually describing
Speaker 3: what's actually happening. But I would assume there's like evidence
Speaker 3: that is what's actually happening, that this is not these
Speaker 3: positions are not have experimentally been shown to not be
Speaker 3: like determined by the universe.
Speaker 1: Yeah, there's a whole really fascinating set of experiments that
Speaker 1: explore this question, like is it just something we don't
Speaker 1: know or is it really undetermined by the universe. Is
Speaker 1: there some like extra information the electron is carrying that
Speaker 1: we're just not aware of that actually tells where the
Speaker 1: universe is, like keeping track of where it really is,
Speaker 1: and we just don't know. And it's a set of
Speaker 1: experiments proposed by John Bell to probe a theory called
Speaker 1: Bell's inequalities, and we have a whole set of podcasts
Speaker 1: about those Whether quantum mechanics really is random or not.
Speaker 1: And the upshot is that it seems like it really
Speaker 1: is random. There are some loopholes there, how you might
Speaker 1: have like some sort of like non local pilot wave
Speaker 1: that's controlling the whole universe. But the most mainstream interpretation
Speaker 1: is that it really is random. There really is some
Speaker 1: non determinism to the universe that you could do the
Speaker 1: same experiment twice, exactly the same setup and get different answers.
Speaker 1: Like you're shoot an electron into an experiment with exactly
Speaker 1: the same conditions twice and it'll end up going left
Speaker 1: once and it'll end up going right on another time.
Speaker 1: There's like a die being thrown by the universe to
Speaker 1: determine where an electron goes. It's crazy, it's bonkers, but
Speaker 1: that's the universe we live in.
Speaker 3: So it'd be like if you like, you know, there's
Speaker 3: the classic thing that even babies. This is so interesting
Speaker 3: about human cognition is that babies have a sort of
Speaker 3: baseline understanding of physics. It seems like if they see
Speaker 3: a little marble hit a big marble, they don't expect
Speaker 3: the big marble to go flying off.
Speaker 2: And if you show them that, they.
Speaker 3: Look they kind of stare at it because it's surprising
Speaker 3: to them. But you know, because we kind of have
Speaker 3: this this innate understanding that if a little thing hits
Speaker 3: a big thing, the big thing isn't going to go
Speaker 3: shooting off, whereas if the big thing hits the little thing,
Speaker 3: it's going to go shooting off. And like, if we
Speaker 3: hit things at a certain angle, it's gonna, you know,
Speaker 3: go at a certain direction, just like I guess that's
Speaker 3: how people can be good at pool, not me, but
Speaker 3: other people. And so it would be shocking though, if
Speaker 3: you're if you're good at pool and you something at
Speaker 3: a certain angle and it's just completely random about of
Speaker 3: whether it goes left or right, or forward or backwards
Speaker 3: or up or down.
Speaker 1: It is a really weird way to think about the universe.
Speaker 1: I was recently trying to explain this stuff to my
Speaker 1: sixteen year old who's taking chemistry and was learning about
Speaker 1: the atomic structure and all this stuff and photons and probabilities,
Speaker 1: and it was pretty bewildering. But it was a fun
Speaker 1: experience to try to download into his mind this new
Speaker 1: way of thinking about the universe. But it really is
Speaker 1: counterintuitive because you don't ever experience it. And that's one
Speaker 1: of the big mysteries of quantum mechanics, is why not.
Speaker 1: Because when we interact with quantum stuff, it tends to collapse.
Speaker 1: It says, Oh, I have a bunch of possibilities, but
Speaker 1: I'm just going to pick one now. When a photon
Speaker 1: hits your eyeball, it decides, Oh, I'm here or I'm there.
Speaker 1: When a electron hits the screen, the universe decides. For
Speaker 1: some reason, the universe has this distinction between tiny little
Speaker 1: stuff that can exist with uncertainty and bigger stuff which can't.
Speaker 1: People sometimes describe this as acting like a particle or
Speaker 1: acting like a wave. Really is between classical physics like
Speaker 1: general relativity that's talking about stuff having specific locations and
Speaker 1: quantum physics, where stuff can still have.
Speaker 3: Uncertainty, So quantum physics would be the particle, and general
Speaker 3: relativity would be the wave, or vice versa.
Speaker 1: So quantu physics is about tiny little stuff, but it's
Speaker 1: the wave like behavior of that stuff that's really weird
Speaker 1: because the wave appears in the Shortener equation, and people
Speaker 1: tend to think about particles as having like a definite location,
Speaker 1: like you've seen this particle on the screen. So general
Speaker 1: relativity and classical physics more broadly thinks about stuff as
Speaker 1: having definitive locations. It is here, it is there, it
Speaker 1: was here, And quantum mechanics says that there can be uncertainty.
Speaker 1: So quantum is the more wavy stuff, and in this case,
Speaker 1: the classical theory is more like definitive locations, which people
Speaker 1: sometimes describe as acting like a particle.
Speaker 3: So quantum mechanics is kind of whibbly wobbly.
Speaker 1: Yeah, that's exactly right. So these are two very different
Speaker 1: pictures of the world. Right, things moving along classical pass
Speaker 1: where they always have a definitive location at every time,
Speaker 1: or things being wibbly wobbling, being undetermined. And you might think, well,
Speaker 1: it should be pretty easy to figure out which is right,
Speaker 1: can't we do experiments to tell us which one is
Speaker 1: predicting things correctly. Right, Often you have two theories, you
Speaker 1: just do an experiment, you say, well, which one is right,
Speaker 1: And the problem is that it's so hard to do
Speaker 1: an experiment where both of them have something to say.
Speaker 1: Most of the universe is divided up into stuff where
Speaker 1: general relativity is important and quantum mechanics can be ignored,
Speaker 1: like the motion of planets, or stuff where quantum mechanics
Speaker 1: is important and general relativity can be ignored, like two
Speaker 1: electrons bouncing off of each other.
Speaker 3: Right, Like you could do a physics experiment on a baseball,
Speaker 3: But then to do a physics experiment and a quantum
Speaker 3: level experiment on the baseball's electrons at the same time
Speaker 3: in a way that makes sense seems very difficult.
Speaker 1: Exactly when you do an experiment with baseballs, you can
Speaker 1: pretty much ignore the fact that it's made from ten
Speaker 1: to twenty nine tiny buzzing particles, and you can just
Speaker 1: use Newton's laws F equals MA to describe its path
Speaker 1: very very accurately. That's because the quantum effects tend to
Speaker 1: average out for reasons. Again, we don't really know how
Speaker 1: that works or why that works. But it does, so
Speaker 1: quantum effects tend to disappear when you zoom out far enough.
Speaker 1: On the other hand, when you zoom in far enough,
Speaker 1: gravity is so weak that it becomes irrelevant. Like we
Speaker 1: do collisions between protons all the time at the Large
Speaker 1: Hadron Collider, but we always ignore their gravity, Like there
Speaker 1: is a gravitational attraction we think between the protons, but
Speaker 1: protons have such tiny masses that we can essentially ignore
Speaker 1: their gravity when we do those calculations.
Speaker 3: I mean that makes sense because even though technically, even
Speaker 3: as people, we have gravity, it's not like we can
Speaker 3: suck things into ourselves. I know that's not how gravity works,
Speaker 3: but still we're not. We are not generating enough of
Speaker 3: a gravitational effect that things, you know, fall into our bodies.
Speaker 2: And so what chance does a proton have?
Speaker 1: Exactly, you can't blame gravity for the reason you ate
Speaker 1: that pint of ice cream. It didn't just like fall
Speaker 1: into your body.
Speaker 2: That was my alibi.
Speaker 1: But that's exactly right. We could hardly even measure the
Speaker 1: gravity between things that are like a kilogram. The smallest
Speaker 1: thing we've ever measured gravity for is just about a kilogram,
Speaker 1: and protons are a tiny, tiny fraction of that. We're
Speaker 1: like thirty orders of magnitude away from being able to
Speaker 1: measure the gravity of a proton. And more than that,
Speaker 1: we don't even understand what the gravity of a proton
Speaker 1: would look like. You know, say you have a particle
Speaker 1: with uncertainty to it. Maybe it's here, maybe it's there,
Speaker 1: maybe it's in this third location you don't know. The
Speaker 1: universe says, that's cool, the particle can be uncertain, all right,
Speaker 1: But then what is the gravity of an uncertain particle?
Speaker 1: Does it have a little bit of curvature over here
Speaker 1: because it might be over there, and a little bit
Speaker 1: of curvature over there because it might be over there.
Speaker 1: Is the curvature of space itself uncertain? We don't know
Speaker 1: how to unify these two ideas of quantum mechanics and
Speaker 1: of gravity. Nobody really knows how that can be done.
Speaker 3: That's so interesting and uncomfortable from a sort of biology perspective,
Speaker 3: because when you look at biology, big stuff is made
Speaker 3: out of small stuff, and so that tracks. But when
Speaker 3: you look at biological processes, like you look at a cell,
Speaker 3: and it's interesting because, of course, on a certain level,
Speaker 3: each cell's activity does not necessarily explain everything about a
Speaker 3: human being or a cat or a dog their behavior.
Speaker 3: But you can generally track how the small stuff creates
Speaker 3: the big stuff. And there's generally some like the rules
Speaker 3: that govern the small stuff, these biological processes that govern
Speaker 3: the small stuff. You can track how that is impacting
Speaker 3: the big stuff. Like you chug a bunch of soy sauce,
Speaker 3: and those salt ions are you know, messing up your
Speaker 3: or your ion channels in your brain, and then that's
Speaker 3: why you're in a coma. So it's you know, it's
Speaker 3: very uncomfortable, this idea that you couldn't track, like, okay,
Speaker 3: so this proton is acting in a certain way, and
Speaker 3: then we can scale up to you know, an item
Speaker 3: like a watermelon, because it has a bunch of protons
Speaker 3: in it.
Speaker 2: We know how that the behavior.
Speaker 3: Of those protons would somehow affect the behavior of the
Speaker 3: watermelon exactly.
Speaker 1: And we'd love to do an experiment where we could
Speaker 1: study that right, where we could take something where quantum
Speaker 1: mechanics was relevant and also gravity was relevant, Like if
Speaker 1: we could take enough protons and squeeze them together and
Speaker 1: keep them in a small enough space so they're still
Speaker 1: being quantum mechanical, but we had enough protons where we
Speaker 1: could also measure its gravity. That way we could understand,
Speaker 1: like how the small stuff is affecting the big stuff.
Speaker 1: So in order to keep the quantum mechanical effects relevant,
Speaker 1: you've got to keep it like really really small. And
Speaker 1: so what happens when you try to do that, when
Speaker 1: you add enough stuff together so that it stays quantum
Speaker 1: mechanical and gravity starts to get relevant, you get a
Speaker 1: black hole. That's what a black hole is is a
Speaker 1: huge amount of mass in a tiny little space. And so,
Speaker 1: on one hand, that's exciting, Wow, the answer is inside
Speaker 1: a black hole. On the other hand, all that's really frustrating.
Speaker 1: The answer is hidden inside a black hole. We can't
Speaker 1: see it. We think that probably inside a black hole
Speaker 1: is evidence that would point us in the direction of
Speaker 1: how to bring these two theories together, how to explain
Speaker 1: what happens when you have a bunch of quantum stuff
Speaker 1: that has enough gravity that you can't ignore it anymore.
Speaker 3: It feels like a sick joke, right to put all
Speaker 3: the answers inside a thing that we can't see inside,
Speaker 3: and if we tried to get someone in there, it
Speaker 3: would destroy them.
Speaker 1: Exactly, and they might actually survive going inside the black
Speaker 1: hole and seeing the answer, But then they could never
Speaker 1: tell us even come collect their Nobel prize. We'd have
Speaker 1: to send in the Nobel Prize after them, assuming that
Speaker 1: they'd figured it out.
Speaker 3: Like I feel like, if someone dives into a black hole,
Speaker 3: they just deserve a Nobel Prize, whether they discover.
Speaker 2: Anything or not.
Speaker 3: But we can study black holes, we just can't like
Speaker 3: see inside them. So is there any way to study
Speaker 3: a black hole such that it gives us any clues
Speaker 3: about this?
Speaker 1: Well, there is one possible crack in the veneer of
Speaker 1: black holes, which is their hawking radiation. Black holes are
Speaker 1: not totally black. They do emit some radiation. It's even
Speaker 1: talking to the calculation a few decades ago, and he
Speaker 1: didn't have a theory for what is the gravity of particles,
Speaker 1: but he did some sort of like clever handwavey approximations,
Speaker 1: and he showed that if you have a quantum field
Speaker 1: near something with an event horizon, then there has to
Speaker 1: be radiation leaving the event horizon. So now we interpret
Speaker 1: this as like the black hole is evaporating, it's like
Speaker 1: giving up some of its energy. The idea is that
Speaker 1: maybe in that radiation, maybe as particles are being generated
Speaker 1: by the event horizon, there might be clues as to
Speaker 1: what's inside the black hole. It's sort of very speculative,
Speaker 1: cutting edge research, but it's possible that if we did
Speaker 1: see hawking radiation, we could maybe infer from it something
Speaker 1: about what's inside the black hole. But hawking radiation would
Speaker 1: be very very faint, and black holes are very very
Speaker 1: far away and hidden by all sorts of other, very
Speaker 1: noisy stuff like hot gases emitting all sorts of radiation.
Speaker 1: So we've never seen hawking radiation, and frankly, we don't
Speaker 1: seem very likely to anytime in the near future. So
Speaker 1: until then, the only frontier really is mental. Can we
Speaker 1: come up with a new theory that brings these two
Speaker 1: things together that reconciles the uncertainty of quantum mechanics and
Speaker 1: the determinism of relativity.
Speaker 2: Well, give me like three minutes while ads play, and
Speaker 2: I'll try to come up with something.
Speaker 1: All right, The Katie Golden tries to win the Nobel
Speaker 1: Prize in three minutes challenge.
Speaker 2: Go all right, I think I've got it, Daniel.
Speaker 1: Oh wow, I'm so desperate to hear what you came
Speaker 1: up with.
Speaker 3: Did you guys remember to carry the one.
Speaker 1: Hold on a second? Did we miss a minus science?
Speaker 1: Is that the whole problem? Oh my gosh, Katie, pause
Speaker 1: this recording right now to rush off to Sweden to
Speaker 1: collecting about rice.
Speaker 3: Well you're very welcome, but yes, let's talk about how
Speaker 3: to go from like our observational science to bringing it
Speaker 3: into the brain. How could we possibly do science from
Speaker 3: inside our own heads?
Speaker 1: Well, sometimes it comes down to just being creative. You
Speaker 1: know a lot of big advances in human history have
Speaker 1: come from just people sitting in their dank study thinking
Speaker 1: about the nature of the universe and pulling ideas together.
Speaker 1: You know, Einstein's revolution with a photoelectric effect. He didn't
Speaker 1: do that experiment. He didn't have a piece of metal
Speaker 1: and a bright light in his laboratory. Guy didn't have
Speaker 1: a laboratory. He read a paper or somebody else did
Speaker 1: this experiment, and he just thought about it and had
Speaker 1: this idea for how to explain it and combined it
Speaker 1: with something he heard from Max Plank about how to
Speaker 1: explain how stuff glows and the temperature at which things glow.
Speaker 1: And decades earlier, Maxwell brought together electricity and magnetism just
Speaker 1: by writing them down nicely on a sheet of paper
Speaker 1: and noticing that there were symmetries between them. So we
Speaker 1: can make a lot of progress in physics just by
Speaker 1: having new ideas.
Speaker 3: So are there people in dank rooms I imagine them
Speaker 3: with like maybe one light bulb lighting the entire room,
Speaker 3: hard at work trying to figure this out. Has there
Speaker 3: been any progress made on trying to come up with
Speaker 3: a philosophical or mathematical explanation.
Speaker 1: So people have been working on this for a long time,
Speaker 1: and it's very challenging. Mathematically. It's hard to see how
Speaker 1: you can get this sort of uncertainty of quantum mechanics
Speaker 1: and the rigor and determination of general relativity to play
Speaker 1: nicely together. There's been a lot of attempts, and a
Speaker 1: lot of them have failed. But there is a new
Speaker 1: idea out there, and that's quantum relativity what we're talking
Speaker 1: about today, and the idea is instead of taking general
Speaker 1: relativity and trying to change it so that it's like uncertain,
Speaker 1: rather than saying maybe the curvature or space time is
Speaker 1: uncertain in the way we're talking about earlier, it's wondering
Speaker 1: can we actually see how quantum mechanics comes naturally from relativity,
Speaker 1: Like maybe the weirdness of quantum mechanics just emerges from
Speaker 1: relativity itself, the way the ideal gas law emerges from
Speaker 1: the motion of particles, or hurricanes emerge from the swirling
Speaker 1: of droplets in the atmosphere. Is it possible to find
Speaker 1: hints in relativity from which we could build the weirdness
Speaker 1: of quantum mechanics directly. That's why it's called quantum relativity.
Speaker 1: Take relativity and find a way to build quantum mechanics
Speaker 1: on top of it, rather than like jamming quantum uncertainty
Speaker 1: directly into relativity.
Speaker 3: That's interesting because I think of when I think of
Speaker 3: sort of the direction of causality, I think of, like
Speaker 3: the small things cause the big things to happen, right,
Speaker 3: the little particles there's some causality of like the small
Speaker 3: particles that make up the big things, you know, cause
Speaker 3: some effect, so that I would always kind of intuitively
Speaker 3: think like, well, we have to figure out how the
Speaker 3: small things behavior explains the big things. But it seems
Speaker 3: like this is more like you're taking the kind of
Speaker 3: behavior of big things with general relativity and seeing how
Speaker 3: that could either explain or how you could see quantum
Speaker 3: mechanics grow out of that.
Speaker 1: Yeah, exactly, and so let's drill in on some of
Speaker 1: the details to make this a little bit more concrete.
Speaker 2: You know.
Speaker 1: One of the crucial things we have in quantum mechanics
Speaker 1: that we don't have in relativity is this uncertainty, this
Speaker 1: possibility for things to be in two locations. Right, a particle,
Speaker 1: for example, we say maybe it does this and maybe
Speaker 1: it does that, and we said, that's uncertain It has
Speaker 1: both possibilities, whereas in relativity we have a lot of determination.
Speaker 1: Like you shoot a particle, even if it's near the
Speaker 1: speed of light, it's going in some direction, you know
Speaker 1: what it's going to do. You can calculate it. One
Speaker 1: of the core conflicts between these two theories is just that.
Speaker 1: So the authors of this theory quantum relativity have found
Speaker 1: a way to try to find multiple possibilities in relativity.
Speaker 1: They say, hmm, maybe there's some overlooked mathematics that shows
Speaker 1: us how relativity actually can have like multiple solutions simultaneously.
Speaker 1: One of the founding principles of relativity is that light
Speaker 1: always moves at the speed of light. Right, all observers
Speaker 1: see light moving at the speed of light, no matter
Speaker 1: how fast you're going. So you're moving in half the
Speaker 1: speed of light relative to the Earth. You turn on
Speaker 1: a flashlight, you're going to see that light being moving
Speaker 1: at the speed of light relative you. Somebody on the
Speaker 1: ground who sees you moving at half the speed of
Speaker 1: light and turning on your flashlight, they look at that
Speaker 1: light beam, they also see it moving at the speed
Speaker 1: of light. They don't see it moving at the speed
Speaker 1: of light plus half the speed of light. It's one
Speaker 1: of the really weird things about special relativity.
Speaker 3: Right, so light there is a constant speed of light
Speaker 3: that can't really be slowed down or sped up exactly.
Speaker 1: And this is the founding assumption of special relativity, at
Speaker 1: least to a whole bunch of mathematics. It tells us
Speaker 1: how to see things from different perspectives. Tells us like,
Speaker 1: how is it possible to see light moving at this
Speaker 1: speed for this observer and seeing it move at the
Speaker 1: same speed for that observer. It helps us tie it
Speaker 1: all together, tells a different story for how the universe works,
Speaker 1: and time goes weird sometimes and things get short, and
Speaker 1: we have podcasts digging into all those details. But it
Speaker 1: gives us this picture of like how different people can
Speaker 1: see the universe from different velocities, and this is called
Speaker 1: the Lorentz transforms. It tells you how to transform between
Speaker 1: one observer and another observer. Because it turns out to
Speaker 1: not as simple as we thought.
Speaker 3: Yeah, I'm looking at this formula and doesn't look super
Speaker 3: simple to me.
Speaker 1: No, it's not simple, and it's nonlinear, and it's got
Speaker 1: square roots in it, and it gets really wonky, which
Speaker 1: is why relativity is so weird and time flows strangely
Speaker 1: and you have the twin paradox and all that stuff. Now,
Speaker 1: that's fine, But it turns out there's actually a second solution.
Speaker 1: There's another way you could describe the transformation how people
Speaker 1: see things in different velocities. That also satisfies this requirement
Speaker 1: that the speed of light is the same for everybody,
Speaker 1: sort of like a second solution to an equation. You know,
Speaker 1: if you have like X squared equals nine, one solution is, oh,
Speaker 1: X equals three. Another solution is what if X equals
Speaker 1: minus three. This is the kind of thing that crops
Speaker 1: up all the time in mathematics and sometimes in physics,
Speaker 1: we like, well, minus three doesn't make sense. We'll just
Speaker 1: ignore that. We'll just drop the unphysical solution.
Speaker 3: Yeah, you can't have negative three apples, missus Birch.
Speaker 1: You can actually go into debt for apples, and you
Speaker 1: can be an apple or prison. So yeah, thanks financial
Speaker 1: engineers for inventing negative money.
Speaker 3: I forgot that our currency was based on the Apple standard.
Speaker 1: Exactly. So in this scenario, there's one solution to these
Speaker 1: transformations to tell you, like how different observers see the
Speaker 1: universe different velocities, And that's the one that assumes that
Speaker 1: everything travels at the speed of light or less. It's
Speaker 1: actually a second solution, a second way to transform between
Speaker 1: these frames that holds for velocities greater than the speed
Speaker 1: of light. And that's like, what, hold on a second,
Speaker 1: I thought the whole assumption of special relativity was that
Speaker 1: you can only move slower than the speed of light, right,
Speaker 1: That is one way to interpret these transformations. There's another
Speaker 1: way to interpret them for velocities greater than the speed
Speaker 1: of light. So these would mean particles moving faster than
Speaker 1: the speed of light.
Speaker 2: What kind of particles are these? Do we know?
Speaker 1: So there's a theory about particles moving faster than the
Speaker 1: speed of light. They're called tachyons, and they do satisfy
Speaker 1: the mathematics of relativity, though nobody's ever seen one. One
Speaker 1: problem with anything moving faster than the speed of light
Speaker 1: is that you can end up with tricky paradoxes about
Speaker 1: the order of things and causality, because remember that observers
Speaker 1: moving at high speeds can see stuff happening at different times.
Speaker 1: Like if I see event A happening before event B,
Speaker 1: you might see the opposite order of stuff because you're
Speaker 1: flying by me at a high speed. That's one of
Speaker 1: the consequences of special relativity that you're not guaranteed simultaneity
Speaker 1: for all frames. That different observers can see the order
Speaker 1: of events differently, and that's usually fine, it's not a
Speaker 1: big deal. But if you can move faster than the
Speaker 1: speed of light, then you start to see things that
Speaker 1: are causally linked be reversed. Like, for example, if I
Speaker 1: fire an arrow, then somebody moving past me is faster
Speaker 1: than the speed of light could see the arrow hit
Speaker 1: the apple before I even fire it. That seems sort
Speaker 1: of problematic, and people are like, yeah, let's just cross
Speaker 1: that off and say that doesn't happen, but actually opens
Speaker 1: the door and exactly the way we might need to
Speaker 1: link relativity with quantum mechanics, because now we have like
Speaker 1: two explanations for those events, like does Daniel fire the
Speaker 1: arrow before it hits the apple or does it hit
Speaker 1: the apple before I fire the arrow? So the idea
Speaker 1: of quantum relativity is to say, well, what if you
Speaker 1: look at these things both from the less than the
Speaker 1: speed of light perspective and the greater than the speed
Speaker 1: of life perspective, Like if you allow both views of it,
Speaker 1: then you have sort of like two different ideas for
Speaker 1: what might be happening here, and there isn't a deterministic
Speaker 1: explanation for which is the right one.
Speaker 3: I mean, you had mentioned earlier that this was kind
Speaker 3: of dismissed, right, because like the idea is that you
Speaker 3: can't observe causally linked events in reverse. What is the
Speaker 3: assumption behind that that says that you can't do that?
Speaker 2: Because like, I.
Speaker 3: Know, it sounds obvious, right, like, of course you can't.
Speaker 3: I would assume there's actually some kind of law in
Speaker 3: physics that does link to that, because you know what
Speaker 3: we know about like assumptions, like we have all sorts
Speaker 3: of assumptions about the world works because that's how we
Speaker 3: observe it. We as humans never observe things in reverse.
Speaker 3: But is there an actual law in either physics or
Speaker 3: general relativity that would prohibit that observation from coming before
Speaker 3: the event?
Speaker 1: Yeah, that's a great question. Why do we assume that
Speaker 1: there's causality in the universe, that things have to be linked?
Speaker 1: And it's just sort of like part of how we
Speaker 1: think about physics. It's a core assumption we make. We
Speaker 1: don't know that it's true, but it sort of makes
Speaker 1: sense to us, and so we try to hold on
Speaker 1: to it as long as possible, build theories on that
Speaker 1: assumption and see if they work. But it might be
Speaker 1: that we have to give it up. There are other
Speaker 1: hints in other theories of physics, sort of the cutting edge,
Speaker 1: that maybe causality isn't the fundamental aspect of the universe.
Speaker 1: It might be something we are trying to impose on it.
Speaker 1: You know, think about the way that we explain the universe.
Speaker 1: We tend to tell stories. Stories are like little causal links.
Speaker 1: I did this, and then she did that, and then
Speaker 1: this happened. It's like A, then B and C, then D.
Speaker 1: It's sort of embedded deeply in how we think. It
Speaker 1: doesn't mean it has to be embedded deeply into the universe.
Speaker 1: And so this is sort of like giving up that
Speaker 1: causal chain and saying, well, maybe A cause B, but
Speaker 1: maybe B caused A. And that's where you get your
Speaker 1: crack indeterminism In relativity, it says, maybe there are two
Speaker 1: ways to view these events. One subliminal, sorry, one subluminal,
Speaker 1: not subliminal as in slower than the speed.
Speaker 3: Of lfemptoms about the superliminal messaging, yeah.
Speaker 1: And one super illuminal, like a view from an observer
Speaker 1: moving fast than the speed of light that sees an
Speaker 1: opposite order of events. And this is basically the crack
Speaker 1: that this whole theory of quantum relativity is built on.
Speaker 1: It says, within relativity, maybe you can have nondeterminism, because
Speaker 1: maybe the superluminal view of the universe is different from
Speaker 1: the subluminal view, that the order of events can be different.
Speaker 1: From within relativity, we now see a little bit of uncertainty,
Speaker 1: a loss of de herminism, and that's basically the starting
Speaker 1: place for quantum relativity.
Speaker 3: I think we have to remind ourselves that physicists are
Speaker 3: human beings and they have the same kind of mental fallacies,
Speaker 3: or not necessarily fallacies, but just habits the routine that
Speaker 3: all humans have, which is viewing things in terms of
Speaker 3: what we have adapted to as human beings or earlier
Speaker 3: as primates, and it's such a strong thing. There have
Speaker 3: been studies on people's behavior where when you look at
Speaker 3: like a screen that has like randomly moving dots on
Speaker 3: a screen or something like, people will try to impose
Speaker 3: some kind of like rules on this or like volition
Speaker 3: to these things, like that these feel alive because they're
Speaker 3: moving randomly, and so you think, well, then there must
Speaker 3: be some kind of autonomy of these things, like some
Speaker 3: reason that it's doing is so like this causality link,
Speaker 3: like I mentioned earlier. It's even found in like babies,
Speaker 3: where you'll see, like if they see something that defies
Speaker 3: the laws of very simple physics of like a ball
Speaker 3: hitting a ball and that ball kind of moving, they
Speaker 3: stare at that because.
Speaker 2: That's not what they're expecting.
Speaker 3: So it seems like a huge challenge to overcome our
Speaker 3: humanness when we're also trying to answer these questions about
Speaker 3: the universe that do not necessarily play by the same
Speaker 3: rules as say, like a primate that has somehow gotten
Speaker 3: smart enough to start writing down numbers.
Speaker 1: Yeah, and we've often seen the appearance of autonomy and
Speaker 1: action in the universe, you know, explaining whether in terms
Speaker 1: of some big guy in the sky throwing thunderbolts, et cetera,
Speaker 1: et cetera. And so we do have to be careful
Speaker 1: and question our assumptions. And sometimes when we are failing
Speaker 1: to describe the universe that we see, we need to
Speaker 1: circle back and say, well, maybe there's something wrong in
Speaker 1: the foundations of our science itself. Maybe we need to
Speaker 1: be asking questions about whether all of these assumptions really
Speaker 1: hold and what breaks if we get rid of them,
Speaker 1: or what breakthroughs we might be able to make.
Speaker 3: So, once we get rid of this assumption that there
Speaker 3: has to be this causality, has there been any breakthroughs
Speaker 3: in terms of then connecting this potential new model of
Speaker 3: general relativity to quantum mechanics, Like, have there been successful
Speaker 3: sort of developments in quantum relativity beyond? Just like maybe
Speaker 3: we can issue the causality.
Speaker 1: Not yet. It's sort of like a promising direction for
Speaker 1: people to build on. What it has generated is a
Speaker 1: whole series of papers arguing about it. So a bunch
Speaker 1: of physicis are like, hey, you can't do that. This
Speaker 1: doesn't make sense, and other people be like, no, actually,
Speaker 1: maybe it does. And so, you know, it's a healthy conversation.
Speaker 1: So far hasn't led anywhere concrete yet, but you know,
Speaker 1: it might be that we look back in one hundred
Speaker 1: years and tell stories about this moment where people are like,
Speaker 1: wait a second, what about this basic assumption, or this
Speaker 1: could just end up on the very very deep trash
Speaker 1: can of the theories that have attempted to unify general
Speaker 1: relativity and quantum mechanics and failed.
Speaker 3: I mean, you need to fill a few trash cans
Speaker 3: full of crumpled up sheets to make a physics aline,
Speaker 3: as I understand it.
Speaker 1: Exactly. But it's fun to examine all these assumptions to
Speaker 1: try to explain our universe in terms of the tiniest
Speaker 1: little particles, and to try to unify those theories, the
Speaker 1: ones that describe the really big, heavy stuff and the
Speaker 1: ones that describe the tiniest little particles flitting around inside
Speaker 1: our atoms. Maybe one day we'll figure it out. Until then,
Speaker 1: thanks very much Kinnie for joining me on this journey
Speaker 1: to our lack of understanding about the universe.
Speaker 3: Thanks for having me, and really do check on whether
Speaker 3: you guys just forgot to carry the one, because you know,
Speaker 3: we all make mistakes.
Speaker 1: I'm on it, and if it turns out you were right,
Speaker 1: we'll definitely cite you. Thanks everyone for listening, See you
Speaker 1: next time. For more science and curiosity, come find us
Speaker 1: on social media, where we answer questions and post videos.
Speaker 1: We're on Twitter, disc Org, Insta, and now TikTok. Thanks
Speaker 1: for listening and remember that Daniel and Jorge Explain the
Speaker 1: Universe is a production of iHeartRadio. For more podcasts from iHeartRadio,
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