Speaker 1: Hey, jorgey, do you think there's anything good about getting older?
Speaker 1: Why are you asking me? I'm only twenty three. How
Speaker 1: long you've been twenty three for a while? Yeah? All right,
Speaker 1: But do you think like there's any advantage to getting
Speaker 1: old and slowing down? I guess fewer speeding tickets. Maybe
Speaker 1: like new kinds of joint pain to feel so new experiences. Yeah,
Speaker 1: the early bird specials at restaurants. Sometimes I wonder if
Speaker 1: it's good to forget some of those painful memories of youth.
Speaker 1: So there are advantages. Maybe physics should try slowing down.
Speaker 1: You want me to tell these photons to take it easy,
Speaker 1: you know. I know they're billion years old and they've
Speaker 1: been going at the speed of light for a long time,
Speaker 1: but maybe it's time for them to slow down. They
Speaker 1: can get the early Photon special. Hi'm Jorge Mae, cartoonist
Speaker 1: and the creator of PhD comments. Hi. I'm Daniel. I'm
Speaker 1: a particle physicist and I hope to be aging gracefully
Speaker 1: and welcome to our podcast. Daniel and Jorge age and
Speaker 1: explain the universe. At the same time, Daniel and Jorge
Speaker 1: explained the aging of the universe, which is mostly my
Speaker 1: knees at this point, which is technically happening right now,
Speaker 1: right now, as you're listening to us. We are getting older, yes,
Speaker 1: and the universe is getting older. You will finish this
Speaker 1: podcast in a different, older universe than the when you
Speaker 1: started it in, right, A little bit bigger, a little
Speaker 1: bit older and wiser, a little bit cooler, a little
Speaker 1: bit darker. The universe is getting older and colder and slower.
Speaker 1: Um though dark energy, of course is accelerating. But those things,
Speaker 1: when they get older, so to slow down, just like us,
Speaker 1: it gets a little bit more boring. No, we are
Speaker 1: getting funnier as we get older. Jorge, Oh right, right, No,
Speaker 1: I mean like entropy, Like entropy is increasing in the universe,
Speaker 1: and so is the entropy of our knees and jokes. Well,
Speaker 1: maybe as we get older we don't get funnier, but
Speaker 1: we think we're funnier, So I laugh more at your jokes,
Speaker 1: even as they decay in quality. It's all about perspective.
Speaker 1: It's all about perspective. Just like in relativity, there is
Speaker 1: no universal time or distance in comedy, right, there is
Speaker 1: no universal humor. There's no universal law for jokes. Is
Speaker 1: there no theory of special comedy. Um, well, there are
Speaker 1: a lot of jokes about relatives, but everybody jokes about
Speaker 1: their family, right, Yeah. Yeah, this idea that everything is
Speaker 1: slowing down is kind of inevitable. But there are some
Speaker 1: things in the universe and maybe we'll never slow down.
Speaker 1: That's right. Even though photons travel through billions of light
Speaker 1: years of space, when they get here, they're still moving
Speaker 1: at the speed of light. You you fired that photon
Speaker 1: from your flashlight at Alpha Centauri, It's gonna get there,
Speaker 1: and it's going to be going the same speed when
Speaker 1: it does. Yeah, I kind of thought about it. I
Speaker 1: guess photons are going at the same speed wherever they go,
Speaker 1: no matter how long they've been going. Yeah, photons don't
Speaker 1: get tired, right. You push a photon and it goes,
Speaker 1: and it just goes and goes and goes and goes
Speaker 1: and goes, and it doesn't like run out of energy,
Speaker 1: you know, unless it gets absorbed by something or bounces
Speaker 1: off something. It will just keep going forever. It's sort
Speaker 1: of amazing at the maximum speed of the universe, not
Speaker 1: just at any speed. At the maximum speed of the universe. Yeah,
Speaker 1: and photons. People have been asking me on Twitter whether
Speaker 1: photons experienced time, Like do photons even get old? You know,
Speaker 1: because photon has taken a billion years to get here
Speaker 1: from somewhere else, And they wonder do photons experienced time?
Speaker 1: And it's a tricky question because you have to imagine,
Speaker 1: like a photon having a clock. What is that clock
Speaker 1: made out of? If it has mass than the photons can,
Speaker 1: how does it look at the clock? Photons to look
Speaker 1: at the clock. What is it like to be a photon? Man?
Speaker 1: It seems like maybe more of a philosophical question than
Speaker 1: a physics question. Yeah, I don't think photons even have
Speaker 1: knees to feel their joint. Paine, I'm not asking whether
Speaker 1: we have anything in common with photons. There are weird
Speaker 1: quantum mechanical little particles. But where we ended up with
Speaker 1: that question was that photons are moving at the speed
Speaker 1: of light, and so they see most of the universe contracted.
Speaker 1: So a photon leaves here and it feels like it
Speaker 1: hasn't gone very far because the universe has been sort
Speaker 1: of shortened. To them, the universe is just it's it's
Speaker 1: it's basically tiny, right, It's the size of a point. Maybe, Yeah,
Speaker 1: that's right, And it's bizarre to imagine what it might
Speaker 1: be like to travel as a photon. But again, I
Speaker 1: don't think we want to get into the question of
Speaker 1: what is it like to be a photon? But it
Speaker 1: is sort of a good life example to not slow down,
Speaker 1: you know, take some inspiration. Photons are my new heroes.
Speaker 1: But other folks have been writing in and asking about
Speaker 1: whether photons always do at the speed of light? Can
Speaker 1: they not go at the speed of light? Can they
Speaker 1: throttle down? Yeah? When photons get old, is there any
Speaker 1: way they can sort of chill out a little bit
Speaker 1: and relax? So to the on the podcast, we'll be
Speaker 1: askering this question dead several, he says. Several readers wrote
Speaker 1: in about there are a bunch of people who've been
Speaker 1: reading articles online about physicists managing to slow down light,
Speaker 1: and they thought, what we better get Daniel and Jorge
Speaker 1: to explain that to us, So to be on the program,
Speaker 1: we'll be asking the question can light be slowed down?
Speaker 1: It's fascinating because people think that, of course, photons travel
Speaker 1: at the speed of light, right, that's why we call
Speaker 1: it the speed of light, And we make a big
Speaker 1: deal about how that's constant. How if you shoot a
Speaker 1: photon out you measure traveling at the speed of light,
Speaker 1: somebody else measures it traveling at the speed of light.
Speaker 1: This sort of this like fundamental constancy, This like stubbornness
Speaker 1: of photons to always go with the same speed. Other
Speaker 1: things can vary their speed, right, Electrons orcs sure, pretty
Speaker 1: much all the other trinos. Right, they can go slow,
Speaker 1: they can sit in the palm of your hand, or
Speaker 1: they can go at nearly the speed of light. Yeah,
Speaker 1: anything that's massive that has any mass to it, electrons,
Speaker 1: even newtrinos, anything like that has a rest mass, Like
Speaker 1: you can catch up to it and have no relative velocity.
Speaker 1: You can exist next to it, hold it, throw it around, etcetera.
Speaker 1: But things that have no mass, what would happen if
Speaker 1: you caught up to them? Right, If there's a photon
Speaker 1: and you caught up to it, a photon is just motion, right,
Speaker 1: There's nothing to it other than it's motion. So if
Speaker 1: you catch up to it and there's no motion, there's
Speaker 1: no velocity relative to the photon, it's not there anymore.
Speaker 1: So that's why you can never catch up to a photon.
Speaker 1: It just doesn't make sense. It's like what happens if
Speaker 1: you catch a wave. It's no longer a wave. Yeah,
Speaker 1: that's right. If you're surfing right and you look down,
Speaker 1: then it's not really a wave anymore. It's just sort
Speaker 1: of like a stationary shape of the water, and so
Speaker 1: there's no relative motion there. Yeah, So don't surf on
Speaker 1: photons people. Not a good idea, especially as you get older. Yeah,
Speaker 1: and so this is an interesting question and so that
Speaker 1: we're going to tackle it today. We're gonna talk about
Speaker 1: whether or not you can slow light down and whether
Speaker 1: it seems that people some people have. Yeah, there's been
Speaker 1: some pretty exciting experiments with click baby headlines about slowing
Speaker 1: down light and stopping light, and so we're gonna dig
Speaker 1: into that today. And see doesn't make any sense. What
Speaker 1: are they actually doing and is it cool or what?
Speaker 1: Oh stopping You're gonna slow it down to the point
Speaker 1: of maybe stopping light. Yeah, yeah, wow, these faces are
Speaker 1: trying to break the rules of the universe. Well, as usual,
Speaker 1: I was curious, do people think it's possible to slow
Speaker 1: down light or is that just sound like crazy talk?
Speaker 1: So I walked around campus at you see Irvine. Yeah,
Speaker 1: so before you listen to these answers, think about it
Speaker 1: for a second, do you think that light can be
Speaker 1: slowed down? Here's what people have to say. I don't
Speaker 1: think so. I don't know. I would say no, theoretically right, yes, yes,
Speaker 1: how would you do it? I'm no clue. I don't
Speaker 1: know that that photons within the sun, they it takes
Speaker 1: very long time until they actually reach the surface of
Speaker 1: the sun and are released into space. I don't know.
Speaker 1: I mean it's not actually it's it's learned on the photons.
Speaker 1: I mean, there's there's relativity obviously, so I closed down time.
Speaker 1: But that's that's time. But that's light is supposed to
Speaker 1: be the constant nation. Because it is a constant. I
Speaker 1: think if you put light through different media, that should
Speaker 1: be slow. But I don't think that it is like
Speaker 1: I would expect that if you put light through water,
Speaker 1: I would expect there would be some sort of effect.
Speaker 1: But but we have a constant for light, So how
Speaker 1: can it be how can it change through different media?
Speaker 1: And if we have a constant for it, that's like,
Speaker 1: but we that's constants for an error? Yes, isn't it okay?
Speaker 1: So maybe it is okay? So I think there might
Speaker 1: be slight changes possibly, but I think it's inherently supposed
Speaker 1: to be constant. No, because it isn't like a constant number.
Speaker 1: I think somehow through velocity or something of that, changing
Speaker 1: velocity at a very high rate might be able to
Speaker 1: I'm not too sure. Maybe like a black hole type
Speaker 1: gravity type of situation. Yeah, No, cool, some pretty cool
Speaker 1: answers here. A lot of a lot of yeses and
Speaker 1: a lot of maybes. I don't know how how did
Speaker 1: people react to the question itself, because it's not a
Speaker 1: question that I had heard much about before you send
Speaker 1: me the email this morning. Uh, you know it's you
Speaker 1: don't think about the slowing down light down much. Well.
Speaker 1: I think that feeling is backed up by these people's experience,
Speaker 1: because when I asked them, do you think it's possible
Speaker 1: to slow down light? I got a lot of quizzical
Speaker 1: looks and a lot of long pauses as people thought
Speaker 1: about it, And you can hear people reaching for answers.
Speaker 1: They're like, I don't know, is a black hole involved? Maybe?
Speaker 1: Or you kind of have to stop and parse the
Speaker 1: words a little bit, like slow down light, slow down
Speaker 1: something that is not quite there, yep, And parsing the
Speaker 1: words is going to be a solution to today's question
Speaker 1: because the answer is sort of technical and legalistic. It's
Speaker 1: sort of one of these pole loopholes in the laws
Speaker 1: of physics, like have you really slowed it down? Some
Speaker 1: people would say they have. Some people would, you know,
Speaker 1: quibble with that. All right, So we have to put
Speaker 1: on our physics lawyer heads today. Whenever you're reading the
Speaker 1: laws of physics, you've got to be very careful, you know,
Speaker 1: to understand exactly what they mean and what they don't mean.
Speaker 1: Are we sort of the shark type of physics lawyer?
Speaker 1: Are we been nice type of physics lawyers today? Are
Speaker 1: we out to get the universe? Are we up to?
Speaker 1: Are we out for justice? Danny? We are not the
Speaker 1: physics police, right, we are on this. We're on the
Speaker 1: defense side here. We are trying to make sure physicists
Speaker 1: can do whatever they like. We're trying to allow physics
Speaker 1: to do weird stuff with the universe because in the end,
Speaker 1: that's how we learn what the rules really are. We
Speaker 1: find the cracks and we exploit them, try to figure
Speaker 1: out what's actually possible given the rules that we know.
Speaker 1: It seems like people had a sense that, you know,
Speaker 1: the universe is interesting enough that maybe there are situations
Speaker 1: in which you can slow light down. Like that didn't
Speaker 1: seem impossible to a lot of people. Yeah, that's an
Speaker 1: optimistic way to look at it. Like, no matter how
Speaker 1: constant you think that law is, there must be some way,
Speaker 1: someplace in the universe where we could break and we
Speaker 1: could find something crazy happening. I like thinking that people
Speaker 1: are open to the fact that the universe is filled
Speaker 1: with crazy bunker stuff. Okay, so let's break it down
Speaker 1: for folks here, Daniel, and let's talk about light and
Speaker 1: how facet travels and what we know about light. And
Speaker 1: it's the first thing to understand, which I think most
Speaker 1: people already do, is that light does always travel at
Speaker 1: the same speed in a vacuum. And remember what light
Speaker 1: is like. You can think about light as a photon
Speaker 1: is a little particle, and it is quantized. But if
Speaker 1: fundamentally think about light is a sort of a ripple.
Speaker 1: Space is filled with quantum fields. Even empty space has
Speaker 1: the possibility to have these particles in it because it
Speaker 1: contains within it these quantum fields, like the electromagnetic field
Speaker 1: that can ripple. So I think of space is sort
Speaker 1: of like having these different possible sort of sheets rubber
Speaker 1: sheets in it, and mostly they're just sort of spread.
Speaker 1: It's smooth, but occasionally you can get a ripple in one,
Speaker 1: and that ripple is like a particle. I see. So
Speaker 1: I think the main idea is that light is a
Speaker 1: photon is not a thing. It's not like a little
Speaker 1: spherical thing. It's more like like a little divid in
Speaker 1: the kind of the fabric of the universe. Yeah, it's
Speaker 1: got no stuff to it, if that's what you mean
Speaker 1: by it's not a thing. It's a it's a transient property, right,
Speaker 1: It's that's why it's always moving. It's a it's a ripple.
Speaker 1: It's like a change in information. It's saying, oh, the
Speaker 1: electromag than the field was this, so now it's that,
Speaker 1: And it's that change that is the photon. That's why
Speaker 1: we say that photons carry information because they're like they're
Speaker 1: carrying information about how these fields are changing, the fields
Speaker 1: going up, and then it's going down, the fields going
Speaker 1: up and then it's going down. That is, the photon
Speaker 1: doesn't actually move like a like a thing. We can
Speaker 1: think of a coffee mug moving from one side of
Speaker 1: my desk the other side of the desk, but a particle.
Speaker 1: A quantum particle is more like um like an effect.
Speaker 1: This part tells the other part, and then that part
Speaker 1: there's the next part, and then it just propagates. Yeah,
Speaker 1: Like if you and I hold it ump rope between
Speaker 1: us and we spind the jump rope, no part of
Speaker 1: the jump rope is moving sideways, like closer to me
Speaker 1: or to you. That's just moving up and down. But
Speaker 1: we can send pulses down that jump rope. Right, if
Speaker 1: I wiggled it really fast, I can send what looks
Speaker 1: like a pulse, But no part of the rope is
Speaker 1: moving sideways. But the pulse is moving sideways that the
Speaker 1: wiggle is moving, but the rope isn't moving. Yeah, and
Speaker 1: even the coffee cup, and the coffee cup is made
Speaker 1: of particles, and those particles are ripples in their fields,
Speaker 1: electron fields, cork fields, whatever, So when the coffee cup moves,
Speaker 1: it's actually the same thing. It's just like a bunch
Speaker 1: of little tiny ripples are moving sideways through the universe.
Speaker 1: That's such a hard warming image, you know, the two
Speaker 1: of us jumping rope together. I feel like I feel
Speaker 1: like I imagine we're in some you know, like city
Speaker 1: block and we're jumping rope and there's children singing, and
Speaker 1: we're having the time of our lives and there's leaves
Speaker 1: blowing everywhere. And afterwards we're sipping hot cocoa and sort
Speaker 1: of a warm, fuzzy camera glow, and we're being interviewed
Speaker 1: by Oprah Like, that's what you're imagining. Yeah, you're sure
Speaker 1: that's going to happen for us. I feel so much
Speaker 1: lighter there. Well, that's good because we're talking about light.
Speaker 1: And so that's what photons are, right, their ripples in
Speaker 1: this electromagnetic field. And the reason that they move at
Speaker 1: the speed of light in a vacuum is that then
Speaker 1: it's just pure electromagnetic field, and they move at the
Speaker 1: maximum speed of information, which is the speed of light
Speaker 1: in a vacuum. So things that are not photons, like
Speaker 1: electrons and corks, they're also you're saying, they're also a
Speaker 1: little perturbations in fields as well. They're just like photons
Speaker 1: in that they're They also don't move in the universe.
Speaker 1: They just propagate. Yes, they propagate through the electron field
Speaker 1: or the cork field, for example. And so an electron
Speaker 1: moves through the universe and it moves at whatever speed
Speaker 1: it's moving, and it's a wiggle in that field. And
Speaker 1: you might ask, well, how come the electron field wiggles
Speaker 1: and it doesn't wiggle the same speed as the photon field? Right, Yeah,
Speaker 1: how come an electron wiggle can variate its speed? Boom?
Speaker 1: We have a gray answer for that. It's the Higgs
Speaker 1: boson because the electron field is not free, it's tied
Speaker 1: to this other field, the Higgs field, that changes how
Speaker 1: it wiggles. And that's what it means for a particle
Speaker 1: to have mass, is that it interacts with this Higgs
Speaker 1: Boson field that changes how ripples move through it, and
Speaker 1: it changes it exactly the way you would expect if
Speaker 1: something had mass. It gives those fields inertia. So mass
Speaker 1: is more like whether or not it interacts with the
Speaker 1: Higgs field, which would slow it down as it moves
Speaker 1: through the universe. Yeah, it doesn't actually slow it down.
Speaker 1: It gives it inertia. It makes it harder to speed
Speaker 1: up and harder to slow down. Right, It's a tiny
Speaker 1: bit more complicated than just slowing down. The Higgs field
Speaker 1: is not like molasses that tries to get everything to
Speaker 1: go to zero speed. It just keeps things at the
Speaker 1: same speed. It makes it hard to change velocity. Oh,
Speaker 1: I see, but light light doesn't interact with the Higgs field,
Speaker 1: so it just always kind of ignores the Higgs field
Speaker 1: and just goes as fast as it can. Yeah, and
Speaker 1: it's actually fascinating. We should do an entire podcast on
Speaker 1: this electroweak symmetry. Like the photon doesn't interact with the
Speaker 1: Higgs field at all, but the W and the Z particles,
Speaker 1: which are very similar to the photon, do interact with
Speaker 1: the Higgs field and become really heavy, and that's why
Speaker 1: the weak field is weak. All right. So there's a
Speaker 1: lot of details in there, but the main idea is
Speaker 1: that a light is a wiggle and it always travels
Speaker 1: at this speed of light in a vacuum, in a
Speaker 1: vacuum precisely. All right, Let's get into this idea of
Speaker 1: maybe whether or not you can slow this wiggle of
Speaker 1: light and how you would do that and why you
Speaker 1: would want to do that. First, let's take a quick
Speaker 1: break up. Okay, Daniel, So you're telling me that light
Speaker 1: always moves at the speed of light. Yeah, deep inside
Speaker 1: here from did you know horge also always travels at
Speaker 1: the speed of Horge that's gonna to a hundred dollars
Speaker 1: physics consulting feed speed of X moves at the speed
Speaker 1: of X. Yeah, but I guess on like light, my
Speaker 1: the horhead, the speed of horhead slows down, is going
Speaker 1: to be slowing down, is slowing down, is going to
Speaker 1: slow down as I get older. But the speed of
Speaker 1: light doesn't seem to change at all. Yeah, And so
Speaker 1: we should separate because again, physics has been terrible about naming,
Speaker 1: because when we talk about the speed of light, often
Speaker 1: what we mean is maximum speed of information in the universe.
Speaker 1: Light in a vacuum happens to travel at that speed,
Speaker 1: and because of historical reasons, we called that speed the
Speaker 1: speed of light. Oh man, you mean physicists name things wrong, Yes, badly,
Speaker 1: and they could have really named it that really the
Speaker 1: speed of light, We should just call it the maximum
Speaker 1: speed of the universe. Yes, the maximum speed the universe
Speaker 1: is separate from the speed of light, because it turns
Speaker 1: out there are lots of different ways to make light
Speaker 1: move slower than the maximum speed of the universe. So
Speaker 1: it's really like a definitions thing, like we just have
Speaker 1: to wrap our shift that little lever in our heads
Speaker 1: and not call it the speed of light anymore. That's right,
Speaker 1: Welcome to physics legalities. Right, But officer, I was not
Speaker 1: traveling faster than the maximum speed of the universe. It
Speaker 1: technically didn't break the speed limit of this highway. It's
Speaker 1: just that the speed limit of this highway is not
Speaker 1: the maximum speed of the universe. I'm sure that that's
Speaker 1: going to get you off that ticket yet. Well, well, well,
Speaker 1: and in the ideal scenario, the officer is a fan
Speaker 1: of our show and just pulled you over to get
Speaker 1: your autograph. That's right on this speeding ticket. And we
Speaker 1: talked in the podcast UM recently actually about drink off
Speaker 1: radiation and what happens when life gets slowed down as
Speaker 1: it passes through a material and other particles zip passed it.
Speaker 1: That's a whole fun, complicated topic. Okay, so we can't
Speaker 1: decrease the maximum speed of the universe, but you can
Speaker 1: make the light go slower than it would in a vacuum,
Speaker 1: or slower than the maximum pet Yeah, you can make
Speaker 1: photons move slower than the maximum speed. And the way
Speaker 1: you do it is you get them to go through
Speaker 1: some material. Because we said that photons move at the
Speaker 1: maximum speed when it's just a pure electromagnetic field and
Speaker 1: a ripple. But if you put other stuff in there,
Speaker 1: like an electron field. Electrons interact with electromagnetic fields, right,
Speaker 1: They have charge and so they will interact with it.
Speaker 1: And like a photon can get absorbed by an electron,
Speaker 1: you have an electron that's zipping around a nucleus, it
Speaker 1: can absorb that photon, hang onto it for a minute,
Speaker 1: and then re emit it. So that effectively slows down
Speaker 1: the photon because it gets from A to B in
Speaker 1: more time than it would if it hadn't been absorbed. Right,
Speaker 1: Like if you want to slow down Hussain Bolt, you
Speaker 1: would have him run through a crowd of people, not
Speaker 1: on an empty track, That's right. Or Jorge driving to
Speaker 1: work takes less time than Jorge driving to work past
Speaker 1: the banana shop because he stops, he takes some bananas.
Speaker 1: It takes some ten minutes. Everybody wonders why he's late.
Speaker 1: You know, I'm not sure anyone wonders anymore why I'm late.
Speaker 1: Daniel put, I'm just glad that you didn't say that
Speaker 1: I drove through a crowd of people. That's where where
Speaker 1: you were going. I'm like, oh, it just just got
Speaker 1: really dark though this is a family friendly podcast, that's right, right, Yeah,
Speaker 1: I guess what you mean is if you want to
Speaker 1: slow light down, you sort of keep it busy. Yeah,
Speaker 1: you interact with it. You you know, Jorge passing through
Speaker 1: a crowd of his admirers is going to have to
Speaker 1: stop and sign autographs more often, and so he's not
Speaker 1: going to get to the other side of the room
Speaker 1: as quickly. Yeah, although these days people don't ask for
Speaker 1: autograph date just asked for selfies mostly. Well, that saves
Speaker 1: your risk, I hope. And to listeners that might feel
Speaker 1: like a technicality, like is the light really traveling less
Speaker 1: than the speed of light? Because it's not really. It's
Speaker 1: between interactions. It's still moving at the maximum speed limit.
Speaker 1: It's just that those interactions take some time. And and
Speaker 1: that's that's totally fair. And again it just depends on
Speaker 1: how you define it. Like you shoot a beam of
Speaker 1: light into glass, when does it come out the other
Speaker 1: side more time? It would take more time than if
Speaker 1: you shot a beam into vacuum. So that's what we
Speaker 1: mean when we say have we slowed down the light?
Speaker 1: I guess you know the image I have in my
Speaker 1: head is sort of like a pinball machine or like
Speaker 1: a pachinko machine. Have you seen those Japanese pinball games
Speaker 1: where the little ball wants to go in a straight line,
Speaker 1: but it keeps bumping into things in between? Now, is
Speaker 1: that sort of what's happening where it's like bumping between
Speaker 1: things or is it really more like the interaction slow
Speaker 1: the light down? Both. It can't move in a straight
Speaker 1: line through material. It's getting deflected. But all deflections are
Speaker 1: also interactions, and sort of a philosophical question here, right,
Speaker 1: If the photon is deflected, is it the same photon
Speaker 1: as the one that came in? It seems like a
Speaker 1: clear question if it gets like fully absorbed and then
Speaker 1: re emitted. But if it gets deflected, it's still there's
Speaker 1: an interaction there, and so it's a different quantum state.
Speaker 1: Oh it actually does get deflected. Well, yeah, Photons moving
Speaker 1: through material don't move in a straight line. They get
Speaker 1: bounced around like a pachinko machine between particles. Sometimes they
Speaker 1: get absorbed and re emitted, sometimes just deflected um. And
Speaker 1: you know, some could argue that those are very different
Speaker 1: kind of experiences for the photons. Some could argue they're
Speaker 1: all interactions so it's all the same deal. But yeah,
Speaker 1: they interact and they get deflected, so it takes longer
Speaker 1: to get from one side of the material to the other.
Speaker 1: I see. So is what slows the light down the
Speaker 1: detours that's taking or is there actually kind of time
Speaker 1: wasted in getting absorbed and re emitted by something in
Speaker 1: the material. It's both both. Those are two different kinds
Speaker 1: of interactions, but they both contribute to making light go
Speaker 1: most more slowly through the material. And it's sort of
Speaker 1: similar to like, you know, making waves move more slowly
Speaker 1: through some material, Like if you if you make waves
Speaker 1: in water, it's different than if you make waves in
Speaker 1: honey or in molasses. Right, there's just a different sort
Speaker 1: of speed of information traveling through that material. And again
Speaker 1: it's because the interactions, like honey holds itself together with
Speaker 1: more wrongly than water does. It's really the same deal.
Speaker 1: So then it sort of depends on what you mean
Speaker 1: by light, like it's light natural photon or is light
Speaker 1: kind of the beam of light? Because the photon itself
Speaker 1: doesn't slow down, does it? It just it just gets busier.
Speaker 1: That's right. The photon itself doesn't slow down unless you're
Speaker 1: averaging right, if you're averaging over it's time through the material,
Speaker 1: then its effective speed is slower. So again it's a
Speaker 1: bit technical. But what these folks have done with these
Speaker 1: experiments that we've been hearing about slowing down light and
Speaker 1: stopping light is even something different than that. It's even
Speaker 1: more of a technicality than just slowing down light. Overall,
Speaker 1: there are different ways to slow light down. One as
Speaker 1: you can slow the photon as it goes across the material.
Speaker 1: And then there's another way, which is what these physicists
Speaker 1: have done. Yeah, because slowing things down as it goes
Speaker 1: through material, that's old news. Like Isaac Newton did that, right,
Speaker 1: he used prisms. Everybody is known for years that you
Speaker 1: can slow things down as they move through a material. Right,
Speaker 1: it's old news. That's from the time of Yeah, this
Speaker 1: it's old news. What these folks have done is not
Speaker 1: just slow things down by moving through ice or water
Speaker 1: or blast. That's last centuries physics news. What they've done
Speaker 1: is something different. Or they claim that it's a big
Speaker 1: step forward, all right, well, um, step us store it.
Speaker 1: What have they done? What did these physicists due to
Speaker 1: slow down light? So what they're doing is not slowing
Speaker 1: down like a beam of light by slowing down individual photons.
Speaker 1: What they're doing is they're slowing down sort of a pulse.
Speaker 1: And when you send a pulse of light, it's not
Speaker 1: just one photon, it's like a collection of photons, the
Speaker 1: way like if you send wiggles down a jump rope,
Speaker 1: it's not a single like sign wave doesn't have a
Speaker 1: single frequency. It has a bunch of different frequencies all
Speaker 1: added up inside of it to make that one shape.
Speaker 1: So are we still talking about individual photons? Are we
Speaker 1: just talking about kind of the the shape of the
Speaker 1: light pulse. We're talking about the pulse, but the pulse
Speaker 1: is made up of a bunch of different photons. It's
Speaker 1: like if you have a group of bike riders and
Speaker 1: you send them all out in a pack. You've got
Speaker 1: a hundred of them or something, and they're all biking together.
Speaker 1: You've got some fast ones and some slow ones and
Speaker 1: sort of like the you know, the shape of the
Speaker 1: pack is changing as it travels, and so the whole
Speaker 1: How old are these cyclists. They're twenty three, just like
Speaker 1: you are. So they're excellent shape. Okay, I just want
Speaker 1: to paint a complete picture here, and any of you
Speaker 1: out there who know anything about like Fourier analysis, that
Speaker 1: you can break down wiggles into sort of their component
Speaker 1: frequencies or so you know, if you're like listening to
Speaker 1: audio and you're looking at equalizer, it shows you, like,
Speaker 1: am I hearing the high pitches or the low pitches
Speaker 1: and the medium pitches? All sound is just a bunch
Speaker 1: of combinations of different wiggles at different frequencies. The same
Speaker 1: thing is true for a pulse of light. If you
Speaker 1: want a pulse of light, you have to make some
Speaker 1: high wiggles and some slower wiggles and patch them all
Speaker 1: together to make that pulse. Right. And and is it
Speaker 1: that different photons of different these different frequencies or is
Speaker 1: it okay? Yes? And so what these researchers have done
Speaker 1: is not slow down individual photons, because that's old news,
Speaker 1: is to try to slow down this whole pulse. To say,
Speaker 1: if we're gonna like send information through fiber optics or whatever,
Speaker 1: you do that by sending pulses of information, you flick
Speaker 1: the switch on and off and that sense whole. But
Speaker 1: a grouping of photons that's a that's a pulse. That's
Speaker 1: a pulse. And so what these experiments are focused on
Speaker 1: is taking one of those pulses and trying to make
Speaker 1: it go more slowly through a material the entire pulse.
Speaker 1: And the key thing there is that, as you said,
Speaker 1: the pulse is made of photons at different frequencies, So
Speaker 1: you've got some that wiggle fast and some the wiggle slow.
Speaker 1: And that's the key idea, because what they do is
Speaker 1: they construct some crazy material, some weird quantum material or
Speaker 1: something where the speed of light through the material is
Speaker 1: different for different frequencies. So the light is slowed down
Speaker 1: differently based on how much it wiggles, Like the really
Speaker 1: blue light is slowed down more than the really red light.
Speaker 1: So it's not that they slowed light down, is that
Speaker 1: they made a material that selectively slows different frequencies. Yes,
Speaker 1: And the consequence is that you like spread out the pulse,
Speaker 1: like you have that group of riders and you said,
Speaker 1: all right, I'm gonna make all the old people ride
Speaker 1: more slowly. Now, then they're gonna start to fall behind,
Speaker 1: and the pulse of riders, this group of bikers is
Speaker 1: going to get more and more spread out, and so
Speaker 1: when the trailing edge of the pulse arrives is going
Speaker 1: to be later, and so sort of the whole pulse
Speaker 1: takes longer to get there. Uh, you stretched it out.
Speaker 1: When it gets there later, well you stretched it out
Speaker 1: and sort of so if you look at like where
Speaker 1: the peak of the pulse is, it moves back because
Speaker 1: part of the pulse got stretched backwards. But doesn't that
Speaker 1: happen normally when you shoot light through glass or ice?
Speaker 1: Doesn't it normally get spread out? It does normally get
Speaker 1: spread out because there's this dispersion relationship, that's what we
Speaker 1: call it, where the slowing downiness depends on the frequency.
Speaker 1: And that's how a prism works, right. A prism works
Speaker 1: because you shoot light into it and the mount that
Speaker 1: it bends depends on this frequency and that's the same
Speaker 1: thing that down so it spreads out exactly, And so
Speaker 1: is what have they done? Then? That's different? Well, these
Speaker 1: materials have like a very strong dispersion. It's like extremely
Speaker 1: extra extra so you can Yeah, so you can shoot
Speaker 1: like a laser, like let's say you want to slow
Speaker 1: it do on a laser pulse. A laser pulse has
Speaker 1: a bunch of frequencies really close together. Because you know,
Speaker 1: a laser is usually like a single color, so it's
Speaker 1: all a bunch of really tightly packed frequencies, it's harder
Speaker 1: to spread out. So what they've done is developed these
Speaker 1: materials where the dispersion is really strong. So even a
Speaker 1: tightly packed laser pulse, which is a bunch of frequencies
Speaker 1: really similar to each other, gets spread out and effectively
Speaker 1: slowed down. It gets blurry. Yeah, yeah, so it gets blurry.
Speaker 1: You smush it. You just gonna smooche the laser. But
Speaker 1: then you know, But then, but like the leading edge
Speaker 1: of the poles, like the first electrons that go in
Speaker 1: there are the fastest, still come out the other side
Speaker 1: as fast as they can. Yeah, the first photons get
Speaker 1: there um at a very high speed. It's not exactly
Speaker 1: the speed of light, because every photon is slowed down
Speaker 1: as it goes through a material for the reasons we
Speaker 1: talked about before. But you're right there. The difference now
Speaker 1: in the speed between the leading edge and the trailing edge.
Speaker 1: And this is where it gets kind of technical. These
Speaker 1: folks talk not about phase velocity, which is a velocity
Speaker 1: of any individual photon in the pulse, a group velocity,
Speaker 1: which is like where is the location of the peak
Speaker 1: half ast is the peak moving. It's like slowing light
Speaker 1: down in the sense that in the sense of what
Speaker 1: happens when you slow down a song or the audio
Speaker 1: of of somebody speaking, it's just goods sort of you know,
Speaker 1: more on the lower it gets blurrier, and it gets
Speaker 1: more in the lower tones. You know, goods slow. But
Speaker 1: they're not technically slowing down the sound pulled the wave.
Speaker 1: They're just kind of spreading it out. And so that's
Speaker 1: what they mean by slowing light down. Yeah, that's what
Speaker 1: they mean by slowing down light. And so you're gonna
Speaker 1: be like clever lawyers, clever lawyers, you gotta sort of
Speaker 1: dig and several layers there before you figure out, like
Speaker 1: what do you really mean by slowing down? Like it
Speaker 1: is sort of more like slowing down in the audio sense, right,
Speaker 1: like you're slowing down a song or speech. Yes, in
Speaker 1: the sense of audio, like the analogy would be that
Speaker 1: you're extending the wavelength of every part of that sound.
Speaker 1: But then you know, as I say to you, hey, Jorge, um,
Speaker 1: you're slowing down like the lower frequencies even more so,
Speaker 1: like you not not only would it sound deeper, would
Speaker 1: I sound more like you know, al green? But also
Speaker 1: the length of the Jorge phrase would take longer to
Speaker 1: get there because the trailing edge of it would take
Speaker 1: longer because you're slowing down the even lower bits. Folks.
Speaker 1: And that was not just Jorge ad living. That was
Speaker 1: actual scientific experimentation, right. That wasn't me burping a banana.
Speaker 1: That was an actual physics. Yeah. And there's one group
Speaker 1: that claims to have even stopped light. Okay, let's get
Speaker 1: into this idea, and maybe you can stop light. That's
Speaker 1: pretty crazy. But first let's take a quick break. Okay,
Speaker 1: so my lawyer says I can slow light down if
Speaker 1: by slowing down I mean like spreading out the wavelengths
Speaker 1: and making it just sort of smooshier. But you're saying
Speaker 1: some scientists can actually or have claim to have actually
Speaker 1: stopped light. Yes, and this is a physics topic, which
Speaker 1: is sort of amazing and then also like sort of
Speaker 1: disappointing and nonsensical because I feel like I stopped light
Speaker 1: all the time. Just you know, I've always been able
Speaker 1: to do that. Half of that power. I just go
Speaker 1: outside and I seem to stop all the light from
Speaker 1: the sun. You do make a better door than a window.
Speaker 1: It's true. I cast a long shadow that you. Well,
Speaker 1: what these folks did when they say they stop light
Speaker 1: is they shoot a laser into some kind of material
Speaker 1: and then the laser gets absorbed by that material, and
Speaker 1: then they can flick a switch and the beam shoots
Speaker 1: back out the other side and an arbitrary later moment. Okay,
Speaker 1: that does sound pretty cool. It sounds pretty cool. They're
Speaker 1: like shoot a beam in, it gets like absorbed, it
Speaker 1: gets he stored, and you can wait like you know,
Speaker 1: a second, an hour, a day, and then you flip
Speaker 1: another laser switch and then the beam shoots it back
Speaker 1: out the other side. Wow, Like, did they trapped it
Speaker 1: inside of this material and then they can let it
Speaker 1: go later? Yes, they've trapped inside the material. All right,
Speaker 1: I mean I'm intrigued. You might ask like, well, did
Speaker 1: they stop the photons? Like and no, of course they
Speaker 1: can't stop the photons. It's not like if they zoomed
Speaker 1: in with a microscope they could see these photons just
Speaker 1: like sitting there. They didn't freeze them, right, they didn't
Speaker 1: freeze the photons. What's that comic book character with the
Speaker 1: with the freezing powers? Oh? Mr Freeze did you just
Speaker 1: make that up? And over see? I tell you they
Speaker 1: right if out of I what's that guy with the
Speaker 1: cartoon powers for particle physics? Is it? Mr particle Physics
Speaker 1: booms exactly? That's how clever that idea sounds. Anyway, Mr
Speaker 1: Freeze didn't like Mr Freeze. These photons, we can like
Speaker 1: look at them covered in ice or anything. What do
Speaker 1: they do? They keep them busy, or they record them
Speaker 1: or what they get. I feel like that comes comes
Speaker 1: from parenting. You're like, all right, I'm gonna run all
Speaker 1: these crazy kids into this room, keep them busy, and
Speaker 1: they'll shoot out the other side. Here's my phone if
Speaker 1: if you want to see a room full of children,
Speaker 1: slow down and maybe Freeze just hand them your phone. Yeah.
Speaker 1: They just have a little phone for these for these photons. Yeah,
Speaker 1: there you go, and these phones admit photons. Now now
Speaker 1: it is getting too deep. Yeah. Essentially, what they do
Speaker 1: is they build some system that can absorb the light,
Speaker 1: store the information from that light, and then re emit
Speaker 1: it at an arbitrary later time based on some external input.
Speaker 1: Isn't that called a camera? Yes, exactly exactly. So I'm
Speaker 1: one sense, it's like, wow, that's awesome. This cloud of
Speaker 1: atoms absorbed this laser and can re emit it. On
Speaker 1: the other hand, like, well, every photograph is basically stopping
Speaker 1: light and later re emitting it. Um. So in one
Speaker 1: sense it's awesome because it's something that nobody's ever done before,
Speaker 1: and another sense, it is accomplishing something we've been doing forever. Well,
Speaker 1: I mean, a photograph and the TV is pretty complicated, right,
Speaker 1: because you need all these different things. But it might
Speaker 1: get in the sense and maybe these guys did it
Speaker 1: in a much more fundamental sense, like they actually build
Speaker 1: a material that takes a photographs and and admits it. Well,
Speaker 1: I wouldn't say it's less complicated, Like I think a
Speaker 1: camera and a screen is less complicated than having like
Speaker 1: you know, um Millie kelvin refrigerator and high intensity lasers.
Speaker 1: But this thing does it sort of all at once,
Speaker 1: like it both absorbs the photons and then later re
Speaker 1: emits it. It's not like it's you know, stored electronically
Speaker 1: and then regenerated. But again you might say it's still
Speaker 1: it's not the same photons, like they were absorbed by
Speaker 1: the material and then re emitted. Is it the same photons?
Speaker 1: Not really stem me through it? What did they do?
Speaker 1: How does this material work. Well. They used a Bose
Speaker 1: Einstein condensate, which is a very cold collection of atoms
Speaker 1: in a really weird quantum state. We'll do a whole
Speaker 1: podcast on what a Bose Einstein condensate is. But what
Speaker 1: they did is they shoot a laser into it from
Speaker 1: the side and then that's sort of like holds it.
Speaker 1: What do you mean, hold it? Like it the light
Speaker 1: is absorbed by the atoms and the condensate, and then
Speaker 1: they just sort of hold it. This first laser is
Speaker 1: like the switch laser, just like gets the atoms in
Speaker 1: the right situation and puts them in the right sort
Speaker 1: of quantum state to do this trick. Then they have
Speaker 1: the second laser, the one they actually want to absorb
Speaker 1: and re emit. They fire that into this pile of
Speaker 1: atoms and then it gets absorbed and then when they
Speaker 1: want to release it, they just turn off the first
Speaker 1: laser and then it emits the pulse from the second
Speaker 1: laser in the same direction and with the same shape
Speaker 1: and intensity everything. Yeah, precisely, and you know, there's some
Speaker 1: loss of information there, but mostly it captures the you know, light.
Speaker 1: That is pretty cool. I think that it's pretty awesome.
Speaker 1: Otherwise it's just a superpower that only a comic book
Speaker 1: character Mr. Light Freezer would have. Mr. Laser Freeze. Okay,
Speaker 1: so oh wow, so um, I mean that that sounds
Speaker 1: pretty impressive that you shoot it and then the atoms themselves,
Speaker 1: not some like memory or some electronic it's like the
Speaker 1: atoms themselves somehow remember this laser and then admit it
Speaker 1: when you want to wanted to in the same way
Speaker 1: that it came in. Yeah, that is pretty cool, And
Speaker 1: I think it's awesome that people just try to make
Speaker 1: materials do new stuff, Like does this whole field of
Speaker 1: you know, atomic physics and condensed matter physics where people
Speaker 1: are like, hey, can we make some new kind of
Speaker 1: goo that has this weird property? Can make some new
Speaker 1: kind of good that has that weird property. And it's
Speaker 1: sort of just like an exploration of the way things
Speaker 1: can be in the universe. And you know, we're used
Speaker 1: to like different kinds of stuff water, metals, rocks, whatever,
Speaker 1: but it's possible that there's all different kinds of stuff
Speaker 1: in the universe that we've never experienced just because doesn't
Speaker 1: occur naturally here on Earth. So these folks are like
Speaker 1: pushing the boundaries right, they're trying to make things do
Speaker 1: new things. Yes, exactly, they're trying to bring the rules.
Speaker 1: They're like, well, nobody thought things could do this, Let's
Speaker 1: see if we can make it work. It's kind of like,
Speaker 1: you know, nobody ever thought you could walk on water,
Speaker 1: but hey, it turns out if you freeze it, you
Speaker 1: can walk on water. Yes, And in some sense it's
Speaker 1: as unsatisfying as that. It's like, are you really walking
Speaker 1: on water if you're walking on a frozen lake? Technically yes,
Speaker 1: what have you shoot a lasers through it? Is it
Speaker 1: still technically a miracle? Well, you know, if you're ice skating,
Speaker 1: then you're walking water because you're making this very thin
Speaker 1: layer of water between your blades and the ice. So
Speaker 1: you know, there you go. More Jesus lawyer. And people
Speaker 1: try to say, maybe there's some application to this, like
Speaker 1: if you could slow down light, you could make circuits
Speaker 1: that use less power or something interesting. Yeah, rank Frankly,
Speaker 1: I don't find any of that convincing. I think that
Speaker 1: the motivation for this is like, hey, can we make
Speaker 1: something in the universe that's weird and different? And I
Speaker 1: think there's there's a there's a lot of value to
Speaker 1: that well, there's a lot of applications that they say
Speaker 1: so in solid state physics, where if you get these
Speaker 1: materials to do these weird things, that they could maybe
Speaker 1: be the basis for like a quantum computer. Yeah, precisely,
Speaker 1: there are ways and you could find applications for materials
Speaker 1: that do weird stuff. And you know, people were building
Speaker 1: atom traps and bose Einstein particles for years before they
Speaker 1: had ideas for how to apply them. So it's a
Speaker 1: good idea to develop new kinds of materials because they
Speaker 1: can inspire new applications. And sometimes you work on something
Speaker 1: for ten years and then people realize, hey, that's exactly
Speaker 1: what we needed for this other totally unrelated problem. So
Speaker 1: you know, we want to make progress as a species,
Speaker 1: we've got to like explore broadly and try all sorts
Speaker 1: of weird stuff. And you never know, like it could
Speaker 1: have been that they didn't make light stop, but something
Speaker 1: else totally weird and unexpected happened and discovered something crazy.
Speaker 1: You never know. When you do research right or just
Speaker 1: that improving these things, you learn something new about the
Speaker 1: materials themselves, or how atoms are like behave, or if
Speaker 1: in order to make this happen. You have to invent
Speaker 1: something new and weird and that turns out to be
Speaker 1: really useful for something else, you know, like the whole
Speaker 1: semiconductor industry and computers exist because of basic research into
Speaker 1: stuff that wasn't motivated at building computers. Like, for example,
Speaker 1: I just got this great idea to shoot myself with
Speaker 1: a laser to stop aging or at least on my knees.
Speaker 1: There is laser therapy for everything, Like you can get
Speaker 1: laser therapy to like stop smoking. I wonder, like what
Speaker 1: part do you are they sting with the laser? Probably
Speaker 1: your wallet and your Yeah, I don't know. I wouldn't
Speaker 1: recommend any of those laser treatments. Okay, well it is.
Speaker 1: It does sound like they maybe have technically slowed down
Speaker 1: light and maybe sort of in a ways stop light.
Speaker 1: So that's pretty pretty interesting, pretty cool. It's pretty cool.
Speaker 1: They've definitely done something nobody has done before. And today
Speaker 1: we only talked about a couple of groups doing a
Speaker 1: couple of experiments, but it's a big field and people
Speaker 1: are doing it will all sorts of new kinds of
Speaker 1: materials and in new ways, and applying it to different
Speaker 1: kinds of light and higher intensity, lower intensity, and bigger
Speaker 1: packets and smaller packets. We couldn't possibly review all the
Speaker 1: recent work on it. It's a whole burgeoning industry. All right. Well,
Speaker 1: I think that answers that question that a lot of
Speaker 1: people wrote in about you can slow down light and
Speaker 1: you can stop light. Have you defined things in the
Speaker 1: right way and use both speakers? Was that the main
Speaker 1: lesson here? Yes? And so if you find a bottle
Speaker 1: and the genie comes out and he's a physicist, and
Speaker 1: you ask for some new special power, make sure you
Speaker 1: are very clear about what you're asking for, because these
Speaker 1: physicists will find a way to squirrel out of it
Speaker 1: and not give you what you were hoping for. Right,
Speaker 1: You might just hand you a six pack of light
Speaker 1: beer and then you say your way. This light will
Speaker 1: make you slow down. That's one way to slow down. There,
Speaker 1: you go do that a laser and you can sell
Speaker 1: it for a lot more. Yeah, you don't want us
Speaker 1: as your physics genies may that that's what would make
Speaker 1: hell a little bit more tolerable. Sin, you can freeze
Speaker 1: some beer down and that you can drink it with
Speaker 1: the physicists. All right, Well, thank you very much to
Speaker 1: everybody who wrote in to ask us about this weird headline.
Speaker 1: And if you read something online about weird discoveries and
Speaker 1: physics or something you're not quite sure about, send it
Speaker 1: to us. We will break it down for you. You
Speaker 1: hope you enjoyed that. Thanks for listening. Let's see you
Speaker 1: next time. Before you still have a question after listening
Speaker 1: to all these explanations, please drop us a line. We'd
Speaker 1: love to hear from you. You can find us on Facebook, Twitter,
Speaker 1: and Instagram at Daniel and Jorge That's one word, or
Speaker 1: email us at Feedback at Daniel and Jorge dot com.
Speaker 1: Thanks for listening, and remember that Daniel and Jorge explained.
Speaker 1: The Universe is a production of I Heart Radio More
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Speaker 1: Yeah