Daniel and Kelly’s Extraordinary Universe - Can you slow down light?

Episode Date: February 6, 2020

The speed of light is constant but is it possible to slow it down? Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

This is an I-Heart podcast. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System

On the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want or gone. Hold up. Isn't that against school policy? That seems inappropriate.

Maybe find out how it ends by listening to the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. In sitcoms, when someone has a problem, they just blurt it out and move on. Well, I lost my job and my parakeet is missing. How is your day? But the real world is different. Managing life's challenges can be overwhelming. So, what do we do? We get support. The Huntsman Mental Health Institute and the Ad Council have mental health resources available for you at loveyourmindday.org. That's loveyourmindtay.org.

See how much further you can go when you take care of your mental health. Hey, Jorge, do you think there's anything good about getting older? Why are you asking me? I'm only 23. long you've been 23 for, like 10 years, 20 years? Yeah. For a while, yeah. All right, but do you think like there's any advantage to getting old and slowing down?

I guess fewer speeding tickets? Maybe like new kinds of joint pain to feel, so new experiences. Yeah, the early bird specials at restaurants. Sometimes I wonder if it's good to forget some of those painful memories of youth. So there are advantages. Maybe physics should try slowing down. You want me to tell these photons to take it easy? You know, I know they're billion years old and they've been going at the speed of light for a long time,

but maybe it's time for them to slow down. They can get the early photon special. Hi, I'm Jorge. I'm a cartoonist and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist and I hope to be aging gracefully. And welcome to our podcast, Daniel and Jorge, age and explain the universe at the same time. Daniel and Jorge explain the aging of the universe, which is mostly my knees at this point. Which is technically happening right now. Right now, as you're listening to us, we are getting older. Yes, and the universe is getting older. You will finish this podcast in a different,

universe than the one you started it in. Right, a little bit bigger, a little bit older and wiser. A little bit cooler. A little bit darker. The universe is getting older and colder and slower, though dark energy, of course, is accelerating. But the most things, when they get older, sort of slow down. Just like us, it gets a little bit more boring.

No, we are getting funnier as we get older, Jorge. Oh, right, right. No, I mean like entropy. Like entropy is increasing in the universe. And so is the entropy of our knees and jokes. Well, maybe as we get older, we don't get funnier, but we think we're funnier. So I laugh more at your jokes, even as they decay in quality. It's all about perspective.

It's all about perspective. Just like in relativity, there is no universal time or distance in comedy, right? There is no universal humor. There's no universal law for jokes. Is there no theory of special comedy? Well, there are a lot of jokes about relatives, but not. Everybody jokes about their family, right? Yeah, this idea that everything is slowing down is kind of inevitable,

but there are some things in the universe that maybe will never slow down. That's right, even though photons travel through billions of light years of space, when they get here, they're still moving at the speed of light. You fire that photon from your flashlight at Alpha Centauri. It's going to get there, and it's going to be going the same speed when it does. Yeah, I hadn't thought about it. I guess photons are going at the same speed wherever they go, no matter how long they've been going.

Yeah, photons don't get tired, right? You push a photon and it goes, and it just goes and goes and goes and goes and goes, and it doesn't like run out of energy. You know, unless it gets absorbed by something or bounces off something, it will just keep going forever. It's sort of amazing. At the maximum speed of the universe. Not just at any speed, at the maximum speed of the universe.

Yeah, and photons, people have been asking me on Twitter or whether photons experience time. Like, do photons even get old? You know, because a photon has taken a billion years to get here from somewhere else. And they wonder, do photons experience time? And it's a tricky question because you have to imagine, like, a photon having a clock?

What is that clock made out of? If it has mass, then the photons can't. How does it look at the clock? Does it use photons to look at the clock? What is it like to be a photon, man? It seems like maybe more of a philosophical question than a physics question. Yeah, I don't think photons even have knees.

to feel their joint pain. I'm not asking whether we have anything in common with photons. They are weird quantum mechanical little particles. But where we ended up with that question was that photons are moving at the speed of light and so they see most of the universe contracted. So a photon leaves here and it feels like it hasn't gone very far because the universe has been sort of shortened.

To them the universe is just, it's basically tiny, right? It's the size of a point maybe? Yeah, that's right. and it's bizarre to imagine what it might be like to travel as a photon. But again, I don't think we want to get into the question of what is it like to be a photon. But it is sort of a good life example to not slow down, you know? Take some inspiration. Photons are my new heroes.

But other folks have been writing in and asking about whether photons always do go at the speed of light. Can they not go at the speed of light? Can they throttle down? Yeah. When photons get old, is there any way they can sort of chill out a little bit and relax? So to the end of the podcast, we'll be asking, this question that several, you said several readers wrote in about. There are a bunch of people who have been reading articles online

about physicists managing to slow down light. And they thought, what? We better get Daniel and Jorge to explain that to us. So to the end of the program, we'll be asking the question, Can light be slowed down? It's fascinating because people think that, of course, photons travel at the speed of light, right? That's why we call it the speed of light.

And we make a big deal about how that's constant. If you shoot a photon out, you measure it traveling at the speed of light. Somebody else measures it traveling at the speed of light. There's sort of this like fundamental constancy, this like stubbornness of photons to always go at the same speed. Right. Other things can vary their speed, right? Electrons, quarks, pretty much all the other neutrinos, right?

They can go slow. They can sit in the palm of your hand or they can go at nearly the speed of light. Yeah. Anything that's massive. that has any mass to it, electrons, even neutrinos, anything like that, has a rest mass. Like, you can catch up to it and have no relative velocity. You can exist next to it, hold it, throw it around, et cetera. But things that have no mass, what would happen if you caught up to them, right?

If there's a photon and you caught up to it, a photon is just motion, right? There's nothing to it other than its motion. So if you catch up to it and there's no motion, there's no velocity relative to the photon, it's not there anymore. So that's why you can never catch up to a photon. It just doesn't make sense. It's like what happens if you catch a wave? It's no longer a wave. Yeah, that's right.

If you're surfing, right, and you look down, then it's not really a wave anymore. It's just sort of like a stationary shape of the water. And so there's no relative motion there. Yeah, so don't surf on photons, people. Not a good idea, especially as you get older. Yeah. And so this is an interesting question. And so we're going to tackle it today.

We're going to talk about whether or not you can slow. light down and whether it seems that some people have. Yeah, there have been some pretty exciting experiments with click-baiting headlines about slowing down light and stopping light. And so we're going to dig into that today and see it doesn't make any sense. What are they actually doing? And is it cool or what? Oh, stopping.

You can slow it down to the point of maybe stopping light. Yeah. Yeah. Oh, wow. These physicists are trying to break the rules of the universe. Well, as usual, I was curious, do people think it's possible to slow down light or or does that just sound like crazy talk? So I walked around campus at UC Irvine.

Yeah, so before you listen to these answers, think about it for a second. Do you think that light can be slowed down? Here's what people had to say. I don't think so. Don't know? I would say no. Theoratically. You're right? Yes.

How would you do it? I have no clue. I know that photons within the sun, it takes very long time until they actually reach the surface of the sun and are released into space. I don't know. I mean, it's not actually slowing down the photons, but... I mean, there's relativity, obviously, so... That's close down time, but that's... Right.

That's time, but that's... And light is supposed to be the constant in that case. Right, because it is a constant, right? But I think if you put light through different media, but it should be slower, but I don't think that it is. I would expect that if you put light through water. I would expect there would be some sort of effect, but... But we have a constant for light, so how can it be... How can it change through a different medium if we have a constant for it?

That's why I'm, like... But we, that's constants for an error. Yes. Isn't it? Okay, so maybe it is. Or an in a vacuum. Right, in a vacuum, okay. So I think there might be slight changes possibly,

but I think it's inherently supposed to be constant. No, because isn't like a constant number? I think somehow through velocity or something like that, changing velocity at a very high rate might be able to. I'm not too sure. Maybe like a black hole type gravity type situation. Yeah. No?

Cool. Some pretty cool answers here. a lot of yeses and a lot of maybes, I don't know. How did people react to the question itself? Because it's not a question that I had heard much about before you send me the email this morning. You know, you don't think about slowing the light down much.

Well, I think that feeling is backed up by these people's experience because when I ask them, do you think it's possible to slow down light? I got a lot of quizzical looks and a lot of long pauses as people thought about it. And you can hear people reaching for answers. They're like, I don't know, is a black hole involved, maybe? You kind of have to stop and parse the words a little bit. Like slow down light, slow down something that is not quite there.

Yep. And parsing the words is going to be the solution to today's question because the answer is sort of technical and legalistic. It's sort of one of these loopholes in the laws of physics. Like, have you really slowed it down? Some people would say they have. Some people would, you know, quibble. with that. All right, so we have to put on our physics lawyer hats today. Whenever you're

reading the laws of physics, you've got to be very careful, you know, to understand exactly what they mean and what they don't mean. Are we sort of the shark type of physics lawyer or are the nice type of physics lawyers today? Are we out to get the universe? Are we out to, are we out for justice, Daniel? We are not the physics police, right? We are on this, we're on the defense side here. We are trying to make sure physicists can do whatever they like. We're trying to allow is this to do weird stuff with the universe? Because in the end, that's how we learn what the rules really are. We find the cracks that may exploit them, try to figure out what's actually possible given the rules that we know. It seems like people had a sense that, you know,

the universe is interesting enough that maybe there are situations in which you can slow light down. Like, that didn't seem impossible to a lot of people. Yeah, that's an optimistic way to look at it. Like, no matter how constant you think that law is, there must be some way, some place in the universe where we could break or we could find something crazy happening. I like thinking that people are open to the fact the universe is filled with crazy bunker stuff. Okay, so let's break it down for folks here, Daniel, and let's talk about light and how fast it travels and what we know about light and its speed. The first thing to understand, which I think most people already do, is that light does always travel at the same speed in a vacuum. And remember what light is. Like,

You can think about light as a photon as a little particle, and it is quantized, but if fundamentally think about light as a sort of a ripple, space is filled with quantum fields. Even empty space has the possibility to have these particles in it because it contains within it these quantum fields, like the electromagnetic field, that can ripple. So I think a space is sort of like having these different possible sort of sheets, rubber sheets in it, and mostly they're just sort of spread smooth, but occasionally you can get a ripple in one. And that ripple is like a particle. I see.

So I think the main idea is that light is a photon, it's not a thing. It's not like a little spherical thing. It's more like a little divot in the kind of the fabric of the universe. Yeah, it's got no stuff to it. If that's what you mean by, it's not a thing. It's a transient property, right? That's why it's always moving. It's a ripple.

It's like a change in information. It's saying, oh, the electromagnetic field was this. Oh, now it's that. And it's that change that is the photon. That's why we say that photons carry information because they're like, they're carrying information about how these fields are changing. The field's going up and then it's going down.

The field's going up and then it's going down. That is the photon. It doesn't actually move like a thing. We can think of a coffee mug moving from one side of my desk, the other side of the desk, but a particle, a quantum particle is more like an effect. This part tells the other part and then that part there's the next part and then just propagates.

Yeah, like if you and I hold a jump rope between us, and we spin the jump rope, no part of the jump rope is moving sideways, like closer to me or to you that's just moving up and down. But we can send pulses down that jump rope, right? If I wiggle it really fast, I can send what looks like a pulse. But no part of the rope is moving sideways, but the pulse is moving sideways. The wiggle is moving, but the rope isn't moving. Yeah.

And even the coffee cup, man, the coffee cup is made of particles, and those particles are ripples in their fields, electron fields, quark fields, whatever. So when the coffee cup moves, it's actually the same thing. It's just like a bunch of little tiny ripples are moving sideways through the universe. That's such a hardwarming image, you know, the two of us jumping rope together. I feel like, I imagine we're in some, you know, like city block, and we're jumping rope, and there's children singing, and we're having the time of our lives. And there's leaves blowing everywhere, and afterwards we're sipping hot cocoa and sort of like a warm, fuzzy camera glow.

and we're being interviewed by Oprah, like that's what you're imagining? Yeah, yeah. I'm sure that's going to happen for us. Good feelings. I feel so much lighter now. Well, that's good because we're talking about light. And so that's what photons are. There are ripples in this electromagnetic field,

and the reason that they move at the speed of light in a vacuum is that then it's just pure electromagnetic field and they move at the maximum speed of information, which is the speed of light in a vacuum. Right. So things that are not photons, like electrons and quarks, They're also, you're saying they're also little perturbations in fields as well. They're just like photons in that they also don't move in the universe.

They just propagate. Yes. They propagate through the electron field or the cork field, for example. And so an electron moves through the universe, and it moves at whatever speed it's moving, and it's a wiggle in that field. And you might ask, well, how come the electron field wiggles and it doesn't wiggle the same speed as the photon field, right? Yeah. How come an electron wiggle can vary its speed?

Boom, we have a great answer for that. It's the Higgs boson because the electron field is not free. It's tied to this other field, the Higgs field, that changes how it wiggles. And that's what it means for a particle to have mass, is that it interacts with this Higgs boson field that changes how ripples move through it, and it changes it exactly the way you would expect if something had mass. It gives those fields inertia. So mass is more like whether or not it interacts with the,

the Higgs field, which would slow it down as it moves through the universe. Yeah, or it doesn't actually slow it down. It gives it inertia. It makes it harder to speed up and harder to slow down, right? It's a tiny bit more complicated than just slowing it down. The Higgs field is not like molasses that tries to get everything to go to zero speed. It just keeps things at the same speed. It makes it hard to change velocity.

Oh, I see. But light, light doesn't interact with the Higgs field, so it just always kind of ignores the Higgs field and just goes as fast as it can. Yeah, and it's actually fascinating. We should do an entire podcast on this electro-week symmetry, like the photon doesn't interact with the Higgs field at all, but the W and the Z particles, which are very similar to the photon, do interact with the Higgs field and become really heavy, and that's why the weak field is weak.

All right, so there's a lot of details in there. But the main idea is that a light is a wiggle, and it always travels at this speed of light in a vacuum. Mm-hmm, in a vacuum, precisely. All right, let's get into this idea of maybe whether or not you can slow this wiggle of light and how you would do that and why you would want to do that. But first, let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys, then,

At 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass. The injured were being loaded into ambulances. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back.

In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on. on the OK Story Time podcast, so we'll find out soon.

This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating.

He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the Iheart Radio app, Apple podcast, or wherever you get your podcast. I'm Dr. Joy Harden Bradford. And in session 421 of Therapy for Black Girls, I sit down with Dr. Othia and Billy Shaka to explore how our hair connects to our identity, mental health, and the ways we heal. Because I think hair

is a complex language system, right? In terms of it can tell how old you are. your marital status, where you're from, you're a spiritual belief. But I think with social media, there's like a hyperfixation and observation of our hair, right? That this is sometimes the first thing someone sees when we make a post or a reel. It's how our hair is styled. You talk about the important role hairstylists play in our community, the pressure to always look put together, and how breaking up with perfection can actually free us.

Plus, if you're someone who gets anxious about flying, Don't miss Session 418 with Dr. Angela Neil Barnett, where we dive into managing flight anxiety. Listen to Therapy for Black Girls on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Okay, Daniel, so you're telling me that light always moves at the speed of light. Yeah, deep insight here from Daniel Watson, right? Did you know, Jorge also always travels at the speed of Jorge. That's going to cost you $100 physics consulting fee. The speed of X moves at the speed of X.

Yeah, but I guess unlike light, the horse head, the speed of Jorge slows down. It's going to be slowing down. It's slowing down and it's going to slow down as I get older. But the speed of light doesn't seem to change at all. Yeah, and so we should separate because, again, physics has been terrible about naming. because when we talk about the speed of light, often what we mean is maximum speed of information in the universe. Light in a vacuum happens to travel at that speed,

and because of historical reasons, we call that speed the speed of light. Oh, man, you mean physicists name things wrong. Yes, badly. Confusingly. Or they could have really named it better. So really, the speed of light, we should just call it the maximum speed of the universe.

Yes, the maximum speed of the universe. is separate from the speed of light because it turns out there are lots of different ways to make light move slower than the maximum speed of the universe. So it's really like a definitions thing. Like we just have to wrap our...

Shift that little lever in our heads and not call it the speed of light anymore. That's right. Welcome to physics legalities, right? But officer, I was not traveling faster than the maximum speed of the universe. I technically didn't break the speed limit of this highway.

It's just that the speed limit of this highway is not the maximum speed of the universe. I'm sure that that's going to get you off that ticket yet. Well, and in the ideal scenario, the officer is a fan of our show. And just pulled you over to get your autograph. That's right. On this speeding ticket. And we talked in the podcast recently, actually, about churinkoff radiation and what happens

when light gets slowed down as it passes through a material. and other particles zip past it. That's a whole fun, complicated topic. Okay, so we can't decrease the maximum speed of the universe, but you can make light go slower than it would in a vacuum, or slower than the maximum speed of the universe. Yeah, you can make photons move slower than the maximum speed. And the way you do it is you get them to go through some material

because we said that photons move at the maximum speed when it's just a pure electromagnetic field and a ripple. But if you put other stuff in there, like an electron field, electrons interact with electromagnetic fields, right? They have charge. And so they will interact with it. And like a photon can get absorbed by an electron. You have an electron that's zipping around a nucleus,

it can absorb that photon, hang on to it for a minute, and then re-emit it. So that effectively slows down the photon because it gets from A to B in more time than it would if it hadn't been absorbed. Right. Like if you want to slow down Usain Bolt, you would have him run through a crowd of people,

not on an empty track. That's right. Or Jorge driving to work takes less time than Jorge driving to work past a banana shop because he stops, he picks some bananas,

it takes him 10 minutes, everybody wonders why he's late, you know. I'm not sure anyone wonders anymore why I'm late, Daniel, but I'm just glad that you didn't say

that I drove through a crowd of people. Is that where you thought I was going? I thought that was where you were going. I'm like, oh, this just got really dark. No, this is a family-friendly podcast. That's right.

That's right. Yeah. I guess what do you mean is if you want to slow light down, you sort of keep it busy. Yeah, you interact with it. You know, Jorge passing through a crowd of his admirers is going to have to stop and sign autographs more often. And so he's not going to get to the other side of the room as quickly. Yeah. Although these days, people don't ask for autograph date. Just ask for selfies mostly. Well, that saves your wrist, I hope. And to listeners, that might feel like a technicality. Like, is the light really traveling less than the speed of light? Because it's not really. Between interactions, it's still moving at the maximum speed limit. It's just that those interactions take some time.

And that's totally fair. Again, it just depends on how you define it. Like, you shoot a beam of light into glass. When does it come out the other side? More time, it would take more time than if you shot a beam into vacuum. So that's what we mean when we say, have we slowed down the light. I guess, you know, the image I have in my head is sort of like a pinball machine or like a Pachinko machine.

Have you seen those Japanese pinball game? where the little ball wants to go in a straight line, but it keeps bumping into things in between. Now, is that sort of what's happening where it's like bumping between things, or is it really more like the interaction slow the light down? Both. It can't move in a straight line through material.

It's getting deflected. But all deflections are also interactions. It's sort of a philosophical question here, right? If a photon is deflected, is it the same photon as the one that came in? It seems like a clear question if it gets fully absorbed and then re-emitted. But if it gets deflected, it's still there's an interaction there. And so it's a different quantum state. Oh, it actually does get deflected?

Well, yeah, photons moving through material don't move in a straight line. They get bounced around like a pachinko machine between particles. Sometimes they get absorbed and re-emitted, sometimes just deflected. And some could argue that those are very different kind of experiences for the photons. Some could argue they're all interactions, so it's all the same deal. But yeah, they interact and they get deflected. So it takes longer to get from one side of the material to the other. I see.

So is what slows the light down the detours it's taking? Or is there actually kind of time wasted in getting absorbed and re-emitted by something in the material? It's both. Both. Those are two different kinds of interactions, but they both contribute to making light go more slowly through the material. And it's sort of similar to like, you know, making waves move more slowly through some material. Like if you make waves in water, it's different than if you make waves in honey or in molasses, right? There's just a different sort of speed of information traveling through that material.

And again, it's because of the interactions, like honey holds itself together more strongly than water does. It's really the same deal. So then it sort of depends on what you mean by light. Like, it's light an actual photon or is light kind of the beam of light? Because the photon itself doesn't slow down, does it? It just gets busier. That's right. The photon itself doesn't slow.

down unless you're averaging, right? If you're averaging over its time through the material, then its effective speed is slower. So again, it's a bit technical. But what these folks have done with these experiments that we've been hearing about slowing down light and stopping light is even something different than that. It's even more of a technicality than just slowing down light overall. There are different ways to slow light down. One is you can slow the photon as it goes across the material. And then there's another way, which is what these physicists have done. Yeah, because slowing things down as it goes through material, that's old news. Like, Isaac Newton did that, right?

He used prisms. Everybody's known for years that you can slow things down as they move through a material, right? It's old news. That's old old news. That's old news. What these folks have done is not just slow things down by moving it through ice or water or glass. That's last century's physics news. What they've done is something different, or they claim that it's a big step forward.

All right. Well, step us through it. What have they done? What did these physicists do to slow down light? So what they're doing is not slowing down like a beam of light by slowing down individual photons. What they're doing is they're slowing down sort of a pulse. And when you send a pulse of light, it's not just one photon.

It's like a collection of photons. The way like if you send wiggles down a jump rope, it's not a single like sine wave. It doesn't have a single frequency. It has a bunch of different frequencies all added up inside of it to make that one shape. So are we still talking about individual photons, or are we just talking about kind of the shape of the light pulse? We're talking about the pulse, but the pulse is made up of a bunch of different photons.

It's like if you have a group of bike riders, right, and you send them all out in a pack. You got a hundred of them or something, and they're all biking together. You got some fast ones and some slow ones and sort of like the, you know, the shape of the pack is changing as it travels. And how old are these cyclists? They're 23, just like you are, so they're in excellent shape. Okay, I just want to paint a complete picture here. And any of you out there who know anything about like Fourier analysis, that you can break down wiggles into sort of their component frequencies.

So you know if you're like listening to audio and you're looking at an equalizer, it shows you like, am I hearing the high pitches or the low pitches or the medium pitches? All sound is just a bunch of combinations of different wiggles at different frequencies. the same thing is true for a pulse of light. If you want a pulse of light, you have to make some high wiggles and some slower wiggles and patch them all together to make that pulse. Right.

And is it that different photons have these different frequencies? Yes. Is it, okay. Yes. And so what these researchers have done is not slow down individual photons, because that's old news, is to try to slow down this whole pulse.

It's to say, if we're going to like send information through fiber optics or whatever, you do that by sending pulses of information. You flick the switch on and off, and that sends a grouping of photons, that's a pulse. That's a pulse. And so what these experiments are focused on is taking one

of those pulses and trying to make it go more slowly through a material, the entire pulse. And the key thing there is that, as you said, the pulse is made of photons at different frequencies. So you got some that wiggle fast and some that wiggle slow. And that's the key idea because what they do is

they construct some crazy material, some weird quantum material or something, where the speed of light through the material is different for different frequencies. So the light is slowed down differently based on how much it wiggles. Like the really blue light is slow down more than the really red light.

So it's not that they slowed light down is that they made a material that selectively slows different frequencies? Yes. And the consequence is that you like spread out the pulse. Like you have that group of riders and you say, all right, I'm going to make all the old people ride more slowly now, then they're going to start to fall behind.

And the pulse of riders, this group of bikers is going to get more and more spread out. And so when the trailing edge of the pulse arrives is going to be later. And so sort of the whole pulse takes longer to get there. Oh, you stretched it out when it gets there later? Well, you stretched it out. And sort of, so if you look at like where the peak of the pulse is, it moves back because part of the pulse got stretched backwards. But doesn't that happen normally when you shoot light through glass or ice?

Doesn't it normally get spread out? It does normally get spread out because there's this dispersion relationship. That's what we call it, where the slowing downiness depends on the frequency. And that's how a prism works, right? A prism works because you shoot light into it and the amount that light bends depends on its frequency. And that's the same thing is slowing out. So it spreads out, exactly. So what have they done then that's different?

Well, these materials have like a very strong dispersion. It's like extremely extra. Oh, extra. So you can shoot, for example. Yeah, so you can shoot like a laser. Like, well, say you want to slow it on a laser pulse, a laser pulse has a bunch of frequencies really close together because, you know, a laser is usually like a single color.

So it's all a bunch of really tightly packed frequencies. It's harder to spread out. So what they've done is develop these materials where the dispersion is really strong. So even a tightly packed laser pulse, which is a bunch of frequencies really similar to each other, gets spread out and effectively slowed down. Oh, it gets blurry. Yeah, yeah, so it gets blurry.

You smush it, you just kind of smooch the laser. But then, but like the leading edge of the pulse, like the first electrons that go in that are the fastest, still come out the other side as fast as they can. Yeah, the first photons get there at a very high speed. It's not exactly the speed of light because every photon is slowed down as it goes through a material

for the reasons we talked about before. But you're right, there's a difference now in the speed between the leading edge and the trailing edge. And this is where it gets kind of technical. These folks talk not about phase velocity, which is the velocity of any individual photon

in the pulse, but group velocity, which is like, where is the location of the peak? How fast is the peak moving? It's like slowing light down in the sense that, in the sense of what happens when you slow down a song. or the audio of somebody speaking, it just gets sort of, you know,

more in the lower, it gets blurrier and it gets more in the lower tones, you know, it gets slow down. But they're not technically slowing down the sound pole, the wave, they're just kind of spreading it out. And so that's what they mean by slowing light down. Yeah, that's what they mean by slowing down light.

And so you've got to like, clever lawyers. You've got to sort of dig in several layers there before you figure out, like, what do you really mean by slowing down life? It is sort of more like slowing down in the audio sense, right? Like you're slowing down a song or speech. Yes, in the sense of audio, like the analogy would be that you're extending the wavelength of every part of that sound. But then, you know, as I say to you, hey, Jorge, you're slowing down like the lower frequencies even more. So, like, not only would it sound deeper, would I sound more like, you know, Al Green, but also the length of the Jorge phrase would take longer to get there because the trailing edge of it would take longer because you're slowing down the even lower bits.

Folks, and that was not just Jorge Adlibbing. That was actual scientific experimentation right there. That wasn't me burping a banana. That was an actual physics experiment. Yeah. And there's one group that claims to have even. even stopped light. Okay, let's get into this idea then of maybe you can stop light.

That's pretty crazy. But first, let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush. Parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m. everything changed. There's been a bombing at the TWA terminal.

Apparently, the explosion actually impelled metal, glass. The injured were being loaded into ambulances. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to us. threat that hides in plain sight that's harder to predict and even harder to stop listen to the new

season of law and order criminal justice system on the iHeart radio app apple podcasts or wherever you get your podcasts my boyfriends professor is way too friendly and now i'm seriously suspicious well wait a minute sam maybe her boyfriend's just looking for extra credit well dakota it's back to school week on the okay story time podcast so we'll find out soon this person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up.

Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated?

with his professor or not. To hear the explosive finale, listen to the OK Storytime podcast on the Iheart radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Joy Harden Bradford. And in session 421 of therapy for black girls, I sit down with Dr. Othia and Billy Shaka to explore how our hair connects to our identity, mental health, and the ways we heal. Because I think hair is a complex language system, right?

In terms of it can tell how old you are, your marital status, where you're from, you're spiritual belief. But I think with social media, there's like a hyper fixation and observation of our hair, right? That this is sometimes the first thing someone sees when we make a post or a reel is how our hair is styled. You talk about the important role hairstylists play in our communities, the pressure to always look put together, and how breaking up with perfection can actually free us. Plus, if you're someone who gets anxious about flying, don't miss session 418 with Dr. Angela Neil Barnett, where we dive into managing flight anxiety. Listen to therapy for black girls on the IHeartRadio app, Apple Podcasts, or wherever you get your

podcast. Okay, so my lawyer says I can slow light down. If by slowing down, I mean like spreading out the wavelengths and making it just sort of a musier, but you're saying some scientists can actually or have claimed to have actually stopped light. Yes, and this is a physics topic which is sort of amazing and then also like sort of disappointing and nonsensical. Because I feel like I stop light all the time.

I just, you know, I've always been able to do that, have that power. I just go outside and I seem to stop all the light from the sun. You do make a better door than a window, it's true. I cast a long shadow, Dano. Well, what these folks did when they say they stopped light is they shoot a laser into some kind of material and then the laser gets absorbed by that material and then they can flick a switch and the beam shoots back out the other side at an arbitrary later moment. Okay, that does sound pretty cool. It sounds pretty cool. They're like shoot a beam in.

It gets like absorbed. It gets stored and you can wait like a second, an hour, a day and then you flip another laser switch and then the beam shoots it back out the other. other side. Wow. Like they trapped it inside of this material and then they can let it go later. Yes. They've trapped it inside the material. All right. I'm intrigued. You might ask like, well, did they stop the photons? Like, and no, of course, they

can't stop the photons. It's not like, if they zoomed in with a microscope, they could see these photons just like sitting there. They didn't freeze them. Right. They didn't freeze the photons. What's that comic book character with the with the freezing powers? Oh, Mr. Freeze?

Did you just make that up? Is that the best you can come up with? That is the, I told you, they ran out of ideas in 1986. What's that guy of the cartoon powers for particle physics? Is it? Mr. Particle Physics. Boom, exactly. That's how clever that idea sounds.

Anyway, Mr. Freeze didn't like, Mr. Freeze these photons, we can like look at them covered in ice or anything. What do they do? They keep them busy or they record them? Or what do they do? Keep them busy. I feel like that idea comes from parenting. You're like, all right, I'm going to run all these crazy kids into this room.

Keep them busy and they'll shoot out the other side. That's right. Here's my phone. If you want to see a room full of children, slow down and maybe freeze, just hand them your phone. Yeah, they just have a little phone for these photons. Yeah, there you go. And these phones emit photons? Now this is getting too deep. Yeah, essentially what they do is they build some system that can absorb the light, store the information from that light, and then re-emmit it at an arbitrary later time based on some external input. Isn't that called a camera? Yes, exactly. Exactly.

So in one sense, it's like, wow, that's awesome. This cloud of atoms absorbed this laser and can reemit it. On the other hand, like, well, every photograph is basically stopping light and later reemitting it. So in one sense, it's awesome because it's something nobody's ever done before. And another sense is accomplishing something we've been doing forever. Well, I mean, a photograph and a TV is pretty complicated, right? Because you need all these different things. but it might get in the sense

that maybe these guys sit in a much more fundamental sense, like they actually build a material that takes a photograph and emits it? Well, I wouldn't say it's less complicated. Like I think a camera and a screen is less complicated than having like, you know, millic Kelvin refrigerator and high

intensity lasers. But this thing does it sort of all at once. Like it both absorbs the photons and then later reemits it. It's not like it's stored electronically and then regenerated. But Again, you might say it's not, still, it's not the same photons. Like they were absorbed by the material and then re-emitted.

Is it the same photons? Not really. Stem me through it. What did they do? How does this material work? Well, they used a Bose-Einstein condensate, which is a very cold collection of atoms in a really weird quantum state. We'll do a whole podcast on what a Bose-Einstein condensate is. But what they did is they shoot a laser into it from the side, and then that sort of like holds it. What do you mean hold it? Like the light is absorbed by the atoms and the condensate, and then they just sort of hold it? This first laser is like the switch laser.

It just like gets the atoms in the right situation. It puts them in the right sort of quantum state to do this trick. Then they have the second laser, the one they actually want to absorb and re-emmit. They fire that into this pile of atoms and then it gets absorbed. And then when they want to release it, they just turn off the first laser and then it emits the pulse from the second laser. In the same direction and with the same shape and intensity, everything? Yeah, precisely. And, you know, there's some loss of information there, but mostly it captures the original

light. That is pretty cool. I think that it's pretty awesome. Yeah. Otherwise, it's just a superpower that only a comic book character named what Mr. Light Freezer would have. Mr. Laser Freeze. Okay, so, oh, wow.

So, I mean, that sounds pretty impressive, that you shoot it and then the atoms themselves, not some memory or some electronic. It's like the atoms themselves, somehow remember this laser and then emit it when you wanted to in the same way that it came in. Yeah, that is pretty cool. And I think it's awesome

that people just try to make materials do new stuff. Like there's this whole field of atomic physics and condensed matter physics where people are like, hey, can we make some new kind of goo that has this weird property? Can we make some new kind of goo that has that weird property?

And it's sort of just like an exploration of the way things can be in the universe. And, you know, we're used to, like, different kinds of stuff, water, metals, rocks, whatever. But it's possible that there's all different kinds of stuff in the universe that we've never experienced just because it doesn't occur naturally here on Earth. So these folks are, like, pushing the boundaries. Right. They're trying to make things do new things. Yes, exactly. They're trying to break the rules.

They're like, well, nobody thought things could do this. Let's see if we can make it work. Right. It's kind of like, you know, nobody ever thought you could walk on water. But, hey, it turns out if you freeze it, you can walk on water. Yes. And in some sense, it's as unsatisfying as that. It's like, are you really walking on water if you're walking on a frozen lake?

Technically, yes. What if you shoot a laser through it? Is it still technically a miracle? Well, you know, if you're ice skating, then you're walking in water because you're making this very thin layer of water between your blades and the ice. So, you know, there you go. More Jesus lawyer. And people try to say maybe there's some application to this.

Like, if you could slow down light, you could make circuits that use less power or something. Oh, interesting. Yeah, frankly, I don't find any of that convincing. I think that the motivation for this is like, hey, can we make something in the universe that's weird and different? And I think there's a lot of value to that. Well, there's a lot of applications they say now in solid state physics, where, if you get these materials to do these weird things, they could maybe be the basis for like a quantum computer.

Yeah, precisely. There are ways that you could find applications for materials that do weird stuff. And, you know, people were building atom traps and Bose Einstein particles for years before they had ideas for how to apply them. So it's a good idea to develop new kinds of materials because they can inspire new applications. And sometimes you work on something for 10 years. And then people realize, hey, that's exactly what we needed for this other totally unrelated problem. So, you know, we want to make progress as a species. We've got to, like, explore broadly

and try all sorts of weird stuff. And you never know. Like, it could have been that they didn't make light stop, but something else totally weird and unexpected happened and they discovered something crazy. You never know when you do research, right? Or just that in proving these things, you learn something new about the materials themselves or how atoms or light behave. Or if in order to make this happen, you have to invent something new and weird. And that turns out to be really useful for something else. You know, like the whole semiconductor industry and computers exist

because of basic research into stuff that wasn't motivated at building computers. Like, for example, I just got this great idea to shoot myself with a laser to stop aging. Or at least at my knees.

There is laser therapy for everything. Like, you can get laser therapy to, like, stop smoking. I wonder, like, what part of you are they shooting with the laser? Probably your wallet. and your credit card number, yeah.

I don't know. I wouldn't recommend any of those laser treatments. Okay, well, it does sound like they maybe have technically slowed down light and maybe sort of, in a way, stoplight. So that's pretty interesting, pretty cool. It's pretty cool. They've definitely done something nobody's done before. And today we only talked about a couple of groups doing a couple of experiments,

but it's a big field, and people are doing it with all sorts of new kinds of materials and in new ways and applying it to different. kinds of light and higher intensity, lower intensity, and bigger packets and smaller packets. We couldn't possibly review all the recent work on it. It's a whole burgeoning industry. All right. Well, I think that answers that question that a lot of people wrote in about. You can slow down light and you can stop light if you define things in the right way and you use both speakers. Was that the main lesson here? Yes. And so if you find a bottle and a genie comes out and he's a physicist and you ask for some new special power, make sure you are

very clear about what you're asking for because these physicists will find a way to squirrel out of it and not give you what you were hoping for. Right. You might just hand you a six pack of light beer and then you'd have blowing your wish. This light will make you slow down. Yeah. That's one way to slow down. There you go. Just add a laser and you can sell it for a lot more. Yeah. You don't want us as your physics genius. Maybe that's what would make hell a little bit more tolerables if you bring some beer down and then you can drink. it with the physicists. Yeah.

All right, well, thank you very much to everybody who wrote in to ask us about this weird headline. And if you read something online about weird discoveries in physics or something you're not quite sure about, send it to us. We will break it down for you.

You hope you enjoyed that. Thanks for listening. See you next time. If you still have a question after listening to all these explanations, please drop us a line. We'd love to hear. from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge, that's one word,

or email us at Feedback at Danielandhorpe.com. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene.

In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of long. and order criminal justice system on the iHeart radio app apple podcasts or wherever you get your podcasts my boyfriend's professor is way too friendly and now i'm seriously suspicious wait a minute sam maybe her boyfriend's just looking for extra credit well dakota luckily it's back to school week on the okay story time podcast so we'll find out soon this person writes my boyfriend's been hanging out with his young professor a lot he doesn't think it's a problem but i don't trust her now he's insisting we get to know each other but i just want her

gone. Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Have you ever wished for a change but weren't sure how to make it? Maybe you felt stuck in a job, a place, or even a relationship. I'm Emily Tish Sussman, and on she pivots, I dive into the inspiring pivots of women who have taken big leaps in their lives and careers. I'm Gretchen Whitmer, Jody Sweetie. Monica Patton. Elaine Welteroth. Learn how to get comfortable pivoting because your life is going to be full of them. Listen to these women and more on She Pivotts now on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

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