Daniel and Kelly’s Extraordinary Universe - Why are some things transparent?

Episode Date: June 13, 2023

Daniel and Jorge try to see through the mysteries of transparency.See 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. It's important that we just reassure people that they're not alone and there is help out there. The Good Stuff Podcast Season 2 takes a deep look into One Tribe Foundation, a non-profit fighting suicide in the veteran community. September is National Suicide Prevention Month, so join host, Jay, Jacob and Ashley Schick as they bring you to the front lines of One Tribe's mission. One Tribe, save my life twice. Welcome to Season 2 of the Good Stuff.

Listen to the Good Stuff podcast on the Iheart Radio app, Apple Podcasts, or wherever you get your podcast. Every case that is a cold case that has DNA. Right now in a backlog will be identified in our lifetime. On the new podcast, America's Crime Lab, every case has a story to tell. And the DNA holds the truth. He never thought he was going to get caught. And I just looked at my computer screen. I was just like, ah, gotcha.

This technology is already solving so many cases. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hey, Jorge, have you ever seen a glass frog? You mean one of those transparent amphibians? Or is it like a little keepsake man out of class? I mean, they're real live frog. I was reading that they are native to Central America, including Panama, where you grew up. Yeah, I have heard that.

But to be honest, I haven't seen one in person. You could probably find them in the jungle, but it's not like they're jumping around my house. Would you ever wonder what it would be like to be transparent yourself? Sounds terrible, I guess. You want people to see, right? Everyone wants to be seen these days. Unless you want to sneak around the house and be invisible. I guess if you have the option of turning transparent, that's cool.

Like, I think all kids dream of being invisible at some point. I always wondered what happens. If you're invisible and you take a bite of an apple, like, can everybody see that apple work its way through you? I guess it depends on, you know, like how the invisibility works. Like, are you a space that is transparent or is it just your molecules are transparent? Or you can just eat a cookie made out of glass frogs. Or eat glass, I guess. that sounds less tasty.

I don't think I want to take a bite out of that. Yeah, I see you, man. I see you. Hi, I'm Jorge McCartunist and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine. And even though you can only hear my voice, I feel seen. Well, that's good. Everyone wants to be seen. I think mostly we just feel heard in this podcast.

That's right. We feel heard, not hurt. Because we love sharing with you our passion and curiosity about the universe. And when I hear back from listeners that something we have said has touched on their deep-seated need to understand the universe, I do feel heard and seen. Yeah, because it is a pretty amazing universe with lots to see out there and to hear. I guess if you have the right kinds of ears because sound doesn't travel in space, does it? It actually does just very, very slowly. Why are you kidding?

Are you serious? No, space is not totally empty. And so in principle, there are sound waves that do propagate through the solar wind, for example. But in practice, if you're in outer space, you're going to freeze before you hear anything. Also, you would be hearing it in slow motion, I guess, right? If sound moves slower. You're like, don't go out in spoo. Too late, you're dead.

that's right you should shout at your friends in space like a year before they go spacewalking without a suit on so they can hear you yeah oh that's not going to help them also how do you shout in space like you have to take off your helmet to shout and then that's not good either in space nobody can hear you or you shouldn't be hurt or you might get hurt but you should turn your eyeballs up to the night sky and wonder how everything works and you should also look down on the ground beneath you and see if you can puzzle out the mysteries of everyday objects. The nature of our universe, how everything works,

how it weaves itself together to make this incredible cosmos. That's one of the deep mysteries that humans want to unravel. And those are the topics we like to take a part on this podcast. Yeah, and it's amazing and lucky that we can see so many things out there in the universe and around us so that we know where they are. And we can also study them and figure out how they work, what they're made out of and what the rules of this crazy universe are. But anyways, welcome to our podcast, Daniel and Jorge.

explain the universe, a production of iHeard Radio. In which we try to do exactly that. Take apart the whole universe, see how it works, and explain it to you. Some of the questions we love to tackle involve the tiniest things in the universe, what the rules are for how they work, or the biggest things in the universe, like the whole universe itself or supermassive black holes at the hearts of galaxies. But there's also a lot of fascinating physics in between, how those tiny little objects pull themselves together to behave in weird and wonderful ways.

The reason ice cream is so tasty, the reason metals conduct electricity, the reason your chair holds you up is because of zillions of atoms all working together to have fascinating phenomena. Yeah, and thankfully we can see them all and hear them all so we can study them. It'd be kind of hard to know and study the universe if everything was invisible, right? Or if we didn't have eyeballs in ears. That's true. And recently we've discovered the amazing fact that most of the universe is invisible.

The dark matter that's out there is most of the stuff. in the universe and we didn't even know it existed until recently because it's invisible to us light passes right through it and there's lots of things going on out there in the universe that you just cannot see because your eyeballs can't pick them up you can't taste them you can't smell them so most of the universe is actually invisible transparency turns out to be the name of the game so the universe got its kid wish of being invisible is that what you're saying what's it trying to sneak around and do i don't know but those dark matter kids are probably eating dark matter cookies all night long and they're made out of dark chocolate and tastes better

too man my new wish is to be a dark matter person they get to eat dark meat and their chicken well it also answers that other question of what happens when a dark matter kid eats a dark matter cookie of course it goes through them and becomes dark matter on the way out dark term matter you mean the darkest matter because of black hole that's where black That's exactly right. Black holes are dark matter toilets. They're worse. They're the things that go into the toilet. Here we are elevating the discourse of the nature of the universe. Yeah, I mean, listeners want to be reached into their soul and touched, right?

And seen and hurt. I'm not sure they want to have this particular taste, however. Well, who said anything about tasting? We're talking about eating dark matter cookies. You're fantasizing about dark matter chocolate over there. It's all about taste. That's right. We're all about taste here.

Good taste, bad taste, you decide. That's right. We're scientists. We explore the full range of tastes available to the human experience. But it is interesting that even the things that are invisible, we can still somehow see them through other things, right? I mean, if dark matter, dark energy was completely invisible, we wouldn't even know it was there. But somehow it has an influence on things that we can see, thankfully, and that's how we know they're there. Yes, transparency turns out to be quite a subtle issue.

Some things can be transparent to one kind of light, but not to another. Some kinds of light can pass through some objects, but not other objects. As always, when you dig into it, you discover there's a fascinating physics story that underlines how things work. Yep, this is an interesting topic. And so today on the podcast, we'll be tagging the question. How does transparency work? Subtitled, how can your kids eat cookies without you knowing? Well, I don't think they need to be.

transparent to do that depending how sneaky they are and how early you go to sleep or wake up now this is an interesting question daniel i imagine it means what makes things see through not like how to transparencies work or how does government transparency work because that that apparently doesn't work that well or sometimes it works too well that's right we want sunlight on all the operations of the universe but in particular here we're wondering about why light can pass through some kinds of of things. Why, you can see through glass, but you can't see through stone. Why x-rays reveal your soft tissues, but not your bones. What is the underlying physics? What is the microscopic picture of transparency? We're exploring the full range of transparent behavior. We're just trying

to be transparent about how the universe works. We're trying to be transparent about how the podcast works, is what I'm saying. And to be fully transparent, I have not read the outline for today's episode. I am kind of winging it today, which is totally different. from other days. Right, exactly. If you don't notice a difference between this episode and the other episode,

then folks, you learn something about how the sausage is made. You learned that Jorge's good thinking on the fly and reading really quickly. But anyways, as usual, we were wondering

how many people out there had thought about things that are transparent and if they know how transparency works. So thanks very much to everybody who answers these questions.

It gives us a great insight into what people already know and don't know if you'd like to help us out for a future episode of the podcast. Please don't be shy. Write to us to questions at Danielanhorpe.com. So think about it for a second.

Do you know how transparency works? Here's what people had to say. Transparency works, in my opinion, by not refracting or the medium that the light is passing through does not refract in any way or change the path of the light. And that way you don't get any kind of interference. and you can see through something as transparent, so perfectly clear. I'm pretty sure that transparency works by, like, the light can travel through the material without being absorbed. So maybe there's a lot of spaces between it.

And so, yeah, that light just doesn't get absorbed, so it goes through on its merry way. At first I thought it was simple because material density would need to more or less transparency, like air or some gas. and low density would be transparent to some point because of the particle density, but then again, glass has quite a high density, right, and it's still transparent. So maybe it's about a refractive index, and, yeah, like if you put glass in a water that comes invisible because it's fully transparent because of the refractive indices. I would guess transparency has to do with interactions between different forces and particles and whether they interact or not, if they interact, they are not transparent to each other,

and if they don't interact, they're transparent to each other. It's like a relay race. So a photon gets emitted. It's absorbed by the first atom in the glass, for instance, and then it gets retransmitted to the next and so on and so forth, until it goes over the other side of the glass or whatever transparent material we are talking about. In order to reflect light, the photon would have to be absorbed. then re-admitted, I think. So I guess in order to be transparent, it would have to be something

that doesn't absorb photons for whatever reason. That'd be interesting one, that. All right. Some pretty intricate answers. I feel like we had some hardcore physicists here in the pool today. Did you ask people on the internet or in your department? These are all internet answers. And they really reflect the incredible complexity of light and matter. We've dug into it in a few episodes, what happens when things reflect and what color means, but there really is a whole lot going on here. Light bouncing off of matter or passing through matter or refracting through matter is really a very complicated phenomenon and very tricky to understand from the microphysics point of view. Yes, I like how it reflects,

how smart our listeners are. But so many really interesting answers, a lot of which really get at the heart of the question, which is that it's about the interactions of the photons with the material. There's also some misunderstanding there, like the idea that light goes through things if there are spaces for it to like wiggle its way through. That's not really the way that we think about it, but we'll dig into it and explain it. I guess it sort of depends, like the difference between transparency in air and transparency in glass and transparency through different kinds of light, right? It sort of depends. There's definitely differences between air and glass, but the basic physics of transparency is quite similar. In either case,

are the photons like avoiding the atoms? It's not like they're finding a pathway through. That's maybe the way transparency works for like a screen door. You can see through a screen because there are literally holes that a photon can pass through. But the reason you can see glass is not because it's like a micro screen. The glass is finding tiny little holes in the glass to wiggle its way through. I guess we'll dig into that. And so let's jump right in.

Daniel, what are the basics? What makes something transparent? So first let's clarify what we mean by transparent, right? By transparent really just mean that you can see through it. It means if you shine a light from one side, the light comes out the other side with basically no scattering. Like the light is still coherent. If you have an image of an ice cream cone on one side, you're going to see the ice cream cone still on the other side. It might be refracted a little bit or bent or distorted, but it's transparent if those images are preserved.

I see. So like if light can pass through it basically is what it means to be transparent. Or information from light passes through it without any distortions. Exactly. And even glass, which we think of as transparent, does distort it a little bit. Like if you stick your finger behind a pane of glass and only half of your finger is sticking behind it, you'll notice the finger no longer looks like a whole finger. It's like broken in half because the path of the light through the glass changes a little bit relative to the path of the light through the air. That's refraction, which is a whole other complicated topic that we dug into in another episode. But still you can see your finger, right?

The same way you can see through water and you can see through air. You can identify things, you can recognize things, even if the path of the light is slightly changed. All right. So that means that a light can, or at least information that the light had before it went through the material, makes it through unscathed. That's what it means to be transparent. Yeah. And the fundamental thing that's happening there relates to how photons either interact or don't interact with the electrons in that material. And to understand that, we have to understand a little bit about the quantum mechanics of those electrons, what energies they're allowed, and how.

the photons decide whether or not to interact with those electrons. And you were saying it's not like it's a screen door where like somehow the light is finding a path to it, but that can also happen, can it? Like if you have something really thin maybe or something really sparse or light like air, there has to be some photons that are making it through without interacting with anything, right? Well, most materials, even like a thin sheet of paper, are dense enough that photons are not like finding holes in them. The reason that light gets through is because the photons are ignoring the atoms. It's not that they're missing them.

It's just that they're passing through without interacting. Because when a photon passes by an atom, it doesn't always interact with it. There are rules about whether or not photons can interact with atoms. And in a solid, it's complicated because you have lots and lots of atoms. But the easiest way to understand it is to start with an individual atom. Just think about like a single hydrogen atom in space and you shoot a photon at it. Is that photon going to get absorbed by the atom? or is the photon going to ignore the atom?

And that depends on the energy of the photon, because these atoms can only absorb photons of certain energies. Well, I guess it also maybe depends on where you shoot the photon, right? Like if I have a hydrogen atom floating out there in the air and I shoot a laser beam, you know, a mile to one side of it, it's not going to interact with the hydrogen, is it? No, that's right. But if you have a huge wall of hydrogen atoms

and you shoot the laser beam at it, then it's not going to be able to avoid the hydrogen. right it's going to have to get through the other side it's going to have to pass through the hydrogen and that's what makes things transparent I mean one thing is to have holes in it sure you can see through a screen door even if it's made of metal or stone as long as there are holes in it but I think the physics of transparency is more interesting if we think about what happens when light ignores the material if it passes through the material rather than finding holes or ways around it Well, I know it's more interesting to you as a physicist,

but I guess for me, I'm just curious about which has more of an effect to make something transparent, right? Because, you know, people always talk about, like, materials, like our skin, our bodies. They're made out of atoms, but the atoms are really sort of far apart. And the nucleus is really far apart from the electrons. So there's a lot of sort of, like, supposedly empty space, even within solid matter like ourselves. I'm just wondering, like, you know, there's, it seems like there's a lot of space for light to squeeze. through or to pass by without even knowing there are other things there. That's an interesting point.

And I think a lot of people have maybe the wrong mental picture of what an atom sort of looks like to a photon. You know, even if you have a grid of atoms, like a sheet of atoms making up of material, you might imagine that it's mostly empty space, as you said. And it's true that the nucleus is small compared to the distances between the atoms. Right. So you have this like grid of atoms. And there is a lot of space between the nuclei.

But that space is not empty, right? That space is filled with electrons. and electronic fields and forces that are holding the nucleus and the electrons together. So the electrons are in these buzzy clouds all around the nucleus. And the electrons weave the atoms together, right? So it's not like there's space between the atoms. The atoms are held together. They're in these bonds that tie them together into a big grid, into a big lattice.

And the electrons can sometimes slide back and forth and move between the atoms. So there isn't a lot of space between the atoms. And then inside the atom, all that space you imagine, might be empty, is really filled with electrons. So from the point of view of a photon hitting like a sheet of material, a sheet of paper or a sheet of glass or whatever, it really is hitting a wall of electrons that it can't find a way around unless you like physically punch holes in it. You just made me wonder like when you have a material, how close together are the electrons

shells between atoms? Like are they bumping up against each other or is there a certain amount of space between It depends a little bit on the kind of atom you have, but atoms tend to bond with their outer most electrons. And we'll dig into that if you let me talk about how these electrons move between the atoms. But you really are tying the outer levels of the electron orbitals together and then forming these common electron energy levels. So these atoms are sharing electrons that really are woven together. I see. I think what you're saying is that to a photon, a grid of electrons, it's like a solid wall almost because it's full of electron.

fields and photons interact with electrons, but like if you were something else that was not an electron, you would maybe see a lot of empty space. But because you are a photon, then, it's like you're walking into a solid wall of electron fuzziness. Yeah, if you're a neutrino, for example, and you don't feel electric charge, then the fact that there are electromagnetic fields all through these materials is irrelevant to you and you pass right through it. So like even a block of lead is basically transparent to a neutrino. Because it doesn't interact with the stuff. So transparency comes down to whether you interact with the material there, not really whether

there are holes there. So photons, they can either pass through a material or they can interact with it. And that depends on the atomic structure and the energy levels of the electrons have and whether or not they interact with that photon. Even though a photon sees a wall of material, a buzzing blob of electrons in front of it, it can still sometimes pass right through without interacting. And that's what transparency is. Yeah, I guess you can be transparent, not just too light, but to other things, right?

Like, isn't there a famous, like, gold foil experiment that kind of help people figure out the structure of the atom? Yeah, that's right. Rutherford shot alpha particles, which are helium nuclei, and a very thin tissue of gold, and he expected it to mostly just pass through, occasionally get distorted a little bit by forces. What he found was that occasionally, like, one in eight thousand times. The alpha particle, the helium nucleus, bounced right back, which told him that it was interacting with some. something hard at the core. So that's what told him that the sheet of gold actually was made out of a grid of hard

nuclei, that most of the gold was transparent to the alpha particle, but that occasional little dots of it were not. Because I guess the helium nuclei would only interact with the nuclei of the gold, right? To the helium particle, it did look like a screen. Because there is a lot of empty space to a helium atom in between the gold atoms. Yeah, that's mostly true. The nuance there is that the helium does interact with the electrons. It's just that the electrons don't have the mass or the kinetic energy to bounce it back.

They can only like slightly change its direction. So if the helium goes to the gold and only interacts with the electrons, it gets a little bit of change of direction. Whereas if it hits one of the nuclei, those have the mass to like push it all the way back. So there's sort of two different kinds of interaction the helium can do, one where it punches through and the other one where it bounces back. All right. So you're saying let's maybe focus on.

light transparency. And we know that light interacts with electrons. And so material stuff to a photon looks pretty dense. And so you can't sort of just go through it without possibly interacting with things. But you're saying maybe the key to transparency is that sometimes light doesn't interact with the thing that's there. That's right. Even if you have a bunch of electrons, photons aren't necessarily able to interact with them. The photon has to have the right amount of energy so the electron can accept it, can absorb it. If a photon has the wrong energy, it'll pass right through without interacting with that electron.

And that all comes down to how the electrons are confined in the material. I mean, a random free electron in space. So you just have like an electron flying through the universe and a photon hits it, it's going to absorb that photon no problem. Because electrons flying through space can have any energy. There's no restriction. You can have any arbitrary amount of energy. So it will almost always absorb that photon.

But an electron around an atom has different rules because of the quantum mechanics, it can only exist on like a ladder of energy levels. So it can only absorb photons that move it up one or two or ten steps on that ladder. It can't move up like one and a half steps or two point seven steps. That limits the kinds of photons that an electron can absorb. Interesting. It's like the electrons are stuck and they don't want to move from where they are. and so let's get a little bit deeper into that and then also talk about what happens

when something is transparent so we'll talk about 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 633 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. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit.

Well, Dakota, it's back to school week on the OK Storytime 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 boy? friend 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, your 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. 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. Get fired up, y'all. Season two of Good Game with Sarah Spain is underway.

We just welcomed one of my favorite people and an incomparable soccer icon, Megan Rapino to the show, and we had a blast. We talked about her recent 40th birthday celebrations, co-hosting a podcast with her fiancé Sue Bird, watching former teammates retire and more. Never a dull moment with Pino. Take a listen.

What do you miss the most about being a pro athlete? The final. The final. And the locker room. I really, really, like, you just, you can't replicate, you can't get back. Showing up to locker room every morning just to shit talk. We've got more incredible guests like the legendary Candace Parker and college superstar A.Z. Fudd.

I mean, seriously, y'all, the guest list is absolutely stacked for season two. And, you know, we're always going to keep you up to. to speed on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHeart Women's Sports. We're talking about transparency here today and what makes things see through. Daniel, you mentioned that it's kind of about how.

light can go into a material, see the material, be near the material, but not interact with it. And you say it has something to do with the energy levels of the electron because you said that an electron floating out in space will always absorb an electron no matter what? Does it have to be like fly near it? Does it have to hit the electron right in the middle or does it interact when it's flying nearby? How does that free space case work? If you zap an electron with a photon and the Electron is out in free space. It means that there are no rules that govern the energy that the electrons can have. I think something that's really cool and not like widely enough understood is where quantization comes from.

Like why electrons in materials have energy levels, where these quantum energy levels come from. And it really comes from boundary conditions. It comes from forcing the electron to live within a certain location, like putting it in a box. So that electron out in empty space, it can be here, it can be there, it can be have any location, it can have any momentum. And so it's free to absorb a photon of any energy. There's a probability for an electron and a photon to interact. There's still a chance, of course, that a photon will not interact with an electron. It depends on the strength of the force, essentially, that controls like the probability for these things to happen.

But for today's conversation, we can imagine that it basically just always happens. You zap an electron with a photon, it doesn't matter what the energy of that photon is. The electron can accept it because it could have a higher momentum of any value. That's not true for electrons around an atom. It can only have energies of certain values because it's confined into the box of the atom. Now, in that free space electron, when that light hits it, what happens to that electron? It gets faster or it gets hotter? Does it start spinning faster?

What happens when you zap an electron in space with light? Well, it absorbs the momentum of that photon because of conservation momentum and now it carries that momentum as well. And so if the photon was moving in the same direction as the electron, then it gives it a zip. It's going faster. If the photon was moving in the opposite direction, the electron hits the photon sort of head on, then it gets slowed down, right? We talked about like laser cooling once on the podcast. You can use lasers to slow things down also if you zap things in the right direction. Yeah, that was pretty cool.

And so it's sort of like a billiard ball, I guess. Like if you have an electron out there in space and you hit it with a photon, it basically happens like it does when you hit a billiard ball, right, with the white ball. Yeah, the quantum mechanics comes in with the probability. There's like a chance that that interaction will happen, a chance that it won't. But for today's conversation, we can think of it like a billiard ball. You're giving it a push and it's absorbing that energy. And because a free electron, one out in the middle of space can have any energy,

quantum mechanics is fine with that. Now you take that same electron, you say, okay, you're now in orbit around a hydrogen atom. Well, you still have to obey the rules of quantum mechanics. And in this case, quantum mechanics says, all right, there's only certain solutions to the math here. Only certain energies of the electron make the math work. The wave function of the electron has to satisfy some conditions. And that's only true for certain values of the electron energy. So you can't have an electron with an arbitrary energy around a proton.

There's a ladder of values there. And that determines whether the electron can absorb the energy of a passing photon. I guess it's sort of like, you know, the Earth is going around the sun in an orbit, but the Earth is not restricted to what that orbit can be. Like if a meteor hits Earth within a force, it is going to speed us up or slow us down and it's going to change the path of our orbit. But you're saying sort of like an electron around an atom, it's not like it can be in any orbit. It can only be in like certain slots of that orbit.

Like it can orbit here or over there or in this circle or in that circle. I know it's not really a circle, but it's sort of that. It's what I mean? It can only circle around the nuclei or a certain grooves, right? Yeah, that's a great contrast because the example of Earth is a classical example. There's no quantum mechanics there. We're talking about gravity, which is a classical theory, and there's an infinite number of possible solutions for an orbit. If you pick a radius for the Earth's orbit, I can tell you exactly what velocity it has to have in order to have that orbit. So there's an infinite number of possible orbits there. In the case of the electrons, it's really very different mathematics that

determines whether the electron can be in a particular state or not. As you said, it's not really in an orbit. It's in a quantum state, which means it's satisfying a different equation. In this case, it's Schrodinger's equation, which is a quantum equation of the wave function and that wave function has periodicity to it. So the wave function basically has to wrap itself around the atom in a way that builds upon itself. It doesn't cancel itself out.

So you can fit in like an integer number of half wavelengths of this wave function so the things like support each other. You get like a standing wave. solution effectively instead of things like canceling themselves out just the same with it like on a guitar string you can have a certain number of modes of a guitar string right you can oscillate the whole string or you can have a node in the middle so both halves are oscillating or you can have two nodes either like three little oscillating pieces in the same way the electron has to satisfy a wave

equation not a gravitational equation and that's where the energy levels come from it's from it comes from confining it to being around the atom which changes the solutions to the equation Okay. So now I have an electron orbiting around a nuclei. It's a wave function. It's a quantum object. It's sort of like snaps into a certain wave shape around the nuclei. And you're saying that a photon hits it and the electron's like, nope, I like where I am now. No, thanks. Or that's not enough to get me to the next step in the ladder. I'm just going to totally ignore you. Is that what's happening? That's exactly what's happening. If a photon comes along and it has enough energy to bump the electron to next stage, it gets absorbed. If it has too much energy to get the electron to the next stage and not enough to get it like two steps up, then it gets ignored, right? So it gets absorbed if it has the right energy

to move the electron of one or two or seven, some integer number of levels, and it gets ignored if the electron would not have a solution anymore if it absorbed this photon, then it just doesn't happen. Wait, wait, wait. So like if an electron is going around a nuclei, it's in a cloud, and it gets one and a half as much energy from a photon that it needs to get to the next level,

it's not going to take that one and then throw away the remainder. It's just totally going to ignore the whole thing. Just totally going to ignore the whole thing. It can absorb something that has two steps and then emit one, right? Or it can absorb something that has like seven and emit four photons, but it has to be on that ladder. How exact does it need to be? Like exactly to the one infinite decimal?

You know what I mean? Like where are the chances that a photon will have the exact amount? of energy needs or does it just need to be around the same energy? Well, there's always uncertainty in quantum mechanics, right? So every photon has an uncertain amount of energy. You can never measure it precisely. Is that true? Really? I thought they had specific frequencies.

Well, a photon is created by a quantum process, which usually means that there is some uncertainty there, right? There's always a little bit of fuzz in all of these processes, which allow these things to overlap. The energy levels that we're talking about come from a simplified model of the nucleus, right? And in reality, these things are a little bit fuzzier. right? The physics is a little bit more complicated. There's other interaction. So there's always a little bit of fuzz on these energy levels. And the atom that produced the photon on the other side of the universe or whatever may have produced at a certain energy level or a little bit higher, a little bit lower. So there's enough fuzz in quantum mechanics to mean that there's a non-zero probability for the photon to have the right energy to be absorbed by the electron. I guess when they interact, then the wave functions collapse and then you figure out if it has the right amount. But it seems very on the right.

likely they would have the exact same amount. Yeah, that's where the fuzz comes in. So you get a little bit of width to these things. So you have a probability for them to overlap. It's not like you're throwing a dart in an infinitely sized board and having to hit exactly the right spot. I see. It's like you have a fuzzy dart and the target is fuzzy too.

And as long as you sort of get it in the right ballpark, then it's going to knock that electron or not. Yeah, exactly. And that explains a lot of atomic physics, right? That explains why certain gases look certain colors. That explains why when you have a fire, you might. get like green or blue flashes in it, or if you did that experiment in high school chemistry where you put copper in your Bunsen burner and it glows green, explains a lot of atomic physics

because different kinds of materials have different energy levels. So they glow with different frequency photons and they can absorb different frequency photons. And that's really cool because it means we can like tell what's in distant stars because we can look at the spectrum of energy that they emit. We can say, oh look, these things are emitting photons from the energy level that only comes from copper so we can tell there's copper in that star. Sometimes these things appear as spikes in the spectrum. Sometimes they appear as dips in the spectrum because like the atmosphere of the star is absorbing those photons.

But the point is that there are energy levels to the atom and those determine whether the photon can interact with the electrons around the atom or whether it gets ignored. All right. So then we're talking about transparency. And so if I shoot a photon at an atom, it's going to get up to the electron cloud there. And it's going to be like, no, I'm not the right energy. I'm just going to keep going, or is it the case that they do interact, but then the end result is the same, and it just spits out a photon of the same energy in the same direction? No, if they're the wrong energy, they just do not interact. If they're the right energy, it gets absorbed and then it can get re-emitted, and that's a whole complicated phenomena about reflection and refraction and all sorts of stuff.

In this case, for transparency, it's more about whether there's an interaction. If it has the wrong energy levels, it just doesn't interact. But that's the case for a single atom, which is not really what's going. going on when you're looking at light going through glass or when you're wondering why light doesn't go through metal. It's much more complicated because now you're packing a lot of atoms together. And so the rules about what happens to those electrons now change. Let's dig into that. What's going on there? So remember the picture we were talking about earlier, when a photon is approaching like

a sheet of metal or a sheet of iron or a sheet of marble or something, it's facing a whole wall of atoms, not individual atoms. We talked about the energy levels of an. individual atom, but when you bring these things together to make a grid, then the atoms bond. They're not just like near each other. They really are bonding. And if you remember your high school chemistry, that means that they are sharing electrons. Sometimes the electron would like be around one nucleus, sometimes around another nucleus. So from the point of view of the electron, what happens is that you no longer really belonging to one nucleus. Now you can think of like

the whole grid of nuclei as having a bunch of energy levels for the electrons. Some of the The inner electrons are trapped around the nucleus, but the outer electrons can flow between them. And that creates a whole complicated set of energy levels. Instead of having these very specific ladders, now you have this like spectrum energy levels. The electrons have lots more options of the energy levels they can be at. I guess I wonder if it's sort of like, you know, we're orbiting around the sun and we're sort of stuck in this orbit. But if another solar system came pretty close, maybe Jupiter might be like, oh, sometimes it might do like a little figure eight and sometimes leave our solar system and go take a loop around that other sun and then

come back. Is that sort of what's happening to the electrons? Yeah, that's exactly what's happening to the electrons. There's lots more options for them. They don't have to just stick around one nucleus. They interact with lots of different nuclei. So that has the consequence of sort of spreading these sharper atomic orbitals and making them even fuzzier. So instead of even really thinking about energy levels now, physicists talk about the possibilities for electrons in these materials as energy bands. You may have heard of like the valence band or the conduction band. These are like a spectra of energy levels available to the electron. Instead of being more like a ladder, they get blurred together. So there's lots of really, really fine steps. It's still technically a ladder,

but there's many, many more steps there. I guess it's sort of like in one atom, the electron is stuck in one particular rut or groove or orbit. That's one extreme. The other extreme is a free-floating electron out in space by itself. When atoms are sort of bonded together in a material, you're saying the electrons are sort of in the middle. Like they're not quite stuck to one particular atom, but they're not quite free either. And so they have limited options, but they don't have just one option. And so there's sort of a range of photons they can absorb. Yeah, exactly. And it depends a little bit on the temperature of the object. If the object is really, really cold and the electrons don't have a lot of energy, then they've all like settled down to their minimum energy. And mostly they are

orbiting an individual nuclei, and they're mostly stuck, and so the electrons don't flow very much. If the thing is hot, then a lot of the electrons have more energy. They have enough energy to like hop from nuclei to nuclei, and so they can flow a little bit better. Wait, what? So that if I heat something up or cool it down, I can make it go transparent or not transparent? No, by heating it up, you're not changing the energy levels that are available. You're just changing where the electrons are. Like instead of all being in the lowest energy levels, now they're in higher energy levels. I'm just talking about which energy levels are filled up. In some cases, the electrons are sort of stuck. When the stuff is cold, the electrons fill the lower energy levels and they're

more stuck to the nuclei. And when the object is warmer, they sort of jump out of those and they're freer to move around from nucleus to nucleus. Cool. Well, let's get a little bit deeper into the material and see what happens when photons of different frequencies try to go through it and what it all means about transparency in the universe. But first, let's take. take another 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. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime 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. out 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. Afea 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. We 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 Neal-Barnett, where we dive into managing flight anxiety. Listen to therapy for black girls on the IHeart Radio app, Apple Podcast. or wherever you get your podcast. Get fired up, y'all.

Season two of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people and an incomparable soccer icon, Megan Rapino, to the show, and we had a blast. We talked about her recent 40th birthday celebrations, co-hosting a podcast with her fiancé Sue Bird, watching former teammates retire and more. Never a dull moment with Pino. Take a listen.

What do you miss the most about being a pro athlete? The final. final and the locker room. I really, really, like, you just, you can't replicate, you can't get back. Showing up to locker room every morning just to shit talk. We've got more incredible guests like the legendary Candace Parker and college superstar AZ Fudd. I mean, seriously, y'all, the guest list is absolutely stacked for season two. And, you know, we're always going to keep you up to speed on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

Presented by Capital One, founding partner of IHeart Women's Sports. We're talking about transparency, and something that comes to mind is, I don't know if you read old comic books or you read comic books when you were a kid. There was always an ad in the bag for, like, x-ray glasses. And I always wondered, like, are those for real or like, how can they sell something so bogus? What's going on? I always wanted to order one, but I couldn't because I was in Panama. Do you know what I'm talking about? Do you know what they were actually selling?

Do know those ads. And I also wanted those. And I wanted them to be real. But I also never bought them because I was pretty sure they were bogus. I mean, you can see through things with x-rays. And we'll talk about why that happens, why high-energy photons from x-rays can pass through. materials sometimes when lower energy photons can't but those glasses can't let you see x-rays and they definitely don't generate x-rays right you're not shooting x-rays through stuff so i'm pretty

sure it was totally bogus or maybe not i don't know we can't say for sure well folks out there if you bought those x-ray glasses and they did let you see through things please write to us and let us know those people are probably rich from a you know stealing bank vaults and things like that all right so Talking about transparency and, you know, when you put a bunch of atoms together in the material, they form this kind of extended fuzzy cloud of electrons that might block light or not. And so whether a photon gets through that depends on its energy. If it has the energy that the electrons in that material like, then I guess it's going to get absorbed, right?

And not go through it. Exactly. So the basic picture is the same. Photon approaches this now grid of atoms. And if it finds an electron that can accept its energy. If the electron can go from its current quantum state to an allowed quantum state, it will absorb that photon. But the picture of the energy levels is different from a single atom than with the grid of atoms. And the single atom, you had the latter that was sort of sharper energy levels.

In the grid of atoms, now you have these bands of energy levels. And you might think, oh, that makes it possible with the electron to absorb basically any photon. It's a little bit more complicated than that because we discovered that there are these gaps in the energy levels. It's not like any possible energy level is allowed for an electron. in these materials, the way it is for an electron in free space. There are still electron energy levels that are not allowed. So there's this band of electron energies called the valence band, where the electrons mostly hang out in a random material.

And then there's a band of energies called the conduction band, where electrons can move around really freely from atom to atom. And there's sometimes a gap between them where electrons can't be. And that can prevent electrons from absorbing energy of a passing photon. You're saying like you can have a material that accepts or lets through lights of a certain range of frequencies then it doesn't let them through and then it does for a different range of frequencies it does let light through. Exactly. Just like with the atom, it can absorb some frequencies and not other frequencies. For a grid of atoms, for a whole solid material, it can absorb some frequencies,

frequencies where it can hit the electron and jump it over this gap between the bands. And it can't absorb photons of other frequencies, photons that don't have enough energy to get the electrons from one band to another. And so different kinds of materials have a different size gap between these bands. And so in solid state physics, they call this the band gap, right? The gap between the typical energy levels of the electron and the conduction band where electrons are good at like flowing. And some kind of materials like metals have a very, very small band gap. The conduction band is basically right on top of the valence band. There's basically no gap there.

And so electrons are very good at absorbing photons of a huge range of energies because there's a huge spectrum there. And other materials, there's a big gap. And in order for an electron to absorb a photon, it has to have enough energy. And lots of photons just don't have enough energy. And so the photons would pass right through the material without interacting. Now, when you're talking about light and energy, the light of a particular photon is related to its frequency, right?

mostly to it almost or everything to its frequency. And so you're really talking about its color, right? Yeah, exactly. The energy of a photon doesn't relate to its speed, right? When we think about the energy of an electron, we think about its speed. But photons are all moving at the same speed. The thing that differentiates a high and low energy electron is its frequency, how fast the electromagnetic fields are wiggling. And as you say, that frequency we interpret as color.

The photons themselves don't have color. It's not like a photon is a red photon or a green photon. It just has a certain frequency. When it hits our eyeballs, our brains give us the experience of red or green or blue or whatever. And that's a whole philosophical question. But yeah, we associate colors with certain frequencies. Yes, but we don't talk about philosophy here. But like if a photon has a certain frequency, it is a red photon, right?

Like to our eyes, it would read as red. It would read as red, yeah. And some photons are above the visible spectrum. And so we say they're x-ray photons or their gamma rays or their UV photons. photons, right? So we can give names to the different parts of the frequency spectrum. Some of them we give them colors, some of them we just give them labels. Radio waves, for example, are photons a very, very long frequency, well below what we can see, even below the infrared. Right. And so that determines whether or not a material is transparent to different kinds of light. Because x-rays sort of

led you see through your body and your bones, right? That's because they have a high energy and the electrons in your body can absorb them, so they sort of go through. Yeah, really interestingly, X-rays can pass through the soft tissues of your body, but they can't pass through your bones, which is why when you see an X-ray, what you're looking at is basically only the bones, because that's the thing that the X-rays didn't pass through. So it passes through everything else. Your body is transparent to X-rays except for your bones. That's why you can tell the difference between the bones and the not-bones part on the X-ray.

Now, is that because the, I guess, bones are made out of the different material than my muscles? And so my muscles don't absorb x-rays, what my bones do because of the, you know, the bonds between the atoms. Exactly. It's the band gap of the material that determines whether or not you can absorb photons of a specific frequency. So, for example, in a conductor, like a metal, like a sheet of steel, the band gap is really, really small. It's very easy to get an electron up into that conduction band where it can flow around. And that's why these things conduct electricity very easily because it's easy to have electrons that slide around in the material. So a conductor like a metal, right, it's really easy to get those electrons flying around.

It also means it's easy to absorb that energy. So that's why things like metals and conductors are good at conducting electricity and good at absorbing photons and bad at being see-through. So that's why a sheet of metal, for example, is not transparent. Unless it's, I guess, a wire mesh. Yeah, exactly. Unless it's a screen, which is why, if you remember, like, Star Trek and they had, like, transparent aluminum in Star Trek 4 or whatever, I was like, well, you can't really do that. It is not something we know how to do. Although, you know, far future societies, maybe they figured it out.

I'm not sure I'm familiar with that level of trivia for the Star Trek movies, but I'll take your word for it. You remember, they got the whales and they had to build an aquarium for the whales and how were they going to hold all this water? I remember the whales, yes. All right. But I guess what do you mean, though, like aluminum is not transparent to visible light, but it is still transparent to other kinds of light, right? Like x-rays sort of go through metal, no? Or do metals, like, block all light?

It's always the case that it depends on the frequency, right? And so you have to have the right frequency to match the energy levels that the object can absorb. If you have a huge amount of energy, then probably you're going to knock the electrons out of the material. Right? then we're getting into the case of like the photoelectric effect. So you zap like gamma rays against aluminum, then there's definitely going to be an interaction

there, but it's going to knock the whole electron out of the material. It's not just going to like push it up to some energy level. So at some point this picture breaks down. Oh, what? So at some point, you have enough energy where the electron jets doesn't want to stay in any groove. It just flies out into space really. Yeah, exactly.

You can shine light on metal and boil off electrons if you have enough energy. There's like a highest level band and above that, then electrons are just free again. You've like broken it out of physics jail. You have to pay $200, though. Exactly. Now, what happens on the other spectrum? Like, what if a photon has too little energy, like a super infrared or something like that or a radio wave? As you said, that still goes through metal and other things, right?

No, radio waves do not go through metal, right? That's why, for example, your phone call is dropped if you're in an elevator because metal is like a Faraday cage. It will block radio waves. Even classically, right, the electrons in the material will reorganize themselves to cancel out an electric field. But from a quantum mechanical point of view, a conductor can absorb very, very low energy photons because the gap there is very small. And so it can absorb very, very low energy photons. But I guess what's going on there, though, like if it's just a single atom and have an electron orbiting, if the photon has very little energy, I'm going to ignore it too, aren't I? Yeah, absolutely. You

are. In the case of an individual atom, then there are photons that have too low an energy to move the electron up from level one to level two or level seven to level eight. Exactly, that can happen. In a solid, now you have a whole spectrum of energy levels. And so there's lots of very, very fine gradations allowed there. So materials can absorb low energy electrons because there's a very, very fine mesh of energy levels. Is there a bottom limit there? Like, is there an energy for my photon, for which it's even outside of the gap of a material with lots of electrons. There might be a lower limit there. I mean, even conductors do have some kind of a band gap. So you might need a minimum energy to get them up from the valence band to the conduction band.

And there might even be a limit within those bands, a minimum energy. So yeah, there might be a limit very, very low energy photons could be ignored even by conductors. But the other side of the coin are materials like. insulators. Take glass, for example. Glass is not a conductor because it has a large gap between these energy levels. So most electrons in the glass are not free to move around. They're mostly stuck to the atom that they are around. And there's a band gap there. If you want to push an electron up to the next energy level, there's like a big gap between the energy level that's normally in and the first one that's available. It's like a few electron bolts. And so photons that hit

glass in the visible spectrum mostly do not have enough energy to get the electron up to the conduction band. And so that's why visible light photons do pass through glass. They pass right through this whole grid of atoms and all those electrons, but they don't have enough energy to move the electrons up to the next band. And so they're ignored and they pass right through. You mean like a material like glass. It's like the atoms are basically it's just a bunch of individual atoms hanging out together. They're not sharing a lot of electrical. which is what you need to make a good conductor, they're mostly just doing what they would do normally on their own. And so you have a very limited number of frequencies that it blocks.

The picture is a little bit more complicated. I mean, the glass atoms still do interact with each other. So they do form this band of energy levels for the electrons because they are bonded together. I mean, glass is not a crystal, but still there are bonds between the atoms. They are interacting. So there is a spectrum of energy levels the electrons can be in for a glass that's not just like an atom. It's not just like a sharp layer, but it's mostly a full band of electrons, but that band is mostly filled and the electrons can't really go anywhere. It's like if you're on a plane, every seat is taken, then you can't like move from seat to seat.

And the next energy level above that is kind of high, or you can't like get to first class. You need a lot of energy to get to first class in a glass. And so everybody's basically stuck in their seat in coach and the electrons can't really absorb little amounts of energy. They need a lot of energy to get promoted up to first class, which is the next band of energy levels in a glass. In a conductor, that band is much, much lower, so it doesn't take as much energy to get up there. In glass, the band is really large.

It's really hard to get promoted up to the next set of energy levels. I think what you're saying is that glass is transparent for a wider range of frequencies of light, which just happened to be in our visible spectrum. But glass is opaque. It is not transparent to. certain frequencies of light. That's exactly right. For example, ultraviolet, right? Ultraviolet, right? Ultraviolet is light with higher energy. You can't see ultraviolet light. It's the kind

that's going to give you a sunburn or can hurt your eyeballs, but it has more energy. And it has enough energy to bump one of these electrons up over this gap into the conduction band. And so glass can absorb UV photons. That's why you don't get a sunburn if you're sunbathing through glass. Glass is like sunscreen. Wait, what? I can just put a glass over. me and I'm going to get you sunburn? Is that a solid medical advice there? That is not solid medical advice. And just to be transparent, we're not medical doctors, right? That's right. But it does block some of the UV so it would reduce your sunburn. I still totally advise you to wear sunscreen. But glass is not transparent to UV the same way it is to visible light. It absorbs a lot

more of the UV. Is that kind of what's going on with sunscreens like a lotion, right? It has materials that absorb UV, right? Yeah, exactly. your sunscreen is just opaque to UV. It has stuff in it that could accept those photons and absorb it, rather than letting those UV photons pass into your body and then cause damage. Okay, now what makes a piece of glass, like a piece of red glass and or a piece of blue glass? So that often is because of doping. You like change the energy levels of the glass by adding impurities.

And so these other molecules change the band gap. So they make it possible for different kinds of photons to be absorbed. And so... I guess you sort of narrow the band gap, right? Like regular glass, a wide range of photon frequencies that it lets through. But like blue glass, I imagine, has a narrow gap where it only lets through light that is bluish, for example. That's right. So sometimes people add like aluminum oxide to glass.

And that makes glass pink or red because it absorbs the green and the blue photons. And so I actually got an email from a listener, Matt Cleveland, who says, what is it about the photons of sunlight that cause some objects to fade and lose their color? What is it that's breaking down? Why do some objects lose their color from this interaction with the sun's photons and others do not? That's an interesting question. Yeah, like if you leave your t-shirt out in the sun, it's going to get faded, right? It's going to get bleached.

That's kind of why your hair also gets bleached a little bit of you stay out in the sun a lot. Yeah, exactly. And that's mostly the UV light, right? These chemicals absorb UV light, and the UV light has a lot of energy. So sometimes it breaks down those chemicals, right? We talked about like photons hitting electrons and banging them out of materials. Well, UV light, sometimes these atoms can absorb it, but it also damages the atoms, the same way it can damage things in your body. And so chemicals in objects can sometimes break down when they absorb UV light.

And what you'll notice is that red stuff is especially susceptible to this because they absorb more high energy, more blue and more UV photons. So things that look red are things. things that absorb in the blue spectrum and therefore absorb more UV light and are likely to fade more in sunlight than things that are blue. Because if they're red, then that means they're mostly reflecting the red part, but they're absorbing the blue light. Yeah, exactly. And UV is like super blue.

But sometimes materials get harder in the sun, right? Like if you leave a piece of rubber or a rubber band or your car tires, they get more brittle as they stay out in the sun longer. Yeah, that's a similar process. you're not changing their transparency, but still the UV light is changing the chemical composition because it's being absorbed and it's breaking down some of the bonds and it's changing the chemical nature of the substance. So if you put your car inside of a glass house, then they'll stay the same color and the tires

will stay bouncing. Is that what you're saying? Yeah, or if you smear your car in sunscreen, either one. Although I guess you have to be careful, you know what to see about cars that live in glass houses. All right. Well, I guess it's an interesting look. into a very familiar thing that is all around this, right? Like the screen on your phone is made out of transparent glass and your windows. And every time you go to the doctor or the dentist and they take x-rays, it's like physics going on, right?

There is physics going on everywhere. What's amazing to me is that sometimes we can even unravel this like microphysical picture of what's happening to explain our everyday experience. Why things are squishy, why things are hard, why things conduct electricity, why things are see-through. It all comes down to what's happening. at the atomic level or the subatomic level. And incredibly, that's a story we can sometimes understand

and even explain to you. Yes, it's almost like the universe is transparent to science. Or it's like scientists have x-ray glasses. Or maybe the UV photons of the universe are just frying our brains. Because your skull is made at a glass? What's going on there? I'm going to go put sunscreen on my brain.

Yeah, or a hat. You know, the physicists have invented hats. also, which helps with sun damage. Quantum hats. We should sell those. All right. Well, we hope you enjoyed that. Thanks for joining us.

See you next time. Thanks for listening. And remember that Daniel and Jorge Explain the Universe is a production of IHeart Radio. For more podcasts from IHeart Radio, 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 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 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. Your entire identity has been fabricated. Your beloved brother goes missing without a trace.

You discover the depths of your mother's illness. I'm Danny Shapiro, and these are just a few of the powerful stories I'll be mining on our upcoming 12th season of Family Secrets. We continue to be moved and inspired by our guests and their courageously told stories. Listen to Family Secrets Season 12 on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.