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Speaker 1: Hey, or hey, have you ever seen a glass frog?

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Speaker 5: M you mean one of those transparent amphibians or is

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Speaker 5: it like a it'll keep taking me out of class?

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Speaker 1: I mean they're a real live frog. I was reading

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Speaker 1: that they are native to Central America, including Panama, where

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Speaker 1: you grew up. Yeah.

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Speaker 5: I have heard that, but to be honest, I haven't

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Speaker 5: seen one in person. You could probably find them in

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Speaker 5: the jungle, but it's not like they're jumping around my house.

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Speaker 1: Will Do you ever wonder what it would be like

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Speaker 1: to be transparent yourself?

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Speaker 5: Sounds terrible. I guess you want people to see, right.

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Speaker 5: Everyone wants to be seen these.

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Speaker 1: Days, unless you want to sneak around the house and

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Speaker 1: be invisible.

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Speaker 5: I guess if you have the auction of turning transparent,

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Speaker 5: that's cool. Like I think all kids dream of being

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Speaker 5: invisible at some point.

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Speaker 1: I always wondered what happens if you're invisible and you

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Speaker 1: take a bite of an apple. I can everybody see

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Speaker 1: that apple work its way through you.

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Speaker 5: I guess it depends on you, know, like how the

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Speaker 5: invisibility works, Like are you a space that is transparent

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Speaker 5: or is it just your molecules are transparent? Or you

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Speaker 5: can just see the cookie mid out of glass frogs

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Speaker 5: or eat glass. I guess that sounds less tasty.

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Speaker 1: I don't think I want to take a bite out

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Speaker 1: of that.

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Speaker 5: Yeah, I see you, man, I see you. I am

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Speaker 5: morehem a cartoonists and the creator of PhD comics.

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Speaker 1: Hi, I'm Daniel. I'm a particle physicist and a professor.

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Speaker 1: You see Irvine, And even though you can only hear

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Speaker 1: my voice, I feel seen.

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Speaker 5: Well, that's good everyone to be seen. I think mostly

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Speaker 5: we just feel heard in this podcast.

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Speaker 1: That's right. We feel heard, not hurt, because we love

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Speaker 1: sharing with you our passion and curiosity about the universe.

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Speaker 1: And when I hear back from listeners that something we

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Speaker 1: have said has touched on their deep seated need to

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Speaker 1: understand the universe, I do feel heard and seen.

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Speaker 5: Yeah, because it is a pretty amazing universe with lots

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Speaker 5: to see out there and to hear. I guess if

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Speaker 5: you have to write kinds of ears because sound doesn't

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Speaker 5: travel in space.

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Speaker 1: It actually does just very very slowly.

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Speaker 5: Why are you kidding or are you serious?

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Speaker 1: No, space is not totally empty, and so in principle

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Speaker 1: there are sound waves that do propagate through the solar wind,

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Speaker 1: for example. But in practice, if you're in outer space,

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Speaker 1: you're going to freeze before you hear anything.

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Speaker 5: Also, you would be hearing it in slow motion. I

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Speaker 5: guess right. If sound mos slower, like, don't go out

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Speaker 5: in space too late, you're dead.

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Speaker 1: That's right. You should shout at your friends in space

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Speaker 1: like a year before they go space walking without a

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Speaker 1: suit on so they can hear you.

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Speaker 5: Yeah, Oh, that's not going to help them. Also, how

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Speaker 5: do you shout in space? Like you have to take

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Speaker 5: off your helmet to shout. Then that's not good. Either

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Speaker 5: in space nobody can hear you. Or you shouldn't be

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Speaker 5: hurt or you might get hurt.

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Speaker 1: But you should turn your eyeballs up to the night

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Speaker 1: sky and wonder how everything works. And you should also

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Speaker 1: look down on the ground beneath you and see if

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Speaker 1: you can puzzle out the mysteries of everyday objects, the

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Speaker 1: nature of our universe, how everything works, how it weaves

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Speaker 1: itself together to make this incredible cosmos. That's one of

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Speaker 1: the deep mysteries that humans want to unravel, and those

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Speaker 1: are the topics we like to take a part on

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Speaker 1: this podcast.

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Speaker 5: Yeah, and it's amazing and lucky that we can see

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Speaker 5: so many things out there in the universe and around us,

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Speaker 5: so that we know where they are and we can

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Speaker 5: also study them and figure out how they work, what

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Speaker 5: they're made out of, and what the rules of this

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Speaker 5: crazy universe are. But anyways, welcome to our podcast, Daniel

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Speaker 5: and Jorge Explain the Universe, a production of iHeartRadio.

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Speaker 1: In which we try to do exactly that, take apart

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Speaker 1: the whole universe, see how works, and explain it to you.

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Speaker 1: Some of the questions we love to tackle involve the

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Speaker 1: tiniest things in the universe, what the rules are for

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Speaker 1: how they work, or the biggest things in the universe,

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Speaker 1: like the whole universe itself or supermassive black holes at

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Speaker 1: the hearts of galaxies. But there's also a lot of

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Speaker 1: fascinating physics in between. How those tiny little objects pull

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Speaker 1: themselves together to behave in weird and wonderful ways. The

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Speaker 1: reason ice cream is so tasty, the reason metals conduct electricity,

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Speaker 1: the reason your chair holds you up is because of

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Speaker 1: zillions of atoms all working together to have fascinating phenomena.

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Speaker 5: Yeah, and thankfully we can see them all and hear

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Speaker 5: them all so we can study them. It'd be kind

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Speaker 5: of hard to know and study the universe if everything

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Speaker 5: was invisible, right, or if we didn't have eyeballs.

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Speaker 1: In years, that's true, and recently we've discovered the amazing

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Speaker 1: fact that most of the universe is invisible. The dark

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Speaker 1: matter that's out there is most of the stuff in

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Speaker 1: the universe, and we didn't even know it existed until recently.

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Speaker 1: Because it's invisible to us. Life passes right there through it,

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Speaker 1: and there's lots of things going on out there in

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Speaker 1: the universe that you just cannot see because your eyeballs

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Speaker 1: can't pick them up, you can't taste them, you can't

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Speaker 1: smell them. So most of the universe is actually invisible.

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Speaker 1: Transparency turns out to be the name of the game.

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Speaker 5: So the universe got its kid wish of being invisible.

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Speaker 5: Is that what you're saying? What's it trying to sneak

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Speaker 5: around and do?

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Speaker 1: I don't know, but those dark matter kids are probably

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Speaker 1: eating dark matter cookies all night long.

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Speaker 5: And they're made out of dark chocolate and taste better too.

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Speaker 5: And my new wish used to be a dark matter person.

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Speaker 5: They get to eat dark meat their chicken.

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Speaker 1: Well, it also answers that other question. What happens when

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Speaker 1: a dark matter kid eats a dark matter cookie? Of course,

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Speaker 1: it goes through them and becomes dark matter on the

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Speaker 1: way out.

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Speaker 5: Darker matter, you mean, the darkest matter, because a black hole.

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Speaker 5: That's where black holes come from.

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Speaker 1: That's exactly right. Black holes are dark matter toilets.

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Speaker 5: They're are worse through the things that go into the toilet.

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Speaker 1: We are elevating the discourse of the nature of the universe.

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Speaker 5: Yeah, I mean listeners want to be reached into their

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Speaker 5: soul and touched right and seen and hurt.

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Speaker 1: I'm not sure they want to have this particular taste, however.

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Speaker 5: Well, who said anything about tasting.

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Speaker 1: We're talking about eating dark matter cookies. You're fantasizing about

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Speaker 1: dark matter chocolate over there. It's all about taste.

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Speaker 5: That's why we're all about taste here.

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Speaker 1: Good taste, bad taste, you.

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Speaker 5: Decide, that's right. We're we're scientists. We explore the full

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Speaker 5: range of tastes available to the human experience. But it

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Speaker 5: is interesting that even the things that are invisible, we

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Speaker 5: can still somehow see them through other things, right. I mean,

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Speaker 5: if dark matter dark energy was completely invisible, we wouldn't

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Speaker 5: even know it was there. But somehow it has an

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Speaker 5: influence on things that we can see, thankfully, and that's

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Speaker 5: how we know they're there.

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Speaker 1: Yes, transparency turns out to be quite a subtle issue.

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Speaker 1: Some things can be transparent to one kind of light

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Speaker 1: but not to another. Some kinds of light can pass

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Speaker 1: through some objects but not other objects. As always, when

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Speaker 1: you dig into it, you discover there's a fascinating physics

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Speaker 1: story that lines how things work.

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Speaker 5: Yep, this is an interesting topic, and so today on

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Speaker 5: the podcast we'll be taping the question how does transparency work?

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Speaker 1: Some titled how can your kids eat cookies without you knowing?

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Speaker 5: Well, I don't think they need to be transparent to

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Speaker 5: do that, depending how sneaky they are and how how

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Speaker 5: early you go to sleep or wake up. Now, this

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Speaker 5: is an interesting question, Daniel, I imagine it means what

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Speaker 5: makes things see through? Not like how do transparencies work,

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Speaker 5: or how does government transparency work? Because that apparently doesn't

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Speaker 5: work that well, or sometimes it works too well.

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Speaker 1: That's right. We want sunlight on all the operations of

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Speaker 1: the universe, but in particular here we're wondering about why

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Speaker 1: light can pass through some kinds of things, Why you

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Speaker 1: can see through glass but you can't see through stone.

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Speaker 1: Why X rays reveal your soft tissues but not your bones,

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Speaker 1: What is the underlying physics, what is the microscopic picture

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Speaker 1: of transparency.

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Speaker 5: We're exploring the full range of transparent behavior.

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Speaker 1: We're just trying to be transparent about how the universe works.

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Speaker 5: We're trying to be transparent about how the podcast works,

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Speaker 5: is what I'm saying, and to be fully transparent. I

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Speaker 5: have not read the outline for today's episode. I am

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Speaker 5: kind of winging it today, which is totally different from

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Speaker 5: other days.

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Speaker 1: Right exactly. If you don't notice the difference between this

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Speaker 1: episode and the other episode, then folks, you learn something

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Speaker 1: about how the sausage is made.

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Speaker 5: You learned that Jorges could thinking on the fly and

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Speaker 5: reading really quickly. But anyways, as usually, we were wondering

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Speaker 5: how many people out there had thought about things that

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Speaker 5: are transparent and if they know how transparency works.

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Speaker 1: So thanks very much to everybody who answers these questions.

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Speaker 1: It gives us a great insight into what people already

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Speaker 1: know and don't know. If you'd like to help us

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Speaker 1: out for a future episode of the podcast, please don't

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Speaker 1: be shy. Write to us two questions at Danielandhorge dot com.

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Speaker 5: So think about it for a second. Do you know

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Speaker 5: how transparency works? Here's what people had to say.

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Speaker 6: Transparency works, in my opinion by not refracting, or the

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Speaker 6: medium that the light is passing through does not refract

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Speaker 6: in any way or change the path of the light,

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Speaker 6: and that way you don't get any kind of interference

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Speaker 6: and you can see through something. It is transparent so

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Speaker 6: perfectly clear.

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Speaker 7: I'm pretty sure that transparency works by like the light

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Speaker 7: can travel through the material without being absorbed, so maybe

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Speaker 7: there's a lot of spaces between it, and so yeah,

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Speaker 7: that light just doesn't get absorbed, so it goes through

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Speaker 7: and it's merry.

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Speaker 8: Way.

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Speaker 9: At first, I thought it was simple because the material

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Speaker 9: density would lead to more or less transparency, like air

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Speaker 9: or some gas and low density would be transparent to

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Speaker 9: some point because of the particle density. But then again,

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Speaker 9: glass is quite a high density, right, and it's still transparent,

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Speaker 9: So maybe it's about reflective index. And yeah, like if

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Speaker 9: you put glass in a water that comes invisible because

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Speaker 9: it's fully transparent because of the reflective in thesease.

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Speaker 10: I would guess transparency has to do with interactions between

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Speaker 10: different forces and particles and whether they interact or not.

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Speaker 10: If they interact, they are not transparent to each other,

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Speaker 10: and if they don't interact, they're transparent to each other.

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Speaker 8: It's like a relay race. So the photon gets emitted,

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Speaker 8: it's absorbed by the first atom in the glass, for instance,

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Speaker 8: and then it gets retransmitted to the next and so

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Speaker 8: on and so forth until it goes over the other

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Speaker 8: side of the of the glass or whatever transparent material

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Speaker 8: we are talking about.

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Speaker 11: In order to reflect light, the photon would have to

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Speaker 11: be absorbed and then re emitted, I think so. I

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Speaker 11: guess in order to be transparent, it would have to

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Speaker 11: be something that doesn't absorb photons for whatever reason. That'd

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Speaker 11: be interesting one.

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Speaker 5: That all right, some pretty intricate answers. I feel like

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Speaker 5: we had some hardcore physicists here in the pool today.

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Speaker 5: Did you ask people on the internet or in your department?

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Speaker 1: These are all Internet answers, and they really reflect the

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Speaker 1: incredible complexity of light and matter. We've dug into it

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Speaker 1: in a few episodes, what happens when things reflect, what

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Speaker 1: color means, But there really is a whole lot going

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Speaker 1: on here. Light bouncing off of matter, or passing through matter,

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Speaker 1: or refracting through matter is really a very complicated phenomenon,

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Speaker 1: very tricky to understand from the microphysics point of view.

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Speaker 5: Yes, I like how it reflects how smarter our listeners are.

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Speaker 1: But so many really interesting answers, a lot of which

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Speaker 1: really get at the heart of the question, which is

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Speaker 1: that it's about the interactions of the photons with the material.

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Speaker 1: There's also some misunderstanding there, like the idea that light

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Speaker 1: goes through things if there are spaces for it to

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Speaker 1: like wiggle its way through. That's not really the way

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Speaker 1: that we think about it, but we'll dig into it

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Speaker 1: and explain it.

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Speaker 5: I guess it depends, like the difference between transparency and

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Speaker 5: air and transparency in glass, and transparency to different kinds

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Speaker 5: of light right bends.

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Speaker 1: There are definitely differences between air and glass, but the

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Speaker 1: basic physics of transparency is quite similar in either case.

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Speaker 1: Are the photons like avoiding the atoms, It's not like

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Speaker 1: they're finding a pathway through. That's maybe the way transparency

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Speaker 1: works for like a screen door. You can see through

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Speaker 1: a screen because there are literally holes that a photon

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Speaker 1: can pass through. But the reason you can see glass

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Speaker 1: is not because it's like a microscreen. That glass is

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Speaker 1: finding tiny little holes in the glass to wiggle its

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Speaker 1: way through.

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Speaker 5: I guess we'll dig into that, and so let's jump

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Speaker 5: right in, Daniel Water are the basics what makes something transparent.

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Speaker 1: So first, let's clarify what we mean by transparent. Right,

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Speaker 1: by transparent really just mean that you can see through it.

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Speaker 1: It means if you shine a light from one side,

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Speaker 1: the light comes out the other side with basically no scattering,

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Speaker 1: like the light is still coherent. If you have an

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Speaker 1: image of an ice cream cone on one side, you're

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Speaker 1: going to see the ice cream cone still on the

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Speaker 1: other side. It might be refracted a little bit or

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Speaker 1: bent or distorted, but it's transparent if those images are preserved.

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Speaker 1: I see.

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Speaker 5: So like, if light can pass through it basically is

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Speaker 5: what it means to be transparent, or information from light

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Speaker 5: passes through it without any distortions exactly.

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Speaker 1: And even glass, which we think of as transparent, does

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Speaker 1: distort it a little bit, like if you stick your

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Speaker 1: finger behind a pane of glass. And only half of

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Speaker 1: your finger is sticking behind it. You'll notice the finger

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Speaker 1: no longer looks like a whole finger. It's like broken

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Speaker 1: in half. Because the path of the light through the

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Speaker 1: glass changes a little bit relative to the path of

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Speaker 1: the light through the air. That's refraction, which is a

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Speaker 1: whole other complicated topic that we dug into in another episode.

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Speaker 1: But still, you can see your finger right the same

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Speaker 1: way you can see through water and you can see

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Speaker 1: through air. You can identify things. You can recognize things

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Speaker 1: even if the path of the light is slightly.

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Speaker 5: Changed, all right, So that means that a light can

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Speaker 5: or at least information that the light had before it

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Speaker 5: went through the material makes it through unscales. That's what

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Speaker 5: it means to be transparent.

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Speaker 1: Yeah, and the fundamental thing that's happening there relates to

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Speaker 1: how photons either interact or don't interact with the electrons

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Speaker 1: in that material. And understand that we have to understand

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Speaker 1: a little bit about the quantum mechanics of those electrons,

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Speaker 1: what energy is they're allowed, and how photons decide whether

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Speaker 1: or not to interact with those electrons.

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Speaker 5: And you were saying, it's not like it's a screen door,

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Speaker 5: where like some other light is finding a path through it.

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Speaker 5: But that can also happen Kennet Like, if you have

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Speaker 5: something really thin maybe, or something really sparse or light

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Speaker 5: like air, there has to be some phonons that are

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Speaker 5: making it through without interacting with anything.

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Speaker 12: Right.

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Speaker 1: Well, most materials, even like a thin sheet of paper,

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Speaker 1: are dense enough that photons are not like finding holes

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Speaker 1: in them. The reason that light gets through is because

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Speaker 1: the photons are ignoring the atoms. It's not that they're

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Speaker 1: missing them, it's that they're passing through without interacting. Because

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Speaker 1: when a photon passes by an atom, it doesn't always

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Speaker 1: interact with it. There are rules about whether or not

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Speaker 1: photons can interact with atoms, and in a solid it's

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Speaker 1: complicated because you have lots and lots of atoms. But

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Speaker 1: the easiest way to understand it is to start with

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Speaker 1: an individual atom. Just think about like a single hydrogen

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Speaker 1: atom in space and you shoot a photon at it.

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Speaker 1: Is that photon going to get absorbed by the atom

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Speaker 1: or is the photon going to ignore the atom? And

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Speaker 1: that depends on the energy of the photon because these

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Speaker 1: atoms can only absorb photons of certain energies.

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Speaker 5: Well, I guess it also maybe depends on where you

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Speaker 5: shoot the photon, right, Like, if I have an hydrogen

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Speaker 5: atom floating out there in the air and I shoot

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Speaker 5: a laser beam a mile to one side of it,

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Speaker 5: it's not going to interact with the hydrogen, is it.

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Speaker 1: No, that's right. But if you have a huge wall

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Speaker 1: of hydrogen atoms and you shoot the laser beam at it,

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Speaker 1: then it's not going to be able to avoid the hydrogen, right,

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Speaker 1: It's going to have to get through the other side.

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Speaker 1: It's going to have to pass through the hydrogen. And

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Speaker 1: that's what makes things transparent. I mean, one thing is

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Speaker 1: to have holes in it. Sure, you can see through

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Speaker 1: a screen door even if it's made of metal or stone,

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Speaker 1: as long as there are holes in it. But I

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Speaker 1: think the physics of transparency is more interesting if we

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Speaker 1: think about what happens when light ignores the material, if

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Speaker 1: it passes through the material, rather than finding holes or

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Speaker 1: ways around.

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Speaker 5: Well, I know it's more interesting as a physicist, but

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Speaker 5: I guess for me, I'm just curious about which has

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Speaker 5: more of an effect to make something transparent, right, Because

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Speaker 5: you know, people always talk about like materials like our skin,

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Speaker 5: our bodies, they're made out of atoms, but the atoms

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Speaker 5: are really sort of far apart, and the nucleus is

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Speaker 5: really far apart from the electron. So there's a lot

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Speaker 5: of sort of like supposedly empty space, even within solid

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Speaker 5: matter like ourselves. I'm just wondering, like, you know, there's

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Speaker 5: it seems like there's a lot of space for a

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Speaker 5: light to squeeze through or to pass by without even

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Speaker 5: knowing there are other things there.

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Speaker 1: That's an interesting point, and I think a lot of

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Speaker 1: people have maybe the wrong mental picture of what an

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Speaker 1: atom sort of looks like to a photon. You know,

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Speaker 1: even if you have a grid of atoms, like a

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Speaker 1: sheet of atoms making the material, you might imagine that

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Speaker 1: it's mostly empty space, as you said, And it's true

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Speaker 1: that the nucleus is small compared to the distances between

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Speaker 1: the atoms, right, So you have this like grid of

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Speaker 1: atoms and there is a lot of space between the nuclei,

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Speaker 1: But that space is not empty, right. That space is

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Speaker 1: filled with electrocrons and electronic fields and forces that are

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Speaker 1: holding the nucleus and the electrons together. So the electrons

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Speaker 1: are in these buzzy clouds all around the nucleus and

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Speaker 1: the electrons weave the atoms together, right, So it's not

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Speaker 1: like the space between the atoms. The atoms are held together,

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Speaker 1: they're in these bonds that tie them together into a

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Speaker 1: big grid, into a big lattice, and the electrons can

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Speaker 1: sometimes slide back and forth and move between the atoms,

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Speaker 1: so there isn't a lot of space between the atoms.

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Speaker 1: And then inside the atom, all that space you imagine

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Speaker 1: might be empty is really filled with electrons. So from

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Speaker 1: the point of view of a photon hitting like a

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Speaker 1: sheet of material, a sheet of paper or a sheet

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Speaker 1: of glass or whatever, it really is hitting a wall

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Speaker 1: of electrons that it can't find a way around unless

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Speaker 1: you like physically punch holes in it.

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Speaker 5: You just made me wonder, like when you have a material,

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Speaker 5: how close together are the electrons shells between atoms, Like

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Speaker 5: are are they bumping up against each other? Or is

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Speaker 5: there a certain amount of space?

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Speaker 1: It depends a little bit on the kind of atom

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Speaker 1: you have, But atoms tend to bond with their outermost electrons,

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Speaker 1: and we'll dig into that if you let me talk

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Speaker 1: about how these electrons move between the atoms. But you

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Speaker 1: really are tying the outer levels of the electron orbitals

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Speaker 1: together and then informing these common electron energy levels. So

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Speaker 1: these atoms are sharing electrons that really are woven together.

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Speaker 5: I see. I think what you're saying is that to

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Speaker 5: a photon a grid of electrons, it's like a solid

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Speaker 5: wall almost because it's full of electron fields and photons

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Speaker 5: interact with electrons. But like, if you were something else

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Speaker 5: that was not an electron, you would maybe see a

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Speaker 5: lot of empty space, But because you are a photon,

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Speaker 5: then you're walking into a solid wall of electron fuzziness.

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Speaker 1: Yeah, if you're a neutrino, for example, and you don't

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Speaker 1: feel electric charge, then the fact that there are electromagnetic

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Speaker 1: fields all through these materials is relevant to you, and

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Speaker 1: you pass right through it. So like even a block

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Speaker 1: of lead is basically transparent to a neutrino because it

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Speaker 1: doesn't interact with the stuff. So transparency comes down to

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Speaker 1: whether you interact with the material there, not really whether

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Speaker 1: there are holes there. So photons they can either pass

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Speaker 1: through a material or they can interact with it, and

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Speaker 1: that depends on the atomic structure and the energy levels

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Speaker 1: that the electrons have and whether or not they interact

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Speaker 1: with that photon. Even though photon sees a wall of material,

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Speaker 1: a buzzing blob of electrons in front of it, it

441
00:21:24,560 --> 00:21:28,800
Speaker 1: can still sometimes pass right through without interacting, and that's

442
00:21:28,840 --> 00:21:29,840
Speaker 1: what transparency is.

443
00:21:30,040 --> 00:21:32,040
Speaker 5: Yeah, I guess it can be transparent not just to

444
00:21:32,119 --> 00:21:34,560
Speaker 5: light but to other things. Right, Like, isn't there a

445
00:21:34,600 --> 00:21:38,440
Speaker 5: famous like gold foil experiment that kind of help people

446
00:21:38,480 --> 00:21:39,960
Speaker 5: figure out the structure of the atom?

447
00:21:40,040 --> 00:21:43,080
Speaker 1: Yeah, that's right. Rutherford shot alpha particles, which are helium

448
00:21:43,200 --> 00:21:46,320
Speaker 1: nuclei and a very thin tissue of gold, and he

449
00:21:46,359 --> 00:21:50,000
Speaker 1: expected it to mostly just pass through, occasionally get distorted

450
00:21:50,000 --> 00:21:53,040
Speaker 1: a little bit by forces. What he found was that occasionally,

451
00:21:53,080 --> 00:21:56,520
Speaker 1: like one in eight thousand times, the alpha particle the

452
00:21:56,520 --> 00:21:59,199
Speaker 1: helium nucleus bounced right back, which told him that it

453
00:21:59,280 --> 00:22:02,320
Speaker 1: was interacting with something hard at the core. So that's

454
00:22:02,359 --> 00:22:04,560
Speaker 1: what told him that the sheet of gold actually was

455
00:22:04,640 --> 00:22:08,040
Speaker 1: made out of a grid of hard nuclei, that most

456
00:22:08,040 --> 00:22:11,000
Speaker 1: of the gold was transparent to the alpha particle, but

457
00:22:11,000 --> 00:22:12,800
Speaker 1: that occasional little dots of it were not.

458
00:22:13,840 --> 00:22:16,840
Speaker 5: Because I guess the helium nuclei would only interact with

459
00:22:16,880 --> 00:22:19,760
Speaker 5: the nuclei of the gold right to the helium particle.

460
00:22:19,880 --> 00:22:22,560
Speaker 5: It did look like a screen because there is a

461
00:22:22,560 --> 00:22:25,920
Speaker 5: lot of empty space to a helium atom in between

462
00:22:26,800 --> 00:22:27,600
Speaker 5: the gold atoms.

463
00:22:27,680 --> 00:22:29,639
Speaker 1: Yeah, that's mostly true. The nuance there is that the

464
00:22:29,680 --> 00:22:32,600
Speaker 1: helium does interact with the electrons. It's just that the

465
00:22:32,640 --> 00:22:35,600
Speaker 1: electrons don't have the mass or the kinetic energy to

466
00:22:35,640 --> 00:22:38,399
Speaker 1: bounce it back. They can only slightly change its direction.

467
00:22:38,960 --> 00:22:40,879
Speaker 1: So if the helium goes through the gold and only

468
00:22:40,920 --> 00:22:43,480
Speaker 1: interacts with the electrons because a little bit of change

469
00:22:43,480 --> 00:22:45,639
Speaker 1: of direction, whereas if it hits one of the nuclei,

470
00:22:45,840 --> 00:22:47,960
Speaker 1: those have the mass to like push it all the

471
00:22:48,000 --> 00:22:50,480
Speaker 1: way back. So the sort of two different kinds of

472
00:22:50,520 --> 00:22:53,520
Speaker 1: interaction the helium can do, one where it punches through

473
00:22:53,560 --> 00:22:55,200
Speaker 1: and the other one where it bounces back.

474
00:22:55,240 --> 00:22:59,720
Speaker 5: All right, So you're saying, let's maybe focus on light transparency.

475
00:23:00,160 --> 00:23:02,840
Speaker 5: And we know that light interacts with electrons, and so

476
00:23:03,640 --> 00:23:06,800
Speaker 5: material stuff to a photon looks pretty dense and so

477
00:23:06,920 --> 00:23:09,800
Speaker 5: you can't sort of just go through it without possibly

478
00:23:09,800 --> 00:23:12,480
Speaker 5: interacting with things. But you're saying, maybe the key to

479
00:23:12,520 --> 00:23:15,879
Speaker 5: transparency is it sometimes light doesn't interact with the thing

480
00:23:15,920 --> 00:23:16,359
Speaker 5: that's there.

481
00:23:16,560 --> 00:23:18,920
Speaker 1: That's right. Even if you have a bunch of electrons,

482
00:23:19,000 --> 00:23:22,280
Speaker 1: photons aren't necessarily able to interact with them. The photon

483
00:23:22,359 --> 00:23:24,840
Speaker 1: has to have the right amount of energy so the

484
00:23:24,880 --> 00:23:27,960
Speaker 1: electron can accept it can absorb it. I photon has

485
00:23:28,000 --> 00:23:32,359
Speaker 1: the wrong energy, it'll pass right through without interacting without electron.

486
00:23:32,640 --> 00:23:34,920
Speaker 1: And that all comes down to how the electrons are

487
00:23:34,960 --> 00:23:38,200
Speaker 1: confined in the material. I mean a random free electron

488
00:23:38,280 --> 00:23:40,359
Speaker 1: in space. So you just have like an electron flying

489
00:23:40,359 --> 00:23:42,800
Speaker 1: through the universe and a photon hits it. It's going

490
00:23:42,840 --> 00:23:46,160
Speaker 1: to absorb that photon no problem, because electrons flying through

491
00:23:46,160 --> 00:23:49,040
Speaker 1: space can have any energy, there's no restriction, can have

492
00:23:49,280 --> 00:23:52,840
Speaker 1: any arbitrary amount of energy, so it will almost always

493
00:23:52,880 --> 00:23:56,240
Speaker 1: absorb that photon. But an electron around an atom has

494
00:23:56,280 --> 00:23:59,000
Speaker 1: different rules. Because of the quantum mechanics, it can only

495
00:23:59,040 --> 00:24:01,960
Speaker 1: exist on like a latter of energy levels, so it

496
00:24:01,960 --> 00:24:04,880
Speaker 1: can only absorb with photons that move it up one

497
00:24:05,040 --> 00:24:07,800
Speaker 1: or two or ten steps on that ladder. It can't

498
00:24:07,800 --> 00:24:09,720
Speaker 1: move up like one and a half steps or two

499
00:24:09,720 --> 00:24:12,919
Speaker 1: point seven steps. That limits the kinds of photons that

500
00:24:12,920 --> 00:24:14,159
Speaker 1: an electron can absorb.

501
00:24:15,200 --> 00:24:18,600
Speaker 5: Interesting, it's like the electrons are stuck and they don't

502
00:24:18,600 --> 00:24:21,440
Speaker 5: want to move from where they are, And so let's

503
00:24:21,440 --> 00:24:24,439
Speaker 5: get a little bit deeper into that and then also

504
00:24:24,560 --> 00:24:27,080
Speaker 5: talk about what happens when something is transparent, so we'll

505
00:24:27,080 --> 00:24:29,359
Speaker 5: talk about that. But first let's take a quick break.

506
00:24:33,560 --> 00:24:36,560
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557
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560
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563
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Speaker 5: All right, we're talking about transparency here today and what

575
00:28:14,280 --> 00:28:17,640
Speaker 5: makes things see through. Daniel, you mentioned that it's kind

576
00:28:17,640 --> 00:28:21,760
Speaker 5: of about how light can go into material, see the material,

577
00:28:21,840 --> 00:28:23,879
Speaker 5: be near the material, but not interact with it. And

578
00:28:23,920 --> 00:28:26,960
Speaker 5: you say it has something to do with the energy

579
00:28:27,040 --> 00:28:30,080
Speaker 5: levels of the electron, because you said that an electron

580
00:28:30,119 --> 00:28:33,000
Speaker 5: floating out in space will always absorb an electron no

581
00:28:33,000 --> 00:28:35,760
Speaker 5: matter what does it have to be, like fly near it,

582
00:28:35,800 --> 00:28:38,120
Speaker 5: does it have to hit the electron right in the middle,

583
00:28:38,440 --> 00:28:41,200
Speaker 5: or does it interact when it's flying nearby. How does

584
00:28:41,200 --> 00:28:43,240
Speaker 5: that free space case work.

585
00:28:43,520 --> 00:28:46,040
Speaker 1: If you zap an electron with a photon and the

586
00:28:46,200 --> 00:28:48,880
Speaker 1: electron is out in free space, it means that there

587
00:28:48,920 --> 00:28:52,080
Speaker 1: are no rules that govern the energy that the electrons

588
00:28:52,080 --> 00:28:54,880
Speaker 1: can have. I think something that's really cool and not

589
00:28:55,080 --> 00:28:59,560
Speaker 1: like widely enough understood, is where quantization comes from, Like

590
00:29:00,040 --> 00:29:04,480
Speaker 1: why electrons in materials have energy levels. Where these quantum

591
00:29:04,600 --> 00:29:08,520
Speaker 1: energy levels come from, And it really comes from boundary conditions.

592
00:29:08,520 --> 00:29:11,720
Speaker 1: It comes from forcing the electron to live within a

593
00:29:11,760 --> 00:29:14,440
Speaker 1: certain location, like putting it in a box, so that

594
00:29:14,560 --> 00:29:17,280
Speaker 1: electron out in empty space. It can be here, it

595
00:29:17,320 --> 00:29:19,400
Speaker 1: can be there, it can have any location, it can

596
00:29:19,480 --> 00:29:22,200
Speaker 1: have any momentum, and so it's free to absorb a

597
00:29:22,240 --> 00:29:25,640
Speaker 1: photon of any energy. There's a probability for an electron

598
00:29:25,680 --> 00:29:27,800
Speaker 1: and a photon to interact. There's still a chance, of course,

599
00:29:27,840 --> 00:29:30,160
Speaker 1: that a photon will not interact with an electron. It

600
00:29:30,200 --> 00:29:34,160
Speaker 1: depends on the strength of the force essentially that controls

601
00:29:34,160 --> 00:29:36,960
Speaker 1: like the probability for these things to happen. But for

602
00:29:37,040 --> 00:29:40,120
Speaker 1: today's conversation, we can imagine that it basically just always happens.

603
00:29:40,360 --> 00:29:43,200
Speaker 1: You zap an electron with a photon. It doesn't matter

604
00:29:43,600 --> 00:29:46,600
Speaker 1: what the energy of that photon is the electron can

605
00:29:46,640 --> 00:29:49,040
Speaker 1: accept it because it could have a higher momentum of

606
00:29:49,120 --> 00:29:52,880
Speaker 1: any value. That's not true for electrons around an atom.

607
00:29:52,960 --> 00:29:56,200
Speaker 1: It can only have energies of certain values because it's

608
00:29:56,200 --> 00:29:58,760
Speaker 1: confined into the box of the atom.

609
00:29:58,800 --> 00:30:01,800
Speaker 5: Now within that freez space electron, when that light hits it,

610
00:30:01,840 --> 00:30:04,240
Speaker 5: what happens to that electron? It gets faster or it

611
00:30:04,280 --> 00:30:07,000
Speaker 5: gets hotter? Does it start spinning faster? What happens when

612
00:30:07,000 --> 00:30:09,040
Speaker 5: you use zap an electron in space would like.

613
00:30:09,240 --> 00:30:12,440
Speaker 1: Well, it absorbs the momentum of that photon because of

614
00:30:12,480 --> 00:30:15,200
Speaker 1: conservation momentum, and now it carries that momentum as well.

615
00:30:15,320 --> 00:30:17,480
Speaker 1: And so if the photon was moving in the same

616
00:30:17,520 --> 00:30:20,000
Speaker 1: direction as the electron, then it gives it a zip.

617
00:30:20,200 --> 00:30:22,400
Speaker 1: It's going faster. If the photon is moving in the

618
00:30:22,400 --> 00:30:25,440
Speaker 1: opposite direction, the electron hits the photon sort of head on,

619
00:30:25,840 --> 00:30:28,760
Speaker 1: then it gets slowed down. Right. We talked about like

620
00:30:28,840 --> 00:30:32,000
Speaker 1: laser cooling once on the podcast. You can use lasers

621
00:30:32,080 --> 00:30:35,520
Speaker 1: to slow things down. Also if you zap things in

622
00:30:35,560 --> 00:30:36,240
Speaker 1: the right direction.

623
00:30:36,600 --> 00:30:39,120
Speaker 5: Yeah, that was pretty cool. And so it's sort of

624
00:30:39,160 --> 00:30:40,680
Speaker 5: like a Billier ball. I guess, like if you have

625
00:30:40,680 --> 00:30:42,480
Speaker 5: an electron outher in space and you hit it with

626
00:30:42,560 --> 00:30:45,160
Speaker 5: a photon. It basically happens like it does when you

627
00:30:45,280 --> 00:30:47,080
Speaker 5: hit a billier ball, right with the white ball.

628
00:30:47,240 --> 00:30:50,000
Speaker 1: Yeah, the quantum mechanics comes in with the probability there's

629
00:30:50,040 --> 00:30:52,120
Speaker 1: like a chance that that in direction will happen, a

630
00:30:52,240 --> 00:30:54,760
Speaker 1: chance that it won't. But for today's conversation, we can

631
00:30:54,800 --> 00:30:56,320
Speaker 1: think of it like a billiard ball. You're giving it

632
00:30:56,320 --> 00:30:58,840
Speaker 1: a push and it's absorbing that energy. And because a

633
00:30:58,960 --> 00:31:01,120
Speaker 1: free electron one out in the middle of space can

634
00:31:01,160 --> 00:31:03,680
Speaker 1: have any energy, quantum mechanics is fine with that. Now

635
00:31:03,720 --> 00:31:05,880
Speaker 1: you take that same electron, you say, okay, you're now

636
00:31:05,920 --> 00:31:08,440
Speaker 1: in orbit around a hydrogen atom. Well, you still have

637
00:31:08,480 --> 00:31:10,560
Speaker 1: to obey the rules of quantum mechanics, and in this case,

638
00:31:10,600 --> 00:31:15,080
Speaker 1: quantum mechanics says are there's only certain solutions to the math. Here,

639
00:31:15,240 --> 00:31:19,040
Speaker 1: Only certain energies of the electron make the math work.

640
00:31:19,320 --> 00:31:22,480
Speaker 1: The wave function of the electron has to satisfy some conditions,

641
00:31:22,720 --> 00:31:26,480
Speaker 1: and that's only true for certain values of the electron energy.

642
00:31:26,600 --> 00:31:29,520
Speaker 1: So you can't have an electron with an arbitrary energy

643
00:31:29,920 --> 00:31:32,760
Speaker 1: around a proton. There's a ladder of values there, and

644
00:31:32,840 --> 00:31:35,960
Speaker 1: that determines whether the electron can absorb the energy of

645
00:31:36,000 --> 00:31:36,920
Speaker 1: a passing photon.

646
00:31:37,280 --> 00:31:39,040
Speaker 5: I guess it's sort of like, you know, the Earth

647
00:31:39,080 --> 00:31:41,200
Speaker 5: is going around the Sun in an orbit, but the

648
00:31:41,200 --> 00:31:43,840
Speaker 5: Earth is not restricted to what that orbit can be.

649
00:31:43,960 --> 00:31:46,800
Speaker 5: Like if a meteor hits Earth within a force, it

650
00:31:46,840 --> 00:31:48,720
Speaker 5: is going to speed us up or slow us down,

651
00:31:48,760 --> 00:31:51,320
Speaker 5: and it's going to change the path of our orbit.

652
00:31:51,920 --> 00:31:54,760
Speaker 5: But you're saying, sort of like an electron around an atom,

653
00:31:55,080 --> 00:31:57,000
Speaker 5: it's not like it can be in any orbit. It

654
00:31:57,040 --> 00:32:00,360
Speaker 5: can only be in like certain slots of that orbit,

655
00:32:00,400 --> 00:32:03,280
Speaker 5: Like it can orbit here or over there, or in

656
00:32:03,320 --> 00:32:05,360
Speaker 5: this circle or in that circle. I know it's not

657
00:32:05,400 --> 00:32:06,920
Speaker 5: really a circle, but it's sort of that. So I

658
00:32:07,000 --> 00:32:10,479
Speaker 5: mean it can only circle around the nuclei or a

659
00:32:10,480 --> 00:32:11,840
Speaker 5: certain grooves, right.

660
00:32:12,000 --> 00:32:15,000
Speaker 1: Yeah, that's a great contrast because the example of Earth

661
00:32:15,120 --> 00:32:17,959
Speaker 1: is a classical example. There's no quantum mechanics there. We're

662
00:32:18,000 --> 00:32:20,800
Speaker 1: talking about gravity, which is a classical theory, and there's

663
00:32:20,840 --> 00:32:24,360
Speaker 1: an infinite number of possible solutions for an orbit. If

664
00:32:24,400 --> 00:32:26,239
Speaker 1: you pick a radius for the Earth's orbit, I can

665
00:32:26,280 --> 00:32:28,600
Speaker 1: tell you exactly what velocity it has to have in

666
00:32:28,720 --> 00:32:31,480
Speaker 1: order to have that orbit. So there's an infinite number

667
00:32:31,480 --> 00:32:33,720
Speaker 1: of possible orbits there. In the case of the electrons,

668
00:32:33,760 --> 00:32:37,520
Speaker 1: it's really very different mathematics that determines whether the electron

669
00:32:37,560 --> 00:32:39,760
Speaker 1: can be in a particular state or not. As you said,

670
00:32:39,760 --> 00:32:42,600
Speaker 1: it's not really in an orbit. It's in a quantum state,

671
00:32:42,640 --> 00:32:45,040
Speaker 1: which means it's satisfying a different equation. In this case,

672
00:32:45,080 --> 00:32:48,120
Speaker 1: it's Schrodinger's equation, which is a quantum equation of the

673
00:32:48,160 --> 00:32:51,600
Speaker 1: wave function, and that wave function has periodicity to it,

674
00:32:51,800 --> 00:32:54,120
Speaker 1: So the wave function basically has to wrap itself around

675
00:32:54,160 --> 00:32:56,520
Speaker 1: the atom in a way that builds upon itself. It

676
00:32:56,520 --> 00:32:58,960
Speaker 1: doesn't cancel itself out. So you can fit in like

677
00:32:59,000 --> 00:33:02,280
Speaker 1: an integer number of half wavelengths of this wave function

678
00:33:02,680 --> 00:33:04,920
Speaker 1: so that things like support each other. You get like

679
00:33:04,960 --> 00:33:08,600
Speaker 1: a standing wave solution effectively, instead of things like canceling

680
00:33:08,600 --> 00:33:10,520
Speaker 1: themselves out. Just the same way that like on a

681
00:33:10,560 --> 00:33:13,680
Speaker 1: guitar string, you can have a certain number of modes

682
00:33:13,880 --> 00:33:16,560
Speaker 1: of a guitar string, right, you can oscillate the whole string,

683
00:33:16,880 --> 00:33:18,240
Speaker 1: or you can have a node in the middle so

684
00:33:18,320 --> 00:33:20,560
Speaker 1: both halves are oscillating, or you can have two nodes,

685
00:33:20,600 --> 00:33:23,720
Speaker 1: or you get like three little oscillating pieces. In the

686
00:33:23,760 --> 00:33:26,600
Speaker 1: same way, the electron has to satisfy a wave equation,

687
00:33:27,080 --> 00:33:30,320
Speaker 1: not a gravitational equation, and that's where the energy levels

688
00:33:30,360 --> 00:33:33,400
Speaker 1: come from, comes from confining it to being around the atom,

689
00:33:33,600 --> 00:33:35,680
Speaker 1: which changes the solutions to the equation.

690
00:33:36,440 --> 00:33:39,440
Speaker 5: Okay, so now I have an electron orbiting around a nuclei.

691
00:33:39,640 --> 00:33:42,720
Speaker 5: It's a wave function, it's a quantum object. It's sort

692
00:33:42,720 --> 00:33:46,000
Speaker 5: of like snaps into a certain wave shape around the nuclei.

693
00:33:46,160 --> 00:33:48,720
Speaker 5: And you're saying that a pooton headset, and the electron

694
00:33:48,800 --> 00:33:52,080
Speaker 5: is like nope, I like where I am now, no thanks,

695
00:33:52,840 --> 00:33:54,680
Speaker 5: or that's not enough to get me to the next

696
00:33:54,720 --> 00:33:57,640
Speaker 5: step in the ladder. I'm just gonna totally ignore you.

697
00:33:57,760 --> 00:33:58,520
Speaker 5: Is that what's happening.

698
00:33:58,720 --> 00:34:01,800
Speaker 1: That's exactly what's happening. A photon comes along and it

699
00:34:01,840 --> 00:34:04,800
Speaker 1: has enough energy to bump the electron to the next stage,

700
00:34:04,920 --> 00:34:07,720
Speaker 1: it gets absorbed. If it has too much energy to

701
00:34:07,760 --> 00:34:09,799
Speaker 1: get the electron to the next stage and not enough

702
00:34:09,800 --> 00:34:13,279
Speaker 1: to get it like two steps up, then it gets ignored. Right,

703
00:34:13,360 --> 00:34:16,000
Speaker 1: So it gets absorbed if it has the right energy

704
00:34:16,080 --> 00:34:18,600
Speaker 1: to move the electron up one or two or seven

705
00:34:18,880 --> 00:34:22,560
Speaker 1: some integer number of levels, and it gets ignored. If

706
00:34:22,600 --> 00:34:25,360
Speaker 1: the electron would not have a solution anymore, if it

707
00:34:25,400 --> 00:34:28,040
Speaker 1: absorbed this photon, then it just doesn't happen.

708
00:34:28,320 --> 00:34:30,560
Speaker 5: Wait wait, wait, So like if an electron is going

709
00:34:30,600 --> 00:34:33,280
Speaker 5: around a nuclei, it's in a cloud, and it gets

710
00:34:33,400 --> 00:34:36,400
Speaker 5: one and a half as much energy from a photon

711
00:34:36,719 --> 00:34:38,680
Speaker 5: that it needs to get to the next level, it's

712
00:34:38,680 --> 00:34:40,439
Speaker 5: not going to take that one and then throw away

713
00:34:40,480 --> 00:34:43,680
Speaker 5: the remainder. It's just totally gonna ignore the whole thing.

714
00:34:44,040 --> 00:34:46,880
Speaker 1: Just totally gonna ignore the whole thing. It can absorb

715
00:34:46,960 --> 00:34:49,760
Speaker 1: something that has two steps and then emit one, right,

716
00:34:50,040 --> 00:34:52,080
Speaker 1: or it can absorb something that has like seven and

717
00:34:52,160 --> 00:34:55,400
Speaker 1: emit four photons, but it has to be on that ladder.

718
00:34:55,840 --> 00:34:58,000
Speaker 5: How exact does it need to be like exactly to

719
00:34:58,080 --> 00:35:01,200
Speaker 5: the one infinite decimal you know what I mean? Like,

720
00:35:01,200 --> 00:35:04,120
Speaker 5: where are the chances that the photon will have the

721
00:35:04,239 --> 00:35:07,120
Speaker 5: exact amount of energy needs or does it just need

722
00:35:07,160 --> 00:35:08,720
Speaker 5: to be around the same energy.

723
00:35:08,880 --> 00:35:11,839
Speaker 1: Well, there's always uncertainty in quantum mechanics, right, so every

724
00:35:11,840 --> 00:35:13,960
Speaker 1: photon has an uncertain amount of energy. You can ever

725
00:35:14,040 --> 00:35:15,000
Speaker 1: measure it precisely?

726
00:35:15,239 --> 00:35:18,440
Speaker 5: Is that true? Really? I thought they had like specific frequencies.

727
00:35:18,520 --> 00:35:20,919
Speaker 1: Well, a photon is created by a quantum process, which

728
00:35:21,000 --> 00:35:23,560
Speaker 1: usually means that there is some uncertainty there, Right, there's

729
00:35:23,560 --> 00:35:25,600
Speaker 1: always a little bit of fuzz in all of these

730
00:35:25,640 --> 00:35:28,680
Speaker 1: processes which allow these things to overlap. The energy levels

731
00:35:28,680 --> 00:35:31,560
Speaker 1: that we're talking about come from a simplified model of

732
00:35:31,600 --> 00:35:34,600
Speaker 1: the nucleus, right, and in reality these things are a

733
00:35:34,600 --> 00:35:37,239
Speaker 1: little bit fuzzier. Right. The physics is a little bit

734
00:35:37,320 --> 00:35:39,959
Speaker 1: more complicated this other interaction. So there's always a little

735
00:35:40,000 --> 00:35:43,200
Speaker 1: bit of fuzz on these energy levels, and the atom

736
00:35:43,239 --> 00:35:45,239
Speaker 1: that produce the photon on the other side of the

737
00:35:45,320 --> 00:35:47,640
Speaker 1: universe or whatever, may have produced it at a certain

738
00:35:47,800 --> 00:35:50,040
Speaker 1: energy level or a little bit higher, a little bit lower.

739
00:35:50,120 --> 00:35:52,520
Speaker 1: So there's enough fuzz than quantum mechanics to mean that

740
00:35:52,520 --> 00:35:55,120
Speaker 1: there's a non zero probability for the photon to have

741
00:35:55,160 --> 00:35:57,759
Speaker 1: the right energy to be absorbed by the electron.

742
00:35:58,040 --> 00:35:58,320
Speaker 9: Mmm.

743
00:35:59,120 --> 00:36:01,960
Speaker 5: I guess when they interact, then the wave functions collapse,

744
00:36:02,040 --> 00:36:04,280
Speaker 5: and then you figure out if it has the right amount,

745
00:36:04,440 --> 00:36:06,560
Speaker 5: But it seems very unlikely they would have the exact

746
00:36:06,560 --> 00:36:07,120
Speaker 5: same amount.

747
00:36:07,480 --> 00:36:09,359
Speaker 1: Yeah, that's where the fuzz comes in. So you get

748
00:36:09,400 --> 00:36:11,319
Speaker 1: a little bit of width to these things, so you

749
00:36:11,320 --> 00:36:13,680
Speaker 1: have a probability for them to overlap. It's not like

750
00:36:13,719 --> 00:36:15,960
Speaker 1: you're throwing a dart in an infinitely sized board and

751
00:36:16,080 --> 00:36:17,760
Speaker 1: having to hit exactly the right spot.

752
00:36:17,880 --> 00:36:19,799
Speaker 5: I see. It's like you have a fuzzy dart and

753
00:36:19,880 --> 00:36:22,160
Speaker 5: the target is fuzzy too, and as long as you

754
00:36:22,239 --> 00:36:24,560
Speaker 5: sort of get it in the Rhine ballpark, then it's

755
00:36:24,600 --> 00:36:27,239
Speaker 5: gonna knock that electron or not.

756
00:36:27,480 --> 00:36:30,359
Speaker 1: Yeah, exactly. And that explains a lot of atomic physics, right.

757
00:36:30,360 --> 00:36:33,960
Speaker 1: That explains why certain gases look certain colors. That explains

758
00:36:34,080 --> 00:36:35,560
Speaker 1: why when you have a fie you might get like

759
00:36:35,640 --> 00:36:37,719
Speaker 1: green or blue flashes in it. Or if you did

760
00:36:37,760 --> 00:36:40,760
Speaker 1: that experiment in high school chemistry where you put copper

761
00:36:40,760 --> 00:36:43,440
Speaker 1: in your Bunsen burner and it glows green. Explains a

762
00:36:43,440 --> 00:36:46,520
Speaker 1: lot of atomic physics because different kinds of materials have

763
00:36:46,560 --> 00:36:50,320
Speaker 1: different energy levels, so they glow with different frequency photons,

764
00:36:50,320 --> 00:36:53,600
Speaker 1: and they can absorb different frequency photons. And that's really

765
00:36:53,600 --> 00:36:56,520
Speaker 1: cool because it means we can tell what's in distant

766
00:36:56,600 --> 00:36:59,200
Speaker 1: stars because we can look at the spectrum of energy

767
00:36:59,239 --> 00:37:01,799
Speaker 1: that they emit. We could say, oh, look, these things

768
00:37:01,840 --> 00:37:04,520
Speaker 1: are emitting photons from the energy level that only comes

769
00:37:04,560 --> 00:37:07,200
Speaker 1: from copper, so we can tell there's copper in that star.

770
00:37:07,520 --> 00:37:10,280
Speaker 1: Sometimes these things appear as spikes in the spectrum. Sometimes

771
00:37:10,320 --> 00:37:12,520
Speaker 1: they appear as dips in the spectrum because like the

772
00:37:12,560 --> 00:37:15,719
Speaker 1: atmosphere of the star is absorbing those photons. But the

773
00:37:15,719 --> 00:37:18,080
Speaker 1: point is that there are energy levels to the atom,

774
00:37:18,120 --> 00:37:20,319
Speaker 1: and those determine whether the photon can interact with the

775
00:37:20,320 --> 00:37:22,840
Speaker 1: electrons around the atom or whether it gets ignored.

776
00:37:23,480 --> 00:37:25,680
Speaker 5: All right, So then we're talking about transparency. And so

777
00:37:25,800 --> 00:37:28,760
Speaker 5: if I shoot a photon at an atom, it's gonna

778
00:37:29,239 --> 00:37:31,400
Speaker 5: get up to the electron cloud there and it's going

779
00:37:31,440 --> 00:37:34,000
Speaker 5: to be like, no, I'm not the right energy. I'm

780
00:37:34,040 --> 00:37:36,319
Speaker 5: just going to keep going. Or is it the case

781
00:37:36,360 --> 00:37:39,080
Speaker 5: that they do interact, But then the end result is

782
00:37:39,080 --> 00:37:42,360
Speaker 5: the same and it just spits out a photon of

783
00:37:42,360 --> 00:37:43,760
Speaker 5: the same energy in the same direction.

784
00:37:43,960 --> 00:37:46,480
Speaker 1: Now, if they're the wrong energy, they just do not interact.

785
00:37:46,520 --> 00:37:48,640
Speaker 1: If they're the right energy, it gets absorbed and then

786
00:37:48,640 --> 00:37:50,719
Speaker 1: it can get re emitted. And that's a whole complicated

787
00:37:50,719 --> 00:37:54,120
Speaker 1: phenomena about reflection and refraction and all sorts of stuff.

788
00:37:54,200 --> 00:37:56,799
Speaker 1: In this case, for transparency, it's more about whether there's

789
00:37:56,840 --> 00:37:59,000
Speaker 1: an interaction. If it has the wrong energy levels, it

790
00:37:59,120 --> 00:38:02,320
Speaker 1: just doesn't. But that's the case for a single atom,

791
00:38:02,360 --> 00:38:04,879
Speaker 1: which is not really what's going on when you're looking

792
00:38:04,920 --> 00:38:07,160
Speaker 1: at like going through glass, or when you're wondering why

793
00:38:07,400 --> 00:38:11,320
Speaker 1: light doesn't go through metal. It's much more complicated because

794
00:38:11,360 --> 00:38:13,799
Speaker 1: now you're packing a lot of atoms together, and so

795
00:38:13,840 --> 00:38:16,840
Speaker 1: the rules about what happens to those electrons now change.

796
00:38:17,200 --> 00:38:20,319
Speaker 5: M let's dig into that. What's going on there?

797
00:38:20,400 --> 00:38:22,640
Speaker 1: So remember the picture we were talking about earlier. When

798
00:38:22,640 --> 00:38:25,200
Speaker 1: a photon is approaching, like a sheet of metal or

799
00:38:25,239 --> 00:38:28,320
Speaker 1: a sheet of iron, or a sheet of marble or something,

800
00:38:28,440 --> 00:38:31,800
Speaker 1: it's facing a whole wall of atoms, not individual atoms.

801
00:38:31,840 --> 00:38:34,360
Speaker 1: We talked about the energy levels of an individual atom.

802
00:38:34,480 --> 00:38:37,000
Speaker 1: But when you bring these things together to make a grid,

803
00:38:37,280 --> 00:38:40,000
Speaker 1: then the atoms bond. They're not just like near each other,

804
00:38:40,360 --> 00:38:42,520
Speaker 1: they really are bonding. And if you remember your high

805
00:38:42,520 --> 00:38:46,040
Speaker 1: school chemistry, that means that they are sharing electrons. Sometimes

806
00:38:46,080 --> 00:38:48,600
Speaker 1: the electron will like be around one nucleus, sometimes around

807
00:38:48,640 --> 00:38:52,040
Speaker 1: another nucleus. So from the point of view of the electron,

808
00:38:52,120 --> 00:38:55,200
Speaker 1: what happens is that you're no longer really belonging to

809
00:38:55,280 --> 00:38:58,080
Speaker 1: one nucleus. Now you can think of like the whole

810
00:38:58,200 --> 00:39:01,520
Speaker 1: grid of nuclei as have a bunch of energy levels

811
00:39:01,760 --> 00:39:04,680
Speaker 1: for the electrons. Some of the inner electrons are trapped

812
00:39:04,680 --> 00:39:08,080
Speaker 1: around nucleus, but the outer electrons can flow between them,

813
00:39:08,239 --> 00:39:11,120
Speaker 1: and that creates a whole complicated set of energy levels.

814
00:39:11,160 --> 00:39:14,400
Speaker 1: And instead of having these very specific ladders, now you

815
00:39:14,440 --> 00:39:17,800
Speaker 1: have this like spectrum energy levels. The electrons have lots

816
00:39:17,840 --> 00:39:20,719
Speaker 1: more options of the energy levels they can be at.

817
00:39:21,400 --> 00:39:23,239
Speaker 5: I guess I wonder if it's sort of like, you know,

818
00:39:23,320 --> 00:39:26,319
Speaker 5: we're orbiting around the Sun and we're sort of stuck

819
00:39:26,320 --> 00:39:29,400
Speaker 5: in this orbit, but if another solar system came pretty close,

820
00:39:29,800 --> 00:39:33,000
Speaker 5: maybe Jupiter might be like, oh, sometimes it might do

821
00:39:33,080 --> 00:39:35,600
Speaker 5: like a little figure eight and sometimes leave our solar

822
00:39:35,600 --> 00:39:37,719
Speaker 5: system and go take a loop around that other Sun

823
00:39:37,800 --> 00:39:39,799
Speaker 5: and then come back. And is that sort of what's

824
00:39:39,800 --> 00:39:40,920
Speaker 5: happening to the electrons.

825
00:39:41,040 --> 00:39:43,879
Speaker 1: Yeah, that's exactly what's happening to the electrons. There's lots

826
00:39:43,960 --> 00:39:45,959
Speaker 1: more options for them. They don't have to just stick

827
00:39:46,000 --> 00:39:49,160
Speaker 1: around one nucleus. They interact with lots of different nuclei.

828
00:39:49,400 --> 00:39:52,359
Speaker 1: So that has the consequence of sort of spreading these

829
00:39:52,520 --> 00:39:56,400
Speaker 1: sharper atomic orbitals and making them even fuzzier. So instead

830
00:39:56,400 --> 00:39:59,640
Speaker 1: of even really thinking about energy levels, now, physicists talk

831
00:39:59,680 --> 00:40:03,880
Speaker 1: about the possibilities for electrons in these materials as energy bands.

832
00:40:04,400 --> 00:40:06,400
Speaker 1: And you may have heard of like the valance band

833
00:40:06,520 --> 00:40:09,160
Speaker 1: or the conduction band. These are like a spectra of

834
00:40:09,280 --> 00:40:12,440
Speaker 1: energy levels available to the electron instead of being more

835
00:40:12,480 --> 00:40:15,400
Speaker 1: like a ladder. They can blurred together, so there's lots

836
00:40:15,440 --> 00:40:18,840
Speaker 1: of really really fine steps. It's still technically a ladder,

837
00:40:18,920 --> 00:40:20,800
Speaker 1: but there's many many more steps there.

838
00:40:20,880 --> 00:40:22,760
Speaker 5: Yeah, I guess it's sort of like in one atom,

839
00:40:22,840 --> 00:40:26,880
Speaker 5: the electron's stuck in one particular rut or groove or orbit.

840
00:40:27,000 --> 00:40:29,840
Speaker 5: That's one extreme. The electron is a free floating electron

841
00:40:29,840 --> 00:40:33,279
Speaker 5: admit in space by itself. When atoms are sort of

842
00:40:33,440 --> 00:40:36,359
Speaker 5: bonded together in the material you're saying, the electrons are

843
00:40:36,400 --> 00:40:38,360
Speaker 5: sort of in the middle, like they're not quite stuck

844
00:40:38,400 --> 00:40:41,000
Speaker 5: to one particular atom, but they're not quite free either,

845
00:40:41,600 --> 00:40:44,080
Speaker 5: and so they have limited options. But they don't have

846
00:40:44,400 --> 00:40:46,360
Speaker 5: just one option, and so there's sort of a range

847
00:40:46,400 --> 00:40:47,600
Speaker 5: of photons they can absorb.

848
00:40:47,680 --> 00:40:49,520
Speaker 1: Yeah, exactly. And it depends a little bit on the

849
00:40:49,560 --> 00:40:52,239
Speaker 1: temperature of the object. If the object is really really

850
00:40:52,320 --> 00:40:54,600
Speaker 1: cold and the electrons don't have a lot of energy,

851
00:40:54,640 --> 00:40:57,760
Speaker 1: then they've all like settled down to their minimum energy.

852
00:40:58,200 --> 00:41:01,799
Speaker 1: And mostly they are orbiting in individual nuclei and they're

853
00:41:01,840 --> 00:41:04,040
Speaker 1: mostly stuck, and so the electrons don't flow very much.

854
00:41:04,080 --> 00:41:06,120
Speaker 1: If the thing is hot, then a lot of the

855
00:41:06,120 --> 00:41:08,719
Speaker 1: electrons have more energy. They have enough energy to like

856
00:41:08,760 --> 00:41:11,680
Speaker 1: hop from nuclei to nuclei, and so they can flow

857
00:41:11,719 --> 00:41:12,520
Speaker 1: a little bit better.

858
00:41:12,600 --> 00:41:14,719
Speaker 5: Wait, what so that if I heat something up or

859
00:41:14,760 --> 00:41:17,600
Speaker 5: cool it down, I can make it go transparent or

860
00:41:17,640 --> 00:41:18,240
Speaker 5: not transparent.

861
00:41:18,440 --> 00:41:20,560
Speaker 1: No, by heating it up, you're not changing the energy

862
00:41:20,640 --> 00:41:24,520
Speaker 1: levels that are available. You're just changing where the electrons are. Like,

863
00:41:24,600 --> 00:41:26,839
Speaker 1: instead of all being in the lowest energy levels, now

864
00:41:26,840 --> 00:41:29,200
Speaker 1: they're in higher energy levels. I'm just talking about which

865
00:41:29,320 --> 00:41:32,040
Speaker 1: energy levels are filled up. In some cases, the electrons

866
00:41:32,040 --> 00:41:34,080
Speaker 1: are sort of stuck. When this stuff is cold, the

867
00:41:34,080 --> 00:41:36,600
Speaker 1: electrons fill the lower energy levels and they're more stuck

868
00:41:36,600 --> 00:41:38,839
Speaker 1: to the nuclei, And when the object is warmer, they

869
00:41:38,880 --> 00:41:40,759
Speaker 1: sort of jump out of those and they're freer to

870
00:41:40,800 --> 00:41:43,120
Speaker 1: move around from nucleus to nucleus.

871
00:41:43,440 --> 00:41:47,239
Speaker 5: Cool. Well, let's get a little bit deeper into the

872
00:41:47,280 --> 00:41:50,839
Speaker 5: material and see what happens when photons of different frequencies

873
00:41:51,120 --> 00:41:54,360
Speaker 5: try to go through it, and what it all means

874
00:41:54,400 --> 00:41:57,840
Speaker 5: about transparency in the universe. But first, let's take another

875
00:41:57,920 --> 00:41:58,399
Speaker 5: quick break.

876
00:42:02,520 --> 00:42:04,320
Speaker 1: When you pop a piece of cheese into your mouth

877
00:42:04,440 --> 00:42:07,560
Speaker 1: or enjoy a rich spoonful of Greek yogurt. You're probably

878
00:42:07,600 --> 00:42:11,640
Speaker 1: not thinking about the environmental impact of each and every bite,

879
00:42:11,680 --> 00:42:14,320
Speaker 1: but the people in the dairy industry are. US Dairy

880
00:42:14,360 --> 00:42:18,640
Speaker 1: has set themselves some ambitious sustainability goals, including being greenhouse

881
00:42:18,680 --> 00:42:21,239
Speaker 1: gas neutral by twenty to fifty. That's why they're working

882
00:42:21,280 --> 00:42:23,640
Speaker 1: hard every day to find new ways to reduce waste,

883
00:42:23,680 --> 00:42:27,879
Speaker 1: conserve natural resources, and drive down greenhouse gas emissions. Take water,

884
00:42:27,960 --> 00:42:31,040
Speaker 1: for example, most dairy farms reuse water up to four

885
00:42:31,080 --> 00:42:34,560
Speaker 1: times the same water cools the milk, cleans equipment, washes

886
00:42:34,600 --> 00:42:37,400
Speaker 1: the barn, and irrigates the crops. How is US Dairy

887
00:42:37,400 --> 00:42:41,160
Speaker 1: tackling greenhouse gases. Many farms use anaerobic digestors that turn

888
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Speaker 1: the methane from maneuver into renewable energy that can power farms, towns,

889
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Speaker 1: and electric cars. So the next time you grab a

890
00:42:47,239 --> 00:42:49,279
Speaker 1: slice of pizza or lick an ice cream cone, know

891
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Speaker 1: that dairy farmers and processors around the country are using

892
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Speaker 1: the latest practices and innovations to provide the nutrient dense

893
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Speaker 1: dairy products we love with less of an impact. Visit

894
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895
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Speaker 14: There are children, friends and families walking riding on paths

896
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897
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898
00:43:09,000 --> 00:43:09,800
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899
00:43:10,000 --> 00:43:13,400
Speaker 14: Protect our cyclists and pedestrians because they're people too. Go safely,

900
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Speaker 14: California from the California Office of Traffic Safety and Caltrans.

901
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917
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Speaker 15: Styfarm nos Making smarter financial moves today secures your financial

918
00:44:23,880 --> 00:44:27,360
Speaker 15: freedom for a second tomorrow. On Mychaeltuda podcast Network, we

919
00:44:27,480 --> 00:44:30,239
Speaker 15: believe this too by sharing money management tips that help

920
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Speaker 15: you realize your dreams, like on our show Life as

921
00:44:33,000 --> 00:44:34,560
Speaker 15: a Gringle with DJ Dramos.

922
00:44:37,120 --> 00:44:39,160
Speaker 12: Now, we have a level of privilege that our parents

923
00:44:39,320 --> 00:44:39,839
Speaker 12: never had.

924
00:44:39,880 --> 00:44:40,880
Speaker 5: So what do we do with it?

925
00:44:41,000 --> 00:44:41,280
Speaker 1: Right?

926
00:44:41,440 --> 00:44:44,239
Speaker 12: How do we utilize the opportunities that we have that

927
00:44:44,320 --> 00:44:47,440
Speaker 12: they don't right? And a lot of that is educating ourselves,

928
00:44:47,560 --> 00:44:50,480
Speaker 12: educating ourselves on how to not make the same mistakes

929
00:44:50,520 --> 00:44:52,880
Speaker 12: they did, how to not fall into those same traps,

930
00:44:52,920 --> 00:44:57,400
Speaker 12: and how to not you know, create the same difficult

931
00:44:57,440 --> 00:44:59,600
Speaker 12: situations that many of us grew up in. Like I

932
00:44:59,640 --> 00:45:02,799
Speaker 12: started podcast earlier saying for me, in my family, one

933
00:45:02,840 --> 00:45:06,640
Speaker 12: of the biggest points of contention was finances, and I know,

934
00:45:06,760 --> 00:45:09,520
Speaker 12: as I'd gotten older, I made it a promise to

935
00:45:09,560 --> 00:45:11,359
Speaker 12: myself to say, I don't want to relive.

936
00:45:11,040 --> 00:45:16,600
Speaker 15: That like a good neighbor. State Farm is there? State

937
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938
00:45:28,080 --> 00:45:30,719
Speaker 5: All right, We're talking about transparency, and something that comes

939
00:45:30,760 --> 00:45:33,239
Speaker 5: to mind is, I don't know if you read old

940
00:45:33,280 --> 00:45:35,200
Speaker 5: comic books, or you read comic books when you were

941
00:45:35,200 --> 00:45:37,479
Speaker 5: a kid, there was always an ad in the bag

942
00:45:37,600 --> 00:45:40,719
Speaker 5: for like X gray glasses, and I always wondered, like

943
00:45:40,840 --> 00:45:44,120
Speaker 5: are those for real? Or like how can they sell

944
00:45:44,160 --> 00:45:46,560
Speaker 5: something so bogas out of what's going on. I always

945
00:45:46,560 --> 00:45:48,200
Speaker 5: wanted to order one, but I couldn't because I was

946
00:45:48,520 --> 00:45:50,520
Speaker 5: in Panola. Do you know what I'm talking about? Do

947
00:45:50,520 --> 00:45:51,960
Speaker 5: you know what they were actually selling?

948
00:45:52,120 --> 00:45:55,080
Speaker 1: Do know those ads? And I also wanted those and

949
00:45:55,120 --> 00:45:57,480
Speaker 1: I wanted them to be real, but I also never

950
00:45:57,520 --> 00:46:00,760
Speaker 1: bought them because I was pretty sure they were bogus.

951
00:46:01,160 --> 00:46:03,680
Speaker 1: I mean, you can see through things with X rays,

952
00:46:03,680 --> 00:46:07,160
Speaker 1: and we'll talk about why that happens, why high energy

953
00:46:07,200 --> 00:46:11,000
Speaker 1: photons from X rays can pass through materials sometimes when

954
00:46:11,040 --> 00:46:14,120
Speaker 1: lower energy photons can't. But those glasses can't let you

955
00:46:14,239 --> 00:46:17,600
Speaker 1: see X rays, and they definitely don't generate X rays, right,

956
00:46:17,719 --> 00:46:21,200
Speaker 1: You're not shooting X rays through stuff. So I'm pretty

957
00:46:21,239 --> 00:46:23,320
Speaker 1: sure it was totally bogus.

958
00:46:23,280 --> 00:46:26,319
Speaker 5: Or maybe not, I don't know. We can't say for sure.

959
00:46:26,560 --> 00:46:28,560
Speaker 1: Well, folks out there, if you bought those X ray

960
00:46:28,600 --> 00:46:30,800
Speaker 1: glasses and they did let you see through things. Please

961
00:46:30,840 --> 00:46:31,960
Speaker 1: write to us and let us hear.

962
00:46:33,120 --> 00:46:36,120
Speaker 5: Those people are probably rich from a you know, stealing

963
00:46:36,600 --> 00:46:38,759
Speaker 5: a bank vaults and things like that. All right, So

964
00:46:38,840 --> 00:46:41,719
Speaker 5: we're talking about transparency. And you know, when you put

965
00:46:41,719 --> 00:46:44,160
Speaker 5: a bunch of adoms together in the material, they form

966
00:46:44,239 --> 00:46:47,600
Speaker 5: this kind of extended fuzzy cloud of electrons that might

967
00:46:47,960 --> 00:46:51,680
Speaker 5: blocklide or not. And so whether a photon gets through

968
00:46:51,719 --> 00:46:54,040
Speaker 5: that depends on its energy. If it has the energy

969
00:46:54,120 --> 00:46:57,560
Speaker 5: that the electrons in that material like, then it gets

970
00:46:57,600 --> 00:47:00,520
Speaker 5: is going to get absorbed right and not go through exactly.

971
00:47:00,600 --> 00:47:04,120
Speaker 1: So the basic picture is the same photon approaches this

972
00:47:04,239 --> 00:47:07,560
Speaker 1: now grid of atoms, and if it finds an electron

973
00:47:07,600 --> 00:47:10,200
Speaker 1: that can accept its energy, if the electron can go

974
00:47:10,280 --> 00:47:13,120
Speaker 1: from its current quantum state to an allowed quantum state,

975
00:47:13,360 --> 00:47:15,799
Speaker 1: it will absorb that photon. But the picture of the

976
00:47:15,880 --> 00:47:18,799
Speaker 1: energy levels is different from a single atom than with

977
00:47:18,840 --> 00:47:20,719
Speaker 1: the grid of atoms, and the single atom you had

978
00:47:20,719 --> 00:47:23,480
Speaker 1: the ladder that was sort of sharper energy levels in

979
00:47:23,560 --> 00:47:26,480
Speaker 1: the grid of atoms. Now you have these bands of

980
00:47:26,600 --> 00:47:28,360
Speaker 1: energy levels, and you might think, oh, that makes it

981
00:47:28,400 --> 00:47:31,239
Speaker 1: possible for the electron to absorb basically any photon. It's

982
00:47:31,239 --> 00:47:33,720
Speaker 1: a little bit more complicated than that because we discovered

983
00:47:33,760 --> 00:47:35,920
Speaker 1: that there are these gaps in the energy levels. It's

984
00:47:35,960 --> 00:47:38,880
Speaker 1: not like any possible energy level is allowed for an

985
00:47:38,920 --> 00:47:40,960
Speaker 1: electron in these materials, the way it is for an

986
00:47:40,960 --> 00:47:44,480
Speaker 1: electron in free space. There are still electron energy levels

987
00:47:44,480 --> 00:47:47,640
Speaker 1: that are not allowed. So there's this band of electron

988
00:47:47,800 --> 00:47:50,799
Speaker 1: energies called the valiance band, where the electrons mostly hang

989
00:47:50,840 --> 00:47:53,359
Speaker 1: out in a random material, and then there's a band

990
00:47:53,400 --> 00:47:56,719
Speaker 1: of energies called the conduction band, where electrons can move

991
00:47:56,760 --> 00:47:59,800
Speaker 1: around really freely from atom to atom, and this sometimes

992
00:48:00,120 --> 00:48:03,520
Speaker 1: gap between them where electrons can't be and that can

993
00:48:03,520 --> 00:48:06,600
Speaker 1: prevent electrons from absorbing energy of a passing photon.

994
00:48:06,880 --> 00:48:09,640
Speaker 5: M you're saying, like, you can have a material that

995
00:48:10,200 --> 00:48:14,640
Speaker 5: accepts or lets through lights of a certain range of frequencies,

996
00:48:15,000 --> 00:48:17,400
Speaker 5: then it doesn't let them through, and then it does

997
00:48:17,560 --> 00:48:20,080
Speaker 5: for a different range of frequencies, it does lead light.

998
00:48:19,960 --> 00:48:22,880
Speaker 1: Through exactly just like with the atom, it can absorb

999
00:48:22,960 --> 00:48:26,440
Speaker 1: some frequencies and not other frequencies for a grid of atoms.

1000
00:48:26,440 --> 00:48:30,040
Speaker 1: For a whole solid material, it can absorb some frequencies,

1001
00:48:30,239 --> 00:48:32,880
Speaker 1: frequencies where it can hit the electron and jump it

1002
00:48:33,000 --> 00:48:36,600
Speaker 1: over this gap between the bands, and it can't absorb

1003
00:48:36,680 --> 00:48:39,760
Speaker 1: photons of other frequencies, photons that don't have enough energy

1004
00:48:39,960 --> 00:48:43,200
Speaker 1: to get the electrons from one band to another, and

1005
00:48:43,280 --> 00:48:46,080
Speaker 1: so different kind of materials have a different sized gap

1006
00:48:46,239 --> 00:48:48,839
Speaker 1: between these bands, and so in solid state physics they

1007
00:48:48,840 --> 00:48:51,600
Speaker 1: call this the band gap, right, the gap between the

1008
00:48:51,640 --> 00:48:55,000
Speaker 1: typical energy levels of the electron and the conduction band

1009
00:48:55,000 --> 00:48:57,680
Speaker 1: where electrons are good at like flowing, and some kind

1010
00:48:57,719 --> 00:49:01,080
Speaker 1: of materials like metals have a very very small band gap.

1011
00:49:01,160 --> 00:49:03,800
Speaker 1: The conduction band is basically right on top of the

1012
00:49:03,840 --> 00:49:07,239
Speaker 1: valiance band. There's basically no gap there, and so electrons

1013
00:49:07,280 --> 00:49:10,200
Speaker 1: are very good at absorbing photons of a huge range

1014
00:49:10,200 --> 00:49:13,040
Speaker 1: of energies because there's a huge spectrum there, and other

1015
00:49:13,080 --> 00:49:15,640
Speaker 1: materials is a big gap, and in order for an

1016
00:49:15,680 --> 00:49:18,920
Speaker 1: electron to absorb a photon, it has to have enough energy,

1017
00:49:19,160 --> 00:49:21,400
Speaker 1: and lots of photons just don't have enough energy, and

1018
00:49:21,440 --> 00:49:24,920
Speaker 1: so the photons would pass right through the material without interacting.

1019
00:49:25,719 --> 00:49:28,279
Speaker 5: Now, when you're talking about light and energy, the light

1020
00:49:28,520 --> 00:49:32,160
Speaker 5: of a particular photon is related to its frequency right

1021
00:49:32,200 --> 00:49:34,719
Speaker 5: mostly to it almost or everything to its frequency, and

1022
00:49:34,719 --> 00:49:36,920
Speaker 5: so you're really talking about its color, right.

1023
00:49:36,840 --> 00:49:39,000
Speaker 1: Yeah, exactly. The energy of a photon doesn't relate to

1024
00:49:39,080 --> 00:49:41,600
Speaker 1: its speed. Right. When we think about the energy of

1025
00:49:41,600 --> 00:49:43,799
Speaker 1: an electron, we think about its speed. But photons are

1026
00:49:43,840 --> 00:49:46,880
Speaker 1: all moving at the same speed. The thing that differentiates

1027
00:49:46,920 --> 00:49:50,799
Speaker 1: a high and low energy electron is its frequency, how

1028
00:49:50,840 --> 00:49:54,439
Speaker 1: fast the electromagnetic fields are wiggling. And as you say

1029
00:49:54,480 --> 00:49:58,359
Speaker 1: that frequency we interpret as color. The photons themselves don't

1030
00:49:58,400 --> 00:50:00,359
Speaker 1: have color. It's not like a photon is a red

1031
00:50:00,400 --> 00:50:03,640
Speaker 1: photon or a green photon, just has a certain frequency

1032
00:50:03,880 --> 00:50:06,239
Speaker 1: when it hits our eyeballs. Our brains give us the

1033
00:50:06,320 --> 00:50:08,759
Speaker 1: experience of red or green or blue or whatever. And

1034
00:50:08,760 --> 00:50:12,280
Speaker 1: that's a whole philosophical question. But yeah, we associate colors

1035
00:50:12,280 --> 00:50:13,360
Speaker 1: with certain frequencies.

1036
00:50:13,520 --> 00:50:16,960
Speaker 5: Yes, but we don't talk about philosophy here. But like that,

1037
00:50:17,160 --> 00:50:20,480
Speaker 5: if a photon has a certain frequency, it is a

1038
00:50:20,520 --> 00:50:23,040
Speaker 5: red photon, right, Like to our eyes it would read

1039
00:50:23,040 --> 00:50:23,439
Speaker 5: as red.

1040
00:50:23,520 --> 00:50:26,279
Speaker 1: It would read as red. Yeah, And some photons are

1041
00:50:26,360 --> 00:50:28,600
Speaker 1: above the visible spectrum, and so we say they're X

1042
00:50:28,719 --> 00:50:32,920
Speaker 1: ray photons or their gamma rays or their UV photons, right,

1043
00:50:32,920 --> 00:50:35,160
Speaker 1: so we can give names to the different parts of

1044
00:50:35,200 --> 00:50:37,760
Speaker 1: the frequency spectrum. Some of them we give them colors.

1045
00:50:37,800 --> 00:50:40,520
Speaker 1: Some of them, we just give them labels. Radio waves.

1046
00:50:40,520 --> 00:50:45,120
Speaker 1: For example, our photons a very very long frequency, well

1047
00:50:45,120 --> 00:50:48,160
Speaker 1: below what we can see, even below the infrared.

1048
00:50:48,000 --> 00:50:51,520
Speaker 5: Right, And so that determines whether or not a materialst

1049
00:50:51,520 --> 00:50:54,680
Speaker 5: transparent to different kinds of light because X rays sort

1050
00:50:54,680 --> 00:50:57,799
Speaker 5: of lead you see through your body and your bones, right.

1051
00:50:57,840 --> 00:51:00,759
Speaker 5: That's because they have a high energy and the electrons

1052
00:51:00,760 --> 00:51:03,120
Speaker 5: in your body can absorb them, so they sort of

1053
00:51:03,120 --> 00:51:03,480
Speaker 5: go through.

1054
00:51:03,640 --> 00:51:06,920
Speaker 1: Yeah. Really interestingly, X rays can pass through the soft

1055
00:51:06,960 --> 00:51:10,480
Speaker 1: tissues of your body, but they can't pass through your bones,

1056
00:51:10,840 --> 00:51:12,759
Speaker 1: which is why when you see an X ray, what

1057
00:51:12,800 --> 00:51:15,480
Speaker 1: you're looking at is basically only the bones, because that's

1058
00:51:15,480 --> 00:51:18,440
Speaker 1: the thing that the X rays didn't pass through, so

1059
00:51:18,520 --> 00:51:21,160
Speaker 1: it passes through everything else. Your body is transparent to

1060
00:51:21,239 --> 00:51:23,920
Speaker 1: X rays except for your bones. That's why you can

1061
00:51:23,920 --> 00:51:26,120
Speaker 1: tell the difference between the bones and the not bones

1062
00:51:26,160 --> 00:51:27,759
Speaker 1: part on the X ray.

1063
00:51:27,920 --> 00:51:30,640
Speaker 5: Now is that because the I guess bones are made

1064
00:51:30,680 --> 00:51:33,839
Speaker 5: out of the different material than my muscles, and so

1065
00:51:34,160 --> 00:51:37,399
Speaker 5: my muscles don't absorb X rays what my bones do

1066
00:51:37,560 --> 00:51:42,800
Speaker 5: because of the you know, the bonds between the atoms exactly.

1067
00:51:42,840 --> 00:51:45,840
Speaker 1: It's the band gap of the material that determines whether

1068
00:51:45,960 --> 00:51:49,920
Speaker 1: or not you can absorb photons of a specific frequency. So,

1069
00:51:49,960 --> 00:51:52,560
Speaker 1: for example, in a conductor like a metal, like a

1070
00:51:52,560 --> 00:51:55,400
Speaker 1: sheet of steel, the band gap is really really small.

1071
00:51:55,520 --> 00:51:57,640
Speaker 1: It's very easy to get an electron up into that

1072
00:51:57,680 --> 00:51:59,719
Speaker 1: conduction band where it can flow around. And that's why

1073
00:51:59,760 --> 00:52:03,000
Speaker 1: these things conduct electricity very easily, because it's easy to

1074
00:52:03,000 --> 00:52:06,400
Speaker 1: have electrons that slide around in the material. So conductor

1075
00:52:06,520 --> 00:52:08,520
Speaker 1: like a metal, right, it's really easy to get those

1076
00:52:08,520 --> 00:52:11,600
Speaker 1: electrons flying around. It also means it's easy to absorb

1077
00:52:12,040 --> 00:52:15,120
Speaker 1: that energy. So that's why things like metals and conductors

1078
00:52:15,520 --> 00:52:18,920
Speaker 1: are good at conducting electricity and good at absorbing photons

1079
00:52:18,960 --> 00:52:21,640
Speaker 1: and bad at being see through. So that's why a

1080
00:52:21,640 --> 00:52:24,720
Speaker 1: sheet of metal, for example, is not transparent.

1081
00:52:25,080 --> 00:52:27,720
Speaker 5: Unless it's I guess a wire mesh.

1082
00:52:27,840 --> 00:52:31,160
Speaker 1: Yeah, exactly, unless it's a screen, which is why if

1083
00:52:31,160 --> 00:52:33,920
Speaker 1: you remember like Star Trek and had like transparent aluminum

1084
00:52:34,000 --> 00:52:36,640
Speaker 1: in Star Trek four or whatever, I always like, well, you

1085
00:52:36,680 --> 00:52:38,799
Speaker 1: can't really do that. That is not something we know

1086
00:52:38,840 --> 00:52:41,759
Speaker 1: how to do. Although you know, far future societies maybe

1087
00:52:41,760 --> 00:52:42,560
Speaker 1: they figured it out.

1088
00:52:42,640 --> 00:52:45,280
Speaker 5: I'm not sure I familiar with that level of trivia

1089
00:52:45,400 --> 00:52:46,799
Speaker 5: for the Story Trek movies, but.

1090
00:52:48,560 --> 00:52:50,520
Speaker 1: I remember they got the whales and they had to

1091
00:52:50,520 --> 00:52:52,480
Speaker 1: build an aquarium for the whales, and how are they

1092
00:52:52,480 --> 00:52:53,480
Speaker 1: going to hold all this water?

1093
00:52:53,680 --> 00:52:56,480
Speaker 5: I remember the whales? Yeah right, but I guess what

1094
00:52:56,480 --> 00:52:59,520
Speaker 5: do you mean though, Like aluminium is not transparent to

1095
00:52:59,600 --> 00:53:02,560
Speaker 5: visible but it is still transparent to other kinds of light, right,

1096
00:53:02,840 --> 00:53:05,319
Speaker 5: Like X rays sort of go through metal, No, or

1097
00:53:05,640 --> 00:53:07,239
Speaker 5: do metals like block all light.

1098
00:53:07,520 --> 00:53:10,600
Speaker 1: It's always the case that it depends on the frequency, right,

1099
00:53:10,680 --> 00:53:12,759
Speaker 1: and so you have to have the right frequency to

1100
00:53:13,040 --> 00:53:16,120
Speaker 1: match the energy levels that the object can absorb. If

1101
00:53:16,160 --> 00:53:19,640
Speaker 1: you have a huge amount of energy, then probably you're

1102
00:53:19,680 --> 00:53:22,040
Speaker 1: going to knock the electrons out of the material. Right.

1103
00:53:22,080 --> 00:53:24,560
Speaker 1: Then we're getting into the case of like the photoelectric effect.

1104
00:53:24,960 --> 00:53:28,960
Speaker 1: So you zapp like gamma rays against aluminium, then there's

1105
00:53:28,960 --> 00:53:30,719
Speaker 1: definitely going to be an interaction there, but it's going

1106
00:53:30,760 --> 00:53:33,160
Speaker 1: to knock the whole electron out of the material. It's

1107
00:53:33,200 --> 00:53:34,960
Speaker 1: not just going to like push it up to some

1108
00:53:35,200 --> 00:53:37,680
Speaker 1: energy level. So at some point this picture breaks down.

1109
00:53:37,960 --> 00:53:41,600
Speaker 5: Oh what So at some point you have enough energy

1110
00:53:41,600 --> 00:53:44,120
Speaker 5: where the electron jade doesn't someone to say in any groove,

1111
00:53:44,120 --> 00:53:45,400
Speaker 5: it just flies out into space.

1112
00:53:45,440 --> 00:53:48,360
Speaker 1: Really, yeah, exactly, you can shine light on metal and

1113
00:53:48,520 --> 00:53:51,880
Speaker 1: boil off electrons if you have enough energy, it's like

1114
00:53:51,920 --> 00:53:55,000
Speaker 1: a highest level band, and above that then electrons are

1115
00:53:55,000 --> 00:53:57,799
Speaker 1: just free. Again, you've like broken it out of physics jail.

1116
00:53:58,960 --> 00:54:02,560
Speaker 5: You have to pay two hundred buck though exactly now,

1117
00:54:03,000 --> 00:54:05,279
Speaker 5: what happens on the other spectrum, Like what if a

1118
00:54:05,360 --> 00:54:09,440
Speaker 5: futlan has too little energy like a super infrared or

1119
00:54:09,480 --> 00:54:12,080
Speaker 5: something like that, or radio wave as you said, that

1120
00:54:12,160 --> 00:54:14,640
Speaker 5: still goes through metal and other things.

1121
00:54:14,719 --> 00:54:16,960
Speaker 1: Right, No, radio waves do not go through metal. Right.

1122
00:54:16,960 --> 00:54:19,560
Speaker 1: That's why, for example, your phone call is dropped if

1123
00:54:19,600 --> 00:54:22,840
Speaker 1: you're in an elevator because metal is like a Faraday cage.

1124
00:54:22,840 --> 00:54:27,040
Speaker 1: It will block radio waves even classically, right, the electrons

1125
00:54:27,040 --> 00:54:29,719
Speaker 1: in the material will reorganize themselves to cancel out an

1126
00:54:29,760 --> 00:54:31,960
Speaker 1: electric field. But from a quantum mechanical point of view,

1127
00:54:32,000 --> 00:54:35,480
Speaker 1: a conductor can absorb very very low energy photons because

1128
00:54:35,520 --> 00:54:37,879
Speaker 1: the gap there is very small, and so it can

1129
00:54:37,920 --> 00:54:40,279
Speaker 1: absorb very very low energy photons.

1130
00:54:40,440 --> 00:54:42,759
Speaker 5: But I guess what's going on there though, Like if

1131
00:54:42,800 --> 00:54:44,920
Speaker 5: it's just a single atom and have an electron orbiting,

1132
00:54:45,520 --> 00:54:48,840
Speaker 5: if the fourth then has very little energy, I'm going

1133
00:54:48,880 --> 00:54:50,399
Speaker 5: to ignore it too, all right, I.

1134
00:54:50,480 --> 00:54:53,160
Speaker 1: Yeah, absolutely, you are. In the case of an individual atom,

1135
00:54:53,560 --> 00:54:56,200
Speaker 1: then there are photons that have too low an energy

1136
00:54:56,239 --> 00:54:59,040
Speaker 1: to move the electron up from level one to level

1137
00:54:59,080 --> 00:55:01,879
Speaker 1: two or level seven to level eight exactly. That can

1138
00:55:01,920 --> 00:55:04,800
Speaker 1: happen in a solid. Now you have a whole spectrum

1139
00:55:04,840 --> 00:55:07,879
Speaker 1: of energy levels, and so there's lots of very very

1140
00:55:07,920 --> 00:55:12,200
Speaker 1: fine gradations allowed there. So materials can absorb low energy

1141
00:55:12,200 --> 00:55:15,280
Speaker 1: electrons because there's a very very fine mesh of energy levels.

1142
00:55:15,440 --> 00:55:18,120
Speaker 5: Is there a bottom limit? There is there an energy

1143
00:55:18,200 --> 00:55:22,160
Speaker 5: for my photon for which it's even outside of the

1144
00:55:22,200 --> 00:55:25,320
Speaker 5: gap of material with lots of electrons.

1145
00:55:24,880 --> 00:55:27,520
Speaker 1: There might be a lower limit there. I mean, even

1146
00:55:27,560 --> 00:55:30,799
Speaker 1: conductors do have some kind of a band gap, so

1147
00:55:30,920 --> 00:55:33,479
Speaker 1: you might need a minimum energy to get them up

1148
00:55:33,760 --> 00:55:37,040
Speaker 1: from the valiance band to the conduction band, and there

1149
00:55:37,120 --> 00:55:40,560
Speaker 1: might even be a limit within those bands a minimum energy,

1150
00:55:40,680 --> 00:55:43,040
Speaker 1: so the other might be a limit. Very very low

1151
00:55:43,160 --> 00:55:46,319
Speaker 1: energy photons could be ignored even by conductors. But the

1152
00:55:46,360 --> 00:55:49,120
Speaker 1: other side of the coin are materials like insulators. Take

1153
00:55:49,160 --> 00:55:53,000
Speaker 1: glass for example. Glass is not a conductor because it

1154
00:55:53,000 --> 00:55:55,399
Speaker 1: has a large gap between these energy levels. So mostly

1155
00:55:55,400 --> 00:55:57,360
Speaker 1: electrons in the glass are not free to move around.

1156
00:55:57,400 --> 00:56:00,600
Speaker 1: They're mostly stuck to the atom that they are around,

1157
00:56:00,840 --> 00:56:02,319
Speaker 1: and there's a band gap there if you want to

1158
00:56:02,320 --> 00:56:04,960
Speaker 1: push an electron up to the next energy level, there's

1159
00:56:05,080 --> 00:56:07,560
Speaker 1: like a big gap between the energy levels that's normally

1160
00:56:07,560 --> 00:56:10,440
Speaker 1: in and the first one that's available. It's like a

1161
00:56:10,480 --> 00:56:14,480
Speaker 1: few electron bolts, and so photons that hit glass in

1162
00:56:14,520 --> 00:56:18,239
Speaker 1: the visible spectrum mostly do not have enough energy to

1163
00:56:18,320 --> 00:56:21,120
Speaker 1: get the electron up to the conduction band. And so

1164
00:56:21,200 --> 00:56:25,400
Speaker 1: that's why visible light photons do pass through glass. They

1165
00:56:25,440 --> 00:56:27,719
Speaker 1: pass right through this whole grid of atoms and all

1166
00:56:27,760 --> 00:56:30,440
Speaker 1: those electrons, but they don't have enough energy to move

1167
00:56:30,480 --> 00:56:33,279
Speaker 1: the electrons up to the next band, and so they're

1168
00:56:33,320 --> 00:56:34,760
Speaker 1: ignored and they pass right through.

1169
00:56:35,040 --> 00:56:37,640
Speaker 5: You mean, like a material like glass. It's like the

1170
00:56:37,680 --> 00:56:40,880
Speaker 5: atoms are basically it's just a bunch of individual atoms

1171
00:56:40,880 --> 00:56:44,160
Speaker 5: hanging out together. They're not sharing a lot of electrons,

1172
00:56:44,200 --> 00:56:46,480
Speaker 5: which is what you need to make a good conductor.

1173
00:56:46,520 --> 00:56:49,239
Speaker 5: They're mostly just doing what they would do normally on

1174
00:56:49,280 --> 00:56:52,040
Speaker 5: their own, and so you have a very limited number

1175
00:56:52,080 --> 00:56:53,680
Speaker 5: of frequencies that it blocks.

1176
00:56:53,719 --> 00:56:55,759
Speaker 1: The picture is a little bit more complicated. I mean,

1177
00:56:55,800 --> 00:56:58,239
Speaker 1: the glass atoms still do interact with each other, so

1178
00:56:58,280 --> 00:57:00,960
Speaker 1: they do form this band of energy levels for the

1179
00:57:01,040 --> 00:57:04,080
Speaker 1: electrons because they are bonded together, right, I mean, glass

1180
00:57:04,200 --> 00:57:06,560
Speaker 1: is not a crystal, but still there are bonds between

1181
00:57:06,600 --> 00:57:09,360
Speaker 1: the atoms they are interacting, so there is a spectrum

1182
00:57:09,360 --> 00:57:12,360
Speaker 1: of energy levels the electrons can be in. For a glass,

1183
00:57:12,680 --> 00:57:14,600
Speaker 1: that's not just like an atom, it's not just like

1184
00:57:14,640 --> 00:57:18,640
Speaker 1: a sharp layer, but it's mostly a full band of electrons.

1185
00:57:18,640 --> 00:57:20,880
Speaker 1: But that band is mostly filled. Then the electrons can't

1186
00:57:20,880 --> 00:57:23,080
Speaker 1: really go anywhere. It's like if you're on a plane,

1187
00:57:23,240 --> 00:57:25,840
Speaker 1: every seat is taken, then you can't like move from

1188
00:57:25,880 --> 00:57:28,520
Speaker 1: seat to seat, and the next energy level above that

1189
00:57:28,680 --> 00:57:30,600
Speaker 1: is kind of high, right, you can't like get to

1190
00:57:30,640 --> 00:57:32,520
Speaker 1: first class. You need a lot of energy to get

1191
00:57:32,560 --> 00:57:36,080
Speaker 1: to first class in a glass, and so everybody's basically

1192
00:57:36,120 --> 00:57:39,080
Speaker 1: stuck in their seat in coach, and the electrons can't

1193
00:57:39,120 --> 00:57:42,080
Speaker 1: really absorb little amounts of energy. They need a lot

1194
00:57:42,120 --> 00:57:44,919
Speaker 1: of energy to get promoted up to first class, which

1195
00:57:44,960 --> 00:57:48,080
Speaker 1: is the next band of energy levels. In a glass

1196
00:57:48,080 --> 00:57:50,440
Speaker 1: and a conductor, that band is much much lower, so

1197
00:57:50,480 --> 00:57:52,520
Speaker 1: it doesn't take as much energy to get up there,

1198
00:57:52,720 --> 00:57:55,280
Speaker 1: and glass the band is really large. It's really hard

1199
00:57:55,320 --> 00:57:58,120
Speaker 1: to get promoted up to the next set of energy levels.

1200
00:57:58,680 --> 00:58:02,400
Speaker 5: I think what're you're saying is that as is transparent

1201
00:58:02,600 --> 00:58:05,960
Speaker 5: for a wider range of frequencies of light, which just

1202
00:58:06,000 --> 00:58:09,360
Speaker 5: happened to be in our visible spectrum. But glass is opaque,

1203
00:58:09,640 --> 00:58:12,600
Speaker 5: it is not transparent to certain frequencies of light.

1204
00:58:12,800 --> 00:58:16,439
Speaker 1: That's exactly right. For example ultraviolet, right, ultraviolet is light

1205
00:58:16,560 --> 00:58:19,680
Speaker 1: with higher energy. You can't see ultraviolet light. It's the

1206
00:58:19,760 --> 00:58:21,360
Speaker 1: kind that's going to give you a sunburn or it

1207
00:58:21,360 --> 00:58:24,000
Speaker 1: can hurt your eyeballs. But it has more energy, and

1208
00:58:24,080 --> 00:58:27,400
Speaker 1: it has enough energy to bump one of these electrons

1209
00:58:27,520 --> 00:58:30,520
Speaker 1: up over this gap into the conduction band, and so

1210
00:58:30,640 --> 00:58:34,000
Speaker 1: glass can absorb UV photons. That's why you don't get

1211
00:58:34,000 --> 00:58:37,840
Speaker 1: a sunburn if you're sunbathing through glass glasses like sunscreen.

1212
00:58:38,080 --> 00:58:41,440
Speaker 5: Wait what I can just put a glass over me

1213
00:58:41,520 --> 00:58:44,200
Speaker 5: and I going to give you sunburn? Is that a

1214
00:58:44,280 --> 00:58:45,640
Speaker 5: solid medical advice there?

1215
00:58:45,760 --> 00:58:47,560
Speaker 1: That is not solid medical advice, And.

1216
00:58:47,600 --> 00:58:50,040
Speaker 5: Just to be transparent, we're non medical doctors, right.

1217
00:58:50,800 --> 00:58:53,280
Speaker 1: That's right. But it does block some of the UV,

1218
00:58:53,520 --> 00:58:56,080
Speaker 1: so it would reduce your sunburn. It still totally advise

1219
00:58:56,120 --> 00:58:59,160
Speaker 1: you to wear sunscreen. But glass is not transparent to

1220
00:58:59,360 --> 00:59:02,320
Speaker 1: UV the same way is to visible light. It absorbs

1221
00:59:02,360 --> 00:59:03,720
Speaker 1: a lot more of the UV.

1222
00:59:03,880 --> 00:59:06,480
Speaker 5: Is that kind of what's going on with sunscreens like

1223
00:59:06,600 --> 00:59:09,960
Speaker 5: E lotion right, right, it has materials that absorb UV.

1224
00:59:10,200 --> 00:59:13,720
Speaker 1: Right, yeah, exactly, your sunscreen is just opaque to UV.

1225
00:59:13,840 --> 00:59:16,800
Speaker 1: It has stuff in it that could accept those photons

1226
00:59:16,840 --> 00:59:19,440
Speaker 1: and absorb it rather than letting those UV photons pass

1227
00:59:19,440 --> 00:59:21,520
Speaker 1: into your body and then cause damage.

1228
00:59:21,600 --> 00:59:24,200
Speaker 5: Okay, Now, what makes a piece of glass like a

1229
00:59:24,240 --> 00:59:26,560
Speaker 5: piece of red glass or a piece of blue glass?

1230
00:59:26,600 --> 00:59:30,000
Speaker 1: So that often is because of doping. You like change

1231
00:59:30,040 --> 00:59:34,040
Speaker 1: the energy levels of the glass by adding impurities, and

1232
00:59:34,080 --> 00:59:37,080
Speaker 1: so these other molecules change the band gap and make

1233
00:59:37,120 --> 00:59:40,120
Speaker 1: it possible for different kinds of photons to be absorbed.

1234
00:59:40,600 --> 00:59:44,160
Speaker 5: And so I guess you sort of narrow the band gap, right,

1235
00:59:44,200 --> 00:59:48,040
Speaker 5: like regular glass wide range of photon frequencies that it

1236
00:59:48,120 --> 00:59:50,640
Speaker 5: lets through, but like blue glass I imagine has a

1237
00:59:50,720 --> 00:59:53,920
Speaker 5: narrow gap where it only lets through light that is

1238
00:59:53,960 --> 00:59:55,000
Speaker 5: bluish for example.

1239
00:59:55,080 --> 00:59:57,920
Speaker 1: That's right. So sometimes people add like aluminum oxide to glass,

1240
00:59:58,280 --> 01:00:01,360
Speaker 1: and that makes glass pink or red because it absorbs

1241
01:00:01,400 --> 01:00:04,120
Speaker 1: the green and the blue photons. And so I actually

1242
01:00:04,120 --> 01:00:07,160
Speaker 1: got an email from a listener, Matt Cleveland, who says,

1243
01:00:07,440 --> 01:00:09,680
Speaker 1: what is it about the photons of sunlight that costs

1244
01:00:09,680 --> 01:00:12,800
Speaker 1: some objects to fade? And lose their color. What is

1245
01:00:12,840 --> 01:00:15,400
Speaker 1: it that's breaking down? Why do some objects lose their

1246
01:00:15,400 --> 01:00:18,080
Speaker 1: color from this interaction with the sun's photons and others

1247
01:00:18,240 --> 01:00:18,560
Speaker 1: do not.

1248
01:00:19,600 --> 01:00:21,800
Speaker 5: That's an interesting question. Yeah, Like if you leave your

1249
01:00:21,840 --> 01:00:24,000
Speaker 5: T shirt out in the sun, it's going to get faded, right,

1250
01:00:24,080 --> 01:00:25,920
Speaker 5: It's going to get bleached. That's kind of why your

1251
01:00:25,920 --> 01:00:27,919
Speaker 5: hair also gets bleached a little bit of view. Stay

1252
01:00:27,920 --> 01:00:29,000
Speaker 5: out in the sun a lot.

1253
01:00:29,000 --> 01:00:32,520
Speaker 1: Yeah, exactly, And that's mostly the UV light, right, These

1254
01:00:32,600 --> 01:00:35,120
Speaker 1: chemicals absorb UV light, and the UV light has a

1255
01:00:35,160 --> 01:00:39,320
Speaker 1: lot of energy, so sometimes it breaks down those chemicals. Right,

1256
01:00:39,360 --> 01:00:42,520
Speaker 1: we talked about like photons hitting electrons and banging them

1257
01:00:42,520 --> 01:00:45,680
Speaker 1: out of materials. Well, UV light sometimes these atoms can

1258
01:00:45,760 --> 01:00:48,439
Speaker 1: absorb it, but it also damages the atoms the same

1259
01:00:48,440 --> 01:00:50,960
Speaker 1: way like can damage things in your body. And so

1260
01:00:51,080 --> 01:00:54,680
Speaker 1: chemicals in objects can sometimes break down when they absorb

1261
01:00:54,840 --> 01:00:57,480
Speaker 1: UV light. And which you'll notice is that red stuff

1262
01:00:57,680 --> 01:01:02,200
Speaker 1: is especially susceptible to this because they absorb more high energy,

1263
01:01:02,240 --> 01:01:05,360
Speaker 1: more blue and more UV photons. So things that look

1264
01:01:05,400 --> 01:01:08,120
Speaker 1: red are things that absorb in the blue spectrum and

1265
01:01:08,160 --> 01:01:11,640
Speaker 1: therefore absorb more UV light and are likely to fade

1266
01:01:11,680 --> 01:01:13,960
Speaker 1: more in sunlight than things that are.

1267
01:01:13,800 --> 01:01:17,400
Speaker 5: Blue, because if they're red, then that means they're mostly

1268
01:01:17,440 --> 01:01:19,680
Speaker 5: reflecting the red part, but they're absorbing the blue light.

1269
01:01:19,880 --> 01:01:22,640
Speaker 1: Yeah, exactly, And UV is like super blue.

1270
01:01:22,840 --> 01:01:25,800
Speaker 5: But sometimes materials get harder in the sun, right, Like

1271
01:01:25,840 --> 01:01:28,720
Speaker 5: if you leave a piece of rubber or a rubber band,

1272
01:01:28,840 --> 01:01:31,840
Speaker 5: or your car tires, they get more brittle as they

1273
01:01:31,840 --> 01:01:32,880
Speaker 5: stay out in the sun longer.

1274
01:01:32,960 --> 01:01:35,960
Speaker 1: Yeah, that's a similar process. You're not changing their transparency,

1275
01:01:36,080 --> 01:01:38,840
Speaker 1: but still the UV light is changing the chemical composition

1276
01:01:38,960 --> 01:01:41,320
Speaker 1: because it's being absorbed and it's breaking down some of

1277
01:01:41,360 --> 01:01:44,520
Speaker 1: the bonds and it's changing the chemical nature of the substance.

1278
01:01:44,640 --> 01:01:46,960
Speaker 5: So if you put your car inside of a glass house,

1279
01:01:49,160 --> 01:01:51,320
Speaker 5: then they'll stay the same color and the tires will

1280
01:01:51,320 --> 01:01:52,680
Speaker 5: stay bouncing. Is that what you're saying?

1281
01:01:52,760 --> 01:01:55,200
Speaker 1: Yeah? Or if you smear your car and sunscreen either one.

1282
01:01:55,280 --> 01:01:56,840
Speaker 5: Oh, I guess you have to be careful. You know,

1283
01:01:57,080 --> 01:01:58,600
Speaker 5: you know what to say about cars that live in

1284
01:01:58,800 --> 01:02:03,640
Speaker 5: glass houses. All right, Well, I guess it's an interesting

1285
01:02:03,920 --> 01:02:07,040
Speaker 5: look into a very familiar thing that is all around us, right,

1286
01:02:07,080 --> 01:02:08,880
Speaker 5: Like the screen on your phone is made out of

1287
01:02:08,880 --> 01:02:11,920
Speaker 5: transparent glass, and your windows and every time you go

1288
01:02:11,960 --> 01:02:14,120
Speaker 5: to the doctor or the dentist and they take X rays.

1289
01:02:14,160 --> 01:02:15,960
Speaker 5: It's like physics going on, right.

1290
01:02:15,960 --> 01:02:19,440
Speaker 1: There is physics going on everywhere. What's amazing to me

1291
01:02:19,720 --> 01:02:23,560
Speaker 1: is that sometimes we can even unravel this microphysical picture

1292
01:02:23,560 --> 01:02:27,200
Speaker 1: of what's happening. Do explain our everyday experience. Why things

1293
01:02:27,240 --> 01:02:30,640
Speaker 1: are squishy, why things are hard, why things conduct electricity,

1294
01:02:30,680 --> 01:02:33,360
Speaker 1: why things are see through. It all comes down to

1295
01:02:33,400 --> 01:02:36,920
Speaker 1: what's happening at the atomic level or the subatomic level.

1296
01:02:37,200 --> 01:02:40,400
Speaker 1: And incredibly that's a story we can sometimes understand and

1297
01:02:40,440 --> 01:02:41,480
Speaker 1: even explain to you.

1298
01:02:42,240 --> 01:02:45,880
Speaker 5: Yes, it's almost like the universe is transparent to science,

1299
01:02:47,160 --> 01:02:49,800
Speaker 5: or it's like scientists have X ray glasses, or.

1300
01:02:49,720 --> 01:02:52,720
Speaker 1: Maybe the UV photons of the universe are just frying

1301
01:02:52,760 --> 01:02:54,960
Speaker 1: our brains because.

1302
01:02:54,760 --> 01:02:57,400
Speaker 5: Your skull is made at a glass. What's going on there?

1303
01:02:58,240 --> 01:03:00,960
Speaker 1: I'm going to go put sunscreen on my brain, yeah.

1304
01:03:00,880 --> 01:03:04,680
Speaker 5: Or a hat, you know. They physics have invented hats also,

1305
01:03:05,680 --> 01:03:07,680
Speaker 5: which helps with sun damage.

1306
01:03:08,200 --> 01:03:10,520
Speaker 1: Quantum hats. We should sell those all right.

1307
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Speaker 5: Well, we hope you enjoyed that. Thanks for joining us,

1308
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Speaker 5: See you next time.

1309
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Speaker 1: Thanks for listening, and remember that. Daniel and Jorge Explain

1310
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Speaker 1: the Universe is a production of iHeartRadio. For more podcasts,

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Speaker 1: from iHeartRadio. Visit the iHeartRadio app, Apple Podcasts, or wherever

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