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Henry Reich of MinutePhysics ( joins the show to talk about fluorescence and then Jessi from Animal Wonders ( shows up with her Half-moon Conure Loulou.

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Hank: Hello, and welcome to the SciShow Talk Show, the episode of SciShow where we talk about things with cool people. Today we have a very special guest, who you may recognize the voice of, this is Henry Reich, the creator of MinutePhysics.

Henry: Indeed.

Hank: I have something that I need to show you.

Henry: Wait, wait, wait, let's wait on that.

Hank: Ok.

Henry: Cuz today,

Hank: Wait.

Henry: Today I want to talk about pennies.

Hank: Oh, wow!

Henry: Which is why I'm wearing my CGP Grey t-shirt.

Hank: So that's why you're wearing your CGP Grey shirt, and just by coincidence, I am also wearing the exact same shirt. But I wanted to tell people about, a little bit about you first.

Henry: Sure.

Hank: So you, what's your, uh, background, wha- how did you get into making videos about physics?

Henry: Um, it's a long story, and the short version is that I always was interested in making videos, but I also studied physics in school. And then I took some time after grad school and went to L.A. and managed to somehow get a job working with FreddieW and Brandon, and learned that YouTube was a thing, and, uh, and thought, well maybe if I were making videos on YouTube, they would be about physics. And I can't really do anything other than draw really crappy stick figures so I draw stick figures.

Hank: That's beautiful, it is a beautiful creation, thank you for creating it. What did you study in school?

Henry: Uh, I studied Math, and Physics in undergrad, and Theoretical Physics for my degree.

Hank: What was your, what, what did you, uh, 

Henry: I studied General Relativity.

Hank: Give me, what is the title of your thesis?

Henry: Um, I think it was, I don't remember. It was something to do with multi-metric gravity, um, and,

Hank: Yeah, that's what I wanted to hear.

Henry: extensions of general relativity.

Hank: into multi-metric gravity.

Henry: into multi-metric gravity, yes.

Hank: So like, no one has any idea what that means and I just want to leave it that way. For now.

Henry: All right, we can do that. 'Cause we're going to talk about pennies.

Hank: 'Cause it's better to talk about pennies, 'cause we're both wearing CGP Grey shirts.

Henry: So, this is a cup of pennies.

Hank: Okay. I agree.

Henry: Do you notice something interesting about the pennies?

Hank: Yes, they all have little red dots on them.

Henry: They all have little red dots on them. Now, in my pocket, if I can get it out -

Hank: On both sides.

Henry: On both sides, yeah, that's an important point.​ So pennies normally have two sides.

Hank: Correct.

Henry: A head side and a tails side. But these pennies have two sides: one is a fluorescent side 

Hank: Okay.
Henry: and one is a non-fluorescent side.

Hank: Okay.

Henry: So, for example that one has a shiny fluorescent side,

Hank: Yeah

Henry: and not.

Hank: Ah, okay.

Henry: And you can't tell them apart when I don't have the UV light on.

Hank: That is true.

Henry: So, it's like heads and tails but you can't see which one is which. The idea here is that I don't have to blindfold you for the entire episode.

Hank: Okay

Henry: Um, so what I'm going to do, is I'm going to pour a bunch of pennies on the table, right, how's that, and I want you to split those pennies into two piles. And I want each pile to have the same number of pennies with the fluorescent side up.

Hank: Okay. That's 

Henry: Go ahead.

Hank: Is there a way to do this right?

Henry: Well, okay, so the first, this is the first - we're gonna do this two times.

Hank: Okay.

Henry: The first time you do it is this way. Do you think it's possible?

Hank: No.

Henry: No.

Hank: I mean it's not gonna be exactly the same. I mean, it's possible that it could be exactly the same, but

Henry: Is there a piece of information you think I could tell you that would allow you to do it?

Hank: I mean, unless there's some kind of correlation between the fluorescent side and the visible things, but there isn't.

Henry: No, there isn't. They're random, I promise. So, so you're going to divide them into two groups and unless you're super lucky there won't be the same number of fluorescent sides and regular ones there.

Hank: Correct

Henry: Now, what I'm going to do is I'm going to blindfold you just for a second because I need to be able to count -

Hank: I do get blindfolded.

Henry: You do get blindfolded, but only for a brief period of time. Um, no peeking out from below.

Hank: Okay.

Henry: Okay, what I'm going to do is I'm going to count how many there are total fluorescent ones so... [counts to 17]. There are a lot of fluorescent ones in here. [counts to 21]. Okay, so twenty-one of these pennies are fluorescent and just for good measure in case you were counting my counting of pennies, I'ma add a couple that aren't fluorescent just to skew you off.

Hank: Ah, I was.

Henry: So, twenty-one are fluorescent.

Hank: Okay.

Henry: Now the question is - you can take your blindfold off - can you split them into two groups that each have the same number of, you can flip coins as well. You're allowed to flip them.

Hank: Oh God. I mean, by the way that you're asking the question, yes, there is a way. But to be clear I have no idea what it is.

Henry: All right.

Hank: So there are twenty-one - how many total coins are there, do you know?

Henry: Um, it doesn't matter. If you count I'm gonna add more so you don't know. The point is you don't know how many total coins there are.

Hank: Okay.

Henry: There's some number of coins, and twenty-one of them in this case happen to be fluorescent. And the question is can you, by just moving them and flipping them, can you put them into two piles that are both the same number, number of fluorescents?

Hank: Apparently so.

Henry: Yes.

Hank: But you're going to have to tell me how to do that.

Henry: Okay.

Hank: To find out how to do this - I have no idea - you can go click over to a second video, which will have the answer. [Video annotation appears: "click here to find out the answer!"] But first, try and figure it out on your own, because apparently there is a way.

Henry: It's actually beautifully simple.

Hank: It's beautifully simple. Well, that makes me want to figure it out myself.

Henry: Do you want to figure it out for yourself?

Hank: In any case, go click on that video. Go watch that video and you will find out. But just stick around here if you want to continue watching and we'll talk about fluorescence, and also have an animal guest from Jessi from Animal Wonders. Ah yeah, so clear off the pennies.

Henry: Yeah, so let's, let's talk about - oh no,

Hank: Oh gosh.

Henry: Pennies are going everywhere.

Hank: So now what you're going to explain to me -

Henry: Let's talk about fluorescence. Like, what's going on here.

Hank: Okay. So black lights and raves and

Henry: Black lights, raves, educational experiences. Um, this is a UV flashlight. [Hands Hank the flashlight]

Hank: Yes, they use them at the airport to look at my I.D.

Henry: I don't understand that. Well actually I do, because I have a passport here, if I can find it.

Hank: Well I also have my, my driver's license. 

Henry: But the passport's more interesting. The passport, when you shine the light on it [shines light on it]

Hank: Oh, it has little hairs!

Henry: It has little fibers, and the fibers are different on the cover. They're glowing fibers, and then here there's like little, tiny ones.

Hank: Yep.

Henry: And if you open it up, um, to the pages, there's like this line along the outer edge of the paper. If you look carefully on it, right up here, what does that say?

Hank: It says passport.

Henry: Passport. So they have this, uh, security features

Hank: In case you were confused about what it was. You can look at it with a UV light and it will tell you that it is passport.

Henry: There are other things as well that, uh, UV light will, that fluorescence is used for. I think there's a security feature in this twenty dollar bill. Where is it?

Hank: Oh yeah, yeah, there's a line

Henry: There a line over there

Hank: What's that say? It says twenty. 

Henry: Twenty. The U.S. government is incredibly original. Twenty. Passport.

Hank: So creative.

Henry: There you go. [Hands Hank the UV flashlight]. I have some other things as well, um

Hank: [Shines torch in his eyes] It kind of hurts to look at.

Henry: [covers torch] Don't, yeah, that's - you know the whole thing about using sunglasses with UV light?

Hank: [laughs]. You're saving me.

Henry: Um, here's my visa card.

Hank: You're covering up your -

Henry: I'm covering up my number, but there's a little V,

Hank: Ah, there's a V there.

Henry: in the corner, that lights up. Um, and, and it's also used, so I have, I guess I just, I'll show you the markers I used for this. [gets out markers]. So I have these markers, the two orange markers - if you move back farther, be a bit more obvious

Hank: Oh yeah, yeah.

Henry: One is glowing a lot more than the other one. On, off, on, off; so. So, now the question is what is fluorescence? What's going on? Um, do you know what fluorescence is?

Hank: I do not.

Henry: Here, let's not shine that in people's eye's.

(Hank shines light in people's eyes.)

Hank: I do not.

Henry: So fluorescence is a phenomenon that happens when you excite the electrons in the atoms in a material using some incident light - in this case it's UV light - and they go to a higher energy level and then they fall back down. But they don't fall back down from that high energy level back, 'cause then they'd just re-emit the UV light. They kind of, before they fall back down they'll, what's called "relax", where they kind of jiggle around and lose some energy due to thermal fluctuations and things, and so when relax, finally relax back down, um, to the ground state they emit light that's at a lower frequency, which means it's visible instead of ultraviolet.

Hank: So, just to get this, uh, this all lined up, so atoms have electrons - 
Henry: Atoms have electrons.

Hank: and the electrons in a ground state exist in a sort of a, that's like their normal place and then when they get hit by photons they might get excited.

Henry: Yep, they might get more energy and then,

Hank: Jump up to other energy levels and then when they fall back down they emit photons.

Henry: They emit photons.

Hank: Is that how normal light works? Is that like, like the colors of this table, the colors of your skin

Henry: Well, the colors of this table is scattering off of, of light coming in.

Hank: So that's not emitting light.

Henry: Yes, so it's not being absorbed and re-emitted. 

Hank: Okay.

Henry: It's scattering. So when you shine this on, you know, something that's fluorescent, there will be some scattering and then there's also some absorption and re-emission.

Hank: So the re-emission is where the fluorescence comes in. That's why it looks like it's glowing rather than it's just being lit up.

​Henry: Exactly. And phosphorescence, which I have this glow-in-the-dark water bottle, we might be able to see - it might be really hard, you might have to make it dark. It's not going to work. But a glow-in-the-dark water bottle will glow for a long period of time after it's in the light, which is different from fluorescence. And phosphorescence does that because in the relaxation period, when the electrons go to a stage which isn't emitting light, they, the state that they end up getting into is something that is much harder for the light to then escape to. It ends up, normally they end up going to some different spin state which, for which they have to like quantum tunnel back down - or something, something weird.

Hank: Oh, okay. 

​Henry: It's complicated but, but the point is it just basically takes longer. So with fluorescence it's happening on the scale of like nanoseconds. It absorbs and then re-emits, whereas phosphorescence it's over the scale of minutes or even hours. So that's, that's fluorescence, and it, it's used actually not just in security devices -

Hank: but also in raves.

​Henry: Yeah, also in raves. But also in, you know, like in biomarkers, um, and

Hank: Right. Right. 

​Henry: you know, if you want to make something that's fluorescent and then put it in your body you can see where, where everything goes.

Hank: Where it ended up, yeah. I don't have anything in me right now. 

​Henry: you don't. I have some on my hand though, I think.

Hank: Yeah, from coloring.

​Henry: Yep, got some marker on my hand. So that is fluorescence. 

Hank: That is how fluorescence works. And now, we're going to talk to an animal.

Henry: Excellent.

Hank: Generally, when Jessi comes in it's either terrifying or adorable; I don't know what's in store for us. 

Jessi appears to have brought us a conure. I had a conure growing up, so I know this. Not this species though.

Henry: It's not a parakeet? It's a parrot?

Jessi: So, I like how you used the work conure. A lot of people don't know what conure means, and it means small parrot with a long tail. It's the same as a parakeet. 

Henry: Or a budgerigar?

Jessi: No. So that's where the confusion happens. A budgerigar, and I can almost never pronounce that name, I call them budgies - um, so budgies are not parakeets. 

​Henry: Right. Oh, 'cause they're, they're Australian, the parakeet's North American.

Jessi: Yes. Um - Americans.

Henry: Or American.

Jessi: Yeah. So - and not just American. They can be over in the old world too. They're just different. So, so conure means small parrot with a long tail, also known as a parakeet; we just get confused sometimes, so we've made up another word, so conure. So this is a half-moon conure, and there are lot of species of different kinds of conures. And he's friendly, so if you want to have him step on your finger?

Hank: Hi. How you doing?

Jessi: You can feed him some little treats.

Hank: I like feeding treats. Oh, yes. They have those like dry tongues.

Jessi: Yeah, it is dry. Some are black, or grey, and some are tan, and it's like a little finger inside your mouth.

Hank: Yeah, like a little old scaly finger in your mouth. 

Jessi: Mm-mm. 

Hank: And you're not very efficient at the eating. 

Jessi: They're really messy - they're supposed to be messy though. 

Hank: Well, I mean he's getting maybe like 25% of the food inside of him. 

Jessi: Well, that's - if he were super, super hungry he wouldn't waste as much, but they're kind of made to be messy because anything that they drop - yeah -

Hank: Yeah, he's like, "can I have more please?"

Jessi: - anything that they drop is going to help the animals below them, and if they drop parts of - you know, if they grab a big chunk of millet or something like that, and then, yeah, they're dropping whole seeds 

Hank: They're distributing. Thanks. 

Jessi: And otherwise all the little decomposers are gonna eat- see how he keeps his head. Yup

Jessi: So we were talking about UV light

Henry: UV light. Exactly.

Jessi: So birds, parrots, psittacines, can see UV light, so they can see stuff that they can't see.

Henry: But if we shine the UV light on, on the, Is it a him or a her?

Jessi: It's a him, if it was a her than 

Hank: How you going, it's okay

Henry: So if we shine the UV light on, we don't really

Hank: We don't see anything, but the birds very well might. Because they see in wavelengths that we don't see in. 

Henry: So it's not fluorescent. But it is reflecting UV light. 

Hank: Yeah

Henry: And the bird can probably see that.

Jessi: So yeah, they have very colorful patterns, some of them do. And we can see their colorful patterns in what we can see, but then they may have patterns on there that we can't perceive, and maybe some of that's gonna be the sexual dimorphism in them, because a lot of times birds look identical to us.

Henry: Males and Females?

Jessi: Yeah but they can tell each other apart but just looking at each other sometimes. 

Hank: So where Lulu come from?

Jessi: Lulu was born at Animal Wonders, uh, one of the only animals born at Animal Wonders. 

Hank: Oh wow

Jessi: Yeah that's 

Hank: We raised a fledgling. 

Jessi: Yeah he had a whole spiky hairdo when he was a baby and that was really interesting. It was um 

Hank: Do you have baby pictures?

Jessi: We have baby pictures.

Hank: We need to get some baby pictures.

Henry: Is he the offspring of another bird you had there?

Jessi: Yes. Yeah, uh, we had a pair of birds and yep, they had babies. So they laid a little clutch of eggs and it was really interesting to see how that whole process worked, and how they grew and uh, it was just really interesting. 

Hank: [to bird] Look what I got. Look what I got.

Jessi: I know you have a seed. Nice work.


Jessi: So Lulu knows a couple things, he doesn't really like to say them in public, he's a little shy. He says 'Whatcha doing' and it sounds just like me, its kinda creepy. 


Jessi:And he says 'MMmm' and 'Thank you'

Hank: My conure, every morning my mom would say 'Hank, get up!' and then  my conure would say 'Hank, get up!'. And I'm like this is perfect, I'm so glad that I take care of you and treat you nice so that you can

Jessi: Nag you.

Hank: Yup

Henry: Which one was more inspiring?

Hank: Oh the bird was much louder.  Because it was there in the room, and also much louder. 

Jessi: Conures, they pack a huge punch, they are so loud

Hank: Be careful if your interested in purchasing a conure because they will, they will prevent the sleep.

Jessi: [Laughs] They are, they're really, really loud. These guys are re-homed so often because people get them because of their pretty colors. You know, the sun conures. One of the prettiest ones. And then just, people have them for a little while, and then they just can't stand how loud they are. And uh, they're messy like you experienced as well. So they're messy and loud, and it's like having a two year old child. For 30 years.

Hank: But Lulu is being very polite.

Jessi: He is. He is until he gets excited, you know. 


Jessi: He definitely screams and chatters and warbles and um. He can be quite loud.

Hank: But yeah 30 years, birds live an amazingly long time, for such small animals.

Jessi: Small little guy and the bigger they get the older they live and 

Hank: Thanks for coming on the show Lulu. Jessi from Animal Wonders, thank you, as always for coming in. Um, is there a YouTube channel or website we should be talking about?

Jessi: Oh, yeah we have a YouTube channel. You can see more of the amazing animals and learn some interesting stuff.

Hank: We'll put a link to it.

Jessi: Okay!

Hank: Okay.

Jessi: Great.

Hank: And Henry of course, people already know about MinutePhysics. But its

Henry: Thanks for having me on.

Hank: Thanks for coming in.

Henry: Its been a lot of fun. 

Hank: And thank you for watching this episode of SciShow talk show. We'll be back next time where we'll have more special guests. If you want to keep getting smarter with us here at SciShow you can go to and subscribe. 

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