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Speaker 1: Katie, what is your favorite color? I'm gonna say blue. Well,

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Speaker 1: you can't just say blue. There's like a million different

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Speaker 1: shades of blue. Okay, I guess say more blue green

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Speaker 1: than a navy blue. Oh, you can do better than that.

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Speaker 1: Pretend you're like writing copy for a paint catalog. Give

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Speaker 1: us a really descriptive name. Okay, something like ce foam

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Speaker 1: mermaid tears or radiant peacock party. Now we're talking, But

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Speaker 1: for this podcast, can you give us like a really

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Speaker 1: good physics name for your shade of blue? How about

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Speaker 1: sparsely hydrogenated blue dwarf. That sounds awesome for me. I'm

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Speaker 1: personally looking forward to the day when somebody launches physics

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Speaker 1: paint colors and I can go to the store and

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Speaker 1: ask for a gallon of sultry supernova sky arlette. That

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Speaker 1: might blow up your her face. Hi. I'm Daniel. I'm

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Speaker 1: a particle physicist and a professor at UC Irvine, and

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Speaker 1: I've never met a color I didn't like. And I'm Katie.

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Speaker 1: I'm stepping in for Jorge this week. I am the

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Speaker 1: host of Creature Feature and I like all colors all

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Speaker 1: the time simultaneously. It makes me hesitate to ask what

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Speaker 1: your closet looks like. Katie Brown, I remember wondering as

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Speaker 1: a kid if there was a possibility for you to

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Speaker 1: imagine a color you hadn't seen before, you know, like,

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Speaker 1: if you thought hard enough, could you invent a color

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Speaker 1: in your mind that didn't exist out there in the world.

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Speaker 1: What do you think do you think that's possible? Yeah?

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Speaker 1: I mean I used to have that same exact thought,

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Speaker 1: thinking of, well, couldn't there be other colors than what

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Speaker 1: we know on the spectrum? And what would that be like?

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Speaker 1: And I would imagine that that experience of this new

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Speaker 1: color might be something beyond just vision, maybe accompanied by

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Speaker 1: a feeling like a tingling or something, I like the

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Speaker 1: connection of the senses. There. Maybe you see a new

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Speaker 1: kind of fruit and it has a new kind of taste,

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Speaker 1: and it opens up a whole new branch of philosophy.

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Speaker 1: Now we're getting into synesthesia territory exactly. But this question

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Speaker 1: of color is it really deep and fascinating one because

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Speaker 1: it extends all the way from philosophy, like what is

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Speaker 1: it like to experience a color? Down to biology how

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Speaker 1: does the human eye respond to photons? And finally to physics,

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Speaker 1: what exactly is a red photon and a blue photon

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Speaker 1: and a green photon, and that's exactly the kind of

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Speaker 1: topic we love to dive into on this podcast. So well,

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Speaker 1: welcome to the podcast Daniel and Jorge Exploding the Universe,

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Speaker 1: in which we ask the deepest, the reddest, the bluest,

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Speaker 1: the whitest, the darkest questions about the nature of the universe.

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Speaker 1: We ask questions that go all the way from your

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Speaker 1: eyeball deep deep down through your brain, and all the

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Speaker 1: way into your soul, whether or not it exists. I'm

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Speaker 1: so excited to smash biology and physics together and create

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Speaker 1: some kind of new particle and we're very excited to

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Speaker 1: have you with us today, Katie, Thanks very much for

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Speaker 1: filling in for Jorge. We always love talking about the

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Speaker 1: biological side of physics with you, Yes, the the squashy

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Speaker 1: side of physics as I call it. And today we

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Speaker 1: are going to be talking about all the things that

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Speaker 1: we can see, because vision plays such an important role

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Speaker 1: in how we perceive the world and how we imagine it.

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Speaker 1: I think if you close your eyes and try to

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Speaker 1: imagine the room around you, probably the image in your

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Speaker 1: mind would be an image. It would be something built

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Speaker 1: out of your visual perception of the world around you.

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Speaker 1: That might be different, of course for blind listeners or

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Speaker 1: other people who don't have strong vision. There's also people

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Speaker 1: with a fantasia who can see, but they actually don't

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Speaker 1: think in pictures, they don't imagine pictures. That blows my

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Speaker 1: mind that you can see things but that you can't

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Speaker 1: have images in your head. Yeah, there's just so many

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Speaker 1: different types of ways that humans can perceive the world exactly,

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Speaker 1: and that means that there are so many layers to

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Speaker 1: these kinds of questions, like what is happening at which stage,

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Speaker 1: How is your eyeball seeing a photon, how is it

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Speaker 1: sending a message, how is that message interpreted, how is

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Speaker 1: that message experienced by your brain? How is that used

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Speaker 1: to make decisions and think about the world. But it's

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Speaker 1: clear that eyeballs are an important part of understanding the

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Speaker 1: world around us, and not just the eyeballs that we

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Speaker 1: have in our skulls, but the other kinds of eyeballs

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Speaker 1: that we build to look at the universe. Our X

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Speaker 1: ray telescopes and are infrared telescopes and our gamma ray

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Speaker 1: telescopes that can see photons that are well out of

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Speaker 1: our visual spectrum, and so understanding how photons work and

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Speaker 1: how we see them is pretty core to understanding the universe.

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Speaker 1: See not just with the eyes and our schools, but

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Speaker 1: the eyes in our hearts, and also the eyes attached

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Speaker 1: to a giant telescope. It would be really weird if

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Speaker 1: we built the telescope that was literally made out of

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Speaker 1: human eyeballs, like strung together. That sounds pretty That's a

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Speaker 1: real biology physics collaboration right there. But the eyeball does

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Speaker 1: touch on a lot of deep questions. There are questions

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Speaker 1: their philosophy, there are questions of biology, and there are

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Speaker 1: also questions of quantum physics. And so today on the podcast,

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Speaker 1: we're going to be peering into all of these questions

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Speaker 1: and asking can the human eye see a single photon?

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Speaker 1: So what do you think, Katie? Is the human eyeball

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Speaker 1: a quantum device? I mean, this is a really interesting question,

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Speaker 1: and I really love how people are kind of thinking

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Speaker 1: about this in terms of like, well, it seems really

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Speaker 1: tiny and you need to magnify it when you need

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Speaker 1: to make it bigger? How can you see one wavelength?

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Speaker 1: And when you think about the eyeball, it certainly seems

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Speaker 1: like the eye is too big right to see just

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Speaker 1: a little tiny particle. But I think when you examine

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Speaker 1: inside the eye and see how teeny tiny and delicate

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Speaker 1: some of these cells that actually allow us to see,

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Speaker 1: makes me a little more convinced that maybe we could

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Speaker 1: see something even as small as a single photon. Yeah.

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Speaker 1: I think when people think about quantum mechanics, they think physics,

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Speaker 1: and then they think about mechanical devices that humans have built,

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Speaker 1: optics and semiconductors and specialized materials, things that you don't

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Speaker 1: typically associate with biology. But of course our bodies are

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Speaker 1: built out of molecules and atoms, the same building blocks

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Speaker 1: as what's in that crazy quantum lab in the basement

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Speaker 1: of your building. And so in principle, it's possible for

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Speaker 1: the human body or anybody to have quantum effects. And

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Speaker 1: I think there's a whole burgeoning field now of people

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Speaker 1: studying quantum biology, things that happen in bodies that rely

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Speaker 1: on quantum mechanics. And so, in principle, as you say,

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Speaker 1: it's possible for biological cells to develop capabilities which rely

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Speaker 1: fundamentally on quantum mechanics, I mean the fact that we

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Speaker 1: can step outside and get burned by u V rays

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Speaker 1: from the sun is pretty compelling evidence to me of

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Speaker 1: the direct impact of physics, even at the very small scale,

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Speaker 1: on our bodies. And I deal with that all the time, exactly.

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Speaker 1: And so I went outside and walked around the campus

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Speaker 1: of UC Irvine and asked a bunch of random students,

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Speaker 1: I Ranto and one chemistry professor if they thought that

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Speaker 1: the human eye could see a single photon. That is,

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Speaker 1: if you were in a dark room and I shot

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Speaker 1: one photon at your eyeball, would you see a flash

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Speaker 1: of light or not? To think about it for a

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Speaker 1: minute before you hear these answers, do you think the

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Speaker 1: human eye could see a single photon? Years what folks

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Speaker 1: on the U c Irvine campus had to say, there's

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Speaker 1: a neurological sense and also a physical sense. I mean,

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Speaker 1: if physical sense doesn't happen, then you will neuroinologically you

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Speaker 1: cannot sense it. So it's like I think it's physically

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Speaker 1: it makes sense then yeah, I mean and fultonic absorbing

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Speaker 1: content in the content sense. I think a single is possible.

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Speaker 1: I just don't know the threshold. I don't think so. No,

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Speaker 1: I don't think so. Why not? Uh, probably because it's

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Speaker 1: too small. I don't think so, just because this is

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Speaker 1: the size of it, Like even the human eye it's

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Speaker 1: only capable of seeing so much, so we even need

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Speaker 1: to magnify it or make it a little larger. No,

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Speaker 1: I don't think so. Why not? Just I just think

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Speaker 1: it's too minute for the eye to like distinguished. Yes,

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Speaker 1: I'm just guessing. Honestly. I feel like it's you can't

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Speaker 1: see one single wavelength? Right, So how many photons do

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Speaker 1: you think it takes before your eyeball response. I don't

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Speaker 1: know if it's like an amount of photons. Maybe it's

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Speaker 1: like a unit of energy one probably not. Isn't light

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Speaker 1: just photons? So, yes, you can see it. Do you

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Speaker 1: think you could see a single a single one? No? No, no,

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Speaker 1: why not? Um, I'm not sure. I don't feel like

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Speaker 1: you could see it. Well, I don't know if my

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Speaker 1: brain could register it, but I feel like a rotter

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Speaker 1: cone gonna pick it up. But it might just like

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Speaker 1: consider it some kind of like random you know, burst

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Speaker 1: of something or some some miss neural mis spider or something.

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Speaker 1: So there's a lot of nose there. What do you think, Katie?

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Speaker 1: I understand the skepticism because it really does seem like

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Speaker 1: that would be too small of a stimulus too for

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Speaker 1: us to really pick up on. Why would we need

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Speaker 1: to see a single photon? Humans aren't necessarily known for

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Speaker 1: being the most sensitive of animals. Not to be mean

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Speaker 1: about it, but we we don't have the best sense

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Speaker 1: of smell, We don't certainly don't have the best sense

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Speaker 1: of vision or the best hearing, So why would we

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Speaker 1: be able to see a single photon? And I really

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Speaker 1: like people kind of questioning whether, even if we could

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Speaker 1: pick it up at the cellular level, whether the brain

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Speaker 1: could even process that. So I under understand the skepticism,

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Speaker 1: but I do I think that the fact that the

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Speaker 1: inner workings of the eyeball are so incredibly small and precise,

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Speaker 1: I'm somewhat leaning towards yes, we might be able to

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Speaker 1: see a single photon. Yeah, I was a little disappointed

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Speaker 1: that these folks didn't have more confidence in our eyeballs.

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Speaker 1: Though I think you're right, I don't understand why we

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Speaker 1: would need to be sensitive to a single photon. It's

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Speaker 1: not like we typically go hunting in the dark for rodents, right,

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Speaker 1: Like if an owl could see a single photon or

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Speaker 1: an eagle could see a single photon, I get it,

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Speaker 1: but human like, we're pretty much napping at night anyway.

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Speaker 1: I was interested in learning more about the fundamental science

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Speaker 1: at the heart of this process, where photons are sorbed

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Speaker 1: by cells in your eye and converted into signals. So

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Speaker 1: I reached out to an expert we have here at

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Speaker 1: You See Irvine. Rachel Martin is a professor of chemistry

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Speaker 1: and she studies of vision, and I asked her to

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Speaker 1: share some thoughts with us about why vision is cool.

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Speaker 1: I'm Rachel Martin, and I'm a professor of chemistry and

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Speaker 1: molecular biology and biochemistry at you See Irvine. Great, and

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Speaker 1: I understand that one of the focuses of your research

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Speaker 1: is vision in the eye. So tell me what do

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Speaker 1: you love about eyeballs? Wind about your career to the

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Speaker 1: study of vision. What entrances you about vision? Vision is amazing.

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Speaker 1: I mean, for one thing, um, humans are very visual animals.

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Speaker 1: This is mostly how we perceive our world. It's you know,

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Speaker 1: it's one of the most important senses for us, which

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Speaker 1: is not true for a lot of mammals. A lot

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Speaker 1: of mammals experienced the world through smell, but for us

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Speaker 1: it's really a lot of it is about seeing things

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Speaker 1: and that's that's kind of our main detection system for

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Speaker 1: the world. And I think that's really neat. And I

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Speaker 1: also think it's pretty amazing that vision works at all.

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Speaker 1: There are a lot of kind of happy accidents of

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Speaker 1: physics that have to be the way they are to

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Speaker 1: enable vision. I mean, so, for instance, the human visual

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Speaker 1: range overlaps almost exactly with um the kind of the

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Speaker 1: whole in the absorption spectrum of water. So you know,

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Speaker 1: water absorbs at a lot of frequencies, but there's just

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Speaker 1: this tiny little window that where it doesn't, and that's

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Speaker 1: where we're we're able to see. And I think that's

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Speaker 1: really neat all. Right, So Rachel is clearly very excited

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Speaker 1: about the eyeball. She has devoted her entire research career

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Speaker 1: to studying the human eye. And I love that about

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Speaker 1: science that every time we're making progress, it's because one

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Speaker 1: person has decided this is the most important question in

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Speaker 1: the universe, and I'm going to devote my entire research

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Speaker 1: career to studying the lens in the human eyeball. I

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Speaker 1: love it. I mean, the eyeball is so bizarre that

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Speaker 1: it even works. It has caused things like people to

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Speaker 1: be skeptical of evolution, thinking, well, the I is such

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Speaker 1: a complex device, how could it possibly naturally evolve? Which

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Speaker 1: I'm sure we're going to talk about. But I am

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Speaker 1: not surprised by the fascination with eyeballs because they're so

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Speaker 1: clever and how they work and it is not straightforward

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Speaker 1: at all. I totally agree. And so let's dig into

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Speaker 1: it a little bit. Since you're the biologist of the

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Speaker 1: pair of us, why don't you give us a rundown

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Speaker 1: on how the eye works? What are the essential elements

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Speaker 1: of it? What comes into play when you are seeing

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Speaker 1: a photon? Right? I mean the ie weirdly enough, is

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Speaker 1: basically like a little camera. So if you've ever played

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Speaker 1: with like a big lens or magnifying glass or something,

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Speaker 1: you know how you can like focus the sun's light

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Speaker 1: into a little dot burned some ants with it if

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Speaker 1: you're evil. So the eye actually has lenses in it

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Speaker 1: that can have like come in, refracts and focuses on

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Speaker 1: a spot. So first, outside of your eye, uh, you

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Speaker 1: have the cornea, So that's the thing that you may

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Speaker 1: directly place the contact lens on, or if you're unlucky,

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Speaker 1: you can scratch the corny and that's really bad. But

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Speaker 1: that's basically this uh it's a convex shape and so

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Speaker 1: light comes in and the light is refracted in this

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Speaker 1: cornya and then uh it goes through the pupil and

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Speaker 1: the iris can constrict or expand, allowing more or less

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Speaker 1: light in and just like the aperture of a camera.

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Speaker 1: And after that, you actually have the lens, which is

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Speaker 1: like the focus on the camera. It you have these

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Speaker 1: two little muscles that attached to the lynching can like

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Speaker 1: pull it or kind of relax and let it contract,

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Speaker 1: and that allows you to focus the light. So if

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Speaker 1: you've ever tried to focus on something and then you could,

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Speaker 1: it's blurry it first and then it comes into focus.

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Speaker 1: That's your lens actually squashing and stretching in order for

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Speaker 1: you to focus on something, and that will focus the

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Speaker 1: light onto the retina, so that is the back of

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Speaker 1: your eye. And on the retina are these uh photosensitive receptors.

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Speaker 1: So there are rods and cones. There are three kinds

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Speaker 1: of cones and only one type of rod. And it

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Speaker 1: is through the way that these rods and cones detect

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Speaker 1: this light that you can see everything from colors to

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Speaker 1: shapes two distances. It's really incredible. And then where we

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Speaker 1: haven't even talked about how it gets to the brain.

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Speaker 1: You have a bundle of nerves. Basically you do you

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Speaker 1: do good cable management, Daniel, Uh, My cable management is

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Speaker 1: a disaster. Actually, yeah, I'm no one to preach about

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Speaker 1: cable management. But our eyes bundle all of these basically

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Speaker 1: cables that run to all of these photo sensitive cells

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Speaker 1: and then into the optic nerve at the back of

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Speaker 1: the eye. It actually creates a blind spot in eye

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Speaker 1: because there's this cluster of of nerves that can't perceive

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Speaker 1: any light, but they're just transmitting the signals from these

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Speaker 1: cells and that runs all the way back to the

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Speaker 1: back of our brain and the occipital lobe. So it

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Speaker 1: is not it is not a straightforward system, but it

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Speaker 1: works really well. It's really amazing. I like the way

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Speaker 1: you've in an analogy to a camera. Um, so we

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Speaker 1: have just to review the cornea bend the light onto

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Speaker 1: the lens. The iris decides how much light goes into

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Speaker 1: the eye. The lens itself focuses light on the retina

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Speaker 1: and the retina sort of like the film or the

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Speaker 1: digital sensors that formed the image. And then translates it

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Speaker 1: into these neurological signals, and that's stuff to me is

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Speaker 1: super fascinating because the thing that you observe, the thing

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Speaker 1: that you experience, are just the messages along the nerve itself,

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Speaker 1: right your brain, your subjective experience. You don't observe the

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Speaker 1: photons themselves. You just get these messages in your brain

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Speaker 1: plays that in your head sort of as an experience

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Speaker 1: of color. But we'll dig into that in a minute.

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Speaker 1: I think that's really interesting and it's fascinating to me

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Speaker 1: that the way we constructed a camera is so similar

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Speaker 1: to the way the eyeball worked. Do you think that

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Speaker 1: we like stole, we cribbed from the eyeball, We're like,

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Speaker 1: this is a good design, let's do it like that.

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Speaker 1: Or do you think it's an example of like convergent

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Speaker 1: evolution of technology and biology. You know, that's a really

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Speaker 1: good question. I don't know, but I could believe either,

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Speaker 1: because we have been studying the eye for for many years,

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Speaker 1: even long before our sort of modern understanding of biology.

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Speaker 1: So I could definitely see there being some inspiration from

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Speaker 1: the eye. But it could also have just been from coincidence,

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Speaker 1: because you know, the very earliest camera, the camera obscure

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Speaker 1: where it's just basically a little pinhole where light comes in.

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Speaker 1: It's such a small pinhole, you have this refraction of

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Speaker 1: light that turns up an image that's upside down in

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Speaker 1: the wall behind it. I could see that having been

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Speaker 1: just discovered kind of by by coincidence or accident. And

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Speaker 1: then we essentially reverse engineered the eyeball only in a

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Speaker 1: mechanical sense. And again what's really cool is that with

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Speaker 1: the camera's the same thing. The image is upside down

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Speaker 1: in the camera, it's the same way, and that I

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Speaker 1: actually the image as it's projected onto the retina, that

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Speaker 1: area where all of the photoreceptors are is upside down

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Speaker 1: and it flips because our brain is able to flip

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Speaker 1: that image right side up. So there's so many middlemen

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Speaker 1: happening in our brain to interpret what we're seeing. You

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Speaker 1: can't always trust your eyes to be exact reporters of reality.

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Speaker 1: And there's another layer of similarity there because the evolution

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Speaker 1: of the technology of the camera, as you say, we

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Speaker 1: started with pinhole cameras and then we've got fancy lenses

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Speaker 1: also mirrors, doesn't it the evolution of the eyeball in

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Speaker 1: biology right, like we think that early eyes actually were

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Speaker 1: more like pinhole cameras. Can you take us through roughly,

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Speaker 1: like how do the human eye evolved? Because this is

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Speaker 1: an argument some creation is to use sometime to say

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Speaker 1: that evolution can possibly be reality, because how could you

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Speaker 1: evolve the eyeball? Can you take us through sort of

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Speaker 1: the rough picture of how the eyeball evolved? Yeah, So,

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Speaker 1: first of all, it's funny to me about people who

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Speaker 1: are so skeptical of the eyeball being able to evolve.

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Speaker 1: It's like, not only has it evolved, it's evolved multiple times.

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Speaker 1: So um, actually, cephalopods including octopuses, completely independently evolved their

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Speaker 1: eye from almost every other animal on the planet. And

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Speaker 1: so this is not just some kind of ridiculous look.

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Speaker 1: It does make it seem a little bit more inevitable.

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Speaker 1: So when we were basically flat worms, we would have

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Speaker 1: kind of just like, uh, some cluster of photosensitive cells

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Speaker 1: that could detect light or dark, not really images, just

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Speaker 1: kind of like hey that's light, I go towards it,

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Speaker 1: or this is dark, I go towards it. So at

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Speaker 1: this very basic level, something like a flat worm and

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Speaker 1: the you know, very early ocean could go up towards

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Speaker 1: the sunlight, or recede back down into the darkness, or

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Speaker 1: go towards a spot obscured by the sunlight, maybe some

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Speaker 1: something to eat or something. But it couldn't form like

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Speaker 1: an actual image. But already that's a huge step forward.

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Speaker 1: That's recognizing that the universe around you is filled with

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Speaker 1: useful information, information you were literally blind to before you

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Speaker 1: develop this capacity. And now that you can sense the

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Speaker 1: fact that there are a bunch of photons over here

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Speaker 1: and not a bunch of photons over there, easy, useful

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Speaker 1: always makes me fantasize that we might be able to

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Speaker 1: like develops some new kind of cell that's sensitive to

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Speaker 1: dark matter or neutrinos or something, you know, in the

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Speaker 1: form the basis of seeing the universe in another way, right, like,

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Speaker 1: because we've done that before, we've developed the capacity to

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Speaker 1: see a previously invisible part of the universe anyway. That

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Speaker 1: just gives me hope, you know, for future evolution if

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Speaker 1: we live a few more million years, I think it's

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Speaker 1: definitely possible. Al Right, So how do you go from

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Speaker 1: having cells that can sense the existence of light to

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Speaker 1: you know, forming images and watching TV shows? Well, first,

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Speaker 1: there's something important that's missing with just this cluster of photoreceptors.

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Speaker 1: It's that you don't necessarily understand what direction something is,

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Speaker 1: or what's up and what's down. And so if you

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Speaker 1: actually recede those cells into like a little cave, like

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Speaker 1: a little socket, it matters which way the light is shining,

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Speaker 1: because you've limited the entry point of the light, and

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Speaker 1: now your aim can tell whether the light is coming

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Speaker 1: from up or from down. And then from there, now

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Speaker 1: that you've got basically an empty eye socket with receptors

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Speaker 1: at the back of the socket, once you start to

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Speaker 1: close that opening to the socket, now you're getting that pinhole.

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Speaker 1: So we're getting to the camera obscure apart where you

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Speaker 1: will get this the light. Not only are you able

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Speaker 1: to better tell what direction the light is, not just

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Speaker 1: up and down, but maybe side to side three sixty

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Speaker 1: kind of understanding of where the lights coming from. You

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Speaker 1: could also start to form very simple images because now

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Speaker 1: you're able to actually bend the light such that it

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Speaker 1: can become refracted and hit the back of your eye

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Speaker 1: in this image. I think that's a little counterintuitive that

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Speaker 1: you go from here's a slab where I can see photons,

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Speaker 1: and the step forward is to hide that is, to

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Speaker 1: like bury that inside you so that it's only can

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Speaker 1: be hit by a few photons that happened to pass

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Speaker 1: through like a little hole you make. That's counterintuitive because

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Speaker 1: you're getting less information, it seems like, because you're getting

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Speaker 1: fewer photons, but you're right, it's more information because you're

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Speaker 1: restricting the photons. So now you can tell this photon

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Speaker 1: must have come from up or must have come from down,

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Speaker 1: and based on where it hits on the inside of

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Speaker 1: this cavity, as you say, you can form an image.

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Speaker 1: That's a pretty cool technology. I don't know if I

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Speaker 1: would have thought of that myself. I mean, that is

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Speaker 1: one of the fascinating things about the senses. So much

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Speaker 1: of it isn't just the ability to sense something, but

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Speaker 1: the ability to prune out information, to restrict the information

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Speaker 1: you're getting so that your brain can make sense of

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Speaker 1: what is happening. Because if you're just getting all the

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Speaker 1: information all the time, you can't differentiate it, and so

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Speaker 1: you're not actually going to form a clear picture of

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Speaker 1: what is happening around you. And I think you're right.

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Speaker 1: It's that differentiation that's key. If you're seeing photons on

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Speaker 1: one side of the cavity and not the other. The

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Speaker 1: relative intensity there is what is telling you this source

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Speaker 1: of light is only coming from that direction and not

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Speaker 1: from the other. So it's about like comparative processing of

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Speaker 1: those signals, not just are their photons or not, but

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Speaker 1: like looking at where you're getting the signals and where

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Speaker 1: you're not getting the signals and using that to form

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Speaker 1: like a mental model of what's going on out there

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Speaker 1: in the world. Right, And so as we're tracing this

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Speaker 1: evolution of the eye, now we've got this cave right,

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Speaker 1: this this eyeball shaped cave with this little pinhole now

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Speaker 1: allowing us to see better direction and maybe start to

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Speaker 1: form these very blurry images. And then you can seal

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Speaker 1: that off right to protect the photoreceptors. And however, you

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Speaker 1: need to make sure that that inside of the eye

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Speaker 1: is still fluid filled. We are remember at this point

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Speaker 1: we are marine animals, probably some kind of very early

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Speaker 1: predecessor to uh, some species of fish, and you can't

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Speaker 1: just have an air pocket as an As a fish,

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Speaker 1: you typically want to have your organs filled with fluid.

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Speaker 1: Since your eye has been evolving to be able to

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Speaker 1: refract light in water. If you have the sudden air

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Speaker 1: pocket that's not going to allow you to see, so

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Speaker 1: you actually have this fluid filled I now of this

431
00:25:22,200 --> 00:25:25,119
Speaker 1: vitreous humor, and we actually still have that in the

432
00:25:25,200 --> 00:25:29,080
Speaker 1: human eye. It is not just an empty balloon filled

433
00:25:29,080 --> 00:25:32,240
Speaker 1: with air. It is filled with fluid. And then all

434
00:25:32,280 --> 00:25:35,879
Speaker 1: you need to start to get to the eye of

435
00:25:35,920 --> 00:25:40,440
Speaker 1: a more complex animal that can see more detailed images

436
00:25:41,119 --> 00:25:46,360
Speaker 1: is a lens and a cornea. So once you've started

437
00:25:46,359 --> 00:25:48,200
Speaker 1: to get this lens in that corner, you're able to

438
00:25:48,200 --> 00:25:52,760
Speaker 1: actually focus and make these specific images. And then uh,

439
00:25:53,040 --> 00:25:56,560
Speaker 1: from there, you have so many possibilities opened up to you.

440
00:25:56,600 --> 00:25:59,959
Speaker 1: Even though animals since of vision, can be really different,

441
00:26:00,480 --> 00:26:04,320
Speaker 1: the thing that they all share is they're really useful, uh,

442
00:26:04,359 --> 00:26:08,119
Speaker 1: in terms of their specific evolutionary niche. It's amazing that

443
00:26:08,200 --> 00:26:10,600
Speaker 1: we can reconstruct this story and that along with this

444
00:26:10,680 --> 00:26:13,719
Speaker 1: story gives us a clue about our own history seeing

445
00:26:13,760 --> 00:26:16,400
Speaker 1: things underwater from our great great great great great great

446
00:26:16,400 --> 00:26:19,680
Speaker 1: great great great ancestors, and also helps explain why some

447
00:26:19,760 --> 00:26:22,600
Speaker 1: eyeballs are different from other eyeballs. Here's a nice little

448
00:26:22,600 --> 00:26:26,639
Speaker 1: story from Rachel Martin explaining why fish eyeballs look different

449
00:26:26,760 --> 00:26:30,520
Speaker 1: from ours. When a photon hits your eyeball. You know,

450
00:26:30,640 --> 00:26:33,720
Speaker 1: first it has to go through the cornea and the lens,

451
00:26:34,840 --> 00:26:37,359
Speaker 1: and those things are really important because that's where we

452
00:26:37,400 --> 00:26:41,040
Speaker 1: get a lot of the focusing power, and particularly in

453
00:26:41,280 --> 00:26:44,240
Speaker 1: terrestrial organisms, you know, a lot of the focusing power

454
00:26:44,280 --> 00:26:46,560
Speaker 1: of your eyelands actually comes from that air water interface

455
00:26:46,600 --> 00:26:49,399
Speaker 1: at the cornea. And it's something that we don't necessarily

456
00:26:49,400 --> 00:26:52,880
Speaker 1: think about. And I know when I was a little kid,

457
00:26:53,480 --> 00:26:56,520
Speaker 1: you know, I really liked swimming, and I was really

458
00:26:56,560 --> 00:26:59,760
Speaker 1: sure that if I practiced enough, I would be able

459
00:26:59,800 --> 00:27:03,359
Speaker 1: to see underwater without goggles. And so you know, I

460
00:27:03,359 --> 00:27:05,359
Speaker 1: would try and try and try, and I thought it

461
00:27:05,400 --> 00:27:07,520
Speaker 1: was just you know, I have to keep trying and

462
00:27:07,640 --> 00:27:10,960
Speaker 1: keep practicing. But you know, my eyes are not optimized

463
00:27:11,000 --> 00:27:15,200
Speaker 1: to work underwater because I'm a terrestrial organism and so um.

464
00:27:15,240 --> 00:27:18,320
Speaker 1: You know, so no matter how much do you practice,

465
00:27:18,640 --> 00:27:21,920
Speaker 1: you need that air layer in front of your eye

466
00:27:21,960 --> 00:27:24,360
Speaker 1: for the you know, for the light to be properly

467
00:27:24,520 --> 00:27:27,199
Speaker 1: refracted to make an image. Our eyes are optimized that

468
00:27:27,240 --> 00:27:30,440
Speaker 1: way because you know, the lens is kind of flattened

469
00:27:30,920 --> 00:27:36,480
Speaker 1: and uh also, you know, the distribution of proteins structural

470
00:27:36,480 --> 00:27:39,320
Speaker 1: proteins inside the lens is optimized to work with that

471
00:27:39,400 --> 00:27:42,040
Speaker 1: air water interface at the cornea, whereas if you look

472
00:27:42,080 --> 00:27:47,280
Speaker 1: at a fish is lends, that's usually very spherical. And

473
00:27:47,440 --> 00:27:51,359
Speaker 1: that's because in a fish lens there's no air. Of course,

474
00:27:51,400 --> 00:27:53,480
Speaker 1: the fish is underwater, and so the proteins in that

475
00:27:53,600 --> 00:27:55,159
Speaker 1: lens have to do all the work. And this is

476
00:27:55,200 --> 00:27:58,360
Speaker 1: a really interesting thing too to notice. Next time you're

477
00:27:58,400 --> 00:28:01,879
Speaker 1: at like a public aquarium, you find the biggest fish

478
00:28:01,960 --> 00:28:04,159
Speaker 1: you can and look at their eyes, you can usually

479
00:28:04,160 --> 00:28:06,320
Speaker 1: see the lens. It's you know, it's often you know,

480
00:28:06,400 --> 00:28:09,439
Speaker 1: pretty easy to see in the fish eye, so you

481
00:28:09,440 --> 00:28:11,760
Speaker 1: can see the shapes. All right, So I think now

482
00:28:11,760 --> 00:28:13,879
Speaker 1: we have an understanding of what the eyeball is and

483
00:28:13,920 --> 00:28:16,679
Speaker 1: the basic mechanism and geometry of it. I want to

484
00:28:16,720 --> 00:28:19,960
Speaker 1: dig into the physics of color, what color means, and

485
00:28:20,000 --> 00:28:23,240
Speaker 1: how our eyeballs see these photons. But first let's take

486
00:28:23,440 --> 00:28:38,560
Speaker 1: a quick break. All right, we're back and we're talking

487
00:28:38,600 --> 00:28:42,280
Speaker 1: about eyeballs. We're not eating eyeballs. We're talking about shooting

488
00:28:42,320 --> 00:28:46,040
Speaker 1: photons into eyeballs and thinking about how they respond and

489
00:28:46,120 --> 00:28:48,960
Speaker 1: what that means and what your brain tells you about

490
00:28:49,000 --> 00:28:52,400
Speaker 1: the signals that crawl up the optic nerves O, Katie,

491
00:28:52,440 --> 00:28:55,080
Speaker 1: what color are you surrounded by right now? What color

492
00:28:55,080 --> 00:28:57,680
Speaker 1: are you looking at as we talk about this, I'm

493
00:28:57,720 --> 00:29:01,480
Speaker 1: actually looking at a very lovely shape of teal because

494
00:29:02,320 --> 00:29:08,360
Speaker 1: this apartment has painted in beautiful colors. Um the owner

495
00:29:08,400 --> 00:29:11,640
Speaker 1: of this apartment really loves teal, and so almost all

496
00:29:11,640 --> 00:29:14,160
Speaker 1: the walls are painted teal. It's it's very nice. I'm

497
00:29:14,200 --> 00:29:17,920
Speaker 1: not complaining. It's just you can really tell he loves

498
00:29:18,080 --> 00:29:22,239
Speaker 1: he loved teal, the guy who painted this apartment. My

499
00:29:22,320 --> 00:29:25,200
Speaker 1: daughter Hazel loves teal also, and she loves a very

500
00:29:25,200 --> 00:29:28,680
Speaker 1: particular shade of it. And for me, I'm like, well,

501
00:29:28,720 --> 00:29:30,520
Speaker 1: it's all just sort of this blue, and she's like,

502
00:29:30,520 --> 00:29:33,120
Speaker 1: oh my god, it's not just all blue, Like this

503
00:29:33,160 --> 00:29:35,360
Speaker 1: is blue and that's teal and this is something else

504
00:29:35,440 --> 00:29:42,000
Speaker 1: and monster. It's interesting to me that we do have

505
00:29:42,040 --> 00:29:45,040
Speaker 1: this very rich experience of color. You know that we

506
00:29:45,120 --> 00:29:48,280
Speaker 1: have a very different reaction to photons of one frequency

507
00:29:48,440 --> 00:29:50,560
Speaker 1: and another. So I think it's important that we dig

508
00:29:50,560 --> 00:29:53,080
Speaker 1: into what that means, what the physics is of it,

509
00:29:53,120 --> 00:29:55,160
Speaker 1: why it is that some photons give us a different

510
00:29:55,200 --> 00:29:58,200
Speaker 1: reaction from other colors. When I was a kid and

511
00:29:58,240 --> 00:30:01,760
Speaker 1: I learned there were only three to front wavelengths of white.

512
00:30:02,360 --> 00:30:05,120
Speaker 1: It was really bewildering because it's like, Okay, how do

513
00:30:05,240 --> 00:30:08,040
Speaker 1: we see so many different colors than if we there

514
00:30:08,040 --> 00:30:12,360
Speaker 1: are only these three wavelengths of why you would think

515
00:30:12,400 --> 00:30:16,480
Speaker 1: we would only see like red or green or blue. Yeah,

516
00:30:16,480 --> 00:30:19,040
Speaker 1: that's really interesting. And of course there are more than

517
00:30:19,080 --> 00:30:22,040
Speaker 1: just three wavelengths of light, all right, There are an

518
00:30:22,080 --> 00:30:25,840
Speaker 1: infinite number. So in the end, what is light? Light

519
00:30:25,880 --> 00:30:30,040
Speaker 1: are these little packets of energy, these photon, these quantized

520
00:30:30,120 --> 00:30:34,280
Speaker 1: little wiggles in the electromagnetic field. So the electromagnetic field

521
00:30:34,280 --> 00:30:37,280
Speaker 1: is something that fills all of space. The whole universe

522
00:30:37,400 --> 00:30:39,680
Speaker 1: has the field in it, and when there's energy in

523
00:30:39,720 --> 00:30:41,760
Speaker 1: the field, they can travel through that field. It consort

524
00:30:41,800 --> 00:30:45,080
Speaker 1: of like wiggle. Imagine like a guitar string and you're

525
00:30:45,080 --> 00:30:47,840
Speaker 1: sending a pulse along it. That's a photon. It's a

526
00:30:47,840 --> 00:30:50,920
Speaker 1: wiggle in the electromagnetic field. And it's a very special

527
00:30:51,000 --> 00:30:53,680
Speaker 1: kind of wiggle because it's self perpetuating. You know, it

528
00:30:53,720 --> 00:30:56,160
Speaker 1: can exist and then it can zoom across the universe

529
00:30:56,160 --> 00:30:59,080
Speaker 1: and exists somewhere else. It doesn't like the fuse or

530
00:30:59,120 --> 00:31:02,400
Speaker 1: spread out. It's like persistent and discreet, and that's in

531
00:31:02,440 --> 00:31:05,040
Speaker 1: the end, what we call a particle. All particles that

532
00:31:05,080 --> 00:31:07,800
Speaker 1: we see and experience in the universe are these little

533
00:31:07,840 --> 00:31:12,640
Speaker 1: discretized wiggles in quantum fields. Now people think about photons

534
00:31:12,760 --> 00:31:16,560
Speaker 1: as photons, as quantum particles, as discreet, and it's true

535
00:31:16,600 --> 00:31:18,960
Speaker 1: that they are quantized. Like you can have one photon

536
00:31:19,320 --> 00:31:22,880
Speaker 1: or two photons or seventy four photons. You can't have

537
00:31:23,040 --> 00:31:26,560
Speaker 1: one and a half photons or one point seven two photons.

538
00:31:26,880 --> 00:31:30,120
Speaker 1: You can only have integer numbers of photons. For those

539
00:31:30,120 --> 00:31:31,800
Speaker 1: of you curious about the physics of it and how

540
00:31:31,800 --> 00:31:34,320
Speaker 1: it is discovered, we have a whole podcast episode about

541
00:31:34,440 --> 00:31:38,080
Speaker 1: the photoelectric effect and how Einstein realized that photons came

542
00:31:38,120 --> 00:31:41,680
Speaker 1: in these little numbered packets. But there's another really important

543
00:31:41,680 --> 00:31:45,120
Speaker 1: fact about each photon, and that's its energy, and that's

544
00:31:45,120 --> 00:31:48,960
Speaker 1: something that is not quantized. So a single photon can

545
00:31:49,000 --> 00:31:53,480
Speaker 1: have any energy, meaning to have any wavelength. So typical

546
00:31:53,600 --> 00:31:56,240
Speaker 1: visible light is like four hundred to six hundred and

547
00:31:56,240 --> 00:31:59,960
Speaker 1: fifty nanometers, but there's an infinite number of different way

548
00:32:00,120 --> 00:32:03,080
Speaker 1: links between four hundred and six fifty. Just because of

549
00:32:03,120 --> 00:32:07,240
Speaker 1: photon is quantized doesn't mean it's energy levels are quantized.

550
00:32:07,400 --> 00:32:10,440
Speaker 1: So if there's an infinite number of frequencies. Would that

551
00:32:10,520 --> 00:32:13,520
Speaker 1: mean there are an infinite number of colors? Great question

552
00:32:13,560 --> 00:32:15,960
Speaker 1: and a really deep philosophy question, And the way I

553
00:32:16,000 --> 00:32:19,000
Speaker 1: think about it is that photons don't have colors. Color

554
00:32:19,120 --> 00:32:22,160
Speaker 1: is your brain's interpretation of the signals that it's getting.

555
00:32:22,200 --> 00:32:24,479
Speaker 1: There are an infinite number of different photons with an

556
00:32:24,480 --> 00:32:28,360
Speaker 1: infinite number of different frequencies, right, But those frequencies don't

557
00:32:28,360 --> 00:32:31,320
Speaker 1: necessarily all have a color assigned to them. The color

558
00:32:31,400 --> 00:32:34,280
Speaker 1: is something that your brain does, assigning it to the

559
00:32:34,320 --> 00:32:38,120
Speaker 1: response of the optical nerve. But in theory, if you

560
00:32:38,240 --> 00:32:43,000
Speaker 1: get enough living organisms that have some kind of eyeball

561
00:32:43,680 --> 00:32:47,000
Speaker 1: and some kind of brain that can detect some kind

562
00:32:47,040 --> 00:32:51,760
Speaker 1: of frequencies, we get enough, including all life on Earth

563
00:32:51,760 --> 00:32:55,360
Speaker 1: and probably a bunch of aliens, could we all perceive

564
00:32:56,040 --> 00:33:02,000
Speaker 1: infinite colors. It's a great question of neurology and philosophy

565
00:33:02,040 --> 00:33:05,000
Speaker 1: that I don't know the answer to, and you know,

566
00:33:05,080 --> 00:33:07,640
Speaker 1: we don't know the answer to even more basic questions

567
00:33:07,720 --> 00:33:10,840
Speaker 1: like is the red that you perceive the same read

568
00:33:10,920 --> 00:33:13,320
Speaker 1: as I perceive. It's a really old question that people

569
00:33:13,320 --> 00:33:16,640
Speaker 1: have been asking since they've been smoking bananappeals around the campfire,

570
00:33:16,800 --> 00:33:19,400
Speaker 1: and one that we still don't have an answer to.

571
00:33:19,720 --> 00:33:21,680
Speaker 1: And I think it's a great kind of question because

572
00:33:21,680 --> 00:33:25,680
Speaker 1: it shows us so the limitations of science. People think

573
00:33:25,680 --> 00:33:28,960
Speaker 1: about sciences maybe all powerful ways to reveal the nature

574
00:33:29,000 --> 00:33:32,040
Speaker 1: of the universe, and science is very powerful, but not

575
00:33:32,160 --> 00:33:36,600
Speaker 1: every question is necessarily a scientific question. You can't conduct

576
00:33:36,600 --> 00:33:39,320
Speaker 1: an experiment or come up with a theory that helps

577
00:33:39,360 --> 00:33:42,520
Speaker 1: you probe it, then science isn't necessarily the best tool.

578
00:33:42,960 --> 00:33:45,320
Speaker 1: And so the question of like is your red the

579
00:33:45,360 --> 00:33:49,720
Speaker 1: same as my red, relies purely on our subjective experiences,

580
00:33:49,760 --> 00:33:52,520
Speaker 1: which we can't translate from my brain to your brain,

581
00:33:52,640 --> 00:33:54,240
Speaker 1: so we have no way of knowing. I can't like,

582
00:33:54,600 --> 00:33:57,920
Speaker 1: measure the redness of your experience. So some of these

583
00:33:57,960 --> 00:34:00,760
Speaker 1: really deep and fascinating questions are for us treadingly just

584
00:34:00,800 --> 00:34:03,240
Speaker 1: past the fingertips of science. Well, I have a really

585
00:34:03,240 --> 00:34:05,880
Speaker 1: easy answer to that, and that my red is a

586
00:34:06,160 --> 00:34:11,480
Speaker 1: fire truck red. So question solved exactly when we point

587
00:34:11,480 --> 00:34:13,440
Speaker 1: to a fire truck and we say that's red. We

588
00:34:13,520 --> 00:34:16,200
Speaker 1: of course don't know what you're seeing and what I'm seeing.

589
00:34:16,239 --> 00:34:19,400
Speaker 1: If that actually looks like teal to my daughter, we'll see.

590
00:34:19,760 --> 00:34:22,280
Speaker 1: Let's go through a little bit the mechanism of how

591
00:34:22,320 --> 00:34:25,359
Speaker 1: your eye can tell which photons have hit it, like

592
00:34:25,440 --> 00:34:28,719
Speaker 1: which frequencies of light are hitting it. But before we

593
00:34:28,760 --> 00:34:31,400
Speaker 1: do that, let's just remind ourselves, like why are there

594
00:34:31,440 --> 00:34:34,239
Speaker 1: different frequencies? You know? Why is it that the fire

595
00:34:34,280 --> 00:34:37,880
Speaker 1: truck is red and blueberries are blue, and that leaves

596
00:34:37,880 --> 00:34:40,680
Speaker 1: are green and the sky is blue. Why are there

597
00:34:40,680 --> 00:34:43,520
Speaker 1: these different colors in our world? And the fundamental level

598
00:34:43,560 --> 00:34:47,600
Speaker 1: of reason from physics is to one is that sometimes

599
00:34:47,680 --> 00:34:51,920
Speaker 1: things get hot and hot things and glow at different temperatures.

600
00:34:51,960 --> 00:34:54,279
Speaker 1: Like the reason that we get light from the sun

601
00:34:54,400 --> 00:34:56,839
Speaker 1: is because the Sun is super duper hot, and as

602
00:34:56,880 --> 00:34:59,600
Speaker 1: things get hotter, they tend to emit light in higher

603
00:34:59,640 --> 00:35:03,200
Speaker 1: freak and see photons. So things that are cold in

604
00:35:03,320 --> 00:35:06,640
Speaker 1: midlight in the infrared, things that are warmer in mid

605
00:35:06,760 --> 00:35:09,200
Speaker 1: light in the visible like the sun. Things that are

606
00:35:09,239 --> 00:35:13,439
Speaker 1: super duper hot like accretion disks around black holes, emit

607
00:35:13,600 --> 00:35:16,239
Speaker 1: light in the ultraviolet or even up to the X

608
00:35:16,360 --> 00:35:19,480
Speaker 1: rays and gamma rays. These are all just different frequencies

609
00:35:19,520 --> 00:35:22,560
Speaker 1: along the electromagnetic spectrum. Is this is why when you

610
00:35:22,680 --> 00:35:26,680
Speaker 1: have a fire, you have sort of a really really

611
00:35:26,719 --> 00:35:29,960
Speaker 1: hot fire, it's going to be like white hot versus

612
00:35:30,080 --> 00:35:32,799
Speaker 1: orange hot. And blue hot exactly. And if you are

613
00:35:32,840 --> 00:35:36,000
Speaker 1: an amateur at home black smith, you know that white

614
00:35:36,000 --> 00:35:38,920
Speaker 1: hot and red hot are different temperatures of your steel.

615
00:35:38,960 --> 00:35:41,520
Speaker 1: That's something people have known for thousands of years before

616
00:35:41,520 --> 00:35:44,920
Speaker 1: we understood the physics involved. Right, that's like folk physics.

617
00:35:45,160 --> 00:35:47,680
Speaker 1: It's pretty cool. And the other way that color comes

618
00:35:47,680 --> 00:35:52,239
Speaker 1: into play physically isn't how materials absorb and reflect color. Like,

619
00:35:52,280 --> 00:35:55,000
Speaker 1: if you're looking at an object and it's red, it's

620
00:35:55,040 --> 00:35:58,560
Speaker 1: because you're getting red photons. You're getting photons of a

621
00:35:58,600 --> 00:36:01,120
Speaker 1: frequency that your brain is signed to. The color red

622
00:36:01,280 --> 00:36:04,399
Speaker 1: to your eyeball from that object, I say it's being

623
00:36:04,480 --> 00:36:07,440
Speaker 1: hit by white light. Light from the sun tends to

624
00:36:07,480 --> 00:36:10,120
Speaker 1: cover the whole visible spectrum. The reason you see it

625
00:36:10,160 --> 00:36:13,760
Speaker 1: is red is not because it's absorbing red. Right, doesn't

626
00:36:13,840 --> 00:36:16,800
Speaker 1: get red from the red photons. It's because it's absorbing

627
00:36:16,880 --> 00:36:20,280
Speaker 1: everything but red, and only the red light is getting

628
00:36:20,320 --> 00:36:23,279
Speaker 1: reflected to your eyeball. Right, A general thing with our

629
00:36:23,400 --> 00:36:28,120
Speaker 1: senses is anything you sense, from hearing to vision has

630
00:36:28,160 --> 00:36:32,160
Speaker 1: to physically hit you. Like your eyes have to be

631
00:36:32,320 --> 00:36:36,919
Speaker 1: physically smacked by photons for you to see them. Your

632
00:36:36,960 --> 00:36:41,440
Speaker 1: ears have to be physically smacked by sound. Waves. It's like,

633
00:36:41,800 --> 00:36:44,319
Speaker 1: you know our sense of touch. We understand you have

634
00:36:44,400 --> 00:36:47,120
Speaker 1: to physically touch something to feel it, but it's the

635
00:36:47,200 --> 00:36:49,319
Speaker 1: same thing with our eyes and our ears, even if

636
00:36:49,320 --> 00:36:51,680
Speaker 1: it doesn't feel that way, because you don't have to

637
00:36:52,080 --> 00:36:54,839
Speaker 1: press a leaf to your eye to see that it's green,

638
00:36:55,480 --> 00:36:59,799
Speaker 1: but you are technically feeling that leaf with your eye

639
00:37:00,000 --> 00:37:03,799
Speaker 1: all because the photons that are bouncing from the leaf

640
00:37:03,840 --> 00:37:07,480
Speaker 1: are hitting your eyeball physically. And that's exactly why things

641
00:37:07,480 --> 00:37:10,840
Speaker 1: that look green are things that reflect green, not things

642
00:37:10,880 --> 00:37:14,160
Speaker 1: that absorb green. Like if you eat a bunch of blueberries,

643
00:37:14,360 --> 00:37:16,520
Speaker 1: it makes you blue on the inside. You might think

644
00:37:16,640 --> 00:37:18,200
Speaker 1: that's the same way it works for light, but the

645
00:37:18,239 --> 00:37:21,239
Speaker 1: reason blueberries are blue is because they reflect blue, they

646
00:37:21,239 --> 00:37:26,080
Speaker 1: don't absorb blue. Isn't that why black things like a

647
00:37:26,160 --> 00:37:29,640
Speaker 1: black shirt gets really hot in the sun because it's

648
00:37:29,800 --> 00:37:33,319
Speaker 1: not it's not that it's absorbing black, which you can't

649
00:37:33,400 --> 00:37:36,640
Speaker 1: really absorb black, because black is just the absence of light.

650
00:37:37,120 --> 00:37:40,520
Speaker 1: It's absorbing that white light, which is a really high

651
00:37:40,600 --> 00:37:43,279
Speaker 1: energy light, which makes it hot. And that's why in

652
00:37:43,320 --> 00:37:46,719
Speaker 1: the desert people wear white because white is more reflective,

653
00:37:46,760 --> 00:37:50,080
Speaker 1: it doesn't absorb as many photons as black. Does, and

654
00:37:50,120 --> 00:37:53,120
Speaker 1: so that's why snow, for example, doesn't melt unless it

655
00:37:53,120 --> 00:37:55,960
Speaker 1: gets dirty. When snow gets dirty, it absorbs more light

656
00:37:56,000 --> 00:37:59,000
Speaker 1: and then it melts. But pure crystal white snow can

657
00:37:59,040 --> 00:38:01,680
Speaker 1: reflect a lot of on light and doesn't melt as quickly.

658
00:38:01,760 --> 00:38:04,680
Speaker 1: And you can actually get sunburned from the reflections of

659
00:38:04,760 --> 00:38:07,640
Speaker 1: snow because it's reflecting a lot of light at you.

660
00:38:08,080 --> 00:38:12,080
Speaker 1: And I learned this while skiing. You can get sunburned

661
00:38:12,120 --> 00:38:16,040
Speaker 1: on the bottom of your nose. Yes, it's fun exactly.

662
00:38:16,120 --> 00:38:19,160
Speaker 1: So now let's trace those photons into your eyes. You say,

663
00:38:19,200 --> 00:38:21,840
Speaker 1: they go through the cornea and the iris and the lens,

664
00:38:22,080 --> 00:38:24,000
Speaker 1: and they hit the retina. And what's going on on

665
00:38:24,080 --> 00:38:26,760
Speaker 1: the retina that allows you to see these things. Well, essentially,

666
00:38:26,840 --> 00:38:30,400
Speaker 1: you have a huge number of sensors, millions and millions

667
00:38:30,440 --> 00:38:33,440
Speaker 1: of these sensors of two kinds. You have the rods

668
00:38:33,560 --> 00:38:36,040
Speaker 1: and you have the cones. Rods are really good at

669
00:38:36,080 --> 00:38:39,120
Speaker 1: seeing small numbers of photons. They're good at seeing in

670
00:38:39,160 --> 00:38:41,279
Speaker 1: the dark, but you only have one kind of them,

671
00:38:41,600 --> 00:38:43,840
Speaker 1: and so they basically just say like yes or no.

672
00:38:44,239 --> 00:38:46,800
Speaker 1: The cones, however, you have three kinds of those, and

673
00:38:46,840 --> 00:38:49,279
Speaker 1: you refer to them earlier as blue, green, and red.

674
00:38:49,440 --> 00:38:52,040
Speaker 1: And the reason we call them that sometimes is because

675
00:38:52,040 --> 00:38:54,880
Speaker 1: they're good at seeing different frequencies of light. It's not

676
00:38:54,920 --> 00:38:57,400
Speaker 1: like they can only see one frequency. There's sort of

677
00:38:57,440 --> 00:38:59,000
Speaker 1: like a width to it. If you look at a

678
00:38:59,000 --> 00:39:02,359
Speaker 1: graph of like how likely one of these cones is

679
00:39:02,760 --> 00:39:05,800
Speaker 1: to see a photon of a different frequency, you see

680
00:39:05,840 --> 00:39:09,200
Speaker 1: that the ones we call s for short wavelength, the

681
00:39:09,200 --> 00:39:12,040
Speaker 1: ones that see blue light, peeking about four hundred and twenty,

682
00:39:12,160 --> 00:39:14,960
Speaker 1: but they can still see four hundred fifty nanimeter photons.

683
00:39:15,120 --> 00:39:18,040
Speaker 1: They're less likely to see five hundred and almost impossible

684
00:39:18,080 --> 00:39:19,759
Speaker 1: for them to see six hundred, but you know it

685
00:39:19,800 --> 00:39:23,239
Speaker 1: never goes to zero. And the red ones, the ones

686
00:39:23,320 --> 00:39:27,080
Speaker 1: we call long cones, those peaking about five hundred and

687
00:39:27,120 --> 00:39:30,120
Speaker 1: sixteen nanimeters, but they could still see a photon at

688
00:39:30,120 --> 00:39:33,319
Speaker 1: four fifties, just less likely. So they're like good at

689
00:39:33,360 --> 00:39:37,120
Speaker 1: different kinds of things. They're more likely or less likely

690
00:39:37,160 --> 00:39:40,000
Speaker 1: to see photons at different frequencies. And that's what your

691
00:39:40,000 --> 00:39:43,040
Speaker 1: brain is pulling together to say, oh, we're seeing something

692
00:39:43,080 --> 00:39:45,880
Speaker 1: that's red because it's tends to be lighting up the

693
00:39:45,960 --> 00:39:48,719
Speaker 1: long cones and not the short cones, or oh we're

694
00:39:48,719 --> 00:39:51,239
Speaker 1: looking at something that deal because it tends to be

695
00:39:51,320 --> 00:39:53,719
Speaker 1: lighting up their short cones and not the medium or

696
00:39:53,800 --> 00:39:56,720
Speaker 1: long cones as much. So there's a lot of interpretation.

697
00:39:56,760 --> 00:39:58,880
Speaker 1: They're just like back when you were talking about how

698
00:39:58,920 --> 00:40:02,320
Speaker 1: the eye evolved, and you're explaining how we have a cave,

699
00:40:02,680 --> 00:40:05,400
Speaker 1: and we're deducing where the light came from based on

700
00:40:05,640 --> 00:40:07,440
Speaker 1: where we are seeing light and where we are not.

701
00:40:07,600 --> 00:40:09,680
Speaker 1: Now we're deducing the color of the source of that

702
00:40:09,800 --> 00:40:12,440
Speaker 1: light based on which cones are lighting up and which

703
00:40:12,440 --> 00:40:17,920
Speaker 1: cones are not. And it's the relative excitement of the cones,

704
00:40:18,200 --> 00:40:22,160
Speaker 1: like if something's getting really lit up versus a little

705
00:40:22,200 --> 00:40:25,320
Speaker 1: bit lit up. That allows us to tell the difference

706
00:40:25,320 --> 00:40:30,080
Speaker 1: between bluish green and a greenish blue exactly. And there's

707
00:40:30,120 --> 00:40:32,719
Speaker 1: a lot of analysis there that's going on in your head.

708
00:40:32,920 --> 00:40:35,480
Speaker 1: And so I was curious, like how this actually works.

709
00:40:35,840 --> 00:40:38,680
Speaker 1: Why is it that this cone is better at that

710
00:40:38,760 --> 00:40:41,319
Speaker 1: frequency of light and this other cone is better at

711
00:40:41,360 --> 00:40:43,840
Speaker 1: the other frequency of light. What is the real mechanism

712
00:40:43,960 --> 00:40:46,440
Speaker 1: of it? So I asked the professor Martin to explain

713
00:40:46,480 --> 00:40:48,759
Speaker 1: to us what is actually happening when photons hit these

714
00:40:48,760 --> 00:40:52,600
Speaker 1: sensitive cells. And here's her explanation. The rods have ward

715
00:40:52,640 --> 00:40:55,800
Speaker 1: option and then the cones have they're just called options,

716
00:40:56,760 --> 00:41:00,319
Speaker 1: and these are proteins that undergo a confirmational chan change

717
00:41:00,640 --> 00:41:03,080
Speaker 1: when a photon hits them. And so the photon hits

718
00:41:03,080 --> 00:41:06,720
Speaker 1: the protein and then it's confirmation changes and that sends

719
00:41:06,719 --> 00:41:09,719
Speaker 1: a signal inside the cell. That is what transmits the

720
00:41:09,760 --> 00:41:12,759
Speaker 1: signal for that detection to our brains. I have an

721
00:41:12,840 --> 00:41:15,720
Speaker 1: understanding of a protein is like a little molecular machine,

722
00:41:16,200 --> 00:41:18,319
Speaker 1: and you're saying it can absorb a single photon and

723
00:41:18,320 --> 00:41:22,240
Speaker 1: that like chunks over mechanically from like one physical shape

724
00:41:22,239 --> 00:41:25,600
Speaker 1: to another physical shape, and that reflects having absorbed that energy.

725
00:41:25,640 --> 00:41:28,000
Speaker 1: And then something detects that the protein has shifted, is

726
00:41:28,000 --> 00:41:30,600
Speaker 1: that a little lever has been pushed by thee. Isn't

727
00:41:30,640 --> 00:41:33,759
Speaker 1: that amazing? So so it undergoes a conformational change, and

728
00:41:33,800 --> 00:41:37,040
Speaker 1: then something on the other side of the cell transmits

729
00:41:37,040 --> 00:41:39,200
Speaker 1: a signal and then that's some you know, that's how

730
00:41:39,239 --> 00:41:42,080
Speaker 1: your brain detects that that you saw that photon. And

731
00:41:42,080 --> 00:41:45,319
Speaker 1: the rods and cones are different in the proteins that

732
00:41:45,360 --> 00:41:47,719
Speaker 1: can absorb the photons, so they're can absorb photons of

733
00:41:47,760 --> 00:41:50,720
Speaker 1: different frequencies because it's a different protein they absorbed photons

734
00:41:50,719 --> 00:41:53,319
Speaker 1: at different frequencies, and the and the reason that they

735
00:41:53,320 --> 00:41:55,760
Speaker 1: have that difference in absorption is all about the protein.

736
00:41:55,840 --> 00:41:58,000
Speaker 1: So it's about the specifics of the you know, the

737
00:41:58,040 --> 00:42:01,400
Speaker 1: amino acid sequence and the structure of the protein. And

738
00:42:01,400 --> 00:42:03,759
Speaker 1: so why is it that the cones can't respond to

739
00:42:03,800 --> 00:42:06,280
Speaker 1: a single photon? Like do they need five or seven?

740
00:42:06,440 --> 00:42:08,880
Speaker 1: Is it because that lever and the protein is harder

741
00:42:08,920 --> 00:42:11,680
Speaker 1: to push? So, yeah, the rood option is the most

742
00:42:11,800 --> 00:42:16,080
Speaker 1: sensitive one. But like that's kind of a weak answer, right,

743
00:42:16,120 --> 00:42:17,719
Speaker 1: Like why is it the most sensitive one? I'm not

744
00:42:17,760 --> 00:42:20,200
Speaker 1: actually sure. Well, speaking of mysteries of the eye, what

745
00:42:20,280 --> 00:42:23,040
Speaker 1: are some sort of frontiers of research? Is there any

746
00:42:23,120 --> 00:42:25,239
Speaker 1: unknown physics that's happening in the eye, or there any

747
00:42:25,280 --> 00:42:28,879
Speaker 1: processes that go on that we don't understand funds? So,

748
00:42:29,000 --> 00:42:31,400
Speaker 1: for one thing, a really active area of research is

749
00:42:31,440 --> 00:42:35,880
Speaker 1: just how do the rhodoptions work? Because um, this is

750
00:42:35,880 --> 00:42:39,480
Speaker 1: one of the fastest known processes in biology, like the

751
00:42:39,520 --> 00:42:42,320
Speaker 1: early steps of what happens when a photon hits that

752
00:42:42,440 --> 00:42:45,800
Speaker 1: rhodopson So I mentioned that it undergoes a confirmational change,

753
00:42:45,800 --> 00:42:48,640
Speaker 1: So it actually has a small molecule that's bound inside

754
00:42:48,680 --> 00:42:52,520
Speaker 1: the protein. That's it's a retinal and it changes confirmation,

755
00:42:53,239 --> 00:42:56,040
Speaker 1: so you know, it goes from like a bent confirmation

756
00:42:56,080 --> 00:42:58,920
Speaker 1: to a straight confirmation. That's what makes the protein undergo

757
00:42:58,960 --> 00:43:03,400
Speaker 1: the confirmational change. But the first steps of that happened

758
00:43:03,480 --> 00:43:06,160
Speaker 1: really really fast, and so you need you need a

759
00:43:06,200 --> 00:43:08,080
Speaker 1: fast laser to be able to study it, and you

760
00:43:08,120 --> 00:43:10,480
Speaker 1: also need to do the whole thing in the dark. Alright,

761
00:43:10,480 --> 00:43:13,480
Speaker 1: So I thought that was super cool that basically we

762
00:43:13,520 --> 00:43:17,800
Speaker 1: have these proteins inside these rods and cones that change

763
00:43:17,800 --> 00:43:21,040
Speaker 1: configuration when a photon hits them. My mental picture is

764
00:43:21,080 --> 00:43:23,480
Speaker 1: like we have a little machine there. I think of

765
00:43:23,560 --> 00:43:27,320
Speaker 1: proteins is little machines, and like the photon like shifts

766
00:43:27,360 --> 00:43:30,680
Speaker 1: a lever, like you know, flips a switch almost physically.

767
00:43:30,719 --> 00:43:33,440
Speaker 1: That's incredible. Do you like to watch videos of Rube

768
00:43:33,440 --> 00:43:38,239
Speaker 1: Goldberg machines. It's like when you have a marble hit

769
00:43:38,280 --> 00:43:41,359
Speaker 1: a thing and then that releases a domino, and then

770
00:43:41,480 --> 00:43:45,120
Speaker 1: soon you've got a teapot boiling, and then that pops

771
00:43:45,160 --> 00:43:47,759
Speaker 1: a balloon and then a hammer lands on a lever.

772
00:43:48,400 --> 00:43:51,440
Speaker 1: That's how I like to visualize a lot of these

773
00:43:51,560 --> 00:43:56,040
Speaker 1: complex cellular processes, and that is very true of how

774
00:43:56,280 --> 00:43:59,600
Speaker 1: these rods and cones work so like you have a

775
00:44:00,040 --> 00:44:04,440
Speaker 1: photon literally hit like a little ever, it's changing the

776
00:44:04,600 --> 00:44:11,759
Speaker 1: molecules shape, which triggers a cascade of responses inside of

777
00:44:11,800 --> 00:44:15,360
Speaker 1: the cell. But you can visualize like a Rube Goldberg

778
00:44:15,440 --> 00:44:18,239
Speaker 1: machine or like a domino effect. And it's not just

779
00:44:18,320 --> 00:44:20,799
Speaker 1: something that happens once and then somebody spends like three

780
00:44:20,800 --> 00:44:23,080
Speaker 1: hours setting it up again, and not just response to

781
00:44:23,120 --> 00:44:26,680
Speaker 1: a photon and then unresponds and gets ready for another photon,

782
00:44:27,000 --> 00:44:30,759
Speaker 1: sometimes like milliseconds later. Right, Rachel was saying, this is

783
00:44:30,800 --> 00:44:34,560
Speaker 1: one of the fastest processes we know of in biology. Yeah,

784
00:44:34,600 --> 00:44:38,120
Speaker 1: and it is interesting because as fast as your cells

785
00:44:38,200 --> 00:44:41,640
Speaker 1: can be in responding to this, you can also overload

786
00:44:41,719 --> 00:44:45,759
Speaker 1: your cells if they're too sensitive, which is also it's

787
00:44:45,800 --> 00:44:48,479
Speaker 1: not just happening on the cellular level. This is something

788
00:44:48,520 --> 00:44:52,080
Speaker 1: that happens inside the brain. So as you're getting this

789
00:44:52,200 --> 00:44:55,440
Speaker 1: information right, because these sensors are sensing it and sending

790
00:44:55,480 --> 00:44:58,359
Speaker 1: that information to the brain, But it doesn't just go

791
00:44:58,480 --> 00:45:00,760
Speaker 1: directly to brain and say hey, look at this color.

792
00:45:01,320 --> 00:45:04,279
Speaker 1: It has to activate your neurons and then that's a

793
00:45:04,320 --> 00:45:07,640
Speaker 1: whole other roup Goldberg machine that happens at the neural level,

794
00:45:07,760 --> 00:45:11,160
Speaker 1: and you may have some threshold of activation for these neurons,

795
00:45:11,200 --> 00:45:14,560
Speaker 1: and so you get some really weird things that happened

796
00:45:14,640 --> 00:45:18,840
Speaker 1: with this interplay between the sensitivity of your photoreceptors in

797
00:45:18,880 --> 00:45:21,520
Speaker 1: your eye and the sensitivity of your neurons and your

798
00:45:21,560 --> 00:45:24,439
Speaker 1: occipital lobe, the vision center of the brain. And that's

799
00:45:24,440 --> 00:45:27,000
Speaker 1: why if you like stare at a bright color and

800
00:45:27,000 --> 00:45:28,719
Speaker 1: then you look at the wall, you see this like

801
00:45:28,840 --> 00:45:32,480
Speaker 1: weird afterimage. So it's a really interesting, I guess, just

802
00:45:32,800 --> 00:45:37,279
Speaker 1: thinking about these little, tiny machines working really hard, but

803
00:45:37,360 --> 00:45:39,600
Speaker 1: it's happening so quickly. It's the kind of thing that

804
00:45:39,640 --> 00:45:42,520
Speaker 1: makes you amaze that it ever works, and suddenly doubt

805
00:45:42,520 --> 00:45:44,800
Speaker 1: that it will continue to. You know, whenever I learned

806
00:45:44,840 --> 00:45:48,000
Speaker 1: how delicate these things are inside my body, I'm immediately terrified, like,

807
00:45:48,040 --> 00:45:50,760
Speaker 1: oh my gosh, what's how has this thing been going

808
00:45:50,800 --> 00:45:53,400
Speaker 1: for so long? Isn't it about to just fall apart?

809
00:45:53,640 --> 00:45:56,400
Speaker 1: But it's amazing it really works. Something was really interesting

810
00:45:56,440 --> 00:45:59,840
Speaker 1: to me was thinking about why the cones are sensitive

811
00:45:59,880 --> 00:46:03,120
Speaker 1: to different frequencies, and it's because they have different proteins

812
00:46:03,160 --> 00:46:06,400
Speaker 1: inside them which are better or worse at absorbing photons

813
00:46:06,440 --> 00:46:10,200
Speaker 1: of different frequencies, and why the rods are more sensitive

814
00:46:10,200 --> 00:46:13,880
Speaker 1: than the cones. Why make cones less sensitive than rods

815
00:46:14,080 --> 00:46:16,960
Speaker 1: and why make rods more sensitive than cones. I think

816
00:46:17,000 --> 00:46:19,680
Speaker 1: the answer is just diversification. Like you want to do

817
00:46:19,719 --> 00:46:21,759
Speaker 1: two different things. One is you want to be able

818
00:46:21,760 --> 00:46:23,719
Speaker 1: to see in low light conditions, and the others you

819
00:46:23,719 --> 00:46:25,359
Speaker 1: want to be able to see color so you can

820
00:46:25,600 --> 00:46:28,439
Speaker 1: spot that fruit or spot that predator. And being able

821
00:46:28,480 --> 00:46:32,040
Speaker 1: to see in low light conditions is actually somewhat mutually

822
00:46:32,120 --> 00:46:35,319
Speaker 1: exclusive to being able to see in higher light conditions,

823
00:46:35,360 --> 00:46:39,719
Speaker 1: because that requires your rods to be really, really sensitive

824
00:46:39,800 --> 00:46:43,000
Speaker 1: to light. And the more sensitive they are to light,

825
00:46:43,200 --> 00:46:47,080
Speaker 1: the more hyperactive they'll be when you have too much lights.

826
00:46:47,080 --> 00:46:51,440
Speaker 1: So your rods aren't that useful in highlight conditions, but

827
00:46:51,520 --> 00:46:54,319
Speaker 1: they're really useful in low light conditions. That's why if

828
00:46:54,360 --> 00:46:58,080
Speaker 1: you've ever stepped from a bright theater lobby into a

829
00:46:58,200 --> 00:47:01,360
Speaker 1: dark movie theater, you can't see where you're going and

830
00:47:01,440 --> 00:47:03,400
Speaker 1: you fall over and you land in a puddle of

831
00:47:03,719 --> 00:47:08,280
Speaker 1: coke and popcorn. Uh, it's because your eyes haven't adjusted

832
00:47:08,320 --> 00:47:11,440
Speaker 1: to the dark. But then as those rods kind of

833
00:47:11,480 --> 00:47:15,920
Speaker 1: like calm down, they adjust to that low light of

834
00:47:16,040 --> 00:47:18,840
Speaker 1: the dark room, and you can actually see in the dark.

835
00:47:19,120 --> 00:47:23,759
Speaker 1: And so yeah, the the rods being hyper sensitive is

836
00:47:23,840 --> 00:47:26,680
Speaker 1: useful for us to be able to see in low

837
00:47:26,760 --> 00:47:29,120
Speaker 1: light conditions. But then we have the cones that allow

838
00:47:29,239 --> 00:47:31,839
Speaker 1: us to see in brighter light, and not only that,

839
00:47:31,960 --> 00:47:34,680
Speaker 1: but differentiate color. And the cones are in the very

840
00:47:34,719 --> 00:47:37,200
Speaker 1: center of your eyeballs. When you're just looking straight at something,

841
00:47:37,239 --> 00:47:39,640
Speaker 1: you're good at seeing colors, and the rods tend to

842
00:47:39,640 --> 00:47:42,080
Speaker 1: be distributed in the other parts of the eyeball, which

843
00:47:42,120 --> 00:47:45,640
Speaker 1: means that like your peripheral vision is better at seeing

844
00:47:45,640 --> 00:47:48,400
Speaker 1: in low light conditions than your central vision is. So

845
00:47:48,480 --> 00:47:50,719
Speaker 1: for example, if you're an amateur astronomer and you like

846
00:47:50,800 --> 00:47:53,400
Speaker 1: looking at the night sky, sometimes you might notice a

847
00:47:53,480 --> 00:47:55,719
Speaker 1: star out of the corner of your eye. If you

848
00:47:55,760 --> 00:47:58,719
Speaker 1: then turn your eyeball to it, it can disappear. And

849
00:47:58,760 --> 00:48:01,280
Speaker 1: that's why because the scent or of your eyeball doesn't

850
00:48:01,320 --> 00:48:03,239
Speaker 1: have a lot of rods. So if you want to

851
00:48:03,239 --> 00:48:06,520
Speaker 1: observe faint things in the sky, don't look straight at

852
00:48:06,520 --> 00:48:10,040
Speaker 1: them where they disappear. It seems almost magical, which is

853
00:48:10,560 --> 00:48:13,839
Speaker 1: interesting evolutionarily right, because you think of when we would

854
00:48:13,960 --> 00:48:17,880
Speaker 1: need this low light vision, it probably would be at

855
00:48:18,000 --> 00:48:20,799
Speaker 1: night when we're trying to avoid getting eaten by a

856
00:48:20,840 --> 00:48:24,520
Speaker 1: nocturnal predator, so being able to see movement out of

857
00:48:24,560 --> 00:48:28,120
Speaker 1: the corner of our eye and flee or hide is

858
00:48:28,200 --> 00:48:31,560
Speaker 1: really important. Whereas in lower light having being able to

859
00:48:31,640 --> 00:48:35,719
Speaker 1: like focus on something specifically, Well, this is when we're sleeping.

860
00:48:35,800 --> 00:48:38,759
Speaker 1: We don't really need to hunt at night. We're not

861
00:48:38,880 --> 00:48:43,200
Speaker 1: nocturnal predators, so our eyes are optimized for being able

862
00:48:43,239 --> 00:48:47,000
Speaker 1: to see somewhat in low lights so we can protect ourselves,

863
00:48:47,120 --> 00:48:52,399
Speaker 1: but not optimized for being predators. Nocturnal predators, that's right.

864
00:48:52,440 --> 00:48:55,120
Speaker 1: And some of us have a different kind of eyeball

865
00:48:55,480 --> 00:48:57,840
Speaker 1: than the rest of us. Most of us have three

866
00:48:58,040 --> 00:49:01,240
Speaker 1: kinds of cones, so we can see light that peaks

867
00:49:01,239 --> 00:49:04,560
Speaker 1: in three different places. But some people have special eyes.

868
00:49:04,640 --> 00:49:08,200
Speaker 1: They are called tetra chromats, and they have a fourth

869
00:49:08,400 --> 00:49:11,520
Speaker 1: kind of cone, which means they have another kind of

870
00:49:11,560 --> 00:49:14,200
Speaker 1: thing in their eye that peaks at a different place.

871
00:49:14,239 --> 00:49:18,279
Speaker 1: It peaks bluer than blue on the spectrum. And this

872
00:49:18,320 --> 00:49:20,800
Speaker 1: to me was fascinating when I first learned about I thought, wow,

873
00:49:20,880 --> 00:49:23,279
Speaker 1: maybe they can see another kind of color. Maybe this

874
00:49:23,360 --> 00:49:26,240
Speaker 1: is like my childhood fantasy. There's like a super blue

875
00:49:26,239 --> 00:49:29,400
Speaker 1: that they can see in their minds that we can't see.

876
00:49:29,560 --> 00:49:31,759
Speaker 1: But unfortunately it's not like that. What it means is

877
00:49:31,800 --> 00:49:35,280
Speaker 1: that they are better at distinguishing between shades of blue.

878
00:49:35,280 --> 00:49:38,000
Speaker 1: They're like my daughter who can tell teal from slightly

879
00:49:38,080 --> 00:49:41,280
Speaker 1: not teal because they get more information about the relative

880
00:49:41,320 --> 00:49:45,600
Speaker 1: intensities of those photons, and so they're better at distinguishing colors.

881
00:49:45,760 --> 00:49:49,600
Speaker 1: They can't necessarily see or experience any new colors. And

882
00:49:49,800 --> 00:49:52,400
Speaker 1: I mean, on the opposite end of the visual spectrum,

883
00:49:52,440 --> 00:49:55,880
Speaker 1: you have people who are color blind or partially color blind.

884
00:49:55,920 --> 00:50:00,279
Speaker 1: And it's not that people necessarily only see in grace gale,

885
00:50:00,360 --> 00:50:03,239
Speaker 1: but they can be like blue green color blind, where

886
00:50:03,239 --> 00:50:07,640
Speaker 1: they have trouble distinguishing between blues and greens. So yeah,

887
00:50:07,680 --> 00:50:11,799
Speaker 1: there's this whole range of human vision, and it makes

888
00:50:11,840 --> 00:50:15,399
Speaker 1: me wonder, like your earlier question, whether there's a lot

889
00:50:15,440 --> 00:50:20,000
Speaker 1: of difference in vision amongst people who are not necessarily

890
00:50:20,040 --> 00:50:24,200
Speaker 1: tetrachromace or people who have color blindness, but just like

891
00:50:24,560 --> 00:50:30,040
Speaker 1: whether vision comes in a spectrum like many other human experiences, right,

892
00:50:30,080 --> 00:50:33,560
Speaker 1: because people experience chocolate differently, right, Like some people actually

893
00:50:33,640 --> 00:50:36,719
Speaker 1: enjoy white chocolate and aren't just pretending. You know, it's

894
00:50:36,719 --> 00:50:43,320
Speaker 1: a mystery they're just wrong. Thank you, thank you. People

895
00:50:43,360 --> 00:50:47,400
Speaker 1: respond subjectively very differently to stimuli, and so it would

896
00:50:47,440 --> 00:50:51,360
Speaker 1: make sense if people responded differently to different kinds of photons.

897
00:50:51,560 --> 00:50:53,360
Speaker 1: And we know that out there in the animal kingdom

898
00:50:53,360 --> 00:50:57,320
Speaker 1: there's also an incredible wide variety of eyeballs, right, Different

899
00:50:57,400 --> 00:51:00,160
Speaker 1: kinds of critters are have evolved too, dear for in

900
00:51:00,200 --> 00:51:03,480
Speaker 1: scenarios where they need more or less kinds of vision.

901
00:51:03,719 --> 00:51:06,880
Speaker 1: For example, we know that owls have incredible vision, especially

902
00:51:06,920 --> 00:51:10,200
Speaker 1: in low light because they have an enormous number of these.

903
00:51:10,320 --> 00:51:14,440
Speaker 1: Rods and geckos have really good actually night color vision

904
00:51:15,080 --> 00:51:17,760
Speaker 1: so that they can survive. Plus they have a tongue

905
00:51:17,760 --> 00:51:20,399
Speaker 1: that lets them clean their own eyeballs, which I think

906
00:51:20,480 --> 00:51:24,279
Speaker 1: is pretty crazy. It's adorable. Yeah, no, I It is

907
00:51:24,360 --> 00:51:28,200
Speaker 1: one of the most fascinating things in evolutionary biology, the

908
00:51:28,320 --> 00:51:35,080
Speaker 1: difference in vision. It's mysterious because we cannot objectively measure

909
00:51:35,120 --> 00:51:38,560
Speaker 1: what an animals experience of vision is. We can only

910
00:51:39,160 --> 00:51:42,960
Speaker 1: guests basically based on their eye structure and based on

911
00:51:43,000 --> 00:51:46,879
Speaker 1: their brain. So there, when you research it can come

912
00:51:46,920 --> 00:51:50,560
Speaker 1: to some really surprising results that are hard to conceptualize. So,

913
00:51:50,640 --> 00:51:56,440
Speaker 1: for instance, rants actually have double vision and can somewhat

914
00:51:56,480 --> 00:52:00,520
Speaker 1: move their eyes independently of each other. And we discovered

915
00:52:00,520 --> 00:52:05,000
Speaker 1: this by putting little teeny tiny high speed cameras attached

916
00:52:05,000 --> 00:52:08,240
Speaker 1: to little hats on rats and looking at their eye gays,

917
00:52:08,640 --> 00:52:11,120
Speaker 1: and they found that their eye gays indicates that they

918
00:52:11,160 --> 00:52:14,560
Speaker 1: prioritize keeping a view of the sky as well as

919
00:52:14,560 --> 00:52:18,120
Speaker 1: their surroundings so that they can avoid that owl who

920
00:52:18,400 --> 00:52:21,439
Speaker 1: has that great night vision. So rats are running along

921
00:52:21,480 --> 00:52:23,920
Speaker 1: the ground with one eye up and one eye down.

922
00:52:24,280 --> 00:52:29,399
Speaker 1: That's crazy, basically, Yeah. And what's so weird is that

923
00:52:29,600 --> 00:52:33,560
Speaker 1: researchers think that these fields of vision in either I

924
00:52:33,800 --> 00:52:37,280
Speaker 1: are too different to be fused into a single image.

925
00:52:37,320 --> 00:52:41,680
Speaker 1: So there's a possibility that rants basically have like two

926
00:52:41,719 --> 00:52:45,320
Speaker 1: TV monitors in their head that they're both keeping track

927
00:52:45,400 --> 00:52:51,400
Speaker 1: of and unlike us, where we have basically one combined image.

928
00:52:51,760 --> 00:52:55,880
Speaker 1: And I mean just the the ingenuity that animals have

929
00:52:55,920 --> 00:52:59,279
Speaker 1: when it comes to eyeballs can be completely baffling. Like

930
00:52:59,360 --> 00:53:01,360
Speaker 1: this is a fun named one, but it's a brown

931
00:53:01,440 --> 00:53:06,200
Speaker 1: nose spook fish, which is a species of barrel eye fish.

932
00:53:06,360 --> 00:53:10,160
Speaker 1: It's this very weird looking fish. It's not very big.

933
00:53:10,200 --> 00:53:13,440
Speaker 1: It's like about seven inches maybe like the length of

934
00:53:13,440 --> 00:53:16,680
Speaker 1: your hand, it's got a transparent body. It looks kind

935
00:53:16,680 --> 00:53:19,680
Speaker 1: of creepy, like some kind of ghost of a fish.

936
00:53:20,040 --> 00:53:23,960
Speaker 1: And it is actually only vertebrate that is known to,

937
00:53:24,760 --> 00:53:29,120
Speaker 1: in addition to a lens, have an actual mirror in

938
00:53:29,160 --> 00:53:33,760
Speaker 1: their eye. So the way that animals can have mirrors

939
00:53:33,880 --> 00:53:37,759
Speaker 1: is they use guanting crystals to form a mirror, because

940
00:53:37,760 --> 00:53:41,520
Speaker 1: a guanting crystal is a protein that an organic animal

941
00:53:41,640 --> 00:53:47,600
Speaker 1: can produce, but it's structure is reflective, and so this

942
00:53:47,680 --> 00:53:51,200
Speaker 1: is actually also used in scallops. Scalops have eyes. In fact,

943
00:53:51,200 --> 00:53:54,160
Speaker 1: they have hundreds of eyes, which is a fun thought

944
00:53:54,320 --> 00:53:57,520
Speaker 1: next time you enjoy your scalp. But yes, so so

945
00:53:57,560 --> 00:54:02,839
Speaker 1: this brown snout spook fish, it has a normal eye

946
00:54:03,239 --> 00:54:07,160
Speaker 1: that looks upwards, and then in addition to that, it

947
00:54:07,200 --> 00:54:09,680
Speaker 1: actually has an annex ee like just stuck to the

948
00:54:09,719 --> 00:54:12,880
Speaker 1: side of it, like a side view mirror on a car.

949
00:54:13,280 --> 00:54:16,200
Speaker 1: It has a mirror that allows it to look downwards.

950
00:54:16,200 --> 00:54:19,560
Speaker 1: So this fish can look both upwards and downwards at

951
00:54:19,600 --> 00:54:22,279
Speaker 1: the same time. Well, that's a very useful kind of

952
00:54:22,320 --> 00:54:24,839
Speaker 1: side eye. One of my favorite kind of eyeballs out

953
00:54:24,880 --> 00:54:27,720
Speaker 1: there in the world is the mantis shrimp. The mantis

954
00:54:27,719 --> 00:54:30,680
Speaker 1: shrimp doesn't just have three or four kinds of cones.

955
00:54:30,960 --> 00:54:35,000
Speaker 1: They estimate it might have fifteen or sixteen different kinds

956
00:54:35,000 --> 00:54:37,279
Speaker 1: of cones in its eye. And when you first read

957
00:54:37,320 --> 00:54:39,360
Speaker 1: about that, you think, wow, the mantis strip must have

958
00:54:39,440 --> 00:54:43,239
Speaker 1: like a really vibrant visual experience. It's like MARTAGRAI every

959
00:54:43,280 --> 00:54:45,200
Speaker 1: day for the mantis shrimp. Right, Well, it turns out

960
00:54:45,239 --> 00:54:49,000
Speaker 1: the mantis strip actually isn't any better than humans at

961
00:54:49,000 --> 00:54:51,960
Speaker 1: distinguishing colors. They do these experiments where they train the

962
00:54:52,000 --> 00:54:54,400
Speaker 1: shrimp like go to food if you can see the

963
00:54:54,440 --> 00:54:57,359
Speaker 1: difference between the colors, and they aren't any better at

964
00:54:57,360 --> 00:54:59,600
Speaker 1: distinguishing colors than we are. And we only have three

965
00:54:59,680 --> 00:55:02,000
Speaker 1: kinds of codes. And the reason is that the mantis

966
00:55:02,000 --> 00:55:05,920
Speaker 1: shrimp basically has much more specific hardware, but it doesn't

967
00:55:05,920 --> 00:55:08,560
Speaker 1: have the processing power to really take advantage of that.

968
00:55:08,760 --> 00:55:12,040
Speaker 1: Their brains are really simple. So we have like simpler

969
00:55:12,120 --> 00:55:16,040
Speaker 1: hardware only three sensors, but very complicated software to interpret

970
00:55:16,200 --> 00:55:18,600
Speaker 1: and analyze that. And the manti strimp has made like

971
00:55:18,640 --> 00:55:21,720
Speaker 1: a different optimization, like go all in on the hardware

972
00:55:21,760 --> 00:55:25,839
Speaker 1: and have really simple software to interpret it. It's pretty fascinating, right,

973
00:55:25,880 --> 00:55:29,200
Speaker 1: And the reason for that is that the mantis shrimp

974
00:55:29,280 --> 00:55:33,439
Speaker 1: is optimizing the speed of its site rather than sort

975
00:55:33,440 --> 00:55:36,680
Speaker 1: of the detail of its perception. So it's thought that

976
00:55:36,719 --> 00:55:41,080
Speaker 1: with less software and more hardware, you can actually sense

977
00:55:41,120 --> 00:55:44,239
Speaker 1: something much more quickly, like the because the speed of

978
00:55:44,360 --> 00:55:47,759
Speaker 1: light is quite fast. Uh. And then if you can

979
00:55:47,920 --> 00:55:52,360
Speaker 1: have these photoreceptors pick up on that photon really quickly

980
00:55:52,360 --> 00:55:55,799
Speaker 1: because you just have so many, then even if your

981
00:55:55,920 --> 00:55:58,879
Speaker 1: software is relatively simple of just like, hey, there's a thing,

982
00:55:59,320 --> 00:56:03,320
Speaker 1: if it's quick enough, it will have incredible reflexes. That

983
00:56:03,400 --> 00:56:04,799
Speaker 1: makes a lot of sense of speed of light is

984
00:56:04,800 --> 00:56:07,560
Speaker 1: faster than the speed of brains. I definitely, I definitely

985
00:56:07,560 --> 00:56:10,759
Speaker 1: don't think at the speed of light and like, is

986
00:56:10,800 --> 00:56:13,160
Speaker 1: that a shark? Or is that dinner? Oops? Too late,

987
00:56:13,239 --> 00:56:17,000
Speaker 1: I'm being eaten already. Well. One of my favorite stories

988
00:56:17,040 --> 00:56:20,680
Speaker 1: about color and animals comes again from Rachel Martin, who

989
00:56:20,680 --> 00:56:23,319
Speaker 1: told us the story about how birds that seems sort

990
00:56:23,320 --> 00:56:25,839
Speaker 1: of boring and blue turned out to be actually ultra

991
00:56:25,920 --> 00:56:29,160
Speaker 1: violet and spectacular. So here's Rachel talking about one of

992
00:56:29,160 --> 00:56:33,160
Speaker 1: her favorite studies. One of my favorite papers in this

993
00:56:33,239 --> 00:56:37,880
Speaker 1: area is one where these scientists were looking at blue tips,

994
00:56:37,880 --> 00:56:42,040
Speaker 1: so a little birds, and they thought that these birds

995
00:56:42,040 --> 00:56:45,960
Speaker 1: didn't really have a strong sexual selection system because they

996
00:56:46,000 --> 00:56:47,480
Speaker 1: all kind of look the same. And you know, for

997
00:56:47,520 --> 00:56:49,520
Speaker 1: a lot of birds, like the males are really pretty

998
00:56:49,560 --> 00:56:52,360
Speaker 1: and showy, and they have markings that the females are choosing,

999
00:56:53,200 --> 00:56:55,720
Speaker 1: and for these birds, they didn't seem to They seemed

1000
00:56:55,719 --> 00:56:58,760
Speaker 1: to all look the same. And then somebody finally thought

1001
00:56:58,880 --> 00:57:03,000
Speaker 1: of doing some ex erments with whether these they had

1002
00:57:03,000 --> 00:57:06,120
Speaker 1: pigments in the UV. So they put m vast lean

1003
00:57:06,239 --> 00:57:08,799
Speaker 1: on the bird's heads. So they discovered that they had

1004
00:57:08,920 --> 00:57:12,440
Speaker 1: some markings in the UV, like on their heads, and

1005
00:57:12,440 --> 00:57:14,760
Speaker 1: so if they put vast lean over it so that

1006
00:57:14,760 --> 00:57:20,000
Speaker 1: that blocked the UV, the females, you know, didn't you

1007
00:57:20,080 --> 00:57:22,800
Speaker 1: weren't able to see those markings, and so then there

1008
00:57:22,840 --> 00:57:24,920
Speaker 1: was a big difference in the sexual selection. So the

1009
00:57:24,960 --> 00:57:27,320
Speaker 1: males that were really popular before because they had these

1010
00:57:27,360 --> 00:57:29,720
Speaker 1: beautiful UV markings on their heads, when you put bass

1011
00:57:29,800 --> 00:57:32,400
Speaker 1: lean on them, then they don't get any attention because

1012
00:57:32,800 --> 00:57:36,680
Speaker 1: the females can't see this. And so it led to

1013
00:57:37,080 --> 00:57:39,600
Speaker 1: you know, one of my favorite paper titles of all time,

1014
00:57:39,880 --> 00:57:43,400
Speaker 1: which was blue Tips Are Ultra Violet Tits. I love

1015
00:57:43,400 --> 00:57:45,320
Speaker 1: that story and I wish I get to write a

1016
00:57:45,320 --> 00:57:48,320
Speaker 1: paper using the phrase ultra violet tits. I wish I

1017
00:57:48,320 --> 00:57:53,800
Speaker 1: had gotten to rub vassilene on a bird's head. So

1018
00:57:53,880 --> 00:57:57,640
Speaker 1: many adventures in science, you know, the more animals we

1019
00:57:57,760 --> 00:58:01,800
Speaker 1: stick under black light them, or we're finding have this

1020
00:58:02,000 --> 00:58:07,000
Speaker 1: like biofluorescence exactly. So we see a little slice of

1021
00:58:07,040 --> 00:58:09,680
Speaker 1: the universe that's out there, and a lot of animals

1022
00:58:09,720 --> 00:58:13,120
Speaker 1: can see further into that spectrum and are advertising to

1023
00:58:13,200 --> 00:58:16,000
Speaker 1: each other in that spectrum, and so it's like we're

1024
00:58:16,000 --> 00:58:18,520
Speaker 1: not seeing what's going on out there. Maybe there are

1025
00:58:18,560 --> 00:58:21,360
Speaker 1: some animals that can see neutrinos and are sending neutrino

1026
00:58:21,480 --> 00:58:24,040
Speaker 1: messages to each other, you know, they have like pigments

1027
00:58:24,080 --> 00:58:27,360
Speaker 1: in their feathers that glow in neutrinos. No, I'm sure

1028
00:58:27,400 --> 00:58:30,120
Speaker 1: they don't. But that sounds like a fun science fiction story.

1029
00:58:30,240 --> 00:58:33,080
Speaker 1: But let's get back to the actual science of the universe.

1030
00:58:33,120 --> 00:58:35,720
Speaker 1: And I want to answer our question about whether a

1031
00:58:35,800 --> 00:58:40,000
Speaker 1: human eye can respond to a single polton human eyeball

1032
00:58:40,040 --> 00:58:43,440
Speaker 1: as a quantum device. But first let's take a second break.

1033
00:58:56,080 --> 00:58:58,600
Speaker 1: All right, we're back, and we have explained to ourselves

1034
00:58:58,720 --> 00:59:01,960
Speaker 1: how the eyeball works, how it receives photon, how it

1035
00:59:02,040 --> 00:59:06,280
Speaker 1: triggers this ridiculous Rube Goldberg machine of flipping levers and

1036
00:59:06,360 --> 00:59:09,960
Speaker 1: rolling balls and cascading signals so that you can experience

1037
00:59:10,160 --> 00:59:14,560
Speaker 1: the reddest read that there is. Yeah, I'm really excited

1038
00:59:14,600 --> 00:59:19,160
Speaker 1: about this because I would love to see a single photon.

1039
00:59:19,760 --> 00:59:23,160
Speaker 1: They're responsible for so much stuff that happens in the universe,

1040
00:59:23,160 --> 00:59:25,720
Speaker 1: and I'd like to personally thank it for being there.

1041
00:59:25,840 --> 00:59:27,920
Speaker 1: And we could finally answer one of the most ancient

1042
00:59:27,960 --> 00:59:31,600
Speaker 1: questions in philosophy, which is what does a photon look like?

1043
00:59:31,960 --> 00:59:34,520
Speaker 1: But it's interesting and relevant to physics because if you

1044
00:59:34,560 --> 00:59:36,919
Speaker 1: look up at the night sky, you see some things

1045
00:59:36,920 --> 00:59:39,960
Speaker 1: that are very bright, the moon or nearby planets and stars,

1046
00:59:40,200 --> 00:59:42,680
Speaker 1: but you also see some things that are very, very dim,

1047
00:59:42,800 --> 00:59:46,080
Speaker 1: just at the edge of your perception. And I've often wondered,

1048
00:59:46,080 --> 00:59:48,640
Speaker 1: when looking at the night sky, how many photons am

1049
00:59:48,680 --> 00:59:53,000
Speaker 1: I seeing? You know, imagine some incredibly huge, bright star

1050
00:59:53,200 --> 00:59:56,440
Speaker 1: that's billions and billions of miles away, shooting ten to

1051
00:59:56,440 --> 00:59:59,800
Speaker 1: the fifty photons per second out into the cosmos. All

1052
00:59:59,840 --> 01:00:02,720
Speaker 1: the those photons, just a few have managed to cross

1053
01:00:02,840 --> 01:00:06,720
Speaker 1: that enormous ocean of dark and hit your eyeball. But

1054
01:00:06,760 --> 01:00:09,800
Speaker 1: it makes me wonder how many photons have to make

1055
01:00:09,840 --> 01:00:13,280
Speaker 1: it before I can see that star. What happens to

1056
01:00:13,360 --> 01:00:17,840
Speaker 1: those photons on the way from the star to our eyeball?

1057
01:00:17,960 --> 01:00:21,800
Speaker 1: Do they get knocked around by other particles? They have

1058
01:00:21,840 --> 01:00:24,880
Speaker 1: a great adventure along the way, They make friends, they

1059
01:00:25,000 --> 01:00:28,800
Speaker 1: you know, complete quests. No, it's incredible. Mostly those photons

1060
01:00:28,840 --> 01:00:32,080
Speaker 1: just fly unimpeded through the universe because space is mostly

1061
01:00:32,120 --> 01:00:35,640
Speaker 1: transparent to those photons. There are things out there, the

1062
01:00:35,680 --> 01:00:39,120
Speaker 1: solar wind and particles that will interact with really high

1063
01:00:39,240 --> 01:00:42,480
Speaker 1: energy photons, but lower energy photons like the ones in

1064
01:00:42,480 --> 01:00:46,240
Speaker 1: the visible spectrum, can mostly fly untouched through space. The

1065
01:00:46,320 --> 01:00:48,800
Speaker 1: last thing they interacted with was the surface of the Sun,

1066
01:00:48,840 --> 01:00:51,520
Speaker 1: and the next thing they interact with is your eyeball.

1067
01:00:51,680 --> 01:00:53,720
Speaker 1: The reason, of course you don't see ten to the

1068
01:00:53,800 --> 01:00:57,080
Speaker 1: fifty photons from that star is just because the photons

1069
01:00:57,080 --> 01:00:59,720
Speaker 1: are going in every single direction. So if you have

1070
01:00:59,760 --> 01:01:02,440
Speaker 1: ten of the fifty covering the surface of the star

1071
01:01:02,760 --> 01:01:05,680
Speaker 1: and they all shoot out than a year later, now

1072
01:01:05,720 --> 01:01:08,680
Speaker 1: that same number of photons is painting the inside of

1073
01:01:08,720 --> 01:01:11,479
Speaker 1: a spear that has a radius of one light year,

1074
01:01:11,800 --> 01:01:14,880
Speaker 1: and so like per area, there are many fewer photons

1075
01:01:15,040 --> 01:01:17,960
Speaker 1: by the time it gets to you, billions of miles away,

1076
01:01:18,080 --> 01:01:21,320
Speaker 1: there's just very few photons per square meter. That's why

1077
01:01:21,320 --> 01:01:23,960
Speaker 1: the star feels distant, and that's why the intensity of

1078
01:01:24,040 --> 01:01:27,880
Speaker 1: light falls like one over the radius squared, because that's

1079
01:01:27,880 --> 01:01:30,280
Speaker 1: the surface area of the inside of a sphere of

1080
01:01:30,320 --> 01:01:32,760
Speaker 1: that radius. Well, I'm glad it's a little bit diffused,

1081
01:01:32,880 --> 01:01:35,960
Speaker 1: because otherwise I think it might just kind of instantly

1082
01:01:36,080 --> 01:01:39,560
Speaker 1: vaporize our eyeballs. And it's a question that scientists have

1083
01:01:39,680 --> 01:01:43,360
Speaker 1: been asking since we understood what photons were like, could

1084
01:01:43,360 --> 01:01:46,680
Speaker 1: we see an individual photon? Is that even possible? At first,

1085
01:01:46,680 --> 01:01:48,959
Speaker 1: we have to separate into two questions. One is could

1086
01:01:48,960 --> 01:01:51,920
Speaker 1: you see a photon which hits the outside of your eye?

1087
01:01:52,320 --> 01:01:54,200
Speaker 1: And the second is could you see a photon which

1088
01:01:54,240 --> 01:01:57,480
Speaker 1: hits the actual receptors on the back of your eye?

1089
01:01:57,640 --> 01:01:59,960
Speaker 1: Because it turns out something that's pretty easy to measure

1090
01:02:00,160 --> 01:02:02,400
Speaker 1: is the efficiency for photons to get to the back

1091
01:02:02,520 --> 01:02:05,920
Speaker 1: of your eyeball. And only like one inten photons that

1092
01:02:06,040 --> 01:02:08,640
Speaker 1: hits the surface of your eye actually makes it to

1093
01:02:08,720 --> 01:02:11,960
Speaker 1: the retina. Is it getting uh, sort of lost on

1094
01:02:12,040 --> 01:02:14,880
Speaker 1: the way, is it not reaching the pupil or is

1095
01:02:14,880 --> 01:02:19,280
Speaker 1: it bouncing off something on your eye before reaching the

1096
01:02:19,320 --> 01:02:21,640
Speaker 1: back of your eye? Yeah, they get scattered and they

1097
01:02:21,640 --> 01:02:25,080
Speaker 1: get absorbed. Remember that has light traveled through materials. If

1098
01:02:25,120 --> 01:02:28,440
Speaker 1: you change the reflectivity or basically the index of refraction

1099
01:02:28,480 --> 01:02:31,800
Speaker 1: of the material, you're gonna get some reflection at that surface.

1100
01:02:32,240 --> 01:02:35,640
Speaker 1: Even when photons go from air, which is transparent, to glass,

1101
01:02:35,680 --> 01:02:39,080
Speaker 1: which is transparent, there's always some reflection. And so as

1102
01:02:39,080 --> 01:02:41,360
Speaker 1: you go through the vitreous humor and go through the

1103
01:02:41,440 --> 01:02:43,840
Speaker 1: lens and go through the cornea, there's little bits of

1104
01:02:43,840 --> 01:02:47,160
Speaker 1: reflection here and there and scattering and absorption. It's not

1105
01:02:47,200 --> 01:02:51,680
Speaker 1: a transparent so only one in ten photons actually makes

1106
01:02:51,680 --> 01:02:54,360
Speaker 1: it to the back of the eyeball, which is crazy. Yeah,

1107
01:02:54,400 --> 01:02:57,760
Speaker 1: it seems like we're losing a lot of photons on

1108
01:02:57,800 --> 01:03:00,400
Speaker 1: the way over there. We gotta put some like signs

1109
01:03:00,520 --> 01:03:04,720
Speaker 1: up on our eyeballs, like photons inter here don't get lost.

1110
01:03:05,000 --> 01:03:07,840
Speaker 1: So people started doing experiments to see how sensitive the

1111
01:03:07,880 --> 01:03:10,920
Speaker 1: eye was. Back in like the nineteen forties, they didn't

1112
01:03:10,920 --> 01:03:15,360
Speaker 1: experiment Columbia University where they shot very very low intensity

1113
01:03:15,480 --> 01:03:18,200
Speaker 1: light into the eyeball to try to understand what the

1114
01:03:18,240 --> 01:03:21,000
Speaker 1: threshold was. But back then they didn't have like a

1115
01:03:21,040 --> 01:03:24,160
Speaker 1: great understanding of quantum mechanics and quantum optics, it was

1116
01:03:24,200 --> 01:03:27,120
Speaker 1: not easy for them to manipulate the light to really

1117
01:03:27,120 --> 01:03:29,720
Speaker 1: get a handle on having a single photon. So what

1118
01:03:29,760 --> 01:03:32,000
Speaker 1: they could tell was that the human eye was very,

1119
01:03:32,160 --> 01:03:35,920
Speaker 1: very sensitive to small numbers of photons, but they couldn't

1120
01:03:35,920 --> 01:03:39,800
Speaker 1: conclusively pin it down because it's very difficult to provide

1121
01:03:39,920 --> 01:03:44,920
Speaker 1: a single photon source, one individually wrapped photon. Yeah, and

1122
01:03:45,000 --> 01:03:47,680
Speaker 1: to know that that's when the photon was there, right.

1123
01:03:47,960 --> 01:03:50,920
Speaker 1: The basic experiment you want is to shoot a photon

1124
01:03:51,000 --> 01:03:53,240
Speaker 1: at somebody's eyeball, to know that you shot the photon

1125
01:03:53,320 --> 01:03:55,400
Speaker 1: there and when you did it, and then have them

1126
01:03:55,440 --> 01:03:57,320
Speaker 1: press a button and say I saw a photon, And

1127
01:03:57,360 --> 01:04:00,320
Speaker 1: that way you can correlate the button presses with when

1128
01:04:00,320 --> 01:04:03,080
Speaker 1: the photons arrived. You could say, yeah, there are reliable

1129
01:04:03,120 --> 01:04:05,880
Speaker 1: indicators of when the photon arrives. And if they're always

1130
01:04:05,920 --> 01:04:08,200
Speaker 1: just pressing the button right, then you can tell this

1131
01:04:08,240 --> 01:04:11,560
Speaker 1: person is crazy. This it is useless. And so to

1132
01:04:11,640 --> 01:04:14,000
Speaker 1: prove that somebody could see a single photon, you need

1133
01:04:14,040 --> 01:04:17,439
Speaker 1: to know when that single photon is hitting the eye.

1134
01:04:17,480 --> 01:04:19,800
Speaker 1: That's the crucial thing. And if all you have our

1135
01:04:19,880 --> 01:04:22,280
Speaker 1: light sources that are sort of classical, like hot things

1136
01:04:22,360 --> 01:04:24,640
Speaker 1: glowing like a light bulb, you know, which has a

1137
01:04:24,720 --> 01:04:27,520
Speaker 1: tongusen filament in it which glows because it gets hot

1138
01:04:27,560 --> 01:04:30,600
Speaker 1: and shoots out of photons. It's difficult to manage because

1139
01:04:30,720 --> 01:04:32,400
Speaker 1: you can turn it down and you can make it

1140
01:04:32,560 --> 01:04:35,120
Speaker 1: very low intensity, but you don't have control over when

1141
01:04:35,120 --> 01:04:37,760
Speaker 1: the photons are admitted, so you never know, for example,

1142
01:04:37,840 --> 01:04:40,320
Speaker 1: like was that one photon that came out or two

1143
01:04:40,520 --> 01:04:42,800
Speaker 1: that Katie pressed the button? Because that was the one

1144
01:04:42,840 --> 01:04:45,280
Speaker 1: time when a couple of photons actually hit her eyeball

1145
01:04:45,320 --> 01:04:47,720
Speaker 1: and not the time when a single photon hit the eyeball.

1146
01:04:47,840 --> 01:04:50,840
Speaker 1: And so the breakthrough in these experiments actually wasn't until

1147
01:04:50,880 --> 01:04:55,360
Speaker 1: about ten years ago when people developed really crazy nonlinear

1148
01:04:55,440 --> 01:04:59,600
Speaker 1: quantum optics to separate individual photons. So is it like

1149
01:04:59,640 --> 01:05:03,960
Speaker 1: a little little gun that shoots a photon. It would

1150
01:05:04,000 --> 01:05:05,680
Speaker 1: be pretty cool to have like a button you could

1151
01:05:05,680 --> 01:05:08,520
Speaker 1: press to shoot a single photon. The key idea actually

1152
01:05:08,560 --> 01:05:11,160
Speaker 1: is to split a photon. So you have a very

1153
01:05:11,240 --> 01:05:14,240
Speaker 1: low intensity source that shoots out photons at you, and

1154
01:05:14,240 --> 01:05:15,920
Speaker 1: what you do is you pass it through a special

1155
01:05:16,080 --> 01:05:19,000
Speaker 1: kind of crystal it's called a down converter, and it

1156
01:05:19,040 --> 01:05:21,680
Speaker 1: takes a single photon and it splits it into two

1157
01:05:21,720 --> 01:05:24,400
Speaker 1: photons of less energy. Now, one you can use for

1158
01:05:24,440 --> 01:05:26,320
Speaker 1: your experiment, and the other one you can use is

1159
01:05:26,360 --> 01:05:28,800
Speaker 1: a tag that tells you, like, oh, a photon just

1160
01:05:28,920 --> 01:05:32,640
Speaker 1: came through. You can measure those using very high precision optics,

1161
01:05:32,880 --> 01:05:36,760
Speaker 1: so you know when the experiment tee is observing photons

1162
01:05:36,760 --> 01:05:38,640
Speaker 1: and when they're not, and so you can tell, oh,

1163
01:05:38,640 --> 01:05:40,840
Speaker 1: there are two photons in the experiment right now, let's

1164
01:05:40,880 --> 01:05:43,680
Speaker 1: disregard this, and you can tell when a single photon

1165
01:05:43,720 --> 01:05:46,400
Speaker 1: has arrived and no other photons have come through. So

1166
01:05:46,440 --> 01:05:49,360
Speaker 1: it's more about being able to count the photons and

1167
01:05:49,520 --> 01:05:53,120
Speaker 1: actually manipulating the photons themselves. Oh that's so interesting, yeah,

1168
01:05:53,200 --> 01:05:56,120
Speaker 1: because like if you want to detect a photon, you

1169
01:05:56,200 --> 01:05:59,720
Speaker 1: kind of have to have whatever thing detect the photon

1170
01:06:00,080 --> 01:06:03,600
Speaker 1: interact with the photon, which would not necessarily allow it

1171
01:06:03,680 --> 01:06:06,520
Speaker 1: to also reach the eye right exactly, you don't want

1172
01:06:06,520 --> 01:06:09,040
Speaker 1: to interfere with that photon which is headed towards the eyeball.

1173
01:06:09,480 --> 01:06:13,360
Speaker 1: So this crazy quantum optics, these strange crystals split it

1174
01:06:13,400 --> 01:06:16,120
Speaker 1: and give you one photon for your accounting and another

1175
01:06:16,160 --> 01:06:19,800
Speaker 1: photon for your experiment, and there of course entangled together.

1176
01:06:19,840 --> 01:06:21,680
Speaker 1: And so you know that when you see a photon,

1177
01:06:21,760 --> 01:06:24,480
Speaker 1: and your little detector that the eyeball should also have

1178
01:06:24,560 --> 01:06:27,120
Speaker 1: seen one. So then they could have people sitting there

1179
01:06:27,120 --> 01:06:29,640
Speaker 1: pressing a button and answering like, oh I saw one, No,

1180
01:06:29,720 --> 01:06:31,760
Speaker 1: I didn't see one. It's like one of those uh

1181
01:06:31,960 --> 01:06:35,000
Speaker 1: those like heart necklaces you'd get at Chuck E Cheese

1182
01:06:35,080 --> 01:06:38,320
Speaker 1: is with your best friend forever. It's like split in

1183
01:06:38,400 --> 01:06:41,320
Speaker 1: half and each one of you got one piece of

1184
01:06:41,320 --> 01:06:44,960
Speaker 1: the heart necklace. Yeah, it's just like that. In fact,

1185
01:06:45,040 --> 01:06:47,120
Speaker 1: it's called the Chuck E Cheese Experiment just for that.

1186
01:06:49,200 --> 01:06:52,280
Speaker 1: And so it's only in two sixteen that they finally

1187
01:06:52,280 --> 01:06:55,440
Speaker 1: put all of this together, this crazy experimental apparatus, and

1188
01:06:55,480 --> 01:06:59,680
Speaker 1: confirmed that the human eye can see a single photon.

1189
01:06:59,800 --> 01:07:02,120
Speaker 1: If it makes it to the retina, it will be

1190
01:07:02,160 --> 01:07:04,200
Speaker 1: able to detect it. So if you're sitting in a

1191
01:07:04,280 --> 01:07:07,040
Speaker 1: dark room and a single photon from a distant star

1192
01:07:07,200 --> 01:07:10,480
Speaker 1: HiT's your retina, you will see a flash of light.

1193
01:07:10,840 --> 01:07:14,160
Speaker 1: So in with people in this experiment, they're pressing this

1194
01:07:14,240 --> 01:07:17,720
Speaker 1: button when they're seeing a flash of light, did they

1195
01:07:17,800 --> 01:07:21,680
Speaker 1: describe like what that experience was like? Yeah, they see

1196
01:07:21,720 --> 01:07:24,600
Speaker 1: like a tiny little pinprick of light, like the smallest

1197
01:07:24,640 --> 01:07:28,200
Speaker 1: little flashlight possible. That's amazing. It is amazing, and it

1198
01:07:28,280 --> 01:07:30,880
Speaker 1: tells you like sort of the limit of your ability,

1199
01:07:31,000 --> 01:07:33,800
Speaker 1: like lights up a single pixel in your brain, so

1200
01:07:33,840 --> 01:07:35,760
Speaker 1: now you can tell like how big is one of

1201
01:07:35,800 --> 01:07:41,120
Speaker 1: your brain pixels. I think it's super cool, And people,

1202
01:07:41,160 --> 01:07:43,840
Speaker 1: of course have gone beyond that and started to ask

1203
01:07:43,960 --> 01:07:47,400
Speaker 1: questions about the quantum mechanics of it. Now we know

1204
01:07:47,520 --> 01:07:51,160
Speaker 1: the human eyeball is basically a quantum opsticks device. It

1205
01:07:51,200 --> 01:07:54,360
Speaker 1: can interact with single photons, So now we can ask

1206
01:07:54,400 --> 01:07:57,600
Speaker 1: interesting questions like what happens if we send photon to

1207
01:07:57,680 --> 01:08:01,160
Speaker 1: the eyeball that are in an undert Rman's state. You

1208
01:08:01,160 --> 01:08:04,520
Speaker 1: know that quantum mechanical objects can have like the possibility

1209
01:08:04,560 --> 01:08:07,320
Speaker 1: of being in two different locations at once. But the

1210
01:08:07,360 --> 01:08:10,160
Speaker 1: strange thing about us is that we don't observe things

1211
01:08:10,200 --> 01:08:13,560
Speaker 1: quantum mechanically. When you look at something, it's either here

1212
01:08:13,760 --> 01:08:15,720
Speaker 1: or it's there. And this is one of the deepest

1213
01:08:15,800 --> 01:08:19,280
Speaker 1: questions in quantum physics is why we can't observe things

1214
01:08:19,439 --> 01:08:22,640
Speaker 1: to be in superpositions. Why if quantum particles can have

1215
01:08:22,720 --> 01:08:25,400
Speaker 1: like probabilities to be in two different states, we only

1216
01:08:25,400 --> 01:08:27,960
Speaker 1: ever observe them to be in one so people are

1217
01:08:27,960 --> 01:08:31,519
Speaker 1: doing experiments to see can the eyeball see photons that

1218
01:08:31,520 --> 01:08:34,280
Speaker 1: are in a superposition. So they take like this single

1219
01:08:34,320 --> 01:08:38,559
Speaker 1: photon and they pass it through a half silvered mirror.

1220
01:08:38,760 --> 01:08:41,560
Speaker 1: This is a mirror which sometimes sends the photon to

1221
01:08:41,600 --> 01:08:43,880
Speaker 1: the left and sometimes sends it to the right. And

1222
01:08:43,880 --> 01:08:46,400
Speaker 1: it's a quantum mechanical thing. It's random. So now what

1223
01:08:46,479 --> 01:08:48,800
Speaker 1: happens when the photon passes through it is that, because

1224
01:08:48,800 --> 01:08:51,880
Speaker 1: it's quantum mechanical, it doesn't like actually go left or

1225
01:08:51,960 --> 01:08:54,800
Speaker 1: actually go right every time. It has a probability to

1226
01:08:54,880 --> 01:08:57,320
Speaker 1: go left and the probability to go right. This is

1227
01:08:57,320 --> 01:08:59,559
Speaker 1: sort of like the double slit experiment. So then what

1228
01:08:59,640 --> 01:09:02,400
Speaker 1: happened when it hits your eyeball is that when the

1229
01:09:02,439 --> 01:09:05,479
Speaker 1: measurement collapses in the universe says, okay, we have to

1230
01:09:05,560 --> 01:09:09,599
Speaker 1: decide which way the photon went. Or can your eye

1231
01:09:09,680 --> 01:09:13,840
Speaker 1: somehow see a quantum mechanically superimposed photon. Do you get

1232
01:09:13,880 --> 01:09:16,679
Speaker 1: like two little flashes, one on the left and one

1233
01:09:16,760 --> 01:09:19,000
Speaker 1: on the right. These are the kind of experiments people

1234
01:09:19,000 --> 01:09:22,800
Speaker 1: are doing right now. That's incredible. I love that so much.

1235
01:09:23,280 --> 01:09:27,479
Speaker 1: There's something about these kinds of experiments where you are

1236
01:09:27,920 --> 01:09:32,800
Speaker 1: seeing how we're perceiving things in the world, especially like

1237
01:09:32,840 --> 01:09:35,160
Speaker 1: on the quantum level. That it's like it kind of

1238
01:09:35,200 --> 01:09:40,000
Speaker 1: gives me chills that we can actually have that direct

1239
01:09:40,880 --> 01:09:46,559
Speaker 1: human observation of quantum physics. It is really amazing, and

1240
01:09:46,600 --> 01:09:49,760
Speaker 1: there are some fun theories of quantum mechanics that we

1241
01:09:49,880 --> 01:09:53,040
Speaker 1: might actually be able to test using this kind of scenario.

1242
01:09:53,479 --> 01:09:56,760
Speaker 1: People wonder like when does the wave function collapse? When

1243
01:09:56,800 --> 01:09:59,080
Speaker 1: does the universe decide or the photon went left or

1244
01:09:59,120 --> 01:10:01,680
Speaker 1: went right? With theories we've talked about with experts on

1245
01:10:01,720 --> 01:10:04,720
Speaker 1: this podcast, some ideas being that the universe splits and

1246
01:10:04,800 --> 01:10:07,360
Speaker 1: one goes left and one goes rights. Others that it's

1247
01:10:07,360 --> 01:10:10,840
Speaker 1: actually dependent on sensitive details of the initial conditions. But

1248
01:10:10,880 --> 01:10:14,680
Speaker 1: there are some theories called spontaneous collapse that says that

1249
01:10:14,720 --> 01:10:17,640
Speaker 1: the collapse to the side, left or right depends in

1250
01:10:17,760 --> 01:10:20,760
Speaker 1: some way on like the size of the object that

1251
01:10:20,800 --> 01:10:24,080
Speaker 1: it's interacting with, which is a little weird, and in

1252
01:10:24,120 --> 01:10:27,439
Speaker 1: that scenario, different size parts of the eye might be

1253
01:10:27,560 --> 01:10:30,639
Speaker 1: more or less likely to induce this collapse. You could

1254
01:10:30,640 --> 01:10:34,360
Speaker 1: actually test this theory by doing this experiment. So this

1255
01:10:34,400 --> 01:10:36,840
Speaker 1: is the kind of thing people are working on right now.

1256
01:10:37,320 --> 01:10:42,440
Speaker 1: Quantum eyeball experiments. That's great. So we're turning humans into

1257
01:10:42,920 --> 01:10:48,519
Speaker 1: sort of like an actual quantum detection instrument. Yeah, because

1258
01:10:48,560 --> 01:10:52,000
Speaker 1: the critical question in all of these experiments is when

1259
01:10:52,080 --> 01:10:55,160
Speaker 1: does the wave function collapse? And if you're interacting with

1260
01:10:55,200 --> 01:10:58,200
Speaker 1: a quantum object using a classical device like a finger

1261
01:10:58,640 --> 01:11:01,479
Speaker 1: or an eyeball, then has to collapse at some point.

1262
01:11:01,560 --> 01:11:03,640
Speaker 1: But the device you're interacting it with, of course, is

1263
01:11:03,680 --> 01:11:06,719
Speaker 1: made of little quantum bits. And so if your eyeball

1264
01:11:06,760 --> 01:11:09,879
Speaker 1: can stay a quantum object then interact with the quantum

1265
01:11:09,880 --> 01:11:12,880
Speaker 1: photon in a quantum way and maintain its superposition, then

1266
01:11:12,920 --> 01:11:16,680
Speaker 1: maybe your eyeball can be in a superposition of quantum states. Right,

1267
01:11:16,760 --> 01:11:19,160
Speaker 1: your eyeball can be in two probabilities, like it saw

1268
01:11:19,160 --> 01:11:20,920
Speaker 1: it on left and it's saw it on the right,

1269
01:11:21,400 --> 01:11:23,519
Speaker 1: And then how does your brain interpret that? Right? Does

1270
01:11:23,560 --> 01:11:26,439
Speaker 1: it collapse when it gets the optical nerve? We don't know.

1271
01:11:26,800 --> 01:11:29,160
Speaker 1: These are super fun questions that we'll be digging into

1272
01:11:29,240 --> 01:11:32,000
Speaker 1: probably for hundreds of years. Well, you just made me

1273
01:11:32,080 --> 01:11:36,080
Speaker 1: go cross side, all right. Well, I think we dove

1274
01:11:36,200 --> 01:11:40,320
Speaker 1: deep into Supernova Scarlet and crazy Blue on this podcast,

1275
01:11:40,439 --> 01:11:42,800
Speaker 1: and we do know now that the human eye can

1276
01:11:43,000 --> 01:11:46,479
Speaker 1: actually see a single photon, and that's going to allow

1277
01:11:46,560 --> 01:11:49,439
Speaker 1: us to probe the frontiers of quantum mechanics and understand

1278
01:11:49,479 --> 01:11:52,800
Speaker 1: crazy things about superpositions and what it's like to be

1279
01:11:52,840 --> 01:11:55,880
Speaker 1: a mantis shrimp. I just love that when I see

1280
01:11:55,920 --> 01:12:01,360
Speaker 1: a star, I'm directly kissing the protons from star with

1281
01:12:01,400 --> 01:12:04,280
Speaker 1: my eyeballs. Unfortunately, you don't have to put the whole

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Speaker 1: star against your eyeball in order to see it. All right, Well,

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Speaker 1: thank you very much Katie for joining us on this

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Speaker 1: examination of the physics of the human eyeball, and thanks

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Speaker 1: to everybody out there for listening and coming with us

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01:12:16,280 --> 01:12:19,840
Speaker 1: on this journey of curiosity and discovery. Thanks for having

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Speaker 1: me tune in next time. Everyone, Thanks for listening, and

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01:12:30,320 --> 01:12:33,040
Speaker 1: remember that Daniel and Jorge explained. The universe is a

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01:12:33,120 --> 01:12:36,559
Speaker 1: production of I Heart Radio. For more podcast For my

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01:12:36,640 --> 01:12:40,240
Speaker 1: Heart Radio, visit the I heart Radio app, Apple Podcasts,

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01:12:40,360 --> 01:12:42,719
Speaker 1: or wherever you listen to your favorite shows.