Latest / Daniel and Kelly’s Extraordinary Universe / Can the human eye see a single photon?

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Can the human eye see a single photon? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Katie, what is your favorite color? I'm gonna say blue. Well,
• 0:14
  Speaker 1: you can't just say blue. There's like a million different
• 0:16
  Speaker 1: shades of blue. Okay, I guess say more blue green
• 0:21
  Speaker 1: than a navy blue. Oh, you can do better than that.
• 0:24
  Speaker 1: Pretend you're like writing copy for a paint catalog. Give
• 0:28
  Speaker 1: us a really descriptive name. Okay, something like ce foam
• 0:32
  Speaker 1: mermaid tears or radiant peacock party. Now we're talking, But
• 0:39
  Speaker 1: for this podcast, can you give us like a really
• 0:41
  Speaker 1: good physics name for your shade of blue? How about
• 0:45
  Speaker 1: sparsely hydrogenated blue dwarf. That sounds awesome for me. I'm
• 0:51
  Speaker 1: personally looking forward to the day when somebody launches physics
• 0:55
  Speaker 1: paint colors and I can go to the store and
• 0:57
  Speaker 1: ask for a gallon of sultry supernova sky arlette. That
• 1:02
  Speaker 1: might blow up your her face. Hi. I'm Daniel. I'm
• 1:19
  Speaker 1: a particle physicist and a professor at UC Irvine, and
• 1:24
  Speaker 1: I've never met a color I didn't like. And I'm Katie.
• 1:27
  Speaker 1: I'm stepping in for Jorge this week. I am the
• 1:30
  Speaker 1: host of Creature Feature and I like all colors all
• 1:34
  Speaker 1: the time simultaneously. It makes me hesitate to ask what
• 1:40
  Speaker 1: your closet looks like. Katie Brown, I remember wondering as
• 1:47
  Speaker 1: a kid if there was a possibility for you to
• 1:50
  Speaker 1: imagine a color you hadn't seen before, you know, like,
• 1:53
  Speaker 1: if you thought hard enough, could you invent a color
• 1:56
  Speaker 1: in your mind that didn't exist out there in the world.
• 2:00
  Speaker 1: What do you think do you think that's possible? Yeah?
• 2:02
  Speaker 1: I mean I used to have that same exact thought,
• 2:05
  Speaker 1: thinking of, well, couldn't there be other colors than what
• 2:09
  Speaker 1: we know on the spectrum? And what would that be like?
• 2:12
  Speaker 1: And I would imagine that that experience of this new
• 2:15
  Speaker 1: color might be something beyond just vision, maybe accompanied by
• 2:20
  Speaker 1: a feeling like a tingling or something, I like the
• 2:24
  Speaker 1: connection of the senses. There. Maybe you see a new
• 2:27
  Speaker 1: kind of fruit and it has a new kind of taste,
• 2:30
  Speaker 1: and it opens up a whole new branch of philosophy.
• 2:33
  Speaker 1: Now we're getting into synesthesia territory exactly. But this question
• 2:37
  Speaker 1: of color is it really deep and fascinating one because
• 2:39
  Speaker 1: it extends all the way from philosophy, like what is
• 2:43
  Speaker 1: it like to experience a color? Down to biology how
• 2:46
  Speaker 1: does the human eye respond to photons? And finally to physics,
• 2:50
  Speaker 1: what exactly is a red photon and a blue photon
• 2:54
  Speaker 1: and a green photon, and that's exactly the kind of
• 2:56
  Speaker 1: topic we love to dive into on this podcast. So well,
• 3:00
  Speaker 1: welcome to the podcast Daniel and Jorge Exploding the Universe,
• 3:03
  Speaker 1: in which we ask the deepest, the reddest, the bluest,
• 3:05
  Speaker 1: the whitest, the darkest questions about the nature of the universe.
• 3:09
  Speaker 1: We ask questions that go all the way from your
• 3:11
  Speaker 1: eyeball deep deep down through your brain, and all the
• 3:14
  Speaker 1: way into your soul, whether or not it exists. I'm
• 3:17
  Speaker 1: so excited to smash biology and physics together and create
• 3:21
  Speaker 1: some kind of new particle and we're very excited to
• 3:24
  Speaker 1: have you with us today, Katie, Thanks very much for
• 3:26
  Speaker 1: filling in for Jorge. We always love talking about the
• 3:29
  Speaker 1: biological side of physics with you, Yes, the the squashy
• 3:33
  Speaker 1: side of physics as I call it. And today we
• 3:36
  Speaker 1: are going to be talking about all the things that
• 3:38
  Speaker 1: we can see, because vision plays such an important role
• 3:42
  Speaker 1: in how we perceive the world and how we imagine it.
• 3:45
  Speaker 1: I think if you close your eyes and try to
• 3:47
  Speaker 1: imagine the room around you, probably the image in your
• 3:51
  Speaker 1: mind would be an image. It would be something built
• 3:54
  Speaker 1: out of your visual perception of the world around you.
• 3:58
  Speaker 1: That might be different, of course for blind listeners or
• 4:00
  Speaker 1: other people who don't have strong vision. There's also people
• 4:03
  Speaker 1: with a fantasia who can see, but they actually don't
• 4:08
  Speaker 1: think in pictures, they don't imagine pictures. That blows my
• 4:12
  Speaker 1: mind that you can see things but that you can't
• 4:14
  Speaker 1: have images in your head. Yeah, there's just so many
• 4:17
  Speaker 1: different types of ways that humans can perceive the world exactly,
• 4:21
  Speaker 1: and that means that there are so many layers to
• 4:23
  Speaker 1: these kinds of questions, like what is happening at which stage,
• 4:26
  Speaker 1: How is your eyeball seeing a photon, how is it
• 4:28
  Speaker 1: sending a message, how is that message interpreted, how is
• 4:31
  Speaker 1: that message experienced by your brain? How is that used
• 4:34
  Speaker 1: to make decisions and think about the world. But it's
• 4:37
  Speaker 1: clear that eyeballs are an important part of understanding the
• 4:40
  Speaker 1: world around us, and not just the eyeballs that we
• 4:42
  Speaker 1: have in our skulls, but the other kinds of eyeballs
• 4:45
  Speaker 1: that we build to look at the universe. Our X
• 4:48
  Speaker 1: ray telescopes and are infrared telescopes and our gamma ray
• 4:51
  Speaker 1: telescopes that can see photons that are well out of
• 4:54
  Speaker 1: our visual spectrum, and so understanding how photons work and
• 4:57
  Speaker 1: how we see them is pretty core to understanding the universe.
• 5:01
  Speaker 1: See not just with the eyes and our schools, but
• 5:04
  Speaker 1: the eyes in our hearts, and also the eyes attached
• 5:06
  Speaker 1: to a giant telescope. It would be really weird if
• 5:10
  Speaker 1: we built the telescope that was literally made out of
• 5:12
  Speaker 1: human eyeballs, like strung together. That sounds pretty That's a
• 5:18
  Speaker 1: real biology physics collaboration right there. But the eyeball does
• 5:22
  Speaker 1: touch on a lot of deep questions. There are questions
• 5:25
  Speaker 1: their philosophy, there are questions of biology, and there are
• 5:27
  Speaker 1: also questions of quantum physics. And so today on the podcast,
• 5:31
  Speaker 1: we're going to be peering into all of these questions
• 5:34
  Speaker 1: and asking can the human eye see a single photon?
• 5:44
  Speaker 1: So what do you think, Katie? Is the human eyeball
• 5:47
  Speaker 1: a quantum device? I mean, this is a really interesting question,
• 5:52
  Speaker 1: and I really love how people are kind of thinking
• 5:56
  Speaker 1: about this in terms of like, well, it seems really
• 5:59
  Speaker 1: tiny and you need to magnify it when you need
• 6:01
  Speaker 1: to make it bigger? How can you see one wavelength?
• 6:06
  Speaker 1: And when you think about the eyeball, it certainly seems
• 6:10
  Speaker 1: like the eye is too big right to see just
• 6:13
  Speaker 1: a little tiny particle. But I think when you examine
• 6:17
  Speaker 1: inside the eye and see how teeny tiny and delicate
• 6:20
  Speaker 1: some of these cells that actually allow us to see,
• 6:24
  Speaker 1: makes me a little more convinced that maybe we could
• 6:27
  Speaker 1: see something even as small as a single photon. Yeah.
• 6:30
  Speaker 1: I think when people think about quantum mechanics, they think physics,
• 6:34
  Speaker 1: and then they think about mechanical devices that humans have built,
• 6:37
  Speaker 1: optics and semiconductors and specialized materials, things that you don't
• 6:41
  Speaker 1: typically associate with biology. But of course our bodies are
• 6:45
  Speaker 1: built out of molecules and atoms, the same building blocks
• 6:48
  Speaker 1: as what's in that crazy quantum lab in the basement
• 6:51
  Speaker 1: of your building. And so in principle, it's possible for
• 6:54
  Speaker 1: the human body or anybody to have quantum effects. And
• 6:58
  Speaker 1: I think there's a whole burgeoning field now of people
• 7:00
  Speaker 1: studying quantum biology, things that happen in bodies that rely
• 7:05
  Speaker 1: on quantum mechanics. And so, in principle, as you say,
• 7:09
  Speaker 1: it's possible for biological cells to develop capabilities which rely
• 7:12
  Speaker 1: fundamentally on quantum mechanics, I mean the fact that we
• 7:16
  Speaker 1: can step outside and get burned by u V rays
• 7:20
  Speaker 1: from the sun is pretty compelling evidence to me of
• 7:23
  Speaker 1: the direct impact of physics, even at the very small scale,
• 7:28
  Speaker 1: on our bodies. And I deal with that all the time, exactly.
• 7:33
  Speaker 1: And so I went outside and walked around the campus
• 7:36
  Speaker 1: of UC Irvine and asked a bunch of random students,
• 7:39
  Speaker 1: I Ranto and one chemistry professor if they thought that
• 7:43
  Speaker 1: the human eye could see a single photon. That is,
• 7:46
  Speaker 1: if you were in a dark room and I shot
• 7:49
  Speaker 1: one photon at your eyeball, would you see a flash
• 7:53
  Speaker 1: of light or not? To think about it for a
• 7:55
  Speaker 1: minute before you hear these answers, do you think the
• 7:57
  Speaker 1: human eye could see a single photon? Years what folks
• 8:00
  Speaker 1: on the U c Irvine campus had to say, there's
• 8:03
  Speaker 1: a neurological sense and also a physical sense. I mean,
• 8:06
  Speaker 1: if physical sense doesn't happen, then you will neuroinologically you
• 8:10
  Speaker 1: cannot sense it. So it's like I think it's physically
• 8:13
  Speaker 1: it makes sense then yeah, I mean and fultonic absorbing
• 8:17
  Speaker 1: content in the content sense. I think a single is possible.
• 8:21
  Speaker 1: I just don't know the threshold. I don't think so. No,
• 8:23
  Speaker 1: I don't think so. Why not? Uh, probably because it's
• 8:26
  Speaker 1: too small. I don't think so, just because this is
• 8:30
  Speaker 1: the size of it, Like even the human eye it's
• 8:33
  Speaker 1: only capable of seeing so much, so we even need
• 8:36
  Speaker 1: to magnify it or make it a little larger. No,
• 8:39
  Speaker 1: I don't think so. Why not? Just I just think
• 8:42
  Speaker 1: it's too minute for the eye to like distinguished. Yes,
• 8:47
  Speaker 1: I'm just guessing. Honestly. I feel like it's you can't
• 8:51
  Speaker 1: see one single wavelength? Right, So how many photons do
• 8:55
  Speaker 1: you think it takes before your eyeball response. I don't
• 8:58
  Speaker 1: know if it's like an amount of photons. Maybe it's
• 9:00
  Speaker 1: like a unit of energy one probably not. Isn't light
• 9:05
  Speaker 1: just photons? So, yes, you can see it. Do you
• 9:07
  Speaker 1: think you could see a single a single one? No? No, no,
• 9:12
  Speaker 1: why not? Um, I'm not sure. I don't feel like
• 9:15
  Speaker 1: you could see it. Well, I don't know if my
• 9:18
  Speaker 1: brain could register it, but I feel like a rotter
• 9:20
  Speaker 1: cone gonna pick it up. But it might just like
• 9:23
  Speaker 1: consider it some kind of like random you know, burst
• 9:25
  Speaker 1: of something or some some miss neural mis spider or something.
• 9:29
  Speaker 1: So there's a lot of nose there. What do you think, Katie?
• 9:32
  Speaker 1: I understand the skepticism because it really does seem like
• 9:37
  Speaker 1: that would be too small of a stimulus too for
• 9:41
  Speaker 1: us to really pick up on. Why would we need
• 9:44
  Speaker 1: to see a single photon? Humans aren't necessarily known for
• 9:48
  Speaker 1: being the most sensitive of animals. Not to be mean
• 9:52
  Speaker 1: about it, but we we don't have the best sense
• 9:54
  Speaker 1: of smell, We don't certainly don't have the best sense
• 9:57
  Speaker 1: of vision or the best hearing, So why would we
• 10:00
  Speaker 1: be able to see a single photon? And I really
• 10:05
  Speaker 1: like people kind of questioning whether, even if we could
• 10:09
  Speaker 1: pick it up at the cellular level, whether the brain
• 10:12
  Speaker 1: could even process that. So I under understand the skepticism,
• 10:16
  Speaker 1: but I do I think that the fact that the
• 10:20
  Speaker 1: inner workings of the eyeball are so incredibly small and precise,
• 10:29
  Speaker 1: I'm somewhat leaning towards yes, we might be able to
• 10:32
  Speaker 1: see a single photon. Yeah, I was a little disappointed
• 10:35
  Speaker 1: that these folks didn't have more confidence in our eyeballs.
• 10:38
  Speaker 1: Though I think you're right, I don't understand why we
• 10:41
  Speaker 1: would need to be sensitive to a single photon. It's
• 10:43
  Speaker 1: not like we typically go hunting in the dark for rodents, right,
• 10:46
  Speaker 1: Like if an owl could see a single photon or
• 10:48
  Speaker 1: an eagle could see a single photon, I get it,
• 10:51
  Speaker 1: but human like, we're pretty much napping at night anyway.
• 10:54
  Speaker 1: I was interested in learning more about the fundamental science
• 10:57
  Speaker 1: at the heart of this process, where photons are sorbed
• 11:00
  Speaker 1: by cells in your eye and converted into signals. So
• 11:03
  Speaker 1: I reached out to an expert we have here at
• 11:05
  Speaker 1: You See Irvine. Rachel Martin is a professor of chemistry
• 11:09
  Speaker 1: and she studies of vision, and I asked her to
• 11:11
  Speaker 1: share some thoughts with us about why vision is cool.
• 11:15
  Speaker 1: I'm Rachel Martin, and I'm a professor of chemistry and
• 11:17
  Speaker 1: molecular biology and biochemistry at you See Irvine. Great, and
• 11:21
  Speaker 1: I understand that one of the focuses of your research
• 11:24
  Speaker 1: is vision in the eye. So tell me what do
• 11:26
  Speaker 1: you love about eyeballs? Wind about your career to the
• 11:29
  Speaker 1: study of vision. What entrances you about vision? Vision is amazing.
• 11:34
  Speaker 1: I mean, for one thing, um, humans are very visual animals.
• 11:38
  Speaker 1: This is mostly how we perceive our world. It's you know,
• 11:42
  Speaker 1: it's one of the most important senses for us, which
• 11:45
  Speaker 1: is not true for a lot of mammals. A lot
• 11:46
  Speaker 1: of mammals experienced the world through smell, but for us
• 11:50
  Speaker 1: it's really a lot of it is about seeing things
• 11:53
  Speaker 1: and that's that's kind of our main detection system for
• 11:57
  Speaker 1: the world. And I think that's really neat. And I
• 11:59
  Speaker 1: also think it's pretty amazing that vision works at all.
• 12:03
  Speaker 1: There are a lot of kind of happy accidents of
• 12:06
  Speaker 1: physics that have to be the way they are to
• 12:08
  Speaker 1: enable vision. I mean, so, for instance, the human visual
• 12:11
  Speaker 1: range overlaps almost exactly with um the kind of the
• 12:15
  Speaker 1: whole in the absorption spectrum of water. So you know,
• 12:19
  Speaker 1: water absorbs at a lot of frequencies, but there's just
• 12:21
  Speaker 1: this tiny little window that where it doesn't, and that's
• 12:25
  Speaker 1: where we're we're able to see. And I think that's
• 12:29
  Speaker 1: really neat all. Right, So Rachel is clearly very excited
• 12:33
  Speaker 1: about the eyeball. She has devoted her entire research career
• 12:36
  Speaker 1: to studying the human eye. And I love that about
• 12:40
  Speaker 1: science that every time we're making progress, it's because one
• 12:43
  Speaker 1: person has decided this is the most important question in
• 12:46
  Speaker 1: the universe, and I'm going to devote my entire research
• 12:49
  Speaker 1: career to studying the lens in the human eyeball. I
• 12:53
  Speaker 1: love it. I mean, the eyeball is so bizarre that
• 12:58
  Speaker 1: it even works. It has caused things like people to
• 13:02
  Speaker 1: be skeptical of evolution, thinking, well, the I is such
• 13:06
  Speaker 1: a complex device, how could it possibly naturally evolve? Which
• 13:11
  Speaker 1: I'm sure we're going to talk about. But I am
• 13:14
  Speaker 1: not surprised by the fascination with eyeballs because they're so
• 13:19
  Speaker 1: clever and how they work and it is not straightforward
• 13:22
  Speaker 1: at all. I totally agree. And so let's dig into
• 13:24
  Speaker 1: it a little bit. Since you're the biologist of the
• 13:27
  Speaker 1: pair of us, why don't you give us a rundown
• 13:29
  Speaker 1: on how the eye works? What are the essential elements
• 13:32
  Speaker 1: of it? What comes into play when you are seeing
• 13:35
  Speaker 1: a photon? Right? I mean the ie weirdly enough, is
• 13:39
  Speaker 1: basically like a little camera. So if you've ever played
• 13:43
  Speaker 1: with like a big lens or magnifying glass or something,
• 13:47
  Speaker 1: you know how you can like focus the sun's light
• 13:50
  Speaker 1: into a little dot burned some ants with it if
• 13:53
  Speaker 1: you're evil. So the eye actually has lenses in it
• 13:57
  Speaker 1: that can have like come in, refracts and focuses on
• 14:01
  Speaker 1: a spot. So first, outside of your eye, uh, you
• 14:06
  Speaker 1: have the cornea, So that's the thing that you may
• 14:10
  Speaker 1: directly place the contact lens on, or if you're unlucky,
• 14:13
  Speaker 1: you can scratch the corny and that's really bad. But
• 14:16
  Speaker 1: that's basically this uh it's a convex shape and so
• 14:22
  Speaker 1: light comes in and the light is refracted in this
• 14:26
  Speaker 1: cornya and then uh it goes through the pupil and
• 14:32
  Speaker 1: the iris can constrict or expand, allowing more or less
• 14:37
  Speaker 1: light in and just like the aperture of a camera.
• 14:41
  Speaker 1: And after that, you actually have the lens, which is
• 14:46
  Speaker 1: like the focus on the camera. It you have these
• 14:49
  Speaker 1: two little muscles that attached to the lynching can like
• 14:52
  Speaker 1: pull it or kind of relax and let it contract,
• 14:57
  Speaker 1: and that allows you to focus the light. So if
• 15:00
  Speaker 1: you've ever tried to focus on something and then you could,
• 15:03
  Speaker 1: it's blurry it first and then it comes into focus.
• 15:05
  Speaker 1: That's your lens actually squashing and stretching in order for
• 15:10
  Speaker 1: you to focus on something, and that will focus the
• 15:12
  Speaker 1: light onto the retina, so that is the back of
• 15:16
  Speaker 1: your eye. And on the retina are these uh photosensitive receptors.
• 15:22
  Speaker 1: So there are rods and cones. There are three kinds
• 15:27
  Speaker 1: of cones and only one type of rod. And it
• 15:31
  Speaker 1: is through the way that these rods and cones detect
• 15:34
  Speaker 1: this light that you can see everything from colors to
• 15:38
  Speaker 1: shapes two distances. It's really incredible. And then where we
• 15:43
  Speaker 1: haven't even talked about how it gets to the brain.
• 15:46
  Speaker 1: You have a bundle of nerves. Basically you do you
• 15:51
  Speaker 1: do good cable management, Daniel, Uh, My cable management is
• 15:55
  Speaker 1: a disaster. Actually, yeah, I'm no one to preach about
• 16:00
  Speaker 1: cable management. But our eyes bundle all of these basically
• 16:04
  Speaker 1: cables that run to all of these photo sensitive cells
• 16:08
  Speaker 1: and then into the optic nerve at the back of
• 16:12
  Speaker 1: the eye. It actually creates a blind spot in eye
• 16:15
  Speaker 1: because there's this cluster of of nerves that can't perceive
• 16:21
  Speaker 1: any light, but they're just transmitting the signals from these
• 16:24
  Speaker 1: cells and that runs all the way back to the
• 16:27
  Speaker 1: back of our brain and the occipital lobe. So it
• 16:32
  Speaker 1: is not it is not a straightforward system, but it
• 16:35
  Speaker 1: works really well. It's really amazing. I like the way
• 16:38
  Speaker 1: you've in an analogy to a camera. Um, so we
• 16:40
  Speaker 1: have just to review the cornea bend the light onto
• 16:43
  Speaker 1: the lens. The iris decides how much light goes into
• 16:47
  Speaker 1: the eye. The lens itself focuses light on the retina
• 16:50
  Speaker 1: and the retina sort of like the film or the
• 16:52
  Speaker 1: digital sensors that formed the image. And then translates it
• 16:56
  Speaker 1: into these neurological signals, and that's stuff to me is
• 16:59
  Speaker 1: super fascinating because the thing that you observe, the thing
• 17:02
  Speaker 1: that you experience, are just the messages along the nerve itself,
• 17:06
  Speaker 1: right your brain, your subjective experience. You don't observe the
• 17:10
  Speaker 1: photons themselves. You just get these messages in your brain
• 17:13
  Speaker 1: plays that in your head sort of as an experience
• 17:16
  Speaker 1: of color. But we'll dig into that in a minute.
• 17:18
  Speaker 1: I think that's really interesting and it's fascinating to me
• 17:20
  Speaker 1: that the way we constructed a camera is so similar
• 17:23
  Speaker 1: to the way the eyeball worked. Do you think that
• 17:26
  Speaker 1: we like stole, we cribbed from the eyeball, We're like,
• 17:29
  Speaker 1: this is a good design, let's do it like that.
• 17:31
  Speaker 1: Or do you think it's an example of like convergent
• 17:33
  Speaker 1: evolution of technology and biology. You know, that's a really
• 17:36
  Speaker 1: good question. I don't know, but I could believe either,
• 17:40
  Speaker 1: because we have been studying the eye for for many years,
• 17:44
  Speaker 1: even long before our sort of modern understanding of biology.
• 17:50
  Speaker 1: So I could definitely see there being some inspiration from
• 17:53
  Speaker 1: the eye. But it could also have just been from coincidence,
• 17:57
  Speaker 1: because you know, the very earliest camera, the camera obscure
• 18:01
  Speaker 1: where it's just basically a little pinhole where light comes in.
• 18:04
  Speaker 1: It's such a small pinhole, you have this refraction of
• 18:08
  Speaker 1: light that turns up an image that's upside down in
• 18:11
  Speaker 1: the wall behind it. I could see that having been
• 18:14
  Speaker 1: just discovered kind of by by coincidence or accident. And
• 18:18
  Speaker 1: then we essentially reverse engineered the eyeball only in a
• 18:22
  Speaker 1: mechanical sense. And again what's really cool is that with
• 18:26
  Speaker 1: the camera's the same thing. The image is upside down
• 18:29
  Speaker 1: in the camera, it's the same way, and that I
• 18:32
  Speaker 1: actually the image as it's projected onto the retina, that
• 18:37
  Speaker 1: area where all of the photoreceptors are is upside down
• 18:40
  Speaker 1: and it flips because our brain is able to flip
• 18:44
  Speaker 1: that image right side up. So there's so many middlemen
• 18:47
  Speaker 1: happening in our brain to interpret what we're seeing. You
• 18:51
  Speaker 1: can't always trust your eyes to be exact reporters of reality.
• 18:56
  Speaker 1: And there's another layer of similarity there because the evolution
• 19:00
  Speaker 1: of the technology of the camera, as you say, we
• 19:02
  Speaker 1: started with pinhole cameras and then we've got fancy lenses
• 19:05
  Speaker 1: also mirrors, doesn't it the evolution of the eyeball in
• 19:08
  Speaker 1: biology right, like we think that early eyes actually were
• 19:12
  Speaker 1: more like pinhole cameras. Can you take us through roughly,
• 19:15
  Speaker 1: like how do the human eye evolved? Because this is
• 19:18
  Speaker 1: an argument some creation is to use sometime to say
• 19:21
  Speaker 1: that evolution can possibly be reality, because how could you
• 19:25
  Speaker 1: evolve the eyeball? Can you take us through sort of
• 19:27
  Speaker 1: the rough picture of how the eyeball evolved? Yeah, So,
• 19:30
  Speaker 1: first of all, it's funny to me about people who
• 19:33
  Speaker 1: are so skeptical of the eyeball being able to evolve.
• 19:36
  Speaker 1: It's like, not only has it evolved, it's evolved multiple times.
• 19:40
  Speaker 1: So um, actually, cephalopods including octopuses, completely independently evolved their
• 19:47
  Speaker 1: eye from almost every other animal on the planet. And
• 19:51
  Speaker 1: so this is not just some kind of ridiculous look.
• 19:55
  Speaker 1: It does make it seem a little bit more inevitable.
• 19:59
  Speaker 1: So when we were basically flat worms, we would have
• 20:03
  Speaker 1: kind of just like, uh, some cluster of photosensitive cells
• 20:09
  Speaker 1: that could detect light or dark, not really images, just
• 20:13
  Speaker 1: kind of like hey that's light, I go towards it,
• 20:16
  Speaker 1: or this is dark, I go towards it. So at
• 20:19
  Speaker 1: this very basic level, something like a flat worm and
• 20:23
  Speaker 1: the you know, very early ocean could go up towards
• 20:28
  Speaker 1: the sunlight, or recede back down into the darkness, or
• 20:32
  Speaker 1: go towards a spot obscured by the sunlight, maybe some
• 20:36
  Speaker 1: something to eat or something. But it couldn't form like
• 20:38
  Speaker 1: an actual image. But already that's a huge step forward.
• 20:42
  Speaker 1: That's recognizing that the universe around you is filled with
• 20:46
  Speaker 1: useful information, information you were literally blind to before you
• 20:50
  Speaker 1: develop this capacity. And now that you can sense the
• 20:53
  Speaker 1: fact that there are a bunch of photons over here
• 20:55
  Speaker 1: and not a bunch of photons over there, easy, useful
• 20:58
  Speaker 1: always makes me fantasize that we might be able to
• 21:00
  Speaker 1: like develops some new kind of cell that's sensitive to
• 21:03
  Speaker 1: dark matter or neutrinos or something, you know, in the
• 21:06
  Speaker 1: form the basis of seeing the universe in another way, right, like,
• 21:09
  Speaker 1: because we've done that before, we've developed the capacity to
• 21:12
  Speaker 1: see a previously invisible part of the universe anyway. That
• 21:16
  Speaker 1: just gives me hope, you know, for future evolution if
• 21:19
  Speaker 1: we live a few more million years, I think it's
• 21:22
  Speaker 1: definitely possible. Al Right, So how do you go from
• 21:25
  Speaker 1: having cells that can sense the existence of light to
• 21:29
  Speaker 1: you know, forming images and watching TV shows? Well, first,
• 21:33
  Speaker 1: there's something important that's missing with just this cluster of photoreceptors.
• 21:38
  Speaker 1: It's that you don't necessarily understand what direction something is,
• 21:43
  Speaker 1: or what's up and what's down. And so if you
• 21:46
  Speaker 1: actually recede those cells into like a little cave, like
• 21:51
  Speaker 1: a little socket, it matters which way the light is shining,
• 21:55
  Speaker 1: because you've limited the entry point of the light, and
• 21:58
  Speaker 1: now your aim can tell whether the light is coming
• 22:02
  Speaker 1: from up or from down. And then from there, now
• 22:06
  Speaker 1: that you've got basically an empty eye socket with receptors
• 22:11
  Speaker 1: at the back of the socket, once you start to
• 22:14
  Speaker 1: close that opening to the socket, now you're getting that pinhole.
• 22:18
  Speaker 1: So we're getting to the camera obscure apart where you
• 22:22
  Speaker 1: will get this the light. Not only are you able
• 22:26
  Speaker 1: to better tell what direction the light is, not just
• 22:29
  Speaker 1: up and down, but maybe side to side three sixty
• 22:32
  Speaker 1: kind of understanding of where the lights coming from. You
• 22:35
  Speaker 1: could also start to form very simple images because now
• 22:40
  Speaker 1: you're able to actually bend the light such that it
• 22:44
  Speaker 1: can become refracted and hit the back of your eye
• 22:47
  Speaker 1: in this image. I think that's a little counterintuitive that
• 22:50
  Speaker 1: you go from here's a slab where I can see photons,
• 22:54
  Speaker 1: and the step forward is to hide that is, to
• 22:57
  Speaker 1: like bury that inside you so that it's only can
• 23:00
  Speaker 1: be hit by a few photons that happened to pass
• 23:03
  Speaker 1: through like a little hole you make. That's counterintuitive because
• 23:06
  Speaker 1: you're getting less information, it seems like, because you're getting
• 23:08
  Speaker 1: fewer photons, but you're right, it's more information because you're
• 23:12
  Speaker 1: restricting the photons. So now you can tell this photon
• 23:15
  Speaker 1: must have come from up or must have come from down,
• 23:18
  Speaker 1: and based on where it hits on the inside of
• 23:20
  Speaker 1: this cavity, as you say, you can form an image.
• 23:22
  Speaker 1: That's a pretty cool technology. I don't know if I
• 23:24
  Speaker 1: would have thought of that myself. I mean, that is
• 23:26
  Speaker 1: one of the fascinating things about the senses. So much
• 23:29
  Speaker 1: of it isn't just the ability to sense something, but
• 23:34
  Speaker 1: the ability to prune out information, to restrict the information
• 23:39
  Speaker 1: you're getting so that your brain can make sense of
• 23:44
  Speaker 1: what is happening. Because if you're just getting all the
• 23:46
  Speaker 1: information all the time, you can't differentiate it, and so
• 23:50
  Speaker 1: you're not actually going to form a clear picture of
• 23:54
  Speaker 1: what is happening around you. And I think you're right.
• 23:56
  Speaker 1: It's that differentiation that's key. If you're seeing photons on
• 23:59
  Speaker 1: one side of the cavity and not the other. The
• 24:01
  Speaker 1: relative intensity there is what is telling you this source
• 24:04
  Speaker 1: of light is only coming from that direction and not
• 24:07
  Speaker 1: from the other. So it's about like comparative processing of
• 24:09
  Speaker 1: those signals, not just are their photons or not, but
• 24:12
  Speaker 1: like looking at where you're getting the signals and where
• 24:14
  Speaker 1: you're not getting the signals and using that to form
• 24:17
  Speaker 1: like a mental model of what's going on out there
• 24:19
  Speaker 1: in the world. Right, And so as we're tracing this
• 24:23
  Speaker 1: evolution of the eye, now we've got this cave right,
• 24:26
  Speaker 1: this this eyeball shaped cave with this little pinhole now
• 24:30
  Speaker 1: allowing us to see better direction and maybe start to
• 24:33
  Speaker 1: form these very blurry images. And then you can seal
• 24:38
  Speaker 1: that off right to protect the photoreceptors. And however, you
• 24:44
  Speaker 1: need to make sure that that inside of the eye
• 24:46
  Speaker 1: is still fluid filled. We are remember at this point
• 24:49
  Speaker 1: we are marine animals, probably some kind of very early
• 24:55
  Speaker 1: predecessor to uh, some species of fish, and you can't
• 25:00
  Speaker 1: just have an air pocket as an As a fish,
• 25:04
  Speaker 1: you typically want to have your organs filled with fluid.
• 25:08
  Speaker 1: Since your eye has been evolving to be able to
• 25:11
  Speaker 1: refract light in water. If you have the sudden air
• 25:14
  Speaker 1: pocket that's not going to allow you to see, so
• 25:17
  Speaker 1: you actually have this fluid filled I now of this
• 25:22
  Speaker 1: vitreous humor, and we actually still have that in the
• 25:25
  Speaker 1: human eye. It is not just an empty balloon filled
• 25:29
  Speaker 1: with air. It is filled with fluid. And then all
• 25:32
  Speaker 1: you need to start to get to the eye of
• 25:35
  Speaker 1: a more complex animal that can see more detailed images
• 25:41
  Speaker 1: is a lens and a cornea. So once you've started
• 25:46
  Speaker 1: to get this lens in that corner, you're able to
• 25:48
  Speaker 1: actually focus and make these specific images. And then uh,
• 25:53
  Speaker 1: from there, you have so many possibilities opened up to you.
• 25:56
  Speaker 1: Even though animals since of vision, can be really different,
• 26:00
  Speaker 1: the thing that they all share is they're really useful, uh,
• 26:04
  Speaker 1: in terms of their specific evolutionary niche. It's amazing that
• 26:08
  Speaker 1: we can reconstruct this story and that along with this
• 26:10
  Speaker 1: story gives us a clue about our own history seeing
• 26:13
  Speaker 1: things underwater from our great great great great great great
• 26:16
  Speaker 1: great great great ancestors, and also helps explain why some
• 26:19
  Speaker 1: eyeballs are different from other eyeballs. Here's a nice little
• 26:22
  Speaker 1: story from Rachel Martin explaining why fish eyeballs look different
• 26:26
  Speaker 1: from ours. When a photon hits your eyeball. You know,
• 26:30
  Speaker 1: first it has to go through the cornea and the lens,
• 26:34
  Speaker 1: and those things are really important because that's where we
• 26:37
  Speaker 1: get a lot of the focusing power, and particularly in
• 26:41
  Speaker 1: terrestrial organisms, you know, a lot of the focusing power
• 26:44
  Speaker 1: of your eyelands actually comes from that air water interface
• 26:46
  Speaker 1: at the cornea. And it's something that we don't necessarily
• 26:49
  Speaker 1: think about. And I know when I was a little kid,
• 26:53
  Speaker 1: you know, I really liked swimming, and I was really
• 26:56
  Speaker 1: sure that if I practiced enough, I would be able
• 26:59
  Speaker 1: to see underwater without goggles. And so you know, I
• 27:03
  Speaker 1: would try and try and try, and I thought it
• 27:05
  Speaker 1: was just you know, I have to keep trying and
• 27:07
  Speaker 1: keep practicing. But you know, my eyes are not optimized
• 27:11
  Speaker 1: to work underwater because I'm a terrestrial organism and so um.
• 27:15
  Speaker 1: You know, so no matter how much do you practice,
• 27:18
  Speaker 1: you need that air layer in front of your eye
• 27:21
  Speaker 1: for the you know, for the light to be properly
• 27:24
  Speaker 1: refracted to make an image. Our eyes are optimized that
• 27:27
  Speaker 1: way because you know, the lens is kind of flattened
• 27:30
  Speaker 1: and uh also, you know, the distribution of proteins structural
• 27:36
  Speaker 1: proteins inside the lens is optimized to work with that
• 27:39
  Speaker 1: air water interface at the cornea, whereas if you look
• 27:42
  Speaker 1: at a fish is lends, that's usually very spherical. And
• 27:47
  Speaker 1: that's because in a fish lens there's no air. Of course,
• 27:51
  Speaker 1: the fish is underwater, and so the proteins in that
• 27:53
  Speaker 1: lens have to do all the work. And this is
• 27:55
  Speaker 1: a really interesting thing too to notice. Next time you're
• 27:58
  Speaker 1: at like a public aquarium, you find the biggest fish
• 28:01
  Speaker 1: you can and look at their eyes, you can usually
• 28:04
  Speaker 1: see the lens. It's you know, it's often you know,
• 28:06
  Speaker 1: pretty easy to see in the fish eye, so you
• 28:09
  Speaker 1: can see the shapes. All right, So I think now
• 28:11
  Speaker 1: we have an understanding of what the eyeball is and
• 28:13
  Speaker 1: the basic mechanism and geometry of it. I want to
• 28:16
  Speaker 1: dig into the physics of color, what color means, and
• 28:20
  Speaker 1: how our eyeballs see these photons. But first let's take
• 28:23
  Speaker 1: a quick break. All right, we're back and we're talking
• 28:38
  Speaker 1: about eyeballs. We're not eating eyeballs. We're talking about shooting
• 28:42
  Speaker 1: photons into eyeballs and thinking about how they respond and
• 28:46
  Speaker 1: what that means and what your brain tells you about
• 28:49
  Speaker 1: the signals that crawl up the optic nerves O, Katie,
• 28:52
  Speaker 1: what color are you surrounded by right now? What color
• 28:55
  Speaker 1: are you looking at as we talk about this, I'm
• 28:57
  Speaker 1: actually looking at a very lovely shape of teal because
• 29:02
  Speaker 1: this apartment has painted in beautiful colors. Um the owner
• 29:08
  Speaker 1: of this apartment really loves teal, and so almost all
• 29:11
  Speaker 1: the walls are painted teal. It's it's very nice. I'm
• 29:14
  Speaker 1: not complaining. It's just you can really tell he loves
• 29:18
  Speaker 1: he loved teal, the guy who painted this apartment. My
• 29:22
  Speaker 1: daughter Hazel loves teal also, and she loves a very
• 29:25
  Speaker 1: particular shade of it. And for me, I'm like, well,
• 29:28
  Speaker 1: it's all just sort of this blue, and she's like,
• 29:30
  Speaker 1: oh my god, it's not just all blue, Like this
• 29:33
  Speaker 1: is blue and that's teal and this is something else
• 29:35
  Speaker 1: and monster. It's interesting to me that we do have
• 29:42
  Speaker 1: this very rich experience of color. You know that we
• 29:45
  Speaker 1: have a very different reaction to photons of one frequency
• 29:48
  Speaker 1: and another. So I think it's important that we dig
• 29:50
  Speaker 1: into what that means, what the physics is of it,
• 29:53
  Speaker 1: why it is that some photons give us a different
• 29:55
  Speaker 1: reaction from other colors. When I was a kid and
• 29:58
  Speaker 1: I learned there were only three to front wavelengths of white.
• 30:02
  Speaker 1: It was really bewildering because it's like, Okay, how do
• 30:05
  Speaker 1: we see so many different colors than if we there
• 30:08
  Speaker 1: are only these three wavelengths of why you would think
• 30:12
  Speaker 1: we would only see like red or green or blue. Yeah,
• 30:16
  Speaker 1: that's really interesting. And of course there are more than
• 30:19
  Speaker 1: just three wavelengths of light, all right, There are an
• 30:22
  Speaker 1: infinite number. So in the end, what is light? Light
• 30:25
  Speaker 1: are these little packets of energy, these photon, these quantized
• 30:30
  Speaker 1: little wiggles in the electromagnetic field. So the electromagnetic field
• 30:34
  Speaker 1: is something that fills all of space. The whole universe
• 30:37
  Speaker 1: has the field in it, and when there's energy in
• 30:39
  Speaker 1: the field, they can travel through that field. It consort
• 30:41
  Speaker 1: of like wiggle. Imagine like a guitar string and you're
• 30:45
  Speaker 1: sending a pulse along it. That's a photon. It's a
• 30:47
  Speaker 1: wiggle in the electromagnetic field. And it's a very special
• 30:51
  Speaker 1: kind of wiggle because it's self perpetuating. You know, it
• 30:53
  Speaker 1: can exist and then it can zoom across the universe
• 30:56
  Speaker 1: and exists somewhere else. It doesn't like the fuse or
• 30:59
  Speaker 1: spread out. It's like persistent and discreet, and that's in
• 31:02
  Speaker 1: the end, what we call a particle. All particles that
• 31:05
  Speaker 1: we see and experience in the universe are these little
• 31:07
  Speaker 1: discretized wiggles in quantum fields. Now people think about photons
• 31:12
  Speaker 1: as photons, as quantum particles, as discreet, and it's true
• 31:16
  Speaker 1: that they are quantized. Like you can have one photon
• 31:19
  Speaker 1: or two photons or seventy four photons. You can't have
• 31:23
  Speaker 1: one and a half photons or one point seven two photons.
• 31:26
  Speaker 1: You can only have integer numbers of photons. For those
• 31:30
  Speaker 1: of you curious about the physics of it and how
• 31:31
  Speaker 1: it is discovered, we have a whole podcast episode about
• 31:34
  Speaker 1: the photoelectric effect and how Einstein realized that photons came
• 31:38
  Speaker 1: in these little numbered packets. But there's another really important
• 31:41
  Speaker 1: fact about each photon, and that's its energy, and that's
• 31:45
  Speaker 1: something that is not quantized. So a single photon can
• 31:49
  Speaker 1: have any energy, meaning to have any wavelength. So typical
• 31:53
  Speaker 1: visible light is like four hundred to six hundred and
• 31:56
  Speaker 1: fifty nanometers, but there's an infinite number of different way
• 32:00
  Speaker 1: links between four hundred and six fifty. Just because of
• 32:03
  Speaker 1: photon is quantized doesn't mean it's energy levels are quantized.
• 32:07
  Speaker 1: So if there's an infinite number of frequencies. Would that
• 32:10
  Speaker 1: mean there are an infinite number of colors? Great question
• 32:13
  Speaker 1: and a really deep philosophy question, And the way I
• 32:16
  Speaker 1: think about it is that photons don't have colors. Color
• 32:19
  Speaker 1: is your brain's interpretation of the signals that it's getting.
• 32:22
  Speaker 1: There are an infinite number of different photons with an
• 32:24
  Speaker 1: infinite number of different frequencies, right, But those frequencies don't
• 32:28
  Speaker 1: necessarily all have a color assigned to them. The color
• 32:31
  Speaker 1: is something that your brain does, assigning it to the
• 32:34
  Speaker 1: response of the optical nerve. But in theory, if you
• 32:38
  Speaker 1: get enough living organisms that have some kind of eyeball
• 32:43
  Speaker 1: and some kind of brain that can detect some kind
• 32:47
  Speaker 1: of frequencies, we get enough, including all life on Earth
• 32:51
  Speaker 1: and probably a bunch of aliens, could we all perceive
• 32:56
  Speaker 1: infinite colors. It's a great question of neurology and philosophy
• 33:02
  Speaker 1: that I don't know the answer to, and you know,
• 33:05
  Speaker 1: we don't know the answer to even more basic questions
• 33:07
  Speaker 1: like is the red that you perceive the same read
• 33:10
  Speaker 1: as I perceive. It's a really old question that people
• 33:13
  Speaker 1: have been asking since they've been smoking bananappeals around the campfire,
• 33:16
  Speaker 1: and one that we still don't have an answer to.
• 33:19
  Speaker 1: And I think it's a great kind of question because
• 33:21
  Speaker 1: it shows us so the limitations of science. People think
• 33:25
  Speaker 1: about sciences maybe all powerful ways to reveal the nature
• 33:29
  Speaker 1: of the universe, and science is very powerful, but not
• 33:32
  Speaker 1: every question is necessarily a scientific question. You can't conduct
• 33:36
  Speaker 1: an experiment or come up with a theory that helps
• 33:39
  Speaker 1: you probe it, then science isn't necessarily the best tool.
• 33:42
  Speaker 1: And so the question of like is your red the
• 33:45
  Speaker 1: same as my red, relies purely on our subjective experiences,
• 33:49
  Speaker 1: which we can't translate from my brain to your brain,
• 33:52
  Speaker 1: so we have no way of knowing. I can't like,
• 33:54
  Speaker 1: measure the redness of your experience. So some of these
• 33:57
  Speaker 1: really deep and fascinating questions are for us treadingly just
• 34:00
  Speaker 1: past the fingertips of science. Well, I have a really
• 34:03
  Speaker 1: easy answer to that, and that my red is a
• 34:06
  Speaker 1: fire truck red. So question solved exactly when we point
• 34:11
  Speaker 1: to a fire truck and we say that's red. We
• 34:13
  Speaker 1: of course don't know what you're seeing and what I'm seeing.
• 34:16
  Speaker 1: If that actually looks like teal to my daughter, we'll see.
• 34:19
  Speaker 1: Let's go through a little bit the mechanism of how
• 34:22
  Speaker 1: your eye can tell which photons have hit it, like
• 34:25
  Speaker 1: which frequencies of light are hitting it. But before we
• 34:28
  Speaker 1: do that, let's just remind ourselves, like why are there
• 34:31
  Speaker 1: different frequencies? You know? Why is it that the fire
• 34:34
  Speaker 1: truck is red and blueberries are blue, and that leaves
• 34:37
  Speaker 1: are green and the sky is blue. Why are there
• 34:40
  Speaker 1: these different colors in our world? And the fundamental level
• 34:43
  Speaker 1: of reason from physics is to one is that sometimes
• 34:47
  Speaker 1: things get hot and hot things and glow at different temperatures.
• 34:51
  Speaker 1: Like the reason that we get light from the sun
• 34:54
  Speaker 1: is because the Sun is super duper hot, and as
• 34:56
  Speaker 1: things get hotter, they tend to emit light in higher
• 34:59
  Speaker 1: freak and see photons. So things that are cold in
• 35:03
  Speaker 1: midlight in the infrared, things that are warmer in mid
• 35:06
  Speaker 1: light in the visible like the sun. Things that are
• 35:09
  Speaker 1: super duper hot like accretion disks around black holes, emit
• 35:13
  Speaker 1: light in the ultraviolet or even up to the X
• 35:16
  Speaker 1: rays and gamma rays. These are all just different frequencies
• 35:19
  Speaker 1: along the electromagnetic spectrum. Is this is why when you
• 35:22
  Speaker 1: have a fire, you have sort of a really really
• 35:26
  Speaker 1: hot fire, it's going to be like white hot versus
• 35:30
  Speaker 1: orange hot. And blue hot exactly. And if you are
• 35:32
  Speaker 1: an amateur at home black smith, you know that white
• 35:36
  Speaker 1: hot and red hot are different temperatures of your steel.
• 35:38
  Speaker 1: That's something people have known for thousands of years before
• 35:41
  Speaker 1: we understood the physics involved. Right, that's like folk physics.
• 35:45
  Speaker 1: It's pretty cool. And the other way that color comes
• 35:47
  Speaker 1: into play physically isn't how materials absorb and reflect color. Like,
• 35:52
  Speaker 1: if you're looking at an object and it's red, it's
• 35:55
  Speaker 1: because you're getting red photons. You're getting photons of a
• 35:58
  Speaker 1: frequency that your brain is signed to. The color red
• 36:01
  Speaker 1: to your eyeball from that object, I say it's being
• 36:04
  Speaker 1: hit by white light. Light from the sun tends to
• 36:07
  Speaker 1: cover the whole visible spectrum. The reason you see it
• 36:10
  Speaker 1: is red is not because it's absorbing red. Right, doesn't
• 36:13
  Speaker 1: get red from the red photons. It's because it's absorbing
• 36:16
  Speaker 1: everything but red, and only the red light is getting
• 36:20
  Speaker 1: reflected to your eyeball. Right, A general thing with our
• 36:23
  Speaker 1: senses is anything you sense, from hearing to vision has
• 36:28
  Speaker 1: to physically hit you. Like your eyes have to be
• 36:32
  Speaker 1: physically smacked by photons for you to see them. Your
• 36:36
  Speaker 1: ears have to be physically smacked by sound. Waves. It's like,
• 36:41
  Speaker 1: you know our sense of touch. We understand you have
• 36:44
  Speaker 1: to physically touch something to feel it, but it's the
• 36:47
  Speaker 1: same thing with our eyes and our ears, even if
• 36:49
  Speaker 1: it doesn't feel that way, because you don't have to
• 36:52
  Speaker 1: press a leaf to your eye to see that it's green,
• 36:55
  Speaker 1: but you are technically feeling that leaf with your eye
• 37:00
  Speaker 1: all because the photons that are bouncing from the leaf
• 37:03
  Speaker 1: are hitting your eyeball physically. And that's exactly why things
• 37:07
  Speaker 1: that look green are things that reflect green, not things
• 37:10
  Speaker 1: that absorb green. Like if you eat a bunch of blueberries,
• 37:14
  Speaker 1: it makes you blue on the inside. You might think
• 37:16
  Speaker 1: that's the same way it works for light, but the
• 37:18
  Speaker 1: reason blueberries are blue is because they reflect blue, they
• 37:21
  Speaker 1: don't absorb blue. Isn't that why black things like a
• 37:26
  Speaker 1: black shirt gets really hot in the sun because it's
• 37:29
  Speaker 1: not it's not that it's absorbing black, which you can't
• 37:33
  Speaker 1: really absorb black, because black is just the absence of light.
• 37:37
  Speaker 1: It's absorbing that white light, which is a really high
• 37:40
  Speaker 1: energy light, which makes it hot. And that's why in
• 37:43
  Speaker 1: the desert people wear white because white is more reflective,
• 37:46
  Speaker 1: it doesn't absorb as many photons as black. Does, and
• 37:50
  Speaker 1: so that's why snow, for example, doesn't melt unless it
• 37:53
  Speaker 1: gets dirty. When snow gets dirty, it absorbs more light
• 37:56
  Speaker 1: and then it melts. But pure crystal white snow can
• 37:59
  Speaker 1: reflect a lot of on light and doesn't melt as quickly.
• 38:01
  Speaker 1: And you can actually get sunburned from the reflections of
• 38:04
  Speaker 1: snow because it's reflecting a lot of light at you.
• 38:08
  Speaker 1: And I learned this while skiing. You can get sunburned
• 38:12
  Speaker 1: on the bottom of your nose. Yes, it's fun exactly.
• 38:16
  Speaker 1: So now let's trace those photons into your eyes. You say,
• 38:19
  Speaker 1: they go through the cornea and the iris and the lens,
• 38:22
  Speaker 1: and they hit the retina. And what's going on on
• 38:24
  Speaker 1: the retina that allows you to see these things. Well, essentially,
• 38:26
  Speaker 1: you have a huge number of sensors, millions and millions
• 38:30
  Speaker 1: of these sensors of two kinds. You have the rods
• 38:33
  Speaker 1: and you have the cones. Rods are really good at
• 38:36
  Speaker 1: seeing small numbers of photons. They're good at seeing in
• 38:39
  Speaker 1: the dark, but you only have one kind of them,
• 38:41
  Speaker 1: and so they basically just say like yes or no.
• 38:44
  Speaker 1: The cones, however, you have three kinds of those, and
• 38:46
  Speaker 1: you refer to them earlier as blue, green, and red.
• 38:49
  Speaker 1: And the reason we call them that sometimes is because
• 38:52
  Speaker 1: they're good at seeing different frequencies of light. It's not
• 38:54
  Speaker 1: like they can only see one frequency. There's sort of
• 38:57
  Speaker 1: like a width to it. If you look at a
• 38:59
  Speaker 1: graph of like how likely one of these cones is
• 39:02
  Speaker 1: to see a photon of a different frequency, you see
• 39:05
  Speaker 1: that the ones we call s for short wavelength, the
• 39:09
  Speaker 1: ones that see blue light, peeking about four hundred and twenty,
• 39:12
  Speaker 1: but they can still see four hundred fifty nanimeter photons.
• 39:15
  Speaker 1: They're less likely to see five hundred and almost impossible
• 39:18
  Speaker 1: for them to see six hundred, but you know it
• 39:19
  Speaker 1: never goes to zero. And the red ones, the ones
• 39:23
  Speaker 1: we call long cones, those peaking about five hundred and
• 39:27
  Speaker 1: sixteen nanimeters, but they could still see a photon at
• 39:30
  Speaker 1: four fifties, just less likely. So they're like good at
• 39:33
  Speaker 1: different kinds of things. They're more likely or less likely
• 39:37
  Speaker 1: to see photons at different frequencies. And that's what your
• 39:40
  Speaker 1: brain is pulling together to say, oh, we're seeing something
• 39:43
  Speaker 1: that's red because it's tends to be lighting up the
• 39:45
  Speaker 1: long cones and not the short cones, or oh we're
• 39:48
  Speaker 1: looking at something that deal because it tends to be
• 39:51
  Speaker 1: lighting up their short cones and not the medium or
• 39:53
  Speaker 1: long cones as much. So there's a lot of interpretation.
• 39:56
  Speaker 1: They're just like back when you were talking about how
• 39:58
  Speaker 1: the eye evolved, and you're explaining how we have a cave,
• 40:02
  Speaker 1: and we're deducing where the light came from based on
• 40:05
  Speaker 1: where we are seeing light and where we are not.
• 40:07
  Speaker 1: Now we're deducing the color of the source of that
• 40:09
  Speaker 1: light based on which cones are lighting up and which
• 40:12
  Speaker 1: cones are not. And it's the relative excitement of the cones,
• 40:18
  Speaker 1: like if something's getting really lit up versus a little
• 40:22
  Speaker 1: bit lit up. That allows us to tell the difference
• 40:25
  Speaker 1: between bluish green and a greenish blue exactly. And there's
• 40:30
  Speaker 1: a lot of analysis there that's going on in your head.
• 40:32
  Speaker 1: And so I was curious, like how this actually works.
• 40:35
  Speaker 1: Why is it that this cone is better at that
• 40:38
  Speaker 1: frequency of light and this other cone is better at
• 40:41
  Speaker 1: the other frequency of light. What is the real mechanism
• 40:43
  Speaker 1: of it? So I asked the professor Martin to explain
• 40:46
  Speaker 1: to us what is actually happening when photons hit these
• 40:48
  Speaker 1: sensitive cells. And here's her explanation. The rods have ward
• 40:52
  Speaker 1: option and then the cones have they're just called options,
• 40:56
  Speaker 1: and these are proteins that undergo a confirmational chan change
• 41:00
  Speaker 1: when a photon hits them. And so the photon hits
• 41:03
  Speaker 1: the protein and then it's confirmation changes and that sends
• 41:06
  Speaker 1: a signal inside the cell. That is what transmits the
• 41:09
  Speaker 1: signal for that detection to our brains. I have an
• 41:12
  Speaker 1: understanding of a protein is like a little molecular machine,
• 41:16
  Speaker 1: and you're saying it can absorb a single photon and
• 41:18
  Speaker 1: that like chunks over mechanically from like one physical shape
• 41:22
  Speaker 1: to another physical shape, and that reflects having absorbed that energy.
• 41:25
  Speaker 1: And then something detects that the protein has shifted, is
• 41:28
  Speaker 1: that a little lever has been pushed by thee. Isn't
• 41:30
  Speaker 1: that amazing? So so it undergoes a conformational change, and
• 41:33
  Speaker 1: then something on the other side of the cell transmits
• 41:37
  Speaker 1: a signal and then that's some you know, that's how
• 41:39
  Speaker 1: your brain detects that that you saw that photon. And
• 41:42
  Speaker 1: the rods and cones are different in the proteins that
• 41:45
  Speaker 1: can absorb the photons, so they're can absorb photons of
• 41:47
  Speaker 1: different frequencies because it's a different protein they absorbed photons
• 41:50
  Speaker 1: at different frequencies, and the and the reason that they
• 41:53
  Speaker 1: have that difference in absorption is all about the protein.
• 41:55
  Speaker 1: So it's about the specifics of the you know, the
• 41:58
  Speaker 1: amino acid sequence and the structure of the protein. And
• 42:01
  Speaker 1: so why is it that the cones can't respond to
• 42:03
  Speaker 1: a single photon? Like do they need five or seven?
• 42:06
  Speaker 1: Is it because that lever and the protein is harder
• 42:08
  Speaker 1: to push? So, yeah, the rood option is the most
• 42:11
  Speaker 1: sensitive one. But like that's kind of a weak answer, right,
• 42:16
  Speaker 1: Like why is it the most sensitive one? I'm not
• 42:17
  Speaker 1: actually sure. Well, speaking of mysteries of the eye, what
• 42:20
  Speaker 1: are some sort of frontiers of research? Is there any
• 42:23
  Speaker 1: unknown physics that's happening in the eye, or there any
• 42:25
  Speaker 1: processes that go on that we don't understand funds? So,
• 42:29
  Speaker 1: for one thing, a really active area of research is
• 42:31
  Speaker 1: just how do the rhodoptions work? Because um, this is
• 42:35
  Speaker 1: one of the fastest known processes in biology, like the
• 42:39
  Speaker 1: early steps of what happens when a photon hits that
• 42:42
  Speaker 1: rhodopson So I mentioned that it undergoes a confirmational change,
• 42:45
  Speaker 1: So it actually has a small molecule that's bound inside
• 42:48
  Speaker 1: the protein. That's it's a retinal and it changes confirmation,
• 42:53
  Speaker 1: so you know, it goes from like a bent confirmation
• 42:56
  Speaker 1: to a straight confirmation. That's what makes the protein undergo
• 42:58
  Speaker 1: the confirmational change. But the first steps of that happened
• 43:03
  Speaker 1: really really fast, and so you need you need a
• 43:06
  Speaker 1: fast laser to be able to study it, and you
• 43:08
  Speaker 1: also need to do the whole thing in the dark. Alright,
• 43:10
  Speaker 1: So I thought that was super cool that basically we
• 43:13
  Speaker 1: have these proteins inside these rods and cones that change
• 43:17
  Speaker 1: configuration when a photon hits them. My mental picture is
• 43:21
  Speaker 1: like we have a little machine there. I think of
• 43:23
  Speaker 1: proteins is little machines, and like the photon like shifts
• 43:27
  Speaker 1: a lever, like you know, flips a switch almost physically.
• 43:30
  Speaker 1: That's incredible. Do you like to watch videos of Rube
• 43:33
  Speaker 1: Goldberg machines. It's like when you have a marble hit
• 43:38
  Speaker 1: a thing and then that releases a domino, and then
• 43:41
  Speaker 1: soon you've got a teapot boiling, and then that pops
• 43:45
  Speaker 1: a balloon and then a hammer lands on a lever.
• 43:48
  Speaker 1: That's how I like to visualize a lot of these
• 43:51
  Speaker 1: complex cellular processes, and that is very true of how
• 43:56
  Speaker 1: these rods and cones work so like you have a
• 44:00
  Speaker 1: photon literally hit like a little ever, it's changing the
• 44:04
  Speaker 1: molecules shape, which triggers a cascade of responses inside of
• 44:11
  Speaker 1: the cell. But you can visualize like a Rube Goldberg
• 44:15
  Speaker 1: machine or like a domino effect. And it's not just
• 44:18
  Speaker 1: something that happens once and then somebody spends like three
• 44:20
  Speaker 1: hours setting it up again, and not just response to
• 44:23
  Speaker 1: a photon and then unresponds and gets ready for another photon,
• 44:27
  Speaker 1: sometimes like milliseconds later. Right, Rachel was saying, this is
• 44:30
  Speaker 1: one of the fastest processes we know of in biology. Yeah,
• 44:34
  Speaker 1: and it is interesting because as fast as your cells
• 44:38
  Speaker 1: can be in responding to this, you can also overload
• 44:41
  Speaker 1: your cells if they're too sensitive, which is also it's
• 44:45
  Speaker 1: not just happening on the cellular level. This is something
• 44:48
  Speaker 1: that happens inside the brain. So as you're getting this
• 44:52
  Speaker 1: information right, because these sensors are sensing it and sending
• 44:55
  Speaker 1: that information to the brain, But it doesn't just go
• 44:58
  Speaker 1: directly to brain and say hey, look at this color.
• 45:01
  Speaker 1: It has to activate your neurons and then that's a
• 45:04
  Speaker 1: whole other roup Goldberg machine that happens at the neural level,
• 45:07
  Speaker 1: and you may have some threshold of activation for these neurons,
• 45:11
  Speaker 1: and so you get some really weird things that happened
• 45:14
  Speaker 1: with this interplay between the sensitivity of your photoreceptors in
• 45:18
  Speaker 1: your eye and the sensitivity of your neurons and your
• 45:21
  Speaker 1: occipital lobe, the vision center of the brain. And that's
• 45:24
  Speaker 1: why if you like stare at a bright color and
• 45:27
  Speaker 1: then you look at the wall, you see this like
• 45:28
  Speaker 1: weird afterimage. So it's a really interesting, I guess, just
• 45:32
  Speaker 1: thinking about these little, tiny machines working really hard, but
• 45:37
  Speaker 1: it's happening so quickly. It's the kind of thing that
• 45:39
  Speaker 1: makes you amaze that it ever works, and suddenly doubt
• 45:42
  Speaker 1: that it will continue to. You know, whenever I learned
• 45:44
  Speaker 1: how delicate these things are inside my body, I'm immediately terrified, like,
• 45:48
  Speaker 1: oh my gosh, what's how has this thing been going
• 45:50
  Speaker 1: for so long? Isn't it about to just fall apart?
• 45:53
  Speaker 1: But it's amazing it really works. Something was really interesting
• 45:56
  Speaker 1: to me was thinking about why the cones are sensitive
• 45:59
  Speaker 1: to different frequencies, and it's because they have different proteins
• 46:03
  Speaker 1: inside them which are better or worse at absorbing photons
• 46:06
  Speaker 1: of different frequencies, and why the rods are more sensitive
• 46:10
  Speaker 1: than the cones. Why make cones less sensitive than rods
• 46:14
  Speaker 1: and why make rods more sensitive than cones. I think
• 46:17
  Speaker 1: the answer is just diversification. Like you want to do
• 46:19
  Speaker 1: two different things. One is you want to be able
• 46:21
  Speaker 1: to see in low light conditions, and the others you
• 46:23
  Speaker 1: want to be able to see color so you can
• 46:25
  Speaker 1: spot that fruit or spot that predator. And being able
• 46:28
  Speaker 1: to see in low light conditions is actually somewhat mutually
• 46:32
  Speaker 1: exclusive to being able to see in higher light conditions,
• 46:35
  Speaker 1: because that requires your rods to be really, really sensitive
• 46:39
  Speaker 1: to light. And the more sensitive they are to light,
• 46:43
  Speaker 1: the more hyperactive they'll be when you have too much lights.
• 46:47
  Speaker 1: So your rods aren't that useful in highlight conditions, but
• 46:51
  Speaker 1: they're really useful in low light conditions. That's why if
• 46:54
  Speaker 1: you've ever stepped from a bright theater lobby into a
• 46:58
  Speaker 1: dark movie theater, you can't see where you're going and
• 47:01
  Speaker 1: you fall over and you land in a puddle of
• 47:03
  Speaker 1: coke and popcorn. Uh, it's because your eyes haven't adjusted
• 47:08
  Speaker 1: to the dark. But then as those rods kind of
• 47:11
  Speaker 1: like calm down, they adjust to that low light of
• 47:16
  Speaker 1: the dark room, and you can actually see in the dark.
• 47:19
  Speaker 1: And so yeah, the the rods being hyper sensitive is
• 47:23
  Speaker 1: useful for us to be able to see in low
• 47:26
  Speaker 1: light conditions. But then we have the cones that allow
• 47:29
  Speaker 1: us to see in brighter light, and not only that,
• 47:31
  Speaker 1: but differentiate color. And the cones are in the very
• 47:34
  Speaker 1: center of your eyeballs. When you're just looking straight at something,
• 47:37
  Speaker 1: you're good at seeing colors, and the rods tend to
• 47:39
  Speaker 1: be distributed in the other parts of the eyeball, which
• 47:42
  Speaker 1: means that like your peripheral vision is better at seeing
• 47:45
  Speaker 1: in low light conditions than your central vision is. So
• 47:48
  Speaker 1: for example, if you're an amateur astronomer and you like
• 47:50
  Speaker 1: looking at the night sky, sometimes you might notice a
• 47:53
  Speaker 1: star out of the corner of your eye. If you
• 47:55
  Speaker 1: then turn your eyeball to it, it can disappear. And
• 47:58
  Speaker 1: that's why because the scent or of your eyeball doesn't
• 48:01
  Speaker 1: have a lot of rods. So if you want to
• 48:03
  Speaker 1: observe faint things in the sky, don't look straight at
• 48:06
  Speaker 1: them where they disappear. It seems almost magical, which is
• 48:10
  Speaker 1: interesting evolutionarily right, because you think of when we would
• 48:13
  Speaker 1: need this low light vision, it probably would be at
• 48:18
  Speaker 1: night when we're trying to avoid getting eaten by a
• 48:20
  Speaker 1: nocturnal predator, so being able to see movement out of
• 48:24
  Speaker 1: the corner of our eye and flee or hide is
• 48:28
  Speaker 1: really important. Whereas in lower light having being able to
• 48:31
  Speaker 1: like focus on something specifically, Well, this is when we're sleeping.
• 48:35
  Speaker 1: We don't really need to hunt at night. We're not
• 48:38
  Speaker 1: nocturnal predators, so our eyes are optimized for being able
• 48:43
  Speaker 1: to see somewhat in low lights so we can protect ourselves,
• 48:47
  Speaker 1: but not optimized for being predators. Nocturnal predators, that's right.
• 48:52
  Speaker 1: And some of us have a different kind of eyeball
• 48:55
  Speaker 1: than the rest of us. Most of us have three
• 48:58
  Speaker 1: kinds of cones, so we can see light that peaks
• 49:01
  Speaker 1: in three different places. But some people have special eyes.
• 49:04
  Speaker 1: They are called tetra chromats, and they have a fourth
• 49:08
  Speaker 1: kind of cone, which means they have another kind of
• 49:11
  Speaker 1: thing in their eye that peaks at a different place.
• 49:14
  Speaker 1: It peaks bluer than blue on the spectrum. And this
• 49:18
  Speaker 1: to me was fascinating when I first learned about I thought, wow,
• 49:20
  Speaker 1: maybe they can see another kind of color. Maybe this
• 49:23
  Speaker 1: is like my childhood fantasy. There's like a super blue
• 49:26
  Speaker 1: that they can see in their minds that we can't see.
• 49:29
  Speaker 1: But unfortunately it's not like that. What it means is
• 49:31
  Speaker 1: that they are better at distinguishing between shades of blue.
• 49:35
  Speaker 1: They're like my daughter who can tell teal from slightly
• 49:38
  Speaker 1: not teal because they get more information about the relative
• 49:41
  Speaker 1: intensities of those photons, and so they're better at distinguishing colors.
• 49:45
  Speaker 1: They can't necessarily see or experience any new colors. And
• 49:49
  Speaker 1: I mean, on the opposite end of the visual spectrum,
• 49:52
  Speaker 1: you have people who are color blind or partially color blind.
• 49:55
  Speaker 1: And it's not that people necessarily only see in grace gale,
• 50:00
  Speaker 1: but they can be like blue green color blind, where
• 50:03
  Speaker 1: they have trouble distinguishing between blues and greens. So yeah,
• 50:07
  Speaker 1: there's this whole range of human vision, and it makes
• 50:11
  Speaker 1: me wonder, like your earlier question, whether there's a lot
• 50:15
  Speaker 1: of difference in vision amongst people who are not necessarily
• 50:20
  Speaker 1: tetrachromace or people who have color blindness, but just like
• 50:24
  Speaker 1: whether vision comes in a spectrum like many other human experiences, right,
• 50:30
  Speaker 1: because people experience chocolate differently, right, Like some people actually
• 50:33
  Speaker 1: enjoy white chocolate and aren't just pretending. You know, it's
• 50:36
  Speaker 1: a mystery they're just wrong. Thank you, thank you. People
• 50:43
  Speaker 1: respond subjectively very differently to stimuli, and so it would
• 50:47
  Speaker 1: make sense if people responded differently to different kinds of photons.
• 50:51
  Speaker 1: And we know that out there in the animal kingdom
• 50:53
  Speaker 1: there's also an incredible wide variety of eyeballs, right, Different
• 50:57
  Speaker 1: kinds of critters are have evolved too, dear for in
• 51:00
  Speaker 1: scenarios where they need more or less kinds of vision.
• 51:03
  Speaker 1: For example, we know that owls have incredible vision, especially
• 51:06
  Speaker 1: in low light because they have an enormous number of these.
• 51:10
  Speaker 1: Rods and geckos have really good actually night color vision
• 51:15
  Speaker 1: so that they can survive. Plus they have a tongue
• 51:17
  Speaker 1: that lets them clean their own eyeballs, which I think
• 51:20
  Speaker 1: is pretty crazy. It's adorable. Yeah, no, I It is
• 51:24
  Speaker 1: one of the most fascinating things in evolutionary biology, the
• 51:28
  Speaker 1: difference in vision. It's mysterious because we cannot objectively measure
• 51:35
  Speaker 1: what an animals experience of vision is. We can only
• 51:39
  Speaker 1: guests basically based on their eye structure and based on
• 51:43
  Speaker 1: their brain. So there, when you research it can come
• 51:46
  Speaker 1: to some really surprising results that are hard to conceptualize. So,
• 51:50
  Speaker 1: for instance, rants actually have double vision and can somewhat
• 51:56
  Speaker 1: move their eyes independently of each other. And we discovered
• 52:00
  Speaker 1: this by putting little teeny tiny high speed cameras attached
• 52:05
  Speaker 1: to little hats on rats and looking at their eye gays,
• 52:08
  Speaker 1: and they found that their eye gays indicates that they
• 52:11
  Speaker 1: prioritize keeping a view of the sky as well as
• 52:14
  Speaker 1: their surroundings so that they can avoid that owl who
• 52:18
  Speaker 1: has that great night vision. So rats are running along
• 52:21
  Speaker 1: the ground with one eye up and one eye down.
• 52:24
  Speaker 1: That's crazy, basically, Yeah. And what's so weird is that
• 52:29
  Speaker 1: researchers think that these fields of vision in either I
• 52:33
  Speaker 1: are too different to be fused into a single image.
• 52:37
  Speaker 1: So there's a possibility that rants basically have like two
• 52:41
  Speaker 1: TV monitors in their head that they're both keeping track
• 52:45
  Speaker 1: of and unlike us, where we have basically one combined image.
• 52:51
  Speaker 1: And I mean just the the ingenuity that animals have
• 52:55
  Speaker 1: when it comes to eyeballs can be completely baffling. Like
• 52:59
  Speaker 1: this is a fun named one, but it's a brown
• 53:01
  Speaker 1: nose spook fish, which is a species of barrel eye fish.
• 53:06
  Speaker 1: It's this very weird looking fish. It's not very big.
• 53:10
  Speaker 1: It's like about seven inches maybe like the length of
• 53:13
  Speaker 1: your hand, it's got a transparent body. It looks kind
• 53:16
  Speaker 1: of creepy, like some kind of ghost of a fish.
• 53:20
  Speaker 1: And it is actually only vertebrate that is known to,
• 53:24
  Speaker 1: in addition to a lens, have an actual mirror in
• 53:29
  Speaker 1: their eye. So the way that animals can have mirrors
• 53:33
  Speaker 1: is they use guanting crystals to form a mirror, because
• 53:37
  Speaker 1: a guanting crystal is a protein that an organic animal
• 53:41
  Speaker 1: can produce, but it's structure is reflective, and so this
• 53:47
  Speaker 1: is actually also used in scallops. Scalops have eyes. In fact,
• 53:51
  Speaker 1: they have hundreds of eyes, which is a fun thought
• 53:54
  Speaker 1: next time you enjoy your scalp. But yes, so so
• 53:57
  Speaker 1: this brown snout spook fish, it has a normal eye
• 54:03
  Speaker 1: that looks upwards, and then in addition to that, it
• 54:07
  Speaker 1: actually has an annex ee like just stuck to the
• 54:09
  Speaker 1: side of it, like a side view mirror on a car.
• 54:13
  Speaker 1: It has a mirror that allows it to look downwards.
• 54:16
  Speaker 1: So this fish can look both upwards and downwards at
• 54:19
  Speaker 1: the same time. Well, that's a very useful kind of
• 54:22
  Speaker 1: side eye. One of my favorite kind of eyeballs out
• 54:24
  Speaker 1: there in the world is the mantis shrimp. The mantis
• 54:27
  Speaker 1: shrimp doesn't just have three or four kinds of cones.
• 54:30
  Speaker 1: They estimate it might have fifteen or sixteen different kinds
• 54:35
  Speaker 1: of cones in its eye. And when you first read
• 54:37
  Speaker 1: about that, you think, wow, the mantis strip must have
• 54:39
  Speaker 1: like a really vibrant visual experience. It's like MARTAGRAI every
• 54:43
  Speaker 1: day for the mantis shrimp. Right, Well, it turns out
• 54:45
  Speaker 1: the mantis strip actually isn't any better than humans at
• 54:49
  Speaker 1: distinguishing colors. They do these experiments where they train the
• 54:52
  Speaker 1: shrimp like go to food if you can see the
• 54:54
  Speaker 1: difference between the colors, and they aren't any better at
• 54:57
  Speaker 1: distinguishing colors than we are. And we only have three
• 54:59
  Speaker 1: kinds of codes. And the reason is that the mantis
• 55:02
  Speaker 1: shrimp basically has much more specific hardware, but it doesn't
• 55:05
  Speaker 1: have the processing power to really take advantage of that.
• 55:08
  Speaker 1: Their brains are really simple. So we have like simpler
• 55:12
  Speaker 1: hardware only three sensors, but very complicated software to interpret
• 55:16
  Speaker 1: and analyze that. And the manti strimp has made like
• 55:18
  Speaker 1: a different optimization, like go all in on the hardware
• 55:21
  Speaker 1: and have really simple software to interpret it. It's pretty fascinating, right,
• 55:25
  Speaker 1: And the reason for that is that the mantis shrimp
• 55:29
  Speaker 1: is optimizing the speed of its site rather than sort
• 55:33
  Speaker 1: of the detail of its perception. So it's thought that
• 55:36
  Speaker 1: with less software and more hardware, you can actually sense
• 55:41
  Speaker 1: something much more quickly, like the because the speed of
• 55:44
  Speaker 1: light is quite fast. Uh. And then if you can
• 55:47
  Speaker 1: have these photoreceptors pick up on that photon really quickly
• 55:52
  Speaker 1: because you just have so many, then even if your
• 55:55
  Speaker 1: software is relatively simple of just like, hey, there's a thing,
• 55:59
  Speaker 1: if it's quick enough, it will have incredible reflexes. That
• 56:03
  Speaker 1: makes a lot of sense of speed of light is
• 56:04
  Speaker 1: faster than the speed of brains. I definitely, I definitely
• 56:07
  Speaker 1: don't think at the speed of light and like, is
• 56:10
  Speaker 1: that a shark? Or is that dinner? Oops? Too late,
• 56:13
  Speaker 1: I'm being eaten already. Well. One of my favorite stories
• 56:17
  Speaker 1: about color and animals comes again from Rachel Martin, who
• 56:20
  Speaker 1: told us the story about how birds that seems sort
• 56:23
  Speaker 1: of boring and blue turned out to be actually ultra
• 56:25
  Speaker 1: violet and spectacular. So here's Rachel talking about one of
• 56:29
  Speaker 1: her favorite studies. One of my favorite papers in this
• 56:33
  Speaker 1: area is one where these scientists were looking at blue tips,
• 56:37
  Speaker 1: so a little birds, and they thought that these birds
• 56:42
  Speaker 1: didn't really have a strong sexual selection system because they
• 56:46
  Speaker 1: all kind of look the same. And you know, for
• 56:47
  Speaker 1: a lot of birds, like the males are really pretty
• 56:49
  Speaker 1: and showy, and they have markings that the females are choosing,
• 56:53
  Speaker 1: and for these birds, they didn't seem to They seemed
• 56:55
  Speaker 1: to all look the same. And then somebody finally thought
• 56:58
  Speaker 1: of doing some ex erments with whether these they had
• 57:03
  Speaker 1: pigments in the UV. So they put m vast lean
• 57:06
  Speaker 1: on the bird's heads. So they discovered that they had
• 57:08
  Speaker 1: some markings in the UV, like on their heads, and
• 57:12
  Speaker 1: so if they put vast lean over it so that
• 57:14
  Speaker 1: that blocked the UV, the females, you know, didn't you
• 57:20
  Speaker 1: weren't able to see those markings, and so then there
• 57:22
  Speaker 1: was a big difference in the sexual selection. So the
• 57:24
  Speaker 1: males that were really popular before because they had these
• 57:27
  Speaker 1: beautiful UV markings on their heads, when you put bass
• 57:29
  Speaker 1: lean on them, then they don't get any attention because
• 57:32
  Speaker 1: the females can't see this. And so it led to
• 57:37
  Speaker 1: you know, one of my favorite paper titles of all time,
• 57:39
  Speaker 1: which was blue Tips Are Ultra Violet Tits. I love
• 57:43
  Speaker 1: that story and I wish I get to write a
• 57:45
  Speaker 1: paper using the phrase ultra violet tits. I wish I
• 57:48
  Speaker 1: had gotten to rub vassilene on a bird's head. So
• 57:53
  Speaker 1: many adventures in science, you know, the more animals we
• 57:57
  Speaker 1: stick under black light them, or we're finding have this
• 58:02
  Speaker 1: like biofluorescence exactly. So we see a little slice of
• 58:07
  Speaker 1: the universe that's out there, and a lot of animals
• 58:09
  Speaker 1: can see further into that spectrum and are advertising to
• 58:13
  Speaker 1: each other in that spectrum, and so it's like we're
• 58:16
  Speaker 1: not seeing what's going on out there. Maybe there are
• 58:18
  Speaker 1: some animals that can see neutrinos and are sending neutrino
• 58:21
  Speaker 1: messages to each other, you know, they have like pigments
• 58:24
  Speaker 1: in their feathers that glow in neutrinos. No, I'm sure
• 58:27
  Speaker 1: they don't. But that sounds like a fun science fiction story.
• 58:30
  Speaker 1: But let's get back to the actual science of the universe.
• 58:33
  Speaker 1: And I want to answer our question about whether a
• 58:35
  Speaker 1: human eye can respond to a single polton human eyeball
• 58:40
  Speaker 1: as a quantum device. But first let's take a second break.
• 58:56
  Speaker 1: All right, we're back, and we have explained to ourselves
• 58:58
  Speaker 1: how the eyeball works, how it receives photon, how it
• 59:02
  Speaker 1: triggers this ridiculous Rube Goldberg machine of flipping levers and
• 59:06
  Speaker 1: rolling balls and cascading signals so that you can experience
• 59:10
  Speaker 1: the reddest read that there is. Yeah, I'm really excited
• 59:14
  Speaker 1: about this because I would love to see a single photon.
• 59:19
  Speaker 1: They're responsible for so much stuff that happens in the universe,
• 59:23
  Speaker 1: and I'd like to personally thank it for being there.
• 59:25
  Speaker 1: And we could finally answer one of the most ancient
• 59:27
  Speaker 1: questions in philosophy, which is what does a photon look like?
• 59:31
  Speaker 1: But it's interesting and relevant to physics because if you
• 59:34
  Speaker 1: look up at the night sky, you see some things
• 59:36
  Speaker 1: that are very bright, the moon or nearby planets and stars,
• 59:40
  Speaker 1: but you also see some things that are very, very dim,
• 59:42
  Speaker 1: just at the edge of your perception. And I've often wondered,
• 59:46
  Speaker 1: when looking at the night sky, how many photons am
• 59:48
  Speaker 1: I seeing? You know, imagine some incredibly huge, bright star
• 59:53
  Speaker 1: that's billions and billions of miles away, shooting ten to
• 59:56
  Speaker 1: the fifty photons per second out into the cosmos. All
• 59:59
  Speaker 1: the those photons, just a few have managed to cross
• 1:00:02
  Speaker 1: that enormous ocean of dark and hit your eyeball. But
• 1:00:06
  Speaker 1: it makes me wonder how many photons have to make
• 1:00:09
  Speaker 1: it before I can see that star. What happens to
• 1:00:13
  Speaker 1: those photons on the way from the star to our eyeball?
• 1:00:17
  Speaker 1: Do they get knocked around by other particles? They have
• 1:00:21
  Speaker 1: a great adventure along the way, They make friends, they
• 1:00:25
  Speaker 1: you know, complete quests. No, it's incredible. Mostly those photons
• 1:00:28
  Speaker 1: just fly unimpeded through the universe because space is mostly
• 1:00:32
  Speaker 1: transparent to those photons. There are things out there, the
• 1:00:35
  Speaker 1: solar wind and particles that will interact with really high
• 1:00:39
  Speaker 1: energy photons, but lower energy photons like the ones in
• 1:00:42
  Speaker 1: the visible spectrum, can mostly fly untouched through space. The
• 1:00:46
  Speaker 1: last thing they interacted with was the surface of the Sun,
• 1:00:48
  Speaker 1: and the next thing they interact with is your eyeball.
• 1:00:51
  Speaker 1: The reason, of course you don't see ten to the
• 1:00:53
  Speaker 1: fifty photons from that star is just because the photons
• 1:00:57
  Speaker 1: are going in every single direction. So if you have
• 1:00:59
  Speaker 1: ten of the fifty covering the surface of the star
• 1:01:02
  Speaker 1: and they all shoot out than a year later, now
• 1:01:05
  Speaker 1: that same number of photons is painting the inside of
• 1:01:08
  Speaker 1: a spear that has a radius of one light year,
• 1:01:11
  Speaker 1: and so like per area, there are many fewer photons
• 1:01:15
  Speaker 1: by the time it gets to you, billions of miles away,
• 1:01:18
  Speaker 1: there's just very few photons per square meter. That's why
• 1:01:21
  Speaker 1: the star feels distant, and that's why the intensity of
• 1:01:24
  Speaker 1: light falls like one over the radius squared, because that's
• 1:01:27
  Speaker 1: the surface area of the inside of a sphere of
• 1:01:30
  Speaker 1: that radius. Well, I'm glad it's a little bit diffused,
• 1:01:32
  Speaker 1: because otherwise I think it might just kind of instantly
• 1:01:36
  Speaker 1: vaporize our eyeballs. And it's a question that scientists have
• 1:01:39
  Speaker 1: been asking since we understood what photons were like, could
• 1:01:43
  Speaker 1: we see an individual photon? Is that even possible? At first,
• 1:01:46
  Speaker 1: we have to separate into two questions. One is could
• 1:01:48
  Speaker 1: you see a photon which hits the outside of your eye?
• 1:01:52
  Speaker 1: And the second is could you see a photon which
• 1:01:54
  Speaker 1: hits the actual receptors on the back of your eye?
• 1:01:57
  Speaker 1: Because it turns out something that's pretty easy to measure
• 1:02:00
  Speaker 1: is the efficiency for photons to get to the back
• 1:02:02
  Speaker 1: of your eyeball. And only like one inten photons that
• 1:02:06
  Speaker 1: hits the surface of your eye actually makes it to
• 1:02:08
  Speaker 1: the retina. Is it getting uh, sort of lost on
• 1:02:12
  Speaker 1: the way, is it not reaching the pupil or is
• 1:02:14
  Speaker 1: it bouncing off something on your eye before reaching the
• 1:02:19
  Speaker 1: back of your eye? Yeah, they get scattered and they
• 1:02:21
  Speaker 1: get absorbed. Remember that has light traveled through materials. If
• 1:02:25
  Speaker 1: you change the reflectivity or basically the index of refraction
• 1:02:28
  Speaker 1: of the material, you're gonna get some reflection at that surface.
• 1:02:32
  Speaker 1: Even when photons go from air, which is transparent, to glass,
• 1:02:35
  Speaker 1: which is transparent, there's always some reflection. And so as
• 1:02:39
  Speaker 1: you go through the vitreous humor and go through the
• 1:02:41
  Speaker 1: lens and go through the cornea, there's little bits of
• 1:02:43
  Speaker 1: reflection here and there and scattering and absorption. It's not
• 1:02:47
  Speaker 1: a transparent so only one in ten photons actually makes
• 1:02:51
  Speaker 1: it to the back of the eyeball, which is crazy. Yeah,
• 1:02:54
  Speaker 1: it seems like we're losing a lot of photons on
• 1:02:57
  Speaker 1: the way over there. We gotta put some like signs
• 1:03:00
  Speaker 1: up on our eyeballs, like photons inter here don't get lost.
• 1:03:05
  Speaker 1: So people started doing experiments to see how sensitive the
• 1:03:07
  Speaker 1: eye was. Back in like the nineteen forties, they didn't
• 1:03:10
  Speaker 1: experiment Columbia University where they shot very very low intensity
• 1:03:15
  Speaker 1: light into the eyeball to try to understand what the
• 1:03:18
  Speaker 1: threshold was. But back then they didn't have like a
• 1:03:21
  Speaker 1: great understanding of quantum mechanics and quantum optics, it was
• 1:03:24
  Speaker 1: not easy for them to manipulate the light to really
• 1:03:27
  Speaker 1: get a handle on having a single photon. So what
• 1:03:29
  Speaker 1: they could tell was that the human eye was very,
• 1:03:32
  Speaker 1: very sensitive to small numbers of photons, but they couldn't
• 1:03:35
  Speaker 1: conclusively pin it down because it's very difficult to provide
• 1:03:39
  Speaker 1: a single photon source, one individually wrapped photon. Yeah, and
• 1:03:45
  Speaker 1: to know that that's when the photon was there, right.
• 1:03:47
  Speaker 1: The basic experiment you want is to shoot a photon
• 1:03:51
  Speaker 1: at somebody's eyeball, to know that you shot the photon
• 1:03:53
  Speaker 1: there and when you did it, and then have them
• 1:03:55
  Speaker 1: press a button and say I saw a photon, And
• 1:03:57
  Speaker 1: that way you can correlate the button presses with when
• 1:04:00
  Speaker 1: the photons arrived. You could say, yeah, there are reliable
• 1:04:03
  Speaker 1: indicators of when the photon arrives. And if they're always
• 1:04:05
  Speaker 1: just pressing the button right, then you can tell this
• 1:04:08
  Speaker 1: person is crazy. This it is useless. And so to
• 1:04:11
  Speaker 1: prove that somebody could see a single photon, you need
• 1:04:14
  Speaker 1: to know when that single photon is hitting the eye.
• 1:04:17
  Speaker 1: That's the crucial thing. And if all you have our
• 1:04:19
  Speaker 1: light sources that are sort of classical, like hot things
• 1:04:22
  Speaker 1: glowing like a light bulb, you know, which has a
• 1:04:24
  Speaker 1: tongusen filament in it which glows because it gets hot
• 1:04:27
  Speaker 1: and shoots out of photons. It's difficult to manage because
• 1:04:30
  Speaker 1: you can turn it down and you can make it
• 1:04:32
  Speaker 1: very low intensity, but you don't have control over when
• 1:04:35
  Speaker 1: the photons are admitted, so you never know, for example,
• 1:04:37
  Speaker 1: like was that one photon that came out or two
• 1:04:40
  Speaker 1: that Katie pressed the button? Because that was the one
• 1:04:42
  Speaker 1: time when a couple of photons actually hit her eyeball
• 1:04:45
  Speaker 1: and not the time when a single photon hit the eyeball.
• 1:04:47
  Speaker 1: And so the breakthrough in these experiments actually wasn't until
• 1:04:50
  Speaker 1: about ten years ago when people developed really crazy nonlinear
• 1:04:55
  Speaker 1: quantum optics to separate individual photons. So is it like
• 1:04:59
  Speaker 1: a little little gun that shoots a photon. It would
• 1:05:04
  Speaker 1: be pretty cool to have like a button you could
• 1:05:05
  Speaker 1: press to shoot a single photon. The key idea actually
• 1:05:08
  Speaker 1: is to split a photon. So you have a very
• 1:05:11
  Speaker 1: low intensity source that shoots out photons at you, and
• 1:05:14
  Speaker 1: what you do is you pass it through a special
• 1:05:16
  Speaker 1: kind of crystal it's called a down converter, and it
• 1:05:19
  Speaker 1: takes a single photon and it splits it into two
• 1:05:21
  Speaker 1: photons of less energy. Now, one you can use for
• 1:05:24
  Speaker 1: your experiment, and the other one you can use is
• 1:05:26
  Speaker 1: a tag that tells you, like, oh, a photon just
• 1:05:28
  Speaker 1: came through. You can measure those using very high precision optics,
• 1:05:32
  Speaker 1: so you know when the experiment tee is observing photons
• 1:05:36
  Speaker 1: and when they're not, and so you can tell, oh,
• 1:05:38
  Speaker 1: there are two photons in the experiment right now, let's
• 1:05:40
  Speaker 1: disregard this, and you can tell when a single photon
• 1:05:43
  Speaker 1: has arrived and no other photons have come through. So
• 1:05:46
  Speaker 1: it's more about being able to count the photons and
• 1:05:49
  Speaker 1: actually manipulating the photons themselves. Oh that's so interesting, yeah,
• 1:05:53
  Speaker 1: because like if you want to detect a photon, you
• 1:05:56
  Speaker 1: kind of have to have whatever thing detect the photon
• 1:06:00
  Speaker 1: interact with the photon, which would not necessarily allow it
• 1:06:03
  Speaker 1: to also reach the eye right exactly, you don't want
• 1:06:06
  Speaker 1: to interfere with that photon which is headed towards the eyeball.
• 1:06:09
  Speaker 1: So this crazy quantum optics, these strange crystals split it
• 1:06:13
  Speaker 1: and give you one photon for your accounting and another
• 1:06:16
  Speaker 1: photon for your experiment, and there of course entangled together.
• 1:06:19
  Speaker 1: And so you know that when you see a photon,
• 1:06:21
  Speaker 1: and your little detector that the eyeball should also have
• 1:06:24
  Speaker 1: seen one. So then they could have people sitting there
• 1:06:27
  Speaker 1: pressing a button and answering like, oh I saw one, No,
• 1:06:29
  Speaker 1: I didn't see one. It's like one of those uh
• 1:06:31
  Speaker 1: those like heart necklaces you'd get at Chuck E Cheese
• 1:06:35
  Speaker 1: is with your best friend forever. It's like split in
• 1:06:38
  Speaker 1: half and each one of you got one piece of
• 1:06:41
  Speaker 1: the heart necklace. Yeah, it's just like that. In fact,
• 1:06:45
  Speaker 1: it's called the Chuck E Cheese Experiment just for that.
• 1:06:49
  Speaker 1: And so it's only in two sixteen that they finally
• 1:06:52
  Speaker 1: put all of this together, this crazy experimental apparatus, and
• 1:06:55
  Speaker 1: confirmed that the human eye can see a single photon.
• 1:06:59
  Speaker 1: If it makes it to the retina, it will be
• 1:07:02
  Speaker 1: able to detect it. So if you're sitting in a
• 1:07:04
  Speaker 1: dark room and a single photon from a distant star
• 1:07:07
  Speaker 1: HiT's your retina, you will see a flash of light.
• 1:07:10
  Speaker 1: So in with people in this experiment, they're pressing this
• 1:07:14
  Speaker 1: button when they're seeing a flash of light, did they
• 1:07:17
  Speaker 1: describe like what that experience was like? Yeah, they see
• 1:07:21
  Speaker 1: like a tiny little pinprick of light, like the smallest
• 1:07:24
  Speaker 1: little flashlight possible. That's amazing. It is amazing, and it
• 1:07:28
  Speaker 1: tells you like sort of the limit of your ability,
• 1:07:31
  Speaker 1: like lights up a single pixel in your brain, so
• 1:07:33
  Speaker 1: now you can tell like how big is one of
• 1:07:35
  Speaker 1: your brain pixels. I think it's super cool, And people,
• 1:07:41
  Speaker 1: of course have gone beyond that and started to ask
• 1:07:43
  Speaker 1: questions about the quantum mechanics of it. Now we know
• 1:07:47
  Speaker 1: the human eyeball is basically a quantum opsticks device. It
• 1:07:51
  Speaker 1: can interact with single photons, So now we can ask
• 1:07:54
  Speaker 1: interesting questions like what happens if we send photon to
• 1:07:57
  Speaker 1: the eyeball that are in an undert Rman's state. You
• 1:08:01
  Speaker 1: know that quantum mechanical objects can have like the possibility
• 1:08:04
  Speaker 1: of being in two different locations at once. But the
• 1:08:07
  Speaker 1: strange thing about us is that we don't observe things
• 1:08:10
  Speaker 1: quantum mechanically. When you look at something, it's either here
• 1:08:13
  Speaker 1: or it's there. And this is one of the deepest
• 1:08:15
  Speaker 1: questions in quantum physics is why we can't observe things
• 1:08:19
  Speaker 1: to be in superpositions. Why if quantum particles can have
• 1:08:22
  Speaker 1: like probabilities to be in two different states, we only
• 1:08:25
  Speaker 1: ever observe them to be in one so people are
• 1:08:27
  Speaker 1: doing experiments to see can the eyeball see photons that
• 1:08:31
  Speaker 1: are in a superposition. So they take like this single
• 1:08:34
  Speaker 1: photon and they pass it through a half silvered mirror.
• 1:08:38
  Speaker 1: This is a mirror which sometimes sends the photon to
• 1:08:41
  Speaker 1: the left and sometimes sends it to the right. And
• 1:08:43
  Speaker 1: it's a quantum mechanical thing. It's random. So now what
• 1:08:46
  Speaker 1: happens when the photon passes through it is that, because
• 1:08:48
  Speaker 1: it's quantum mechanical, it doesn't like actually go left or
• 1:08:51
  Speaker 1: actually go right every time. It has a probability to
• 1:08:54
  Speaker 1: go left and the probability to go right. This is
• 1:08:57
  Speaker 1: sort of like the double slit experiment. So then what
• 1:08:59
  Speaker 1: happened when it hits your eyeball is that when the
• 1:09:02
  Speaker 1: measurement collapses in the universe says, okay, we have to
• 1:09:05
  Speaker 1: decide which way the photon went. Or can your eye
• 1:09:09
  Speaker 1: somehow see a quantum mechanically superimposed photon. Do you get
• 1:09:13
  Speaker 1: like two little flashes, one on the left and one
• 1:09:16
  Speaker 1: on the right. These are the kind of experiments people
• 1:09:19
  Speaker 1: are doing right now. That's incredible. I love that so much.
• 1:09:23
  Speaker 1: There's something about these kinds of experiments where you are
• 1:09:27
  Speaker 1: seeing how we're perceiving things in the world, especially like
• 1:09:32
  Speaker 1: on the quantum level. That it's like it kind of
• 1:09:35
  Speaker 1: gives me chills that we can actually have that direct
• 1:09:40
  Speaker 1: human observation of quantum physics. It is really amazing, and
• 1:09:46
  Speaker 1: there are some fun theories of quantum mechanics that we
• 1:09:49
  Speaker 1: might actually be able to test using this kind of scenario.
• 1:09:53
  Speaker 1: People wonder like when does the wave function collapse? When
• 1:09:56
  Speaker 1: does the universe decide or the photon went left or
• 1:09:59
  Speaker 1: went right? With theories we've talked about with experts on
• 1:10:01
  Speaker 1: this podcast, some ideas being that the universe splits and
• 1:10:04
  Speaker 1: one goes left and one goes rights. Others that it's
• 1:10:07
  Speaker 1: actually dependent on sensitive details of the initial conditions. But
• 1:10:10
  Speaker 1: there are some theories called spontaneous collapse that says that
• 1:10:14
  Speaker 1: the collapse to the side, left or right depends in
• 1:10:17
  Speaker 1: some way on like the size of the object that
• 1:10:20
  Speaker 1: it's interacting with, which is a little weird, and in
• 1:10:24
  Speaker 1: that scenario, different size parts of the eye might be
• 1:10:27
  Speaker 1: more or less likely to induce this collapse. You could
• 1:10:30
  Speaker 1: actually test this theory by doing this experiment. So this
• 1:10:34
  Speaker 1: is the kind of thing people are working on right now.
• 1:10:37
  Speaker 1: Quantum eyeball experiments. That's great. So we're turning humans into
• 1:10:42
  Speaker 1: sort of like an actual quantum detection instrument. Yeah, because
• 1:10:48
  Speaker 1: the critical question in all of these experiments is when
• 1:10:52
  Speaker 1: does the wave function collapse? And if you're interacting with
• 1:10:55
  Speaker 1: a quantum object using a classical device like a finger
• 1:10:58
  Speaker 1: or an eyeball, then has to collapse at some point.
• 1:11:01
  Speaker 1: But the device you're interacting it with, of course, is
• 1:11:03
  Speaker 1: made of little quantum bits. And so if your eyeball
• 1:11:06
  Speaker 1: can stay a quantum object then interact with the quantum
• 1:11:09
  Speaker 1: photon in a quantum way and maintain its superposition, then
• 1:11:12
  Speaker 1: maybe your eyeball can be in a superposition of quantum states. Right,
• 1:11:16
  Speaker 1: your eyeball can be in two probabilities, like it saw
• 1:11:19
  Speaker 1: it on left and it's saw it on the right,
• 1:11:21
  Speaker 1: And then how does your brain interpret that? Right? Does
• 1:11:23
  Speaker 1: it collapse when it gets the optical nerve? We don't know.
• 1:11:26
  Speaker 1: These are super fun questions that we'll be digging into
• 1:11:29
  Speaker 1: probably for hundreds of years. Well, you just made me
• 1:11:32
  Speaker 1: go cross side, all right. Well, I think we dove
• 1:11:36
  Speaker 1: deep into Supernova Scarlet and crazy Blue on this podcast,
• 1:11:40
  Speaker 1: and we do know now that the human eye can
• 1:11:43
  Speaker 1: actually see a single photon, and that's going to allow
• 1:11:46
  Speaker 1: us to probe the frontiers of quantum mechanics and understand
• 1:11:49
  Speaker 1: crazy things about superpositions and what it's like to be
• 1:11:52
  Speaker 1: a mantis shrimp. I just love that when I see
• 1:11:55
  Speaker 1: a star, I'm directly kissing the protons from star with
• 1:12:01
  Speaker 1: my eyeballs. Unfortunately, you don't have to put the whole
• 1:12:04
  Speaker 1: star against your eyeball in order to see it. All right, Well,
• 1:12:08
  Speaker 1: thank you very much Katie for joining us on this
• 1:12:10
  Speaker 1: examination of the physics of the human eyeball, and thanks
• 1:12:13
  Speaker 1: to everybody out there for listening and coming with us
• 1:12:16
  Speaker 1: on this journey of curiosity and discovery. Thanks for having
• 1:12:19
  Speaker 1: me tune in next time. Everyone, Thanks for listening, and
• 1:12:30
  Speaker 1: remember that Daniel and Jorge explained. The universe is a
• 1:12:33
  Speaker 1: production of I Heart Radio. For more podcast For my
• 1:12:36
  Speaker 1: Heart Radio, visit the I heart Radio app, Apple Podcasts,
• 1:12:40
  Speaker 1: or wherever you listen to your favorite shows.