Latest / Daniel and Kelly’s Extraordinary Universe / Can you imagine a color you've never seen?

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Can you imagine a color you've never seen? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: When I was a kid, I was fascinated by color,
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Speaker 1: and in particular, there was one question which had me
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Speaker 1: up late at night thinking about it, which was this,
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Speaker 1: can you think up a new color? Now? If you've
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Speaker 1: seen a rainbow, then you know that the whole spectrum
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Speaker 1: of visible light is reflected there. You have all the reds,
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Speaker 1: all the oranges, all the greens, all the yellows, all
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Speaker 1: the way up to the blues and the violets, and
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Speaker 1: you can see they're all of the colors that you
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Speaker 1: can perceive. And of course it makes you wonder about color,
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Speaker 1: How does color work? What is it really? And it
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Speaker 1: also connects to some deep questions about philosophy, not just physics.
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Speaker 1: For example, many people have wondered the color that I'm
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Speaker 1: seeing red, how do I know that other people are
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Speaker 1: seeing the same color? Right? Maybe the thing that I
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Speaker 1: see is red somebody else sees as blue. Fascinating question
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Speaker 1: in philosophy. But there's another question there, which is can
1:01
Speaker 1: you think up a new color? If these colors that
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Speaker 1: I'm seeing are just perceptions in my mind? Is my
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Speaker 1: brain capable of coming up with a new color? Can
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Speaker 1: I generate in my own head a new experience of color.
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Speaker 1: I spent many nights thinking about whether it was possible
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Speaker 1: to concentrate hard enough to come up with a new
1:22
Speaker 1: color Hie. I'm Daniel. I'm a particle physicist and a
1:43
Speaker 1: part time podcast host and the co author of the
1:45
Speaker 1: book We Have No Idea, A Guide to the Unknown Universe,
1:49
Speaker 1: which takes you on a tour about all the things
1:51
Speaker 1: we don't understand about the universe. And you're listening to
1:55
Speaker 1: the podcast Daniel and Jorge Explain the Universe production of
1:59
Speaker 1: My Heart Radio. My co host Jorge Ham and co
2:02
Speaker 1: author in that book, can't be here today, so I'm
2:05
Speaker 1: talking to you on my own about all the amazing
2:08
Speaker 1: things in the universe. Our podcast tries to find incredible,
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Speaker 1: mind blowing, really hard to think about things and explain
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Speaker 1: them to you in a way that you actually understand
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Speaker 1: and maybe even entertains you along the way. Today on
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Speaker 1: the program, we're gonna be walking a fine line between
2:24
Speaker 1: physics and philosophy, because there's a deep connection between these fields.
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Speaker 1: Sometimes in physics we discover something that reveals the truth
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Speaker 1: of the universe, and that truth can make us feel
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Speaker 1: differently about our relationship with life and the universe and
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Speaker 1: how everything works. This, of course is true when we're
2:40
Speaker 1: talking about the beginning of the universe and how it
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Speaker 1: all came to be in its potential future end, but
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Speaker 1: also about how we perceive the universe, the very everyday thing,
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Speaker 1: and one of the most tangible ways we have to
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Speaker 1: perceive the universe, of course, is with light, and specifically
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Speaker 1: with color. Color is so physical, it's so tangible, it's
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Speaker 1: so such an intense experience. But what is it? What
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Speaker 1: does physics have to say about color? And so that's
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Speaker 1: the topic we're gonna be tackling on today's podcast. What
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Speaker 1: is the physics of color? And there's lots of different
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Speaker 1: aspects to this question. How many colors are there? Why
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Speaker 1: do we see things in different colors? Why some objects
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Speaker 1: different colors than other objects? Has it all work? And
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Speaker 1: there's a great history here of physicists diving into color.
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Speaker 1: Even Isaac Newton did some of his original best work
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Speaker 1: with lenses and optics and prisms, and he studied spreading
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Speaker 1: of white light into the rainbow. And in the early
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Speaker 1: part of this century, color was a big clue that
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Speaker 1: helped us understand quantum mechanics. People saw all sorts of
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Speaker 1: weird patterns that they didn't understand, and it took some
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Speaker 1: clever brains and some interesting experiments to untangle it. Now,
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Speaker 1: everybody has some understanding of color. Everybody has some experience
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Speaker 1: of color. Well, some people out there might be color blind.
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Speaker 1: But does everybody understand color? Do people know how color works?
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Speaker 1: Why we see things different color, why some things reflect
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Speaker 1: blue and other things reflect green? Do people really understand
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Speaker 1: what color is? So to get a sense of the
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Speaker 1: general level of knowledge of color, I walked around this
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Speaker 1: time in Aspen, Colorado, and I asked people what they
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Speaker 1: knew about color and light and why different things were
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Speaker 1: different colors. Listen to what they have to say, but
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Speaker 1: first think to yourself. Do you understand color? Do you
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Speaker 1: understand light? Do you understand why things are different colors?
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Speaker 1: Can you imagine a new color in your mind? Think
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Speaker 1: about those things as you listen to these answers. I
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Speaker 1: couldn't tell you that one something about the light, but
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Speaker 1: I don't know reflecting light. I don't know the spectrum
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Speaker 1: from the sun. There's infrared colors. We can't see the colors.
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Speaker 1: We can see the spectrum of the colors and the
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Speaker 1: light causing, uh, what you see for colors? I don't
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Speaker 1: know physical light is a certain wavelength. Your I C
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Speaker 1: is visible light and has more to do it's the
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Speaker 1: light bouncing after the objects. I also don't all. I'm sorry,
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Speaker 1: it's something to do with the light with our eyes
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Speaker 1: the color of white. So you're probably hear in those
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Speaker 1: answers that there's definitely some understanding of light and wavelengths
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Speaker 1: and color, and that there's definitely some physics to it. Right.
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Speaker 1: People understand that behind color is a lot of physics,
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Speaker 1: and that's great because we're gonna dig into all of
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Speaker 1: that physics today. But there's not a lot of understanding
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Speaker 1: for why different things are different colors. Why is this
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Speaker 1: bench blue, why is the grass green? All of these things?
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Speaker 1: How does that work? On a sort of microscopic level.
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Speaker 1: One of my favorite things about physics is that we
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Speaker 1: can take the macroscopic universe, the one that we experience,
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Speaker 1: and take it apart and explain it in terms of
5:52
Speaker 1: microscopic stuff. We understand the difference, for example, between frozen
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Speaker 1: water and liquid water in terms of the motion of
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Speaker 1: the little articles inside, and everything we are experiencing around
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Speaker 1: us is in the end, just an emergent phenomenon of
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Speaker 1: these microscopic events, And so we'd like to understand basically
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Speaker 1: everything around us in terms of the microscopic principles. Right,
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Speaker 1: what is really happening on the tiniest level that makes
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Speaker 1: something green or makes something else red. And by the
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Speaker 1: end of today's podcast, I hope you'll have a solid
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Speaker 1: understanding of why things are different colors. So let's dig
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Speaker 1: into it first. What is light and what is color? Well,
6:29
Speaker 1: let's begin with light. Light, of course, is just electromagnetic radiation.
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Speaker 1: We talked about this on the podcast fairly often. You
6:36
Speaker 1: go all the way down from radio waves up to
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Speaker 1: gamma rays and X rays. All of these things are
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Speaker 1: just electromagnetic fields that are wiggling. That's why they can
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Speaker 1: get to you across the vast distances of space. It's
6:48
Speaker 1: not like sound, where you have the air that's shaking.
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Speaker 1: Light is the waving of electromagnetic fields. And electromagnetic fields
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Speaker 1: are a property of space itself, like all the quantum
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Speaker 1: fields that we talked about on another podcast, Every element
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Speaker 1: of space has the possibility to have light in it,
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Speaker 1: or electrons in it, or any of the other quantum fields.
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Speaker 1: So when a photon passes through space, what that really
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Speaker 1: means is the electromagnetic fields in that space are oscillating,
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Speaker 1: and so all kinds of light are just electromagnetic radiation.
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Speaker 1: Right in the middle of the spectrum is visible light
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Speaker 1: at about a few hundred nanometers and it's no different
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Speaker 1: from the light at higher energies and lower energies, except
7:28
Speaker 1: of course, for that energy. So the properties that a
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Speaker 1: photon has that you need to understand are just its energy. Now,
7:36
Speaker 1: its energy is very closely connected to its frequency. The
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Speaker 1: more energy the photon has, the faster it wiggles, and
7:42
Speaker 1: the faster it wiggles, the shorter its wavelength. All these
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Speaker 1: photons have the same speed. They all travel the speed
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Speaker 1: of light, but they have different amounts of energy per photon.
7:53
Speaker 1: And every photon you can translate its energy directly into
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Speaker 1: its frequency, and its frequency directly into its wavelength. It's
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Speaker 1: really just one piece of information expressed in different ways.
8:04
Speaker 1: I want to talk a little bit more about that,
8:05
Speaker 1: but first let's take a quick break. So photons, of course,
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Speaker 1: are quantum mechanical particles. We've talked on this podcast many
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Speaker 1: times about how they can be seen as particles, they
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Speaker 1: can be seen as waves, and it's true, and you
8:29
Speaker 1: should think about them as quantum mechanical, but only in
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Speaker 1: the sense that you can only have a certain integer
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Speaker 1: number of photons. Like you turn on your laser. You
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Speaker 1: can have one photon, or two photons, or three photons
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Speaker 1: or seventy four photons. You can't have one and a
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Speaker 1: half photons. You can't have two point seven two photons.
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Speaker 1: That's where the quantum mechanics comes in. It's it's a
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Speaker 1: discrete number of photons. But this other property of photons,
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Speaker 1: the energy of a photon equivalent again to its frequency
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Speaker 1: and therefore wavelength that can have any value. A given
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Speaker 1: photon can have any amount of energy, from very very low,
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Speaker 1: making it like a radio wave, to very very high,
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Speaker 1: making an X ray or a gamma ray. We'll talk
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Speaker 1: later about how photons are generated, and there are some
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Speaker 1: objects that can only generate photons of certain energy, but
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Speaker 1: in principle of photon can have any energy. What that
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Speaker 1: means to the context of color is that every individual
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Speaker 1: photon can have any energy level, which means you could
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Speaker 1: have any frequency, which means it could have any wavelength,
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Speaker 1: And of course the wavelength of the photon is connected
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Speaker 1: to the color. We perceive photons of different wavelength as
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Speaker 1: having different colors than a four D nimeters. For example,
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Speaker 1: we perceive things as very very red up but seven
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Speaker 1: d nanometers we perceive things as very very blue or
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Speaker 1: very very violent. So there's a close connection between the
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Speaker 1: wavelength of the photon and the color that we perceive.
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Speaker 1: But don't be confused. The color is not a property
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Speaker 1: of a photon. Sure people say a red photon, but
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Speaker 1: what they mean is that the photon has a certain wavelength.
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Speaker 1: We perceive it as red, but the redness is inside us.
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Speaker 1: There's nothing red about the photon. The photon just has
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Speaker 1: a certain wavelength. So when we're talking about the physics
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Speaker 1: of color, let's separate what property the photon has and
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Speaker 1: our perception, our experience of it. Alright, so back to
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Speaker 1: the photon. You can have any infinite number of different
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Speaker 1: wavelengths for a photon. What that means is that potentially
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Speaker 1: it is an infinite number of colors. If every wavelength
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Speaker 1: corresponds to a color, then there's an infinite number of
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Speaker 1: colors out there. Can we perceive an infinite number of colors.
10:44
Speaker 1: Let's talk for a moment about what about how we
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Speaker 1: perceive color. Imagine this spectrum of different wavelengths from four
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Speaker 1: d nimeters up to seven hundred nimeters. Yes, there's an
10:54
Speaker 1: infinite number of different wavelengths you could stick into that spectrum. Right,
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Speaker 1: it's the real numbers and an infinite number. Just the
11:01
Speaker 1: same way, there's an infinite number of numbers between one
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Speaker 1: and two. Right, there's one, one point one, one point one, one,
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Speaker 1: one point one, seven, etcetera. I could go on literally
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Speaker 1: forever and name numbers between one and two. In the
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Speaker 1: same way, there's an infinite number of wavelengths photons can have,
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Speaker 1: but we are limited in how we can perceive them.
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Speaker 1: We can't necessarily tell the difference between two slightly different
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Speaker 1: wavelength photons. We might perceive them the same way. That's
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Speaker 1: just a matter of resolution. It's like in your camera
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Speaker 1: has a certain number of pixels, and so something falls
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Speaker 1: in one pixel, you can't tell where in the pixel
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Speaker 1: it landed. Did it land in the center, did it
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Speaker 1: land towards the edge. You can't tell because your camera
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Speaker 1: has a certain spatial resolution, a certain number of pixels,
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Speaker 1: and of course the more pixels it has, the better
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Speaker 1: it at it is at figuring out exactly where those
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Speaker 1: photons landed. In the same way, your eye is not
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Speaker 1: capable of distinguishing between every time need a little difference
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Speaker 1: in wavelengths. Two photons that have almost the same wavelength
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Speaker 1: will register exactly the same way in your eye. Now,
12:07
Speaker 1: in your eyeball, there are actually three different kinds of
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Speaker 1: cells in the back of the eyeball that's see color.
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Speaker 1: What they do is they respond differently to photons at
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Speaker 1: different wavelengths. One of them peaks very very low, it's
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Speaker 1: mostly responsive around four hundred and fifty nanimeters. The second
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Speaker 1: kind peaks sort of in the middle of the spectrum,
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Speaker 1: like five hundred fifty nanimeters, and the third kind peaks
12:29
Speaker 1: a little bit higher, just under six hundred nanimeters. So
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Speaker 1: I have three kind of cells. Each one is sensitive
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Speaker 1: to different wavelength photons. So the way that it works
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Speaker 1: is that the photon hits your eyeball and then some
12:41
Speaker 1: of these light up. If the photon has a wavelength
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Speaker 1: which corresponds to the peak of the sensitivity for one
12:47
Speaker 1: of those cells, it'll light up really strongly, like the
12:49
Speaker 1: one at four fifty. If you send a photon and
12:52
Speaker 1: at four hundred fifty nimes right at that one, it's
12:54
Speaker 1: gonna light up, And the other ones are not going
12:56
Speaker 1: to light up very strongly, whereas if you send a
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Speaker 1: photon around six hundred nimes, then the third kind is
13:02
Speaker 1: going to light up really strongly and the other two
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Speaker 1: are going to be dimmer. And then your brain takes
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Speaker 1: that information. It says, the low wavelength one lit up
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Speaker 1: and the other two didn't, so therefore the light we're
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Speaker 1: seeing must be low wavelength, or if it gets messages,
13:17
Speaker 1: it say that only the high wavelength sensor lit up,
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Speaker 1: and then it knows that the light you're seeing must
13:22
Speaker 1: be high wavelength. It's not that your your eye specifically
13:26
Speaker 1: measures the wavelength of any individual photon. What it does
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Speaker 1: is it asks how much does it light up each
13:34
Speaker 1: of these three sensors, and then it has to reverse
13:36
Speaker 1: engineer and estimate what was the wavelength of the light
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Speaker 1: that hit it. It's sort of like triangulation. Your cell
13:44
Speaker 1: phone knows where it is because it can talk to
13:47
Speaker 1: like three different cell phone towers, and it can ask
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Speaker 1: those towers how far away from you am I? And
13:52
Speaker 1: if one of the tower says, oh, you're real close,
13:54
Speaker 1: and the other two say no, you're pretty far, then
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Speaker 1: your phone knows it's pretty close to one of those towers,
14:00
Speaker 1: and it can tell exactly where it is because it
14:02
Speaker 1: has the messages from all three. That's called triangulation. Well,
14:06
Speaker 1: your eye is doing the same thing with the sensors
14:08
Speaker 1: in the eyeball. It gets three pieces of information about
14:11
Speaker 1: the light that's coming in, and each of those gives
14:14
Speaker 1: it different information, right, information about how close are you
14:18
Speaker 1: to the wavelength that this sensor is good at seeing,
14:21
Speaker 1: and then it can use that information to decide what
14:24
Speaker 1: wavelength of the light actually hits you. So the final
14:27
Speaker 1: perception is sort of mixed from these three different measurements
14:31
Speaker 1: we make. And this is why you can build up
14:34
Speaker 1: any sort of color that humans can experience out of
14:37
Speaker 1: just three sort of basis colors. You often hear about
14:40
Speaker 1: the primary colors or red, green, and blue, and any
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Speaker 1: color the humans perceive can be built up with some
14:47
Speaker 1: combination of red, green, and blue. And this blew my
14:50
Speaker 1: mind the first time I thought about it. I thought, Wow,
14:52
Speaker 1: there's like colors live in some sort of mental, abstract
14:56
Speaker 1: mathematical space, and red, green, and blue, or like the eye,
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Speaker 1: the invectors of it, and any color you can imagine
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Speaker 1: is just a linear combination of those three colors. That
15:06
Speaker 1: was incredible to me, but it's not actually true that
15:10
Speaker 1: just encompassed the human experience of color. Remember, there's an
15:13
Speaker 1: infinite number of colors in the spectrum because it's an
15:16
Speaker 1: infinite number of wavelengths. What r GB does is it
15:20
Speaker 1: plays with human responses. We have three ways to measure colors,
15:24
Speaker 1: and so it triggers those three sensors in different ways
15:27
Speaker 1: to give you the experience of different colors. The same
15:30
Speaker 1: way in the case of the cell phone towers, if
15:32
Speaker 1: you could pack those cell phone towers with different distances,
15:34
Speaker 1: you could stimulate being any place between those towers in
15:39
Speaker 1: that same way. All right, So to recap photons have
15:43
Speaker 1: any arbitrary wavelength, which is which is controlled by the
15:47
Speaker 1: energy that they carry. And if we imagine the relationship
15:51
Speaker 1: between wavelength and color, color is part of the human perception.
15:55
Speaker 1: Color is what we experience. There's nothing red about the photon.
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Speaker 1: Per se. It has a certain wavelength which your brain
16:02
Speaker 1: measures your eyeballs like a device for measuring the wavelength
16:06
Speaker 1: of those colors by using those three different sensors to
16:09
Speaker 1: triangulate it, and then it gives you the experience of
16:13
Speaker 1: that color. But because there's nothing in particularly red about
16:16
Speaker 1: the photon. Where does redness come from? And this is
16:21
Speaker 1: where physics crosses into the realm of philosophy, or physics
16:25
Speaker 1: inspires fascinating questions in philosophy. And one of the really
16:30
Speaker 1: interesting wrinkles here is that not everybody out there has
16:34
Speaker 1: three color sensors in their eye. There are some folks
16:38
Speaker 1: out there that have a mutation. They have four kinds
16:41
Speaker 1: of sensors in their eye. They are called tetra chromats,
16:45
Speaker 1: and they have an extra way to sense color in
16:48
Speaker 1: their eye. When I first learned about this, I thought, oh,
16:52
Speaker 1: does that mean that they have like another color in
16:54
Speaker 1: their mind? Is this fourth kind of cell that can
16:57
Speaker 1: detect another element of the spectrum give them a new
17:01
Speaker 1: kind of experience that I can't have. Is there some
17:03
Speaker 1: color out there that they can experience that I will
17:06
Speaker 1: never know? That's not the case. Actually, it's just a
17:10
Speaker 1: fourth way of sensing the wavelength of the light that
17:13
Speaker 1: you're seeing. So it gives them better ability to nail
17:17
Speaker 1: down the wavelength of the light. They don't necessarily see
17:19
Speaker 1: any new colors. It's like adding a fourth tower to
17:23
Speaker 1: your triangulation. It gives it helps you separate in cases
17:27
Speaker 1: where it's hard to tell. It gives you extra information
17:29
Speaker 1: to tell where that cell phone is, it doesn't necessarily
17:33
Speaker 1: give you a totally new experience of distance. So tetrachromats
17:37
Speaker 1: are interesting and fascinating, but they don't necessarily see color
17:41
Speaker 1: differently than we do. They're just better at it. It's
17:44
Speaker 1: like if you're measuring the length of something and your
17:46
Speaker 1: ruler has more little marking, so you can make a
17:48
Speaker 1: more precise measurement of the length of whatever it is
17:51
Speaker 1: you're looking at. All right, but back to the sense
17:54
Speaker 1: of philosophy, perception has to be something in the mind,
17:58
Speaker 1: because again, there's nothing blue or purple or orange about
18:01
Speaker 1: the photon. That's something that your brain is doing. And
18:04
Speaker 1: that's why, of course people wonder, is the read that
18:07
Speaker 1: I'm experiencing different from the red that you're experiencing. Maybe
18:12
Speaker 1: the red that I'm experiencing is you're blue. That seems
18:15
Speaker 1: unlikely because we all sort of like the same kind
18:17
Speaker 1: of art and the same kind of combinations of colors.
18:19
Speaker 1: But we don't really know, because we can never really
18:22
Speaker 1: experience what's in somebody else's mind. And this is a
18:25
Speaker 1: famous question in philosophy. Can you describe redness? Can you
18:30
Speaker 1: communicate somehow. Is there any possible way to capture the
18:34
Speaker 1: experience of redness to convey that to somebody else without
18:38
Speaker 1: them experiencing your redness? Can you describe redness in other terms?
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Speaker 1: Or is it unique? Is it? Is it its own
18:46
Speaker 1: sort of basis concept in the idea structure of your mind.
18:51
Speaker 1: And there's this famous thought experiment. Say you take a
18:54
Speaker 1: genius scientist and you put her in a room, and
18:57
Speaker 1: and the scientists only ever see black and white, and
19:00
Speaker 1: she can learn all about the world, and she can
19:02
Speaker 1: learn all about science, but she only ever sees black
19:05
Speaker 1: and white. There's only black and white. Thinks in the room,
19:07
Speaker 1: and the TV she's using only has black and white,
19:10
Speaker 1: so she never sees any color. And this person is
19:13
Speaker 1: super duper smart. Is there any way that she can
19:17
Speaker 1: understand color so that when she opens the door and
19:21
Speaker 1: you let her out of this terrible mind experiment you
19:23
Speaker 1: can never actually do on people. So when she emerges
19:25
Speaker 1: into the world and sees color and experiences it for
19:28
Speaker 1: the first time, she will have already understood. Is there
19:32
Speaker 1: any way to give her that understanding without the experience.
19:36
Speaker 1: If so, then it means that color is something that
19:39
Speaker 1: you can translate into other ideas and convey from mind
19:43
Speaker 1: to mind. If not, then it means it's something purely internal,
19:47
Speaker 1: something that cannot be described in any other way, meaning
19:51
Speaker 1: that we can never know if my red is the
19:53
Speaker 1: same as your red. So it's a famous unanswered question
19:56
Speaker 1: and philosophy. But it stimulates in me another question, which
20:01
Speaker 1: is how many colors are there in our mind? I mean,
20:04
Speaker 1: if they are just in our mind, If the red
20:07
Speaker 1: that I'm seeing as I look at this T shirt
20:09
Speaker 1: right now is something an experience that my brain is
20:12
Speaker 1: generating for me, then can it also generate other colors?
20:17
Speaker 1: Obviously you can. You can generate blue, can generate orange,
20:19
Speaker 1: You can generate purple. Right. It takes some external stimulation
20:23
Speaker 1: to make that happen. But the generation and the experience
20:27
Speaker 1: itself is in my mind. It's after the information from
20:30
Speaker 1: the wavelength has been transformed into some sort of pulse
20:33
Speaker 1: in my brain, and that's when the experience of purple happens.
20:36
Speaker 1: So then the question is could I generate a novel
20:39
Speaker 1: one could I think of? Could I imagine new color
20:44
Speaker 1: that nobody has ever imagined, or at least that I
20:46
Speaker 1: have never imagined? You know, say I had never seen
20:49
Speaker 1: anything green before in my life. I had only ever
20:53
Speaker 1: seen red and blue. Could I think up green? Could
20:56
Speaker 1: I envision green in my mind without having ever seen it?
21:00
Speaker 1: Or even if I've seen red, green and blue, can
21:02
Speaker 1: I come up with a new color? So I honestly
21:05
Speaker 1: spent many afternoons as a kid trying to come up
21:07
Speaker 1: with a new color, and it always ended up something
21:10
Speaker 1: weird and orange. But I never succeeded, and so to
21:13
Speaker 1: this day, I still do not know the answer to
21:16
Speaker 1: that question. So that tells us a little bit about
21:20
Speaker 1: the physics of color. What is color? How is it
21:23
Speaker 1: connected to the wavelength of light and electromagnetic radiation, and
21:27
Speaker 1: how we perceive it and what that means. How you
21:30
Speaker 1: translate from the photons that are out there in the
21:32
Speaker 1: universe to our perception of color, which is fascinating, but
21:35
Speaker 1: it doesn't tell us about what's happening microscopically in stuff.
21:39
Speaker 1: Why is that shirt blue? In this shirt red? Why
21:42
Speaker 1: is it generating photons at different colors? So I see
21:45
Speaker 1: those things, so I experience those We'll dig into all that,
21:48
Speaker 1: but first let's take a little break. Okay, we're talking
22:04
Speaker 1: about the physics of color and the experience of color.
22:08
Speaker 1: And this is something which goes back to the early
22:11
Speaker 1: nine hundreds when there was a really interesting scientific puzzle
22:14
Speaker 1: that people were trying to understand, which is that some
22:17
Speaker 1: gases have color. You've probably experienced this if you've ever
22:20
Speaker 1: played with like a Bunsen burner and put some weird
22:22
Speaker 1: stuff in it and you see it, Oh, it glows green.
22:25
Speaker 1: Or if you put this metal in it, you get
22:26
Speaker 1: something purple. If you put this metal in it, you
22:28
Speaker 1: get a red flame. And so fire has different colors.
22:32
Speaker 1: And remember the fire is just essentially ionized gas. You're
22:35
Speaker 1: heating something up and it's glowing and emitting photons, and
22:38
Speaker 1: that's what you're seeing. But back on the day before
22:40
Speaker 1: we had a really detailed understanding of the quantum mechanics
22:43
Speaker 1: of it, people were wondering why do different gases have
22:46
Speaker 1: different colors? And more specifically, there were two things that
22:50
Speaker 1: people noticed. First of all, they noticed the gases absorbed colors.
22:55
Speaker 1: So if you're shown, for example, a white light through
22:58
Speaker 1: a bunch of gas, you measure the wavelength of the
23:01
Speaker 1: light that came through, you'd notice that the gas absorbed
23:04
Speaker 1: certain wavelengths, but only certain wavelengths, and it depended on
23:08
Speaker 1: the gas. Nitrogen would absorb different things than hydrogen would
23:11
Speaker 1: absorb different things than oxygen. So each gas seemed to
23:14
Speaker 1: have its own pattern. These little slices of the spectrum
23:18
Speaker 1: that we get taken out of the white light when
23:20
Speaker 1: they pass through the gas. So you pass white light
23:23
Speaker 1: through a gas and it removes a certain little slices
23:26
Speaker 1: of that spectrum, and it's like a fingerprint. You can
23:29
Speaker 1: tell what gas is there based on which slices of
23:32
Speaker 1: the spectrum it takes out. But nobody understood why does
23:36
Speaker 1: this gas take out that those colors and why does
23:39
Speaker 1: that gas take out the other colors? And the second
23:42
Speaker 1: thing is the inverse of that. You took those same
23:45
Speaker 1: gases and you heated them up, and they would glow,
23:48
Speaker 1: but they wouldn't glow in every color. They don't glow
23:51
Speaker 1: white necessarily. They glow in certain colors. And the colors
23:54
Speaker 1: they glow in match exactly the colors that they would
23:58
Speaker 1: take out of the spec drum when you pass white
24:01
Speaker 1: light through them. So, for any particular gas, if you
24:05
Speaker 1: passed white light through it, it would slice out little
24:07
Speaker 1: parts of the spectrum. But then if you took that
24:10
Speaker 1: same gas and you heated it up, it would emit
24:12
Speaker 1: light and exactly those little wavelengths that it had sliced out.
24:16
Speaker 1: So something interesting was going on. And before people understood
24:19
Speaker 1: the microscopic physics of it, there was a lot of
24:21
Speaker 1: study and just a lot of sort of thought about it.
24:24
Speaker 1: People measured the wavelengths, of course, very carefully and did
24:27
Speaker 1: detailed experiments to try to understand it, because data, of
24:30
Speaker 1: course is the source of insight and much of the science,
24:33
Speaker 1: and especially in physics, and a lot of mathematicians looked
24:36
Speaker 1: at those spectrum and they noticed patterns. They noticed that
24:39
Speaker 1: there was spacing between the wavelengths that the that the
24:42
Speaker 1: gases would absorb, and they saw these patterns that the
24:45
Speaker 1: spacing would grow larger and larger and larger, and they're
24:48
Speaker 1: able to fit mathematical equations to those spacings. Now, they
24:52
Speaker 1: didn't understand where those equations came from, but they noticed
24:55
Speaker 1: that they were there. So Ridberg, for example, came up
24:58
Speaker 1: with this formula, and he had no understanding for what
25:01
Speaker 1: causes formula could couldn't explain the formula at all, but
25:04
Speaker 1: it worked perfectly. And that's a great clue because it
25:08
Speaker 1: tells you what's the mathematical structure and the end physics
25:11
Speaker 1: is always trying to describe the universe in terms of mathematics.
25:15
Speaker 1: The stated goal of physics, of course, is to write
25:18
Speaker 1: down an equation that describes everything in the universe and
25:21
Speaker 1: then look at that equation and understand from the mathematical
25:24
Speaker 1: structure of that equation, what do we learn about the
25:27
Speaker 1: nature of the universe. So math is our language. So
25:30
Speaker 1: as soon as we can turn a big pile of
25:32
Speaker 1: data into sort of a compressed mathematical equation, then we
25:36
Speaker 1: can ask questions about the structure that equation and wonder
25:39
Speaker 1: why is it this way, what is it? Why is
25:40
Speaker 1: it that way? And it was Neil's bore that figured
25:43
Speaker 1: it out when he built his atomic theory, the one
25:47
Speaker 1: that has little electrons orbiting the center. And of course
25:50
Speaker 1: that's passe because we don't think these days about electrons
25:53
Speaker 1: orbiting because they're not classical objects that have paths, and
25:56
Speaker 1: we'll dig into that in a future episode about quantum mechanics.
26:00
Speaker 1: In his model, electrons were orbiting the nucleus of the atom,
26:04
Speaker 1: and they could only have certain energy levels. And what
26:06
Speaker 1: happened when an electron jumped down an energy level It
26:10
Speaker 1: had to give up some of that energy, and it
26:12
Speaker 1: gave up that energy in terms of a photon. So
26:15
Speaker 1: if an atom has certain restricted energy levels, then the
26:19
Speaker 1: electron can jump down only certain distances, and those distances
26:23
Speaker 1: correspond to the energy of the photons that can be
26:26
Speaker 1: emitted by that atom, and therefore correspond to the wavelength
26:30
Speaker 1: of the light that you see. So if you take
26:32
Speaker 1: any particular atom, it has certain energy levels, and if
26:36
Speaker 1: you heat that up, then the electrons jump up energy levels.
26:39
Speaker 1: They're absorbing that energy, and then sometimes they jump down,
26:42
Speaker 1: and when they jump down they give off those photons.
26:45
Speaker 1: So that explained why certain gases emitted only in certain spectrum,
26:50
Speaker 1: and every gas has its own particular set of wavelengths
26:53
Speaker 1: that it can emit in those wavelengths again controlled exactly
26:57
Speaker 1: by the difference in the energy levels of the electrons
27:01
Speaker 1: going around the center. And it also, awesomely also explained
27:06
Speaker 1: the absorption because if you take white light and you
27:09
Speaker 1: shine it at that gas, it can't absorb any arbitrary photon.
27:14
Speaker 1: It can only absorb photons that will take the electron
27:17
Speaker 1: up one energy level, or two energy levels, or three
27:20
Speaker 1: energy levels. And it's this mathematics that explain that spectrum
27:25
Speaker 1: that the electrons have to move up or down one
27:28
Speaker 1: or two or three steps, no half steps, no quarter steps,
27:31
Speaker 1: no one point to seven steps that determine which photons
27:35
Speaker 1: the atoms can absorb and can emit. So that helps
27:39
Speaker 1: us understand sort of the physical basis of why different
27:42
Speaker 1: things give off different colors, why different things look different colors.
27:46
Speaker 1: So let's put it all together. You have light from
27:48
Speaker 1: the sun. Now, life from the sun is in lots
27:51
Speaker 1: of different frequencies, is a broad spectrum. It peaks in
27:54
Speaker 1: the yellow or sometimes people say it's a little bit green,
27:57
Speaker 1: but mostly you have life from the sun all all
28:00
Speaker 1: over the visible spectrum. And that's not a coincidence that
28:02
Speaker 1: the sun happens that you give off photons in the
28:05
Speaker 1: same spectrum that we can see things. Right, our eyes
28:08
Speaker 1: evolved in the presence of this sun in order to
28:11
Speaker 1: be able to see photons which were around us. We
28:14
Speaker 1: can think of it as evenly spread across all of
28:16
Speaker 1: the wavelength. Now, what happens when that light hits your
28:21
Speaker 1: red T shirt. Well, when light hits your red T shirt,
28:25
Speaker 1: it gets reflected off the T shirt, but not entirely.
28:29
Speaker 1: Some of the colors of that white light get absorbed
28:31
Speaker 1: by your red T shirt. Why does your red T
28:33
Speaker 1: shirt absorbed only some colors Because the atoms in your
28:38
Speaker 1: red T shirt have electrons which can jump up one
28:41
Speaker 1: energy level and accept photons at just the right wavelength. So,
28:46
Speaker 1: just like the gas where if you pass white light
28:48
Speaker 1: through it, it will delete certain wavelengths, your T shirt
28:52
Speaker 1: will delete a bunch of wavelengths from white light. And
28:56
Speaker 1: your T shirt is red not because it's absorbed photon
29:00
Speaker 1: on which are in the red part of the spectrum,
29:02
Speaker 1: but because it's reflected them. This is a common misperception.
29:06
Speaker 1: People think white light comes from the sun and your
29:08
Speaker 1: T shirt is red because it's absorbed the red parts
29:11
Speaker 1: and reflected everything else. Remember that you are seeing photons
29:14
Speaker 1: only when they hit your eyeball, and so I see
29:17
Speaker 1: your shirt is red because your shirt has reflected those
29:20
Speaker 1: red photons. To me, right, light is something I'm experiencing
29:24
Speaker 1: based on the photons that are being reflected or emitted
29:28
Speaker 1: from an object, not some like inherent property that it has.
29:32
Speaker 1: Something absorbs red photons, It doesn't turn that object red.
29:36
Speaker 1: To see something as red, you have to see red
29:38
Speaker 1: photons leaving it, which means they have to reflect from
29:41
Speaker 1: that object. So something that's blue, for example, absorbs red photons.
29:46
Speaker 1: Something that's red absorbs blue photons to a little bit
29:50
Speaker 1: backwards right. Or more specifically, something that looks blue absorbs
29:55
Speaker 1: photons of every wavelength except for blue. Something that looks green, mean,
30:00
Speaker 1: absorbs photons of every wavelength except for green. And this
30:05
Speaker 1: is a model of color we call subtractive color because
30:08
Speaker 1: you start from the white light, which is every kind
30:10
Speaker 1: of wavelength, and you remove stuff. When something hits your
30:14
Speaker 1: blue t shirt, a bunch of photons get absorbed, right,
30:17
Speaker 1: they get removed, So we call that subtractive color. There's
30:20
Speaker 1: another way to think of color, and that's additive color.
30:23
Speaker 1: Instead of its starting from full white light and talking
30:27
Speaker 1: about the color you perceive. If you start from nothing,
30:29
Speaker 1: you start from blackness, for example a computer monitor, as
30:33
Speaker 1: opposed to a piece of paper. Start from a computer monitor,
30:36
Speaker 1: then you can add light to make various mixtures. But
30:40
Speaker 1: but it's a little bit complicated. The two different ways
30:42
Speaker 1: of thinking about light are fundamentally equivalent in the end.
30:45
Speaker 1: But if you design something, for example, on your computer monitor,
30:48
Speaker 1: and then you print it out on a white piece
30:51
Speaker 1: of paper, it might look a little bit different from
30:53
Speaker 1: you expected. So those are you out there who are
30:55
Speaker 1: artists know all the details about the difference between subtractive
30:58
Speaker 1: color models and additive color models. All right, So we've
31:01
Speaker 1: been talking about color and photons, and now I think
31:04
Speaker 1: we have a pretty good understanding of the physics of it. Remember,
31:07
Speaker 1: photons have certain wavelength which corresponds to their energy, and
31:10
Speaker 1: they're just flying around the universe having a certain energy
31:13
Speaker 1: per photon. The experience of color is something that happens
31:17
Speaker 1: inside our brain, is the interpretation of signals along the
31:20
Speaker 1: optic nerve that comes from the eyeball. The eyeball has
31:23
Speaker 1: done its best to measure the wavelength of the light
31:26
Speaker 1: that's hitting it. But the experience of color is something internal,
31:29
Speaker 1: something in the mind, something that philosophers can probe and
31:33
Speaker 1: physicists can wonder about. But it also makes us wonder
31:36
Speaker 1: what it's like to experience the world, and whether we
31:39
Speaker 1: could see the world differently if we had different kinds
31:41
Speaker 1: of eyeballs. So we've got a great question from a
31:44
Speaker 1: listener which I want to actually answer right now. Here's
31:47
Speaker 1: the question. Hi, Daniel Hire, This word that looks pretty
31:51
Speaker 1: good and sharp in the visible spectrum, of light. But
31:55
Speaker 1: what would it look like if you could only see
31:58
Speaker 1: lowware or eh our frequency is off flight? Would a
32:02
Speaker 1: low frequency world be all transparent? Thank you, what a
32:06
Speaker 1: great question. I love imagining alternative universes where we had
32:10
Speaker 1: different kinds of eyeballs or different kinds of experiences. So
32:14
Speaker 1: it's an interesting question and actually one that you could
32:16
Speaker 1: answer yourself because we have technology for this. For example,
32:20
Speaker 1: night vision goggles do this sort of frequency shift, and
32:24
Speaker 1: they'll let you see light that's out there that your
32:27
Speaker 1: eyeballs cannot measure. They'll let you see at night because
32:31
Speaker 1: there are actually photons flying around just that your eyes
32:34
Speaker 1: cannot see them, in the same way that like infrared cameras.
32:38
Speaker 1: Infrared cameras see photons that are have too long a wavelength,
32:42
Speaker 1: wavelength that your eyes cannot see, but that are out there.
32:46
Speaker 1: And so in the infrared, the world certainly does look different.
32:50
Speaker 1: Have you seen the Predator movies, for example, where you've
32:53
Speaker 1: seen any sort of military action movie, you know that
32:55
Speaker 1: infrared you can see people's heat, you can tell what's
32:58
Speaker 1: hot and what's not because things glow in the infrared
33:03
Speaker 1: when they're hot, and so you can definitely have a
33:06
Speaker 1: different experience of the world if you could see a
33:08
Speaker 1: different wavelengths, and yes, different things would be transparent and
33:12
Speaker 1: different things would be opaque because the opacity of something
33:15
Speaker 1: and its transparency is a function of its wavelength. Right,
33:18
Speaker 1: glass is transparent in the visible light, but not necessarily
33:22
Speaker 1: in other wavelengths, and at higher energies more things are
33:26
Speaker 1: transparent because the photons sort of have enough energy to
33:29
Speaker 1: get through them. So if you could see it higher
33:32
Speaker 1: energy photons, then you could see through more stuff. You
33:35
Speaker 1: could have X ray vision, for example, if you could
33:38
Speaker 1: see X rays, which in the end are just higher
33:41
Speaker 1: energy photons, then you could literally see through people. You
33:45
Speaker 1: could see whether they have a broken bone. You can
33:47
Speaker 1: detect all sorts of different fascinating things about the world.
33:50
Speaker 1: So absolutely, yes, the world would look very different if
33:53
Speaker 1: we could see in lower, higher frequencies of light. And
33:56
Speaker 1: don't forget that this information is out there all around you.
33:59
Speaker 1: There's a huge, uge amount of information about the world
34:01
Speaker 1: that you are missing because you just do not have
34:03
Speaker 1: the sensors to pick it up. And while we're on
34:06
Speaker 1: the topic of listener questions about light, I want to
34:08
Speaker 1: tackle one more. Here's another amazing question. What happens when too. Obviously,
34:13
Speaker 1: wavelengths light winds contact each other, where do they go?
34:17
Speaker 1: In the fourth donation, So what if you have a
34:20
Speaker 1: photon out there at five nanometers and a photon at
34:22
Speaker 1: seven d animeters and you shoot them at each other,
34:25
Speaker 1: then what's going to happen? I think that's sort of
34:27
Speaker 1: the source of the question. Well, unfortunately, not much, because
34:31
Speaker 1: photons don't interact with things that don't have electric charge. Remember,
34:36
Speaker 1: photons are the force carrying boson of the electromagnetic interaction.
34:41
Speaker 1: So anytime there's a magnet or there's electricity, photons are
34:45
Speaker 1: the thing that's sort of carrying that information. And electromagnetism
34:49
Speaker 1: works on things that have electric charges. You only have
34:52
Speaker 1: electrical forces on things that have positive or negative charges,
34:56
Speaker 1: even magnets. Magnets are generated by little, tiny spinning charges.
35:00
Speaker 1: So photons only interact with things that have charges, meaning electrons,
35:04
Speaker 1: meaning protons meaning positrons. They don't interact with things that
35:08
Speaker 1: don't have charges like other photons. So mostly what happens
35:12
Speaker 1: when one photon is in the same space as another
35:14
Speaker 1: photon is nothing. They just pass right through each other. Now,
35:18
Speaker 1: very occasionally you can have photons interacting with other photons. Remember,
35:23
Speaker 1: photons are quantum particles, so they're always doing crazy stuff,
35:27
Speaker 1: and every photon is occasionally turning into a matter antimatter
35:30
Speaker 1: pair like an electron, as a kind o positron. This
35:33
Speaker 1: happens very briefly and then it goes back to being
35:35
Speaker 1: a photon, but it might do that at the same
35:39
Speaker 1: moment that another photon coming the other direction does the
35:43
Speaker 1: same thing, and then you'll have an electron an oppositron
35:46
Speaker 1: from the first photon and an electronpositon from the second photons,
35:50
Speaker 1: and those the guys can interact. So photons can interact,
35:54
Speaker 1: but not directly. They have to sort of transform into
35:57
Speaker 1: other particles briefly, which can then interact. We call that
36:00
Speaker 1: light by light scattering, and it's actually quite a fascinating experiment.
36:04
Speaker 1: All right, So we've dug into the physics of light.
36:06
Speaker 1: We talked about what light is. It's just wiggling electromagnetic fields.
36:11
Speaker 1: We talked about how light has different frequencies and how
36:14
Speaker 1: those frequencies translate into color, and the complicated things that
36:18
Speaker 1: are going on inside your eyeball so that you perceive
36:20
Speaker 1: those different colors, and the amazing question of whether you
36:24
Speaker 1: could ever describe your red to somebody else where that
36:27
Speaker 1: you could think up the new color in somebody's mind.
36:29
Speaker 1: I love all these questions, and I'm never gonna stop
36:32
Speaker 1: trying to think up a new color. I'll align my
36:34
Speaker 1: bed tonight, closing my eyes and trying to imagine a new,
36:38
Speaker 1: weird kind of colors. Can't be orange, it can't be purple,
36:42
Speaker 1: it can't be a new kind of green. It's got
36:43
Speaker 1: to be something totally new. So thanks for tuning in
36:47
Speaker 1: and listen to me talk and explain all about the
36:49
Speaker 1: physics of light. Hope you enjoyed that. And if you
36:52
Speaker 1: have a topic you'd like to hear us talk about,
36:54
Speaker 1: please send it in to questions at Daniel and Jorge
36:58
Speaker 1: dot com. Yeah, if you still have a question after
37:08
Speaker 1: listening to all these explanations, please drop us a line.
37:12
Speaker 1: We'd love to hear from you. You can find us
37:14
Speaker 1: at Facebook, Twitter, and Instagram at Daniel and Jorge that's
37:18
Speaker 1: one word, or email us at Feedback at Daniel and
37:21
Speaker 1: Jorge dot com. Thanks for listening and remember that Daniel
37:24
Speaker 1: and Jorge Explain the Universe is a production of I
37:27
Speaker 1: Heart Radio. For more podcast from my Heart Radio, visit
37:31
Speaker 1: the i heart radio, app, Apple podcasts, or wherever you
37:34
Speaker 1: listen to your favorite shows.