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

Episode Date: October 15, 2019

What is color and how do we perceive it? How many colors are there? UCI particle physicist Professor Daniel Whiteson explains the science of colors and answers some listener questions as well. Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

This is an I-Heart podcast. I was diagnosed with cancer on Friday and cancer-free the next Friday. No chemo, no radiation, none of that. On a recent episode of Culture Raises Us podcast, I sat down with Warren Campbell, Grammy-winning producer, pastor, and music executive to talk about the beats, the business, and the legacy behind some of the biggest names in gospel, R&B, and hip-hop. Professionally, I started at Deadwell Records. From Mary Mary to Jennifer Hudson, we get into the soul of the music and the purpose that

drives it. Listen to Culture raises us on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. The U.S. Open is here, and on my podcast, Good Game with Sarah Spain. I'm breaking down the players, the predictions, the pressure, and of course, the honey deuses, the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very wonderfully experiential sporting event. To hear this and more, listen to Good Game with Sarah Spain, an IHeart women's sports production in partnership with Deep Blue Sports and Entertainment on the IHeart radio app, Apple Podcasts, or wherever you get your podcasts. Brought to you by Novartis, founding partner of IHeart Women's Sports Network.

Hey, I'm Kurt Brown-Oller. And I am Scotty Landis, and we host Bananas, the podcast where we share the weirdest, funniest, real news stories from all around the world. And sometimes from our guest personal lives, too. Like when Whitney Cummings recently revealed her origin story on the show. There's no way I don't already have rabies. This is probably just why my personality is like this. I've been surviving rabies for the past.

20 years. New episodes of bananas drop every Tuesday in the exactly right network. Listen to bananas on the IHeart radio app, Apple Podcasts, or wherever you get your podcasts. When I was a kid, I was fascinated by color, and in particular, there was one question which had me up late at night thinking about it, which was this. Can you think up? a new color. Now, if you've seen a rainbow, then you know that the whole spectrum of visible light is reflected there. You have all the reds, all the oranges, all the greens, all the yellows, all the way up to the blues and the violets. And you can see there all of the colors that you can perceive. And of course, it makes you wonder about color. How does color work? What is it really?

And it also connects to some deep questions about philosophy, not just physics. For example, many people have wondered, the color that I'm seeing red, how do I know that other people are seeing the same color, right? Maybe the thing that I see is red, somebody else sees as blue. A fascinating question in philosophy. But there's another question there, which is, can you think up a new color? If these colors that I'm seeing are just perceptions in my mind, is my brain capable of coming up with a new color? Can I generate in my own head a new experience? of color. I spent many nights thinking about whether it was possible to concentrate hard enough to come up with a new color.

Hi, I'm Daniel. I'm a particle physicist and a part-time podcast host. And the co-author of the book, We Have No Idea, a Guide to the Unknown Universe, which takes you on a tour about all the things we don't understand about the universe. And you're listening to the podcast, Daniel and Jorge Explain the Universe, a production of IHeart Radio. My co-host, Jorge Cham, and co-author in that book, can't be here today, so I'm talking to you on my own about all the amazing things in the universe. Our podcast tries to find incredible, mind-blowing, really hard to think about things,

and explain them to you in a way that you actually understand and maybe even entertains you along the way. Today on the program, we're going to be walking a fine line between physics and philosophy because there's a deep connection between these fields. Sometimes in physics we discover something that reveals a truth of the universe, and that truth can make us feel differently about our relationship with life and the universe and how everything works. This, of course, is true when we're talking about the beginning of the universe and how it all came to be and its potential future ends.

but also about how we perceive the universe, the very everyday thing. And one of the most tangible ways we have to perceive the universe, of course, is with light and specifically with color. Color is so physical, it's so tangible, it's such an intense experience. But what is it? What does physics have to say about color? And so that's the topic we're going to be tackling on today's podcast. What is the physics?

of color. And there's lots of different aspects to this question. How many colors are there? Why do we see things in different colors? Why are some objects different colors than other objects? Has it all work? And there's a great history here of physicists diving into color. Even Isaac Newton did some of his original best work with lenses and optics and prisms, and he studied spreading of white light into the rainbow. And in the early part of this century, color was a big clue that helped us understand quantum mechanics. People saw all sorts of weird patterns that they didn't understand. It took some clever brains and some interesting experiments to untangle it. Now, everybody has some understanding of color. Everybody has some experience of color. Well,

some people out there might be colorblind. But does everybody understand color? Do people know how color works? Why we see things in different color? Why some things reflect blue and other things reflect green? Do people really understand what color is? So to get a sense of the general level of knowledge of color, I walked around this time in Aspen, Colorado, and I asked people what they knew about color and light and why different things were different colors. Listen to what they have to say, but first, think to yourself. Do you understand color? Do you understand light? Do you understand why things are different colors? Can you imagine a new color in your mind? Think about those things as you listen to these answers.

Go ahead and tell you that one either. Something about the light, but I don't know. Pigments? Reflecting light. I don't know. The spectrum from the sun. There's infrared colors we can't see, the colors we can see. The spectrum of the colors and the light causing what you see for colors. I don't know.

Visible light is a certain wavelength. Your eye sees visible light. and has more to do with the light bouncing off the object. I also don't know. I'm sorry. It's something to do with the light, with our eyes,

and with the color of white. So you're probably hearing those answers that there's definitely some understanding of light and wavelengths and color, and that there's definitely some physics to it, right? People understand that behind color is a lot of physics. And that's great, because we're going to dig into all that physics today.

But there's not a lot of understanding for why different things are different colors. Why is this bench blue? Why is the grass green? All of these things. How does that work on a sort of microscopic level? One of my favorite things about physics is that we can take the macroscopic universe, the one that we experience, and take it apart and explain it in terms of microscopic stuff.

We understand the difference, for example, between frozen water and liquid water in terms of the motion of the little particles inside. And everything we are experiencing around us is in the end just an emergent phenomenon of these microscopic events. And so we'd like to understand basically everything around us in terms of the microscopic principles, right? What is really happening on the tiniest level that makes something green or makes something else red? And by the end of today's podcast, I hope you'll have a solid understanding of why things are different colors. So let's dig into it first. What is light and what is color?

Well, let's begin with light. Light, of course, is just electromagnetic radiation. We talk about this on the podcast fairly often. You go all the way down from radio waves up to gamma rays and x-rays. All of these things are just electromagnetic fields that are wiggling. That's why they can get to you across the vast distances of space. It's not like sound where you have the air that's shaking. Light is the waving of electromagnetic fields.

And electromagnetic fields are a property of space itself. Like all the quantum fields that we talked about, on another podcast, every element of space has the possibility to have light in it or electrons in it or any of the other quantum fields. So when a photon passes through space, what that really means is the electromagnetic fields in that space are oscillating. And so all kinds of light are just electromagnetic radiation. Right in the middle of the spectrum is visible light at about a few hundred nanometers. And it's no different from the light at higher energies and lower energies except, of course, for that energy.

So the properties that a photon has that you need to understand are just its energy. Now, its energy is very closely connected to its frequency. The more energy the photon has, the faster it wiggles. And the faster it wiggles, the shorter its wavelength. All these photons have the same speed. They all travel to the speed of light, but they have different amounts of energy per photon.

And every photon, you can translate its energy directly into its frequency and its frequency directly into its wavelength. It's really just one piece of information expressed in different ways. I want to talk a little bit more about that, but first, let's take a quick break. I'm Dr. Joy Harden Bradford, and in session 421 of therapy for black girls, I sit down with Dr. Ophia and Billy Shaka to explore how our hair connects to our identity, mental health, and the ways we heal. Because I think hair is a complex.

language system, right, in terms of it can tell how old you are, your marital status, where you're from, you're a spiritual belief. But I think with social media, there's like a hyperfixation and observation of our hair, right? That this is sometimes the first thing someone sees when we make a post or a reel is how our hair is styled. You talk about the important role hairstyles play in our community, the pressure to always look put together, and how breaking up with perfection can actually free us. Plus, if you're someone who gets anxious about flying, don't miss session 418 with Dr. Angela Neil Barnett, where we dive into managing flight anxiety. Listen to therapy for black girls on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Get fired up, y'all.

Season two of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people and an incomparable soccer icon, Megan Rapino, to the show, and we had a blast. We talked talked about her recent 40th birthday celebrations, co-hosting a podcast with her fiancé Sue Bird, watching former teammates retire and more. Never a dull moment with Pino. Take a listen. What do you miss the most about being a pro athlete?

The final. The final. And the locker room. I really, really, like, you just, you can't replicate, you can't get back. Showing up to locker room every morning just to shit talk. We've got more incredible guests

like the legendary Candice Parker and college superstar A. Z. Fudd. I mean, seriously, y'all. The guest list is absolutely stacked for season two. And, you know, we're always going to keep you up to speed on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

Presented by Capital One, founding partner of IHeart Women's Sports. The OGs of Uncensored Motherhood are back and badder than ever. I'm Erica. And I'm Mila. And we're the host of the Good Mom's Bad Choices Podcast. Brought to you by the Black Effect Podcast Network every Wednesday. Historically, men talk too much. And women have quietly listened.

And all that stops here. If you like witty women, then this is your tribes. With guests like Corinne Steffens. I've never seen so many women protect predatory men. And then me too happened. And then everybody else wanted to get pissed off because the white said it was okay. Problem.

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You actually sent it? Listen to the Good Mom's Bad Choices podcast every Wednesday on the Black Effect Podcast Network. The IHeart Radio app, Apple Podcast, or wherever you go to find your podcast. So photons, of course, are quantum mechanical particles. We've talked on this podcast many times about how they can be seen as particles, they can be seen as waves. And it's true, and you should think about them as quantum mechanical, but only in the sense that you can only have a certain integer number of photons. Like you turn on your laser, you can have one photon or two photons or three photons or 974 photons. You can't have one and a half photons.

You can't have 2.72 photons. That's where the quantum mechanics comes in. It's a discrete number of photons. But this other property of photons, the energy of a photon, equivalent again to its frequency and therefore its wavelength, that can have any value. A given photon can have any amount of energy from very, very low, making it like a radio wave, to very, very high, making it an x-ray or a gamma ray. We'll talk later about how photons are generated, and there are some object

that can only generate photons of certain energy, but in principle, a photon can have any energy. What that means to the context of color is that every individual photon can have any energy level, which means it could have any frequency, which means it could have any wavelength. And of course, the wavelength of the photon is connected to the color. We perceive photons of different wavelength as having different colors. Down at 400 nanometers, for example, we perceive things as very, very red. Up at 700 nanometers, we perceive things as very, very blue or very, very violet. So there's a close connection between the wavelength of the photon and the color that we perceive.

But don't be confused. The color is not a property of the photon. Sure, people say a red photon, but what they mean is that the photon has a certain wavelength. We perceive it as red, but the redness is inside us. There's nothing red about the photon. The photon just has a certain wavelength. So when we're talking about the physics of color, let's separate what property the photon has

and our perception, our experience of it. All right. So back to the photon, you can have any infinite number of different wavelengths for a photon. What that means is that potentially there's an infinite number of colors. If every wavelength corresponds to a color, then there's an infinite number of colors out there. Can we perceive an infinite number of colors?

Let's talk for a moment about how we perceive color. Imagine this spectrum of different wavelengths, from 400 nanometers up to 700 nanometers. Yes, there's an infinite number of different wavelengths you could stick into that spectrum, right? It's the real numbers, and there's an infinite number. Just the same way, there's an infinite number of numbers between one and two, right? There's one, 1.1, 1.11, 1.17, etc. I could go on literally forever and name numbers between one and two. In the same way, there's an infinite number of wavelengths photons can have.

But we are limited in how we can perceive them. We can't necessarily tell the difference between two slightly different wavelength photons. We might perceive them the same way. That's just a matter of resolution. It's like in your camera has a certain number of pixels. And so if something falls in one pixel, you can't tell where in the pixel at length. landed. Did it land in the center? Did it land towards the edge? You can't tell because your camera has a certain spatial resolution, a certain number of pixels. And of course, the more pixels it has, the better

it is at figuring out exactly where those photons landed. In the same way your eye is not capable of distinguishing between every tiny little difference in wavelengths. Two photons that have almost the same wavelength will register exactly the same way in your eye. Now, in your eyeball, there actually three different kinds of cells in the back of the eyeball that see color. What they do is they respond differently to photons at different wavelengths. One of them peaks very, very low. It's mostly responsive around 450 nanometers. The second kind peaks sort of in the middle of the spectrum, like 550 nanometers.

And the third kind peaks a little bit higher, just under 600 nanometers. So you have three kind of cells, each one is sensitive to different wavelength photons. the way that it works is that the photon hits your eyeball and then some of these light up. If the photon has a wavelength, which corresponds to the peak of the sensitivity for one of those cells, it'll light up really strongly. Like the one at 450, if you send a photon at 450 nanometers right at that one, it's going to light up and the other ones are not going to light up very strongly. Whereas if you send a photon around 600 nanometers, then the third kind is going to light up

really strongly and the other two are going to be dimmer. And then your brain takes that information. It says the low wavelength one lit up and the other two didn't, so therefore the light we're seeing must be low wavelength. Or if it gets messages that say that only the high wavelength sensor lit up, then it knows that the light you're seeing must be high wavelength. It's not that your eye specifically measures the wavelength of any individual photon. What it does is it asks, how much does it light up each of these three sensors? And then it has to reverse engineer and estimate what was the wavelength of the light that hit it. It's sort of like triangulation.

Your cell phone knows where it is because it can talk to like three different cell phone towers. And it can ask those towers, how far away from you am I? And if one of the tower says, oh, you're real close. And the other two say, no, you're pretty far. Then your phone knows it's pretty close to one of those towers. And it can tell exactly where it is because it has the messages from all three. That's called triangulation. Well, your eye is doing the same thing with the sensors in the eyeball.

It gets three pieces of information about the light that's coming in, and each of those gives it different information, right? Information about how close are you to the wavelength that this sensor is good at seeing, and then it can use that information to decide what wavelength of the light actually hit you. So the final perception is sort of mixed from these three different measurements we make. And this is why you can build up any sort of color that humans can experience out of just three sort of basis colors. You often hear about the primary colors or red, green, and blue.

And any color the humans perceive can be built up with some combination of red, green, and blue. And this blew my mind the first time I thought about it. I thought, wow, there's like colors live in some sort of mental abstract mathematical space. And red, green, and blue are like the eigenvectors of it. And any color you can imagine is just a linear combination of those three colors. That was incredible to me. But it's not actually true. They just encompass the human experience of color.

Remember, there's an infinite number of colors in the spectrum because this is an infinite number of wavelengths. What RGB does is it plays with human responses. We have three ways to measure colors. And so it triggers those three sensors in different ways to give you the experience of different colors. The same way in the case of the cell phone towers, if you could ping those cell phone towers with different distances, you could stimulate being any place between those towers in that same way. All right. So to recap, photons have any arbitrary wavelength, which is

controlled by the energy that they carry. And if we imagine the relationship between wavelength and color, color is part of the human perception. Color is what we experience. There's nothing red about the photon per se, it has a certain wavelength which your brain measures, your eyeball is like a device for measuring the wavelength of those colors by using those three different sensors to triangulate it. And then it gives you the experience of that color. But because there's nothing particularly red about the photon, where does redness come from? And this is where physics crosses into the realm of philosophy, or physics inspires fascinating questions in philosophy. And one of the really interesting wrinkles here is that not everybody out there has three

color sensors in their eye. There are some folks out there that have a mutation. They have four kinds of sensors in their eye. They are called tetachromats, and they have an extra way to sense color in their eye. When I first learned about this, I thought, ooh, does that mean that they have like another color in their mind? Is this fourth kind of cell that can detect another element of the spectrum, give them a new kind of experience that I can't have? Is there some color out there that they can experience that I will never know? That's not the case actually. It's just a fourth way of sensing the wavelength of the light that you're seeing. So it gives them better ability to nail down the wavelength of the light. They don't necessarily see any new

colors. It's like adding a fourth tower to your triangulation. It helps you separate in cases where it's hard to tell. It gives you extra information to tell where that cell phone is. It doesn't necessarily give you a totally new experience of distance. So tetachromats are interesting and fascinating, but they don't necessarily see color differently than we do. They're just better at it. It's like if you're measuring the length of something and your ruler has more little markings, so you can make a more precise measurement of the length of whatever it is you're looking at. All right, but back to the sense of philosophy. Perception has to be something in the mind because, again, there's nothing blue or purple

or orange about the photon. That's something that your brain is doing. And that's why, of course, people wonder, is the red that I'm experiencing, different from the red that you're experiencing? Maybe the red that I'm experiencing is you're blue. That seems unlikely because we all sort of like the same kind of art and the same kind combinations of colors, but we don't really know because we can never really experience what's in somebody else's mind. And this is a famous question in philosophy. Can you describe redness?

Can you communicate somehow? Is there any possible way to capture the experience of redness to convey that to somebody else without them experiencing your redness? Can you describe redness in other terms? Or is it unique? Is it, is it its own sort of basis concept in? in the idea structure of your mind. And there's this famous thought experiment. Say you take a genius scientist and you put her in a room and the scientist only ever sees black and white

and she can learn all about the world and she can learn all about science, but she only ever sees black and white. There's only black and white things in the room and the TV she's using only has black and white. So she never sees any color. And this person is super duper smart. Is there any way that she can understand color

so that when she opens the door and you let her out of this terrible mind experiment you could never actually do on people, so when she emerges into the world and sees color and experiences it for the first time, she will have already understood. Is there any way to give her that understanding without the experience? If so, then it means that color is something that you can translate into other ideas and convey from mind to mind. If not, then it means it's something purely internal, something that cannot be described in any other way, meaning that we can never know if my red is the same as your red. So it's a famous unanswered question of philosophy, but it stimulates in me another question, which is how many colors are there in our

mind? I mean, if they are just in our mind, if the red that I'm seeing as I look at this t-shirt right now is something, an experience that my brain is generating for me, then can it also generate other colors. Obviously, it can. It can generate blue. It can generate orange. You can generate purple, right? It takes some external stimulation to make that happen. But the generation of the experience itself is in my mind. It's after the information from the wavelength has been transformed into some sort of pulse in my brain. And that's when the experience of purple happens. So then the question is, could I generate a novel one? Could I think of? Could I imagine new color that nobody has ever imagined, or at least that I have never imagined.

You know, say I'd never seen anything green before my life. I'd only ever seen red and blue. Could I think up green? Could I envision green in my mind without having ever seen it? Or even if I've seen red, green, and blue, can I come up with a new color? So I honestly spent many afternoons as a kid trying to come up with a new color, and it always ended up something weird and orange, but I never succeeded. And so to this day, I still do not know the answer to that question.

So that tells us a little bit about the physics of color. What is color? How is it connected to the wavelength of light and electromagnetic radiation and how we perceive it? And what that means, how you translate from the photons that are out there in the universe to our perception of color, which is fascinating. But it doesn't tell us about what's happening microscopically in stuff. Why is that shirt blue and this shirt red? Why is it generating photons at different colors so I see those things? So I experience those.

We'll dig into all that. But first, let's take a little break. I'm Dr. Joy Harden Bradford. And in session 421 of therapy for black girls, I sit down with Dr. Othia and Billy Shaka to explore how our hair connects to our identity, mental health, and the ways we heal. Because I think hair is a complex language system, right, in terms of, can tell how old you are, your marital status, where you're from, you're a spiritual belief. But I think with social media, there's like a hyperfixation and observation of our hair, right?

That this is sometimes the first thing someone sees when we make a post or a reel is how our hair is styled. We talk about the important role hairstylists play in our community, the pressure to always look put together, and how breaking up with perfection can actually free us. Plus, if you're someone who gets anxious about flying, Don't miss session 418 with Dr. Angela Neil Barnett, where we dive into managing flight anxiety. Listen to therapy for black girls on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Get fired up, y'all. Season two of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people and an incomparable soccer icon, Megan Rapino, to the show.

And we had a blast. We talked about her recent 40th birthday celebrations, co-hosting a podcast with her fiance Sue Bird, watching former teammates retire and more. Never a dull moment with Pino. Take a listen. What do you miss the most about being a pro athlete? The final. The final. And the locker room.

I really, really, like, you just, you can't replicate, you can't get back. Showing up to locker room every morning just to shit talk. We've got more incredible guests like the legendary Candace Parker and college superstar A.Z. Fudd. I mean, seriously, y'all. The guest list is. is absolutely stacked for season two. And, you know, we're always going to keep you up to speed

on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHeart Women's Sports. The OGs of Uncensored Motherhood are back and badder than ever. I'm Erica. And I'm Mila. And we're the host of the Good Mom's Bad Choices podcast, brought to you by the Black

Black Effect Podcast Network every Wednesday. Historically, men talk too much. And women have quietly listened, and all that stops here. If you like witty women, then this is your tribes, with guests like Corinne Steffens. I've never seen so many women protect predatory men. And then me too happened. And then everybody else wanted to get pissed off because the white said it was okay. Problem.

My oldest daughter, her first day in ninth grade, and I called to ask how I was going. She was like, oh, dad, all they were doing was talking about your thing in class. I ruined my baby's first day of high school. And slumflower. What turns me on is when a man sends me money. Like, I feel the moisture between my legs when a man sends me money. I'm like, oh my God, it's go time. You actually sent it?

Listen to the Good Mom's Bad Choices podcast every Wednesday on the Black Effect Podcast Network. The IHeart Radio app, Apple Podcast, or wherever you go to find your podcast. Okay, we're talking about the first. physics of color and the experience of color. And this is something which goes back to the early 1900s when there was a really interesting scientific puzzle that people were trying to understand, which is that some gases have color. You've probably experienced this if you've ever played with like a Bunsen burner and put some weird stuff in it and you see it, oh, it glows green. Or if

you put this metal in it, you get something purple. If you put this metal in it, you get a red flame. And so fire has different colors. And remember the fire is just essentially ionized gas. You're heating something up and it's glowing and emitting photons and that's what you're seeing. But back in the day, before we had a really detailed understanding of the quantum mechanics of it, people were wondering, why do different gases have different colors? And more specifically, there were two things that people noticed. First of all, they noticed the gases absorbed colors. So if you shone, for example, a white light through a bunch of gas, you measure the wavelength of the light that came through, you'd notice that the gas absorbed certain wavelength.

but only certain wavelengths, and it depended on the gas. Nitrogen would absorb different things than hydrogen would absorb different things than oxygen. So each gas seemed to have its own pattern, these little slices of the spectrum that would get taken out of the white light when they pass through the gas. So you pass white light through a gas and it removes a certain little slices of that spectrum. And it's like a fingerprint. You can tell what gas is there based on which slices of the spectrum it takes out. But nobody understood why does this gas take out those colors?

And why does that gas take out the other colors? And the second thing is the inverse of that. You took those same gases and you heated them up and they would glow. But they wouldn't glow in every color. They don't glow white necessarily. They glow in certain colors. And the colors they glow in match exactly the colors that they would take out of the spectrum when you pass white light through them.

So for any particular gas, if you passed white light through it, it would slice out little parts of the spectrum. But then if you took that same gas and you heated it up, it would emit light in exactly those little wavelengths that it had sliced out. So something interesting was going on. And before people understood the microscopic physics of it, there was a lot of study and just a lot of sort of thought about it. People measured the wavelengths, of course, very carefully and did detailed experiments to try to understand it. because data, of course, is the source of insight in much of the science, and especially in physics. And a lot of mathematicians looked at those spectrum, and they noticed patterns. They noticed that there was spacing between the wavelengths that the gases would absorb.

And they saw these patterns that the spacing would grow larger and larger and larger. And they were able to fit mathematical equations to those spacings. Now, they didn't understand where those equations came from, but they noticed that they were there. So Rydberg, for example, came up with this formula. and he had no understanding for what caused this formula. He could know, couldn't explain the formula at all, but it worked perfectly. And that's a great clue because it tells you what's the mathematical structure. In the end, physics is always trying to describe the universe in terms of mathematics.

The stated goal of physics, of course, is to write down an equation that describes everything in the universe and then look at that equation and understand from the mathematical structure of that equation, what do we learn about the nature of the universe? So math is our language. So as soon as we can turn a big pile of data into sort of a compressed mathematical equation, then we can ask questions about the structure of that equation and wonder, why is it this way? Why is it that way? And it was Neal's Bohr that figured it out.

When he built his atomic theory, the one that has little electrons orbiting in the center, and of course, that's passe because we don't think these days about electrons orbiting because they're not classical objects that have paths, and we'll dig into that in a future episode about quantum mechanics. In his model, electrons were orbiting the nucleus of the atom, and they could only have certain energy levels. And what happened when an electron jumped down an energy level? It had to give up some of that energy,

and it gave up that energy in terms of a photon. So if an atom has certain restricted energy levels, then the electron can jump down only certain distances. And those distances correspond to the energy of the photons that can be emitted by that atom, and therefore correspond to the wavelength of the light that you see. So if you take any particular atom, it has certain energy levels. And if you heat that up, then the electrons jump up energy levels.

They're absorbing that energy. And then sometimes they jump down. And when they jump down, they give off those photons. So that explained why certain gases emitted only in certain spectrum. And every gas has its own particular set of wavelengths that it can emit in. Those wavelengths, again, controlled exactly by the difference in the energy levels of the electrons going around the center. And it also, awesomely also explained the absorption, because if you take white light and you shine it at that gas, it can't absorb any arbitrary photon.

It can only absorb photons that will take the electron up one energy level, or two energy levels, or three energy levels. And it's this mathematics that explain that spectrum. that the electrons have to move up or down one or two or three steps, no half steps, no quarter steps, no 1.27 steps that determine which photons the atoms can absorb and can emit. So that helps us understand sort of the physical basis of why different things give off different colors, why different things look different colors. So let's put it all together. You have light from the sun. Now light from the sun is in lots of different frequencies. It's a broad spectrum. It peaks in the yellow or sometimes people say it's a little bit green, but mostly you have

light from the sun all over the visible spectrum. And that's not a coincidence that the sun happens to give off photons in the same spectrum that we can see things, right? Our eyes evolved in the presence of this sun in order to be able to see photons which were around us. We can think of it as evenly spread across all of the wavelength. Now what happens when that light hits your red t-shirt? well when light hits your red t-shirt it gets reflected off the t-shirt but not entirely some of the colors of that white light get absorbed by your red t-shirt why does your red t-shirt absorb only some colors because the atoms in your red t-shirt have electrons which can jump up one energy level and accept photons at just the right wavelength so just like the gas where if you pass white light through it it will delete certain wavelengths your t-shirt will delete a bunch of wavelengths from white light and your t-shirt is red not because it's absorbed photons which are in the red part of the spectrum but because it's reflected them this is a common misperception people think white light comes from the sun and your t-shirt is red because it's absorbed the red parts and reflected everything else remember that you are seeing photons only when they hit your eyeball and so i see your shirt as red because your shirt has reflected those red photons to me, right? Light is something I'm experiencing based on the photons that are being reflected or emitted from an object, not some like inherent property that it has. Something absorbs red

photons. It doesn't turn that object red. To see something as red, you have to see red photons leaving it, which means they have to reflect from that object. So something that's blue, for example, absorbs red photons. Something that's red absorbs blue photons. It's a little bit backwards, right or more specifically something that looks blue absorbs photons of every wavelength except for blue something that looks green absorbs photons of every wavelength except for green and this is a model of color we call subtractive color because you start from the white light which is every kind of wavelength and you remove stuff when something hits your blue t-shirt a bunch of photons get absorbed right they get removed so we call that subtractive color there's another way

way to think of color, and that's additive color. Instead of starting from full white light and talking about the color you perceive, if you start from nothing, you start from blackness. For example, a computer monitor as opposed to a piece of paper. Start from a computer monitor, then you can add light to make various mixtures. But it's a little bit complicated. The two different ways of thinking about light are fundamentally equivalent in the end. But if you design something, for example, on your computer monitor, and then you print it out on a white piece of paper, it might look a little bit different from you expected. So those of you out there who are artists know all the details about the difference between subtractive color

models and additive color models. All right, so we've been talking about color and photons, and now I think we have a pretty good understanding of the physics of it. Remember, photons have a certain wavelength, which corresponds to their energy, and they're just flying around the universe, having a certain energy per photon. The experience of color is something that happens inside our brain. It's the interpretation of signals along the optic nerve that come from the eyeball. The eyeball has done its best to measure the wavelength of the light that's hitting it, but the experience of color is something internal, something in the mind, something that philosophers can probe and physicists can wonder about. It also makes us wonder what it's

like to experience the world and whether we could see the world differently if we had different kinds of eyeballs. So we got a great question from a listener, which I want to actually answer right now. Here's the question. Hi, Daniel. Hi, Ray. This word looks pretty good and sharp in the visible spectrum of light. But what would it look like if you could only see lower or higher frequencies of light? Would a low frequency world be all transparent? Thank you. What a great question. I love imagining alternative universes where we had different kinds of eyeballs or different kinds of experiences. So it's an interesting question. And actually,

that you could answer yourself because we have technology for this. For example, night vision goggles do this sort of frequency shift. And they let you see light that's out there that your eyeballs cannot measure. They let you see at night because there are actually photons flying around, just that your eyes cannot see them. In the same way that like infrared cameras, infrared cameras, see photons that have too long a wavelength, a wavelength that your eyes cannot see,

but that are out there. And so in the infrared, the world certainly does look different. If you've seen the Predator movies, for example, or you've seen any sort of military action movie, you know, that in infrared, you can see people's heat. You can tell what's hot and what's not, because things glow in the infrared when they're hot. And so you can definitely have a different experience of the world

if you could see at different wavelengths. And yes, different things would be transparent and different things would be opaque, because the opacity of something and its transparency is a function of its wavelength, right? Glass is transparent in the visible light, but not necessarily in other wavelengths. And at higher energies, more things are transparent because the photons sort of have enough energy to get through them.

So if you could see at higher energy photons, then you could see through more stuff. You could have x-ray vision, for example. If you could see x-rays, which in the end are just higher energy photons, then you could literally see through people. You could see whether they have a broken bone. You could detect all sorts of different fascinating things about the world. So absolutely, yes, the world would look very different if we could see in lower, higher frequencies of light. And don't forget that this information is out there. All around you, there's a huge amount of information about the world that you are missing because you just do not have the sensors to pick it up. And while we're

on the topic of listener questions about light, I want to tackle one more. Here's another amazing question. What happens when two opposite way links, lightways contact each other? Where do they go in the fourth dimension? So what if you have a photon out there at 500 nanometers and a photon at 700 nanometers and you shoot them at each other? Then what's going to happen? I think that's sort of the source of the question. Well, unfortunately, not much because photons don't interact with things that don't have electric charge. Remember, photons are the force-carrying boson of the electromagnetic interaction. So anytime there's a magnet or there's electricity, photons are the thing that's sort of carrying that information. And electromagnetism works on things that have electric charges. You only

have electrical forces on things that have positive or negative charges. Even magnets, magnets are generated by little tiny spinning charges. So photons only interact with things that have charges, meaning electrons, meaning positrons. They don't interact with things that don't have charges like other photons. So mostly what happens when one photon is in the same space as another photon is nothing. They just pass right through each other. Now very occasionally, you can have photons interacting with other photons. Remember, photons are quantum particles, so they're always doing crazy stuff. And every photon is occasionally turning into a matter, anti-matter pair, like an electron as a positron. This happens very briefly, and then it goes back to being a photon.

But it might do that at the same moment that another photon coming the other direction does the same thing. And then you'll have an electron and a positron from the first photon and an electron and positron from the second photons. And those guys can interact. So photons can interact, but not directly. They have to sort of transform into other particles briefly, which can then interact. We call that light by light scattering. And it's actually quite a fascinating experiment. All right.

So we've dug into the physics. of light. We talked about what light is. It's just wiggling electromagnetic fields. We talked about how light has different frequencies and how those frequencies translate into color and the complicated things that are going on inside your eyeballs so that you perceive those different colors. And the amazing question of whether you could ever describe your red to somebody else or whether you could think up a new color in somebody's mind, I love all these questions and I'm never going to stop trying to think up a new color. I'll lie in my bed tonight. Closing my eyes and trying to imagine a new weird kind of color, it can't be orange, it can't be purple, it can't be a new kind of green.

It's got to be something totally new. So thanks for tuning in and listen to me talk and explain all about the physics of light. Hope you enjoyed that. And if you have a topic you'd like to hear us talk about, please send it in to questions at danielanhorpe.com. If you still have a question after listening to all these explanations, please drop us a line. We'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge, that's one word,

or email us at Feedback at Danielandhorpe.com. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. Culture eats strategy for breakfast, right? On a recent episode of Culture Raises Us, I was joined by Belisha Butterfield, media founder, political strategist, and tech powerhouse

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