Daniel and Jorge Explain the UniverseWhat 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.
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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 as 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 iHeartRadio. My co host Jorge Chan 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 in its potential future end, 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 so such an intense experience. But what is what does physics have to say about color? And so that's a 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, and 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 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 ask 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.
I couldn't tell you that one.
Something about the light, but I don't know pigments reflecting light.
I don't know the spectrum from the sun.
If there's infra red colors, we can't see the colors. We can see the spectrum of the colors and the light causing what you say for colors, I don't know.
Physical light is a certain length. Your ic is visible lights and has more to do it's the light bouncing off the objects. I also don't know.
I'm sorry, it's something to do with the light with our eyes. And there's the color of white.
So you probably hear in 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 colors is a lot of physics, and that's great because we're going to dig into all of 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're 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 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 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. With big wireless providers, what you see is never what you get. Somewhere between the store and your first month's bill, the price, your thoughts you were paying magically skyrockets. With mint Mobile, you'll never have to worry about gotcha's ever again. When mint Mobile says fifteen dollars a month for a three month plan, they really mean it. I've used mint Mobile and the call quality is always so crisp and so clear. I can recommend it to you so say bye bye to your overpriced wireless plans, jaw dropping monthly bills and unexpected overages. You can use your own phone with any mint Mobile plan and bring your phone number along with your existing contacts. So dit your overpriced wireless with Mint Mobiles deal and get three months a premium wireless service for fifteen bucks a month. To get this new customer offer and your new three month premium wireless plan for just fifteen bucks a month, go to mintmobile dot com slash universe. That's mintmobile dot com slash universe. Cut your wireless bill to fifteen bucks a month. At mintmobile dot slash Universe. Forty five dollars upfront payment required equivalent to fifteen dollars per month new customers on first three month plan only speeds slower about forty gigabytes On unlimited plan. Additional taxi spees and restrictions apply. Seement Mobile for details.
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You can't have two point seven two 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 objects 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 wave wavelength of the photon is connected to the color. We perceive photons of different wavelength as having different colors than at four hundred nanometers, for example, we perceive things as very very red. Up at seven hundred nanometers we perceive things as very very blue, are very very violent. 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 what about how we perceive color. Imagine this spectrum of different wavelengths from four hundred nanimeters up to seven hundred nanimeters. 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, one point one, one point one, one, one point one, seven, et cetera. 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 something falls in one pixel, you can't tell where in the pixel it 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 at 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 are 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 four hundred and fifty nanimeters. The second kind peaks sort of in the middle of a spectrum, like five hundred and fifty nanimeters, and the third kind peaks a little bit higher, just under six hundred nane. So you have three kind of cells. Each one is sensitive to different wavelength photons. So 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 will light up really strongly, like the one at four fifty. If you send a photon added four hundred and fifty nanimeters 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 six hundred nanimeters, 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 towers 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 hits 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 basist colors. You often hear about the primary colors or red, green, and blue, and any color that 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. That just encompassed 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 but 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 tetrachromats, 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 wherein 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 tetrachromats 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 your blue. That seems unlikely because we all sort of like the same kind of art and the same kind of 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 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 its own sort of basist concept 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 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 in 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, can generate orange, you can generate purple.
Right.
It takes an 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 transfer formed 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've never seen anything green before in 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 in 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? In 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. When you pop a piece of cheese into your mouth or enjoy a rich spoonful of Greek yogurt, you're probably not thinking about the environmental impact of each and every bite. But the people in the dairy industry are. US Dairy has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty to fifty. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. Take water, for example, most dairy farms reuse water up to four times. The same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is US dairy tackling greenhouse gases? Many arms use anaerobic digestors that turn the methane from maneuver into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient deents dairy products we love with less of an impact. Visit us dairy dot com slash sustainability to learn more.
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Okay, we're talking about the physics of color and the experience of color. And this is something which goes back to the early nineteen hundreds 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, ooh, 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 color? And more specifically, there were two things that people noticed. First of all, they noticed the gases absorbed colors. So if you've shown, 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 wavelengths, 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 we 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 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're 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 Ridberg, for example, came up with this formula, and he had no understanding for what causes formula. He 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 and 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 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 Neil's bore that figured it out when he built his atomic theory, the one that has little electrons orbiting 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 and 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 they 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 spectrums, 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 one point two seven 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 you 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 of 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 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. Now, 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 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 exp 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. But 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 Hira, 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 off 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 one 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'll 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 an 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 a 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 it 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 wig links right waves contact each other.
Where do they go in the fourth dimension? So what if you have a photon out there at five hundred nanimeters and a photon at seven hundred nanimeters 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 in For me, an 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 protons 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 mat or antimatter pair like an electrons and 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 electronic 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 eyeball 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. A'lllign 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 Danielandhorge dot 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 Danielandhorge dot 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. When you pop a piece of cheese into your mouth, you're probably probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. Howse us Dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
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