1 00:00:08,640 --> 00:00:11,040 Speaker 1: When I was a kid, I was fascinated by color, 2 00:00:11,240 --> 00:00:14,319 Speaker 1: and in particular, there was one question which had me 3 00:00:14,520 --> 00:00:16,520 Speaker 1: up late at night thinking about it, which was this, 4 00:00:17,280 --> 00:00:21,560 Speaker 1: can you think up a new color? Now? If you've 5 00:00:21,600 --> 00:00:24,560 Speaker 1: seen a rainbow, then you know that the whole spectrum 6 00:00:24,560 --> 00:00:27,720 Speaker 1: of visible light is reflected there. You have all the reds, 7 00:00:28,120 --> 00:00:30,320 Speaker 1: all the oranges, all the greens, all the yellows, all 8 00:00:30,320 --> 00:00:31,960 Speaker 1: the way up to the blues and the violets, and 9 00:00:32,000 --> 00:00:34,360 Speaker 1: you can see they're all of the colors that you 10 00:00:34,400 --> 00:00:37,520 Speaker 1: can perceive. And of course it makes you wonder about color, 11 00:00:37,560 --> 00:00:40,239 Speaker 1: How does color work? What is it really? And it 12 00:00:40,280 --> 00:00:44,120 Speaker 1: also connects to some deep questions about philosophy, not just physics. 13 00:00:44,240 --> 00:00:48,120 Speaker 1: For example, many people have wondered the color that I'm 14 00:00:48,200 --> 00:00:50,519 Speaker 1: seeing red, how do I know that other people are 15 00:00:50,560 --> 00:00:52,920 Speaker 1: seeing the same color? Right? Maybe the thing that I 16 00:00:52,960 --> 00:00:56,960 Speaker 1: see is red somebody else sees as blue. Fascinating question 17 00:00:57,160 --> 00:01:00,959 Speaker 1: in philosophy. But there's another question there, which is can 18 00:01:01,040 --> 00:01:04,319 Speaker 1: you think up a new color? If these colors that 19 00:01:04,400 --> 00:01:07,759 Speaker 1: I'm seeing are just perceptions in my mind? Is my 20 00:01:07,840 --> 00:01:11,800 Speaker 1: brain capable of coming up with a new color? Can 21 00:01:11,840 --> 00:01:15,639 Speaker 1: I generate in my own head a new experience of color. 22 00:01:16,160 --> 00:01:19,080 Speaker 1: I spent many nights thinking about whether it was possible 23 00:01:19,319 --> 00:01:22,800 Speaker 1: to concentrate hard enough to come up with a new 24 00:01:22,880 --> 00:01:43,039 Speaker 1: color Hie. I'm Daniel. I'm a particle physicist and a 25 00:01:43,160 --> 00:01:45,840 Speaker 1: part time podcast host and the co author of the 26 00:01:45,880 --> 00:01:49,440 Speaker 1: book We Have No Idea, A Guide to the Unknown Universe, 27 00:01:49,560 --> 00:01:51,680 Speaker 1: which takes you on a tour about all the things 28 00:01:51,720 --> 00:01:55,080 Speaker 1: we don't understand about the universe. And you're listening to 29 00:01:55,120 --> 00:01:59,120 Speaker 1: the podcast Daniel and Jorge Explain the Universe production of 30 00:01:59,160 --> 00:02:02,720 Speaker 1: My Heart Radio. My co host Jorge Ham and co 31 00:02:02,920 --> 00:02:05,280 Speaker 1: author in that book, can't be here today, so I'm 32 00:02:05,280 --> 00:02:07,960 Speaker 1: talking to you on my own about all the amazing 33 00:02:08,000 --> 00:02:11,440 Speaker 1: things in the universe. Our podcast tries to find incredible, 34 00:02:11,680 --> 00:02:15,480 Speaker 1: mind blowing, really hard to think about things and explain 35 00:02:15,520 --> 00:02:17,680 Speaker 1: them to you in a way that you actually understand 36 00:02:17,680 --> 00:02:21,120 Speaker 1: and maybe even entertains you along the way. Today on 37 00:02:21,160 --> 00:02:24,280 Speaker 1: the program, we're gonna be walking a fine line between 38 00:02:24,320 --> 00:02:28,720 Speaker 1: physics and philosophy, because there's a deep connection between these fields. 39 00:02:28,760 --> 00:02:32,040 Speaker 1: Sometimes in physics we discover something that reveals the truth 40 00:02:32,120 --> 00:02:34,519 Speaker 1: of the universe, and that truth can make us feel 41 00:02:34,520 --> 00:02:38,040 Speaker 1: differently about our relationship with life and the universe and 42 00:02:38,080 --> 00:02:40,519 Speaker 1: how everything works. This, of course is true when we're 43 00:02:40,520 --> 00:02:42,840 Speaker 1: talking about the beginning of the universe and how it 44 00:02:42,880 --> 00:02:45,400 Speaker 1: all came to be in its potential future end, but 45 00:02:45,520 --> 00:02:49,560 Speaker 1: also about how we perceive the universe, the very everyday thing, 46 00:02:50,520 --> 00:02:52,440 Speaker 1: and one of the most tangible ways we have to 47 00:02:52,480 --> 00:02:55,600 Speaker 1: perceive the universe, of course, is with light, and specifically 48 00:02:55,639 --> 00:02:59,160 Speaker 1: with color. Color is so physical, it's so tangible, it's 49 00:02:59,200 --> 00:03:02,640 Speaker 1: so such an intense experience. But what is it? What 50 00:03:02,720 --> 00:03:05,560 Speaker 1: does physics have to say about color? And so that's 51 00:03:05,560 --> 00:03:13,680 Speaker 1: the topic we're gonna be tackling on today's podcast. What 52 00:03:14,000 --> 00:03:17,000 Speaker 1: is the physics of color? And there's lots of different 53 00:03:17,000 --> 00:03:20,080 Speaker 1: aspects to this question. How many colors are there? Why 54 00:03:20,080 --> 00:03:23,200 Speaker 1: do we see things in different colors? Why some objects 55 00:03:23,200 --> 00:03:26,480 Speaker 1: different colors than other objects? Has it all work? And 56 00:03:26,520 --> 00:03:29,960 Speaker 1: there's a great history here of physicists diving into color. 57 00:03:30,200 --> 00:03:33,120 Speaker 1: Even Isaac Newton did some of his original best work 58 00:03:33,320 --> 00:03:37,000 Speaker 1: with lenses and optics and prisms, and he studied spreading 59 00:03:37,000 --> 00:03:39,720 Speaker 1: of white light into the rainbow. And in the early 60 00:03:39,800 --> 00:03:42,800 Speaker 1: part of this century, color was a big clue that 61 00:03:42,880 --> 00:03:45,880 Speaker 1: helped us understand quantum mechanics. People saw all sorts of 62 00:03:45,960 --> 00:03:48,240 Speaker 1: weird patterns that they didn't understand, and it took some 63 00:03:48,360 --> 00:03:52,920 Speaker 1: clever brains and some interesting experiments to untangle it. Now, 64 00:03:52,960 --> 00:03:57,040 Speaker 1: everybody has some understanding of color. Everybody has some experience 65 00:03:57,080 --> 00:03:59,920 Speaker 1: of color. Well, some people out there might be color blind. 66 00:04:00,600 --> 00:04:04,320 Speaker 1: But does everybody understand color? Do people know how color works? 67 00:04:04,680 --> 00:04:07,840 Speaker 1: Why we see things different color, why some things reflect 68 00:04:07,880 --> 00:04:11,040 Speaker 1: blue and other things reflect green? Do people really understand 69 00:04:11,360 --> 00:04:13,920 Speaker 1: what color is? So to get a sense of the 70 00:04:14,000 --> 00:04:16,720 Speaker 1: general level of knowledge of color, I walked around this 71 00:04:16,760 --> 00:04:19,839 Speaker 1: time in Aspen, Colorado, and I asked people what they 72 00:04:19,960 --> 00:04:23,279 Speaker 1: knew about color and light and why different things were 73 00:04:23,400 --> 00:04:26,000 Speaker 1: different colors. Listen to what they have to say, but 74 00:04:26,120 --> 00:04:28,800 Speaker 1: first think to yourself. Do you understand color? Do you 75 00:04:28,920 --> 00:04:31,839 Speaker 1: understand light? Do you understand why things are different colors? 76 00:04:32,120 --> 00:04:35,080 Speaker 1: Can you imagine a new color in your mind? Think 77 00:04:35,120 --> 00:04:37,719 Speaker 1: about those things as you listen to these answers. I 78 00:04:37,760 --> 00:04:41,000 Speaker 1: couldn't tell you that one something about the light, but 79 00:04:41,080 --> 00:04:47,080 Speaker 1: I don't know reflecting light. I don't know the spectrum 80 00:04:47,240 --> 00:04:51,679 Speaker 1: from the sun. There's infrared colors. We can't see the colors. 81 00:04:51,720 --> 00:04:55,160 Speaker 1: We can see the spectrum of the colors and the 82 00:04:55,279 --> 00:04:59,320 Speaker 1: light causing, uh, what you see for colors? I don't 83 00:04:59,360 --> 00:05:03,320 Speaker 1: know physical light is a certain wavelength. Your I C 84 00:05:03,480 --> 00:05:06,839 Speaker 1: is visible light and has more to do it's the 85 00:05:06,960 --> 00:05:11,120 Speaker 1: light bouncing after the objects. I also don't all. I'm sorry, 86 00:05:11,839 --> 00:05:14,880 Speaker 1: it's something to do with the light with our eyes 87 00:05:15,920 --> 00:05:18,640 Speaker 1: the color of white. So you're probably hear in those 88 00:05:18,680 --> 00:05:22,760 Speaker 1: answers that there's definitely some understanding of light and wavelengths 89 00:05:22,800 --> 00:05:25,560 Speaker 1: and color, and that there's definitely some physics to it. Right. 90 00:05:25,600 --> 00:05:29,120 Speaker 1: People understand that behind color is a lot of physics, 91 00:05:29,160 --> 00:05:31,039 Speaker 1: and that's great because we're gonna dig into all of 92 00:05:31,040 --> 00:05:33,840 Speaker 1: that physics today. But there's not a lot of understanding 93 00:05:33,880 --> 00:05:37,240 Speaker 1: for why different things are different colors. Why is this 94 00:05:37,320 --> 00:05:40,520 Speaker 1: bench blue, why is the grass green? All of these things? 95 00:05:40,520 --> 00:05:42,960 Speaker 1: How does that work? On a sort of microscopic level. 96 00:05:43,279 --> 00:05:45,840 Speaker 1: One of my favorite things about physics is that we 97 00:05:45,880 --> 00:05:49,479 Speaker 1: can take the macroscopic universe, the one that we experience, 98 00:05:49,839 --> 00:05:52,280 Speaker 1: and take it apart and explain it in terms of 99 00:05:52,320 --> 00:05:56,960 Speaker 1: microscopic stuff. We understand the difference, for example, between frozen 100 00:05:57,000 --> 00:05:59,359 Speaker 1: water and liquid water in terms of the motion of 101 00:05:59,400 --> 00:06:03,320 Speaker 1: the little articles inside, and everything we are experiencing around 102 00:06:03,400 --> 00:06:06,039 Speaker 1: us is in the end, just an emergent phenomenon of 103 00:06:06,080 --> 00:06:10,320 Speaker 1: these microscopic events, And so we'd like to understand basically 104 00:06:10,360 --> 00:06:13,760 Speaker 1: everything around us in terms of the microscopic principles. Right, 105 00:06:13,800 --> 00:06:17,000 Speaker 1: what is really happening on the tiniest level that makes 106 00:06:17,000 --> 00:06:20,120 Speaker 1: something green or makes something else red. And by the 107 00:06:20,200 --> 00:06:22,279 Speaker 1: end of today's podcast, I hope you'll have a solid 108 00:06:22,360 --> 00:06:25,880 Speaker 1: understanding of why things are different colors. So let's dig 109 00:06:25,880 --> 00:06:29,120 Speaker 1: into it first. What is light and what is color? Well, 110 00:06:29,200 --> 00:06:32,800 Speaker 1: let's begin with light. Light, of course, is just electromagnetic radiation. 111 00:06:32,880 --> 00:06:36,200 Speaker 1: We talked about this on the podcast fairly often. You 112 00:06:36,279 --> 00:06:38,520 Speaker 1: go all the way down from radio waves up to 113 00:06:38,680 --> 00:06:41,400 Speaker 1: gamma rays and X rays. All of these things are 114 00:06:41,440 --> 00:06:44,720 Speaker 1: just electromagnetic fields that are wiggling. That's why they can 115 00:06:44,760 --> 00:06:48,320 Speaker 1: get to you across the vast distances of space. It's 116 00:06:48,360 --> 00:06:51,239 Speaker 1: not like sound, where you have the air that's shaking. 117 00:06:51,680 --> 00:06:55,839 Speaker 1: Light is the waving of electromagnetic fields. And electromagnetic fields 118 00:06:55,880 --> 00:06:59,040 Speaker 1: are a property of space itself, like all the quantum 119 00:06:59,160 --> 00:07:02,760 Speaker 1: fields that we talked about on another podcast, Every element 120 00:07:02,760 --> 00:07:05,479 Speaker 1: of space has the possibility to have light in it, 121 00:07:05,640 --> 00:07:08,960 Speaker 1: or electrons in it, or any of the other quantum fields. 122 00:07:09,000 --> 00:07:11,840 Speaker 1: So when a photon passes through space, what that really 123 00:07:11,840 --> 00:07:15,880 Speaker 1: means is the electromagnetic fields in that space are oscillating, 124 00:07:16,240 --> 00:07:19,320 Speaker 1: and so all kinds of light are just electromagnetic radiation. 125 00:07:19,880 --> 00:07:22,240 Speaker 1: Right in the middle of the spectrum is visible light 126 00:07:22,440 --> 00:07:25,480 Speaker 1: at about a few hundred nanometers and it's no different 127 00:07:25,800 --> 00:07:28,560 Speaker 1: from the light at higher energies and lower energies, except 128 00:07:28,560 --> 00:07:31,920 Speaker 1: of course, for that energy. So the properties that a 129 00:07:31,920 --> 00:07:36,280 Speaker 1: photon has that you need to understand are just its energy. Now, 130 00:07:36,320 --> 00:07:39,480 Speaker 1: its energy is very closely connected to its frequency. The 131 00:07:39,520 --> 00:07:42,760 Speaker 1: more energy the photon has, the faster it wiggles, and 132 00:07:42,800 --> 00:07:46,320 Speaker 1: the faster it wiggles, the shorter its wavelength. All these 133 00:07:46,320 --> 00:07:48,960 Speaker 1: photons have the same speed. They all travel the speed 134 00:07:49,000 --> 00:07:52,560 Speaker 1: of light, but they have different amounts of energy per photon. 135 00:07:53,240 --> 00:07:56,400 Speaker 1: And every photon you can translate its energy directly into 136 00:07:56,440 --> 00:08:00,240 Speaker 1: its frequency, and its frequency directly into its wavelength. It's 137 00:08:00,280 --> 00:08:03,880 Speaker 1: really just one piece of information expressed in different ways. 138 00:08:04,160 --> 00:08:05,600 Speaker 1: I want to talk a little bit more about that, 139 00:08:05,640 --> 00:08:21,200 Speaker 1: but first let's take a quick break. So photons, of course, 140 00:08:21,240 --> 00:08:24,520 Speaker 1: are quantum mechanical particles. We've talked on this podcast many 141 00:08:24,520 --> 00:08:26,600 Speaker 1: times about how they can be seen as particles, they 142 00:08:26,600 --> 00:08:29,560 Speaker 1: can be seen as waves, and it's true, and you 143 00:08:29,560 --> 00:08:32,160 Speaker 1: should think about them as quantum mechanical, but only in 144 00:08:32,160 --> 00:08:34,599 Speaker 1: the sense that you can only have a certain integer 145 00:08:34,800 --> 00:08:38,240 Speaker 1: number of photons. Like you turn on your laser. You 146 00:08:38,280 --> 00:08:40,840 Speaker 1: can have one photon, or two photons, or three photons 147 00:08:40,920 --> 00:08:44,280 Speaker 1: or seventy four photons. You can't have one and a 148 00:08:44,320 --> 00:08:47,920 Speaker 1: half photons. You can't have two point seven two photons. 149 00:08:48,200 --> 00:08:51,320 Speaker 1: That's where the quantum mechanics comes in. It's it's a 150 00:08:51,400 --> 00:08:55,800 Speaker 1: discrete number of photons. But this other property of photons, 151 00:08:56,160 --> 00:08:59,400 Speaker 1: the energy of a photon equivalent again to its frequency 152 00:08:59,480 --> 00:09:03,440 Speaker 1: and therefore wavelength that can have any value. A given 153 00:09:03,480 --> 00:09:06,679 Speaker 1: photon can have any amount of energy, from very very low, 154 00:09:07,040 --> 00:09:09,240 Speaker 1: making it like a radio wave, to very very high, 155 00:09:09,320 --> 00:09:12,240 Speaker 1: making an X ray or a gamma ray. We'll talk 156 00:09:12,320 --> 00:09:14,720 Speaker 1: later about how photons are generated, and there are some 157 00:09:14,800 --> 00:09:17,960 Speaker 1: objects that can only generate photons of certain energy, but 158 00:09:18,000 --> 00:09:21,080 Speaker 1: in principle of photon can have any energy. What that 159 00:09:21,120 --> 00:09:24,400 Speaker 1: means to the context of color is that every individual 160 00:09:24,400 --> 00:09:27,280 Speaker 1: photon can have any energy level, which means you could 161 00:09:27,320 --> 00:09:30,640 Speaker 1: have any frequency, which means it could have any wavelength, 162 00:09:31,000 --> 00:09:33,920 Speaker 1: And of course the wavelength of the photon is connected 163 00:09:33,960 --> 00:09:38,000 Speaker 1: to the color. We perceive photons of different wavelength as 164 00:09:38,080 --> 00:09:41,720 Speaker 1: having different colors than a four D nimeters. For example, 165 00:09:41,880 --> 00:09:45,000 Speaker 1: we perceive things as very very red up but seven 166 00:09:45,040 --> 00:09:47,839 Speaker 1: d nanometers we perceive things as very very blue or 167 00:09:47,960 --> 00:09:52,200 Speaker 1: very very violent. So there's a close connection between the 168 00:09:52,240 --> 00:09:55,319 Speaker 1: wavelength of the photon and the color that we perceive. 169 00:09:55,760 --> 00:09:59,679 Speaker 1: But don't be confused. The color is not a property 170 00:09:59,760 --> 00:10:02,880 Speaker 1: of a photon. Sure people say a red photon, but 171 00:10:02,920 --> 00:10:06,079 Speaker 1: what they mean is that the photon has a certain wavelength. 172 00:10:06,400 --> 00:10:10,120 Speaker 1: We perceive it as red, but the redness is inside us. 173 00:10:10,160 --> 00:10:13,280 Speaker 1: There's nothing red about the photon. The photon just has 174 00:10:13,320 --> 00:10:16,480 Speaker 1: a certain wavelength. So when we're talking about the physics 175 00:10:16,480 --> 00:10:20,200 Speaker 1: of color, let's separate what property the photon has and 176 00:10:20,320 --> 00:10:24,320 Speaker 1: our perception, our experience of it. Alright, so back to 177 00:10:24,360 --> 00:10:28,280 Speaker 1: the photon. You can have any infinite number of different 178 00:10:28,280 --> 00:10:33,200 Speaker 1: wavelengths for a photon. What that means is that potentially 179 00:10:33,240 --> 00:10:36,720 Speaker 1: it is an infinite number of colors. If every wavelength 180 00:10:36,760 --> 00:10:40,160 Speaker 1: corresponds to a color, then there's an infinite number of 181 00:10:40,200 --> 00:10:44,360 Speaker 1: colors out there. Can we perceive an infinite number of colors. 182 00:10:44,679 --> 00:10:46,840 Speaker 1: Let's talk for a moment about what about how we 183 00:10:47,000 --> 00:10:51,240 Speaker 1: perceive color. Imagine this spectrum of different wavelengths from four 184 00:10:51,480 --> 00:10:54,559 Speaker 1: d nimeters up to seven hundred nimeters. Yes, there's an 185 00:10:54,559 --> 00:10:58,679 Speaker 1: infinite number of different wavelengths you could stick into that spectrum. Right, 186 00:10:58,679 --> 00:11:01,200 Speaker 1: it's the real numbers and an infinite number. Just the 187 00:11:01,240 --> 00:11:04,880 Speaker 1: same way, there's an infinite number of numbers between one 188 00:11:04,960 --> 00:11:08,400 Speaker 1: and two. Right, there's one, one point one, one point one, one, 189 00:11:08,720 --> 00:11:11,800 Speaker 1: one point one, seven, etcetera. I could go on literally 190 00:11:11,880 --> 00:11:15,320 Speaker 1: forever and name numbers between one and two. In the 191 00:11:15,360 --> 00:11:18,600 Speaker 1: same way, there's an infinite number of wavelengths photons can have, 192 00:11:19,400 --> 00:11:22,360 Speaker 1: but we are limited in how we can perceive them. 193 00:11:22,400 --> 00:11:26,960 Speaker 1: We can't necessarily tell the difference between two slightly different 194 00:11:27,000 --> 00:11:30,680 Speaker 1: wavelength photons. We might perceive them the same way. That's 195 00:11:30,679 --> 00:11:33,480 Speaker 1: just a matter of resolution. It's like in your camera 196 00:11:33,559 --> 00:11:36,600 Speaker 1: has a certain number of pixels, and so something falls 197 00:11:36,760 --> 00:11:39,760 Speaker 1: in one pixel, you can't tell where in the pixel 198 00:11:39,800 --> 00:11:42,199 Speaker 1: it landed. Did it land in the center, did it 199 00:11:42,280 --> 00:11:45,000 Speaker 1: land towards the edge. You can't tell because your camera 200 00:11:45,080 --> 00:11:48,440 Speaker 1: has a certain spatial resolution, a certain number of pixels, 201 00:11:48,520 --> 00:11:51,240 Speaker 1: and of course the more pixels it has, the better 202 00:11:51,280 --> 00:11:53,520 Speaker 1: it at it is at figuring out exactly where those 203 00:11:53,520 --> 00:11:56,800 Speaker 1: photons landed. In the same way, your eye is not 204 00:11:56,960 --> 00:12:00,760 Speaker 1: capable of distinguishing between every time need a little difference 205 00:12:00,800 --> 00:12:03,960 Speaker 1: in wavelengths. Two photons that have almost the same wavelength 206 00:12:04,200 --> 00:12:07,720 Speaker 1: will register exactly the same way in your eye. Now, 207 00:12:07,760 --> 00:12:10,240 Speaker 1: in your eyeball, there are actually three different kinds of 208 00:12:10,280 --> 00:12:12,880 Speaker 1: cells in the back of the eyeball that's see color. 209 00:12:13,240 --> 00:12:15,720 Speaker 1: What they do is they respond differently to photons at 210 00:12:15,720 --> 00:12:19,360 Speaker 1: different wavelengths. One of them peaks very very low, it's 211 00:12:19,440 --> 00:12:23,360 Speaker 1: mostly responsive around four hundred and fifty nanimeters. The second 212 00:12:23,440 --> 00:12:25,559 Speaker 1: kind peaks sort of in the middle of the spectrum, 213 00:12:25,760 --> 00:12:29,480 Speaker 1: like five hundred fifty nanimeters, and the third kind peaks 214 00:12:29,520 --> 00:12:32,520 Speaker 1: a little bit higher, just under six hundred nanimeters. So 215 00:12:32,640 --> 00:12:35,240 Speaker 1: I have three kind of cells. Each one is sensitive 216 00:12:35,280 --> 00:12:38,880 Speaker 1: to different wavelength photons. So the way that it works 217 00:12:39,240 --> 00:12:41,839 Speaker 1: is that the photon hits your eyeball and then some 218 00:12:41,920 --> 00:12:44,600 Speaker 1: of these light up. If the photon has a wavelength 219 00:12:44,679 --> 00:12:47,280 Speaker 1: which corresponds to the peak of the sensitivity for one 220 00:12:47,320 --> 00:12:49,960 Speaker 1: of those cells, it'll light up really strongly, like the 221 00:12:49,960 --> 00:12:51,880 Speaker 1: one at four fifty. If you send a photon and 222 00:12:52,000 --> 00:12:54,719 Speaker 1: at four hundred fifty nimes right at that one, it's 223 00:12:54,720 --> 00:12:56,560 Speaker 1: gonna light up, And the other ones are not going 224 00:12:56,600 --> 00:12:59,000 Speaker 1: to light up very strongly, whereas if you send a 225 00:12:59,000 --> 00:13:02,360 Speaker 1: photon around six hundred nimes, then the third kind is 226 00:13:02,360 --> 00:13:04,199 Speaker 1: going to light up really strongly and the other two 227 00:13:04,240 --> 00:13:07,320 Speaker 1: are going to be dimmer. And then your brain takes 228 00:13:07,320 --> 00:13:11,320 Speaker 1: that information. It says, the low wavelength one lit up 229 00:13:11,320 --> 00:13:13,360 Speaker 1: and the other two didn't, so therefore the light we're 230 00:13:13,400 --> 00:13:17,160 Speaker 1: seeing must be low wavelength, or if it gets messages, 231 00:13:17,200 --> 00:13:20,720 Speaker 1: it say that only the high wavelength sensor lit up, 232 00:13:20,800 --> 00:13:22,760 Speaker 1: and then it knows that the light you're seeing must 233 00:13:22,800 --> 00:13:26,800 Speaker 1: be high wavelength. It's not that your your eye specifically 234 00:13:26,920 --> 00:13:30,960 Speaker 1: measures the wavelength of any individual photon. What it does 235 00:13:30,960 --> 00:13:34,040 Speaker 1: is it asks how much does it light up each 236 00:13:34,040 --> 00:13:36,600 Speaker 1: of these three sensors, and then it has to reverse 237 00:13:36,679 --> 00:13:40,440 Speaker 1: engineer and estimate what was the wavelength of the light 238 00:13:40,480 --> 00:13:44,800 Speaker 1: that hit it. It's sort of like triangulation. Your cell 239 00:13:44,800 --> 00:13:47,040 Speaker 1: phone knows where it is because it can talk to 240 00:13:47,160 --> 00:13:49,360 Speaker 1: like three different cell phone towers, and it can ask 241 00:13:49,360 --> 00:13:52,600 Speaker 1: those towers how far away from you am I? And 242 00:13:52,640 --> 00:13:54,600 Speaker 1: if one of the tower says, oh, you're real close, 243 00:13:54,800 --> 00:13:57,120 Speaker 1: and the other two say no, you're pretty far, then 244 00:13:57,120 --> 00:14:00,000 Speaker 1: your phone knows it's pretty close to one of those towers, 245 00:14:00,080 --> 00:14:01,960 Speaker 1: and it can tell exactly where it is because it 246 00:14:02,000 --> 00:14:06,120 Speaker 1: has the messages from all three. That's called triangulation. Well, 247 00:14:06,160 --> 00:14:08,800 Speaker 1: your eye is doing the same thing with the sensors 248 00:14:08,840 --> 00:14:11,800 Speaker 1: in the eyeball. It gets three pieces of information about 249 00:14:11,800 --> 00:14:14,520 Speaker 1: the light that's coming in, and each of those gives 250 00:14:14,559 --> 00:14:18,120 Speaker 1: it different information, right, information about how close are you 251 00:14:18,240 --> 00:14:20,760 Speaker 1: to the wavelength that this sensor is good at seeing, 252 00:14:21,440 --> 00:14:24,440 Speaker 1: and then it can use that information to decide what 253 00:14:24,520 --> 00:14:27,880 Speaker 1: wavelength of the light actually hits you. So the final 254 00:14:27,920 --> 00:14:31,320 Speaker 1: perception is sort of mixed from these three different measurements 255 00:14:31,360 --> 00:14:34,560 Speaker 1: we make. And this is why you can build up 256 00:14:34,640 --> 00:14:37,480 Speaker 1: any sort of color that humans can experience out of 257 00:14:37,520 --> 00:14:40,760 Speaker 1: just three sort of basis colors. You often hear about 258 00:14:40,760 --> 00:14:44,120 Speaker 1: the primary colors or red, green, and blue, and any 259 00:14:44,160 --> 00:14:47,200 Speaker 1: color the humans perceive can be built up with some 260 00:14:47,400 --> 00:14:50,200 Speaker 1: combination of red, green, and blue. And this blew my 261 00:14:50,280 --> 00:14:52,160 Speaker 1: mind the first time I thought about it. I thought, Wow, 262 00:14:52,200 --> 00:14:56,120 Speaker 1: there's like colors live in some sort of mental, abstract 263 00:14:56,240 --> 00:14:59,920 Speaker 1: mathematical space, and red, green, and blue, or like the eye, 264 00:15:00,000 --> 00:15:03,000 Speaker 1: the invectors of it, and any color you can imagine 265 00:15:03,360 --> 00:15:06,320 Speaker 1: is just a linear combination of those three colors. That 266 00:15:06,400 --> 00:15:09,880 Speaker 1: was incredible to me, but it's not actually true that 267 00:15:10,080 --> 00:15:13,600 Speaker 1: just encompassed the human experience of color. Remember, there's an 268 00:15:13,680 --> 00:15:16,560 Speaker 1: infinite number of colors in the spectrum because it's an 269 00:15:16,560 --> 00:15:20,600 Speaker 1: infinite number of wavelengths. What r GB does is it 270 00:15:20,680 --> 00:15:24,360 Speaker 1: plays with human responses. We have three ways to measure colors, 271 00:15:24,440 --> 00:15:27,160 Speaker 1: and so it triggers those three sensors in different ways 272 00:15:27,480 --> 00:15:30,120 Speaker 1: to give you the experience of different colors. The same 273 00:15:30,160 --> 00:15:32,320 Speaker 1: way in the case of the cell phone towers, if 274 00:15:32,320 --> 00:15:34,600 Speaker 1: you could pack those cell phone towers with different distances, 275 00:15:34,840 --> 00:15:38,960 Speaker 1: you could stimulate being any place between those towers in 276 00:15:39,000 --> 00:15:43,120 Speaker 1: that same way. All right, So to recap photons have 277 00:15:43,800 --> 00:15:47,080 Speaker 1: any arbitrary wavelength, which is which is controlled by the 278 00:15:47,200 --> 00:15:51,040 Speaker 1: energy that they carry. And if we imagine the relationship 279 00:15:51,080 --> 00:15:55,000 Speaker 1: between wavelength and color, color is part of the human perception. 280 00:15:55,400 --> 00:15:58,960 Speaker 1: Color is what we experience. There's nothing red about the photon. 281 00:15:59,120 --> 00:16:02,080 Speaker 1: Per se. It has a certain wavelength which your brain 282 00:16:02,360 --> 00:16:06,239 Speaker 1: measures your eyeballs like a device for measuring the wavelength 283 00:16:06,240 --> 00:16:09,160 Speaker 1: of those colors by using those three different sensors to 284 00:16:09,240 --> 00:16:13,000 Speaker 1: triangulate it, and then it gives you the experience of 285 00:16:13,040 --> 00:16:16,960 Speaker 1: that color. But because there's nothing in particularly red about 286 00:16:16,960 --> 00:16:21,400 Speaker 1: the photon. Where does redness come from? And this is 287 00:16:21,400 --> 00:16:24,960 Speaker 1: where physics crosses into the realm of philosophy, or physics 288 00:16:25,000 --> 00:16:30,120 Speaker 1: inspires fascinating questions in philosophy. And one of the really 289 00:16:30,200 --> 00:16:34,080 Speaker 1: interesting wrinkles here is that not everybody out there has 290 00:16:34,320 --> 00:16:38,040 Speaker 1: three color sensors in their eye. There are some folks 291 00:16:38,040 --> 00:16:41,880 Speaker 1: out there that have a mutation. They have four kinds 292 00:16:41,880 --> 00:16:45,520 Speaker 1: of sensors in their eye. They are called tetra chromats, 293 00:16:45,840 --> 00:16:48,400 Speaker 1: and they have an extra way to sense color in 294 00:16:48,440 --> 00:16:51,960 Speaker 1: their eye. When I first learned about this, I thought, oh, 295 00:16:52,080 --> 00:16:54,360 Speaker 1: does that mean that they have like another color in 296 00:16:54,400 --> 00:16:57,440 Speaker 1: their mind? Is this fourth kind of cell that can 297 00:16:57,480 --> 00:17:01,000 Speaker 1: detect another element of the spectrum give them a new 298 00:17:01,080 --> 00:17:03,400 Speaker 1: kind of experience that I can't have. Is there some 299 00:17:03,680 --> 00:17:05,960 Speaker 1: color out there that they can experience that I will 300 00:17:06,040 --> 00:17:10,040 Speaker 1: never know? That's not the case. Actually, it's just a 301 00:17:10,119 --> 00:17:13,359 Speaker 1: fourth way of sensing the wavelength of the light that 302 00:17:13,400 --> 00:17:17,000 Speaker 1: you're seeing. So it gives them better ability to nail 303 00:17:17,080 --> 00:17:19,840 Speaker 1: down the wavelength of the light. They don't necessarily see 304 00:17:19,920 --> 00:17:23,679 Speaker 1: any new colors. It's like adding a fourth tower to 305 00:17:23,800 --> 00:17:27,399 Speaker 1: your triangulation. It gives it helps you separate in cases 306 00:17:27,440 --> 00:17:29,840 Speaker 1: where it's hard to tell. It gives you extra information 307 00:17:29,880 --> 00:17:33,240 Speaker 1: to tell where that cell phone is, it doesn't necessarily 308 00:17:33,280 --> 00:17:37,720 Speaker 1: give you a totally new experience of distance. So tetrachromats 309 00:17:37,880 --> 00:17:41,399 Speaker 1: are interesting and fascinating, but they don't necessarily see color 310 00:17:41,480 --> 00:17:44,320 Speaker 1: differently than we do. They're just better at it. It's 311 00:17:44,359 --> 00:17:46,439 Speaker 1: like if you're measuring the length of something and your 312 00:17:46,520 --> 00:17:48,760 Speaker 1: ruler has more little marking, so you can make a 313 00:17:48,760 --> 00:17:51,879 Speaker 1: more precise measurement of the length of whatever it is 314 00:17:51,880 --> 00:17:54,240 Speaker 1: you're looking at. All right, but back to the sense 315 00:17:54,280 --> 00:17:57,919 Speaker 1: of philosophy, perception has to be something in the mind, 316 00:17:58,240 --> 00:18:01,760 Speaker 1: because again, there's nothing blue or purple or orange about 317 00:18:01,760 --> 00:18:04,760 Speaker 1: the photon. That's something that your brain is doing. And 318 00:18:04,800 --> 00:18:07,359 Speaker 1: that's why, of course people wonder, is the read that 319 00:18:07,440 --> 00:18:12,040 Speaker 1: I'm experiencing different from the red that you're experiencing. Maybe 320 00:18:12,040 --> 00:18:15,080 Speaker 1: the red that I'm experiencing is you're blue. That seems 321 00:18:15,119 --> 00:18:17,640 Speaker 1: unlikely because we all sort of like the same kind 322 00:18:17,680 --> 00:18:19,840 Speaker 1: of art and the same kind of combinations of colors. 323 00:18:19,880 --> 00:18:22,200 Speaker 1: But we don't really know, because we can never really 324 00:18:22,200 --> 00:18:25,199 Speaker 1: experience what's in somebody else's mind. And this is a 325 00:18:25,240 --> 00:18:30,359 Speaker 1: famous question in philosophy. Can you describe redness? Can you 326 00:18:30,720 --> 00:18:34,480 Speaker 1: communicate somehow. Is there any possible way to capture the 327 00:18:34,520 --> 00:18:38,600 Speaker 1: experience of redness to convey that to somebody else without 328 00:18:38,640 --> 00:18:43,600 Speaker 1: them experiencing your redness? Can you describe redness in other terms? 329 00:18:43,720 --> 00:18:46,560 Speaker 1: Or is it unique? Is it? Is it its own 330 00:18:46,600 --> 00:18:50,720 Speaker 1: sort of basis concept in the idea structure of your mind. 331 00:18:51,400 --> 00:18:54,439 Speaker 1: And there's this famous thought experiment. Say you take a 332 00:18:54,480 --> 00:18:57,639 Speaker 1: genius scientist and you put her in a room, and 333 00:18:57,640 --> 00:19:00,560 Speaker 1: and the scientists only ever see black and white, and 334 00:19:00,640 --> 00:19:02,719 Speaker 1: she can learn all about the world, and she can 335 00:19:02,800 --> 00:19:05,320 Speaker 1: learn all about science, but she only ever sees black 336 00:19:05,359 --> 00:19:07,720 Speaker 1: and white. There's only black and white. Thinks in the room, 337 00:19:07,720 --> 00:19:10,520 Speaker 1: and the TV she's using only has black and white, 338 00:19:10,520 --> 00:19:13,639 Speaker 1: so she never sees any color. And this person is 339 00:19:13,680 --> 00:19:16,960 Speaker 1: super duper smart. Is there any way that she can 340 00:19:17,080 --> 00:19:21,119 Speaker 1: understand color so that when she opens the door and 341 00:19:21,119 --> 00:19:23,320 Speaker 1: you let her out of this terrible mind experiment you 342 00:19:23,320 --> 00:19:25,920 Speaker 1: can never actually do on people. So when she emerges 343 00:19:25,960 --> 00:19:28,840 Speaker 1: into the world and sees color and experiences it for 344 00:19:28,880 --> 00:19:32,000 Speaker 1: the first time, she will have already understood. Is there 345 00:19:32,040 --> 00:19:36,080 Speaker 1: any way to give her that understanding without the experience. 346 00:19:36,359 --> 00:19:39,679 Speaker 1: If so, then it means that color is something that 347 00:19:39,720 --> 00:19:43,560 Speaker 1: you can translate into other ideas and convey from mind 348 00:19:43,600 --> 00:19:47,440 Speaker 1: to mind. If not, then it means it's something purely internal, 349 00:19:47,480 --> 00:19:51,119 Speaker 1: something that cannot be described in any other way, meaning 350 00:19:51,160 --> 00:19:53,760 Speaker 1: that we can never know if my red is the 351 00:19:53,800 --> 00:19:56,480 Speaker 1: same as your red. So it's a famous unanswered question 352 00:19:56,520 --> 00:20:01,119 Speaker 1: and philosophy. But it stimulates in me another question, which 353 00:20:01,200 --> 00:20:04,760 Speaker 1: is how many colors are there in our mind? I mean, 354 00:20:04,760 --> 00:20:07,320 Speaker 1: if they are just in our mind, If the red 355 00:20:07,400 --> 00:20:09,320 Speaker 1: that I'm seeing as I look at this T shirt 356 00:20:09,480 --> 00:20:12,560 Speaker 1: right now is something an experience that my brain is 357 00:20:12,680 --> 00:20:16,920 Speaker 1: generating for me, then can it also generate other colors? 358 00:20:17,320 --> 00:20:19,879 Speaker 1: Obviously you can. You can generate blue, can generate orange, 359 00:20:19,880 --> 00:20:23,640 Speaker 1: You can generate purple. Right. It takes some external stimulation 360 00:20:23,720 --> 00:20:27,080 Speaker 1: to make that happen. But the generation and the experience 361 00:20:27,119 --> 00:20:30,520 Speaker 1: itself is in my mind. It's after the information from 362 00:20:30,520 --> 00:20:33,399 Speaker 1: the wavelength has been transformed into some sort of pulse 363 00:20:33,440 --> 00:20:36,400 Speaker 1: in my brain, and that's when the experience of purple happens. 364 00:20:36,920 --> 00:20:39,800 Speaker 1: So then the question is could I generate a novel 365 00:20:39,880 --> 00:20:43,960 Speaker 1: one could I think of? Could I imagine new color 366 00:20:44,119 --> 00:20:46,239 Speaker 1: that nobody has ever imagined, or at least that I 367 00:20:46,280 --> 00:20:49,119 Speaker 1: have never imagined? You know, say I had never seen 368 00:20:49,200 --> 00:20:53,040 Speaker 1: anything green before in my life. I had only ever 369 00:20:53,080 --> 00:20:56,960 Speaker 1: seen red and blue. Could I think up green? Could 370 00:20:56,960 --> 00:21:00,320 Speaker 1: I envision green in my mind without having ever seen it? 371 00:21:00,600 --> 00:21:02,639 Speaker 1: Or even if I've seen red, green and blue, can 372 00:21:02,680 --> 00:21:05,000 Speaker 1: I come up with a new color? So I honestly 373 00:21:05,040 --> 00:21:07,919 Speaker 1: spent many afternoons as a kid trying to come up 374 00:21:07,960 --> 00:21:10,399 Speaker 1: with a new color, and it always ended up something 375 00:21:10,520 --> 00:21:13,600 Speaker 1: weird and orange. But I never succeeded, and so to 376 00:21:13,680 --> 00:21:16,439 Speaker 1: this day, I still do not know the answer to 377 00:21:16,480 --> 00:21:20,159 Speaker 1: that question. So that tells us a little bit about 378 00:21:20,280 --> 00:21:23,199 Speaker 1: the physics of color. What is color? How is it 379 00:21:23,280 --> 00:21:27,239 Speaker 1: connected to the wavelength of light and electromagnetic radiation, and 380 00:21:27,280 --> 00:21:29,960 Speaker 1: how we perceive it and what that means. How you 381 00:21:30,040 --> 00:21:32,280 Speaker 1: translate from the photons that are out there in the 382 00:21:32,359 --> 00:21:35,840 Speaker 1: universe to our perception of color, which is fascinating, but 383 00:21:35,920 --> 00:21:39,600 Speaker 1: it doesn't tell us about what's happening microscopically in stuff. 384 00:21:39,920 --> 00:21:42,640 Speaker 1: Why is that shirt blue? In this shirt red? Why 385 00:21:42,680 --> 00:21:45,800 Speaker 1: is it generating photons at different colors? So I see 386 00:21:45,840 --> 00:21:48,760 Speaker 1: those things, so I experience those We'll dig into all that, 387 00:21:48,920 --> 00:22:04,960 Speaker 1: but first let's take a little break. Okay, we're talking 388 00:22:04,960 --> 00:22:08,200 Speaker 1: about the physics of color and the experience of color. 389 00:22:08,960 --> 00:22:11,040 Speaker 1: And this is something which goes back to the early 390 00:22:11,119 --> 00:22:14,320 Speaker 1: nine hundreds when there was a really interesting scientific puzzle 391 00:22:14,320 --> 00:22:17,040 Speaker 1: that people were trying to understand, which is that some 392 00:22:17,160 --> 00:22:20,479 Speaker 1: gases have color. You've probably experienced this if you've ever 393 00:22:20,520 --> 00:22:22,800 Speaker 1: played with like a Bunsen burner and put some weird 394 00:22:22,840 --> 00:22:25,000 Speaker 1: stuff in it and you see it, Oh, it glows green. 395 00:22:25,119 --> 00:22:26,920 Speaker 1: Or if you put this metal in it, you get 396 00:22:26,960 --> 00:22:28,639 Speaker 1: something purple. If you put this metal in it, you 397 00:22:28,680 --> 00:22:31,800 Speaker 1: get a red flame. And so fire has different colors. 398 00:22:32,200 --> 00:22:35,200 Speaker 1: And remember the fire is just essentially ionized gas. You're 399 00:22:35,200 --> 00:22:37,879 Speaker 1: heating something up and it's glowing and emitting photons, and 400 00:22:38,240 --> 00:22:40,520 Speaker 1: that's what you're seeing. But back on the day before 401 00:22:40,600 --> 00:22:43,120 Speaker 1: we had a really detailed understanding of the quantum mechanics 402 00:22:43,200 --> 00:22:46,679 Speaker 1: of it, people were wondering why do different gases have 403 00:22:46,840 --> 00:22:50,679 Speaker 1: different colors? And more specifically, there were two things that 404 00:22:50,760 --> 00:22:55,360 Speaker 1: people noticed. First of all, they noticed the gases absorbed colors. 405 00:22:55,920 --> 00:22:58,840 Speaker 1: So if you're shown, for example, a white light through 406 00:22:58,880 --> 00:23:01,119 Speaker 1: a bunch of gas, you measure the wavelength of the 407 00:23:01,200 --> 00:23:04,040 Speaker 1: light that came through, you'd notice that the gas absorbed 408 00:23:04,320 --> 00:23:08,040 Speaker 1: certain wavelengths, but only certain wavelengths, and it depended on 409 00:23:08,080 --> 00:23:11,600 Speaker 1: the gas. Nitrogen would absorb different things than hydrogen would 410 00:23:11,640 --> 00:23:14,760 Speaker 1: absorb different things than oxygen. So each gas seemed to 411 00:23:14,800 --> 00:23:18,240 Speaker 1: have its own pattern. These little slices of the spectrum 412 00:23:18,480 --> 00:23:20,760 Speaker 1: that we get taken out of the white light when 413 00:23:20,760 --> 00:23:23,320 Speaker 1: they pass through the gas. So you pass white light 414 00:23:23,359 --> 00:23:26,760 Speaker 1: through a gas and it removes a certain little slices 415 00:23:26,800 --> 00:23:29,240 Speaker 1: of that spectrum, and it's like a fingerprint. You can 416 00:23:29,240 --> 00:23:32,840 Speaker 1: tell what gas is there based on which slices of 417 00:23:32,840 --> 00:23:36,640 Speaker 1: the spectrum it takes out. But nobody understood why does 418 00:23:36,680 --> 00:23:39,840 Speaker 1: this gas take out that those colors and why does 419 00:23:39,880 --> 00:23:42,600 Speaker 1: that gas take out the other colors? And the second 420 00:23:42,640 --> 00:23:45,240 Speaker 1: thing is the inverse of that. You took those same 421 00:23:45,359 --> 00:23:48,520 Speaker 1: gases and you heated them up, and they would glow, 422 00:23:48,960 --> 00:23:51,160 Speaker 1: but they wouldn't glow in every color. They don't glow 423 00:23:51,200 --> 00:23:54,800 Speaker 1: white necessarily. They glow in certain colors. And the colors 424 00:23:54,800 --> 00:23:58,880 Speaker 1: they glow in match exactly the colors that they would 425 00:23:58,880 --> 00:24:01,359 Speaker 1: take out of the spec drum when you pass white 426 00:24:01,400 --> 00:24:04,960 Speaker 1: light through them. So, for any particular gas, if you 427 00:24:05,040 --> 00:24:07,760 Speaker 1: passed white light through it, it would slice out little 428 00:24:07,800 --> 00:24:09,960 Speaker 1: parts of the spectrum. But then if you took that 429 00:24:10,040 --> 00:24:12,560 Speaker 1: same gas and you heated it up, it would emit 430 00:24:12,640 --> 00:24:15,760 Speaker 1: light and exactly those little wavelengths that it had sliced out. 431 00:24:16,000 --> 00:24:19,680 Speaker 1: So something interesting was going on. And before people understood 432 00:24:19,680 --> 00:24:21,879 Speaker 1: the microscopic physics of it, there was a lot of 433 00:24:21,880 --> 00:24:23,920 Speaker 1: study and just a lot of sort of thought about it. 434 00:24:24,320 --> 00:24:27,080 Speaker 1: People measured the wavelengths, of course, very carefully and did 435 00:24:27,520 --> 00:24:30,600 Speaker 1: detailed experiments to try to understand it, because data, of 436 00:24:30,600 --> 00:24:33,440 Speaker 1: course is the source of insight and much of the science, 437 00:24:33,480 --> 00:24:36,720 Speaker 1: and especially in physics, and a lot of mathematicians looked 438 00:24:36,720 --> 00:24:39,800 Speaker 1: at those spectrum and they noticed patterns. They noticed that 439 00:24:39,800 --> 00:24:42,800 Speaker 1: there was spacing between the wavelengths that the that the 440 00:24:42,840 --> 00:24:45,760 Speaker 1: gases would absorb, and they saw these patterns that the 441 00:24:45,760 --> 00:24:48,480 Speaker 1: spacing would grow larger and larger and larger, and they're 442 00:24:48,480 --> 00:24:52,280 Speaker 1: able to fit mathematical equations to those spacings. Now, they 443 00:24:52,280 --> 00:24:55,480 Speaker 1: didn't understand where those equations came from, but they noticed 444 00:24:55,520 --> 00:24:58,199 Speaker 1: that they were there. So Ridberg, for example, came up 445 00:24:58,200 --> 00:25:01,080 Speaker 1: with this formula, and he had no understanding for what 446 00:25:01,280 --> 00:25:04,639 Speaker 1: causes formula could couldn't explain the formula at all, but 447 00:25:04,720 --> 00:25:08,080 Speaker 1: it worked perfectly. And that's a great clue because it 448 00:25:08,119 --> 00:25:11,639 Speaker 1: tells you what's the mathematical structure and the end physics 449 00:25:11,760 --> 00:25:15,280 Speaker 1: is always trying to describe the universe in terms of mathematics. 450 00:25:15,720 --> 00:25:18,560 Speaker 1: The stated goal of physics, of course, is to write 451 00:25:18,560 --> 00:25:21,280 Speaker 1: down an equation that describes everything in the universe and 452 00:25:21,280 --> 00:25:24,440 Speaker 1: then look at that equation and understand from the mathematical 453 00:25:24,520 --> 00:25:27,399 Speaker 1: structure of that equation, what do we learn about the 454 00:25:27,480 --> 00:25:30,080 Speaker 1: nature of the universe. So math is our language. So 455 00:25:30,119 --> 00:25:32,199 Speaker 1: as soon as we can turn a big pile of 456 00:25:32,280 --> 00:25:36,040 Speaker 1: data into sort of a compressed mathematical equation, then we 457 00:25:36,080 --> 00:25:38,760 Speaker 1: can ask questions about the structure that equation and wonder 458 00:25:39,000 --> 00:25:40,680 Speaker 1: why is it this way, what is it? Why is 459 00:25:40,720 --> 00:25:43,639 Speaker 1: it that way? And it was Neil's bore that figured 460 00:25:43,640 --> 00:25:47,040 Speaker 1: it out when he built his atomic theory, the one 461 00:25:47,080 --> 00:25:50,320 Speaker 1: that has little electrons orbiting the center. And of course 462 00:25:50,480 --> 00:25:53,200 Speaker 1: that's passe because we don't think these days about electrons 463 00:25:53,320 --> 00:25:56,600 Speaker 1: orbiting because they're not classical objects that have paths, and 464 00:25:56,640 --> 00:25:59,960 Speaker 1: we'll dig into that in a future episode about quantum mechanics. 465 00:26:00,320 --> 00:26:03,960 Speaker 1: In his model, electrons were orbiting the nucleus of the atom, 466 00:26:04,000 --> 00:26:06,679 Speaker 1: and they could only have certain energy levels. And what 467 00:26:06,800 --> 00:26:10,280 Speaker 1: happened when an electron jumped down an energy level It 468 00:26:10,359 --> 00:26:12,200 Speaker 1: had to give up some of that energy, and it 469 00:26:12,280 --> 00:26:14,960 Speaker 1: gave up that energy in terms of a photon. So 470 00:26:15,800 --> 00:26:19,240 Speaker 1: if an atom has certain restricted energy levels, then the 471 00:26:19,280 --> 00:26:23,560 Speaker 1: electron can jump down only certain distances, and those distances 472 00:26:23,640 --> 00:26:26,520 Speaker 1: correspond to the energy of the photons that can be 473 00:26:26,560 --> 00:26:30,080 Speaker 1: emitted by that atom, and therefore correspond to the wavelength 474 00:26:30,200 --> 00:26:32,320 Speaker 1: of the light that you see. So if you take 475 00:26:32,359 --> 00:26:36,320 Speaker 1: any particular atom, it has certain energy levels, and if 476 00:26:36,359 --> 00:26:39,680 Speaker 1: you heat that up, then the electrons jump up energy levels. 477 00:26:39,680 --> 00:26:42,760 Speaker 1: They're absorbing that energy, and then sometimes they jump down, 478 00:26:42,840 --> 00:26:45,720 Speaker 1: and when they jump down they give off those photons. 479 00:26:45,760 --> 00:26:50,600 Speaker 1: So that explained why certain gases emitted only in certain spectrum, 480 00:26:50,680 --> 00:26:53,919 Speaker 1: and every gas has its own particular set of wavelengths 481 00:26:53,920 --> 00:26:57,679 Speaker 1: that it can emit in those wavelengths again controlled exactly 482 00:26:57,760 --> 00:27:01,400 Speaker 1: by the difference in the energy levels of the electrons 483 00:27:01,480 --> 00:27:06,119 Speaker 1: going around the center. And it also, awesomely also explained 484 00:27:06,240 --> 00:27:09,760 Speaker 1: the absorption because if you take white light and you 485 00:27:09,840 --> 00:27:14,040 Speaker 1: shine it at that gas, it can't absorb any arbitrary photon. 486 00:27:14,480 --> 00:27:17,240 Speaker 1: It can only absorb photons that will take the electron 487 00:27:17,440 --> 00:27:20,560 Speaker 1: up one energy level, or two energy levels, or three 488 00:27:20,760 --> 00:27:25,159 Speaker 1: energy levels. And it's this mathematics that explain that spectrum 489 00:27:25,200 --> 00:27:28,120 Speaker 1: that the electrons have to move up or down one 490 00:27:28,240 --> 00:27:31,399 Speaker 1: or two or three steps, no half steps, no quarter steps, 491 00:27:31,400 --> 00:27:35,480 Speaker 1: no one point to seven steps that determine which photons 492 00:27:35,760 --> 00:27:39,280 Speaker 1: the atoms can absorb and can emit. So that helps 493 00:27:39,320 --> 00:27:42,520 Speaker 1: us understand sort of the physical basis of why different 494 00:27:42,520 --> 00:27:45,880 Speaker 1: things give off different colors, why different things look different colors. 495 00:27:46,000 --> 00:27:48,680 Speaker 1: So let's put it all together. You have light from 496 00:27:48,680 --> 00:27:51,520 Speaker 1: the sun. Now, life from the sun is in lots 497 00:27:51,520 --> 00:27:54,800 Speaker 1: of different frequencies, is a broad spectrum. It peaks in 498 00:27:54,840 --> 00:27:57,120 Speaker 1: the yellow or sometimes people say it's a little bit green, 499 00:27:57,440 --> 00:28:00,160 Speaker 1: but mostly you have life from the sun all all 500 00:28:00,200 --> 00:28:02,919 Speaker 1: over the visible spectrum. And that's not a coincidence that 501 00:28:02,960 --> 00:28:05,280 Speaker 1: the sun happens that you give off photons in the 502 00:28:05,359 --> 00:28:08,720 Speaker 1: same spectrum that we can see things. Right, our eyes 503 00:28:08,840 --> 00:28:11,879 Speaker 1: evolved in the presence of this sun in order to 504 00:28:11,880 --> 00:28:14,800 Speaker 1: be able to see photons which were around us. We 505 00:28:14,800 --> 00:28:16,960 Speaker 1: can think of it as evenly spread across all of 506 00:28:16,960 --> 00:28:20,840 Speaker 1: the wavelength. Now, what happens when that light hits your 507 00:28:21,119 --> 00:28:24,879 Speaker 1: red T shirt. Well, when light hits your red T shirt, 508 00:28:25,400 --> 00:28:28,720 Speaker 1: it gets reflected off the T shirt, but not entirely. 509 00:28:29,160 --> 00:28:31,440 Speaker 1: Some of the colors of that white light get absorbed 510 00:28:31,440 --> 00:28:33,680 Speaker 1: by your red T shirt. Why does your red T 511 00:28:33,800 --> 00:28:38,080 Speaker 1: shirt absorbed only some colors Because the atoms in your 512 00:28:38,080 --> 00:28:41,680 Speaker 1: red T shirt have electrons which can jump up one 513 00:28:41,840 --> 00:28:46,280 Speaker 1: energy level and accept photons at just the right wavelength. So, 514 00:28:46,360 --> 00:28:48,800 Speaker 1: just like the gas where if you pass white light 515 00:28:48,840 --> 00:28:52,720 Speaker 1: through it, it will delete certain wavelengths, your T shirt 516 00:28:52,760 --> 00:28:56,000 Speaker 1: will delete a bunch of wavelengths from white light. And 517 00:28:56,080 --> 00:29:00,080 Speaker 1: your T shirt is red not because it's absorbed photon 518 00:29:00,000 --> 00:29:01,840 Speaker 1: on which are in the red part of the spectrum, 519 00:29:02,000 --> 00:29:05,960 Speaker 1: but because it's reflected them. This is a common misperception. 520 00:29:06,040 --> 00:29:08,479 Speaker 1: People think white light comes from the sun and your 521 00:29:08,480 --> 00:29:11,320 Speaker 1: T shirt is red because it's absorbed the red parts 522 00:29:11,320 --> 00:29:14,800 Speaker 1: and reflected everything else. Remember that you are seeing photons 523 00:29:14,880 --> 00:29:17,520 Speaker 1: only when they hit your eyeball, and so I see 524 00:29:17,560 --> 00:29:20,720 Speaker 1: your shirt is red because your shirt has reflected those 525 00:29:20,800 --> 00:29:24,880 Speaker 1: red photons. To me, right, light is something I'm experiencing 526 00:29:24,880 --> 00:29:28,040 Speaker 1: based on the photons that are being reflected or emitted 527 00:29:28,080 --> 00:29:31,840 Speaker 1: from an object, not some like inherent property that it has. 528 00:29:32,400 --> 00:29:35,840 Speaker 1: Something absorbs red photons, It doesn't turn that object red. 529 00:29:36,280 --> 00:29:38,040 Speaker 1: To see something as red, you have to see red 530 00:29:38,080 --> 00:29:41,480 Speaker 1: photons leaving it, which means they have to reflect from 531 00:29:41,520 --> 00:29:46,800 Speaker 1: that object. So something that's blue, for example, absorbs red photons. 532 00:29:46,800 --> 00:29:50,440 Speaker 1: Something that's red absorbs blue photons to a little bit 533 00:29:50,480 --> 00:29:55,120 Speaker 1: backwards right. Or more specifically, something that looks blue absorbs 534 00:29:55,160 --> 00:30:00,160 Speaker 1: photons of every wavelength except for blue. Something that looks green, mean, 535 00:30:00,720 --> 00:30:05,000 Speaker 1: absorbs photons of every wavelength except for green. And this 536 00:30:05,080 --> 00:30:08,080 Speaker 1: is a model of color we call subtractive color because 537 00:30:08,080 --> 00:30:10,840 Speaker 1: you start from the white light, which is every kind 538 00:30:10,880 --> 00:30:14,360 Speaker 1: of wavelength, and you remove stuff. When something hits your 539 00:30:14,360 --> 00:30:17,080 Speaker 1: blue t shirt, a bunch of photons get absorbed, right, 540 00:30:17,200 --> 00:30:20,360 Speaker 1: they get removed, So we call that subtractive color. There's 541 00:30:20,400 --> 00:30:23,400 Speaker 1: another way to think of color, and that's additive color. 542 00:30:23,840 --> 00:30:27,160 Speaker 1: Instead of its starting from full white light and talking 543 00:30:27,200 --> 00:30:29,480 Speaker 1: about the color you perceive. If you start from nothing, 544 00:30:29,480 --> 00:30:33,400 Speaker 1: you start from blackness, for example a computer monitor, as 545 00:30:33,400 --> 00:30:36,400 Speaker 1: opposed to a piece of paper. Start from a computer monitor, 546 00:30:36,720 --> 00:30:40,040 Speaker 1: then you can add light to make various mixtures. But 547 00:30:40,040 --> 00:30:42,320 Speaker 1: but it's a little bit complicated. The two different ways 548 00:30:42,360 --> 00:30:45,120 Speaker 1: of thinking about light are fundamentally equivalent in the end. 549 00:30:45,640 --> 00:30:48,720 Speaker 1: But if you design something, for example, on your computer monitor, 550 00:30:48,840 --> 00:30:51,360 Speaker 1: and then you print it out on a white piece 551 00:30:51,360 --> 00:30:53,320 Speaker 1: of paper, it might look a little bit different from 552 00:30:53,360 --> 00:30:55,320 Speaker 1: you expected. So those are you out there who are 553 00:30:55,400 --> 00:30:58,000 Speaker 1: artists know all the details about the difference between subtractive 554 00:30:58,000 --> 00:31:01,120 Speaker 1: color models and additive color models. All right, So we've 555 00:31:01,120 --> 00:31:04,280 Speaker 1: been talking about color and photons, and now I think 556 00:31:04,280 --> 00:31:07,360 Speaker 1: we have a pretty good understanding of the physics of it. Remember, 557 00:31:07,400 --> 00:31:10,880 Speaker 1: photons have certain wavelength which corresponds to their energy, and 558 00:31:10,920 --> 00:31:13,680 Speaker 1: they're just flying around the universe having a certain energy 559 00:31:13,720 --> 00:31:16,800 Speaker 1: per photon. The experience of color is something that happens 560 00:31:17,000 --> 00:31:20,479 Speaker 1: inside our brain, is the interpretation of signals along the 561 00:31:20,480 --> 00:31:23,360 Speaker 1: optic nerve that comes from the eyeball. The eyeball has 562 00:31:23,400 --> 00:31:26,280 Speaker 1: done its best to measure the wavelength of the light 563 00:31:26,320 --> 00:31:29,520 Speaker 1: that's hitting it. But the experience of color is something internal, 564 00:31:29,640 --> 00:31:33,280 Speaker 1: something in the mind, something that philosophers can probe and 565 00:31:33,360 --> 00:31:36,480 Speaker 1: physicists can wonder about. But it also makes us wonder 566 00:31:36,640 --> 00:31:39,120 Speaker 1: what it's like to experience the world, and whether we 567 00:31:39,160 --> 00:31:41,520 Speaker 1: could see the world differently if we had different kinds 568 00:31:41,520 --> 00:31:44,360 Speaker 1: of eyeballs. So we've got a great question from a 569 00:31:44,360 --> 00:31:47,560 Speaker 1: listener which I want to actually answer right now. Here's 570 00:31:47,600 --> 00:31:51,720 Speaker 1: the question. Hi, Daniel Hire, This word that looks pretty 571 00:31:51,720 --> 00:31:55,040 Speaker 1: good and sharp in the visible spectrum, of light. But 572 00:31:55,560 --> 00:31:58,040 Speaker 1: what would it look like if you could only see 573 00:31:58,280 --> 00:32:01,840 Speaker 1: lowware or eh our frequency is off flight? Would a 574 00:32:02,000 --> 00:32:06,840 Speaker 1: low frequency world be all transparent? Thank you, what a 575 00:32:06,880 --> 00:32:10,240 Speaker 1: great question. I love imagining alternative universes where we had 576 00:32:10,320 --> 00:32:14,520 Speaker 1: different kinds of eyeballs or different kinds of experiences. So 577 00:32:14,680 --> 00:32:16,880 Speaker 1: it's an interesting question and actually one that you could 578 00:32:16,880 --> 00:32:20,240 Speaker 1: answer yourself because we have technology for this. For example, 579 00:32:20,400 --> 00:32:24,080 Speaker 1: night vision goggles do this sort of frequency shift, and 580 00:32:24,120 --> 00:32:27,440 Speaker 1: they'll let you see light that's out there that your 581 00:32:27,440 --> 00:32:31,400 Speaker 1: eyeballs cannot measure. They'll let you see at night because 582 00:32:31,440 --> 00:32:34,000 Speaker 1: there are actually photons flying around just that your eyes 583 00:32:34,120 --> 00:32:38,160 Speaker 1: cannot see them, in the same way that like infrared cameras. 584 00:32:38,240 --> 00:32:42,480 Speaker 1: Infrared cameras see photons that are have too long a wavelength, 585 00:32:42,880 --> 00:32:46,280 Speaker 1: wavelength that your eyes cannot see, but that are out there. 586 00:32:46,680 --> 00:32:50,320 Speaker 1: And so in the infrared, the world certainly does look different. 587 00:32:50,400 --> 00:32:53,000 Speaker 1: Have you seen the Predator movies, for example, where you've 588 00:32:53,000 --> 00:32:55,640 Speaker 1: seen any sort of military action movie, you know that 589 00:32:55,880 --> 00:32:58,960 Speaker 1: infrared you can see people's heat, you can tell what's 590 00:32:58,960 --> 00:33:02,760 Speaker 1: hot and what's not because things glow in the infrared 591 00:33:03,000 --> 00:33:06,000 Speaker 1: when they're hot, and so you can definitely have a 592 00:33:06,040 --> 00:33:08,840 Speaker 1: different experience of the world if you could see a 593 00:33:08,920 --> 00:33:12,200 Speaker 1: different wavelengths, and yes, different things would be transparent and 594 00:33:12,240 --> 00:33:15,240 Speaker 1: different things would be opaque because the opacity of something 595 00:33:15,280 --> 00:33:18,680 Speaker 1: and its transparency is a function of its wavelength. Right, 596 00:33:18,800 --> 00:33:22,760 Speaker 1: glass is transparent in the visible light, but not necessarily 597 00:33:22,800 --> 00:33:26,160 Speaker 1: in other wavelengths, and at higher energies more things are 598 00:33:26,200 --> 00:33:29,240 Speaker 1: transparent because the photons sort of have enough energy to 599 00:33:29,320 --> 00:33:32,040 Speaker 1: get through them. So if you could see it higher 600 00:33:32,120 --> 00:33:35,360 Speaker 1: energy photons, then you could see through more stuff. You 601 00:33:35,360 --> 00:33:38,600 Speaker 1: could have X ray vision, for example, if you could 602 00:33:38,640 --> 00:33:41,240 Speaker 1: see X rays, which in the end are just higher 603 00:33:41,360 --> 00:33:45,200 Speaker 1: energy photons, then you could literally see through people. You 604 00:33:45,200 --> 00:33:47,520 Speaker 1: could see whether they have a broken bone. You can 605 00:33:47,560 --> 00:33:50,200 Speaker 1: detect all sorts of different fascinating things about the world. 606 00:33:50,280 --> 00:33:53,720 Speaker 1: So absolutely, yes, the world would look very different if 607 00:33:53,720 --> 00:33:56,200 Speaker 1: we could see in lower, higher frequencies of light. And 608 00:33:56,240 --> 00:33:59,440 Speaker 1: don't forget that this information is out there all around you. 609 00:33:59,520 --> 00:34:01,640 Speaker 1: There's a huge, uge amount of information about the world 610 00:34:01,800 --> 00:34:03,880 Speaker 1: that you are missing because you just do not have 611 00:34:03,960 --> 00:34:06,160 Speaker 1: the sensors to pick it up. And while we're on 612 00:34:06,200 --> 00:34:08,360 Speaker 1: the topic of listener questions about light, I want to 613 00:34:08,400 --> 00:34:13,600 Speaker 1: tackle one more. Here's another amazing question. What happens when too. Obviously, 614 00:34:13,760 --> 00:34:17,360 Speaker 1: wavelengths light winds contact each other, where do they go? 615 00:34:17,560 --> 00:34:19,960 Speaker 1: In the fourth donation, So what if you have a 616 00:34:20,000 --> 00:34:22,719 Speaker 1: photon out there at five nanometers and a photon at 617 00:34:22,760 --> 00:34:25,319 Speaker 1: seven d animeters and you shoot them at each other, 618 00:34:25,480 --> 00:34:27,440 Speaker 1: then what's going to happen? I think that's sort of 619 00:34:27,480 --> 00:34:31,400 Speaker 1: the source of the question. Well, unfortunately, not much, because 620 00:34:31,480 --> 00:34:36,400 Speaker 1: photons don't interact with things that don't have electric charge. Remember, 621 00:34:36,560 --> 00:34:41,520 Speaker 1: photons are the force carrying boson of the electromagnetic interaction. 622 00:34:41,880 --> 00:34:45,400 Speaker 1: So anytime there's a magnet or there's electricity, photons are 623 00:34:45,400 --> 00:34:49,320 Speaker 1: the thing that's sort of carrying that information. And electromagnetism 624 00:34:49,360 --> 00:34:52,160 Speaker 1: works on things that have electric charges. You only have 625 00:34:52,239 --> 00:34:55,840 Speaker 1: electrical forces on things that have positive or negative charges, 626 00:34:56,160 --> 00:34:59,800 Speaker 1: even magnets. Magnets are generated by little, tiny spinning charges. 627 00:35:00,200 --> 00:35:04,120 Speaker 1: So photons only interact with things that have charges, meaning electrons, 628 00:35:04,200 --> 00:35:08,080 Speaker 1: meaning protons meaning positrons. They don't interact with things that 629 00:35:08,160 --> 00:35:12,240 Speaker 1: don't have charges like other photons. So mostly what happens 630 00:35:12,239 --> 00:35:14,960 Speaker 1: when one photon is in the same space as another 631 00:35:14,960 --> 00:35:18,799 Speaker 1: photon is nothing. They just pass right through each other. Now, 632 00:35:18,960 --> 00:35:23,400 Speaker 1: very occasionally you can have photons interacting with other photons. Remember, 633 00:35:23,400 --> 00:35:26,720 Speaker 1: photons are quantum particles, so they're always doing crazy stuff, 634 00:35:27,000 --> 00:35:30,319 Speaker 1: and every photon is occasionally turning into a matter antimatter 635 00:35:30,480 --> 00:35:33,600 Speaker 1: pair like an electron, as a kind o positron. This 636 00:35:33,680 --> 00:35:35,839 Speaker 1: happens very briefly and then it goes back to being 637 00:35:35,840 --> 00:35:39,440 Speaker 1: a photon, but it might do that at the same 638 00:35:39,560 --> 00:35:42,960 Speaker 1: moment that another photon coming the other direction does the 639 00:35:43,040 --> 00:35:46,239 Speaker 1: same thing, and then you'll have an electron an oppositron 640 00:35:46,360 --> 00:35:50,280 Speaker 1: from the first photon and an electronpositon from the second photons, 641 00:35:50,480 --> 00:35:54,200 Speaker 1: and those the guys can interact. So photons can interact, 642 00:35:54,280 --> 00:35:57,160 Speaker 1: but not directly. They have to sort of transform into 643 00:35:57,200 --> 00:36:00,759 Speaker 1: other particles briefly, which can then interact. We call that 644 00:36:00,920 --> 00:36:04,400 Speaker 1: light by light scattering, and it's actually quite a fascinating experiment. 645 00:36:04,480 --> 00:36:06,719 Speaker 1: All right, So we've dug into the physics of light. 646 00:36:06,960 --> 00:36:11,240 Speaker 1: We talked about what light is. It's just wiggling electromagnetic fields. 647 00:36:11,280 --> 00:36:14,520 Speaker 1: We talked about how light has different frequencies and how 648 00:36:14,560 --> 00:36:18,080 Speaker 1: those frequencies translate into color, and the complicated things that 649 00:36:18,080 --> 00:36:20,440 Speaker 1: are going on inside your eyeball so that you perceive 650 00:36:20,560 --> 00:36:24,080 Speaker 1: those different colors, and the amazing question of whether you 651 00:36:24,080 --> 00:36:26,960 Speaker 1: could ever describe your red to somebody else where that 652 00:36:27,000 --> 00:36:29,520 Speaker 1: you could think up the new color in somebody's mind. 653 00:36:29,880 --> 00:36:32,160 Speaker 1: I love all these questions, and I'm never gonna stop 654 00:36:32,160 --> 00:36:34,640 Speaker 1: trying to think up a new color. I'll align my 655 00:36:34,719 --> 00:36:38,560 Speaker 1: bed tonight, closing my eyes and trying to imagine a new, 656 00:36:38,680 --> 00:36:42,040 Speaker 1: weird kind of colors. Can't be orange, it can't be purple, 657 00:36:42,320 --> 00:36:43,960 Speaker 1: it can't be a new kind of green. It's got 658 00:36:43,960 --> 00:36:47,479 Speaker 1: to be something totally new. So thanks for tuning in 659 00:36:47,719 --> 00:36:49,920 Speaker 1: and listen to me talk and explain all about the 660 00:36:49,960 --> 00:36:52,560 Speaker 1: physics of light. Hope you enjoyed that. And if you 661 00:36:52,640 --> 00:36:54,640 Speaker 1: have a topic you'd like to hear us talk about, 662 00:36:54,719 --> 00:36:58,480 Speaker 1: please send it in to questions at Daniel and Jorge 663 00:36:58,640 --> 00:37:08,800 Speaker 1: dot com. Yeah, if you still have a question after 664 00:37:08,840 --> 00:37:11,959 Speaker 1: listening to all these explanations, please drop us a line. 665 00:37:12,000 --> 00:37:14,160 Speaker 1: We'd love to hear from you. You can find us 666 00:37:14,160 --> 00:37:17,960 Speaker 1: at Facebook, Twitter, and Instagram at Daniel and Jorge that's 667 00:37:18,000 --> 00:37:21,360 Speaker 1: one word, or email us at Feedback at Daniel and 668 00:37:21,480 --> 00:37:24,920 Speaker 1: Jorge dot com. Thanks for listening and remember that Daniel 669 00:37:24,960 --> 00:37:27,480 Speaker 1: and Jorge Explain the Universe is a production of I 670 00:37:27,719 --> 00:37:31,160 Speaker 1: Heart Radio. For more podcast from my Heart Radio, visit 671 00:37:31,160 --> 00:37:34,680 Speaker 1: the i heart radio, app, Apple podcasts, or wherever you 672 00:37:34,760 --> 00:37:36,280 Speaker 1: listen to your favorite shows.