1 00:00:09,400 --> 00:00:13,040 Speaker 1: Hey, they're listeners. You're into physics. So here's a tribua 2 00:00:13,160 --> 00:00:16,160 Speaker 1: question for you. Do you know who won a Nobel 3 00:00:16,280 --> 00:00:19,760 Speaker 1: Prize for relativity? That might feel like it's your question 4 00:00:19,840 --> 00:00:22,600 Speaker 1: because you want to say Einstein, because they think relativity 5 00:00:22,840 --> 00:00:26,200 Speaker 1: and Einstein will I'll tell you it's not Einstein. Now, 6 00:00:26,239 --> 00:00:28,440 Speaker 1: maybe you're scrambling through your mind to think about the 7 00:00:28,520 --> 00:00:31,320 Speaker 1: names of other physicists. You might know. How many physicists 8 00:00:31,360 --> 00:00:36,120 Speaker 1: can you name? Anyway, you got Einstein, you got me. Well, 9 00:00:36,159 --> 00:00:39,159 Speaker 1: I'll give you a clue. It's neither Einstein nor me. 10 00:00:39,760 --> 00:00:43,440 Speaker 1: So who was it? Right? Well, some folks wanted for 11 00:00:43,640 --> 00:00:47,400 Speaker 1: proving that relativity was correct. There were Nobel Prizes for 12 00:00:47,440 --> 00:00:51,839 Speaker 1: gravitational waves and for binary pulsars. But the answer is 13 00:00:51,880 --> 00:00:55,400 Speaker 1: that nobody wanted for relativity. Nobody who came up with 14 00:00:55,400 --> 00:00:58,960 Speaker 1: this incredible earth shattering idea that now frames all of 15 00:00:59,040 --> 00:01:03,120 Speaker 1: modern physics won the Nobel Prize for it. But you 16 00:01:03,200 --> 00:01:06,240 Speaker 1: might be thinking, hold on, didn't Einstein win a Nobel Prize? 17 00:01:06,640 --> 00:01:10,240 Speaker 1: And he did, but he wanted essentially for quantum mechanics. 18 00:01:26,800 --> 00:01:30,680 Speaker 1: Hello everyone, I'm Daniel. I'm a particle physicist, and I'm 19 00:01:30,720 --> 00:01:34,400 Speaker 1: the co host of this podcast together with Korge cham 20 00:01:34,520 --> 00:01:37,400 Speaker 1: who can't be here this week, So you're just listening 21 00:01:37,400 --> 00:01:40,600 Speaker 1: to me talking about the joys of physics and trying 22 00:01:40,640 --> 00:01:43,679 Speaker 1: to simulate Jorge in my mind. Every time i'm talking, 23 00:01:43,720 --> 00:01:46,639 Speaker 1: I'm thinking, here's what Jorge would say. At this moment, 24 00:01:46,720 --> 00:01:49,360 Speaker 1: I'm trying to interject a little Jorge Ism for you, 25 00:01:49,680 --> 00:01:52,280 Speaker 1: since we all miss him and you were listening to 26 00:01:52,320 --> 00:01:57,200 Speaker 1: our podcast, Daniel and Jorge Explain the Universe, a production 27 00:01:57,360 --> 00:02:00,240 Speaker 1: of I Heart Radio in which we zoom all around 28 00:02:00,240 --> 00:02:03,520 Speaker 1: the universe and try to find interesting, fascinating, cool little 29 00:02:03,600 --> 00:02:06,640 Speaker 1: nuggets of physics that would blow your mind, but take 30 00:02:06,680 --> 00:02:09,280 Speaker 1: them apart so they don't actually explode your head and 31 00:02:09,360 --> 00:02:13,519 Speaker 1: cause your brains displatter anywhere. Instead, we want to smoothly 32 00:02:13,600 --> 00:02:16,919 Speaker 1: and calmly insert them into your mind so you understand them, 33 00:02:16,960 --> 00:02:18,680 Speaker 1: so you can talk to your friends about them, so 34 00:02:18,760 --> 00:02:22,760 Speaker 1: you can actually comprehend these amazing, wonderful facts that we 35 00:02:22,840 --> 00:02:26,000 Speaker 1: have learned about the universe, and also understand all the 36 00:02:26,080 --> 00:02:29,200 Speaker 1: things we don't know about the universe, which is my 37 00:02:29,360 --> 00:02:32,040 Speaker 1: favorite part of physics, and that's why Jorge and I 38 00:02:32,120 --> 00:02:35,079 Speaker 1: wrote the book We Have No Idea, A Guide to 39 00:02:35,120 --> 00:02:37,760 Speaker 1: the Unknown universe, which takes you on an amazing tour 40 00:02:37,840 --> 00:02:40,960 Speaker 1: of all the big and basic questions about the universe 41 00:02:41,000 --> 00:02:43,600 Speaker 1: that we still have no idea what the answers are. 42 00:02:43,880 --> 00:02:46,359 Speaker 1: And on the podcast, we've been doing something fun, which 43 00:02:46,400 --> 00:02:49,399 Speaker 1: is taking a little tour of how we know what 44 00:02:49,480 --> 00:02:53,480 Speaker 1: we know, and specifically how we know anything about particle physics. 45 00:02:53,800 --> 00:02:55,960 Speaker 1: It's still incredible to me when I look around at 46 00:02:56,000 --> 00:02:58,799 Speaker 1: the world that everything is made out of these tiny 47 00:02:58,840 --> 00:03:02,519 Speaker 1: microscopic object so we can't see that we've taken thousands 48 00:03:02,520 --> 00:03:05,640 Speaker 1: of years to even discover that they exist. Yet we 49 00:03:05,720 --> 00:03:11,040 Speaker 1: have this really complex, really elaborate, really amazingly effective model 50 00:03:11,080 --> 00:03:14,480 Speaker 1: of what's happening down there at the microscopic scale, all 51 00:03:14,480 --> 00:03:18,920 Speaker 1: these tiny quantum particles interacting and zooming around. Physicists can 52 00:03:18,919 --> 00:03:21,440 Speaker 1: do calculations to tell you exactly what's going to happen 53 00:03:21,440 --> 00:03:25,000 Speaker 1: when this particle hits that particle. It's really incredibly complex 54 00:03:25,040 --> 00:03:28,040 Speaker 1: and mature. Though of course we have lots of questions, 55 00:03:28,320 --> 00:03:30,160 Speaker 1: but I think a lot of times people think of 56 00:03:30,200 --> 00:03:33,760 Speaker 1: this as sort of like an idea, something people came 57 00:03:33,840 --> 00:03:37,480 Speaker 1: up with a description of the universe. But it's critical 58 00:03:37,800 --> 00:03:40,600 Speaker 1: that everybody understand that this isn't just an idea that 59 00:03:40,640 --> 00:03:43,600 Speaker 1: came out of our heads. This is something born out 60 00:03:43,640 --> 00:03:47,360 Speaker 1: of desperation. This is our attempt to grapple with the 61 00:03:47,480 --> 00:03:53,040 Speaker 1: weird and bizarre and counterintuitive and frankly mind blowing experiments 62 00:03:53,080 --> 00:03:56,480 Speaker 1: that have shattered our perceptions of reality. We thought the 63 00:03:56,560 --> 00:03:59,760 Speaker 1: universe worked a certain way. We thought everything was smooth, 64 00:04:00,040 --> 00:04:03,000 Speaker 1: You could cut objects as many times as you wanted 65 00:04:03,040 --> 00:04:06,480 Speaker 1: to infinitely small pieces, but you can't. We thought the 66 00:04:06,560 --> 00:04:09,520 Speaker 1: universe was deterministic, that if you did the same experiment 67 00:04:09,560 --> 00:04:12,040 Speaker 1: twice you would get the same outcome. Right, that would 68 00:04:12,120 --> 00:04:15,920 Speaker 1: make sense, But it's not. It's fundamentally random. And the 69 00:04:15,960 --> 00:04:18,440 Speaker 1: core of that is particle physics, because it attempts to 70 00:04:18,440 --> 00:04:22,400 Speaker 1: describe the entire universe in terms of these tiny, weird, 71 00:04:22,760 --> 00:04:27,240 Speaker 1: nondeterministic little particles, in terms of these tiny, little, weird, 72 00:04:27,520 --> 00:04:30,880 Speaker 1: nondeterministic particles that seem to follow rules that just do 73 00:04:30,960 --> 00:04:34,040 Speaker 1: not describe the world that we are familiar with. So 74 00:04:34,360 --> 00:04:36,000 Speaker 1: my goal is to take you on a tour of 75 00:04:36,040 --> 00:04:38,640 Speaker 1: those experiments, the ones that change the way we think 76 00:04:38,680 --> 00:04:41,440 Speaker 1: about the universe, that showed us that the universe is 77 00:04:41,520 --> 00:04:44,480 Speaker 1: different from what we imagined, because it's not just the 78 00:04:44,520 --> 00:04:47,040 Speaker 1: final idea that you want that I want you to understand. 79 00:04:47,400 --> 00:04:49,880 Speaker 1: I want you to know what the evidence is. How 80 00:04:49,920 --> 00:04:53,080 Speaker 1: do we know what we know? Now? Recently we talked 81 00:04:53,080 --> 00:04:56,440 Speaker 1: about the discovery of the first particle, the first experiment 82 00:04:56,640 --> 00:05:00,520 Speaker 1: that revealed this incredible revelation that the Uni verse is 83 00:05:00,600 --> 00:05:03,360 Speaker 1: made out of time to little dots. And so today 84 00:05:03,360 --> 00:05:12,200 Speaker 1: we are continuing that tour. We are talking about how 85 00:05:12,240 --> 00:05:15,760 Speaker 1: do we know the photon is a thing? You're familiar 86 00:05:15,760 --> 00:05:18,440 Speaker 1: with photons? To you, photon is a very normal word 87 00:05:18,480 --> 00:05:21,479 Speaker 1: you hear bandied about here, talked about but how do 88 00:05:21,560 --> 00:05:24,120 Speaker 1: we know that photons are there? How do we know 89 00:05:24,160 --> 00:05:26,520 Speaker 1: that light is made out of photons that is chopped 90 00:05:26,600 --> 00:05:28,920 Speaker 1: up into these little pieces that can't be cut down 91 00:05:29,000 --> 00:05:32,240 Speaker 1: even further. What is the actual experiment that proves to 92 00:05:32,440 --> 00:05:35,760 Speaker 1: us that photons are a thing, that light is not 93 00:05:35,880 --> 00:05:39,279 Speaker 1: just electromagnetic waves, but it does these other weird things 94 00:05:39,279 --> 00:05:42,159 Speaker 1: that you have to give it particle status to explain. So, 95 00:05:42,240 --> 00:05:44,800 Speaker 1: as usual, I was wondering how many people out there 96 00:05:44,920 --> 00:05:47,479 Speaker 1: know why we think the photon is a thing, Why 97 00:05:47,560 --> 00:05:50,840 Speaker 1: we don't just think about light as electromagnetic waves. So 98 00:05:50,960 --> 00:05:52,960 Speaker 1: I walked around the campus of U see Irvine and 99 00:05:53,040 --> 00:05:56,919 Speaker 1: accosted a bunch of friendly and unsuspecting students, and I 100 00:05:57,000 --> 00:05:59,839 Speaker 1: asked them, do you know how the photon was discovered? 101 00:06:00,080 --> 00:06:02,640 Speaker 1: Do you have an idea of why we think the 102 00:06:02,640 --> 00:06:06,120 Speaker 1: photon is a thing. So before you listen to these answers, 103 00:06:06,160 --> 00:06:08,839 Speaker 1: think to yourself, or pause the podcast, or just take 104 00:06:08,880 --> 00:06:11,640 Speaker 1: a moment. How do you know photons are a thing? 105 00:06:11,640 --> 00:06:14,479 Speaker 1: Are you just believing physicists when they tell you, or 106 00:06:14,520 --> 00:06:18,119 Speaker 1: do you know what the data says? I'm not entirely sure. 107 00:06:18,400 --> 00:06:21,359 Speaker 1: I feel I shouldn't have that. I I'm sorry, I 108 00:06:21,440 --> 00:06:27,000 Speaker 1: probably should know. But it was the slit experiments, wasn't it. 109 00:06:27,080 --> 00:06:32,200 Speaker 1: And they projected a laser beam onto a single slit 110 00:06:32,320 --> 00:06:35,240 Speaker 1: or double slits and it diffracted the beam and that's 111 00:06:35,240 --> 00:06:38,919 Speaker 1: how they discovered it. Particle wave duality. Yeah, the photo 112 00:06:38,960 --> 00:06:41,520 Speaker 1: electrical facts. You shone a light on a metal and 113 00:06:41,520 --> 00:06:46,880 Speaker 1: then the metal you cross. Uh, you start for Einstein ninth. 114 00:06:46,960 --> 00:06:48,880 Speaker 1: I don't remember the year. Yeah, I don't remember who 115 00:06:48,920 --> 00:06:51,120 Speaker 1: did it, but I remember that you shine a light 116 00:06:51,160 --> 00:06:54,559 Speaker 1: on a metal, do you give the electron enough energy 117 00:06:54,640 --> 00:06:59,479 Speaker 1: to start conducting it's particles? Well, we know it's a 118 00:06:59,520 --> 00:07:01,960 Speaker 1: wave because it travels through vacuum, and we know that 119 00:07:02,000 --> 00:07:07,360 Speaker 1: it's a particle because you can transfer energy from it. Right, Yeah, 120 00:07:07,360 --> 00:07:11,960 Speaker 1: it has it hasn't defined momentum, even though it has 121 00:07:12,000 --> 00:07:15,960 Speaker 1: no mass. But the slit experiment double slip one showed 122 00:07:16,000 --> 00:07:19,239 Speaker 1: that it was a wave, like a single slit showed 123 00:07:19,240 --> 00:07:24,800 Speaker 1: that a particle. Well, it's not necessarily a particle. It's 124 00:07:25,320 --> 00:07:28,120 Speaker 1: both a particle and a wave. And for a really 125 00:07:28,160 --> 00:07:31,040 Speaker 1: long time we thought it was just a wave. But 126 00:07:31,840 --> 00:07:36,000 Speaker 1: I believe the first time we figured out that it 127 00:07:36,080 --> 00:07:42,720 Speaker 1: was a particle had to do um exciting metals to 128 00:07:43,800 --> 00:07:49,480 Speaker 1: release photons and realized that the distributions were discreet. So 129 00:07:49,600 --> 00:07:52,080 Speaker 1: I was really impressed with these answers. A lot of 130 00:07:52,160 --> 00:07:56,600 Speaker 1: understanding here that photons are particles and that they're part 131 00:07:56,600 --> 00:07:59,480 Speaker 1: of this larger idea of light being a wave and 132 00:07:59,520 --> 00:08:02,679 Speaker 1: a particle. Even some discussion of the double slit experiment, 133 00:08:02,720 --> 00:08:05,080 Speaker 1: which I'm dying to get into in a future podcast 134 00:08:05,120 --> 00:08:08,120 Speaker 1: and talk all about the amazing facts of quantum mechanics. 135 00:08:08,680 --> 00:08:10,720 Speaker 1: But the double slit experiment actually shows you that the 136 00:08:10,720 --> 00:08:13,600 Speaker 1: photon is a wave. But there was somebody out there 137 00:08:13,600 --> 00:08:16,880 Speaker 1: who talked about the photoelectric effect, and that's the key 138 00:08:17,080 --> 00:08:20,080 Speaker 1: that was the experiment that showed us that photons were 139 00:08:20,120 --> 00:08:23,440 Speaker 1: a thing. But before we talk about the crazy experiment 140 00:08:23,520 --> 00:08:26,920 Speaker 1: to prove that quantum mechanics is our reality, that showed 141 00:08:27,040 --> 00:08:29,920 Speaker 1: us that the universe is probably sliced up into little 142 00:08:29,920 --> 00:08:33,600 Speaker 1: bits and not infinitely smooth. Let's set the stage. Okay, 143 00:08:33,640 --> 00:08:36,240 Speaker 1: let's you remember how people thought about light, and to 144 00:08:36,280 --> 00:08:38,640 Speaker 1: get the context of the story, you have to rewind 145 00:08:38,720 --> 00:08:41,400 Speaker 1: all the way back to Isaac Newton. Isaac Newton, of 146 00:08:41,440 --> 00:08:44,760 Speaker 1: course very famous not just for the cookies, but also 147 00:08:44,840 --> 00:08:48,120 Speaker 1: for his discovery of his theory of gravity, which unified 148 00:08:48,280 --> 00:08:51,040 Speaker 1: motion of objects here on Earth with motion of objects 149 00:08:51,040 --> 00:08:53,520 Speaker 1: in the heavens. Really gave us access to the whole 150 00:08:53,640 --> 00:08:57,800 Speaker 1: universe to imagine, Wow, maybe physics can actually describe things 151 00:08:58,120 --> 00:09:00,280 Speaker 1: not just here in front of us, but out there 152 00:09:00,280 --> 00:09:02,680 Speaker 1: in the universe. Those are things out there that follow 153 00:09:02,800 --> 00:09:07,920 Speaker 1: laws of physics. Incredible accomplishments. But Newton also also made 154 00:09:07,960 --> 00:09:11,040 Speaker 1: amazing discoveries in the field of optics. He spent a 155 00:09:11,080 --> 00:09:14,199 Speaker 1: lot of time with lenses and with prisms, and he 156 00:09:14,280 --> 00:09:17,000 Speaker 1: was convinced that light was a particle, and he thought 157 00:09:17,000 --> 00:09:19,240 Speaker 1: a lot about how light traveled. He saw it moving 158 00:09:19,240 --> 00:09:21,160 Speaker 1: in straight lines, except when he was bent by these 159 00:09:21,240 --> 00:09:23,760 Speaker 1: lenses and he was convinced that light was a particle. 160 00:09:23,800 --> 00:09:27,520 Speaker 1: And because he was a genius and he's a staggering 161 00:09:27,600 --> 00:09:30,319 Speaker 1: influence on the field of physics, people listen to him 162 00:09:30,320 --> 00:09:33,120 Speaker 1: and rightly so. And for hundreds of years people were 163 00:09:33,160 --> 00:09:35,920 Speaker 1: convinced that it was a particle, even though other folks 164 00:09:36,040 --> 00:09:39,400 Speaker 1: had really nice theories of light as a wave. And 165 00:09:39,440 --> 00:09:42,720 Speaker 1: it wasn't until the eighteen hundreds when people started observing, 166 00:09:43,120 --> 00:09:46,600 Speaker 1: like doing things that particles couldn't do, that they had 167 00:09:46,640 --> 00:09:49,840 Speaker 1: to adapt their mindset. And that's the key. There you 168 00:09:49,880 --> 00:09:54,120 Speaker 1: see experiment rearing its uncomfortable head again saying, oh no, no, 169 00:09:54,559 --> 00:09:57,360 Speaker 1: you thought you understood the universe. You have an idea 170 00:09:57,400 --> 00:09:59,520 Speaker 1: in your mind, you have a mental model of how 171 00:09:59,559 --> 00:10:03,240 Speaker 1: this is working, but it can't describe what's actually happening. 172 00:10:03,600 --> 00:10:06,760 Speaker 1: And that's why I'm an experimentalist. That's why I think 173 00:10:06,760 --> 00:10:09,520 Speaker 1: experiment is the place to be, because experimentalists are the 174 00:10:09,520 --> 00:10:12,320 Speaker 1: ones who make the discoveries. They are on the forefront 175 00:10:12,400 --> 00:10:16,040 Speaker 1: of knowledge. They're out there exploring the universe, discovering things 176 00:10:16,080 --> 00:10:19,720 Speaker 1: that don't make sense. Theorists, of course, do an incredible job. 177 00:10:19,760 --> 00:10:22,600 Speaker 1: They tied all together they understand they predict future phenomenon. 178 00:10:22,640 --> 00:10:25,599 Speaker 1: But for me, the bit about physics that's wonderful is 179 00:10:25,720 --> 00:10:29,160 Speaker 1: the experimental side, is making those discoveries, is asking nature 180 00:10:29,200 --> 00:10:32,760 Speaker 1: a question and demanding an answer, pinning nature in a 181 00:10:32,800 --> 00:10:35,440 Speaker 1: corner so that nature has to tell you is the 182 00:10:35,520 --> 00:10:38,760 Speaker 1: universe this way or that way? And so the thing 183 00:10:38,800 --> 00:10:42,400 Speaker 1: that told people that photons couldn't just be a particle 184 00:10:42,720 --> 00:10:46,840 Speaker 1: were wave like effects, things like interference. And you're familiar 185 00:10:46,880 --> 00:10:50,800 Speaker 1: with interference, maybe you have noise canceling headphones. Now is 186 00:10:50,840 --> 00:10:54,920 Speaker 1: canceling headphones work via interference? Sound is a wave. It's 187 00:10:54,920 --> 00:10:58,040 Speaker 1: a shaking of air, and the air comes towards your head, 188 00:10:58,520 --> 00:11:00,840 Speaker 1: and if you can create waves shake in the other 189 00:11:00,880 --> 00:11:04,160 Speaker 1: direction at the same time, they basically cancel out those 190 00:11:04,160 --> 00:11:06,920 Speaker 1: waves that are coming in your head. So sound canceling 191 00:11:06,920 --> 00:11:09,080 Speaker 1: headphones are proof that sound is a wave because they 192 00:11:09,120 --> 00:11:12,240 Speaker 1: can do this wave like thing that particles just cannot do. 193 00:11:12,840 --> 00:11:15,000 Speaker 1: In the same way, people saw light behaving in a 194 00:11:15,040 --> 00:11:18,000 Speaker 1: way that could only be described by a wave, and 195 00:11:18,040 --> 00:11:20,360 Speaker 1: so you had interference effects, and you had all sorts 196 00:11:20,360 --> 00:11:23,000 Speaker 1: of theories sort of built momentum until you get to 197 00:11:23,120 --> 00:11:27,240 Speaker 1: James Clerk Maxwell his incredible genius pulled together lots of 198 00:11:27,280 --> 00:11:31,440 Speaker 1: ideas about electricity and magnetism into his unified theory of 199 00:11:31,480 --> 00:11:37,040 Speaker 1: electromagnetism that described light as oscillations of electromagnetic fields. And 200 00:11:37,040 --> 00:11:39,200 Speaker 1: when he pulled all these equations together, he saw the 201 00:11:39,240 --> 00:11:42,439 Speaker 1: equations fit together in a way to describe the oscillations 202 00:11:42,440 --> 00:11:45,640 Speaker 1: of electromagnetic fields moving at a certain speed, a speed 203 00:11:45,679 --> 00:11:48,640 Speaker 1: he could calculate, and that speed came out to be boom, 204 00:11:48,840 --> 00:11:51,960 Speaker 1: exactly the speed of light. What a moment of epiphany 205 00:11:52,000 --> 00:11:54,400 Speaker 1: that must have been for him. He pulls together all 206 00:11:54,400 --> 00:11:56,360 Speaker 1: of this knowledge, he gets new insight, he looks at 207 00:11:56,400 --> 00:11:59,080 Speaker 1: the world in a new way, and then it pops 208 00:11:59,080 --> 00:12:02,719 Speaker 1: out this obvious, amazing prediction that light moves at this 209 00:12:02,920 --> 00:12:05,760 Speaker 1: speed of light, this number that we had already known. 210 00:12:06,320 --> 00:12:09,280 Speaker 1: So what amazing confirmation for him. So that was dominant, 211 00:12:09,320 --> 00:12:12,160 Speaker 1: and people thought, okay, well, light's definitely a wave, right, 212 00:12:12,280 --> 00:12:14,720 Speaker 1: does all these wave like things we have this beautiful theory, 213 00:12:14,920 --> 00:12:18,000 Speaker 1: it's got to be a wave. Okay. So if light 214 00:12:18,120 --> 00:12:20,280 Speaker 1: is a wave, right, we think about it in terms 215 00:12:20,280 --> 00:12:23,680 Speaker 1: of electromagnetic radiation. It's just the waving of the field, 216 00:12:23,960 --> 00:12:26,400 Speaker 1: just the same way sound is waving of the air. 217 00:12:26,640 --> 00:12:29,560 Speaker 1: Different kinds of waves, but that doesn't really matter. And 218 00:12:29,600 --> 00:12:33,640 Speaker 1: the key thing to understand if light is just electromagnetic radiation, 219 00:12:33,679 --> 00:12:38,200 Speaker 1: it's just oscillations of electromagnetic fields. That means they can 220 00:12:38,280 --> 00:12:42,120 Speaker 1: have any value. You can just turn up the intensity 221 00:12:42,120 --> 00:12:44,000 Speaker 1: of the light right to make the light brighter. What 222 00:12:44,040 --> 00:12:46,680 Speaker 1: happens when you make light brighter in the wave theory 223 00:12:47,160 --> 00:12:49,720 Speaker 1: is to just increase how much the waves are shaking, right, 224 00:12:49,760 --> 00:12:52,360 Speaker 1: They're just shaking more so they have more energy. So 225 00:12:52,400 --> 00:12:55,600 Speaker 1: that's sort of the classical theory of electromagnetic radiation of 226 00:12:55,679 --> 00:12:58,040 Speaker 1: light as just these wiggling of the waves that can 227 00:12:58,080 --> 00:12:59,920 Speaker 1: have any value at all. You can turn it up, 228 00:13:00,240 --> 00:13:02,480 Speaker 1: you can turn it down, just the same way you 229 00:13:02,480 --> 00:13:05,280 Speaker 1: can make music louder or softer, and you can have 230 00:13:05,360 --> 00:13:08,080 Speaker 1: essentially any value to that volume. So that was the 231 00:13:08,080 --> 00:13:10,720 Speaker 1: sort of prevailing thinking at the time before the photon 232 00:13:10,800 --> 00:13:15,160 Speaker 1: was discovered. But then, of course, an experiment came along 233 00:13:15,240 --> 00:13:17,800 Speaker 1: that couldn't be explained, and experiment came along that just 234 00:13:18,200 --> 00:13:21,240 Speaker 1: had answers that did not make sense in the wave 235 00:13:21,440 --> 00:13:24,320 Speaker 1: theory of the universe. So we'll dig into what that 236 00:13:24,400 --> 00:13:27,640 Speaker 1: experiment was and how it worked. But first let's take 237 00:13:27,679 --> 00:13:42,880 Speaker 1: a quick break. So we're back and we're talking about 238 00:13:43,040 --> 00:13:45,959 Speaker 1: why we think the photon is a thing. What experiment 239 00:13:46,040 --> 00:13:49,240 Speaker 1: back there in history convinced people that photons had to 240 00:13:49,240 --> 00:13:52,760 Speaker 1: be a particle. And remember that in the context of 241 00:13:52,800 --> 00:13:55,040 Speaker 1: this experiment, light was thought to be a wave. It 242 00:13:55,080 --> 00:13:58,720 Speaker 1: was thought to be electromagnetic radiation, just this oscillation of 243 00:13:58,760 --> 00:14:02,760 Speaker 1: the fields. Somebody essentially shouting in the electromagnetic spectrum, and 244 00:14:02,840 --> 00:14:05,840 Speaker 1: then came along this crazy experiment. The name of the 245 00:14:05,840 --> 00:14:08,559 Speaker 1: experiment is not critical, but what it studied with something 246 00:14:08,640 --> 00:14:12,920 Speaker 1: called the photoelectric effect. Essentially, what you're doing here is 247 00:14:12,960 --> 00:14:16,959 Speaker 1: you're shining a really powerful beam of light at some surface. 248 00:14:17,320 --> 00:14:19,080 Speaker 1: And a surface, of course we know now is made 249 00:14:19,080 --> 00:14:21,760 Speaker 1: out of atoms. And what they observed is that if 250 00:14:21,800 --> 00:14:24,800 Speaker 1: you shone light at a surface, electrons would boil off 251 00:14:24,800 --> 00:14:27,160 Speaker 1: of it. You could pull them off by putting them 252 00:14:27,160 --> 00:14:29,640 Speaker 1: in an electric field, and then you can measure their energy. 253 00:14:30,520 --> 00:14:33,840 Speaker 1: People thought, oh, that's cool, we can boil particles off 254 00:14:33,840 --> 00:14:36,160 Speaker 1: of the surface by shooting light beams at it. What 255 00:14:36,200 --> 00:14:39,280 Speaker 1: would a physicist do in this scenario? She would probably think, Oh, 256 00:14:39,400 --> 00:14:41,200 Speaker 1: let me see what I can do and what happens 257 00:14:41,200 --> 00:14:42,680 Speaker 1: that I turn it up? What happens if I turn 258 00:14:42,760 --> 00:14:44,640 Speaker 1: it down? What happens? So I made the light purple? 259 00:14:44,760 --> 00:14:47,520 Speaker 1: What happens if I make the light green? Right, a 260 00:14:47,560 --> 00:14:49,960 Speaker 1: physicist would want to know if the results make sense 261 00:14:50,040 --> 00:14:53,400 Speaker 1: under all conditions. Sure, maybe we can understand how this 262 00:14:53,440 --> 00:14:56,360 Speaker 1: works in this scenario. But can we push our limits 263 00:14:56,360 --> 00:14:59,400 Speaker 1: of knowledge? Can we find some wrinkle, some corner of 264 00:14:59,440 --> 00:15:01,920 Speaker 1: the space in which it doesn't make sense? That's right, 265 00:15:02,120 --> 00:15:05,400 Speaker 1: experimentalists are always just trying to spoil everything for theorists. 266 00:15:05,520 --> 00:15:08,760 Speaker 1: That's not true at all. Actually, as Jorge would say, 267 00:15:08,800 --> 00:15:12,560 Speaker 1: because every time experimentalists do something and find a result 268 00:15:12,640 --> 00:15:15,800 Speaker 1: that doesn't make sense, that's an amazing clue. That's the 269 00:15:15,840 --> 00:15:18,240 Speaker 1: clue the theorists need to come up with a new 270 00:15:18,360 --> 00:15:22,000 Speaker 1: theory of the universe. Anyway, back to the photoelectric effect. 271 00:15:22,320 --> 00:15:25,720 Speaker 1: What happens when you shine light at the surface Electrons 272 00:15:25,760 --> 00:15:29,680 Speaker 1: come off. Now, if you're thinking of light as electromagnetic waves, 273 00:15:29,920 --> 00:15:33,280 Speaker 1: then what should happen if you turn up the intensity. 274 00:15:33,600 --> 00:15:36,360 Speaker 1: If you turn up the intensity, then electron should shoot 275 00:15:36,360 --> 00:15:39,320 Speaker 1: off with more energy. Because under the classical idea, the 276 00:15:39,360 --> 00:15:42,200 Speaker 1: original idea of light is a wave. Then if you 277 00:15:42,240 --> 00:15:44,600 Speaker 1: turn up the intensity of the light, the strength of 278 00:15:44,600 --> 00:15:47,320 Speaker 1: the light beam, then you're putting more energy. Is just 279 00:15:47,560 --> 00:15:51,440 Speaker 1: electromagnetic waves oscillating with more energy, and so there should 280 00:15:51,440 --> 00:15:54,720 Speaker 1: be more energy there to dump into the electrons, and 281 00:15:54,760 --> 00:15:57,680 Speaker 1: so the electron should boil off with more energy, and 282 00:15:57,720 --> 00:16:00,480 Speaker 1: there should be no dependence on the frequency. You can 283 00:16:00,560 --> 00:16:03,080 Speaker 1: just get the energy out of the electromagnetic waves. It 284 00:16:03,120 --> 00:16:05,640 Speaker 1: doesn't matter how fast they're shaking, as long as the 285 00:16:05,760 --> 00:16:09,320 Speaker 1: energy is there. The energy they're depending just on the intensity. 286 00:16:09,440 --> 00:16:12,040 Speaker 1: So that's the idea. They thought, if we turn up 287 00:16:12,080 --> 00:16:14,520 Speaker 1: the intensity of the light, we make the light brighter, 288 00:16:15,000 --> 00:16:18,320 Speaker 1: then you should get electrons coming off with more energy, 289 00:16:18,360 --> 00:16:21,440 Speaker 1: and there should be no dependence on the color. All right, 290 00:16:21,480 --> 00:16:24,080 Speaker 1: So that's what they thought makes perfect sense. And then 291 00:16:24,120 --> 00:16:26,440 Speaker 1: because their experimentalist, because they actually want to go out 292 00:16:26,480 --> 00:16:29,840 Speaker 1: and explore the universe, not just do thought experiments in 293 00:16:29,880 --> 00:16:32,520 Speaker 1: their head the way the old Greeks did, they went 294 00:16:32,520 --> 00:16:35,120 Speaker 1: out and they actually tried this, and what they found, 295 00:16:35,120 --> 00:16:38,760 Speaker 1: of course, blew their mind. Where they found is two 296 00:16:38,840 --> 00:16:42,960 Speaker 1: things that didn't make any sense at all. First of all, 297 00:16:43,280 --> 00:16:46,400 Speaker 1: the energy the electrons that came off the surface didn't 298 00:16:46,400 --> 00:16:49,640 Speaker 1: depend on the intensity at all. You could turn up 299 00:16:49,640 --> 00:16:52,680 Speaker 1: the intensity and the energy the electrons wouldn't change. You 300 00:16:52,680 --> 00:16:55,920 Speaker 1: could turn down the intensity and the energy the electrons 301 00:16:55,920 --> 00:17:00,400 Speaker 1: wouldn't change. Weirdly, if you turned up the intensity got 302 00:17:00,440 --> 00:17:03,720 Speaker 1: more electrons. You didn't get any electrons with more energy, 303 00:17:03,840 --> 00:17:07,040 Speaker 1: but you got more electrons boiling off. And if you 304 00:17:07,119 --> 00:17:10,000 Speaker 1: made the light dimmer, if you turned down the intensity again, 305 00:17:10,040 --> 00:17:13,600 Speaker 1: the energy didn't change, but the number of electrons dropped. 306 00:17:13,920 --> 00:17:15,679 Speaker 1: And this didn't make any sense at all in the 307 00:17:15,720 --> 00:17:18,640 Speaker 1: classical idea, if light is just a wave, if it's 308 00:17:18,640 --> 00:17:22,520 Speaker 1: just oscillation of the electromagnetic field, then it should depend 309 00:17:22,520 --> 00:17:24,840 Speaker 1: on the intensity, but there was no dependence on the 310 00:17:24,880 --> 00:17:28,800 Speaker 1: intensity at all. Instead, changing the intensity didn't change the 311 00:17:28,920 --> 00:17:31,679 Speaker 1: energy the electrons coming off. It only changed the number 312 00:17:31,720 --> 00:17:35,080 Speaker 1: of electrons we saw. So then they said, ah, that's weird, 313 00:17:35,600 --> 00:17:38,239 Speaker 1: So let's try changing the frequency of the light. So 314 00:17:38,280 --> 00:17:40,760 Speaker 1: they go from blue light down to red light and 315 00:17:40,800 --> 00:17:42,880 Speaker 1: back to purple light and just to see, and they 316 00:17:42,880 --> 00:17:45,960 Speaker 1: found that the energy to electrons, weirdly, did depend on 317 00:17:46,000 --> 00:17:49,399 Speaker 1: the frequency of the light. At higher frequencies, the electrons 318 00:17:49,440 --> 00:17:52,959 Speaker 1: had more energy, and at low enough frequencies you wouldn't 319 00:17:53,000 --> 00:17:56,280 Speaker 1: get any electrons at all. So this made no sense 320 00:17:56,320 --> 00:17:59,520 Speaker 1: to anybody. People who are thinking, who are confident that 321 00:17:59,640 --> 00:18:03,240 Speaker 1: light with just electromagnetic radiation could not explain either of 322 00:18:03,240 --> 00:18:06,880 Speaker 1: these effects. One the fact that the energy to electrons 323 00:18:07,000 --> 00:18:10,160 Speaker 1: didn't depend on the intensity of the radiation, which made 324 00:18:10,160 --> 00:18:13,240 Speaker 1: no sense because they thought these are just classical waves 325 00:18:13,240 --> 00:18:15,560 Speaker 1: and the intensity means more energy, so why aren't we 326 00:18:15,560 --> 00:18:18,480 Speaker 1: getting more energy out of the electrons? And number two 327 00:18:18,920 --> 00:18:21,800 Speaker 1: that the energy the electrons coming off did depend on 328 00:18:21,880 --> 00:18:24,120 Speaker 1: the color of the light. But it made no sense 329 00:18:24,119 --> 00:18:27,800 Speaker 1: to people because people were thinking about light as waves. 330 00:18:28,359 --> 00:18:31,399 Speaker 1: Now there was somebody thinking about light in other terms, 331 00:18:31,640 --> 00:18:35,440 Speaker 1: and that was Plunk. Plunk was studying a totally different problem, 332 00:18:35,520 --> 00:18:38,840 Speaker 1: another unsolved question in physics, which had to do with 333 00:18:38,920 --> 00:18:42,160 Speaker 1: black body radiation, which we'll talk about in another episode, 334 00:18:42,520 --> 00:18:44,080 Speaker 1: and he was trying to solve that problem and he 335 00:18:44,160 --> 00:18:46,639 Speaker 1: just couldn't. He was trying to explain why we didn't 336 00:18:46,640 --> 00:18:49,200 Speaker 1: see in the lab what we expected to see based 337 00:18:49,200 --> 00:18:52,320 Speaker 1: on the theory, and to solve his problem he had 338 00:18:52,359 --> 00:18:54,560 Speaker 1: to come up with a crazy idea. He said, well, 339 00:18:54,880 --> 00:18:57,880 Speaker 1: I don't know why, and I can justify this at all, 340 00:18:58,320 --> 00:19:03,160 Speaker 1: But if I assume whom that light comes in little 341 00:19:03,240 --> 00:19:06,000 Speaker 1: packets of energy that you can have like zero or 342 00:19:06,080 --> 00:19:09,240 Speaker 1: one or two little bits of energy, but you can't 343 00:19:09,280 --> 00:19:12,440 Speaker 1: have into your numbers in between. Then it solves my problem. 344 00:19:12,520 --> 00:19:14,320 Speaker 1: And for him it was sort of a mathematical thing 345 00:19:14,720 --> 00:19:17,600 Speaker 1: because like, I'm trying to do this calculation, it's not working. 346 00:19:17,840 --> 00:19:20,000 Speaker 1: Nobody can figure it out. Oh look if I make 347 00:19:20,040 --> 00:19:24,280 Speaker 1: this totally unjustified assumption that my calculation works and explains 348 00:19:24,280 --> 00:19:26,920 Speaker 1: the data, and that's cool. That's a totally valid way 349 00:19:26,960 --> 00:19:28,960 Speaker 1: to do theory and to do physics. And then you 350 00:19:29,000 --> 00:19:31,520 Speaker 1: got to go back and say, well, what does that mean? Right? 351 00:19:32,080 --> 00:19:34,960 Speaker 1: And it was Einstein who put it together. Einstein heard 352 00:19:35,000 --> 00:19:38,280 Speaker 1: about Plunk's idea, he said, that's fascinating, and he heard 353 00:19:38,280 --> 00:19:41,480 Speaker 1: about the photo electric effect and said, oh, interesting puzzle, 354 00:19:41,760 --> 00:19:45,399 Speaker 1: and he put them together. And so Einstein, who never 355 00:19:45,560 --> 00:19:48,919 Speaker 1: actually won the Nobel Prize for relativity, did win the 356 00:19:48,960 --> 00:19:52,439 Speaker 1: Nobel Prize later for putting these two ideas together. And 357 00:19:52,480 --> 00:19:55,600 Speaker 1: though he didn't do the experiments for the photo electric effect, 358 00:19:55,880 --> 00:19:58,560 Speaker 1: and he also didn't have the original idea to break 359 00:19:58,640 --> 00:20:01,520 Speaker 1: light down into little pieces, he just put the idea 360 00:20:01,720 --> 00:20:03,959 Speaker 1: in the right place to solve the problem and explain 361 00:20:04,040 --> 00:20:07,520 Speaker 1: this experiment. All right, So let's talk about how the 362 00:20:07,560 --> 00:20:10,919 Speaker 1: idea that photons might be little particles, little packets of 363 00:20:11,000 --> 00:20:15,119 Speaker 1: energy explains this experiment. But first, let's take another break. 364 00:20:28,240 --> 00:20:30,840 Speaker 1: All right, we're back and we're talking about why photons 365 00:20:30,920 --> 00:20:35,000 Speaker 1: are a thing. We reminded ourselves why people originally thought 366 00:20:35,000 --> 00:20:37,639 Speaker 1: that photons were waves, and then we talked about the 367 00:20:37,640 --> 00:20:40,720 Speaker 1: photo electric effect. This experiment with a weird result and 368 00:20:40,760 --> 00:20:44,840 Speaker 1: a result that could not be explained using classical theory 369 00:20:44,880 --> 00:20:47,880 Speaker 1: that could not be understood if you thought about light 370 00:20:48,000 --> 00:20:50,560 Speaker 1: as a wave. So how do we explain the photo 371 00:20:50,560 --> 00:20:53,440 Speaker 1: electric effect? How do we understand the weird results of 372 00:20:53,520 --> 00:20:56,680 Speaker 1: this experiment just by saying that light comes in little packets? 373 00:20:56,960 --> 00:21:00,080 Speaker 1: All right, Well, Einstein said, I'm gonna assume that likes 374 00:21:00,080 --> 00:21:03,800 Speaker 1: in these little packets, and that the energy inside one 375 00:21:03,840 --> 00:21:07,520 Speaker 1: packet is proportional to the frequency. That means that higher 376 00:21:07,560 --> 00:21:11,919 Speaker 1: frequencies things like blue, have more energy than photons at 377 00:21:11,960 --> 00:21:15,760 Speaker 1: lower frequencies, things like red. What that means is, if 378 00:21:15,760 --> 00:21:18,200 Speaker 1: you want more energy in your photon, you need purple 379 00:21:18,240 --> 00:21:20,440 Speaker 1: er photons. If you want less energy in your photons, 380 00:21:20,680 --> 00:21:24,800 Speaker 1: you need redder photons. His microscopic understanding, what's happening is 381 00:21:24,800 --> 00:21:27,280 Speaker 1: you have this surface of metal and it's got electrons 382 00:21:27,320 --> 00:21:30,600 Speaker 1: in it, and electrons need a certain amount of energy 383 00:21:30,680 --> 00:21:33,680 Speaker 1: in order to escape. They're bound to their atoms. They're happy, 384 00:21:33,720 --> 00:21:36,800 Speaker 1: they're they're circling the nuclei right, They don't necessarily want 385 00:21:36,800 --> 00:21:38,480 Speaker 1: to leave. In order for them to leave, they have 386 00:21:38,520 --> 00:21:41,919 Speaker 1: to get a certain minimum of energy. So what happens 387 00:21:41,920 --> 00:21:45,000 Speaker 1: when a photon comes and hits the surface. While photon 388 00:21:45,160 --> 00:21:48,919 Speaker 1: hits the electron and either it has enough energy to 389 00:21:49,080 --> 00:21:51,879 Speaker 1: kick the electron off or it doesn't. If it doesn't know, 390 00:21:51,960 --> 00:21:54,600 Speaker 1: electron is kicked off. And what that means is that 391 00:21:54,680 --> 00:21:57,280 Speaker 1: the frequency of the light has to be right high 392 00:21:57,400 --> 00:21:59,840 Speaker 1: enough frequency to have a high enough energy to kick 393 00:22:00,000 --> 00:22:03,040 Speaker 1: off any electrons. And that explains why when they turned 394 00:22:03,080 --> 00:22:06,160 Speaker 1: the frequency down on the light, no matter how bright 395 00:22:06,200 --> 00:22:08,520 Speaker 1: it was, if they turned the color down to deep 396 00:22:08,560 --> 00:22:11,560 Speaker 1: deep red, they just didn't see any electrons coming off. 397 00:22:12,359 --> 00:22:14,520 Speaker 1: And they couldn't explain that with their classical theory. With 398 00:22:14,520 --> 00:22:16,919 Speaker 1: their classical theory, they thought, well, lights a wave, the 399 00:22:16,920 --> 00:22:19,600 Speaker 1: color doesn't matter. We can make it red. As long 400 00:22:19,640 --> 00:22:22,680 Speaker 1: as we make it really really bright, electron should still 401 00:22:22,720 --> 00:22:26,159 Speaker 1: come off. But they didn't. And this theory explains why. 402 00:22:26,200 --> 00:22:29,560 Speaker 1: Because the photons in little chunks, and each electron can 403 00:22:29,600 --> 00:22:33,240 Speaker 1: only absorb energy from one photon at a time, and 404 00:22:33,400 --> 00:22:36,480 Speaker 1: that's the critical idea. You can only interact with one 405 00:22:36,480 --> 00:22:39,439 Speaker 1: photon at a time, so you if the photon doesn't 406 00:22:39,440 --> 00:22:42,760 Speaker 1: have enough energy because it's too low frequency, it's too red, 407 00:22:43,080 --> 00:22:45,359 Speaker 1: then it just can't get you out of your atom trap. 408 00:22:45,840 --> 00:22:47,639 Speaker 1: And you have there are other photons coming down the 409 00:22:47,680 --> 00:22:50,240 Speaker 1: pike if you have a really really intense beam, but 410 00:22:50,320 --> 00:22:53,760 Speaker 1: those don't help because once that first photon has failed 411 00:22:53,760 --> 00:22:55,720 Speaker 1: to get you out of the atom, then your back 412 00:22:55,720 --> 00:22:57,480 Speaker 1: on the atom again, and the next one is also 413 00:22:57,520 --> 00:23:01,000 Speaker 1: going to fail. The photons can't work together. So that's 414 00:23:01,040 --> 00:23:02,960 Speaker 1: the key idea, the fact that the beam of light 415 00:23:03,080 --> 00:23:06,840 Speaker 1: is not just one wave that's shaking the electrons so 416 00:23:06,840 --> 00:23:08,600 Speaker 1: that if you turn it up, you're shaking them more 417 00:23:08,640 --> 00:23:11,360 Speaker 1: and getting them enough energy to get out of those atoms. 418 00:23:11,359 --> 00:23:14,200 Speaker 1: But it's broken up into pieces, and each piece needs 419 00:23:14,320 --> 00:23:17,960 Speaker 1: enough energy on its own to get those electrons out 420 00:23:17,960 --> 00:23:20,000 Speaker 1: of the atom. So the way you do it, the 421 00:23:20,040 --> 00:23:22,200 Speaker 1: way you can get the electrons out of the atom 422 00:23:22,320 --> 00:23:25,200 Speaker 1: is by changing the frequency because that gets more energy 423 00:23:25,280 --> 00:23:29,520 Speaker 1: into each photon. And so if a purple one comes, 424 00:23:29,520 --> 00:23:32,840 Speaker 1: remember purple being very high frequency, it has enough energy 425 00:23:33,040 --> 00:23:35,119 Speaker 1: to get the electrons out of the atom and a 426 00:23:35,160 --> 00:23:38,440 Speaker 1: little bit left over. So as you increase the frequency 427 00:23:38,440 --> 00:23:42,240 Speaker 1: of the light, you're increasing the energy per photon, essentially 428 00:23:42,280 --> 00:23:45,560 Speaker 1: the energy that each electron has access to, and then 429 00:23:45,600 --> 00:23:47,320 Speaker 1: it has enough energy get out of the atom and 430 00:23:47,359 --> 00:23:49,840 Speaker 1: to zoom off with a good amount of speed. So 431 00:23:49,920 --> 00:23:52,399 Speaker 1: the higher the frequency of the light, the more energy 432 00:23:52,400 --> 00:23:55,320 Speaker 1: in each photon, the more energy these electrons come out at. 433 00:23:55,520 --> 00:23:58,080 Speaker 1: And that is exactly what they saw in the experiment, 434 00:23:58,440 --> 00:24:01,720 Speaker 1: and that can only be explained if electrons can only 435 00:24:01,800 --> 00:24:05,320 Speaker 1: interact with one particle of light at a time, and 436 00:24:05,440 --> 00:24:08,240 Speaker 1: the light is in fact a particle. It also explains 437 00:24:08,359 --> 00:24:11,320 Speaker 1: why the energy of electrons does not depend on the 438 00:24:11,359 --> 00:24:14,679 Speaker 1: intensity of the beam. You can have a really powerful 439 00:24:14,720 --> 00:24:17,760 Speaker 1: red beam, but it's too low frequency. All those photons 440 00:24:17,760 --> 00:24:20,200 Speaker 1: are wasted because none of them have enough energy to 441 00:24:20,240 --> 00:24:23,040 Speaker 1: get the electrons out. It doesn't matter how high you 442 00:24:23,080 --> 00:24:25,639 Speaker 1: turn it up. And even if you're turn it up 443 00:24:25,680 --> 00:24:28,240 Speaker 1: to green and you have enough energy to get the 444 00:24:28,240 --> 00:24:31,639 Speaker 1: electrons out of there, you don't get more energetic electrons 445 00:24:31,760 --> 00:24:34,919 Speaker 1: by increasing the intensity. Again, you have to change the 446 00:24:35,040 --> 00:24:38,320 Speaker 1: energy in each photon. That's hitting the electron. You can 447 00:24:38,400 --> 00:24:41,680 Speaker 1: only do that by changing the frequency. And this assumes 448 00:24:41,720 --> 00:24:45,040 Speaker 1: again that electrons can only interact with one photon at 449 00:24:45,080 --> 00:24:48,200 Speaker 1: a time, which is pretty solid assumption. So the amazing 450 00:24:48,240 --> 00:24:51,119 Speaker 1: thing is that this idea, which really came from Plank, 451 00:24:51,600 --> 00:24:54,879 Speaker 1: explain these experiments which really were done by other people. 452 00:24:55,240 --> 00:24:58,760 Speaker 1: But the unification of it, the bringing together the idea, 453 00:24:58,840 --> 00:25:02,840 Speaker 1: the moment of inside the explanation of this weird experiment, 454 00:25:03,240 --> 00:25:05,840 Speaker 1: was done by Einstein. And that's what Einstein won the 455 00:25:05,840 --> 00:25:08,840 Speaker 1: Nobel Prize for, not for doing the experiment, not for 456 00:25:08,880 --> 00:25:10,879 Speaker 1: having the idea, but for being sort of in the 457 00:25:11,000 --> 00:25:13,679 Speaker 1: right place at the right time to bring that idea 458 00:25:14,000 --> 00:25:17,240 Speaker 1: to solve this open problem. Now, the photon was not 459 00:25:17,440 --> 00:25:20,159 Speaker 1: named as a particle for decades later. All of this 460 00:25:20,240 --> 00:25:23,119 Speaker 1: happened just around the turn of the nineteenth century, and 461 00:25:23,160 --> 00:25:25,639 Speaker 1: Einstein won the Nobel Prize later for it, but it 462 00:25:25,680 --> 00:25:29,120 Speaker 1: wasn't until nineteen twenty six that people started calling these 463 00:25:29,119 --> 00:25:32,360 Speaker 1: things photons. And it comes from the Greek word for light. 464 00:25:32,960 --> 00:25:35,560 Speaker 1: But it also touches on something I think is really interesting, 465 00:25:35,600 --> 00:25:38,000 Speaker 1: which is the sort of concept of a particle. I 466 00:25:38,160 --> 00:25:41,679 Speaker 1: like to imagine what we're physicists thinking back then, what 467 00:25:41,720 --> 00:25:44,040 Speaker 1: did they think that the universe looked like at a 468 00:25:44,080 --> 00:25:48,120 Speaker 1: microscopic scale, Because to us, the notion of a particle 469 00:25:48,359 --> 00:25:50,480 Speaker 1: is kind of familiar. I mean, they're weird, they do 470 00:25:50,600 --> 00:25:52,919 Speaker 1: things that we don't understand. They follow rules and make 471 00:25:52,960 --> 00:25:56,280 Speaker 1: no sense to us. But we're comfortable with the idea 472 00:25:56,400 --> 00:25:59,440 Speaker 1: that the universe is atomic, meaning that's made up of 473 00:25:59,600 --> 00:26:00,960 Speaker 1: little bit it and all we have to do is 474 00:26:00,960 --> 00:26:03,639 Speaker 1: sort of figure out what those bids do. But at 475 00:26:03,640 --> 00:26:06,440 Speaker 1: the time, this whole concept of a particle was kind 476 00:26:06,440 --> 00:26:09,520 Speaker 1: of new. Remember where they had discovered the electron. That 477 00:26:09,640 --> 00:26:12,840 Speaker 1: was only recently. That was the first piece of evidence 478 00:26:12,880 --> 00:26:14,600 Speaker 1: that there was something as a particle. Sort of the 479 00:26:14,600 --> 00:26:17,720 Speaker 1: invention of the concept of a particle was the discovery 480 00:26:17,720 --> 00:26:20,040 Speaker 1: of the electron. And all he really did there was 481 00:26:20,080 --> 00:26:24,439 Speaker 1: identify something tiny that had both mass and charge, and 482 00:26:24,440 --> 00:26:26,800 Speaker 1: so he said, oh, look there's a thing there as 483 00:26:26,840 --> 00:26:29,320 Speaker 1: these two attributes. I'm going to call it a particle. 484 00:26:29,320 --> 00:26:32,000 Speaker 1: Actually he called it a corpus skule. But the concept 485 00:26:31,760 --> 00:26:36,399 Speaker 1: of intellectual groundwork was laid then for a particle. So 486 00:26:36,520 --> 00:26:39,479 Speaker 1: then you get to the photon. Now the photon has energy, 487 00:26:39,680 --> 00:26:43,159 Speaker 1: it has direction, but it doesn't have mass. It's not 488 00:26:43,280 --> 00:26:46,600 Speaker 1: a thing in that sense, there's no stuff to it, 489 00:26:47,160 --> 00:26:50,320 Speaker 1: So that immediately sort of bends your mind around what 490 00:26:50,600 --> 00:26:54,439 Speaker 1: is this concept of a particle. Anyway, we've created this 491 00:26:54,480 --> 00:26:57,680 Speaker 1: idea to accommodate the discovery the electron. We hope, oh, 492 00:26:57,760 --> 00:27:00,560 Speaker 1: maybe there are other particles, And later on the podcasts 493 00:27:00,640 --> 00:27:02,880 Speaker 1: will take a tour of the discoveries of other particles, 494 00:27:02,880 --> 00:27:06,840 Speaker 1: which have hilarious and amazing and dramatic stories to them. 495 00:27:06,920 --> 00:27:09,680 Speaker 1: But very early in the history of particles we had 496 00:27:09,680 --> 00:27:11,640 Speaker 1: to already bend the rules and say, oh, well, we 497 00:27:11,640 --> 00:27:13,760 Speaker 1: were talking about particles is a little bits of stuff. 498 00:27:13,760 --> 00:27:16,440 Speaker 1: But they can also be not stuff, right, they can 499 00:27:16,600 --> 00:27:19,880 Speaker 1: also just be energy. And so to me, it's amazing 500 00:27:20,240 --> 00:27:22,680 Speaker 1: that this field of particle physics was founded on such 501 00:27:22,840 --> 00:27:25,800 Speaker 1: crazy discoveries. So to me, it's wonderful that the field 502 00:27:25,800 --> 00:27:29,040 Speaker 1: of particle physics is founded on such crazy discoveries. And 503 00:27:29,040 --> 00:27:31,120 Speaker 1: you've got to give a lot of credit to the theorists, 504 00:27:31,119 --> 00:27:34,040 Speaker 1: of course, who put these ideas together and helped us 505 00:27:34,440 --> 00:27:37,320 Speaker 1: understand what we were seeing. But to me, the most 506 00:27:37,359 --> 00:27:41,639 Speaker 1: exciting moments are those moments of experimental surprise when the 507 00:27:41,760 --> 00:27:45,200 Speaker 1: universe does something that we don't understand when the unit, 508 00:27:45,240 --> 00:27:47,600 Speaker 1: when we predict the universe will do a and instead 509 00:27:47,680 --> 00:27:50,479 Speaker 1: it does be because that's the universe talking to us, 510 00:27:50,600 --> 00:27:53,639 Speaker 1: or that's the universe answering our questions, that's the universe 511 00:27:53,920 --> 00:27:56,919 Speaker 1: being the subject of our interrogation when we say we 512 00:27:56,960 --> 00:27:58,840 Speaker 1: want to know how this works, prove it to us, 513 00:27:58,920 --> 00:28:02,480 Speaker 1: or reveal to us the underlying mechanism. And that's what 514 00:28:02,600 --> 00:28:05,439 Speaker 1: experimental physics is about. Is about cornering the universe and 515 00:28:05,520 --> 00:28:08,399 Speaker 1: forcing it to reveal something new to you. And a 516 00:28:08,440 --> 00:28:10,960 Speaker 1: lot of times that revelation happens when you didn't expect that. 517 00:28:11,000 --> 00:28:13,160 Speaker 1: You thought, oh, we're just double checking this over here. 518 00:28:13,160 --> 00:28:15,800 Speaker 1: We're pretty sure we understand it. Just dotting the eyes 519 00:28:15,840 --> 00:28:17,520 Speaker 1: and crossing the teas and all of a sudden, oops, 520 00:28:17,560 --> 00:28:20,880 Speaker 1: you get something totally surprising. But those are the moments 521 00:28:21,080 --> 00:28:23,120 Speaker 1: that we learned something new about the universe, And those 522 00:28:23,160 --> 00:28:26,320 Speaker 1: are the moments I'm striving for my own personal research. 523 00:28:26,520 --> 00:28:29,920 Speaker 1: When I'm smashing particles together at the LHC. We think 524 00:28:29,960 --> 00:28:32,320 Speaker 1: we understand what's going to happen, but I'm always secretly 525 00:28:32,359 --> 00:28:35,560 Speaker 1: hoping that a student will come to me and say, hey, Daniel, 526 00:28:35,720 --> 00:28:37,880 Speaker 1: what's this. I found this weird thing in our data 527 00:28:37,920 --> 00:28:41,000 Speaker 1: that just doesn't make any sense, and that's only happened 528 00:28:41,040 --> 00:28:43,520 Speaker 1: once or twice in my entire career, and I look 529 00:28:43,560 --> 00:28:46,320 Speaker 1: forward to it happening again. So maybe one day we'll 530 00:28:46,360 --> 00:28:48,840 Speaker 1: be hearing about a crazy discovery we made at the 531 00:28:48,920 --> 00:28:52,320 Speaker 1: Large Adeon Collider. Until then, thanks for listening to this 532 00:28:52,400 --> 00:28:54,800 Speaker 1: description of how we know the photon is a thing, 533 00:28:55,360 --> 00:28:57,640 Speaker 1: and please, if you're interested in learning more about the 534 00:28:57,680 --> 00:29:00,720 Speaker 1: history of physics or understanding how we know how the 535 00:29:00,840 --> 00:29:03,720 Speaker 1: universe works and what we don't know, please send me 536 00:29:03,760 --> 00:29:07,840 Speaker 1: a suggestion to feedback at Daniel and Jorge dot com. 537 00:29:07,840 --> 00:29:17,880 Speaker 1: Thanks for tuning in. If you still have a question 538 00:29:17,920 --> 00:29:21,360 Speaker 1: after listening to all these explanations, please drop us a line. 539 00:29:21,400 --> 00:29:23,520 Speaker 1: We'd love to hear from you. You can find us 540 00:29:23,560 --> 00:29:27,360 Speaker 1: at Facebook, Twitter, and Instagram at Daniel and Jorge That's 541 00:29:27,400 --> 00:29:30,760 Speaker 1: one word, or email us at Feedback at Daniel and 542 00:29:30,880 --> 00:29:34,320 Speaker 1: Jorge dot com. Thanks for listening, and remember that Daniel 543 00:29:34,360 --> 00:29:36,880 Speaker 1: and Jorge Explain the Universe is a production of I 544 00:29:37,120 --> 00:29:40,560 Speaker 1: Heart Radio. For more podcast from my Heart Radio, visit 545 00:29:40,560 --> 00:29:44,080 Speaker 1: the I heart Radio app, Apple Podcasts, or wherever you 546 00:29:44,160 --> 00:29:45,680 Speaker 1: listen to your favorite shows.