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Do you know who won a Nobel 39 00:02:14,080 --> 00:02:17,520 Speaker 1: Prize for relativity? That might feel like it's your question 40 00:02:17,639 --> 00:02:20,440 Speaker 1: because you want to say Einstein, because you think relativity 41 00:02:20,639 --> 00:02:24,040 Speaker 1: and Einstein. Well, I'll tell you it's not Einstein. Now, 42 00:02:24,040 --> 00:02:26,240 Speaker 1: maybe you're scrambling through your mind to think about the 43 00:02:26,320 --> 00:02:29,120 Speaker 1: names of other physicists. You might know. How many physicists 44 00:02:29,200 --> 00:02:33,959 Speaker 1: can you name? Anyway, you got Einstein, you got me. Well, 45 00:02:34,000 --> 00:02:36,960 Speaker 1: I'll give you a clue. It's neither Einstein nor me. 46 00:02:37,560 --> 00:02:38,639 Speaker 1: So who was it? 47 00:02:38,720 --> 00:02:38,919 Speaker 4: Right? 48 00:02:39,320 --> 00:02:43,440 Speaker 1: Well, some folks wanted for proving that relativity was correct. 49 00:02:43,919 --> 00:02:48,000 Speaker 1: There were Nobel Prizes for gravitational waves and for binary pulsars. 50 00:02:48,320 --> 00:02:52,519 Speaker 1: But the answer is that nobody wanted for relativity. Nobody 51 00:02:52,560 --> 00:02:55,640 Speaker 1: who came up with this incredible earth shattering idea that 52 00:02:55,680 --> 00:02:59,440 Speaker 1: now frames all of modern physics won the Nobel Prize 53 00:02:59,480 --> 00:03:02,440 Speaker 1: for it. But you might be thinking, hold on, didn't 54 00:03:02,520 --> 00:03:05,920 Speaker 1: Einstein win a Nobel Prize? And he did, but he 55 00:03:05,960 --> 00:03:26,799 Speaker 1: wanted essentially for quantum mechanics. Hello everyone, I'm Daniel. I'm 56 00:03:26,840 --> 00:03:29,639 Speaker 1: a particle physicist, and I'm the co host of this 57 00:03:29,720 --> 00:03:33,800 Speaker 1: podcast together with Jorge cham who can't be here this week. 58 00:03:34,040 --> 00:03:37,160 Speaker 1: So you're just listening to me talking about the joys 59 00:03:37,200 --> 00:03:40,080 Speaker 1: of physics and trying to simulate Jorge in my mind 60 00:03:40,480 --> 00:03:43,400 Speaker 1: every time I'm talking, and I'm thinking, here's what Jorge 61 00:03:43,480 --> 00:03:45,600 Speaker 1: would say at this moment, I'm trying to interject a 62 00:03:45,600 --> 00:03:49,080 Speaker 1: little orgeism for you, since we all miss him and 63 00:03:49,160 --> 00:03:53,040 Speaker 1: you are listening to our podcast, Daniel and Jorge Explain 64 00:03:53,160 --> 00:03:57,360 Speaker 1: the Universe, a production of iHeartRadio in which we zoom 65 00:03:57,440 --> 00:04:00,640 Speaker 1: all around the universe and trying to find interesting, thing, fascinating, 66 00:04:00,760 --> 00:04:03,840 Speaker 1: cool little nuggets of physics that would blow your mind. 67 00:04:04,120 --> 00:04:06,760 Speaker 1: But take them apart so they don't actually explode your 68 00:04:06,760 --> 00:04:10,040 Speaker 1: head and cause your brains to splatter anywhere. Instead, we 69 00:04:10,080 --> 00:04:13,440 Speaker 1: want to smoothly and calmly insert them into your mind 70 00:04:13,720 --> 00:04:15,680 Speaker 1: so you understand them, so you can talk to your 71 00:04:15,680 --> 00:04:19,120 Speaker 1: friends about them, so you can actually comprehend these amazing, 72 00:04:19,480 --> 00:04:22,120 Speaker 1: wonderful facts that we have learned about the universe and 73 00:04:22,279 --> 00:04:26,080 Speaker 1: also understand all the things we don't know about the universe, 74 00:04:26,080 --> 00:04:29,159 Speaker 1: which is my favorite part of physics, and that's why 75 00:04:29,279 --> 00:04:32,279 Speaker 1: Jorge and I wrote the book We Have No Idea, 76 00:04:32,360 --> 00:04:34,680 Speaker 1: A Guide to the Unknown Universe, which takes you on 77 00:04:34,720 --> 00:04:38,000 Speaker 1: an amazing tour of all the big and basic questions 78 00:04:38,040 --> 00:04:40,600 Speaker 1: about the universe that we still have no idea what 79 00:04:40,640 --> 00:04:43,320 Speaker 1: the answers are. And on the podcast, we've been doing 80 00:04:43,360 --> 00:04:46,119 Speaker 1: something fun, which is taking a little tour of how 81 00:04:46,160 --> 00:04:49,400 Speaker 1: we know what we know, and specifically how we know 82 00:04:49,520 --> 00:04:53,040 Speaker 1: anything about particle physics. It's still incredible to me when 83 00:04:53,040 --> 00:04:55,440 Speaker 1: I look around at the world that everything is made 84 00:04:55,440 --> 00:04:58,760 Speaker 1: out of these tiny microscopic objects that we can't see, 85 00:04:58,800 --> 00:05:01,840 Speaker 1: that we've taken foul of years to even discover that 86 00:05:01,880 --> 00:05:06,520 Speaker 1: they exist. Yet we have this really complex, really elaborate, 87 00:05:06,720 --> 00:05:10,520 Speaker 1: really amazingly effective model of what's happening down there at 88 00:05:10,520 --> 00:05:14,839 Speaker 1: the microscopic scale, all these tiny quantum particles interacting and 89 00:05:14,920 --> 00:05:18,440 Speaker 1: zooming around. Physicists can do calculations to tell you exactly 90 00:05:18,520 --> 00:05:20,960 Speaker 1: what's going to happen when this particle hits that particle. 91 00:05:21,200 --> 00:05:24,760 Speaker 1: It's really incredibly complex and mature, though of course we 92 00:05:24,839 --> 00:05:26,960 Speaker 1: have lots of questions. But I think a lot of 93 00:05:27,000 --> 00:05:30,160 Speaker 1: times people think of this as sort of like an idea, 94 00:05:30,480 --> 00:05:34,039 Speaker 1: something people came up with a description of the universe. 95 00:05:34,400 --> 00:05:37,720 Speaker 1: But it's critical that everybody understand that this isn't just 96 00:05:37,760 --> 00:05:40,120 Speaker 1: an idea that came out of our heads. This is 97 00:05:40,160 --> 00:05:44,080 Speaker 1: something born out of desperation. This is our attempt to 98 00:05:44,200 --> 00:05:48,760 Speaker 1: grapple with the weird and bizarre and counterintuitive and frankly 99 00:05:49,000 --> 00:05:53,480 Speaker 1: mind blowing experiments that have shattered our perceptions of reality. 100 00:05:53,760 --> 00:05:56,200 Speaker 1: We thought the universe worked a certain way. We thought 101 00:05:56,480 --> 00:05:59,719 Speaker 1: everything was smooth, that you could cut objects as many 102 00:05:59,800 --> 00:06:03,360 Speaker 1: times you wanted to infinitely small pieces, but you can't. 103 00:06:03,839 --> 00:06:06,320 Speaker 1: We thought the universe was deterministic, that if you did 104 00:06:06,320 --> 00:06:09,480 Speaker 1: the same experiment twice you would get the same outcome. Right, 105 00:06:09,520 --> 00:06:12,880 Speaker 1: that would make sense, But it's not. It's fundamentally random. 106 00:06:13,480 --> 00:06:15,680 Speaker 1: And the core of that is particle physics, because it 107 00:06:15,720 --> 00:06:20,200 Speaker 1: attempts to describe the entire universe in terms of these tiny, weird, 108 00:06:20,600 --> 00:06:25,080 Speaker 1: non deterministic little particles, in terms of these tiny, little, weird, 109 00:06:25,360 --> 00:06:28,400 Speaker 1: non deterministic particles that seem to follow rules that just 110 00:06:28,520 --> 00:06:31,120 Speaker 1: do not describe the world that we are familiar with. 111 00:06:31,680 --> 00:06:33,680 Speaker 1: So my goal is to take you on a tour 112 00:06:33,760 --> 00:06:36,200 Speaker 1: of those experiments, the ones that change the way we 113 00:06:36,279 --> 00:06:39,039 Speaker 1: think about the universe, that showed us that the universe 114 00:06:39,120 --> 00:06:42,120 Speaker 1: is different from what we imagined. Because it's not just 115 00:06:42,200 --> 00:06:45,320 Speaker 1: the final idea that I want you to understand. I 116 00:06:45,360 --> 00:06:47,800 Speaker 1: want you to know what the evidence is. How do 117 00:06:47,920 --> 00:06:51,120 Speaker 1: we know what we know now? Recently we talked about 118 00:06:51,120 --> 00:06:54,520 Speaker 1: the discovery of the first particle, the first experiment that 119 00:06:54,680 --> 00:06:58,920 Speaker 1: revealed this incredible revelation that the universe is made out 120 00:06:58,960 --> 00:07:02,120 Speaker 1: of tiny little dots. And so today we are continuing 121 00:07:02,160 --> 00:07:10,600 Speaker 1: that tour. We are talking about how do we know 122 00:07:10,720 --> 00:07:14,400 Speaker 1: the photon is a thing? You're familiar with photons. To you, 123 00:07:14,720 --> 00:07:17,400 Speaker 1: photon is a very normal word. You hear bandied about, 124 00:07:17,680 --> 00:07:19,840 Speaker 1: you hear talked about. But how do we know that 125 00:07:19,880 --> 00:07:22,600 Speaker 1: photons are there? How do we know that light is 126 00:07:22,680 --> 00:07:24,960 Speaker 1: made out of photons that is chopped up into these 127 00:07:24,960 --> 00:07:27,920 Speaker 1: little pieces that can't be cut down even further. What 128 00:07:28,040 --> 00:07:31,600 Speaker 1: is the actual experiment that proves to us that photons 129 00:07:31,640 --> 00:07:35,120 Speaker 1: are a thing, that light is not just electromagnetic waves, 130 00:07:35,120 --> 00:07:37,600 Speaker 1: but it does these other weird things that you have 131 00:07:37,680 --> 00:07:40,600 Speaker 1: to give it particle status to explain. So, as usual, 132 00:07:40,640 --> 00:07:43,560 Speaker 1: I was wondering how many people out there know why 133 00:07:43,640 --> 00:07:45,720 Speaker 1: we think the photon is a thing. Why we don't 134 00:07:45,760 --> 00:07:48,880 Speaker 1: just think about light as electromagnetic waves. So why I 135 00:07:48,920 --> 00:07:51,400 Speaker 1: walked around the campus if you see irvine and accosted 136 00:07:51,400 --> 00:07:55,320 Speaker 1: a bunch of friendly and unsuspecting students, and I asked them, 137 00:07:55,560 --> 00:07:58,160 Speaker 1: do you know how the photon was discovered? Do you 138 00:07:58,240 --> 00:08:01,080 Speaker 1: have an idea of why we think the photon is 139 00:08:01,120 --> 00:08:04,120 Speaker 1: a thing. So before you listen to these answers, think 140 00:08:04,160 --> 00:08:07,080 Speaker 1: to yourself, pause, the podcast or just take a moment. 141 00:08:07,600 --> 00:08:09,720 Speaker 1: How do you know photons are a thing? Are you 142 00:08:09,840 --> 00:08:12,560 Speaker 1: just believing physicists when they tell you, or do you 143 00:08:12,680 --> 00:08:15,920 Speaker 1: know what the data says. I'm not entirely sure. 144 00:08:16,200 --> 00:08:16,800 Speaker 5: I just don't know. 145 00:08:16,880 --> 00:08:18,080 Speaker 6: I feel I shouldn't I have, but I don't. 146 00:08:18,120 --> 00:08:24,320 Speaker 7: Sorry, I probably should know. But it was the slit experiments, 147 00:08:24,400 --> 00:08:29,360 Speaker 7: wasn't it. And they projected a laser beam onto a 148 00:08:29,400 --> 00:08:32,559 Speaker 7: single slit or double slits and it diffracted the beam 149 00:08:32,760 --> 00:08:33,880 Speaker 7: and that's how they discovered it. 150 00:08:33,920 --> 00:08:37,920 Speaker 5: Particle wave duality, photo electric, Yeah, the photoelectric facts. Okay, 151 00:08:38,000 --> 00:08:39,560 Speaker 5: you shone a light on a metal, and then the 152 00:08:39,559 --> 00:08:42,360 Speaker 5: metal you cross, you start conducting. 153 00:08:42,440 --> 00:08:45,679 Speaker 8: Guys for Einstein. I don't remember the year. 154 00:08:45,760 --> 00:08:47,679 Speaker 5: Yeah, I don't remember who did it, but I remember 155 00:08:47,720 --> 00:08:50,360 Speaker 5: that you shine a light on a metal, you give 156 00:08:50,480 --> 00:08:53,319 Speaker 5: the electron enough energy to start conducting. 157 00:08:53,320 --> 00:08:56,080 Speaker 1: It's photons of particles. 158 00:08:56,600 --> 00:08:59,160 Speaker 5: Well, we know it's a wave because it travels through vacuum. 159 00:08:59,200 --> 00:09:02,520 Speaker 5: And we know that it's a particle because you can 160 00:09:02,520 --> 00:09:06,520 Speaker 5: transfer energy from it. Right, Yeah, it has it hasn't 161 00:09:06,520 --> 00:09:10,760 Speaker 5: defined momentum even though it has no mass. 162 00:09:10,960 --> 00:09:14,320 Speaker 8: Well, the slit experiment double slid one showed that it 163 00:09:14,360 --> 00:09:17,800 Speaker 8: was a wave like a single slit shows that's a particle. 164 00:09:18,080 --> 00:09:23,840 Speaker 9: Well, it's not necessarily a particle. It's both a particle 165 00:09:23,880 --> 00:09:26,600 Speaker 9: and a wave. And for a really long time we 166 00:09:26,640 --> 00:09:31,720 Speaker 9: thought it was just a wave. But I believe the 167 00:09:32,000 --> 00:09:35,520 Speaker 9: first time we figured out that it was a particle 168 00:09:35,679 --> 00:09:44,960 Speaker 9: had to do exciting metals to release photons and realize 169 00:09:45,000 --> 00:09:46,719 Speaker 9: that the distributions were discreete. 170 00:09:47,160 --> 00:09:49,760 Speaker 1: So I was really impressed with these answers. A lot 171 00:09:49,800 --> 00:09:54,200 Speaker 1: of understanding here that photons are particles and that they're 172 00:09:54,200 --> 00:09:57,120 Speaker 1: part of this larger idea of light being a wave 173 00:09:57,200 --> 00:10:00,520 Speaker 1: and a particle. Even some discussion of the double slid experiment, 174 00:10:00,520 --> 00:10:02,880 Speaker 1: which I'm dying to get into in a future podcast 175 00:10:02,920 --> 00:10:05,960 Speaker 1: and talk all about the amazing facts of quantum mechanics. 176 00:10:06,480 --> 00:10:08,520 Speaker 1: But the double slit experiment actually shows you that the 177 00:10:08,559 --> 00:10:11,400 Speaker 1: photon is a wave. But there was somebody out there 178 00:10:11,400 --> 00:10:14,280 Speaker 1: who talked about the photoelectric effect, and that's the key. 179 00:10:14,880 --> 00:10:17,920 Speaker 1: That was the experiment that showed us that photons were 180 00:10:17,920 --> 00:10:21,240 Speaker 1: a thing. But before we talk about the crazy experiment 181 00:10:21,320 --> 00:10:24,720 Speaker 1: to prove that quantum mechanics is our reality that showed 182 00:10:24,800 --> 00:10:27,680 Speaker 1: us that the universe is probably sliced up into little 183 00:10:27,720 --> 00:10:31,360 Speaker 1: bits and not infinitely smooth. Let's set the stage, Okay, 184 00:10:31,440 --> 00:10:34,280 Speaker 1: let's remember how people thought about light. And to get 185 00:10:34,280 --> 00:10:36,800 Speaker 1: the context of the story, you have to rewind all 186 00:10:36,840 --> 00:10:39,480 Speaker 1: the way back to Isaac Newton. Isaac Newton, of course, 187 00:10:39,800 --> 00:10:42,720 Speaker 1: very famous not just for the cookies, but also for 188 00:10:42,800 --> 00:10:46,320 Speaker 1: his discovery of his theory of gravity, which unified motion 189 00:10:46,440 --> 00:10:48,920 Speaker 1: of objects here on Earth with motion of objects in 190 00:10:48,960 --> 00:10:51,320 Speaker 1: the heavens. It really gave us access to the whole 191 00:10:51,440 --> 00:10:55,640 Speaker 1: universe to imagine, Wow, maybe physics can actually describe things 192 00:10:55,960 --> 00:10:58,040 Speaker 1: not just here in front of us, but out there 193 00:10:58,080 --> 00:11:00,880 Speaker 1: in the universe. Those are things out there follow laws 194 00:11:00,920 --> 00:11:06,319 Speaker 1: of physics. Incredible accomplishments. But Newton also also made amazing 195 00:11:06,400 --> 00:11:09,040 Speaker 1: discoveries in the field of optics. He spent a lot 196 00:11:09,040 --> 00:11:12,200 Speaker 1: of time with lenses and with prisms, and he was 197 00:11:12,280 --> 00:11:14,920 Speaker 1: convinced that light was a particle. And he thought a 198 00:11:14,920 --> 00:11:17,439 Speaker 1: lot about how light traveled, saw it moving in straight 199 00:11:17,480 --> 00:11:19,800 Speaker 1: lines except when it was bent by these lenses. And 200 00:11:19,880 --> 00:11:22,160 Speaker 1: he was convinced that light was a particle. And because 201 00:11:22,200 --> 00:11:26,000 Speaker 1: he was a genius and he has a staggering influence 202 00:11:26,080 --> 00:11:28,760 Speaker 1: on the field of physics, people listened to him rightly 203 00:11:28,840 --> 00:11:31,520 Speaker 1: so and for hundreds of years people were convinced that 204 00:11:31,600 --> 00:11:34,400 Speaker 1: it was a particle, even though other folks had really 205 00:11:34,559 --> 00:11:37,680 Speaker 1: nice theories of light as a wave. And it wasn't 206 00:11:37,760 --> 00:11:41,560 Speaker 1: until the eighteen hundreds when people started observing light doing 207 00:11:41,640 --> 00:11:44,960 Speaker 1: things that particles couldn't do that they had to adapt 208 00:11:45,000 --> 00:11:46,720 Speaker 1: their mindset. And that's the key. 209 00:11:47,240 --> 00:11:47,440 Speaker 5: There. 210 00:11:47,520 --> 00:11:51,959 Speaker 1: You see experiment rearing its uncomfortable head again, saying, oh no, no, 211 00:11:52,400 --> 00:11:55,160 Speaker 1: you thought you understood the universe. You have an idea 212 00:11:55,200 --> 00:11:57,360 Speaker 1: in your mind, you have a mental model of how 213 00:11:57,360 --> 00:12:01,000 Speaker 1: this is working, but he can't describe what's actually happening. 214 00:12:01,400 --> 00:12:04,520 Speaker 1: And that's why I'm an experimentalist. That's why I think 215 00:12:04,600 --> 00:12:07,319 Speaker 1: experiment is the place to be, because experimentalists are the 216 00:12:07,320 --> 00:12:10,120 Speaker 1: ones who make the discoveries. They are on the forefront 217 00:12:10,160 --> 00:12:13,880 Speaker 1: of knowledge. They're out there exploring the universe discovering things 218 00:12:13,880 --> 00:12:17,520 Speaker 1: that don't make sense. Theorists, of course, do an incredible job. 219 00:12:17,559 --> 00:12:20,360 Speaker 1: They tie it all together, they understand, they predict future phenomena. 220 00:12:20,440 --> 00:12:23,400 Speaker 1: But for me, the bit about physics that's wonderful is 221 00:12:23,520 --> 00:12:26,960 Speaker 1: the experimental side is making those discoveries, is asking nature 222 00:12:27,000 --> 00:12:30,559 Speaker 1: a question and demanding an answer, pinning nature in a 223 00:12:30,600 --> 00:12:33,120 Speaker 1: corner so that nature has to tell you, oh, is 224 00:12:33,160 --> 00:12:36,320 Speaker 1: the universe this way or that way? And so the 225 00:12:36,360 --> 00:12:39,720 Speaker 1: thing that told people that photons couldn't just be a 226 00:12:39,760 --> 00:12:44,680 Speaker 1: particle were wavelike effects, things like interference. And you're familiar 227 00:12:44,679 --> 00:12:49,000 Speaker 1: with interference, maybe you have noise canceling headphones. Noise canceling 228 00:12:49,040 --> 00:12:52,800 Speaker 1: headphones work via interference. Sound is a wave. It's a 229 00:12:52,880 --> 00:12:56,199 Speaker 1: shaking of air, and the air comes towards your head. 230 00:12:56,320 --> 00:12:58,360 Speaker 1: And if you can create waves that shake in the 231 00:12:58,400 --> 00:13:01,640 Speaker 1: other direction at the same time, they basically cancel out 232 00:13:01,760 --> 00:13:04,240 Speaker 1: those waves that are coming in your head. So sound 233 00:13:04,280 --> 00:13:06,800 Speaker 1: canceling headphones are proof that sound is a wave because 234 00:13:06,800 --> 00:13:09,960 Speaker 1: they can do this wavelike thing that particles just cannot do. 235 00:13:10,679 --> 00:13:12,840 Speaker 1: In the same way, people saw light behaving in a 236 00:13:12,840 --> 00:13:15,800 Speaker 1: way that could only be described by a wave. And 237 00:13:15,840 --> 00:13:18,120 Speaker 1: so you had interference effects, and you had all sorts 238 00:13:18,160 --> 00:13:20,840 Speaker 1: of theories sort of built momentum until you get to 239 00:13:20,920 --> 00:13:25,040 Speaker 1: James Clerk Maxwell, his incredible genius pull together lots of 240 00:13:25,040 --> 00:13:29,280 Speaker 1: ideas about electricity and magnetism into his unified theory of 241 00:13:29,320 --> 00:13:34,840 Speaker 1: electromagnetism that described light as oscillations of electromagnetic fields. And 242 00:13:34,840 --> 00:13:37,000 Speaker 1: when he pulled all these equations together, he saw the 243 00:13:37,040 --> 00:13:40,240 Speaker 1: equations fit together in a way to describe the oscillations 244 00:13:40,240 --> 00:13:43,439 Speaker 1: of electromagnetic fields moving at a certain speed, a speed 245 00:13:43,480 --> 00:13:46,480 Speaker 1: he could calculate, and that speed came out to be boom, 246 00:13:46,720 --> 00:13:49,800 Speaker 1: exactly the speed of light. What a moment of epiphany 247 00:13:49,800 --> 00:13:52,200 Speaker 1: that must have been for him. He pulls together all 248 00:13:52,280 --> 00:13:54,280 Speaker 1: this knowledge, he gets new insight, he looks at the 249 00:13:54,280 --> 00:13:57,079 Speaker 1: world in a new way, and then it pops out 250 00:13:57,080 --> 00:14:01,000 Speaker 1: this obvious, amazing prediction that light moves at this speed 251 00:14:01,040 --> 00:14:04,240 Speaker 1: of light, this number that we had already known. So 252 00:14:04,280 --> 00:14:07,160 Speaker 1: what amazing confirmation for him. So that was dominant and 253 00:14:07,160 --> 00:14:10,280 Speaker 1: people thought, okay, well, life's definitely a wave, right, does 254 00:14:10,320 --> 00:14:12,920 Speaker 1: all these wavelike things we have this beautiful theory it's 255 00:14:12,960 --> 00:14:16,000 Speaker 1: got to be a wave. Okay, So if light is 256 00:14:16,000 --> 00:14:18,120 Speaker 1: a wave, right, we think about it in terms of 257 00:14:18,160 --> 00:14:21,880 Speaker 1: electromagnetic radiation. It's just the waving of the field, just 258 00:14:21,920 --> 00:14:24,760 Speaker 1: the same way sound is waving of the air. Different 259 00:14:24,840 --> 00:14:27,480 Speaker 1: kinds of waves, but that doesn't really matter. And the 260 00:14:27,560 --> 00:14:31,360 Speaker 1: key thing to understand if light is just electromagnetic radiation, 261 00:14:31,480 --> 00:14:36,000 Speaker 1: it's just oscillations of electromagnetic fields. That means they can 262 00:14:36,120 --> 00:14:39,440 Speaker 1: have any value. You can just turn up the intensity 263 00:14:39,920 --> 00:14:42,120 Speaker 1: of the light to make the light brighter. What happens 264 00:14:42,160 --> 00:14:45,040 Speaker 1: when you make light brighter in the wave theory is 265 00:14:45,080 --> 00:14:47,480 Speaker 1: to just increase how much the waves are shaking, right, 266 00:14:47,520 --> 00:14:50,200 Speaker 1: They're just shaking more so they have more energy. So 267 00:14:50,200 --> 00:14:53,400 Speaker 1: that's sort of the classical theory of electromagnetic radiation of 268 00:14:53,480 --> 00:14:55,840 Speaker 1: light as just these wiggling of the waves that can 269 00:14:55,920 --> 00:14:57,760 Speaker 1: have any value at all. You can turn it up, 270 00:14:58,040 --> 00:15:00,440 Speaker 1: you can turn it down, the same where you can 271 00:15:00,480 --> 00:15:03,560 Speaker 1: make music louder or softer, and you can have essentially 272 00:15:03,600 --> 00:15:06,120 Speaker 1: any value to that volume. So that was the sort 273 00:15:06,120 --> 00:15:09,240 Speaker 1: of prevailing thinking at the time before the photon was discovered. 274 00:15:09,480 --> 00:15:13,640 Speaker 1: But then, of course an experiment came along that couldn't 275 00:15:13,640 --> 00:15:16,680 Speaker 1: be explained. An experiment came along that just had answers 276 00:15:16,720 --> 00:15:19,800 Speaker 1: that did not make sense in the wave theory of 277 00:15:19,840 --> 00:15:22,920 Speaker 1: the universe. So we'll dig into what that experiment was 278 00:15:23,160 --> 00:15:26,200 Speaker 1: and how it worked. But first let's take a quick break. 279 00:15:30,760 --> 00:15:33,720 Speaker 1: With big wireless providers, what you see is never what 280 00:15:33,800 --> 00:15:36,440 Speaker 1: you get. Somewhere between the store and your first month's bill. 281 00:15:36,520 --> 00:15:39,560 Speaker 1: The price you thought you were paying magically skyrockets. With 282 00:15:39,680 --> 00:15:43,120 Speaker 1: mint Mobile, You'll never have to worry about Gotcha's ever again. 283 00:15:43,160 --> 00:15:45,400 Speaker 1: When mint Mobile says fifteen dollars a month for a 284 00:15:45,440 --> 00:15:48,280 Speaker 1: three month plan, they really mean it. 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So we're back and we're 328 00:18:10,359 --> 00:18:12,840 Speaker 1: talking about why we think the photon is a thing. 329 00:18:13,240 --> 00:18:16,960 Speaker 1: What experiment back there in history convinced people that photons 330 00:18:17,000 --> 00:18:20,199 Speaker 1: had to be a particle. And remember that in the 331 00:18:20,240 --> 00:18:23,000 Speaker 1: context of this experiment, light was thought to be a wave. 332 00:18:23,040 --> 00:18:26,480 Speaker 1: It was thought to be electromagnetic radiation, just this oscillation 333 00:18:26,760 --> 00:18:30,840 Speaker 1: of the fields, somebody essentially shouting in electromagnetic spectrum, and 334 00:18:30,920 --> 00:18:33,920 Speaker 1: then came along this crazy experiment. The name of the 335 00:18:33,960 --> 00:18:36,679 Speaker 1: experiment is not critical, but what it's studied was something 336 00:18:36,720 --> 00:18:41,000 Speaker 1: called the photoelectric effect. Essentially, what you're doing here is 337 00:18:41,040 --> 00:18:45,040 Speaker 1: you're shining a really powerful beam of light at some surface, 338 00:18:45,400 --> 00:18:47,160 Speaker 1: and a surface, of course we know now is made 339 00:18:47,160 --> 00:18:49,920 Speaker 1: out of atoms. What they observed is that if you 340 00:18:50,040 --> 00:18:53,119 Speaker 1: shine light at a surface, electrons would boil off of it. 341 00:18:53,560 --> 00:18:55,399 Speaker 1: You could pull them off by putting them in an 342 00:18:55,440 --> 00:18:58,520 Speaker 1: electric field, and then you can measure their energy. So 343 00:18:58,560 --> 00:19:01,920 Speaker 1: people thought Ooh, that's cool. We can boil particles off 344 00:19:01,920 --> 00:19:04,280 Speaker 1: of a surface by shooting light beams at it. What 345 00:19:04,320 --> 00:19:07,360 Speaker 1: would a physicist do in this scenario? She would probably think, Ooh, 346 00:19:07,480 --> 00:19:09,280 Speaker 1: let me see what I can do and what happens 347 00:19:09,280 --> 00:19:10,800 Speaker 1: if I turn it up? What happens if I turn 348 00:19:10,840 --> 00:19:12,760 Speaker 1: it down? What happens if I make the light purple? 349 00:19:12,840 --> 00:19:15,639 Speaker 1: What happens if I make the light green? Right? A 350 00:19:15,640 --> 00:19:18,040 Speaker 1: physicists would want to know if the results make sense 351 00:19:18,160 --> 00:19:21,439 Speaker 1: under all conditions. Sure, maybe we can understand how this 352 00:19:21,520 --> 00:19:24,439 Speaker 1: works in this scenario, but can we push our limits 353 00:19:24,440 --> 00:19:27,480 Speaker 1: of knowledge? Can we find some wrinkle, some corner of 354 00:19:27,520 --> 00:19:30,080 Speaker 1: the space in which it doesn't make sense? That's right, 355 00:19:30,200 --> 00:19:33,480 Speaker 1: experimentalists are always just trying to spoil everything for theorists. 356 00:19:33,600 --> 00:19:36,560 Speaker 1: That's not true at all. Actually, as Jorge would say, 357 00:19:36,880 --> 00:19:40,679 Speaker 1: because every time experimentalists do something and find a result 358 00:19:40,720 --> 00:19:43,919 Speaker 1: that doesn't make sense, that's an amazing clue. That's the 359 00:19:43,960 --> 00:19:46,320 Speaker 1: clue the theorists need to come up with a new 360 00:19:46,440 --> 00:19:50,160 Speaker 1: theory of the universe. Anyway, back to the photoelectric effect. 361 00:19:50,400 --> 00:19:53,840 Speaker 1: What happens when you shine light at the surface, electrons 362 00:19:53,840 --> 00:19:57,760 Speaker 1: come off. Now, if you're thinking of light as electromagnetic waves. 363 00:19:58,040 --> 00:20:01,440 Speaker 1: Then what should happen if you turn up the intensity. 364 00:20:01,680 --> 00:20:04,400 Speaker 1: If you turn up the intensity, then electrons should shoot 365 00:20:04,440 --> 00:20:07,399 Speaker 1: off with more energy. Because under the classical idea, the 366 00:20:07,480 --> 00:20:10,280 Speaker 1: original idea of light is a wave. Then if you 367 00:20:10,320 --> 00:20:12,679 Speaker 1: turn up the intensity of the light, the strength of 368 00:20:12,720 --> 00:20:15,479 Speaker 1: the light beam, then you're putting more energy. It's just 369 00:20:15,640 --> 00:20:19,520 Speaker 1: electromagnetic waves oscillating with more energy, and so there should 370 00:20:19,520 --> 00:20:22,800 Speaker 1: be more energy there to dump into the electrons, and 371 00:20:22,880 --> 00:20:25,760 Speaker 1: so the electrons should boil off with more energy, and 372 00:20:25,800 --> 00:20:28,600 Speaker 1: there should be no dependence on the frequency. You can 373 00:20:28,680 --> 00:20:31,199 Speaker 1: just get the energy out of the electromagnetic waves. It 374 00:20:31,200 --> 00:20:33,720 Speaker 1: doesn't matter how fast they're shaking, as long as the 375 00:20:33,840 --> 00:20:37,439 Speaker 1: energy is there. The energy there depending just on the intensity. 376 00:20:37,520 --> 00:20:40,159 Speaker 1: So that's the idea. They thought, if we turn up 377 00:20:40,160 --> 00:20:42,680 Speaker 1: the intensity of the light, we make the light brighter, 378 00:20:43,080 --> 00:20:46,200 Speaker 1: then you should get electrons coming off with more energy, 379 00:20:46,440 --> 00:20:49,520 Speaker 1: and there should be no dependence on the color. All right, 380 00:20:49,600 --> 00:20:52,159 Speaker 1: So that's what they thought makes perfect sense. And then 381 00:20:52,200 --> 00:20:54,520 Speaker 1: because their experimentalist, because they actually want to go out 382 00:20:54,560 --> 00:20:57,960 Speaker 1: and explore the universe, not just do thought experiments in 383 00:20:58,000 --> 00:21:00,600 Speaker 1: their head the way the old Greeks did. They went 384 00:21:00,640 --> 00:21:03,200 Speaker 1: out and they actually tried this, and what they found, 385 00:21:03,200 --> 00:21:06,760 Speaker 1: of course, blew their mind. What they found is two 386 00:21:06,960 --> 00:21:11,000 Speaker 1: things that didn't make any sense at all. First of all, 387 00:21:11,359 --> 00:21:13,960 Speaker 1: the energy of the electrons that came off the surface 388 00:21:14,200 --> 00:21:17,560 Speaker 1: didn't depend on the intensity at all. You could turn 389 00:21:17,640 --> 00:21:20,639 Speaker 1: up the intensity and the energy the electrons wouldn't change. 390 00:21:20,680 --> 00:21:23,480 Speaker 1: You could turn down the intensity, and the energy the 391 00:21:23,520 --> 00:21:27,879 Speaker 1: electrons wouldn't change. Weirdly, if you turned up the intensity, 392 00:21:27,960 --> 00:21:31,119 Speaker 1: you got more electrons. You didn't get any electrons with 393 00:21:31,160 --> 00:21:34,919 Speaker 1: more energy, but you got more electrons boiling off. And 394 00:21:34,960 --> 00:21:37,000 Speaker 1: if you made the light dimmer, if you turned down 395 00:21:37,040 --> 00:21:40,479 Speaker 1: the intensity again, the energy didn't change, but the number 396 00:21:40,480 --> 00:21:43,359 Speaker 1: of electrons dropped. And this didn't make any sense at 397 00:21:43,359 --> 00:21:46,359 Speaker 1: all in the classical idea, if light is just a wave, 398 00:21:46,440 --> 00:21:49,920 Speaker 1: if it's just oscillation of the electromagnetic field, then it 399 00:21:49,960 --> 00:21:52,720 Speaker 1: should depend on the intensity. But there was no dependence 400 00:21:52,760 --> 00:21:56,440 Speaker 1: on the intensity at all. Instead, changing the intensity didn't 401 00:21:56,520 --> 00:21:59,200 Speaker 1: change the energy the electrons coming off. It only changed 402 00:21:59,240 --> 00:22:02,280 Speaker 1: the number of electrons we saw. So then they said, 403 00:22:02,280 --> 00:22:05,639 Speaker 1: all right, that's weird, so let's try changing the frequency 404 00:22:05,680 --> 00:22:08,120 Speaker 1: of the light. So they go from blue light down 405 00:22:08,160 --> 00:22:09,960 Speaker 1: to red light and back to purple light and just 406 00:22:10,000 --> 00:22:11,879 Speaker 1: to see. And they found that the energy to the 407 00:22:11,880 --> 00:22:15,160 Speaker 1: electrons weirdly did depend on the frequency of the light. 408 00:22:15,359 --> 00:22:19,520 Speaker 1: At higher frequencies, the electrons had more energy, and at 409 00:22:19,560 --> 00:22:22,720 Speaker 1: low enough frequencies you wouldn't get any electrons at all. 410 00:22:23,200 --> 00:22:25,919 Speaker 1: So this made no sense to anybody. People who are thinking, 411 00:22:26,040 --> 00:22:30,119 Speaker 1: who are confident that light was just electromagnetic radiation, could 412 00:22:30,119 --> 00:22:33,840 Speaker 1: not explain either of these effects. One the fact that 413 00:22:33,840 --> 00:22:36,800 Speaker 1: the energy the electrons didn't depend on the intensity of 414 00:22:36,840 --> 00:22:39,880 Speaker 1: the radiation, which made no sense because they thought these 415 00:22:39,880 --> 00:22:43,000 Speaker 1: are just classical waves and the intensity means more energy, 416 00:22:43,040 --> 00:22:45,360 Speaker 1: so why aren't we getting more energy out of the electrons? 417 00:22:45,840 --> 00:22:48,720 Speaker 1: And number two that the energy the electrons coming off 418 00:22:48,920 --> 00:22:51,560 Speaker 1: did depend on the color of the light. But it 419 00:22:51,560 --> 00:22:55,000 Speaker 1: made no sense to people because people were thinking about 420 00:22:55,080 --> 00:22:58,560 Speaker 1: light as waves. Now there was somebody thinking about light 421 00:22:58,640 --> 00:23:02,000 Speaker 1: in other terms. That was Plunk. Plank was studying a 422 00:23:02,119 --> 00:23:06,600 Speaker 1: totally different problem, another unsolved question in physics, which had 423 00:23:06,600 --> 00:23:09,240 Speaker 1: to do with black body radiation, which we'll talk about 424 00:23:09,320 --> 00:23:11,639 Speaker 1: in another episode, and he was trying to solve that 425 00:23:11,680 --> 00:23:13,880 Speaker 1: problem and he just couldn't. He was trying to explain 426 00:23:14,080 --> 00:23:16,640 Speaker 1: why we didn't see in the lab what we expected 427 00:23:16,680 --> 00:23:19,240 Speaker 1: to see based on the theory, and to solve his 428 00:23:19,440 --> 00:23:22,000 Speaker 1: problem he had to come up with a crazy idea. 429 00:23:22,080 --> 00:23:24,679 Speaker 1: He said, well, I don't know why, and I can't 430 00:23:24,760 --> 00:23:29,680 Speaker 1: justify this at all. But if I assume that light 431 00:23:29,880 --> 00:23:32,840 Speaker 1: comes in little packets of energy that you can have 432 00:23:32,960 --> 00:23:36,639 Speaker 1: like zero or one or two little bits of energy, 433 00:23:36,760 --> 00:23:39,480 Speaker 1: but you can't have integer numbers in between, then it 434 00:23:39,520 --> 00:23:41,439 Speaker 1: solves my problem. And for him it was sort of 435 00:23:41,440 --> 00:23:44,360 Speaker 1: a mathematical thing. He's like, I'm trying to do this calculation. 436 00:23:44,720 --> 00:23:47,480 Speaker 1: It's not working. Nobody can figure it out. Oh look, 437 00:23:47,600 --> 00:23:51,240 Speaker 1: if I make this totally unjustified assumption, then my calculation 438 00:23:51,359 --> 00:23:54,080 Speaker 1: works and it explains the data. And that's cool. That's 439 00:23:54,080 --> 00:23:56,640 Speaker 1: a totally valid way to do theory and to do physics. 440 00:23:56,760 --> 00:23:58,280 Speaker 1: And then you've got to go back and say, well 441 00:23:58,359 --> 00:23:59,120 Speaker 1: what does that mean? 442 00:23:59,359 --> 00:23:59,600 Speaker 6: Right? 443 00:24:00,160 --> 00:24:03,120 Speaker 1: And it was Einstein who put it together. Einstein heard 444 00:24:03,119 --> 00:24:06,199 Speaker 1: about Plank's idea, he said, hm, that's fascinating, and he 445 00:24:06,200 --> 00:24:09,560 Speaker 1: heard about the photoelectric effect. He said, ooh, interesting puzzle, 446 00:24:09,800 --> 00:24:13,520 Speaker 1: and he put them together. And so Einstein, who never 447 00:24:13,680 --> 00:24:17,040 Speaker 1: actually won the Nobel Prize for relativity, did win the 448 00:24:17,040 --> 00:24:20,520 Speaker 1: Nobel Prize later for putting these two ideas together. And 449 00:24:20,560 --> 00:24:23,680 Speaker 1: though he didn't do the experiments for the photoelectric effect, 450 00:24:23,960 --> 00:24:26,640 Speaker 1: and he also didn't have the original idea to break 451 00:24:26,720 --> 00:24:29,760 Speaker 1: light down into little pieces, he just put the idea 452 00:24:29,840 --> 00:24:32,040 Speaker 1: in the right place to solve the problem and explain 453 00:24:32,119 --> 00:24:35,560 Speaker 1: this experiment. All right, So let's talk about how the 454 00:24:35,640 --> 00:24:39,000 Speaker 1: idea that photons might be little particles, little packets of 455 00:24:39,119 --> 00:24:43,240 Speaker 1: energy explains this experiment. But first, let's take another break. 456 00:24:47,920 --> 00:24:49,720 Speaker 1: When you pop a piece of cheese into your mouth 457 00:24:49,800 --> 00:24:52,960 Speaker 1: or enjoy a rich spoonful of greeky oogurt, you're probably 458 00:24:53,000 --> 00:24:57,040 Speaker 1: not thinking about the environmental impact of each and every bite. 459 00:24:57,080 --> 00:24:59,680 Speaker 1: But the people in the dairy industry are. US Dairy 460 00:24:59,680 --> 00:25:03,360 Speaker 1: has said let themselves some ambitious sustainability goals, including being 461 00:25:03,440 --> 00:25:06,400 Speaker 1: greenhouse gas neutral by twenty to fifty. That's why they're 462 00:25:06,400 --> 00:25:09,040 Speaker 1: working hard every day to find new ways to reduce waste, 463 00:25:09,080 --> 00:25:13,280 Speaker 1: conserve natural resources, and drive down greenhouse gas emissions. Take water, 464 00:25:13,320 --> 00:25:16,920 Speaker 1: for example, most dairy farms reuse water up to four times. 465 00:25:16,960 --> 00:25:20,359 Speaker 1: The same water cools the milk, cleans equipment, washes the barn, 466 00:25:20,440 --> 00:25:24,160 Speaker 1: and irrigates the crops. How is US dairy tackling greenhouse gases? 467 00:25:24,200 --> 00:25:27,199 Speaker 1: Many farms use anaerobic digestors that turn the methane from 468 00:25:27,240 --> 00:25:30,600 Speaker 1: maneure into renewable energy that can power farms, towns, and 469 00:25:30,640 --> 00:25:32,880 Speaker 1: electric cars. So the next time you grab a slice 470 00:25:32,920 --> 00:25:34,800 Speaker 1: of pizza or lick an ice cream cone, know that 471 00:25:34,880 --> 00:25:37,520 Speaker 1: dairy farmers and processors around the country are using the 472 00:25:37,600 --> 00:25:41,359 Speaker 1: latest practices and innovations to provide the nutrient dense dairy 473 00:25:41,400 --> 00:25:44,080 Speaker 1: products we love with less of an impact. Visit us 474 00:25:44,160 --> 00:25:46,680 Speaker 1: dairy dot com slash sustainability to learn more. 475 00:25:47,720 --> 00:25:51,160 Speaker 10: There are children, friends, and families walking, riding on pass 476 00:25:51,200 --> 00:25:53,680 Speaker 10: and roads every day. Remember they're real people with loved 477 00:25:53,680 --> 00:25:55,879 Speaker 10: ones who need them to get home safely. Protect our 478 00:25:55,880 --> 00:25:59,400 Speaker 10: cyclists and pedestrians because they're people too. Go safely California 479 00:25:59,440 --> 00:26:01,760 Speaker 10: from the californ On your Office of Traffic Safety and Caltrans. 480 00:26:01,920 --> 00:26:05,119 Speaker 6: Hey there, fellow globetrotters and destination dreamers. If you're anything 481 00:26:05,200 --> 00:26:07,399 Speaker 6: like us, you'd note that life's too short for boring 482 00:26:07,440 --> 00:26:10,080 Speaker 6: toasters and towels. That's why we decided to ditch the 483 00:26:10,119 --> 00:26:13,720 Speaker 6: traditional wedding registry and went with honeyfund dot com. Imagine 484 00:26:13,800 --> 00:26:15,760 Speaker 6: your friends and family chipping in to send you on 485 00:26:15,840 --> 00:26:20,560 Speaker 6: a dreamy, exotic honeymoon, practical check, meaningful double check. Plus 486 00:26:20,600 --> 00:26:23,520 Speaker 6: it's fee free and so fun for wedding guests to shop. 487 00:26:23,680 --> 00:26:27,120 Speaker 6: So why get more stuff when you can have unforgettable experiences. 488 00:26:27,240 --> 00:26:30,840 Speaker 6: Join the revolution at honey fund dot com and start 489 00:26:30,920 --> 00:26:35,800 Speaker 6: your adventure today. 490 00:26:40,880 --> 00:26:43,520 Speaker 1: All right, we're back and we're talking about why photons 491 00:26:43,560 --> 00:26:47,600 Speaker 1: are a thing. We reminded ourselves why people originally thought 492 00:26:47,640 --> 00:26:50,240 Speaker 1: that photons were waves, and then we talked about the 493 00:26:50,280 --> 00:26:53,440 Speaker 1: photoelectric effect. This experiment with a weird result and a 494 00:26:53,560 --> 00:26:57,560 Speaker 1: result that could not be explained using classical theory that 495 00:26:57,680 --> 00:27:00,800 Speaker 1: could not be understood if you thought about light as 496 00:27:00,840 --> 00:27:03,959 Speaker 1: a wave. So how do we explain the photoelectric effect? 497 00:27:03,960 --> 00:27:06,840 Speaker 1: How do we understand the weird results of this experiment? 498 00:27:07,240 --> 00:27:10,040 Speaker 1: Just by saying that light comes in little packets? All right, Well, 499 00:27:10,040 --> 00:27:12,880 Speaker 1: Einstein said, I'm going to assume that light comes into 500 00:27:12,880 --> 00:27:16,879 Speaker 1: these little packets and that the energy inside one packet 501 00:27:16,960 --> 00:27:20,920 Speaker 1: is proportional to the frequency. That means that higher frequencies 502 00:27:21,119 --> 00:27:25,520 Speaker 1: things like blue, have more energy than photons at lower frequencies, 503 00:27:25,720 --> 00:27:28,680 Speaker 1: things like red. What that means is, if you want 504 00:27:28,720 --> 00:27:31,520 Speaker 1: more energy in your photon, you need purpler photons. If 505 00:27:31,520 --> 00:27:34,760 Speaker 1: you want less energy in your photons, you need redder photons. 506 00:27:35,119 --> 00:27:37,840 Speaker 1: His microscopic understanding of what's happening is you have this 507 00:27:37,960 --> 00:27:40,600 Speaker 1: surface of metal and it's got electrons in it, and 508 00:27:40,680 --> 00:27:44,280 Speaker 1: electrons need a certain amount of energy in order to escape. 509 00:27:44,359 --> 00:27:47,359 Speaker 1: They're bound to their atoms. They're happy there. They're circling 510 00:27:47,440 --> 00:27:49,840 Speaker 1: the nuclei, right, They don't necessarily want to leave. In 511 00:27:49,920 --> 00:27:51,520 Speaker 1: order for them to leave, they have to get a 512 00:27:51,560 --> 00:27:55,240 Speaker 1: certain minimum of energy. So what happens when a photon 513 00:27:55,320 --> 00:27:58,119 Speaker 1: comes and hits the surface, Well, a photon hits the 514 00:27:58,160 --> 00:28:01,880 Speaker 1: electron and either it has an enough energy to kick 515 00:28:01,920 --> 00:28:04,520 Speaker 1: the electron off or it doesn't. If it doesn't, no 516 00:28:04,600 --> 00:28:07,280 Speaker 1: electron is kicked off. And what that means is that 517 00:28:07,320 --> 00:28:09,920 Speaker 1: the frequency of the light has to be right high 518 00:28:10,040 --> 00:28:12,560 Speaker 1: enough frequency you'd have a high enough energy to kick 519 00:28:12,600 --> 00:28:15,680 Speaker 1: off any electrons. And that explains why when they turned 520 00:28:15,680 --> 00:28:18,800 Speaker 1: the frequency down on the light, no matter how bright 521 00:28:18,840 --> 00:28:21,160 Speaker 1: it was, if they turned the color down to deep 522 00:28:21,200 --> 00:28:24,240 Speaker 1: deep red, they just didn't see any electrons coming off. 523 00:28:25,000 --> 00:28:27,159 Speaker 1: And they couldn't explain that with their classical theory. With 524 00:28:27,160 --> 00:28:29,560 Speaker 1: their classical theory, they thought, well, light's a wave, the 525 00:28:29,560 --> 00:28:32,199 Speaker 1: color doesn't matter. We can make it red as long 526 00:28:32,240 --> 00:28:35,280 Speaker 1: as we make it really really bright, electrons should still 527 00:28:35,320 --> 00:28:38,600 Speaker 1: come off. But they didn't, and this theory explains why, 528 00:28:38,840 --> 00:28:42,200 Speaker 1: because the photons in little chunks, and each electron can 529 00:28:42,240 --> 00:28:46,280 Speaker 1: only absorb energy from one photon at a time. That's 530 00:28:46,320 --> 00:28:49,560 Speaker 1: the critical idea. You can only interact with one photon 531 00:28:49,600 --> 00:28:52,480 Speaker 1: at a time, So if the photon doesn't have enough 532 00:28:52,560 --> 00:28:55,880 Speaker 1: energy because it's too low frequency, it's too red, then 533 00:28:55,920 --> 00:28:58,040 Speaker 1: it just can't get you out of your atom trap. 534 00:28:58,440 --> 00:29:00,320 Speaker 1: And yeah, there are other photons coming down down the 535 00:29:00,320 --> 00:29:02,920 Speaker 1: pike if you have a really really intense beam, but 536 00:29:02,960 --> 00:29:06,400 Speaker 1: those don't help because once that first photon has failed 537 00:29:06,400 --> 00:29:08,360 Speaker 1: to get you out of the atom, then you're back 538 00:29:08,360 --> 00:29:10,280 Speaker 1: in the atom again, and the next one's also going 539 00:29:10,360 --> 00:29:13,680 Speaker 1: to fail. The photons can't work together. So that's the 540 00:29:13,760 --> 00:29:15,800 Speaker 1: key idea, the fact that the beam of lights is 541 00:29:15,800 --> 00:29:19,560 Speaker 1: not just one wave that's shaking the electrons so that 542 00:29:19,600 --> 00:29:21,360 Speaker 1: if you turn it up, you're shaking them more and 543 00:29:21,400 --> 00:29:23,800 Speaker 1: getting them enough energy to get out of those atoms. 544 00:29:24,000 --> 00:29:26,880 Speaker 1: But it's broken up into pieces, and each piece needs 545 00:29:26,960 --> 00:29:30,560 Speaker 1: enough energy on its own to get those electrons out 546 00:29:30,600 --> 00:29:32,640 Speaker 1: of the atom. So the way you do it, the 547 00:29:32,680 --> 00:29:34,600 Speaker 1: way you can get the electrons out of the atom 548 00:29:34,920 --> 00:29:37,880 Speaker 1: is by changing the frequency, because that gets more energy 549 00:29:37,920 --> 00:29:42,160 Speaker 1: into each photon. And so if a purple one comes 550 00:29:42,200 --> 00:29:45,520 Speaker 1: remember purple being very high frequency, it has enough energy 551 00:29:45,680 --> 00:29:47,680 Speaker 1: to get the electrons out of the atom and it's 552 00:29:47,720 --> 00:29:50,480 Speaker 1: a little bit left over. So as you increase the 553 00:29:50,520 --> 00:29:54,160 Speaker 1: frequency of the light, you're increasing the energy per photon, 554 00:29:54,520 --> 00:29:58,000 Speaker 1: essentially the energy that each electron has access to, and 555 00:29:58,040 --> 00:29:59,440 Speaker 1: then it has enough energy to get out of the 556 00:29:59,480 --> 00:30:01,720 Speaker 1: atom to zoom off with a good amount of speed. 557 00:30:02,360 --> 00:30:04,600 Speaker 1: So the higher the frequency of the light, the more 558 00:30:04,760 --> 00:30:07,600 Speaker 1: energy in each photon, the more energy these electrons come 559 00:30:07,640 --> 00:30:09,920 Speaker 1: out at. And that is exactly what they saw in 560 00:30:09,960 --> 00:30:13,840 Speaker 1: the experiment, and that can only be explained if electrons 561 00:30:13,880 --> 00:30:17,400 Speaker 1: can only interact with one particle of light at a time, 562 00:30:17,760 --> 00:30:20,320 Speaker 1: and that light is in fact a particle. It also 563 00:30:20,360 --> 00:30:23,840 Speaker 1: explains why the energy the electrons does not depend on 564 00:30:23,880 --> 00:30:26,640 Speaker 1: the intensity of the beam. You can have a really 565 00:30:26,800 --> 00:30:29,920 Speaker 1: powerful red beam, but it's too low frequency. All those 566 00:30:29,920 --> 00:30:32,760 Speaker 1: photons are wasted because none of them have enough energy 567 00:30:32,760 --> 00:30:35,480 Speaker 1: to get the electrons out. It doesn't matter how high 568 00:30:35,560 --> 00:30:38,080 Speaker 1: you turn it up. And even if you're turn it 569 00:30:38,160 --> 00:30:40,760 Speaker 1: up too green and you have enough energy to get 570 00:30:40,760 --> 00:30:43,560 Speaker 1: the electrons out of there. You don't get more energetic 571 00:30:43,640 --> 00:30:47,320 Speaker 1: electrons by increasing the intensity. Again, you have to change 572 00:30:47,440 --> 00:30:50,760 Speaker 1: the energy in each photon that's hitting the electron. You 573 00:30:50,800 --> 00:30:53,880 Speaker 1: can only do that by changing the frequency. And this 574 00:30:53,920 --> 00:30:57,480 Speaker 1: assumes again that electrons can only interact with one photon 575 00:30:57,560 --> 00:31:00,440 Speaker 1: at a time, which is pretty solid assumption. So the 576 00:31:00,440 --> 00:31:03,760 Speaker 1: amazing thing is that this idea, which really came from Plank, 577 00:31:04,240 --> 00:31:07,560 Speaker 1: explained these experiments which really were done by other people. 578 00:31:07,880 --> 00:31:11,440 Speaker 1: But the unification of it, the bringing together the idea, 579 00:31:11,480 --> 00:31:15,480 Speaker 1: the moment of insight, the explanation of this weird experiment 580 00:31:15,880 --> 00:31:18,480 Speaker 1: was done by Einstein. And that's what Einstein won the 581 00:31:18,480 --> 00:31:21,440 Speaker 1: Nobel Prize for, not for doing the experiment, not for 582 00:31:21,480 --> 00:31:23,520 Speaker 1: having the idea, but for being sort of in the 583 00:31:23,600 --> 00:31:26,520 Speaker 1: right place at the right time to bring that idea 584 00:31:26,640 --> 00:31:29,880 Speaker 1: to solve this open problem. Now, the photon was not 585 00:31:30,080 --> 00:31:33,280 Speaker 1: named as a particle for decades later. All this happened 586 00:31:33,440 --> 00:31:36,360 Speaker 1: just around the turn of the nineteenth century, and Einstein 587 00:31:36,400 --> 00:31:38,560 Speaker 1: won the Nobel Prize later for it, But it wasn't 588 00:31:38,600 --> 00:31:42,760 Speaker 1: until nineteen twenty six that people started calling these things photons. 589 00:31:43,040 --> 00:31:45,680 Speaker 1: And it comes from the Greek word for light, but 590 00:31:45,720 --> 00:31:48,160 Speaker 1: it also touches on something I think is really interesting, 591 00:31:48,200 --> 00:31:50,680 Speaker 1: which is the sort of concept of a particle. I 592 00:31:50,840 --> 00:31:54,360 Speaker 1: like to imagine what we're physicists thinking back then, What 593 00:31:54,400 --> 00:31:56,680 Speaker 1: did they think that the universe looked like at a 594 00:31:56,720 --> 00:32:00,760 Speaker 1: microscopic scale, Because to us, the notion of a particle 595 00:32:00,960 --> 00:32:03,120 Speaker 1: is kind of familiar. I mean, they're weird. They do 596 00:32:03,240 --> 00:32:05,560 Speaker 1: things that we don't understand. They follow rules and make 597 00:32:05,600 --> 00:32:08,520 Speaker 1: no sense to us. But we're comfortable with the idea 598 00:32:09,000 --> 00:32:12,080 Speaker 1: that the universe is atomic, meaning that's made up of 599 00:32:12,240 --> 00:32:13,760 Speaker 1: little bits, and all we have to do is sort 600 00:32:13,800 --> 00:32:16,680 Speaker 1: of figure out what those bits do. But at the time, 601 00:32:16,880 --> 00:32:19,440 Speaker 1: this whole concept of a particle was kind of new. 602 00:32:19,800 --> 00:32:23,160 Speaker 1: Remember where they had discovered the electron. That was only recently. 603 00:32:23,800 --> 00:32:26,000 Speaker 1: That was the first piece of evidence that there was 604 00:32:26,040 --> 00:32:28,080 Speaker 1: something as a particle. Sort of the invention of the 605 00:32:28,120 --> 00:32:31,280 Speaker 1: concept of a particle was the discovery of the electron. 606 00:32:31,440 --> 00:32:34,560 Speaker 1: And all he really did there was identify something tiny 607 00:32:34,760 --> 00:32:37,600 Speaker 1: that had both mass and charge, and so he said, oh, 608 00:32:37,680 --> 00:32:40,560 Speaker 1: look there's a thing there. It has these two attributes. 609 00:32:40,760 --> 00:32:42,520 Speaker 1: I'm going to call it a particle. Actually he called 610 00:32:42,560 --> 00:32:45,760 Speaker 1: it a corpuscule. But the concept that sort of intellectual 611 00:32:45,840 --> 00:32:49,520 Speaker 1: groundwork was laid then for a particle. So then you 612 00:32:49,560 --> 00:32:52,400 Speaker 1: get to the photon. Now the photon has energy, it 613 00:32:52,440 --> 00:32:56,080 Speaker 1: has direction, but it doesn't have mass. It's not a 614 00:32:56,200 --> 00:33:00,200 Speaker 1: thing in that sense, there's no stuff to it. That 615 00:33:00,320 --> 00:33:03,480 Speaker 1: immediately sort of bends your mind around what is this 616 00:33:03,760 --> 00:33:07,840 Speaker 1: concept of a particle? Anyway, we've created this idea to 617 00:33:07,880 --> 00:33:10,760 Speaker 1: accommodate the discovery the electron. We hope, oh, maybe there 618 00:33:10,760 --> 00:33:13,600 Speaker 1: are other particles. And later on the podcast we'll take 619 00:33:13,600 --> 00:33:15,880 Speaker 1: a tour of the discoveries of other particles which have 620 00:33:16,080 --> 00:33:20,120 Speaker 1: hilarious and amazing and dramatic stories to them. But very 621 00:33:20,160 --> 00:33:22,840 Speaker 1: early in the history of particles we had to already 622 00:33:22,920 --> 00:33:24,600 Speaker 1: bend the rules and say, oh, well, we were talking 623 00:33:24,640 --> 00:33:27,000 Speaker 1: about particles. There's little bits of stuff, but they can 624 00:33:27,120 --> 00:33:30,920 Speaker 1: also be not stuff, right, they can also just be energy. 625 00:33:31,280 --> 00:33:33,520 Speaker 1: And so to me, it's amazing that this field of 626 00:33:33,520 --> 00:33:37,120 Speaker 1: particle physics was founded on such crazy discoveries. So to me, 627 00:33:37,200 --> 00:33:39,800 Speaker 1: it's wonderful that the field of particle physics is founded 628 00:33:39,840 --> 00:33:42,360 Speaker 1: on such crazy discoveries. And you've got to give a 629 00:33:42,400 --> 00:33:45,040 Speaker 1: lot of credit to the theorists, of course, who put 630 00:33:45,040 --> 00:33:48,600 Speaker 1: these ideas together and helped us understand what we were seeing. 631 00:33:48,960 --> 00:33:51,880 Speaker 1: But to me, the most exciting moments are those moments 632 00:33:51,880 --> 00:33:56,000 Speaker 1: of experimental surprise when the universe does something that we 633 00:33:56,040 --> 00:33:58,960 Speaker 1: don't understand. When the unit when we predict the universe 634 00:33:58,960 --> 00:34:01,680 Speaker 1: will do a and it's dead, it does be because 635 00:34:01,720 --> 00:34:04,280 Speaker 1: that's the universe talking to us, or that's the universe 636 00:34:04,520 --> 00:34:07,560 Speaker 1: answering our questions. That's the universe being the subject of 637 00:34:07,600 --> 00:34:10,239 Speaker 1: our interrogation when we say we want to know how 638 00:34:10,280 --> 00:34:12,640 Speaker 1: this works, prove it to us or reveal to us 639 00:34:12,680 --> 00:34:16,520 Speaker 1: the underlying mechanism. And that's what experimental physics is about, 640 00:34:16,600 --> 00:34:19,600 Speaker 1: is about cornering the universe and forcing it to reveal 641 00:34:19,640 --> 00:34:21,839 Speaker 1: something new to you. And a lot of times that 642 00:34:21,880 --> 00:34:24,120 Speaker 1: revelation happens when you didn't expect that. You thought, oh, 643 00:34:24,120 --> 00:34:26,399 Speaker 1: we're just double checking this over here. We're pretty sure 644 00:34:26,440 --> 00:34:28,880 Speaker 1: we understand it. We just dotting the eyes and crossing 645 00:34:28,880 --> 00:34:30,440 Speaker 1: the t's, and all of a sudden, oops, you get 646 00:34:30,480 --> 00:34:33,960 Speaker 1: something totally surprising. But those are the moments that we 647 00:34:34,080 --> 00:34:35,960 Speaker 1: learned something new about the universe, And those are the 648 00:34:35,960 --> 00:34:39,480 Speaker 1: moments I'm striving for my own personal research when I'm 649 00:34:39,520 --> 00:34:43,120 Speaker 1: smashing particles together at the LEDC. We think we understand 650 00:34:43,120 --> 00:34:45,719 Speaker 1: what's going to happen. But I'm always secretly hoping that 651 00:34:45,800 --> 00:34:48,240 Speaker 1: a student will come to me and say, Hey, Daniel, 652 00:34:48,320 --> 00:34:50,480 Speaker 1: what's this. I found this weird thing in our data 653 00:34:50,560 --> 00:34:53,640 Speaker 1: that just doesn't make any sense. And that's only happened 654 00:34:53,640 --> 00:34:56,120 Speaker 1: once or twice in my entire career, and I look 655 00:34:56,160 --> 00:34:58,960 Speaker 1: forward to it happening again. So maybe one day we'll 656 00:34:59,000 --> 00:35:01,440 Speaker 1: be hearing about a career easy discovery we made at 657 00:35:01,440 --> 00:35:04,840 Speaker 1: the Large Hadron Collider. Until then, thanks for listening to 658 00:35:04,880 --> 00:35:07,439 Speaker 1: this description of how we know the photon is a thing, 659 00:35:08,000 --> 00:35:10,239 Speaker 1: and please, if you're interested in learning more about the 660 00:35:10,280 --> 00:35:13,360 Speaker 1: history of physics or understanding how we know how the 661 00:35:13,440 --> 00:35:16,360 Speaker 1: universe works and what we don't know, please send me 662 00:35:16,400 --> 00:35:20,840 Speaker 1: a suggestion to feedback at Danielanjorge dot com. Thanks for 663 00:35:20,880 --> 00:35:31,200 Speaker 1: tuning in. If you still have a question after listening 664 00:35:31,239 --> 00:35:34,279 Speaker 1: to all these explanations, please drop us a line. We'd 665 00:35:34,360 --> 00:35:37,200 Speaker 1: love to hear from you. You can find us at Facebook, Twitter, 666 00:35:37,280 --> 00:35:40,960 Speaker 1: and Instagram at Daniel and Jorge that's one word, or 667 00:35:41,080 --> 00:35:45,800 Speaker 1: email us at feedback at Danielandhorge dot com. Thanks for listening, 668 00:35:45,800 --> 00:35:48,520 Speaker 1: and remember that Daniel and Jorge explain the universe is 669 00:35:48,560 --> 00:35:53,160 Speaker 1: a production of iHeartRadio. For more podcasts from iHeartRadio, visit 670 00:35:53,200 --> 00:35:57,279 Speaker 1: the iHeartRadio app, Apple Podcasts, or wherever you listen to 671 00:35:57,320 --> 00:36:08,759 Speaker 1: your favorite shows. 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