1 00:00:08,640 --> 00:00:11,520 Speaker 1: If you've done some traveling, then you know the experience 2 00:00:11,520 --> 00:00:14,840 Speaker 1: of feeling out of place. There are still some places 3 00:00:14,880 --> 00:00:18,400 Speaker 1: on Earth where the culture is sufficiently different from ours 4 00:00:18,520 --> 00:00:20,600 Speaker 1: or from yours, then you can no longer sort of 5 00:00:20,640 --> 00:00:24,080 Speaker 1: trust your instincts. You don't intuitively know how to behave 6 00:00:24,160 --> 00:00:26,760 Speaker 1: and how to get around. Maybe you don't know what 7 00:00:26,760 --> 00:00:29,160 Speaker 1: people are saying, and you can't read the street signs, 8 00:00:29,200 --> 00:00:32,120 Speaker 1: and things just seem to work differently. The street food 9 00:00:32,120 --> 00:00:35,880 Speaker 1: has weird eyeballs in it where looks like it's fried scorpions. Hey, 10 00:00:35,920 --> 00:00:39,720 Speaker 1: maybe it is. Well, that's the experience physicists have when 11 00:00:39,720 --> 00:00:43,000 Speaker 1: we discover that the rules of the universe are totally 12 00:00:43,000 --> 00:00:46,519 Speaker 1: different from what we are familiar with. That's exactly the 13 00:00:46,560 --> 00:00:48,919 Speaker 1: feeling we're going for, and that's the feeling we get 14 00:00:49,040 --> 00:01:08,640 Speaker 1: very often when we travel to the quantum realm. Yeah. Hi, 15 00:01:08,959 --> 00:01:13,160 Speaker 1: I'm Daniel. I'm a particle physicist and I'm one half 16 00:01:13,200 --> 00:01:16,959 Speaker 1: of the dynamic duo known as Daniel and Jorge, hosts 17 00:01:16,959 --> 00:01:21,280 Speaker 1: of this podcast, Daniel and Jorge Explain the Universe, brought 18 00:01:21,360 --> 00:01:24,520 Speaker 1: to you by I Heart Radio. My co host today, 19 00:01:24,640 --> 00:01:27,000 Speaker 1: Jorge Champ can't be with us, so I'll be talking 20 00:01:27,040 --> 00:01:29,959 Speaker 1: to you myself about the amazing secrets of the universe. 21 00:01:30,520 --> 00:01:34,319 Speaker 1: This podcast is dedicated to revealing truths about the universe, 22 00:01:34,360 --> 00:01:37,880 Speaker 1: to taking things that seem amazing and mystifying that maybe 23 00:01:37,880 --> 00:01:40,160 Speaker 1: you've heard about or people talk about when they want 24 00:01:40,160 --> 00:01:43,160 Speaker 1: to sound smart, but you never really understood. Well, we 25 00:01:43,200 --> 00:01:45,560 Speaker 1: are here to break it down and make sure you 26 00:01:45,600 --> 00:01:48,280 Speaker 1: can walk away actually understanding it. You can talk about 27 00:01:48,280 --> 00:01:51,640 Speaker 1: it like an intelligent person. So if you have questions 28 00:01:51,680 --> 00:01:53,960 Speaker 1: about what you heard today, please send them to us 29 00:01:54,240 --> 00:01:57,320 Speaker 1: two questions at Daniel and Jorge dot com. It is 30 00:01:57,360 --> 00:02:00,720 Speaker 1: our goal that you actually understand everything we are talking 31 00:02:00,760 --> 00:02:04,040 Speaker 1: about and hopefully maybe even get a chuckle along the way. 32 00:02:04,240 --> 00:02:07,120 Speaker 1: Since it's just me today, we'll probably have fewer jokes 33 00:02:07,120 --> 00:02:10,600 Speaker 1: than usual. It's often Hooree that injects the humor into 34 00:02:10,639 --> 00:02:14,000 Speaker 1: these conversations. So we're little humans. We're here on Earth, 35 00:02:14,080 --> 00:02:16,799 Speaker 1: and we're used to a certain kind of experience. We 36 00:02:16,960 --> 00:02:19,040 Speaker 1: used to things a certain size and moving on a 37 00:02:19,080 --> 00:02:22,200 Speaker 1: certain speed. But the universe is a big place and 38 00:02:22,240 --> 00:02:24,320 Speaker 1: there are lots of things out there that are not 39 00:02:24,440 --> 00:02:28,080 Speaker 1: like our experience, that are really big or moving really fast. 40 00:02:28,600 --> 00:02:31,680 Speaker 1: And what we've learned as humans is that most of 41 00:02:31,680 --> 00:02:34,440 Speaker 1: the universe is different from what we expected, and that 42 00:02:34,560 --> 00:02:37,760 Speaker 1: it follows rules that are different. And when we try 43 00:02:37,800 --> 00:02:39,840 Speaker 1: to understand the rest of the universe, the things that 44 00:02:39,840 --> 00:02:43,040 Speaker 1: are not balls rolling down planes or how water flows 45 00:02:43,080 --> 00:02:46,200 Speaker 1: down a hill, that we need to do something mentally difficult. 46 00:02:46,320 --> 00:02:49,000 Speaker 1: We need to do some sort of extrapolation. And that's 47 00:02:49,040 --> 00:02:50,880 Speaker 1: the job of physics is to take us from the 48 00:02:50,919 --> 00:02:54,359 Speaker 1: known into the unknown, to say, well, we understand how 49 00:02:54,400 --> 00:02:57,320 Speaker 1: these things happen here on Earth. Can we also understand 50 00:02:57,320 --> 00:02:59,720 Speaker 1: how the Earth moves around the sun. Can we understand 51 00:02:59,720 --> 00:03:02,880 Speaker 1: the origins of the universe. Can we peel back layers 52 00:03:02,880 --> 00:03:05,840 Speaker 1: of reality and see how things are built underneath? And 53 00:03:05,880 --> 00:03:08,240 Speaker 1: in order to do that, we have to describe things 54 00:03:08,280 --> 00:03:11,080 Speaker 1: we haven't seen in terms of things that we have seen. 55 00:03:11,600 --> 00:03:13,760 Speaker 1: We talk about particles, and we like to describe them 56 00:03:13,800 --> 00:03:16,280 Speaker 1: as kind of like waves and kind of like little 57 00:03:16,280 --> 00:03:20,000 Speaker 1: spinning balls, because those are familiar mental constructs. Those are 58 00:03:20,040 --> 00:03:22,280 Speaker 1: things we understand, so we can talk to each other 59 00:03:22,480 --> 00:03:25,160 Speaker 1: about them. It's like if you drink a new wine 60 00:03:25,200 --> 00:03:26,800 Speaker 1: and you try to describe it to your friends and 61 00:03:26,800 --> 00:03:29,840 Speaker 1: you say, oh, it has flavors of oak and maybe BlackBerry. 62 00:03:30,320 --> 00:03:32,200 Speaker 1: It's a way to describe things that you don't know 63 00:03:32,320 --> 00:03:34,480 Speaker 1: in terms of things that you know. It's a basic 64 00:03:34,760 --> 00:03:39,160 Speaker 1: mental strategy for understanding things. But what happens when you 65 00:03:39,240 --> 00:03:43,840 Speaker 1: run into something fundamentally different, something unlike anything you've seen before, 66 00:03:44,280 --> 00:03:48,520 Speaker 1: something where all of your mental constructs fail or are limited, 67 00:03:49,000 --> 00:03:52,240 Speaker 1: when our experience has just not prepared us for something. 68 00:03:52,680 --> 00:04:04,040 Speaker 1: That's the topic of today's podcast, Can we ever understand 69 00:04:04,320 --> 00:04:07,480 Speaker 1: quantum mechanics? And before we dive in, I want to 70 00:04:07,480 --> 00:04:10,320 Speaker 1: give a music shout out to Casey Hagman who sent 71 00:04:10,400 --> 00:04:13,000 Speaker 1: in that alternative quest in music. Thank you very much. 72 00:04:13,040 --> 00:04:15,760 Speaker 1: We loved it. And quantum mechanics is one of the 73 00:04:15,800 --> 00:04:18,320 Speaker 1: most difficult things for people to grasp, one of the 74 00:04:18,320 --> 00:04:21,359 Speaker 1: most intimidating topics, because people feel like it just can't 75 00:04:21,400 --> 00:04:26,279 Speaker 1: make sense to them, and they hear eminent scientists, researchers, philosophers, 76 00:04:26,279 --> 00:04:29,640 Speaker 1: physicists talking about quantum mechanics as if they don't understand 77 00:04:29,680 --> 00:04:32,000 Speaker 1: it either. And it's true, there's a lot left to 78 00:04:32,000 --> 00:04:35,320 Speaker 1: be understood about quantum mechanics. Folks like Sean Carroll talk 79 00:04:35,360 --> 00:04:38,440 Speaker 1: about it very intelligently, and there's lots of lively discussion 80 00:04:38,440 --> 00:04:40,919 Speaker 1: about what quantum mechanics really means, But I want to 81 00:04:40,920 --> 00:04:44,360 Speaker 1: talk about something simpler. Just what does quantum mechanics say? 82 00:04:44,440 --> 00:04:47,160 Speaker 1: What have we learned about the universe via quantum mechanics? 83 00:04:47,400 --> 00:04:51,200 Speaker 1: Is it possible for us to develop an intuition to 84 00:04:51,360 --> 00:04:55,360 Speaker 1: understand quantum mechanics? Is? Will it always forever be foreign 85 00:04:55,400 --> 00:04:58,600 Speaker 1: to us? Or can we become comfortable with it? Will 86 00:04:58,640 --> 00:05:02,200 Speaker 1: we by spending enough time? And it by thinking? Is 87 00:05:02,200 --> 00:05:05,760 Speaker 1: it possible that by spending enough time marinating in these 88 00:05:05,800 --> 00:05:08,520 Speaker 1: concepts and thinking about them in the right way, that 89 00:05:08,640 --> 00:05:11,800 Speaker 1: we could eventually become familiar with them, sort of the 90 00:05:11,839 --> 00:05:15,679 Speaker 1: way Chinese might seem impenetrable to a Western person at first, 91 00:05:15,720 --> 00:05:18,200 Speaker 1: but you spend enough time there and it becomes part 92 00:05:18,200 --> 00:05:21,679 Speaker 1: of your brain. Your brain develops sort of new ways 93 00:05:21,720 --> 00:05:24,880 Speaker 1: of thinking, new patterns, new ideas flow through it, so 94 00:05:24,920 --> 00:05:27,640 Speaker 1: that the new language and the topics and the strategies 95 00:05:27,680 --> 00:05:30,800 Speaker 1: and the tones of that language eventually become familiar. They 96 00:05:30,880 --> 00:05:33,760 Speaker 1: become how you think. So the strategy there, of course, 97 00:05:33,880 --> 00:05:37,640 Speaker 1: is immerging. You don't learn a new language effectively by 98 00:05:37,720 --> 00:05:41,080 Speaker 1: learning vocabulary and studying in the classroom. The best way 99 00:05:41,160 --> 00:05:44,160 Speaker 1: I've always found really learned to speak a new language, 100 00:05:44,160 --> 00:05:47,039 Speaker 1: to think in a new language. Is to spend time 101 00:05:47,240 --> 00:05:49,400 Speaker 1: doing it, is to go to that country and be 102 00:05:49,560 --> 00:05:52,400 Speaker 1: part of those people and be there and use that 103 00:05:52,520 --> 00:05:54,800 Speaker 1: as part of your life. And that's how your brain works. 104 00:05:55,240 --> 00:05:58,480 Speaker 1: So our strategy today for helping you understand quantum mechanics 105 00:05:58,760 --> 00:06:01,159 Speaker 1: is not to give you the math medical basics, but 106 00:06:01,279 --> 00:06:03,960 Speaker 1: to spend some time in the quantum realm until we 107 00:06:04,040 --> 00:06:07,560 Speaker 1: develop an intuition for how it works. But before we 108 00:06:07,600 --> 00:06:10,240 Speaker 1: go there, I wanted to know what people understood about 109 00:06:10,279 --> 00:06:14,240 Speaker 1: quantum mechanics and also whether they thought they understood quantum mechanics. 110 00:06:14,640 --> 00:06:17,080 Speaker 1: Is quantum mechanics something that everybody out there feels like 111 00:06:17,240 --> 00:06:20,720 Speaker 1: is impossible to understand or are most people under the 112 00:06:20,760 --> 00:06:23,760 Speaker 1: impression that they have it figured out. I walked around 113 00:06:23,760 --> 00:06:26,160 Speaker 1: campus that you see Irvine, and I asked people if 114 00:06:26,200 --> 00:06:29,360 Speaker 1: they thought they could understand quantum mechanics. Before you hear 115 00:06:29,400 --> 00:06:32,440 Speaker 1: these answers, think to yourself, how good is your grasp 116 00:06:32,720 --> 00:06:35,880 Speaker 1: on the basic tenets of quantum mechanics. Do you feel fluent? 117 00:06:36,080 --> 00:06:38,440 Speaker 1: Can you explain this stuff? Do you feel like you 118 00:06:38,480 --> 00:06:42,760 Speaker 1: can navigate that strange quantum realm? Here's what people on 119 00:06:42,800 --> 00:06:44,960 Speaker 1: the street that you see Irvine had to say. Do 120 00:06:45,000 --> 00:06:49,440 Speaker 1: you feel like you understand quantum mechanics? Not anyone who 121 00:06:49,480 --> 00:06:52,760 Speaker 1: answers yes to that doesn't really have an understanding of quantum. 122 00:06:52,880 --> 00:06:56,960 Speaker 1: So no, very basically, I have working knowledge of quantum mechanics, 123 00:06:57,000 --> 00:06:59,760 Speaker 1: but I would not say that I understand it at 124 00:06:59,760 --> 00:07:04,960 Speaker 1: the a PhD physicist, I say I understand it decently. Well. 125 00:07:05,000 --> 00:07:09,000 Speaker 1: Are you familiar with the double slit experiment? Yes, um 126 00:07:09,320 --> 00:07:13,520 Speaker 1: show that particles. I think it was electrons that they use, 127 00:07:14,000 --> 00:07:16,760 Speaker 1: and they move in waves, So if you're to fire 128 00:07:16,800 --> 00:07:20,880 Speaker 1: the electrons and observe them, they'd only go on like 129 00:07:20,920 --> 00:07:23,520 Speaker 1: a line. But then if you cover it you can 130 00:07:23,560 --> 00:07:26,080 Speaker 1: see a wave like pattern in the back or something 131 00:07:26,120 --> 00:07:29,040 Speaker 1: like that. I honestly don't even know about quantum mechanics. 132 00:07:29,040 --> 00:07:31,160 Speaker 1: I'm just the goal nature of light. It's both a 133 00:07:31,160 --> 00:07:33,360 Speaker 1: wave and a particle. So, as usual, we've got a 134 00:07:33,440 --> 00:07:36,000 Speaker 1: very nice breath of answers from people who felt like 135 00:07:36,080 --> 00:07:38,880 Speaker 1: they hardly understood anything about quantum mechanics the people who 136 00:07:39,000 --> 00:07:42,440 Speaker 1: clearly had some working knowledge. So that's great, and we're 137 00:07:42,480 --> 00:07:45,200 Speaker 1: hoping to bring everyone who listens to this podcast up 138 00:07:45,240 --> 00:07:47,120 Speaker 1: to at least the very basic level of being able 139 00:07:47,200 --> 00:07:50,960 Speaker 1: to intelligently think about and understand quantum topics, and I 140 00:07:51,000 --> 00:07:53,160 Speaker 1: think the best way to start off is to hear 141 00:07:53,200 --> 00:07:56,840 Speaker 1: a listener question. Here's a question from a young listener. Hi, 142 00:07:56,960 --> 00:07:59,480 Speaker 1: Daniel Lynn Whole. Hey, my name is Robin, and I 143 00:07:59,480 --> 00:08:02,239 Speaker 1: would love to know what the key differences between quantum 144 00:08:02,240 --> 00:08:05,040 Speaker 1: and classical mechanics are and to what extent they agree 145 00:08:05,080 --> 00:08:07,080 Speaker 1: with each other. This is a great way to start 146 00:08:07,440 --> 00:08:10,920 Speaker 1: because classical physics is what we're familiar with. Classical physics 147 00:08:11,000 --> 00:08:14,200 Speaker 1: is what describes how basketball moves, or how rocks roll 148 00:08:14,320 --> 00:08:17,400 Speaker 1: down hills, or how things move in the atmosphere, things 149 00:08:17,440 --> 00:08:19,880 Speaker 1: that we are familiar with that we have spent hundreds 150 00:08:19,960 --> 00:08:23,320 Speaker 1: or thousands of years developing an intuition for things that 151 00:08:23,360 --> 00:08:26,760 Speaker 1: probably our brains have evolved to be good at understanding, 152 00:08:26,840 --> 00:08:29,480 Speaker 1: so that in some way they are natural objects to 153 00:08:29,560 --> 00:08:33,240 Speaker 1: our mental worlds. Right, So the question really is what's 154 00:08:33,240 --> 00:08:37,040 Speaker 1: the biggest difference between the classical world and the quantum world. 155 00:08:37,440 --> 00:08:39,200 Speaker 1: What is it when you go to the quantum world 156 00:08:39,200 --> 00:08:42,559 Speaker 1: that you can no longer assume that is obviously true 157 00:08:42,600 --> 00:08:46,800 Speaker 1: in the classical world. The basic difference between classical objects 158 00:08:46,840 --> 00:08:50,920 Speaker 1: and quantum mechanical objects is that quantum mechanical objects do 159 00:08:50,960 --> 00:08:54,640 Speaker 1: not have a path. They don't have a trajectory through space, 160 00:08:54,679 --> 00:08:57,920 Speaker 1: a well defined stead of where they were at any 161 00:08:58,040 --> 00:09:00,559 Speaker 1: given time. That's the key, l Us and I want 162 00:09:00,600 --> 00:09:03,000 Speaker 1: you to come away from today's podcast with. So let's 163 00:09:03,000 --> 00:09:06,160 Speaker 1: talk about what that means. If you have a baseball 164 00:09:06,360 --> 00:09:09,840 Speaker 1: and it's at one location now and ten seconds later 165 00:09:09,920 --> 00:09:13,520 Speaker 1: it's across the baseball field, you imagine that it went 166 00:09:13,760 --> 00:09:17,199 Speaker 1: from where it was to where it is now. You say, well, 167 00:09:17,240 --> 00:09:20,040 Speaker 1: if it was over there before and it's over here 168 00:09:20,080 --> 00:09:22,160 Speaker 1: and now, how did it get there. It must have 169 00:09:22,520 --> 00:09:26,079 Speaker 1: gone between those two locations. You have two pieces of data, 170 00:09:26,320 --> 00:09:30,080 Speaker 1: and you naturally interpolate because you make this assumption that 171 00:09:30,160 --> 00:09:33,960 Speaker 1: a classical object has a location at every time, and 172 00:09:33,960 --> 00:09:37,480 Speaker 1: that you can stitch those together into a path that 173 00:09:37,640 --> 00:09:41,800 Speaker 1: traverses space time in some continuous way. And you might 174 00:09:41,840 --> 00:09:45,280 Speaker 1: be thinking, well, of course everything does. Everything has a 175 00:09:45,280 --> 00:09:48,760 Speaker 1: location at a given time, and only one location. But 176 00:09:48,840 --> 00:09:52,240 Speaker 1: that's an intuition you've developed from experiencing the natural world, 177 00:09:52,280 --> 00:09:55,440 Speaker 1: from playing baseball, or from being chased by people throwing 178 00:09:55,520 --> 00:09:58,040 Speaker 1: rocks at you. You're used to things moving through the 179 00:09:58,080 --> 00:10:01,480 Speaker 1: world in a responsible and understandable way. So you've made 180 00:10:01,480 --> 00:10:05,960 Speaker 1: this assumption. Quantum objects do not have paths like that. 181 00:10:06,360 --> 00:10:10,199 Speaker 1: They don't have locations that translate through time. For a 182 00:10:10,280 --> 00:10:13,439 Speaker 1: quantum object like an electron, you can measure it at 183 00:10:13,480 --> 00:10:16,720 Speaker 1: one location A and then later measure it at another 184 00:10:16,800 --> 00:10:20,480 Speaker 1: location B, but it doesn't mean that it's flown through 185 00:10:20,520 --> 00:10:24,520 Speaker 1: the universe from A to B in that intervening time. 186 00:10:24,920 --> 00:10:27,760 Speaker 1: It can be at A later be at B, but 187 00:10:27,840 --> 00:10:30,880 Speaker 1: it's not true that it's moved from A to B, 188 00:10:31,400 --> 00:10:34,320 Speaker 1: meaning that if you've made a measurement halfway, you would 189 00:10:34,320 --> 00:10:37,760 Speaker 1: have found it going from A to B. Now that's 190 00:10:37,920 --> 00:10:40,600 Speaker 1: very confusing, that's very hard to understand. How can an 191 00:10:40,600 --> 00:10:43,720 Speaker 1: object be here and later be there and never be 192 00:10:44,000 --> 00:10:47,000 Speaker 1: in between? And the reason is that quantum objects are 193 00:10:47,040 --> 00:10:50,320 Speaker 1: just different from the classical objects. They are not the 194 00:10:50,360 --> 00:10:52,240 Speaker 1: same kind of thing. And this assumption that you have 195 00:10:52,320 --> 00:10:56,319 Speaker 1: made about the universe comes from only experiencing classical objects 196 00:10:56,400 --> 00:11:00,000 Speaker 1: things on our scale, but the smaller level the universe 197 00:11:00,240 --> 00:11:02,960 Speaker 1: just does not work that way, and that's pretty hard 198 00:11:03,000 --> 00:11:05,959 Speaker 1: to digest. But don't worry. There are things at the 199 00:11:06,040 --> 00:11:09,040 Speaker 1: quantum realm which do follow your intuition in which you 200 00:11:09,160 --> 00:11:12,520 Speaker 1: can use to help understand and develop an intuitive sense 201 00:11:12,559 --> 00:11:16,000 Speaker 1: of the of the universe, and that's the quantum wave function. 202 00:11:16,600 --> 00:11:19,240 Speaker 1: So how do the quantum object work. Well, a quantum 203 00:11:19,320 --> 00:11:22,600 Speaker 1: object is here and later it's there. What determines that. 204 00:11:22,720 --> 00:11:25,960 Speaker 1: It's not like quantum objects don't follow the laws of physics. 205 00:11:26,200 --> 00:11:28,640 Speaker 1: And you probably know the quantum objects could also be random, 206 00:11:28,920 --> 00:11:30,760 Speaker 1: that you can do the same thing to a quantum 207 00:11:30,800 --> 00:11:34,880 Speaker 1: object twice and get different outcomes. And that's true. All 208 00:11:35,000 --> 00:11:37,840 Speaker 1: those things are true. But the quantum object is ruled 209 00:11:37,880 --> 00:11:41,440 Speaker 1: by something, and that's this quantum wave function. You don't 210 00:11:41,440 --> 00:11:43,560 Speaker 1: have to know a lot of complicated math. All you 211 00:11:43,600 --> 00:11:45,480 Speaker 1: need to know is that the wave function tells you 212 00:11:45,800 --> 00:11:48,800 Speaker 1: where a quantum object is most likely to be. You 213 00:11:48,920 --> 00:11:52,160 Speaker 1: probably have heard that electrons don't have a specific location 214 00:11:52,200 --> 00:11:55,559 Speaker 1: to have a probability cloud around an atom. That's an 215 00:11:55,559 --> 00:11:58,040 Speaker 1: extrapolation of the wave function. The wave function tells you 216 00:11:58,400 --> 00:12:01,120 Speaker 1: where the electron is most like it to be. If 217 00:12:01,120 --> 00:12:03,559 Speaker 1: it's large over here, has it's more likely to be there. 218 00:12:03,600 --> 00:12:06,320 Speaker 1: If it's small somewhere else, it's less likely to be there. 219 00:12:06,360 --> 00:12:09,880 Speaker 1: If it's zero somewhere, it means the particle cannot be there. 220 00:12:10,600 --> 00:12:14,440 Speaker 1: Where is the particle? Actually, we don't know, and there's 221 00:12:14,440 --> 00:12:16,920 Speaker 1: a lot of discussion about whether the wave function means 222 00:12:17,120 --> 00:12:20,800 Speaker 1: the particle isn't actually anywhere or just we don't know 223 00:12:20,920 --> 00:12:24,360 Speaker 1: where it is, but we do know that quantum mechanics 224 00:12:24,400 --> 00:12:28,160 Speaker 1: says that that information does not need to exist. It's 225 00:12:28,240 --> 00:12:30,679 Speaker 1: not necessarily the case that there's hidden knowledge that the 226 00:12:30,720 --> 00:12:34,080 Speaker 1: electron is actually somewhere and we don't know. So the 227 00:12:34,080 --> 00:12:36,199 Speaker 1: best way to think about the wave function is that 228 00:12:36,240 --> 00:12:39,800 Speaker 1: it's physics saying what's allowed and what's more likely, and 229 00:12:39,840 --> 00:12:42,360 Speaker 1: this wave function is what we can grab onto, what 230 00:12:42,480 --> 00:12:46,480 Speaker 1: we can understand because the wave function does follow rules, 231 00:12:46,760 --> 00:12:50,000 Speaker 1: and the wave function has a path that makes sense. 232 00:12:50,240 --> 00:12:53,079 Speaker 1: It flows from one spot to the other. It doesn't 233 00:12:53,120 --> 00:12:55,880 Speaker 1: just disappear and appear somewhere else. So you have to 234 00:12:56,000 --> 00:12:59,720 Speaker 1: let go of your intuitive desire to understand the path 235 00:12:59,840 --> 00:13:02,800 Speaker 1: of of an electron the path of a quantum object, 236 00:13:02,800 --> 00:13:05,600 Speaker 1: because those things don't exist. But instead, when you let 237 00:13:05,600 --> 00:13:07,840 Speaker 1: that go, you can grasp onto the next layer. The 238 00:13:07,880 --> 00:13:10,840 Speaker 1: next layer is this wave function, the thing that determines 239 00:13:11,160 --> 00:13:13,760 Speaker 1: where the electron is, the thing that determines where the 240 00:13:13,800 --> 00:13:17,200 Speaker 1: electron is likely to be somewhere else. And that's the 241 00:13:17,280 --> 00:13:19,400 Speaker 1: key thing, is that the wave function tells you where 242 00:13:19,440 --> 00:13:23,160 Speaker 1: the electron is, and it responds to stimulation, it responds 243 00:13:23,200 --> 00:13:25,959 Speaker 1: to the world, and it flows just like a wave, 244 00:13:26,679 --> 00:13:28,600 Speaker 1: and you can use that you can understand how that 245 00:13:28,600 --> 00:13:31,760 Speaker 1: wave flows through time to understand where the electron is 246 00:13:31,840 --> 00:13:34,280 Speaker 1: likely to be in the future. Even if the electron 247 00:13:34,320 --> 00:13:37,240 Speaker 1: itself doesn't have a path from A to B, it's 248 00:13:37,360 --> 00:13:40,640 Speaker 1: wave function does. So the key to being comfortable with 249 00:13:40,760 --> 00:13:44,040 Speaker 1: quantum mechanics is to get comfortable with the objects wave 250 00:13:44,080 --> 00:13:47,880 Speaker 1: function rather than the object. All right, So the best 251 00:13:47,880 --> 00:13:50,520 Speaker 1: way to learn a new language is to get practice, 252 00:13:50,600 --> 00:13:52,800 Speaker 1: is to immerse yourself in it. So the next thing 253 00:13:52,800 --> 00:13:55,280 Speaker 1: we're gonna do is a bunch of exercises of diving 254 00:13:55,320 --> 00:13:58,280 Speaker 1: into the quantum realm and being comfortable with the wave 255 00:13:58,280 --> 00:14:01,079 Speaker 1: function understanding how it flows. And to do that, we're 256 00:14:01,080 --> 00:14:03,960 Speaker 1: going to explore in some detail the famous double slit 257 00:14:04,040 --> 00:14:07,320 Speaker 1: experiment that shows us the crazy behavior of quantum mechanics. 258 00:14:07,360 --> 00:14:08,760 Speaker 1: And at the end of it, I hope it all 259 00:14:08,800 --> 00:14:10,880 Speaker 1: makes sense and the weird results of the double slit 260 00:14:10,920 --> 00:14:14,840 Speaker 1: experiment feel totally natural. But first, let's take a quick break. 261 00:14:27,880 --> 00:14:30,400 Speaker 1: All right, So we are talking about quantum mechanics and 262 00:14:30,400 --> 00:14:33,000 Speaker 1: we're trying to get an intuitive grasp of quantum mechanics. 263 00:14:33,000 --> 00:14:35,400 Speaker 1: We want not just that you say things about quantum 264 00:14:35,400 --> 00:14:37,880 Speaker 1: mechanics that sound intelligent. We want to actually get an 265 00:14:37,960 --> 00:14:41,200 Speaker 1: understanding how do things work at the lowest level. What 266 00:14:41,240 --> 00:14:43,800 Speaker 1: intuition do we have that we can apply? And the 267 00:14:43,920 --> 00:14:46,920 Speaker 1: key thing, again, remember, is the wave function. You have 268 00:14:47,040 --> 00:14:50,560 Speaker 1: quantum mechanical objects like electrons and protons and photons. They 269 00:14:50,560 --> 00:14:55,360 Speaker 1: are difficult to describe using our classical ideas of balls 270 00:14:55,400 --> 00:14:58,720 Speaker 1: and objects that move through space because quantum objects don't 271 00:14:58,760 --> 00:15:02,160 Speaker 1: have paths. And said, we're gonna focus on their wave function, 272 00:15:02,200 --> 00:15:04,440 Speaker 1: the thing that says where they are likely to be, 273 00:15:04,640 --> 00:15:08,080 Speaker 1: and we're gonna understand how that wave function changes through time. 274 00:15:08,280 --> 00:15:10,880 Speaker 1: And we're gonna grab onto that instead of having a 275 00:15:10,920 --> 00:15:13,920 Speaker 1: classical path with the object, we're gonna understand how the 276 00:15:13,960 --> 00:15:16,880 Speaker 1: wave function changes through time, because that's the thing that's 277 00:15:16,960 --> 00:15:20,200 Speaker 1: most like a classical path. All right, So we're gonna 278 00:15:20,200 --> 00:15:22,440 Speaker 1: start very simple, and we're gonna work up to more 279 00:15:22,480 --> 00:15:26,520 Speaker 1: complicated situations. Imagine that you are a photon. You are 280 00:15:26,560 --> 00:15:29,160 Speaker 1: a tiny little quantum particle, and you're shot out of 281 00:15:29,160 --> 00:15:31,520 Speaker 1: a laser with a bunch of your friends towards the screen. 282 00:15:32,080 --> 00:15:36,240 Speaker 1: What happens while you leave the laser right later you 283 00:15:36,360 --> 00:15:40,400 Speaker 1: hit the screen. Does that mean that you flew through 284 00:15:40,520 --> 00:15:45,080 Speaker 1: the room from the laser to the screen. Not necessarily, right, 285 00:15:45,200 --> 00:15:48,760 Speaker 1: You do not have a classical path. Just because you 286 00:15:48,880 --> 00:15:52,120 Speaker 1: left the laser and later hit the screen doesn't mean 287 00:15:52,240 --> 00:15:55,240 Speaker 1: you have a trajectory. Doesn't mean that you necessarily can 288 00:15:55,280 --> 00:16:00,640 Speaker 1: be found in between things in the quantum realm. Don't go, however, 289 00:16:01,000 --> 00:16:05,360 Speaker 1: your wave function does. When you are created inside the laser, 290 00:16:05,440 --> 00:16:07,880 Speaker 1: just at the aperture of the laser, your wave function 291 00:16:07,960 --> 00:16:10,520 Speaker 1: says where you're likely to be, And then your wave 292 00:16:10,600 --> 00:16:15,080 Speaker 1: function flows through the room. If it isn't interacting with everything, 293 00:16:15,360 --> 00:16:18,280 Speaker 1: it just flows nicely through the room, showing the most 294 00:16:18,320 --> 00:16:21,160 Speaker 1: likely place to find your location. This is not the 295 00:16:21,200 --> 00:16:23,080 Speaker 1: same as having a classical path. This is sort of 296 00:16:23,080 --> 00:16:26,560 Speaker 1: the path of your wave function. Then it hits the screen, 297 00:16:26,880 --> 00:16:29,640 Speaker 1: and the screen essentially measures it. It says, okay, wave function, 298 00:16:30,000 --> 00:16:32,720 Speaker 1: where is this photon? And that's the moment when the 299 00:16:32,800 --> 00:16:36,359 Speaker 1: universe has to decide. Instead of having a probability distribution 300 00:16:36,360 --> 00:16:40,080 Speaker 1: about where you are, it says where is this actual photon? 301 00:16:40,600 --> 00:16:42,880 Speaker 1: So you have two measurements. When you leave the laser 302 00:16:43,240 --> 00:16:45,840 Speaker 1: and when you hit the screen. What happens in between 303 00:16:46,240 --> 00:16:49,320 Speaker 1: we don't know, but the wave function tells us, given 304 00:16:49,320 --> 00:16:52,240 Speaker 1: that you've left the laser, what's the likely place to 305 00:16:52,320 --> 00:16:54,000 Speaker 1: land on the screen. And then when you land on 306 00:16:54,000 --> 00:16:56,480 Speaker 1: the screen, the universe rolls a die and says where 307 00:16:56,480 --> 00:17:00,440 Speaker 1: you actually are. Okay, that's easy. Now let's do the 308 00:17:00,440 --> 00:17:03,000 Speaker 1: experiment again. A bunch of photons flying out from a 309 00:17:03,080 --> 00:17:06,120 Speaker 1: laser towards the wall. Let's bring in some black walls 310 00:17:06,200 --> 00:17:08,560 Speaker 1: so that instead of having a totally clear path of 311 00:17:08,640 --> 00:17:11,000 Speaker 1: the screen, you have sort of a narrow gap, not 312 00:17:11,119 --> 00:17:13,600 Speaker 1: too small, you know, a few inches. So what's going 313 00:17:13,640 --> 00:17:17,240 Speaker 1: to happen, Well, some of the photons that leave the 314 00:17:17,320 --> 00:17:20,480 Speaker 1: laser are going to go right through that gap and 315 00:17:20,560 --> 00:17:22,639 Speaker 1: hit the screen, just like before. Some of them are 316 00:17:22,640 --> 00:17:24,760 Speaker 1: gonna hit the walls that block a fraction of the 317 00:17:24,840 --> 00:17:28,080 Speaker 1: laser and so on the screen behind. What you'll get 318 00:17:28,119 --> 00:17:31,080 Speaker 1: is sort of a geometric shadow places where the photon 319 00:17:31,160 --> 00:17:33,000 Speaker 1: made it through the gap. You're gonna hit the screen 320 00:17:33,040 --> 00:17:35,359 Speaker 1: at the back, places where they hit the walls that 321 00:17:35,400 --> 00:17:37,720 Speaker 1: we introduced to make this a little gap. They're going 322 00:17:37,760 --> 00:17:39,320 Speaker 1: to hit those walls and they're not going to make 323 00:17:39,359 --> 00:17:42,520 Speaker 1: it to the screen. All right, So instead of having 324 00:17:42,600 --> 00:17:45,200 Speaker 1: just the laser splash on the back screen, now we 325 00:17:45,240 --> 00:17:48,520 Speaker 1: have something called a geometric shadow. Geometric because it has 326 00:17:48,600 --> 00:17:51,600 Speaker 1: crisp edges and it follows the shape of the of 327 00:17:51,680 --> 00:17:55,760 Speaker 1: the thing that the laser went through. No big deal. Now, 328 00:17:56,480 --> 00:18:00,520 Speaker 1: let's narrow the gap. Let's squeeze those two walls that 329 00:18:00,560 --> 00:18:03,199 Speaker 1: can find the laser. Two very very small, something like 330 00:18:03,280 --> 00:18:06,920 Speaker 1: hundreds of nanometers approximately the wavelength of light that's going 331 00:18:06,920 --> 00:18:09,800 Speaker 1: through it. Now what we see on the back wall changes. 332 00:18:10,040 --> 00:18:12,399 Speaker 1: Instead of seeing a geometric shadow, what we see is 333 00:18:12,440 --> 00:18:15,000 Speaker 1: sort of a spray of light. The light is spreading 334 00:18:15,000 --> 00:18:18,199 Speaker 1: out a little bit. It doesn't just become as narrow 335 00:18:18,320 --> 00:18:20,720 Speaker 1: as the gap it's shining through. It spreads out a 336 00:18:20,720 --> 00:18:24,280 Speaker 1: little bit. This is a wave effect. It happens anytime 337 00:18:24,359 --> 00:18:27,000 Speaker 1: a wave passes through a slit that's narrow compared to 338 00:18:27,040 --> 00:18:29,800 Speaker 1: its wavelength. We could do a deep dive under fraction, 339 00:18:29,840 --> 00:18:31,840 Speaker 1: and maybe we will in a future podcast, but it's 340 00:18:31,880 --> 00:18:34,440 Speaker 1: not critical to understand here. The only thing you need 341 00:18:34,480 --> 00:18:37,800 Speaker 1: to understand is at anytime a wave meaning sound or 342 00:18:37,880 --> 00:18:42,040 Speaker 1: light or bathtub splashes or wave functions pass through a 343 00:18:42,119 --> 00:18:44,920 Speaker 1: narrow slit, they spread out a little bit. You can 344 00:18:44,960 --> 00:18:47,639 Speaker 1: do the same kind of experiment in a bathtub. If 345 00:18:47,680 --> 00:18:50,040 Speaker 1: you send water waves through a very narrow gap, you 346 00:18:50,119 --> 00:18:51,800 Speaker 1: notice that when they come out of that gap they 347 00:18:51,840 --> 00:18:54,800 Speaker 1: spread out. Then we'll just shoot out in a narrow column, 348 00:18:55,119 --> 00:18:57,359 Speaker 1: all right. So now we have a very narrow gap, 349 00:18:57,800 --> 00:18:59,439 Speaker 1: and on the backscreen we have a sort of a 350 00:18:59,520 --> 00:19:02,240 Speaker 1: spray of results. We have a spray, not just a 351 00:19:02,320 --> 00:19:05,360 Speaker 1: very narrow geometric shadow. We have a spray of results 352 00:19:05,359 --> 00:19:08,119 Speaker 1: with a light can land, all right, and now we're 353 00:19:08,160 --> 00:19:10,879 Speaker 1: going to make a second narrow gap. So we have 354 00:19:10,960 --> 00:19:13,960 Speaker 1: sources of light in the back maybe lasers, maybe flashlights, 355 00:19:13,960 --> 00:19:16,520 Speaker 1: it doesn't matter. And they shoot light out, and then 356 00:19:16,520 --> 00:19:19,080 Speaker 1: we have two narrow gaps for the light to fly through. 357 00:19:19,680 --> 00:19:22,000 Speaker 1: And so we have light coming through both of those 358 00:19:22,040 --> 00:19:25,240 Speaker 1: gaps towards the wall. What do you see on the 359 00:19:25,280 --> 00:19:28,200 Speaker 1: back screen? You might think, oh, I have two copies 360 00:19:28,359 --> 00:19:30,200 Speaker 1: of what I saw when I had one narrow gap, 361 00:19:30,240 --> 00:19:32,680 Speaker 1: because now I have two narrow gaps, So how hard 362 00:19:32,720 --> 00:19:35,840 Speaker 1: can this be? That's not quite true. What you see 363 00:19:36,119 --> 00:19:39,800 Speaker 1: is an interference pattern. An interference pattern is what happens 364 00:19:39,840 --> 00:19:44,120 Speaker 1: when two waves collide. Because remember that waves are oscillation. 365 00:19:44,560 --> 00:19:47,880 Speaker 1: For example, if you have waves in your bathtub, those 366 00:19:47,920 --> 00:19:50,239 Speaker 1: waves are just the motion of the water moving up 367 00:19:50,240 --> 00:19:52,560 Speaker 1: and down. They're not their own thing. There a motion 368 00:19:52,640 --> 00:19:55,560 Speaker 1: of the water. Same way sound waves, These sounds that 369 00:19:55,600 --> 00:19:57,840 Speaker 1: I'm making into the microphone that you're hearing in your 370 00:19:57,840 --> 00:20:01,640 Speaker 1: earbuds or wherever you're listening, those are oscillations of the air. 371 00:20:02,000 --> 00:20:04,760 Speaker 1: The air itself is shaking, and because it's the shaking 372 00:20:04,760 --> 00:20:07,320 Speaker 1: of a medium, if something else comes along and shakes 373 00:20:07,359 --> 00:20:10,639 Speaker 1: it in another way, those that shaking can interfere, and 374 00:20:10,640 --> 00:20:12,840 Speaker 1: you can have two kinds of interference. You can have 375 00:20:12,920 --> 00:20:16,040 Speaker 1: constructive interference two things are shaking it the same way, 376 00:20:16,040 --> 00:20:18,239 Speaker 1: so you cant sort of double shaking. Or you can 377 00:20:18,280 --> 00:20:21,439 Speaker 1: have destructive interference where two things are shaking it in 378 00:20:21,440 --> 00:20:25,240 Speaker 1: the opposite way and they cancel each other out. For example, 379 00:20:25,480 --> 00:20:28,920 Speaker 1: this is how noise canceling headphones work. They very rapidly 380 00:20:29,000 --> 00:20:32,000 Speaker 1: hear the noises that are around you and admit exactly 381 00:20:32,040 --> 00:20:35,840 Speaker 1: the right sound to cancel out the sound. You can 382 00:20:35,880 --> 00:20:39,320 Speaker 1: create sound which will negate the other sound by shaking 383 00:20:39,320 --> 00:20:42,760 Speaker 1: it the opposite direction. So when the two shakings add up, 384 00:20:42,960 --> 00:20:45,800 Speaker 1: they add up to zero. So this is an interference 385 00:20:45,840 --> 00:20:48,680 Speaker 1: pattern places where things add up to be stronger in 386 00:20:48,720 --> 00:20:51,560 Speaker 1: place where things can cancel each other out. If you 387 00:20:51,560 --> 00:20:53,440 Speaker 1: look on that screen, what you'll see is a very 388 00:20:53,440 --> 00:20:56,399 Speaker 1: bright band in the middle where the two sources of 389 00:20:56,480 --> 00:20:58,480 Speaker 1: light from the two narrow gaps are adding up on 390 00:20:58,560 --> 00:21:01,240 Speaker 1: top of each other. And to the left of it 391 00:21:01,320 --> 00:21:03,920 Speaker 1: is a dark band, a band where the things are 392 00:21:03,960 --> 00:21:06,560 Speaker 1: canceling each other out. And as you move along the 393 00:21:06,600 --> 00:21:08,880 Speaker 1: screen you get bands of light and bands of dark, 394 00:21:09,040 --> 00:21:11,640 Speaker 1: bands of light and bands of dark, and the exact 395 00:21:11,720 --> 00:21:13,959 Speaker 1: width of those things depends on the wavelength of the 396 00:21:13,960 --> 00:21:18,320 Speaker 1: thing that's interfering with itself. Now you're probably thinking, oh, well, 397 00:21:18,480 --> 00:21:20,960 Speaker 1: the light is a wave, right, and if light is 398 00:21:20,960 --> 00:21:23,920 Speaker 1: a wave, it makes perfect sense for light to interfere 399 00:21:23,920 --> 00:21:26,320 Speaker 1: with itself the same way sound does, in the same 400 00:21:26,320 --> 00:21:29,919 Speaker 1: way waves in your bathtub night. That intuition makes sense, 401 00:21:30,119 --> 00:21:33,600 Speaker 1: But unfortunately that is not what's happening, and the next 402 00:21:33,640 --> 00:21:37,960 Speaker 1: experiment reveals that it's something much weirder, much more fascinating, 403 00:21:37,960 --> 00:21:41,399 Speaker 1: which reveals the true quantum nature of light. So we 404 00:21:41,440 --> 00:21:45,479 Speaker 1: have two narrow gaps and we're shining light through both gaps, 405 00:21:45,520 --> 00:21:47,800 Speaker 1: and we see an interference pattern on the back screen, 406 00:21:48,160 --> 00:21:51,199 Speaker 1: and we think well, that's fascinating. I bet it's because 407 00:21:51,280 --> 00:21:54,320 Speaker 1: light is interfering. That light is coming through both gaps, 408 00:21:54,320 --> 00:21:56,439 Speaker 1: and when it comes out the other side, either it 409 00:21:56,480 --> 00:21:59,600 Speaker 1: adds up constructively we get a bright patch, or it 410 00:21:59,680 --> 00:22:01,720 Speaker 1: can't as itself out and we get a dark patch. 411 00:22:02,440 --> 00:22:04,720 Speaker 1: So now let's do an experiment to discover if that's 412 00:22:04,760 --> 00:22:07,520 Speaker 1: actually true. What we're gonna do is we're gonna dial 413 00:22:07,640 --> 00:22:10,040 Speaker 1: down the source of the light. Maybe we had a laser, 414 00:22:10,119 --> 00:22:12,080 Speaker 1: maybe we had a flash light, doesn't matter too much, 415 00:22:12,520 --> 00:22:15,199 Speaker 1: but let's turn down the source of the light. And 416 00:22:15,240 --> 00:22:18,120 Speaker 1: as we talked about in a podcast very recently, light 417 00:22:18,280 --> 00:22:22,040 Speaker 1: is not continuous. It's not just the smooth oscillations of 418 00:22:22,040 --> 00:22:25,680 Speaker 1: the electromagnetic waves. Light is made of packets, and those 419 00:22:25,720 --> 00:22:29,240 Speaker 1: packets are photons. So you can't actually turn a light 420 00:22:29,280 --> 00:22:32,000 Speaker 1: down to any arbitrary value. You have to turn it 421 00:22:32,040 --> 00:22:35,040 Speaker 1: down for example, one photon a second, or two photons 422 00:22:35,080 --> 00:22:37,439 Speaker 1: a second, or three photons a second. You can't have 423 00:22:37,760 --> 00:22:40,600 Speaker 1: one point five photons a second. But what we can 424 00:22:40,600 --> 00:22:43,520 Speaker 1: do is something really fascinating. We can turn the light 425 00:22:43,560 --> 00:22:46,320 Speaker 1: down so we're shooting out one photon at a time, 426 00:22:46,760 --> 00:22:49,399 Speaker 1: maybe one photon, and then you wait five seconds, you 427 00:22:49,400 --> 00:22:52,280 Speaker 1: shoot out another photon. The idea is that one photon 428 00:22:52,320 --> 00:22:54,720 Speaker 1: has had plenty of time to go through the whole 429 00:22:54,720 --> 00:22:58,640 Speaker 1: experiment before the next photon comes through. Now, if the 430 00:22:58,680 --> 00:23:02,720 Speaker 1: interference comes from light coming through both of those narrow 431 00:23:02,760 --> 00:23:06,840 Speaker 1: gaps and then interfering, then the interference pattern should vanish 432 00:23:06,920 --> 00:23:09,639 Speaker 1: when we slow the experiment down to one photon at 433 00:23:09,640 --> 00:23:13,119 Speaker 1: a time. Because there's only one photon in the experiment 434 00:23:13,240 --> 00:23:17,040 Speaker 1: at a time, there's no other photon to interfere. That's 435 00:23:17,080 --> 00:23:19,760 Speaker 1: what you would expect if the interference pattern came from 436 00:23:19,800 --> 00:23:23,520 Speaker 1: the interference of the light waves. But it doesn't, because 437 00:23:23,560 --> 00:23:26,400 Speaker 1: what happens when we do this experiment is that we 438 00:23:26,480 --> 00:23:29,720 Speaker 1: still get an interference pattern. I remember learning about this 439 00:23:29,760 --> 00:23:32,520 Speaker 1: in college and it blew my mind. You shoot one 440 00:23:32,560 --> 00:23:35,760 Speaker 1: photon at a time, one photon goes here, another one 441 00:23:35,800 --> 00:23:39,760 Speaker 1: goes there. And remember, quantum mechanics is random, So there's 442 00:23:39,800 --> 00:23:42,919 Speaker 1: a wave function for each photon, and that wave function 443 00:23:42,960 --> 00:23:46,720 Speaker 1: says the probability of any given photon going somewhere. But 444 00:23:46,800 --> 00:23:49,760 Speaker 1: two photons shot in exactly the same direction under the 445 00:23:49,800 --> 00:23:53,159 Speaker 1: same conditions don't have to land in the same place. 446 00:23:53,600 --> 00:23:56,720 Speaker 1: The universe throws a new quantum number for every photon, 447 00:23:57,080 --> 00:23:59,240 Speaker 1: So the first one might land here and the next 448 00:23:59,240 --> 00:24:01,679 Speaker 1: one might land there. And what you do as you 449 00:24:01,920 --> 00:24:04,439 Speaker 1: do this experiment, which now takes longer because you're shooting 450 00:24:04,480 --> 00:24:07,800 Speaker 1: a lot of individual photons, what you see is that 451 00:24:07,880 --> 00:24:11,520 Speaker 1: you very gradually build up the interference pattern. Again. You 452 00:24:11,560 --> 00:24:14,720 Speaker 1: get a lot more photons landing where the interference pattern 453 00:24:14,840 --> 00:24:17,800 Speaker 1: was bright, and you get no photons landing where the 454 00:24:17,840 --> 00:24:20,800 Speaker 1: screen was previously dark, and you've got a few landing 455 00:24:20,800 --> 00:24:23,160 Speaker 1: where the where the screen was a little bit bright. 456 00:24:23,600 --> 00:24:27,600 Speaker 1: So the photons follow this interference pattern. It's like for 457 00:24:27,640 --> 00:24:30,480 Speaker 1: each one it says, all right, well we gotta have 458 00:24:30,560 --> 00:24:32,199 Speaker 1: a bunch over here and a few over there and 459 00:24:32,280 --> 00:24:34,160 Speaker 1: none over there, so let's roll a die and see 460 00:24:34,200 --> 00:24:36,959 Speaker 1: where you're gonna go. And eventually you just build up 461 00:24:37,000 --> 00:24:40,920 Speaker 1: exactly the same pattern that you saw before. So how 462 00:24:41,000 --> 00:24:43,320 Speaker 1: is that possible? How is it possible to have an 463 00:24:43,359 --> 00:24:46,840 Speaker 1: interference pattern if you don't have two photons in the 464 00:24:46,880 --> 00:24:50,919 Speaker 1: experiment at once, What is doing the interfering? Well, the 465 00:24:51,000 --> 00:24:53,320 Speaker 1: problem with this thinking is that you're thinking of the 466 00:24:53,320 --> 00:24:57,040 Speaker 1: photons as flying through the experiment. But remember they don't 467 00:24:57,119 --> 00:25:00,720 Speaker 1: have quantum paths. These things ex this when they leave 468 00:25:00,760 --> 00:25:03,000 Speaker 1: the light source, and then they exist when they hit 469 00:25:03,000 --> 00:25:06,040 Speaker 1: the screen. But in between they don't necessarily have a 470 00:25:06,119 --> 00:25:09,239 Speaker 1: location that we can think about sensibly. But what they 471 00:25:09,280 --> 00:25:12,960 Speaker 1: do have is a wave function. So instead of trying 472 00:25:12,960 --> 00:25:15,440 Speaker 1: to follow the photon through the experiment and making sense 473 00:25:15,440 --> 00:25:17,679 Speaker 1: of it, let's follow the wave function. That's the thing 474 00:25:17,680 --> 00:25:19,879 Speaker 1: we're gonna grab onto and try to make sense of 475 00:25:20,240 --> 00:25:23,399 Speaker 1: things that it's something that we can actually understand. So 476 00:25:23,480 --> 00:25:25,920 Speaker 1: let's start from the beginning. The photon is shot out 477 00:25:26,040 --> 00:25:28,720 Speaker 1: from this laser or this flashlight whatever, and has a 478 00:25:28,760 --> 00:25:31,600 Speaker 1: certain way function to be there. Now, the wave function 479 00:25:31,680 --> 00:25:34,520 Speaker 1: flies across the room and it spreads out a little 480 00:25:34,520 --> 00:25:36,800 Speaker 1: bit because that's the source of the light, and then 481 00:25:36,840 --> 00:25:39,240 Speaker 1: it hits the wall, the wall that has two narrow 482 00:25:39,280 --> 00:25:42,960 Speaker 1: gaps in it. Then what happens, Well, nobody has made 483 00:25:43,000 --> 00:25:45,720 Speaker 1: a measurement yet. The photon is interacting with this wall, 484 00:25:45,760 --> 00:25:49,719 Speaker 1: but nobody's looking, nobody's asked where is the photon? So 485 00:25:49,760 --> 00:25:54,080 Speaker 1: it has chance to go through one slit and chance 486 00:25:54,160 --> 00:25:56,640 Speaker 1: to go through the other slit. So what happens when 487 00:25:56,680 --> 00:26:00,200 Speaker 1: the wave function hits the wall? And remember it's hey 488 00:26:00,240 --> 00:26:02,520 Speaker 1: to talk about the wave function moving through space. The 489 00:26:02,560 --> 00:26:04,800 Speaker 1: wave function has a path that we can think about. 490 00:26:05,520 --> 00:26:08,240 Speaker 1: So when the wave function hits the wall, it splits 491 00:26:08,240 --> 00:26:11,680 Speaker 1: into half of it goes through one slit and half 492 00:26:11,720 --> 00:26:14,480 Speaker 1: of it goes through the other slid. And that reflects 493 00:26:14,520 --> 00:26:16,960 Speaker 1: the fact that the photon itself has a fifty percent 494 00:26:17,040 --> 00:26:19,280 Speaker 1: chance of hitting one slit and a fifty percent chance 495 00:26:19,320 --> 00:26:22,399 Speaker 1: of hitting the other slid. And if nobody has asked 496 00:26:22,480 --> 00:26:24,639 Speaker 1: which slip did it go through, it just has fifty 497 00:26:24,680 --> 00:26:26,960 Speaker 1: percent chance of going through one and a fifty pc 498 00:26:27,119 --> 00:26:29,720 Speaker 1: chance of going through the other. Now, let's follow the 499 00:26:29,720 --> 00:26:32,160 Speaker 1: wave function. The wave function comes out the other side 500 00:26:32,160 --> 00:26:34,320 Speaker 1: of these slits, and there's a little bit of source 501 00:26:34,359 --> 00:26:37,120 Speaker 1: of wave function from one slit and source of wave 502 00:26:37,119 --> 00:26:39,800 Speaker 1: function of the other slit. And a wave function, of course, 503 00:26:40,240 --> 00:26:43,320 Speaker 1: is a wave. So what happens when you get two 504 00:26:43,359 --> 00:26:46,240 Speaker 1: sources of a wave coming out from the wall towards 505 00:26:46,240 --> 00:26:50,560 Speaker 1: the screen, of course you get interference and so on 506 00:26:50,600 --> 00:26:54,000 Speaker 1: the screen. What's actually happening is that the wave function 507 00:26:54,080 --> 00:26:57,399 Speaker 1: is interfering with itself, and it gives the photon a 508 00:26:57,480 --> 00:27:00,480 Speaker 1: high probability to be in some locations and a low 509 00:27:00,560 --> 00:27:04,000 Speaker 1: probability to be in other locations, and a zero probability 510 00:27:04,000 --> 00:27:06,840 Speaker 1: to be in some locations. So for the wave function, 511 00:27:06,920 --> 00:27:10,639 Speaker 1: it determines where that photon, that individual photon that we 512 00:27:10,680 --> 00:27:14,040 Speaker 1: put into our experiment is likely to land. And so 513 00:27:14,080 --> 00:27:16,800 Speaker 1: the thing that's doing the interfering is not light because 514 00:27:16,840 --> 00:27:19,000 Speaker 1: you have a single photon in the experiment at once. 515 00:27:19,359 --> 00:27:21,520 Speaker 1: And if you're not convinced that this is the wave 516 00:27:21,640 --> 00:27:26,200 Speaker 1: function interfering, because you think maybe it's really just light interfering, 517 00:27:26,240 --> 00:27:29,880 Speaker 1: wouldn't that be simpler. But remember that we're sending a 518 00:27:29,920 --> 00:27:32,840 Speaker 1: single photon through a time in order to prevent the 519 00:27:32,840 --> 00:27:36,520 Speaker 1: photons from interacting, from interfering with each other. But the 520 00:27:36,600 --> 00:27:40,560 Speaker 1: real killer is that they did this experiment not with photons, 521 00:27:40,560 --> 00:27:44,440 Speaker 1: but later with electrons and they got the same result. 522 00:27:44,800 --> 00:27:48,200 Speaker 1: But what's doing the interfering is the wave function. Another 523 00:27:48,200 --> 00:27:50,720 Speaker 1: way to think about it is that the photon has 524 00:27:50,800 --> 00:27:53,639 Speaker 1: equal probability to go through one slit and the other, 525 00:27:54,119 --> 00:27:57,600 Speaker 1: and that probability is doing the interfering because remember the 526 00:27:57,600 --> 00:28:01,320 Speaker 1: way functions what controls where the partal has a probability 527 00:28:01,359 --> 00:28:04,240 Speaker 1: to be. So because it has a probability to be 528 00:28:04,280 --> 00:28:09,119 Speaker 1: through slit one and through slit two, those probabilities interfere 529 00:28:09,160 --> 00:28:13,120 Speaker 1: with each other, and those probabilities determine where the photon 530 00:28:13,200 --> 00:28:16,840 Speaker 1: can land on the back screen, and that's what we see, 531 00:28:16,960 --> 00:28:19,080 Speaker 1: and that's why it builds up one at a time 532 00:28:19,400 --> 00:28:23,080 Speaker 1: because for photon number one, it follows that distribution, and 533 00:28:23,119 --> 00:28:25,439 Speaker 1: the universe rolls a die only when it gets to 534 00:28:25,480 --> 00:28:27,840 Speaker 1: the back screen. That's when we're measuring it. That's when 535 00:28:27,840 --> 00:28:30,720 Speaker 1: we're interacting with it. That's when we're saying, Okay, a photon, 536 00:28:31,040 --> 00:28:34,399 Speaker 1: where are you? So remember that the quantum wave function 537 00:28:34,440 --> 00:28:37,640 Speaker 1: determines where you are most likely you the photon are 538 00:28:37,680 --> 00:28:40,280 Speaker 1: most likely to be found, and there are parts of 539 00:28:40,280 --> 00:28:42,320 Speaker 1: the screen where the photon has a high chance of 540 00:28:42,400 --> 00:28:46,760 Speaker 1: landing because the wave function interferes constructively and places on 541 00:28:46,800 --> 00:28:49,320 Speaker 1: the screen where has no chance of landing because the 542 00:28:49,360 --> 00:28:52,080 Speaker 1: two halves of its wave function are interfering with each 543 00:28:52,080 --> 00:28:55,840 Speaker 1: other destructively. They're canceling each other out. And you might 544 00:28:55,880 --> 00:28:58,600 Speaker 1: be thinking, well, is the wave function of physical thing? 545 00:28:58,680 --> 00:29:01,560 Speaker 1: Is it just a tool where you using to calculate things, 546 00:29:01,920 --> 00:29:04,440 Speaker 1: or is it something that's real and part of the universe. 547 00:29:04,840 --> 00:29:07,880 Speaker 1: That's a hard question to answer. It's philosophical, but here 548 00:29:07,920 --> 00:29:11,520 Speaker 1: we're seeing real physical effects of the existence of the 549 00:29:11,520 --> 00:29:14,840 Speaker 1: wave function. The wave function really does act like a wave, 550 00:29:14,880 --> 00:29:17,120 Speaker 1: and a wave that you can grasp on the way 551 00:29:17,160 --> 00:29:19,720 Speaker 1: that you can use your intuition to understand. You can 552 00:29:19,760 --> 00:29:21,640 Speaker 1: think of this wave function the same way you think 553 00:29:21,640 --> 00:29:25,160 Speaker 1: of waves in water, flowing through things and diffracting and 554 00:29:25,240 --> 00:29:28,840 Speaker 1: interfering and doing all those wave like things. And this 555 00:29:28,960 --> 00:29:31,680 Speaker 1: is the key to understanding quantum mechanics is grabbing onto 556 00:29:31,680 --> 00:29:34,280 Speaker 1: the wave function because it flows and it moves just 557 00:29:34,360 --> 00:29:37,640 Speaker 1: like a classical wave. It's just that it determines the 558 00:29:37,680 --> 00:29:40,480 Speaker 1: performance and the behavior in the location of a crazy 559 00:29:40,560 --> 00:29:43,880 Speaker 1: quantum object. So while that sinks into your brain, you're 560 00:29:43,960 --> 00:29:47,840 Speaker 1: understanding your classical intuition for the quantum wave function and 561 00:29:47,880 --> 00:29:51,520 Speaker 1: how a single photons wave function can interfere with itself 562 00:29:51,720 --> 00:29:54,600 Speaker 1: to give you this crazy pattern on the screen. While 563 00:29:54,640 --> 00:29:57,560 Speaker 1: that's in your mind, let's take a quick break before 564 00:29:57,600 --> 00:30:01,200 Speaker 1: we think about the last, the craziest, the most amazing 565 00:30:01,320 --> 00:30:04,880 Speaker 1: part of this double slit experiment. Just after this break, 566 00:30:17,920 --> 00:30:20,280 Speaker 1: all right, So we are spending time in the quantum 567 00:30:20,280 --> 00:30:23,120 Speaker 1: realm trying to become familiar, trying to develop an intuition. 568 00:30:23,560 --> 00:30:25,680 Speaker 1: And the key point I'm trying to make today is 569 00:30:25,720 --> 00:30:28,760 Speaker 1: that your intuition cannot be applied to a quantum object 570 00:30:28,840 --> 00:30:31,200 Speaker 1: because it's just different from the kind of things you're 571 00:30:31,240 --> 00:30:33,920 Speaker 1: familiar with. It is not a tiny spinning ball, It 572 00:30:34,080 --> 00:30:36,480 Speaker 1: is not a wave. It is neither. It is both 573 00:30:36,520 --> 00:30:40,360 Speaker 1: into something new and weird that possibly we will never understand. 574 00:30:40,720 --> 00:30:43,120 Speaker 1: But in my view, the best chance to understanding it 575 00:30:43,160 --> 00:30:45,680 Speaker 1: is to spend time with it, to develop an intuition 576 00:30:45,760 --> 00:30:48,320 Speaker 1: by immersion. So that's what we're doing today. We are 577 00:30:48,320 --> 00:30:51,800 Speaker 1: flying our way through experiments conducted by a physicist trying 578 00:30:51,800 --> 00:30:54,400 Speaker 1: to reveal the true nature of the universe. So we 579 00:30:54,480 --> 00:30:57,680 Speaker 1: started out just shooting photons against the screen to get 580 00:30:57,720 --> 00:31:00,200 Speaker 1: familiar with the idea that the photons don't move move 581 00:31:00,320 --> 00:31:02,240 Speaker 1: from one side of the screen to the other. They 582 00:31:02,240 --> 00:31:04,920 Speaker 1: have a probability to be in a certain place where 583 00:31:05,000 --> 00:31:07,640 Speaker 1: they only exist where they are measured and in between. 584 00:31:07,640 --> 00:31:11,040 Speaker 1: They do not necessarily have a path. You measure something, 585 00:31:11,520 --> 00:31:13,440 Speaker 1: you see the photon coming out of the light source 586 00:31:13,600 --> 00:31:15,720 Speaker 1: and later you see it on the screen. Doesn't mean 587 00:31:15,760 --> 00:31:17,760 Speaker 1: you can draw a straight line between those and say 588 00:31:17,880 --> 00:31:20,680 Speaker 1: the light was here. But what you can do is 589 00:31:20,720 --> 00:31:23,360 Speaker 1: talk about its wave function. The wave function leaves the 590 00:31:23,440 --> 00:31:26,240 Speaker 1: light source and later hits the screen, where eventually the 591 00:31:26,280 --> 00:31:29,440 Speaker 1: universe demands a measurement, and so the universe has to 592 00:31:29,480 --> 00:31:32,080 Speaker 1: decide based on where the wave function is, where to 593 00:31:32,160 --> 00:31:35,200 Speaker 1: actually put the photon. But that wave function is something 594 00:31:35,240 --> 00:31:38,000 Speaker 1: you can grasp, something you can follow through space in 595 00:31:38,040 --> 00:31:41,200 Speaker 1: a way that your intuition will be satisfied with. So 596 00:31:41,280 --> 00:31:44,760 Speaker 1: then we added these barriers. So instead of just splashing 597 00:31:44,960 --> 00:31:47,320 Speaker 1: light on the back screen, we saw a geometric shadow. 598 00:31:47,720 --> 00:31:50,640 Speaker 1: Then we narrowed the barriers until we saw the effects 599 00:31:50,680 --> 00:31:53,840 Speaker 1: of waves. We saw that the fact that waves coming 600 00:31:53,840 --> 00:31:56,240 Speaker 1: through a very narrow gap will spread out a little bit, 601 00:31:56,720 --> 00:31:59,480 Speaker 1: and then we added a second narrow gap, so we 602 00:31:59,560 --> 00:32:03,480 Speaker 1: had to sources of waves. And those waves apparently were interfering, 603 00:32:03,840 --> 00:32:06,280 Speaker 1: and your intuition was suggested that maybe it was light 604 00:32:06,280 --> 00:32:08,160 Speaker 1: doing the interfering, because we like to think of light 605 00:32:08,160 --> 00:32:11,080 Speaker 1: as a wave. But then we played a trick. We said, 606 00:32:11,480 --> 00:32:15,400 Speaker 1: let's slow down the experiment, only shoot one photon at 607 00:32:15,400 --> 00:32:18,400 Speaker 1: a time. And this, in theory, if light was a 608 00:32:18,400 --> 00:32:21,600 Speaker 1: wave and it was waves doing the interacting, this should 609 00:32:21,640 --> 00:32:24,960 Speaker 1: destroy the interference pattern because only one photon was going 610 00:32:25,000 --> 00:32:27,880 Speaker 1: through the experiment at a time. But it didn't. It 611 00:32:28,000 --> 00:32:31,040 Speaker 1: slowed down the interference pattern and it showed us that 612 00:32:31,080 --> 00:32:34,320 Speaker 1: there was still something they're doing the interfering, and that's 613 00:32:34,360 --> 00:32:36,760 Speaker 1: the key is letting go of this idea that the 614 00:32:36,840 --> 00:32:40,480 Speaker 1: light is flowing through the experiment, because quantum objects don't flow, 615 00:32:40,520 --> 00:32:44,040 Speaker 1: they don't go, and they don't have they don't have paths. Instead, 616 00:32:44,400 --> 00:32:47,800 Speaker 1: what's flowing through the experiment is the quantum wave of 617 00:32:47,840 --> 00:32:50,440 Speaker 1: the photon, and the quantum wave of the photon can 618 00:32:50,480 --> 00:32:53,400 Speaker 1: go through either slit as a fifty percent chance to 619 00:32:53,440 --> 00:32:55,440 Speaker 1: go through one and a fifty percent chance to go 620 00:32:55,520 --> 00:32:58,240 Speaker 1: through the other, and then it interferes with itself. It 621 00:32:58,320 --> 00:33:01,080 Speaker 1: gives us this interference pattern, and it's hard to get 622 00:33:01,200 --> 00:33:03,400 Speaker 1: your mind around what it means for the photon to 623 00:33:03,480 --> 00:33:06,080 Speaker 1: have a chance to go through both slits at once. 624 00:33:06,720 --> 00:33:08,840 Speaker 1: Most likely you think of it like this. You think, well, 625 00:33:09,280 --> 00:33:11,920 Speaker 1: the photon either went through one slit or the other. 626 00:33:12,120 --> 00:33:14,959 Speaker 1: We just don't know. And it's true that often in 627 00:33:15,040 --> 00:33:18,480 Speaker 1: science and in physics, we use probability to describe our 628 00:33:18,560 --> 00:33:21,240 Speaker 1: lack of knowledge. We say the universe is thirteen point 629 00:33:21,280 --> 00:33:24,320 Speaker 1: eight billion years old plus or minus a hundred million, 630 00:33:24,680 --> 00:33:26,760 Speaker 1: and it reflects not the fact that the universe doesn't 631 00:33:26,800 --> 00:33:29,000 Speaker 1: have a specific age, but just the fact that we 632 00:33:29,040 --> 00:33:31,120 Speaker 1: don't know it well enough that we haven't been able 633 00:33:31,160 --> 00:33:34,520 Speaker 1: to measure it. But this is different. It's not true 634 00:33:34,680 --> 00:33:37,200 Speaker 1: that the photon went through one slit or went through 635 00:33:37,240 --> 00:33:39,440 Speaker 1: the other and we just don't know. The truth is 636 00:33:39,440 --> 00:33:42,719 Speaker 1: that its wave went through both. It needed to go 637 00:33:42,800 --> 00:33:46,240 Speaker 1: through both in order to give us the interference pattern. Remember, 638 00:33:46,680 --> 00:33:49,560 Speaker 1: we didn't collapse the wave, We didn't interfere, We didn't 639 00:33:49,560 --> 00:33:52,880 Speaker 1: interact with the photon um when it's going through the slit. 640 00:33:52,960 --> 00:33:55,240 Speaker 1: We just let it fly through one slit or the other. 641 00:33:55,560 --> 00:33:57,920 Speaker 1: We don't pay attention. We only are looking at the 642 00:33:57,920 --> 00:34:01,160 Speaker 1: back screen. So le stick into that. Let's try to 643 00:34:01,240 --> 00:34:04,080 Speaker 1: probe that. What if we try to figure out which 644 00:34:04,120 --> 00:34:06,960 Speaker 1: slit the photon actually went through, because we are a 645 00:34:07,000 --> 00:34:09,880 Speaker 1: hardcore classicist and we want to know did it go 646 00:34:09,920 --> 00:34:12,080 Speaker 1: through one or the other. So we build a little 647 00:34:12,080 --> 00:34:15,040 Speaker 1: detector detector that doesn't change the direction of the photon 648 00:34:15,280 --> 00:34:17,520 Speaker 1: in a measurable way, but just tells us whether a 649 00:34:17,600 --> 00:34:19,920 Speaker 1: photon went through a slit, and we attach it to 650 00:34:19,960 --> 00:34:22,439 Speaker 1: one of the slits, and we do our experiment again. 651 00:34:22,440 --> 00:34:26,040 Speaker 1: And the idea here is just to confirm our intuition, 652 00:34:26,080 --> 00:34:29,240 Speaker 1: our classical intuition that the photon went through one slit 653 00:34:29,320 --> 00:34:31,480 Speaker 1: or the other. We turn on the experiment again. We 654 00:34:31,520 --> 00:34:34,440 Speaker 1: shoot one single photon at a time, and for every photon, 655 00:34:34,880 --> 00:34:37,680 Speaker 1: our detector tells us whether it went through slit one 656 00:34:37,719 --> 00:34:39,880 Speaker 1: because it beeps, or whether it went through slit two 657 00:34:40,000 --> 00:34:42,600 Speaker 1: because it doesn't beep. Do we get the same result 658 00:34:42,640 --> 00:34:45,960 Speaker 1: on the back screen. The answer is we do not. 659 00:34:46,760 --> 00:34:49,560 Speaker 1: We do not get the interference pattern on the back screen. Instead, 660 00:34:49,600 --> 00:34:53,280 Speaker 1: what we get our two geometrical shadows. And at first 661 00:34:53,320 --> 00:34:55,440 Speaker 1: this might be nonsensical. You might think, well, but the 662 00:34:55,480 --> 00:34:58,359 Speaker 1: detector is just telling you whether the photon went through 663 00:34:58,440 --> 00:35:01,040 Speaker 1: one or the other. It's not changing the photon in 664 00:35:01,080 --> 00:35:04,480 Speaker 1: any measurable way. What's the issue? How could it possibly 665 00:35:04,560 --> 00:35:07,399 Speaker 1: change what we're seeing in the back screen. But that's 666 00:35:07,440 --> 00:35:09,720 Speaker 1: because you're thinking about the photon is having a path, 667 00:35:09,840 --> 00:35:12,439 Speaker 1: is flying through When you think, well, it either went 668 00:35:12,480 --> 00:35:14,719 Speaker 1: through one slit or the other, it doesn't matter if 669 00:35:14,760 --> 00:35:18,200 Speaker 1: I know that, don't shouldn't change what happens. It's like 670 00:35:18,239 --> 00:35:21,520 Speaker 1: if you're watching a horse race, just watching what happens 671 00:35:21,560 --> 00:35:25,160 Speaker 1: around the first bend shouldn't change who wins the race? Right, Well, 672 00:35:25,200 --> 00:35:28,040 Speaker 1: that's not the case, because remember what's flying through your 673 00:35:28,040 --> 00:35:30,960 Speaker 1: experiment is not a photon. Photons don't fly through things. 674 00:35:31,000 --> 00:35:34,440 Speaker 1: They're not classical objects with paths. What's flying through the 675 00:35:34,480 --> 00:35:38,359 Speaker 1: experiment is a quantum wave, and the quantum wave is 676 00:35:38,440 --> 00:35:41,560 Speaker 1: sensitive to being watched. When you watch a quantum wave, 677 00:35:41,560 --> 00:35:43,720 Speaker 1: when you interact with it, when you say, okay, quantum 678 00:35:43,719 --> 00:35:46,759 Speaker 1: wave of this photon, where's the photon now? Then it 679 00:35:46,880 --> 00:35:49,320 Speaker 1: changes it it collapses and it says, okay, the photon 680 00:35:49,440 --> 00:35:52,360 Speaker 1: is here, and then the quantum wave can continue. But 681 00:35:52,480 --> 00:35:54,960 Speaker 1: you've narrowed it down. You pinned it down and said, okay, 682 00:35:55,000 --> 00:35:58,200 Speaker 1: it's right here, and then the quantum wave continues from 683 00:35:58,239 --> 00:36:01,200 Speaker 1: that location. So in the first scenario, when we didn't 684 00:36:01,239 --> 00:36:05,000 Speaker 1: have the detector, the quantum wave flies, it hits the 685 00:36:05,040 --> 00:36:07,520 Speaker 1: two slits, and it splits in half, and some of 686 00:36:07,520 --> 00:36:11,200 Speaker 1: the quantum wave goes through both slits. Each slit emits 687 00:36:11,360 --> 00:36:14,080 Speaker 1: some portion of the quantum wave, and those two halves 688 00:36:14,239 --> 00:36:16,840 Speaker 1: interfere with each other. In the version where you have 689 00:36:17,000 --> 00:36:21,040 Speaker 1: the detector on, then you're asking the universe to decide 690 00:36:21,440 --> 00:36:24,000 Speaker 1: which slit the photon went through, not just to reveal, 691 00:36:24,239 --> 00:36:27,279 Speaker 1: but to decide which slit the photon went through. So 692 00:36:27,320 --> 00:36:29,680 Speaker 1: the quantum wave can only go through one of the 693 00:36:29,719 --> 00:36:32,880 Speaker 1: slits and not the other one. Because the detector tells 694 00:36:32,920 --> 00:36:35,600 Speaker 1: you which slit it went through, it has no probability 695 00:36:35,640 --> 00:36:38,000 Speaker 1: to go through the other slit, So all it can 696 00:36:38,000 --> 00:36:40,640 Speaker 1: do is then emits some quantum wave from one of 697 00:36:40,640 --> 00:36:44,000 Speaker 1: the slits. If you hadn't looked, then it's free to 698 00:36:44,040 --> 00:36:46,960 Speaker 1: emit quantum wave from both slits, which can then interfere. 699 00:36:47,080 --> 00:36:49,200 Speaker 1: But if you look, if you demand an answer, if 700 00:36:49,200 --> 00:36:52,000 Speaker 1: you want to know which slit it went through, then 701 00:36:52,000 --> 00:36:54,720 Speaker 1: the quantum wave can only emit from the other slit 702 00:36:55,440 --> 00:36:58,040 Speaker 1: and then there's no interference pattern. There's just it's just 703 00:36:58,080 --> 00:37:00,759 Speaker 1: like as if you had one slit. And this is 704 00:37:00,800 --> 00:37:04,000 Speaker 1: the thing that blows most people's minds that asking questions 705 00:37:04,040 --> 00:37:07,600 Speaker 1: of the universe changes the answer. And it's true because 706 00:37:07,719 --> 00:37:11,040 Speaker 1: quantum waves respond to measurement. They like to be uncertain. 707 00:37:11,200 --> 00:37:14,680 Speaker 1: They're happy to fly through the universe keeping their uncertainty 708 00:37:14,680 --> 00:37:18,080 Speaker 1: their probability distribution until they are asked, and that moment 709 00:37:18,120 --> 00:37:20,280 Speaker 1: that you ask it, then it collapses and it says 710 00:37:20,440 --> 00:37:23,279 Speaker 1: the photon is here, the photon is there. So this 711 00:37:23,320 --> 00:37:25,640 Speaker 1: is an object we can grasp onto because it helps 712 00:37:25,680 --> 00:37:29,560 Speaker 1: us understand how things move through the universe, but also 713 00:37:29,680 --> 00:37:31,799 Speaker 1: is something new and something weird and something we have 714 00:37:31,880 --> 00:37:33,960 Speaker 1: to get familiar with. But the only way to do that, 715 00:37:34,040 --> 00:37:36,719 Speaker 1: of course, is to spend some time with it. So 716 00:37:36,760 --> 00:37:38,799 Speaker 1: I hope that's helped you understand a little bit about 717 00:37:38,880 --> 00:37:42,279 Speaker 1: quantum mechanics. The first step in becoming familiar with the 718 00:37:42,360 --> 00:37:45,200 Speaker 1: quantum realm is to abandon your idea of a quantum path, 719 00:37:45,440 --> 00:37:48,040 Speaker 1: that things have to move through the universe in a 720 00:37:48,080 --> 00:37:51,399 Speaker 1: continuous manner, that if you're over here and later you're 721 00:37:51,400 --> 00:37:54,239 Speaker 1: over there, you have to have somehow moved from one 722 00:37:54,320 --> 00:37:57,279 Speaker 1: to the other. But instead, instead of grabbing onto this 723 00:37:57,360 --> 00:38:00,400 Speaker 1: quantum path, there is something else you can grab onto, 724 00:38:00,560 --> 00:38:04,120 Speaker 1: this quantum wave function, which behaves in very understandable ways, 725 00:38:04,160 --> 00:38:06,800 Speaker 1: and we have equations that govern exactly how it moves. 726 00:38:07,160 --> 00:38:10,279 Speaker 1: And those equations, like the Shortinger wave equation, treat these 727 00:38:10,320 --> 00:38:12,960 Speaker 1: things like waves. Waves that we can understand that we 728 00:38:13,000 --> 00:38:16,719 Speaker 1: can actually apply our wave like intuition too, So if 729 00:38:16,760 --> 00:38:19,200 Speaker 1: you want to develop an intuition for quantum mechanics, get 730 00:38:19,280 --> 00:38:21,960 Speaker 1: cozy with the wave function. Now. The wave function, of 731 00:38:22,000 --> 00:38:26,080 Speaker 1: course has other mysteries, mysteries that continue to confound us 732 00:38:26,360 --> 00:38:29,879 Speaker 1: and the biggest one is this business about measurement. How 733 00:38:29,960 --> 00:38:32,560 Speaker 1: is it the wave function knows to collapse that We've 734 00:38:32,600 --> 00:38:35,000 Speaker 1: asked it a question and it's given us an answer 735 00:38:35,360 --> 00:38:38,000 Speaker 1: that when the wave function hits the screen, it says 736 00:38:38,120 --> 00:38:41,160 Speaker 1: the photon has various probabilities to be in various locations. 737 00:38:41,280 --> 00:38:43,680 Speaker 1: But then it actually makes a decision. When does the 738 00:38:43,760 --> 00:38:47,359 Speaker 1: universe decide to roll this dice and say, all right, 739 00:38:47,400 --> 00:38:50,320 Speaker 1: photon number seventy four, you are over here. Phot to 740 00:38:50,440 --> 00:38:53,360 Speaker 1: number seventy eight, you are over there. That is a 741 00:38:53,480 --> 00:38:56,759 Speaker 1: deep and recurring mystery of quantum mechanics that nobody really knows. 742 00:38:56,800 --> 00:38:59,440 Speaker 1: The answer to this description I've given you today is 743 00:38:59,480 --> 00:39:03,719 Speaker 1: sometimes as the Copenhagen interpretation of quantum mechanics, and it 744 00:39:03,800 --> 00:39:07,120 Speaker 1: has deep flaws in it. Flaws like who's doing the measuring? 745 00:39:07,400 --> 00:39:10,560 Speaker 1: You might ask, for example, if we if the photons 746 00:39:10,640 --> 00:39:13,040 Speaker 1: hit the screen but nobody looks, if there are no 747 00:39:13,200 --> 00:39:16,000 Speaker 1: humans in that universe, no scientists to do the observing, 748 00:39:16,400 --> 00:39:19,120 Speaker 1: then does the universe collapse the way of function or 749 00:39:19,120 --> 00:39:21,759 Speaker 1: does it keep it vague. We don't know the answer 750 00:39:21,800 --> 00:39:24,160 Speaker 1: to that question because we can't do the experiment in 751 00:39:24,200 --> 00:39:28,400 Speaker 1: which nobody looks and also know the answer, So that's frustrating, 752 00:39:28,640 --> 00:39:30,399 Speaker 1: and that's the source of a lot of discussion about 753 00:39:30,440 --> 00:39:33,080 Speaker 1: quantum mechanics. And there are other interpretations out there, like 754 00:39:33,120 --> 00:39:36,560 Speaker 1: the many Worlds interpretations that clever people like Sean Carroll 755 00:39:36,600 --> 00:39:39,400 Speaker 1: find much more natural, but they require you to accept 756 00:39:39,440 --> 00:39:42,800 Speaker 1: the existence of a huge number of other alternative universes. 757 00:39:43,040 --> 00:39:46,000 Speaker 1: So every interpretation of quantum mechanics comes with some sort 758 00:39:46,000 --> 00:39:48,760 Speaker 1: of cognitive load. And today we're not going to understand 759 00:39:48,840 --> 00:39:51,680 Speaker 1: all of the nuances and open questions of quantum mechanics. 760 00:39:51,880 --> 00:39:54,120 Speaker 1: We just wanted to spend some time becoming familiar with 761 00:39:54,120 --> 00:39:57,359 Speaker 1: the quantum realm. So the next time you read about 762 00:39:57,440 --> 00:40:00,680 Speaker 1: quantum mechanics, or think about quantum computers, or even just 763 00:40:00,719 --> 00:40:03,759 Speaker 1: are on a trip somewhere weird and unusual, remember you 764 00:40:03,880 --> 00:40:06,640 Speaker 1: can become familiar with something strange, something out of your 765 00:40:06,640 --> 00:40:09,400 Speaker 1: experience as long as you spent enough time immersing it, 766 00:40:09,840 --> 00:40:13,360 Speaker 1: marinating in the mathematics and the logic of it. Eventually 767 00:40:13,600 --> 00:40:16,080 Speaker 1: it would become part of who you are. Thanks for 768 00:40:16,160 --> 00:40:19,239 Speaker 1: listening to this explanation of our amazing and crazy and 769 00:40:19,320 --> 00:40:22,560 Speaker 1: totally bonkers universe. And if you have things that you'd 770 00:40:22,600 --> 00:40:25,520 Speaker 1: like us to discuss and break down in an accessible way. 771 00:40:25,560 --> 00:40:28,440 Speaker 1: Please send them to us at feedback at Daniel and 772 00:40:28,520 --> 00:40:39,520 Speaker 1: Joge dot com. Thanks for tuning in. If you still 773 00:40:39,600 --> 00:40:42,560 Speaker 1: have a question after listening to all these explanations, please 774 00:40:42,840 --> 00:40:45,160 Speaker 1: drop us the line. We'd love to hear from you. 775 00:40:45,160 --> 00:40:48,000 Speaker 1: You can find us at Facebook, Twitter, and Instagram at 776 00:40:48,320 --> 00:40:51,440 Speaker 1: Daniel and Jorge That's one word, or email us at 777 00:40:51,719 --> 00:40:55,440 Speaker 1: feedback at Daniel and Jorge dot com. Thanks for listening, 778 00:40:55,440 --> 00:40:58,160 Speaker 1: and remember that Daniel and Jorge Explaining the Universe is 779 00:40:58,200 --> 00:41:01,799 Speaker 1: a production of High Heart Reading More podcast for my 780 00:41:01,880 --> 00:41:05,680 Speaker 1: Heart Radio, visit the I Heart Radio, Apple podcasts, or 781 00:41:05,719 --> 00:41:13,320 Speaker 1: wherever you listen to your favorite shows. Yeah