WEBVTT - What is Quantum Tunneling? 0:00:00.080 --> 0:00:10.720 Yeah, okay, are you any good at bowling? By any chance? 0:00:10.800 --> 0:00:14.080 I am either the world's best or worst bull? All right? 0:00:14.120 --> 0:00:15.720 But when you go bowling, do you ever get any 0:00:15.800 --> 0:00:19.560 like gutter balls? I can't deny that I get gutter balls, 0:00:19.640 --> 0:00:21.880 all right? But are you so off the mark that 0:00:22.000 --> 0:00:24.920 sometimes your bowling ball ends up like in the next lane. 0:00:25.239 --> 0:00:27.520 I also can't deny that that's ever happened to me. 0:00:27.720 --> 0:00:30.200 Oh man, Well, in that case, you might have a 0:00:30.240 --> 0:00:33.960 special physics distinction. Oh how's that? You might be the 0:00:33.960 --> 0:00:37.839 world's first quantum bowler? Is that another TV show? Like 0:00:37.960 --> 0:00:43.720 Quantum Leap, but about quantum bowling? That's right, it's the 0:00:43.760 --> 0:01:03.040 Big Lebowski meets Quantum Leap. It's my new pitch. Hi. 0:01:03.160 --> 0:01:06.600 I'm Jorge. I'm a cartoonists and the creator of PhD Comments. 0:01:06.640 --> 0:01:10.160 And I'm Daniel. I'm a particle physicist, a terrible bowler, 0:01:10.640 --> 0:01:13.039 and the co author of a book with Jorge called 0:01:13.120 --> 0:01:16.120 We Have No Idea About All the Mysteries of the Universe. 0:01:16.240 --> 0:01:19.640 So welcome to our podcast Daniel and Jorge Explain the Universe, 0:01:19.800 --> 0:01:22.160 a production of I Heart Radio. That's Right, in which 0:01:22.240 --> 0:01:24.200 we take things around us in the universe that we 0:01:24.240 --> 0:01:28.120 find amazing or crazy, or wet and sticky, or just 0:01:28.360 --> 0:01:31.520 weird and interesting, and we try to explain them to you. Right, 0:01:31.560 --> 0:01:34.119 all the strikes, all the gutter balls, and all those 0:01:34.120 --> 0:01:38.120 spars out there in the universe, that's right, even the splits, 0:01:38.480 --> 0:01:40.480 We'll roll it right down the middle for you and 0:01:40.520 --> 0:01:44.200 into your brain. Right. Sometimes there's even quantum spin on 0:01:44.240 --> 0:01:46.200 the ball. Right. I have no idea how to do 0:01:46.280 --> 0:01:48.600 spin on the ball. I see people do that. I've 0:01:48.640 --> 0:01:51.600 tried to do that. It's failed miserably. I'm all about 0:01:51.600 --> 0:01:54.120 the straight and Grandma rule. It's been actually helped you. 0:01:54.240 --> 0:01:56.080 Do you think, as a particle physicist would be all 0:01:56.120 --> 0:01:59.360 pro spinning balls and all that stuff. But I found 0:01:59.360 --> 0:02:02.400 an impossible My wistomost breaks every time I try to 0:02:02.440 --> 0:02:05.080 do it well. On the program, we usually talk about 0:02:05.160 --> 0:02:07.600 topics that people have questions about or people are really 0:02:07.600 --> 0:02:10.320 curious about about the universe. But physics about how the 0:02:10.360 --> 0:02:14.520 world and the how reality really works. And so today 0:02:14.560 --> 0:02:17.560 we're tackling a pretty interesting topic, right, Daniel, that's right. 0:02:17.600 --> 0:02:19.760 This is a topic people wrote in and asked us 0:02:19.800 --> 0:02:22.680 to explain. And I think it's because they here talked 0:02:22.720 --> 0:02:25.520 about in physics podcasts, and you read about it in 0:02:25.560 --> 0:02:28.880 physics books. There's a bunch of online videos talking about it, 0:02:28.960 --> 0:02:32.840 but frankly, there are very few actually satisfying explanations, and 0:02:32.880 --> 0:02:34.760 I think people wanted us to dig into it and 0:02:34.760 --> 0:02:36.799 see if you can explain to them what's going on. 0:02:37.120 --> 0:02:39.840 It's definitely one of those topics that sound cool for sure, 0:02:40.440 --> 0:02:43.519 Like just those two words put together, Well, anything after 0:02:43.600 --> 0:02:48.760 quantum sounds cool, right, Quantum banana, quantum bowling, even that 0:02:48.800 --> 0:02:52.240 sounds interesting. An evening of quantum bowling with Daniel and Jorge. 0:02:52.400 --> 0:02:54.120 That sounds like an event you pay twenty bucks to 0:02:54.160 --> 0:02:56.160 go to. Right. Well, Today, on the program, we'll be 0:02:56.200 --> 0:03:00.800 tackling a subject that is almost seems like maybe and 0:03:00.880 --> 0:03:05.240 that a lot of people associate with perhaps teleportation, the 0:03:05.320 --> 0:03:07.720 idea that maybe you can move from one spot to 0:03:07.760 --> 0:03:11.120 another spot kind of instantly or through a wall or 0:03:11.160 --> 0:03:13.200 something like that, so they On the podcast, we'll be 0:03:13.240 --> 0:03:21.320 talking about quantum tunneling. Quantum tunneling is one of my 0:03:21.360 --> 0:03:24.680 favorite topics because it's one of those really weird effects 0:03:24.760 --> 0:03:27.200 you see in quantum mechanics. You know, when you zoom 0:03:27.200 --> 0:03:30.320 in on the world and you discover it's microscopic nature. 0:03:30.560 --> 0:03:32.960 You try to understand it in terms of things we 0:03:33.000 --> 0:03:35.400 know and understand, and your brain is trying to use 0:03:35.440 --> 0:03:37.840 particles and waves and all this stuff. This is one 0:03:37.880 --> 0:03:40.120 of those effects that really just stumps us when it 0:03:40.280 --> 0:03:43.680 when we try to explain it in terms of macroscopic things. 0:03:43.720 --> 0:03:45.960 We try to get intuitive handle on it, and so 0:03:46.000 --> 0:03:48.440 it just shows us that the world is so different 0:03:48.520 --> 0:03:50.640 from the world that we actually understand. I guess my 0:03:50.720 --> 0:03:52.720 question annially, is am I going to spend this episode 0:03:52.760 --> 0:03:55.320 complaining about the naming of this effect? Like is this 0:03:55.440 --> 0:03:59.160 really like a tunnel like every other episode, like every 0:03:59.240 --> 0:04:04.760 other episode out of this podcast? Um? Probably? Yes, Probably, UM, 0:04:04.960 --> 0:04:06.920 spend most of the time you complenty with the name 0:04:07.000 --> 0:04:09.640 and me trying to argue that the physics version is 0:04:09.680 --> 0:04:12.400 different from the cultural version or whatever, and that there's 0:04:12.440 --> 0:04:16.040 poetry in physics. There is some poetry and physics there's 0:04:16.080 --> 0:04:19.520 also plenty of clumsiness. Now, this is a fascinating topic 0:04:19.600 --> 0:04:22.520 because it's the kind of thing that's really impossible to 0:04:22.600 --> 0:04:26.159 explain in terms of classical analogs. You know, things that 0:04:26.200 --> 0:04:29.359 you have intuition for particles and waves and bowling balls. 0:04:29.800 --> 0:04:32.760 It's just something that those things can't do, and so 0:04:32.839 --> 0:04:35.280 it opens the door in our minds. It says the 0:04:35.400 --> 0:04:38.640 universe is weirder than you will ever understand, right, And 0:04:39.360 --> 0:04:41.240 that's the kind of thing that got me into physics, 0:04:41.240 --> 0:04:45.640 you know, the revealing that the universe operates under rules, 0:04:45.680 --> 0:04:48.520 but rules that are weird and in some ways alien 0:04:48.720 --> 0:04:50.760 to the to the world that we know. So, yeah, 0:04:50.800 --> 0:04:53.640 it's got two cool words, quantum and tunneling, and so 0:04:53.800 --> 0:04:55.440 I don't know, that makes me think of like a 0:04:55.800 --> 0:04:59.279 something that drills deep down into the quantum realm or 0:04:59.440 --> 0:05:03.159 you know, something that um lets me like travel to 0:05:03.240 --> 0:05:06.400 the quantum realm or something. What is the what is 0:05:06.440 --> 0:05:08.480 the quantum realm? Where is it? How do you get there? 0:05:08.640 --> 0:05:11.040 That's a whole other podcast episode. It's on the Admin 0:05:11.120 --> 0:05:13.360 Movies obviously. All right, well, we'll have to have Paul 0:05:13.440 --> 0:05:16.400 Rudd on as a guest, and uh and Michael Douglas 0:05:16.440 --> 0:05:18.440 since he's professor PIM. I mean, they can explain to 0:05:18.480 --> 0:05:21.279 us all about the PM particles in the quantum realm. 0:05:21.279 --> 0:05:23.760 But you're at quantum tunneling does have a really cool 0:05:23.800 --> 0:05:27.320 sound to it, and so, as usual, I was wondering, like, 0:05:27.400 --> 0:05:29.600 what do people know about quantum tunneling to people. Does 0:05:29.640 --> 0:05:32.040 everybody already understand this and we don't need to explain it? 0:05:32.200 --> 0:05:35.039 Or is it a huge mystery to people have misconceptions? 0:05:35.560 --> 0:05:37.719 And so I walked around campus a you see Irvine, 0:05:38.120 --> 0:05:41.400 and it costed friendly strangers to ask them. So before 0:05:41.400 --> 0:05:43.600 you listen to these answers, think about it for a second. 0:05:43.680 --> 0:05:46.799 If somebody asked you randomly on the street and didn't 0:05:46.800 --> 0:05:49.320 give you the option of googling it, would you know 0:05:49.520 --> 0:05:53.160 what quantum tunneling is? That's right, no googling allowed. Here's 0:05:53.160 --> 0:05:55.560 what people had to say. Do you know what quantum 0:05:55.640 --> 0:05:59.000 tunneling is? Um? I don't know what makes me think 0:05:59.040 --> 0:06:01.000 of like the mountain since Wwitzerland and how they have 0:06:01.080 --> 0:06:03.320 to like build tunnels underneath them and then that's where 0:06:03.360 --> 0:06:06.560 certain is. So there's probably some quantum tunneling down there. 0:06:06.920 --> 0:06:10.039 I have Can you explain it? No? I have not? 0:06:10.800 --> 0:06:15.200 No um not really probably not. Well, I've heard, I've 0:06:15.240 --> 0:06:17.320 heard of it, but I'm not sure what the concept is. 0:06:17.760 --> 0:06:20.480 I don't know what's that mean? No, I have not, 0:06:20.760 --> 0:06:22.480 I do not. I have not heard of that. I 0:06:22.960 --> 0:06:24.880 have not. Something has to do with light and like hell, 0:06:24.960 --> 0:06:27.919 the transflor on something like that alright, not a popular 0:06:28.120 --> 0:06:31.440 or familiar topic, but half the people had never heard 0:06:31.440 --> 0:06:34.920 of it. That's right. Um, people were pretty clueless, though 0:06:34.960 --> 0:06:38.520 some people were pretty creative. I love the answer about 0:06:38.720 --> 0:06:42.120 tunnels near certain that was very creative. Yeah, they said 0:06:42.200 --> 0:06:45.920 that made them think of the tunnels underneath the mountains 0:06:46.000 --> 0:06:49.920 of Switzerland, because Switzerland has tunnels and they do physics experiments. 0:06:50.000 --> 0:06:53.880 So therefore two and two together. Obviously that's what a 0:06:53.960 --> 0:06:57.040 quantum tunnel is. It's not a terrible answer, like, you know, 0:06:57.320 --> 0:06:59.120 what kind of tunnel do you need to build a 0:06:59.200 --> 0:07:02.159 large age uncle it? You know, hey, a quantum tunnel, right, 0:07:02.240 --> 0:07:04.719 a tunnel in which you do quantum experiments. That's not 0:07:04.800 --> 0:07:07.200 a terrible answer. Maybe that's more of a quantum ingunnel. 0:07:08.000 --> 0:07:10.840 And the truth is the Swiss are awesome in building tunnels, 0:07:10.840 --> 0:07:12.280 and they could sort of have to be because they're 0:07:12.320 --> 0:07:15.400 surrounded by mountains, but they really are world class in 0:07:15.800 --> 0:07:18.920 building these tunneling machines. And so it's still surprised that 0:07:18.960 --> 0:07:21.320 the large Hadron collider is in Switzerland because that really 0:07:21.360 --> 0:07:24.320 is the best place to build tunnels for your quantum experiments. Yea, 0:07:24.360 --> 0:07:26.080 they have to dig all those tunnels to burial, that 0:07:26.240 --> 0:07:29.760 money that they keep for rich people. Oh, that illicitly 0:07:30.080 --> 0:07:32.120 elicitly gotten gold. You know, hey, what do you mean 0:07:32.160 --> 0:07:36.040 I have a Swiss bank account in my dream? Well, 0:07:36.080 --> 0:07:39.840 you know, true story. I discovered, um by opening her mail, 0:07:39.920 --> 0:07:44.480 that my wife has a Swiss bank account. She has 0:07:44.480 --> 0:07:47.400 a retirement plan in Switzerland. All right, what what other 0:07:47.440 --> 0:07:52.120 secrets have you covered by opening her mail? The best 0:07:52.120 --> 0:07:54.000 part of the story is that she didn't know she 0:07:54.040 --> 0:07:56.840 had a Swiss bank account until I told her. Feels 0:07:56.880 --> 0:08:00.280 like a Born movie here. No, it has actually pretty 0:08:00.320 --> 0:08:03.360 mundate explanation. When we were in Switzerland so I could 0:08:03.360 --> 0:08:05.520 work on the large age on collider, she had a 0:08:05.600 --> 0:08:09.040 job working in research in Switzerland, and unbeknownst to her, 0:08:09.400 --> 0:08:11.680 they opened an account in her name and deposited some 0:08:11.800 --> 0:08:14.960 retirement funds there and uh, and then we discovered it 0:08:15.040 --> 0:08:17.120 later and like, oh my gosh, look, Katrina has a 0:08:17.160 --> 0:08:19.640 Swiss Bank acount with money in it. That's how banking 0:08:19.680 --> 0:08:22.880 work in Switzerland. They just give it away. Yeah exactly. So, um, yeah, 0:08:22.920 --> 0:08:25.280 she has a Swiss Bank account, but I don't. Well anyway, 0:08:25.320 --> 0:08:28.400 so people were not very familiar with quantum tunneling, which 0:08:28.440 --> 0:08:30.480 means that hey, we can. We can talk about it 0:08:30.520 --> 0:08:34.040 on the podcast. That's right, It's an awesome topic to demystify. 0:08:34.320 --> 0:08:36.360 First we'll explain what it is, and then we'll explain 0:08:36.400 --> 0:08:39.760 how it works and how it's not teleportation. Right, That's 0:08:39.800 --> 0:08:42.640 my big question is is it like teleportation? Is it 0:08:42.800 --> 0:08:46.720 associated with teleportation? Can we teleport with quantum tunneling? All right? 0:08:46.800 --> 0:08:49.320 Start us off, Daniel, What how would you describe what 0:08:49.400 --> 0:08:51.800 quantum tunneling is? So I think the best place to 0:08:51.840 --> 0:08:54.840 start is to sort of warm up our intuition, Like, 0:08:54.920 --> 0:08:57.960 let's think about this problem using things were familiar with, 0:08:58.120 --> 0:09:00.920 and then we can make the analogy to the quantum 0:09:01.000 --> 0:09:03.280 version and we can understand where that breaks down, like 0:09:03.440 --> 0:09:06.000 where our intuition goes wrong. So let's start with our 0:09:06.000 --> 0:09:08.680 intuition and the sort of the problem. The kind of 0:09:08.679 --> 0:09:11.360 problem we're trying to describe is sort of like playing 0:09:11.360 --> 0:09:15.719 with a bowling ball inside an empty swimming pool. This 0:09:15.880 --> 0:09:19.040 is still for the bowling ball and swimming pool. Yeah, 0:09:19.120 --> 0:09:21.200 I mean, isn't that a familiar thing when you see 0:09:21.200 --> 0:09:23.520 a swimming, empty swimming pool and you think, I wonder 0:09:23.559 --> 0:09:25.640 what would happen if I threw a bowling ball in there? Well, 0:09:25.720 --> 0:09:28.480 let's give our listeners just a quick idea of what 0:09:28.520 --> 0:09:31.040 we're talking about. So, quantum tunneling is kind of this 0:09:31.120 --> 0:09:35.040 idea that a particle or or in the usual case 0:09:35.040 --> 0:09:38.480 it's an electron, it consider be on one side of 0:09:38.480 --> 0:09:41.439 a barrier in one moment and then the next moment 0:09:41.480 --> 0:09:43.559 it's on the other side of the barrier. Right. The 0:09:43.679 --> 0:09:46.080 generally they have quantum tunneling is that it's really hard 0:09:46.120 --> 0:09:48.880 to keep electrons in a little trap or in a 0:09:48.880 --> 0:09:51.760 little hole. That they really they're hard to pin down. 0:09:51.760 --> 0:09:53.720 And people are probably familiar with that because the Heisenberg 0:09:53.760 --> 0:09:56.760 and certainty principle, like, you know, you can't really isolate 0:09:56.800 --> 0:10:01.000 a quantum particle in one little spot in space very long, 0:10:01.480 --> 0:10:03.440 but you know if you try to do it, then 0:10:03.480 --> 0:10:05.360 you know eventually it's going to leak out. And and 0:10:05.400 --> 0:10:08.120 the point of quantum tunneling is that electrons can build 0:10:08.120 --> 0:10:12.040 these tunnels or burrow through these barriers to to you know, 0:10:12.080 --> 0:10:14.640 adjacent little holes or adjacent little wells. So that's the 0:10:14.640 --> 0:10:17.160 idea is that it's like you have a particle, there's 0:10:17.160 --> 0:10:20.200 a barer in front of it, and at some point 0:10:20.720 --> 0:10:23.400 it just moves to the other side of the barrier. Yeah, exactly. 0:10:23.400 --> 0:10:24.800 You can see it on one side of the barrier, 0:10:25.240 --> 0:10:27.200 and even if it doesn't have enough energy to get 0:10:27.240 --> 0:10:29.880 over the barrier, sometimes you see it on the other 0:10:29.960 --> 0:10:31.840 side and you have to ask, like, how did it 0:10:31.840 --> 0:10:34.920 get here? Right, right, like spontaneously just appears on the 0:10:34.960 --> 0:10:37.400 other side or what. Yeah, well, sometimes on one side 0:10:37.400 --> 0:10:38.599 and then it's on the other side, and then it 0:10:38.640 --> 0:10:41.079 goes back right, And there's a lot of interesting stuff 0:10:41.120 --> 0:10:43.720 there about like, um, you know, if the particle was 0:10:43.800 --> 0:10:46.440 here and then later it's there, how did it get 0:10:46.520 --> 0:10:49.360 from one place from the first place to the next place. 0:10:49.840 --> 0:10:52.560 Right In your mind, you're used to things. If it's 0:10:52.600 --> 0:10:54.600 in one spot and then later it's in another spot, 0:10:54.600 --> 0:10:57.160 you imagine it took a path from one spot to 0:10:57.200 --> 0:10:59.600 the other spot. Right, That's the way classical things work, 0:10:59.640 --> 0:11:03.920 based balls, hamsters, whatever. But that's not true for quantum objects. 0:11:03.960 --> 0:11:06.400 Quantum bologists are here and then later they're there, and 0:11:06.440 --> 0:11:09.800 there iss not necessarily any path between those places that 0:11:09.840 --> 0:11:12.800 the particle took. It didn't move, It just was here 0:11:12.920 --> 0:11:16.400 and then it was there. Yeah, it's frustrating because quantum 0:11:16.400 --> 0:11:20.640 particles don't have this underlying hidden truth, right, it's not 0:11:20.720 --> 0:11:24.160 like there is a true story about where the particle 0:11:24.280 --> 0:11:26.120 was at every moment and we just don't know it. 0:11:26.120 --> 0:11:29.560 It doesn't have that story. That story doesn't exist. You know, 0:11:29.679 --> 0:11:32.200 it's it's it's in a location only when you ask 0:11:32.280 --> 0:11:34.480 where is it? And then it's in a location later 0:11:34.559 --> 0:11:36.960 when you ask where is it? You're saying it particles 0:11:37.000 --> 0:11:39.880 don't really have a here or there. It's like they're 0:11:39.960 --> 0:11:42.120 around here. Well, they have a here, Like at some 0:11:42.200 --> 0:11:44.120 moment you can say it's here, and another moment you 0:11:44.160 --> 0:11:47.560 can say it's there. But you can't connect the dots, right, 0:11:47.960 --> 0:11:50.920 You can't say that there must be a line between 0:11:50.920 --> 0:11:54.120 those two dots and the particle took that line or there. 0:11:54.160 --> 0:11:56.720 There doesn't have to necessarily be aligned. It's just here 0:11:56.760 --> 0:11:59.280 and then later it's there. It's you know, it's like 0:11:59.400 --> 0:12:04.720 um frames in a movie, but without the intervening um connections. 0:12:04.920 --> 0:12:06.920 Like if you're watching a movie, you know, the person 0:12:06.960 --> 0:12:09.120 would be standing here, and then suddenly they'd be standing 0:12:09.120 --> 0:12:11.440 over there, and then they'll be studying this other part 0:12:11.440 --> 0:12:16.320 of the frame, right, almost like they were teleporting between spots. 0:12:18.200 --> 0:12:20.559 I was just going to say that that's not teleportation. 0:12:20.640 --> 0:12:22.800 Right when you're watching a movie, and you know, and 0:12:22.840 --> 0:12:25.200 you watch this frame by frame, you don't imagine they're 0:12:25.200 --> 0:12:27.560 teleporting from frame to frame. Right, you're just saying, well, 0:12:27.720 --> 0:12:29.400 I know he's here in this frame and he's there 0:12:29.400 --> 0:12:32.439 at that frame. Right. That's not teleportation. You're saying. A 0:12:32.480 --> 0:12:35.480 quantum particle doesn't have a path between these two things. 0:12:35.480 --> 0:12:37.240 It's like, if you ask you where it is, it'll 0:12:37.280 --> 0:12:39.520 just kind of pop around all over the place. Yeah, 0:12:39.559 --> 0:12:41.199 you can ask a particle where it is and it 0:12:41.240 --> 0:12:43.640 will answer, right, and then later you can ask it 0:12:43.640 --> 0:12:46.120 where it is and it will answer, But you don't 0:12:46.160 --> 0:12:49.560 necessarily know anything about where it is in the intervening time, 0:12:49.600 --> 0:12:53.120 and you can't assume that there's some classical path. You know, 0:12:53.160 --> 0:12:55.960 if you if you ask where's my baseball and what's 0:12:56.000 --> 0:12:58.920 his velocity? Right, then you can actually predict exactly where 0:12:58.920 --> 0:13:01.319 it's going to go any moment. And so it has 0:13:01.360 --> 0:13:04.000 this thing we call the classical path. It's position and 0:13:04.080 --> 0:13:07.000 velocity at any point in time, and when you're looking 0:13:07.040 --> 0:13:09.000 at it, you're just sort of sampling that. Right. But 0:13:09.040 --> 0:13:11.560 for a quantum particle that doesn't exist, you can ask 0:13:11.559 --> 0:13:14.079 where is it? And you're gonna ask where is it later? Right? 0:13:14.320 --> 0:13:16.560 But you can't connect the dots between those two and 0:13:16.600 --> 0:13:19.360 assume that there's a path that it's following. Well, this 0:13:19.440 --> 0:13:35.800 is a perfect point to take a break, Okay. So 0:13:35.880 --> 0:13:38.920 then the idea of quantum tunneling is that a particle 0:13:39.840 --> 0:13:41.720 is on one side of a wall or a barrier, 0:13:41.880 --> 0:13:44.800 and then the next instant it's in the other side 0:13:44.800 --> 0:13:46.560 of the barrier. And so that what we want to 0:13:46.559 --> 0:13:49.160 do here today is sort of explain how that happens 0:13:49.320 --> 0:13:51.800 and why it's not teleportation. Exactly how does that happened 0:13:52.080 --> 0:13:54.960 and what does it mean and why it's not teleportation. 0:13:55.000 --> 0:13:57.080 And so you you think a great way to think 0:13:57.320 --> 0:13:59.680 get into this topic is to think about bowling balls. 0:13:59.720 --> 0:14:02.560 And yeah, well, I mean, what is a barrier after all? Right, 0:14:02.559 --> 0:14:05.440 Like I think people think about electrons is tiny little balls. 0:14:05.640 --> 0:14:07.560 So I was thinking about let's use a bowling ball 0:14:07.600 --> 0:14:11.240 because that's macroscopic and what is really a barrier? Right, 0:14:11.240 --> 0:14:12.679 I mean people might be thinking like, what kind of 0:14:12.720 --> 0:14:15.640 barriers are we talking about? And so let's imagine a 0:14:15.679 --> 0:14:19.840 macroscopic barrier, like a familiar one. Right, You're the bottom 0:14:19.840 --> 0:14:21.840 of swimming pool with a bowling ball. By the way, 0:14:21.920 --> 0:14:24.720 this is amazing video of a guy. This what inspired 0:14:24.760 --> 0:14:26.600 me is this amazing video online of a guy with 0:14:26.640 --> 0:14:28.520 the bowling ball in a swimming pool and he can 0:14:28.560 --> 0:14:31.160 do these hilarious tricks where he puts like the pins 0:14:31.200 --> 0:14:33.240 behind him and he rolls the bowling ball and it 0:14:33.280 --> 0:14:37.080 does these crazy moves and he knocks off all the pins. Anyway, 0:14:37.200 --> 0:14:39.400 so you're the bottom of the swimming pool with the 0:14:39.400 --> 0:14:41.400 bowling ball, right, and what happens you just put it down. 0:14:41.560 --> 0:14:44.000 Let's make it clear the pool is empty. I'm not 0:14:44.120 --> 0:14:49.200 drowning here, I'm not empty swimming pool. I'm not holding 0:14:49.440 --> 0:14:51.720 onto his heavy ball. And and then sitting at the 0:14:51.720 --> 0:14:55.800 bar of gear does not make this anymore complicated. Yeah, 0:14:55.880 --> 0:14:58.080 it's an empty swimming pool with a bowling ball. But 0:14:58.200 --> 0:14:59.800 let's also make it clear it's one of these swimming 0:14:59.800 --> 0:15:02.800 pool is that it has a curved floor, right, like 0:15:02.840 --> 0:15:05.320 a bowl shaped floor, right like if if it's a 0:15:05.360 --> 0:15:09.160 swimming pool with straight edges at the bottom, this is 0:15:09.200 --> 0:15:11.520 not going to work, that's right. Also, there's no like 0:15:11.680 --> 0:15:15.680 chain saws or you know, traps or you know, rabbit 0:15:15.720 --> 0:15:17.920 hamsters or anything else in the swimming pool. Just you know, 0:15:18.000 --> 0:15:20.120 to be clear, just just the bowling ball in an 0:15:20.160 --> 0:15:22.960 empty curved pool, you know, or if it's easier for you, 0:15:23.000 --> 0:15:25.320 imagine a grape in the bottom of a bowl or whatever. 0:15:25.520 --> 0:15:27.720 But the point is what happens when you put the 0:15:27.720 --> 0:15:29.680 bowling ball at the bottom of the swimming pool. It 0:15:29.760 --> 0:15:32.400 just sits there, right, It doesn't leave. You're never going 0:15:32.440 --> 0:15:35.440 to find it in your neighbor's empty swimming pool, right, 0:15:35.560 --> 0:15:38.200 It's always going to be in that pool. And the 0:15:38.320 --> 0:15:40.880 barrier in this case is the edge of the swimming pool. 0:15:40.920 --> 0:15:42.200 You mean, like, if you don't touch it, if you 0:15:42.240 --> 0:15:44.200 don't push it, if the wind doesn't blow, it is 0:15:44.240 --> 0:15:46.480 just going to stay there. That's right exactly. And you 0:15:46.560 --> 0:15:48.680 expected to stay there. You don't expect to come by 0:15:48.720 --> 0:15:51.320 one day and find it in your neighbor's swimming pool. Right. 0:15:51.520 --> 0:15:53.680 It is that if something does disturb it, like a 0:15:53.800 --> 0:15:56.160 raccoon comes by and pushes it, it's just going to 0:15:56.360 --> 0:15:59.080 roll back down to the bottom of the pool again. Right, 0:15:59.080 --> 0:16:01.480 that's kind of the idea. That's right exactly, because the 0:16:01.560 --> 0:16:04.080 walls of the pool are the barrier, right, That's where 0:16:04.080 --> 0:16:06.880 we talk about. It's a potential barrier. And if a 0:16:06.960 --> 0:16:09.520 raccoon comes and pushes it, you know, and he pushes it, 0:16:09.680 --> 0:16:11.800 you know, as hard as a raccoon can. Then it's 0:16:11.800 --> 0:16:13.840 gonna roll up, and then it's gonna roll back down, 0:16:13.840 --> 0:16:16.080 and it might roll back up the other side, but 0:16:16.120 --> 0:16:20.120 it's never gonna roll higher than it then it went originally, Right, 0:16:20.400 --> 0:16:23.000 It's just gonna eventually relax down to the bottom of 0:16:23.000 --> 0:16:25.680 the swimming pool. And so if you don't give it 0:16:25.800 --> 0:16:28.560 enough energy to go over the lip, then it's trapped 0:16:28.600 --> 0:16:30.800 in the pool. Right, It's never going to get out 0:16:30.800 --> 0:16:33.320 of the pool unless it has enough energy to go 0:16:33.480 --> 0:16:35.760 up and over the edge of the swimming pool, right, 0:16:35.800 --> 0:16:38.880 And so that's the barrier, like that's the wall, yeah, exactly, 0:16:38.880 --> 0:16:41.400 And your intuition says it's trapped, right, if you don't 0:16:41.400 --> 0:16:45.000 give enough energy, it's never ever, ever, ever, ever, ever 0:16:45.040 --> 0:16:47.760 ever ever going to end up in your neighbor swimming pool, right, 0:16:47.760 --> 0:16:50.040 that's where your intuition says, right, unless there are some 0:16:50.120 --> 0:16:53.160 really strong raccoons. But that's what different. I don't know 0:16:53.240 --> 0:16:54.920 what kind of neighborhood this is with all these empty 0:16:54.920 --> 0:16:59.120 swimming pools and like tough gangs of raccoons pushing bowling balls. 0:16:59.160 --> 0:17:01.880 But we're to get out quite the science fiction dystopia here. 0:17:02.120 --> 0:17:04.359 But Yeah, you don't expect it to ever be able 0:17:04.400 --> 0:17:07.160 to get out of the pool by itself. That's right, 0:17:07.200 --> 0:17:10.720 exactly that barrier you can consider it to be perfect. Right. 0:17:10.880 --> 0:17:13.800 The only way um to the next swimming pools to 0:17:13.800 --> 0:17:16.080 go over the barrier. Right, You can never go through 0:17:16.160 --> 0:17:18.040 the barrier. These raccoons are not tough enough to throw 0:17:18.080 --> 0:17:21.240 the bowling ball like and crush the ground and get 0:17:21.240 --> 0:17:24.560 through it. Right. Wait, what are their Swiss raccoons and 0:17:24.600 --> 0:17:31.000 they dig a tunnel? Yeah, or they're like superhero raccoons 0:17:31.040 --> 0:17:33.520 like um in one of those Marvel movies system, isn't 0:17:33.520 --> 0:17:35.320 there some super raccoon or is he just look like 0:17:35.359 --> 0:17:37.280 a raccoon and he's not actually a raccoon and never 0:17:37.320 --> 0:17:41.160 actually in genetically modified raccoon aliens that look like human 0:17:41.240 --> 0:17:43.360 like Earth raccoons And never quite figured that one out. 0:17:43.440 --> 0:17:50.680 But we digress, we do, we do digress. That's the analogy. 0:17:50.800 --> 0:17:53.280 Right now, Think instead of the bowling ball, think of 0:17:53.320 --> 0:17:56.440 an electron. And then when we talk about barriers, we're 0:17:56.440 --> 0:18:00.480 talking about you know, barriers to that electron. So maybe 0:18:00.760 --> 0:18:03.760 made by other particles, you know, protons or something that 0:18:03.800 --> 0:18:06.000 would repel it, right, something that would you would build 0:18:06.000 --> 0:18:08.960 to try to keep the electron localized like a little trap, 0:18:09.320 --> 0:18:12.879 like a like a little magnetic field. Maybe he is 0:18:12.960 --> 0:18:16.200 keeping it trapped or something. Yeah, a little magnetic field 0:18:16.280 --> 0:18:19.080 or electrostatic potential or something anything you can do to 0:18:19.080 --> 0:18:21.360 trap an electron. And people do this, right, they want 0:18:21.359 --> 0:18:24.720 to study individual electrons or individual ions. They build atom 0:18:24.760 --> 0:18:27.800 traps the pretty cool um and so people actually do this. 0:18:28.080 --> 0:18:30.879 But it's also a good case study for quantum mechanics 0:18:30.920 --> 0:18:33.200 because it helps us think about how these things work 0:18:33.240 --> 0:18:35.200 and don't work. So it's a it's a very popular 0:18:35.240 --> 0:18:38.959 sort of junior level quantum mechanics problem in college. So 0:18:39.000 --> 0:18:42.240 what happens. You put the electron in this little well, right, 0:18:42.280 --> 0:18:43.920 and it's like a barry. It's like a swimming pool, 0:18:44.440 --> 0:18:47.359 and you think, if the electron doesn't have enough energy 0:18:47.400 --> 0:18:49.800 to go over the edge, then it's trapped, right, just 0:18:49.880 --> 0:18:52.000 like the bowling ball. If it doesn't have enough energy, 0:18:52.080 --> 0:18:54.920 how could it ever get into the neighboring swimming pool. Well, 0:18:54.920 --> 0:18:57.760 the thing you find is that even though it doesn't 0:18:57.800 --> 0:19:01.040 have enough energy, sometimes it appears is in your neighbor's 0:19:01.040 --> 0:19:04.760 swimming pool. Like it gets through that barrier. It appears 0:19:05.040 --> 0:19:07.680 in the adjacent well. Like if you have a series 0:19:08.000 --> 0:19:11.160 of these um potential wells, you know, these these little 0:19:11.200 --> 0:19:13.720 traps made for electrons, and you put it in one, 0:19:14.040 --> 0:19:15.600 you come back the next day and find it in 0:19:15.640 --> 0:19:18.119 the next one. Even though it didn't have enough energy 0:19:18.160 --> 0:19:21.120 to go over that barrier, even though it was trapped 0:19:21.119 --> 0:19:25.119 by a magnetic field, it somehow slipped out, yes, exactly, 0:19:25.840 --> 0:19:28.719 And so that's the that's what we call quantum tunneling. Right, 0:19:28.800 --> 0:19:31.800 how did it get through the barrier? In principle, the 0:19:31.840 --> 0:19:35.639 barrier should be should bar it, right, that's what barriers do. 0:19:35.720 --> 0:19:38.280 It should borrow it from passing, just the way you're 0:19:38.440 --> 0:19:40.760 the ground does, the end of the swimming pool does. 0:19:41.119 --> 0:19:44.800 So the question is why does an electron not get stuck, right, 0:19:44.840 --> 0:19:47.000 because if it tried to move, the field would push 0:19:47.000 --> 0:19:50.000 it back into the trap. But somehow it's able to 0:19:51.040 --> 0:19:55.080 live out or create a tunnel exactly exactly. And your 0:19:55.080 --> 0:19:58.720 instinct might be to say, well, maybe like momentarily goes 0:19:58.800 --> 0:20:01.600 over the barrier, like you know, I don't know Heisenberg 0:20:01.680 --> 0:20:04.879 Uncertainty blog blog. You know, maybe it borrows a little energy, 0:20:04.960 --> 0:20:08.639