WEBVTT - Why can't two electrons be in the same place? 0:00:08.480 --> 0:00:11.600 Hey, Joe, if you could only eat one flavor of 0:00:11.640 --> 0:00:14.560 ice cream for the rest of your life, would it 0:00:14.600 --> 0:00:17.840 be chocolate or vanilla? Who do I have to choose? 0:00:18.440 --> 0:00:21.720 Can I do like a quantum superposition of the tooth flavors? No, 0:00:21.920 --> 0:00:24.919 you are not a quantum Jorge, so you can only 0:00:24.960 --> 0:00:28.680 be in vanilla or chocolate. States It's a classic dilemma 0:00:28.680 --> 0:00:31.640 of classical physics, isn't it is? And so does your 0:00:31.640 --> 0:00:35.760 wave function collapse to vanilla or chocolate? Obviously vanilla my 0:00:35.800 --> 0:00:38.639 favorite flavor. Are you telling me for real you'd give 0:00:38.680 --> 0:00:41.680 up chocolate ice cream forever? What if I break the 0:00:41.760 --> 0:00:44.519 loss of physics? Can I do something like a swirl? 0:00:44.600 --> 0:00:46.239 Then you go to physics jail whether they don't have 0:00:46.280 --> 0:00:49.320 either flavor of ice cream? It haves swirls in physics jail, 0:00:50.440 --> 0:00:52.159 not even for my last meal. All they have in 0:00:52.200 --> 0:00:55.520 physics jail is physics homework problems. That seems a little inhumane, 0:00:56.120 --> 0:01:13.280 the ice cream part, not the homework part. I am 0:01:13.319 --> 0:01:16.200 more hammy cartoonist and the creator of PhD comics. Hi, 0:01:16.319 --> 0:01:19.119 I'm Daniel. I'm a particle physicist and a professor at 0:01:19.240 --> 0:01:22.440 UC Irvine, And I choose the chocolate ice cream in 0:01:22.640 --> 0:01:28.000 one hundred out of one hundred multiverses. Big fan of chocolate, huh, 0:01:28.080 --> 0:01:31.040 there's just no comparison. I mean, chocolate is delicious, but 0:01:31.120 --> 0:01:34.640 chocolate ice cream, it just elevates it beyond understanding, No, 0:01:34.840 --> 0:01:36.679 I think. I guess My question is when you say 0:01:36.760 --> 0:01:38.360 chocolate I thing for the rest of your life. Do 0:01:38.360 --> 0:01:41.119 you mean like you only get to eat chocolate ice 0:01:41.160 --> 0:01:44.679 cream for all your meals? Or is this like only 0:01:44.720 --> 0:01:47.120 for desserts subtimes? I think even I would get tired 0:01:47.160 --> 0:01:50.440 of chocolate ice cream if I ate nothing but that breakfast, 0:01:50.560 --> 0:01:53.520 ludge and dinner, eventually it would get old. Though. You 0:01:53.560 --> 0:01:56.160 know this milk chocolate ice cream is dark chocolate ice cream. 0:01:56.320 --> 0:01:59.080 There's chocolate and salt. There are lots of variations there. 0:01:59.080 --> 0:02:01.160 But that's what I was going to ask, Like what 0:02:01.320 --> 0:02:04.200 kind of chocolate? There's so many the flavors to choose from. Yeah, 0:02:04.280 --> 0:02:07.680 and chocolate from all around the world. You know, Madagascar chocolate, 0:02:07.720 --> 0:02:10.840 and then it's whale and chocolate. They're all subtly different. Now, 0:02:10.840 --> 0:02:14.120 what's your stand on Like chips like chunks of chocolate 0:02:14.120 --> 0:02:16.600 in your ice cream? Honestly, I think that ruins the texture. 0:02:16.639 --> 0:02:19.440 You know, a frozen blob. It's like chewing on a pebble, 0:02:19.480 --> 0:02:22.760 Like nobody wants to eat rocks, right, right, right, So 0:02:22.919 --> 0:02:25.760 you're you're against some chocolate ice cream. I'm saying chocolate 0:02:25.840 --> 0:02:29.520 chunks ruined the chocolate ice cream experience. Let's just have 0:02:29.600 --> 0:02:31.880 pure ice cream and not chunks. But then now you've 0:02:31.880 --> 0:02:34.360 got to define a size limit, like what sized limit 0:02:34.400 --> 0:02:38.840 of chocolate particle are you willing to tolerate? Chocolate ice 0:02:38.880 --> 0:02:42.799 cream is fundamental, man, It's not composite. It's so important 0:02:42.840 --> 0:02:45.480 to the universe. There's a chocolate ice cream field that 0:02:45.560 --> 0:02:48.960 permeates the whole universe. I see, I see, But I mean, 0:02:49.000 --> 0:02:51.680 I'm sure there's this size of chocolate particle that will 0:02:52.080 --> 0:02:54.120 fly under your radar. Yeah, you know. I think this 0:02:54.240 --> 0:02:56.840 calls from more experiments for sure. And I actually did 0:02:56.880 --> 0:02:59.560 a little Twitter experiment myself. I was wondering if our 0:02:59.600 --> 0:03:02.960 support orders sided with the obviously correct me on the 0:03:03.040 --> 0:03:06.680 chocolate camp or the obviously incorrect you on the vanilla camp. 0:03:06.960 --> 0:03:08.680 So I went out into the little pole to ask 0:03:08.760 --> 0:03:12.360 people chocolate versus vanilla? But did you say chocolate vanilla? What? 0:03:12.520 --> 0:03:16.120 I didn't? I just said chocolate versus vanilla? Important science question. 0:03:16.560 --> 0:03:19.840 Oh yeah, it sounds like an ill designed experiment, Danny, 0:03:20.000 --> 0:03:22.240 I would expect more from a scientist. Well, I didn't 0:03:22.280 --> 0:03:24.160 want to be over specific. I wanted a sample, you know, 0:03:24.240 --> 0:03:29.880 people's general vibe about these flavors, the word chocolate and vanilla. Yeah, exactly. 0:03:30.040 --> 0:03:31.919 It wasn't a question of like, which one you preferred 0:03:31.960 --> 0:03:35.720 to spell? Obviously, it's about the flavor. And anyway, the 0:03:35.760 --> 0:03:38.840 Internet came down on my side, chocolate fifty eight percent 0:03:38.880 --> 0:03:42.920 to vanilla forty two percent. Wow, that's relatively closed, I 0:03:42.920 --> 0:03:45.200 would say, don't you think I actually was surprised. I 0:03:45.200 --> 0:03:47.000 thought chocolate was going to blow vanilla out of the 0:03:47.040 --> 0:03:49.600 water a little bit more. Here you go, Hey, you 0:03:49.640 --> 0:03:52.680 know I'll take a twenty point differential. Well, we all 0:03:52.720 --> 0:03:55.680 know that whatever the Internet things is the best choice 0:03:55.800 --> 0:03:58.800 for anything. Well, I would say whatever our listeners thing 0:03:59.000 --> 0:04:01.800 is definitely you know, sampling the truth of the universe. 0:04:02.040 --> 0:04:03.920 I see, did you have everyone to sign a little 0:04:04.040 --> 0:04:07.640 like waiver to testify that they're listeners? This is getting 0:04:07.640 --> 0:04:09.680 more unscientific by the moment. By the way, they all 0:04:09.680 --> 0:04:11.640 follow us on Twitter. Why would somebody follow us on 0:04:11.640 --> 0:04:14.280 Twitter and not listen to the podcast that just makes 0:04:14.280 --> 0:04:17.880 no sense exactly. If they're already listening to us in 0:04:17.880 --> 0:04:19.920 our podcast, why would they follow us on Twitter for 0:04:20.120 --> 0:04:23.840 important science questions like chocolate versus Vanilla, the chance to 0:04:23.839 --> 0:04:26.000 weigh in on the ultimate debate in the universe. Well, 0:04:26.040 --> 0:04:27.839 I guess if you'd like to go with the majority, 0:04:28.160 --> 0:04:31.240 you know, the mainstream, I guess that's your thing, right. 0:04:31.320 --> 0:04:33.799 Vanilla is definitely not the boring, middle of the road choice, 0:04:33.880 --> 0:04:37.359 for sure. Vanilla is the rebel choice. Yeah, it's the 0:04:37.520 --> 0:04:41.760 indie minority choice. But anyways, welcome to our podcast Daniel 0:04:41.800 --> 0:04:44.919 and Horry Explain the Universe, a production of iHeartRadio in 0:04:44.960 --> 0:04:48.000 which we appreciate all of the flavors of the universe, 0:04:48.240 --> 0:04:51.360 the quantum, the classical, the things that make sense, the 0:04:51.360 --> 0:04:54.000 things that don't make sense. We blend them all together 0:04:54.160 --> 0:04:57.360 into chunks so tiny and so smooth that you can 0:04:57.400 --> 0:05:01.200 appreciate them without having to chew on a intellectual pebbles. 0:05:01.279 --> 0:05:03.880 It's right because it is a delicious universe, full of 0:05:03.920 --> 0:05:07.640 amazing textures and flavors and temperatures of treats. And so 0:05:07.680 --> 0:05:09.080 there's a lot to talk about it in a lot 0:05:09.120 --> 0:05:11.400 to try to explain to everyone, And there's a wonderful 0:05:11.440 --> 0:05:14.320 and long history of trying to understand the universe, just 0:05:14.360 --> 0:05:16.640 sort of looking at the stuff around us, seeing if 0:05:16.680 --> 0:05:19.920 it makes sense, breaking into smaller pieces and seeing those 0:05:19.960 --> 0:05:23.240 pieces make sense, digging in even deeper to smaller and 0:05:23.480 --> 0:05:27.000 smaller pieces, until eventually we get the stuff that seems 0:05:27.000 --> 0:05:31.120 to follow weird and different rules, rules that surprise and 0:05:31.320 --> 0:05:34.600 confuse us. The universe is full of rules, interesting rules 0:05:34.640 --> 0:05:38.600 that are sometimes helpful, like Newton's laws or general relativity 0:05:38.640 --> 0:05:40.760 by Einstein. But sometimes there are rules that kind of 0:05:40.839 --> 0:05:42.919 don't quite make a lot of sense, at least to 0:05:43.120 --> 0:05:46.640 a human because our tendency is to think about things 0:05:46.680 --> 0:05:48.880 in terms of the things we know. When we discover 0:05:49.040 --> 0:05:51.200 a new object, we think, oh, maybe it's a little 0:05:51.240 --> 0:05:53.000 bit like a grain of sand, or maybe it's a 0:05:53.000 --> 0:05:55.480 little bit like a basketball. Can I apply the rules 0:05:55.520 --> 0:05:57.840 of waves to this thing? Can I apply what I 0:05:57.880 --> 0:06:00.800 know about bananas to this new discovery? So when we 0:06:00.880 --> 0:06:03.800 unearthed quantum particles, our first guests is to think, oh, 0:06:03.839 --> 0:06:06.600 these are like tiny little dots that follow the rules 0:06:06.640 --> 0:06:09.200 of classical physics. Maybe they move through space, they have 0:06:09.279 --> 0:06:12.600 velocity and position, they're just super duper tiny. But what 0:06:12.640 --> 0:06:15.680 we've discovered is that they are not like anything we 0:06:15.760 --> 0:06:18.320 have ever seen before. They're not tiny little dots of 0:06:18.400 --> 0:06:21.800 sand just like baseballs, but much much smaller. They're not 0:06:21.880 --> 0:06:25.240 even just like waves. There's something else, something weird, that 0:06:25.360 --> 0:06:27.800 follows a new set of rules that we have to 0:06:27.800 --> 0:06:30.599 discover and savor. Yeah. I feel like whenever we start 0:06:30.640 --> 0:06:33.279 to talk about things that don't make sense, it probably 0:06:33.320 --> 0:06:36.560 means that we're going to the quantum realm, that we're 0:06:36.600 --> 0:06:38.440 going to talk about quantum things. Yeah, but this is 0:06:38.440 --> 0:06:42.360 our experience every time we extrapolate from our intuitive experience, 0:06:42.480 --> 0:06:45.400 from our understanding of the world around us, not just 0:06:45.440 --> 0:06:47.600 the tiny and the quantum, but also the very very 0:06:47.680 --> 0:06:50.359 big right thinking about the universe as a whole, and 0:06:50.400 --> 0:06:53.440 maybe having an edge or having a beginning. All those 0:06:53.480 --> 0:06:56.919 things defy our understanding because they're not part of our experience, 0:06:57.120 --> 0:06:59.720 so we don't have like a natural vocabulary, a way 0:06:59.760 --> 0:07:02.680 of thinking about them that's comfortable. Instead, we have to 0:07:02.720 --> 0:07:06.000 rely on mathematics to bridge us into a new language, 0:07:06.040 --> 0:07:08.640 a new way of thinking about the world. Yeah, but 0:07:08.680 --> 0:07:10.240 I guess it's part of that is I wonder if 0:07:10.240 --> 0:07:12.960 it's just like the context in which we came up 0:07:13.000 --> 0:07:15.560 in as a species, like our size that we just 0:07:15.600 --> 0:07:18.920 happen to evolve into. Like if we were much much 0:07:18.960 --> 0:07:22.960 tinier as a living thing, you know, maybe the quantum 0:07:23.280 --> 0:07:25.560 rules of the universe would make more sense than the 0:07:25.600 --> 0:07:28.880 classical rules of the universe. I think that's probably true, 0:07:28.960 --> 0:07:32.640 And one day we might meet like microscopic aliens whose 0:07:32.680 --> 0:07:36.000 scientists of all finding quantum mechanics we totally intuitive and 0:07:36.160 --> 0:07:39.240 classical physics to be very very weird. Of course, they 0:07:39.240 --> 0:07:41.360 wouldn't call it classical physics. They would call it like, 0:07:41.600 --> 0:07:44.520 you know, huge physics or something. They would think it's 0:07:44.640 --> 0:07:46.920 very strange that if you take ten to the twenty 0:07:47.000 --> 0:07:50.280 nine quantum particles, they somehow come together to act like 0:07:50.400 --> 0:07:53.480 one big particle. That's an interesting question. I wonder, like, 0:07:53.520 --> 0:07:57.280 what's the smallest living sentient thing you can have? Like 0:07:57.360 --> 0:08:00.160 can you make a being out of straight up of 0:08:00.280 --> 0:08:02.120 a few quarks, you know what I mean? Or the 0:08:02.120 --> 0:08:05.040 strings inside of quarks. It's a really fun question. And 0:08:05.240 --> 0:08:08.560 Max Tegmark, who's a physicist at MIT, has this really 0:08:08.600 --> 0:08:12.160 fun paper about where consciousness comes from, and he thinks 0:08:12.160 --> 0:08:14.520 it's actually a state of matter. We're going to dig 0:08:14.560 --> 0:08:17.320 into it in a future podcast episode. But it might 0:08:17.360 --> 0:08:20.000 be that everything in the universe is aware, and that 0:08:20.120 --> 0:08:24.280 even small combinations of objects can somehow do calculations and 0:08:24.400 --> 0:08:28.440 maybe even be conscious. Dude, they gonna have to smoke 0:08:28.520 --> 0:08:32.959 some special things in order to get into that topic. Bananappeals, 0:08:33.000 --> 0:08:36.360 for sure, Well, the quantum universe is full of interesting 0:08:36.400 --> 0:08:39.600 and weird rules, sometimes rules that don't seem to make sense, 0:08:39.679 --> 0:08:41.640 or that even seem kind of fair, And as we 0:08:41.679 --> 0:08:44.560 explore the quantum universe we discover these rules. A lot 0:08:44.600 --> 0:08:46.720 of the time, these rules are just descriptive. They just 0:08:46.800 --> 0:08:50.280 describe what we see. They don't always fundamentally explain it. 0:08:50.320 --> 0:08:53.160 But sometimes we can actually find a reason for it. 0:08:53.200 --> 0:08:55.280 So that's sort of the strategy is like, look out 0:08:55.280 --> 0:08:57.680 in the universe, see what's going on, see what's not 0:08:57.840 --> 0:09:00.440 going on, so we can understand what the dues and 0:09:00.480 --> 0:09:02.959 don't have other particle world and then try to extract 0:09:03.000 --> 0:09:06.200 from that some fundamental reason why the universe is this 0:09:06.240 --> 0:09:09.200 way and not some other way. So to the other podcast, 0:09:09.240 --> 0:09:17.600 we'll be tackling the question why can't two fermions be 0:09:17.840 --> 0:09:21.120 in the same quantum state. Now, first of all, Danny, 0:09:21.200 --> 0:09:23.120 let me just say that I'm glad you're a bored 0:09:23.160 --> 0:09:25.840 with the faith the quantum realm? Have you sold out 0:09:25.880 --> 0:09:29.760 to the Marvel corporate machine yet to ching? No, it's true. 0:09:29.800 --> 0:09:31.679 I have the new ant Man movie on the brain. 0:09:31.800 --> 0:09:34.440 Can't wait to see it. Oh really, you're excited even 0:09:34.440 --> 0:09:37.080 though they're jumping into the quantum realm and finding all 0:09:37.160 --> 0:09:39.760 kinds of things inside of it. M Yeah, absolutely, I 0:09:39.840 --> 0:09:43.000 like those movies. I mean, they are scientifically mostly nonsense, 0:09:43.040 --> 0:09:46.240 but they also don't take themselves too seriously, and they 0:09:46.240 --> 0:09:48.120 have fun with it, and I think they're really creative. 0:09:48.160 --> 0:09:51.360 The first couple had some really beautiful visuals of like 0:09:51.400 --> 0:09:53.640 what the quantum realm might look like or what it 0:09:53.720 --> 0:09:56.319 might be like to visit the quantum realm, so I 0:09:56.320 --> 0:09:58.160 think they're a lot of fun. Oh wow, I feel 0:09:58.200 --> 0:10:01.440 like you are getting paid by Marvel, right, You're like, 0:10:01.600 --> 0:10:05.800 is this the Daniel? I know what science you like? 0:10:05.960 --> 0:10:08.640 The random use of the word quantum. No, I don't 0:10:08.640 --> 0:10:11.560 only like hard science fiction. I dislike hard science fiction 0:10:11.600 --> 0:10:13.640 that gets it wrong. You know, if you want to 0:10:13.640 --> 0:10:15.840 pretend to be serious about your science and then you 0:10:15.880 --> 0:10:17.720 get it wrong, then you get the merits from me. 0:10:17.760 --> 0:10:19.240 But if you're going to make fun of yourself along 0:10:19.280 --> 0:10:21.280 the way and just have a good time. Then let's 0:10:21.280 --> 0:10:23.400 go for it. Well, in this case, we're asking a 0:10:23.600 --> 0:10:27.000 kind of an interesting question here about the quantum nature 0:10:27.000 --> 0:10:29.560 of things. So why can't two fermions be in the 0:10:29.640 --> 0:10:32.440 same quantum state? No, I imagine this is maybe not 0:10:32.480 --> 0:10:35.360 a question most people have thought about before. This is 0:10:35.400 --> 0:10:38.600 something people run into in high school chemistry when they're 0:10:38.600 --> 0:10:41.760 like learning about electrons and electron orbitals. But it's a 0:10:41.800 --> 0:10:45.760 really deep and important concept in particle physics theory that 0:10:45.880 --> 0:10:48.840 relates to how particles operate, what it means for particles 0:10:48.840 --> 0:10:51.840 to be identical, what it means to like swap particles 0:10:51.840 --> 0:10:54.240 from one state to another. Turns out to be a 0:10:54.240 --> 0:10:57.720 really deep and important concept in particle physics, and something 0:10:57.720 --> 0:10:59.719 a couple of listeners wanted to know more about. How 0:10:59.760 --> 0:11:02.600 does it actually work and why does it happen? Maybe 0:11:02.600 --> 0:11:04.439 it'll be the plot of the next ant Men movie. 0:11:04.520 --> 0:11:06.240 You can't have two ant Men in the same place 0:11:06.240 --> 0:11:10.000 at the same time. Yeah, I think they have multiple 0:11:10.080 --> 0:11:14.400 ones in this latest movie, So maybe that's the plotline 0:11:14.480 --> 0:11:16.360 is toasted, Or maybe it just means ant Man is 0:11:16.360 --> 0:11:19.040 a Boson and not a Fermion, Or maybe he's an 0:11:19.080 --> 0:11:27.440 ant t particle. I wasped right into that was usually 0:11:27.480 --> 0:11:29.200 we were wondering how many people out there had thought 0:11:29.200 --> 0:11:33.360 about this rule that applies to fermions or electrons, and so, 0:11:33.400 --> 0:11:36.400 as usual, Danny went out there to ask the internet, right, 0:11:36.640 --> 0:11:39.960 that's right. Thank you very much to everybody who participates 0:11:40.000 --> 0:11:41.800 for this segment of the podcast, and if you would 0:11:41.800 --> 0:11:45.280 like to share your thoughts for our education and entertainment, 0:11:45.360 --> 0:11:48.120 please don't be shy write to us two questions at 0:11:48.240 --> 0:11:50.800 Daniel and Jorge dot com. So think about it for 0:11:50.800 --> 0:11:54.560 a second. Do you know why two fermions can't be 0:11:54.760 --> 0:11:58.320 in the same quantum state? Here's would be glad to say. 0:11:58.600 --> 0:12:02.360 I'm not sure of the terminology. I think there is 0:12:02.400 --> 0:12:06.239 an exclusion principle something that says that they can't occupy 0:12:06.360 --> 0:12:09.400 the same state or same space. I don't know if 0:12:09.400 --> 0:12:12.800 it's called the poly exclusion principle. I'm not sure. So 0:12:12.840 --> 0:12:17.199 I think the fermions are the force caring ones. Why 0:12:17.240 --> 0:12:19.960 can't they be in the same quantum state? You know, 0:12:20.040 --> 0:12:23.320 maybe they're all entangled with each other and so they 0:12:23.360 --> 0:12:25.920 all have to have like opposing states of some sort. 0:12:26.200 --> 0:12:29.800 I am merely guessing that two fermions cannot have the 0:12:29.800 --> 0:12:34.000 same quantum state because they have different properties. Well maybe 0:12:34.000 --> 0:12:37.120 because they have the same charges, and then they need 0:12:37.160 --> 0:12:41.560 to find more stable spots to be related to some 0:12:41.640 --> 0:12:45.839 other opposite charge particle. I think deferments cannot be in 0:12:45.880 --> 0:12:48.240 the same quint of state for the same reason that 0:12:48.440 --> 0:12:51.880 a magnet cannot have a same pool in booth sides. 0:12:52.640 --> 0:12:57.079 I'm a bit fuzzy on what fermions are, but if 0:12:57.120 --> 0:13:01.360 they can't be in the same quantum state, I think 0:13:01.600 --> 0:13:04.319 it might be to do with the fact that's kind 0:13:04.320 --> 0:13:08.200 of like magnets, where you need in order for them 0:13:08.200 --> 0:13:11.079 to be magnetic, you have to have one pole opposite 0:13:11.080 --> 0:13:13.680 to the other. Something similar like that, where the one 0:13:13.720 --> 0:13:16.800 needs to spin up one needs to spin down. All right, 0:13:17.120 --> 0:13:19.839 A lot of fun answers here. Nobody mentioned Paul Rudd. 0:13:21.320 --> 0:13:23.320 Nobody else out there is a shill from Marble like 0:13:23.400 --> 0:13:28.760 I am. Apparently you keep bringing it up. You rather, 0:13:28.880 --> 0:13:31.440 Paul Rudd. I want in on this. By the way, 0:13:31.480 --> 0:13:33.480 if you if you have a hook up with Marvel, 0:13:33.960 --> 0:13:36.760 I'm totally in. All right, sounds good now. These answers 0:13:36.800 --> 0:13:38.720 are pretty good. They're sort of all over the place. 0:13:38.800 --> 0:13:40.840 I was a little surprised. I thought we'd hear more 0:13:40.880 --> 0:13:43.920 mentions of the poll exclusion principle. More people need to 0:13:44.000 --> 0:13:47.040 take or remember their high school chemistry. You mean you 0:13:47.080 --> 0:13:50.800 were expecting more people to mention the poll exclusion principle. Yeah. Absolutely, 0:13:50.800 --> 0:13:53.040 I thought it was something people knew pretty well. I 0:13:53.040 --> 0:13:56.080 mean I remember suffering through it in high school chemistry. 0:13:56.240 --> 0:13:58.600 I imagine a lot of other people have. Well, let's 0:13:58.760 --> 0:14:01.800 step into it, Danny. What is the poly exclusion principle 0:14:01.880 --> 0:14:05.160 and how does it apply to quantum states and fermions. 0:14:05.160 --> 0:14:08.360 So the poly exclusion principle basically just says that you 0:14:08.440 --> 0:14:12.120 cannot have two fermions in the same quantum state, right, 0:14:12.120 --> 0:14:14.680 It's basically a statement of the problem. Of course, it 0:14:14.720 --> 0:14:19.000 references these particles fermions, named after Enrico Fermi. But these 0:14:19.000 --> 0:14:21.480 are the particles that make up matter. So quarks and 0:14:21.560 --> 0:14:25.760 electrons are fermions, and this is why, for example, you 0:14:25.800 --> 0:14:28.840 can't have two electrons in the same state around a 0:14:28.920 --> 0:14:32.840 hydrogen atom. The poly exclusion principle forbids it. Okay, so 0:14:33.240 --> 0:14:35.280 let me go back a little bit to a fermion. 0:14:35.440 --> 0:14:37.680 It's what you call the matter particles, right, Yeah, we 0:14:37.800 --> 0:14:40.920 have two different kinds of particles. In the standard model, 0:14:40.960 --> 0:14:43.280 we have the particles that make up matter, so the electron, 0:14:43.400 --> 0:14:45.600 the quarks, for example, and that of that you can 0:14:45.640 --> 0:14:48.920 build protons and neutrons, from which you can make the nucleus. 0:14:49.200 --> 0:14:51.600 At electrons you get atoms. Buy them all together, you 0:14:51.600 --> 0:14:55.160 get molecules. We're basically built out of those things. There 0:14:55.160 --> 0:14:58.280 are also other particles. These are the force particles. The 0:14:58.320 --> 0:15:02.360 particles like the photon that bind the electron to the nucleus, 0:15:02.400 --> 0:15:05.000 and the w and the z bosons for the weak force, 0:15:05.040 --> 0:15:08.520 and the gluons for the strong force. These particles are 0:15:08.560 --> 0:15:11.840 the force particles. There's an interesting difference between these two 0:15:11.960 --> 0:15:14.720 kinds of particles. The first one the fermions. You can 0:15:14.760 --> 0:15:16.640 never have two of them in the same state. Two 0:15:16.640 --> 0:15:18.840 electrons can never be in the same state. But the 0:15:18.880 --> 0:15:22.880 other group, the force carrying particles, these bosons. There's no limit, 0:15:23.040 --> 0:15:25.200 Like you can have two photons in the same state, 0:15:25.480 --> 0:15:28.400 ten photons in the same state, a million photons all 0:15:28.440 --> 0:15:31.800 piled on top of each other. So fermions can never 0:15:31.840 --> 0:15:33.920 be in the same state. Those are the matter particles, 0:15:34.120 --> 0:15:37.000 and bosons can be in the same state. That's this 0:15:37.120 --> 0:15:40.560 weird division Okay, now let's maybe define for people what 0:15:40.720 --> 0:15:43.040 is a quantum state, Like what does it mean to 0:15:43.240 --> 0:15:45.840 have a state, and what can those states be? So 0:15:45.880 --> 0:15:48.560 what can quantum particles do well. They can be in 0:15:48.600 --> 0:15:51.520 some location. They can also have a certain amount of energy, 0:15:51.720 --> 0:15:53.960 They can have a certain kind of spin, like some 0:15:54.000 --> 0:15:56.600 of these particles can have spin up or spin down 0:15:57.040 --> 0:16:00.720 or other various weird kinds of spin. So basically, anything 0:16:00.760 --> 0:16:04.480 that describes the particle is part of its quantum state. 0:16:04.480 --> 0:16:07.360 A quantum state is just a description of the particle, 0:16:07.520 --> 0:16:11.120 Like you mean, like where is it and what's it doing? Yeah, exactly, 0:16:11.200 --> 0:16:13.440 that's what a state is. The way you might describe 0:16:13.520 --> 0:16:16.440 like a classical object by saying where is it, how 0:16:16.520 --> 0:16:19.000 fast is it going? What is it? Location and velocity? 0:16:19.000 --> 0:16:21.960 That describes the classical object. A quantum state is just 0:16:22.000 --> 0:16:24.480 a description of the quantum particle. Like the state of 0:16:24.480 --> 0:16:27.400 a baseball might be like it's over here, it's moving 0:16:27.440 --> 0:16:30.880 in this direction, and it's also spinning in place, and 0:16:30.960 --> 0:16:33.320 maybe also like it's temperature. Would that be kind of 0:16:33.360 --> 0:16:36.720 like what you need to describe a baseball. Imagine, for example, 0:16:36.760 --> 0:16:39.280 we live in a simulation and you're the programmer of 0:16:39.320 --> 0:16:42.400 the simulation. What details do you need to keep track 0:16:42.520 --> 0:16:46.640 of to run your simulation? That's the quantum state of 0:16:46.800 --> 0:16:48.880 a particle. I see. Well, I'm not sure how many 0:16:48.880 --> 0:16:52.320 people out there know how to program, but I think 0:16:52.320 --> 0:16:55.240 maybe it's sort of like a list that identifies everything 0:16:55.320 --> 0:16:58.080 that we know about a particle. That's kind of what 0:16:58.080 --> 0:17:00.960 you're saying, right, And so for small particles that list 0:17:01.040 --> 0:17:03.320 it's not like an infinite list, right, Like it's a 0:17:03.360 --> 0:17:05.920 list of maybe like five things exactly. It depends a 0:17:05.960 --> 0:17:08.840 little bit on where that particle is. An electron in 0:17:08.920 --> 0:17:11.800 free space doesn't have energy levels the way an electron 0:17:11.840 --> 0:17:15.000 around a hydrogen atom does. Wait, what it depends on 0:17:15.040 --> 0:17:16.800 the situation. So like, if I have just have a 0:17:16.800 --> 0:17:19.520 particle out there in space by itself, what are its 0:17:19.600 --> 0:17:22.800 quantum state variables? A particle just out there in space 0:17:22.880 --> 0:17:26.360 with like no potential, no forces on anything, a free particle, 0:17:26.800 --> 0:17:29.280 then the quantum states are just the location and the 0:17:29.400 --> 0:17:31.760 energy and the energy. What do you mean by energy, Well, 0:17:31.800 --> 0:17:36.920 it's velocity, right, it's kinetic energy, and it's spin as well. Yes, absolutely, 0:17:36.960 --> 0:17:39.440 and it's spin. But remember out there in free space, 0:17:39.440 --> 0:17:43.400 the kinetic energy can have any value. Electrons are quantized 0:17:43.440 --> 0:17:46.879 into energy levels around a hydrogen atom because they're confined. 0:17:47.240 --> 0:17:50.359 The quantization only comes from the confinement. Electrons at in 0:17:50.400 --> 0:17:53.600 free space don't have like energy levels, whereas electrons around 0:17:53.600 --> 0:17:56.200 a hydrogen atom, for example, do. So there's an important 0:17:56.200 --> 0:18:00.400 distinction there about the quantum state of these particles. Are space, 0:18:00.400 --> 0:18:03.000 you would just say the energy around the hydrogenontom, you 0:18:03.040 --> 0:18:05.159 would say the energy level. But when it's out in 0:18:05.200 --> 0:18:07.560 space you also count like the spin of it too, Right, 0:18:07.680 --> 0:18:10.280 are there any other quantum variables? I guess each kind 0:18:10.280 --> 0:18:13.680 of particle has different kind of variables attached to it. Yeah, exactly. 0:18:13.720 --> 0:18:16.120 And electrons can have two different kinds of spin, spin 0:18:16.200 --> 0:18:19.040 up and spin down. Photons can have three different kinds 0:18:19.040 --> 0:18:22.440 of spin. The Higgs boson doesn't have any spin at all, 0:18:22.800 --> 0:18:24.280 So it depends a little bit on a kind of 0:18:24.320 --> 0:18:26.840 particle and also the situation that it's in. Okay, So 0:18:26.880 --> 0:18:29.960 now the rule here is that no two particles can 0:18:30.000 --> 0:18:32.959 have the same quantum state. Now what does that mean 0:18:33.000 --> 0:18:35.480 for like particles out there in the open floating around 0:18:35.480 --> 0:18:38.800 space like that means that no two electrons can be 0:18:38.840 --> 0:18:41.119 in the same spot with the same velocity in the 0:18:41.160 --> 0:18:44.040 same spin. So the rules not that no, two particles 0:18:44.080 --> 0:18:46.600 can be in the same state, but no, two fermions number. 0:18:46.680 --> 0:18:49.399 Half of the particles we call them fermions, they can't 0:18:49.400 --> 0:18:51.600 be in the same state. The other half we call 0:18:51.640 --> 0:18:54.240 them bosons. They have no problem being in the same state. 0:18:54.600 --> 0:18:57.240 So electrons and quarks they can't pile up on top 0:18:57.280 --> 0:18:59.480 of each other in the same state, whereas photons can. 0:19:00.160 --> 0:19:02.600 Question is, like, what happens out there in empty space? Well, yeah, 0:19:02.600 --> 0:19:05.119 two electrons cannot be in the same state, meaning it 0:19:05.160 --> 0:19:07.240 can't be in the same location with the same spin 0:19:07.359 --> 0:19:10.840 and the same energy. That's just not possible. Well that's interesting, 0:19:10.920 --> 0:19:13.080 Like that just seems to be like a rule the 0:19:13.160 --> 0:19:17.040 universe has, right, Like that's something that you think can't happen. 0:19:17.240 --> 0:19:19.600 But I guess is anyone actually tried to see if 0:19:19.640 --> 0:19:22.080 you can fit to electrons in the same spot. Oh yeah, 0:19:22.080 --> 0:19:24.720 the universe tries to do it all the time. Remember, 0:19:24.760 --> 0:19:27.480 the universe likes to have things relax down to the 0:19:27.520 --> 0:19:30.560 lowest energy. That's really what forces are. Forces are things 0:19:30.600 --> 0:19:33.800 that push things down to lower energy configurations. So think 0:19:33.800 --> 0:19:37.320 about what happens when you put electrons around an atom, Right, 0:19:37.359 --> 0:19:39.320 the first one goes down to the lost energy level, 0:19:39.400 --> 0:19:41.439 and then the second one can't go down to the 0:19:41.480 --> 0:19:44.399 lost energy level because that's filled. Right. It's sort of 0:19:44.440 --> 0:19:46.639 like playing connect for you put one piece in, the 0:19:46.720 --> 0:19:49.760 next one can't slot into that lowest level anymore. It 0:19:49.760 --> 0:19:51.760 has to go to energy level two. I guess I'm 0:19:51.800 --> 0:19:54.880 trying to understand like this rule on the free space 0:19:55.280 --> 0:19:57.840 situation first, and then maybe we can get into the 0:19:58.560 --> 0:20:02.240 going around an atom situation and after that because like electrons, 0:20:02.240 --> 0:20:04.760 for example, don't have a volume to them, right, they 0:20:04.760 --> 0:20:07.280 don't have a solidness to them. So technically, like you 0:20:07.320 --> 0:20:10.320 could have an electron on top of another electron, but 0:20:10.400 --> 0:20:13.520 you're saying the universe somehow, for some reason, doesn't like that. Yeah. Well, 0:20:13.560 --> 0:20:15.840 I think the free space example is a little artificial 0:20:15.840 --> 0:20:18.439 because you bring two electrons together, they will have a 0:20:18.480 --> 0:20:20.520 force between them. They will try to repel each other, 0:20:20.600 --> 0:20:23.480 so they're no longer free electrons, right, So that examples 0:20:23.480 --> 0:20:26.919 a little bit artificial. I think you know, out in space, 0:20:27.000 --> 0:20:30.800 the universe does try to compress electrons down into tiny dots. 0:20:30.800 --> 0:20:33.840