WEBVTT - Does particle spin affect life on Earth? 0:00:08.440 --> 0:00:11.440 Okay, I realized I've never asked you this. Are you 0:00:11.680 --> 0:00:15.040 left or right handed? Usually draw with my right hand, 0:00:15.640 --> 0:00:18.200 so I'm sure you've tried to draw with your other hand. 0:00:18.440 --> 0:00:21.040 What's that like? It's it's pretty tricky. Yeah, if you're 0:00:21.079 --> 0:00:23.759 used to doing things with one hand, it's hard to switch. Well, 0:00:23.800 --> 0:00:26.279 what about driving? Have you ever driven on the left 0:00:26.280 --> 0:00:29.920 side of the road, you mean, on purpose or against 0:00:29.960 --> 0:00:32.360 the law or following the laws of Well, you know 0:00:32.400 --> 0:00:34.720 there are some places in the world where they drive 0:00:34.760 --> 0:00:38.800 on the other side. I have driven in Australia and England. Yeah, 0:00:38.880 --> 0:00:41.000 it's pretty tricky, but after a while you get used 0:00:41.000 --> 0:00:43.000 to it. What would you say is better your left 0:00:43.040 --> 0:00:46.120 side of the road driving or your left handed drawing. Well, 0:00:46.200 --> 0:00:49.560 I've fortunately have not had an accident on either side 0:00:49.840 --> 0:00:52.239 of the road, so the data says that I am 0:00:52.320 --> 0:00:54.840 equally good. Well, I'm glad you're even handed. That sounds 0:00:54.840 --> 0:00:56.959 like a left handed compliment, Daniel, I think that's right. 0:01:00.280 --> 0:01:15.720 Hi am poor handed cartoonists and the creator of PhD comics. Hi, 0:01:15.800 --> 0:01:18.720 I'm Daniel. I'm a particle physicist and a professor. And 0:01:18.880 --> 0:01:21.759 you see Irvine and I have tried to do math 0:01:21.920 --> 0:01:23.960 left handed. I mean you write out math with your 0:01:24.040 --> 0:01:25.600 left hand. Is that what you mean? Yeah? I try 0:01:25.640 --> 0:01:27.520 to write out math with my left hand or sometimes 0:01:27.600 --> 0:01:30.800 upside down. Sometimes when I'm teaching math to my kids, 0:01:31.120 --> 0:01:33.000 I have to write it so that they can see it, 0:01:33.040 --> 0:01:36.360 which requires a little bit of awkward gymnastics. But if 0:01:36.360 --> 0:01:39.119 you use your left hand and maybe it's it's it's normal. 0:01:40.160 --> 0:01:42.160 If I use my left hand and my handwriting looks 0:01:42.160 --> 0:01:44.640 as sloppy as theirs. I know people who would aspire 0:01:44.680 --> 0:01:48.520 to be ambidexterous, so they purposely used the mouths even 0:01:48.560 --> 0:01:50.440 though they're right handed. They use their mouse but their 0:01:50.520 --> 0:01:52.440 left hand so that they're you know, are able to 0:01:52.520 --> 0:01:54.040 do both. How would you give my right arm to 0:01:54.080 --> 0:01:56.440 be ambidextrous. Well, if you give your right arm, then 0:01:56.440 --> 0:01:59.760 you wouldn't be ambidexterous. Sounds like you're caught in a paradox. 0:02:00.080 --> 0:02:02.800 Welcome to a podcast Daniel and Jorge Explain the Universe, 0:02:02.880 --> 0:02:05.440 a production of I Heart Radio, in which we try 0:02:05.480 --> 0:02:07.640 to tickle the right side of your brain and the 0:02:07.760 --> 0:02:10.360 left side of your brain. We want to understand the 0:02:10.600 --> 0:02:13.800 entire universe, the top half, the bottom half, the left side, 0:02:13.840 --> 0:02:17.280 the right side, and everything in between even the backside, 0:02:18.080 --> 0:02:21.040 the backside, the front side, the dark side, and the 0:02:21.120 --> 0:02:24.360 light side. Every side of the universe deserves to be understood, 0:02:24.360 --> 0:02:27.200 and we think it's possible. And on this podcast we 0:02:27.240 --> 0:02:30.240 ask those big questions about the nature of reality, the 0:02:30.320 --> 0:02:32.560 nature of life, why we are all here, what it 0:02:32.560 --> 0:02:34.919 all means, how long we will be here, and whether 0:02:35.080 --> 0:02:37.920 we're alone, and we try to explain all of them 0:02:37.960 --> 0:02:41.480 to you. And today I want to especially explain things 0:02:41.520 --> 0:02:44.359 to Walter Bloom, a long time listener of the pod 0:02:44.440 --> 0:02:47.880 from Switzerland, whose girlfriend Victoria wants to wish him a 0:02:48.000 --> 0:02:51.919 happy thirty eighth birthday. Happy birthday, Walter, Yeah, it is 0:02:51.960 --> 0:02:55.239 a big universe to explain. It is a wide universe, 0:02:55.280 --> 0:02:57.840 full of many sides to it, many different ways that 0:02:57.919 --> 0:03:00.040 you can look at things, and also many different in 0:03:00.120 --> 0:03:03.440 ways that things can be put together. There are almost 0:03:03.440 --> 0:03:05.440 an infinite way for a matter to arrange itself. And 0:03:05.480 --> 0:03:08.640 one of the joys of physics is figuring out how 0:03:08.680 --> 0:03:11.320 the universe works, because then we get to ask why. 0:03:11.520 --> 0:03:13.320 When we discover that we are put together out of 0:03:13.360 --> 0:03:16.040 time of little particles, we get to wonder, like, why 0:03:16.280 --> 0:03:18.639 is the universe arranged out of these time little particles. 0:03:18.800 --> 0:03:21.440 Why does it have these patterns? What does that really mean? 0:03:21.600 --> 0:03:23.800 The joy physics is really that it's setting us up 0:03:23.840 --> 0:03:26.840 to ask philosophy questions. Oh, is that the main goal 0:03:26.880 --> 0:03:30.200 of physics just to be a primer, like a trailer 0:03:30.240 --> 0:03:33.480 to philosophy, just the opening act for philosophy. Example, what 0:03:33.720 --> 0:03:36.240 you're saying businesses are just there to warm up the crowd. 0:03:36.320 --> 0:03:38.080 In the end, I think the almost science really is 0:03:38.120 --> 0:03:41.720 motivated by philosophy questions. You know, at the heart of 0:03:41.800 --> 0:03:45.000 almost every science question we ask, there is a why question, 0:03:45.040 --> 0:03:48.320 which is in the end fundamentally philosophical. Yeah, and we 0:03:48.360 --> 0:03:51.320 ask these questions not just because it's interesting and fascinating 0:03:51.360 --> 0:03:54.160 and we understand more about the universe. But sometimes these 0:03:54.280 --> 0:03:57.520 questions and these issues have a big impact on our daily, 0:03:57.960 --> 0:04:02.800 everyday lives, even maybe on life itself. Yeah, we notice 0:04:02.840 --> 0:04:05.560 these patterns in the universe. The universe seems to organize 0:04:05.560 --> 0:04:07.960 itself in this way and not some other way. We 0:04:08.040 --> 0:04:10.800 noticed sometimes there are symmetries in the universe, like you 0:04:10.800 --> 0:04:13.920 could rotate everything and the laws of physics wouldn't change. 0:04:14.160 --> 0:04:17.320 But also sometimes we notice that there are not symmetries 0:04:17.360 --> 0:04:19.720 in the universe, that the universe has a strong opinion 0:04:20.080 --> 0:04:22.839 about how things should be done, and the opposite way 0:04:22.960 --> 0:04:26.880 just does not happen. Time flows forwards and not backwards, 0:04:26.920 --> 0:04:29.960 and these are the things that inspire our philosophical musings 0:04:29.960 --> 0:04:32.240 to wonder what it would be like for universe or 0:04:32.320 --> 0:04:34.760 time flowed backwards, or what it would be like for 0:04:34.920 --> 0:04:38.080 universe in the mirror of our universe. Yeah, and so 0:04:38.120 --> 0:04:41.000 our universe likes to put things together in a particular way, 0:04:41.200 --> 0:04:45.360 and you can trace sometimes that to the very properties 0:04:45.400 --> 0:04:48.320 of the smallest particles in the universe, the things that 0:04:48.360 --> 0:04:51.039 everything is made out of, and some of these properties 0:04:51.040 --> 0:04:54.200 can have a pretty big impact on what gets formed 0:04:54.200 --> 0:04:56.840 in the universe and even whether we would be here 0:04:56.920 --> 0:04:59.320 or not. It does seem sometimes like at the smallest 0:04:59.400 --> 0:05:02.000 level of the universe, US follows really different rules, really 0:05:02.040 --> 0:05:05.599 strange quantum rules that don't really affect our lives, Like 0:05:05.640 --> 0:05:08.400 how a particle moves through space is totally different from 0:05:08.440 --> 0:05:11.240 how a baseball flies through space. But as you say, 0:05:11.320 --> 0:05:14.040 sometimes there is a connection. Sometimes we can even find 0:05:14.040 --> 0:05:17.680 a portal from the timeliest particle to our everyday lives. 0:05:17.880 --> 0:05:19.520 So to be on the podcast, we will be tackling 0:05:19.520 --> 0:05:29.240 the question does particle spin affect life on Earth? Are 0:05:29.240 --> 0:05:31.800 we trying to put a positive spin here on life 0:05:31.800 --> 0:05:34.359 on Earth? I'm trying to put a positive spin on particles. 0:05:34.440 --> 0:05:37.240 I'm like, look, particles are relevant. Give me money, is 0:05:37.279 --> 0:05:40.080 what you're saying. Well, you know that's the philosophy that's 0:05:40.160 --> 0:05:43.200 underlying all of it. And yes, we're trying to make 0:05:43.200 --> 0:05:45.640 our science relevant. Do you share any of your funding 0:05:45.640 --> 0:05:48.680 with philosophers? Philosophers really need funding? I mean, how much 0:05:48.720 --> 0:05:52.120 does paper and pencil cost? Anyway? Isn't that aren't dose 0:05:52.160 --> 0:05:56.479 the tools of your research as well? Um? Ten billion 0:05:56.560 --> 0:05:59.440 dollar particle colliders. You can build those out of pencil 0:05:59.480 --> 0:06:02.240 and paper. You could, You just haven't tried the paper 0:06:02.279 --> 0:06:05.400 mache particle collider. Put that on the table next time 0:06:05.400 --> 0:06:07.800 we're discussing the future of the field. Can you demonstrate 0:06:07.839 --> 0:06:11.159 mathematically that you cannot build a particle collider with paper mache. 0:06:11.240 --> 0:06:13.640 Let's show the spitball collider. Yeah, let's see what we 0:06:13.680 --> 0:06:17.480 can learn my colliding spitballs at nearly the speed of light. Yeah, 0:06:17.560 --> 0:06:19.680 it's possible, right, it is possible. I have to do 0:06:19.760 --> 0:06:22.359 some pencil and paper calculations to see what kind of 0:06:22.400 --> 0:06:24.680 experiments we could do and what we might learn about 0:06:24.720 --> 0:06:27.760 the universe from a paper machee collider. Yeah, i'll fund 0:06:27.760 --> 0:06:31.640 out here. Here's five bucks. But this is an interesting question. 0:06:31.960 --> 0:06:35.440 We're trying to link life on Earth to something as 0:06:35.520 --> 0:06:40.799 small and maybe and seemingly insignificant as the spin fundamental 0:06:40.839 --> 0:06:43.240 particle of nature. That's a pretty big leap. It is 0:06:43.279 --> 0:06:45.320 a pretty big leap, And you might think it sounds 0:06:45.320 --> 0:06:47.440 a little bit desperate, like is Daniel just trying to 0:06:47.480 --> 0:06:50.240 be irrelevant to life? But remember that I'm actually doing 0:06:50.240 --> 0:06:53.960 this research mostly because I think it's irrelevant honestly, because 0:06:54.240 --> 0:06:57.120 it doesn't affect everyday life on Earth, which means you 0:06:57.160 --> 0:06:59.480 can't use it to build weapons. Wait, did you just 0:06:59.640 --> 0:07:03.000 admit your research is irrelevant to all life on Earth. 0:07:03.200 --> 0:07:05.520 It's irrelevant in the sense that it doesn't have immediate 0:07:05.560 --> 0:07:09.039 practical applications the way that you admit your research has 0:07:09.040 --> 0:07:12.600 no immediate practical applications. Oh, absolutely, yes, learning about particles 0:07:12.600 --> 0:07:15.920 has no immediate practical applications. I can't tell you tomorrow 0:07:16.240 --> 0:07:18.800 that it's going to improve technology or even next year. 0:07:19.200 --> 0:07:21.680 It's basic research in the sense that we might discover 0:07:21.760 --> 0:07:24.120 something crazy and new about the universe. Will down the road, 0:07:24.160 --> 0:07:27.120 I'm sure will benefit society, but in terms of life 0:07:27.160 --> 0:07:30.960 immediate impact and you know tomorrow's weapons systems, No, we 0:07:31.000 --> 0:07:34.840 have no relevance. All right, Well, I guess possible deniabilities 0:07:34.960 --> 0:07:38.120 is important for some people. But this is an interesting 0:07:38.200 --> 0:07:41.160 question to wonder if maybe the spin of particles could 0:07:41.160 --> 0:07:43.600 have affected how life on Earth evolved, or even if 0:07:43.640 --> 0:07:46.680 life itself evolved at all on this planet. Yeah, it's 0:07:46.680 --> 0:07:49.840 a fascinating hypothesis with a little bit of evidence to 0:07:49.880 --> 0:07:51.760 back it up. Well, as usually, we were wondering how 0:07:51.800 --> 0:07:54.240 many people have thought about this question. I had thought 0:07:54.240 --> 0:07:57.840 about maybe the properties of particles having an impact on 0:07:57.920 --> 0:08:00.280 life on Earth, so it's usual Daniel went out there 0:08:00.320 --> 0:08:03.240 to ask people do you think particle spin can affect 0:08:03.320 --> 0:08:05.920 life on Earth? So thank you very much to everybody 0:08:05.920 --> 0:08:08.559 who participates in this segment of the podcast. We really 0:08:08.560 --> 0:08:11.520 appreciate hearing your thoughts and I think everybody out there 0:08:11.720 --> 0:08:13.720 enjoys it as well. If you'd like to share your 0:08:13.760 --> 0:08:16.480 thoughts on the topic of the day for future episodes, 0:08:16.720 --> 0:08:19.320 please don't be shy right to us. Two questions at 0:08:19.440 --> 0:08:22.000 Daniel and Jorge dot com. It's what people have to say. 0:08:22.080 --> 0:08:26.560 I betterly know what particle spin is, but I could 0:08:27.000 --> 0:08:30.800 surely say that it does not affect life on other 0:08:30.840 --> 0:08:35.800 planets from the Solar System. Well, everything is spinning. Particles 0:08:35.840 --> 0:08:41.720 are spinning, the earthy spinning, the galaxy and spinning. Realms 0:08:41.720 --> 0:08:46.240 are spinning. Everything is spinning. So yeah, the life is spinning. 0:08:46.400 --> 0:08:50.160 I'm going to say yes, because it affects the way 0:08:50.320 --> 0:08:53.440 matter is made up. But I really don't know what 0:08:53.480 --> 0:08:56.160 would happen if particles spin were to be reversed. I 0:08:56.200 --> 0:08:59.440 don't know for you would even recognize the effects of that. 0:09:00.040 --> 0:09:03.280 It will be interpreted maybe a couple of ways outside 0:09:03.280 --> 0:09:07.320 of like the necessity it's spen make physics work, I 0:09:07.320 --> 0:09:10.840 would say probably not very much impact life. I don't think. 0:09:10.880 --> 0:09:14.199 I don't think like DNA is interacting with particles spin. 0:09:14.480 --> 0:09:16.840 All right, Some people said yes, some people said no. 0:09:17.200 --> 0:09:20.440 There are strong opinions here. There are positive and negative spins. 0:09:20.520 --> 0:09:22.439 On one hand, it does seem hard to imagine that 0:09:22.480 --> 0:09:25.200 the behaviors of tiny little particles could affect something like 0:09:25.360 --> 0:09:29.040 life on Earth. On the other hand, if you believe reductionism, 0:09:29.120 --> 0:09:32.040 if you believe that everything in the universe comes out 0:09:32.040 --> 0:09:35.080 of how tiny little bits are dancing around and tooing 0:09:35.120 --> 0:09:38.240 and frowing that in principle, everything about life comes down 0:09:38.320 --> 0:09:40.640 to how particles work. Well, yeah, I mean I guess 0:09:40.679 --> 0:09:44.920 if particles, for example, didn't feel the electromagnetic force, I mean, 0:09:44.960 --> 0:09:47.199 the whole universe would be different. Yeah, I'm sitting here 0:09:47.200 --> 0:09:50.559 trying to imagine what a universe would be like without electromagnetism. 0:09:50.679 --> 0:09:52.760 I mean, it would be a dark universe for sure, right, 0:09:52.760 --> 0:09:55.520 there would be no light at all in that universe. Yeah. 0:09:55.640 --> 0:09:58.120 Or I guess even m if the particles had a 0:09:58.120 --> 0:10:01.200 different mass, it would also change the ole universe, right, 0:10:01.360 --> 0:10:04.840 like planets would form differently, galaxies would form differently. Who knows, 0:10:04.840 --> 0:10:08.120 And maybe life can or could have would have formed 0:10:08.160 --> 0:10:10.280 here on Earth. And yeah, it's a deep mystery why 0:10:10.320 --> 0:10:13.199 the parameters of the universe seem to be set up 0:10:13.240 --> 0:10:16.080 to allow life. Although you know, that's just sort of 0:10:16.080 --> 0:10:18.720 like life that we can imagine. It's possible that if 0:10:18.760 --> 0:10:21.760 you tweaked all those parameters, you might have completely different chemistry. 0:10:21.800 --> 0:10:24.760 But that might allow for different kinds of biology, different 0:10:24.800 --> 0:10:28.640 kinds of life, maybe even different kinds of intelligence. So 0:10:28.679 --> 0:10:31.360 while the universe does sort of seem fine tuned for us, 0:10:31.840 --> 0:10:34.000 it might be that other fine tunings are good for 0:10:34.120 --> 0:10:36.839 other kinds of beings. All right, Well, the question at 0:10:36.840 --> 0:10:40.160 hand is does particle spin affect life on Earth? And 0:10:40.320 --> 0:10:44.480 so I guess particle spin is something that is the 0:10:44.559 --> 0:10:46.600 property of particles. Maybe we can get a little bit 0:10:46.640 --> 0:10:49.560 into that first. Particle spin is a really fun and 0:10:49.800 --> 0:10:54.680 super weird property of particles, and it's especially fascinating because 0:10:54.720 --> 0:10:57.240 the universe seems to have a preference for one kind 0:10:57.240 --> 0:11:00.840 of spin over another kind of spin. Fundamentally, we don't 0:11:00.880 --> 0:11:04.040 really know what particle spin is. I mean, you might 0:11:04.080 --> 0:11:07.360 imagine that it's like a little ball and it's spinning. 0:11:07.440 --> 0:11:10.720 The problem is that particles are not little balls, and 0:11:10.760 --> 0:11:13.400 they don't really have surfaces, so we don't think that 0:11:13.440 --> 0:11:16.319 they are physically spinning. But they do have a property 0:11:16.320 --> 0:11:18.440 which is very similar to the kind of things we 0:11:18.559 --> 0:11:20.800 call spin, for like the Earth is spinning and the 0:11:20.920 --> 0:11:24.800 galaxy is spinning. Particles have properties which have similar mathematical 0:11:24.880 --> 0:11:28.320 behaviors to spin of like big objects, and so we 0:11:28.440 --> 0:11:33.040 call it spin even though it's not like technically physically spinning, right, 0:11:33.160 --> 0:11:36.360 because quantum particles are not like little balls, as you said, 0:11:36.400 --> 0:11:39.720 they're like little dots basically, and so they have this 0:11:39.760 --> 0:11:42.880 property called spin. And if it's not related to it 0:11:42.960 --> 0:11:45.320 actually spinning, why did you call it spin? Or not 0:11:45.400 --> 0:11:48.360 you specifically, but you know the physics physicism birth did it? 0:11:48.880 --> 0:11:50.600 Why did they call it spin? They call it spin 0:11:50.720 --> 0:11:54.120 because even if it isn't actually physically spinning, it is 0:11:54.160 --> 0:11:57.720 a form of angular momentum. Right, things in the universe 0:11:57.760 --> 0:11:59.960 can spin, and they can have momentum in the same 0:12:00.040 --> 0:12:02.520 way that things can have normal momentum. Right, momentum is 0:12:02.559 --> 0:12:04.880 just like if you push an object, it keeps going, 0:12:05.000 --> 0:12:07.200 or if you don't push it, it doesn't go anywhere. 0:12:07.360 --> 0:12:10.000 The same thing holds true for spin. If you spin something, 0:12:10.080 --> 0:12:12.240 it will keep spinning, like out in space where there 0:12:12.280 --> 0:12:14.480 isn't any air to slow it down. Or if you 0:12:14.559 --> 0:12:17.360 don't push an object, it won't spin. Right, It's something 0:12:17.400 --> 0:12:20.320 floating in space won't spin unless you push it. That's 0:12:20.360 --> 0:12:22.880 angular momentum, and that's conserved in the universe. That's why 0:12:22.920 --> 0:12:25.080 if you push something to make it spin, it'll just 0:12:25.160 --> 0:12:27.960 keep spinning out there in space until something stops it. 0:12:28.000 --> 0:12:30.840 But you can transfer that angular momentum to something else, right, 0:12:30.880 --> 0:12:32.839 it can bump into something else and make that spin. 0:12:32.960 --> 0:12:36.200 We call particles spin spin because it's a kind of 0:12:36.240 --> 0:12:39.080 angular momentum. You can take anglar momentum and convert it 0:12:39.160 --> 0:12:42.880 into particle spin and back. So when the universe does 0:12:42.960 --> 0:12:45.760 its accounting to make sure that angular momentum is conserved, 0:12:45.840 --> 0:12:49.120 particle spin is part of its balance book, you're allowed 0:12:49.120 --> 0:12:52.200 to move some angle momentum into that category. So it 0:12:52.240 --> 0:12:55.520 really is a kind of angular momentum, even if it's 0:12:55.520 --> 0:12:59.120 a weird quantum kind. But you said that, like regular 0:12:59.160 --> 0:13:02.640 objects in space and have zero angular momentum or a 0:13:02.679 --> 0:13:05.679 little bit or a lot of angular momentum, can particles 0:13:05.720 --> 0:13:09.400 have zero or a lot of angular momentum? And also 0:13:09.480 --> 0:13:12.079 why not just call it angular momentum? Yes, particles can 0:13:12.160 --> 0:13:15.880 have different amounts of spin. Of Photons, for example, can 0:13:15.960 --> 0:13:19.960 have spin up or down or zero. Electrons can only 0:13:20.000 --> 0:13:22.600 have spin one half or negative one half. They can't 0:13:22.640 --> 0:13:26.280 have zero spin. They're different kind of particles. So matter 0:13:26.360 --> 0:13:28.720 particles are all either spin up or spin down by 0:13:28.760 --> 0:13:31.880 one half, whereas forest particles those can be up or 0:13:31.920 --> 0:13:36.120 down or zero. Can the same particle have zero and 0:13:36.120 --> 0:13:37.800 then I give it a spin and then it starts 0:13:37.800 --> 0:13:40.280 spinning or is it just an inherent property of that 0:13:40.400 --> 0:13:43.760 particle that's a really interesting philosophy question. Right, Essentially, you're 0:13:43.760 --> 0:13:46.960 saying a photon moving through the universe with zero spin, 0:13:47.440 --> 0:13:50.640 if you give it spin, is it's still the same photon. Well, 0:13:50.640 --> 0:13:53.000 to give it spin, you have to impart angular momentum 0:13:53.080 --> 0:13:56.360 on it, which means an interaction, and so philosophically it 0:13:56.559 --> 0:14:00.200 is changed. Right, It's like interacts with some particle, and 0:14:00.240 --> 0:14:02.520 you think of that as like being absorbed and re emitted. 0:14:02.880 --> 0:14:05.280 So I think philosophically you can think of it it's 0:14:05.280 --> 0:14:07.719 like a new particle, or it's at least a new 0:14:07.800 --> 0:14:11.160 quantum state. But yes, photons can have zero spin, or 0:14:11.200 --> 0:14:13.240 they can have spin one, or they're gonna have spin 0:14:13.360 --> 0:14:16.960 minus one m. And the spin it's quantized as well, 0:14:16.960 --> 0:14:21.040 Like you have a photon with like three point five spin, No, 0:14:21.200 --> 0:14:23.200 you can't, And you can't have photons with like half 0:14:23.240 --> 0:14:26.600 a spin or point seven to nine spin. It's absolutely quantized. 0:14:26.880 --> 0:14:30.040 So photons have three possible states plus one, zero or 0:14:30.040 --> 0:14:33.200 minus one, and electrons have two states plus a half 0:14:33.440 --> 0:14:35.880 or minus a half. And that's true for all fer meon's. 0:14:35.920 --> 0:14:38.720 All fermons are either plus a half or minus a half. 0:14:38.920 --> 0:14:41.920 They have half integer spins. That's why we call them fermons. 0:14:41.960 --> 0:14:44.960 They all observe the Firmi exclusion principle, which means they 0:14:44.960 --> 0:14:47.720 can't be in the same quantum state as each other. Bosons, 0:14:47.720 --> 0:14:50.000 which have integer spin, they can hang out in the 0:14:50.040 --> 0:14:52.040 same state, So you can have like a million photons 0:14:52.320 --> 0:14:55.280 all in the same state. Now, you said earlier that 0:14:55.520 --> 0:14:59.160 spin is up or down, right, that's kind of the 0:14:59.360 --> 0:15:02.920 possibility ane's of it. But in a in space there 0:15:03.000 --> 0:15:04.760 is no up and there's no down. So what does 0:15:04.800 --> 0:15:06.520 it mean for a spin to be up or down 0:15:06.560 --> 0:15:08.480 for a particle. Well, in the same way that you 0:15:08.520 --> 0:15:11.600 can pick any access to calculate ingle momentum, you can 0:15:11.600 --> 0:15:14.200 pick any access to project the spin. So you have 0:15:14.240 --> 0:15:16.800 a particle, you pick an access, you say, here's my axis. 0:15:16.840 --> 0:15:18.360 I want to know if it's spin is up or 0:15:18.400 --> 0:15:21.400 down along this axis, and you can pick any access 0:15:21.440 --> 0:15:24.200 you like and call it up or down. Typically, what 0:15:24.240 --> 0:15:27.080 we do is we choose the axis of the particle's motion, 0:15:27.440 --> 0:15:30.080 and we ask is the particle spin in the direction 0:15:30.120 --> 0:15:33.400 of its motion or in the opposite direction of its motion? 0:15:33.680 --> 0:15:36.360 But isn't. Then then the problem the motion and not 0:15:36.480 --> 0:15:39.320 the spin. Like if I throw a baseball face up 0:15:39.440 --> 0:15:41.960 or if I toss a frisbee face up or face down, 0:15:42.040 --> 0:15:43.720 it's not that it's a whole different frisbee. It's the 0:15:43.720 --> 0:15:45.640 same frisbee. I just threw it upside down. Yeah. And 0:15:45.680 --> 0:15:47.840 in the case of particles, you can measure their spin 0:15:47.960 --> 0:15:51.120 along any direction, or you can measure it along their motion, 0:15:51.240 --> 0:15:53.480 or you can measure it perpendicular to their motion or 0:15:53.480 --> 0:15:55.960 in any direction, and you'll always get either plus a 0:15:56.000 --> 0:15:59.520 half or minus a half or particles. Okay, So it's 0:15:59.520 --> 0:16:02.720 just some sort of like an arbitrary label. You're saying, like, 0:16:02.880 --> 0:16:05.880 particles have this thing called spin, and we're gonna there's 0:16:06.000 --> 0:16:08.080 kind of two kinds of the spin. There's the upspin 0:16:08.160 --> 0:16:11.240 and there's down spin exactly. And the universe seems to 0:16:11.280 --> 0:16:16.360 have a preference for particles who spin is pointed away 0:16:16.440 --> 0:16:19.440 from the direction of their emotion, like an electron is 0:16:19.480 --> 0:16:22.960 flying through space in the positive ex direction. The universe 0:16:22.960 --> 0:16:25.600 seems to have a preference for those particles to spin 0:16:25.760 --> 0:16:28.640 the opposite direction of their motion, for their spin to 0:16:28.680 --> 0:16:31.760 be sort of like back along the negative X axis. 0:16:31.800 --> 0:16:34.280 If their motion is in the positive X axis, we 0:16:34.320 --> 0:16:37.880 call those particles left handed. If their spin is the 0:16:37.920 --> 0:16:40.720 opposite direction of their motion. I guess it's kind of 0:16:40.760 --> 0:16:43.680 like a clock. Like a clock can move through space 0:16:44.000 --> 0:16:46.640 where it's either the face of the clock is facing 0:16:46.640 --> 0:16:48.840 where it's going, or the face of the clock is 0:16:49.000 --> 0:16:51.760 facing away from where it's going, or facing back. And 0:16:51.800 --> 0:16:54.720 so you're saying that particles tend to be the kind 0:16:54.760 --> 0:16:57.920 where the clock face is facing back. Those kind of 0:16:57.960 --> 0:17:00.240 particles where the clock is facing backwards with a spin 0:17:00.360 --> 0:17:02.440 is the opposite direction of motion. We call them left 0:17:02.480 --> 0:17:05.480 handed particles. In our universe, we have left and right 0:17:05.480 --> 0:17:08.840 handed versions of most particles, but one of the forces, 0:17:08.920 --> 0:17:13.040 the weak nuclear force, which is responsible for like beta decay, 0:17:13.119 --> 0:17:16.920 it will only talk to left handed particles. It does 0:17:16.960 --> 0:17:19.960 not interact at all with right handed particles. So that's 0:17:19.960 --> 0:17:21.639 when we mean when we say the universe seems to 0:17:21.720 --> 0:17:25.720 have a preference for left handed particles. The other forces, electromagnetism, 0:17:25.800 --> 0:17:28.080 the strong force, they don't care. They're happy to talk 0:17:28.119 --> 0:17:30.560 to right or left handed particles, but the weak force 0:17:30.880 --> 0:17:34.560 only talks to left handed particles. So it's almost like 0:17:34.560 --> 0:17:39.479 the universe um is not ambidexterous, like the universe seems 0:17:39.520 --> 0:17:43.320 to prefer or at least favor, left handed particles. Over 0:17:43.400 --> 0:17:46.480 right handed particles. Yeah, and it's a slight preference, right, 0:17:46.520 --> 0:17:49.240 because remember, the weak force is a feeble force. It 0:17:49.320 --> 0:17:52.280 is not a powerful force. Does not control the structure 0:17:52.320 --> 0:17:54.560 of our galaxies, it does not control the structure of 0:17:54.600 --> 0:17:58.119 your body. It does not control lightning. Right, It's not 0:17:58.200 --> 0:18:00.719 a very powerful force. And so it's a subtle effect. 0:18:01.119 --> 0:18:03.960 And this was actually overlooked for years and years and years. 0:18:04.119 --> 0:18:07.480 Even well after the weak force was discovered, people hadn't 0:18:07.560 --> 0:18:10.600 really checked to see if it was symmetric, if it 0:18:10.680 --> 0:18:13.399 talked to both kinds of particles. There was this moment 0:18:13.440 --> 0:18:16.119 in the middle of last century when people realized, wow, 0:18:16.160 --> 0:18:19.280 nobody's ever actually checked this to see if the weak 0:18:19.280 --> 0:18:22.200 force was symmetric. And every thought, of course, it's symmetric. 0:18:22.240 --> 0:18:26.560 Everything in the universe is symmetric, strong forces, symmetric, electromagnetism 0:18:26.640 --> 0:18:29.440 is symmetric. It would be bonkers if the weak force 0:18:29.520 --> 0:18:32.199 was not symmetric. But nobody had checked, and so very 0:18:32.240 --> 0:18:36.119 quickly a famous scientist at Columbia skipped or Christmas vacation 0:18:36.200 --> 0:18:39.399 to do this experiment and discover the shocking result that 0:18:39.480 --> 0:18:42.560 the weak force is not just a little bit anti symmetric, 0:18:42.640 --> 0:18:46.400 it's completely antisymmetric. It only talks to left handed particles. 0:18:46.720 --> 0:18:48.680 It was a huge shock wave that went through the 0:18:48.680 --> 0:18:51.600 physics community about fifty years ago. Yeah, I think we 0:18:51.640 --> 0:18:54.600 had a whole episode about this experiment that demonstrated the 0:18:54.680 --> 0:18:57.560 universe has a little bit of a left handed preference, 0:18:57.720 --> 0:19:00.480 and so this preference has pretty big imp cations and 0:19:00.520 --> 0:19:03.679 how the universe works and maybe even how life on 0:19:03.760 --> 0:19:07.560 Earth developed. So let's get into right and left handedness 0:19:07.600 --> 0:19:10.000 of the universe and life on Earth. But first let's 0:19:10.119 --> 0:19:25.080 take a quick break. All right, we're asking the question 0:19:25.200 --> 0:19:29.359 does particle spin affect life on Earth? And so we 0:19:29.400 --> 0:19:31.960 talked about what spin is. It's a property of particles. 0:19:32.320 --> 0:19:35.400 Particles can spin up or down. They can be left 0:19:35.440 --> 0:19:38.679 handed or right handed. And this handedness is something we 0:19:38.720 --> 0:19:41.880 see all throughout, not just the universe, but nature itself. Right, 0:19:41.920 --> 0:19:43.919 I mean in Chemis City they talk about hand in 0:19:43.960 --> 0:19:46.399 this as well of molecules. Yeah, you can apply this 0:19:46.520 --> 0:19:49.399 principle in general to anything. You can ask if something 0:19:49.480 --> 0:19:52.760 is left handed or right handed, and basically you're asking 0:19:53.200 --> 0:19:56.400 would it look the same in the mirror? Right, if 0:19:56.440 --> 0:19:58.639 you flip something in the mirror, would you get something 0:19:58.680 --> 0:20:01.000 the same? And You can literally do this experiment in 0:20:01.080 --> 0:20:04.520 front of yourself with your hands. Like, take your left hand. 0:20:04.880 --> 0:20:07.000 It's not the same as your right hand right. There's 0:20:07.040 --> 0:20:10.359 a different orientation of the fingers relative to the thumb. 0:20:10.359 --> 0:20:12.320 If you put your left hand in the mirror, then 0:20:12.359 --> 0:20:15.680 it looks like your right hand. Right. The mirror flips 0:20:15.720 --> 0:20:18.399 your left hand to a right handed sort of shape. 0:20:18.440 --> 0:20:20.240 But if you just take your right hand, you can't 0:20:20.240 --> 0:20:22.080 like turn around or twist it in any way to 0:20:22.119 --> 0:20:25.680 make it look exactly like your left hand. They're different, right. 0:20:25.680 --> 0:20:28.119 We call that chirality, the one is left handed and 0:20:28.200 --> 0:20:30.800 one is right handed, that they're not the same, right. 0:20:30.920 --> 0:20:33.800 I guess if you're doing the mirror experiment, you would 0:20:33.800 --> 0:20:36.480 see that maybe some parts in your body are symmetric 0:20:36.640 --> 0:20:39.040 and are are not handed right. Like if you take, 0:20:39.119 --> 0:20:41.520 for example, your eyeball, if you put it in front 0:20:41.560 --> 0:20:44.479