WEBVTT - Listener Questions #12 0:00:06.040 --> 0:00:10.200 Why are neutrons so complicated? And why is white chocolate 0:00:10.440 --> 0:00:11.640 not more widely hated? 0:00:11.840 --> 0:00:15.200 Are the bananas we eat all the same? Can we 0:00:15.280 --> 0:00:16.800 save them from that fungal strain? 0:00:17.200 --> 0:00:20.880 Is Jupiter really only made of gas? It's definitely got 0:00:20.920 --> 0:00:21.680 a lot of. 0:00:21.720 --> 0:00:27.360 Mess biology, physics, archaeology, forestry. Thanks for not asking about chemistry. 0:00:28.520 --> 0:00:31.440 What diseases do you get from your cat? Well, we'll 0:00:31.480 --> 0:00:33.159 find the answers to all of that. 0:00:33.479 --> 0:00:36.440 Whatever questions keep you up at night, Daniel and Kelly's 0:00:36.440 --> 0:00:37.600 answers will make it right. 0:00:37.960 --> 0:00:41.479 Welcome to another Listener Questions episode on Daniel and Kelly's 0:00:41.560 --> 0:00:43.120 Extraordinary Universe. 0:00:56.880 --> 0:00:58.240 Hello, I'm Kelly Waitersmith. 0:00:58.280 --> 0:01:01.680 I study parasites and s and you are surprisingly good 0:01:01.720 --> 0:01:02.520 at limericks. 0:01:02.760 --> 0:01:04.959 Well, I don't know about that. I gave a talk 0:01:05.080 --> 0:01:08.720 in Kentucky and a woman who is a poet was invited, 0:01:09.120 --> 0:01:12.840 and she gave a poem about our book, and she 0:01:13.040 --> 0:01:16.960 encouraged me to be bolder about poetry and not so 0:01:17.120 --> 0:01:22.120 self conscious. And I know it's not good my rhymes, 0:01:22.400 --> 0:01:24.160 but I have so much fun, and I'm like, that's 0:01:24.240 --> 0:01:26.880 kind of the point for me. For me, that's the point. 0:01:27.040 --> 0:01:30.119 Well, I'm Daniel I'm a particle physicist. I don't pretend 0:01:30.200 --> 0:01:32.600 to be a poet, but I think the universe is 0:01:32.720 --> 0:01:33.680 kind of poetic. 0:01:33.880 --> 0:01:36.400 Ah See, I think you're a poet in your own 0:01:36.400 --> 0:01:38.760 way because you say very poetic things. 0:01:39.720 --> 0:01:42.399 Well, if being corny and curious about the universe counts 0:01:42.440 --> 0:01:45.040 as being poetic, then put me on that list. 0:01:45.160 --> 0:01:49.760 It's a dad kind of poetry. 0:01:48.000 --> 0:01:52.400 Dad poetry. Oh my gosh, science dad poetry. That is 0:01:52.440 --> 0:01:56.000 a new genre we are pioneering here, science parent poetry. Really. 0:01:56.200 --> 0:01:59.720 Yes, Well, you might ask yourself why would Kelly make 0:01:59.760 --> 0:02:03.520 her poems public. I don't really know. I have a 0:02:03.760 --> 0:02:06.400 confidence beyond what I ought to. But you know, there 0:02:06.480 --> 0:02:09.160 are other questions out there, and our listeners have loads 0:02:09.160 --> 0:02:10.000 of them. 0:02:10.200 --> 0:02:13.880 Questions deeper than Kelly's ability to rhyme. We love hearing 0:02:13.960 --> 0:02:16.840 your questions about the universe. How did it begin? How 0:02:16.880 --> 0:02:18.560 is it going to end? What does it all mean? 0:02:18.680 --> 0:02:21.839 How does it come together to explain everything we are 0:02:22.000 --> 0:02:24.960 and everything we eat and all the poems we listen to. 0:02:25.440 --> 0:02:27.520 If you have questions about the nature of the universe 0:02:27.520 --> 0:02:29.920 and you can't find answers, you've been googling, you've been 0:02:29.960 --> 0:02:34.240 asking your neighbors, you don't know any physicists or parasitologists yourself. 0:02:34.440 --> 0:02:38.560 Please write into us to questions at Danielankelly dot org. 0:02:38.840 --> 0:02:41.200 We love, love, love to hear from you, and you 0:02:41.240 --> 0:02:42.919 will definitely hear from us. 0:02:43.040 --> 0:02:45.840 And everybody should have a parasitologist and a physicist in 0:02:45.840 --> 0:02:47.400 their lives, and we are here for you. 0:02:48.400 --> 0:02:51.080 That's right. We are feeling that whole you didn't know 0:02:51.120 --> 0:02:54.240 you had in your life exactly. And so today we 0:02:54.280 --> 0:02:58.240 have a bunch of really fun questions about neutrons, about bananas, 0:02:58.280 --> 0:03:01.120 and about Jupiter, and there's a theme that's going to 0:03:01.200 --> 0:03:04.079 tie them all together. We'll reveal it at the end. 0:03:04.320 --> 0:03:06.399 Oh, Daniel's going to be revealing this to Kelly too, 0:03:06.440 --> 0:03:09.200 because I didn't see a theme well, I was reading 0:03:09.200 --> 0:03:11.440 our outline. Can't wait to find out. 0:03:11.800 --> 0:03:13.920 This first question is from Scott Lewis, who thought that 0:03:13.960 --> 0:03:17.000 neutrons also needed some Daniel and Kelly love after hearing 0:03:17.000 --> 0:03:18.880 our episode about protons. 0:03:19.320 --> 0:03:21.840 Hi, Kelly and Daniel. There have been a number of 0:03:21.919 --> 0:03:26.440 articles lately discussing the internal complexity of the proton and 0:03:26.560 --> 0:03:30.040 everything we are learning about it. One article went so 0:03:30.120 --> 0:03:33.440 far as to describe it as the most complicated thing 0:03:33.520 --> 0:03:38.160 you can possibly imagine. I've read of unusual tetri quark 0:03:38.400 --> 0:03:42.720 configurations and other weird things that show up in the 0:03:42.720 --> 0:03:46.840 colliders from time to time. Is the internal structure of 0:03:46.880 --> 0:03:50.920 a neutron similarly complex? Do we know less about the 0:03:50.960 --> 0:03:54.000 guts of a neutron? And if so, is there a 0:03:54.080 --> 0:03:58.360 reason why they are perhaps more difficult to study? Thank 0:03:58.400 --> 0:04:01.839 you for everything you guys do great job on the program. 0:04:02.560 --> 0:04:04.880 This is a great question. And you know, Daniel, whenever 0:04:04.960 --> 0:04:07.320 I hear about neutrons, I think about one of those 0:04:07.360 --> 0:04:10.520 disaster movies with John Cusack in it, where the world 0:04:10.680 --> 0:04:15.520 was like falling apart because the neutrons had mutated. Yeah, 0:04:16.279 --> 0:04:19.240 I know, I almost walked out of that movie. I 0:04:19.279 --> 0:04:21.600 loved John Cusack as a child of the eighties. 0:04:21.640 --> 0:04:23.880 You know, you can say anything, but don't say anything 0:04:23.920 --> 0:04:25.160 about neutrons mutating. 0:04:25.400 --> 0:04:29.240 That's right, That's a line for me, a line. But 0:04:29.279 --> 0:04:31.360 I gotta say, I don't really understand neutrons very well. 0:04:31.440 --> 0:04:34.240 So let's start at the beginning. What are neutrons? And 0:04:34.279 --> 0:04:36.800 hopefully by the end I'll be convinced that they won't 0:04:36.839 --> 0:04:38.320 mutate and I don't have to worry about the world 0:04:38.320 --> 0:04:38.960 being destroyed. 0:04:39.040 --> 0:04:41.800 Well, I agree with Scott. Neutrons are just as fascinating, 0:04:41.880 --> 0:04:44.240 if not more so, than protons, and they don't get 0:04:44.279 --> 0:04:46.720 as much attention because we don't think of them as 0:04:46.720 --> 0:04:49.800 the building blocks of matter, but they really are. They're essential. 0:04:49.839 --> 0:04:52.640 Without neutrons, we wouldn't have big, complicated atoms that you 0:04:52.680 --> 0:04:56.880 need for biology and chemistry and bananas for example. But 0:04:56.960 --> 0:04:59.920 protons and neutrons are very closely related. Both of them 0:05:00.160 --> 0:05:03.480 are made of the same fundamental objects, just different amounts 0:05:03.480 --> 0:05:07.120 of them. So a proton is made of two upcorks 0:05:07.320 --> 0:05:09.880 and a down cork, and so the upcork is charged 0:05:09.920 --> 0:05:12.520 two thirds and then down cork is charged minus one third. 0:05:12.760 --> 0:05:15.200 So you add two upquarks and a down cork you 0:05:15.279 --> 0:05:17.719 get a total charge of one. That's the proton. If 0:05:17.800 --> 0:05:20.560 you switch one of those upcorks for a down cork, 0:05:20.640 --> 0:05:23.599 and they have one upcork with charge two thirds and 0:05:23.680 --> 0:05:26.919 two down corks with charge minus one third each, you 0:05:26.960 --> 0:05:31.040 get a neutron because it's neutral as zero electric charge. 0:05:31.120 --> 0:05:33.800 So two downs and an up neutron, two ups and 0:05:33.839 --> 0:05:34.440 a down. 0:05:34.440 --> 0:05:37.280 Proton got it. So usually on this show you hear 0:05:37.320 --> 0:05:40.440 me complain about how bad physicists are at naming things 0:05:40.640 --> 0:05:44.080 because we are exactly Yeah, I'm making an accurate observation, 0:05:45.000 --> 0:05:47.520 but I love that y'all have named the thing that 0:05:47.600 --> 0:05:51.120 holds it all together gluons, and I'm assuming that's because 0:05:51.160 --> 0:05:52.479 it sounds like glue, right. 0:05:53.520 --> 0:05:56.160 Well, the gluons aren't very sticky. Yes, yeah, they do 0:05:56.279 --> 0:05:59.880 hold these things together. And so upquarks and down quarks 0:06:00.000 --> 0:06:03.200 are super fascinating because they are similar to other particles 0:06:03.200 --> 0:06:06.159 we know, like electrons, but they also feel another force, 0:06:06.240 --> 0:06:09.520 the strong nuclear force, So they are charged. We talked 0:06:09.520 --> 0:06:12.000 about them having two thirds or negative one third charge, 0:06:12.040 --> 0:06:15.280 so they feel electromagnetism. They can shoot off photons, they 0:06:15.279 --> 0:06:18.279 feel electric fields, but there's another field in the universe 0:06:18.320 --> 0:06:21.039 that they feel that electrons ignore, and that's the color 0:06:21.080 --> 0:06:25.839 field of the strong nuclear force and vibrations of that field. 0:06:25.920 --> 0:06:30.000 They're actually eight different ones are called gluons, and so 0:06:30.120 --> 0:06:33.080 gluons are the mediator of the strong force, the way 0:06:33.120 --> 0:06:36.599 photons are the mediator of the electromagnetic force. It's just 0:06:36.680 --> 0:06:39.800 one of the things the universe can do. And electrons 0:06:39.839 --> 0:06:42.279 have zero color charge, so they just fly through and 0:06:42.320 --> 0:06:45.080 ignore it the way neutrinos, for example, ignore electric fields. 0:06:45.680 --> 0:06:48.120 But quarks they feel all of the fields. The weak feel, 0:06:48.200 --> 0:06:50.960 the strong field, the electromagnetic field, they feel all of them, 0:06:51.240 --> 0:06:53.960 and the strong field is the strongest one, and so 0:06:54.040 --> 0:06:56.960 it binds these particles together very very tightly. So the 0:06:57.000 --> 0:06:59.880 proton and the neutron are both bound together using gluon. 0:07:00.520 --> 0:07:03.400 And is there a history behind gluons that's going to 0:07:03.560 --> 0:07:06.200 like make me think y'all aren't clever or was it 0:07:06.240 --> 0:07:08.880 called gluons because it like seems to glue things together. 0:07:10.240 --> 0:07:12.640 No, we're called the gluons because they glue the nucleus 0:07:12.680 --> 0:07:15.600 together exactly. And there's a whole fascinating history about the 0:07:15.640 --> 0:07:19.360 discovery of gluons and the personalities involved. It was really 0:07:19.400 --> 0:07:22.120 interesting moment with fascinating history. But basically every discovery in 0:07:22.160 --> 0:07:25.760 particle physics has like cool personalities and controversies. 0:07:25.840 --> 0:07:28.200 You would say that as a prominent member of that community. 0:07:30.840 --> 0:07:34.040 They're not always positive stories. You know, there's like arguments 0:07:34.040 --> 0:07:36.880 and people peeing on other people's experiments, and like, you know, 0:07:36.960 --> 0:07:40.360 these are human stories, because hey, physicists are people, you know, 0:07:40.400 --> 0:07:42.800 we're just curious about the universe, and there are Nobel 0:07:42.880 --> 0:07:45.880 prizes at stake, so you don't always get the best 0:07:45.880 --> 0:07:46.760 side of everybody. 0:07:46.880 --> 0:07:49.120 They sure smell like people. You walk up to them, 0:07:49.120 --> 0:07:51.640 you're like, yeah, you're a person. But anyway, okay, one 0:07:51.720 --> 0:07:54.040 day we should get the great story behind gluons. But 0:07:54.560 --> 0:07:56.160 let's talk about how neutrons decay. 0:07:56.400 --> 0:07:58.880 Yeah, so the fascinating thing that neutrons can do that 0:07:58.920 --> 0:08:01.920 protons do not do is that they decay. They don't 0:08:02.000 --> 0:08:05.280 last forever. You have a neutron out there in the universe, 0:08:05.400 --> 0:08:08.840 just by itself, it's gonna turn into a proton. And 0:08:08.880 --> 0:08:11.840 the way it does this is that one of those quarks, 0:08:11.840 --> 0:08:14.960 the dcork, turns into an upcork, so it goes from 0:08:15.040 --> 0:08:18.160 D to up. Now it starts out as a D cork, 0:08:18.200 --> 0:08:21.600 which is charged negative one third, and becomes an upcork, 0:08:21.760 --> 0:08:24.840 which is charged two thirds. So to conserve electric charge, 0:08:24.840 --> 0:08:27.840 it has to emit a negatively charged particle, so it 0:08:27.880 --> 0:08:30.880 emits a W minus which has charged negative one So 0:08:30.960 --> 0:08:34.320 all the charges balance out. So this dcork emits a 0:08:34.440 --> 0:08:38.280 W minus and turns into an upcork, turning the neutron 0:08:38.480 --> 0:08:41.840 into a proton, and then shooting off this W minus particle. 0:08:42.080 --> 0:08:45.880 Okay, so neutron, when it becomes a proton, you get 0:08:45.920 --> 0:08:48.160 a proton and an electron that shoots off. 0:08:48.440 --> 0:08:51.360 You get a W minus, not an electron, but you're close. 0:08:51.400 --> 0:08:53.880 Because the W minus doesn't live for very long. It 0:08:53.920 --> 0:08:58.600 turns into an electron and an anti neutrino, and so 0:08:58.880 --> 0:09:02.160 that's basically the process is the neutron turns into a 0:09:02.160 --> 0:09:04.560 proton in order to balance the charge it has to 0:09:04.600 --> 0:09:07.200 carry along an electron eventually, right, because you start with 0:09:07.240 --> 0:09:09.400 a neutron it's zero charge, you end up with a 0:09:09.400 --> 0:09:11.600 proton with plus one, and you need the electron with 0:09:11.679 --> 0:09:15.319 minus one to balance the electric charges. But the universe 0:09:15.400 --> 0:09:18.760 is not happy with that because the universe also conserves 0:09:18.800 --> 0:09:22.520 the number of electrons. Like, you can't just create electrons 0:09:22.559 --> 0:09:25.640 willy nilly. The universe keeps tabs on that. So if 0:09:25.640 --> 0:09:27.480 you create an electron, you also have to create an 0:09:27.520 --> 0:09:31.360 anti electron or it turns out electron neutrinos also count. 0:09:31.559 --> 0:09:34.199 So if you create an electron and an anti electron 0:09:34.240 --> 0:09:37.600 neutrino at the same time, then everything balances out. You've 0:09:37.600 --> 0:09:40.040 accounted for everything the universe cares about. 0:09:40.280 --> 0:09:43.720 I think the up down quarks give me this maybe 0:09:43.760 --> 0:09:45.960 false sense of understanding what's going on, because I just 0:09:46.000 --> 0:09:48.040 imagine an up arrow and a down arrow and I'm like, oh, 0:09:48.080 --> 0:09:49.600 I got it. You just flip the down arrow. Now 0:09:49.640 --> 0:09:51.520 it's pointing up. But what does it mean to say 0:09:51.559 --> 0:09:54.400 it emits a W minus? Is it just like the 0:09:55.000 --> 0:09:58.480 change in energy gets expelled, and that's what it means 0:09:58.480 --> 0:09:59.960 to say emitting a W minus. 0:10:00.400 --> 0:10:02.600 We really do think about these things as a pair, 0:10:02.800 --> 0:10:04.640 or the up on the top and the D on 0:10:04.679 --> 0:10:07.079 the bottom, And the way we think about it from 0:10:07.080 --> 0:10:09.439 a sort of theoretical point of view is that the 0:10:09.640 --> 0:10:11.840 W is the way to go up or down. So 0:10:11.840 --> 0:10:14.680 there's actually two w's, the W plus and the W minus. 0:10:14.800 --> 0:10:16.439 If you want to go from the D to the U, 0:10:16.760 --> 0:10:18.560 you emit a W minus. If you want to go 0:10:18.600 --> 0:10:21.120 from the U to the D, you emit a W plus. 0:10:21.400 --> 0:10:24.000 So these are sort of like stair steps in order 0:10:24.000 --> 0:10:26.120 to go from one to the other. That's sort of 0:10:26.120 --> 0:10:28.560 the same way around an atom. An electron can go 0:10:28.640 --> 0:10:30.720 up and down energy levels, and to do so, it 0:10:30.840 --> 0:10:35.200 either emits or absorbs a photon. These ws change the 0:10:35.240 --> 0:10:37.280 state from a D to a U, and there is 0:10:37.320 --> 0:10:40.640 a connection to the sort of underlying theoretical structure which 0:10:40.640 --> 0:10:44.040 we usually represent using these things called groups, where you 0:10:44.040 --> 0:10:46.440 can transform an object, but it stays within a little 0:10:46.440 --> 0:10:49.079 pre defined set that's called a group, and so it's 0:10:49.080 --> 0:10:51.320 deeply connected to the sort of group theory structure, which 0:10:51.360 --> 0:10:53.480 I think we should dig into sometime on the podcast. 0:10:53.960 --> 0:10:56.120 But the basic version is that the up is sort 0:10:56.120 --> 0:10:58.439 of the higher state and the down is the lower state. 0:10:58.600 --> 0:11:01.400 But you can move between them using these ws. 0:11:01.640 --> 0:11:03.679 Okay, awesome, all right, I think I get that. Thank you. 0:11:03.960 --> 0:11:07.400 So you can go from neutron to proton. But protons 0:11:07.440 --> 0:11:10.959 don't decay into neutrons. Why do neutrons decay? 0:11:11.280 --> 0:11:15.320 Yeah, great question. Why do neutrons decay and protons don't. Well, 0:11:15.360 --> 0:11:18.440 neutrons have a higher mass than protons, and so when 0:11:18.559 --> 0:11:20.679 a neutron decays, it gives off a little bit of 0:11:20.760 --> 0:11:23.640 energy and turns into a proton. Why does a neutron 0:11:23.720 --> 0:11:25.600 have a higher mass than a proton. Well, remember, the 0:11:25.640 --> 0:11:29.199 mass of these guys comes from the bonds between the quarks. 0:11:29.280 --> 0:11:31.600 It's not because the neutron is made of heavier stuff 0:11:31.640 --> 0:11:34.080 than the protons. These up and down quarks have almost 0:11:34.200 --> 0:11:37.000 no mass, basically zero compared to the mass of the 0:11:37.000 --> 0:11:39.640 proton and the neutron. All of the mass of these 0:11:39.720 --> 0:11:43.120 guys comes from the gluons, the arrangements of the particles, 0:11:43.320 --> 0:11:46.240 and so the neutron state up down down is a 0:11:46.320 --> 0:11:49.880 higher energy configuration than the up, up down proton state, 0:11:50.280 --> 0:11:52.360 and so it's just like a higher energy level the 0:11:52.400 --> 0:11:54.320 way like around an atom. You know, there's like the 0:11:54.360 --> 0:11:57.000 five two S state is a higher energy level than 0:11:57.040 --> 0:11:59.280 like the two P or whatever. There's all these different 0:11:59.400 --> 0:12:01.480 energy levels, and they have to do with the arrangements 0:12:01.480 --> 0:12:05.000 between the particles, the configurations, and so the strong nuclear 0:12:05.000 --> 0:12:08.960 force super duper complicated. But this neutron state, the UDD state, 0:12:09.360 --> 0:12:12.400 is higher energy than the UUD and so it can 0:12:12.440 --> 0:12:14.640 decay down. And that's what the universe does. It always 0:12:14.800 --> 0:12:18.040 starts with massive particles which decay down into lighter particles. 0:12:18.480 --> 0:12:22.080 The proton can't decay because there's nothing lighter than the proton. 0:12:22.800 --> 0:12:25.560 Like you can't find a state that's lighter than the proton. 0:12:25.559 --> 0:12:27.920 If you turned that other D into a U for example, 0:12:28.040 --> 0:12:31.120 it actually would be a higher energy state than the proton. 0:12:31.520 --> 0:12:33.040 So the proton is sort of like the bottom of 0:12:33.080 --> 0:12:35.800 the ladder, the same way the electron is. The muon 0:12:35.880 --> 0:12:38.280 can decay into an electron and other stuff. Why doesn't 0:12:38.320 --> 0:12:40.920 the electron decay because there's nothing for it to decay into. 0:12:41.040 --> 0:12:44.040 It's the lightest particle, and therefore it's stable. Now, we 0:12:44.080 --> 0:12:46.520 don't know that the proton is actually stable, we've just 0:12:46.600 --> 0:12:49.680 never seen it decay, and so we can estimate that 0:12:49.720 --> 0:12:52.720 its lifetime is super duper long because we've watched a 0:12:52.760 --> 0:12:54.440 bunch of protons for a long time to see if 0:12:54.440 --> 0:12:56.720 any of them decay and never seen a single one decay, 0:12:56.720 --> 0:12:59.880 which means either they're totally stable, like they live forever, 0:13:00.679 --> 0:13:02.960 or they live for such a long time that we 0:13:03.040 --> 0:13:05.440 just haven't seen one yet, and that lifetime would be 0:13:05.480 --> 0:13:08.200 like billions and billions of years. So neutrons are super 0:13:08.200 --> 0:13:11.240 fascinating because they actually do decay, so we can learn 0:13:11.280 --> 0:13:13.400 something about what's going on inside them. 0:13:13.720 --> 0:13:16.120 So, in the nucleus of an atom, you have the 0:13:16.120 --> 0:13:18.800 same number of protons and neutrons, but the number of 0:13:18.800 --> 0:13:22.440 protons isn't changing over time, but neutrons are decaying into protons. 0:13:22.920 --> 0:13:26.360 What's gonna happen? Are we eventually not gonna have enough 0:13:26.360 --> 0:13:27.520 neutrons for everything? 0:13:28.240 --> 0:13:30.840 Yeah, this is really amazing because remember we were talking 0:13:30.880 --> 0:13:33.640 about neutrons by themselves. A single neutron in the middle 0:13:33.679 --> 0:13:37.120 of space will decay in about eleven to twelve minutes, 0:13:37.679 --> 0:13:40.120 So you might be wondering, why isn't everything inside me? 0:13:40.160 --> 0:13:42.400 Why aren't all my neutrons turning into protons? And then 0:13:42.480 --> 0:13:46.360 like you know, everything's going haywire because the neutron is stable. 0:13:46.520 --> 0:13:49.440 If it's inside the atom, it's unstable and will decay 0:13:49.440 --> 0:13:52.920 into a proton when it's outside by itself, but inside 0:13:52.920 --> 0:13:55.439 the atom, all of its other neutron and proton buddies 0:13:55.520 --> 0:13:59.000 stabilize it. That's really weird, right, what's going on was 0:13:59.080 --> 0:14:02.360 some really interesting stuff is happening there because when the 0:14:02.400 --> 0:14:05.400 neutrons and the protons are together in the nucleus, they're 0:14:05.440 --> 0:14:08.359 not just like packed in like tennis balls. They're interacting 0:14:08.360 --> 0:14:11.600 with each other. Right, These things are quarks with gluons 0:14:11.600 --> 0:14:14.199 holding them together, but they're not completely sealed off from 0:14:14.200 --> 0:14:16.679 anything else. If you're like on one side of the gluon, 0:14:16.720 --> 0:14:18.280 you might be closer to one of the quarks or 0:14:18.400 --> 0:14:20.680 closer to one of the other quarks. So you can 0:14:20.720 --> 0:14:24.640 actually feel the quarks inside the neutron if you're nearby it. 0:14:25.000 --> 0:14:26.600 And so the atom is not just like a bunch 0:14:26.640 --> 0:14:29.680 of tennis balls totally sealed off. They're interacting with each other. 0:14:29.880 --> 0:14:33.080 There's this little residual strong force that's actually what holds 0:14:33.080 --> 0:14:34.080 the nucleus together. 0:14:34.400 --> 0:14:36.480 Friends help you hold everything together. 0:14:36.600 --> 0:14:40.360 Yes, exactly, And so inside of the nucleus, neutrons can 0:14:40.400 --> 0:14:43.080 live a long long time. Sometimes they can live forever. 0:14:43.600 --> 0:14:45.840 Like take a carbon atom. Carbon has a bunch of 0:14:45.880 --> 0:14:49.480 neutrons in the nuclei. Those neutrons will live forever. You 0:14:49.520 --> 0:14:51.120 have a carbon atom, we think it could just sit 0:14:51.200 --> 0:14:54.600 in space for a zillion zillion zillion years. Other elements 0:14:54.600 --> 0:14:57.600 are not as stable, like uranium, for example, will break down, 0:14:58.000 --> 0:14:59.760 and one of the ways it does is through these 0:14:59.800 --> 0:15:03.240 kind of decays. And so neutrons can either crack open 0:15:03.280 --> 0:15:06.200 your nucleus if they're not quite stable enough, or they 0:15:06.240 --> 0:15:09.080 can help it stay together. Like the reason the nucleus 0:15:09.080 --> 0:15:11.640 stays together all these protons which otherwise are pushing each 0:15:11.680 --> 0:15:14.320 other apart, is because the neutrons are there in between 0:15:14.360 --> 0:15:16.840 you to help stabilize it, to pull them together with 0:15:16.920 --> 0:15:19.080 the strong force, and to keep the protons from pulling 0:15:19.160 --> 0:15:22.440 themselves apart. So neutrons are really the glue that holds 0:15:22.440 --> 0:15:23.560 the whole universe together. 0:15:23.680 --> 0:15:26.800 I feel like you could write nerdy Hallmark cards. 0:15:28.520 --> 0:15:30.040 I love you and your neutrons. 0:15:30.120 --> 0:15:36.280 That's right. You hold me together, you're my proton, you 0:15:36.400 --> 0:15:38.560 keep me from decay. That's right. 0:15:41.120 --> 0:15:44.000 But there's also still a bunch of mysteries about the neutron, 0:15:44.080 --> 0:15:47.200 Like we think we understand the basic story here, but 0:15:47.480 --> 0:15:50.440 you know, particle physicist nerds always want to drill down 0:15:50.440 --> 0:15:52.320 and said, do we really understand it. Let's make a 0:15:52.360 --> 0:15:55.200 bunch of really precise measurements in different ways and see 0:15:55.200 --> 0:15:58.520 if there's anything surprising. So there's this mystery right now 0:15:58.560 --> 0:16:01.520 in exactly how long the neutron does live? 0:16:01.920 --> 0:16:03.480 How do we ask that question? 0:16:03.720 --> 0:16:06.040 So people came up with two very different ways to measure, 0:16:06.120 --> 0:16:09.080 like how long does a neutron take to decay? There's 0:16:09.120 --> 0:16:12.120 the bottle method and the beam method. And the bottle 0:16:12.160 --> 0:16:14.840 method is pretty simple. It says, take a bunch of neutrons, 0:16:15.160 --> 0:16:17.560 cool them down so they're not flying around everywhere, put 0:16:17.560 --> 0:16:20.360 them in a bottle, and then just wait and see 0:16:20.360 --> 0:16:23.200 how many you have, like you know, plot them over time. 0:16:23.840 --> 0:16:26.120 The way we study radioactive decay or any kind of 0:16:26.240 --> 0:16:28.360 random process is you start with a bunch of them 0:16:28.360 --> 0:16:29.680 and you wait to see how long does it take 0:16:29.760 --> 0:16:32.720 until you have half as many and that's the characteristic lifetime. 0:16:33.320 --> 0:16:35.000 And so that's what they do, and they get a number. 0:16:35.040 --> 0:16:37.920 It's like fourteen minutes and thirty nine seconds. It's the 0:16:38.000 --> 0:16:41.160 characteristic lifetime of a neutron. This is a really cool 0:16:41.160 --> 0:16:44.440 experiment they do in Los Alamos, New Mexico, actually my hometown, 0:16:45.120 --> 0:16:48.080 and they have these ultra cold neutrons. They've chilled them 0:16:48.080 --> 0:16:51.520 down to like milli kelvin inside this container they call 0:16:51.760 --> 0:16:54.800 the bathtub. It's like one meter in diameter. They just 0:16:54.840 --> 0:16:57.080 like fill it with neutrons and count them and then 0:16:57.160 --> 0:16:59.560 wait to see what happens. And so they get their number. 0:16:59.640 --> 0:17:01.840 And you know, these are serious dudes. They take it 0:17:01.920 --> 0:17:04.159 very seriously. They've account for all sorts of uncertainty, they 0:17:04.160 --> 0:17:06.960 have cross checks whatever. They're very confident in their number. 0:17:07.200 --> 0:17:10.400 But there's another experiment, the beam experiment, and they don't 0:17:10.440 --> 0:17:11.359 get the same answer. 0:17:11.640 --> 0:17:13.760 What how much does it differ by the. 0:17:13.640 --> 0:17:16.919 Beam experiment makes a neutron beam? And you know we 0:17:16.920 --> 0:17:19.359 said that neutrons decay into protons, right, So they had 0:17:19.359 --> 0:17:22.000 this clever idea like, oh, neutrons are actually really hard 0:17:22.000 --> 0:17:24.600 to count. The other guys have this complicated, sophisticated equipment 0:17:24.640 --> 0:17:27.560 to count neutrons. They're hard. Let's just count the protons. 0:17:27.600 --> 0:17:30.440 If neutrons are decaying into protons, let's just count the protons. 0:17:30.640 --> 0:17:33.200 And so they fly it through an electromagnetic field, filter 0:17:33.280 --> 0:17:36.040 out the protons and count those and they get a 0:17:36.040 --> 0:17:39.600 different answer. They get a slightly longer answer by nine seconds. 0:17:39.880 --> 0:17:42.280 So instead of fourteen minutes and thirty nine seconds, they 0:17:42.280 --> 0:17:45.120 get fourteen minutes and forty eight seconds. So they think 0:17:45.200 --> 0:17:47.960 neutrons live a little bit longer than the bathtub. 0:17:48.080 --> 0:17:49.879 Guys, but don't you have to at least know how 0:17:49.880 --> 0:17:53.240 many neutrons you're starting with, because if you get ten protons, 0:17:53.840 --> 0:17:55.760 but you don't know how many neutrons you started with, 0:17:55.960 --> 0:17:58.159 how do you know the rate of decay? 0:17:58.440 --> 0:18:01.200 Yeah, good question. They know how many neutrons they've started 0:18:01.200 --> 0:18:03.800 with because they know how they produce the neutrons, Okay, 0:18:03.800 --> 0:18:06.000 and so they think they've accounted for that. But you 0:18:06.040 --> 0:18:09.280 know something is going on here, like it's the same process. 0:18:09.280 --> 0:18:11.880 They should get the same answer. So either somebody's made 0:18:11.880 --> 0:18:15.760 a subtle air totally possible, right, and they both work 0:18:15.880 --> 0:18:19.400 really really hard to reduce these uncertainties. Often in this scenario, 0:18:19.440 --> 0:18:21.960 you get two experiments. They get different measurements, but they 0:18:22.000 --> 0:18:24.119 both have large uncertainties and they overlap, and then they 0:18:24.160 --> 0:18:27.040 both work really really hard to refine their experiments, and 0:18:27.119 --> 0:18:30.560 usually as the uncertainty shrink, the results converge into one answer. 0:18:30.560 --> 0:18:33.920 You're like, Okay, cool, the universe is coherent. But what's 0:18:33.920 --> 0:18:36.840 happening here is that the uncertainties are shrinking, but the 0:18:36.880 --> 0:18:39.520 answers are not getting closer together, so they're getting more 0:18:39.560 --> 0:18:43.360 and more confident in their discrepancy, which means, hey, maybe 0:18:43.359 --> 0:18:46.840 there's some new interesting physics. Maybe the neutron, like the 0:18:46.880 --> 0:18:50.320 boring vanilla particle most people aren't excited about, is actually 0:18:50.320 --> 0:18:53.800 the portal to discovering the nature of the universe. You 0:18:53.880 --> 0:18:58.240 all are pros at Silver Linings, Well, this is really 0:18:58.280 --> 0:19:01.760 fun idea that maybe neutrons don't just decay to protons. 0:19:02.080 --> 0:19:06.440 Maybe sometimes neutrons decay into something else, like dark matter, 0:19:06.920 --> 0:19:09.520 and so in the neutron beam, what's happening is these 0:19:09.560 --> 0:19:12.320 neutrons are just disappearing into dark matter, and those guys 0:19:12.320 --> 0:19:14.919 are not measuring it. So maybe the bathtub guys are 0:19:15.000 --> 0:19:18.000 right because they're actually measuring the neutrons, whereas the guys 0:19:18.000 --> 0:19:20.600 who are assuming they turn into protons. They're the ones 0:19:20.640 --> 0:19:24.240 getting the wrong answer because it's not always going to protons. 0:19:24.240 --> 0:19:25.639 Sometimes it's going to dark matter. 0:19:25.840 --> 0:19:28.280 And we can't measure dark matter right. 0:19:28.240 --> 0:19:30.080 We do not have ways to measure dark matter is 0:19:30.119 --> 0:19:32.400 certainly not in these beams, and so this is really 0:19:32.400 --> 0:19:35.240 interesting and really important because it could be an indication 0:19:35.359 --> 0:19:38.080 of something that's happening. And it's also important because it 0:19:38.080 --> 0:19:40.960 helps us understand the early universe. You know, in the 0:19:41.080 --> 0:19:43.840 very early universe, we had like quarks and gluons flying 0:19:43.880 --> 0:19:47.920 around and things cool down into hydrogen and briefly also 0:19:48.080 --> 0:19:52.000 forming some helium. And that ratio of hydrogen helium is 0:19:52.040 --> 0:19:55.000