What is a Neutrino?

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Speaker 1: Or Hey, did you know that there's a whole universe of particles that exists all around us, passing through us, and you can't feel any of it. You mean like a like a ghost world. Yeah, like zillions of particles and you can't see or touch or detect or really could even know that they're there. So what do you mean it's like a whole universe passing through me, Like there's stuff but we can't see it or touch it. I mean that there's a huge amount of stuff in the universe that you can't detect. It's there, it's interacting, it's doing things, but you can't notice it. You don't only notice things with your senses. That doesn't access everything in the universe. In fact, we have no idea what for acting in the universe We can't see at all. Right, there could be huge amounts of crazy, invisible purple monsters that we can't touch and never will. Well, those that can't see sometimes you know, yeah, sometimes we can see a little hints of it, and that gives us a clue that there are vast amounts of things happening in the universe that we only rarely get to see. Whoa WHOA is right. Hi, I'm je and I'm Daniel, and this is Daniel and Jorge Explain the universe. The universe, The Universe, the universe. Yeah, it's a podcast where we try to talk about all the crazy and amazing things that make up this universe we live in. We want to take the whole universe, wrap it up in about twenty minutes and make it digestible to you fitted inside of your brain, through your ears, or you know, really, maybe we could grind it up, dry it and you could snort the universe. That'd be pretty That's what we just say. Or however you consume your podcasts, that's very important in whatever, in whatever form you smoke or snort or listen to your podcasts. But on today's program, we're gonna talk about something mysterious, something you can't eat, but something which is all around you right now. Billions and billions of them are passing through you right now. And we're not talking about last night's pizza. I know. The topic of today's episode is the neutrino called the ghostly particle, right, that's right. Some two people call it the ghostly particle. The word neutrino is Italian for little neutral one. It's a nickname given to the particle well before it was discovered, and it's a really weird little particle. So we thought, let's break it down to explain to people what it actually is, because it's a fascinating mystery. Yeah, I imagine not a lot of people who have heard of I mean maybe some people have heard of the neutron, but the neutrino that may not be as well known. In order to get a sense for what people knew about the neutrino, I went out and I asked people around campus that you see Irvine what they knew. So play along at home, think to yourself, what do you know about the neutrino? And then listen to these interviews. Here's what people had to say. I don't watch about it, but it's I often hear that got like a cosmic some one of those cosmic race and people try to detect using specialized tools. I heard of it, but I don't exactly what it is. Great, I do not know what that is now, um no, no, alright, I'm not exactly sure. So like some kind of funk esdays and nutrition, I don't know what is it? Alright? Not a popular particle. No, Almost nobody on campus had any idea what the neutrina was. One person thought it was some sort of fungus that might grow on your toes, which you could still be I mean, well, I mean, we don't know a lot about it. Right well, it could have potentially contribute to fungi, or you could could be accumulating in your toes right now, Daniel. More likely somebody creates or just or discovers a new form of fungus and names it after the neutrino right after this podcast goes wild. But yeah, pretty much across the board, everyone said I've never heard of this, And let me tell you how deeply disappointing that is to me as a particle physicist. Work you see, Irvine, and let me tell you why. The reason is that the guy who discovered the new trino and won the Nobel Prize for it. Okay, and down at you See Irvine. We have a few Nobel Prize winners. But it's not like we have dozens and dozens. It's not like Berkeley where they have a special parking lot for Nobel Prize winners. Nobel Prize, Daniel, I do not have a Nobel Prize as the recording of this podcast Breaking News, Breaking News. You think that's something you would already know, because if I had a Nobel Prize, I'd be wearing it around my chest. Um So, so it was discovered by somebody in your campus, right there, Fred Ryness. Yeah. In fact, the building is now named after him. I work in Ryness Hall, named after Fred Ryness, the discoverer of the new Trino, and he won the Nobel Prize. This is It's a pretty big deal around campus, and so you think maybe somebody on campus here, you see Irvine, would know that. What's one of the things that we're famous for? Is it part of like the tours when people, you know, people tour campuses and they say, this is where the nutrina was discovered. Oh my god, don't even get me started. It is part of the tour. But it drives me crazy because every time they walk by my building and they hear the tour and they say, oh, this is the building named after Fred Ryan is so won the Nobel Prize. Then they give a little spiel about the neutrino and they get almost everything about it totally wrong. And I'm tempted every time to step into the referende. Excuse me, Actually, you're going to train our round run with that voice. I love it. I know how that's gonna go over. Nobody cares. But do you know I feel like people visiting the campuses deserve a good explanation. It might factor into their decision to go to u c R. Vine. Let's record an excellent podcast about the neutrino, and then it will make it required listening for all the tour guides, and then I won't have to explain it to every single one of them one aever. Well, just just put it on a speaker. You'll stand outside your building with a boom box playing the podcast, like you to say anything that's right. Yeah, I definitely will not get picked up by campus security to nanoseconds. Absolutely, that's a great idea, Thank you, y. So let's break it down. What is a neutrina all right? A neutrino is a fundamental particle. What does that mean? Well, a fundamental particle, as we see it, is a point in space. It's a tiny dot, right, It's a place in space where we think there might be electric charge, there might be matter, there might be all sorts of quantum properties. Other examples are the electron right or the corks. These are all particles we think are not made of other little particles. That's why we call them fundamental. So particles are not like little balls. You're saying there's special points in space. That's right. We're made out of atoms, which are made out of particles and things we're made out of. They're not little balls. They're actually just like little special points in space. That's kind of your definition of a particle. Yeah, exactly. And it's very tempting to think of particles a little balls because, for example, cartoonists frea balls and slaggers. Shame on them. Well, it's very difficult to draw a ball that has no volume because it's literally not there. Right, Any tiny point you draw is going to have a left side and a right side, which means it has a size right. But a particle is just a single point in space. There's no extent to it. The left side and the right side are at the same place because there's no space there. It's a zero volume dot in space with some quantum mechanical properties, electric charge, mass, all sorts of stuff. So the universe is filled with these little points that you call particles, and they're all different. There's electrons, there, protons. The neutrino is one of these particles that the universe likes to make, that's right. But the proton is not one of them. Proton is not a fundamental particle. Right, So let's review. You're made out of atoms. Atoms have electrons and and then have a nucleus. The nucleus is made out of protons and neutrons, and the protons and neutrons are made out of quarks. So all the atoms that build up you and me and hamsters and ice cream are made out of quirks and electrons. Right. So the up cork and the down cork make up the proton and the neutron which gives the nucleus, and the electron surrounds it. And that you can make any atom. You can make uranium, you can make you know, hydrogen, you can make lithium. Anything. It's just made out of those three particles. So these are just things that the universe likes to make. And there's not just the kind that we're made out of. But there's more much more than that, that's right. And uh, it's fascinating because most of the stuff in the universe that we know about, you know, gas and planets, whatever is made out of these three particles up corks, down corks, and electrons. In fact, that is the recipe for almost everything, and I was thinking about it the other day. It's sort of incredible. It's not just the recipe for everything, but it's everything in the same proportions. That is, every atom that makes up you has the same number of up corks and down corks and electrons, and every atom that makes up ice cream or lava or hamsters, it's the same number of particles. Right, So we're getting off in a bit of tangent here, but it's sort of fascinating because, I mean it's like there's a similar list of ingredients in the same proportions, not just similar, exactly the same. So if you had a kilogram of hamsters, or a kilogram of ice cream or a kilogram of Jorge, it would be made out of the same particles. The only difference is in the arrangement of them. I mean, some some arrangements are more awesome than others. I mean, come on, that's right. Ice cream is really pretty awesome. I totally. The interesting thing is that, as you were saying, there are other particles, right, there's not just those three particles. You can make all this crazy stuff out of those three particles, but there are other particles out there. And that's the first mistake that's made. On the u c I campus tour. They describe the newtrino as a sub atomic particle, the smallest part of the atom. But the neutrino is not part of the atom. It's not in there. You take the atom apart, and there's only up corks, down corks and electrons and neutrino. It's a particle. It's in the universe, but you don't need it to make hydrogen or lithium or uranium or any of the other eums. But maybe they mean subpotomic in terms of its size, like it's much much smaller than an atom in the sense that particles have no size. That's true, yes, maybe in the sense that it's false, it's true, right, Well, every particle is subatomic, and from from that definition, fundamental particles have no size. Yeah, but it's just as small as the electron or the up cork or the down cork, and then it has zero volume. But the interesting thing about it is that it's not part of matter, right, So it's like, why is it there? Um? But the neutrino is weird in in a few ways. Right. Not only does it not make up the atom, it also doesn't feel a lot of the forces. Like the neutrino can pass right through you without interacting. That's what we're talking about, the top of the episode is that neutrinos are passing through us all the time in great numbers and we don't feel them at all, which isn't true for electrons, right, it's a huge rain of electrons. You would definitely feel them, and you would get cancer pretty quick. Yeah. And it's interesting because pretty much anything has the capacity to move through other things things, Right, Because if everything is made out of point particles, which have zero volume they're just little points in space, then technically, if you take a whole bunch of nothing, you should be able to pass it through another whole bunch of nothing. Right, that's right, that's right exactly. So if you take a bunch of point particles that don't interact with each other at all, then they will pass through each other. There's no chance that they will collide because they have zero volume. So that's sort of overlapping area. What we call the cross section particle physics is zero, right, you can't make two things that have zero volume hit each other. It's vable, And so yeah, you're right. You could have a huge density of them and a new one can come along and just pass right through it. Yeah, because like the reason I can't go through the wall here, the reason I can't pass through it like a ghost. It's not that like my particles hit against the other particles like they bump against each other. It's just like they want to get closed. But then there's other forces that that prevent me from going near them. Exactly. The particles that make up the wall have no volume to them at all. Right, It's like a it's just a bunch of dots, and you're a bunch of dots, and so you should be able to pass through it. Except, of course, the particles that make up the wall are not just a disconnected bunch of dots. They're bound very tightly together with forces, and those forces hold them together into sheets and structures, and also those forces repel other particles that feel those forces. So when your finger is pushing against the wall, what's happening is not that the ball particles in your finger are bouncing off the ball particles in the wall, but they're repelling each other using mostly electromagnetism. So the sensation of touching things and holding things and standing on top of things that it's really just like we're all kind of magnets repelling each other. Yeah, they're electrostatic forces mostly their chemical bonds, right. And so you can think of like a surface of something is like a chain link fence, right, lots of big gaps, but then there's links holding it together. And you know, another chain link fence coming up to it, which is also mostly air, can't pass through it because they both have these links. So that's the thing is that something can only touch you or affect you, or you can only feel it if it's affected by electromagnetic forces. That's kind of the key, right. Yeah, So there's two elements of the universe, not just particles, but also forces, right, and those are the basic building blocks of how we do science and particle physics. We got the particles and we've got the forces. I mean, another time we can talk about quantum field theory. And for those listeners out there who know that, you know that everything is actually just a quantum field. But let's talk about particles and forces today extra credit podcast. That's right. So at this level that we say it's particles and they're connected by forces, the forces are how the particles talk to each other. And if my particles are talking to your particles, then when you punch me in the face, then that's why I feel it right now. If you say when, as if, it happens often, I'm trying to make this a concrete example for the listeners, you know, not abstract type of if I slowly caress your cheek. Hold on. I noticed that you made that an if, not a when. Um, let's keep this PG. Imagine that you were built out of particles. It felt different forces than me than when we high fived. Our hands would pass right through each other because those forces would not pay attention to each other or tract or repell or anything. We would like phase right through each other because the particles that make us up don't interact, right, So it's all about interacting. Okay, So the neutrino is one of these particles that doesn't speak the same language that our particles speak. That's right. The neutrino is neutral. It has no electric charge. That's one of the reasons it's called neutrino. Neutrino is Italian for little neutral particle. And so it doesn't feel electromagnetism at all. And not only does it not feel electromagnetism like the electron does feel it, but it also doesn't feel the strong nuclear force that's the one that holds the corks together in the nucleus and affects the proton and the neutron. So it doesn't feel the two strongest forces in the universe, the strong nuclear force and electromagnetism. Generally just likes to avoid conflict. Yeah, well, it's kind of snob mostly ignores everything. It's nay or shy. I don't know. You could see it both ways, says the introvert, right standing up for the introverted particle, aren't you. Well, let's get it more into it, but let's take a quick break first. Okay, So the neutrino is a particle in the universe that's there. There's a lot of them out there, but it just doesn't feel the same forces. It doesn't speak the same language that you and I and all the particles that make us speak or use right, that's right. Yeah, it's like, um, you know, it's like it's a it's deaf or something. You can walk through the loudest bar, you know, with thump thump thump music, right, and not even hear anything, not even notice it's there. Right, it's not purposely ignoring you, it just does not hear it. Interesting. I was thinking a good analogy could also be you know how in the Internet today people communicated using Facebook or Twitter, or Instagram or email. Those are all different ways that people interact with each other on the Internet. But what if there was somebody who said, you know what, I'm not going to use Twitter or Instagram or Facebook. I'm just gonna respond to people if they write me a handwritten letter. That's right. Yeah, those people are social media neutrinos. Yes, yeah, that's kind of what it is. It's like everybody else is talking to each other in one way, but this one particle just says, you know what, I'm going to ignore those different ways to interact. I'm just gonna do my thing. Yeah, and given the toxicity of social media, that probably means the neutrino is the happiest particle. Yeah, you know, they made. That's the key we should all learn from newtrinos. Yeah. Um, So let's remind people though, what the forces are. So there's the strong nuclear force that ties the nucleus together. There's electromagnetism that's responsible for electricity and magnetism and light and all that kind of stuff. And then there's the weak nuclear force that's the weakest of of these forces. And then there's gravity. Everything with mass feels gravity, right, but in the case of particles, we don't really think about gravity very much because particles have hardly any mass at all, and so gravity doesn't really affect them to really those other three. So the corks, the corks, they feel the strong nuclear force and electromagnetism and the weak force. Okay, so they feel everything. Electrons, they feel electromagnetism, and they feel the weak nuclear force. Neutrinos only feel the weak nuclear force, which is called the weak nuclear force because it's super duper weak, not because it takes a week to act or something like that. So it doesn't just ignore some of the forces that everybody else fields, but it only it's like the one it chose to interact with the rest of the universe is like the week is one. It's like the most incossequential one, right exactly. It's like, you know, if you could only interact with somebody by sending them a letter to the south pole, and the letters only go every six months or something, right, And you know, if the neutrino didn't feel any forces at all, then we would have no way to even know it existed. There could be a whole set of particles that speak even maybe a whole different set of forces. Yeah, like people think about dark matter, right, dark matter, we don't know if it feels any of these forces, and that's what makes it so difficult to look for and to understand. Dark amount, as far as we know, only speaks gravity, which is why you can only study it when there's like a galaxy sized blob of it. Neutrinos do feel one of these forces, which is why we can talk about them and study them. Well, let's talk about some of these properties that I was reading about the neutrino. I read that it has a mass that's maybe one less than one million of the mass of the electron. That's right. Neutrinos are super duper duper low mass, and we don't understand why at all. You know, we look at the mass of these particles, the electron, the corks, the other ones. We have no idea why these particles are different masses. We did a whole episode on how they get their masses, which is about interacting with the Higgs boson. Some of them interact a lot with the Higgs boson and so they get a lot of mass, and some them don't interact hardly at all, so they get almost no mass. But we don't know why, Like, why does this one interact with the Higgs a lot and this one almost none. It's like a bunch of parameters in the control panel the universe, and we don't know if there's a pattern to it, or if they just set randomly at the beginning of the universe. We have no clue, but it seems like an important hint that the neutrinos are so close to zero mass but not actually zero. Yeah, so they are kind of tiny, right, I mean, I know everything is a point mass mathematically, but these things, I mean they're not just a point mass, but they're a point mass that are really really really really really almost no mass. That's right. But if again, it doesn't affect their size right. Their physical size is a different thing from their mass. Their mass is like a quantum mechanical label, like electric charge. Right, it's not like something with more mass. It is more stuffed to it. But yeah, you're right. Neutrinos are weird because they have almost no mass but not zero, like they're not the lightest thing in the universe though. Right. Photons have no mass exactly zero. They travel to speed of light. Neutrinos just less than the speed of light because they have just more than zero mass. These particles only choose to interact with the rest of the universe using the weak force. And the weak force is not just weak, but it's also really short, meaning that it doesn't work over long distances. You have to be within the diameter of a proton just to feel this force. That's right. The weak force is super limited, right, And not only is it weak, as you're saying, but it's short range. And the reason is that the particles that communicate that force. Remember, we have particles that make up matter, and then we also have forces, and the forces themselves are communicated using particles. So, for example, electromagnetism is communicated using the photon, right, And electromagnetism goes everywhere in the universe has infinite range, and the reason is that the photon is massless. Right, the photon has no mass. But the particles that communicate the weak force, they're called the w and the z bosons are really really v particles, sort of ironic. The lightest particle of all the matter particles in neutrino uses the heaviest force particles, which means that they don't go very far. So this particle not only is it um ignoring a lot of the forces, but the forces that it does feel are super weak. And this particle is super light. It's almost like it's almost not there, you know, like what is the not at all? Not at all? In fact, there's zillions of neutrinos. I mean, it's not there in the sense that you can almost not tell that it's there. But there are a huge number of neutrinos. Like if you hold out your fingernail, it's approximately one square centimeter. There are a hundred billion neutrinos passing through your fingernail every second. D yes ten to the eleven neutrinos per square centimeter per second. Let's count. So look at your fingernail one one, two, three hundred billion neutrinos just went in my fingernail, that's right, and ignored you. Right, And neutrinos, I mean, not only can we not detect them, they can't really detect us right to them, we are like an invisible haze in the universe. Right then, don't even know where I would exist, right, They hardly interact with. A neutrino interact with the rest of the universe so weakly that it can pass right through the Earth without interacting. Again, not because it's small. It's not that it like wiggles through cracks between atoms, right, It's that it doesn't interact. It just doesn't care. It just yeah, it just flies right through. Um. A neutrino can pass through a light year of lead. Okay, So imagine a blob of lead that's a light year long, which is how far light travels any year, which is really really far, and lead it's a really kind of like dense metal. Right, Yeah, it's a huge amount of stuff. Right. Um, neutrino can pass through a wall that thick and have about a fifty percent chance of interacting. So it's just going through the universe doing its own thing. Yeah, making us feel even more insignificant. It's all about you, Jorge, It's all about you. It's something insignificant. Is making us feel even more insignificant. Well, we are pretty insignificant. Nothing we do is important. Um, But it turns out that neutrinos are not just ignoring us, they're also ignoring the whole Earth and other suns and everything. And you might be asking, like, why are there so many neutrinos? Where are they coming from? And the answer is that they come from the Sun. They're produced in the fusion reaction at the core of the Sun. Well, I think the question that I want to know is, if they're so light, so inconsequential, so ignoring, how do we even know that it's there? And why should we even care that it's there? All right? Great, great question? How do we know that it's there? Well, it does interact, right, so it can interact with our world. And because there are so many of them, the big number of how many there are and the small number of the probability of them to interact actually balance out to give us a reasonable number of times. And neutrinos do interact with normal matter. And so if you set up a big experiment. You can catch neutrinos right, because there's a huge number of them. So out of the hundreds of billions fault flowing through my fingernail, every once in a while, one mom would be like, oh, hey, what's this. It's a fingernail exactly. I don't know what a fingernail is, but I just ran into it. Yeah. So what you do if you want to catch new trinos is you set up a big vat, for example, of water underground, and you shield it from everything else, so you make sure you don't get any background from muans or anything else crazy, and you wait until one of those atoms of water and gets bumped by something mysterious, and there are ways to tell whether or not it was bumped by something like a neutrino. And that's the way that we measure neutrinos. Today. We have these huge detectors, like the ones called super Comioconda in Japan that measure neutrinos from the Sun and from other sources. And they do about having these big tanks of heavy water and waiting for one of them to get bumped by neutrino. So that's how we know where they were there, like, can definitely see them, You can definitely see them interacting. Yeah, and that's how fred Ryan saw them. He signed neutrinos bouncing off of protons and turning into a very characteristic signal that you couldn't mimic with anything else. And so I mean in that sense, he doesn't see the neutrinos themselves directly. It's not like he captured one, put it in the box, said ah ha, look here's my Nobel Prize winning discovery. What he saw was something that happened that only a neutrino could do. Well, I have more questions, but let's take a quick break. So, I think a lot of particle physics laboratories in the country and across the world. Now there's kind of a renewed interest in neutrinos now that we found the Higgs boson and and a lot of these particles in the standard model of physics. There's a lot of interest down the netrino. So why is that, Well, why is the neutrino interesting or why is it a big deal? Yeah, it's a big deal, and not just because it's weird, but one of the things we want to do in particle physics is understand the universe at its smallest scale, right, understand the tiniest little bits. And to do that, we need to look not just at the kind of matter that makes us up, but the kind of matter that's everywhere in the universe. Because we're looking for ideas and patterns that go bigger than humanity, right, that that are tell us something fundamental and deep about the universe. So for that we need to cast our net as widely as possible and understand how this kind of matter works, how other kinds of matter works. And so it's important to understand neutrinos because they are there their clue somehow about how the universe is put together. Right, And it could be and I said, neutrinos are fundamental, that they're not made of other things. That's our current state of knowledge. It could be the neutrinos and corks and electrons and every particle we know are actually made out of something smaller neutrinos. Neutrinos. To answer your question, why should we study them, Well, they give us clues as to how the whole principles working together. Right. We wanted to get the big picture so we can see all the patterns because those patterns give us clues as to what's going on to underneath, what these things are all made out of, and what the answers are. But also because neutrinos themselves are really weird. They can do things that other particles can't, Like they can change from one type into the other. You know, for example, an electron is an electron is an electron. It's never going to change into a muan, but an electron neutrino. Neutrinos come in three different flavors electron, muon, and taw. They can switch from one to the other. So you create one type in the Sun and as it's flying to the Earth that has about a one third chance to change into another kind of neutrino. That's really strange. It's not something we've seen before, and it actually breaks a pretty basic rule in the standard model of particle physics that you can't switch from one kind of flavor to another. So we don't know why that is when, don't know what it means. Lots of possibilities. It's like it's not only ignoring Twitter and Facebook and Instagram, it's changing its address every three months, like it really doesn't want to be found. That's right. Yeah, it's a pretty weird little particle can do all sorts of things, and so we're hoping that figuring out what he can do and how it interacts and nailing down all these details will give us a clue as to some of the deeper mysteries. You know, how did all the matter come to be? Why do we have the matter or not antimatter? What are all these things made out of? We're hoping that just nailing down and tying up the loose ends and new trinos gives us clues to answer these other bigger, deeper questions, because that's kind of how science works, you know, right. I mean, science doesn't just study human beings and our biology. Science also studies other animals and other organisms, because that tells us a lot about why we're here, or what the rules are for why we're here. Yeah, exactly exactly. To understand humanity, you understand all of our closest cousins and our distant relatives and the whole spectrum of life on Earth to get the context. And so we want to understand how particles work. We want to we need to study all of them. Yeah, I mean, the weird ones that don't want to be found. That's right, We're going to ignore all of their preferences and study him anyway. Yeah, I'm not a particle physicist. I'm a particle stalker. Yeah, particle hunter. Isn't that what they sometimes they call you guys, particle hunters? Particle hunters? Yeah, look, I found one, this one right here. So what do you think learning about this ghostly particle is going to teach us? Like, what are the possibilities of things we can learn from it? Well, we could learn that there are other kinds of particles out there. Some people think that there might be four kinds of neutrinos out there. There's a new kind of of neutrino called the sterile neutrino, which doesn't even feel the weak force. Right, people think that there there might be this other kind of particle out there. Um, it might tell us something about why we have matter and antimatter because it it might be related to how things switch back and forth. Um. But most likely I think it's going to contain some surprises. You know, particle physics, the history of us has been full of surprises. Do you think think this is happening? Turns out bad's happening, and the only way to dig into it is to just explore, dig into it and figure it out and see what nature has to tell us. The asked, he would be neutral. That's right. And so I hope after listening to this episode those folks out there, I'll know now what a neutrino is. That's not a fungus on your toneail, and that it's a tiny particle. Yes, And also it was that it was discovered in the campus of UC Berkeley, Irvine, UC Irvine. That's wait, it's not UC Berkeley. Actually you know that. You just said that to Ryan me up. All right, Well, thank you for joining us. See you next time. Another piece of the universe explained before. You still have a question after listening to all these explanations, please drop us a line. We'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge that's one word, or email us at Feedback at Daniel and Jorge dot com.