How long does a neutron live?

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Speaker 1: Hey, Katie, how do your particles feel today? I guess it depends on which particle you ask. All right, well, let's start with your protons. How are they feeling this morning? They're feeling pretty positive. And your electrons any negativity there? Well, I would say they're all charged up. And what about those neutrons. We don't want to overlook them? How are they doing? There? Come scums? All right, well, let's see if this podcast can get them excited. Well, I'm excited even if my neutrons are kind of just meth. Hello. I'm Daniel. I'm a particle of physicist and a professor at UC Irvine, and I contain multitudes of particles. And I am Katie Golden. I host the podcast Creature feature about animals and my particles. Uh, I think I've got at least ten of them. You know, really, your podcast is also about particles, since all animals are also made of particles. That's right, So who's the physicist? Now? We're all physicists. That's the point. Every podcast is really about particles, even those true crime podcasts, even the Bigfoot podcast, even those paranormal e sp podcasts that consistently outrank ours in the natural science category, but welcome to the podcast. Daniel and Jorge explain the universe in which we treat the entire universe as a crazy swarm of particles. Particles that are mysterious, particles that are weird, particles that follow very strange quantum rules, but particles that do follow rules in the end, rules that we think we can understand, we can digest, that we can explain to you. On this podcast, we hope to wrap our minds around everything in the universe, break it down to its time little particles, and feed them to you one by one. My co host and friend, Jorge Champ can't be here today, but we are very lucky to have our regular co host, Katie. Katie thanks a lot for joining us. Of course, I am ready to learn about particles because you know, they seem important, given that I need them in me to make me, me, to make you you. Indeed, but you know what is the units of you? Diving right into the philosophical questions at the heart of particle physics, one thing we have learned recently about particles and the universe is that we all seem to be made up of the same kinds of particles. I'm made of protons, neutrons, and electrons. You're made of protons, neutrons and electrons. What's the difference? Are there Katie particles and Daniel particles? No, it turns out that the only different it's between Daniel and Katie fundamentally, or between an apple and a banana, or between kittens and lava, is how those particles are put together. You take that same basic set of building box and you can make anything. You're blowing my mind. So if we sort of melted down Katie and Daniel into just the particles and then rearranged all the Katie particles into Daniel particle like the Daniel blueprints, then now would just create a Daniel even though uh, those were originally my particles. That's exactly right. It seems like our universe follows the same principles as legos, that the same basic building blox can be used to make anything. Right, if your little brother used your legos to make a huge dinosaur and then you smashed it and used it to build a pirate boat, you could reuse those dinosaur legos to make your pirate hip. Now Here, of course, I have to quibble with the fundamental flaw of Lego toys. The original Legos, We're just the basic building blocks, and I love that simplicity that I had no bias to them. You you could use them to make anything. These fancy new modern Legos, you know, they come with stuff printed on the sides or specific shapes, right, so the sort of like predetermine what you have to build. I'm talking about the true original Legos. Yeah. I usually just built the tallest tower I could make out of my Legos, and then usually put a bunch of guys on it, so it's like just this big tower of Babel. I don't know what that says about me, but yeah, I agree, Although I do like that modern legos do have different kinds of Legos. Like it started out, I think, with just the one Lego block unit, but now you have all sorts of different types of Legos. You have like the sort of o G blocks, but you also have these long, skinny ones, you have ones that can rotate, you have like connector legos. But is that at all similar to how the universe works? Seems to be very similar to how the universe works. You know, I'm made of protons and neutrons and electrons and store are you and so is basically everything that you've ever eaten, everything you've ever tripped over, everything you've ever thrown at your sibling. They're all made of the same ingredients. And if you look at the periodic table, you can see that that's true, right, Every element on the periodic table is just made of protons and neutrons and electrons arranged in different numbers. You start with one proton and electron, you have hydrogen. You added another proton, you get helium. Keep adding protons, do you get different elements? You're just adding more of the same basic building blocks, but you make fundamentally different elements. But those different elements are not really fundamentally different. The only difference between carbon and neon, or between lead and gold is the number of protons inside those nuclei. So really you can build anything with the same basic building blocks. It's so hard to wrap my head around that. So, you know, just like it's just seems that it's a numbers game, because like usually with legos, if you just have like five legos, it doesn't suddenly turn into from like you know, a sugar into like gold or something like that. But with these on the atomic levels. When you change just the number of these these tiny particles, it turns from you know, something that if you eat nothing would happen to you, to something if you eat it it would be bad and drive you crazy, like eating lead versus drinking air. I guess we don't really drink air, but you get the idea. Yeah. Absolutely. It might seem like a small difference. You're just adding a proton, what's the big deal, But it completely changes its emergent behavior. All these characteristics that were familiar with the way metals are shiny and conduct electricity, the way some of these elements are float around and ignore the other ones that are not very active. All of those properties are determined by how many protons and how many electrons there are in each atom, and so like, the fact that metals are metallic and conductive comes from the fact that their electron shells are not filled, which is determined by the number of protons inside the nucleus. So it's not just an relevant detail, it's a totally determining fact. But it's fascinating they're all made out of the same bits. The other fascinating thing to me is that we're all made out of roughly the same ratios of bits, Like any given atom has basically a one to one to one proton to neutron to electron ratio. So lead has more protons than hydrogen, but it also has more neutrons and also has more electrons. That means that not only are we all made out of the same three basic building blocks, but we're made out of them in the same proportions. It's not like Katie has more electrons and Daniel has more protons, right, where the same building blocks in the same proportions just rearranged differently. So you you mentioned that the number of protons sort of changes the element. In the number of electrons, it's kind of changes the characteristic of these elements, But you didn't mention neutrons too much being sort of the determinant of what these elements are. Why are neutrons different in terms of pro tons and electrons. Yeah, it's a good point, and neutrons are sadly often overlooked, which is why we are dedicating almost our entire podcast today to talking about these mysterious, funny particles. But you're right that neutrons don't really determine as much the identity of the atom, and that's because they are electrically neutral. Like if you add another proton to the atom, then in order to make it electrically neutral, you have to add another electron in orbit around it, and that really changes the chemical properties. It changes how this thing interacts, whether or not it's electron orbitals are filled, or whether it's got an opening that very strongly affects the behavior of the atom. You add another neutron, then you don't need to add another electron. So you can add neutrons, no big deal. You can't just add neutrons anytime you like to any atom. It doesn't make them heavier, and it makes these other versions of the elements. These are called isotopes. So, for example, you can have hydrogen, which is just a proton, but you can also have deuterium, which is a proton and a neutron. So you put those together inside the nucleus, you have an electron around it. It's still called hydrogen, but it's like a heavy version of hydrogen. For example, if you put that together into H two O, but instead of the hydrogen, you have this heavy version of hydrogen with a neutron also in the nucleus. Then you get what's called heavy water, which we sometimes use in nuclear experiments. Right, so it does change a little bit sort of the flavor of the element to add neutron, sort to take them away, but it doesn't change its fundamental identity, which is determined by the charged objects of proton and the electron. So that's really interesting to me. Why is the neutron involved at all in the atomic structure if it's just kind of this It seems like this neutral fluff particle just this like dead weight, But is that really true. No, the neutron often overlooked, but it does play a vital role in keeping the nucleus together. We're gonna dig into it a bit more on the podcast, but very briefly, think about how the nucleus stays together. Right, If you have the nucleus of an atom that has like twenty five protons in it, those things are all positive of lee charged. Why don't they just like bust apart? You know, why don't they repel each other because they all have the same positive charge. The answer is that the nucleus is held together by the strong force, which is much more powerful than electromagnetism and neutrons. Even though they are neutral electromagnetically, they do involve the strong force. Turns out, the nucleus is a bit of a delicate puzzle keeping those protons from flying apart. You need the neutrons. It's a little bit of a spacer, and so it's easier to make stable nuclei if you include the neutrons. I see, So without the neutrons, the protons would not be able to stand each other's presence. I know people like that and like in group dynamics, that kind of keep the peace. So that's that is really interesting. So I guess without neutrons we wouldn't exist, we would not be held together. But it's odd to me though, that that neutrons have. It seems like they're fundamentally different from like a proton or an election because they don't have this charge. So you know, how did that even really happen? Yeah, well, these are deep questions about the universe, like why do we have neutrons anyway? Right, it's just sort of how the universe coalesces. Remember, we go back to the very early part of the universe where everything is just energy, and the universe then expands and cools and as it cools. It's sort of like crystallizes into lower energy states. Things sort of like come together and form stable particles. And by looking around in the universe and seeing sort of what was made, we can tell sort of like what the options were. We don't know like why it's possible to build neutrons necessarily, but we see that a lot of them sort of emerged from the chaos of the early universe. And that's another really fascinating aspect of these particles is their age. Like protons, we think that protons probably live forever. Like you make a proton, you can just hang out forever and stick around till the end of time. Same with an electron. Electron is stable, right, you have an electron sitting in empty space, it will just stay an electron for a billion years, maybe a trillion years, a quadrillion years. And what that means is that the protons and electrons inside your body were probably made during the Big Bang. So you are made of ancient multitudes. I mean, you know, thank you for that, thank you for calling me old. So neutrons weren't necessarily made during the Big Bang. You're saying, so neutrons were also made during the Big bang, right as the universe cooled, we got protons, we've got electrons, we've got neutrons. But there's a difference between protons, electrons, and neutrons that goes beyond just their electric charge. Neutrons don't seem to last forever the same way that protons and electrons do. In fact, they don't last very long at all. So that makes them fundamentally weird and different. And by studying the details of how long the neutron lives and what it turns into, we might get some clues to these questions about like why are there neutrons after all? What's going on inside the neutrons? Are they irrelevant little particles? Are they the most important clue we have to the nature of the universe? So yeah, no, I'm really curious, like what does it mean for a neutron to be alive? And then how does it die? And how long does that process take? And so today on the podcast we'll be answering the question how long does a neutron live? Alright, Katie, and you've already called me out, I see for using the word live in the title, because our neutrons alive after all, and you know, as a particle physicist, I think about these particles as sort of having a lifetime. But you're right, neutrons are not alive, nor are they dead in any sort of biological sense. I mean, if you corner a biologist and try to get them to answer the question what is life, They're gonna start sweating and giving you a really complex answer. So it's not a simple question. But but no, I get it. So it's like a neutron does not always remain a neutron in the sense that it does not stay the same forever, and so that could be seen as it, you know, essentially decaying or dying. Right exactly, When we talk about particle lifetimes, we're talking about how long the particle exists before it turns into something else. So some particles in the universe are stable, like electrons and protons and the corks that make up those protons and photons. For example, you can create a photon with a flashlight, shoot it out into space, and it might fly for billions or trillions of years. Some of the photons received by your eyeballs when you look up at night have been crawling across the universe for billions of years. It's incredible how long they have survived. So some particles sort of live forever. And again we're using to live in a sort of anthropomorphic biological analogy to life. Really we just mean exists, but other particles don't. Other particles are not stable, and the neutron is one of those. That's really interesting. So yeah, I didn't really think of neutrons as being an impermanent thing. I think about the building blocks of life. I mean I pictured them as these like little permanent speares that you know, make everything and just stay the same, and you know that is just this kind of like solid foundation to everything. But now you're shaking that all up. What if I told you that one of your legos a specific kind of lego, if you didn't use it, it would just like evaporate or turn into other kinds of legos. That sounds like an excuse a little brother would give when you're stealing all my legos. All right, but this is not a family therapy podcast, at least not yet. So I was curious if other people had thought about the lifetime of the neutron, if people were aware that neutrons don't live forever, and how long they thought it might live. So I went out there to our cadre of Internet volunteers who are willing to answer hard physics questions without any opportunity to prepare themselves. Thank you very much, and if you would like to join this hearty group, then please, they'll be shy right to me. Two questions at Daniel and Jorge dot com. So think about it for a moment. Do you know how long a neutron lives? Here's what people had to say. I guess. My guess would be that it would live indefinitely until some other force overpowers the forces that hold it together. Tron lives um like a free nel tron shouldn't been that long, but I don't know, probably not more than a few minutes. I think that actually this is something that's really confused me as I've started to look into and tried to understand particle physics and quantum physics and everything, and I think that possibly it's just an instant. Yeah, neutrons, just like like a lot of particles, just exists for an instant. On the other hand, it could be they could last for by entire lifetime, so yeah, it could be a long time as well. Well. Neutrons makeup part of stomic nuclei, so they live for at least as long as the longest lived elements UM, so at least a few million years. But I think UH universe skills tend to be quite extreme, so I guess since they don't live for only fractions of a millisecond, I'm going to guess they live for billions of years. I don't know if a neutron lives forever, and I think the answer to that question is we don't know if neutrons live forever. I know that proton decay is still actively being studied and debated, and I don't think a neutron would be much different. And as of now, I believe we do not know how long they live or if they decay away. I know that protons decay inter neutrons UM because they emit a positron, so I'm gonna wonder whether neutrons can also emit an electron and in a sense decay into protons. But this process doesn't happen, so all the proton has a lifetime of I don't know if the order of a few seconds UM, and you'tron. I know it's a number of years and I think it's the amount amount of time is comfortable to the age of the universe something like that. I really like the answer, probably just an instant, or maybe my entire lifetime, because even though that seems funny, like how could you compare an instant to an entire lifetime? How could you be so equivocal? On the universal scale, those are almost the same in a certain way, right, Like when you look at the entire lifetime of the universe, an instant in one human lifetime or not that different exactly. And that's the incredible thing about all of these numbers in physics that when you're talking about how long something lives, it could be some crazy, tiny tiny number ten to the minus twenty seconds, or it could be cosmic the scale of the lifetime of the universe, right, which is like, you know, six tillions of seconds, and so it's hard to know, like on that huge scale where to put these numbers, And so if you don't have any information, then you're right, his entire lifetime does feel sort of like an instant. And that's one of my favorite things about physics that it may think about these cosmic sweeps of time and recognize the fact that something that might take our entire lifetime is basically meaningless on the time scale of the universe. Well, way to make me feel both old and small. So in terms of neutrons, like it is interesting, like if they live like a human lifetime, that makes me feel a little less alone, or if they live like an instant, that almost makes me feel sorry for them. It's really hard not to anthropomorphize something once we're talking about how long it lasts, as if the neutron particularly cares. But I guess I want to know, like, what what is the neutron? Should I feel sorry for it? Well, I'm not going to tell you how to feel about the particles, but I'm happy to tell you how they're put together and what they mean. And so in the case of a neutron, we've been talking about it as if it was a particle in itself, like atoms. We said are made out of protons and neutrons in the nucleus surrounded by electrons. And that's true, but we can also drill one step deeper to understand what is the neutron itself made out of? Now, in the case of some fundamental particles like the electron, we don't know if they're actually fundamental or made out of even smaller lego building blocks. So far, the electron just looks like it's only made out of itself, but that might just be because we haven't zoomed in far enough. We don't have colliders capable of blowing up electrons and seeing what's inside them. In the case of protons and neutrons, we actually have been able to break them up and see what's inside. For about the last fifty years or so, we have had colliders capable of smashing these particles and showing us what they are made out of. And fascinatingly, the proton and the neutron are made out of the same two building blocks, up quarks and down corks, so there are two funny little particles. They have weird fractional electric charges, which allows them to get added up to make a neutron or a proton. So, for example, a neutron is an up cork which is charged two thirds, and then two down corks, each of which are charged minus one third. So neutron is an up, down, down Three of these corks put together, and you get zero electric charge. So physicists, when you're asked what's up cork? Do you just say not much what's up cork with you? Or do you have an actual answer to what's an up cork? And I guess what's a down cork? I don't know what's up is down, what's down is up? Sometimes in physics, you know, as I always say, I'm not going to be held responsible for the names of these particles, but you know, there are some reasons why we called them up corks and down corks. They're organized together by the weak force into this pair, this up and down pair that get linked together by the w boson, which we're going to talk about in just a minute. But actually in the nucleus, the upcorks and down corks are not held together by the weak force. They're held together by the strong force. So quarks have electric charges, but that's not what's holding them together. Like you think about the way molecules are held together, they're held together because of the electric charges. These electrons are like whizzing around and making these ionic bonds or covalent bonds. The electric charges are basically irrelevant once you get inside the proton and the neutron because there's a much more powerful force at play. And that's the strong nuclear force, which totally overwhelms the electromagnetic force, is able to hold all of these particles together. And the strong nuclear force does that by using gluons. So your mental picture of a neutron shouldn't be like three little lego pieces that clicked neatly together and that's it. Instead, it's more like three tiny little dots surrounded by a swarm of these gluons that are holding it together. So it's more like a bag of gluons with three hard dots in it. So, oh my gosh, so gluons. It's just this sort of like swarm of these things that hold together the up quarks and down corks. So like, the more we split things apart and try to think about like the even smaller thing that holds the smaller things together, it gets really difficult for my brain not to start hurting. But all right, So, so do we know like how many gluons are in a neutron or is it just kind of this mass of stuff that we know holds together of corks and down corks, But we can't necessarily quantify how many of these things there are. Yeah, that is a great question because probably you're wanting to put together a model of what's going on inside the neutron that has like a basic recipe, and those things clicked together to make a neutron way like pieces of a jigsaw puzzle get clicked together to make a bigger picture. Right, But that's not really the way we think about these gluons. Luans in this case are force particles. They're not matter particles. What that means is that they don't really exist in the same way that the matter particles do. They exist as a representation of the force between the matter particles. So you have the up cork and the two down corks. They're sitting there and they're pulling on each other, the strong forces holding them together there. How do you think about that force, Well, there's a few different ways of doing it. One is to think about them exchanging particles like zooming gluons back together. That's how they hold themselves together. And you can use that same strategy to think about how other particles talk to each other, Like what happens when two electrons push against each other because they have the same electric charge. How does that actually work microscopically, Well, you can think of them as shooting photons towards each other because photons are the force particle for the electromagnetic force. So inside the neutron, these corks are holding onto each other by shooting gluons at each other. That's one way of thinking about how the forces are working inside the neutron. There's another way of thinking about it, which doesn't use this sort of like virtual particles, these gluons sipping back and forth. You just think about fields. Like if you're more comfortable thinking about an electron being surrounded by its electric field and the way that it pushes on other electrons is that it's electric field pushes on it, then you can think about the interior of the neutron that same way as having three quarks each surrounded by a field from the strong force, and those fields are tugging on each other. Those are gluonic fields. You can think about them as either like a huge tower or virtual gluons which appear and disappear very quickly, or you can think about them in terms of fields. Are two equivalent mental pictures for the same fundamental process that's going on. But you can't really like count the number of gluons because they're not particles that exist in the same way as the corks. So, Okay, in my recipe that I'm writing for home baked neutrons, I'm just gonna put down a pinch of gluons. So you said that this is these are strong, uh, strong forces holding this neutron together. But we were just talking about how maybe these neutrons break apart. So how would they break apart if you have these really strong forces holding them together? Great question, and it reveals something about the way I think a lot of people think about particles and their decay. What happens when a particle decays? Is it breaking apart? Are you taking its pieces and they're reassembling them to build something else? Right, Well, what's happening when a neutron decays is not actually that is breaking apart at all. It's that one piece of its internal structure, one of those corks, changes its nature. So remember that a neutron is up, down, down right tow down corks and an up cork. Well, what happens if one of those down corks changes its flavor and becomes an up cork? Then you have two upcorks in a down instead of two down corks and an up. Remember that up coorks are charged plus two thirds and a down cork is charged minus one third, So now you have plus two third plus two third minus one third gives you a charge of plus one. That's a proton. So what happens when a neutron decays is that one of its down corks converts into an upcork and the neutron becomes a proton. So it doesn't break apart. It flips from being a neutron to being a proton. That's amazing. So it's less of a death of a particle in more of a tram information of a particle. Do we have any idea of why a down cork would become up cork? Yeah, Like you know, why does it down cork decide it wants to be an upcork one day? You know, like why isn't it just happy being an upcork. It's a great question, and it's a really deep question. It's like why does any particle decay? You know, why do muance just hang out and be muance? Why do they decay to electrons and a couple of neutrinos? Why does anything decay? And the reason is that the universe is constantly getting colder and spreading out. Entropy and statistical mechanics tells us that the universe doesn't like to have energy localized in a little spot. It likes for it to spread out. Sort of fascinating quantum mechanical, the universe likes to occupy multiple quantum states instead of like being focused on a single quantum state. What that means essentially is that any particle will always decay into a lower mass particle. If it's possible for you to take a step down the mass ladder to break up into smaller particle with less mass than you, always will the universe is its constant pressure. It's the same as if you have like a hot object sitting on a surface, it's going to spread its energy out to the neighboring stuff. The same way you have a very high mass particle. It wants to break up into lower mass particles. And it turns out that the neutron is heavier than the proton just by a little bit, and so the neutron can do this. It can take a step down into a lower energy configuration. So the neutron is a higher energy state, which means it has a little bit more mass. And decays down into a proton. It does this by flipping one of the down corks into an upcorp. So it's my freshly biked neutron. It's kind of like a hot soup flay. And then if I leave that out, it's going to cool down and then collapse into a proton. I got it. Oh, speaking of su fla, I did leave one out, so we're gonna need to take a quick break while I go check on that. I'm sure it's fine, uh, And then we hopefully will come back and I'll still have my neutron soup fla attack and we'll continue talking about how long do these neutrons live? How do I resuscitate my neutron souflay? So we'll be right back. Okay, So bad news is that my soup fla did collapse. The good news is I guess it's now our proton, so all isn't lost. That's always the backup plan for your neutron souflay. Turns out, charge it up to a proton south lag. Like you know, a sou flay that collapses is still gonna taste pretty good. So a neutron that decays into a proton is still a particle. It'll still build things like delicious soufleas exactly. And so we were talking about how neutrons decay and how they turn into protons, and people might be wondering, like what's going on with the electric charges? Like can you just turn a down cork which is charged minus a third into an upcork, which is charged plus two thirds? Like charge doesn't just come for fruit. You can't just like create charge. How do you just convert a neutron into a plus one charged proton? Right? The answer is that the universe does do the accounting quite carefully. And when a downcourt converts into an upcork, it also emits a W particle. Okay, now you're just making up particles. What's the W particle? So a W particle is the force particle for the weak nuclear force. Right, we got all these different forces. We have electromagnetism, we have a strong force, we have the weak force. Each one we think of as carried by a particle. So photons carry the electromagnetic force, gluons carry these strong force. W particles carry the weak nuclear force. The weak nuclear force is like the weirdest, strangest, most amazing sporce there is. It's not very powerful, but it can do all sorts of really strange stuff. And we have a couple of podcast episodes dedicated just to under standing the weak force and parity violation and all that crazy stuff. But in this case, the weak force is here to help balance the books. When a down cork becomes an upcork, that sort of costs one electric charge. You've gone from a neutron to a proton. So to balance the books, you also need to create something with negative charge. The amazing thing about these W particles is that they do have charge, so the W can have a positive or a negative charge. In this case, you emit a W minus which balances the charges. So have you've gone from a neutron to a proton and a W minus. So the proton is plus one, the W minus is minus one. That all adds up to zero. The W minus itself doesn't live for very long and it turns into an electron and an anti neutrino. Okay, so an electron does have a negative charge, so it still retains that negative charge. What is an anti neutrino? Yeah, and anti neutrino is one of these little ghostly particles. So you and I are made of protons and neutrons and electrons, which are made of upcorks and down corks. But there's this other particle, this neutrino, which exists in the universe and can be made, and the Sun is pumping out like jillions of them every second. But they're very strange little particles because they don't appear normally inside matter, Like I am not made out of neutrinos, and you're not made out of neutrinos in any way. But it's something that the universe can exist. It's like a Lego building block that's never used in making anything bigger or larger. It's just sort of like floating around in the universe. Yeah, I remember those Lego blocks. They're usually like these like weirdly shaped, clear little ones, and they would just kind of not be used in anything, get quickly lost or eaten exactly. And neutrinos are strange because they're very very low mass, they're almost massless but not entirely, and they also hardly interact. They don't have any electric charge, they don't have the strong force, so they basically just fly through everything. So neutrino when it's produced, can fly through like a star without blinking an eye into a neutrino. The whole universe is transparent, and so that just sort of flies out. And so to summarize them, when a neutron decays, it turns into a proton, an electron, and then an anti neutrino, and so that's what happens when a neutron decase. That's spooky. So neutron does kind of create a ghost when it decays scientifically speaking exactly. And we should also be clear about what we mean about neutron decay because people might be wondering, like, does that mean that the neutrons that are in my body right now are going to like break up, like they don't last for long? Like, am I dying because my neutrons are decaying? Yeah, I want to know if I will spontaneously turn into a pile of protons, electrons and ghost particles in my best interest to know. And that's one of the really fascinating mysteries about neutron decay is that neutrons do decay, but only sort of like when they're on their own, floating out in the universe. When a neutron is inside a nucleus when it's hanging out with other protons. When it and it's proton brethren have built something larger, then he can last forever. You know, you have a stable nucleus like iron, right, iron can live forever. We think if you have an iron atom sitting alone in the universe, it's made of protons and neutrons and electrons, it can sit there, we think forever. We think it's stable. If it's not perturbed, it will just hang out until the end of time. That includes the neutrons inside the iron right there there. They're neutrons. They will hang out forever. Their down corks are not going to flip into up corks, turning them into protons. This is like the ultimate ziplock bag techniques. So keeping neutrons fresh forever. I love that technology for my strawberries. They're so good, but they go bad so fast. Exactly so, the neutrons in your body are in atoms, and so they are likely to last as long as those atoms last. But if you take a neutron out of the atom and you have it by itself hanging out in free space, now we can talk about the lifetime of that neutron. What does it do when it's left alone? Well, the neutrons sitting there in empty space last till end of time or will it decay? So if you put like a proton and then a neutron and electron, you have them just hanging out in free space and you just wait. The proton will last forever, we think, the electron will last forever, we think, but the neutron will not. The neutron by itself will decay. One of those down corks will flip. That's the actual sound it makes, and it will turn into a proton electron and an anti neutrino. So when we talked about the neutron last time, we're talking about the isolated neutron, not a neutron that's inside the nucleus. So, when it's inside the nucleus, what is that zip block effect that is keeping it from decaying. Yeah, it's a great question, and there's a lot of mysteries there because we don't really understand very well how the strong force works. We talked about it briefly a little earlier, but when protons and neutrons are locked together inside a nucleus, it's not like you just have these particles and they're stuck together like legos. They're also talking to each other because remember a proton and a neutron, they're not just linked together quarks, they're little bags of gluons. When you get a proton and neutron close enough together, then their gluons talk to each other. Those bags leak a little bit. They're not totally separate from each other, and really they sort of like weave themselves into a larger mosaic. You might wonder inside a heavy hydrogen atom, where you have not just a proton, but a proton or a neutron, what's making the proton and neutron stick to each other? Right, the proton is positively charged, the neutron is negatively charged. Why did they stick together at all? Why don't they just float apart? The answer is their gluons. When you get them that close together, then the gluons inside each other's bags talk to each other, and they click together into sort of a larger object which is not really anymore just and isolated proton, not really any more isolated neutron, but this combined object that has these linkages together. So is that why when you keep adding neutrons to an atom that it becomes maybe less stable because you start to weaken those gluon forces. Yeah, you can make it less stable or more stable. Right, The way that you organize the protons and the neutrons inside the nucleus totally determined whether something is stable or not. We have a fun podcast episode about the islands of stability and how heavy you can make something and keep it stable. We don't know the answer to that because the strong force is very difficult to do calculations with, Like we can't sit down with pencil and paper and solve the quantum mechanics of the nucleus the way we can with the hydrogen atom. Folks who have done physics in college have done like the shortening your equation for the hydrogen atom. When we know those equations, we can solve them, we can find the states of the electron. We don't know how to do those calculations for the strong force because it's much more powerful and much more sensitive to tiny details, So we don't actually know like the answer to those We can't do it with pencil and paper. We have massive computers trying to do those calculations, but it's really challenging, So mostly it's experimental. We try to like build heavier stuff and see if we can keep it together. People shoot like neutrons at atoms and see like, oh, can I get one to stick in there and make something which lasts longer. So it's a whole area of research. How do weave protons and neutrons together into stable objects? We think that they organize themselves in terms of these shells. Is this nuclear shell model that tells you how to build protons and neutrons together into a stable nucleus sort of analogous to the way electrons organize themselves in shells on the outside of the atom. It's really fascinating. So I am feeling more and more like a physicist based on my childhood because I would try to just build the biggest thing out of legos and then kind of hold it up and see if it could sustain and self for if it would fall apart. And it sounds like that's what you guys are doing, just with more expensive equipment. But yeah, so that that is interesting is you're saying that, like maybe they arrange themselves into shells. When you're talking about shells, I'm assuming this is not like a mollusk shell or something. So what is a shell in terms of particle physics. Yes, when we talk about shells we think of like spheres and other arrangements. We think of The protons and neutrons inside the nucleus have somehow found stable ways to organize themselves into these like little mosaics. Instead of thinking about them really as protons and neutrons anymore, you really should think about them as components of this fabric, this nuclear fabric, which likes to weave itself together. And the incredible thing is that it's stable, like in many configurations, even for very very heavy elements, these things are quite stable. Again, we don't really understand it. And so there's two different communities of physicists here, the ones that like to make really big blobs of protons and neutrons and understand like how are they working together? And then there's the folks who just want to like dig inside one neutron and say, well, let's just study the neutron by itself. Let's zoom inside the neutron and see if we can understand what makes that cork flip from one to the other. How often does that happen? How long does it take? And what does that mean about the neutron. So you've got like the nuclear physicists studying like huge blobs of neutrons and protons inside the nucleus, and they have us particle physicists looking to break it apart and see what's inside. That's really interesting. So now that we have isolated the neutron, it's we've broken apart that atom. It's outside, it's vulnerable. Now what happens? So now we can see how long it takes to pop into a proton and electron and a neutrino. And so this is a really interesting question, just like how long does it take? Remember, protons will live for trillions of years. There's two amazing things about the neutron lifetime how long a neutron will survive on its own. First is that it's very short. It's like fifteen minutes. The neutron does not last very long. The person is that it's basically instantaneous on a cosmic timescale. That's right, you know, neutron's last for like fifteen minutes. It's it's nothing. You know, cosmically, do you make a neutron? You leave it there, you go to get a coffee and you come back it's gone. You know, that's kind of sad to me. I don't know why. Again, I'm like attributing emotions to these things in the universe that, as far as I know, don't feel emotions, but it does. It seems very um disconcerting. That's something as fundamental as a neutron, less about as long as it takes for my soup to cool down. Yeah, So if you want to build something out of neutrons, and you make yourself a big pile of neutrons, you better get to work. No time for a coffee break, you know, before you get started. Like you got to use them or lose them. The other fascinating thing about the neutron lifetime is we don't actually know what it is. We've tried to measure it, and we have two very different ways of measuring the neutron lifetime, like two very different experimental setups, and they get different results. Like one group put a bunch of them in a bottle and wait to see how many they have like ten minutes later, and they get an answer of like fourteen minutes and thirty nine seconds. And other folks use a beam of neutrons and count how many protons come out, and they get a different answer. They get fourteen minutes and forty eight seconds, So there's like a nine second difference, so we don't even actually know. Well, I see what the problem is. Probably one group is using one Mississippis and the other group is using one potato to potato. You have solved this mystery. It is funded physicists for decades and today you have figured it out. Katie. Wow, thank you so much your contributions to particle physics. So you're welcome everyone for me solving this physics problem. And when we get back, um, I'm sure Daniel will make some kind of argument that no, it's not as simple as one Mississippi or one potato, but you know all of them have a short break to work that one out, because I think my argument is prettier tight. Okay, And so we're back and we've got this. Two teams of I would assume, very smart, very professional scientists, but they're coming to slightly different answers on how long it takes for a neutron on to decay. One group fourteen minutes thirty nine seconds, the other group fourteen minutes and forty eight seconds. So what the heck is going wrong? Is one group just wrong? We don't know. It's really fascinating to have watched this series of experiments over a couple of decades. You know, whenever you do something in physics, you try to do it a couple of ways because it's easy to make mistakes. You're doing something hard, you're making assumptions, you're doing the best you can, but it's very easy for mistakes to creep in, and so it's great practice to have two different groups of people doing it two different ways, making different mistakes. In the end, we're supposed to be measuring the same thing about the universe. The neutron should just have a certain lifetime and we should be able to measure it and get the same answer. And if we don't, that means that one of our assumptions is wrong, where somebody is making a mistake, or there's something deeper going on. Right, something is happening in one of these experiments that we don't understand, which could be like a clue as to how the universe works. So originally these two groups made these measurements and they didn't get the same answer, But nobody was worried because their airbor were pretty large. You know, the difference was like eight or nine seconds, but the uncertainty was like thirty seconds. So people have thought, we'll just keep working and maybe the numbers will creep together as they get more precise. The opposite has happened. Both groups have been working hard to reduce those uncertainties, you know, figure out the sources of error and potential bias in their experiments, shaving them off, calibrating them, cross checking them. And as the uncertainties have decreased, and now those uncertainties are like less than a second or two, the size of the difference between the two experiments has stayed the same. In fact, it's even crept up a little bit, from like eight to almost ten seconds. Okay, so we have Team Bottle, I'm going to say, and then Team Beam. So what are these teams doing? Because they have very different methods going on here, which that may somewhat explain why they're getting different results. So first let's go over like Team Bottle. What is Team Bottle doing just you know, shaking up some neutrons and a bottle, seeing what happens to them. That's basically, yeah, they have a new tron source. This is actually at Los Alumos, New Mexico, where I grew up. I was wasn't involved in this experiment. It's a huge facility there. As far as you know. Anyways, go on, I may have been unwittingly roped into this experiment. They have a bunch of neutrons there and basically they put them in a bottle. They get them ultra cold, so they're not moving very fast, and neutrons are a bit hard to store because they don't have electric charts, so you can't use magnetic fields or electric fields to control them. You have to use gravity to get them cold. So they slow down and let them just like fall into this container. They call it the bathtub, And basically they just collect a bunch of neutrons. They very carefully count how many introns they start with, and then they measure the number of neutrons in their bottle, and then they come back ten minutes later, measured again. And they come back ten minutes later and they measure it again. And that's the essence of the experiment, is like, if you think something doesn't last very long, put a bunch of them in a bottle. Count how many you have come back later and count them again. So it's very simple experiment in that way. So you've got this this ice cold bottle of delicious new atron's man that makes me thirsty. And so they would measure these and they would find that they are sort of disappearing at a certain rate, and that is how they got at fourteen minutes and thirty nine seconds exactly. The important thing to understand is that the neutron lifetime doesn't mean that every neutron has a clock in it and it expires exactly after fourteen minutes and thirty nine seconds. It's an exponential decay. Every neutron has a probability to decay in any moment. And if some fraction of your neutrons will decay in shorter time, and a fraction of the neutrons will last longer, just like radioactive decay, it's the same fundamental process. In fact, it is that process protons turning into neutrons, which drives also radioactive decay. So you don't like watch one neutron, just ask how long did it live. Have a whole population of neutrons, and you count how many you have over time, and you fit that to a function and exponential decay, and you measure sort of the parameter the slope of that function. So it's a bit more than just watching one neutron decay. That's why you have a population of them. So they have these in a little bathtub and then every once in a while they're trying to count all of them. They pushed them against this counter which is covered in boron and zinc, and that makes the neutrons give off a little flash of light, and they count how many flashes of light they saw, and that tells them how many neutrons they have left I see. So these two experiments would be like two groups of alien scientists measuring the average lifespan of a human. Like, sure, our lifespans are going to differ, but they're not going to differ by like hundreds of years. They're going to differ by a matter of a few years. And so you should in theory, even if these two alien scientists groups have different methods of measuring our lifespan, they should in theory be able to both come up with the same average lifespan. But in this case they're not. So then what is what is Team Beam doing? The Team Beam is taking the opposite approach, where his team Bottle is saying, let's count how many neutrons we still have left, Team Beam is asking how many neutrons disappear. So they have a beam of neutrons that they create, and they count how many protons are created within these beams, because remember a neutron decays and it decays into a proton, So to count how many neutrons have disappeared, they count how many protons are created. And so instead of counting how many neutrons they still have, like the Bottle guys are doing, they're counting how many neutrons have left the room. So in the analogy you were talking about with human lifetime, instead of counting how many humans do we still have left, they're counting graves. I see. I mean it makes me wonder. And again this is probably you know, me strolling in without having done the rigorous testing that Team Beam has done. But like, could there be like some infiltration of protons, like protons coming from some other source that is messing with their results. Absolutely, that's the kind of thing that they've been thinking about for like the last twenty years. So you're right, it's something to be worried about, but they're very careful. They shield their experiments that magnetic fields to prevent anything from creeping in, and they filter these protons out using magnetic fields and very careful to only count the protons that they think come from their beam. So each experiment has like a long list of ways that they can get it wrong. And over the last ten years they've been like going down that list and thinking, how can we check this, How do we really know this is true? Can we do this another way just to verify, just like as a sanity check, maybe there's something going wrong here. And they've gone down that list and nobody's found any basic mistakes, and as a result, they've been able to shave down their uncertainty because now they have like multiple ways of doing every step of their experiment to convinced themselves that their number is correct. So we still have Team Bottle and Team Beam doing very careful work. Nobody has an idea for what might be different where the mistake could be, but they're still getting different answers. Also, bringing it back to the aliens observing Earth analogy, I mean, I wonder if maybe there could like these teams could be doing everything perfectly and executing the experiments perfectly, still getting the different results, but not because they made an error, but because there's something else going on. So, for instance, maybe if the Team Alien one is just counting the number of humans left after a certain amount of time and average getting the lifespan average from that, they may not be taking into account like a new births or something. And then for Team Alien just measuring the graves. You know, what if you have a grave that has like more than one person in it, So could there be something going on where these these two you know, let's not blame the groups of scientists or the intern or the janitor. Nobody's doing anything wrong. But they are actually correct. But just because their method of measurement is different, there is some some mysterious mechanism going on that is creating that difference. Yes, absolutely, that is sort of the hope, right. The boring answer is like, oh, it turns out the cable wasn't plugged in right, or this temperature was set to the wrong number, and like you know, from an experimental point of view, that would be satisfied to figure it out. More exciting would be is if it reveals that one of the assumptions that are made that suggests that these two experiments should be getting the same answer are fundamentally wrong. So people have been very creative about this, and there is one cool idea floating out there that maybe when the neutron decays, it doesn't always decay into a proton. Maybe sometimes it decays into something else like dark matter. Some tiny fraction of time, the neutron turns into dark matter, and that would explain this difference because remember that the beam folks, they won't see it if the neutron decays into something else. They only count the number of times the neutron decays into a proton because they assume it always decays into a proton. Now the bottle folks, they will see that neutron disappear because they're counting the neutrons themselves. So if the neutrons sometimes decay into something which is not a proton, then these two groups will get different numbers. So this is fun idea out there about how maybe neutrons will sometimes decay into dark matter instead of into protons. That is really cool. I love that when in science, like if you get an unexpected result bolt or something that seems like a mistake, it could actually lead you to an even bigger, even more interesting discovery. And there's so many times in the history of science when you do that, When people do experiments, they think just like wrapping up everything, tying up the loose ends. We're pretty sure we understand what we're gonna see. And then there's a discrepancy and it's persistent and it won't go away, and sometimes you tug on that thread and it unravels like everything we thought we knew about the universe. You know, the whole discovery of quantum mechanics was from people like m that's weird. You don't really understand what's going on with the photoelectric effect. So these little discrepancies are very important. They're very powerful ways to test your assumptions and to maybe get a clue that there's something new going on in the universe we don't know. And the dark matter idea is just sort of like a category of possibilities. The specific theory that was bounced around for a few years about the neutrons decay in the dark matter doesn't look like it works. They made this very specific prediction that it would decay into a new state, and in that state, we decay into dark matter, and along the way it would make a tiny little lash, a very specific light. And so the bottle folks looked for this flash of light, but they didn't see it. But that doesn't mean that it's wrong. There might be some other explanation in the same vein the neutrons could be turning into something else. We don't expect a new kind of dark matter or even something else weirder, So, are are they looking into new experiments that they could potentially do to sort of find out what's going on here exactly? They're trying to develop like a third way to measure the neutron lifetime, because that will give us a handle. It's like a vote, right, we develop a third, totally independent way with different assumptions than either the first two. It will tell us which of those first two is correct and which one is not. Actually measuring the neutron lifetime the way we thought it was. A third way to measure this is actually in space because one way to make neutrons is to smash protons against the Earth's atmosphere, which happens all the time out there in space because space is filled with high energy cosmic rays. Protons from the center of the galaxy or from other solar systems smashing into Earth's atmosphere, creating these showers of particles, including neutron on. Now, most of these neutrons then like rain down on the Earth's surface, and as they do, because they're by themselves, they're not inside atomic nuclei, they turn into protons. So if you can count like the number of neutrons created at the edge of the atmosphere with a number of protons you then see raining down, you can get a sense for how many of those neutrons have converted from neutrons into protons. And that's a way to measure the neutron lifetime. It's a bit tricky and it's more complicated, which is why it wasn't like the first option or the second option. But now we need a third option and we need to figure this out. And so people are even talking about like building probes that an orbit Venus, because Venus might have the perfect atmosphere to do this kind of experiment, because it's got so much C O two in it, So it's using a whole planet as a test tube exactly. Particle physicists are not content to just do experiments in one tiny little lab. We want to use the whole universe as our experiment. I see you're just trying to use your research budget for travel. I get it, exactly. What's this first class ticket to Venus? Daniel? Can you explain this charge? But this is something that's really important, you know, not just because we want to understand what's inside the neutron and how does it work and is the neutron turning into something else? The neutron lifetime is a really important component of our universe. You know, in the early universe, neutrons were made, as we talked about, but if they didn't last for long enough, they couldn't get served up into atomic nuclei. So the length of the neutron lifetime sort of determines how many isotopes are made, how much helium is made, and so it's important to get this number right. You know. They determines like the hydrogen to helium ratio that's made during the Big Bang, but also determines like how long stars will live, because the more helium you get, the smaller and heavier the stars are that are made, which don't burn as long. So this is like a fundamental ingredient to the early universe calculations. It's something we really need to understand. So even a discrepancy of a few seconds is very important to determine what is causing that and what the answer is to this right, and it goes to really deep questions in particle physics about the strong force. You know, this is something that we can't sit down and predict very confidently. It takes massive calculation to try to get a sense for how corks talk to each other because the forces are so strong and so difficult to calculate with. It's something physicists called non perturbative, which means that we can't make many of our typical assumptions and simplifications when we do these calculations. So this is a great laboratory to force the universe to teach us something about how the strong force actually works, to force it to like tell us, here's how this happens. Here's the result of this calculation. So it's a really powerful way to try to get some inside how these little particles are talking to each other. And in the end, I got neutrons and you got neutrons. So this should be important to all of us. Yeah, it is interesting. It's such a humble particle that you think of this like neutral doesn't seem to have such a big role to play, But really it's so important to not only to keep us together apparently, like I don't want to fall apart into a bunch of protons and w minuses and then which turns into ghost particles and electrons. I want to stay me for as long as possible, but also just it seems like it's really important to understand them, to understand the universe. Yeah, and it's an enduring mystery. We're gonna stay tuned to figure out what's going on with these neutrons, how long they live, and whether Team Bottle or Team Beam got it right. This is exciting. I want to print shirts Team Bottle, Team Beam and see we're the dialay. Thank you everybody for joining us on this journey, the journey inside our atoms and your atoms and the universe's atoms, where tiny little clocks determine the fate of neutrons and the fate of stars. And thanks very much Katie for joining us on this very particular podcast. Thanks for having me, and good luck with your neutron soup. Flay tune in next time. Everybody, thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I heart Radio. For more podcast from my heart Radio, visit the i heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows. Ye