The Marvelous Mystery of the Muon Magnetic Moment

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Speaker 1: Hey, or hey, I have a really practical question for you. Well, you know I'm an engineer, so practical is my middle name. All right, Well, here's the question. Who would you trust more to build a spare room off of your house? A physicist, board engineer. I think you know the answer to that, Daniel, Not to physicists. All right, but tell me why. You know. Physicists are awesome, but I wouldn't say they're very precise. You know, they approximate everything. You know, everything's like plus or minus a galactic idea. So you want to know how big this bedroom is going to be in advance, for example. I just don't want like a spherical room or like a quantum on certain room. You know, I want to know where I'm sluting. Well, you might appreciate a surprise, but I think that's fair, that's reasonable. But you know that sometimes physicists can actually get really hardcore about the detail. You're still not building my spare room. I am more hammy cartoonists and the creator of PhD comics. Hi, I'm Daniel. I'm a particle of physicist and you definitely don't want me building your spare room. Is that because of you or because you're a physicist, or is it all packaged together. You know, there's a whole spectrum of physicists. There's the kind that really likes to build stuff, crawl around on the detector with a hammer and a wrench and and get dirty. And then there's the kind of like to sit in front of a laptop and analyze data and think about statistics. And I'm definitely more of that second kind. Well, you can check out my house in your laptop and think about it for a long time. I'll build you a virtual spare room. There you go. I'll program another spare room in the simulation of your universe. It sometimes exists in this universe and sometimes it doesn't. It's theoretical. That's right. Just step through this black hole into your new spare rooms and cozy but welcome to our podcast Daniel and Jorge Explain the Universe, a production of our Heart Radio in which we talk about all the amazing things that are happening in this universe, all the things we'd like to understand from the very very large, very very dense, all the way down to the very very small and the very very weird. Yeah, because the universe has a lot of amazing things and all kinds of skills, you know, galactic cosmological skills, But there are also amazing things happening at the smallest scales of reality and nature. That's right, and these really tiny things they give us an amazing opportunity. They let us test our understanding and not just do we mostly get things right, They let us really push our limit to understand exactly how these things are working. Do our models predict what's happening or is there something a little bit wrong? And that kind of raises a question of how well do we know what's happening at these really tiny scales, Like we can measure distances from here to the moon, for example, or here to maybe the next star, But how do you measure things that are that small? And how do you know if you're right? It definitely takes a certain skill. You have to come up experimentally with really clever devices, things that isolate individual particles, or get a bunch of particles and get them all aligned and then separate them from any other effect. It's a really particular skill in science to devise an experiment that forces nature to reveal something for you that pushes everything else away. Like we learned about the Lego experiment that measures gravitational waves. There's a huge amount of cleverness involved in isolating those things so you can see tiny little wiggles in space. Well, this is sort of experimental cleverness, and when you deal with particles, you need this sort of the same kind of skill. You need to set the universe up in a way that it has to reveal to you very precisely the answer to your question. Right, But sometimes a problem, right, Daniel, is that you measure something and you don't get what you expect. You measure something, you think it's going to be this big or this long or this heavy, and then when you measure in reality, it's different. Yeah, well that's not a problem. That's fantastic, that's exciting. That's an opportunity, you know, Like, yeah, because we have two branches of our work. We have the experimental side that's going out and doing stuff and measuring things and answering questions, you know, sort of asking the universe, what do we conclude from that? How do we interpret that and build a model of the universe in our heads, and then turn around and predict future measurements and when those predictions disagree with the things we observe. That gives us an opportunity to update that model, to say, oh, something was wrong. There's a new particle, or this particle works differently, or black holes are actually bigger than we thought. Those are the moments when we learn. So when theory and experiment disagree, I smell opportunity. But how do you know who's right. You never do, And usually they're both wrong, and they're both wrong in different ways because there are very very different challenges, you know, split the difference. Calculating something theoretically has challenges of computing time and getting minus signs right and sort of organized in your mind, and and getting answers experimentally has all sorts of different challenges, making things clean, making them distinct, getting a big sample of something, getting enough material, you know, we're sometimes just getting enough money to build the device that you need. That's the hard part. But there is one of these big mysteries in nature that it has to do with a weird kind of discrepancy between what the theory predicts and what we actually measure. So today on the podcast, we'll be talking about mystery of the muance magnetic moment. That sounds marvelous and magnificent. It is one of the most amazing and marvelous moments in magnetic field history. You know, it's an opportunity for physics to learn something because it's something that we know how to calculate very very very precisely. You know, if you want to find out what's wrong with your theory, you need to find something that you can predict very accurately and then measure you're very very accurately, so you can compare the two and that tells you if your theory is right or and or if you're measuring device is working right and not just giving you weird things. Yeah, and if you hope that your experiment is correct, then you know, if you see a discrepancy, tells you that your theory is wrong. And sometimes we do this as a way to detect the presence of new particles or you know, just to see if anything is right, because some of these calculations are very very sensitive, so it's a very good way to tell whether there's anything missing in your ideas. You know, it's sort of like if you walk around your house and you could take a really precise measurement, you could see where everything was, and you compared that to the drawings you have of your house. Right, that would tell you, like, you know, whether your house is well described by your idea of it, or whether it was a mistake to hire you to clearly actually probably not. How are you to measure it also build it? I would say, Wow, this is perfect work. You should pay your contract or double. I guess that's a big question. And the question is how good or physics isn't measuring things? And so we were wondering, we were curious about how many people out there. So if I've thought about how good our measurements of the universe are, and in particular, what's the most precisely measured quantity in physics? So, as usual Daniel went out there into the wilds of the Internet to ask people what's the most precisely measured quantity in physics? That's right, And if you're interested in answering random internet questions without any preparation, please right to me at feedback at Daniel and Jorge dot com and I'll send you some questions to answer. So think about it for a second. If you were asked, what's the most precisely measured thing in physics. What would you answer? Here's what people had to say. My best guess is increments of time, accusing an atomic clock. I don't know. I don't know, Sorry that I don't know. Is this something to do with the plank Clint? Maybe aliens? I'm not sure what you mean about quantity, whether that be amount of things, how many bananas it takes to create a black hole. I'm going to guess it's mass. Maybe I like this question. Well, I think first we have to define what do we mean by precisely? Maybe temperature mass would be the most precisely measured quantity in physics because it holds a tangible value. I reckon they can measure pretty small, like maybe an adam. All ride a broad range of answers, from aliens to bananas to the plank scale. I feel like our audience is very much in tune with what we cover here in the podcast. Yeah, these are great answers, and I have to confess I think that some of these answers make me rethink how I should have asked this question, because I asked, what's the most precisely measured quantity in physics? Like you go out, you do an experiment, you measure something. But I think really the question we should have asked is what's the most precisely calculated quantity in physics? And there's a difference. For example, the atomic clock answer is a really good one. You know, atomic clocks are precise us too, like one part and tend to the sixteen. You know, it takes like ten to the sixteen seconds before they're off by one second. So you would agree with a lot of these alien, Yeah, some of these are really very accurate. And for example, Lego, like we mentioned before, gravitational waves. To detect gravitational waves, they have to measure, you know, the change in length of something by one part in tend to the twenty or tend to the twenty one, which is really incredibly precise experimentally. But what I was going for was a question of, like, what's the most precise test we have of our theories, which requires not just a really precise experiment, but also a really precise prediction. Oh, I see, like what's the most precise that physicists have been right about stuff? Is that kind of what you mean? Yeah, because for gravitational waves, for example, that's a very precise experimental measurement but we didn't know in advance how big it would be, and we don't know necessarily how big those should be. It depends on the size of the black holes that are the same with the tomic clocks. We can't calculate the those things as well as we can measure them. In order to get some insight into the universe, you need something where you can calculate it really well and you can predict it really precisely. Interesting, so you're kind of talking about like, according to the laws of physics, we think that dis quantity should be this, and then how well does it match with what we actually measure of it exactly? Because it's those discrepancies we need to learn something. It doesn't matter if you measure the length of your house to one picometer, because we don't know how big your house should be and doesn't really tell us anything about the universe. But if you measure something really precisely that we can also predict that we can calculate that has to be a certain value because of our understanding of physics. Then measuring it and finding out it's something else gives you a clue that something is wrong about our model. Right, Well, it seems like there's one such thing that we're trying to predict and measure at the same time, and that there's a big mystery about why those two things don't match. And that's the magnetic moment of muance, which is a great alliteration there. I'm so pleased to have some positive feedback for a name in particle physics from you. That's a high, high standard for your poetic writing. Here, the mystery of the muon magnetic moment. Yes, it's really marvelous, all right. So this is a quantity that we have predicted using theory and that we've measured using big machines. But those two things don't match. That's right, all right, So let's get into it, Daniel. Let's start with the first m What is the magnetic moment. So when you think about particles, remember we like to think of them as little dots in space that have labels, and those labels can be like what's the spin or what's the charge or how much mass do they have. We don't think of particles is like little physical balls that actually do these things. They're weird quantum objects and they have these labels. And so this is one of the labels of a particle. But it's a little weird because it's not like a direct label. It's not like something you can put right on the particle. Because particles they don't have a magnetic charge. They have electric charge. That's how they feel electric fields. But as we talked about on the podcast before, there are no particles that just have like a north or a south magnetic charge on their own. See, they have an electric charge, but they don't have like a pole like you say, like a magnet, like a north and south. That's right, they don't have just a north and just a south. What they have is this weird magnetic field. It's a dipole to have a north and a south, just like every magnet we've ever discovered has a north and a south. And that comes from the combination of having charge and having spin because charge and spin together gives you some sort of magnetic interaction. Okay, so particles have spin and charge and together they have a like a pole, like a magnet, little magnet inside of it. Yeah, and that's what we call the magnetic moment. It's the part of the muan that is affected by a magnetic field. And you know, fundamentally it comes from having charge and from spinning. And that's because it has a magnetic moment. It doesn't have a magnetic charge. It's not a north or a south, but it is affected by the magnetic field. And that's what we mean when we say the magnetic moment of the muan. How a muan is affected by a magnet. It's not the moment for like an electron looks at a positron and they feel that attraction towards. No, it's not. It's not a dramatic moment. It's not something exists in like theory of screenplays or anything like that, unless you're writing a movie about particles, in which case there probably is an electrifying moment for the muan. Wow, you would totally watch that movie. Um, I totally have that movie script already in a drawer in my house. It's been sent to several Hollywood agents, but nobody seems to be writing. Consider this podcast my pitch for this project. I would definitely watch that movie, but I have not yet written the script anyway. So we're interested in you know, what happens when you put a magnetic field on a muan. And this is something we can measure because we can do that experiment, and it's also something we can calculate, and it turns out to be really sensitive to exactly what's happening into some other big questions about how particles work well, And maybe let's go back a step and cover the other m which is the muon. So muan is like an electron, Is it like a quirk? Yeah, So we are made out of quirks and electrons. Right, We have quirks that make up the protons and neutrons inside our atom, and then we have electrons whizzing around them. But each of those particles have other copies. There are other kinds of quirks, and there are also other kinds of electrons. So there's a heavier version of the electron. We call that a muan, exactly the same as the electron, except has a lot more mass. And there's another one even called the towel. So the electron has these two cousins, the muon and the towel that have all the same interactions and all the same properties, like the same charge, the same spin, but just heavier match, just heavier mass. Yeah, and it's weird. We don't know why they exist, Like why do we have the muan. Why do we have the tow Why does the electron have two cousins and not nine cousins or seventeen cousins or any cousins like my cousin? Are they good for anything? I'm not going to get in the middle of that family dispute. We have cousins, so we want specified which one I'm talking about. But what I guess what I mean is like, is it good for anything? Like does it form part of you know, can you make an atom out of them? Or do we just know them kind of theoretically, or we know that they formed, but then they disappear quickly. That's right. They're not stable, so you can form atoms out of them. You can take a proton and put a mu on around it and form a bound state. But the muan lasts for you know, a few microseconds. Remember that heavy particles don't survive very long in the universe. Actually, in its reference frame, if you were riding on the back of a muan, you'd see that it lasts a few microseconds. But because they move so fast, their clocks are slowed down. So as we watch the muan, we see them live their three microsecond lifetime. Over a longer period because of time dilation, so they don't last terribly long. It's still you know, seconds or minutes. But muans don't last in our universe because they're heavy. They effectively turn into electrons. All right, So there's a big mystery regarding the magnetic moment of the eu on. So let's get into the theory and the experiment and talk about what it means. But first let's take a quick break a right, Daniel, we're talking about the magnificent mystery of the marvelous muon magnetic moment. Momentarily, hi rolls in your mouth. It's delicious. Um, So yeah, so tell me about this mystery. So we know about the muan and you're saying that we can the theory predicts its magnetic moment. How can the theory predict something like that, Well, we think about it in terms of particles, right, We're talking about how the muon is affected by a magnetic field. But a magnetic field we know is really carried by photons. Like when things interact electromagnetically, we can imagine that as being done by photons moving through space carrying information. Remember, every force that we think about electromagnetism, the strong force the weak force has these particles to sort of do its job, and in the case of the electromagnetic interaction, it's the photon. So when you think about how a muon is affected by a magnetic field, really on the sort of particle level, what you're thinking about is what happens when a photon hits a muon, or how does a photon interact with a muon. That's sort of like the basic tinker toy element of particle physics that lets muans be affected by magnetic fields, right, because magnetic fields are transmitted by photons. Yeah, magnetic fields are basically photons. We can think about like our fields particles or particles fields, but they're very tightly connected. So like if I throw a muon at a bunch of magnets and it curves one way, it's not because it's something in it. It's because it's like hitting and interacting with photons. Yeah, exactly, it's getting bent by the magnetic field. And very natural way to think about that is in terms of photons being generated by you know whatever where the source of your magnetic field is and pushing the muan. All right, So then we think of its interactions is hitting photons, and so how does that help us predict its magnetic moment. Well, it's fascinating because there's a whole bunch of different ways that a photon can hit that mu on. Like the simplest thing is photon hits the muon and bounces off, right, So you have photon muan interaction very simple, Like in your mind, you have a couple just little lines of particles that intersect and then they go their separate ways. That's the simplest thing, and you can use that to calculate, all right, what's the strength of the magnetic moment of the muan? And if you did that calculation, you get a pretty simple answer. This was done first by a guy named Julian Schwinger, and he was so proud of this calculation that he actually had this number. It's alpha and the fine structure constant over to pie. He put this number on his tombstone. He's like, don't forget I came up with this. Seriously, it's like it's a beautiful calculation. He was so proud. This guy did a huge amount of physics in his lifetime. He's basically the person who proved that Fynman's theory of quantum electro dynamics actually work. Finding like sketched a bunch of doodles and had a few ideas, but never like actually made it work. And Julian Schwinger was like, all right, let's do all the calculations and see if this is right. But that benefit in his tool stone, I guess this is a really succinct way to just sort of like sum up the guy's life. Anyway, the point is that there are other things the photon can do also. It doesn't just have to bounce off the muan on its way there. It could like split into an electron and positron and then convert back into a photon and then go off. Or it can emit a particle and then reabsorb that first particle. So if you'd like drawing these Fineman diagrams these ideas for how this happens, all you have to do is add a couple more lines, and all these things describe totally valid things the photon could do as it interacts with the muon, and those change effectively the muan's magnetic moment. See, so it's kind of like the muon doesn't really have a magnetic moment. How does it interact with a photon? Its interaction with the photon is essentially what determines how it reacts to magnetic fields, which is its magnetic moment. And photons are crazy, they're like always turning into other stuff and spewing off particles and reabsorbing them. And the real actual thing that happens between a mean and a photon is some some of all those things, all those things mixed together, which you can and that you can predict with the theory. Like your theory, you can like write this down in a piece of paper, like what happens if a photon hits the muan, and you can in a piece of paper you can work out how that muan should bend its path or how we should get deflected. And then you can say, well, what if it was a little bit more complicated, what if it also emitted another particle at the same time, Then it would change your calculation. And you know, as you make these things more complex, there are more and more possibilities, so it becomes very challenging theoretically to account for all the different things. But that's also gives you an opportunity because if there are crazy particles out there that you would never considered, then the photon could be turning into them, could be like interacting with them, could be like popping into existence some weird new particle you never imagined. And that would change how it interacts with the muan because it would lose some energy. It would just it would change its angle, it would change its direction, it would change the probability of this thing happening at all. And so in this way, the photon interacting with the muan is sort of like a probe of the whole universe because along the way, the photon can do all sorts of crazy stuff. You can do anything that quantum mechanics lets it do, and what happened affects how it interacts with the muon. And so by calculating this quantity and then measuring it, you can ask, like, is there anything else that the photon is doing along the way that's changing how it interacts with the mu want to see, like how good are we predicting what photons actually do. Yeah, it's like you said to photons, hey, go crazy, do anything you want to do, and then we're going to try to calculate all the things we think you can do, and then let's compare. And you know, if it turns out you're dancing with a new kind of particle we've never heard about before, we're gonna know you're like stalker fans. Yeah, and you know, people like me, I like to discover new particles by sort of making them concretely, like pouring enough energy into a collider so that we have enough energy to make this new particle. And see it's sort of directly, but this is another way to do it, is to like look for these particles just sort of like briefly popping into existence as photons do their crazy dance with muans. And I guess my question is why the mean like couldn't I mean, all these questions and all these magnetic moment ideas we should work for any other particle, right, So why are we focusing on the muon specifically? And you can do these calculations also for the electron and also for the town, right, but the muon is sort of in a sweet spot because it's a little bit heavier, it's sort of easier to handle. The new physics should happen to all of these particles. Right, but it has essentially a proportionately larger effect on the muan because it has a larger mass. I see, So lemon is like the guinea pig. Yeah, the muan is like the best place to get the universe to reveal all these little details, all right, And so you can run the math and it should tell you how the muon should bend in a magnetic field. And you can also measure how, like you can throw me on at a magnetic field and see how it bends. That's the experimental side. Yeah, But before we move on to the experimental side, I gotta sort of shout out to the theory here, because this is what I meant earlier about being really precise. On the theoretical side, this quantity, the magnetic moment of the muan, is the number that theorists know best. It's the most precisely calculated quantity basically in the universe as far as we know, unless there are alien physicists doing it out there. What how can something theoretical be precise? Doesn't precision mean like how right you are. It doesn't mean how right you are. And when we do these calculations, we start with the simplest idea as we say, well, what's the simplest thing of photon can do? And that gets you mostly right, and they think, well, what if it does one weird thing along the way, And there's like nineteen ways for that to happen, So you add nineteen calculations. Well what if it did two weird things along the way. Okay, now there's nineteen squared ways to do that, and each of these gives us smaller and smaller effect. And so as you add up more and more of these ideas you're considering, you get closer to the true answer, but also becomes harder. And so now they're at the point where they're calculating like millions and millions of possibilities. Maybe first to turn to ano electron, and that electron did some weird thing, which turn to into a photon, which then did some weird thing. And so they've estimated sort of theoretically how precise this is, Like it's impossible to get it exactly right because you need to do an infinite number of calculations, so they can estimate how close they get based on how much is the answer changing as they add more ideas, So they're asthm topically approaching the deep truth. I guess there's a you know, an engineering, there's always this issue about the different between accuracy and precision, like accuracies how right you are, and precision is like how sure you are? So is the thing that's happening here? Is it that theories are pretty sure they know what the moment of the muan is, like they think they've covered all the angles, so they're pretty sure, but maybe they don't know if it's the actual value. Yeah, you know, I have equivalent with theoretical physics here because experimentalists trying to be really formal about the statistical statements we make. If we say, okay, there's an uncertainty here, that means something very specific. Statistically, it means if you did the same experiment a hundred times, you would get the answer within your uncertainty bounds sixty percent of the time or something like that, or a different answer if your Bayesian. That's precision. There is are a lot more hand wavy, you know, they're like, well, we tweaked a couple knobs and got different answers, and so you know that's the uncertainty. We multiplied some things by two just to see how things would change. So that's what we're calling the uncertainty. And you know, it's harder, it's different. They're not measuring things about the universe. They're just trying to like guess how closely they are the right answers. So I guess maybe the title should really be the most precisely guessed that theory quantity ever, you know what I mean. Like they put a lot of attention into the They've covered every angle on so they're they're pretty sure that this is what the plan is. Yeah, I suppose so, although you know, there have been moments in this history and this is a decades long project to make the theory more precise and make the experiment more precise. It's a bit of an arms race to see like who's getting more and more precise. There was a moment in the nineties when the theorists discovered that they had gotten the sign wrong, like that a minus sign where there should be a positive sign, and it changed the answer kind of a lot. So they're they're definitely mistakes in there. Oh my gosh, who made the mistake? Are they going to put that in their tombstone as well? One more minus sign? Know, there are different groups, and they're cross checking each other, and so you know, that's another way they try to estimate how correct these things. All right, well, let's get in to now the experiment part of it and how well these two things match up. Who's more precise or less accurate or more marvelous. But first let's take a quick break. All right, we're talking about the magnetic moment of the muan as the most precisely guest at quantity ever, and now we're going to measure it with an experiment, and that just involves throwing a muan at a magnetic field and seeing where it goes or is there is there something special going on? You know, that would work, But what you want is a really precise measurement. You want a measurement which is accurate to like one part in ten to the twelve or ten to the thirteen, and so to do that you need a really clean setup. And so what you described would work, but it's sort of hard to measure it's a single particle. And so what you want is a lot of muans. You want them all basically doing the same thing. So you can get a bunch of measurements and divide by a big number and it sort of averages out some of the mistakes. And so what they do is they get a huge pile of muans, a big blob of muans, and they point the spin of the muan, which is the thing that determines again where this magnetic field is going, and they get them to spin in the direction they're moving, and they move them in a circle. So they have this ring in Chicago where they have a bunch of muans and they move them in a circle. And when muans move around in a circle in a magnetic field, their spin will precess, it will rotate around the access of motion. Because that's how the physics work out. Like if you try to ban the muon, it will also sort of change in other ways. Yeah, Like one thing that happens to a particle and you put it through a magnetic field is that it bends. But a particles moving in a circle through a magnetic field will process, It will will change the direction in which they're pointing. So that's what they can do, is they can measure the difference between the direction of the magnetic field that they're putting on these particles and the direction of the spin of the ones which affects their magnetic moment, And so they have come up with really clever ways to measure these things and to reduce all sorts of uncertainties. And you know, if you're a visual person, it's really very similar in spirit to the experiment that looks for gravitational waves. What you're trying to do is isolate this experiment from any other effect. You know, like, is that the microwave oven in the break room that's changing the answer? You do we understand all the electromagnetic fields nearby. Is the radiation from the ground affecting our result? It's this kind of experiment you're like really isolating any source of noise or uncertainty. All right, So they're spinning these muans in a circle in Chicago, and again not in Minnesota or Milwaukee or Montana. No, it's being done at Fermulab, the accelerator complex just outside Chicago between Batavia and Naperville, where I did my pH d thesis hometown plug. All right. So they're spinning these in a in a circle, and they're measuring how they're processing or changing in the direction of their moment, and that tells you the magnetic moment of the muan experimentally, and now the problem is how well does it match with what the theorists. Yeah, that's right, that's the questions. That we have the number from the theory and the number from the experiment, and if you write these two numbers down on a piece of paper, they agree to the first what is it, like eight or nine digits before they disagree. So it's like it's really a testament to an incredible amount of work. I mean, you call it guessing, but like these theorists have done a huge amount of work to really nail this down, and the experimentalists have done a different, difficult pile of work, and now they have these two numbers. It's incredible to me that they agree this closely at all. All right, so let's maybe sign out the number for the audience here. So the experimentalists say that the magnetic moment of the muan is two point zero zero two three three one eight four one eight close our mind is some small quantity, and what are the units of these These are dimensionless units. Yeah, so okay, that was from the experimentalist. Theorists say it should be two point zero zero two three, three, one eight three six to not fo, that's right. So they agree on you know, after the decimal place, they agree to seven digits, and then they disagree. One of them says four one, eight and the other one says three six two, which is not a huge difference. It's like twelve zeros and then like, yeah, it's a bunch of zeros and fifty six. But the fascinating thing is that both of them are pretty confident in their results. So there's a gap between them, very tiny gap between them, but the uncertainty is smaller than the gap. Right, the difference between them is fifty six, and the uncertainty is like fifteen, So the difference is like three or three and a half times the uncertainty. It seems really it's so weird to me that they're so confident, you know about these numbers, Like you know, I've done experiments, and you know, to get that kind of position is really hard, Like if they ran this experiment next year and the year after that, but they still get the same exact. Yeah. These uncertainties reflect statistical limitations, so like you haven't runned for an infinitely long time, and also systematic uncertainties like things you think will contribute to mismeasurement or or bias on your result, and you know these are estimates. It could be that they're wrong. It could be just a basic mistake somewhere. But this is what we're trying to learn. Like we're trying to learn, like do we understand how to do these precision measurements or do we understand how to do these calculations, or is there a new particle out there that we're not factoring into our calculations that's playing with a magnetic moment of the muant finding a little bit? Is this the hint of the discovery of some new particles, some new supersymmetric particle which is too heavy to make a particle colliders and only appears very briefly and gives these little hints to the mule, like is there something hiding in that zero point zero zero five six difference between the experiment and the theory, or because they're both pretty sure of their numbers, there's now like they're both pretty sure of their numbers. Yeah, it couldn't be like a wire missing here or a plus sign missing over there. They certainly could be and their independent checks, their independent experiments, and we'll talk about that in a moment, but they're both pretty confident. And I remember learning about this in college and I was still learning about quantum mechanics and how it all worked. And at the time, I thought of physics as sort of like a description of what we see about the universe, just like sort of a human internal to our minds approximation of what's happening in the universe. And I read about this calculation, like, wow, it agrees to you know, nine or ten decimal places. That's amazing. And I at this moment where I thought, wait a second, maybe physics isn't just describing approximately what's happening. Maybe we've discovered like the source code, Like maybe this is what the universe itself is doing. Because to get that accurate, to get that precise, it's sort of shocking, you know, to imagine there could be another theory that could also be that precise. So I see, it's like, what if we actually uncover at the code of the simulation of the universe, because it's so we're so right, and we're so right. Yeah, maybe the universe does run on a computer using these equations? Is that kind of what you mean? Sort of you know, but in a more universal way, like maybe the universe does follow laws and it does calculations, and it follows these rules when it does those calculations, you don't have to be embedded in some meta universe and simulated on a computer. Maybe the universe is doing calculations though. Anyway, it's an incredible testament in my mind to the work involved here, and it's amazing that it works at all. I agree, right, But there is sort of an interesting mystery, And I guess the weird thing is that you're telling me that for the electron there's no difference between the experiment and the theory. That's right, Like this difference only shows up in the melee. We can do the same measurement for the electron. We actually a similar number, but there's no discrepancy. Like the electron. When they do the theoretical calculation and they do the experimental measurement, they get those two things to agree to within uncertainty. Now we expect that new is it, new particles whatever, would have a bigger effect on the muan, so it's not a surprise that it doesn't appear there for the electrons. And that's quite fascinating. So maybe there's something going on with the muan that you wouldn't see in the electron. So the electron you check that box or like the theory, and both groups have gone at the electron with the same kind of intensity and precision, and you can do all the same kinds of theoretical calculations for the electron and get a really precise number. And then you can go measure the magnetic moment of the electron, because electrons also bend in magnetic fields, and you can make that measurement really, really precise, and those two numbers agree. Electrons, we understand them like. There are no mysteries hiding under the rug for the magnetic moment of the electron, but for the muan, which is exactly where we would expect to see something weird. First we start to see something weird, all right, But it's different for the muan, which means that it might be hiding a secret. So what does that mean, Daniel, What could be hiding underneath the marvelousness of the muant? Well, you know, we suspect that there are other particles out there that we have not yet discovered. We found six particles that are corks, six particles that are leftons, and then a few of the particles that mediate the interactions between them, and so we have this pile of particles, but we don't know if those the only particles out there. And actually it would make a lot more sense if there were more particles, because there are these weird patterns we found that are unexplained, and some of them would click together really nicely if there were new particles. Like some of the particles we've seen are called fermions. They have spin one half, and the other ones are called bosons because they have spin one. There's one idea that maybe every fermion has a boson version, like the muan has another version of it called the smeu on, and the photon is another version of it called the photino. And these are like just one idea of how there could be new particles out there that sort of solve deep problems in theoretical physics, but we haven't seen them yet, so they could just be too big, too heavy for us to discover them. In particle colliders, remember to see something in the collider, you have to put in enough energy, which means you have to make the collider big enough, which means you have to get enough money from the government to build a really big tunnel, So there's a limitation there. This might be another way to like sneak around that limitation and see these new particles for the first time, at least hint that they're there. And if you do the calculations and what do you expect to see if there are these new particles, this is kind of exactly what you expect to see. So is the idea then that maybe there's a new part that we don't know about that the photon is turning into or like transforming into before it interacts with me. Because the photon can interact with anything that has electric charge. And so if there's some new heavy particle out there that does have electric charge but it's never really exists in the universe because it's too massive, well, occasionally the photon can turn into it or pairs of it, like it's particle and it's antiparticle, and that would change how it interacts with the muan because you have to include it in all of these calculations. Like maybe it admits this new heavy particle and then it interacts with the muan and then it reabsorbs that particle, and that would change the way it interacts with the muan. And so the presence of weird heavy particles changes the basic interaction between two very simple particles, which I think is fascinating. It's like a it's a clever way to leverage you know something about the universe, to force the universe to tell you about what's going on, even if you don't have the energy to build that com eider. I think Danny, what you're saying is that the experimentalist are right and the theories are wrong. Well, you know, the experimentalists are probably wrong in different ways from the theorists. Experimentalists definitely make mistakes. It's really hard to do these things and to get them right and to remove all sources of air. And that's why it's fascinating as a cross check, because if they're wrong, they're probably wrong in different directions or different amounts. And so it's a great way to cross check, and you know, to improve experimental physics and to improve our theoretical understanding of the universe and maybe find new particles in between. And yeah, and maybe make us stop off in Stockholm to collect your Noobile prize. And that's why you know this isn't over. It's not just like, oh, hey, we saw this discripancy were done, because it's kind of indirect, right, This is not like we make these particles, we see them, we understand them. It's just sort of like a clue that the particles are there. And so what they want to do is make these things more precise. They want to get better experimental measurements. They want to push the theoretical measurements to see are these things wrong? Do these stack up? Can we improve this uncertainty? Can we make these things ten times as precise? And does it stick around or disappear? All? Right? Well, I think it all speaks to just again this idea that there may still be amazing things hiding even in tiny little gaps of point zero zero zero zero zero five six. That's right, some of the biggest clues in the universe turn out to be on the smallest numbers. And there is news to come because there's an experiment happening right now again in Chicago that's going to give a measurement of the muan magnetic moment that's going to be four times as precise as the one that we have now. They took this big magnet and they shipped it from Long Island where they did the experiment first, and moved into Chicago and that a cleaner beam with more muans and they're running those results right now. And in eighteen they said that they would have results quote sometime in t and so here we are in no results yet, but we expect any day, any day. These things are hard. We expect any day they'll come out with the new measurement. And the whole physics community is waiting, like, what's going to happen. How's the number going to change? So it's a big deal. They're like, hey, we said we'd be accurate about the muan, not about when we would tell you about the plus or minus five years, plus the minus fifty six years. Oh man, I'm sure that there are some graduate students out there on this experiment it's called muan G minus two, that they are sweating and working hard to get this number out. Well, hopefully we added a little bit more pressure because now I'm curious about what's gonna happen. We're all curious because this is how we learned about the universe. We corner it and force it to tell us what is the answer to this number? We think we know what it should be. Tell us what the real truth is, tells the universe, don't keep it to yourself. Experimental physics is basically a modern day oracle, right, We actually do get to ask questions, will be horrible, and it gives us answer and then it chops off your head or something something Greek and classical like that. It kills your mom. Probably all right, Well, we hope you enjoyed that, and think about all the amazing secrets that could be hiding in the smallest of quantities. That's right. In one of these days, one of these secrets will reveal something deep and true about the universe. See you next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I Heart Radio. Or more podcast from my Heart Radio visit the i heart Radio app, Apple Podcasts, or wherever you listen to your favorite