Daniel and Kelly’s Extraordinary Universe - The Marvelous Mystery of the Muon Magnetic Moment

Episode Date: July 30, 2020

Can physicists discover new particles by watching how muons wiggle in magnetic fields? Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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This technology is already solving so many cases. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hey, Jorge, I have a really practical question for you. Well, you know, I'm an engineer, so practical is my middle lane. All right. Well, here's the question. Who would you trust more to build a spare room off of your house? A physicist or an engineer? I think you know the answer to that, Daniel. Not the physicist. 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 light unit. So you want to know how big this bedroom's 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 sleeping. 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 details. You're still not building my spare room. Hi, I'm Jorge. I'm a cartoonist and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist, and you definitely don't want me. 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 in the detector with a hammer and a wrench and get dirty. And then this is the kind that 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.

Oh, 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 room. Nice and cozy. But welcome to our podcast, Daniel and Jorge, explain the universe, a production of iHeard 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 scales, you know, galactic, cosmological skills, but there are also amazing things happening at the smallest scales of reality in nature. That's right. And these really tiny things, they gave 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? 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 LIGO 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 the 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 the problem, right, Daniel, is that you measure something and you don't get what you expect. Yeah. You measure something, you think it's going to be this big or this long or this heavy. And then when you measure it in reality, it's different. Yeah, well, that's not a problem. That's fantastic. That's exciting. That's an opportunity, you know. Really? 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. You split the difference. Calculating something theoretically has challenges of computing time and getting minus signs right and sort of organizing your mind 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, or sometimes just getting enough money to build the device that you need. That's the hard part. 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 Muons 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 very, very accurately so you can compare the two. And that tells you if your theory is right or and or if your 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, it 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 had of your house, right? that would tell you, like, you know, whether your house is well described by your idea of it, for example. Or whether it was a mistake to hire you to build my house, clearly. I should probably not hire you to measure it also after you build it. I would say, wow, this is perfect work. You should pay your contractor double. I guess that's a big question.

And the question is, how good are physicists measuring things? And so we were wondering, we were curious about how many people out there sort of have 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 write to me at Feedback at danielanhorpe.com and I'll send you some

questions to answer. So think about it for a second. Viewer as 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, like using an atomic clock. I don't know. I don't know. That I don't know.

Is it something to do with the plankland, maybe? Aliens. I'm not sure quite what you mean by quantity, whether that be amount of things. How many bananas it takes to create a black hole? I'm gonna guess it's mass, maybe. I like this question. Well, I think first we have to define. find 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 atom. All right. A broad range of answers from aliens to bananas to the Planck 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 to like one part in 10 to the 16. Wow. You know, it takes like 10 to the 16 seconds before they're off by one second. So you would agree with a lot of these, like bananas and aliens. Yeah, some of these are really very accurate. And for example, LIGO, like we mentioned before, gravitational waves, to detect gravitational waves, they had to measure the change and length of something by one part in 10 to the 20 or 10 to the 21, 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 hole, et cetera, et cetera. The same with atomic clocks. We can't calculate those things as well as we can measure them. I see. 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 loss of physics, we think that this 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. It 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. All 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 muons, which is a great alliteration. I'm so pleased to have some positive feedback for a name in particle physics from you. It's a high, high standard. Praise 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. is 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 as 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 an 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. Oh, I see. They have an electric charge, but they don't have like a pole, like you say, like a magnet, like a north and a 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. They 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 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 muon 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 muon, how a muon is affected by a magnet. It's not the moment for like an electron looks at a positron and they feel that attraction towards each other. No, 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 muon. Wow. You would totally watch that movie, wouldn't you?

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 that. Consider this podcast my pitch for this project. There you go. 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 muon? 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 and to some other big questions

about how particles work. Well, maybe let's go back a step and cover the other M, which is the muon. So muon is like an electron? Is it like a quark? Yeah, so we are made out of quarks and electrons, right? We have quarks 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 quarks, and there are also other kinds of electrons. So there's a heavier version of the electron. We call that a muon. It's exactly the same as the electron, except it has. a lot more mass. And there's another one even called the tau. So the electron has these two cousins, the muon and the tau, that have all the same interactions and all the same properties.

Like the same charge, the same spin, but just heavier mass. Just heavier mass. Yeah. And it's weird. We don't know why they exist. Like, why do we have the muon? Why do we have the tau? Why does the electron have two cousins and not nine cousins or 17 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. So we have 36 cousins, so we won't specify which one I'm talking about. But 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 form, 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 muon around it and form a bound state. But the muon lasts for, you know, a few microseconds. I 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 muon, you'd see that it lasts a few microseconds.

But because they move so fast, their clocks are slowed down. So as we watch a muon, 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 muons 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 muon. So let's get into the theory and the experiment and talk about what it means.

But first, let's take a quick break. Have you ever wished for a change but weren't sure how to make it? Maybe you felt stuck in a job, a place, or even a relationship. I'm Emily Tish Sussman, and on she pivots, I dive into the inspiring pivots of women who have taken big leaps and their lives. lives and careers. I'm Gretchen Whitmer, Jody Sweeten, Monica Patton, Elaine Welteroff. I'm Jessica Voss.

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From Mary Mary to Jennifer Hudson, we get into the soul of the music and the purpose that drives it. Listen to Culture raises us on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. All right, Daniel, we're talking about the magnificent mystery of the marvelous muon magnetic moment, momentarily. Just rolls in your mouth. It's delicious. So, yeah, so tell me about this mystery. So we know about the muon, 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 muons be affected by magnetic fields. Oh, right, because magnetic fields are transmitted by photons.

Yeah, magnetic fields are basically photons. I mean, we can think about like our fields, particles, or our particles fields, but they're very tightly connected. I see. So like if I throw a muon at a bunch of magnets and it curves one way, it's not because 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 a very natural way to think about that is in terms of photons being generated by, you know, whatever the source of your magnetic field is and pushing the muon. All right. So then we think of its interactions as 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 muon.

Like the simplest thing is photon hits the muon and bounces off. Right. So you have photon, muon interaction, very simple. Like in your mind, you have a couple just little lines of particles that intersect and then they go there 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 muon? And if you did that calculation, you get a pretty simple thing. 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 2 pi. He put this number on his tombstone. Wow. 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 Feynman's theory of quantum electrodynamics actually worked. Feynman like sketched a bunch of doodles and had a few ideas, but never, like, actually made it work. And Julian Schringer was like, all right, let's do all the calculations and see if this is

right. But that didn't fit in his tombstone, I guess. No, this was 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 muon. 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 Feynman 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 a muon. And those change effectively the muon's magnetic moment. Oh, I 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 muon and a photon is some sum of all those things, all those things mixed together. That you can predict with the theory. Like your theory, you can like bring this down in a piece of paper. Like what happens if a photon hits a muon and you can, in a piece of paper, you can work out how that

muon should bend its path or how it 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 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 also gives you an opportunity. Because if there are crazy particles out there that you had 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 muon. Because it would lose some energy? Yeah, 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 a muon 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 muon? I see. Like, how good are we predicting what photons actually do? Yeah. It's like you say 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 never heard about before, we're going to 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 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 muons. And I guess my question is why the muon, like couldn't, I mean, all these questions and all these magnetic moment ideas should work for any other particle, right? So why are we focusing on the muon specifically? Yeah, and you can do these calculations also for the electron and also for the tau, 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 proportionally larger effect on the muon because,

it has a larger mass. Oh, I see. So the muon is like the guinea pig. Yeah. The muon 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 a muon 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 got to 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 muon, 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 does mean how right you are. And when we do these calculations, we start with the simplest ideas. We say, well, what's the simplest thing a photon can do? And that gets you mostly right. And you think, well, what if it does one weird thing along the way? And there's like 19 ways for that to happen. So you add 19 calculations. Well, what if it did two weird things along the way? Okay, now there's 19 squared ways to do that. And each of these gives a 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 it turned to

into electron and that electron did some weird thing which turned 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. Right. So they can estimate how close they get based on like how much is the answer changing as they add more ideas. So they're asymptotically approaching the deep truth. I see. I guess there's an engineering, there's always this issue about the difference between accuracy and precision. Accuracy is how right you are

and precision is like how sure you are. So the thing that's happening here is it that theories are pretty sure they know what the moment of the muon is? 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 a quibble with theoretical physics here

because experimentalists try to be really formal about the statistical statements we make. If we say, okay, there's an uncertainty here, Here, that means something very specific statistically. It means if you did the same experiment 100 times, you would get the answer within your uncertainty bounds 68% of the time, something like that, or a different answer if you're Bayesian. Right. That's precision.

There is 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 guess how close they are to the right answer. So I guess maybe the title should really be the most precisely guessed at theory quantity ever. Do you know what I mean? Like they put a lot of attention into the, they've covered every angle and so they're pretty sure that this is what quantity 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 90s when the theorist discovered that they had gotten a sign wrong, like they had a minus sign where there should be a positive sign, and it changed the answer kind of a lot. So there's definitely mistakes in there. Oh, my gosh. Who made that mistake? Are they going to put that in their tombstone as well? One more minus sign.

Whoops. No, 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 are. All right, well, let's get into 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. Have you ever wished for a change but weren't sure how to make it? Maybe you felt stuck in a job, a place, or even a relationship.

I'm Emily Tish Sussman, and on she pivots, I dive into the inspiring pivots of women who have taken big leaps in their lives and careers. I'm Gretchen Whitmer, Jody Sweeten, Monica Penn, Elaine Welteroff. I'm Jessica Voss. And that's when I was like, I got to go. I don't know how, but that kicked off the pivot of how to make the transition. Learn how to get comfortable pivoting because your life is going to be full of them. Every episode gets real about the why behind these changes and gives you the inspiration and maybe the push to make your next pivot.

Listen to these women and more on She Pivots, now on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. The U.S. Open is here. And on my podcast, Good Game with Sarah Spain, I'm breaking down the players from rising stars to legends chasing history. The predictions will we see a first time winner and the pressure? Billy Jean King says pressure is a privilege, you know. Plus, the stories and events off the court and, of course, the honey deuses, the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very fancy, wonderfully experiential sporting events. I mean, listen, the whole aim is to be accessible and inclusive for all tennis fans, whether you play tennis or not. Tennis is full of compelling stories of late. Have you heard about Icon Venus Williams' recent wildcard bids? Or the young Canadian, Victoria Mboko, making a name for herself.

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I think culture is any space that you live in that develops you. On a recent episode of Culture Raises Us podcast, I sat down with Warren Campbell, Grammy-winning producer, pastor, and music executive to talk about the beats, the business, and the legacy behind some of the biggest names in gospel, R&B, and hip-hop. This is like watching Michael Jackson talk about thoroughly before it happens. Was there a particular moment where you realize just how instrumental music culture was to shaping all of our global ecosystem? I was eight years old and the Motown 25 special came on and all the great Motown artists, Marvin, Stevie Wonder, Temptations, Diana Raw. From Mary Mary to Jennifer Hudson, we get into the soul of the music and the purpose that drives it.

Listen to Culture raises us on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. All right, we're talking about the magnetic moment of the muon as the most precisely guessed at quantity ever. And now we're going to measure it with an experiment. And that just involves throwing a muon at a magnetic field and seeing where it goes, or 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 10 to the 12 or 10 to the 13. 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 muons. You want them all basically doing the same thing. 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 muons, a big blob of muons. And they point the spin of the muon, 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 muons and they move them in a circle and when muons move around in a circle in a magnetic field their spin will precess. It will rotate around the axis of motion. Because that's how the physics work out. If you try to bend the muon

it'll also sort of change in other ways. Yeah, like one thing that happens to a particle when 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'll 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 muons, 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 it the microwave oven in the break room that's changing the answer? 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 mons in a circle in Chicago. And again, not in Minnesota or Milwaukee or Montana. No, it's being done at Fermilab, the accelerator complex just outside Chicago, between Batavia and Naperville, where I did my PhD thesis. Oh, hometown plug. Yeah. All right. So they're spinning these in a circle and they're measuring how they're precessing or changing in the direction of their moment.

And that tells you the magnetic moment of the muon experimentally. And now the problem is, how well does it match with what the theory is saying? Yeah, that's right. That's the question. So 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. Wow. All right. So let's maybe sign out the number for the audience here. So the experimentalists say that the magnetic moment of the muon is 2.00233118-184-118. Close our mind is some small quantity.

And what are the units of these? These are dimensionless units. Yeah. Okay. That was from the experimentalists. The theorists say it should be 2.0023118362, not 4188. That's right. So they agree, you know, after the decimal place, they agree to.

seven digits. And then they disagree. One of them says 418 and the other one says 362. Which is not a huge difference. It's like dot 12 zeros and then like 56. Yeah. It's a bunch of zeros and 56. 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. The difference between them is 56 and the uncertainty is like 15. So The difference is like three or three and a half times the uncertainty.

It seems real. 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 precision is really hard. Like, if they ran this experiment next year and the year after that, would they still get the same exact numbers? Yeah, these uncertainties reflect statistical limitations. So, like, you haven't run it for an infinitely long time. And also systematic uncertainties, like things you think will contribute to mismeasurement or, or by, 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 muon a tiny little bit? Is this the hint of the discovery of some new particle, some new super symmetric 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 0.00,000, 056 difference between the experiment and the theory? Or, because they're both pretty sure of their numbers. There's no 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. There certainly could be. And there are independent checks. They're 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 then I read about this calculation like, wow, it agrees to, you know, nine or 10 decimal places. That's

amazing. And I had 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. Oh, I see. It's like, what if we actually uncovered the code of the simulation of the universe? Because it's so, we're so right.

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 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 were telling me that for the electron there's no difference between the experiment and the theory. That's right. This difference only shows up in the muon. Yeah, we can do the same measurement for the electron. We can 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 uncertainties. Now, we expect that new physics, new particles, whatever, would have a bigger effect on the muon. So it's not a surprise that it doesn't appear there for the electrons. That's quite fascinating. I see. maybe there's something going on with the muon that you wouldn't see in the electron. So the electron, you check that box, you're like the theory,

and both groups have gone at the electron with the same kind of intensity and precision. 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 muon, 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 muon, which means that it might be hiding a secret. So what does that mean, Daniel? What could be hiding underneath the marvelousness of the muon? Well, you know, we suspect that there are other particles out there that we have not yet discovered. We found six particles that are quarks, six particles that are leptons. 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 are 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 muon has another version of it called the smuon. And the photon has 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 like too big, too heavy for us to discover them in particle colliders. Remember to see something in a collider, you have to put in a. 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 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 particle we don't know about that the photon is turning into or like transforming into before it interacts with the muon. Yeah, 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 muon because you have to include it in all these calculations. Like maybe it emits this new heavy particle. particle, and then it interacts with the muon, and then it reabsorbs that particle. And that would change the way it interacts with the muon. And so the presence of weird, heavy particles changes the basic interaction between two very simple particles, which I think is fascinating. 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 collider. I think, Daniel, what you're saying is that the experimentalists 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 error. And that's why it's fascinating as a cross-check, because if they're wrong, they're probably wrong in different directions or in 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 a stop off in Stockholm to collect your Nobel Prize. And that's why, you know, this isn't over. It's not just like, oh, hey, we saw this discrepancy, we're 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 this thing 10 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 0.000000-000-5-6. 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 muon 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 they have a cleaner beam with more muons and they're running those results right now. And in 2018, they said that they would have results, quote, sometime in 2019. And so here we are in 2020. 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 muon, not about when we would tell you about the accuracy of the muon. 2019 plus or minus five years. Plus or minus 56 years. Oh, man, I'm sure that there are some graduate students out there on this experiment. It's called muon 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 going to happen here, Daniel. 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. Tell us, universe, don't keep it to yourself. Experimental physics is basically a modern-day oracle, right? We actually do get to ask questions of the oracle, and it gives us answers. And then it chops off your head or 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. From tips for healthy living to the latest medical breakthroughs, WebMD's Health Discovered podcast keeps you up to date on today's most important health issues. Through in-depth conversations with experts from across the health care community, WebMD reveals how today's health news will impact your life tomorrow.

It's not that people don't know that exercise is healthy. It's just that people don't. know why it's healthy, and we're struggling to try to help people help themselves and each other. Listen to WebMD Health Discovered on the IHeart Radio app or wherever you get your podcasts. It's important that we just reassure people that they're not alone, and there is help out there. The Good Stuff podcast, Season 2, takes a deep look into One Tribe Foundation, a non-profit fighting suicide in the veteran community. September is National Suicide Prevention Month, so join host Jacob and Ashley Schick as they bring you to the front lines of One Tribe's mission. One Tribe, save my life.

twice. Welcome to season two of the Good Stuff. Listen to the Good Stuff podcast on the Iheart radio app, Apple Podcasts, or wherever you get your podcast. Do we really need another podcast with a condescending finance brof trying to tell us how to spend our own money? No thank you. Instead, check out Brown Ambition. Each week, I, your host, Mandy Money, gives you real talk, real advice with a heavy dose of I feel uses, like on Fridays when I take your questions for the BAQA. Whether you're trying to invest for your future, navigate a toxic workplace, I got you. Listen to Brown Ambition on the IHeart Radio app, Apple Podcast, or wherever you get your podcast. This is an IHeart podcast.