Daniel and Kelly’s Extraordinary Universe - How can we look for magnetic monopoles?

Episode Date: August 3, 2023

Daniel and Jorge talk about a particle with a pure magnetic charge and how to look for it using a cubic kilometer of ice.See omnystudio.com/listener for privacy information.

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get your podcast. I'm Dr. Scott Barry Kaufman, host of the psychology podcast. Here's a clip from an upcoming conversation about how to be a better you. When you think about emotion regulation, you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome. Avoidance is easier. Ignoring is easier. Denials is easier. Complex problem solving takes effort. Listen to the psychology podcast on the IHeartRadio app, Apple Podcasts, or wherever you get your podcasts. Hey Daniel, does being a scientist require a lot of travel? Yeah, you know, conferences and meetings and all that kind of stuff. Hmm, but that's just talking about science.

What about actually doing science? Like you need to go somewhere into the lab or out into the field? Yeah, you got to do that also. I'm pretty lucky that the collider I work at is in a pretty beautiful spot in Switzerland. But do you actually have to go there? Like, do you have to press buttons or fix the machine? Who else is going to hit that big red button in the control room, if not me, man? Or do you just go there to talk?

There's definitely a lot of talking and coffee drinking. But yeah, somebody has to actually build the thing and make it run. So people got to be there in person. And I guess you've got to talk to them, right? I'm just wondering why you actually have to go to Switzerland. Yeah, some of us have to actually go to build a thing. We built part of the detector and the readout systems that gather the data. And we're responsible for making it work.

And you've got to be there when it breaks. Now, is that the best physics location to get stationed at? I think it's one of the top ones. It's definitely better than the suburbs of Chicago where we worked more recently. Hey, what's wrong with Chicago? Chicago's awesome, the suburbs a little bit less exciting. But there's an experiment on the Mediterranean. So those people basically work on the French Riviera.

Nice. Do they work in speedos and swimsuits or not since it's the French Riviera? I don't think you want to visualize physicists and speedos. Yeah, let's not do that. On the other extreme are experiments at the South Pole. Ooh, that sounds super cool. It's a little too cool for my tastes. That sounds awesome.

Somewhere I want to go at least once in my life. Hi, I'm Horamie Cartoonist and the author of Oliver's Great Big Universe. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I'd be happy to die without ever going to the South Pole. Well, I guess you don't want to go to the South Pole. to die or have those two coincide. But if you had the opportunity, when did you want to go? I actually have had the opportunity, but I said no, thank you. You said no, thank you. I've said no, thank you. Why? The South Pole seems kind of cold and uncomfortable. I'm not that into unpleasant travel. Same reason I don't really want to go to space. Yeah, well, I think space is a little

bit colder than the South Pole. Yeah, don't you want to go for the adventure, see some penguins, some live penguins, not in a zoo? I think when I was younger, I was more into adventure travel than I am now. Now you're more into couch adventures. I'm less into discomfort now than I used to be. But anyways, welcome to our podcast, Daniel and Jorge, explain the universe, a production of Our Heart Radio. A mental adventure, a way to travel the entire universe and think about everything that's

happening out there. How things work at the tiny particle level, how things work at the galactic scale, and everything in between. Physics is our way of exploring this vast universe and trying to make sense of it. And our job on the podcast is to help you make sense of it as well. That's right. We live in an amazing cosmos and we are just tourists making our way through it, observing all the sites and learning all of the languages that it has and eating all the foods it has to offer. We're not tourists to this cosmos. We live here, man. We are home here. We're just trying to understand our own context. It's not like we came here from some other part of the multiverse to

poke and prod and take pictures. Well, we're tourists in the sense that we're only here for a very short amount of time. And we hope that in that time, we can help unravel some of the deep questions of the nature of the universe. Yes, because there are a lot of amazing things out there for us to ask questions about and to explore and to wonder why they exist. Unfortunately, we can't mostly go out there to explore the universe. We have to just see what comes to us here on Earth.

In this tiny little corner of the universe, we can actually gather an incredible amount of information based on all the particles that do arrive here on Earth, the photons, the neutrinos, and sometimes the oddball particles. Wait, we can't just put physicists on a spaceship and send them out to other planets? If you want to fund that, I bet you'll have lots of volunteer physicists. Just not me. What if they have nice chocolates like they do in Switzerland? I don't think chocolate is enough to counterbalance the discomfort, because after all, you can still get pretty nice chocolates without getting in the spaceship.

How do you know? Maybe they taste better in space. I'll let someone else do that experiment and report back. There would be chocolates that are out of this world. Cosmic chocolates. Well, we can do lots of cool experiments just here on Earth and not just building telescopes to capture photons or neutrinos. Sometimes we can actually use the Earth itself to see these particles. Yeah, the Earth is a big place and it catches a lot of stuff from space,

from other parts of the galaxy, from other parts of the universe, and we can use it to try to catch things that maybe we haven't seen some of the telescopes that we build actually rely on the earth being there to induce the particles to interact to reveal themselves without the earth some of these particle telescopes wouldn't even work so today on the podcast we'll be asking the question how can we look for magnetic monopoles now is this related to monopoly the game or the capitalism concept I think it's somewhat related to capitalism. Yeah, having just like one source of chocolate, somebody has a monopoly on chocolate. Monopoles are also like a source of charge. Okay, that's a bit of a stretch.

What are physicists in this stretched analogy here? Are you the boot? Are you the little car? Are you the top hat? We are buying it up. We are trying to purchase knowledge about the universe. Hopefully you don't land and go to jail. Do not pass go.

I will happily go to physics jail. if that's what's required to unravel the mysteries of the universe. I guess research is sort of a little bit like drawing chance cards. Oh, it definitely is. I've had so many conversations with students where they've been like, I've been working for 60 hours a week for a year and haven't gotten anywhere. I'm like, number one, don't work 60 hours a week. Number two, there's no guarantee that time spent means progress made.

There's so much randomness in research. And number three, you should be working 80 hours a week. No, you should definitely not be working 80 hours a week. you've got to take care of your people's mental health, man. But yeah, I guess it's not maybe related to the board game. I'm guessing it's maybe related to magnetism and magnetic poles. Exactly. It has to do with deep questions about where charge comes from in electricity,

where magnetism comes from in magnetism, how the two are connected, why we have quantized amounts of electric charge in this universe and why we have quantized amounts of electric charge in this universe. It's sort of like a big open question in particle physics. Yeah, we're going to jump into what a magnetic monopole is. But first, we were wondering how many people out there had heard of this concept and thought about the idea of how to look for them. So thanks very much to everybody who answers these questions.

If you would like to hear your voice on the podcast answering the question of the day, please write to me to questions at danielanhorpe.com. So think about it for a second. How do you think we can look for magnetic monopoles? Here's what people had to say. I have no idea what that means, but. Maybe if it was a monopole, it'd mess with other magnetic fields, and so we could look for disturbances in dipoles?

First of all, I would ask, do they really exist? I know you have a podcast on that, but I haven't listened to it yet. I actually don't know. I really don't know. Looking forward to hear from you. I would say by closing one eye, but I think they may not exist because there needs to be balanced in nature, and this just seems unbalanced. Where are monocles?

I don't know what a monopole is, so I don't know. Maybe something related to, like, the magnetic field of Earth, just for the universe. Like, maybe the universe has a giant magnetic field. I don't know. I can't wait to search it up. I'm not sure how we could look for magnetic monopoles. If they're large, then maybe we could look at how things act around them out in space. but if they're really small, I have no idea.

I wouldn't even know where to look, never mind how to look. I believe classical electromagnetism doesn't allow for magnetic monopoles, but maybe there is some kind of quantum weirdness that at least theoretically predicts them, but I don't have a clue about how to find them. All right, we've got a couple of comedians here in the batch. Somebody say, maybe you can look for monopoles by wearing monocles. The guy in Monopoly wears a monocle after all, doesn't he?

Oh, yes. It's all there. It was a hidden sign. You don't have a monopoly on jokes and physics, apparently. Apparently, not because two people brought up this joke. Somebody said you can also look for them by closing one eye, but which eye, I guess. That's the question. Maybe you have to roll the die.

Depends if it's a left or right-handed monopole, I suppose. Monopoles are handed. There's handateness in magnetism. If it has spin, then it's going to have handedness, absolutely. All right, well, let's dig into this concept. Maybe a lot of people haven't heard what a monopole is, a magnetic monopole is. So, Daniel explains us, what is a magnetic monopole? A magnetic monopole is easiest to understand if you first get your mind around what an electric monopole is.

If we can understand what a monopole is in electricity, then we can understand what it is in magnetism. And in electricity, a monopole is pretty simple. It's just something that has an overall charge, like an electrical. electron has negative charge. It's a source of charge. And a proton has a positive charge. It's a source of charge. You add up all the charge on the object, it's either positive or it's negative. It's not zero. And that creates a particular kind of field. Gass's law for electricity tells you, for example, that the electric field through a surface depends on the total amount of charge in the volume. So a monopole in electricity is just something that has an overall charge to it. So as you said, like an electron is maybe the ultimate negative electric monopole, right? Like it's just a point particle. It's just a little point in space that has a negative charge to it and it looks negative from all directions. Exactly.

And the atom is the combination of the proton and the electron. It's overall neutral. It has no overall charge. So it's not a monopole. But it is a dipole because the positive charge and the negative charge are not exactly on top of each other. They don't totally cancel out. So if you're closer to one than the other, you'll still feel an electric field. But that's a dipole field.

It's a field that comes from something that has a positive and a negative charge. Right. Dipole means two. So it comes from something where the charge is overall zero, but it has a distribution. So a monopoles and that has an overall charge like the electron of the proton, a dipole has no overall charge, but the distribution of charge inside that neutral object still gives you an electric field, a dipole field. I think what you mean is like the nucleus of an atom is neutral because there are, or at least it's positive, right?

Because it has protons and neutrons in it. And then the outer part of the atom has the electron, which is negative. And the electron is going around the nucleus. So at any given time, there's one side of the atom that's more negative than the other side, right? But it's sort of like electron is flying around, right? So it's changing for an atom all the time. Exactly. And if you're really far away from the atom and the distance between.

the electron and the proton doesn't really matter. You can think of them as on top of each other and the dipole field goes to zero very quickly. But as you get close to it, then that does matter. And so there is an electric field that doesn't cancel out, right? The electric field of the electron and the proton don't cancel out. So you feel a dipole field. Meaning like if you're really close to the atom,

super duper close to the atom and you're like an electron, for example, you might be pushed in one direction more than the other. Yeah, exactly. You can imagine a field from the electron and a field from the proton. If you're really far away, then they're basically canceling each other out. But if you're really close to the two of them, you're going to be closer to one than the other by a big fraction, and they're not going to cancel out. So that's a dipole field. So monopoles do exist.

Like an electron is a monopole, isn't it? Yes, an electric monopole does exist. You can have a piece of matter with an overall charge to it that creates this monopole field, right? Just a very simple field. And dipole fields exist in electricity. In quadrupole fields and octopole fields, actually it's part of this like multipole field. expansion. If you like to think about vector spaces and linear algebra, you can break any field in expansion of these different poles. The first term is the monopole, then the dipole, then the

quadrupole, et cetera, et cetera. But conceptually, you can think about the monopole is coming from something that has an overall charge. All right. So that's an electric monopole. I'm guessing maybe a magnetic monopole is different. A magnetic monopole is the exact analog, except to use magnetic charge instead of electric charge. Wait, wait, wait, wait. What's the difference between magnetic charge an electric charge. I already thought that was the same thing. Well, they're very tightly connected because we've unified electricity and magnetism into one overall force called electromagnetism, right?

But there are two different parts of it. There's electricity and there's magnetism. They're different components of electromagnetism. Like what's the difference? Like if two electrons are repelled from each other, aren't they pushing away from each other using the electromagnetic force? Yes, absolutely they are. And there's components to that which are electric, like this,

the coulombic repulsion, just from the electric charges, but if they're in motion, then one of them can be generating a magnetic field, and that magnetic field can also turn the other electron, for example. So there's both electric and magnetic components to how two electrons interact. So I guess you would maybe have to dig into the equations, but is there a way to sort of explain the difference between magnetism and electricity? Like magnetism has a different set of charges. We call them north and south, right? So you can have a magnet that has a north and a south, and you know that if you bring the north end close to another the north and it repels. Two north's repel and two south repels. So these are the magnetic charges,

the north and the south charges. But aren't there's like immersion properties? Like aren't these all just made out of electrons, which are monopoles? Yes, exactly. All the magnetic fields in the universe are dipoles. All of magnetism is generated by electric monopoles, either moving charges or quantum spin. So all the magnetic fields we have in the universe are generated by electric monopoles. If there are magnetic monopoles, then those would also generate pure magnetic fields, like a pure north field or a pure south field, not a dipole field where you have like a north on one end and a south on the other. If you have a bar magnet, for example, it has a north on one side and a south on the other. You try to crack it in half, you're not going to get a pure north on one side and a pure south on the other. You're going to end up with two bar magnets, each of which is a dipole with a north and a south.

As far as we know, there are no pure magnetic charges out there. no like particles that just have a north or particles that just have a south that would be a magnetic monopole the equivalent of like an electron which is an electric monopole okay so i guess i'm still trying to wrap my head around this difference because i always thought it was maybe the same thing so you're saying like if i have an electron and i spin it it's going to create a dipole it's going to create a magnetic dipole right it's going to have a north and a south so electrons have quantum spin they don't literally spin in the way that like a top spin but their quantum spin does generate a little magnetic field, but that magnetic field has a north and a south. It's not just a north or not just a south. Right, but I guess the question is like, what is a magnetic field? A magnetic field is something that's generated either by a magnetic monopole or induced by an electric current, right?

And electric currents can only induce magnetic dipoles. They can't induce magnetic monopoles. I guess what I mean is like to the layperson, how would you define a magnetic field? In the same way that you think about electric fields, These are sort of theoretical concepts that explain how two particles push on each other. So how does an electron push on another electron? We say it's using the electric field.

Really, that's just our way of saying this is what two electrons do to each other. Magnetic fields are similar. The two are very closely paired electric fields and magnetic fields very tightly coupled. But a magnetic field is different from an electric field, right? It does different things. It's generated in different ways. It applies different forces to charges. Or a magnetic field does different things to magnetic charges than it does to electric charges.

All these things are described by Maxwell's equations. But in the end, it's just descriptive, right? Like we see these things happening to electrons and to bar magnets and to other particles in the universe. We try to boil them down into as compact the description as possible. And then we come up with this story that we tell ourselves about what's happening. And that story includes fields. Are those fields real and physical things that are out there in the universe? We can't like see them directly.

We only see their impact on other. particles. So when you ask me like, well, what is a field? Well, it's sort of a theoretical philosophical construct that explains the motions of the particles that we see. They seem to follow certain rules, and those are best explained by these fields that we've built up in our minds. I guess maybe I think what you're saying is that a field is sort of like an idea that tells you, like, if I put an electron in here relative to this other electron, it's going to feel the repulsive electric force in that direction. Or if I put it over here in this other location, it's going to a field of force in a different direction by a different amount.

And so maybe a magnetic field is sort of the same. Like if I have a magnetic field and I throw an electron at it, it's going to do different things depending on whether it's, you know, flying close to the north side of this magnetic field or it's the south side, right? Yeah, that's right. These fields were invented as a concept to explain action at a distance. Like how did two electrons push in each other if they're not actually touching? And so you create this field concept, say an electron

creates a field through space, and that field can push on the other electron. It transfers momentum to the other electron. So, yeah, magnetic fields have different rules. And these are all described by Maxwell's equations. You throw an electron through a magnetic field. It's going to curve. You throw an electron through an electric field.

It will get accelerated in some direction. So the rules are a little bit different. So I guess the way the universe works, it's kind of weird thing. Like if you take an electron and you spin it, it creates a field around it, or like it has an effect on the things around it so that if you throw another electron

near that spinning electron, then it's going to curve a certain way depending on whether you're going like in the direction or near its north and south poles. That's just a weird thing that happens, right? Yeah, I guess you could say all of physics is explaining the weird things that happen. And if you're not really comfortable with the idea of like quantum spin,

you can also just take electrons and run them in a circle. You take a wire and you coil it and you pass a current through it, that's electrons moving in a circle. that will generate a magnetic field which will bend the path of other electrically charged particles. But the key thing is that all of the magnetic fields we've seen in the universe are generated by the motion of electric charges or the spinning of those electric charges. And those generate dipoles, a combination of a north and a south. In principle, by symmetry, you might imagine why aren't there particles that can generate a pure north or pure south

the way an electron can generate a pure positive or negatively charged electric field? Well, it kind of seems like maybe there isn't such a thing as a magnetic charge. Like, is there such a thing as a magnetic charge? Isn't it more like, I don't know, but maybe does it maybe have more to do with like the direction that these electrons are spinning? Like, is there such a thing as a magnetic charge or is it just the direction that electrons are spinning? There's such a thing as the polarity of a magnetic field, right?

Magnetic fields have a north and a south. When you take two bar magnets, you try to push them together, you flip one over, they'll repel instead of a tract, right? So there's definitely a direction to these magnetic fields. They have a charge to them in that sense. The same way, like, what's the difference between a positive and negative charge? It really is just defined by the effect of a field on it. What's the difference between an electron and an anti-electron?

They have a different charge, which means you put them in an electric field. They go in different directions. That's sort of what charge means. And so in the same way, there's two different kinds of magnetic fields. The north and the south kind, we've only ever seen them paired together. The way, for example, you can make a dipole out of a. positive and negative charge, putting them together to have something an overall neutral, but still has an effect on stuff nearby because it has a dipole field.

We've only ever seen a magnetic dipole field. So you're asking like, is there really a magnetic charge? Well, there's a directionality to the magnetic field. We've never seen a particle that has a pure magnetic charge by itself. So in that sense, everything is generated from the electric charge. But that doesn't mean that they don't exist. And actually, it would be theoretically beautiful and kind of symmetric if they did. did exist. It would complete these equations in this sort of very nice way.

I guess maybe what I'm trying to say is that like an electron, right, has electric charge and it has a spin direction, but it doesn't really have like a magnetic label or value or quantum quantity to it, right? It does not. You're correct. The magnetic field and its magnetic field direction comes from the charge and the spin. And in the same way like for your fridge magnet, it's not like It's a property of the things in it. It's just that the electrons inside of that magnet are all spinning in a certain way, right? Yes, all magnetism we know of in the whole universe are just dipoles, the combinations of north and south, which are generated from the electric charges fundamentally.

But that doesn't mean it's the only thing that can happen. It might be that there are particles out there that have a magnetic charge the way the electron has an electric charge. That would be a magnetic monopole. That's the question. All right. Well, let's dig into that question a little bit more. and also how businesses are trying to look for these monopolies in nature. But first, let's take a quick break.

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Presented by Capital One, founding partner of IHeart Women's Sports. All right, we're talking about a very magnetic subject here today, magnetic monopoles, and whether they exist or can exist in how we're actually looking for that. Now, Daniel, I guess I'm kind of confused here. It seems like magnetic fields are just kind of what happens when you take an electric charge and you spin it, right? either quantum spin or you actually like physically make an electron go around in a circle, you create a magnetic field. And a magnetic field is sort of defined by that, right, by its direction.

Like if you spin it, let's say I spin an electron clockwise. It's going to generate a magnetic field in like going up or going down, right? And so I feel like going up or down automatically gives you a dipole because you need an up and a down to define a direction. And so I don't even know what a monopole would look like. Like, how can something have the same direction from all sides? Same way an electric field does. You have an electron in empty space.

It has an electric field, which, you know, either points towards the electron or away from the electron in every direction simultaneously, right? There's a total overall charge there. There's like a source of electric charge. So then how would it act on something else? Like, let's say that a monopole, magnetic monopold did exist. Let's say I have one in my hand. And now I have a magnet on my other hand with a north and a south pole. what would this thing do?

It would only attract the north part of my magnet or something like that? If you're holding a north charge and then you have another north charge, they would repel. If you have a south charge, they would attract. You can apply all of your intuition from electricity because we think the things are perfectly symmetric. The equations should be the same. So if you think like, well, what happens to a neutral atom if I have an electron nearby, well, the electron repels the other electron and attracts the proton.

So if you have a north charge in your hand and then you have a dipole nearby, then it will attract the south part of the dipole and repel the north part of the dipole. That dipole will align itself in that magnetic field. I see. It will repel the north part, but it'll attract the south part of my magnet. Exactly, yeah.

What if I have like a spinning electron? A spinning electron will create a dipole field, right? So then you'll have two dipoles. Oh, I think I see the difference. Like if I have a monopole in my left hand and a dipole in my right hand, the forces it exerts on my right dipole magnet, are always going to be sort of pointing away from the north monopole, right?

That's kind of what it means to have a monopole. Whereas if I had a dipole in each hand, how they affect each other sort of depends on how I twist my hands or in what direction or where I put them relative to each other. But a monopole, magnetic monopole, would sort of act like a point particle. I think it would you're saying. It would like exert forces the same in all directions. And theoretically, this comes from exactly the kind of questions you're asking.

You're basically saying it seems like magnetism is like just a part of electricity, right? Because electricity is really the source of everything. But the theory says, well, if electric sources can generate magnetic fields, why can't we have like magnetic sources that generate electric fields, right? Why can't we do that also? Why isn't there a symmetry there? Why can't we have things that are just sources of magnetic fields? And then when they spin, they make electric dipoles.

Or if you have a current of magnetic sources, they would generate an electric field, the same way a current of electric charges would generate a magnetic field. Wouldn't it be awesome if there was symmetry to them? And if you look at the equations Maxwell's equations for electromagnetism, there is this weird asymmetry. The universe seems to prefer electricity. It seems to be more primary. And that's because we have electric charges.

And if you say, well, actually, what if there are monopoles in the universe and you change Maxwell's equations to allow for monopoles, then they become perfectly symmetric. All the equations are just like mirror images of each other, Electricity and magnetism are just two sides of exactly the same coin. So if there were monopoles, it would be this like beautiful, theoretical clicking together of these two pieces. Interesting. I guess maybe I wonder if the big question is really sort of related to the idea that like we don't really know why spinning charges create magnetic fields.

Do we know that? I guess it depends on what kind of answer you're looking for for why. I mean, we know that it happens. We have a mathematical description of it. We've invented this concept of a field to explain like the forces on particles and the vicinity of moving charges. What kind of why are you looking for? Like if I have a spinning electron on my right hand and a spinning electron on my left hand, why does the spinning electron in my right hand want to make this other spinning electron spin in the same direction?

I think actually they want to make each other spin in the opposite directions, right? In opposite directions, yeah. Oh, yeah, that's a good question. you know, in our universe, that's what happens, right? We see that's what happens. And if you try to make an explanation for it without magnetic fields, it doesn't work. If you add this thing called a magnetic field, then it does work, right? So far, just descriptive.

You know, you're basically asking like, why do you have magnetic fields? Could you have a universe without magnetic fields? You certainly could, but our universe seems to have them. You're asking, could you have a universe without magnetic fields? I think that would be more complicated. It would be a very different universe. You wouldn't have light, for example. So I'm not sure you could have a universe without magnetic fields.

I think maybe that's the question you're asking, like, why are they here? No, I think I'm more asking, like, in space, if you have a whole bunch of rocks twirling around an object, like the sun, for example, their orbits are going to collapse down into a disk because, like, the forces balance out in the direction that they're not spinning around the sun, but they don't align. You know, there's like a mechanical explanation for why orbits tend to be disks. Yeah, that comes from conservation of angular momentum. Right, right, right.

So now, like, if I have a spinning electron on my right hand, I wonder, I'm just wondering if maybe it wants to make the other electron spin in the opposite way, because if it's spinning, you know what I mean? Like the motion plus the electric forces somehow make it so that if they're spinning in opposite directions, that's the most balanced way that they can be. I don't think there's a simple mechanical explanation for it in that sense. It's just that the kind of thing we see happen in our universe. And I think that theoretically it would be pretty hard to build a universe without magnetic fields.

To me, that's the best answer for why they're here. You know, it's something we see that happens and we don't know how to build a universe without it. All right. Maybe that's the answer. It's just the way it is. It is just the way it is. But in terms of balance, it's like fascinating that the universe has all these electric charges in it. We see them all over the place.

But we've never seen a magnetic charge. And it would be so beautiful and symmetric if it did. not only because it would like balance the equations of Maxwell in this way that like let us have electric charges generating magnetic fields and magnetic charges generating electric fields and all sorts of stuff but it would also answer other deep theoretical questions we have like why is electric charge quantized at all like why is electric charge always this weird number a rational number one-third two-third minus one plus two why is it never like 0.714 all right so it's Like breaking this problem or figuring it out would tell us about why things are the way they are, which is my question in the first place. Yeah, it's really interesting. It actually does have to do with angular momentum as you were talking about a minute ago. In our universe, angular momentum is quantized, right? How fast things spin around other things can't just have any arbitrary value. They have to be quantized. Like linear momentum, how fast you're moving through space, how much momentum you have, your mass times your velocity, doesn't have to be quantized. it can be any number. But your angular momentum, right, how the momentum of spinning does have to be

quantized in our universe. That's a really fascinating fact. But if you have magnetic monopoles in the universe, you have electric charged particle and a magnetically charged particle, then their angular momentum is related to the product of their two charges, like the amount of magnetic charge and the amount of electric charge. And because the product has to be quantized, that means they both have to be quantized. So if there's a single magnetic monopole anywhere, in the universe that its angular momentum has to be quantized, which means its charge has to be quantized, and so does electric charge. So if magnetic monopoles exist, then electric and magnetic charges both have to be quantized. I think you're saying that, you know, are electric charges quantized?

Like, can you have just any amount of electric charge right now, as far as we know? They are quantized. You cannot just have like an arbitrary charge. We've not like seen particles with like 1.000-2 electric charges and 0.9997 electric charges, they seem to be quantized in these discrete units. But then magnetic charge, it sort of depends on that electric charge and how fast it's spinning. Well, magnetic dipoles do, right? If there are magnetic monopoles, there are north charges and south charges out there, then you can also ask the question, are those quantized? And if so, then why? The question is really like, why is electric charge? Why is any charge at all quantized? Why isn't it just some arbitrary value.

Why don't we see like electrons out there with a big spectrum of different charges? Why do they all have the same one? Well, isn't it the case that electric charge is quantized because it's smallest unit that we know. The electron is a particle, right? It is a particle, yeah. You're asking like, why can an electron have half of an electron charge? Yeah, or a real number, right? Or a rational charge.

Why is it always this integer or a rational ratio of the integers? You know, we've seen like one-third or minus two-thirds. or one seems to be quantized. Yes, you're right. All electric charges are bills out of electrons, but the question is like, why do particles themselves have quantized electric charges? And the existence of a single magnetic monopole in the universe would force all electric charges to be quantized because their angular momentum depends on their charge. And angular momentum we know has to be quantized. I think the deep question is like, why are things quantized? To me, that's really fascinating. Like, we could have had a universe where particles have any random charge.

Instead, we seem to have a universe where particles have these fixed charges. It's like a ladder of charges instead of a spectrum. And the question is why. Nobody really has an answer to that except for this one explanation. If there's a monopole out there in the universe, then particles have to have quantized electric charges because it relates to their angular momentum, which we already know has to be quantized. We also think that magnetic multiples were probably made in the early universe. Like when the big bang happened, it made a bunch of particles of all kinds. And if monopoles are a thing, then a lot of them should have also been made in the big bang. And they should still be flying around the universe. But wait, I guess maybe the question is, what would this

monopole be embodied in? Would it be a particle with a monopole? Would it just be like a random monopole that exists out there? Like a random like magnet floating out in space that has this? Is it made out of something? Or is it, would it just exist? It would be a new kind of particle, right? a particle with some kind of mass and other properties, you know, spin, and it would have some kind of overall magnetic charge. The way electric charge doesn't just, like, float around unembodied in the universe. It's attached to particles the same way. A magnetic charge would be attached to this new particle, which we call it magnetic monopole.

That would be the particle. It's like the magnetic version of an electron. Call it the magnetron or whatever. Okay. Now, see, now you're talking about a whole new kind of particle. Yes, a whole new kind of particle, exactly. And so this new particle that we haven't seen yet so far would have mass, maybe, and it would also have electric charge or it would not have electric charge? It probably wouldn't have electric charge the way like an electron doesn't have magnetic charge.

Okay, and so it would just have this magnetic charge to it, no spin either? Don't all particles need to have spin? Not all particles have spin, like the Higgs boson has no spin, but every other particle does. And so this particle probably would have spin. There's a bunch of different theories of magnetic monopoles, but in most cases they have spin. And magnetic monopole spinning would create an electric dipole, the same way that an electron spinning has a little magnetic field.

A magnetic monopole spinning would have a little electric field. All right. And so then this new particle would somehow exist in universe, but we haven't seen it before. We've never seen one. Nobody has ever spotted a magnetic monopole. Wouldn't we have noticed by now? You know, like there are a bunch of North Pole particles out there floating, wouldn't they have been attracted to our South Poles?

And wouldn't we have noticed that they, you know, our South Poles are getting heavier? Mm-hmm, exactly. If magnetic monopoles were as common as electrons, then absolutely, yes, we would have noticed them. And they would play a big role in life and experience of living in this universe would be very different. And magnetism would be very different. And it would have then bubbled up through our primary experience. And when Maxwell wrote his laws, instead of making them. asymmetric and basing everything on electric charges, he would have written magnetic monopoles

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You have the monopoly today here on magnetic confusion for cartoonists. And it sounds like there is a concept out there called a monopole, which is maybe this theoretical or maybe potential particle that might exist that has magnetic charge to it. It attracts north and south or repels north and south magnetic poles, but it doesn't really have a direction to it. It only has either north or south to it as an inherent property of its particleness. Exactly.

And nobody's ever seen one in that sense. It's theoretical, but it's also very theoretically motivated. Like the universe is sort of weird and out of whack. It would make a lot of sense to see monopoles. The same way the universe seems weird and out of whack without antimatter. Right. The equations work for matter and they should also work for antimatter. And so Dirac said like, hmm, let's go look for antimatter.

And then we found it. It's not very much of it. It's pretty rare. but it shows us that the universe has this symmetry. It was also Dirac who said maybe we should go look for monopoles as this sort of symmetric version of electrically charged particles. So it would make a lot of sense if it existed in the universe, but so far we've never seen one.

Okay, which begs the questions? Are we looking for them? Are physicists trying to find these or just sitting back on their couch wondering that they exist? Some physicists are trekking out to the South Pole building crazy amazing telescopes out of the ice in the South Pole. hole to look for neutrinos, but also to look for magnetic monopoles. Nice. So this is a famous experiment or a big experiment?

It's a famous and big experiment. There's a big group here at UC Irvine that works on it. It's called the Ice Cube Neutrino Observatory. And it literally is an ice cube. They take a cubic kilometer of ice on the South Pole. They drill holes in it and they bury cameras on these long strings within the ice. So they basically have instrumented a cubic kilometer of ice looking for flashes of light of particles traveling through that ice. Wait, what? So they just take like an ice shelf down in Antarctica and they drill down like a kilometer or two and they rope down cameras, instruments, but then they're pretty far apart from each other, aren't they? Yeah, they have like 90 of these strings. Each one is like one to two

kilometers long. And as you say, they drill these crazy deep holes in the ice and then they have these strings. So every string has like a lot of cameras on it. A lot of these light sensors. They lower those down into these holes and then they pour water in so the whole thing freezes up again. So then you have this cubic kilometer of ice with about 5,000 sensors distributed through it. You're right they're not like equally distributed. They'd love to have more strings, but this is sort of the best they can do. So then how are they looking for monopoles? So what you can do with this ice is you can look for Cherenkov light. That's light that particles emit when they fly through material faster than photons can fly through that material.

Remember, you can't move faster than light in a vacuum, though when light moves through ice, it moves that's slower than the speed of light in a vacuum. And particles don't always have to follow that same limit. So if a muon, for example, is moving through the ice faster than a photon could, it creates this sort of superluminal wake. The way, for example, if you're on a jet ski in a lake, you're creating a wake behind you because the boat that's making the ripples is moving faster than the ripples. So the ripples sort of like add up to make this wake, this cone of ripples behind you,

the same way particles moving through this material emit this special light, this churrenk off light in a cone as they move. So you can use this to spot particles moving really, really fast through the ice. And they built this thing not to look for monopoles, but to look for neutrinos that move up through the earth. So they come from the sun or somewhere out in deep space. they move up through the earth, interact somewhere in the earth, and they create like a muon which flies through the ice.

And that tells them that a neutrino was there. That's why they built this experiment as a neutrino observatory. Wait, so they built it to detect neutrinos, but you can also use it to detect potentially a monopole particle? Exactly. This is one of the clever, like, reapplications of these things. They build it for one thing, but then they realize, actually, we can also use this to look for something else.

Because a muon and a monopole going to the ice would look very, very different. Magnetic monopoles, if they exist, would make a spectacular signature in the ice. Because of this relationship between the magnetic and electric charges, we know that the minimum magnetic charge of a monopole, if it exists, is basically the equivalent of like 68 electric charges. So a magnetic monopole, if it exists, it's like very, very magnetically charged. So when it flies through the ice, it would create like a series of brilliant flashes of this Durancoff light. Wait, I guess there's so many questions there. Why do you think? a monocle would be so magnetically charge, first of all. Where does that gas come from?

So it comes from this argument that electric and magnetic charges are connected by angular momentum. Probably the two has to be quantized because that's related to angular momentum. So that lets you actually calculate what the minimum magnetic charge has to be if that argument holds. It's sort of like the fine structure constant over two. So that's like 137 over two. So the minimum magnetic charge has to be like 68 and a half times the electric charge. So basically, if there are magnetic models out there, they're very, very magnetic. They're not just like a little bit magnetic. And so as it goes through the ice, this particle wouldn't interact with the water

molecules? It would interact with the water molecules. That's what generates the Trenkoff radiation is the interaction of this particle with the electromagnetic fields of the water. That's what generates this radiation because it's interacting with the material it's moving through and that interaction would generate all of this radiation. It wouldn't interact in the same way an electron interacts, right? Because the electron has a different charge than a magnetic monopole would.

And because this thing is basically more charged than an electron is, even though it also has a different kind of charge, its magnitude is also greater. It emits more radiation, like 8,000 times as much radiation. I guess, you know, we talked last time about neutrinos that they can go through things because they don't feel the electromagnetic force, only the weak force, right? But here is something that is totally super magnetic. You're saying it's very magnetic. Why wouldn't it sort of bounce around when it hits or flies close to all these water molecules?

Why would it keep going? Yeah, that's a good question. If you shoot an electron at a big blob of ice, it doesn't go all the way through, right? It gets absorbed. But if you shoot a muon through it, muon remember is an electron, but with more mass, it can penetrate through because it has more mass. So, like, has more momentum to keep going. And a monopole, we think also would be massive, and so it would survive making it through the ice.

It's more like a muon than an electron. But also has this crazy magnetic charge that makes it radiate a lot as it flies through. Wait, so you think it would also be massive? Why do you think it would be massive? There are lots of different theories for magnetic monopoles. Some of them predict it would be massive. Some of them predict it wouldn't be. Basically, this experiment can only see the ones that are massive.

If there's a magnetic monopole out there that has very, very low mass, then it wouldn't make it through the ice. And so you wouldn't see this signature. So now I feel like this is just getting more theoretical by the minute. So now you're assuming it exists and also that it's massive and also that it has a huge magnetic charge through it. And also that it's going super duper fast. We can only see these things if they're moving like relativistically, right? Cherenkov light is only emitted if the thing is moving faster than photons through that material. If you have a slow massive monopole, it wouldn't emit this light.

We wouldn't see it. But this telescope is capable of seeing massive monopoles with a lot of magnetic charge if they're also moving faster than three quarters of speed of light. So you're right, it can't look for every kind of monopole, but it's definitely worth looking because if they are there, they would be spectacular signature. It would be like very obvious, very easy to see it and very hard to spoof. But I guess hasn't this observatory been out there for a while? Wouldn't this have found these by now?

Or notice these weird streaks? Yeah, you're right. It seems like it would be kind of obvious in their data. Why wouldn't they have noticed it? But, you know, it's not like people are always looking through the data by eye. When you do an analysis of your data in a particle physics experiment, you're looking for a particular kind of thing, usually. And so this might have been missed if nobody was looking for it.

So people went and did a dedicated search. Like, let's look through the data to see if there's any kind of these weird things. So they've been running your eye for like almost a decade. And so they look through all of their data, trying to see if there are any big spectacular signatures. of bright monopoles passing through this cube of ice, and they didn't see any. Won, wom, wamp, wong.

So all this setup was for nothing? All this setup tells us that if there are monopoles out there, they're either not moving fast or they don't have enough mass or there's something very different from what we expected. But it's pretty awesome to take this cube of ice in the South Pole and to look for these things. I love how dramatic the signature is. I love how exciting it is because also they're going to keep running it.

It might be that monopoles are just pretty rare. Maybe there aren't very many left over. Maybe there weren't very many made in the Big Bang. Maybe they're all clustered together in the center of the galaxy. We just don't know. So it's worthwhile to keep looking. So they're going to keep running this experiment and they're going to keep looking for monopoles. And you know, it only really takes one because it's such a dramatic and spectacular signature.

And it sounds like if you find one, it would be pretty significant, right? Like you're just trying to prove its existence. Exactly. Just knowing that it's possible for them to exist would be amazing. game changing, right? The same way that like discovering one single particle of antimatter proved that antimatter is a thing and the symmetry exists in the universe. Like the guy got the Nobel prize for literally a picture of one particle that he found in 1929. And so the discovery of a single monopole would tell us something really deep about the nature of electricity and magnetism

in our universe. It would answer your question. Like why is magnetism a thing? Well, because magnetic monopoles are part of our universe. For the same reason, the charges are a thing. And so to me, that would be really fascinating. And these things are totally worth looking. Every time I hear about magnetic monopoles, I'm like, ooh, I hope they found it. I guess maybe a question you can ask is, what if they don't exist? What does that mean about the universe?

It means the universe is imbalanced in this weird, uncomfortable way. We like symmetry in our equations. We like balance. We like things to not prefer one direction or another. So it's pretty weird if electricity and magnetism have this deep relationship. but the universe prefers electricity for some reason. It's the same as being uncomfortable about why matter is matter and antimatter is pretty rare. We'd like an explanation for that.

And so if there's a symmetry, then we don't need an explanation. If there isn't a symmetry, then we need to know why. Well, it sort of sounds like, you know, generally you can explain magnetism with just electric charge and spin or spin direction. I wonder if you even need magnetism. Yeah, well, that's why we combined electricity and magnetism into one theory. So in that sense, is magnetism even really a thing? Well, electromagnetism is a thing. And so magnetism on its own doesn't really make sense.

It's sort of like saying, you know, do you need elephant tails? Well, they're part of elephants. They don't exist by themselves, but they're also an important part of the elephant, right? Elephants don't want you chopping their tails off. I don't know. I haven't asked any elephants. And they seem to be fine with their tails. I guess what I mean is maybe like a, you know, like maybe I wonder if we're

trying to look for an effect that we can already explain. You know what I mean? Like we have electric charge. We have spin. That kind of explains mechanism, doesn't it? Yeah, absolutely. We can explain all the phenomena we see in the universe without magnetic charges. But the explanation we build has this hole in it, which makes us wonder if we're missing

something. The same way that when we put the periodic table together, we notice there's some holes in it. There's some gaps in there. I wonder if that kind of thing can exist. Let's go out and try to make technetium. Oh, look, it does exist. feels satisfactory, right? It's like an OCD person filling in that last square. So the structure of the theory of electromagnetism seems so tantalizing and tempting. It suggests that they might exist.

So you're right. We don't need them to explain anything we've seen in the universe. In fact, we have to go out and make special experiments just to hunt for effects that can't be explained with electric charges. But we'd love if they did exist because it would just make the theory more beautiful and balanced. And that's what physics is all about. Beauty and balance. It's about finding simple explanations for the complex phenomena. Yeah. All right. Well, good luck to the Ice Cube Neutrino experiment. I hope they find a monopole or a fast-moving heavy monopole, right? Those are the requirements. A highly magnetic, fast-moving massive monopole.

And if they do, I hope they invite you down there to help them celebrate. Oh, man, for sure. In fact, invite me now. I'll totally go. I'll help you dig one of the holes. All right, put that on your tour dates. Sounds good. Well, we hope you enjoyed that. And thanks for joining us. See you next time. Thanks for listening. And remember that Daniel and Jorge Explain the Universe

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