Daniel and Kelly’s Extraordinary Universe - What are quasi-particles

Episode Date: July 21, 2020

Daniel and Jorge talk about phonons, magnons, excitons, anyons and explainons. Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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Okay, now what are all of those particles made out of? Probably smaller particles. So is it particles all the way down? Is there anything that's not a particle? You're asking a particle physicist, so what else do you expect to hear? An actual particle of explanation? Well, I think this podcast is basically a particle. Is it made out of explainions?

Bad punions? Bad Jokesions? I had a bad punyan last week. Didn't go over well. Hi, I'm Jorge, I'm a cartoonist and the creator of PhD comics. Hi, I'm Daniel. I'm a real particle physicist, not a quasi-particle physicist. Welcome to our podcast. Daniel and Jorge quasi-explained the universe, a real production of iHeartRadio. That's right, in which we talk about all the things that are right.

real, all the things that are crazy, and all the things that are imagined and our interpretation of all of them. We break them down for you and try to give you an understanding of what's going on out there and how scientists are thinking about it. All the mysteries of the universe, all the unanswered questions, and all the amazing facts that we have learned. We bring it all to you with a pun or two. That's right. All of the things that are out there and all the things that might also be out there that scientists are not sure actually exist or are even real, even some things that could be semi real. Isn't that a weird term, Daniel, semi real?

Almost real? It's semi weird, yeah. Yeah, well, you know, there's a whole rabbit hole we could get down into there by like, what is real even mean, man? But I don't think we've smoked enough banana peels yet today to get there. Or like, are rabbits even real? That's another rabbit hole in itself. And why are they chasing bananas down rabbit holes?

Like, that never made any sense. Yeah, so everything's a particle. It seems like, you know, all matter in the universe. and so it kind of begs the question like what are particles themselves made out of and what is not made out of particles and could there be something else that's not a particle

but still make up matter. Yeah and particles are sort of an idea that we have I mean we look out in the universe and we break things up and we see them as smaller and smaller bits and then we have this notion that the smallest piece might be this dot but the whole concept of a particle is a little bit fuzzy. We've talked

on the podcast about the discovery of particles what it really means to be a particle. You know, the first particle ever discovered was the electron. It was really just the identification of a point in space that where you had charge and mass at the same time, like this little cluster of quantum labels. And since then we've added stuff to it. You know, particles can have spin. They can have magnetic moments. They can do all sorts of crazy stuff. But still this concept of like, what is a particle? What does it mean? Remains a little bit fuzzy. You know, they don't have any volume. They do all sorts of weird things. Sometimes they act like waves.

And so it begs the question of like, are particles real or are there just something sort of in our mind? And can we apply this notion of particles to other things also? Now, Daniel, as a disclaimer, we should say that you are a particle physicist. So you might not be entirely neutral on this subject. It might be a little biased. Or I'm an expert, right? So you should listen carefully to my thoughts about it because I'm well informed. No, it's certainly true.

And I like to think of the universe in terms of particles. I like to think that the universe can be explained in terms of a, bunch of little microscopic things, that everything is really just an emergent phenomena of the microscopic. Right. I guess to a particle physicist, everything looks like a particle. Yeah. Just like I've heard astronomers say, we're all made out of stars. I'm like, hmm, that's convenient. Yeah. And it's sort of a question of scale. Even astronomers, sometimes they treat like the whole sun as a particle. You know, when you're doing your gravitational calculations about, you know, moving a planet around a star, you don't really care about how big the star is. You're so far

from it that you can effectively treat the whole star as if it was a point mass at the center of mass of the star. And that's basically calling it a particle. It's saying, I don't care about any other details. I'm just going to put it as a point. So it's a very powerful concept, even if you're not gainfully employed in the field. Right. And generally speaking, it just kind of means like a packet of stuff, right?

Yeah. It's sort of like a little cluster of labels. You know, you can put a mass on it, a spin on it, you know, other kind of quantum labels. But yeah, it's like a little... A cluster of labels. Yeah. Like a whole bunch of little labels moving around together. Yeah, like we talked about how the neutrino, you know, it carries a weak label, but it doesn't carry one for the strong force.

And photons don't carry any mass, but they do carry information about electromagnetic fields. And so to me, I think about these things as having their little dots in space that have labels on them. And so there's this concept in physics called a quasi particle. Is it quasi or quasi-particle? I'm quasi-sure that it's quasi-particle. We're obviously quasi-experts in vocabulary. here and pronunciation. Hey, if we're wrong, we're only quasi wrong.

It's better than being semi-wrong, I guess. Or pseudo-wrong, yeah. Or pseudo-experts. There you go. And this came to us from listeners, actually, who had a question about what these things are. Listeners, Linda Campbell, Nick Beatrice, Jack Case, Tim Davis, they all wrote to us asking what a quasi-particle is. That's right.

If you have a question about something you'd like us. to talk about right to us because we will actually answer your email and sometimes even do a podcast on it. And these folks had seen articles about quasi-particles and asked us to explain it. What is a quasi-particle? What does it mean? Yeah, and have we gone too far with this concept of particles? Impossible. You can't have enough particles to a particle physicist. You can't have too many particles. I mean, it's such a nice idea.

No, we don't know, right? Like, we don't know if particles go on forever if you can get down to the smallest possible particle or if you get small and if particles doesn't really work and you need something else like, you know, pixels of space or little strings or something else. But so far it's a very nice idea to explain the world around us. Is it like if you have a hammer, everything looks like a nail? If you have a particle collider, everything looks like a particle.

Yeah. And if particles have worked, then you extend the idea. You're like, well, let's see if this would also help us understand this other problem. And we do that in physics and in math all the time. We take strategies from one field and we apply them somewhere else to see we can make connections. You know, one of Newton's greatest leaps forward conceptually was understanding that the same rules applied in the heavens and on Earth. And that's all we're trying to do. We're trying to use the concept we discover in particle physics, the group theory, the symmetry, the conservation laws, and apply them other places.

Yes, Daniel, but what is heaven made out of? Particles also. Articles. Angelons. Halons. There you go. Halons, exactly. The rest.

So, as usually, we were wondering, how many people out there actually had heard of this concept or, you know, knew what it was. So Daniel went out there into the wilds of the internet to ask this question and get people's responses. So before you listen to these answers, think about it for a second. Have you heard of quasi-particles? And if somebody asked you, what would you say? Here's what people had to say. Sounds like something that has some of the properties of particles, but perhaps doesn't satisfy all of the conditions. Either that or some guy named quasi came up with a new particle. Probably something that wants to trick you that it's a particle and it's not. Do you want to guess that there are particles with more than one part?

Quasi particles are virtual particles that don't follow the rules. Quasi particles are particles which are created in the vacuum because of the background energy of space that sort of are there and they're not there, maybe. I hope that's something. Is that like a virtual particle? or maybe something that we've seen in the data when we've been looking for particles that we can't quite explain. Particles have mass and quasi-particles maybe do and maybe don't, maybe they go through a filter in the universe. Something that's almost a particle or something very similar to one.

I'm not a native speaker and I have to look in dictionary. It means semi. So quasi particle is semi-particle. Quasi means something that looks like something else. So I'm assuming that a quasi-particle is a particle that looks like a particle, but really isn't. I would say a quasi-particle is a particle that may appear to be real, but actually is not. There was something super tiny. Well, those are some pretty good guesses.

Yeah, I like the person who looked it up in the dictionary. I'm like, hmm. I know. some rules here. You're not supposed to look anything up or Google anything, but, you know, not being a native speaker, I'll forgive that one. Maybe they're just quasi rules. So, yeah, let's jump right into it, Daniel. What is a quasi particle? So a quasi particle is called a quasi particle because it's something that behaves like a particle. It has some of the same properties that we typically use to describe particles. Like, it's persistent. You know, it sticks around. It's quantized. You

You know, you can have one or two, but not one and a half. Usually they're discreet. But it's not actually fundamental. It's not like something that is the building block of the universe. It's not a ripple in the quantum field. It's usually like an excited state of some macroscopic solid. It's something that behaves like a particle, but it's not actually a particle. So does that include like the protons and neutrons?

You know, they behave like particles, but they're actually made out of smaller particles inside. Is that kind of what you mean? Or is it, are you talking more like bigger scale? We're talking bigger scale. I mean, and you could argue that protons and neutrons are not particles because they're not fundamental and they don't have their own quantum fields. And so in that sense, they really are emerging phenomenon. We can get into that later on.

I think that's a fascinating question. But I think typically people think when they talk about emerging phenomenon, they think about sort of a larger scale. You know, imagine like you have a glass of water in front of you and it has, it's sparkling water, has bubbles. You can see those bubbles sort of move up through the, water and they move sort of the way a particle does. They hold their shape, they're consistent, you know, they're coherent. They move through the water the same way a particle does. You can apply

a lot of the same mathematics and understanding and intuition that you apply to particles to that bubble in the water, even though nobody thinks that bubbles are a fundamental unit of the universe or that there's like a quantum bubble field that we know of, this thing is a manifestation of. Maybe quarks are made out of bubbles that we have yet discovered. Maybe it's all rainbows and Unicorns. Yeah, it's bubble theory. You know, the same way you can look at like the ocean and you can see a wave moving through it.

A wave is not a fundamental property of the universe. It's an emergent phenomenon of all these thousands and millions and trillions of particles all moving together. But mathematically, it's much more convenient to talk about the wave than to track all the little particles that make it up. So quasi particles in the same way, but not really that big a scale, not the scale of like bubbles and waves, but, you know, like excited states of solids, like wiggles that pass through solids or rotations of things that move in a coherent way and sort of keep their identity

as they pass through a solid. Right. Like sound waves also? Could a sound wave, like a shout or a screen, be considered a quasi-particle? Yes, sound waves, like vibrations, basically. If you break them down, you can go down to like the quantum, the smallest possible sound wave is like the vibration of a single particle. That is a quasi-particle.

It's called a phonon. A phonon is like the quantum. No, you just made that up. I did not just make that up. A phone on. You can phone anybody and ask them about it. It's seriously a thing. I feel like you're phoning it in.

No, it's sort of like a, you know, it's a more general sense of what a particle is. And here you have like a single particle might be vibrating. And then it passes that vibration off to the next particle and to the next particle and the next particle. So it's like a thing that's moving. Yeah. And it's quantized, right? Because these particles that are vibrating, the atoms or whatever in your lattice, you know, say, for example, I knock on the desk in front of me, it's sent.

sound waves through the desk, or if I speak through the air, then those particles, the ones that are doing the wiggling, they're quantum particles. They have quantum states. It's like a minimum amount of vibration that they can have. And so if you have that minimum amount of vibration, it could pass to the next one and pass to the next one. And that's what keeps it like a coherent thing. You can't just disperse out into infinitely smaller things.

It sticks around because of these quantum minima. They're almost like packets of stuff. Mm-hmm. And it's sort of a mental game you can play with yourself, like what's a particle and what's a quasi particle. You know, another great and classical example of a quasi particle is the absence of a particle. What? Yeah. Like you ever play that game where you have like a bunch of tiles and there's one open slot and you have to slide the tiles around to like get them in the right order?

Like the little puzzles. Yeah, those little puzzles. Well, you can think about it like as the motion of a bunch of tiles or you can think about it as the motion of a hole, of a gap. right, that gap is sort of moving through the puzzle. You're moving that gap around. So that little hole is like a particle? That little hole is sort of like another tile, right? And so in the same way, if you have like a whole bunch of electrons,

you can think about one missing electron moving around. Like say you have 10 slots for electrons, but only nine electrons. So there's one hole, right? And then if all the electrons move over, then the hole moves. The opposite way, right? The opposite way, precisely. So you can either think of it as moving, like every single electron over one slot,

or you can just think of it as the whole moving over one in the other direction. There's two equivalent ways to think about it, but one of them is simpler because you've abstracted away a lot of complications so you can think about it in just this one blob. In the same way that watching a bubble rise through water is simpler than thinking about all the billions of little particles that are making that happen. So you sort of like abstracted away some stuff

so you can apply your particle brain to this new kind of thing. I see. You just kind of blew up. my mind a little bit. Yeah, just to think of that bubbles are not actually a thing. They're just like water molecules moving out of the way. That's a bubble. Yeah, exactly. They're just getting

pushed out of the way by that air. But the arrangement is sort of static. There's like a minimum size to those bubbles, right, because of surface tension and whatever. The bubbles can't just like break up into infinitely small bubbles. And that's why they stick around, right, until they eventually they pop. And in the same way, like electrons can't split in half.

And so that's why you don't get these holes like gradually filled in with partial electrons. Now, this sounds kind of very macro, like, you know, we're talking about bowls and waves. Now, is this something that you as a particle physicist deals with? Or is it more like a bigger things physics? Neither, actually. It's not something that I deal with because I usually deal with actual particles, real particles, you know, particles that are excitations of quantum fields. But it's also not something that happens on the macro scale, usually. It's most often on the microscale. So it's something in the adjacent field of condensed matter physics.

People who build like weird materials and superfluidity and think about superconductivity. I mean, another great example of a quasi-particle are pairs of electrons that cause superconductivity. You know, one reason that metals have a hard time being superconductive is because electrons are fermions. They don't like to be in the lowest state together with another one. But in superconducting materials, we did a whole podcast episode about that. Electrons like to group together into pairs. They're called Cooper pairs. And they're pushed together into these pairs.

And together, they're actually bosons. They have the opposite rules from fermions. And so they can cool down and all occupy the same state and flow smoothly over each other. So a Cooper pair is like a pair of electrons, sort of acting like a particle. And so that's another example of a quasi particle. They're often at this micro level. I guess the common threat is that they maintain some sort of quantum property, right? Like a dust particle, a physicist wouldn't call a quasi particle, right?

It has to sort of maintain that quantuminess feeling about it. Yeah. And you know, you could probably argue that anything is a quasi-particle, but I would say that it should be persistent and it should be quantized and it should be discreet. So many key words. Quantai quasi-qualitative quantity of particles. Yeah, exactly. And so it's fun.

It's like an extrapolation. And this is always really fascinating in science when you can see something in the world and then apply those same ideas somewhere else and gain some insight. because it kind of works. It helps you. It simplifies the problem so you can see the larger dynamics and gives you an insight into what's going on.

It lets you use your intuition from somewhere else. And that's what science is all about. It's not about figuring out the rules for A and then for B and then for C. We want rules that explain everything. We want rules that tie everything together. And so, yeah, if you have a hammer and you've hit a bunch of nails successfully,

you're going to go around and hit everything else with that hammer until they look like nails. Until they break apart into particles. Very convenient. It all works. See, it all works. All right, let's get into what are some examples, some fun examples of quasi-particles,

and then let's talk about whether or not they're actually real. But first, let's take a quick break. Imagine that you're on an airplane, and all of a sudden you hear this. Attention passengers, the pilot is having an emergency, and we need someone, anyone, to land this plane. Think you could do it? It turns out that,

Nearly 50% of men think that they could land the plane with the help of air traffic control. And they're saying like, okay, pull this, until this. Do this. Pull that. Turn this. It's just... I can do my eyes close. I'm Manny. I'm Noah. This is Devin. And on our new show, no such thing. We get to the bottom of questions like these. Join us as we talk to the leading expert on overconfidence. Those who lack expertise lack the expertise they need to recognize that they lack expertise. And then as we try the whole thing out for real, wait, what?

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Because, you know, it sort of exists as electrons moving, which are particles, and it gets stored as information, and it gets turned into soundways, which are sort of quasi-particles, too. That's right. This podcast cannot be broken up into smaller pieces. And so it's therefore a quantized podcast and cannot disperse through the universe and must be accepted into your brain in total. And it's both good and bad at the same time. You are welcome, of course, to listen to the podcast in five-minute increments or 12-minute increments

or five all at once so do it as you please of course oh my goodness all right well what are some examples of quasi-particles like we talked a little bit about phonons and being like sound wave particles

yeah phonons are vibrations they're like the quantum of sound waves they're like the minimum component of sound waves all sound waves in a solid are built out of phonons and so the smallest possible sound wave you can have in a solid is one phonon and you know it's just like energy

moving through the solid. This atom vibrating in a lattice and then the next one vibrates and the next one vibrates. And so you can think of that as the phonon moving through. And I think phonon is pretty cool word too. It makes me think of some sort of like Star Trek gun. Like

you know, set your phonon blasters on wiggle. I don't know. It's very reminiscent for me of phoning it in. I feel like physicists phoned it in when they came up with this name. They're like, what do we call a sound wave particle.

I know, a phonon. Phon. I think it's awesome. Yeah, and then all the other quasi-particles all have sort of similar names. You know, the kind of thing that's getting wiggled or, you know, move through and then on at the end of it. Is it related to sort of like the medium

in which these things propagate in or move around in? Because I feel like a sound wave is quantized because the underlying thing that they're on is quantized. So at some point, you know, you can't make a smaller sound wave. because you run into particles.

That's right, because those particles have quantized energy levels. Like, they can't wiggle at half of their energy level. They can wiggle at one energy level or two or three, but there's a minimum amount of wiggle. And that's why it's quantized. You know, that's why, for example, they can't accept a photon of arbitrary energy. They're resonant frequencies,

frequencies that solids like to accept photons because it helps them move exactly one energy level up. And also, that's why solids give off light at certain frequencies, because, you know, that's the resonant frequencies for that gas, for example, it can excite up by absorbing a photon and excite down by giving off that photon. And when it absorbs the photon, like, where does that energy go? It goes into a phonon. Right.

A phonon is the energy moving through the gas. So photons get turned into phonons. Right. Boy, that's fun to say. And so what are some other examples of quasi-particles? Well, basically every quantum property that a particle can have, When you put it in a lattice, you can think about that property moving through the lattice. What do you mean a lattice?

Like a grid of particles? Yeah. Every solid you can think of as like a grid of particles, like a 3D like a Lego set of particles put together. And so they're all stacked together. Each one is touching the one above it and below it into its left, into its right, forwards and backwards. And they're sort of tied together by these bonds. And that's what makes a solid, right? It's sort of like a loose crystal.

And so they're in this lattice so they can pass information, right? It's like if you're in a crowd of people and everybody's whispering into their neighbor's ear, you can pass information through the crowd. And so that same way, like, that's how these bonons get passed through the crowd. But you can do it also with other quantum properties like the particle spin. You say we could do it with holes, but you can also do it with quantum properties, like charge and mass and things like that? That's a good point.

I mean, for charge, it's sort of holes, right? Holes essentially is the moving of charge around, but they're the actual particle moves over, like the electrons have to move over. You can't pass charge from one particle to another, the way you can pass energy. When an electron moves from here there, it moves the charge with it, creating sort of like a hole in the charge. Yeah, so you can have quasi-particles in like a particle gas, right? If the electrons are free to move around, then the absence of a particle is a quasi-particle, that hole. But also in a lattice, you can have quasi-particles like the phonon, but also things like the magnon,

which is the quantum of particle spin that helps create the magnetic field that metals can have, for example. Oh, now that one does sound like a transformer, I have to say, which I'm all for. Wait, so a particle spin can also move around like a wave? How does that work? Like the orientation of it or what does that mean?

Yeah, the orientation of it. Remember, the particle spin is quantized. So, for example, an electron can be spin up or spin down. So say you have a bunch of electrons that are all spin, down except for one that's spin up, then it can sort of pass that spin to the next electron making its spin up. And it can pass that spin to the next electron. It can make its spin up. So the spin-upness can move through this sort of grid of electrons. And you can think of that as like, oh, well, I got a bunch of electrons. Some are spin up and some are spin down. Or you can

think of it like, oh, I have a magnon that's moving through a sea of electrons. Because like one particle will give its spin to the next particle or just from the gap of it? Yeah, they can transfer because they couple to each other a little bit. You know, electrons talk to each other. They bounce around. They share energy. They interact. And spin is conserved. So you can't just

have them all be spin up. If they're all spin down except for one, then you have to have one electron spin up. It's just a question of which one. And because it's quantized, you can't have like half spin up and a third spin up. So you need to pass the whole thing over from electron to electron. And so

the magnon moves around. Is it like the potato in a game of hot potato? Exactly. Exactly. Exactly. But I'm not sure. Maybe the electrons want to be spit up, right? Maybe it's like, hey, give me that hot potato. No, give me that hot potato.

I can't speak for the electrons. We should just rename the game to magnons or quasi potato. And then every time you want to play with your four-year-olds, you have to explain to them quasi-particles and then, you know, they're not interested anymore. And then nobody wants to play. But these are actually really cool. And they have other applications.

particle physics, like if you search for magnons, you can be sensitive to really small effects. Like if you get a field of particles and they're really quiet, then you can look for magnons as evidence that like maybe dark matter has come through and hit one of these electrons and given it a spin. And so you can try to measure these things using very, very sensitive magnetometers because remember the spin of the particle affects its magnetic field. And so that's why we call it a magnon. It all goes back to dark matter, doesn't it? In the end, it's only exciting if it can help you find dark matter. I guess maybe, right?

Because it motivates why you want to study it, maybe? It's a big mystery, yeah. But here it's just like, hey, this is a cool idea, and it gives us a new way to look for something really cool. And it's an example of why it's good to use, like, particle physics ideas in other areas. Like, you can get this inside into condensed matter and how spin moves around in a lattice of electrons.

And then that gives you an idea for how to look for something else cool and new. So, you know, it's sort of like refreshes you creatively, intellectually to like look at something from a new perspective. So is the idea then that like if I have a whole bunch of electrons and they're just hanging out and suddenly there's like a potato in the middle, they're like, hmm, you're like, must have been dark matter that gave us that potato, right? Or, you know, it's been obviously. But is it kind of like that? Like if there's suddenly a potato in the middle, you got to wonder where that potato came from. Yeah, exactly. And eventually one dark matter experiment will have to be called

potato based on this podcast. Yeah, physics, ordinary. What's the right acronym there? Transfer. Well, while you work on that, you know, these things actually do have special power to discover dark matter because the kind of dark matter experiments we have right now are mostly waiting for dark matter to bump into the nucleus of the atom. You know, the big heavy protons and neutrons. And we see that kind of nuclear recoil. We see that getting kicked. And that requires kind of heavy dark matter because you've got to be big enough to like give it a kick. The dark matter is really, really wispy. And it won't move those neutrons and protons, even if it does bump into them. But these magnon detectors could be much more powerful as a way to search for very, very light, very low mass dark matter. And since we haven't found dark matter, the higher masses where we've looked for it, it's kind of exciting to say, oh, look, we can build new detectors that might be sensitive to even wispier dark matter. Because electrons are more sensitive than protons and neutrons? Well, they're just lighter and so they're easier to kick, right? If you are a very light particle, then you're going to have a bigger effect bumping into an electrical. then you are bumping into a proton or neutron, which is like, you know, a boulder in comparison.

I see. So if dark matter can interact with electrons, then you would see it in a very kind of maybe bigger way if you look for these quantum spin quasi-particles. Yeah. If you look for magnons, exactly. I feel like you don't want to say magnon. It's such a fun word. Yeah, no, magnon, magnon. And there are lots of other kinds of quasi-particles.

You know, there are polarons. This is when electrons interact with the polarization of ions. Wait, I just came up with a joke, Daniel. What's that? If you make this project, if you set up this experiment, you should call it the magnon particle interface. Maxon particle interface. MPI? No, Magnon PI.

Then you'd be ready for prion time. Everybody has to unbutton their shirt, two buttons to work on this experiment. Yeah, and have a mustache. I'll start growing it. Then there's the, like, there are rotons. If you have like a fluid. Rotons. A roton.

If you have a fluid that you can get like vortices in it, right? You can get like little whirlpools. And the sort of the minimum amount of vortex that you can get turns out to be quantized because of how these particles can spin. And so that's what a roton is. It's like the minimum quantum of vortices. I guess because the medium again is quantized. So, you know, little like vortices also have to be quantized

because there's a minimum size of these particles. Yeah. And they have energy levels in just the same way that phonons exist because solids and a lattice have energy levels to their vibrations. Fluids also have energy levels. And these particles inside them, these vortices have sort of a minimum energy level. And that's where you get rotons. And then you get other really weird things.

And you can apply this really broadly. And there's been like an explosion of different kinds of quasi-particles. People have sort of created or conceived of, you know, they even have like weird two-dimensional quasi-particles. All right. Let's get into the rest of these quasi-particles. examples of quasi-particles and then let's get into whether or not they're actually real like philosophically could we call them real things and how does that maybe put into question

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All right, Daniel, so we covered the phone online. the magnon and the rotons and what other ons have people sort of discover it or study? One of my favorites is this weird one. It's an excitation in plasma. So plasma is like you take gas and you heat it up so much that the electrons and the nucleus separate. The electron becomes free. You have like a charged gas. And this is really hot and nasty stuff.

And it's, you know, it's what the sun is made out of. And it's what we use to try to do fusion. And sometimes you can get it acting in sort of like sheet. You can get these like sheets of plasma layering on top of each other because these things have charges. And so like you can get like a negatively charged sheet and then a positively charged sheet and then a negatively charged sheet sort of like stack up on top of each other. And weird ripples pass through these 2D sheets of plasma. And these things are called. Let me guess. Plasma.

That would be a good one. But no, they're called for reasons I don't understand, they're called eneons. Oh, no. Like, A-N-Y-O-N-S. And, you know, it makes me wonder, like, how did they come up with that name? Like, maybe all the other ons were taken, and somebody said, you know, is there anything left? Ding, oh, any on. No-ons or something.

Daniel, what do you call a quasi-particle made out of quasi-particles? A quasi-quazi-particle. An onion. An onion, of course. Man, I walked into all these terrible jokes. You are. I am just firing off the quasi-pad jokes here. But there's some really cool mathematical features of these things, like these anions,

they actually act like two-dimensional particles. It's like a mathematical system that we don't see in reality. Our universe is in three dimensions, so our particles move in three dimensions. And there's different mathematics that apply to two dimensions, the surface of things and the surface area of things and how things diffuse, instead of going like one over R square that goes like one over R. and these anions actually exhibit those mathematical properties as if they were 2D particles. And that's really kind of cool.

That's just like test out these mathematics in real life. Interesting. Because then you can have like different kinds of physics, right? Like you can have 2D physics, which could be totally different. Yeah, it is totally different. And it's fascinating to see it. And like, of course, it's made out of 3D things. So it's not really 2D, but it's sort of like a physical simulation of 2D, which is really

pretty cool because you see these effects happening, but sort of, you know, quasi, it's like on the meta level, you're like abstracted it out. And in this interpretation of these plasma wiggles where I call these anions and treat them like particles, then I see that it follows exactly the math you'd expect for actual 2D particles. And that's pretty cool. Like you can describe them with wave functions, even though they're not. Like, they're just gaps in other wave functions. Yeah, exactly. Exactly. You can describe them with wave functions and all the mathematics we use for particle physics, but in 2D. So that's pretty awesome.

What are some other cool quasi-particles? I think maybe the last one I'm excited about is the exciton. I walked into that one, Daniel. There's actually a particle called the exciton. Yeah, and it's not like the quantum unit of Daniel's enthusiasm for science. You know, it's... Which has a minimum, Daniel? Are you saying there's a minimum excitability threshold?

Always above zero. It's always above zero. And this is when you get an electron, which is a particle you know, and a hole. So a hole is already a quasi-particle, right? It's the absence of an electron. It's a gap where you might expect an electron. But sometimes electrons and holes can interact with each other because a hole is in effect positively charged, right?

The absence of a negative charge is like a positive charge. And so the electron and the hole can interact and they can actually form these bound states. What? One electron will drag a hole behind it. And so they're sort of moving together. The electron would drag the hole. Yeah, the electron will drag the hole behind it. Because, you know, a hole is sort of like the absence of an electron.

And these are all things that come out of like complex interactions between the electrons and the positive ions that they're embedded in. And, you know, not all these things last for that long. You know, like Cooper pairs don't tend to last for very long in superconducting materials. But you can still apply the mathematics to them for as long as they do live. And so you call that pairing another particle. So a quasi-particle with a particle, you can group them into a quasi-particle too. Yeah, exactly. So it's just like you were saying before, it's a quasi-particle made out of a particle and a quasi-particle.

Wow. Seems really meta. It is pretty meta. And it lets us explore sort of the theoretical space for particles that we don't see in terms of fundamental particles. Like we talked on the podcast recently about whether neutrinos are their own antiparticle. And this is a special kind of particle called a myerona fermion invented by an Italian guy, Eitori Mayorana. And we've never seen a Myrona Fermion.

Like we don't know if neutrinos are their own antiparticles. We're curious about it. We've never seen it. But in quasi-particles, we've seen quasi-particles that have this property that are their own antiparticles, where two of them, when they bump into each other, they annihilate. And so we sort of have seen the mathematics of Myrona-Fermion's work on the level of quasi-particles, even if we haven't seen it work for fundamental particles. And that tells you that, okay, well, the math is right.

If those particles exist and are out there, we know what they would do. All right. Well, let's get into the question of maybe the more philosophical question, which is, are quasi-particles real? Are they just kind of like phenomenon? Or do you think there's something fundamental about them in the universe? We don't know if they're real. Or I guess we don't know if they're fundamental. We don't know if anything is real, right?

I mean, quasi-particles are a mathematical way to describe, like, some information, some labels moving through a material. You could say the same thing about particles, except there the material is not like a solid or a crystal, it's a quantum field, right? Particles, we say this on the podcast all the time. Particles are just excited little blobs of energy moving through a quantum field. And we had a listener question recently, like, why do we have particles at all? And we said that there's like a minimum energy that a quantum field can store and that energy moves around.

And that's what we think of as a particle. So maybe this whole particle idea is a human idea. It's just our interpretation of a localized packet of energy. And we apply that to what we call fundamental particles that we don't know if they're fundamental. And also two sort of larger groupings of things. So I find that argument kind of persuasive that there really is nothing fundamental. Interesting. Like maybe everything should just be called.

an energy on or something like that. You know what I mean? Like everything is just an excitation. Like everything is just a lip in something else. Yeah, exactly. And maybe it's not fair to have a distinction between particles and quasi-particles. They're all particles, right? They're all really the same.

It's just a question of like, what are you wiggling? Are you wiggling some other matter or are you wiggling a quantum field? What it makes me think is like, what if quantum fields are actually made out of other little things? Do you know what I mean? like maybe, but we just can't see them. Yes, very likely they are. What?

Because our description of the universe in terms of quantum fields doesn't really work at some level. So a lot of open questions we've talked about, you know, why do we have so many of these fields? Why do we have like several different kinds of forces each with their own kind of field? Are they all just part of one field? Is there even really a field or is it an emergent property of something deeper? And so I think that, you know, this era of particle physics

where we talk about the universe in terms of part of, particles and the fields that they wiggle on, this is probably a temporary phase in the sort of the longer history of physics before we dig in and we find some other concept. Right. Because, you know, the concept of a particle is only like 100-something years old. We could very well come up with a new mathematical concept that the universe is based out of. That's what string theory is.

Yeah, the onion. I'm telling you, man. You heard it here first, folks. That's right. It has layers. It's a theory that has layers, Daniel. It makes you cry. It makes me cry, the more I hear about it, exactly.

Slice into it. Yeah, but you know what I mean? Like maybe what we think of as fundamental right now, like quarks and the electron, maybe they're just like holes in a medium of other stuff, smaller particles. Yeah, absolutely. And everything that we have, all these ideas we have, this understanding we have about the universe. These are just ideas in our head to describe the experience that we do and the observations we make. We don't know that any of it is like true in any sense.

It's just useful and seems to work. And it seems awfully true because it really, really works. We're going to do an episode next week about like the super high precision of the predictions. Like the mathematics of these fields and these particles gets things right on to like, you know, 12, 15 decimal places. So it seems really true. But we don't know that it is. I mean, I remember having this moment in college when I was learning about quantum mechanics and seeing one of these calculations where the calculation was done and the experiment was done. two agreed to like 15 decimal places.

And I remember thinking, wow, it's like this theory is not just good. It's like what the universe is doing. And that could be true. It could be that the universe has field and it's doing these field calculations to describe how particles move. But it could also be that that's totally wrong. It's just an emergent picture of something much simpler, much deeper that hopefully we'll stumble across soon.

Like maybe it's just a big coincidence. It could just be. And it could be, you know, that the way that we think about it and who happened to be around when we started thinking about it and the ideas that they had. If you ran like history twice or 10 times or 15 times, you might get very different mathematics and therefore very different sort of like intellectual notions about how to organize our knowledge about the universe.

And that's really what a particle is. It's a human organization of our knowledge of the universe. So you might have come up with a different idea. And science could have followed a very different path. Well, Daniel, I feel definitely a few excitants about the whole endeavor and to learning more about this. It is kind of a cool way to sort of see the universe. Like maybe the universe we see when we look at the stars or when we look at ourselves in

the mirror, you know, we're all just kind of like little packets of excitability of little packets of energy just kind of rippling around. Yeah. And it's fun to think that you can explore that on the micro, micro, micro level. You can break yourself up and think about the smaller and smaller particles. But it also works the other direction. you can build up from there and think of like particles

on another level and a meta level and it still kind of works and that's sort of amazing that tells you that, you know, this concept of like a packet of energy or packet of excitation moving around maybe that is something real and true in the universe.

Interesting. Like everyone listening to this podcast is a you on. A person on. A person on, Daniel. It's already there. I bet they're hoping that you will move on from this joke. All right.

Let's phone it in and phone on it and wrap it up. Time to go on. All right. Well, thanks for joining us. We hope you enjoyed that discussion, that quasi-discussion, and maybe look at the universe

in a slightly different way. And thanks to everybody for writing in with your curiosity. We love hearing what you are curious about. A goal of our podcast is to bring you to the forefront of science. And so when you hear something talked about you don't understand, send it to us.

We will break it down for you. We will explain it to you in a way that makes sense and hopefully makes you giggle on. See you next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio,

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