Daniel and Kelly’s Extraordinary Universe - What Is Quantum Spin?

Episode Date: May 16, 2019

Everybody talks about it, but what IS it? Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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Hey, Daniel, do you ever get caught using a word that you don't really understand? Do you actually always know what you're talking about? I don't think I'm willing to divulge that here on the podcast. I mean, you can have that conversation over a beer sometimes. But the thing that I love is that there are some topics in physics, some idea, some words, that I'm pretty sure nobody actually really understands. I feel like this is taking us to another episode about quantum physics. That's right and wrong at the same time.

No! I mean, yes! Exactly. Both of them at the same time. Hi, I'm a cartoonist and the creator of Ph.D. Comics. Hi, I'm Daniel. I'm a particle physicist. And welcome to our podcast, Daniel and Jorge, explain The Universe, a production of iHeart Radio, in which we take crazy and fascinating and amazing and

hot and wet and nasty things about the universe and try to explain them to you. Today's episode is dedicated to Ilana, whose boyfriend Nick is a local fan of the podcast here in Irvine. Happy birthday, Ilana. Today's topic is a really fun one, and in preparation for it, not only did I go and do the normal street interviews I usually do with random people, but I actually went around the halls of my physics department and I asked a bunch of grad students if they could explain today's topic for me and they found it pretty tough. Wow, that's a pretty interesting spin on the topic on our process. That's right. That's right. Today on the podcast, we're going to be talking about

quantum spin. Exactly. Quantum spin. What is it? What does it mean? Are there things actually spinning. Why is it quantum? We got a lot of people sending in requests to talk about this topic. And I think when people are interested in physics and digging around in videos on the internet and listening to podcasts, you hear this come up a lot. It comes up in quantum entanglement. It's in science fiction everywhere. And of course, people want to know what does it mean? What's going on? Why is it so important? That's right. What is spin? How fast is it spinning? What's the spin on it? Exactly. Is it spinning out of control? That's right. Is it different from political spin?

It's definitely a thing, right? It's something fascinating. And more importantly, if you're an expert in this field, does that make you a spin doctor? Doctor of spin, yes, exactly. You know, we have sort of a bad track record in physics of naming things, naming things using familiar words. Like, we give corks flavors, right? The up quark and the charm cork and the top cork are different flavors of corks. Or colors, right?

And colors, right? When they don't really have color. They don't really have color, and they don't really taste different. I mean, I don't know. I've never actually tasted a top cork, so there you go. I'm speaking on something I don't really understand. But we don't mean it in that way. So sometimes we're like adopting existing words and just using them totally inappropriately.

Other times we're trying to use words that are similar to some other concepts, specifically because we want to call up structures and ideas from those concepts. Like, colors actually pretty cool. because while the particles are not colored, there's something about quantum color, which is similar to color. And so we want to express that. You're sort of trying to grab on to an intuitive idea,

even if you're trying to reference an intuitive idea in our everyday experience and kind of latch that on to a physics concept. Exactly. And we do that all the time, right? That's basically what physics is, is try to explain the unknown in terms of the known, right? like when we try to talk about particles

we're doing that all the time you know we're saying oh it's a particle no it's a wave right it's really neither and it's both and it's something else more complicated and we're just trying to patch together a description of it using ideas in your head right we weave these together into some sort of understanding here's such a suggestion for you guys maybe

you should just instead of calling being bold and calling it like colors or flavors just add the word like at the beginning in your official definitions So the announcement should be like, like, we're calling this color. I mean, like, let's call it a flavor. No, I just call it like quantum like color. It's like color.

I see it. It has a color like property or a spin-like property. Yeah, yeah. Or, you know, I mean, if you want to get mathematical, you just put a little tilde in the front, right? And then nobody would be confused. Yeah, I like that idea a lot. Oh, good. You like, like it.

Yeah, I totally like it. And I think, I hope on Twitter it gets a lot of likes. There you go. I think I'm on to something. I think you're on to something. I think you should be nominated onto the secret international physics naming committee. I don't know where it meets or when it meets or who's in charge of it. But they've been making some dubious decisions recently and they need some fresh blood.

Well, I think if I was in charge, I would just put the tilded in front of physics itself, you know? Oh, snap. Like, what do you study? Tilda physics. What does that mean? Like physics. I'm studying something like physics, but it's not actually physics. I mean, isn't everything like physics, philosophically?

Next thing, you're going to be calling me like a physicist. Not actually a physicist, but something like approximating a physicist, you know. You're going to spread this everywhere. I should just call you a Tilda Daniel. You're sort of like a Daniel. Intuitively, you're a Daniel. No, I'm actually a Daniel. I'm the definition of me, right?

I see. You're Daniel sub-zero. Exactly. I'm not like me. I am me. right? You are, Daniel. I think therefore I am Daniel.

Well, anyways, before we spin out of control here on this side conversation, we're talking about quantum spin. And so it plays a big deal in quantum physics, in quantum entanglement, right? And atomic orbitals. I mean, it's sort of important in everybody's atoms, which are kind of important to people. That's right. I like my atoms, you know. They're not like atoms.

I just like them. But exactly. Spin is everywhere. and you hear it come up, and especially when you're hearing explanations of quantum entanglement or quantum computing or orbitals and this kind of stuff, you hear about it. And when I was a student and I was learning about quantum spin, I was like, okay, but what is it? Like, are these things actually spinning? Why do we call it spin, right? How could a particle spin?

And so let's dig into all that today. Well, as usual, Daniel went out there and asked people on the street if they knew what quantum spin was. and you actually have kind of an interesting spin to it this time, right? Yeah, I went out and I asked people on the UC Irvine campus and then a few other folks at an Irvine mall what they thought quantum spin was, if they could describe it. And if they did understand quantum spin, I also asked them, are these particles actually spinning?

Or is that just like spin? Is that just like a word we use? Well, here's what people had to say. So energy. I just think of energy. Okay. Yeah. Yes. What's quantum spin? Like, quantum spin, as in, like, spin-up, spin-down within molecular orbitals and electrons.

So are those particles, like, actually spinning? Yes. No, I haven't. Quantum spin, no. No? Yeah, it's electron spin that it can be positive or negative. How's it different from normal spin? Like a tennis ball can spin.

Is electrons spin the same thing? Are they physically spinning? I'm not sure. I know some stuff about Polly's principle that the spin should be in a specific way and they're paired. So I know some way in this joint stuff, but I'm not sure about them.

All right. Cool. Yeah, isn't because every electron has a different type of spin. It's like either plus one half or a minus one. I forgot what it would. But yeah. And are they like action? spinning? Is it like the same thing as a tennis ball spinning? Or is it a different kind of thing?

No, because it's not like, because you can't treat it like it's a particle, right? Because it's, like, an electron is a mix of a particle and a wave. I've heard of it, but I'm not familiar with the meaning. Okay. No, I don't know what that is. All right. Yes, there's up and down spin, right? And it's in the, I don't know much more than that. Okay. All right. It seemed very binary. Some people had no idea. I never even heard of it. And some people had a lot to say about this topic.

Yeah. And some people knew some stuff sort of in the vicinity of the topic, but not actually like relevant to the question. In the vicinity. Yeah, yeah, exactly. I like when I asked somebody a question and I can tell, they haven't thought about this in a long time and they have sort of like a free association going off in their mind.

They're like, wait, this is connected to that idea, to that idea, that idea, that idea. And then they go, no, actually, I don't know. I don't know the answer. That's really fun when you can see their process. Yeah, because a lot of people would be heard. heard about it or read about it a long time ago, maybe in high school physics or something. And so you sort of feel like it's in there in your brain. You just need some time to, you know, boot up the hard drives.

Yeah, exactly. But I think my favorite part of this experience asking people these questions was that one gentleman after I asked him, if you knew about quantum spin, he then asked me, he said, is this something you need for your dissertation? And you said, yes, yes, sir. Yes, sir. I am a 25-year-old graduate student. Absolutely. Wait, are you saying that you can't be a grad student at 40-something? There are fewer of them, yes. There are fewer 40-something-year-old grad students. But I have to say, the ones that are 40 years old, like folks that went out into the real world and worked in real estate or law or something and then came back to do physics grad school, they're really good students. They really want it. Yeah, it takes a, it's a lot of work to divert from a path in the real world back into academia.

It's much harder than just like going from undergrad to grad school. So I really respect that. You know, you got to really want it. Oh, cool. So if there are any listeners out there who want to change careers and get a PhD, they should contact you, right? And you have a spot for them. I'm not sure I just offered anybody funding, but I would encourage you.

If you have a deep passion for physics and you find yourself in a dead-end job and you wish you had gone to physics grad school to unravel mystery of the universe, I encourage you, sir, and ma'am. If you'd like to be in another deadest, of awesome knowledge. Then be a cartoonist. Is that what you're going to say? Yes, yes.

All right, so Daniel, let's break it down for people. What is quantum spin? We don't know. Done. Podcast over. That's why we had to diverse so many so much. Just do a fill in the airtime. So people don't know.

Because this don't know what quantum spin is. We don't really know what it is. Now, we know it's a thing, right? So there's this thing, this property of particles. We don't really understand what it is, what it's doing. But there's this thing we've observed, and we call it quantum spin. So let's do it that way. Let's talk about what this thing is that we can observe.

And then we'll talk about why we call it quantum spin and whether it's actually spinning and stuff. Right. Well, what's the origin of this? How did this come to be a thing? Well, it came to be a thing basically because of magnets, right? And you remember that charged particles, so a little particle with the charge on it, like an electron. If you move it in a circle, right, like through a wire or loop or something, then it makes a magnetic field, right? You can turn it on and off, like electromagnets. This is how they work.

Right, like motors, everyday electric motors, motors in your car, and in your electric car, even in your phone, right? There's probably a little motor, a solenoid, doing the vibrations when you put it on vibrate. That's the principle. Like, they just pump electrons through a coil, a little loop, and then that creates a magnetic field, which moves something. That's right. And the cool thing there is you have a magnet you can control electronically or digitally. So that's pretty awesome.

But the important concept there is that things moving in a circle, charges moving in a circle, give you a magnetic field, right? So that's something we know about, right? It's something we understand. And so then people were asking the question, well, do electrons themselves, like individual particles, do they have little magnets on them? Like, not just moving in a circle, but is there a magnetic field just due to the particle? And this is the kind of thing physicists do.

They're like, well, we don't expect this to be this way, but let's just check, right? Let's see if this happens. Because back then, maybe they thought particles were like little balls, right? Maybe. Yeah, well, they didn't know, right? This is in the 1920s. This is almost 100 years ago. The whole idea of a particle was still pretty new.

People discovered electrons and neutrons and, you know, it was a crazy era of discovery. They were maybe asking, like, is one electron maybe like a magnet itself? Yes, exactly, right. And that's what they were wondering about. And so if it's a magnet, it would have a direction, right? Like a field. Exactly.

Would it have its own little magnetic field? So that was the question they were trying to answer. Like, does an electron or a silver atom or whatever, a little particle have its own magnetic field? So what they did is they built this device that would, basically, they put particles in this device, and the device has a magnetic field on it. and they move the particles through the device, not in a circle, but just in a straight line. And the idea is that the device has magnets in it.

So if the particles have their own magnetic field, then they'll get pushed to one side because the magnets and the particle would interact with the magnets from this device and would push the particles to one side or the other. Kind of like if you, not through an electron, but if you threw like an actual magnet, like a fridge magnet,

if you threw it at some other magnets, it would get deflected, right? Yeah, exactly. It would get deflected. Now, most magnets are balanced, right? Most magnets have a north and a south. So say you set up like a really strong pair of magnets, and then you threw a fridge magnet through it.

Probably wouldn't get deflected because it has a north and a south, and so the pulls would get balanced. So what they did was they set it up one really big magnet and then a weaker magnet on the other side. So there's like an uneven magnetic field through it so that if your fridge magnet goes through it, depending on the angle of the magnet,

depending on the angle of the north and the south, it'll get pulled in one direction. or the other. Okay. So they built the particle version of this, right? An uneven magnetic field, and they shot some particles through it. And what they found was really surprising, right? It was really shocking what they discovered.

They found that particles do have magnetic fields? Yeah, well, first of all, they found two things that were surprising. One, particles do have their own little magnetic fields. I mean, first they did it with silver atoms, which is sort of the easiest thing they could do to make a beam. Then this is a long time ago before you could easily make like a beam of particles. they just put a bunch of silver in an oven and like some of it boiled off and they collimated it and got a beam of silver atoms and then later they did the same thing with

electrons and they found that these things have their own little magnets like an electron is a magnet which is kind of perplexing like what does that mean like where does this magnet come from right but what does it mean that it's a magnet like if i just look at an electron it has like a north and south pole to it yes exactly electrons have their own little magnetic fields even when they're not moving in a circle. Even if they're not moving at all. Like if you suspend it an electron, can you can you do that? Yeah. Yeah, exactly. If you have an electron just floating motionless in midair, it will have its own little magnet. And that's really weird to us now, right? Because we know that electrons and particles are not like little balls, they're just points. Yes, exactly. And so

the question of where does that magnet come from, that's where this whole idea of spin came from. But the other really weird thing they found was that the magnets didn't point in every direction. Like if you just throw a bunch of magnets through this device, if they're all pointed in different directions, right, these are just randomly oriented, you'd expect them to get deflected in random directions.

This one goes left, this one goes right? This one goes a little bit up. This one goes a little bit down. But, you know, if they're randomly organized, they should go in all sorts of directions, right? But what they found was that either went left or they went right. there was nothing in between

like it's either left or right and nothing else like those are your two options really and no variations in how much right or how much left yeah they all went exactly the same amount left or this exactly the same amount right what yeah exactly

and that's why we call it quantum right they have this little quantum magnetic field the amazing thing is that say then you rotate the device you're like okay rotate it 90 degrees maybe you were measuring it on the x axis now you're measuring on the y axis right So you're imagining, okay, well, maybe these particles just, you know, were somehow weirdly oriented along the x-axis.

So they either go left or right. So then rotate your device, 90 degrees. Then all the particles are either move up or down, right? No matter how you orient the device, the particles either go along the magnet or against it, right? So it's not like a real magnetic field, right? It's something weirder. It's not like a real magnetic field. Exactly.

It's like a magnetic field. It's like a magnetic field. And that's exactly what they struggled with. They're like, okay, this has some property. Something is generating this magnet, and it's definitely quantum mechanical in some weird way, because we have all these weird properties. Like another weird thing about this magnetic device is, say you send a bunch of electrons through it and you split them left and right, okay?

Then you take the left beam, only the left beam, and you split them through a device that's rotated 90 degrees that goes up and down. then they split up and down, right? Even though beforehand, they would only split left and right. Wait, what if you take the left beam, the ones that went left, what if you try to split them up again horizontally? Do they all go left again? Yes, they do.

But if you split them left right and you take the left beam, then you split them up down, you take the up beam, and then you try to split it left and right again, then they mix. They go both left and right. And that's why it's quantum mechanical. Yeah, because you can split them. You can't measure this weird little quantum magnet that the electron has.

You can't measure it both in X and in Y at the same time. It's the old Heisenberg uncertainty principle. You can't know too much information about the universe. So when you measure it in up-down, it mixes it up again and left-right. Wow. It's like, oh, I see. You can't measure the up and down and the left and right at the same time. It's like you can't know a particle where it is and where it's going at the same time.

The same thing applies to the magnet. Exactly. And that's how we knew it was a quantum mechanical property, right? So we discovered this weird thing about particles that they have their own little magnets, and somehow this magnet is quantum mechanical. And so they were like, what could this be? All right, let's get into what it could be and some of the weird things about that. But first, let's take a quick break. airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys.

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In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's, my boyfriend's professional. is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon.

This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating.

He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast.

Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills and I get eye rolling from teachers or I get students who would be like, it's easier to punch someone in the face. When you think about emotion regulation, like you're not going to choose an adapted strategy which is more effortful to use unless you think there's a good outcome as a result of it if it's going to be beneficial to you. Because it's easy to say like go you go blank yourself, right? It's easy. It's easy to just drink the extra beer. It's easy to ignore to suppress seeing a colleague who's bother me. you and just like walk the other way. Avoidance is easier. Ignoring is easier. Denial is easier. Drinking is

easier. Yelling, screaming is easy. Complex problem solving, meditating, you know, takes effort. Listen to the psychology podcast on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts. So people were measuring electrons and they found that they have sort of like an inherent magnet inside of electrons and that it's quantum mechanical, meaning that it's like really weird. You can't measure up and down and left and right. That's right. So people, that's what people decide to call quantum spin. Yeah, exactly.

Even though it's not really spinning, they just went for that name. That's right. They call it quantum spin. And so let's try to figure out what do they mean by quantum spin. Why did they call it quantum spin? All right. Well, quantum is pretty strong. straightforward. It's definitely it's a property of particles

and it behaves like other quantum things that you can't know too much about it at the same time or you can't measure the X and the Y direction of it at the same time and also it's either up or down, right? There's no in between. So it's quantized. So the quantum stuff, all right,

I buy it, right? You should definitely call this quantum something. If you're going to call it quantum spin or quantum banana, you know, that's another question, but it should definitely have the quantum label. Okay. Well, I feel like maybe they should have called it quantum pole or something, you know, like something that references that

because really you're trying to capture this kind of the magnetic direction of the magnetic field of the electron, right? Which is kind of like the pole. Yeah. Well, what they did is they thought about what generates magnetic poles, right? What generates magnetic fields? And we know that a

particle moving in a circle, right, like orbiting, for example, will generate a magnetic field. So then they thought maybe the particle is spinning. Maybe it's like physically spinning. And if you imagine an electron, like it has charge on it. Think about the surface of the electron has like little bits of its charge distributed across the surface. This is the image they had back then, not the image that we use now.

If that was spinning, then you can imagine that the spinning surface of the electron could be basically particles moving in a circle and that would generate a magnetic field. So they were like, aha, maybe we've discovered that electrons can spin, right? But why didn't they just call it like quantum pole? Because you were born 100 years too late, man. I know, that's what I'm saying. Totally. I'm officially nominating you to be on the secret physics naming committee. I think you're great of this.

I mean, in the sense of people out there who might be trying to understand this, you know, I mean, they're not physicists. They don't really care why they called it a particular thing. But if they had called the quantum magnetic pole or something like that, would that still be accurate and also maybe be easier to understand? I don't think it's accurate because it's describing the effect and not the cause, right? We think something is happening which generates the magnetic field and these other properties. But what we'd like to do is figure out what the cause of it is like, what is the particle doing that generates the magnetic field, right?

What is the source of it? And does that give us insight into other stuff? And it turns out it does, right? We like to think about the particles having this thing we call spin, and we call it spin because it generates a magnetic field, but also because the way the mathematics of the spin is really similar to the mathematics of electrons in orbit. What do you mean it's similar? Well, like the mathematical language we use to describe it

is very, very similar, right? And when you see some phenomenon A and you describe it mathematically and you see phenomenon B and you describe it mathematically, and you notice, hey, look, they're described by the same math, then you have to wonder, are they two sides of the same coin, or are they really the same thing? And so people thought, oh, look at all these relationships

between this thing we call quantum spin and orbital angular momentum, you know, the angular momentum of something moving around in a circle. Right. And it was a lot of connections there. But they turned out to be wrong, right? Like, I know what you were trying to do,

but you sort of missed, kind of. Well, yes and no, right? That's the first rate you think about quantum mechanics. Like, theoretically it does work. Physically, it doesn't. Like, theoretically, it does, it works in this beautiful, really deep way because what we know, for example, is that angular momentum is conserved, right? Like, momentum is this property of particles to keep going in the direction they're going.

Angler momentum is this property of particles to keep spinning the way they were spinning, right? And we know that angular momentum is conserved. If you start something spinning, it's going to keep spinning until you stop it. Now, what's conserved is total angular momentum, not the angular momentum of, like, one thing. So you spin a top, right? And you can stop it by touching it against another top, which then takes its spin, right? So the total spin of those two tops is conserved.

Well, the fascinating thing is that while we don't know what spin is, we know that orbital angular momentum and spin are conserved together, like the sum of them is conserved. So you can change the spin of some particle and it will influence its angular momentum, right? What you need to conserve is the sum of those two things, which tells you that spin really is like a kind of angular momentum. Fundamentally, theoretically, these really are related things. Like a particle has that kind of angular momentum, and so it's appropriate to call it spin. Yes, it's some kind of intrinsic angular momentum.

Like you can transfer angular momentum from the orbital kind to the spin kind and back, right? which tells you that they really are two kinds of the same thing. That in some way, the division between them is just in our minds. It's just mathematical. Oh, I see. So you're saying it's some kind of spin. It's some kind of rotation. Yes, exactly.

So it's like spin. It's like spin. Exactly. And so it's really tantalizing. I got you. I got you. You admitted on air that Jorge Chan was right. It should be called like spin.

It should be called like spin. I completely and totally agree with you. Your ego. But I guess the question is, like, so they decided to call it spin because it's sort of like it, like real spin. But I guess the question is, are these particles actually spinning? Right. And that's the fascinating part, is that they can't. I mean, particles are points, right?

They have no volume. We were talking earlier about the idea of a particle with a surface and maybe bits of it on the surface were spinning. Like the surface was rotating and the bits of charge were moving in a circle to generate. magnetic field. That's hogwash. Like, that can't happen because particles don't have a size, right? Electrons, as far as we know, has zero size. Like, the one side of it is exactly the same place as the other side of it. So there's nothing to spin. You can't turn around a point. It has no direction. It's like a vector of zero length. Like, there's no distance between one end of the particle and the other end of the particle for them to be sort of moving in different directions, right?

exactly because it's a point particle yeah you spin the particle and it's exactly the same as it was before right there's no direction to it right but well isn't it kind of

maybe a philosophical question like maybe a particle a point can't spin who says a point can't spin you just can't see it I just said it that's not enough for you I'm only a like physicists

you're well liked Daniel no imagine a vector right imagine a vector right which is a length and a direction, okay? Right. That can spin, right?

You can turn it 90 degrees or 180 degrees or whatever. Like an arrow, right? Like an arrow, exactly. But if an arrow has zero length, what direction is it pointing in? The one that I tell. The one that it decides to have. I don't know. It's this quantum stuff.

No, it has no direction. It has no length. It can't have a direction, right? Because a direction would imply a length. Right. But you're sort of telling me that it does kind of have a direction, right? It kind of has like spin. Yeah, it has some property.

It can't spin physically, like it can't spin in the way that we would spin a tennis ball, right? Definitely cannot do that. Also, there's other problems. Like, if you imagine an electron, if you say, well, we don't really know maybe an electron does have a size, right? You haven't seen it, but maybe it does. Well, you know, if you say we know the size electron has to be less than like 10 to the minus 20 meters, because that's the best resolution we have on our biggest particle accelerators. And then you calculate, like, well, how fast would the surface the electron be spinning?

will it be spinning faster than the speed of light. So it's definitely not happening. These are not tiny little actually spinning balls, right? But this always happens when we try to describe something quantum mechanical in terms of something that's not, right? You have the tennis ball or the baseball spinning in your head and you're trying to use that as the model. And it works for a while until it doesn't.

And it doesn't work because this thing is not a tiny ball, right? It's some weird thing. It has some weird property. The amazing thing is this spin property, is really similar to this other thing we do understand. Right. I think maybe the problem is that you're saying that, like, position-wise, like, where its constituent matter is can't rotate in space, right?

That's right. But you're saying that it has other properties other than position of its constituent matter that do sort of have a preferred direction. Yes, exactly. That's why we call it intrinsic spin, because it has some property which is very similar mathematically to spin but we know it's not actually spinning

so like intrinsic is like is the physics version of like right because well it's intrinsic spin it's like some kind of spin right so you're saying that it's a point but it is kind of spinning I'm saying it's a point and it has some weird property

which is related to physical spin but is not but mathematically it's kind of equivalent before we keep going let's take a short break December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed.

There's been a bombing at the TWA terminal. Apparently, the explosion, actually. impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and Order Criminal Justice System is back. In Season 2, we're turning our focus to a threat that hides in plain sight.

That's harder to predict and even harder to stop. Listen to the new season of Law and Order. Border Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her.

Now he's insisting we get to know each other. I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. It's even more likely that they're cheating. He insists there's nothing between them.

I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcast, or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the psychology podcast. Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills, and I get eye rolling from teachers or I get students who would be like, it's easier to punch someone in the face.

When you think about emotion regulation, like you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome as a result of it, if it's going to be beneficial to you. Because it's easy to say, like, go blank yourself, right? It's easy. It's easy to just drink the extra beer. It's easy to ignore, to suppress, seeing a colleague who's bothering you and just, like, walk the other way. Avoidance is easier.

Ignoring is easier. Denial is easier. Drinking is easier. Yelling, screaming is easy. Complex problem solving, meditating, you know, takes effort. Listen to the psychology podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. It's really quite fascinating and it's amazing to look at the history

because they did these experiments in the 20s and the 20s was also when they were figuring out quantum mechanics they were like, how does this thing work? And they were still trying to put the math together. And when they were trying to put together the math for relativistic quantum mechanics, that was like the quantum mechanics of tiny particles moving really fast, they discovered

it didn't work. It only worked if you added some new hidden variable to the electrons. Like, there had to be two kinds of them. Not just antiparticles and particles, but every electron also had to have

this other weird hidden property. And then they called it spin. And it's the same, it turned out to be the same spin that the other physicists were looking at? Yes, exactly. It all converged beautifully.

And they were like, cha-ching, look at this. Oh, my God. It all makes sense. Now we understand those experiments. Right. We're the spin master. So you need spin.

Like quantum mechanics doesn't work without spin. Like the Lorentz group and quantum field theory, all that has been deeply built inside of it. So we know it's a thing. And theoretically, it makes sense. What do you mean it needed like a hidden variable? What does that mean? Like it needed like an extra space,

like an extra variable attached to it in order for the math to like work out? Think about an electron as having labels, right? Like it has a certain mass. It has a certain position, it has a certain direction, whatever. Every electron also has to have this other label. You know, it's either up or down, right? And remember, this is spin, so it's not like you're spinning at some random speed. It's quantum spin.

So there's only two options, up or down. And so every electron has to have this weird label. You're spinning up or you're spinning down. And that makes a difference. Like when you fill out atomic orbitals, right, no two electrons can be in the same orbital because they're fermions. They don't like to share. but an electron that spin up is different from an electron that spin down.

So you can have two electrons in the ground state because they have this weird sort of hidden thing that's different about them. It's like black and the red. It's like the exception to the poly exclusion, right? It's like it lets you go around it, right? It's why you can have two atoms in the ground state where otherwise the poly exclusion principle we tell you you can't. It's because, well, they're not really in the ground state.

There's two ground states. You can have a ground state for up and a ground state for down, right? But it's not really up and down, right? It's only up and down if you measure it up and down. It's up and down along whatever direction you measure. So if you measure it in X, every electron will say, I'm up or I'm down. If then you measure it in Y, every electron will say, oh, I'm up or I'm down. But they get mixed up, right?

So they're quantum mechanically confusing because they're either up or down in X, and then later you're up or down in Y, which misses up or downness in X. it's very complicated. So you're saying that electrons can, like, talk? Essentially. It's a way to communicate, yeah. And this is why this comes up all the time in, like, quantum computing, because you can use electrons as sort of a cube bit, right?

Is it spin up or is it spin down? Electron can be in two states. And that's, like, a nice map from a classical bit, which is zero or one. So these quantum mechanical properties are nice because they have two states. So electrons are spin up or spin down. So that's why it comes up all the time. And also in quantum entanglement, like you have some particle create two electrons.

Well, to conserve angular momentum, one has to be spin up and one has to be spin down. Oh, really? Yeah. When you create them out of nothing or out of something else, they can't both come out at the same spin. Yeah, well, for example, Z bosons can have spin zero. What does that even mean, Daniel?

It has no thing which is not really like spin. It's actually even more complicated Z bosons have a total spin of one. That's like the length of their spin. But this is a vector so it can point to different directions, which means they have three waves to spin. So particles, like

electrons are called spin one-half particles. They have one-half of a unit to spin, which means they can be spin up one-half or down one-half. Z-bosons have spin one, right? So they can be spin plus one or minus one or zero. So Z-bosons have three

different ways to spin, whereas electrons have two ways to spin. It's pretty weird. It's considered like spin one way or the other way or not at all. Yes, exactly. But if you have a Z boson with spin zero and it decays into an electron and a positron, then one of them has to be spin up and the other one has to be spin down so that they add up to the original angular momentum of the Z boson, which was zero. What if a plus one divides? Then it turns into an electron and a positron which are spinning in the same direction. So those two one-haves add up to one. I'm going to pretend I understood that.

Well, that's the cool thing about it is that the math of this is really similar. You can use all the math you develop for like angular momentum and understanding spin orbitals and stuff like that. You can use that same math to understand spin, which is really compelling to me. It tells me that theoretically we're dealing with a very similar topic. Right. Or maybe the math we had to understand angular momentum matches the physics of quantum particles, right? Yes, exactly. When the math you're describing

matches the physics, then that's success, right? That says, oh, look, I've described it. I've gotten some insight. I mean, that's all we can ever do, is hope that the math describes the physics. Right. No, what I mean is, like,

maybe if you hadn't called it spin, you call it quantum blookety-blook, right? I'm reconsidering nominating you for that committee after that suggestion. What do you have against bluckety-blooks? I don't even know how to spell it, man.

Anyway, all right, so let's say we had quantum blook-de-blook. Yeah, and then later you find out that angular momentum behaves like quantum blook-de-blook, then that would be, which one would be more correct, right? Which one would be more correct? Well, if you're using the same math for both of them, then you're done, and it's really just a question of how you name it, right? In the end, it's the math, right? The physics is really about the math and not the names.

In the end, it's about the equations on paper and the structures and how we're thinking about it. So really you could have called it anything, but you picked spin because it's sort of related to something that we people had knowledge about or people have kind of intuitive understanding about. That's right. And because we think it really is a kind of angular momentum. What kind is it? And are these things really spinning? And why do electrons have intrinsic angular momentum? That we have no idea. But it seems to be necessary to make quantum field theory work. It seems to be a kind of angular momentum. It's definitely a real thing. but it's kind of a mystery and it's something I like to think about like what are you doing little electron why are you spinning this way what is making you generate that

magnetic field yeah exactly exactly well I guess so then the answer is what is quantum sin it's some property of electrons that sort of behaves similar to rotation but we don't really know what it is but it's there it's real

and it's definitely not actually spinning and it's not just electrons all particles have some kind of spin there's particles with half integer spin we call them fermions and all the matter particles are like that electrons and quarks and then there's particles with integer spin like bosons like photons and w's and zes and gluons and those kind of particles and that's actually the way we distinguish them right

fermions have half integer spin and bosons have integer spin so it's an important deal like in the particle world it's a big deal right and you meet a new particle you want to know what is it spin The Higgs, for example, is spin zero. It's the only particle we know that has no spin at all and never can spin. It's the only particle we've ever found that can never spin. Wow. Now you're just messing with basic arithmetic, man.

You're like, if it's zero, it can only be zero. If it's one, it can be zero and minus. You know what I mean? Like, you're using the same words to describe things. I mean, anyways. Okay, I should be more careful when I say what it means for a particle to have a certain amount of spin. When we say a particle spin one, what we mean is that the last. length of its spin vector is one.

Now that vector can point in different directions. Any individual particle can have spin plus one, zero, or minus one if it's a spin one particle. If a particle is spin one-half, that's like the length of its spin vector. Then its spin vector can point either plus one-half or minus one-half.

Those guys can't be zero. Cool. It's like arithmetic. It's not really arithmetic. Yeah, that's what I mean. It would just be so much easier to understand you guys. If you just said, instead of saying it's quantum spin, it's, It's like spin.

All right. I'm going to say it's like spin from now on. And we'll see how many weird eyebrow races I get in my physics conversations. Yeah, totally. Well, you'll probably get weird eyebrows in your physics department. But I'm saying if you're talking to people out there in the street. Are you suggesting there's like more unibrowes in the physics department than in your average street? More unibrous.

What? Weird eyebrows, man. All right, well, that's what quantum spin is. I know it's confusing and it's complicated, but we hope we at least brought you up to speed to where the physics community is. And remember, even physicists, we don't really know what quantum spin is.

And all those grad students I asked, how would you explain quantum spin to a random person on the street? They got themselves tangled up by their tongues as well. So it's a confusing topic. But if you still have questions about quantum spin, send us an email to feedback at danielanhorpe.com. That's right. You can even send us like emails.

or like questions. Or emails about how much you like us. See you next time. If you still have a question after listening to all these explanations, please drop us a line we'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge, that's one word, or email us at Feedback at Daniel and Jorge.com. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio.

For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever. you get your podcasts.

My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast and the IHart Radio app, Apple Podcasts, or wherever you get your podcasts.

The U.S. Open is here and on my podcast, Good Game with Sarah Spain. I'm breaking down the players, the predictions, the pressure, and of course the honey deuses, the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very wonderfully experiential sporting event. To hear this and more, listen to Good Game with Sarah Spain and IHart Women's Sports production in partnership with deep blue sports and entertainment. on the IHeart radio app, Apple Podcasts, or wherever you get your podcasts. Brought to you by Novartis, founding partner of IHeart Women's Sports Network. This is an IHeart podcast.