Chen Ning Yang — The Man Who Unlocked Symmetry (EP. 14)

Hosted by Lester Nare and Krishna Choudhary, this episode tells the story of Nobel laureate Chen Ning Yang and how his ideas on symmetry and gauge theory transformed modern physics. Summary • Early Years & Mentorship: From China to Chicago — learning under Fermi and Chandrasekhar. • Parity Violation: How Yang & Lee overturned the mirror-symmetry assumption and changed physics forever. • Gauge Symmetry & Yang-Mills Fields: The foundation of the Standard Model of particle physics. • Legacy & Philosophy: Why Yang saw beauty as nature’s signature and symmetry as its language. Show Notes • Nobel Prize in Physics 1957 — Chen Ning Yang & Tsung-Dao Lee • Original Yang–Mills Paper (1954, Physical Review) • Madame Wu’s Parity Violation Experiment (1957) • Biography of Subrahmanyan Chandrasekhar (University of Chicago)

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Lester Nare?

  Ciao, Internet. This is your captain speaking, Lester Nare, joined as always by my co-host and our resident PhD, Krishna Choudhary. This is From First Principles.

• 0:26Lester Nare?

  My friend.

• 0:27Krishna Choudhary?

  How's it going?

• 0:28Lester Nare?

  We have some travel coming up, and so we want to do a quick special episode for this upcoming week, which just so happens to be when the World Series is happening. And so, as you can see, we've prepared accordingly with our Japanese otani jersey, with our Dodgers memorabilia hat, because we know the Dodgers are going to be back-to-back World Series champions.

• 0:50Krishna Choudhary?

  That's right. I mean, we're recording this a week before the World Series, but we already know how it's gonna go down.

• 0:55Lester Nare?

  We already know how it's gonna go.

• 0:56Krishna Choudhary?

  Yeah, it's gonna go down. I mean, we're going up against Canadians.

• 1:00Lester Nare?

  Look, having been on both sides of the pond, born in Montreal, living in the States.

• 1:06Krishna Choudhary?

  You're literally kind of Canadian, but you know, you know what I mean?

• 1:08Lester Nare?

  It's not the same thing. It's not the same thing. We are going to win. But because of our sort of travel schedule, we're gonna do a special episode that's focused on one story. And this story actually comes from a direct message, a DM. Someone slid into the DMs on TikTok, and they mentioned the recent passing of a physicist named Chen Ningyong.

• 1:34Krishna Choudhary?

  Yep.

• 1:35Lester Nare?

  And people are saying he's one of the most influential physicists of the 20th century. And I was unfamiliar with the game, did a little bit of digging. And some of the names that people associate in terms of the class he belongs in include Einstein, Bohr, Heisenberg, Feynman, high praise.

• 1:56Krishna Choudhary?

  Yeah, yeah.

• 1:57Lester Nare?

  Very, very high praise.

• 1:59Krishna Choudhary?

  Yeah.

• 1:59Lester Nare?

  So are we really saying that Yang can be associated in that class of sort of untouchables when it comes to sort of? Physicists who are above reproach in terms of what they've provided over the course of their careers in knowledge and expertise in Nobels.

• 2:19Krishna Choudhary?

  And, I mean, he won the Nobel Prize, but, and everybody talks about that, right? There's a BBC article that came out on his death and it said, you know, Chinese Nobel laureate and physicist Chen Yung dies at the age of 103. That BBC article mostly talks about his Nobel Prize, which was given for discovering the theoretical foundations for something called parity violation, which is what we're going to get to. But that's not actually why he's considered one of the greatest

• 2:49Lester Nare?

  Okay.

• 2:49Krishna Choudhary?

  of the 20th century. I mean, as you said, the 20th century has some of the most influential physicists of all time. Einstein, Bohr, Heisenberg. These are the people who not only contributed to our understanding of the modern world, but totally reshaped how we think about doing physics in the first place. Right? And Yang is one of those people who completely kind of changed the, the way in which we think about trying to do theoretical physics, you know, as theoretical physicists do. And, and he came up with, the thing that really immortalized him was this formulation

• 3:30Krishna Choudhary?

  of something called non-abelian gauge theory, which is known as Yang Mills theory.

• 3:36Lester Nare?

  I remember hearing, oh, gauge theory, gauge theory all the time.

• 3:39Krishna Choudhary?

  This is the guy who kind of started that whole thing. Okay. Yang Mills theory, and you know, in physics circles, we just say Yang Mills theory. It's, it's a bedrock foundation for the standard model, which is one of the most successful theoretical ideas that we've had as human beings. Okay? And. It's rooted in this idea of symmetry, okay? So in this episode, what I really want to do is go through some of Yang's work and talk about symmetry as a principle and how that relates to the to the modern world. Now symmetry, everybody knows what symmetry is, right? The my favorite symmetric object is the Taj Mahal in India.

• 4:22Krishna Choudhary?

  The first time I saw it was actually, I was quite old, even though I was grew up and grew up and was born in India, I didn't see it until after college. And it is one of the most beautiful buildings I have ever seen on planet Earth. And all of that has to do with symmetry. If you look at the Taj Mahal, right? It's an extremely symmetric building. And we kind of know what that means, right? We have this deep sort of intuitive sense that symmetry means balance, beauty, harmony, right? But when we think of symmetry, we think of it as a static property. It's something that we're looking at for a static object, right?

• 5:04Krishna Choudhary?

  But what do we actually mean when we say symmetry? The idea is, and this is something that the great mathematician Hermann Weyl came up with. The idea of symmetry from a mathematical sense is that a thing is symmetrical if there is something we can do to it so that after we have done it, it looks the same as it did before.

• 5:28Lester Nare?

  This is a tongue cluster.

• 5:30Krishna Choudhary?

  It is, but here's what's happening. You've got a thing that is symmetric. What does that mean? That means I can do something to it. And when I'm done doing it, it looks just the same. The Taj Mahal, here's an example, right? Imagine the Taj Mahal in your head.

• 5:44Lester Nare?

  Yes.

• 5:44Krishna Choudhary?

  Flip it. Flip it along the X Y plane.

• 5:47Lester Nare?

  Yes.

• 5:48Krishna Choudhary?

  Not on the X Y plane, on the vertical, right?

• 5:50Lester Nare?

  Yes.

• 5:51Krishna Choudhary?

  So so everything that's on the left goes to the right. So those spires on the left go to the spires on the right. The dome is exactly symmetric to the central axis. The two little domes on the side are symmetric, so they just flip around. So you can imagine if I were to take that photo of the Taj Mahal and then flip it. Right along the middle, I would get the same exact Taj Mahal. That means that it's symmetric.

• 6:14Lester Nare?

  Okay.

• 6:14Krishna Choudhary?

  Does that mean?

• 6:15Lester Nare?

  Yes.

• 6:15Krishna Choudhary?

  Does that make sense?

• 6:16Lester Nare?

  Yes.

• 6:16Krishna Choudhary?

  It's symmetric upon reflection of that central axis.

• 6:19Lester Nare?

  Yes.

• 6:19Krishna Choudhary?

  Now, there's other kinds of symmetry and, and we're used to it. They're like, for example, there's shapes that we can do. And what we can do is not just reflecting along the central line. We can reflect along many lines. For example, the heart, the heart shape, you can reflect along the central line. The butterfly, you can reflect along the central line and the, and the, the wings will go from one to the other. A square, you can reflect along the central line on both axes and also along the diagonals. And the square is going to come back to be the same square. Okay. There's another way to do symmetry, not just with the reflections. You can also do rotations of objects. If you look at like the red cross, the cross of the red cross. Or the thing that's in the middle of the Swiss flag. Right?

• 7:01Krishna Choudhary?

  You can rotate that cross 90 degrees and it'll be the same cross. Right? But if you take an arrow and you rotate it, it's going to point the other direction. Right? It's going to point from up to left or whatever. However, however you do the, the 90 degree rotation. So in that sense, we kind of know what symmetry means for, um, objects, like thingies.

• 7:24Lester Nare?

  Right.

• 7:25Krishna Choudhary?

  Right? 2D things, 3D things, you can even think about a sphere, right? You can rotate a sphere in any direction and it's a continuous symmetry. Because no matter how you rotate the sphere, it's still going to be a sphere.

• 7:36Lester Nare?

  And you can do similarly with a cube, but only not in any direction, but in certain explicit.

• 7:41Krishna Choudhary?

  Yes.

• 7:42Lester Nare?

  Degrees of rotation.

• 7:43Krishna Choudhary?

  Yeah. And actually the five platonic solids that are our logo.

• 7:47Lester Nare?

  Yes.

• 7:47Krishna Choudhary?

  You can, you can rotate them in three dimensions and you'll come back with the same exact platonic solid.

• 7:53Lester Nare?

  Yes.

• 7:53Krishna Choudhary?

  Right? So we're, we're used to objects being symmetric. But in the early 1900s, there was talk about maybe there's symmetry in the physical laws themselves.

• 8:06Lester Nare?

  Okay.

• 8:07Krishna Choudhary?

  Okay? There's stuff you can do to physics laws that leave the physics laws exactly the same.

• 8:14Lester Nare?

  Okay.

• 8:14Krishna Choudhary?

  Okay?

• 8:15Lester Nare?

  Okay. I hear what you're saying.

• 8:16Krishna Choudhary?

  Yeah. So let's, let's, let's dig into that. This was actually first, um, first sort of codified by, um, someone by the name of Emmy Noether, who was a mathematician from Gottingen. She was actually like, she.

• 8:35Krishna Choudhary?

  People didn't want to publish her because she was a woman. So she would publish under her supervisor's name. But there's a theorem called Noether's theorem, which basically codifies this idea that there's something I can do to physical laws that will preserve the action of the physics underlying it. There's, we've actually like, it's quite intuitive at the start. Okay, there's a translation in space. That's a symmetry. For example, the laws of physics are the same here as they are anywhere else in the universe.

• 9:13Lester Nare?

  We've talked about this.

• 9:13Krishna Choudhary?

  So if I, yeah, and we've talked about this before. If I set up an experiment here in one lab and I do somethingy and I measure somethingy. And then I go all the way across the United States to the East Coast. And I set up the experiment. I'm going to measure that same thingy, right?

• 9:30Lester Nare?

  This is, LIGO is a perfect example of this.

• 9:32Krishna Choudhary?

  Yes, exactly. There's one on Livingston, there's in Louisiana, and there's one in Hanford in Washington. They're both operating the same way. This LIGO wouldn't be possible if translation in space wasn't a thing.

• 9:44Lester Nare?

  Right?

• 9:45Krishna Choudhary?

  Yes. Right? And but there's an inherent assumption there that because we're on two separate parts of Earth, the Earth is not really part of the experiment. Right? We're doing enough to cancel out the stuff of Earth and like that local environment to really focus on the physics that we want. And because of the translation symmetry of physics, that experiment in Louisiana is the same as the experiment in Washington. Right? That's a translation in space.

• 10:16Lester Nare?

  Okay.

• 10:17Krishna Choudhary?

  There's also a translation in time, which means if I do an experiment now and then I don't change anything and then I do an experiment, you know, tomorrow or a month later, as long as it doesn't somehow depend on the Earth's position in the solar system or something like that. Obviously, if you're trying to like measure stars or something, yeah, you're not gonna.

• 10:39Lester Nare?

  Sure.

• 10:39Krishna Choudhary?

  Yeah, you know, but. If you're doing something with subatomic particles or like gravitational waves, then yeah, whatever, whatever thing I'm doing now is the same as what I'll be doing tomorrow is the same as what I'll be doing in a month and so on and so forth.

• 10:54Lester Nare?

  Is this the kind of the where this idea of longitudinal longitudinal studies come from? Where you have this long period of time where you're just replicating the same experiment in order to see the impacts like over generational differences or any other kind of category. But because you have this symmetry in time.

• 11:11Krishna Choudhary?

  Yeah, yeah, yeah. You at least can trust that the laws of physics are changing, right?

• 11:16Lester Nare?

  That's not a variable you have to account for.

• 11:18Krishna Choudhary?

  If that weren't true, then it's like whatever thing you're doing, it's like, oh, well, you did it a month later, right? So, so, so there is this, there is this like underlying notion that whatever the laws of physics are today are going to be the same as the laws of physics tomorrow and the day after, right? And another one is the rotation in space. Okay, if I have, if I have an apparatus that's oriented this way and then I just rotate the whole thing, as long as like I rotate everything that has to do with my experiment, my experiment should yield the same results, right?

• 11:56Lester Nare?

  Makes sense.

• 11:56Krishna Choudhary?

  So all of these things are symmetries. The fact that I can change my experiment in a way, but the physics remains the same. This is underlying like, you know, the fact that I can replicate experiments. And if I do an experiment and I publish something with all the methods, somebody from the other side of the world can actually replicate that experiment.

• 12:14Lester Nare?

  It's the bedrock of the scientific process.

• 12:15Krishna Choudhary?

  It is, it is, and, and, and it's been shown to be true. There's so many experiments that show that, you know, this is the laws of physics. There's no special point in space and time or direction in space and time that like yield different laws of physics, right? Emmy Noether, in Noether's theorem, what she actually showed was if we take, if we take the assumption that physics is the same after these translations, that then something must be conserved. Every single time that we have this symmetry. That's something that we can tackle in a later episode. And actually prove Noether's theorem. It's a beautiful proof. And it's quite intuitive.

• 12:56Krishna Choudhary?

  But at the end of the day, what ends up happening is any symmetry is associated with a conservation law. So for example, the fact that I can translate in space, meaning I do an experiment here, then I do an experiment somewhere else. And the physics laws are exactly the same. That leads to a conservation of momentum. Okay.

• 13:15Lester Nare?

  Yes, yes.

• 13:15Krishna Choudhary?

  In any situation.

• 13:16Lester Nare?

  Right.

• 13:18Krishna Choudhary?

  If I do an experiment today and then I do it tomorrow and the, and, and the week after and the month after. And all of the laws of physics are the same. That leads to a conservation of energy. Okay. If I do an experiment here and I change the rotation where I rotate my entire experimental apparatus and I do it again. And the laws of physics are the same. That leads to the conservation of angular momentum. Right? It's a deep, deep notion that we have. Okay, this was in the early 1900s where Emmy Noether came up with this.

• 13:49Lester Nare?

  I've never understood it intuitively because we've talked about all three of the, we've talked about conservation of angular momentum quite a bit. We've talked about the conservation of energy. And, and the conservation of momentum. And I've never understood it intuitively in this context of if you're doing your experiment here today and there tomorrow. There it like it.

• 14:12Krishna Choudhary?

  There is no difference.

• 14:13Lester Nare?

  There's means there.

• 14:14Krishna Choudhary?

  Yeah, yeah.

• 14:15Lester Nare?

  Have to be.

• 14:16Krishna Choudhary?

  Yeah.

• 14:17Lester Nare?

  That's, it's, that's actually very, I just had a light bulb go off in my head.

• 14:21Krishna Choudhary?

  It's, it's so deep, dude.

• 14:22Lester Nare?

  Yeah.

• 14:23Krishna Choudhary?

  To think about, right? That like really like these laws that we have, these rules that these numbers are never going to change in any given setup. Has to do with the fact that the universe wants to conserve the laws of physics regardless of these transformations.

• 14:38Lester Nare?

  Right.

• 14:39Krishna Choudhary?

  Right? It's, it's a very deep statement to make.

• 14:42Lester Nare?

  Yes.

• 14:43Krishna Choudhary?

  Okay, and that's something that Emmy Noether came up with. With Noether's theorem. Now, she did that for classical mechanics. This is before the quantum revolution and things like that. And Hermann Weyl was one of her colleagues at Gottingen. He thought this was one of the. Craziest things he's ever heard, right? The fact that you can connect like an action on the physical laws to a conservation of the physical laws themselves. And he started going further with the new quantum revolution and trying to put that into this same language.

• 15:16Lester Nare?

  Okay.

• 15:17Krishna Choudhary?

  And turns out it gets even deeper when you go into quantum mechanics. In quantum mechanics, for example, you know, everything is a wave function, right? Whatever, whatever that means. But what gets even weirder is that wave function is a complex number. Okay. It's a complex number, which means it has a magnitude and it has a phase. It has a phase with respect to like the some kind of zero, some zero that you arbitrarily choose. That complex number has, it's like a clock hand, right? It's got a length and it's got an angle. Well, according to quantum mechanics, what are the observables? The observables are probabilities of outcomes of experiments.

• 16:00Krishna Choudhary?

  And that comes from taking the magnitude of this complex number, the magnitude meaning only the length. So the, the, the phase actually doesn't matter when it comes to things that we can see, right? Which means if I, if I take an electron, for example, and I change the phase everywhere for that electron all over the universe, right? Cause this wave function is everywhere. That's not going to change the outcome of my experiment. If I add a phase or I subtract a phase, if everywhere I'm just like making the clock go a little bit, a little bit, that's not going to change whatever thing I observe.

• 16:35Lester Nare?

  Right.

• 16:36Krishna Choudhary?

  Okay. And it turns out that that symmetry has to do with the conservation of charge. The fact that I can't create a positive or a negative charge anywhere.

• 16:45Lester Nare?

  Hmm.

• 16:46Krishna Choudhary?

  It's crazy, right? So this is getting real interesting.

• 16:50Lester Nare?

  Interesting.

• 16:51Krishna Choudhary?

  This is getting really, really interesting.

• 16:54Lester Nare?

  Okay, please continue, right? Because it's now it's again, now from that foundation, I'm extrapolating to a variety of other things we've talked about before that are making even more sense, understanding this like correlation or this relationship.

• 17:09Krishna Choudhary?

  Yeah, it's, I mean, physics is is getting really weird and really beautiful at the same time, right? It's like, oh, it's getting weird. In any case, let's talk about, okay, so we've talked about symmetries, right? And like, the laws that are, laws are going to be the same no matter what I do.

• 17:27Lester Nare?

  Yes.

• 17:28Krishna Choudhary?

  Okay.

• 17:28Lester Nare?

  Well, both in a classical sense.

• 17:30Krishna Choudhary?

  And, and we've just touched upon the quantum, quantum sense of things, right?

• 17:36Krishna Choudhary?

  So let's talk about something that does break symmetry, because not every transformation is going to preserve the laws of physics. For example, if you do a change of scale, right? Suppose I make my experiment and it's like, you know, one meter by one meter or whatever, and then I just like increase the the size of my experiment. Am I going to get the same physics? The answer is no, because nature does have a fundamental scale, right? There are such things as atoms, and those atoms are about 10 to the minus 10 meters big, like one angstrom, right? So to make my thingy bigger, I need to use more atoms, and that's going to change the physics of my apparatus. So the physics of scale of stretching and squishing is not a symmetry of the universe,

• 18:21Krishna Choudhary?

  because there is a fundamental scale. The other way, when I was saying, like, you know, the symmetry of time, there's no T equals zero. I guess there is when it comes to the Big Bang, but when it comes to experiments that I do in the lab, there's no T equals zero.

• 18:35Lester Nare?

  In the perception of the way we understand and see the universe, it's a little bit of a different context.

• 18:39Krishna Choudhary?

  Yeah, that's a little bit of, in cosmology, there's a little bit of a different context, right? There is such a thing as T equals zero. But in in the scale of like, experiments that I want to do in the lab, there isn't. There's no X equals zero, Y equals zero. There's no like, origin for the universe. So I can shift my experiment anywhere and the translation of space is going to work. But there is a fundamental scale, right? That has to do with like, how Big atoms are, if you want to get really, really nitty gritty about it, there's a fundamental scale that's the plank length. That has to do with like how big, how, how, how, you know, close I can get electrons before they turn into black holes.

• 19:15Lester Nare?

  Yes.

• 19:15Krishna Choudhary?

  But, but there is such a thing, right? There's some meter stick.

• 19:18Lester Nare?

  Yes.

• 19:18Krishna Choudhary?

  That, that's here. And so this is actually something that was first found by Galileo. Um, in Galileo's Dialogue Concerning Two New Sciences, he published this thing. He had a really funny cartoon. He, he, he thought about like animals and what would happen if I had like a Clifford sized dog?

• 19:35Lester Nare?

  Okay.

• 19:36Krishna Choudhary?

  Okay. Remember Clifford, the big red dog? Yeah. So it's like, I got, I got a normal dog and then I got a Clifford sized dog. What would happen? Well, the Clifford sized dog, um, your, your mass, your weight scales like your volume, right? So it's going to go like the length cubed.

• 19:52Lester Nare?

  Okay.

• 19:52Krishna Choudhary?

  Right?

• 19:53Lester Nare?

  Yes.

• 19:53Krishna Choudhary?

  Uh, the, how much stuff you have goes like length cubed because volume goes like length cubed. On the other hand, tensile strength goes like length squared because it has to do with the cross sectional area of your bone.

• 20:05Lester Nare?

  Yeah.

• 20:06Krishna Choudhary?

  You noticed that?

• 20:08Lester Nare?

  So I was just watching a video about this person hanging from rubber bands and seeing how many rubber bands it took to hold their weight up. And part of the discussion was about the tensile strength that is in the rubber bands in order to enable.

• 20:20Krishna Choudhary?

  Yeah, exactly.

• 20:21Lester Nare?

  Holding it up.

• 20:21Krishna Choudhary?

  Yeah, exactly. Like if he had, that guy, if he had a chain of rubber bands, that wouldn't really help him.

• 20:26Lester Nare?

  Right.

• 20:27Krishna Choudhary?

  On the other hand, if he had a bunch of rubber bands in parallel, that would help him.

• 20:31Lester Nare?

  Exactly.

• 20:31Krishna Choudhary?

  Because the rubber bands in parallel would increase the, the cross sectional area of how much is holding you up.

• 20:38Lester Nare?

  Bingo.

• 20:38Krishna Choudhary?

  Right? And so, um, Galileo has this really cool cartoon of like what, what a super dog bone would look like compared to a normal dog. Where the normal dog is like this, like small bone, and this is one of his drawings. And then the super dog bone is just massive, but not so much scaled in the, in the, along the bone length, but like the air, the, the thickness.

• 21:00Lester Nare?

  Yes.

• 21:00Krishna Choudhary?

  Of the bone is way bigger.

• 21:02Lester Nare?

  The girth one would say.

• 21:03Krishna Choudhary?

  Exactly. The girth of that bone is way bigger and that's where he scaled it. And he's like, if I wanted a super dog.

• 21:09Lester Nare?

  Yes.

• 21:09Krishna Choudhary?

  Or whatever, Clifford, the big red dog, that guy's bones would be, would be really thick. Because it needs to hold up the weight of the dog, right? I don't know why he chose dog, but anyways, maybe he had affinity to dog, dogs, who knows?

• 21:23Lester Nare?

  Look, I have three dogs, so I also have.

• 21:25Krishna Choudhary?

  I love dogs. So yeah, yeah. I, I get it. I get it. If, if he had cats, he would not be my favorite. Nothing against cats. Nothing against Schrodinger. I'm sure, but I'm sure there's, there's cat lovers in the audience. I'm just not a cat person. Okay, here's another broken symmetry, right? We can think about motion. Okay, what if I, what if I, what if I put my experiment? Right? I'm doing some experiment and then I put my experiment on a spaceship that is moving at a constant velocity.

• 21:59Krishna Choudhary?

  Actually, according to Galilean relativity and later Einstein's relativity, my experiment on that moving spaceship that's going at the, on a, in a straight line at constant velocity is going to have exactly the same results as my experiment that's on the ground that is stationary, whatever that means, because turns out if, if I can't tell in my spaceship, I can't do any experiment that tells me if I'm moving and somebody else is stationary and so on and so forth, right? If both of our experiments are exactly the same, I can't tell who's moving and who's stationary. All I can say is somebody is moving relative to me. That was the big, you know, light bulb of Einstein to say that that's actually true. What are the consequences of that? Right?

• 22:42Krishna Choudhary?

  That's something called a Lorentz transformation. So that's, that's a symmetry of the universe. The fact that I can boost myself into a reference frame where I'm moving in a constant velocity, but my laws of physics won't change. On the other hand,

• 22:56Krishna Choudhary?

  you can think, okay, what about if I'm rotating at a constant angular velocity? Is that a symmetry? What that means is if I'm in a spaceship, that's, that's just, let's say stationary, whatever that means. And I do an experiment and then I put myself on a rotating reference frame, for example, the earth. Yes. Right? But take out gravity, somehow I'm rotating, but there's no gravity. Yes. Would the experiment be the same? The answer is no. The answer is no. And I mean, have you been to Griffith Observatory? Yes. Have you seen the big pendulum from the, from the ceiling down? That's called Fokker's pendulum. That's a great example of a pendulum that is behaving differently because it's on a rotating reference frame.

• 23:41Krishna Choudhary?

  Because it's on a rotating reference frame, the pendulum is going to rotate. Within itself and knock over those little tiny

• 23:49Lester Nare?

  Yes.

• 23:49Krishna Choudhary?

  Uh, thingies.

• 23:50Lester Nare?

  Yes.

• 23:51Krishna Choudhary?

  And like showed that the earth is rotating. That was one of the first big, you know, proofs that the earth is really rotating.

• 23:57Lester Nare?

  And you're visually kind of showing that there's like this basin, right? Where there's this pendulum that's floating like imagine a clock, but like it's now as it's as the earth rotates, the pendulum will move to different hours on the clock.

• 24:11Krishna Choudhary?

  Mm hmm.

• 24:12Lester Nare?

  Uh, because that reference frame is changing.

• 24:14Krishna Choudhary?

  Exactly.

• 24:15Lester Nare?

  Uh, just in terms for the listeners visually, like that's what you're describing.

• 24:19Krishna Choudhary?

  Yeah.

• 24:19Lester Nare?

  The rotation makes it so that if the pendulum starts going from 12 to six, as the earth rotates, it's now going from one to seven.

• 24:27Krishna Choudhary?

  Yeah.

• 24:27Lester Nare?

  Two to eight, whatever it might be.

• 24:29Krishna Choudhary?

  Yeah, exactly. And it goes at different, it goes at different speeds based on how far up you are on the earth in terms of um, latitude.

• 24:36Lester Nare?

  Yes.

• 24:36Krishna Choudhary?

  You know, so that is not asymmetry.

• 24:40Lester Nare?

  Right.

• 24:40Krishna Choudhary?

  Okay. Like the fact that I can just like, I can't just take my experiment and start rotating it at a constant velocity. I can turn it and then do stuff. That's, that gets me angular momentum, but I can't like constantly be rotating. Okay?

• 24:55Lester Nare?

  Oh, interesting.

• 24:56Krishna Choudhary?

  Right?

• 24:57Lester Nare?

  Yeah.

• 24:57Krishna Choudhary?

  So, so, so these, so not everything is allowed.

• 25:00Lester Nare?

  Right.

• 25:00Krishna Choudhary?

  By the universe.

• 25:01Lester Nare?

  Right.

• 25:01Krishna Choudhary?

  Okay, certain things are allowed and certain things are not allowed.

• 25:05Lester Nare?

  The admin, the admin exposed some parameters that are

• 25:08Krishna Choudhary?

  Yeah.

• 25:09Lester Nare?

  Yeah, but it's like not, not, not all of them.

• 25:11Krishna Choudhary?

  Not all of it. Yeah, exactly. And so um, in the, in, in the early 1900s, the question started becoming, what are the things that are allowed and what are the things that are not? We've already talked about how uh, translation in space is allowed, so I can move my apparatus from here to there. I can move my apparatus in time, so I can do stuff here. I can do stuff tomorrow and it'll be fine. I can rotate it and it'll be fine. What about parity? Okay, the question of the, the question is, are the laws of physics ambidextrous? Meaning?

• 25:44Krishna Choudhary?

  Does the law of physics, do the laws of physics distinguish left from right? Okay, like the Taj Mahal. The Taj Mahal does not distinguish left from right, right? I can flip the Taj Mahal in the mirror and it'll look exactly the same. If I, if I put a giant mirror in front of the Taj Mahal, right? And then I, I got somebody to, to be in the garden of the Taj Mahal and he's looking one way and he's looking the other way. If the mirror is big enough and if he's not allowed to move around, he could not tell which one's the real Taj Mahal and which one's the fake Taj Mahal. Because the Taj Mahal is symmetric under inversion, right?

• 26:26Krishna Choudhary?

  The question is, can someone devise a physics experiment to show that we are not doing that? Okay, and this is something that I've borrowed from Feynman. He, he proposed a thought experiment. He said, suppose we're making a clock.

• 26:41Krishna Choudhary?

  Okay, we're making a clock that's normal, so it's gonna go, you know, clockwise?

• 26:45Lester Nare?

  Yes.

• 26:45Krishna Choudhary?

  Okay, and now I make a clock with, that, that looks like my grandfather clock, but in the mirror.

• 26:53Lester Nare?

  Right, so we're seeing, we're seeing an image with two clocks, one that looks like a normal clock where the 12, the 3, the 6, the 9, look like normal numbers.

• 27:01Krishna Choudhary?

  Look like normal numbers and the, the, the hand is gonna go from the 12 to the, yeah.

• 27:05Lester Nare?

  And then there's a second clock that's basically inverted.

• 27:08Krishna Choudhary?

  It's the inverse, so, so the 12 is flipped, the 3 is where the 9 should be.

• 27:12Lester Nare?

  Yes.

• 27:13Krishna Choudhary?

  The 9 is where the 3 should be.

• 27:14Lester Nare?

  Yes.

• 27:14Krishna Choudhary?

  And then the, the hand goes from the 12 to the inverted 3.

• 27:18Lester Nare?

  3 to the left, it's rotating counterclockwise instead of clockwise.

• 27:22Krishna Choudhary?

  Instead of clockwise, right? So he's like, can I, can I make a clock like that? Okay, this was part of his Feynman Lectures of Physics, which I'm a huge fan of. Um, so, how do we make such a clock? Well, we gotta be really careful, okay? For example, even the screws, all of the screws are right-handed on our grandfather clocks, right? Because in America, and I think across the world, right? Righty-tighty, lefty-loosey. I think that's just a standard all over the world now. But that's just a human convention. If I wanted to make a truly symmetric mirror image clock, I'd have to, I'd have to call up my guy and have him make left-handed threads, which is like probably super hard because

• 28:06Krishna Choudhary?

  the thingy that's making the thread is itself right-handed. So you'd have to make like custom equipment and all, he'd probably have to 3D print or something like that. But if we did, let's say we, let's say we went through all of that trouble.

• 28:20Lester Nare?

  Yes.

• 28:21Krishna Choudhary?

  Okay? And we made a mirror image clock.

• 28:24Lester Nare?

  Yes.

• 28:24Krishna Choudhary?

  Okay? Would that clock go exactly like the mirror image of my?

• 28:31Lester Nare?

  Normal clock.

• 28:31Krishna Choudhary?

  Normal clock? And intuitively, it seems yes, right?

• 28:36Lester Nare?

  I mean, without thinking too hard about it.

• 28:38Krishna Choudhary?

  Without thinking too hard about it, honestly, like, it does seem yes. Honestly, like if, if the gears are tuned different, if the screws are tuned different, if everything is reversed, then of course the clock is gonna go in reverse, right? And, and that was, that was the way to do it for the longest time. And another, another way to think about this, this parity symmetry, right? We just talked about like, the clock is really a microcosm of like, can I make an experiment that goes one way or the other, right? That can tell the difference. If the clock does in fact do something different, then that means the universe does care about left or right, right? But in this case, I mean, we're pretty convinced that like the clock is gonna, right?

• 29:21Krishna Choudhary?

  All it's relying on is gravity, if there's a pendulum, and then like electromagnetism, which is just like the atoms pushing up against other atoms to like make the gear turn and you've got some motors. I guess not a motor, right? Cause the pendulum is providing the...

• 29:36Lester Nare?

  Yeah.

• 29:37Krishna Choudhary?

  In any case, it seems like it should work. Another experiment that I thought was really cool that I found in his, in his lectures was the alien thought experiment, okay? So here's the challenge. You're on the phone, somehow the aliens have contacted us?

• 29:50Lester Nare?

  Yes.

• 29:50Krishna Choudhary?

  Okay, this is your dream.

• 29:52Lester Nare?

  Yeah. Look, I'm trying to set it up.

• 29:55Krishna Choudhary?

  Yeah.

• 29:56Lester Nare?

  I'm trying to set up the group chat right now.

• 29:57Krishna Choudhary?

  Yeah, yeah, so, okay, imagine we're on a group chat, okay? We can't send them any photos.

• 30:02Lester Nare?

  Okay.

• 30:03Krishna Choudhary?

  Okay, all we can do is like chat with them.

• 30:05Lester Nare?

  Okay.

• 30:05Krishna Choudhary?

  They're on some really far away planet.

• 30:08Lester Nare?

  Okay.

• 30:08Krishna Choudhary?

  All right.

• 30:11Krishna Choudhary?

  How do you explain left or right to them?

• 30:15Krishna Choudhary?

  If, if there was somebody in LA, right? It would be pretty easy to explain left or right. You could just like tell them to look at the Hollywood sign, for example. And then be like, the H is on the left of the D. Easy. Easy clap, you're done. They don't have the Hollywood sign. Okay, so what do you do? Well, you could, um, you could, you know, if, if they're on Mars, then they're still in our local neighborhood.

• 30:40Lester Nare?

  Yes.

• 30:40Krishna Choudhary?

  So you, you could tell them to look at the constellations.

• 30:42Lester Nare?

  Yes.

• 30:43Krishna Choudhary?

  Right, you could be like, oh, look at the Big Dipper and then, yeah, you see how there's like the four that are kind of in a rectangle-y? Like they're to the left of the handle. Okay, yeah, great. So now you've defined left or right. Now suppose they're in a completely different galaxy and somehow we've had a wormhole that lets us text. You know, the, the texts are going through the wormhole. Okay, how do we, how do we, how do we tell them? How do we tell them? He, so Feynman, um, puts out a really funny, like, little failed attempt.

• 31:14Lester Nare?

  Okay.

• 31:15Krishna Choudhary?

  That I thought was, was interesting enough to highlight here. Okay, so he said, okay, well, you know, um, if I take like sugar molecules, like from, you know, sugarcane or something, and I dissolve it in water, and then I have plain polarized light, that's something that I can tell the alien how to make, right? Let's say they understand English, they just don't understand left and right. I can tell them, you know, a, a plain polarized light, meaning like, you know, uh, you guys know what light is? Yes, and they'll be like, yes, and I'll be like, okay, you guys understand that there's a polarization where the electric field is in one direction and the magnetic field is in the perpendicular direction? They're gonna be like, yes. We're gonna be like, okay, so let's get plain polarized light, which means all of the light has the electric field moving in one direction.

• 32:00Krishna Choudhary?

  And they're like, okay, cool, I can do that. Seems like something they can do. And then we're gonna be like, oh, hey, get a bunch of sugars. Sugars meaning C6H1206, glucose. Okay, get a bunch of sugars. And then put the, put your plane polarized light through the sugars. Okay. And what's going to happen is as the plane polarized light goes through these sugars, it's going to rotate. It's going to rotate and this we, we've got it. We've got a little visualization here.

• 32:26Lester Nare?

  Yes.

• 32:27Krishna Choudhary?

  It's gonna, as, as the plane polarized light goes through, the electric field, which is only moving up and down. That's how we prepared it. It's going to start rotating to the right.

• 32:39Lester Nare?

  Okay.

• 32:40Krishna Choudhary?

  Okay.

• 32:41Lester Nare?

  Yes. And so.

• 32:41Krishna Choudhary?

  And so, and so you can tell your alien, hey, okay. So just watch how the, how your light rotates through this sugar water thingy. Okay. And then, you know, the direction that the light comes out, that's the right.

• 32:56Lester Nare?

  That's the right.

• 32:56Krishna Choudhary?

  Okay. And the other way is the left.

• 32:58Lester Nare?

  Okay.

• 32:59Krishna Choudhary?

  Okay.

• 32:59Lester Nare?

  Okay.

• 33:00Krishna Choudhary?

  Seems, seems pretty cool.

• 33:01Lester Nare?

  I'm, I'm, I'm tracking.

• 33:02Krishna Choudhary?

  Seems, seems, seems pretty good. The problem is the sugars that we make on earth all have a certain chirality. Because the, the, the sugars are a C6H12O6 ring. There's a ring of carbons, right? It's a, it's a little hexagon of, of carbons and oxygens. And the way in which they're arranged are always in one particular handedness. Okay. You gotta, you gotta go, you, you, you gotta go clockwise to see the, the, the way that the elements are formed. But you could make sugars in the lab.

• 33:39Lester Nare?

  That are not.

• 33:40Krishna Choudhary?

  That are the exact opposite direction.

• 33:42Lester Nare?

  The corality is the opposite.

• 33:43Krishna Choudhary?

  Okay. The chirality is opposite. It's just that all of life on earth, for some reason, makes one handedness of sugars. And that has to do with the fact that all of the proteins that we have on earth have one handedness. Okay. So there's proteins, like all of the primary amino acids in life, right? Except one glycine are chiral. And so there's isomers of these amino acids where you've got the D isomer and the L isomer. The left-handed form and the right-handed form. And most of our amino acids are the left-handed form. Okay? It just is what it is.

• 34:25Lester Nare?

  Right.

• 34:25Krishna Choudhary?

  Because I, and there's actually, this is a big, um, mystery in like the origin of life. Like, how does everyone, like, in the same, you know, you could have picked two and everyone's picked one, right? And it's probably because whatever primordial ancestor was the first, you know, primordial origin of life on Earth, picked the left-handed form. And then as everyone descended from that, right? The DNA became left-handed, the proteins became left-handed, the glucose that comes out becomes a certain handedness. Everything becomes that handedness. And so you can make stuff in the lab, right? That is both, right? You can, you can have both chirality in the lab.

• 35:09Krishna Choudhary?

  But when it comes to biology, we're always gonna make one-handedness.

• 35:13Lester Nare?

  That is fascinating.

• 35:14Krishna Choudhary?

  So, so if we're, if we're talking now, we're DMing this, this alien, right?

• 35:18Lester Nare?

  Yes.

• 35:19Krishna Choudhary?

  And we're like, make a bunch of C6H1206.

• 35:22Lester Nare?

  Yes.

• 35:24Krishna Choudhary?

  He's actually gonna be like, I'm getting both. I'm getting stuff that's going to the right and to the left. And we're gonna be like, oh, which one can you eat? Right? He'll be like, oh, maybe, maybe he could eat the, the ones that are left. Because the, the primordial life on his planet.

• 35:40Lester Nare?

  Yes, yes.

• 35:40Krishna Choudhary?

  Was the other handedness, right? So that's not gonna work.

• 35:43Lester Nare?

  It's not gonna work.

• 35:44Krishna Choudhary?

  I thought that was such a cool little.

• 35:46Lester Nare?

  That's very.

• 35:48Krishna Choudhary?

  You know?

• 35:49Lester Nare?

  And it's, it's such a simple question that has such deep

• 35:54Lester Nare?

  implications in terms of actually trying to.

• 35:56Krishna Choudhary?

  Yeah.

• 35:57Lester Nare?

  Facilitate, it's again, it starts off like a silly go like, oh, how can you tell an alien what left versus right?

• 36:02Krishna Choudhary?

  Yeah.

• 36:03Lester Nare?

  But there's actually some really deep fundamental.

• 36:04Krishna Choudhary?

  There's deep physics here.

• 36:05Lester Nare?

  Yeah, yeah, yeah.

• 36:06Krishna Choudhary?

  Can you?

• 36:07Lester Nare?

  Yeah, can you?

• 36:07Krishna Choudhary?

  The question is, can you?

• 36:09Lester Nare?

  Can you?

• 36:09Krishna Choudhary?

  Can you, without sending him a photo?

• 36:13Lester Nare?

  Right.

• 36:14Krishna Choudhary?

  Right? If I send him a photo, it's easy.

• 36:16Lester Nare?

  But via strictly.

• 36:17Krishna Choudhary?

  Via just strictly, I need you to do stuff there.

• 36:20Lester Nare?

  Yes. In order to illustrate.

• 36:22Krishna Choudhary?

  Yeah.

• 36:23Lester Nare?

  Left versus right.

• 36:24Krishna Choudhary?

  Left versus right. Can I do this, right? So it's still failing, even if we do these, uh, this, this chemical sort of, okay. So, so the chemistry is failing, right? All right, now let's do a physics attempt. Okay. Okay. Um, in, in physics, we're always talking about something called the right hand rule. Okay. Okay. Um, right hand rule is how we do cross products of vectors and it defines our coordinate system. For example, if you have a wire that's got current moving up, then you put your thumb on your right hand towards the current and then you curl your hand. And the way you curl your hand is the way that the magnetic field is going. So, so in this, in this image, we're seeing, uh, someone with a thumbs up hand with this wire going through it. Mm hmm.

• 37:08Krishna Choudhary?

  Um, and, and the, the current is going up. Current is going up. So the thumb is pointing up and, and there, you know, you can see the hand, the fingernails are pointing like, are in, like in the front. Yeah. Of the image. Yeah. And so the. And the way that I curl the fingers, the fingers are curled counterclockwise. Yes. And the, and then it's also now flowing in the direction. The magnetic field is flowing where my fingers. Fingers are, which is this. Yeah, that, that, so that's called a right hand rule and we live a right hand, we live in a right-handed coordinate system. Okay. What that really means is the following, okay? What that means is if I have my X axis, let's say this way. And my Y axis this way. Okay. Then my Z axis is this way. If, if I have my X axis pointing north. Uh, but yeah, let's say, let's say pointing outward. Outward.

• 37:52Krishna Choudhary?

  And my Y axis to the left. Yes. Then the Z axis is up. Up, okay. Now, somebody who created physics could have easily been left-handed. Right. And said, nah, X axis this way. Outward. Y axis this way, so Z axis is pointing down. The fact that Z axis is pointing up here and not down is just a human construct. It's a choice. It's a choice that we've made because probably the guy who, who made it up, the made up the cross product was like, I'm going to use a right-handed coordinate system. Right? Yes. And so our coordinate system is right-handed just by pure choice, but we could have had our Z axis pointing the other way and it would have been complete, the physics would have been completely fine. It's the same. It's the same. It's just this orientation. So, so we can't really use physics, right?

• 38:37Krishna Choudhary?

  And, and to, to illustrate this further, right? Let's think about what happens to like motions of particles and vectors in a mirror world.

• 38:47Lester Nare?

  Okay.

• 38:47Krishna Choudhary?

  Okay, so if I have a mirror that's right in front of me and I have a particle that's moving away from me.

• 38:54Lester Nare?

  Yes.

• 38:54Krishna Choudhary?

  I would, I would go to the other, the other photo.

• 38:56Lester Nare?

  Yes.

• 38:58Krishna Choudhary?

  If I have a, if I have a, if I have a mirror in front of me and I would go. Let, let's say the particle is going towards the mirror.

• 39:07Lester Nare?

  Okay.

• 39:08Krishna Choudhary?

  Okay, so it's moving away from me.

• 39:10Lester Nare?

  Yes.

• 39:11Krishna Choudhary?

  In the mirror world, what I'm seeing is the particle would come towards me.

• 39:15Lester Nare?

  Yes.

• 39:15Krishna Choudhary?

  Yes?

• 39:16Lester Nare?

  Yes.

• 39:16Krishna Choudhary?

  So, so the, the trajectory of the particle is flipped.

• 39:20Lester Nare?

  Yes.

• 39:21Krishna Choudhary?

  Yes?

• 39:21Lester Nare?

  Yes.

• 39:22Krishna Choudhary?

  Okay, but if I have a current that is, that is, that is now, let, let's say, let's say I've got a current that creates a magnetic field. All magnetic fields are created by currents, right? So if we go to photo 11, we'll actually see on the, on the left hand side, we're gonna see a current that is twisted to the, to the, yeah, to the right.

• 39:45Lester Nare?

  Okay.

• 39:45Krishna Choudhary?

  Okay, so in our world, it's twisted to the right, which means that if I were to follow this loop of current, right, let's say I make a loop out of the current and it's twisted to the right, so my right hand is following the thing, then the B field is pointed up.

• 39:58Lester Nare?

  Yes.

• 39:59Krishna Choudhary?

  Right, but in the mirror world, that current would be pointed to the left and so the B field would be pointing down. Right?

• 40:07Lester Nare?

  Yes.

• 40:07Krishna Choudhary?

  And everything in physics has to do with the, everything when it comes to magnetism and charged particles and how those charged particles move in a magnetic field. In physics, that has to do with the cross product of my velocity

• 40:22Lester Nare?

  Yes.

• 40:23Krishna Choudhary?

  and my magnetic field.

• 40:24Lester Nare?

  Mm-hmm.

• 40:24Krishna Choudhary?

  But what just happened is I just flipped both of those vectors, right? The velocity became the negative.

• 40:31Lester Nare?

  Yes.

• 40:31Krishna Choudhary?

  And the B field also flipped.

• 40:33Lester Nare?

  Yes.

• 40:33Krishna Choudhary?

  So I got a negative times a negative, which becomes a positive.

• 40:36Lester Nare?

  This is, ah, this is, okay.

• 40:38Krishna Choudhary?

  Right?

• 40:38Lester Nare?

  Yeah.

• 40:39Krishna Choudhary?

  So I can't do it. I can't, I can't like.

• 40:42Lester Nare?

  Yes.

• 40:43Krishna Choudhary?

  I can't actually, I can't actually do it.

• 40:49Krishna Choudhary?

  With just pure electromagnetism.

• 40:51Lester Nare?

  You cannot explain to the Martian.

• 40:53Krishna Choudhary?

  Yeah.

• 40:53Lester Nare?

  What is left versus right because of this.

• 40:59Lester Nare?

  Like mirror symmetric.

• 41:01Krishna Choudhary?

  Yeah, because all of the laws of physics so far.

• 41:04Lester Nare?

  Yes.

• 41:05Krishna Choudhary?

  Are exactly mirror symmetric.

• 41:06Lester Nare?

  Right.

• 41:07Krishna Choudhary?

  Right?

• 41:07Lester Nare?

  Right.

• 41:08Krishna Choudhary?

  Everything in the mirror world is the same as my world.

• 41:11Lester Nare?

  Yes.

• 41:12Krishna Choudhary?

  There's no way for me to DM him and explain to him what is left and right.

• 41:16Lester Nare?

  That's so.

• 41:17Krishna Choudhary?

  It's so cool to think about, right? So we've tackled gravity. Gravity doesn't, gravity doesn't care.

• 41:23Lester Nare?

  Yeah.

• 41:23Krishna Choudhary?

  Gravity really doesn't care.

• 41:24Lester Nare?

  Yeah.

• 41:25Krishna Choudhary?

  Electromagnetism, we thought kinda cared because we're, we're always worried about the direction of the magnetic field and like the crossing of the product and the da, da, da. But it turns out like in the mirror, everything is flipped. So the motion of the particle isn't actually gonna change. Right? So, so we're really in a conundrum here.

• 41:43Lester Nare?

  This, yeah, like, right.

• 41:45Krishna Choudhary?

  Like, how are we gonna tell this guy?

• 41:46Lester Nare?

  Right.

• 41:47Krishna Choudhary?

  How, how are we gonna explain to this guy the simple fact that like my heart is on the left hand side?

• 41:53Lester Nare?

  Right.

• 41:54Krishna Choudhary?

  You know?

• 41:54Lester Nare?

  Right.

• 41:55Krishna Choudhary?

  And I write with my right hand side.

• 41:56Lester Nare?

  And what does that actually mean?

• 41:58Krishna Choudhary?

  Yeah, doesn't mean anything.

• 41:59Lester Nare?

  Doesn't mean anything.

• 42:00Krishna Choudhary?

  It becomes, it becomes a very philosophical question, right? Does it mean, like, is there really no difference between left and right? Does the universe really not care?

• 42:08Lester Nare?

  Well, if we're talking about politics, there's certainly a difference.

• 42:11Krishna Choudhary?

  Certainly, there's certainly a difference, right?

• 42:13Lester Nare?

  Maybe that's why we shouldn't be labeling them in these directions because in physics, there's, there's.

• 42:17Krishna Choudhary?

  It seems, it seems there's no difference.

• 42:19Lester Nare?

  Or maybe this is where horseshoe theory comes from.

• 42:21Krishna Choudhary?

  Yeah, yeah, yeah.

• 42:22Lester Nare?

  The extreme is the same.

• 42:23Krishna Choudhary?

  It's the same. Yeah, exactly. Yeah. Exactly. So, so we've been discussing this question, right? Is parity conservation a law of the universe? And so far, it seems yes. Okay, meaning that if I have some experiment and I do some experiment and then I do the mirror image of that experiment, the results of the experiment are exactly gonna be the same. Okay, so let's review a few, a few things, okay? Certain vectors flip sign.

• 42:48Lester Nare?

  Okay.

• 42:48Krishna Choudhary?

  Okay, like position, for example, if I'm moving in this direction, in the mirror image, it's gonna flip sign.

• 42:55Lester Nare?

  When you say this direction, how do you mean?

• 42:56Krishna Choudhary?

  Just, I mean, like, yeah, for example, like, let's say there's a mirror in front of me. If I'm moving towards the mirror.

• 43:02Lester Nare?

  Yes.

• 43:02Krishna Choudhary?

  In the mirror world, that particle is gonna be moving towards me.

• 43:05Lester Nare?

  Got it.

• 43:05Krishna Choudhary?

  Right? So it's like, it's like I'm, I'm moving towards the wall. Let's say the mirror is on the wall and the particle is moving towards the wall. Well, in the mirror world, the particle is moving out of the wall. Right?

• 43:17Lester Nare?

  Yes.

• 43:17Krishna Choudhary?

  So it's, it's flipped its sign.

• 43:19Lester Nare?

  Yes.

• 43:19Krishna Choudhary?

  Right? That's what parity means. We're flipping all of the X's. X becomes negative X, Y becomes negative Y, Z becomes negative Z. Okay? Now. Certain vectors, these true vectors, they flip their sign. But then there's other vectors called axial vectors that do not. For example, angular momentum. Suppose I have, suppose I'm doing this with my hands.

• 43:42Lester Nare?

  Uh, rotating in a clockwise direction.

• 43:44Krishna Choudhary?

  Yeah, rotating in a clockwise direction. So the spin is towards the wall.

• 43:49Lester Nare?

  Okay.

• 43:49Krishna Choudhary?

  Right? It's towards the wall into the wall.

• 43:51Lester Nare?

  Yeah, the righty-tidy idea.

• 43:53Krishna Choudhary?

  Yeah, righty-tidy idea. Well, that rotation is gonna look the same in the mirror, in the mirror world, right? In the mirror world, if I'm doing my hand like this, the mirror's trajectory is also gonna be going clockwise. So in the mirror world, that, the, the, the spin is gonna be going into the wall, right? It's gonna be going like, the, the, the angular momentum actually doesn't change.

• 44:16Lester Nare?

  Wait, this is actually really crazy.

• 44:18Krishna Choudhary?

  I really need you to focus here and think about this.

• 44:20Lester Nare?

  That's actually really crazy, because what you're basically saying is in the mirror.

• 44:24Krishna Choudhary?

  Yeah, and, and if.

• 44:25Lester Nare?

  Pull it back up, yeah.

• 44:26Krishna Choudhary?

  We pull it back up, like on the left hand side, we've got, we've got a, a, a wheel that's turning like this.

• 44:32Lester Nare?

  Yeah.

• 44:32Krishna Choudhary?

  And so the, the spin vector is to the right.

• 44:34Lester Nare?

  Yeah.

• 44:35Krishna Choudhary?

  Now I flipped it along the middle.

• 44:37Lester Nare?

  Mm-hmm.

• 44:38Krishna Choudhary?

  It's spinning, but the spin vector is still, still, right? Because it's, like, imagine, I got, I got, I got, I got a mirror in front of me. I'm doing this. In the mirror world, that thing is, my hand is still doing the same kind of thing.

• 44:50Lester Nare?

  Yes.

• 44:51Krishna Choudhary?

  It's because I've changed both X and Y to be negative and negative. And the spin is a product of my, of the, of those, of those two coordinates. So the negative, you know, it's still gonna be pointing in the same direction. So an electron that's spinning this way into the mirror is gonna be still pointing, like, going the same direction in the mirror world.

• 45:12Lester Nare?

  In the mirror world.

• 45:13Krishna Choudhary?

  It's, this is, this, this is a crucial thing for you to understand.

• 45:17Lester Nare?

  This is, I've never.

• 45:19Krishna Choudhary?

  Right, and can you imagine it?

• 45:20Lester Nare?

  No, so I, I can in my head, yeah, no, I can, I can visually. And it's, it's, it's making me uncomfortable because it doesn't make sense.

• 45:27Krishna Choudhary?

  Yeah.

• 45:28Lester Nare?

  Like, but not, not, not even that it doesn't make sense, but it, it's, it's, the, the distinction between the first use case we just talked about, um, of the, um, position vector.

• 45:43Lester Nare?

  Like versus this axial vector and simply like we it it's it seems like such a simple difference.

• 45:50Krishna Choudhary?

  Yeah.

• 45:51Lester Nare?

  But the implications of that simple difference are are change everything.

• 45:55Krishna Choudhary?

  And and and and the the real underlying substrate here is that axial vectors are not true vectors. They're kind of like.

• 46:02Lester Nare?

  Okay.

• 46:03Krishna Choudhary?

  They're they're products of two vectors, right? Angular momentum is R cross V. So so because you put a negative on one and the negative on the other, it's going to be the same. Right? The position vector is literally like, where am I going from where I went to?

• 46:17Lester Nare?

  It's it's flat, right? There's no dimensionality.

• 46:19Krishna Choudhary?

  Yeah, there's no, it's just, there's nothing tricky.

• 46:21Lester Nare?

  Right.

• 46:21Krishna Choudhary?

  About it.

• 46:22Lester Nare?

  Right.

• 46:22Krishna Choudhary?

  But when it comes to axial vectors like angular momentum, those things do not flip.

• 46:27Lester Nare?

  That's it's it's I'm like, I have so many thoughts.

• 46:31Krishna Choudhary?

  Yeah, it's crazy, dude. So this this, but this is central to the idea.

• 46:36Lester Nare?

  Okay.

• 46:37Krishna Choudhary?

  Some vectors change, other vectors do not.

• 46:40Lester Nare?

  Do not.

• 46:41Krishna Choudhary?

  When it comes to parity, in the mirror world, right? If my angular momentum is that way, in the mirror world, it's also going to be that way. On the other hand, my position, if my position is is this way, the the guy is coming at me. Right? If if if I have like a a bug that's flying away from me towards the mirror, then that bug is flying towards me out of the mirror.

• 47:04Lester Nare?

  Yes.

• 47:05Krishna Choudhary?

  So the position vector is flipped. But if my bug is like rotating like this, it's going to be coming towards me, but it's going to be rotating like like, you know?

• 47:15Lester Nare?

  Yeah, yeah.

• 47:16Krishna Choudhary?

  So so the position is but but it's still going to be rotating in that same clockwise way.

• 47:21Lester Nare?

  Yes, yes, yes. And it's actually like really trippy to think about.

• 47:25Krishna Choudhary?

  It's really trippy to think about, dude.

• 47:29Lester Nare?

  This this, okay, I'm tracking.

• 47:31Krishna Choudhary?

  You know?

• 47:31Lester Nare?

  No, no, I mean, this total side note to this, but this kind of reminds me, it's not similar. But there's like this whole, this is gentleman who's created this thing called the true mirror. Because we're seeing a reflection, a mirrored version of ourselves when we look in a mirror versus what other people see when they look at us.

• 47:48Krishna Choudhary?

  Yeah.

• 47:49Lester Nare?

  And there's actually this like. Physiological response that we as humans have when we see a mirror reflection of ourselves versus like what other people see of ourselves. And so like because like your brain processes the mirror image in a certain way.

• 48:07Krishna Choudhary?

  Yeah.

• 48:07Lester Nare?

  And so when you see it in the opposite, there's like these outcomes like, oh, you tend to like, not be searching, gazing in the eye, like trying to find the eye line. You naturally like are not uncomfortable and smile. Like there's this whole like arena of stuff. It's not the same thing, but it makes me think about that use case because I've never before thought about the idea that the way people see me in the world is not the same thing that I see in the mirror.

• 48:36Krishna Choudhary?

  No.

• 48:37Lester Nare?

  And so everyone sees me the reverse of how I think my existence is.

• 48:40Krishna Choudhary?

  Yes, yes.

• 48:41Lester Nare?

  And that's very weird.

• 48:42Krishna Choudhary?

  Yeah, they're seeing just like, I guess you, I don't know. There's no flipping.

• 48:47Lester Nare?

  There's no flipping.

• 48:48Krishna Choudhary?

  There's no flipping because flipping is a crazy thing, right? You're flipping axes and all this other stuff.

• 48:52Lester Nare?

  But if I was like having angular momentum towards, towards, anyway.

• 48:57Krishna Choudhary?

  Yeah, yeah, exactly, dude. It's crazy. It's crazy to think about.

• 49:01Lester Nare?

  It's very.

• 49:02Krishna Choudhary?

  But but my main point here was some vectors, like my velocity.

• 49:07Lester Nare?

  Yes.

• 49:07Krishna Choudhary?

  Like my position, those are true vectors. Those are going to flip sign.

• 49:11Lester Nare?

  Yes.

• 49:11Krishna Choudhary?

  My angular momentum is not going to flip sign.

• 49:14Lester Nare?

  Right.

• 49:15Krishna Choudhary?

  Okay.

• 49:15Lester Nare?

  Right.

• 49:16Krishna Choudhary?

  Now, you know, we start getting these weird experiments from Otto Laporte. He's a student of Sommerfeld. Sommerfeld, we've talked about at the University of Munich, one of the great physicists of Germany before the war, who tutored the likes of Heisenberg and Pauli and all these people, never got the Nobel Prize. But he showed in experiments with iron that if you have, you know how like in quantum mechanics, you have transitions between energy levels of an atom? The electron is in some energy state and then it goes to another energy state and.

• 49:50Lester Nare?

  And they're discrete.

• 49:51Krishna Choudhary?

  Yeah, and they're discrete. And when that transition happens, it lets out light. And by measuring the light, you can tell what kind of transition that happened.

• 49:59Lester Nare?

  Yes.

• 49:59Krishna Choudhary?

  Well, he found that there's certain transitions that never happen.

• 50:03Lester Nare?

  Okay.

• 50:03Krishna Choudhary?

  Okay. If the electron is in some state, it's never going to go to some of these other states. Okay. And Eugene Wigner.

• 50:11Krishna Choudhary?

  Created these things called selection rules, okay? Turns out that atoms have different, two kinds of energy levels. There's one that has even parity, which means that if I flip the coordinates, it's the same. That's the one, like if it's symmetric about the y-axis, right? And if I flip, it's like the Taj Mahal. Yes. And then there's another one where if I flip the parity, it's gonna be the negative of that. It's like, it's like a flippingness of the Taj Mahal, okay? But there's one state that looks like the Taj Mahal, and then there's another state that looks exactly the opposite. Yes. Okay? Yes. And what he found was that when these electrons switch energy levels, they have to conserve parity, okay? Okay. One of them is even, the other one is odd. You can assign them numbers. Yes. That are even and odd.

• 50:57Krishna Choudhary?

  And the total parity before has to equal the total parity after. So it became, and, and everybody liked it, right? It's like, okay, it's like intuitive, right? If I made a clock that's in the, that's in this opposite mirror world, then it works the same way. Conservation of parity comes from Noether's theorem. Yes. So it's all nice. It's all tracking. It's all tracking. The universe, the universe can't distinguish between left and right. We're in a nice universe that's just agnostic about what is left and right. It doesn't care, okay? Then comes the puzzle of the theta and the tau, okay? These are mesons. Mesons are, um, at the time, they didn't know what it was.

• 51:37Krishna Choudhary?

  But, um, this was, now we know that a meson is basically a quark and anti-quark bound together in a single particle. At the time, we didn't know what it was. In the 1950s, these physicists, they found two particles, the theta and the tau, okay? And they were same, the same in every regard, okay? They had the same mass, they had the same charge, they had the same lifetime even. The lifetime part is weird, okay? Cause they got the same lifetime, but they're different in one tiny thing, okay? And the one tiny thing is in how they decay. One of them decayed into two pions, and the other one decayed into three pions. It's not important what pions are. The main point is pions carry a parity charge. Okay, you know how I was saying that we can assign parity? parity numbers to our states.

• 52:23Krishna Choudhary?

  Well, pions have parity numbers. And all of a sudden, you had two identical particles in every other aspect, but one of them had a different parity decay. And the other one had a different parity decay. Okay, one of them was going into two, the other one was going into three. So one of them had an even parity and the other one had an odd parity. If you think that parity is parity is the same, right? On the left hand side, we've got the the theta, which is sorry, on the left hand side, we've actually got the tau that's going into three pions. And on the right, we've got the the pi that's going into two, right? That this is just a schematic diagram showing like that decay.

• 53:00Lester Nare?

  Yes.

• 53:01Krishna Choudhary?

  This is very weird.

• 53:02Lester Nare?

  Yeah.

• 53:03Krishna Choudhary?

  Because if the law of conservation of parity is true, which everyone assumed it's true, then the decays must end in the same parity. But here we've got the same particle that looks pretty much the same.

• 53:14Lester Nare?

  But they have.

• 53:14Krishna Choudhary?

  In every aspect.

• 53:15Lester Nare?

  Diverging.

• 53:16Krishna Choudhary?

  But they have this diverging decay.

• 53:18Lester Nare?

  The K parity.

• 53:19Krishna Choudhary?

  Okay.

• 53:20Lester Nare?

  Okay.

• 53:20Krishna Choudhary?

  And so now it's like, how how how could these two be so similar and yet have such a different thing?

• 53:29Lester Nare?

  Right.

• 53:30Krishna Choudhary?

  One, one possible resolution is that these are two very different particles.

• 53:37Lester Nare?

  Okay.

• 53:38Krishna Choudhary?

  The other possible ability is that these two are the same particle, but parity is not conserved in this process.

• 53:46Lester Nare?

  Okay.

• 53:46Krishna Choudhary?

  And all the stuff that we've talked about with electromagnetism, with gravity, parity is conserved. But in this particular thing that we are observing.

• 53:55Lester Nare?

  Not.

• 53:56Krishna Choudhary?

  It is not.

• 53:57Lester Nare?

  Okay.

• 53:57Krishna Choudhary?

  Okay?

• 53:58Lester Nare?

  So the conservation of parity is not universal.

• 54:01Krishna Choudhary?

  Yes, maybe not all the laws of physics obey the conservation of parity. Maybe there's an exception.

• 54:08Lester Nare?

  Okay.

• 54:08Krishna Choudhary?

  Maybe gravity is not the exception. Maybe electromagnetism is not the exception, exception, but maybe there's something else. Okay? And this is where the hero of our story, story, Yang Chengning comes in.

• 54:20Lester Nare?

  Okay.

• 54:20Krishna Choudhary?

  Okay, so Yang Chengning, born in nineteen twenty two in Hefei province in China.

• 54:28Krishna Choudhary?

  His dad was actually a professor at Tsinghua University in Beijing. He was a math professor. He's one of the few people who actually did his PhD outside of China and then came back Okay. To teach in China. So he's had exposure to group theory from a very early age. Group theory is the mathematics of symmetry. Okay. Okay, so he's gearing up Yeah. For this fight early on, right? He's forged in war, actually, like during the Japanese invasion of Kunming in 1937. This was before the all-out break of war in the Pacific Theater where the United States got involved after Pearl Harbor. The Japanese were doing all sorts of random, stupid nonsense, terrible stuff in China.

• 55:12Krishna Choudhary?

  And so all of the Chinese academia actually went down to Lianda in the southwestern province. And they sort of conglomerated all of their academic might in the south away from all of the fighting. And this is where Yang Chengning did his undergraduate and his PhD. Okay? No, sorry, not his PhD, his undergraduate and his masters. Okay. Okay? And he actually learned about quantum mechanics at a very early, even back then, I mean, it's quite remarkable because quantum mechanics was still quite early, but he was, the university was so good Right. That he was already getting exposure to quantum mechanics at that early undergrad, masters level.

• 55:55Krishna Choudhary?

  He gets on one of these liberty boats from China to the US. He caught it in Calcutta, actually. These are boats that were set up after the war to bring in people from the Indonesian, Indo-Chinese theater that was happening in Burma Mm-hmm. To the United States. So he goes through Calcutta, through the Red Sea, through the Mediterranean to New York. There were no direct boats to San Francisco. So he actually had to come the other way, all the way around the earth, right? He ends up in New York. He stays, I was just watching some of his interviews from Stony Brook University, which is where he ended up and spent a majority of his academic career. They have these incredible interviews of the man, Yang Chengning, and

• 56:38Krishna Choudhary?

  He was talking about how like, you know, when he first got off the boat, he, he got a hotel room in Times Square, which back then is not, you know, now it's like all touristy, but like back then,

• 56:52Lester Nare?

  Yeah.

• 56:52Krishna Choudhary?

  it's sketches.

• 56:53Lester Nare?

  Yeah, not, not the same thing.

• 56:54Krishna Choudhary?

  It's not the great thing.

• 56:55Lester Nare?

  Had it pretty gentrification.

• 56:56Krishna Choudhary?

  Yeah, so like his first, his first, uh, his first exposure to America was Times Square in the, in the 1940s. Anyway, so, so he gets there, um, he goes to Columbia in search of Fermi, because Fermi was officially on the roster of Columbia. He goes there, he asks the secretary about Fermi. The secretaries don't know who Fermi is, because I don't even know.

• 57:17Lester Nare?

  Yeah.

• 57:18Krishna Choudhary?

  Fermi was, Fermi was, at the time, he was never in Columbia, because he was doing classified research for the government, for the Manhattan Project. But, I mean, come on, you don't know who Fermi is.

• 57:27Lester Nare?

  Yeah.

• 57:28Krishna Choudhary?

  All right, fine. Um, he, he goes to Columbia, he can't find Fermi, he goes to Princeton, he actually meets Eugene Wigner there. Wigner tells him that he's going to sabbatical at Oak Ridge, which is another classified thing.

• 57:41Lester Nare?

  Yep.

• 57:41Krishna Choudhary?

  And because Yang Chengning is Chinese, you know, you can't, you're not gonna, you're not gonna get a job with Wigner.

• 57:47Lester Nare?

  You're not gonna get read into the special access program.

• 57:49Krishna Choudhary?

  No, yeah, it's like, you just got here.

• 57:51Lester Nare?

  Yeah.

• 57:52Krishna Choudhary?

  It's like, so.

• 57:53Lester Nare?

  Especially at that time, too.

• 57:54Krishna Choudhary?

  At that time, yeah, it's like, I, we don't know.

• 57:57Lester Nare?

  It's tough, it's tough.

• 57:58Krishna Choudhary?

  Yeah, it's tough. So then, so then he goes, talks to Wheeler.

• 58:01Lester Nare?

  Yeah.

• 58:01Krishna Choudhary?

  Wheeler, someone that we talked about, another Princeton great.

• 58:04Lester Nare?

  Yes.

• 58:05Krishna Choudhary?

  Um, Wheeler gave him some problems. Those problems didn't really interest him, he tried as much. Um, and then he got word that Fermi was actually, um, permanently going to Chicago, University of Chicago from Columbia. And so he applies there, he sends a telegram to Columbia, to Chicago,

• 58:22Krishna Choudhary?

  gets in immediately, because his grades were so good

• 58:24Lester Nare?

  Yeah.

• 58:24Krishna Choudhary?

  in the Chinese undergrad and masters. So he gets in, he goes to the Chicago's school, um, under the guidance of these giants, Enrico Fermi, Edward Teller, um, the villain of the Oppenheimer movie. He actually got his PhD under Edward Teller.

• 58:42Lester Nare?

  Okay, oh, very interesting.

• 58:43Krishna Choudhary?

  Edward Teller was his PhD advisor.

• 58:45Lester Nare?

  Very interesting.

• 58:45Krishna Choudhary?

  And that's actually a really funny story, because, um, He wanted to at first get his PhD under Enrico Fermi. But Fermi had gone to Argonne National Lab again for classified research.

• 58:57Lester Nare?

  Yes.

• 58:58Krishna Choudhary?

  Right? So he's like, I can't really take you. I'm really sorry. He goes to Teller. Teller gives him problems. These are problems that aren't really interesting to Young, right? So Young's trying, couldn't solve them. He's like, okay, maybe I'll try my hand at experimental physics. Fails miserably, like every theoretical physicist does, who tries to go into the lab, just has no idea what he's doing. In his interview, he's actually talking about how the graduate students would like literally laugh at him. But they were like also best friends with him because he would solve their theoretical problems. Right? But but he was just hopeless in the lab.

• 59:34Lester Nare?

  In the lab.

• 59:34Krishna Choudhary?

  Right? So he's there for three and a half years, just doing nonsense, breaking shit. And he publishes during that time, he publishes independently, some papers about the symmetry groups and group theory, and how that can be applied to nuclear fission and nuclear decay. Okay, this catches the eye of Teller again. And Teller comes up to him and he's like, so at this point, he's kind of, you know, famous in the University of Chicago because there's not a lot of Chinese students. Not not like nowadays when there's so many Chinese students in American universities, so many international students in American universities. Back then, there's few and far bit far in between. And he's so good at theoretical physics. So and he publishes these papers.

• 1:00:17Krishna Choudhary?

  So Teller comes up to him and he's like, so I heard you're you're doing pretty bad in this lab. And he's like, yeah, man, I'm really struggling. And but Teller says, you know, I liked your paper that you put out. You know, if you want to submit that as part of your thesis, I'll be your advisor. Because this was something that Teller hadn't even thought about, Edward Teller. But he's like, you know, this is interesting stuff. So if you want to, if you want to, you know, graduate with a PhD under me, just like make it a little bit longer. You know, I can't be like, I can't submit like a three-page paper as your thesis. But, you know, I could talk if you're doing like a little bit longer. He comes back with a little bit longer paper. Teller's like, this isn't long enough. I was meaning like substantially longer.

• 1:01:01Lester Nare?

  I was trying to be nice.

• 1:01:02Krishna Choudhary?

  Yeah, so like, so so so Young goes back. Comes back with a longer paper and Teller is like, alright, this is fine. Actually, at a, at a later celebration of Yang's birthday, Teller went up to speak and he talked about how the third submission that Yang had of his paper was still too short, but he was just like, this is hopeless. Like, this guy's clearly a very good physicist. Let's just, let's, I'm just gonna talk to his, I'll, I'll go to bat for him, you know?

• 1:01:30Lester Nare?

  Yeah, having Edward Teller go to bat for you is not, that, yeah, a bad thing.

• 1:01:35Krishna Choudhary?

  It's not bad at all. 1948, he gets his, um, his paper. Um, one of the cool things about his time at, his time at Chicago was he was actually in a two-person class with, um, Sung Dao Lee, under the tutelage of Subramaniam Chandrasekhar, okay? Subramaniam Chandrasekhar is one of my heroes personally. He's somebody that I, um, Subramaniam Chandrasekhar is one of the heroes of Indian physics. He, um, discovered the Chandrasekhar limit, which is the white dwarf limit, how big a star can get before it can no longer be a white dwarf. Um, at the age of like 19 or 20, he discovered this.

• 1:02:16Krishna Choudhary?

  He faced intense racism in Great Britain, um, by someone by the name of Arthur Eddington, who himself, great physicist or whatever, but you know, whatever.

• 1:02:28Lester Nare?

  Gatekeeper, we get it.

• 1:02:29Krishna Choudhary?

  Yeah, we, we get it. So he, he was hired by the University of Chicago and at the time he was working at the York's Observatory in Wisconsin. Um, he offered this course, I forget what the course was actually, but only two people signed up. It was Sung Dao Lee and Yang Chengning, okay? Um, he would drive 200 miles from York's Observatory to Chicago every week to, um, do this course and teach this course. But good thing for him because that course holds the world record for number of Nobel Prizes.

• 1:03:08Krishna Choudhary?

  100% of the attendees of that course, 100% of the attendees of that course won the Nobel Prize. No other course has that, you know, because he got two students and both won the Nobel Prize.

• 1:03:23Lester Nare?

  That's actually pretty crazy.

• 1:03:24Krishna Choudhary?

  That's a great, like, like, that's a record that I don't think it's ever going to be beat.

• 1:03:29Lester Nare?

  We're gonna put that in the stat locker for FFP when we start the leaderboard.

• 1:03:32Krishna Choudhary?

  Oh, that'll be a great one. Yeah, it's like classes. Yeah.

• 1:03:35Lester Nare?

  We're gonna build out a stats library, just like all major professional sports do for when they, when the announcer's like, oh, the last time we saw 300 yards, 42 da da da da, was in 19 da da da.

• 1:03:49Krishna Choudhary?

  Yeah.

• 1:03:50Lester Nare?

  We're starting the same stats library, next gen stats.

• 1:03:53Krishna Choudhary?

  Yeah, next gen stats. And that's gonna be, that's gonna be one that's like, never gonna be beat. Okay, you had two students, both won the Nobel Prize, 100% Nobel Prize winner class. Imagine, right? So Sung Dao Lee is actually instrumental in the next part of our story.

• 1:04:10Lester Nare?

  Okay.

• 1:04:10Krishna Choudhary?

  Because Sung Dao Lee and Yang, they are the ones who start looking at that tau theta puzzle that we were talking about, right? You got these two identical particles, they're decaying in weird ways.

• 1:04:25Lester Nare?

  The parity, there's no conservation of the parity, because they're decaying into two and three.

• 1:04:30Krishna Choudhary?

  Yeah.

• 1:04:31Lester Nare?

  Which is weird because there's like same size.

• 1:04:32Krishna Choudhary?

  Yeah, same, same, but different. Why are they different?

• 1:04:35Lester Nare?

  Why are they different?

• 1:04:36Krishna Choudhary?

  Like, is it, is it that they are different? Or is it that the laws of physics are a bit different?

• 1:04:41Lester Nare?

  Right, are not, don't, the conservation of parity has exceptions.

• 1:04:44Krishna Choudhary?

  Exactly. Yeah. So, so Yang Chengning, sorry, Yang and Lee, they propose a revolutionary idea. What they do is they go back and look at all of the literature, okay? There's a funny story here where they were in Colombia at the time, and they're searching for parking, and they're in the car, he talks about this in his memoir, they're in the car discussing this issue of the theta and the tau, and they're like, is parity conserved? Like, what's going on? And they have this. Idea, but they're looking for parking. They can't find parking because it's Manhattan. There's no

• 1:05:23Lester Nare?

  There's no parking.

• 1:05:24Krishna Choudhary?

  Manhattan.

• 1:05:24Lester Nare?

  Yeah.

• 1:05:25Krishna Choudhary?

  Manhattan. So they park in this like restaurant, this Chinese restaurant that hadn't opened yet. But like, you know, they still, the, the restaurant had parking. So they find parking. They go into cafe and they continue their, their discussion. And what they're really focusing on is, has anyone actually checked if beta decay obeys parity? There's been all of these experiments to check that electromagnetism obeys this mirror rule. There's been all of these experiments to show that nuclear stuff, like the strong nuclear force obeys the mirror symmetry, but has anyone actually done it for the weak nuclear force? Which is what's involved in beta decay. So they decide to go through the literature and they actually find out, no.

• 1:06:08Krishna Choudhary?

  No one has said one way or the other, whether beta decay obeys the parity conservation law. So they write up a paper and they actually talk about certain experiments that you could do. To maybe find out if something, i- if beta decay is different in the mirror world.

• 1:06:29Lester Nare?

  Yes.

• 1:06:30Krishna Choudhary?

  Okay.

• 1:06:30Lester Nare?

  Yes.

• 1:06:30Krishna Choudhary?

  Everything else is the same.

• 1:06:31Lester Nare?

  Right.

• 1:06:32Krishna Choudhary?

  But beta decay is something that no one's actually bothered to check. Okay. They, they contact Chen Cheng Wu, who is an experimental physicist at Columbia. She's one of the great, great experimental physicists of the 20th century. And she was basically the expert in the entire world about beta decay.

• 1:06:54Lester Nare?

  Okay.

• 1:06:55Krishna Choudhary?

  And beta decay spectroscopy. They're like, there's one person that we can go to and it's, um, Chen Cheng Wu. They proposed this, they proposed this idea, this like, I want to check if this thing is symmetric. So Wu comes up with this ingenious experiment.

• 1:07:12Lester Nare?

  Okay.

• 1:07:12Krishna Choudhary?

  Okay. Here's what she does. She gets cobalt 60, which is an isotope of cobalt. Okay. It's got 60 neutrons and protons in its nucleus. And what they're going to do is they're going to wait for the cobalt 60 to decay into nickel 60. So notice, the atomic number has remained the same, which means what's happened is a neutron has turned into a proton. A neutron turning into a proton, that's a neutral charge going into a positive charge, which means it has to release a negative charge.

• 1:07:45Lester Nare?

  Release the negative charge.

• 1:07:47Krishna Choudhary?

  Exactly. By the conservation of charge, the charges before and have to remain the same.

• 1:07:52Lester Nare?

  Right.

• 1:07:53Krishna Choudhary?

  So if I've created a positive charge and I started at zero, I need to create a negative charge to balance it out. So, this is a process of beta decay. Okay, this is something that has to do with the weak nuclear force. Okay? The question is, is the electron that gets spit out, does it have a preferred orientation?

• 1:08:14Lester Nare?

  This goes back to our right-handedness, left-handedness thing.

• 1:08:16Krishna Choudhary?

  Exactly. Does it, does the electron that gets spit out, does it have a way of only preferring left or right, or one of the other?

• 1:08:25Lester Nare?

  Yeah.

• 1:08:26Krishna Choudhary?

  That's the question. It's a very simple experiment.

• 1:08:28Lester Nare?

  Yeah, yeah, yeah.

• 1:08:29Krishna Choudhary?

  Right? That's, and this is the genius of Wu. I mean, the, the experiment sounds simple, it's insane, right? You gotta, you gotta get these cobalt 60 atoms, then you gotta cool it down to near absolute zero, because you don't want the cobalt 60 to be, right? You wanna tell which way the electron is moving. So you gotta collimate all of the cobalt 60 so that it's all oriented in the same direction. The cobalt 60 itself has a spin on its own, right? So you want all of the cobalt 60 atoms to be oriented in the same direction, which means you gotta cool everything down to near absolute zero. There's something like 10 milli Kelvin, which is like difficult even now, but back then, like, she had to do it at the NIST, the NIST offices in Washington DC, because they were experts at making really, really cold things.

• 1:09:13Krishna Choudhary?

  So she actually told them, this was in December of 1957. Or 1956, actually. December of 1956, she goes down to Washington DC and she sets up this apparatus. She wants to do it fast, because she knows this is gonna be big. So she's like, no, I, I, I am Lady Wu. I am in charge of beta decay everywhere around the world. I'm gonna do this. So she gets cobalt 60, she cools it down, puts a magnet- Field on it so that all of the cobalt sixty atoms, let's say, are oriented in this direction, let's say, away from me. So they're they're they're pointing in this direction. And she waits for the electrons to come out, right, during this decay.

• 1:09:54Krishna Choudhary?

  Now, here is the critical thing. Okay, there's two scenarios that could happen. The cobalt sixty is oriented in one direction. The electron could go forward, or it could go backwards, right? If my cobalt sixty is oriented in one direction, the electron could spit out forward or backwards.

• 1:10:13Lester Nare?

  Yes.

• 1:10:14Krishna Choudhary?

  Now, they're always gonna be

• 1:10:17Krishna Choudhary?

  the the spin is always gonna be oriented in the same direction as the cobalt sixty because of conservation of angular momentum, right? Like, the the cobalt sixty has an initial angular momentum that is away from me.

• 1:10:30Lester Nare?

  Yes.

• 1:10:30Krishna Choudhary?

  So the electron that's going out is always gonna have an angular momentum that's away from me. The question is, the direction of motion, is it gonna be away from me or towards me? Those are the two scenarios, right? And in a world that doesn't care about left or right handedness, both of those directions should be exactly equally probable.

• 1:10:55Lester Nare?

  Got right.

• 1:10:56Krishna Choudhary?

  I should have an equal number of electrons coming from the front as from the back.

• 1:11:00Lester Nare?

  Yes.

• 1:11:01Krishna Choudhary?

  Because I've oriented the cobalt in in in the front direction, let's say. But if the world doesn't care, then the electrons should come out from the front and from the back equally likely.

• 1:11:11Lester Nare?

  Yes.

• 1:11:11Krishna Choudhary?

  Because they're all oriented. I mean, sure, the electrons are all right handed orientation, but if the universe doesn't care about right handed orientation, then the front and the back should be equally likely. That is not what she saw.

• 1:11:25Lester Nare?

  So, okay, got it.

• 1:11:27Krishna Choudhary?

  All of the electrons came out from the back.

• 1:11:31Lester Nare?

  Interesting.

• 1:11:32Krishna Choudhary?

  All of the electrons came out from the back.

• 1:11:33Lester Nare?

  So the universe does.

• 1:11:35Krishna Choudhary?

  The universe does care.

• 1:11:38Krishna Choudhary?

  That's so funny because after all of that.

• 1:11:41Lester Nare?

  After all of that.

• 1:11:41Krishna Choudhary?

  After all that.

• 1:11:43Lester Nare?

  Yeah.

• 1:11:44Krishna Choudhary?

  But it's insane.

• 1:11:45Lester Nare?

  It does actually matter.

• 1:11:46Krishna Choudhary?

  It does actually matter. Left and right handedness is something that the universe does care about. This is schematic. You've got the magnetic field in one direction. The cobalt 60 is oriented in that one direction. There's two possibilities. The electrons going out front and going out back. But the electrons only come out the back. Because they're constrained by which way they can spin.

• 1:12:06Lester Nare?

  Okay.

• 1:12:07Krishna Choudhary?

  Right? So, so if I could spin this way, I can only come out this way. In some mirror world, let's say that I have an anti cobalt made out of anti protons and anti neutrons. And the thing that's coming out is a positron instead of a electron. Then it would come out the front.

• 1:12:23Lester Nare?

  Hmm. This goes back to the same analogy of, of like when we're looking at the mirror. It's the same direction. It's, it's, okay. So let me take a step back.

• 1:12:35Krishna Choudhary?

  It's crazy, dude.

• 1:12:36Lester Nare?

  So

• 1:12:39Lester Nare?

  the experiment proved that there's not symmetry in the mirror image.

• 1:12:44Krishna Choudhary?

  No, the mirror image physics is different.

• 1:12:47Lester Nare?

  Is different.

• 1:12:47Krishna Choudhary?

  From our image.

• 1:12:48Lester Nare?

  From our image.

• 1:12:49Krishna Choudhary?

  Yeah. Let me, let me, let me get a little bit more specific.

• 1:12:52Lester Nare?

  Okay.

• 1:12:53Krishna Choudhary?

  Okay, let me get a little bit more.

• 1:12:57Krishna Choudhary?

  Yeah, let me, let me, let me say it this way. Okay. I've got my cobalt nucleus, right?

• 1:13:03Lester Nare?

  Yes.

• 1:13:03Krishna Choudhary?

  My cobalt nucleus is in this direction. It's spinning clockwise.

• 1:13:08Lester Nare?

  Yes.

• 1:13:08Krishna Choudhary?

  Right? In my mirror world, the cobalt nucleus is also spinning clockwise.

• 1:13:13Lester Nare?

  Right.

• 1:13:13Krishna Choudhary?

  Yes?

• 1:13:14Lester Nare?

  Yes.

• 1:13:14Krishna Choudhary?

  Okay. So in my world, the cobalt nucleus is spinning clockwise. But the electrons are shooting out towards me.

• 1:13:25Lester Nare?

  Yes.

• 1:13:26Krishna Choudhary?

  Right?

• 1:13:27Lester Nare?

  Yes.

• 1:13:27Krishna Choudhary?

  In the mirror world, if everything was exactly symmetric.

• 1:13:32Krishna Choudhary?

  The electrons should be shooting towards the mirror Krishna.

• 1:13:35Lester Nare?

  Not right, not towards you.

• 1:13:37Krishna Choudhary?

  But it'd be coming towards the real Krishna.

• 1:13:39Lester Nare?

  Right, right, yeah, yeah.

• 1:13:41Krishna Choudhary?

  The physics is different. You see what I'm saying? Because the spin of the cobalt hasn't changed in the mirror world.

• 1:13:47Lester Nare?

  Yes.

• 1:13:47Krishna Choudhary?

  But if the physics is the same, the electron coming towards me in the mirror world, the electron should be going that way.

• 1:13:54Lester Nare?

  Yes.

• 1:13:54Krishna Choudhary?

  But they'd be coming back this way.

• 1:13:56Lester Nare?

  Back this way. So there is not, there is not this conservation of parity.

• 1:14:03Krishna Choudhary?

  There's not a conservation of parity when it comes to beta decay.

• 1:14:05Lester Nare?

  When it comes to the weak nuclear force.

• 1:14:07Krishna Choudhary?

  When it comes to the weak nuclear force.

• 1:14:09Lester Nare?

  Specifically, so there is, it's one of those things where there is an exception specific to, not to gravity, not to the strong nuclear force.

• 1:14:19Krishna Choudhary?

  Not to the, not to the electromagnetism either.

• 1:14:22Lester Nare?

  Not to electromagnetism either, but the weak, the tiny.

• 1:14:27Krishna Choudhary?

  The tiny, the weakling.

• 1:14:28Lester Nare?

  Yeah.

• 1:14:28Krishna Choudhary?

  The weak nuclear force.

• 1:14:30Lester Nare?

  Does not have this conservation law that is true everywhere else, which is fascinating.

• 1:14:35Krishna Choudhary?

  That's crazy.

• 1:14:36Lester Nare?

  No, that is crazy.

• 1:14:37Krishna Choudhary?

  That is, dude, it's like, cause now we can DM our aliens.

• 1:14:41Lester Nare?

  Right, right.

• 1:14:41Krishna Choudhary?

  We can DM our alien and be like, hey, prepare some cobalt 60, right? And then, and then, and then orient it in whatever, whatever way you want. Orient it in whatever magnetic field you want. And the electron that comes out, the way it's gonna come out, now pretend the electron is going out this way, then the way that it turns, the left, my heart is on the left, the way that it turns.

• 1:15:05Lester Nare?

  Yes.

• 1:15:05Krishna Choudhary?

  You know?

• 1:15:06Lester Nare?

  Is left. This was Feynman's original Martian problem?

• 1:15:08Krishna Choudhary?

  This is, this is, Feynman, Feynman like talked about all of these things in the context of this Martian problem.

• 1:15:16Lester Nare?

  Martian problem.

• 1:15:16Krishna Choudhary?

  In his, in his Feynman lectures.

• 1:15:18Lester Nare?

  And this is the actual solution to how can you tell the Martian left or right? Is you can use beta decay or the weak nuclear force as, as the one area where there's an exception to the conservation of parity, as the methodology by which you can communicate left-handedness.

• 1:15:34Krishna Choudhary?

  Left-handed, and now, now we can do that by simply describing an experiment. This is huge.

• 1:15:39Lester Nare?

  Right.

• 1:15:39Krishna Choudhary?

  It means the universe does care.

• 1:15:40Lester Nare?

  Okay, yes. About left and right.

• 1:15:42Krishna Choudhary?

  Yes, which is so funny. That's crazy.

• 1:15:44Lester Nare?

  That's so that in the the story arc we got to get there. And again, this is goes back to why from first principles matters so much because people don't just like make things up out of whole cloth. You know what I mean? There's this decades long conversation.

• 1:16:00Krishna Choudhary?

  Yeah.

• 1:16:00Lester Nare?

  That's going back and forth and people are really thinking about the fundamentals and creating experiments in which to be able to say yes or no. And a lot of times the it's failed. It's it's not a success.

• 1:16:13Krishna Choudhary?

  Yeah.

• 1:16:13Lester Nare?

  Until someone like Wu, in this case, creates that experimental design that just perfectly.

• 1:16:19Krishna Choudhary?

  And it's there's no bells and whistles. It's just it's like so obvious.

• 1:16:24Lester Nare?

  In retrospect.

• 1:16:25Krishna Choudhary?

  In retrospect, it is. Yeah. Yeah, somebody. Yeah, it's.

• 1:16:29Lester Nare?

  That's fascinating.

• 1:16:30Krishna Choudhary?

  Really unfortunate. Actually, she didn't win the Nobel Prize for it. Tsung Dao-Li and Yang won the Nobel Prize, and it really should have been a three part Nobel Prize. And it is one of the most. It's a real shame. It's the one that almost every physicist agrees.

• 1:16:46Lester Nare?

  Right.

• 1:16:47Krishna Choudhary?

  Like, without a doubt, Wu should have won that Nobel Prize. Because there's no Tsung Dao-Li and Yang without Wu.

• 1:16:54Lester Nare?

  Right.

• 1:16:55Krishna Choudhary?

  Actually proving it.

• 1:16:55Lester Nare?

  Right, right. That that was what created the actual experimental.

• 1:16:59Krishna Choudhary?

  Yeah, yeah, yeah. And and and like people like Paul Lee were pissed off about it. Wigner was pissed off. Like, everybody in the community was like, what are you guys doing? That you haven't you didn't give it to Wu. It was almost, yeah, yeah. So it was really unfortunate, you know, for this, this, you know, giant of physics.

• 1:17:19Lester Nare?

  Seminal figure.

• 1:17:20Krishna Choudhary?

  Seminal figure. Like, there's no, like, even you don't have to. There is. It might be because she was a woman, probably, honestly, back then in the 1950s at the time.

• 1:17:31Lester Nare?

  Yeah.

• 1:17:32Krishna Choudhary?

  Probably. It's so it's so unfortunate because, you know, it's it's like clear and obvious. How big of a deal. This is, right?

• 1:17:43Lester Nare?

  We need VAR for the Nobels.

• 1:17:46Krishna Choudhary?

  Yeah.

• 1:17:46Lester Nare?

  Because that was a clear and obvious error by the officials at the time.

• 1:17:49Krishna Choudhary?

  Yeah, and at the time, like, this was in December, she, you know, took off her holidays.

• 1:17:53Lester Nare?

  Yeah.

• 1:17:53Krishna Choudhary?

  She canceled her holidays to do this experiment because she knew how big it would be.

• 1:17:56Lester Nare?

  Right.

• 1:17:57Krishna Choudhary?

  Right? I mean, and in January, when, when all of the results came out, even before the paper was published, everyone in the physics community was talking about it. They were writing letters to each other. It was by telegram. The paper was under peer review, but it spread like the new gospel.

• 1:18:13Lester Nare?

  Yeah.

• 1:18:14Krishna Choudhary?

  That parity is no longer a rule in the universe.

• 1:18:17Lester Nare?

  Which is a big.

• 1:18:18Krishna Choudhary?

  That's a big deal, dude.

• 1:18:19Lester Nare?

  Big deal.

• 1:18:20Krishna Choudhary?

  That's a big deal.

• 1:18:20Lester Nare?

  That's a very big deal.

• 1:18:21Krishna Choudhary?

  Because parity had that pedestal.

• 1:18:23Lester Nare?

  Yeah.

• 1:18:24Krishna Choudhary?

  That was the same as translation in space, translation in time.

• 1:18:27Lester Nare?

  Conservation of the energy.

• 1:18:28Krishna Choudhary?

  Yeah, yeah.

• 1:18:29Lester Nare?

  Imagine if someone rolled up the days like, oh, the conservation of energy actually is not a thing.

• 1:18:32Krishna Choudhary?

  Not a thing, like. Yes, that would be like, yo, what are you talking about? It would be a huge. It would be a huge deal.

• 1:18:39Lester Nare?

  It would be a huge deal.

• 1:18:40Krishna Choudhary?

  Yeah, yeah, it spread like wildfire across, across the world, you know, through the telegrams. Um, so it's really unfortunate that she didn't win the Nobel Prize. Um, and that is what won Yang the Nobel Prize.

• 1:18:55Lester Nare?

  Right.

• 1:18:56Krishna Choudhary?

  Okay, what he's most known for actually nowadays, and I'm just gonna go through this real quick because I don't have the expertise yet. I'm, I'm reading this textbook called Physics from Symmetry.

• 1:19:08Lester Nare?

  Mm-hmm.

• 1:19:08Krishna Choudhary?

  Um, I'll put the, I'll put the, the author, I forget the author, but there's this, it's an amazing textbook, Physics from Symmetry. And it's, and it's going through talking about, um, how to build up physics

• 1:19:21Lester Nare?

  Mm-hmm.

• 1:19:22Krishna Choudhary?

  from an axiomatic perspective of like, what if the symmetries are axioms? How do we build up a universe?

• 1:19:28Lester Nare?

  Based on those.

• 1:19:29Krishna Choudhary?

  Based on those. And that sort of way of thinking about stuff came from something called Young-Mills theory. Okay, this is Young. His tour de force, the reason why he's considered the great, right? Like, this parody stuff is cute.

• 1:19:45Lester Nare?

  Yeah.

• 1:19:46Krishna Choudhary?

  Okay?

• 1:19:46Lester Nare?

  Yeah.

• 1:19:47Krishna Choudhary?

  The real reason why he's considered like, one of the greatest of the 20th century is because of the Yang Mills theory. So Yang's been obsessed with symmetry for the very longest time, right? And while started working on these, Hermann Weyl started working on symmetries in physics. He piggybacked off of Notter to, and he renamed these symmetries, something called gauge symmetries. After like the gauges of railroad tracks and how they're all like, you know, standardized.

• 1:20:15Lester Nare?

  I literally remember being in Terrace at Princeton and hearing any number of you guys talk. Someone was constantly on about gauge theory.

• 1:20:24Krishna Choudhary?

  Because.

• 1:20:25Lester Nare?

  Constantly.

• 1:20:27Krishna Choudhary?

  Dude, gauge theory, once, once, I mean, I'm just getting into it with this textbook and it's, it's like intoxicating. How beautiful it is.

• 1:20:35Lester Nare?

  Okay.

• 1:20:36Krishna Choudhary?

  Like, imagine, it's completely inverting the logic of how you want to study the universe, right? Because it's saying like, it's postulating a symmetry to derive a force. Right? It's saying, we can take it as an axiom, the fact that these symmetries exist.

• 1:20:56Lester Nare?

  Yes.

• 1:20:56Krishna Choudhary?

  And then ask, what is the kind of universe that we would live in if these symmetries exist? Right? It's almost, dude, it's like, dare I say, a little religious in some sense. It's, it's insane, right? So, so here's what I, here's, here's the only thing that I'm going to say about like, sort of how the math that works.

• 1:21:18Krishna Choudhary?

  Well, we talked about how the wave function, right? It's a complex number.

• 1:21:20Lester Nare?

  Yes.

• 1:21:21Krishna Choudhary?

  It's everywhere in space. If I change the phase of that wave function, that complex number, and the only thing I care about in terms of observables is the magnitude of that complex number, then it doesn't matter how, how much I change the phase.

• 1:21:32Lester Nare?

  Yes.

• 1:21:32Krishna Choudhary?

  As long as I change the phase everywhere.

• 1:21:34Lester Nare?

  Yes.

• 1:21:34Krishna Choudhary?

  The observable is going to be the same. That gives me conservation of charge. Okay. Um, we can ask, what if I want to change the phase differently everywhere in space and time?

• 1:21:44Lester Nare?

  Yes.

• 1:21:44Krishna Choudhary?

  Okay, so instead of a global symmetry, which is, which is where I change the phase everywhere, I change the phase locally.

• 1:21:50Lester Nare?

  Yes.

• 1:21:50Krishna Choudhary?

  Is there a local symmetry that I can do? And that's where we, what you can do is you can say, okay, if I change the local phase everywhere, then I can't really do a derivative in the right sense, right? Because the derivative, a spatial derivative in some sense, is the change between this quantity and this quantity divided by how, how far apart they are. Well, if I change this guy and I don't change this guy, now my derivative is really not well-defined. If I change them by the same amount, then that change cancels out and my derivative is fine. But if it's a local thing, then the derivative is no longer well-defined.

• 1:22:25Lester Nare?

  Yes.

• 1:22:25Krishna Choudhary?

  But what I can do is I can compensate for it. And um, there was um, there was a famous physicist who actually said, it's kind of like, you know, if every city had its own local currency and they just decided to change their currency denomination or whatever, you would need some way, some exchange rate

• 1:22:46Lester Nare?

  Yeah.

• 1:22:47Krishna Choudhary?

  to, to make sure that I'm still paying for the right amount of stuff.

• 1:22:50Lester Nare?

  Yes.

• 1:22:50Krishna Choudhary?

  Right? That's where a gauge field comes in. A gauge field is something you introduce to preserve the local symmetry where it's like, okay, I changed the phase here, but not here. What do I have to do to, to compensate for that? To make sure that all of my mathematics is still fine? That my, I can still do a derivative. It's something that becomes like a covariant derivative where it depends on like where I'm taking the derivative. But all of these things introduce this thing called a gauge field, which is a new entity. It can also be known as a connection. And the sole purpose of this field is to connect the different symmetry choices that I have in all of these different neighboring points. And it provides a rule on how to compare all of my different thingies, right?

• 1:23:33Lester Nare?

  It's the like, uh, like a currency exchange.

• 1:23:36Krishna Choudhary?

  Yes.

• 1:23:37Lester Nare?

  It's like, it's like the easiest analogy.

• 1:23:38Krishna Choudhary?

  It's the easiest way to think about it.

• 1:23:39Lester Nare?

  And just in my head right now in this context.

• 1:23:41Krishna Choudhary?

  Exactly, yeah. And um, it turns out that currency exchange is itself a field that is very Very, very much real because that currency exchange has a certain value at each point, right? Depending on this city versus this city, this city versus this city. That that exchange rate has a different value at each point. So it becomes kind of like a field.

• 1:24:02Lester Nare?

  That makes sense.

• 1:24:02Krishna Choudhary?

  Right? Kind of like, and so, and so that field permeates space time. And the real miracle of gauge theory is that that field is when it's curved, when it like changes, that exerts a force on the stuff that it's affecting. And that force is, i- i- it can manifest in real things. For example, in the electromagnetic field, that force is the electromagnetic force. That is the photon, the thing from the field, that gauge field.

• 1:24:38Lester Nare?

  Yeah.

• 1:24:39Krishna Choudhary?

  Is like the elec- the electromagnetic four vector that becomes a photon.

• 1:24:44Lester Nare?

  Okay, now this is.

• 1:24:45Krishna Choudhary?

  This is getting crazy, but that's what Yang Mills was doing, dude.

• 1:24:48Lester Nare?

  Okay.

• 1:24:48Krishna Choudhary?

  That's what, and Yang Mills was like, this is crazy.

• 1:24:51Lester Nare?

  Yeah.

• 1:24:51Krishna Choudhary?

  What if I take this to new heights and I start applying it to the, the strong nuclear force?

• 1:24:57Lester Nare?

  Right.

• 1:24:57Krishna Choudhary?

  And the weak nuclear force. This is, he, he was actually at, um, he, he had a shared office at Brookhaven at the time. Brookhaven had this thing called the Cosmotron and he shared an office with, um, Robert Mills. And the two of them start talking about Mills's like fascination with symmetry, right? And the two of them start thinking, okay, how can I make this something that has to do with nuclear forces? Right? Can I, can I make a quantum field theory for nuclear binding? That explains all of the physics just based on symmetry. It becomes, it, it's the start of something called Yang Mills theory.

• 1:25:31Lester Nare?

  Mm hmm.

• 1:25:31Krishna Choudhary?

  Right? It was not at its, when they devised it, it was not at its final form. There were still problems. They were getting these things called like massless particles. Where like everything had no mass and they're like, nah.

• 1:25:44Lester Nare?

  We have some photons.

• 1:25:45Krishna Choudhary?

  Yeah, yeah, but like not everything has no mass and, and, and there were still a bunch of things that had to happen. Stephen Weinberg came, came in later to, to say, okay, we can actually combine that gauge theory with, with a kind of symmetry breaking, which we don't have to get into, but, but he introduced this idea of symmetry breaking. Then we get something like the Higgs, which comes in to give mass to the W and Z bosons. And so all of the standard model starts percolating out of this idea that we can take symmetries of stuff, right? And and start creating physics.

• 1:26:20Lester Nare?

  From those.

• 1:26:20Krishna Choudhary?

  From that axiomatic kind of framework.

• 1:26:24Lester Nare?

  We we are, we are definitely. I have so many thoughts about this.

• 1:26:28Krishna Choudhary?

  But are you starting to see why he's such a big deal in the 20th century?

• 1:26:33Lester Nare?

  No, I hundred percent get it.

• 1:26:34Krishna Choudhary?

  Right, it's not the parody experiment is nice, but this stuff is just like, whoa.

• 1:26:41Lester Nare?

  I feel the other time I felt the same way as this when we was when we talked about the Heisenberg uncertainty principle. It makes me feel the same level of like, oh.

• 1:26:53Krishna Choudhary?

  Yeah.

• 1:26:53Lester Nare?

  You know what I mean?

• 1:26:54Krishna Choudhary?

  Makes you feel weird in a nice way, but in a weird way.

• 1:26:57Lester Nare?

  Right, like it's it's from just again, for my from my layman's perspective, like that's the easiest like category analogy that I can. Cause I can much more almost intuitively understand like GR and like where Einstein was coming from like. That's just for whatever reason easier for me to.

• 1:27:15Krishna Choudhary?

  Yeah, he was a sage, that's what I mean. He was a sage.

• 1:27:17Lester Nare?

  That's weird, yeah.

• 1:27:18Krishna Choudhary?

  Not a magician.

• 1:27:19Lester Nare?

  Not a magician.

• 1:27:19Krishna Choudhary?

  Yeah.

• 1:27:20Lester Nare?

  But this this just feels like hand wavy and it works.

• 1:27:24Krishna Choudhary?

  And it works.

• 1:27:25Lester Nare?

  And it works and I but it's just like, but like, can we go back to like, wait a minute?

• 1:27:31Krishna Choudhary?

  Yeah, yeah. And I mean, I'm still honestly, I'll be honest, I'm still kind of there with you on that whoa. Right, I still I need to reread this textbook, I need to go through like some quantum field theory textbooks to really try to get. What is going on in in my coursework, I went all the way up to, you know, quantum three in my grad graduate school. So we did like elementary quantum field theory. I had I I know how to derive the Dirac equation and things like that. But young Mills, I'm still sort of wrapping my head around.

• 1:28:03Lester Nare?

  It's it like you're the way you've created the journey.

• 1:28:07Krishna Choudhary?

  But that's the that's the way that I've talked about it now is sort of how I've constructed.

• 1:28:13Lester Nare?

  Right.

• 1:28:13Krishna Choudhary?

  The the understanding in my head.

• 1:28:16Lester Nare?

  Right.

• 1:28:16Krishna Choudhary?

  You know?

• 1:28:16Lester Nare?

  And because I know you so well, it helps me like you've created a construction that I can engage in at a very, very rudimentary level. But you've at least given me the Lego blocks and the building blocks of the framework of like what it is and why it matters. And like, why it's this like this inversion of the way to think about things by starting from this like some axiomatic symmetry.

• 1:28:41Krishna Choudhary?

  Yeah.

• 1:28:42Lester Nare?

  Argument as like your starting point to then build around.

• 1:28:48Krishna Choudhary?

  Yeah.

• 1:28:49Lester Nare?

  Versus like the other, it's just my brain.

• 1:28:54Krishna Choudhary?

  Yeah.

• 1:28:55Lester Nare?

  This is, look, for the, for those watching, this is, well, this is what happens if we only do one story.

• 1:29:00Krishna Choudhary?

  Yeah. Yeah, cuz then, cuz then I like really.

• 1:29:02Lester Nare?

  Then we just go in. And so if you're still listening at this point in the pod, number one, leave a comment so we know.

• 1:29:10Krishna Choudhary?

  Yeah.

• 1:29:11Lester Nare?

  That you, you actually like are on the journey with us.

• 1:29:14Krishna Choudhary?

  Yeah.

• 1:29:15Lester Nare?

  Because part of this, like, I really am trying to grok these concepts.

• 1:29:19Krishna Choudhary?

  Yeah.

• 1:29:19Lester Nare?

  And create at least a framework in my mind of what's happening here, such that as I decide what direction I wanna take my academic interest for the rest of my life, I'm getting this nice potpourri buffet of everything.

• 1:29:33Krishna Choudhary?

  Yeah.

• 1:29:33Lester Nare?

  Like, but QFT is a little interesting, but I think I'm gonna stick with, uh, stick with, you know, whatever. Seag ass thing.

• 1:29:40Krishna Choudhary?

  Yeah.

• 1:29:41Lester Nare?

  Go in that direction.

• 1:29:42Krishna Choudhary?

  I mean, this stuff is just so deep. I just, even I'm like, as I'm like, thinking about it, as, as I read, I have to read the, the sections over and over again to make sure I get every little thing, because it's just so beautiful. And I'm like, this can't be real.

• 1:29:57Lester Nare?

  Right.

• 1:29:57Krishna Choudhary?

  Right?

• 1:29:58Lester Nare?

  Right.

• 1:29:58Krishna Choudhary?

  That like, what, we're just so like, the unitary two by two matrices that have a determinant of one, like, are all of a sudden, like, what? So, so, so that's, that's just the world is just, eh, you know?

• 1:30:17Lester Nare?

  This is, this is nerd paradise.

• 1:30:19Krishna Choudhary?

  Yeah.

• 1:30:20Lester Nare?

  I know there are gonna be some people who will be like, I'm exactly.

• 1:30:23Krishna Choudhary?

  Yeah.

• 1:30:23Lester Nare?

  Like who just can, can empathize and sympathize.

• 1:30:26Krishna Choudhary?

  It doesn't make any sense to me, but at the same time, it's making so much sense.

• 1:30:31Krishna Choudhary?

  That it's just like, eh, what? Why does this work?

• 1:30:35Lester Nare?

  I don't, I don't, I don't.

• 1:30:36Krishna Choudhary?

  It's weird, man. Young. So Young Mill's theory is like really, really crazy.

• 1:30:40Lester Nare?

  I think we.

• 1:30:41Krishna Choudhary?

  Like the fact that the standard model works this way.

• 1:30:44Lester Nare?

  Right.

• 1:30:44Krishna Choudhary?

  Right? And all of the particles obey these, these laws that just come out of symmetry principles of just like, oh, I can do something to my thingy and it doesn't change. That means that there is a conservation of baryon number. That means there's a conservation of charge. That means there's a conservation of color. What are we, what?

• 1:31:05Lester Nare?

  The, the, the fractal community is gonna have a field day.

• 1:31:09Krishna Choudhary?

  It's crazy, dude.

• 1:31:10Lester Nare?

  Everything is fractal.

• 1:31:12Krishna Choudhary?

  Yeah.

• 1:31:12Lester Nare?

  Everything is symmetry.

• 1:31:14Krishna Choudhary?

  Yeah. I mean, okay. So to close out on the story of Young, um, he settled in the Institute for Advanced Study at Princeton for a while.

• 1:31:20Lester Nare?

  Yes.

• 1:31:21Krishna Choudhary?

  Um, that there's a photo of him with all of the classic.

• 1:31:25Lester Nare?

  Wait, it's so funny. When I was studying this stuff, I was like, oh, that looks like Princeton.

• 1:31:27Krishna Choudhary?

  Yeah, it's, you know, the, the window, like the, the table. No, it is. It's, it's the table and the window and, and the way the trees are, you just know it's.

• 1:31:39Lester Nare?

  I love how you also did not say anything.

• 1:31:42Krishna Choudhary?

  No, because I wanted you to, I wanted to be like, yeah, no, that was actually Princeton. That was at the Institute for Advanced Study. The architecture is all the same in that town.

• 1:31:49Lester Nare?

  Yeah.

• 1:31:50Krishna Choudhary?

  In that town, it's like, there's a little bit of Gothic-ness.

• 1:31:52Lester Nare?

  Yes.

• 1:31:53Krishna Choudhary?

  In like the Rocky College and like Blair, but then most of it is just like that classic American.

• 1:31:58Lester Nare?

  Yes.

• 1:31:58Krishna Choudhary?

  Like colonial architecture.

• 1:32:00Lester Nare?

  A hundred percent.

• 1:32:01Krishna Choudhary?

  Um, so he moved to the State University of New York, um, at Stony Brook, where he was the Albert Einstein Professor. Um, then he, uh, he actually became the first director of the Institute for Theoretical Physics there. Now it's called the C N Yang Institute for Institute at Stony Brook University. Um, he was really big on scientific diplomacy. So in 1971, in the Nixon era, when China-US tensions sort of thawed, he went back to China and he helped Chinese physics recover from that Cultural Revolution, um, which was, you know, really bad for academia and all this other stuff.

• 1:32:38Lester Nare?

  Right.

• 1:32:38Krishna Choudhary?

  Um, he established a committee on. Educational exchange with China, he returned to Tsinghua University.

• 1:32:46Krishna Choudhary?

  And in his 1957 Nobel Prize speech, he actually described himself as a product of both Chinese and Western cultures in harmony and in conflict. I thought that was, I thought that was really interesting. So I looked, I looked really into this. There was an interview that was done by Stony Brook University that asked him, what did you mean by that? In harmony? By that? Yeah. What do you mean by in harmony and in conflict? I'm a product of Chinese and Western traditions. He, he went into a lot of Chinese history. He started talking about how China had this amazing, you know, 5,000, 6,000 year old storied history, kind of went into decline in the 19th

• 1:33:31Krishna Choudhary?

  century and the British were trying to carve up China with the Opium Wars and all that other stuff.

• 1:33:40Krishna Choudhary?

  In 1900, there was the Boxer Rebellion. I don't know if you remember this. I remember this from AP World History. I had to learn about it. The Boxer Rebellion was a way for the Chinese to fight back on the imperialists. There was an alliance of eight nations. It was the US, Russia, Germany, Japan, Italy, Britain, France, Austria, Hungary. So all of the guys who were fighting during World War II, all of these imperialist nations, they came together to subdue the Boxer Rebellion in 1900.

• 1:34:14Krishna Choudhary?

  They asked for reparations because that always works and something like hundreds of millions of ounces of silver, which is an astronomical thing at the time from China in, in reparations for the Boxer Rebellion. 10 years after that rebellion, the US Congress passed a law saying that part of the US spoils from all of that silver was going to go back to China to fund academia and scholarships. So they actually funded Tsinghua University in Beijing. They started Tsinghua University, which is where his dad was employed. Right. Where he sort of got his start. Yep. In academia. They also funded scholarships, which is the same scholarship program that

• 1:34:57Krishna Choudhary?

  he came to the US in. So it was this full circle sort of thing that Yang.

• 1:35:05Krishna Choudhary?

  Was involved with, he became very emotional, but that's what he meant when it's in harmony and in conflict, right? Because in conflict, that's what started it. But in harmony, he comes to the United States, he goes to Chicago, earns his degree under Edward Teller, goes on to be one of the great, great physicists of the 20th century. After his retirement from Stony Brook, he goes back to China. He goes back to his alma mater, Tsinghua University, becomes the honorary director of the newly established Institute for Advanced Study over there. He really goes back and returns and pours a lot of effort into advancing fundamental disciplines

• 1:35:49Krishna Choudhary?

  and cultivating a new generation of scientific talent in China. And a lot of people give him a lot of credit for where China is in fundamental physics today.

• 1:35:59Lester Nare?

  I was gonna say, this is what we talked about in a previous episode in this, like in the US, we still have this probably outdated conception around scientific research in China as all being basically driven by this great power war between the US and China. And so there's an incentive to basically fudge the numbers in order to project this idea that they're making these advancements that are effectively hot air. And that conception may have been true 20, 30 years ago. But it is certainly, it is certainly not true today. And you can not only see that in the fundamental research side, but you can also see that in how that research ends up in end user products,

• 1:36:39Lester Nare?

  where the best phones, the best cars, like all the frontier, modern, Western things that we have historically been like, with the exception of really AI right now, which is still, you know, we still have the edge. The Huawei style phones are better, the Yangwang cars are better. Not only, like, that's proven by them selling in the West, right? And feature for feature. And so this is like a really You can certainly say that the, some of these seminal figures have their roots that they've now reestablished are clearly bearing fruit.

• 1:37:13Krishna Choudhary?

  Yeah.

• 1:37:13Lester Nare?

  And the evidence of that is undeniable at this point.

• 1:37:16Krishna Choudhary?

  Exactly, yeah.

• 1:37:17Lester Nare?

  It's, oh my god.

• 1:37:18Krishna Choudhary?

  Yeah, exactly. And, you know, he's, he, he was an instrumental part of that reawakening.

• 1:37:24Lester Nare?

  Right.

• 1:37:24Krishna Choudhary?

  Of China's fundamental science and fundamental physics ecosystem. In 2015, he actually renounced as US citizen so he could obtain and resume his Chinese citizenship. He spoke candidly, pretty much about this journey. He actually said that when he became a US citizen, his father never forgave him for that until he lived, which, that's crazy. And I can understand, like, I mean, my dad would never do that, but if, if your dad does that and you wanna, you know, I can understand. So, so he went back to his, um, his Chinese citizenship. He loved the United States. He called it a beautiful country that had given him, given him incredible opportunities to pursue science. He's also not one of these evangelists, these particle physics evangelists.

• 1:38:08Krishna Choudhary?

  When China wanted to make the next particle accelerator, he was actually against it. Because he was like, particle physics is not, like, going places.

• 1:38:18Lester Nare?

  Yeah, yeah.

• 1:38:19Krishna Choudhary?

  What are you gonna do with a larger accelerator? You're not gonna find new particles. You're just gonna make a bigger accelerator. Which, and everyone in the particle physics community was like, didn't talk to him for like, two years or something. But, you know, he, he was very candid about what he thought about where physics is going. It's, it's, he, it's an incredible life that he lived. You know?

• 1:38:44Lester Nare?

  Yeah.

• 1:38:45Krishna Choudhary?

  Coming up during the war, during World War II in China.

• 1:38:49Lester Nare?

  In China.

• 1:38:49Krishna Choudhary?

  Which is not the best place to be in World War II. It's one of the worst, in fact. Given all of the atrocities that happened under Japanese imperialism there. He managed to make it out, managed to create a name for himself in America, managed to not only create a name, but like, you know, he's, he's sitting down with Einstein and Feynman and, and the big guys, and he's holding his own. And to, to those in the high-energy physics community, and the particle physics community, and the mathematical physics community, Yang is...

• 1:39:24Krishna Choudhary?

  The Mount, one of the Mount Rushmore's, you know? Young-Mills' theory is, is really, really like fundamental. And I hope you get an idea of, now that I've talked to you about like what it really means, like how it turns its head, how it turns the head of all of physics.

• 1:39:41Lester Nare?

  Yes.

• 1:39:41Krishna Choudhary?

  To become this axiomatic kind of pursuit.

• 1:39:44Lester Nare?

  Yes.

• 1:39:44Krishna Choudhary?

  From symmetry to, to laws, rather than from laws to.

• 1:39:48Lester Nare?

  Yes.

• 1:39:48Krishna Choudhary?

  The other way around.

• 1:39:49Lester Nare?

  Everything else.

• 1:39:50Krishna Choudhary?

  Yeah, um, he died very recently and we, we have one final photo of Chinese students lined up at Tsinghua University to pay tribute with photos, with flowers. Um, there was a line to, to, to pay respects to him. He was a huge deal in China, as he should be.

• 1:40:07Lester Nare?

  As he should be.

• 1:40:08Krishna Choudhary?

  He was, he was the first Chinese to win the Nobel Prize, along with Tsung Deli. So, you know, together. But yeah, he's completely transformed physics in the 20th century, right? Um, you, one, one could say there's few people that you could say is the father of the standard model, but he'd be one of them.

• 1:40:30Krishna Choudhary?

  Yeah.

• 1:40:30Lester Nare?

  Just, it's just what a journey.

• 1:40:33Krishna Choudhary?

  Yeah, yeah.

• 1:40:33Lester Nare?

  One big story.

• 1:40:35Krishna Choudhary?

  Yeah.

• 1:40:36Lester Nare?

  Uh, to one of the goats of the 20th century Nobel Prize winner.

• 1:40:40Krishna Choudhary?

  I know it was long, but I really had to, I mean, I, I had to share with you all of the things that I, I found, I mean, I knew about Young-Mills' theory, but not to the extent.

• 1:40:51Lester Nare?

  Yeah.

• 1:40:51Krishna Choudhary?

  Yeah.

• 1:40:52Lester Nare?

  It's just an incredible, an incredible life story. It has everything.

• 1:41:00Krishna Choudhary?

  Yeah.

• 1:41:00Lester Nare?

  It has war, love, geopolitics, fundamental research.

• 1:41:07Lester Nare?

  Uh, you know, those who should have been there with you, those who were not able to be there with you. These, this sort of intersectionality, like, you know, globalists, like everyone's like, oh, the globalists are terrible. I mean, you know, we are, we have now been given this gift. Uh, because again, we have allowed smart folks to come in and go to institutions like Chicago, go to institutions like Princeton, go to Stony Brook.

• 1:41:35Lester Nare?

  And give back something that is just, I'm going to be thinking about this one for, for some time. This was our one big story, uh, on one of the goats of physics, uh, Yang Chengning.

• 1:41:50Lester Nare?

  Both on this parody concept, conservation of parody and Young Mills theory, Nobel Prize winner, we're gonna claim he's a Princetonian.

• 1:41:59Krishna Choudhary?

  Yeah, yeah, yeah, it counts.

• 1:42:01Lester Nare?

  He was there.

• 1:42:01Krishna Choudhary?

  He was there.

• 1:42:02Lester Nare?

  Guys, there's a picture of him there. I sat where he was sitting.

• 1:42:05Krishna Choudhary?

  Yeah, yeah, yeah.

• 1:42:06Lester Nare?

  So we'll take the win, but in all seriousness.

• 1:42:09Krishna Choudhary?

  Probably drank a few beers there on that table, too.

• 1:42:11Lester Nare?

  Hundred percent. To what a wonderful life lived and to, and just, this is meant to be a love letter to the work. And it may be unlocking interest for some listeners who might not have been interested in this area that one day may continue on the legacy and build on the foundation that's been here, or that's been built, rather. As always, my name is Lastonare, joined by my co-host and our resident PhD, Krishna Choudhary. Thank you for joining us for this deep dive special episode. We will be back next week. This is From First Principles.