Short Wave - The Queen of Nuclear Physics (Part One): Chien-Shiung Wu's Discovery

Episode Date: May 20, 2022

In the 1950's, a particle physicist made a landmark discovery that changed what was known about how the universe operates. Chien-Shiung Wu did it while raising a family and an ocean away from her relatives in China. Short Wave's Scientist-In-Residence Regina Barber joins host Emily Kwong to talk about that landmark discovery—what it meant for the physics world, and what it means to Regina personally as a woman and a Chinese and Mexican American in physics. Email the show at [e-mail] pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey everyone, Regina Barber here. So this May is AAPI Heritage Month, and we at Shortwave are celebrating by sharing the stories from the Asian American and Pacific Islander communities. We couldn't let this month pass by without revisiting one of the legends of shortwave lore, a pioneering Chinese American, one of the best experimentalists, and the queen of nuclear physics, Chen Chung-Wu.

In this two-part series, we discuss Wu's life, work, and impact. We talk radioactive cobalt, antimatter, and a secret project that would change her life and the lives of countless others. We hope you enjoy. Okay, short waivers, we have a story in two acts for you about a discovery that changed the world, and it all went down in a particle physics lab in the 1950s. That's where one scientist ran a painstakingly difficult experiment that shattered fundamental ideas about how our universe works at the tiniest levels. We'll talk more about her backstory in part two, which you can listen to tomorrow. For part one, we're going to decipher the science of her

accomplishment with our very own scientist in residence, Dr. Regina Barber, who is an astrophysicist by trade, though her Ph.D. is in physics. Physics was an accident. Astronomy was what I loved. And it was at some point in Regina's physics career in some hallway that she saw a face that made her do a double take, a face that looked like her own. There are these posters that are on many physics department's walls. And they go through each decade of what was happening in physics. So it's like 1900, 1910, 1920s. And in the 1950s panel, there was this, you know, Asian woman.

The woman on that poster was Dr. Qian Shengwu, widely considered the queen of nuclear physics, for an experiment that upended a decades-old assumption in her field. Today on the show, Regina Barber and I dig into the Wu experiment, what it meant for physics at the time, and what it means to Regina personally as a Chinese and Chicana scientist today. I'm Emily Kwong, and you're listening to Shortwave, the Daily Science podcast from NPR.

Okay, so Regina, Dr. Barber, Gina B, for the last few weeks, you've been kind of diving into the life of Dr. Wu and her career as well. Right. What do you now know about who she was to the world of physics? Yeah. So seeing her in that poster really impressed me, just knowing that she did particle physics. And knowing that she was an experimentalist. What's an experimentalist?

So, yeah, experimentalist is somebody who actually, like, does experiments, who actually tests these theories. A theorist usually just does models. on computers, like pen and paper kind of stuff, but an experimentalist, like, has a lab. The experimentalists are doing the work, doing the physics. And that's the kind of scientist that Dr. Wu was? Right. And she was one of the best. Being an experimentalist is, like, rough on your psyche because stuff doesn't work. And sometimes they don't, it doesn't work because of, like, the discoveries you're making.

Sometimes it doesn't work because of you didn't buy the right equipment because something broke. She was highly respected in the science community. And this was on top of her being an immigrant, a woman, and a, you know, a woman of color. So Dr. Wu, she was kind of growing in her career and in prominence in the 1950s. And this was a time when people thought that nature, like the world around us worked in a particular way. What did people think back then? Yeah, so scientists had this idea that they were small, discrete chunks of matter, and we called that atoms. And we knew about the atom, we knew about electrons, and about the nucleus.

But what we know now is that the nucleus can be broken into subatomic particles, much smaller particles that actually relate to forces in our universe. And that interaction between particles and these, like, fundamental forces is where Dr. Wu's story comes into play here. So what did people think about forces back then? Yeah, well, back then people knew all these forces acted on different particles. in different ways, but they thought they all acted symmetrically. But what does that mean exactly? It means that if I were to flip everything, I would flip from top to bottom, I'd flip left to right. If we were in this mirror universe, all the forces would act the exact same way in perfectly

symmetrical ways. Like, everything would work the same. There's no direction that's preferred in the universe. This idea was called conservation of parity. Okay. So that was the dominant idea at the time. And when you say fundamental forces, what do you mean? Like, Star Wars forces?

I wish, kind of. So the four fundamental forces, you'll actually recognize them. One's gravity, mass getting attracted to mass. The other is the electromagnetic force, which is an electron being attracted to a proton or two protons being repelled. And then there are these other two, the nuclear forces. The first one is the strong nuclear force, which kind of keeps that nucleus together, like goes beyond. on those two protons wanting to get away from each other, keeps the nucleus bound. And then there's the weak nuclear force.

What does the weak nuclear force do? So the weak nuclear force, it's responsible for some radioactive decay of atoms, for the beta decay. Oh, right. And Dr. Wu studied beta decay. And you're saying beta decay is caused by the weak force. Right, correct. So let's get to this moment, her moment, which is what Dr. Wu was doing with beta decay at the time. And why these two theoretical physicists, Tidi Lee and Cien Yang, approached her in the first place to help them run these experiments?

So these two theorists, Yang and Lee, they were both Chinese Americans as well. And I remember reading this and thinking, oh, they just went to her because she's also Chinese American. But no, not at all. Like, they went to her because she was like the best in the business. She took a whole bunch of cobalt 60 atoms, a version of cobalt that's radioactive. or unstable. It doesn't really want to stay cobalt 60. And she aligned them. So she made sure that they were all kind of in the same direction. And to do that was so, so difficult. She had to bring these atoms to a really, really cold temperature. Because you have to make sure that these cobalt 60 atoms aren't really moving too much. You want them all to be aligned because as they emit these electrons, as they go through this weak nuclear force process, And start decaying. And start decaying, you want to see if they're emitting these particles in equal direction or in a certain direction.

And what were people expecting to see from this experiment? If the rule, conservation of parity, were true for the weak force. And what did she actually say? Yeah, so if the rule was true, all these aligned cobalt atoms would be emitting these high-energy particles, specifically electrons, equally from the north end and the south end of these cobalt atoms. But what Dr. Wu found is that after all of these atoms were all aligned, most of the electrons were being shot out in a specific direction. In the southerly direction, so think about it like this.

Suddenly your universe, you're now in that mirror universe, you'd be able to distinctly tell that that's the mirror universe, not our universe. And that's not symmetry, right? That is a violation of parents. Right, which proved that the universe is a little asymmetrical when it comes to the weak force. That is a major, major, major, major finding. What did other physicists think about this experiment? The scientific community, the physics community was just blown away by this.

They just assumed this idea of symmetry with these forces would be the same, and it wasn't. But just for this force, just for the weak nuclear force, and that was just, it made no sense. Yeah, I see that. And when we think about physics today, in our time, what are some of the long-term implications of Dr. Wu's finding of this experiment? Well, it led to other parity investigations, so looking at symmetry in other subatomic places. And those parity investigations help scientists distinguish between matter and antimatter. So matter is what we're made up of, right? But antimatter also exists, which is just like matter in its size and mass, but everything is. else is opposite. And if matter and antimatter meet, it explodes. They annihilate each other. Oh, they're like mortal enemies. Yes. So, like, there's this question of why we're here at all. Like, why haven't all the matter and antimatter in the universe just met up and exploded and annihilated

each other? But if something made it so that there's more matter than antimatter, that there's this preference for matter over antimatter, that would explain how we're here, how the universe is made of matter mostly. Oh, my gosh. So what you're saying is that this notion of asymmetry may be why after the Big Bang there's more matter than antimatter, meaning the right conditions for us to even exist, for the world as we know it to exist. Maybe, maybe, maybe, maybe.

Like, ramifications of this are still being discussed. So after this experiment was run and the paper was published, shortly after that, the theoretical physicists who approach Dr. Wu, Dr. Lee and Dr. Yang, they both won the Nobel Prize in physics. Yeah. And Dr. Wu did not. Correct. Why? I think there's a lot of things that kind of go into it. It's that she was a woman, that she was a woman of color, and that she was an experimentalist. And there's this hierarchy in physics where the theorists are seen as the smartest, the ones that are really doing the work. And the experimentalists are just like tech, you know. know the tech people. It's the first thing every other physicists or even non-physicists who know of her say, they say she should have won the Nobel Prize. How was learning about her impacted you? It makes me really proud to have, you know, an Asian American woman in physics, because that's what I am. Seeing her in that poster, I mean, ever since I was a kid, I would really try to look for people like me.

I found a astronaut Chang Diaz, Dr. Chang Diaz, and I was like, oh, that's the closest is going to be to me. I remember seeing that and being like, oh, my gosh, like, I'm not so weird. I can do this. Regina, the last thing I want to ask you is just what part of her story are you going to take with you as a physicist of this generation? The stories that are about her and her just sticking up for herself and her just not putting up with being treated as less, is something that I will really take away. And I'm just so proud of her that she was that brave during that time. I just feel really honored to be able to talk to you about Dr. Wu and hear from you as an Asian American physicist, talking about another Asian American physicist as an Asian American myself.

And to kind of have this space all together is just really, it's really nice. Yeah. Regina, Dr. Barber, thank you so, so much for coming on. shortwave. And I'm really looking forward to working with you as a colleague, too. Yeah, we're having a great time. You're amazing. We really are. Yeah, we are amazing. Yes, I agree. Thanks. This is part one of a two-part episode. So be sure to tune in tomorrow. Dr. Chen Chong-Wu through the eyes of someone who knew her in a totally different way. Her granddaughter, Jada U.N., joins us on Shortwave. Today's episode was produced by Burley McCoy, edited by Gizal Grayson, who is our senior

supervising editor, and fact-checked by Catherine Seifer. The audio engineer for this episode was Patrick Murray. Neil Carruth is our senior director of On-demand news programming, and Anya Grunman is our senior vice president of programming. Special thanks to Brad Johnson and Seth Rittenhouse for helping me through my review of particle physics. We appreciate you. I'm Emily Kwong.

And I'm Regina Barber. And you are listening to Shortwave, the Daily Science podcast from NPR.