AILSA CHANG, HOST:
Most of us don't spend a lot of time thinking deeply about the universe - what it's made of, how it works. But right now we're going to spend a moment remembering a man who devoted his life to those questions. Joseph Polchinski was an influential physicist at the University of California, Santa Barbara. He died last week at the age of 63.
One of the physicists who's mourning this loss is Sean Carroll. He's a professor at the California Institute of Technology, a close friend of Joe's. And he joins us now from member station KPCC. Thank you for joining us.
SEAN CARROLL: Thanks for having me.
CHANG: So Joe Polchinski sounded like quite the character from what I gather. Can you share with us - what was he like as a guy?
CARROLL: Yeah, Joe was great because he was an enormously clear thinker as a physicist, but he also had this mischievous sense of humor. He wrote this gigantic, definitive, two-volume textbook on superstring theory. And what he really wanted to title it was "Joe's Big Book Of String"...
CARROLL: ...As if he were a little kitten playing with a ball of yarn.
CHANG: Did that fly?
CARROLL: And Cambridge University Press eventually put the kibosh on that...
CARROLL: ...And it was just called "String Theory."
CHANG: Oh, bummer.
CARROLL: But he was always working these little jokes, these little sly asides into his deepest questions about physics.
CHANG: Well, about those deepest questions - I was a pretty miserable student in physics during high school, so I need you to get down to my level for a moment here. Can you explain - give us a sense of the work that Polchinski was known for in physics, in string theory.
CARROLL: So string theory is a simple idea. Instead of little particles like electrons and quarks, if we were to look closely at them, we would see they were little loops of string. It's an old idea from the '60s and '70s. But in the 1980s it really caught fire, and that was the first superstring revolution. And people started asking, well, if there are these one-dimensional loops of string, could there be two-dimensional membranes or even higher-dimensional things? And string theory believes in more than the three spatial dimensions around us. And mostly they said, no, that just doesn't work. And Joe came along in 1995 and said, actually, not only does it work, it's necessary. String theory is not just a theory of strings. It's also a theory of these higher-dimensional things called branes.
CHANG: Like brains in my head?
CARROLL: Like branes, B-R-A-N-E-S.
CARROLL: It's a back creation from the word membrane. So a membrane is a two-dimensional thing. What do you call a five-dimensional thing? A fivebrane.
CHANG: Got you.
CARROLL: And so Joe put these out there. And he said, you can't avoid these guys. And people who started thinking about them realized they all actually help the different kinds of string theory fit together. String theory is a much more unified, coherent framework than anyone had ever imagined.
CHANG: So how well-known was Polchinski outside the world of physics for his contributions to string theory?
CARROLL: Not very much, I would say. You know, he was one of those people who was universally admired within the physics community, but he liked not only to sort of stay in his office and do work, but even in his choice of topics he wasn't chasing the latest fads. He tried to think deeply about old problems that people have been thinking about for decades. And he would come back and tell us, look; there's something we missed in the last 20 years. And that's really what made him such a treasure, that he could figure out these things that everyone else had been thinking about for decades.
CHANG: Well, at the end of his life, Joe Polchinski developed a brain tumor and - which made it very hard for him to think through physics problems the way he used to. And he turned towards writing to get through that phase of his life. Can you tell us a little bit about what you learned from him when you read his writing?
CARROLL: Yeah. He - Joe was always an enormously clear expositor. You loved to read his papers, to hear him talk. So he turned to writing sort of his physics memoirs, his life as a physicist. And it was very, very physics-oriented. Like, it wasn't who I met at a party. It was like what calculation I was doing that night. And it's a wonderful experience to read as a physicist because for one thing, you see all the mistakes, right? When you read a physics paper, people don't tell you what mistakes they made along the way. They tell you the answer they finally got. But here he is saying why I didn't do this, why did I do this, what a struggle it was for him. That makes us feel good, the rest of us, the rest of us more human-level physicists, to think that even Joe Polchinski could struggle a little bit.
CHANG: Sean Carroll, thank you so much for joining us.
CARROLL: Sure. It's my pleasure. Thanks for having me on.
CHANG: That's Caltech physics professor Sean Carroll. He joined us to remember physicist Joseph Polchinski, who died last week at age 63. Transcript provided by NPR, Copyright NPR.