Today and tomorrow I’m at the Kavli Institute for Theoretical Physics, on the campus of the University of California at Santa Barbara, attending a conference celebrating the career of one of the world’s great theoretical physicists, Joe Polchinski. Polchinski has shown up on this website a couple of times already (here, here and here). And in yesterday’s post (on string/M theory) I mentioned him, because of his game-changing work from 1995 on “D-branes”, objects that arise in string theory. His paper on the subject has over 2000 citations! And now it’s such a classic that people rarely actually cite it anymore, just as they don’t cite Feynman’s paper on Feynman diagrams; its ideas have surely been used by at least double that number of papers.
Polchinski’s also very well-known for his work on quantum gravity, black holes, cosmic [i.e. astronomically large] strings, and quantum field theory.
Between 2000 and 2006, I had the extraordinary privilege to write four papers with Polchinski, all of them aimed at clarifying the relationship between string theory and quantum field theory. This was the longest collaboration of my career, and a very successful one. Because of this, I have the honor to give one of the talks today at the conference. So I’m going to cut my post short now, and tell you more about what’s happening at the conference when my duty is done.
But I will perhaps tease you with one cryptic remark. Although D-branes arise in string theory, that’s not the only place you’ll find them. As we learned in 1998-2000, there’s a perspective from which protons and neutrons themselves are D-branes. From that point of view, we’re made out of these things.
Someday — not today — I’ll explain that comment. But it’s one of many reasons why Polchinski’s work on D-branes is so important.