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.

## 12 Responses

The proceedings of the conference are going online here http://online.kitp.ucsb.edu/online/joefest-c14/ so you can see video of the talks. Wonderful world wide web! I must say I enjoyed Matt’s provocative talk. 🙂

The open strings attached on the D-brane contain particles that mediate forces and a gauge theory is realized on the D-brane. it is possible to tune a parameter of the theory to make the length of the strings to zero and then, the theory becomes a theory of point particles.

So The Gauge field of photon became a photon particle ?

Due to non-zero effect of the cosmological constant, It can then be shown that the parameter tuning considered above does not lead to zero string length limit, and the system we obtain is a theory of strings living in a certain curved space-time (WHERE GRAVITY IS AGAIN PROMINENT).

The “ Holographic QCD” is the non-perturbative invariance in QCD (or hadronization) ?

For each group generator there necessarily arises a corresponding vector field (TIME?) called the gauge field. Gauge fields are included in the Lagrangian to ensure its invariance under the local group transformations (called gauge invariance).

Is this the clumping of space at planck scale in string theory ?

You evil, evil punster. I applaud.

Congratulations to Joe!

http://science.nasa.gov/science-news/science-at-nasa/2003/25feb_nosoap/

Thanks, Plato. Nice demo of competition between forces.

Sounds a lot like Mem-Branes 🙂

http://4.bp.blogspot.com/-K4WQjBRmtcs/Tm4hhbSOPuI/AAAAAAAACtg/Y8fvBSRe-Ac/s1600/shake2.gif

That’s no accident: the term was derived from the word “membrane”.

I know.

Matt,

Thanks a lot for this post in particular, and its natural follow-up that you have already mentioned that will come in time; besides, thanks a lot for the pun (clearly intended) in the title of this post.

Kind regards, GEN