Comments on: What is a Brane?

By: Peter

Peter — Wed, 31 Dec 1969 19:00:00 +0000

I think you’ll find that if you talk privately to many string theorists, they are very unhappy with the present state of the field. A common opinion would be that the standard picture of a 10/11 d string/M-theory TOE has been incredibly overhyped and now looks unlikely. But they’re not sure what else to work on. One of the few intellectually alive sub-fields of particle theory is that of trying to really understand QCD via its supposed string dual. A lot of people are working on that, keeping quiet about their doubts about the TOE. Siegel is one of the few not keeping so quiet (he has tenure, for one thing…).

By: Anonymous

Anonymous — Wed, 31 Dec 1969 19:00:00 +0000

I read much of Siegel’s webpages and I’m surprised he seems to be able to hold contradictory opinions in the same webpage! In his “serious” pages, he is a proponent of string theory and he describes his work on it but in his parodies, he becomes very critical of string theory.

By: Peter

Peter — Wed, 31 Dec 1969 19:00:00 +0000

Well if some of the features of the physics look like they come from a vibrating string, it’s perfectly reasonable to try to model strong interactions with a quantum string. It just doesn’t work, or at least not in anything like the simplest such way of “quantizing a string”.

I’d heard that lots of people had suggested a fourth quark with the right quantum numbers around 1964, but never that Zweig was one of them. The idea only became really compelling in 1970 with the GIM mechanism.

By: D R Lunsford

D R Lunsford — Wed, 31 Dec 1969 19:00:00 +0000

Peter – you mention Glashow and his 4th quark. Remember that George Zweig had his model of “aces”, which were really just 4 quarks at the outset.

-drl

By: D R Lunsford

D R Lunsford — Wed, 31 Dec 1969 19:00:00 +0000

Peter -

It looks like Siegel is carrying on the parton and Veneziano dual-resonance ideas in his own way, with modern tools. So he’s sort of going back to before gauge theory and s.s.b.!

One thing I never understood – it seems that string theory got started because the dynamics of these models looked like that of a vibrating string. Why did they make the leap of faith to say that it really *is* a string??

-drl

By: Peter

Peter — Wed, 31 Dec 1969 19:00:00 +0000

DMS: Sure, if when particles collide at the LHC, energy starts disappearing into extra dimensions, that would be a big deal. It also would be a big deal if these collisions caused the archangel Michael to appear at the collision point. These both seem about equally likely to me.

Glashow and others had good arguments for a fourth quark. This was a simple extension of the three quark model that made the whole thing simpler and more elegant. The extra dimension stuff is nothing at all like that.

ksh95: Yes p-branes for p>1 are described by a non-renormalizable sigma-model. Look at your favorite way of quantizing the string, increase the dimension of the world-sheet above 2 and see what happens.

Danny: I don’t really understand exactly what Siegel has in mind, but he is clearly more interested in finding a 4d string that would help one understand QCD, rather than a 10d string that would explain gravity.

By: DMS

DMS — Wed, 31 Dec 1969 19:00:00 +0000

Getting to the article, I think I would agree with Nima that *IF* brane concept turns out to be correct, it will indeed be the biggest thing in science in 300 years. Don’t you think?

Of course, I don’t think it will be found, but who knows…

Maybe, it will be like the charm episode in particle physics, when Glashow made a bet that charm would be found with an estimate of the mass, and he won the bet( If my memory serves me right, it was based on the GIM mechanism based one-loop calculation of the K0-K0bar mixing.). But my understanding is that no one believed his prediction (unlike the case now where anyone who “matters” believes in it).

By: ksh95

ksh95 — Wed, 31 Dec 1969 19:00:00 +0000

Whoa, whoa, whoa,

You’re telling me that branes give infinite results, even in perturbation theory?

What’s this about? Are they doing S-matrix calculations or something else?

I’ll ask around, but in the meantime if some one could kindly explain the present state of affairs I’d be much ablidged.

By: Thomas Larsson

Thomas Larsson — Wed, 31 Dec 1969 19:00:00 +0000

A Brane New World always reminds me of a Swedish dotcom company, by Huxley’s original name A Brand New World. It defaulted a couple of years ago, after burning more venture capital than Boo.com.

As they say on the stock market: never try to catch a falling knife. No matter how much the string stock falls, there is always 100% left to the bottom.

By: plato

plato — Wed, 31 Dec 1969 19:00:00 +0000

sorry Peter it won’t happen again