Edward Witten researching non-string LQG-like quantum gravity

**ensabah6** · Jun22-07, 04:20 PM

Edward Witten is the most influential string theorists in the world, is now doing research into gravity that is decidedly non-string, and very similar to LQG.

here's a link
http://gesalerico.ft.uam.es/strings0...1_speakers.htm

his research program is titled " Three-Dimensional Gravity Revisited"

and here's a discussion
http://www.math.columbia.edu/~woit/wordpress/?p=555

Peter Woit writes "If one wants to interpret this new work in light of the the LQG/string theory wars, it’s worth noting that the technique used here, reexpressing gravity in terms of gauge theory variables and hoping to quantize in these variables instead of using strings, is one of the central ideas in the LQG program for quantizing 3+1d gravity."

**marcus** · Jun22-07, 05:13 PM

Last year the UC Berkeley math and physics departments hosted Witten and he gave three 90 minute talks, which I attended all of.

and at no time during the talks did he mention string theory (or superstring or brane or whatever)

it was about the geometric Langlands program which doubtless has implications for all kinds of mathematics including of course string mathematics but the talks did not explicitly bring up string

then at the end of the third talk, when it was time for questions, someone from the audience asked if he had any words about string and he said that he believed it would turn out to have something to do with nature.

**ensabah6** · Jun22-07, 05:37 PM

Originally Posted by marcus

Last year the UC Berkeley math and physics departments hosted Witten and he gave three 90 minute talks, which I attended all of.

and at no time during the talks did he mention string theory (or superstring or brane or whatever)

it was about the geometric Langlands program which doubtless has implications for all kinds of mathematics including of course string mathematics but the talks did not explicitly bring up string

then at the end of the third talk, when it was time for questions, someone from the audience asked if he had any words about string and he said that he believed it would turn out to have something to do with nature.

Hi,
So what's your interpretation of Witten's remark? Is he being more lqg- by the day?

**marcus** · Jun22-07, 05:47 PM

Originally Posted by ensabah6

Hi,
So what's your interpretation of Witten's remark?

As a member of the audience I knew people from both departments who were present and I felt the physicists' frustration with Witten's singleminded focus on his current interest (geometric Langlands). These were the only talks he gave in the course of his brief visit and he avoided saying anything about string or even general ideas like unification.

Beyond reporting what I thought was striking about the emphasis I having nothing to add about Witten.

I think it is more interesting to watch the shift of interest of a whole class of people (the prominent successful string mathematicians of the 1990s) and try to get an idea of where they are going. The example of just one person, no matter how famous, doesn't do it for me.

so I want to take something you said and generalize it to make a broader question:

Originally Posted by ensabah6

... research into gravity that is decidedly non-string, and very similar to LQG.
...

that raises a very interesting general topic, that is not even restricted to the one example of Edward Witten

what other string theorists do you know of who have crossed over into non-string QG or moved in that direction-----despite earlier career success in string?

I can think of several. Jan Ambjorn has many string papers but he was giving the dynamical triangulations talks at the European Union QG school this spring at Zakopane---he made some remarks about string at the beginning that persuade me he is not so amphibious now but is more concentrating on non-string QG.

Steve Giddings and Don Marolf have been successful and prominent in string research, but their most recent joint paper had LQG citations and looked as if it would fit usefully into the non-string QG program. I think of them now as both more ambidextrous---able to contribute ideas and results either way.

Giddings most recent solo paper cited 4 papers by Rovelli, one by Smolin, two by Dittrich, several by Gambini and Pullin---it showed unusually thoughtful reading of non-string QG research (this was his contribution to this year's Gravity Foundation essays)

Of course Leonardo Modesto got out of string at Genoa and went to work with Rovelli in Marseille. Likewise Sergei Alexandrov got his PhD in string in Paris and now is doing interesting work at Montpellier related to LQG. there must be quite a few people who made the transition early, before they had any chance to become known as string mathematicians. What I am wondering about is more the prominent string people who seem to be acquiring a non-string QG interest.

**arivero** · Jun22-07, 07:00 PM

Witten went into strings because of the KK extra dimensions, as he had gone into supergravity before, due to the same reasons. He always kept pushing the theory towards d=11, to meet the standard model embedding, and insisting that string theory at the end should be very diferent from the starting theory.

**ensabah6** · Jun22-07, 10:02 PM

Originally Posted by marcus

As a member of the audience I knew people from both departments who were present and I felt the physicists' frustration with Witten's singleminded focus on his current interest (geometric Langlands). These were the only talks he gave in the course of his brief visit and he avoided saying anything about string or even general ideas like unification.

Beyond reporting what I thought was striking about the emphasis I having nothing to add about Witten.

I think it is more interesting to watch the shift of interest of a whole class of people (the prominent successful string mathematicians of the 1990s) and try to get an idea of where they are going. The example of just one person, no matter how famous, doesn't do it for me.

so I want to take something you said and generalize it to make a broader question:

that raises a very interesting general topic, that is not even restricted to the one example of Edward Witten

what other string theorists do you know of who have crossed over into non-string QG or moved in that direction-----despite earlier career success in string?

I can think of several. Jan Ambjorn has many string papers but he was giving the dynamical triangulations talks at the European Union QG school this spring at Zakopane---he made some remarks about string at the beginning that persuade me he is not so amphibious now but is more concentrating on non-string QG.

Steve Giddings and Don Marolf have been successful and prominent in string research, but their most recent joint paper had LQG citations and looked as if it would fit usefully into the non-string QG program. I think of them now as both more ambidextrous---able to contribute ideas and results either way.

Giddings most recent solo paper cited 4 papers by Rovelli, one by Smolin, two by Dittrich, several by Gambini and Pullin---it showed unusually thoughtful reading of non-string QG research (this was his contribution to this year's Gravity Foundation essays)

Of course Leonardo Modesto got out of string at Genoa and went to work with Rovelli in Marseille. Likewise Sergei Alexandrov got his PhD in string in Paris and now is doing interesting work at Montpellier related to LQG. there must be quite a few people who made the transition early, before they had any chance to become known as string mathematicians. What I am wondering about is more the prominent string people who seem to be acquiring a non-string QG interest.

Thanks. I do think should LHC fail to find evidence of SUSY, what is now a trickle may become a stream.

Lee Smolin I think started out in the supergravity/string theory camp.

**ensabah6** · Jun22-07, 10:02 PM

Originally Posted by arivero

Witten went into strings because of the KK extra dimensions, as he had gone into supergravity before, due to the same reasons. He always kept pushing the theory towards d=11, to meet the standard model embedding, and insisting that string theory at the end should be very diferent from the starting theory.

Do you think Witten still feels this way, with his current research interests? "then at the end of the third talk, when it was time for questions, someone from the audience asked if he had any words about string and he said that he believed it would turn out to have something to do with nature."

doesn't sound like a vote of confidence. Michio Kaku and Briane Greene and other stringers called String theory the Theory of Everything, and the language which God wrote the universe.

**arivero** · Jun23-07, 03:29 PM

Originally Posted by ensabah6

asked if he had any words about string and he said that he believed it would turn out to have something to do with nature."

doesn't sound like a vote of confidence.

Well, it is more of the same: to tell that the "final string theory" will be very different from the current one, is a optimistic way of saying the same thing.

String theory has grown sort of randomly, with no respect with the empirical evidence. So, the fact of having a very adecuate number of extra dimensions (11 better than 10, in any case) and room enough to contain previous extensions of the standard model (GUT models, supergravity) can be interpretated either as telling us that string theoy has something to do with nature or that as string theory has explored in a unified way a range of mathematical objects which have something to do with nature.

**marcus** · Jun23-07, 04:37 PM

Arivero, I think the question on several people's minds can be put more simply than Ensabah stated it. And you may have an illuminating answer.

We see that this is the second year in a row* that Witten goes to the big annual international String conference and gives a paper that is not string.

Naturally people wonder, is this just an isolated case with no special significance?
Or should we draw some conclusion from it?

For my part, I tend to ascribe a lot of stuff to mere random variation---Witten is just one guy, I see him to a large extent as a mathematician and the interests of mathematicians are changeable. If he finds himself not getting results in one field he can jump over and see what he can do in another field.

I would be impressed if there were a trend in the overall NUMBERS involving a lot of experienced top people. But not by one guy, even if he is some people's tribal totem

*Last year at Beijing Strings '06, it was “Gauge Theory and Geometric Langlands Program”. Woit commented: "He has given talks at almost all the Strings conferences since the first in 1995, but this will be the first one at which he won’t be talking about string theory."

**arivero** · Jun23-07, 05:05 PM

Originally Posted by marcus

Witten is just one guy, I see him to a large extent as a mathematician and the interests of mathematicians are changeable. If he finds himself not getting results in one field he can jump over and see what he can do in another field.

http://www.slac.stanford.edu/spires/...ww&SEQUENCE=ds

mathematician?

I would be impressed if there were a trend in the overall NUMBERS involving a lot of experienced top people. But not by one guy, even if he is some people's tribal totem

Well it depends of the initial motivation to be in strings. If it is just training, why to move now that you have got the training?

Also, it is about particle vs cosmology. Even this forum reflects the modern feeling that strings are primarely about cosmology. So people in strings are not ashamed of the failure to predict the particle spectrum.

**arivero** · Jun23-07, 05:42 PM

Check

http://www-hep.phys.cmu.edu/beauty20...ard_Witten.pdf

Except Gross and perhaps Polchiski, I can not imagine the other main speakers of String07 giving a talk on flavour such as this one.

**Dcase** · Jun23-07, 06:47 PM

Hi Arivero,

I do not know how accurate this Wiki biography is, but Witten has a remarkable academic history:

- bachelor's degree in history (with a minor in linguistics) from Brandeis University

- attended the University of Wisconsin for one semester as an economics graduate student before dropping out

- enrolling in applied mathematics at Princeton University before shifting departments and receiving a Ph.D. in physics in 1976 under David Gross

- first physicist to win the Fields Medal for mathematical physics

http://en.wikipedia.org/wiki/Edward_Witten

LD Faddeev. chair Fields Medal Committee comments.
http://www.mathunion.org/Prizes/Fiel...ten/page1.html

M-theory may be an extension of Morse Theory?
http://en.wikipedia.org/wiki/Morse_theory

**marcus** · Jun23-07, 09:00 PM

Originally Posted by arivero

mathematician?
...

Yes. since the categories are not exclusive, if you want to challenge you need to bring evidence that he is NOT a mathematician.

**marcus** · Jun23-07, 09:12 PM

Originally Posted by arivero

...the modern feeling that strings are primarily about cosmology. So people in strings are not ashamed of the failure to predict the particle spectrum.

Alejandro, I should think that string contribution to cosmology would be an embarrassment to many in the community. If that is a primary ground of self-respect, things must be in a bad way. I don't see how that could be so. Perhaps you would explain.

**ensabah6** · Jun24-07, 04:32 AM

Peter Woit responds to Aaron Bergman on the stringness/LQGness of Witten's latest research here http://www.math.columbia.edu/~woit/w...p=570#comments

PW
"....During the talk he brought up the question of LQG, noting that in 3d you could covariantly express gravity in terms of a gauge theory, that the way this was done in 4d (LQG) was non-covariant......"

"....There was nothing at all about string theory in his talk...."

**Boris Leykin** · Jun24-07, 12:03 PM

Originally Posted by marcus

...someone from the audience asked if he had any words about string and he said that he believed it would turn out to have something to do with nature.

Sorry for my dilettantish curiousity.

But isn't everything like I was asking here. Loop quantum gravity is more fundamental than string theory. Look at the picture. What is this quantum foam? Isn't it made of loops?

okounkov1.GIF
No?