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Edward Witten researching non-string LQG-like quantum gravity

  1. Jun 22, 2007 #1
    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/strings07/040_scientific07_contents/041_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."
     
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  3. Jun 22, 2007 #2

    marcus

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    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.
     
    Last edited: Jun 22, 2007
  4. Jun 22, 2007 #3
    Hi,
    So what's your interpretation of Witten's remark? Is he being more lqg- by the day?
     
  5. Jun 22, 2007 #4

    marcus

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    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.
     
    Last edited: Jun 22, 2007
  6. Jun 22, 2007 #5

    arivero

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    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.
     
  7. Jun 22, 2007 #6
    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.
     
    Last edited: Jun 22, 2007
  8. Jun 22, 2007 #7
    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.
     
    Last edited: Jun 22, 2007
  9. Jun 23, 2007 #8

    arivero

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    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.
     
  10. Jun 23, 2007 #9

    marcus

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    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 :biggrin:

    *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."
     
    Last edited: Jun 23, 2007
  11. Jun 23, 2007 #10

    arivero

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    http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+A+WITTEN,+E&FORMAT=www&SEQUENCE=ds

    mathematician?

    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.
     
    Last edited: Jun 23, 2007
  12. Jun 23, 2007 #11

    arivero

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  13. Jun 23, 2007 #12
    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/Fields/1990/Witten/page1.html


    M-theory may be an extension of Morse Theory?
    http://en.wikipedia.org/wiki/Morse_theory
     
  14. Jun 23, 2007 #13

    marcus

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    Yes. since the categories are not exclusive, if you want to challenge you need to bring evidence that he is NOT a mathematician.
     
    Last edited: Jun 23, 2007
  15. Jun 23, 2007 #14

    marcus

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    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.
     
  16. Jun 24, 2007 #15
    Peter Woit responds to Aaron Bergman on the stringness/LQGness of Witten's latest research here http://www.math.columbia.edu/~woit/wordpress/?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...."
     
  17. Jun 24, 2007 #16
    is there a LQG landscape?!

    Sorry for my dilettantish curiousity.:redface:
    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?:biggrin:
    okounkov1.GIF
    No?
     
  18. Jun 24, 2007 #17

    marcus

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    I think the topic of the thread is interesting in its own right---we don't have to get off into our favorite speculations about the nature of reality. Here is what the thread-starter said

    So let's try to follow up on that theme. An influential string theorist is doing non-string gravity research. Is that part of a more general trend?
    Yes. As most of us know---perhaps all of us know---the research publication rate is declining, and the production of heavily-cited papers has dropped to almost nothing compared with 5-10 years ago.

    It could just be a fallow period and will pick up later---just as Witten could post an important M-theory paper later this year. We don't know the future. But it is still worth looking at quantative indices like this because they are part of the picture too.
     
  19. Jun 24, 2007 #18

    marcus

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    In case anyone is not already aware of this.
    If you count peer-review publication of articles whose summary abstracts have string-related keywords (superstring, brane, M-theory, heterotic, AdS/CFT) using the Harvard database you get this:

    for the entire year
    2002: http://adsabs.harvard.edu/cgi-bin/n...txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1

    2006: http://adsabs.harvard.edu/cgi-bin/n...txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1

    2007: http://adsabs.harvard.edu/cgi-bin/n...txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1


    For the first six months of the year

    2002: http://adsabs.harvard.edu/cgi-bin/n...txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1

    2006: http://adsabs.harvard.edu/cgi-bin/n...txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1

    2007: http://adsabs.harvard.edu/cgi-bin/n...txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1

    Obviously not everything is in for the first six months of 2007, much less for the entire year---so those are numbers you can try guessing and see how close you come. The numbers for 2002 and 2006 illustrate the trend in string community activity.

    More significant, perhaps, is the drop-off in the number of recent papers which other string theorists consider important enough, or sufficiently significant for their own research, to cite as references. Each year the number of recent (past five years) papers getting 100 or more citations has declined. From 10 - 20 a few years back, to 2 or 3 last year. Judging by citations there has been an order-of-magnitude drop in the value of recent string research as perceived by the string researchers themselves.

    This slowdown in quantity and quality has been discussed by leading people in the string community. Witten minimized its importance, saying that these things go in cycles and in any line of research there are periods of a few years when it is very hard to get significant results. That seems pretty sensible---don't get excited and wring your hands, just go over into some other line of research and find an interesting problem to work on.

    Others, like David Gross, have had a more profound reaction (in my humble opinion). He has thought deeply about the impasse and has been sounding frustrated and worried on several occasions over the past year.
    Gross remarks after the Solvay Conference and at the end of the recent Jerusalem-Haifa conference were interesting and provocative, I thought.

    Both ways of coping have my respect, needless to say.
     
  20. Jun 24, 2007 #19
    In NEW Peter Woit's view is that the popularity of string theory owes largely to Witten, and that many HEP followed Witten there. If this is true, then should Witten focus more on non-string QG, presumably QG theorists will follow suit, esp in light of a hypothetical null SUSY result from LHC.
     
  21. Jun 24, 2007 #20

    arivero

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    Yes, this point of view is old; it comes from Green & Schwartz, who time ago enjoyed to explain how they got to involve Witten in the project as an strategical move. And after that, the 1995 revolution (dualities) increased his role as prominent figure.

    Frustrated? Pity I have never heard Gross so I can not compare. I will try to check Friday and Saturday, as he has scheduled one technical lecture and then a public one.
     
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