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Serectly developing from the other approach

  1. Mar 17, 2005 #1
    are there any physicists who are working at their university which specailizes in let's say string theory and in the same time are also working on the side on lqg? (or even vice versa).


    p.s
    sorry for the misleading title...
     
  2. jcsd
  3. Mar 17, 2005 #2

    marcus

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    I believe that a significant number of researchers pursue several lines of investigation relating to Quantum Gravity. I cannot estimate numbers for you but I can give a few examples

    Jan Ambjorn publishes string research but also is one of the main developers of dynamical triangulations approach (simplicial QG)

    Roy Maartens has done plenty of brane cosmology but lately has been doing Loop Quantum Cosmology (has published with Bojowald and others in LQC)

    Kristin Schleich lists string theory as a research interest on her homepage at UBC, but she just published a paper about the Kodama state which may be important in LQG.

    Lee Smolin has published a number of string research papers over the years. You just have to look these people up by name at Arxiv.org and you will see the kind of mixed history I am talking about.

    Sergei Alexandrov publishes in string and LQG/spin foam

    Leonardo Modesto was doing string and then started publishing LQG (in one case with Carlo Rovelli)

    these are just a few names that I happened to think of. I am sure I could think of a lot more. Maybe other people will remind us of more. it seems to me very natural that a broadly-trained creative researcher would want to work several approaches. I do not like the "two-camps" mentality. I think the reality must surely be more complicated than "two opposing camps"
     
  4. Mar 19, 2005 #3
    well, lee smolin is the most famous from the list you gave and from his popular science book (three roads to qg), you can argue that he isnt biased (i could not say the same about the author of the elegant universe who doesnt cover broadly about the other approaches which differ from string theories).

    anyway, thanks for the names' list...
     
  5. Mar 19, 2005 #4

    marcus

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    it is a thought-provoking question----glad you asked. Another name that comes to mind is Don Marolf. He has done string research and also has been co-author on several key LQG papers.

    but there is another aspect to this besides the people-overlap.

    there is an area of research where the two approaches are so interconnected that one cannot really draw the line.
    at a certain point one cannot be sure if he is doing Loop research or string.
    or at least making a sharp distinction might raise controversy.

    you can see this emerging if you can take the time to go over the recent (largely incomprehensible to me) paper by the prominent stringtheorists
    Dijkgraaf, Neitzke, Vafa, Gukov that I cited in another thread. At some places they point to where they think Loop methods could play a role in what they call "topological Mtheory". I will try to find a quote. there is a strong example of this in their conclusions right at the end. Maybe i can find it.
    yes the thread is
    https://www.physicsforums.com/showthread.php?t=67709
    the paper is mentioned in post #4 there
    http://arxiv.org/abs/hep-th/0411073
    a sample quote would be on page 56, section 10 "directions for future research"
    ----quote Dijkgraaf, Vafa et al----
    Another natural question we have raised relates to the interpretation of the topological M-theory: does it indeed count domain walls? This is a very natural conjecture based on the links we found between form theories of gravity and the counting of black hole states. It would be important to develop this idea more thoroughly. Another question raised by our work is whether one can reformulate the full M-theory in terms of form theories of gravity. This may not be as implausible as it may sound at first sight. For example, we do know that N = 2 supergravity in 4 dimensions, which is a low energy limit of superstrings compactified on Calabi-Yau manifolds, has a simple low energy action: it is simply the covariantized volume form on (4|4) chiral superspace [74]. In fact, more is true: we could include the Calabi-Yau internal space as and write the leading term in the effective action as the volume element in dimension (10|4). The internal volume theory in this case would coincide with that of Hitchin. Indeed, this is related to the fact that topological string amplitudes compute F-terms in the corresponding supergravity theory. Given this link it is natural to speculate that the full M-theory does admit such a low energy formulation, which could be a basis of another way to quantize M-theory — rather in tune with the notion of quantum gravitational foam.
    ----end quote----

    LQG is the most notable case of a form theory of gravity. I think there is a nonspecific reference to LQG/spinfoam here, which I have boldfaced to make more visible.
     
    Last edited: Mar 19, 2005
  6. Mar 19, 2005 #5

    Chronos

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    The incomprehensible part is not a failing on your part, marcus. The mathematical concepts they blithely throw about are understood by only a handful of people on this planet.
     
  7. Mar 19, 2005 #6

    marcus

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    well that's fair enough, we really cant complain as long as they and a few others understand what they are saying. Lee Smolin seems to be responding to the DGNV paper and selfAdjoint just pointed up something about it in that other thread. Maybe there's a chance we can get something out of it one way or another :smile:

    here's that comment by sA about the DGNV paper
    https://www.physicsforums.com/showthread.php?p=497701#post497701
    I dont understand it now but I'm not totally giving up (and I guess you arent either)
     
    Last edited: Mar 19, 2005
  8. Mar 19, 2005 #7

    Chronos

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    I didn't mean that sarcastically. I think I understand the concepts, and try to nibble around the edges, but I have no clue when they talk about how deep the pond is.
     
  9. Mar 19, 2005 #8

    marcus

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    yeah, I know you didnt mean it sarcastically, I was just making my own situation visavis this stuff explicit, and anyway I have no problem with a bit of sarcasm and other tones of voice which do so much to relieve the monotony.

    I would go even farther than you and say that it peeves me personally that so much of theoretical physics has gotten out-of-control complicated. But I dont feeld I can HARP on that because it doesnt do any good. we just have to wait patiently till most of this theorizing gets blown away by experiment and the rest gets unified and simplified by some stroke of genius. the baroque complexity gripes me but it just aint worth our time (IMHO) to complain about it.

    you see we cant a priori exclude the possibility that nature's laws are hideously clunky.:surprised: you know this as well as I do.
    meanwhile kvetch all you want (I think you are safe as long as you dont attack anyone of us)

    BTW selfAdjoint pointed up something interesting in Smolin's response to the Dijkgraaf et al paper. It was in the other thread. I dont know if it matters or not. any ideas?
     
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