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How do you see the next phase of background independent QG research?

  1. Sep 30, 2007 #1

    marcus

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    How do you see things shaping up during the next few years in Quantum Gravity?

    the last two years have seen a lot of change
    there are some new approaches that have either just been discovered (like Smolin's group finding matter degrees of freedom in spin networks)
    or have recently become prominent (like asymptotic safety approach of Reuter and Percacci groups)

    there are attempts to get different approaches to CONVERGE---like A & G working for the past two years on unifying spin network LQG with Alain Connes Noncommutative Geometry.

    and many people including Rovelli and Freidel working on making spinfoam so it has the right low-energy behavior and also matches LQG----if you read the "new spinfoam vertex" papers you see a major focus on unifying spinfoam with canonical LQG.

    so there is a trend or a groping towards convergence and unification of approaches.

    And Martin Reuter gave a very clear prescription for the next 5 years when they were asked at the end of Loops '07. He wants to see the dimension of the critical hypersurface around the renormalization group fixed point be the same as the number of ambiguities in LQG----some number like three: of parameters that you can nail down and then the theory is predictive. Seriously or not, he gave a vision of equivalence between the two approaches: his and Loop.

    In the Q&A at the end of his Asymptotic Safety chapter for Oriti's book, Percacci also described various way the approaches could converge.

    Those are some things I see happening or vaguely on the horizon. What do you see? Can you describe in better detail what is going on?

    What are some other trends?
     
  2. jcsd
  3. Sep 30, 2007 #2
    LHC results may affect research directions, obviously if SUSY is observed, or Higgs, or new particles, or higher dimensions. Obviously if LHC finds evidence of both higher dimensions and SUSY, it's entirely possible LQG-BI interest will dry up and string's hegemony will continue unabated. Other results, including astronomical or even TEV are important (i.e speed of c)

    I would like to see more research into condense matter models, , although Wen seems to think LQG could be a string net condensation convergence, Volvovik argues that quantizing GR is fundamentally the wrong approach, and that in his view, GR and SM arise from a fermionic vaccuum. (Though he regards string-M-theory as equally misguided as BI LQG)

    There may be in the near future a convergence between Wen's string net condensation and work by Fotini in this direction in her "quantum graphity" papers.
     
  4. Sep 30, 2007 #3

    jal

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    Hi ensabah6!
    I like your assessment.
    jal
     
  5. Sep 30, 2007 #4
    you and I are in substantial agreement.
     
  6. Sep 30, 2007 #5

    marcus

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    Hi you two, thanks for your thoughtful input.

    Just to clarify, I am not asking what you WANT to see happen but what trends you see actually in progress and looking ahead say 5 years. what you actually expect to happen in Background Independent QG research.

    To give an example, I see a pattern of fights and arguments among close relatives. As the various QG approaches converge people will inevitably step on each other's toes more.

    I don't think it is sensible for us to think of ourselves as PICKING WINNERS because that is not how QG is organized. Different approaches constantly MORPH. The things in the "race" don't ever stay the same. What we are watching is different trains evolving as they merge into each other.

    Have to go, more later.
    ======================

    Back now. Another trend is the emergence of cosmology as the proving ground.

    Another is the rising prominence of nonstring QG at international conferences like the GRG, the Marcel Grossmann, and the upcoming ICGC (international conference on gravitation and cosmology).
    For instance at the Spring 2007 APS meeting (american physical society annual meeting) there were an equal number of nonstring QG and string invited speakers. At the Sydney GRG (general relativity and gravitation) it was 2:0 and at the ICGC it will be 6:1---this is just counting the invited plenary speakers. At these big broadgauge meetings they cover a lot of areas including various kinds of observational astronomy, so if you lump nonstring QG and string together it is a small slice of the total. Within that small slice, however, the BI approaches have become much more prominent.
    this means that working cosmologists are increasingly interested in what QG folks have to say. that means, in turn, that more will be expected of them.

    There will be more pressure to answer questions about things like
    dark energy
    accelerated expansion
    structure formation in early universe
    resolution of hole and bang singularities
    inflation alternatives to exotic matter
     
    Last edited: Sep 30, 2007
  7. Oct 1, 2007 #6

    Chronos

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    I agree entirely, marcus. The universe is the ulitimate laboratory. No earthly device will ever compete with the energies attained by inspiralling binary neutron stars. Mathematical models will compete for centuries, IMO. Better telescopes will put the fora of mathematical models in their proper place.
     
  8. Oct 1, 2007 #7
    besides any research leads LHC, TEV, HEP, or astronomy may provide,

    in addition to your list I would add:

    1 more research into the Kodama state, with Randanomo and Eyo Ita leading the way, and
    2 more research into condense matter models (i.e Wen, Markapolou's Quantum graphity, Volvovik) of gravity and SM. Oriti's GFT is inspired by Volvovik's condense matter models.
     
  9. Oct 1, 2007 #8

    marcus

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    Remember we are trying to say what to expect to happen, not what this or that person WANTS. the thread is not about what's your favorite.

    So say we're talking about the next 5 years. One way is to look back over the past 5 years.
    To gauge the influence, see how many papers with say 10+ citations---ten or more is not a lot to ask! Maybe add up the total cites of these 10+ papers.

    So go to Spires http://www.slac.stanford.edu/spires/hep/ and put this in
    FIND EA WEN, XIAO GANG AND DATE > 2002
    I think you will find just one paper-----it has 12 cites
    Tell me if you do a more effective search and there are any besides this with 10 or more cites.
     
    Last edited: Oct 1, 2007
  10. Oct 1, 2007 #9

    marcus

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    Hi Chronos! I am glad you agree. I will test a few names and see about their recent cites, as a pointer to how the immediate future may go. Let me know if you think of anybody.

    As a benchmark we can use Ensabah suggestion of Xiao Gang Wen who in the past five years had ONE paper with 10 or more---and the total was 12 cites. (one, 12)

    Reuter has TEN papers in the same period that each got over 10 cites.
    He also caused a lot of excitment among the grad students and postdocs when he spoke at Loops 05, the Zakopane School, and Loops 07.
    FIND A REUTER, MARTIN AND AFF MAINZ U., INST. PHYS. AND DATE > 2002
    I totaled up what Spires gave me and got 256.
    So we can gradually accumulate some benchmarks

    In case anybody missed Satz blog
    http://realityconditions.blogspot.com/2007/07/loops-07-conference-report-part-3.html
    http://realityconditions.blogspot.com/2007/07/loops-07-conference-report-part-2.html
    http://realityconditions.blogspot.com/2007/07/loops-07-conference-report-part-1.html
    http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_12.html
    ESPECIALLY THIS ONE:
    http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_10.html
    http://realityconditions.blogspot.com/2007/04/report-on-quantum-gravity-school_08.html

    Xiao Gang Wen (one, 12)
    Martin Reuter (ten, 256)

    In trying to get a realistic picture of the next 5 years it helps to gauge how influential someone has been recently and also how much enthusiasm among the young researchers there is, for what they do. I assume everyone here has read Alex Satz blog reporting on the Zakopane school and on Loops 07. If you are talking about Background Independent QG that is where it's at, so it would be naive to try to say anything about the field without carefully studying what went down there. Satz blog is called
    REALITY CONDITIONS. He is a PhD student and knows the others, and he gives an idea of how the various research looked to them and what impressed them.

    that is where the energy comes from to run QG for the next five years.

    Percacci (five, 90)
    he shares collaborators with Reuter, so whoever Reuter draws in will sometime be co-author of a paper with Percacci.

    FIND A BOJOWALD AND DATE > 2002
    Bojowald (thirtysix, 1139)
    that is we are trying to predict the future so we look at RECENT work in background independent QG and with Bojo we find that he has thirtysix recent papers (past five years) that got 10 or more cites and the cites on just those papers totaled up to 1139.

    Reuter, Percacci, Bojowald all have ways of explaining either accelerated expansion or inflation without dark energy or exotic "inflatons" or they have ways of getting over singularities, or both or all three. That is THEY ARE TALKING ISSUES OF CURRENT INTEREST and showing results. And they are moderately or highly influential. And they are attracting young researchers to collaborate.

    So it is a good bet that they have some considerable influence on the next QG phase----the next five years.
    I will try to think of others. Percacci and Reuter are, of course, the asymptotic safety approach. Bojowald and his associates run the quantum cosmology approach. there are signs of convergence, which should be lively to watch!


    Markopoulou (five, 90)
    Percacci (five, 90)
    Reuter (ten, 256)
    Freidel (thirteen, 348)
    Bojowald (thirtysix, 1139)
     
    Last edited: Oct 2, 2007
  11. Oct 2, 2007 #10
    Ok,
    So then why not just tell us which papers to date have the most cites and which topics have the most papers, and we can be done with this? How many Bi-LQG researchers are thoroughly trained in condense matter physics to expand on Wen's or Volvovik's work? (how many condense matter physicists can understand BI QG-SM research?)

    regards,

    BTW, there are a couple of papers on SUSY + LQG, as well as LQG + higher dimensions (Oekcel has published some), with possibly few citations. However, should LHC discover SUSY, current LQG papers that have been published detailing how to incorporate SUSY into LQG would get more citations, (i.e more citations to Oeckel's previously published paper on how to incorporate SUSY in Ashketar variables) and of course, more LQG papers will be focused on SUSY by Oeckel and other researchers (though I think in this event M-theory papers would get much bigger boost).

    Likewise, while LQG DSR in 2+1 has been proved, DSR in 3+1 has not been proved, but should DSR be firmly established (i.e results of Markan be established with other observations) obviously linking LQG to DSR in 3+1 would be a future research direction.

    So observational results, esp from LHC (i.e electroweak symmetry breaking, SUSY, higher dimensions) may determine the course of future LQG research.

     
  12. Oct 2, 2007 #11

    jal

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    ensabah6 .... I still agree with your assessment
    jal
     
  13. Oct 2, 2007 #12
    You and I agree on everything :)

    Where would you place Witten's work on AdS3/CFT2 gravity, in the BI camp or string camp?
     
    Last edited: Oct 2, 2007
  14. Oct 3, 2007 #13
    Without doing too much self-advertising, may i suggest also all the work on the semi-classical behavior of loop gravity and spinfoam model through the study of the "graviton propagator"... The goal of the program is to check whether our (dear?) loop quantum gravity has the right semi-classical limit (general relativity) and what are the unambiguous quantum corrections to the classical theory... actually, if any of you has any comment or opinion about the work in this direction, it'd be great/fun to hear what you think about it (see stuff by Rovelli, Speziale, Modesto... and even me).

    also even i don't think the citations count gives a proper assessment of how promising some work is, but i felt like adding these to your counts:
    Smolin (thirteen, 515)
    Rovelli (ten, 208)
    Livine (ten, 209) - sorry, after seeing the citation counts, i couldn't help but check what i was worth...
     
  15. Oct 3, 2007 #14

    jal

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    I have not given it any though.
    I think along different lines.
    I'm looking for the common pattern from all the approaches that indicate that there might be a quantum structured spacetime.
    I could add more but it would divert this thread by too much.
    jal
     
  16. Oct 3, 2007 #15

    marcus

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    Etera! Great to hear from you!

    thanks for supplying the citation counts. Obviously we are not thinking of cites as the only measure of influence, but it does help quantify a PART of the picture.

    I will merge your list in with mine.

    Markopoulou (five, 90)
    Percacci (five, 90)
    Rovelli (ten, 208)
    Livine (ten, 209)
    Reuter (ten, 256)
    Freidel (thirteen, 348)
    Smolin (thirteen, 515)
    Bojowald (thirtysix, 1139)

    I can hear Rovelli (your PhD thesis advisor i think) laughing if you would tell him that you scored one more point than he. Nobody should care about differences that aren't even an order of magnitude, but when we are trying to predict the progress over the next year or two, then what has just recently happened is a useful guide.

    the work that just recently HAS been cited is more likely to characterize the work to be expected over the next couple of years, than work that so far has barely been noticed. I shouldn't have to say this, it is so obvious.

    It's a reality check.

    OK so what kind of progress can we expect in QG over the next couple of years?

    Clearly the new work in spinfoam is the most or one of the most important developments. It finally solves many problems and gives a new dynamics. Good evidence suggesting that the semiclassical limit is satisfactory----last night I was reading your and Simone Speziale paper with Dan Christensen which means BEOWULF CLUSTER!!!
    Anyway I think that this was supercomputer work using efficient algorithms that Dan and his group have developed.
    I find this exciting and the results in that new paper were good. Pointing towards good behavior both IR and UV if I understand correctly. You said in the outlook section that the next step is to do the same analysis with the new spinfoam model. That all sounds really good. I logged the paper in our bibliography thread yesterday.

    -----------------------------------------------
    If you want a paper to read about that, an obvious one is to get the one by Etera Livine, Simone Speziale, and Dan Christensen that I refer to here. It was posted just last night.

    That paper has references that will lead you back to a lot of work that has happened in the past year and a half or so.

    This is partly in response to the next post by Ensa, and in case anybody else reading didnt notice the reference here to the Christensen, Livine, Speziale paper
     
    Last edited: Oct 3, 2007
  17. Oct 3, 2007 #16
    Hi Marcus,
    I do agree that establishing spinfoam semiclassical limit is GR is probably the #1 priority, otherwise you don't have gravity, but I've not seen any progress that I'm aware of.


    Which specific papers do you have in mind "Clearly the new work in spinfoam is the most or one of the most important developments. It finally solves many problems and gives a new dynamics. Good evidence suggesting that the semiclassical limit is satisfactory---- "
     
  18. Oct 3, 2007 #17

    marcus

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    read my previous post please

    Let's get back to work on this. Please only people who are actually familiar with the QG literature of the past couple of years or so! If you do QG research or follow the field closely enough to know what's been going on---the main papers of 2005-2007---the main areas where progress has been made. If you went to Loops 05, Loops 07 or the Zakopane school or read up on several of the talks. What I mean is, iff you know the QG scene I would very much like your opinion.

    Let's make the horizon a little closer. Lets try to predict QG research TWO YEARS OUT.

    that is, if you have a realistic idea of what's been happening in the past couple of years, and a feel for the momentum of the various approaches, perhaps you could make an educated guess about what will actually happen between now and October 2009.

    So it's a reality check. If it gets to be October 2008 and nothing that you were predicting is happening yet, then it probably won't be happening by 2009 either and better luck next time.

    I am more interested in hearing what other people think who know the situation, than making my own predictions, especially anybody who was at the recent school or conferences. Maybe none of them will help out with savvy guesses:frown: But Etera already did! So things are not so bad! Come what may. I'll go ahead and say what I see happening in the next couple of years.
     
    Last edited: Oct 4, 2007
  19. Oct 4, 2007 #18
    Hi Marcus,

    I'll not dare to make any guesses here, this is such an active field. But I'd say that I hope the GLAST mission will have an important role in shaping some directions. I hope.

    Best,
    Christine
     
  20. Oct 4, 2007 #19

    marcus

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    Christine, congratulations on the publication of your Science Fiction novel Tempo Aberto which I gather just went on sale:
    http://www.lulu.com/content/1100795
    also thanks so much for putting in a word here! With a two-year horizon both GLAST and MAGIC will have an important impact on Quantum Gravity. Let me turn your hope into a prediction. I feel certain of this.

    Regardless of whether the answer is yes or no about dispersion, it will make a big difference either way, and be good for the field. Both telescopes are sensitive enough to help decide the basic question.

    As an astrophysicist, you may have a number of other ways in mind that gammaray observations can contribute to QG development, but I think primarily of the one big issue of energy-dependent speed of light.

    I think with MAGIC it is just a question of their taking the time to observe more AGN flares. A sample of one (or one and a half :smile: ) flares is not enough. They must have more in the pipeline.
     
    Last edited: Oct 4, 2007
  21. Oct 4, 2007 #20
    Thanks! :redface: I'll see whether there is enough interest in my book so that it is worthy the effort of translating it into English. At present, only for the Portuguese speaking world... The title is "Tempo Aberto", which means "Open Time". The book was inspired by the idea of Laplace's demon, and the most part of it was actually written many, many years ago.

    Right, thanks for reminding me of MAGIC as well. I hope they get more data. No need to say that anyone interested in QG must be very interested on the data that these telescopes will bring.

    Christine
     
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