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Asia Pacific Center for Theoretical Physics starts a new LQG group

  1. Aug 18, 2010 #1

    marcus

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    Hanno Sahlmann has announced the formation of a new LQG group, at the APCTP in Korea. There are postdoc and PhD student positions to be filled and he indicates he would like to get them filled by this fall (which is fast approaching!)

    sahlmann@particle.skipthis.uni-karlsruhe.andthis.de

    Sahlmann is the S in the well-known L.O.S.T theorem which established, under fairly general assumptions, uniqueness of the holonomy/flux state space. If I'm not mistaken, his PhD advisor was Thiemann at the Einstein Institute (the T in L.O.S.T). As I recall, Sahlmann postdoc'd with Ashtekar 2003-2005 and at Utrecht 2006-2008 with Renate Loll. Since 2008 he holds a faculty position at Karlsruhe. It looks like he will lead the new LQG group.

    I see that Spires lists PhD advisors:
    http://www.slac.stanford.edu/spires/find/hepnames/www?phdadv=Thiemann,+Thomas [Broken]

    Several new LQG groups have been established in the past couple of years---and previous groups have added permanent positions. 2008-2010 seems to have been a time of growth for the field. Probably the reasons for this are complicated---I'm not sure there is a single explanation.

    To illustrate how many more Lqg venues there are now than there were a few years back, I will copy from Francesca's map. In some cases I think the primary interest of the permanent faculty listed here is in a neighboring field, but I guess it would be possible to do a Loop PhD thesis with almost any of those listed as your advisor.

    AEI Berlin
    Permanents: Bianca Dittrich, Daniele Oriti, Hermann Nicolai. http://www.aei.mpg.de/english/research/teams/ [Broken]

    CPT Marseille
    Permanents: Alejandro Perez, Carlo Rovelli, Simone Speziale. http://www.cpt.univ-mrs.fr/~quantumgravity/ Postdocs: Eugenio Bianchi, Muxin Han, Christian Roeken, Antonino Marcianò, Marco Valerio Battis...

    LSU
    Permanents: Kristina Giesel, Jorge Pullin, Parampreet Singh. http://relativity.phys.lsu.edu/

    QG Nottingham
    Permanents: John Barrett, Kirill Krasnov, Jorma Louko. http://www.maths.nottingham.ac.uk/research/applied_mathematics/quantum_gravity/ [Broken]
    (Affiliated: Ed Copeland http://www.nottingham.ac.uk/physics/research/particles/)

    Morelia
    Permanents: Alejandro Corichi, Robert Oeckl, José Zapata. http://www.matmor.unam.mx/~corichi/lqgindex.html

    PennState
    Permanents: Abhay Ashtekar, Martin Bojowald. Postdocs:Claudio Perini,Elena Magliaro,Jacobo Diaz Polo,William Nelson,Simone Mercuri. PhD:Miguel Campiglia, Adam Henderson, Artur Tsobanjan, Edward Wilson...

    Erlangen
    Permanents: Thomas Thiemann and one more faculty soon! Postdocs: Emanuele Alesci, ..... PhD studens: .....

    Perimeter Institute for Theoretical Physics
    Permanents: Laurent Freidel, Fotini Markopoulou, Lee Smolin.

    IEM-QFT Madrid
    Permanents: Fernando Barbero, Guillermo Mena Marugán. Postdoc: Tomasz Pawlowski. http://www.iem.csic.es/departamentos/qft/index.html

    University of Warsaw
    Permanent: Jerzy Lewandowski. http://www.fuw.edu.pl/~lewand/homepage.html

    Beijing Normal University
    Permanent: Yongge Ma http://physics.bnu.edu.cn/application/research/gravity/LQG/eng/research.html

    Universität Hamburg
    Permanent: Catherine Meusburger. http://www.math.uni-hamburg.de/home/meusburger/ Postdoc: Winston Fairbain.

    Florida Atlantic University
    Permanent: Jonathan Engle, Warner Miller.

    École normale supérieure de Lyon
    Permanent: Etera Livine

    Universite De Paris XI Paris Sud
    Permanent: Vincent Rivasseau http://www.rivasseau.com/index.html

    Tours
    Permanent: Karim Noui

    Universite Montpellier II
    Permanent: Sergei Alexandrov

    Grenoble
    Permanent: Aurelien Barreau http://lpsc.in2p3.fr/ams/aurelien/

    Cinvestav Zacatenco
    Permanent: Merced Montesinos

    Montevideo
    Permanents: Rodolfo Gambini, Michael Reisenberger.

    Cambridge
    Permanent: Ruth M. Williams

    King's College London
    Permanent: Mairi Sakellariadou.
    http://www.kcl.ac.uk/schools/nms/physics/people/academic/sakellariadou/

    UMC Utrecht
    Permanent: Renate Loll http://www.phys.uu.nl/~loll/Web/title/title.html

    Niels Bohr Instituttet
    Permanent: Jan Ambjorn http://www.nbi.ku.dk/english/

    Rheinische Friedrich-Wilhelms-Universität
    Permanent: Klaus Kiefer

    Universität Paderborn
    Permanent: Christian Fleischhack

    Haverford College
    Permanent: Stephon Alexander. Postdoc:Antonino Marcianò.

    Western Ontario
    Permanents: Daniel Christensen

    McMaster University
    Permanent: Seth Major. http://academics.hamilton.edu/physics/smajor/

    New Brunswick
    Permanents: Viqar Husain http://www.math.unb.ca/~husain/ [Broken]

    University of Lethbridge
    Permanents: Saurya Das, Arundhati Dasgupta, Mark Walton. Post-Doc: Wissam Chemissany. Students: Borislav Belchev, Ahmed Farag Ali, Ali Nassar, Steve Sidhu. http://people.uleth.ca/~saurya.das/TPG/TPG.h [Broken]...

    Raman Research Institute
    Permanent: Madhavan Varadarajan

    University of Sydney/Macquarie University
    Permanent: Daniel Terno http://www.qscitech.info/ Postdoc: Florian Girelli

    American University of Beirut
    Permanent: Tamer Tlas.

    Kansas State University
    Permanent: Louis Crane. http://www.math.ksu.edu/main/contact_info/personnel_detail?person_id=1330

    Riverside
    Permanent:John Baez. http://math.ucr.edu/home/baez/README.html

    Caltech
    Permanent: Matilde Marcolli. http://www.its.caltech.edu/~matilde/

    Berkeley
    Permanent: Robert Littlejohn. http://www.physics.berkeley.edu/research/faculty/littlejohn.html [Broken]

    Pavia
    Permanents: Mauro Carfora and Annalisa Marzuoli Students: Hal Haggard and Francesca Vidotto (2011)

    Torino
    Permanent: Lorenzo Fatibene http://www.dm.unito.it/personalpages/fatibene/index.htm

    Sapienza University of Rome
    Permanents: Giovanni Montani, Giovanni Amelino Camelia. Giovanni Montani http://www.icra.it/cgm/welcome.htm http://www.roma1.infn.it/~amelino/

    Uniwersytet Wrocławski Wydział Fizyki i Astronomii Instytut Fizyki Doświadczalnej
    Permanent: Jerzy Kowalski-Glikman.

    Uniwersytet Jagielloński Wydział Fizyki Astronomii i Informatyki Stosowanej
    Permanent: Marek Szydlowski.

    IUCAA Pune
    Permanent: Naresh Dadhich

    National Cheng Kung University
    Permanent: Chopin Soo

    Academia Sinica
    Permanent: Hoi-Lai Yu

    ======================
    The information for some of these is only partial. It comes from this map:
    http://maps.google.com/maps/ms?ie=U...985216139270436.0004843830d27f3e6c50e&t=h&z=0
    In any case, Hanno starting a LQG group at Pohang, Korea is not an isolated example. There seems to be a "Loop diaspora" in progress.
     
    Last edited by a moderator: May 4, 2017
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  3. Aug 19, 2010 #2

    marcus

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    The question came up in another thread "what would it take for Princeton IAS to establish a LQG group?" The question is sociological, but relevant to the progress of science. Science is a community/tradition-based process and can't be understood in isolation from human institutions.

    I won't try to answer the "what would it take?" question but it's worth thinking about a related question: how do you recognize a QG research center? Like for example the first item on the above list: AEI Berlin. Also called Einstein Institute at Potsdam (which is just outside Berlin).

    I guess the focus needs to be on understanding how change happens. Thiemann just moved from AEI to set up a new QG center at University of Erlangen (famous for Felix Klein's "Erlangen Program" in geometry/group theory). What you see at AEI now is kind of a TEMPLATE or model for what to expect at Erlangen, or at the Asia Pacific center where Thiemann's student Sahlmann is forming a QG group.

    Change happens in the list of places which are prominent. For example the heaviest investment in string has been at Princeton and Rutgers. But we hear less and less about Princeton and Rutgers and we hear more and more about AEI, Marseille, Perimeter.


    Well Einstein Potsdam has 3 relevant research teams:

    Canonical and Covariant Dynamics of Quantum Gravity (7 people, Thiemann's student Dittrich is leader)
    http://www.aei.mpg.de/english/research/teams/canonicalCovariantDynamics/index.html [Broken]
    http://www.aei.mpg.de/english/research/teams/canonicalCovariantDynamics/members/index.php [Broken]

    Microscopic Quantum Structure & Dynamics of Spacetime (8 people, Oriti is the group leader)
    http://www.aei.mpg.de/english/research/teams/microscopicQuantumStructure/index.html [Broken]
    http://www.aei.mpg.de/english/research/teams/microscopicQuantumStructure/members/index.php [Broken]

    Quantum Gravity and Unified Theories (only has two specifically Lqg)
    http://www.aei.mpg.de/english/research/teams/quantumGravity/members/index.php [Broken]

    The last here used to be the place for the AEI Loop people, before the two new teams were established. It has Baratin, who got his PhD with Freidel, and is now postdoc---and Tambornino, a PhD student of Dittrich. Most of the specifically Lqg people at the Potsdam Einstein Institute are now in the first two research teams.

    The point is that one should not be looking for the appearance of institutional set-ups labeled "LQG". Look at the team names:
    "dynamics of quantum gravity"
    "microscopic dynamics of spacetime"

    Whatever it takes for Princeton to set up a LQG research group has already happened, but Princeton is stuck and can't move. In effect, AEI is the new "Princeton IAS". It has taken the lead while the IAS is immobilized by its investment in people who are getting old (and who study stuff that is getting old.)
    The new AEI research team titles do not say "LQG". They simply say quantum gravity, or words to that effect. You have to click on the links and look closer to see where it says Lqg, usually in the first paragraph of the mission statement.
     
    Last edited by a moderator: May 4, 2017
  4. Aug 19, 2010 #3

    marcus

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    To get a better understanding of how change takes place in Academia we should look at what IAS Princeton is actually doing.
    What it looks like is a quiet gradual de-emphasis of string and a shift of their HEP emphasis into phenomology relevant to LHC.

    Last year they brought in Nima Arkani-Hamed, and Nima has proposed a program to retrain some young string people and get them into more LHC-relevant research. He got an NSF grant that is partly for that purpose. Here's a November 2009 report on those trends.

    == http://www.math.columbia.edu/~woit/wordpress/?p=2447 ==
    Since the late eighties, the two institutions in the US most heavily invested in string theory have been Princeton and Rutgers. Recently they have been moving aggressively to try and diversify, especially in the direction of LHC phenomenology, with the hiring of Nima Arkani-Hamed at the IAS and Matt Strassler at Rutgers. Last year the two institutions collaborated on a proposal for a new Physics Frontier Center with a budget of $1 million or so per year. This would be called the PARTICLE Center (Princeton And Rutgers Theory Institute for Collaboration with LHC Experiments) and would aim to be the main US center for LHC phenomenology. The proposal promoted the possibility of experimental anomalies to be discovered by the LHC in fall 2009, quickly followed by PARTICLE physicists inventing a model that would explain the data and predict a subtle effect that would require a new triggering strategy to see. The result of this would be a surprising measurement that would explain supersymmetry breaking.

    Anyway, that proposal doesn’t appear to have been funded, with reviewers rather dubious about the idea of retraining Princeton and Rutgers string theorists as LHC phenomenologists, as well as the idea of devoting significant new resources to funding the Princeton and Rutgers theory groups, centralizing LHC phenomenology efforts there. However, two new year-long grants for $130,000 each were awarded to Strassler and Arkani-Hamed, who promise to use them to “create the nucleus of an LHC center on the East Coast” at Princeton and Rutgers. One of the goals of these grants is listed as “to help in the process of … retraining postdocs from more formal areas of high-energy theory”, since the job market for young string theorists has more or less collapsed.
    ==endquote==

    The key phrase here is retraining postdocs. Institution inertia has to do with investment in human capital.

    Some NEW research centers are poised to take the lead in fundamental physics, and are able to move faster, because they are not so heavily invested in string researchers.
    What the older institutions need to work on is gradually shifting emphasis and bit-by-bit redirecting their focus.

    Whatever happens in Academia-USA will happen slowly and will not have a visible "LQG" headline.
    For example one thing is the slow gain in prestige of a place like Penn State. You saw the funding of a big new intitute there last year: Ashtekar's IGC (Institute for Gravitation and Cosmology.) There is no visible "LQG" flag being waved, but we know the kind of research they do and the people that come out of there. And the place has been gaining in prominence.

    Also we have to read the code: what Nima said about getting out of "the more formal areas of high-energy theory" means getting out of string. The older universities with a heavier pre-committment cannot immediately set up new QG groups--that's institutionally too big a jump for their people--first they have to find some way to retrain/redirect the researchers they have already.
     
    Last edited: Aug 19, 2010
  5. Aug 19, 2010 #4

    marcus

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    What are the underlying physical reasons for the rapid expansion of LQG research in the past few years, say since 2005?

    I think one important reason is that it has come to be recognized as the leading form of manifold-less QG where one knows how to calculate.

    Of course there is no sharp border between LQG/spinfoam and group field theory (as pursued by Oriti's group at the Einstein Institute in Potsdam) and simplicial QG (e.g. Dittrich's group at Potsdam combines both approaches).

    The main thing is to have a manifold-less QG where there is enough structure on the table so one can calculate stuff---operator spectra, transition amplitudes, correlations functions, a graviton propagator. There seems to have been a merging of approaches in this direction.

    So we can look at the list that Francesca and friends put up on Google---the LQG map--- and see the potential for what is actually a mix of allied manifold-less approaches.

    And the question to think about is "why manifold-less?"

    It has to do with diff-invariance. I have to go out briefly. Will discuss this later.
     
  6. Aug 19, 2010 #5

    atyy

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    No.

    "LQG is a diffeomorphism invariant theory of fields on manifolds."

    http://arxiv.org/abs/0909.0939
     
  7. Aug 19, 2010 #6

    marcus

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    Something of a cherry-pick :biggrin: In that paper Lewandowski is presenting an excellent valuable result, and finds it convenient to use his own special terminology. He distinguishes between "SFM" (spinfoam models) and what he calls "LQG" which is based on embedded spin-networks. Old LQG.

    That was a 2009 paper by Lewandowski et al, but it harks back to much earlier canonical formulations.
    Rovelli's April 2010 review is more up-to-date and I will try to adhere to his terminology as much as possible. Hope you will do likewise so we don't talk at cross-purposes so much.
     
    Last edited: Aug 19, 2010
  8. Aug 19, 2010 #7

    marcus

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    This reminds me of an earlier thread where there was some confusion as to what a diffeomorphism is.

    A diffeomorphism is simply a smooth 1-1 onto map.

    An example would be let the manifold be the real line R with the usual differential structure---usual idea of smooth map.
    Let the map be x --> 2x
    "multiply every number by 2."

    A smooth map does not assume the existence of a metric and has no automatic connection to one if it exists.
    So it's obvious that one can add the natural metric to the picture: |x-y|. Let us assume we have that metric and no other.

    This example of a diffeomorphism changes the distances between points. In fact it doubles the distances.
    (Clearly a diffeo does not have to be linear, so with a more complicated example it could change distances by lots of different ratios.)

    You can only say that a diffeomorphism preserves distances if you explicitly specify that the metric is mapped as well. You "take the metric along with you" so to speak. There was, I think, a lot of confused talk recently in one or more threads about diff-invariance. Rather than go back to those threads, I will just develop the ideas I need here. Simpler, and avoids wasting time with sematic bickering.
     
    Last edited: Aug 19, 2010
  9. Aug 19, 2010 #8

    atyy

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    I think only Markopoulou is working on a manifoldless approach.

    Maybe Bianca Dittrich.

    I mean, are spin foams manifoldless? I think of them as GFT, which has a manifold.

    BTW, since your list of LQG related researchers is so broad - that's ok - did you consider http://arxiv.org/abs/0907.2994 ?
     
    Last edited: Aug 19, 2010
  10. Aug 19, 2010 #9

    marcus

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    I already commented on that in the "Five Principles" thread, at length :biggrin:. When I say manifold-less I mean no manifold representing the spacetime continuum. One can still use Lie groups! Rovelli's April survey of "new LQG" starts right off with cartesian products of copies of SU(2). It's how one does gauge theory on spin-networks (without a spacetime manifold) and how one defines the Hilbert space of LQG states.
     
  11. Aug 19, 2010 #10

    marcus

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    I guess the point should be made here that General Relativity itself is a prototypical manifold-less theory in the sense that after one does the construction one throws the manifold away.

    The gravitational field, in GR, is not a particular metric on a particular manifold. It is an equivalence class of solutions under diffeos. Two given setups (manifold, metric, distribution of matter) are equivalent if there exists a diffeo which maps one to the other (TAKING EVERYTHING ALONG.)

    Individual points of the spacetime manifold have no physical significance, nor does any particular manifold---the gravitational field is more abstract than that. It is an abstract geometry--an insubstantial bunch of spatial and temporal relationships.

    Since the theory is constructed using a spacetime manifold, people commonly think in terms of some concrete representative of the equivalence class---which works just fine for most things.

    However it doesn't work so well when you do QG, because it is wrong at a fundamental philosophical level. There is no spacetime geometry which we can determine any more than there are particle trajectories which we can determine using a finite number of slits and detectors. GR took us partway on the journey and we must begin where GR took us--we begin with the insight GR attained, by discarding the spacetime manifold as gauge.

    (It's always possible to go back à la Lewandowski and restore continuity with the past. There are useful theorems to prove and things to discover by hooking the present up with earlier LQG development! But the philosophical basis, and the principal formulation, is manifold-less. Specifically it is a type of manifoldless formulation Rovelli calls "combinatorial.")

    I think basically the reason we are seeing rapid growth in LQG since 2005 or 2006 is a spreading realization of the importance of this insight. (Also LQG has made remarkable advances starting in 2008, just technically speaking. That has probably helped.)
     
    Last edited: Aug 19, 2010
  12. Aug 19, 2010 #11

    atyy

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    So is this philosophically wrong? My own hope is that really it is GFT that is fundamental, but historically, spin foams do come from a spacetime manifold. And of course, manifolds are only defined up to diffeomorphism.

    "Spin foam models are discrete versions of a functional integral, usually constructed using a triangulation of the space-time manifold (‘foam’), local variables (‘spins’), and local amplitudes for the simplexes in the triangulation." http://arxiv.org/abs/0907.2440
     
  13. Aug 19, 2010 #12
    do these insights still apply if GR is just an entropic "equation of state"? or, as in string theory, it's just a low-energy quantized spin-2 field of a more complex 11-D M-theory?
     
    Last edited: Aug 19, 2010
  14. Aug 19, 2010 #13

    atyy

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    Or AdS/CFT for that matter. Would the Rovellian philosophy predict that the AdS/CFT conjecture will turn out to be false?
     
  15. Aug 19, 2010 #14

    marcus

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    Certainly not! How can you say such a thing, Atyy! AdS/CFT is a mathematical conjecture concerning differential manifolds! I suspect that it will be proven as a math theorem. Or as several theorems.

    One makes the required assumptions and definitions and one (hopefully eventually) can prove the theorem.

    It would be naive to imagine that the Poincaré conjecture must be "false" if it turns out that there is some better way than a manifold with metric to represent space and the grav. field! :biggrin:
     
  16. Aug 19, 2010 #15

    marcus

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    Yes of course. Ask yourself what "molecules" of geometry underlie the entropy.
     
  17. Aug 19, 2010 #16

    atyy

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    But AdS/CFT is a theory of quantum gravity!

    So is it actually an instantiation then of Rovellian philosophy? If you look at the CFT - there is no spacetime, only its boundary. In my thinking, AdS/CFT is the reason (well, more a gut feeling) that GFT should be primary. Actually there is some indication that Rovelli might agree! "In this sense, this approach has similarities with the philosophy of the Maldacena duality in string theory: a nonperturbative theory is dual to a more quantum field theory. But here there is no conjecture involved: the duality between certain spin-foam models and certain group field theories is a theorem." http://relativity.livingreviews.org/Articles/lrr-2008-5/ [Broken]
     
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  18. Aug 20, 2010 #17

    marcus

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    That's an interesting quote from Rovelli:
    I don't disagree with what you quote, but my perspective (as retired mathematician) is different from what I think yours is. I tend to keep mathematical theorems separate from physical theories of nature.
    I think of the AdS/CFT conjecture as a (not-yet-proven) theorem. The theorem is among other things about manifolds.

    As an interesting piece of mathematics, it could be applicable in several different circumstances (wherever the idealization is a good fit) at several different scales. I don't normally take mathematical tools too literally.

    In any case AdS/CFT is not the topic here. I'm sure you would agree it's a big subject and needs its own thread.
     
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  19. Aug 20, 2010 #18

    marcus

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    I did some organizing and editing on the Google-maps list of LQG "places". I organized it alphabetically by country, and brought it up to date as best I could. I erased some information I thought might be out of date or where a link had gone dead. Can't vouch for everything, but on the whole it matches what I know from other sources.

    Basically what it shows is a kind of explosive growth and a "diaspora". The appearance of new centers. A large number of those I first knew of as students and postdocs have moved into permanent positions.

    I will get the list.


    Some of the senior people on the Google-maps list have only tentative association with LQG, but were included for whatever reason. Marcolli is mainly NCG and has only one recent spinfoam paper. Baez main interests are outside QG, as far as I know. He might be willing to advise PhD students in quantum gravity, but I am not sure. Loll and Ambjorn work with simplicial QG---they actually have a rival approach to LQG. Stephon Alexander has co-authored with LQG people in the past but again I don't think LQG is a central interest of his. So the list as we get it off Google contains periferal people. Rivals and alternatives. Actually I don't know how I would have compiled it myself---distinctions are not sharply drawn. But it seems right to me in the main.
     
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