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Thiemann's Latest - Conroversy

  1. Aug 31, 2006 #1

    selfAdjoint

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    Thomas Thiemann has responded to some critics, with a new conspectus of LQG and his Master Constraint Program. Here is his abstract; note the comment on Helling et al.

    hep-th/0608210
    From: Thomas Thiemann [view email]
    Date: Tue, 29 Aug 2006 19:05:37 GMT (82kb)
    Loop Quantum Gravity: An Inside View
    Authors: Thomas Thiemann
    Comments: 58 pages, no figures
    Report-no: AEI-2006-066
    Subj-class: High Energy Physics - Theory; Mathematical Physics
    This is a (relatively) non -- technical summary of the status of the quantum dynamics in Loop Quantum Gravity (LQG). We explain in detail the historical evolution of the subject and why the results obtained so far are non -- trivial. The present text can be viewed in part as a response to an article by Nicolai, Peeters and Zamaklar [hep-th/0501114]. We also explain why certain no go conclusions drawn from a mathematically correct calculation in a recent paper by Helling et al [hep-th/0409182] are physically incorrect.

    The Helling et al. paper is this:

    hep-th/0409182
    From: Robert C. Helling [view email]
    Date: Fri, 17 Sep 2004 10:53:26 GMT (19kb)
    String quantization: Fock vs. LQG Representations
    Authors: Robert C. Helling, Giuseppe Policastro
    Comments: 19 pages
    Report-no: DAMTP-2004-93
    We set up a unified framework to compare the quantization of the bosonic string in two approaches: One proposed by Thiemann, based on methods of loop quantum gravity, and the other using the usual Fock space quantization. Both yield a diffeomorphism invariant quantum theory. We discuss why there is no central charge in Thiemann's approach but a discontinuity characteristic for the loop approach to diffeomorphism invariant theories. Then we show the (un)physical consequences of this discontinuity in the example of the harmonic oscillators such as an unbounded energy spectrum. On the other hand, in the continuous Fock representation, the unitary operators for the diffeomorphisms have to be constructed using the method of Gupta and Bleuler representing the diffeomorphism group up to a phase given by the usual central charge.


    And Robert Helling has replied to Thiemann's claim here.

    Meanwhile Lubos Motl had a teardown of Thiemann's paper on his blog (I am not going to link to it)., which the physicist who blogs as Capitalist Imperialist Pig then showed to be false (the word "lie" comes up here. Lubos commented with a critique of pig's essay that was typical Lubos: off the point and ending with this sentence: "I would like to help you to avoid similar stupidities in the future, but I have not yet discovered a cure that would change a complete idiot into a reasonable person"

    There is also discussion at Christine Dantas's blog, but I haven't been there yet.
     
  2. jcsd
  3. Aug 31, 2006 #2

    marcus

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    Glad you made a thread about this!
    Good idea. I will go to christine's blog and read what Aaron Bergman had to say.

    We can be proud of Hans Kastrup who was thesis advisor to both the top German nonstring QG people----Thomas Thiemann and Martin Bojowald. He is still in there having a considerable influence on events. TT credits Hans for having prodded him to write this reply to Nicolai---insisting that he had to.

    traditions.
    making the younger generation live up to them.
    germans.

    but I would not like to have to reply to Aaron Bergman. He is a pain.
    If Urs would comment on TT it would be great. I realize Urs is open and fairminded
     
  4. Aug 31, 2006 #3

    marcus

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    I looked at Christine's blog
    http://christinedantas.blogspot.com/2006/08/lqg-inside.html

    Urs is not there. It is basically 3 consecutive posts by A.B.
    It sounds like A.B. wants to read the papers TT posted in November 2004 which go into details and examples. And in the October 2005 paper that you flagged.

    A.B. is asking about detail and example of the kind that TT covered in those half-dozen papers and it sounds from his tone that he hasnt looked at them (or so I would guess). So if TT goes to Christine's he will just be telling Aaron "please look at the following paper", or so I would guess.

    I will gather the links in case anyone myself included might find them useful.

    http://arxiv.org/abs/gr-qc/0510011
    Quantum Spin Dynamics VIII. The Master Constraint
    Thomas Thiemann
    19p
    Class.Quant.Grav. 23 (2006) 2249-2266

    "Recently the Master Constraint Programme (MCP) for Loop Quantum Gravity (LQG) was launched which replaces the infinite number of Hamiltonian constraints by a single Master constraint. The MCP is designed to overcome the complications associated with the non -- Lie -- algebra structure of the Dirac algebra of Hamiltonian constraints and was successfully tested in various field theory models. For the case of 3+1 gravity itself, so far only a positive quadratic form for the Master Constraint Operator was derived. In this paper we close this gap and prove that the quadratic form is closable and thus stems from a unique self -- adjoint Master Constraint Operator. The proof rests on a simple feature of the general pattern according to which Hamiltonian constraints in LQG are constructed and thus extends to arbitrary matter coupling and holds for any metric signature. With this result the existence of a physical Hilbert space for LQG is established by standard spectral analysis."


    http://arxiv.org/abs/gr-qc/0411142
    Testing the Master Constraint Programme for Loop Quantum Gravity V. Interacting Field Theories
    Bianca Dittrich, Thomas Thiemann
    20 pages
    Class.Quant.Grav. 23 (2006) 1143-1162

    http://arxiv.org/abs/gr-qc/0411141
    Title: Testing the Master Constraint Programme for Loop Quantum Gravity IV. Free Field Theories
    Authors: Bianca Dittrich, Thomas Thiemann
    23 pages
    Class.Quant.Grav. 23 (2006) 1121-1142

    http://arxiv.org/abs/gr-qc/0411140
    Testing the Master Constraint Programme for Loop Quantum Gravity III. SL(2,R) Models
    Bianca Dittrich, Thomas Thiemann
    33 pages
    Journal-ref: Class.Quant.Grav. 23 (2006) 1089-1120

    http://arxiv.org/abs/gr-qc/0411139
    Testing the Master Constraint Programme for Loop Quantum Gravity II. Finite Dimensional Systems
    Bianca Dittrich, Thomas Thiemann
    23 pages
    Class.Quant.Grav. 23 (2006) 1067-1088

    http://arxiv.org/abs/gr-qc/0411138
    Testing the Master Constraint Programme for Loop Quantum Gravity I. General Framework
    Bianca Dittrich, Thomas Thiemann
    Comments: 42 pages, no figures
    Class.Quant.Grav. 23 (2006) 1025-1066
     
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