What is Lqg: Definition and 262 Discussions

The Clowes–Campusano LQG (CCLQG; also called LQG 3 and U1.28) is a large quasar group, consisting of 34 quasars and measuring about 2 billion light-years across. It is one of the largest known superstructures in the observable universe. It is located near the larger Huge-LQG. It was discovered by the astronomers Roger Clowes and Luis Campusano in 1991.

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  1. marcus

    What are the best introductory resources for learning Loop Quantum Gravity?

    There were questions in a couple of threads about what books/papers/recorded lectures could serve to give a good introduction to LQG. I gathered some excerpts from Leucippus' posts and want to make a fresh start---trying to understand and to stay more focused on the central problem. In general...
  2. marcus

    Exploring Noncommutative Space in LQG: Gauge Networks and Spin Foams

    This is an exciting development in LQG. They have a proposal for how to generalize the ideas of spin network and spin foam so that the network vertices are made of chunks of noncommutative space instead of ordinary space. I'd be glad if anybody who's looked at the paper and wants to volunteer...
  3. N

    How has LQG resolved the Big Bang Singularity

    I get the impression from the following material that LQG models have 'resolved' the divergent big bang singularity into a finite big crunch... If so, what changed and is this a generally accepted 'new start' at the front end of the FLRW model which follows?? I may have missed some discussions...
  4. atyy

    Relational Observables in LQG: Gauge Invariance and Incorporation of Matter

    It's often said that gauge invariant local observables in quantum gravity must be relational. In classical gravity, relational observables are constructed with matter. LQG for the most part has not had matter, yet it has been said to have observables such as area or volume. Are these...
  5. jfy4

    The Holonomy Expansion for Hamiltonian in LQG

    In Rovelli's book, in chapter 7 it talks about the Hamiltonian operator for LQG. In manipulating the form for the Hamiltonian operator Rovelli makes the following expansions U(A,\gamma_{x,u})=1+\varepsilon u^a A_a(x)+\mathcal{O}(\varepsilon^2) where by fixing a point x and a tangent...
  6. Physics Monkey

    Is Singular Quantization Still Necessary for Loop Quantum Gravity?

    I recently bought "A First Course in Loop Quantum Gravity" by Pullin and Gambini. Partly, I was curious to see what, if anything, had changed in the pedagogy. I also got Bojowald's book a while back. In the final section of "A First Course ..." the authors discuss open problems and broad...
  7. T

    What Should I Study Next: SUSY, LQG, String Theory, or GUT?

    I've been studying, just for pleasure, but studying in the end, a lot about QFT and its prerrequisites reaching some not so bad understanding of the Standard Model. I know that I still have to fill a lot of gaps, but nevertheless, I am looking for some new topic to start reading (while I fill...
  8. marcus

    Speziale-Wieland Twistor LQG paper, July 2012

    There are a lot of open problems in the twistor approach to Loop QG. They take the time to point them out. It's a fairly new approach so there are a lot of different things to work on. It's a 39 page paper, and at least from my perspective quite interesting. The authors are based in Marseille...
  9. soothsayer

    Coexistence of LQG and String Theory?

    Can Loop Quantum Gravity and String Theory coexist? What if String theory was correct in its description of matter and 3 of the 4 forces, with the only difference from modern M theory being that there is simply no real particle called the graviton, and instead, gravity is as is described by LQG...
  10. R

    Schiff conjecture and LQG or m-theory?

    Recently heard about the Schiff conjecture saying that any reasonable theory of gravitation should adhere to the ideas of EEP and UFF. I realize that this isn't a "strong" idea (only a conjecture after all), but to anyones understanding, does either loop quantum gravity or m-theory appear to...
  11. J

    The Future of LQG - Oldey's Perspective

    This is what an oldey in LQG thinks: http://arxiv.org/pdf/1201.4598.pdfs - page 27. It's great to see such confidence expressed in something that has for so long been put to the side because of the popularity in string theory. What most interests you and why? Do you have a different opinion...
  12. C

    Is it possible to combine string theory and LQG?

    Good evening. I am wondering if string theory and loop quantum gravity could be combined into a single theory. I have been trying to decide which of the two I should choose as my "religion," but I feel that both are correct. Could string theory and loop quantum gravity be different...
  13. Z

    Uncovering the Role of K in Canonical Variables of Loop Quantum Gravity

    In LQG the canonical variables are a SU(2) connection A, and the "electric" field E, such that they form a canonical pair, i.e., {A,E}=1. But the constraints that generates diffeomorphisms contains also the variable K (extrinsic curvature). My question is, is this variable an independent one? if...
  14. arivero

    Is there some hint of susy in LQG?

    Point is, Huerta and Baez, building upon the shoulders of M-theoretists, show us that susy is more relevant that just a trick to move the dimension of string theory. And Bott periodicity in Connes models did the same hint. Still, it seems that besides sugra, no model of space time has been able...
  15. tom.stoer

    Constraints, measure and vertex amplitude in LQG

    Have a look at http://arxiv.org/abs/1202.5039 Degenerate Plebanski Sector and its Spin Foam Quantization Authors: Sergei Alexandrov (Submitted on 22 Feb 2012) Abstract: We show that the degenerate sector of Spin(4) Plebanski formulation of four-dimensional gravity is exactly solvable and...
  16. V

    Idea for experimental test of LQG

    Hello! Long time peeker, first time poster. I recently made a GR joke/brainteaser on a pop sci blog I frequent, and the tirade of nutty reactions it provoked drove me to an agitated contemplation of the matter, which gave rise to a few ideas. I was thinking that maybe a Gallileo type...
  17. W

    Can LQG Explain the Existence of Branes in Higher Dimensions?

    Is it possible for LQG to occur in higher dimension (more than 3+1)? If possible. How? If not possible. Do you notice LQG in fixed 4D compared to Strings 10D is pretty boring? Nature doesn't make sense for there to be 4D (3+1T) only when it could create more with no sweat. So this alone may...
  18. M

    Relations between ANY TWO of LQG, TQFT, CFT wanted

    In Tom Stoer's latest thread, he says "there is growing evidence that the incompleteness of the different approaches [LQG / canonical QGR / spin foams] has a common origin", and suprised suggests that "it may be that trying to quantize an effective theory will never work, ie., without...
  19. tom.stoer

    Constraint Algebra & Gupta-Bleuler in LQG & SF Models | W. Wieland

    There's a new paper dealing with constraint algebra and Gupta-Bleuler quantization in LQG and SF models. http://arxiv.org/abs/1012.1738 Complex Ashtekar variables and reality conditions for Holst's action Authors: Wolfgang Wieland (Submitted on 8 Dec 2010) Abstract: From the Holst action...
  20. F

    What exactly is the relation between LQG and the Friedmann equation?

    I'm just beginning to look into loop quantum cosmology, and I've recently run into some fundamental confusion concerning how exactly the Friedmann equation fits in. Is it just that the application of loop quantum gravity yields a modified/effective Friedmann equation, or is it the other way...
  21. atyy

    Is This Gauge Theories' Classification Similar to LQG?

    http://arxiv.org/abs/1108.4389 Gauge Theories Labelled by Three-Manifolds Tudor Dimofte, Davide Gaiotto, Sergei Gukov (Submitted on 22 Aug 2011) We propose a dictionary between geometry of triangulated 3-manifolds and physics of three-dimensional N=2 gauge theories. Under this duality...
  22. romsofia

    Will LQG Survive 10 Years: Outlooks on Loop Quantum Gravity

    Well this upcoming year will be my last year of high school (yes I'm think WAY ahead). Anyways, I was thinking about grad school, and I've been looking into LQG (loop quantum gravity) and am thinking, that I will probably want to do research in something in that field. However, I've read that...
  23. atyy

    Existence of LQG: Investigating Limits of Spin Foam Models

    In http://arxiv.org/abs/1010.1939, Eq 26 & 27, Rovelli used 2 limits to define the current spin foam models. But he doesn't know if those limits exist. In http://arxiv.org/abs/1010.5437, Rovelli and Smerlak further elaborated properties of the limits, assuming their existence. Frank Hellmann...
  24. jfy4

    Is the Lagrangian for LQG similar to that of Yang-Mills theories?

    Hi, There is clearly an analogous relationship between Yang-Mills theories and LQG, for example the covariant derivative, the field strength tensor, the field and its conjugate momentum etc... I am wondering how far this analogy extends. Specifically, is the Lagrangian for LQG the...
  25. tom.stoer

    Exploring the Current Status and Open Issues in LQG: A Comprehensive Review

    I try to read all relevant papers regarding LQG, but of course for an outsider this is no longer not possible, therefore somehow I lost track when it comes to certain special topics. Some years ago authors like Smolin wrote review articles regarding current status, open issues and research...
  26. F

    Quantum grains (String theory & LQG in trouble?)

    http://www.sciencedaily.com/releases/2011/06/110630111540.htm What do you guys think?
  27. atyy

    What is the dimension of LQG (Rovelli's TQFT)?

    In http://arxiv.org/abs/1010.1939 Rovelli describes his present model as a generalized TQFT. The current quantum groups stuff is also strongly TQFT inspired (as spin foams in general are). This makes me wonder whether LQG should not in fact be "higher dimensional". The reason is that I've...
  28. S

    Are the LQG physicist less prepared than the ST physicist?

    I ask this question because some time ago I was attending some course in LQG, and I was very surprised of the lack of knowledge of the teacher in anything that was not completely related to his investigation. Even things that he knew, he only knew it in the particular context of his work and...
  29. Physics Monkey

    Classical Limit in LQG: Has GR Been Shown?

    Hi everyone, I would like to ask a very simple and direct question: has the classical limit of any of the various loopy approaches to quantum gravity been shown to be GR? Perturbative fluctuations around flat space, for example? I've seen what appear to me to be conflicting claims on...
  30. marcus

    Bianchi Haggard volume spectrum paper puts UC Berkeley on Lqg map

    I was glad to see this paper for several reasons. The volume operator in Loop Gravity is the locus of some interesting unresolved questions. The kind that requires and attracts creative mathematicians IMHO. This first paper from Gene Bianchi and Hal Haggard is just a 4-page letter I guess for...
  31. marcus

    Merging NCG matter with Spinfoam LQG spacetime (new Pfaeffle-Stephan)

    This thread is in case discussion of the following paper is wished. http://arxiv.org/abs/1102.0954 The Holst Action by the Spectral Action Principle Frank Pfaeffle, Christoph A. Stephan 11 pages (Submitted on 4 Feb 2011) "We investigate the Holst action for closed Riemannian 4-manifolds with...
  32. S

    Why not unify LQG with Superstring\M theory ?

    Is it possible to unify both theories ? I think it may be possible
  33. marcus

    Signs LQG has the right redefinition (or wrong?)

    LQG was redefined in 2010. The essentials are summarized in two December papers, http://arxiv.org/abs/1012.4707 http://arxiv.org/abs/1012.4719 What indications do you see that this was the right (or wrong) move? How do you understand the 2010 reformulation? How would you characterize it...
  34. marcus

    Piareround's questions about LQG

    Piareround had some questions about LQG. I have to go out for the next hour or so. Maybe someone will take a look and respond. Or I will when I get back.
  35. tom.stoer

    Criticism of LQG - What do we miss?

    It may be more intersting to identify open issues from our perspective instead of "translating" Lubosz. A brainstorming from my side: LQG starts with a quantization of spacetime which is topologically M3*R; it is by no means clear if this "background-dependence" does not throw away physical...
  36. inflector

    Luboš Motl's Criticism of LQG - What Does He Miss?

    I don't normally read Luboš's blog because I find his tendency to belittle others offputting to say the very least. It can also be difficult to find the value hidden in the pile of vitriol and condescension. Further, I find from my past experience that his level of arrogance has been an...
  37. marcus

    Spring schedule for International LQG Seminar

    The ILQGS "conference call" seminars audio and slide go online, so we can listen. They usually have some 5 or so centers hooked up, so during the presentation you may hear comment/question from Marseille, Nottingham, PennState, Warsaw, Waterloo,... Then sometimes the speaker will respond to the...
  38. marcus

    Spinfoam Fermions, Lqg now has matter

    https://www.physicsforums.com/showthread.php?p=3048498#post3048498 This should have its own thread: http://arxiv.org/abs/1012.4719 Spinfoam fermions Eugenio Bianchi, Muxin Han, Elena Magliaro, Claudio Perini, Carlo Rovelli, Wolfgang Wieland 8 pages (Submitted on 21 Dec 2010) "We...
  39. tom.stoer

    Understanding the Relation between LQG and NQC

    Hi, unfortunatey I lost track. I do not understand much reagrding NCG, but I noticed that there seems to be a line of research that tries to harmonize the NCG and the LQG approach, right? Can anybody here explain the relation between LQG and NQC, the "big picture", not so much focussed on...
  40. H

    The mathematics required for mathematical physics (LQG, ST, FT, etc)?

    I realize this might be a little bit of academic advisement, but I think it'd be more useful to have some people who really know a lot about the subject post about this. I like math a lot, and specifically I was wondering about number theory or set theory and logic, which is interesting but I'm...
  41. marcus

    If LQG now satisfactory, how to add matter?

    Currently the two definitive papers are 1004.1780 and 1010.1939, with several others applying spinfoams to cosmology e.g. 1003.3483. LQG is about where one could have predicted back in Fall 2008, with the merger of the canonical, covariant, and cosmological versions. I think in fact one or more...
  42. marcus

    Bianchi's PI talk on quantum polyhedra in LQG

    http://pirsa.org/10110052/ Quantum polyhedra in loop quantum gravity Eugenio Bianchi "Interwiners describe quanta of space in loop quantum gravity. In this talk I show that the Hilbert space of SU(2) intertwiners has as semiclassical limit the phase space of a classical system originally...
  43. MTd2

    In LQG, where do things come from to make the Big Bounce?

    Is it from a Black Hole? Is it from a Cyclic Universe?
  44. Q

    Is there someone who knows the difference between String Theory and LQG?

    Hi, guys. I want to do some research on quantum gravity. I know that there are two theories achieving some success in this direction. Do you know something about that? I want to learn something about that. Thank you!
  45. bcrowell

    Smolin's Scientific American article on LQG

    I would like to step up from the pop-sci level of understanding LQG to something more like a real physicist's understanding, but one thing that's hanging me up is the SU(2) stuff, which I don't understand, even at a hand-wavy level. Falling back to the pop-sci level to regroup, I remembered that...
  46. marcus

    Basic LQG questions raised by 1998 LQG Primer article

    Basic LQG questions raised by 1998 "LQG Primer" article B Crowell asked what would be the best way into LQG and then (on looking over the suggested entry-level "LQG Primer" article by Rovelli and Upadhya http://arxiv.org/abs/gr-qc/9806079 ) made a potentially very helpful list of questions. I...
  47. E

    What is Rovelli's new LQG formulation trying to do?

    What is Rovelli's "new" LQG formulation trying to do? I've wondered about this to
  48. marcus

    Can LSS unification (gravity, gauge, Higgs) be quantized à la new LQG ?

    Can LSS unification (gravity, gauge, Higgs) be quantized à la "new LQG"? This came out in April. We had it on our second quarter MIP ("most important paper") poll. https://www.physicsforums.com/showthread.php?t=413838 So far, this is a classical treatment. And it uses a spacetime manifold...
  49. E

    LQG and Princeton's institute for Advanced Study

    Looking at Marcus list I wonder: What would it take for LQG to be seriously researched (i.e group of phD's publishing papers, post docs, grad students, courses in study) at Princeton's institute for Advanced Study as well as Stanford or Harvard, UChicago, Rutgers, MIT, etc., will be starting an...
  50. marcus

    Asia Pacific Center for Theoretical Physics starts a new LQG group

    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...
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