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

    Spacetime-matter degrees of freedom in current LQG research

    For the purposes of this thread LQG is defined in a pragmatic unrigorous way. Loop gravity is what loop gravitists do. That begs the question who are representative loop gravitists? Well it is a fuzzy set but I think we all have an idea who they are: people like Rovelli, Smolin, Freidel...
  2. kakarukeys

    Why is the classical limit of kinematical LQG still unknown?

    From http://math.ucr.edu/home/baez/week110.html" One could also imagine a huge spin network with lots of vertices and edges, all with small quantum numbers, distributed homogeneously, evenly throughtout the graph. It should look like a flat space when viewed at large scale. If you use a...
  3. ZapperZ

    Does Loop Quantum Gravity Make Testable Predictions?

    At least LQG tries to make measurable predictions! When is String theory going to even try? http://physicsweb.org/articles/news/10/2/2/1 Zz.
  4. marcus

    Smolin video LQG online course

    http://streamer.perimeterinstitute.ca:81/mediasite/viewer/FrontEnd/Front.aspx?&shouldResize=False scroll down the side menu to "Introduction to Quantum Gravity" L.S. announced posting this course on Woit's blog
  5. marcus

    How Standard Model numbers arise from LQG

    One way to achieve a degree of unification in physics would be to show how key aspects of the Standard Model of particle theory emerge from Loop Quantum Gravity. At the October QG conference Lee Smolin offered some ideas as to how that might happen. It involved having the links of the spin...
  6. S

    Understanding Entropy in LQG: Evidence from Spin Network Systems

    This is a great paper :http://arxiv.org/abs/gr-qc?0505111 I know of 4 actual/specific systems that allready exist that are confirmation of the said paper with respect to spin network?
  7. M

    Exploring String Theory & LQG: A Beginner's Guide

    Could Someone Please Explain Exactly What String Theory and LQG Are Trying To Do? I have recently had the opportunity to ask this question to a couple prominent physicists, and they could not answer it. What is the purpsoe of these theories? What do they explain that is not explained by...
  8. marcus

    Who are typical young LQG people?

    Always tricky to try to point to typical anything. Interesting discussion over at Not-Even-Wrong blogsite http://www.math.columbia.edu/~woit/blog/archives/000204.html basically the issue is should young LQG people get more openings and support in the US. Thomas Larsson says no because (if I...
  9. marcus

    Loops 05, this year's big LQG conference

    http://loops05.aei.mpg.de/index_files/Home.html October 10-14 at Potsdam, Albert Einstein Institute The aim of this conference is to summarise the status and open problems of the various approaches to quantum gravity and to present new ideas and research directions. "The topics of this...
  10. wolram

    LQG, SF: Kicking Tyres, Adding Sawdust, and More

    Is this all that LQG, SF is, kicking tyres and adding saw dust to differentials, putting some pluss gas in your engine, to keep it running, how about giving the buyer some grantee.
  11. marcus

    LOST theorem found (important result for LQG)

    http://arxiv.org/abs/gr-qc/0504147 this has been promised for a couple of years now. here at PF we studied the papers leading up to it there was one paper we discussed here by Lewandowski and Okolow (LO) and several by Sahlmann and Thiemann (ST) or by Hanno Sahlmann solo. The four of...
  12. wolram

    Can Spin Foam Model of LQG Survive High-Energy Particles?

    It may be a simplistic question, but i wondered if the spin foam model of LQG could survive a particle of 10-20 Mev ripping through its matrics.
  13. marcus

    Will LQG explain the constants?

    the values of some of the fundamental numerical constants occurring in the standard models of matter and cosmology are considered to be favorable to life and people wonder why they are what they are for example the finestructure constant alpha, why is it around 1/137? for example the...
  14. wolram

    How Does Particle Scattering Work in Loop Quantum Gravity?

    http://arxiv.org/PS_cache/gr-qc/pdf/0502/0502036.pdf Particle scattering in loop quantum gravity Leonardo Modesto and Carlo Rovelli Centre de Physique Th´eorique de Luminy, Universit´e de la M´editerran´ee, F-13288 Marseille, EU (February 9, 2005) We devise a technique for defining and...
  15. marcus

    Small black holes ruled out by LQG?

    http://arxiv.org/abs/gr-qc/0503041 A black hole mass threshold from non-singular quantum gravitational collapse Martin Bojowald, Rituparno Goswami, Roy Maartens, Parampreet Singh 4 pages, 3 figures "Quantum gravity is expected to remove the classical singularity that arises as the...
  16. marcus

    How Does Loop Quantum Gravity Approach Particle Scattering?

    new today http://arxiv.org/abs/gr-qc/0502036 Particle scattering in loop quantum gravity Leonardo Modesto, Carlo Rovelli 4 pages "We devise a technique for defining and computing n-point functions in the context of a background-independent gravitational quantum field theory. We...
  17. wolram

    Gravitating Matter in LQG & String: How Critical is the Density?

    I think this is the right place to ask, how much "gravitating", matter is needed, in LQG and String, for our universe to be as it is. and how critical is this "density".
  18. M

    Exploring the Speed of Light with LQG Theory

    I think the solution to this question of why the speed of light is measured the same by all inertial observers can be answered by background independent theories such as LQG.
  19. marcus

    BF theory is basic to LQG so we should learn about it

    Broda is an important figure in the history of BF theory and Broda has just written an encyclopedia entry on BF which he posted today BF system—encyclopedic entry B. Broda http://arxiv.org/hep-th/0502045 I don't know if this is good or not but it is short and I am going on Broda's...
  20. S

    Topological Unification of M-theory and LQG?

    I don't know if this paper was commented on here while I was away at Christmas time, but I was just pointed to it by a paper on today's arxiv and I think it desrves notice. http://arxiv.org/abs/hep-th/0411073 Robert Dijkgraaf, Sergei Gukov, Andrew Neitzke, and Cumrun Vafa; Toplogical...
  21. J

    Rovelli in effect concedes that lqg is wrong, but still worthwhile

    Let me begin by saying that I won't be the first to post inappropriate responses in this second attempt to treat the above subject. I previously posted the following: In the forward to rovelli's new book "Quantum Gravity", james bjorken states quite plainly that the effective field theory...
  22. marcus

    Progress on LQG dynamics (the Master Constraint program)

    Five new papers by Thomas Thiemann and Bianca Dittrich http://arxiv.org/abs/gr-qc/0411138 Testing the Master Constraint Programme for Loop Quantum Gravity I. General Framework 42 pages "Recently the Master Constraint Programme for Loop Quantum Gravity (LQG) was proposed as a...
  23. T

    What book on String theory or LQG is recommended for pleasure reading?

    What book should I read for pleasure... that's not too large hopefully about either String theory or LQG. I have already read the Elegant Universe. I have to read a book for class.
  24. Y

    New universe predictions by GR and LQG

    The question is whether I am naive to suppose that either GR or LQG predicts new universes. I have also posted essentialy the same question (and post) in the Steller Astrophysics forum. Martin Bojowald has removed the singularities from GR using LQG. See...
  25. marcus

    Robbert Dijkgraaf et al: 4D 2-Form Gravity & Topological M-Theory

    http://lanl.arxiv.org/abs/hep-th/0411073 Robbert Dijkgraaf, Sergei Gukov, Andrew Neitzke, Cumrun Vafa See page 11 section 3.3 "4D 2-Form Gravity" The authors are well-known. Dijkgraaf is in Amsterdam and the others are at Harvard. "4D 2-form gravity" serves as a general pointer in...
  26. R

    Can LQG Explain the EPR Paradox and Instantaneous Action at a Distance?

    In LQG the minimum time is 10^-43 seconds. So how can there be instantaneous action at a distance in LQG between entangled photon pairs? Also, a particle traveling through quantized space would jump from one position to the next and miss some space in between.The standard quantum mechanical...
  27. M

    Paola Zizzi's "Computational LQG" | Modeling Black Holes & Hawking Radiation

    Paola Zizzi is a researcher that is trying to formulate a model of the universe like a quantum computer. She has published several papers about this, for example I remember one where she proposes the possibility of the universe being the "Ultimate Internet". Now she wants to apply these ideas...
  28. marlon

    Unifying Quantum Mechanics and General Relativity: A Debate on Strings vs LQG

    Strings or LQG and why? Hi, I am currently studying LQG and i would like to have an idea on how opinions are devided between String Theory and LQG. I would like to use the outcome of this poll as a reference to the introductory text i am writing on LQG. View the Loop Quantum Gravity-thread...
  29. marcus

    Energy defined in LQG but not in GR?

    selfAdjoint has given a link to a really enlightening post by Steve Carlip Here is the Carlip post https://www.physicsforums.com/showthread.php?p=227804&posted=1#post227804 Carlip is tops. A major reliable authority in General Relativity and Quantum Gravity. Good idea to listen to what he...
  30. marcus

    John Baez: LQG Talk Online: Quantum Geometry, Spin Foams & Black Holes

    A week ago in Dublin John Baez gave one of the plenary talks the title was: Loop Quantum Gravity, Quantum Geometry and Spin Foams this talk is now available online (PS format) from Baez website http://math.ucr.edu/home/baez/lectures.html#lqg click on where it says: "You can see the...
  31. marcus

    LQG predicts inflation and solves horizon problem on its own

    Papers by a number of authors have shown that Loop Quantum Cosmology removes the big bang singularity. Loop Quantum Cosmology development leads that of the full LQG theory because in cosmology one is essentially quantizing the prevailing (Friedman) cosmological model, which is a deal simpler...
  32. J

    The truth about lqg and background-independence

    In the paper Separable Hilbert space in Loop Quantum Gravity carlo rovelli explains why it's not yet known whether lqg is background-independent and discrete. The problem is that isotopic graphs constructed in lqg from spin-networks aren’t in general diffeomorphic, so the isotopy-equivalence...
  33. P

    Compare and Contrast LQG and ST

    Hey everybody. I'm doing an essay on this very subject, the comparisons and contrast between LQG and ST. I've heard things, such as: ST seems to define particles and forces, where LQG seems to discribe strings themselves and They both descibe a fundimental element of nature, but it's I don't...
  34. T

    Branes strings lqg toe and other fancy shortcuts

    Alright I swear that I read in scientific american that Loop Quantum Gravity is trying to put fouth a new toe to compete with string theory. However in discussion with Marcus he told me that they are not trying to have any sort of theory that would lead to toe. Part 2 I was reading in Pop...
  35. M

    Exploring LQG: A Student's Questions and Intuitions

    I am a student just beginning a study of LQG and I would appreciate some comment on a few questions and intuitions that I have as I enter the subject. My background is more in mathematics than in physics, and my perspective on space has been guided more by topology than by the concerns of...
  36. M

    Exploring the Physics of Black Holes in LQG

    This is a thread attempting to comprehend the physics behind the theory in the description of Black holes in LQG. There has been very much debate about the minimum value that a puncture can have in the horizon of a BH. The fact is, if a puncture disappears from the horizon, then the horizon...
  37. marcus

    Josh Willis replies to comment on LQG and the diffeomorphism group

    There has been a lot of internet discussion of a paper by Ashtekar, Fairhurst, and Willis called "Quantum gravity, shadow states, and quantum mechanics" gr-qc/0207106, and one of the authors, Josh Willis, replied on SPR today (in the thread "LQG and diffeomorphism group cocycles") Here is a...
  38. marcus

    Your pick of the latest LQG papers

    These are mostly from 2004 though a couple are from late last year. 1. Velhinho "On the structure of the space of generalized connections" http://arxiv.org/math-ph/0402060 2. Noui and Perez "Three dimensional loop quantum gravity: physical scalar product and spin foam models"...
  39. marcus

    What is the Category Theory formulation of LQG?

    Alejandro recently conducted a poll on Category Theory and the response was remarkably positive out of 7 respondents to the question "Do you know what a Category is?" there were 6 who said they could quote the definition from memory. the poll was in the "Isham New Quantization" thread...
  40. marcus

    Matter-antimatter asymmetry generated by LQG

    Meteor just posted a link in the "surrogate sticky" LQG referemce library to an article by Parampreet Singh. https://www.physicsforums.com/showthread.php?s=&postid=142798#post142798 A propos of Singh, he has had several interesting articles recently relating LQG and the big bang---using Loop...
  41. marcus

    Amazing bid by Thiemann to absorb string theory into LQG

    this just out http://arxiv.org/hep-th/0401172 quoting from the abstracts: The LQG -- String: Loop Quantum Gravity Quantization of String Theory I. Flat Target Space Authors: Thomas Thiemann Comments: 46 p. "We combine I. background independent Loop Quantum Gravity (LQG)...
  42. Tsu

    Is there a support group for spouses of physicists?

    I think, pretty much - never mind. I tried to watch Integral's link to the PBS video, but I need to use Ivan's computer with the high-speed connection and that just isn't going to happen any time soon. I have so many questions, even I can't get them sorted out enough to make sensible posts. I...
  43. M

    Hilbert Spaces in LQG: Is Physical Hilbert Space Infinite?

    Well, you all know that LQG has different kinds of Hilbert spaces (4 in the sake of truth). You start with the kinematical Hilbert space that is the vector space of all possible quantum states of spacetime. However, all these spacetimes are not physically real, not all of them make sense. Then...
  44. S

    100% Efficient machines through LQG?

    I was sitting in my car today, before class, pondering the meaning of the universe. When I thought,"Hey, if there is a smallest unit of matter, then there should also be a smallest unit of energy." Well, then I thought, "If that's true, then if the smallest unit of energy were to act upon the...
  45. M

    LQG & SUSY Particles: Are They Connected?

    I don't know if this has been covered on another thread (haven't been back to this particular forum for some time), but I was wondering (this wondering is, of course, due to my inexcusable ignorance of loop quantum gravity): Are supersymmetric partner particles any part of the LQG paradigm? I...
  46. M

    Good elementary description of LQG

    January 2004 issue of Scientific American contains a good elementary description of LQG. One point he makes in favor of LQG in contrast to string theory is that LQG does not require a background of contiuous space-time, while string theory does. Comments?
  47. D

    Branes and LQG: A Simplified Explanation

    I'm a very ignorant person. Could someone please explain to me what branes and LQG are? I know what a string is (or at least i think i do). I am a firm believer of K.I.S.S. so try to keep it simple for me because I'm just in 11th grade.
  48. marcus

    How area in LQG transforms under Lorentz boosts

    It is an interesting issue. Right at the end of the seminal paper of Livine (Projected Spin Networks for Lorentz connection: Linking Spin Foams and Loop Gravity) that selfAdjoint recently referred to as "Projected..." at the end of the Conclusions and Outlooks section, he says: "Finally...
  49. U

    LQG, strings and the IKKT matrix model

    It is an old observation that both LQG and string theory are fundamentally built from 1-dimensional objects. This is no coincidence. In general, every gauge theory can be formulated in terms of Wilson loops and these can often be described by "a" theory of strings. This was discussed in detail...
  50. E

    Why is LQG a dead end but not m-theory?

    hi, I went to a lecture last january where it was mentioned that physicists don't work much on LQG and why it's such a dead end but m- theory isn't. Could someone explain this? Also, can someone give me references to explain why the problems of LQG are so serious and so why the above is...
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