Lqg Definition and 259 Threads

I've read a lot of arguments in support of LQG over string theory, mainly focusing on ST's lack of background independence. I'm also told that there are some pretty good arguments against LQG. What are some of these arguments? Have they been summarized somewhere?

How i can see the right lorentz invariance in lqg?

Here is some background on Leonardo Modesto's new paper: It is in this context that Leonardo Modesto has shown that LQG also has this curious fractal-like microstructure down near Planck scale. That the dimensionality declines from the usual 4D at large scale down to 2D at the microscopic...

So this is something that's been bothering me for awhile and I seem to be getting no closer to understanding it on my own. I want to quote two things here; one, an Aaron Bergman post about String Theory at Uncertain Principles; two, Rovelli's LQG textbook, "Quantum Gravity"...

I was reading this: https://www.physicsforums.com/showthread.php?t=181830 I was wondering if there is any up to day info about the speed of gamma ray burst that could confirm or debunk these claims. Or are LQG and String Theory in troubles?

This may have been posted somewhere else but, I would like to know. How do LQG theorists reconcile the fact that the universe is expanding at an accelerating rate, and the LQG prediction of the big bounce. Also I have heard that they say the universe is still expanding because of inertia from...

Here is the news: http://www.sciencedaily.com/releases/2008/05/080515092615.htm"

I heard there were currently some tests trying to prove LQG. One had to do with the radiation from distant cosmic explosions called gamma-ray bursts they might provide a way to test whether the theory of loop quantum gravity is correct or not. Does anyone know any up to date info about these...

I've read in a couple books (e.g. in Lee Smolin's three roads to quantum gravity) about the possible union of LQG and string theory. In other words, that string theory and LQG can possibly be reformulated into a single TOE. I've been unable to find anything more on this idea through google and...

Do you think physics departments should give equal time to LQG and string theory? Currently, the top physics research departments at the best Universities, from Princeton to Harvard to Stanford to Rutgers all employ string theorists in various capacities. When I say equal time, I am...

Hello all. I am a layperson that is very interested in science. I am particularly intrigued with what results the LHC will produce and how they affect the various existing theories. I was thinking that a central thread that links to and discusses various predictions on what the LHC will find...

We have had some discussion of this in earlier threads. Alain Connes et al have been able to derive the standard menu of particles from a certain spectral triple, in Noncommutative Geometry (NCG). On the other hand, Loop Quantum Gravity (LQG) as developed by Rovelli, Smolin and many others is...

So I'm trying to read through Baez&Muniain's "Gauge Fields, Knots and Gravity". One thing I was particularly hoping to get out of this was a specific understanding of what a "holonomy group" is. In the relevant section (p. 231-233 in the version I'm looking at), Baez& describe a holonomy by...

Edward Witten on LQG "for lambda > 0, QG does not exist in any dimension" arxiv.org/abs/0706.3359 - page 6 "for lambda > 0, QG does not exist in any dimension" ...the reason... "cannot provide precise observables" As I understand Edward Witten, deSitter space is not stable but metastable, and...

Hello, I'm a 4th year physics undergrad, so I'm about to decide what to do in my undergrad thesis. I'll do pure theoretical work, but I'd like to avoid copy-paste stuff and come up wityh something quite original, however I'm not sure what topic are available, maybe someone here will help...

Kevin Vandersloot is an Ashtekar PhD now at Portsmouth UK with a EU Curie fellowship. He and another EU postdoc, C. Boehmer, have been studying the interior of the LQG black hole. As we know, the big bang can be modeled using LQG and it gives no singularity (no place where the model blows up...

I am interested in loop quantum gravity but am just a college freshman so have none of the mathematical background to learn about it. Are there any "layman's" books out there on LQG, in the same vein of Universe in a Nutshell, The Elegant Universe, etc?

Consistency between string/M-theory and LQG Is there a reason that LQG and other QG theories cannot be consistent with string/M-theories? My naive understanding is that the former theories approach the problems of QG and unification from the perspective of quantising GR, while the latter start...

Three related papers came out today. One posted in astro-ph, and the other two in gr-qc. http://arxiv.org/abs/0710.5734 Dirac Fields in Loop Quantum Gravity and Big Bang Nucleosynthesis Martin Bojowald, Rupam Das, Robert J. Scherrer 15 pages, 2 figures (Submitted on 30 Oct 2007) "Big Bang...

A detailed introduction of the new LQG spinfoam model---flipped version of the Barrett-Crane vertex amplitude---appeared in August*. Quite a lot of follow-up work has been posted, including three papers that appeared yesterday. Recently posted extensions include numerical work by Rovelli et al...

Could someone explain to me why we use a gauge-invariant and diffeomorphism-invariant measure on the quantum configuration space? Is it because we want the inner product to be invariant under gauge transformations. What is a gauge-invariant measure anyway? see http://arxiv.org/abs/hep-th/9305045

One difference between GR and LQG is that LQG is chiral, whereas GR is not. In order to break the electroweak symmetry, a higgs field needs to be introduced by hand. Einstein's understanding of inertia implies a strong EP as gravitational mass and inertia are identical, while a higgs...

Energy dependent speed of gammaray photons may have been observed, by the MAGIC collaboration at its Canary Islands observatory. Lee Smolin has been making the point for several years now that if an energy dependent speed of gammarays is ever observed it will be an enormous stimulus to LQG...

My impression was that only misinformed people argue that LQG discreteness is in conflict with Lorentz invariance. This was resolved a long time ago, i thought. Does anyone disagree? Want to talk about it? Explain something to me that I am missing? http://arxiv.org/abs/gr-qc/0205108 Reconcile...

This is very exciting. I have wondered about this merely as a spectator, because e.g. AFAIK the spinfoam formalism has not confirmed that about the geometric operators. What they say is that discrete spectrum HAS NOT BEEN PROVEN yet for the geometric operators, so it could go either way. Also I...

Jacobson renovates LQG with a roto-Reuter I think the word for it is RENOVATION A roto-rooterTM is a tool for clearing clogged drains. I've been watching Martin Reuter papers since 2004, especially since a possible link with Loll's CDT appeared in 2005, but with reserve. I found Reuter's...

Hi, here in Brazil doesn´t seem to have a researcher specialized in LQG. I think I will have to do my doctorate research in another field and just afterwards study LQG on my own. Could anybody help me to make a list of the disciplines I should study to comprehend and do research in LQG ...

That is the question, if you assume the space-time is discrete then it will be an smallest amount of volume line surface and so on, but how do you know how big this amount is ? for example in usual QM we have that energy is quantizied so the avaliable energy levels are eigenvalues of the...

LQG in the mainstream press "Glimpse of Time Before Big Bang Possible" string theory gets all the headlines, and perhaps, when LHC starts collecting data, justifiably so, but here's one for LQG http://news.yahoo.com/s/space/20070701/sc_space/glimpseoftimebeforebigbangpossible "To see...

Hi all, I asked about this on the academic and career guidance forum but didn't get any useful replies. Which of these maths subjects (all at fourth year level) would you recommend for someone interested in the subjects listed in the title? What would you say is missing from this list...

In order to assist navigation through Ashtekar's recent advances in LQG (see his paper, "href="[PLAIN]http://arxiv.org/abs/0705.2222"[/URL] with links to papers on each research line mentioned by him.

this just out http://arxiv.org/abs/0705.2388 The loop-quantum-gravity vertex-amplitude Jonathan Engle, Roberto Pereira, Carlo Rovelli 6 pages "Spinfoam theories are hoped to provide the dynamics of non-perturbative loop quantum gravity. But a number of their features remain elusive. The best...

One question I have for LQG's derivation of BH entropy is this: would any arbitrarily enclosed sphere in space, whether it's that of the surface of planet earth, or the moon, or the sun, not to mention BH's also have the same BH entropy since as I understand the calculation, it is merely...

LQC is a subset, a symmetry reduced minisuperspace of LQG, which appears to have a Hamiltonian with a good semiclassical limit that reproduces GR. First, Randano papers addresses Witten's earlier paper on Kodama's state being nonrenormalizable. Now, thanks to Marcus, it appears Eyo Eyo Ita...

Specifically what I`m referring to is the final discussion summing up the program in which the weakness of lqg was characterized explicitly as "the whole theory". Was this a constructive way to end the program? Perhaps some of you would rather ignore this.

I'm reading Carlo Rovelli's book "Quantum Gravity". In the second chapter he writes down the Plebanski action by performing a decomposition of the complex Lorentz algebra into self-dual and anti-self dual parts, i.e. so(3, 1, C)=so(3, C)\oplus so(3, C). I sort of appreciate this fact and what it...

My documentary--how many $$$ have been invested in ST & LQG? As part of my documentary I am looking at how many $$$ have been invested in ST & LQG. Does anyone have any ballpark figures? How much total has been invested in ST? How much total has been invested in LQG? Where can I find this...

MNy questions about the QG are vast..i have some math knowledge about GR and only a bit about Regge calculus and Canonical Quantization... 1) if we have the Hamiltonian constraint \bold H =0 then you must have energies (eigenvalues) are all zero¡¡¡ then how does LQG overcome this apparent...

Hello there, I am filming a documentary on cutting-edge physics, and I was wondering what constitutes a "professionally researched theory." What is it about ST and LQG that make them "professionally researched?" Are there other non-profesionally researched theories out there? Thanks...

i think i asked it before already, but if i recall correctly no one has given me a specific detailed answer. what i want to know is what maths does LQG theory use? i mean do you need to know topology,manifolds, what are the main subjects that needed to be learned? btw, as far as i know (im...

it's my understanding that Yershov's Preon Theory can predict particle masses a priori and his paper also describes second and third generation particles, whereas Bilson-Thompson only the first generation. http://arxiv.org/abs/physics/0301034 http://arxiv.org/abs/hep-ph/0207132 Is it...

here's the link http://www.newscientist.com/channel/fundamentals/mg19125675.100-atomic-jitters-hint-at-quantum-spume.htmlin a nut shell 1- pollen in water jiggles - other small particles also jitter in solution. 2- einstein explained this as brownian motion & atoms 3- Einstein did not directly...

http://www.newscientist.com/channel/fundamentals/mg19125645.800 sounds like string theory, all particles from vibrations. how successful has this theory been in comparison to string theory, on particle physics? "physical particles may seem very different from the space-time they inhabit, but...

This is something I thought I should do if nobody else would by the time I had learned enough to do it: gr-qc/0607068: Title: Dirac Quantization of Parametrized Field Theory Authors: Madhavan Varadarajan Comments: 33 pages Parametrized field theory (PFT) is free field...

Today someone has asked me about the evidences about the variations of fundamental constants (mainly alpha) As it is known that variation attemps versus the equivalence principle. So i wonder, if that variation would be irrefutably confirmed how would it affect LQG? I mean, LQG...

So Loop Quantum Gravity predicts a "spinfoam" which goes from one quantum "spin network" state to another in the fashion of a path integral. And each spin network describes the properties of spacetime and is the eigenstate of the QG Hamiltonion. OK. But by what process is the spin network...

Recently, I read a beautiful paper in which it is proven that ANY surface in LQG contains degeneracy, no matter it being a boundary horizon or whatever else. (http://uk.arxiv.org/abs/gr-qc/0603121) This degeneracy is such that the surface degeneracy is A/4. This is a critial discovery in LQG and...

Ok, the problem is that I don't have enough time or money, so I want to be somewhat careful in what books I buy. I am looking to purchase a few books on modern physics that discuss new ideas in physics, and I've found many books with good reviews that cover the topics that I'm interested in...

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...

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.