Quantum gravity Definition and 482 Threads

So, a couple weeks ago I read this article. I came here, expecting that someone would probably talk about it (I've been viewing posts here for a while, but became a member only recently). No one, that I could find, has actually talked about it, so I though it would be a good first post for me...

Let's suppose gravitons exist, and you have a machine that is 100% effective at detecting them. If you were in a room with no windows, and there is an apparent gravitational field, then would using this machine let you tell if you were in a gravitational field or accelerating?

I watched a seminar in particle physics and they mentioned that it was difficult to reconcile general relativity and Quantum field theory, I was just curious as to why it was so difficult considering quantum field theory is already reconciled with special relativity and gauge symmetry. what...

confused about quantum gravity theory? I know that quantum gravity is used to describe the effects of the gravitational interaction under differentg circumstandes, But can anyone please explain,under what circumstances is the theory appropriate, also some examples of the phenomena that are...

In the LQG theory does the universe have to be closed, or can space be infinite in size? What I mean is, is the LQG theory similar to the quasi steady state theory in which the universe does collapse, and then bounces back, but is still infinite in size.

Interesting that Steven Weinberg should cite Asymptotic Safety work by Martin Reuter and Frank Saueressig. And another UV-safety article by Roberto Percacci, that appears in Oriti's new book Approaches to Quantum Gravity: Towards a New Understanding of Space, Time, and Matter. Here's a bit...

If quantum gravity exists, then gravitons are responsible; however, it seems to me as if a body of matter would need to be consuming energy/mass (as the sun does) to create gravitons, because of the Conservation Theory. Have I overlooked something? Almost certainly, but I cannot find it. Any...

Rovelli has given his team and himself just seven months to advance LQG to a new stage. Why do I call this "throwing the eagle"? Because a Roman general would on occasion hurl his legion's eagle standard into the opposing army's midst, confident his side could rout their foes the recover it...

Petr Horava attempts to start at this paper a small quantum gravity theory, like Loop Quantum Gravity, except that he, according to his words: http://arxiv.org/abs/0901.3775v1 "In analogy with Yang-Mills, we are motivated to look for a “small” theory of quantum gravity in 3+1 dimensions...

hi everyone i was wondering if anybody had any suggestions for particularly good places to do a phd in quantum gravity? in the uk or around europe in particular? most theoretical physics positions seem to be focused on high energy theory or strings. i am particularly interested in loop...

A finding that may have interest. http://arxiv.org/PS_cache/arxiv/pdf/0901/0901.0510v1.pdf Quote. Some new challenges for an experiment and observation, which are consequences of the model of low-energy quantum gravity by the author, are considered here. In particular, the property of...

spacetime states in Rovelli's book "Quantum Gravity" happy new year everybody, I am reading "quantum gravity" of Rovelli. He introduces functions f(x,t) defined on compact of space time that are zero outside. They correspond to the time and space needed to a measurement. page 168: they...

As I am fairly new here (been a lurker for a long while), I was not quite sure where to post this topic as it has Relativistic and Quantum Mechanical basis. Apologies if this is the incorrect place. It's not a homework question in any sense, but I'm doing a project for my Advanced Science...

I am trying to understand the meaning of nonlocality and its implications in physics. My concept of locality is not very precise but when I try to read papers myself, I come across terms like "nonlocality", "not-too-local operator", "ultralocal operator" etc. Can anybody help me understand these...

I came across an interesting discussion about LQG's philosophy (through Googling "Cauchy surface" and "loop quantum gravity"): Approaching the Planck Scale From a Relativistic Point of View: A Philosophical Appraisal of Loop Quantum Gravity Christian Wüthrich...

I have just read the book Three Roads to Quantum Grabity... but my mind has gone blank, the three methods are string theory (M-Theory), loop quantum gravity and one other. I can't remember the last :(:( Any help would be great.,..

http://arxiv.org/PS_cache/arxiv/pdf/0811/0811.2161v1.pdf He finds that only twists and knots are conserved in ribbon networks, that is, generalized spin networks. He finds that there is an infinite number of redundant states. He suggests in the end that one might try this...

Hello everyone. Im studying theoretical physics in sweden and I would like to go abroad for my last year to take some courses and write my master thesis within the field of quantum gravity. Do you have any suggestions on where I should try to go? As there is no research within that...

There's an article about Loop Quantum Gravity in this month's Scientific American, and I have a quick question. They assume space itself is made out of "atoms" with definite size (Planck's length if I'm not mistaken). So how exactly does it work with the expansion of the Universe? Do these...

arXiv:0809.4218 [ps, pdf, other] Title: Nonquantum Gravity Authors: Stephen Boughn Comments: submitted to Foundations of Physics Subjects: General Relativity and Quantum Cosmology (gr-qc) One of the great challenges for 21st century physics is to quantize gravity and generate a theory...

Re the article by Bojowald in the October issue of Scientific American about Loop Quantum Gravity. He states that one of the consequences of the theory is that the speed of light is a function of wavelength. Any experimental evidence, or even hint of evidence, that anyone knows of?

Some people talk as if they think the social statistics of science don't matter, but it's hard for me to believe they really think that. Stats on public perceptions and interest in science, and also stats on research publication, citations, faculty hiring etc., must sometimes be important to...

Frank Wilczek has presented a way of looking at the world which is curiously consonant with Lattice Quantum Gravity approaches a la Renate Loll, John Barrett, Lee Smolin, Carlo Rovelli and others. The world as lattice---what Wilczek calls the Grid. It is oddly reminiscent of spin networks...

It is always said, that string theory makes no testable predictions. At least there are some qualitative predictions like supersymmetry and extra dimensions. One prediction of loop quantum gravity is a violation of Lorentz invariance. Are there other predictions of loop quantum gravity? I...

I have made a resource page for loop quantum gravity . I have made a list of books, papers and online tutorials. Check it out. It should be helpful http://mushfiq.net/loop-quantum-gravity/ ....... :wink:MUSHFIQ

This years's grants have been announced. A total of 2.7 million was awarded. FQXi is set up to support investigation of foundational questions. Here is a sampling of the awards, chosen with a hefty componenent of randomness. Gives an idea of some of the kinds of things FQXi supports.Stephon...

Hi: Can anybody tell me what is Quantum gravity?, I tought General relativity was the theory that described gravity, could you explain me more..? Thanks

Major paper by Fairbairn--a way to put matter into 4D quantum gravity I expect this paper will "raise the dead" in the sense of evoking a comment from John Baez :-). It develops some lines of research he was working on three years ago. It references work by Derek Wise, a Baez PhD----also...

Can you tell me about good Math and physics departments has good faculties of mathematical physics or quantum gravity ? I will contact prof about phd information.

Tipler had proposed that the correct QM Lagrangian leading to gravity should be S = \int d^4x\, \sqrt{-g}(\Lambda + \frac{1}{8\pi G}R + c^2_1R^2 +c^3_1R^3 \ldots + c^2_2R_{\mu\nu}R^{\mu\nu} + \ldots + c^3_1R_{\mu\nu;\alpha}R^{\mu\nu;\alpha} + \ldots) however is he right he proposed...

the publication date for the book is given as May 2009 http://www.cambridge.org/catalogue/catalogue.asp?isbn=9780521860451 the list of contributors is C. Rovelli, G ‘t Hooft, R. Sorkin, J. Stachel, N. Savvidou, L. Crane, O. Dreyer, R. Percacci, F. Markopoulou, G. Horowitz, J. Polchinski, T...

The May 20 issue of the journal Physical Review Letters will reveal the results of a National Science Foundation study by Penn State Eberly College of Science grad student, Victo Raveras and Madhavan Varadarajan, a professor at the Raman Research Institute in India that challenge the idea that...

http://arxiv.org/abs/0805.1265 C, P, and T of Braid Excitations in Quantum Gravity Song He, Yidun Wan 28 pages, 5 figures (Submitted on 9 May 2008) "We study the discrete transformations of four-valent braid excitations of framed spin networks embedded in a topological three-manifold. We show...

I understand that it is a quantum take on space-time. I just don't actually understand IT. Can anyone help? Any good online lectures or explanations? Thanks.

using the Schwinger Dyson equations that gives us a differential expression for the functional Z[J] so Z[0] is just the path integral over 4-dimensional spaces .then for Einstein equation (no matter) they read (system of 10 functional equations) R _{a,b}( -i \frac{ \delta Z (J)}{\delta J})+...

Paper: Rovelli's "What is observable in classical and quantum gravity?" I'm reading Rovelli's QG book and found a reference to his own article: "What is observable in classical and quantum gravity?" I fail to find it on arxiv - anyone know if this is available or do you have to buy it from...

Hello everyone, I'm currently occupying myself with Loop Quantum Gravity and wonder about some question. In LQG, space is built up from a spin network. However, how is movement of material particles realized in this network? One could tend to the idea, particles are simply hopping from one...

"Three Roads to Quantum Gravity" So some time back, before "The Trouble with Physics", Lee Smolin wrote a book called "Three Roads to Quantum Gravity". Is "Three Roads" any good? And does it go into any detail on how LQG works? I find LQG a little while back, so I read Smolin's "The Trouble...

I am an undergraduate student of phyiscs major. If i want to work on Quantum Gravity then do i need to continue MSc Physics? Or Others like High energy phyiscs or particle physics or Astro? My aim is to be a teacher at a top University and Research on Quantum Gravity & String theory. Can you...

Simone Speziale is teaching an introductory course on LQG, and Perimeter has the videos online. Lecture #1, 5 February: http://pirsa.org/08020008/ Lecture #2, 7 February: http://pirsa.org/08020012/ ===================== Lee Smolin is giving a more advanced QG course and there are about eight...

Ok, I am by no means an expert in this field I've just read a few books about it (poplular science books) and I'm going to begin a physics major next year. I've got a few questions though: 1. There are many different theories for quantum gravity, what makes physicists think one might be more...

This could be good http://pirsa.org/08010033 ==quote== PIRSA:08010033 Title: Lecture 1 ( Windows Media , Macromedia Flash , MP3 Audio , PDF) Speaker(s): Lee Smolin Abstract: The Problem of Time in Quantum Gravity and Cosmology Date: 09/01/2008 - 7:00 pm Location: 405 URL...

J. Scott Carter from The University of Southern Alabama is a great new QG-TQFT blues performer See and listen here: http://scienceblogs.com/pontiff/2007/12/quantum_gravity_topological_qu.php Thanks to Dave Bacon! Here is the song text: The Quantum Gravity Topological Quantum Field Theory Blues...

At the risk of annoying some people but hopefully also interesting others I would like to mention my new book on the periodic table, which has just been named as one of 7 "outstdanding academic books of the year 2007" in the category for chemistry But the book is as much about physics as it...

Coin raised a cluster of interesting issues for discussion, which need a separate thread. (If we addressed them in the QG links thread it would interfere with its bibliography role.) So I'm copying his post here:

de Sitter Relativity: a New Road to Quantum Gravity--Aldrovandi and Pereira take risk Aldrovandi and Pereira are at the ITP at Sao Paolo State University. They have taken a risky step and proposed to modify General Relativity so that it should be locally de Sitter instead of locally Lorentzian...

I am reading Barton Zwiebach's 'A First Course in String Theory'. I expect I will finish up in about a month. Not that I understand it that well. I will put it aside and perhaps read it again in a couple of years. I took a peek at the book 'String Theory in a Nutshell' by Elias Kiritsis and...

Bee Hossenfelder (who used to post here as "Hossi") has organized a 5-day workshop on XQG. A brief summary with links: http://www.perimeterinstitute.ca/esqg07/ The schedule of talks (5 Nov - 9 Nov) is here...

http://arxiv.org/abs/0710.1548 Propagation and interaction of chiral states in quantum gravity Lee Smolin, Yidun Wan 34 pages, 30 figures (Submitted on 5 Oct 2007) "We study the stability, propagation and interactions of braid states in models of quantum gravity in which the states are...

Hi, does anyone know whether any of the current approaches to Quantum Gravity shed any light on the measurement problem in quantum mechanics? Moreover have there been any attempts to consider the implications of the measurement problem from within either the string theory approach or the quantum...