Talk:Loop quantum gravity

message: am i wrong if i'd suggest to replace "space" by "SPACETIME" in many places, f.e.:
Loop quantum gravity (LQG) is a theory that attempts to describe the quantum properties of the universe and gravity. It is also a theory of quantum space and quantum time because, according to general relativity, the geometry of spacetime is a manifestation of gravity. LQG is an attempt to merge and adapt standard quantum mechanics and standard general relativity. The main output of the theory is a physical picture of space where SPACETIME is granular. The granularity is a direct consequence of the quantization. It has the same nature as the granularity of the photons in the quantum theory of electromagnetism or the discrete levels of the energy of the atoms. Here, it is SPACETIME itself that is discrete. In other words, there is a minimum distance resp. TIME-STEP possible to travel through it.
(=> each of the four dimensions are granular... )
... as well as i found in many articles/places "(havy) matter" as the only reason for "bending/curvation of the spacetime" ! Shouldn't it be "matter or energy" at every place as both are equivalent ?  — Preceding unsigned comment added by TheuDie (talk • contribs) 12:45, 27 December 2014 (UTC)
thread_title:  ?? question ?? 

message: Why are we citing non-peer reviewed, and seemingly unphysical (multiplication of functionals=0 is just wrong) material? Surely we should only cite journal papers, not just what gets posted to arxiv!  —Preceding unsigned comment added by 71.58.64.44 (talk) 01:35, 17 March 2008 (UTC)
replies: text: The way things are done these days arxiv, is the way allot of physics publishing is done.  Some on there don't even bother with paper journals anyway because more people will see an arxiv posting.  Another way is to put it on a scientific bloging site, or on your website then a moderated usenet group.  From there feedback and peer review is public.  By the time something is in a paper journal these days it is old news. --Hfarmer (talk) 02:27, 21 July 2008 (UTC)
thread_title:  Iyo Iyo Ita 

message: It currently appears that nothing forbids coupling anomalous 
- i.e. quantum mechanically inconsistent - chiral fermions to LQG.
:That's not true, LQG is based upon first class constraints and with anomalous chiral fermions, the first class constraints mutate into second class constraints. AnonyScientist (talk) 11:38, 23 August 2008 (UTC)
thread_title:  Chiral fermion anomalies 

message: I've removed the block of original research and synthesis posted in the section previously titled "Diffeomorphism invariance and background independence", and replaced it with what I suppose is an equivalently imperfect summary-style section, presently retitled Loop quantum gravity#General_covariance_and_background_independence. ... Kenosis (talk) 23:34, 8 January 2009 (UTC)
thread_title: Block of original research removed

message: Pra1998 added a reference to a paper about results from Fermi, stating in the article that they "seem to have severe implications for this theory." Is this noncontroversial? There's a recent paper by Amelino-Camelia and Smolin http://arxiv.org/abs/0906.3731 analyzing the results, which does not seem to say "Oh no, we need to give up on LQG." --76.167.77.165 (talk) 02:20, 18 August 2009 (UTC)
thread_title: is interpretation Fermi results controversial?

message: I am a layman who has more than passing interest in this topic. I would like to chime in with my two cents.
====The good====
This is a remarkably well-balanced article in a field in which every researcher thinks he/she has THE answer. Theory is not confused with fact. Limitations are admitted. Contrary opinions are acknowledged. All objectively presented. Kudos to the contributors. I would like to see this objectivity maintained in future editions.
====The bad====
The article is almost completely impenetrable. It's not the concepts; it's the vocabulary. My favorite sentence is:
:"While originally developed in order to quantize vacuum general relativity in 3+1 dimensions, the formalism can accommodate arbitrary spacetime dimensionalities, fermions, an arbitrary gauge group (or even quantum group), and supersymmetry, and results in a quantization of the kinematics of the corresponding diffeomorphism-invariant gauge theory."
This is a cutting-edge subject--some level of knowledge must be assumed. The article cannot go all the way back to explaining photons, electron, protons, and neutrons--that would require an entire encyclopedia. However a better balance needs to be achieved between precision and comprehension. Some suggestions: shorter sentences; fewer "BIG" words per sentence; more analogies; more examples. I don't think a professional physicist is needed--just writing each sentence with conscious attention to the target audience.
====The ugly====
There is no ugly!
:::: The para you quoted can be understood by anyone with even a basic understanding of basic physics, . Dimension10 (talk) 13:53, 23 July 2013 (UTC)
thread_title: The good, the bad, and the ugly

message: There is no ugly!
:::: The para you quoted can be understood by anyone with even a basic understanding of basic physics, . Dimension10 (talk) 13:53, 23 July 2013 (UTC)
thread_title: The ugly

message: I was a bit surprised by the following in the article, "...as of now there is no experimental observation for which loop quantum gravity makes a prediction not made by the Standard Model or general relativity (a problem that plagues all current theories of quantum gravity)." Could someone provide a citation for this as i thought LQG did make a prediction which was supposed to be tested by GLAST.  —Preceding unsigned comment added by 24.222.119.180 (talk) 21:57, 15 May 2011 (UTC)
thread_title: Citation needed?

message: It was the question if a photons 'speed' could vary with its 'energy' that GLAST was supposed to look for, amongst other things. In loop quantum it seems as if this could be a effect of the theory, not invalidating Einstein, but modifying it slightly. Although, be aware of that we are discussing 'energy', as defined from interactions, not 'rest mass'. So those of you wanting to give a photon a 'mass' have to search elsewhere.
.. Can't seem to find anything recent though? http://www.slac.stanford.edu/exp/glast/ground/GlastScience/year2007/JeffScargle/JeffScargle_jan11_07.pdf discuss it. And here is GLAST http://fermi.gsfc.nasa.gov/ .. The best I could find is from 2008 .. http://www.douban.com/group/topic/8577816/ but? I'm surprised that I can't find anything better on it. It should be resolved by now, one way or another..
Ahh a.. http://backreaction.blogspot.com/2010/08/update-on-status-of-dsr.html Hmm :) But, I do like Smolin, he's what all scientists should be, open to change, keeping his cool. Theories are only as good as the experiments proving or disproving them. And Smolin is constantly at the forefront, no matter how controversial he might be deemed to be. Still, as I expect light to be a 'clock' of sorts myself, I'm happy that we haven't found it with several 'beats', not that it's impossible, though. Here is the link to the wiki http://en.wikipedia.org/wiki/Doubly_special_relativity (deformed special relativity) that seems to discuss that idea in more depth, hopefully :)
Yoron 178.30.80.59 (talk) 17:51, 25 June 2011 (UTC)
thread_title:  You are quite right, looking for it as I write. 

message: What's the central formula of this theory? I mean, there has to be something likem a Lagrange density or something similar... --91.4.236.151 (talk) 18:08, 20 July 2011 (UTC)
replies: text:  Yup, the Einstein - Hilbert - Palatini - Ashtekar (EHPA) or Einstein - Hilbert - Ashtekar (EHA) action (Source: LQG for (and by) the bewildered) .. Dimension10 (talk) 13:56, 23 July 2013 (UTC)
replies: text:  Would there be something like a (quantum) physical system, with a Hilbert space of states or whatever is appropriate for LQG, and observables and dynamics? You would be looking for the formula for dynamics of the system? --Telecomtom (talk) 01:33, 3 April 2012 (UTC)

text:  From the article on spin networks: "In loop quantum gravity (LQG), a spin network represents a "quantum state" of the gravitational field on a 3-dimensional hypersurface. The set of all possible spin networks (or, more accurately, "s-knots" - that is, equivalence classes of spin networks under diffeomorphisms) is countable; it constitutes a basis of LQG Hilbert space." Maybe someone will write the formula for the dynamics ... --Telecomtom (talk) 02:08, 3 April 2012 (UTC)
thread_title:  Formula? 

message: Some large aspects of this theory have been seriously overlooked, this article only explains the very basics of loop quantum gravity and a lot more information is needed to give the reader a sufficient understanding of this theory. I'm a physicist, and I'm new to wikipedia, but an expert is not the the only option, for example i can't really help because i specialize in string theory and occasionally  other similar fields. But the truth is that anyone, given they put in a sufficient amount of time and research can construct an understanding of anything, well enough to give a brief outline of it. A large population of the planet have vast amount of information at their disposal, everyone reading this has access to the internet, this allows us to research near enough any topic we desire, including quantum loop gravity. It may be hard to find but i can assure you, it is there. All we need is a team of people, maybe even just one person to research this topic, their understanding to begin with is irrelevant, as long as they put in enough effort to begin with and gain an interest in the desired topic. This person, or people, could then update this page with their findings, sure it would help if there was a specialist who could explain it without research, but the notification that one has been needed has been up there for 2-3 years, so we will have to do the next best thing. Someone with a respectable amount of knowledge of physics could do this brilliantly, they could grasp the concepts of this theory easily, and identify, false or misleading data. I have a 'quite' good understanding of this theory and if no one steps up and does this research I will do it myself, if i have the time. 
Dr J. Hill  — Preceding unsigned comment added by Joehill11 (talk • contribs) 20:59, 6 February 2012 (UTC)
replies: text: Well, hurry the frick up, Doc - and when you get going, leave me a note on my Talk Page so I can follow along behind you as your assistant, tweaking your grammar! :-)
Welcome to Wikipedia! We can use you! And BTW, if you know any lung cancer experts, send them to me - I NEED THE HELP!
Very best regards:
Cliff (a/k/a "Uploadvirus") (talk) 11:47, 8 February 2012 (UTC)
thread_title:  Overlooked aspects and gaining information 

message: Under "The problem of time in quantum gravity", the introduction states:
"Roughly speaking the problem of time is that there is none in general relativity. This is because in general relativity the Hamiltonian is a constraint that must vanish. However, in any canonical theory, the Hamiltonian generates time translations. Therefore we arrive at the conclusion that "nothing moves" ("there is no time") in general relativity."
This is probably a reflection of Rovelli's thinking ("Forget time", "Time does not exist"). The claim that there is no time in general relativity as such is inappropriate, however, as it is at odds with generally accepted descriptions of general relativity.  — Preceding unsigned comment added by 217.162.239.196 (talk) 22:54, 24 March 2014 (UTC)
replies: text: The Problem of Time section belongs on a separate page, and should be removed from this page.  I submitted a request for a "Problem of Time" page ( http://en.wikipedia.org/wiki/Wikipedia_talk:Articles_for_creation/Problem_of_Time ) and added a link to that proposed page as a "main article" link.  — Preceding unsigned comment added by 81.71.198.114 (talk) 12:34, 27 April 2014 (UTC)
thread_title: Time in general relativity

message: In loop quantum gravity there is a limit of ultimate compression and then the Universe bounces for it isn't allowed any greater compression, but nobody cares because dark energy is proliferating faster than dark matter which loses energy.
Loop quantum gravity predicts that there is also an upper limit to the diffusion of space, and the excessive energy fills the missing matter thus we have a new Big Bang, but not out of any singularity.  — Preceding Lee Smolin comment added by Lee Smolin (talk) 02:17, 28 April 2016 (UTC)
thread_title:  The loop quantum gravity diffusion limit 

message: There is some equation on the page which doesnt render, can someone familliar with mathml and lqg take a look and see what is wrong? MiCkE 09:41, 24 June 2016 (UTC)
thread_title:  MathML problem 

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thread_title:  External links modified 

message: I have anotated 'In 1986, Abhay Ashtekar reformulated Einstein's general relativity in a language closer to that of the rest of fundamental physics' with .  My *guess* is that: Ashtekar, Abhay (1986). "New Variables for Classical and Quantum Gravity". Physical Review Letters. 57 (18): 2244–2247 is appropriate, but someone who knows should check that. 31.52.252.245 (talk) 14:42, 5 May 2019 (UTC)
thread_title:  Another citation needed? 

message: 72 through to 79 and 80 through to 81 are all the same, how do i delete these down to a readable number? thanks :D  — Preceding unsigned comment added by Transmission Medium (talk • contribs) 12:02, 11 August 2019 (UTC)
replies: text: Im seconding this, .... I see the footnotes and I could easily delete them, but Im holding off because they look like  they were deliberately stacked there and it's possible that there's something I'm not seeing. —Soap— 23:54, 11 April 2020 (UTC)
thread_title:  Multiple redundant footnotes 

message: In a recent edit User: MosquitoBird11 wrote
"Reverting intro to an older more user friendly and concise version before wordy and off topic WP:TOPIC edits by User:Ibayn and 200.104.142.8 which made the introduction difficult to comprehend, and overly focused and in-depth string theory."
Sorry but your intro:
"Loop quantum gravity (LQG) is a theory of quantum gravity, merging quantum mechanics and general relativity, making it a possible candidate for a theory of everything. Its goal is to unify gravity in a common theoretical framework with the other three fundamental forces of nature, beginning with general relativity and adding quantum features. It competes with string theory that begins with quantum field theory and adds gravity." 
is inaccurate! Loop quantum gravity is not a theory of everything! And doesn't pretend to be. What you are describing by "Its goal is to unify gravity in a common theoretical framework with the other three fundamental forces of nature" is applicable to string theory but not to Loop Quantum Gravity, and as such you being are off topic.
And my intro:
"Loop quantum gravity (LQG) is a theory of quantum gravity, attempting to merge quantum mechanics and general relativity, (including the incorporation of the matter of the standard model into the framework). It takes seriously the key insight from general relativity that space-time is a dynamic entity, not a fixed framework. It competes with string theory that is also is a candidate for a theory of quantum gravity. However, unlike string theory, LQG is not a candidate for a theory of everything the goal of which is to explain all of particle physics, unifying gravity with the other forces at the same time. In contrast to LQG, string theory (for the most part) is a background-dependent (built on a fixed framework), which doesn’t account for the dynamic nature of space-time at the heart of relativity."
is accurate. It is not off-topic at all, what I am eluding to is the driving force (pardon the pun) behind Loop Quantum Gravity research! A very different philosophy to (most of) string theory.
Encyclopedias aren't necessarily supposed to be user-friendly but they are supposed to be accurate! User: IBayn.
:First off, please  don't use all caps because it almost seems as if you're shouting at people and we at Wikipedia are civil in our "conversations" :)  Secondly, I agree with you, but your solution does focus wayyyy too much on string theory and almost the entire second half could be cut. Third, Encyclopedias **are** supposed to be user-friendly. Otherwise, we could just list a series of sources and you could learn everything you wanted from them. If you want, we could brainstorm a better way to incorporate the issues you've brought up in a manner that doesn't ruin the tone, focus, friendliness, and reliability, of the lead.  Integral Python click here to argue with me 15:29, 4 October 2019 (UTC)
replies: text: I fixed it up a little bit to make it clearer and deemphasize string theory a little bit more, hopefully, I didn't re-add any of your original problems back.  Integral Python click here to argue with me 22:02, 8 October 2019 (UTC)

text: Also, are you aware that your signature is not your actual user page? Your signature leads to User: IBayn, but your user page is User:Ibayn and your talk page is User talk:Ibayn  Integral Python click here to argue with me 22:08, 8 October 2019 (UTC)
thread_title:  My intro altered 

message: In the section Loop_quantum_gravity#Geometric_operators,_the_need_for_intersecting_Wilson_loops_and_spin_network_states we have a math equation with a 3! in it.  I assume this is the factorial, which is 6, but why don't we just write 6?  Is there a narrow use of excalamation points in math that Im not aware of?  —Soap— 23:50, 11 April 2020 (UTC)
thread_title:  What does 3! mean? 

message: Not a single connectome of loops exists, but a Feynman set of alternative loop-connectome, with variant significance per section and as a whole (the whole is all mathematically similar or parallel universes; but nowadays we have a problem with very different mathematically nonparallelizable universes which do not belong in our own family of universes; thus don't immediately contribute probabilistically).  — Preceding unsigned comment added by 2A02:587:410B:3A70:D92B:AEE6:8B9F:491E (talk) 13:52, 27 September 2020 (UTC)
thread_title:  Make paragraph: Probabilistic loop quantum gravity 

message: Note the statement "ESA's INTEGRAL satellite measured polarization of photons of different wavelengths... ...13 orders of magnitude below the Planck scale." at the very end.
This statement is quite misleading, and I was questioning it when I first read it, since we cannot physically measure below planck length. I did further digging and apparently this is a quite wrong interpretation/statement and has been refuted on Physics StackExchange a more than a year ago. How should we fix this? I'm afraid if I add anything it would be more complicated than necessary. Captain Chicky (talk) 23:36, 25 November 2022 (UTC)
thread_title:  Last part about granulation of spacetime is misleading? 

message: Affirming that "The most well-developed theory that has been advanced as a direct result of loop quantum gravity is called loop quantum cosmology (LQC)" is absolutely wrong. LQC is not a direct result of LQG in any way. LQC quantises "a la LQG" symmetry reduced models, it is not a direct result from taking LQG and reducing it to a symmetric spacetime. Even though it seems LQC and LQG might be conected (there are some papers by Livine, Tambornino, Garay... on simple models of LQG that show dynamics similar to those of LQC), affirming that LQC is a result of LQG is misleading. Alvinero (talk) 10:13, 18 May 2023 (UTC)
thread_title:  Loop Quantum Cosmology and its links with LQG