Talk:Loop quantum gravity

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12 year old

Isn't it wikipedia policy for a 12 year old to be able to understand... I'm 12 years of age and my dad (37) couldn't understand a word of it except for the words a, the, it, in, science, gravity and physics! please... can this srticle be simplified!

The relevant question is -- is the Wikipedia sufficiently self-contained for a patient enough and diligent enough person (even 12) to find answers needed? You don't need to understand something to understand it. You only need to have access to the background needed to understand it. But the background is part of the Wikipedia, too. You can literally start out at 0 (as long as you're able to read, that is) and work your way from there.

I always understood that's how people normally surf the web anyhow (especially younger people for whom this is supposedly their home turf!). When they don't get something they surf in a matter of milliseconds to another link to bone up on what background they don't know, and then go back to what it was whose background they didn't have.

I think the answer is -- the Wikipedia (and the net, as a whole) are completely self-contained ... even to the point (I might add) of making school and college redundant and superfluous. -- Mark, 2007 February 3 —Preceding unsigned comment added by 4.159.171.124 (talk) 23:32, 3 February 2008 (UTC)

That's the dumbest statement I've ever read. I shudder at the thought of the newer generations being educated by the internet. 201.216.245.25 (talk) 19:26, 25 November 2009 (UTC)

Also, this article has gained WWW status as "difficult to understand"

Please sign your comments in the future. The fact of the matter is that LQG is a very esoteric piece of theoretical physics. As such it cannot be explained to a 12 year old unless that 12 year old knows tensor calculus. When I was 12 I was busy learning the basic laws of motion and general analytical skills which helped me learn what I needed in order to understand topic such as these. --Hfarmer 06:28, 13 July 2007 (UTC)

Absolute rubbish. This obviously bright 12 year old is quite right and you are wrong. There is a perfectly comprehensible description of this field in the January 2004 issue of Scientific American that does not use the word 'tensor' once. Like I said, I have a PhD in solid state chemistry and I found the article totally incomprehensible. Don't blame the igonorance of the audience for your lack of expository skills. Deadlyvices 10:16, 14 July 2007 (UTC)

Your education... I really don't see what that has to do with the topic at hand. You learned chenistry and not nearly as much physics as a physicist would. Please respect the fact that solid state chemistry while complex is not physics, that little you know would be applicable. I certinaly would not pretend to know as much about solid state chemistry as you would. Please pay us, your fellow physical scientist, the same respect. Furthermore I have not edited this article's copy in a long time. When I did I gave it the structure of having a plain english introductory lead section, then more technical guts. It still has that basic structure. Does it not say.

Loop quantum gravity (LQG), also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the seemingly incompatible theories of quantum mechanics and general relativity. This theory is one of a family of theories called canonical quantum gravity. It was developed in parallel with loop quantization, a rigorous framework for nonperturbative quantization of diffeomorphism-invariant gauge theory. In plain English, this is a quantum theory of gravity in which the very space in which all other physics occurs is quantized.

Loop quantum gravity (LQG) is a proposed theory of spacetime which is constructed with the idea of spacetime quantization via the mathematically rigorous theory of loop quantization. It preserves many of the important features of general relativity, while at the same time employing quantization of both space and time at the Planck scale in the tradition of quantum mechanics.

LQG is not the only theory of quantum gravity. The critics of this theory say that LQG is a theory of gravity and nothing more, though some LQG theorists have tried to show that the theory can describe matter as well. There are other theories of quantum gravity, and a list of them can be found on the quantum gravity page.

Just what about that is confusing? where is the word tensor used? There is really no way to make it simpler than the above. Any simpler and the article would be so generic as to be applicable to any theory of quantum gravity. --Hfarmer 13:25, 14 July 2007 (UTC)

Sorry, I should have said I found it almost totally incomprehensible. You don't appear to grasp that the issue is not about education, it's about meeting your audience halfway, and you don't seem to be prepared to budge an inch. Why should I have to be a physicist to understand a Wikipedia article? Kind of makes the writing of it in the first place pretty pointless, wouldn't you say?

I came here looking for a good, clear account of the subject for the intelligent layperson and I found this instead. It's chock-full of material such as

At the core of loop quantum gravity is a framework for nonperturbative quantization of diffeomorphism-invariant gauge theories, which one might call loop quantization. While originally developed in order to quantize vacuum general relativity in 3+1 dimensions, the formalism can accommodate arbitrary spacetime dimensionalities, fermions,[1] an arbitrary gauge group (or even quantum group), and supersymmetry,[2] and results in a quantization of the kinematics of the corresponding diffeomorphism-invariant gauge theory. Much work remains to be done on the dynamics, the classical limit and the correspondence principle, all of which are necessary in one way or another to make contact with experiment.

In a nutshell, loop quantization is the result of applying C*-algebraic quantization to a non-canonical algebra of gauge-invariant classical observables. Non-canonical means that the basic observables quantized are not generalized coordinates and their conjugate momenta. Instead, the algebra generated by spin network observables (built from holonomies) and field strength fluxes is used.

'In a nutshell, loop quantization is the result of applying C*-algebraic quantization to a non-canonical algebra of gauge-invariant classical observables. ' Just what the hell does all this mean? The most impenetrable of nutshells, that's what. I may be a chemist but even with my limited knowledge (which extends to Fermi levels, wave vectors, k-space, Brillouin zones and the suchlike) I imagine I could write a far more accessible account which, although lacking this kind of mathematical detail, reaches a much wider audience. Yet when someone points out that the article is largely incomprehensible, you reply 'As such it cannot be explained to a 12 year old unless that 12 year old knows tensor calculus'. You might as well have said 'go away and play with your Newtonian mechanics, little boy/girl'. If you want to be accorded respect, try showing it in the first place, and to everyone, not just 'fellow physical scientists'. I'd suggest that you start by always underestimating your audience's knowledge and never underestimating their intelligence. This article and your subsequent comments seem to do the complete opposite. Deadlyvices 04:14, 16 July 2007 (UTC)

I am sure your education in chemistry is quite comprehensive. I have no doubt that in that field you are totally qualified. I would have to differ with your assertion that you know enough about this topic to write a good article about it. While you know much about quantum levels of atoms and what not (more knowledge of that than the average physicist to be certain). That kind of "quantum physics" has little to nothing to do with the ultra relativistic quantum mechanics that is LQG (Or M theory for that matter). If you had said you knew Quantum Field Theory that would have been a much stronger credential.

However I understand that this is not about credentials. Wikipedia needs to be understandable to everyone who has graduated at least highschool. That is how I had written the introductory paragraph and subsequent editors continued in that spirit.

To make this article comprehensible to a 18 year old the article could only consist of that introductory section.

I suggest this look at the references in the LQG article. Read and study the matterials then please tell me how to break this down without mentioning tensors, or calculus, or the calculus of tensors, or the algebra of operators, etc, etc. It is inherently very complicated. THAT'S NOT MEANT TO INSULT YOU. It's just a statement of facts. LQG is second in complexity only to M-theory. That's just the nature of Quantum Gravity. --Hfarmer 05:16, 20 July 2007 (UTC)

So, are you telling me that there is no middle ground between the article remaining as it is, that is to say, more or less incomprehensible to anybody without a background in relativistic physics, and it being so superficial that it conveys no usful information whatsoever? That, to be of use, it only is of use to professional theoretical physicists? Give me a break!

The article on Heim Theory also deals with a very complicated and dense subject, probably understood by even fewer people than LQG. Yet I was able to understand all of it, not just the introductory paragraph. This is because the person who wrote it is evidently better at communicating difficult subject matter than the people who wrote this article. I'd bet real money that an entry written on LQG by a comparative non-expert would reach a bigger audience than this one and end up doing more ultimate good for the cause. Don't forget; it's the plebs like me who ultimately pay the salaries of the theoreticians who work in this field and we have every right to know why this field is worth bothering about. The 12-year-old you patronised may well end up being your Senator one day.Deadlyvices 16:53, 20 July 2007 (UTC)

Yes. That's what I am saying. At the level of physics a 12 or even 18 year old knows LQG and M-theory would be indistinguishable. For such a person they would probably stop with reading about "quantum gravity". To be a real smart @$$ I will say that a 12 year old Richard Feynmann would understand just fine. :P--Hfarmer 19:55, 16 September 2007 (UTC)

I tend to concur with the other Richard Feynman, the one who said that if a subject wasn't explicable in a freshman lecture, then it hadn't been understood properly. Every other article I've read on the Web about LQG manages to convey much more than this one. I wonder why that is?Deadlyvices 07:33, 23 September 2007 (UTC)

Like most big Wikipedia topics (Star Wars, Pokemon, computational chemistry...) it's written largely by fans and experts in its particular field, and therefore generally written with a certain amount of assumed knowledge about the field, rather than being aimed at a general audience. It's easy to forget that Wikipedia is meant to be an encyclopedia, and not just a collection of all human knowledge. Technical depth can (and arguably should) be dropped for clarity and brevity, so long as proper references and a bibliography are provided. 137.195.68.169 16:35, 25 October 2007 (UTC)

I agree that the quantum physicists who author these tutorials have little interest in writing down to the layman level since they are playing to their peers, academics who will recognize thier thumbnail descriptions on wiki almost like publications. It is not impossible to explain something this arcane to laymen with some background in math (just read Roger Penrose's article on loop gravity in "Road to Reality") but for a 12 year old without the knowledge of vectors, guage connections, parallel transport, spin networks, etc. it just isn't possible. Piamero (talk) 05:19, 22 September 2008 (UTC)piamero

I like complicated

As an "educated layman" i enjoy being challenged and stimulated by wikipedia physics entries and i'd like to suggest that as long as technical terms are linked to their respective articles, allowing users to investigate to whatever depth they feel comfortable with there should be no attempt to simplify to any great extent - some things are just bloody complicated.

58.105.150.204 (talk) 04:50, 21 January 2008 (UTC)

Jolly good for you. Most of us, when we start off learning about a new subject, prefer 'simple'. And 'comprehensible'. We also don't like having to engage in wild-goose chases across the Web trying to ascertain the meaning of material that could quite easily have been made easy to understand in the first place. Perhaps you have a lot of free time to do this sort of investigation. I don't, personally, and if Wikipedia wants to be recognised as any kind of authoritative resource, it has to be accessible before sets out to be rigorous.Deadlyvices (talk) 18:57, 29 January 2008 (UTC)

Iyo Iyo Ita

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)

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)

Chiral fermion anomalies

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)

Block of original research removed

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)

I proposed the following be removed to their own sections/articles

   * 4.4 LQG and the big bang singularity
   * 4.5 LQG and particle physics
   * 4.6 LQG and the Graviton
   * 4.7 The Kodama state
   * 4.8 Spinfoam
   * 4.9 Non commutative geometry and loop gravity

1. 5 LQG and analogues to condensed matter physics

   * 5.1 LQG and string nets
   * 5.2 LQG and group field theory  —Preceding unsigned comment added by 134.193.253.41 (talk) 18:26, 9 March 2009 (UTC) 

any volunteers to do so? If I do so will someone reverse the edit? —Preceding unsigned comment added by 134.193.253.41 (talk) 18:33, 9 March 2009 (UTC)

is interpretation Fermi results controversial?

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)

I think it is at this time premature to rely on a single observation. —Preceding unsigned comment added by 24.145.243.18 (talk) 18:07, 19 August 2009 (UTC)