Talk:Loop quantum gravity: Difference between revisions

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			{{Archive box\|] (up to May 2004) <br> ] {created 29 November 2004) <br> ] (As of August 2005) <br> ] (Created Oct 2009, content up to mid-2008)}}
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			== ?? question ?? ==
	==Part IV Selection of Open Research Problems ==
			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 ? <small><span class="autosigned">— Preceding ] comment added by ] (] • ]) 12:45, 27 December 2014 (UTC)</span></small><!-- Template:Unsigned --> <!--Autosigned by SineBot-->

			Yes, you are wrong. LQG models sapce using a spin-network, and it predicts that there is a quantum of area, and probably a quantum length. LQG does not work that well with time, and it is not clear in any way that there is a quantum of time in the same way as there are quanta of space.] (]) 09:35, 20 June 2021 (UTC)
	FROM Thiemann - Lectures on Loop Quantum Gravity, please use accordingly to improve the article and get an idea of the issues at hand:

			== 12 year old ==
	Let us summarize the most important open research problems that have come up during the
	discussion in these lectures.

			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!
	i)
	Hamiltonian Constraint and Semiclassical States
	The unsettled correctness of the quantum dynamics is the major roadblock to completing the
	quantization programme of QGR. In order to make progress a better understanding of the
	kinematical semiclassical sector of the theory is necessary.

			Then why don't you go to Simple English Wiki kid? That's clearly your and your father's level. <span style="font-size: smaller;" class="autosigned">—Preceding ] comment added by ] (]) 04:16, 25 November 2010 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->
	ii)
	Physical Inner Product
	Even if we had the correct Hamiltonian constraint and the complete space of solutions, at the
	moment there is no really good idea available of how to construct a corresponding physical
	inner product because the constraint algebra is not a Lie algebra but an open algebra in the
	BRST sense so that techniques from rigged Hilbert spaces are not available. A framework for
	such open algebras must be developed so that an inner product can be constructed at least in
	principle.

			:The relevant question is -- is the Misplaced Pages 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 Misplaced Pages, too. You can literally start out at 0 (as long as you're able to read, that is) and work your way from there.
	iii)
	Dirac Observables
	Not even in classical general relativity do we know enough Dirac observables. For QGR they
	are mandatory for instance in order to select an inner product by adjointness conditions and
	in order to arrive at an interpretation of the final theory. A framework of how to define Dirac
	observables, at least in principle, even at the classical level, would be an extremely important
	contribution.

			: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.
	iv)
	Covariant Formulation
	The connection between the Hamiltonian and the Spin Foam formulation is poorly understood.
	Without such a connection e.g. a proof of covariance of the canonical formulation on the one
	hand and a proof for the correct classical limit of the spin foam formulation on the other cannot
	be obtained using the respective other formulation. One should prove a rigorous Feynman
	Kac like formula that allows to switch between these complementary descriptions.

			:I think the answer is -- the Misplaced Pages (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 <small>—Preceding ] comment added by ] (]) 23:32, 3 February 2008 (UTC)</small><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->
	v)
			::That's the dumbest statement I've ever read. I shudder at the thought of the newer generations being educated by the internet. ] (]) 19:26, 25 November 2009 (UTC)
	vi)
			:::"a matter of milliseconds"? I assume you live somewhere that has Fiber-To-The-Home? ] (]) 22:27, 23 September 2015 (UTC)
	QFT on CST's and Hawking Effect from First Principles
	The low energy limit of the theory in connection with the the construction of semiclassical
	states must be better understood. Once this is done, fundamental issues such as whether
	the Hawking effect is merely an artefact of an invalid description by QFT's on CST's while a
	quantum theory of gravity should be used or whether it is a robust result can be answered.
	Similar remarks apply to the information paradoxon associated with black holes etc.
	Combinatorial Formulation of the Theory
	The description of a theory in terms of smooth and even analytic structures curves, surfaces
	etc. at all scales in which the spectra of geometrical operators are discrete at Planck scales is
	awkward and cannot be the most adequate language. There should be a purely combinatorical
	formulation in which notions such as topology, differential structure etc. can only have a
	semiclassical meaning.

			Also, this article has gained WWW status as "difficult to understand"
	vii)
	Avoidance of Classical and UV Singularities
	That certain classical singularities are absent in loop quantum cosmology and that certain
	operators come out finite in the full theory while in the usual perturbative formulation they
	would suffer from UV singularities are promising results, but they must be better understood.
	If one could make contact with perturbative formulations and pin point exactly why in QGR
	81
	the usual perturbative UV singularities are absent then the theory would gain a lot more
	respect in other communities of high energy physicists. There must be some analog of the
	tenorrealization group and the running of coupling constants that one usually finds in QFT's
	and CST's. Similar remarks apply to the generalization of the loop quantum cosmology result
	to the full theory.

			: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. --] 06:28, 13 July 2007 (UTC)
	viii)
	Contact with String (M) Theory
	If there is any valid perturbative description of quantum gravity then it is almost certainly
	string theory. It is conceivable that both string theory and loop quantum gravity are comple-
	mentary descriptions but by themselves incomplete and that only a fusion of both can reach the
	status of a fundamental theory. To explore these possibilities, Sinolin has launched an ambi-
	tious programme which to our mind so far did not raise the interest that it deserves 8. The
	contact arises through Chern Simons theory which is part of both Loop Quantum Gravity
	and M Theory (when considered as the high energy limit of 11 dimensional Supergravity).
	Another obvious starting point is the definition of M Theory as the quantum supermembrane
	in 11 dimensions , a theory that could be obtained as the quantization of the classical
	supermembrane by our non-perturbative methods. Finally, a maybe even more obvious con-
	nection could be found through the so-called Pohlmeyer String which appears to be a
	method to quantize the string non-perturbatively, without supersymmetry, anomalies or extra
	dimensions, by working directly at the level of Dirac observables which are indeed possible to
	construct explicitly in this case.
	] 09:06, 21 August 2006 (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. ] 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.
	Like many things in physics this is a contentios matter. I have archived the debate thus far because the page was very messy. note that there is a long laundry list of objections to LQG in the third achive which I will link to in the article so please do not add them backin. If you do not "Like" LQG flame it in usenet. This is just an encylopedica article and as such should be brief and aimed at the lay person who just wants to know that the heck it is. This is not a journal please don't take it so serioously. :-)

			<blockquote>
	I just pray this does not reignite the flame/editwar.
			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.
	--] 00:49, 23 August 2005 (UTC)

			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.
			</blockquote>

			:::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. --] 13:25, 14 July 2007 (UTC)
	=== unverified ===

			::::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 Misplaced Pages article? Kind of makes the writing of it in the first place pretty pointless, wouldn't you say?
	For one thing, the critics of this theory cite that it does not predict the existence of extra dimensions and does not predict the masses or charges of particles, such as in String theory.
			::::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
			::::<blockquote>
			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, 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. 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.
	string theory does not predict or allows for post-diction calculation of masses. extradimensions remains unverified as of 2005.
			</blockquote>
			::::'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. ] 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. Misplaced Pages 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.
	== A Long Question ==
	To my understanding, physics is about describing or measuring particular aspects of the nature. This activity is based on the comparison of the subject of discourse such as spatial or chronological distance or the mass with a unit of measure, such as, in a simple case for spatial distance, a yardstick or the measuring unit of length. So the task for example to measure the distance reduces to counting how often, say, a yardstick has to be applied. Derived variables are treated accordingly. For counting numbers are used.
	“In mathematics, the real numbers are intuitively defined as numbers that are in one-to-one correspondence with the points on an infinite line—the number line. The term "real number" is a retronym coined in response to "imaginary number". …Real numbers may be rational or irrational; algebraic or transcendental; and positive, negative, or zero…Real numbers measure continuous quantities.” More details on real numbers are found in Misplaced Pages: http://en.wikipedia.org/Real_numbers).
	That an uncountable number of real numbers exists is one aspect. The other aspect is, that in practice self-adjoint operators on a Hilbert space (for example, self-adjoint square complex matrices) are used, which “generalize the reals in many respects: they can be ordered (though not totally ordered), they are complete, all their eigenvalues are real and they form a real associative algebra. Positive-definite operators correspond to the positive reals and normal operators correspond to the complex numbers” Misplaced Pages (http://en.wikipedia.org/Real_numbers). Why is it necessary to use “CSTAR algebra”?
	If I understand correctly, the set of the real numbers is a subset of the set of the complex numbers.
	So: what is wrong with the simple assumption that complex numbers can also be used for the initially mentioned counting purpose?
	Why is it a problem to use C-Algebra instead of CSTAR-algebra? For instance, one wants to determine the area of a square and the distance between the corner points is artificially counted by using complex numbers instead of a real numbers.
	“...since if two complex numbers are equal, their real parts must be equal and their complex parts must be equal…We must emphasize, however, that this separation into a real part and an imaginary part is not valid in general, but is valid only for equations which are linear, that is for equations, in which x appears in every term only in the first power or the zeroth power. For instance, if there were in the equation a term λ • x2, then when we substitute xr + i•xi, we would get λ•(xr+ixi)2, but when separated into real and imaginary parts this would yield λ(xr2-xi2) as the real part and 2•i•λ•xr•xi as the imaginary part. So we see that the real part of the equation would not involve just λ•xr2, but also – λ•xi2. In this case …the completely artificial thing we introduced in our analysis, mixed in…” (Feynman, „Lectures on Physics” (1977), 23-2).
	So, the outcome would be something that could look like a quantization of a surface. If xi is sufficiently small, the experimental falsification or proof would be as difficult as in case of the theory of loop quantum gravity.
	Friedrich Schmidt, 17 August 2005.

			::::: To make this article comprehensible to a 18 year old the article could only consist of that introductory section.
	== You sound like a matematician ==
	1.) Physicist use real numbers for observable quantities out of convention. All measureing instruments known to man give measurements in real number's. For example your yardstick has no <math>i=\sqrt(-1)</math> on it. You can draw one in if you want, and put an I infront of all your other measurements but why? That's the physicsit reasoning for it. Some people can give you a much more complicated song and dance but the bottom line facts are that measureing instruments give results in real numbers

			::::: 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. --] 05:16, 20 July 2007 (UTC)
	:: Where do you get "measureing instruments known to man give measurements in real number's?" I don't see irrational numbers on my ruler.

			::::::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!
	2.) Why C* Algebra instead of C Algebra? C Algebra probaly leads to needlessly complicated expressions. Physicist are good at math but we thrive on makeing math as simple as it can be.
			::::::The article on ] 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.] 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--] 19:55, 16 September 2007 (UTC)
	3.) The last part of your comment seems to be on string theory and a compariso between LQG and strings based on expreimental testability. I agree with the general idea that theories of gravity will be difficult to test because the effects will always be very very small.
	--] 01:56, 3 November 2005 (UTC)</math>

			::::::::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?] 07:33, 23 September 2007 (UTC)
	== Why Heyting algebra? ==

			:::::::::Like most big Misplaced Pages 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 Misplaced Pages 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. ] 16:35, 25 October 2007 (UTC)
	I'm puzzled by the See Also link to Heyting Algebra.
	There doesn't seem to be any connection between Heyting Algebra
	the contents of the Loop Quantum Gravity article. If there is,
	I'd really like to see it.

			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. ] (]) 05:19, 22 September 2008 (UTC)piamero
	-- hendrik@pooq.com

			I think that of the whole article does a better job that this wikipedia article in explaining what loop quantum gravity is. <span style="font-size: smaller;" class="autosigned">—Preceding ] comment added by ] (]) 11:38, 9 December 2009 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->
	== Stop opinionating! ==

	I agree with Hfarmer. When you state an opinion, don't use the passive voice (see ]) and do cite your authority. I have removed the Problems section. It's nothing but unsupported opinion.

			While I have the greatest respect for people who strive to document these complex topics, I wholeheartedly agree with Deadlyvices' objections. Abstract physical concepts that are very difficult to understand have been documented to accommodate readers of nearly all levels, which means this article '''is''' unnecessarily complicated. The greatest physicists of all time were able to make earth-shattering discoveries because of their ability to think in physical pictures like speeding trains and such. The most famous example is probably the apple falling on Newton's head. I know that this becomes rather difficult when talking about non-Newtonian physics, but Albert Einstein also thought in 'physical pictures', even though the subjects he studied were far more abstract than gravity. I strongly suggest you take it upon you to represent the intensely abstract LQG with more 'graspable' presentations. Highly respected scientists like Michio Kaku do a great job at publishing literature on advanced scientific concepts that is understandable by pretty much anyone. That said, I'm not telling you to drop the more complex content. I'm merely asking you to at least provide interested readers who do not study physics with a solid explanation of the basics of LQG, significantly increasing the importance and value of this article. <span style="font-size: smaller;" class="autosigned">— Preceding ] comment added by ] (]) 18:34, 24 August 2011 (UTC)</span><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->
	"As of now, there is not a single experiment which verifies or refutes any aspect of LQG." "theory without experiment is just faith" The same can be said for string theory, or black holes, for that matter.
	:black holes have been proven through gravitational lensing. hth. ] 01:50, 12 December 2005 (UTC)

			Should there be another LQG entry simplified for popular understanding in popular press?
	"LQG has failed to gain support in the physics community" is an unsupported generalization.

			http://en.wikipedia.org/String_theory
	If one wishes to opinionate or preach, they can place their opinions HERE, like this:
			For a generally accessible and less technical introduction to the topic, see Introduction to M-theory. <span style="font-size: smaller;" class="autosigned">— Preceding ] comment added by ] (]) 03:35, 16 March 2013 (UTC)</span><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->

			== I like complicated ==
	:'''Problems'''
			::::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.
			] (]) 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 Misplaced Pages wants to be recognised as any kind of authoritative resource, it has to be accessible before sets out to be rigorous.] (]) 18:57, 29 January 2008 (UTC)
			::Cool story bro. Fact is, this material has to be abstracted and generalized to the point of distortion in order for it to be 'easy to understand'. The problem is egotistical readers expecting to be able to easily understand whatever they come across, certain that their vast intellects are surely capable of grasping any given topic instantly. If they don't understand something, it's not their fault - it's the material's! Pathetic. Unsigned, because, well, fuck you that's why.
			:::Well, bro, I don't expect anything of the sort. Most people, not me, think that this article is jargonistic and poorly written, and if a professional scientist like me finds it difficult it's not because I'm egotistical to the extent that I expect everything to be handed to me on a plate. Perhaps we have a point. Perhaps its written by a crappy author who is too arrogant to recognise he isn't very good at explaining complex topics. Perhaps it shouldn't be written about at all in an encyclopaedia if it can't be written about comprehendably. And fuck you too, you arrogant, abusive and cowardly little man (that much I'm certain about). ] (]) 22:33, 20 July 2011 (UTC)

			Just revisited this page. Up until the section Constraints and their Poisson bracket algebra it's pretty good. After that it's totally incomprehensible, over-technical shit. ] (]) 11:53, 7 July 2015 (UTC)
	:As of now, there is not a single experiment which verifies or refutes any aspect of LQG. This problem plagues many current theories of quantum gravity. LQG is affected especially, because it applies on a small scale to the weakest forces in nature. There is no work around for this problem, as it is the biggest problem any scientific theory can have; theory without experiment is just faith. The second problem is that a crucial free parameter in the theory known as the Immirzi parameter is a logarithm of a Transcendental number. This has negative implications for the computation of the entropy of a black hole using LQG. To be fair, it must be noted that the transcendental number is the result of a calculation. It does not come from an experiment, which would be the true test of scientific reality. Since Bekenstein and Hawking computed the entropy of a black hole, this computation has become a crucial litmus test for any theory of quantum gravity.

			::I find much of this article incomprehensible. I don't begrudge the presence of the complicated detail as well, but there should be an introductory section that is more clear and simple, without unnecessary jargon. I read ''A Brief History of Time'' at age 12 and understood it as far as it went, so I'm certain that exceedingly complicated and unintuitive concepts can be explained at least a little better than this article does. ] (]) 15:01, 13 June 2019 (UTC)
	:Finally, LQG has failed to gain support in the physics community mainly because of its limited scope. Many scientists believe that LQG could be formulated into a theory of quantum gravity just suited for 4 dimensions. However, by using the String theory or M-theory, scientists have come very close to taking everything we know into account and predicting much that we do not know. Hence, the general feeling is that these competing theories are more potent. Loop theorists disagree, because they believe that we need a proper theory of quantum gravity as a prerequisite for any theory of everything. This philosophical problem could be the most fatal problem that LQG faces in the future. Only time and experimentation can decide the matter.
			:::Sixteen years on from my original gripe, and whoever wrote this article managed to make it even more dense and incomprehensible.
			:::That's one hell of an achievement.
			:::] (]) 12:33, 20 October 2023 (UTC)

			== Iyo Iyo Ita ==
	:Other problems associated with LQG can be found in ]

			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! <small>—Preceding ] comment added by ] (]) 01:35, 17 March 2008 (UTC)</small><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->
	The last paragraph should begin, "''All'' problems..." Unless you're ready to site ''authoritative'' sources, not just other opinion, leave "problems" out of the article.

			::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. --] (]) 02:27, 21 July 2008 (UTC)
	Also, as Hfarmer said, Misplaced Pages is to be read by the educated layman. "Nonperturbative quantization of diffeomorphism-invariant gauge theories" indeed!

			Please nobody take this suggestion seriously. I am a professional chemist and the idea that there are scientist that "dont even bother with paper journals anyway" or that personal websites or "scientific" blogs are reliable sources, is laughable.] (]) 13:44, 18 February 2016 (UTC)
	] 20:47, 25 November 2005 (UTC)

			== Chiral fermion anomalies ==
	== Criticisms to LQG, Shortening the Article, and issues around. ==
			<pre>It currently appears that nothing forbids coupling anomalous
			- i.e. quantum mechanically inconsistent - chiral fermions to LQG.</pre>
			: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. ] (]) 11:38, 23 August 2008 (UTC)

			==Block of original research removed==
	I personally think it is a pity that I have to search all the history until I find the criticisms of the theory. Many theories around wikipedia have a "Criticism" topic. And also, the shortening of the article on the basis that "wikipedia is for the common man, not the physics" was lame. Misplaced Pages should be for both, and elsewhere is stated that it is a project to "compile the sum of all knowledge". Any article can have "soft" and "hardcore" parts. If there is such a problem of people trying to bash LQG, there could be a separate page named ] What do you people think of it? ] 20:29, 29 November 2005 (UTC)
			I've removed the block of ] posted in the section previously titled "Diffeomorphism invariance and background independence", and replaced it with what I suppose is an equivalently imperfect ] section, presently retitled ]. ... ] (]) 23:34, 8 January 2009 (UTC)

	Agreed. ] 14:38, 2 December 2005 (UTC)


			I proposed the following be removed to their own sections/articles
	I second that. Which I why I am readding the problems section. I am not an advocate of either string theory or loop quantum gravity. In fact I have my own theory that is more like LQG than anything else out there.

			#
	Simply ackowledgin the problems of LQG will not discredit it. Active areas of research have problems those problems are what is being researched.

			* 4.4 LQG and the big bang singularity
	As for the problems section being "un supported opinion" The content of that section is based on my own research and the objections cited a few archives back by the likes of Lubos Motl "lumidek" was his username. He is a well known theoretical physicist. I myself am at least googleable. Search for Hontas Farmer Physics and you will find my credentials. As such people like us can act as "verifiable sources" Afterall this is our very area of reasearch being discussed who knows it better?
			* 4.5 LQG and particle physics
	--] 03:49, 7 December 2005 (UTC)
			* 4.6 LQG and the Graviton
			* 4.7 The Kodama state
			* 4.8 Spinfoam
			* 4.9 Non commutative geometry and loop gravity

			# 5 LQG and analogues to condensed matter physics
	== Eh? ==
	The day someone who doesn't already know the theory (aka the only type of person to whom this page would be useful) understands the term "nonperturbative quantization of diffeomorphism-invariant gauge theories," even after following all the links, is the day I eat my hat.

			* 5.1 LQG and string nets
	****As someone how came to this page to try to understand LQG - I must agree with 'Eh?'. This page is entirely useless to the uninitiated.
			* 5.2 LQG and group field theory <span style="font-size: smaller;" class="autosigned">—Preceding ] comment added by ] (]) 18:26, 9 March 2009 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->

			any volunteers to do so? If I do so will someone reverse the edit? <span style="font-size: smaller;" class="autosigned">—Preceding ] comment added by ] (]) 18:33, 9 March 2009 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->
	I agree, the article is unreadable and should be completly rewriten. In addition, the text refers to a discussion archive which is not a part of the encyclopedia at all. --] <small>]</small> 17:53, 30 December 2005 (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." --] (]) 02:20, 18 August 2009 (UTC)

			I think it is at this time premature to rely on a single observation. <span style="font-size: smaller;" class="autosigned">—Preceding ] comment added by ] (]) 18:07, 19 August 2009 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->
	I absolutely agree: I believe that the introduction should ease a reader into learning about the subject, rather than just assume they already understand LQG. What if the reader is looking into it as leisurely research, and not as part of a university course? I do not know more about diffeomorphism than most people, but I am very willing to learn so long as it is explain in terms I understand. Misplaced Pages is about free knowledge, and I am finding it hard to see that in this article.

	== It has become clear that this article needs rewriting ==

			==The good, the bad, and the ugly==
	I do not have the energy to undertake this matter right this minute but I will tomorrow. What needs to be re imposed is the structure I had imposed a year ago. I will re write a plainly worded introduction to the subject matter. Below that introduction a more technical section which will include a discussion of the short commings of Loop Quantum Gravity. (which as far as I can see are as much the result of the sociology of physics and the politics of funding. String theory people attack LQG with the zeal one would expect from religious fanatics.) --] 00:24, 3 January 2006 (UTC)
			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."<br>
			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!

	:I think the important point there is that this theory, like String Theory, is regarded by many as a form of religion. This is discussed extensively in ]. See also the ]. For clarity in this article, I think ] offers a little more digestible prose. ] 02:37, 3 January 2006 (UTC)

			:::: The para you quoted can be understood by anyone with even a basic understanding of basic physics, . ] (]) 13:53, 23 July 2013 (UTC)
	::Er, whoops. That's ]. Got my affairs mixed up. ] 00:30, 5 January 2006 (UTC)

			Uh-huh? So "formalism", "supersymmetry" and "gauge theory" are all part of your "basic understanding of basic physics"? You must be super-duper smart.] (]) 13:47, 18 February 2016 (UTC)
	== NPOV back ==

			I have a high school level physics i got a B in when 17, so basic physics....definitely didn't mention "diffeomorphism-invariant" I agree with the original comment ] (]) <!--Template:Undated--><small class="autosigned">—Preceding ] comment added 23:51, 29 January 2020 (UTC)</small> <!--Autosigned by SineBot-->
	I've returned the NPOV tag on top of this page because someone has slowly deleted absolutely all concrete criticism that effectively explained why loop quantum gravity is an inconsistent ]. I understand that the percentage of LQG fans between those who edit this page exceeds their percentage among the physicists roughly by three orders of magnitude, but that should not be a sufficient justification to allow a Misplaced Pages page that claim such nonsenses such as that LQG only has the same problems like string theory, which is what this page essentially does. See , , for basic summary why LQG is not a ready candidate for a physics theory from the viewpoint of physicists as opposed to crackpots who push some agenda through Misplaced Pages. Best wishes, Lubos Motl, Harvard --] 14:57, 8 January 2006 (UTC)

			==Citation needed?==
	Yeah, you are right. And I dont think it's fair to mix LQG with Bogdanov theory (which in my view represents a real alternative to major problems non solvable in LQG).

			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. <span style="font-size: smaller;" class="autosigned">—Preceding ] comment added by ] (]) 21:57, 15 May 2011 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->

	Lubos Motl's comments above ''are to be read in the context that he is an outspoken '''string theorist''', and not an unbiased/independent authority'' on the merits of Loop Quantum Gravity - ] 23:21, 18 January 2006 (UTC)

			== You are quite right, looking for it as I write. ==

			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.
	This will shock you Dr. Motl but I agree with that. I myself authored a section on the problems with LQG which some people have sought to remove even that modest section at times. if you do not believe me just look at the revision history. I am currently to busy to clean up this mess. But as soon as I do the Npov will be removed. Because I will write it with a neutral POV. I am not a LQG fan or a string fan. I have my own take on canonical quantum gravity separate and apart from LQG. LQG is by no means perfect. However I do not feel that it's encyclopedia entry should be comprised of a smear campaign.
			.. 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/Doubly_special_relativity (deformed special relativity) that seems to discuss that idea in more depth, hopefully :)
	On second thought I feel that one of the former revisions of this page was just about right. I will revert to the revision as of (http://en.wikipedia.org/search/?title=Loop_quantum_gravity&oldid=32572035). I will do this at 1:00AM CST 1/21/06 if nobody objects to that revision. --] 06:30, 20 January 2006 (UTC)

			Yoron ] (]) 17:51, 25 June 2011 (UTC)
	I would also point out two other things to Dr. Motl. you wrote a much longer section full of objections. I placed a link to the talk page where I archived it. I did this from the first rewrite of the page. I though that much of what you had to say was far too technical for the layperson reading the article. I would like you to know that I feel the same way about much of the matterial added going into painful detail on the mathematics of LQG (diffeomorphism invariance indeed!). What use is any of that to the average highschool kid doing a science project who only knows E=mc^2 (and not even F=ma because they have not had a formal physics class)? None. Talk of diffeomorphisms and lack of 11 dimensional super symmetry... will just fly over the heads of 98% of the people served by wikipedia.

			== Formula? ==
	Do you understand that I am not your enemy?

			What's the central formula of this theory? I mean, there has to be something likem a Lagrange density or something similar... --] (]) 18:08, 20 July 2011 (UTC)
	--] 06:50, 20 January 2006 (UTC)

			:::: Yup, the Einstein - Hilbert - Palatini - Ashtekar (EHPA) or Einstein - Hilbert - Ashtekar (EHA) action (Source: LQG for (and by) the bewildered) .. ] (]) 13:56, 23 July 2013 (UTC) . m.
	:I do like that revision more than the present one. I'd be happy to do a copyedit on it if you revert it. Also, before you do any reverting, please make sure that nothing is left out from the current version. No need to lose data. ] 07:43, 20 January 2006 (UTC)

			:: 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? --] (]) 01:33, 3 April 2012 (UTC)

			:: From the article on ]s: "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 ... --] (]) 02:08, 3 April 2012 (UTC)
	::True we do not want to loose data. However we do not want to make the article too long or too technical. As a matter of fact look at the string theory article. It is through, dignified and ackowledges that string theory also has it's problems. It seems pretty neutral. Look at the artilcles about other theories of Quantum gravity. The are neutral brief and to the point. --] 20:02, 20 January 2006 (UTC)

			== Overlooked aspects and gaining information ==
	:::Dear Hfarmer, I apologize because I had to be really sloppy in judging your viewpoint. Incidentally, the list of meaningful papers reviewing LQG rationally has just expanded by one - see that cites the new preprint and explains its points, including the critical ones. I am not sure whether it is physically possible to sustain a realistic page about LQG here. Concerning the technical level of these articles, it seems to me that Misplaced Pages in general does try to explain topics at the technical level, so I don't understand why it should avoid things like diffeomorphisms that are critical for anything about gravity, among other examples of technical terms. In the case of string theory, there have been many quite deeply technical points explained on Misplaced Pages - see lists of string theory topics etc. --] 02:14, 21 January 2006 (UTC)
			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 <small><span class="autosigned">— Preceding ] comment added by ] (] • ]) 20:59, 6 February 2012 (UTC)</span></small><!-- Template:Unsigned --> <!--Autosigned by SineBot-->
			::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 Misplaced Pages! We can use you! And BTW, if you know any lung cancer experts, send them to me - I NEED THE HELP!

			Very best regards:
	:::Think nothing of it Dr. Motl. I have had much worse things said over less important topics. What I was shooting for when I rewrote this about a year ago was an article with two major sections. An introduction in plain language. Laypeople need read no further. Then the technical nuts and bolts of the theory which would include discussion of it's problems and pitfalls. I have learned to be satisfied when a wikipedia page does not contain hidden swearwords and links to pornography. You get what you pay for. --] 04:03, 21 January 2006 (UTC)
			] (]) 11:47, 8 February 2012 (UTC)

			==black hole entropy contradictions ==

			the below 2 passages contradict one another, Carlo Rovelli's edit is based on more recent research which does away with the Immirzi parameter and Carlo Rovelli is a LQG researcher who has written papers and textbooks.
	Dr.Motl. I have read the paper you referenced as well as your interpretation of it. Both the paper and your blog seem to attempt to explain this in the a way that a non theoretical physicist could understand. This seems to be the technical level appropriate for the wikipedia.

			I propose deleting the older bottom paragraph as no longer current.
	What would it take to make this article neutral enough that you would remove the npov tag? The way it is as of 1:43 CST is npov as I see it. Perhaps if you added another paragraph to the problems section that better explained how string theorist look at LQG? Just a suggestion. --] 07:45, 21 January 2006 (UTC)


			Another application of LQG concerns understanding the thermal behavior of black holes. A recent success of the theory in this direction is the computation of the entropy of all non singular black holes . The result is the expected formula S=A/4, where S is the entropy and A the area of the black hole, derived by Bekenstein and Hawking on heuristic grounds. This is the only known derivation of this formula from a fundamental theory, for the case of generic non singular black holes.
	==Balance Restored==

	As Dr. Motl has not responded to my last entry here. I will take it for balance being restored. Whomever alters this article in the future should realize that this is supposed to be an encyclopedia. Simple description of LQG its claims failures and sucesses will do. There is no need for a commercial for or against. The people who read this encyclopedia know that what is written in it would not be gospel truth.
	--] 07:35, 27 January 2006 (UTC)

			Another problem is that a crucial free parameter in the theory, known as the Immirzi parameter, can only be computed by demanding agreement with Bekenstein and Hawking's calculation of the black hole entropy. Loop quantum gravity predicts that the entropy of a black hole is proportional to the area of the event horizon, but does not obtain the Bekenstein-Hawking formula S = A/4 unless the Immirzi parameter is chosen to give this value. A prediction directly from theory would be preferable.
	==External Links== I would like to add a link to Abhay Ashtekar's home page. It has some excellent popular articles suitable for beginners about Space, Time, GR, and LQG.
	http://cgpg.gravity.psu.edu/people/Ashtekar/articles.html
	Also, I'd like to add a link to the new Scientic American Issue on LQG
	http://www.sciam.com/special/toc.cfm?issueid=40&sc=rt_nav_list
	Atoms of Space and Time by Lee Smolin
	"We perceive space and time to be continuous, but if the amazing theory of loop quantum gravity is correct, they actually come in discrete pieces." I"ll wait a few days. in the absence of adverse comment, I"ll made the additions. Take Care! Will314159--Will314159 19:18, 30 March 2006 (UTC)

	Also
	Loop Quantum Gravity. Lee Smolin. Online at
	www.edge.org/3rd–culture/smolin03/smolin03–index.html
	--Will314159 21:33, 30 March 2006 (UTC)

			==Vandalism 180.149.8.81==
	I made the above mentioned external link additions and checked the links. Take Care!--Will314159 13:46, 31 March 2006 (UTC)
	And the reason these resources are under External links and not the Bibliography is because the Ashtekar home page, the SciAmer Special Issue, and Edge has multiple articles in one setting dealing with LQG and associated ideas. Take Care!--Will314159 14:22, 31 March 2006 (UTC)

			Main article: History of loop quantum gravity
	== Experimental verification ==

			In 1986, "someone" reformulated Einstein's general relativity in a language closer to that of the rest of
	It is important and should be mentioned that LQG makes a testable prediction: speed of light is not constant but depends on the energy of the photon. cf
	Smolin sez that GLAST satellite will carry out the experiment. According to NASA, GLAST will go up in 2007.

			changed that to twitch
	== ] and ] ==

			(cur \| prev) 02:18, 14 May 2013‎ AnomieBOT (talk \| contribs)‎ . . (112,172 bytes) (+53)‎ . . (Rescuing orphaned refs ("ReferenceA" from rev 554904443)) (undo)
	I came over here to the LQG talk page to make people aware of some recent changes to the ] article that seemed relevant to those with an interest in LQG. It seems, however, that some of my concerns have already found their way into the LQG article itself, which is probably a more pressing concern.
			(cur \| prev) 16:08, 13 May 2013‎ 180.149.8.81 (talk)‎ . . (112,119 bytes) (+4)‎ . . (→‎History) (undo)
			(cur \| prev) 16:01, 13 May 2013‎ 180.149.8.81 (talk)‎ . . (112,115 bytes) (-9)‎ . . (→‎History) (undo)
			(cur \| prev) 15:56, 13 May 2013‎ 180.149.8.81 (talk)‎ . . (112,124 bytes) (-9,375)‎ . . (→‎An overview) (undo) (Tag: section blanking)
			(cur \| prev) 15:54, 13 May 2013‎ 180.149.8.81 (talk)‎ . . (121,499 bytes) (+7)‎ . . (→‎An overview) (undo)

			i think someone should undo 180.149.8.81 vandals and then lock the article only ibyan and rovelli may add content
	First, there have been numerous people over time who have tried to describe LQG as a would-be "Theory of Everything" in that article. I have done my best to explain that this is false, and that LQG researchers generally view its focus on quantum gravity ''only'' as a strength, not a weakness. (Judging LQG as a TOE rather than on its own terms would be fundamentally unfair.) However, some people have then accused me of trying to suppress and censor rival theories (I happen to be a string theorist, though I'm not of the LQG-hating variety). Getting some support on this point from people who are not string theorists would be appreciated.
			ban 180.149.8.81

			==Time in general relativity==
	And second, there has been a recent effort to elevate the ideas of ] so that they are treated as mainstream physics. "]", as it's called, claims to have predicted a bunch of particle masses and coupling strengths, and a paper about faster than light travel based on Heim's work was recently given a prize by a group of aerospace engineers. As far as I can tell, Heim theory is simply bad physics that hides its fundamental flaws behind complicated-looking mathematics; I seem to recall that only one paper by Heim has been published in a peer reviewed journal (and none on the topic by his current followers). One of the people in the pro-Heim effort at the TOE article (]) also added a reference to Heim to the introduction here.

			Under "The problem of time in quantum gravity", the introduction states:
	I'm not enough of an expert on LQG to feel comfortable changing this article myself (and I don't want to be accused of waging a lone crusade against this stuff), but if anyone who has been active here agrees with my impressions of "Heim theory" then they might want to revert that recent edit. And, of course, any support that you could give over at the TOE article would be appreciated as well. (For discussions of the merits of Heim theory or the lack thereof, take a look at the lengthy (archived) discussions at ], ], and even ].)--] 16:20, 18 April 2006 (UTC)

			"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."
	Obviously, Mr. Steuard, does not like Heim Theory Take Care. --Will314159 10:42, 7 May 2006 (UTC)Edited--Will314159 16:46, 8 May 2006 (UTC)

			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. <span style="font-size: smaller;" class="autosigned">— Preceding ] comment added by ] (]) 22:54, 24 March 2014 (UTC)</span><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->
	Heim theory has nothing at all to do with this theory. Trust me. -]

			: 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/Wikipedia_talk:Articles_for_creation/Problem_of_Time ) and added a link to that proposed page as a "main article" link. <span style="font-size: smaller;" class="autosigned">— Preceding ] comment added by ] (]) 12:34, 27 April 2014 (UTC)</span><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->
	== Crank magnet articles ==

			== The loop quantum gravity diffusion limit ==
	I am looking for information from experienced WP editors on the problem of keeping good editors on Wiki. See the page here ]
			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. <small class="autosigned">— Preceding ] comment added by ] (]) 02:17, 28 April 2016 (UTC)</small>
	This is no more than a list of people who have left Misplaced Pages, or thinking of leaving, or generally cheesed off, for the reason (1) what I will unpolitely call 'cranks', i.e. people engaged in a persistenta and determined campaign to portray their highly idiosyncratic (and dubious) personal opinion as well-established mainstream scientific or historical fact, or 'crank subculture' i.e. fairly sizeable subcultures which adhere strongly to various anti-scientific conspiracy theories (e.g. Free energy suppression) or anti-scientific political movements (e.g. Intelligent design) masquerading as "scholarship". (2) the problem of edit creep, i.e. the tendency of piecemeal editing to make articles worse over time, rather than better.

			== MathML problem ==
	If you are in this category, leave a link to your user page there. If you can, put something on your user page that indicates reason for discontent. I particularly like war stories, so let me have any of those (links please, not on the page).

			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? ] 09:41, 24 June 2016 (UTC)
	There is a more general discussion of this issue on Lina Mishima's page. ] Note I am not in agreement with her title as it is not in my view a problem about experts, but more of adherence to scholarly standards, ability to put polished and balanced articles together. But her idea is good.

			== External links modified ==
	I don’t know much about this subject except that it's a possible crank magnet. If you know of any other, let me know, or even better, cut and paste this message on those pages. I'm going round the obvious places like intelligent design, Goedel, Cantor and so forth, but there must be many such. ] 15:03, 31 August 2006 (UTC)

			Hello fellow Wikipedians,
	==Lorentz violation==

			I have just modified 2 external links on ]. Please take a moment to review ]. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit ] for additional information. I made the following changes:
	I am under the impression that LQG violates (local) Lorentz invariance by proposing a preferred reference frame for the definition of the Planck scale (the spin foam has a characteristic scale of one Planck length only in a particular frame.) My familiarity with this comes from talk of LGQ tests that probe Lorentz violation in GRBs. I'm pretty sure I'm right, so I'm taking out the unsourced opening statement that it preserves LI. ] <small>(])</small> 05:35, 27 September 2006 (UTC)
			*Added archive https://web.archive.org/web/20060820164053/http://sps.nus.edu.sg/~wongjian/lqg.html to http://sps.nus.edu.sg/~wongjian/lqg.html
			*Added archive https://web.archive.org/web/20070928110105/http://www.perimeterinstitute.ca/Events/Introduction_to_Quantum_Gravity/Introduction_to_Quantum_Gravity/ to http://www.perimeterinstitute.ca/Events/Introduction_to_Quantum_Gravity/Introduction_to_Quantum_Gravity/

			When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.
	:That's not necessarily the case, although judging from the literature you've linked to, it ''does'' seem to be a common (convenient?) misconception. LQG satisfies Lorentz invariance in local regimes.
	:To put it more simply than does the matter justice, let's imagine two observers measuring a particular length. One is at rest, the other accelerating. The one at rest measures the length to be minimal, i.e. the Planck length. The idea is that by ]ing, the other observer might see a ''reduction'' in the minimal length (the Plank length) because of ]. However, QM might seem to tell us that length perceived will ''still'' be the ] of an ordinary quantum observable (of course!), which means that it doesn't, some say, Fitzgerald contract: observer 2 cannot measure anything smaller than the Planck length, because it won't be an eigenvalue. Hence it can't Fitzgerald contract, and hence it can't be minimal. However, this overlooks a crucial fact. In LQG, the ] metric is a ]. Measurement is described by a ], but two distinct measurements (as the two observers' measurements are) get two distinct operators. And interestingly, the "length measurement" operators for the two parties involved don't commute: a "length eigenstate" for observer 1 (at rest) is thus not a "length eigenstate" for observer 2 (Lorentz-boosted). But, in ], a property which is not in an eigenstate for a particular observer is described by a ] over a number of states: a ]. This means that the length observed by observer 2 will have a ''mean value'' (over many experiments, say) which is contracted appropriately — weird, isn't it? — but have a minimal ''nonzero'' value which is given by the Planck length (because observer 2 can always measure the distance to be zero, i.e. there ''is'' no length, the two "points" on either side of the length are actually one point, in his reference frame). Ergo, no violation of Lorentz invariance.
	:Now, other theories of ] may have a problem with phenomena of this sort, depending on how they treat the idea of the spacetime metric. But LQG doesn't, precisely because it is a ''quantisation'' of GR. Conversely, we could say that an experiment which ''does'' detect a violation of local Lorentz invariance would probably ''falsify'' LQG!
	:And in future, please cite properly, instead of linking to search engine results. Not only is this wholly inappropriate by any scholarly standards, but the link you placed in the article is nigh unreadable, and renders it very hard to edit. Thanks. ] 11:42, 27 September 2006 (UTC)
	::After reading the above, I reverted the recent edits by ]. I think we need to discuss them here first, before we decide what to do next. 15:39, 27 September 2006 (UTC)

			{{sourcecheck\|checked=false\|needhelp=}}
	This is an interesting argument, but very limited. What you have established essentially is that a minimal length is compatable with invariance under boosts in the same fashion that the quantization of angular momentum is compatable with invariance under rotations. However, the structure of the "spin foam" is more complicated; theories of LQG that are not simply toy models to demonstrate this statement usually require "doubly special" transformations . ] <small>(])</small> 23:19, 27 September 2006 (UTC)

			Cheers.—] <span style="color:green;font-family:Rockwell">(])</span> 02:17, 6 January 2018 (UTC)
	== Recent edits by Sdedeo ==
	A few things here.
	#I hope that the message above this section, which labels this article a "crank magnet", is not leading anyone astray here. LQG is ''not'' a cranky subject: it is a recognised research program in ]. LQG papers have been published in journals such as ]: and it does get more respectable than that as far as scientific publication goes. The only cranks here, as far as I am concerned, are those who have an irrational obsession with discrediting LQG beyond what is reasonable (no names mentioned).
	#As far as the "diffeomorphism invariance" section which ] deleted, I agree that it is not appropriate, as written, for an encyclopaedia...it ''does'' give the impression that the writer is, himself, discovering background independence and diffeomorphism invariance as he writes: this does not work. The article ''needs'' a section on diffeomorphism invariance, as it is a crucial part of LQG, but I shall write something more appropriate when I get the chance. I have recently completed writing an article, and have been intending to fix the page up for some time, but have not wanted to embark upon the project until I can do it justice. I shall be doing it properly soon.
	#Now, regarding this nonsense of "Lorentz invariance violation". In order to support his idea that LQG violates this principle, ] links to the blog of someone known for his anti-LQG polemics. He also provides a set of search results of abstracts as a "citation" of supporters of LQG admitting that this is the case. Among these citations that ] provides, allegedly to "prove" that LQG supporters agree that LQG violates Lorentz invariance, is , which ''proves'', along the lines I discussed above, that this is nonsense: there is no such violation. In fact, it points out that it is a "simple minded" criticism of LQG to insist on this. The paper in question was published in ] D: '''the premier journal for this sort of research'''. So, I have removed the paragraph, which contained typographical errors anyway, as nonsense and OR. The sources are not properly cited, and nor do the "cited" sources support the argument made: they contradict it (other than the blog, but citing blogs in quantum gravity articles is ''not'' appropriate).
	#My intuition tells me that the unreasonable and spurious attack on this article is motivated, at least in part, by the "crank magnet" message above, and is an offshoot of the ] phenomenon. As such, I shall assume that it is happening in ], and I shall not make a fuss about it (yet). Additionally, while I am not so arrogant or presumptuous to term myself an "expert", I ''do'' sympathise wholeheartedly with the project being undertaken on that board. Indeed, I have posted an account of one of my own recent "crank encounters" to ]. I hope that part of the "expert rebellion" is not deliberately harming the integrity of what should be scholarly articles on scholarly subjects!
	#I know my little rant here will probably make me sound a bit like a crank. I am not. I promise. I am simply an editor who feels very strongly about maintaining Misplaced Pages's standards, and is more than a little frazzled himself about the endless stream of nonsense that we have to combat. I am disturbed that someone who is apparently very concerned about the same things as I am, can come and deposit a load of nonsense, without proper citation, and which demonstrates a fundamental misunderstanding of the subject, without even discussing their changes on the talk page, and then go on to rant about the events on their user page! This simply does '''not''' do. ] 22:30, 27 September 2006 (UTC)
	:#''Post scriptum''. I note that Sdedeo has now put a rant about me on his userpage. He claims to "have been involved in research towards detecting Lorentz violation (sic) effects" predicted by the theory. Searching paper abstracts and linking to search results does not really count as "research", in my book. For all I know, he may be more deeply involved, but then I invite him to discuss the problem properly, here. Personally, I think that someone "involved in research" like that would not have addressed the issue as Sdedeo did, and expressed such uncertainty about his understanding on the talk page. Nor, I believe, would they be wanting to restrict Misplaced Pages's scientific reporting to the level of popular science, I don't think, as Sdedeo calls for ]. I could be wrong, again, I know. I apologise in advance if I cause offence by this. I simply do not appreciate this sort of attack, which is '''completely''' uncalled for, and not really very reasonable. ] 22:47, 27 September 2006 (UTC)

			== Another citation needed? ==
	As I have reported on my user page, ], it is a common, mainstream opinion that LQG violates Lorentz invariance. The well-publicised statement that the photon dispersion relation is altered from w=k ''requires'' that ordinary Lorentz invariance be broken. A "pseudo-Lorentz invariance", invariance under "doubly special" Lorentz transformations has be invented, although it is impossible to gauge this and recover General Relativity. I'm certaintly willing to acknolege that a minority of workers in the field may disagree. I personally do not find their argument compelling but wikipedia is not the place to debate such claims and I certaintly mentioned this in my edit as a minority viewpoint.

			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 {{citation needed}}. 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. ] (]) 14:42, 5 May 2019 (UTC)
	At this point, Byrgenwulf finds a single article that holds to the minority viewpoint that standard Lorentz invariance can be recovered. He uses this to decide my edits are "nonsense" and that I have a "fundamental misunderstanding" of the subject. Quite the contrary; the long history of believing in, and searching for, Lorentz violation in LQG can be found pretty easily by someone with an understanding of the field -- see refs in .

			== Multiple redundant footnotes ==
	] <small>(])</small> 22:57, 27 September 2006 (UTC)

			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 <!-- Template:Unsigned --><small class="autosigned">— Preceding ] comment added by ] (] • ]) 12:02, 11 August 2019 (UTC)</small> <!--Autosigned by SineBot-->
	:By all means I can't judge the content dispute here, but I humbly ask both of you ] and ] to consider the possibilty that some sort of misunderstanding his occured here? I've seen you both on other places as decent guys and would like to see a full scale war only if really, really necessary. --] 23:00, 27 September 2006 (UTC)
			: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. ]<span style="background-color: #a6ffe0; padding: 3px; border-radius: 6px 6px 6px 6px;"><b>]</b></span>] 23:54, 11 April 2020 (UTC)

			== My intro altered ==
	I have no desire to revert or otherwise edit war with Byrgenwulf and am no longer involved in editing the page. ] <small>(])</small> 23:01, 27 September 2006 (UTC)

			In a recent edit ] wrote
	:My main point here, Sdedeo, is that citing the blog of Lubos Motl, a noted polemic opponent of LQG, does not cut it. Nor does linking to a search page of abstracts in support of a point, one of which abstracts actually contradicts the point made (the Phys Rev paper). And yes, the article I cited was among the list of abstracts which you "graciously provided" ostensibly to prove that the theory ''does'' violate Lorentz invariance. See for yourself: click on the second link you provided (not Motl's blog, which is worth less than nothing in this discussion), and you will see the paper I cited.
	:I also by no means believe that something is correct just because it is published in Phys Rev. But I ''do'' believe that by any scholarly standards, a Phys Rev citation is worth more than someone's blog. And I believe that the arguments offered in the paper I cited are far more rigorous and correct than the arguments ''contra''.
	:Sdedeo says it is a "common, mainstream" opinion that LQG violates Lorentz invariance. This is not really so. It may be a "common, mainstream" ''misconception'' that it does, and it is certainly a "common, mainstream" string theorist's strawman, but it is not actually the case. While ''some'' (but not all, not by any means all) of LQG's proponents may suggest violation of Lorentz invariance as a possible consequence of the theory, this is ''not'' part of the central "core" of the theory. Indeed, I would argue that the idea is a ''minority'' one among LQG's more respectable proponents, but one which has seized the imagination of many people, without them stopping to check their facts or think about the arguments a little. I never had any idea that this Lorentz invariance nonsense was quite as widespread as it is (this is not specifically my field, though I ''do'' profess a fairly thorough understanding of LQG).
	:I know that ] suggested that it might be a problem, and Sdedeo states on his userpage that he "trumpets" this idea, but this is a bit of an exaggeration. Indeed, Smolin main paper on Lorentz invariance violation (to which it would have been very easy to provide a direct link, by the way, instead of your page of search results), takes the approach that this breaking of Lorentz invariance ''may or may not'' be a problem, but ''if it were'', it doesn't matter, because his form of "]" covers it. As it turns out, this doubly special relativity has its own problems, but Smolin never even suggested that the Lorentz invariance violation was a ''necessary part'' of LQG, and nor did he stipulate that this new Lorentz group was a necessary "fix" to the theory. He merely said that some physicists have pointed to what they think might be a problem, and he offered a possible solution (he never really analysed the problem).
	:As far as Sdedeo's analysis goes, I don't accept it. I also found the paper to back me up ''after'' I had written my explanation above — although I had read it before, of course. I suppose I am used to thinking of LQG in a certain way...
	:Yes, the analysis I provided is for the hbar limit. That's the point of the whole argument, really. The hbar limit is a "minimal length", smaller than which there is nothing. But there is no sound reason to insist that Lorentz invariance ''must only'' occur in the classical limit, as you seem to be doing, that it is some sort of "emergent phenomenon"...whyever ''should'' this be the case? If it is preserved right at the "bottom", then all is well, because this is where the argument is centred. And in the classical limit, obviously, the results will be returned in accordance with expectations, so all is well. The photon dispersion thing, if it is what I am thinking of, is an ''extremely peripheral'' issue in LQG, and doesn't need Lorentz invariance violation anyway: slight differences from expected ratios for sufficiently large numbers should be accounted for by ''gravitational effects'', which is ultimately what the theory is trying to do, last time I checked. The same goes for the ] idea: these are all very much on the fringes, as it were, of LQG, and are neither a crucial or even a necessary part of the theory — they are hardly what might be called "canonical".
	:Sdedeo mentions that the "spin foam" model is more complicated. ''Yes'' the spin foam model ''is'' more complicated in some respects, but strictly speaking the spin foam model is not LQG. While both theories make use of loop quantisation, in LQG proper (the canonical approach) the spin networks are in three dimensions, but in the spin foam model they are in four dimensions. Of ''course'' there will be differences, but problems with the spin foam model belong in that model's article, or ]. The header of the LQG article ''specifically states'' that the article deals with the canonical approach, not theories of loop quantisation in general. But as has been pointed out, this is not the place for such debating these matters.
	:The bottom line is that the recent insertion did not even discuss the issue properly at all, as it ought to have: ''why'' might Lorentz invariance be violated? how is this dealt with? what are the arguments ''pro'' and ''contra''? Linking to a blog and two pages of search results (which do not even properly back up the claims made in the edit!) does not amount to proper citation, I don't think. I am therefore ''well'' entitled to remove the paragraph, and insist that it is done properly. And I am well entitled to claim that the insertion is nonsensical, as well.
	:But I likewise have no lust for edit warring. I think the article needs a complete rewrite, since it manages to say almost nothing. And the whole time, when it ''does'' say something, LQG's critics interject, LQG apologises, and the article hobbles on again. This doesn't work. Ideally, a whole article on loop quantisation would be lovely, and we really do need something on background independence/diffeomorphism invariance in the article — since it's the main idea behind LQG. I certainly do not wish to drive you away, Sdedeo (this article needs all the help it can get). It seems that we have merely had a very unfortunate misunderstanding, which is in all likelihood a side effect of the constant befrazzledness that is plaguing many corners of Misplaced Pages. ] 00:51, 28 September 2006 (UTC)

			"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."
	==Friendly Neighbour and Sdedeo==

			Sorry but your intro:
	A short explanation. I am also a hero of the . I'd like to explain that I do not claim expertise in the field of LQG. However, I am a physicist and I am able to understand the papers in the field. Sdedeo made a very botched job in convincing me that he's right. The abstract lists were not a way to support your views with scientific papers. All the papers I looked in seem to confirm that Byrgenwulf is right. Maybe it is because he has the ability to cite one paper at at time, not a whole repository of them.

			"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."
	I do believe the article needs a rewrite. In the case of Lorenz invariance it should be stated that there are different views on whether it is violated in LQG. As I have on another article discussion page, this is an encyclopedia, not a physics hanbook and all widely reported views should be presented here, even when they are wrong (but they status should be reported as well). Please read the linked edit to see what I mean before you hit me. ] 06:32, 28 September 2006 (UTC)

			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.
	:Here are the facts:

			And my intro:
	:#The article has claimed -- for who knows how many months -- that LQG generically preserves ordinary Lorentz invariance. This is ''incorrect''.
	:#I corrected this error, explained that the mainstream LQG view, held by both critics and proponents and folks in between, is that LQG violates Lorentz invariance, provided references and noted minority views. (For my choice of defining Lorentz invariance as a "minority" view, see comments below.)
	:#My edits were deleted -- not improved upon, not expanded, not refined: deleted -- twice.

			"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."
	:Byrgenwulf now claims that he deleted my contribution because it contained a reference to ], a critic of LQG, in addition to pointing the reader to a unedited list of papers on the question of Lorentz Violation. He also has some personal thoughts on LQG, which are irrelevant and seem mainly fixated on the argument he presented above which prove nothing about Loop Quantum Gravity beyond a toy model whose only input is "granularity on the Planck scale."

			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.
	:Friendly Neighbour claims both to be a physicist and yet also unable to browse a list a papers in the field to determine the truth of my claims. His claim that randomly clicking on the paper abstracts convinced him that Byrgenwulf is correct is hard to believe -- the ''first five papers'' in the list I linked to are discussions of Lorentz violating effects in Loop Quantum Gravity, and an informal count (plus or minus two, let's say) says that out of the ''seventeen'' papers I presented, only two claim unambiguously that standard Lorentz invariance is preserved in LQG (fourteen claim that Lorentz violation is violated in Loop Quantum Gravity and one paper appears to be a "false hit".)

			Encyclopedias aren't necessarily supposed to be user-friendly but they are supposed to be accurate! ].
	:] <small>(])</small> 14:24, 28 September 2006 (UTC)

			:First off, please don't use all caps because it almost seems as if you're shouting at people and we at Misplaced Pages 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. '''<sub>]</sub><sup>'']''</sup>''' 15:29, 4 October 2019 (UTC)
	::I did not say I'n not unable to parse your list. The problem is I do not have time to read 17 papers to check your claims. Even bigger problem is that neither do you! Otherwise you would not include ones that contradict your position. Sorry but if you do not have time to list 2-3 most important papers which confirm your edits (they would be useful as citations, anyway), I'm not going to do your research for you. ] 14:52, 28 September 2006 (UTC)

			I have edited my comments to tone things down ].
	Your claim is now not that you read the papers and they contradicted my statement, but that you did not read them at all. In any case, it is immaterial; you are unfamiliar with the research and yet felt happy to delete the claim as "controversial". ] <small>(])</small> 15:12, 28 September 2006 (UTC)
	:OK, I was not precise. ''Mea culpa''. What I meant was that I looked only into the papers of links provided by ] because he bothered to link actual papers, not search result lists and explain why they are relevant (it saves a lot of time as one needs not read the whole paper to see what it's supposed to prove). However, I did ask you three times (including once on your Talk page) for actual paper links. The time you wasted rebuking me could be used to find some papers which could actually make the article better balanced and better referenced. ] 15:19, 28 September 2006 (UTC)

	::I had dinner on Monday with some friends of mine: a computer scientist and a mathematician. The subject of wikipedia came up and the mathematician said that she found the entire project totally ridiculous. Every time she googles a term and comes to the wikipedia page she finds massive errors. Being a bit of an idealist, I said, yes, wikipedia has problems, but you know, it's a collaborative effort, why not edit the page and fix it -- you have all this valuable knowledge, why not make it available, it's a wonderful thing, etc., etc.. Little did I know that the average lifetime for such a contribution would be measured in hours.

			I have altered the intro - now a compromise between accuracy and reader-friendliness. Please note there is an important difference between:
	::You deleted my content before Byrgenwulf came along, so one assumes that this revert was made in a complete (as opposed to near-complete) state of ignorance. You are certaintly correct that time has been wasted. However, I did not waste my time -- ''you'' did. Further, your unwillingness to acknoledge the incomplete state of your knowledge, your belief that reading papers to correct it is unnecessary (even when a list is provided to you), and the fact that there are appear to be others like you forces me to agree with my friends. ] <small>(])</small> 15:42, 28 September 2006 (UTC)

			"incorporation of the matter of the standard model into the framework established for the pure quantum gravity case"
	:::You're wrong. I reverted you almost four hours after ] gave his reply on the talk page. This is my revert:
	:::*'''15:34, 27 September 2006 Friendly Neighbour''' (Talk \| contribs) (''rv the contested claims by Sdedeo to the last version by Byrgenwulf at least until a consensus emerges'')
	:::and these are the relevant changes on the Talk page:
	:::*'''15:39, 27 September 2006 Friendly Neighbour''' (Talk \| contribs) (›''Lorentz violation - Why I reverted Sdedeo'')
	:::*'''11:42, 27 September 2006 Byrgenwulf''' (Talk \| contribs) (›''Lorentz violation - Nonsense - I'll change the article later'')
	:::I see you are not willing providing any article links. You seem to believe that thrashing my reputation is a better way to improve the article. Which is funny because I was open to discussion and willing to change my mind if only you deigned to provide me the information I needed. So be it. ] 16:30, 28 September 2006 (UTC)

			and
	I have provided article links -- and discussed their content ''over and over'' on this page. Your first contribution was to delete these links. Your later contributions were to explain why you did not, and would not, read them. Yes, the timing does suggest that you read Byrgenwulf's (incorrect) statements before reverting. ] <small>(])</small> 16:34, 28 September 2006 (UTC)

			"unifying gravity with the other forces at the same time."
	:My later contributions can be summed up in one sentence: "''Please help me support you''". But you refused. OK, I'm done with the controversy. I'll not comment here at least until you decide to help yourself with some actual references (not a search result list - I can create them myself). ] 16:46, 28 September 2006 (UTC)

			Unifying forces has a specific meaning, for instance, the electric and magnetic forces were understood as different aspects of the same force, i.e. the electromagnetic force. This unified the electric and magnetic forces. Loop quantum gravity does not attempt to explain gravity and the other forces as being different aspects of an all encompassing single force. In fact gravity is not a force ].
	As I have said, I am no longer involved with editing the page, and I no longer have faith that wikipedia can create and maintain articles on technical subjects beyond a popular level. I will be curious to see if this particular issue is ever corrected given the way editors behave on physics-related articles. You and Byrgenwulf have decided to delete the content I provided; fine -- I will not engage in the usual wikipoliticking to reinstate it. I have provided you and Byrgenwulf with information about an important defect in the article, and, if you did not have them already, the tools to verify this defect and correct it. The rest is up to you. ] <small>(])</small> 17:03, 28 September 2006 (UTC)
			: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. '''<sub>]</sub><sup>'']''</sup>''' 22:02, 8 October 2019 (UTC)
			:Also, are you aware that your signature is not your actual user page? Your signature leads to ], but your user page is ] and your talk page is ] '''<sub>]</sub><sup>'']''</sup>''' 22:08, 8 October 2019 (UTC)

			== What does 3! mean? ==
	:Oh, I see I'm now featured in a name of a section. What a honor! - as ] would say.
	:Here is the contested (it's a fact) section in last version of ]'s edit:
	::<font color=magenta>Unlike General Relativity, LQG is acknoledged by both critics and supporters (see, ''e.g.'', ) not to satisfy local Lorentz invariance -- although controversy exists on this point (see, ''e.g.'', ). Tests of LQG-induced local Lorentz violation through modification of the photon ] have been suggested through searches for energy-dependent photon arrival from distant ] .</font>
	:I did make my search. The Lorenz invariance (not only of LQG but also of string theories) was indeed postulated by many authors. However most recent papers do not see any need for it. The strongest quotation I found comes from the very beginning of Fay Dowker, Joe Henson and Rafael D. Sorkin "", 2004:
	::"''Contrary to what is often stated, a fundamental spacetime discreteness need not contradict Lorentz invariance.''"
	:Therefore it's certainly not true that LQG '''needs''' to break the invariance. Although it's true that a lot of work has really went in proving it must. Therefore I feel that Byrgenwulf (and the third article you cited) say it's a common misconception. I feel some mention of the controversy is indeed needed in the article but probably not a whole section. That were my $0.02. ] 17:49, 28 September 2006 (UTC)

			In the section ] 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? ]<span style="background-color: #a6ffe0; padding: 3px; border-radius: 6px 6px 6px 6px;"><b>]</b></span>] 23:50, 11 April 2020 (UTC)
	As I explained above, a discrete spacetime alone is comptable with Lorentz invariance in the same fashion that quantization of angular momentum is compatable with rotational invariance. LQG postulates much, much more than just a fundamental spacetime discreteness and leads to the Lorentz violation effects that are discussed in at least ''fifteen'' papers I have given you and which you still refuse to read or remark upon. You have apparently still not read them or understood them in any way.

			== Make paragraph: Probabilistic loop quantum gravity ==
	If you had done more than read the first sentence of the abstract of the paper you cite, you would discover that after presenting a toy model, the authors proceed to discuss realistic LQG models. As the authors themselves state:

			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). <!-- Template:Unsigned IP --><small class="autosigned">— Preceding ] comment added by ] (]) 13:52, 27 September 2020 (UTC)</small> <!--Autosigned by SineBot-->
	:We now would like to also give a Lorentz invariant toy model with a fixed discrete length spectrum. Unfortunately, it can not be directly inspired from 3d Lorentzian loop quantum gravity since this theory predicts a continuous spectrum.

			== Last part about granulation of spacetime is misleading? ==
	When moving to a discussion of realistic LQG models, they use DSR:

			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.
	:Deformed Special Relativity (DSR) was especially introduced to address the issue of constructing a relativistic theory, i.e. one in which inertial observers see equivalent physics, with the equivalence being given by a group of transformations with both a invariant speed c and a invariant length lP . A feature of such a theory is now that the speed of light depends on the energy E of the beam and that c is only the speed of light as E → 0 . The theory is still Lorentz invariant, even though the action of the Lorentz transformations becomes non-linear, and the structure of the translations is modified.

			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 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. ] (]) 23:36, 25 November 2022 (UTC)
	It should be emphasised that when they declare the theory to be "Lorentz invariant" here, they do not mean Lorentz invariant under the usual ], but rather a different set -- as the authors say later, the Lorentz invariance is "hidden" (I believe what they mean here is that there is a different representation of SO(3,1) in play because the spacetime coordinates now no longer commute, although this is unclear to me.) See Eq. 64 of where the new Lorentz contraction formula is presented for DSR.

			== Loop Quantum Cosmology and its links with LQG ==
	The violation of Lorentz invariance in the usual sense can be seen trivially by the alteration of the photon dispersion relation. The number of times I must restate this point, and list articles that refer to this, is rapidly approaching infinity. ] <small>(])</small> 18:28, 28 September 2006 (UTC)

			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. ] (]) 10:13, 18 May 2023 (UTC)
	:Do you humbly aim at ] or ambitiously for ]? And what exactly is your point if you do not want to edit the article? ] 18:39, 28 September 2006 (UTC)

			== Theory and hypothesis ==
	First you delete my contribution. Then you refuse to read the relevant articles. Then, when I do attempt an (incomplete) explanation of an article of your choice, you make it clear you're not interested. This argument arose when you objected to my characterization of your and Byrgenwulf's deletions as ill-informed. ] <small>(])</small> 18:50, 28 September 2006 (UTC)

			It would help very much if theory and hypothesis are not used interchangeably.
	==further remarks==

			Loop quantum gravity is still a hypothesis. It might be described mathematically, but as far as I understand, it still explains nothing, can not be used for predictions and it is not yet possible to test it.
	From my talk page: "You should have started with an explanation on the article Talk page. The way you edited the article with no explanation made YOU look like the non-scientist party. That's why I reverted you. I could have been wrong but you seemed to send all the well-known "wiki-kookism" signals. However, I made it clear that I mean the revert as temporary. And you, instead of providing the links to the relevant papers in a human readable way, started a revert war."

			== Proposed Overview for the Page - However, It Requires Citations ==
	:Your claim is now that you reinstated the incorrect statement that LQG generically satisfies Lorentz invariance because it looked like I was a "wiki-kook". Perhaps your version of wikipedia has special ultraviolet coloring that tells you if an edit is by a "kook" -- if it does, you now know that it this coloring can not be trusted and that, in fact, there are better methods to determining the truth of a claim. There is also a strange contention that is not "human readable". ] <small>(])</small> 16:02, 28 September 2006 (UTC)

			Quantum gravity is a field of theoretical physics that aims to describe gravity according to the principles of quantum mechanics. This complex topic encompasses various theories and models:
			String-net liquid: A condensed matter physics model that involves only closed loops. It provides a potential explanation for the emergence of photons, electrons, and other elementary particles as excitations of the string-net liquid.
			String theory: A theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. It is a candidate for the theory of everything, aiming to unify all fundamental forces of nature, including gravity.
			Supersymmetry: A principle that proposes a type of symmetry between bosons (particles that follow Bose-Einstein statistics) and fermions (particles that follow Fermi-Dirac statistics). This symmetry could solve various problems in particle physics, such as the hierarchy problem.
			Topos theory: A branch of mathematical category theory that provides a foundation for geometry and logic. It has applications in the study of quantum mechanics and theoretical computer science.
			Einstein–Cartan theory: A classical theory of gravitation that extends general relativity by incorporating the intrinsic angular momentum (spin) of matter. It predicts different spacetime structures in the presence of spin-torsion interactions.
			These concepts are part of the broader quest to develop a coherent theory of quantum gravity. ] (]) 19:19, 21 October 2024 (UTC)

			:The suggestion introduces various theories and concepts (such as string-net liquid, string theory, supersymmetry, topos theory, and Einstein–Cartan theory) that are not directly related to Loop Quantum Gravity. While LQG is a theory of quantum gravity, the other theories mentioned are distinct and generally belong to different areas of theoretical physics. For example:
			:* '''String theory''' is an alternative approach to quantum gravity, not specifically related to LQG.
			:* '''String-net liquid''' is a condensed matter model. There is a subtle but noteworthy connection between string-nets and LQG, however, it is not central to LQG.
			:* '''Supersymmetry''' is a concept in high-energy physics, not directly part of LQG.
			:* '''Topos theory''' and '''Einstein-Cartan theory''' are also not central to LQG, though they could intersect with broader discussions in theoretical physics.
			:The suggestion is trying to cover a broad range of topics in theoretical physics without focusing specifically on LQG itself. A Misplaced Pages page's "overview" should provide a concise, focused summary of the subject in question—in this case, LQG—without straying into unrelated theories unless there is a specific connection. For example, while LQG does deal with quantum gravity and the quantization of spacetime, it is not directly concerned with supersymmetry or topos theory, so bringing them up here creates confusion.
			:Mentioning concepts like '''string theory''', '''supersymmetry''', and '''Einstein-Cartan theory''' without clearly explaining their relationship (or lack thereof) to LQG could mislead readers into thinking these are all part of the same theory or framework. This can detract from the clarity of what Loop Quantum Gravity is and how it distinguishes itself from other approaches. ] (]) 00:19, 8 November 2024 (UTC)

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?? question ??

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)

Yes, you are wrong. LQG models *sapce* using a spin-network, and it predicts that there is a quantum of area, and probably a quantum length. LQG does not work that well with time, and it is not clear in any way that there is a quantum of time in the same way as there are quanta of space.WKB2020 (talk) 09:35, 20 June 2021 (UTC)

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!

Then why don't you go to Simple English Wiki kid? That's clearly your and your father's level. —Preceding unsigned comment added by 99.227.131.13 (talk) 04:16, 25 November 2010 (UTC)

The relevant question is -- is the Misplaced Pages 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 Misplaced Pages, 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 Misplaced Pages (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)

"a matter of milliseconds"? I assume you live somewhere that has Fiber-To-The-Home? Jimw338 (talk) 22:27, 23 September 2015 (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 Misplaced Pages 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, 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. 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. Misplaced Pages 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 Misplaced Pages 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 Misplaced Pages 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 think that this piece of the whole article does a better job that this wikipedia article in explaining what loop quantum gravity is. —Preceding unsigned comment added by 62.77.56.12 (talk) 11:38, 9 December 2009 (UTC)

While I have the greatest respect for people who strive to document these complex topics, I wholeheartedly agree with Deadlyvices' objections. Abstract physical concepts that are very difficult to understand have been documented to accommodate readers of nearly all levels, which means this article is unnecessarily complicated. The greatest physicists of all time were able to make earth-shattering discoveries because of their ability to think in physical pictures like speeding trains and such. The most famous example is probably the apple falling on Newton's head. I know that this becomes rather difficult when talking about non-Newtonian physics, but Albert Einstein also thought in 'physical pictures', even though the subjects he studied were far more abstract than gravity. I strongly suggest you take it upon you to represent the intensely abstract LQG with more 'graspable' presentations. Highly respected scientists like Michio Kaku do a great job at publishing literature on advanced scientific concepts that is understandable by pretty much anyone. That said, I'm not telling you to drop the more complex content. I'm merely asking you to at least provide interested readers who do not study physics with a solid explanation of the basics of LQG, significantly increasing the importance and value of this article. — Preceding unsigned comment added by 81.243.33.132 (talk) 18:34, 24 August 2011 (UTC)

Should there be another LQG entry simplified for popular understanding in popular press?

http://en.wikipedia.org/String_theory For a generally accessible and less technical introduction to the topic, see Introduction to M-theory. — Preceding unsigned comment added by 75.81.141.8 (talk) 03:35, 16 March 2013 (UTC)

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 Misplaced Pages 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)

Cool story bro. Fact is, this material has to be abstracted and generalized to the point of distortion in order for it to be 'easy to understand'. The problem is egotistical readers expecting to be able to easily understand whatever they come across, certain that their vast intellects are surely capable of grasping any given topic instantly. If they don't understand something, it's not their fault - it's the material's! Pathetic. Unsigned, because, well, fuck you that's why.

Well, bro, I don't expect anything of the sort. Most people, not me, think that this article is jargonistic and poorly written, and if a professional scientist like me finds it difficult it's not because I'm egotistical to the extent that I expect everything to be handed to me on a plate. Perhaps we have a point. Perhaps its written by a crappy author who is too arrogant to recognise he isn't very good at explaining complex topics. Perhaps it shouldn't be written about at all in an encyclopaedia if it can't be written about comprehendably. And fuck you too, you arrogant, abusive and cowardly little man (that much I'm certain about). Deadlyvices (talk) 22:33, 20 July 2011 (UTC)

Just revisited this page. Up until the section *Constraints and their Poisson bracket algebra* it's pretty good. After that it's totally incomprehensible, over-technical shit. Deadlyvices (talk) 11:53, 7 July 2015 (UTC)

I find much of this article incomprehensible. I don't begrudge the presence of the complicated detail as well, but there should be an introductory section that is more clear and simple, without unnecessary jargon. I read A Brief History of Time at age 12 and understood it as far as it went, so I'm certain that exceedingly complicated and unintuitive concepts can be explained at least a little better than this article does. 2601:441:4680:3230:8049:1915:7B9F:826A (talk) 15:01, 13 June 2019 (UTC)

Sixteen years on from my original gripe, and whoever wrote this article managed to make it even more dense and incomprehensible.

That's one hell of an achievement.

Deadlyvices (talk) 12:33, 20 October 2023 (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)

Please nobody take this suggestion seriously. I am a professional chemist and the idea that there are scientist that "dont even bother with paper journals anyway" or that personal websites or "scientific" blogs are reliable sources, is laughable.178.15.151.163 (talk) 13:44, 18 February 2016 (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

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)

The good, the bad, and the ugly

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)

Uh-huh? So "formalism", "supersymmetry" and "gauge theory" are all part of your "basic understanding of basic physics"? You must be super-duper smart.178.15.151.163 (talk) 13:47, 18 February 2016 (UTC)

I have a high school level physics i got a B in when 17, so basic physics....definitely didn't mention "diffeomorphism-invariant" I agree with the original comment 79.64.152.157 (talk) —Preceding undated comment added 23:51, 29 January 2020 (UTC)

Citation needed?

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)

You are quite right, looking for it as I write.

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/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)

Formula?

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)

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) . m.

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)

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)

Overlooked aspects and gaining information

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)

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 Misplaced Pages! 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)

black hole entropy contradictions

the below 2 passages contradict one another, Carlo Rovelli's edit is based on more recent research which does away with the Immirzi parameter and Carlo Rovelli is a LQG researcher who has written papers and textbooks.

I propose deleting the older bottom paragraph as no longer current.

Another application of LQG concerns understanding the thermal behavior of black holes. A recent success of the theory in this direction is the computation of the entropy of all non singular black holes . The result is the expected formula S=A/4, where S is the entropy and A the area of the black hole, derived by Bekenstein and Hawking on heuristic grounds. This is the only known derivation of this formula from a fundamental theory, for the case of generic non singular black holes.

Another problem is that a crucial free parameter in the theory, known as the Immirzi parameter, can only be computed by demanding agreement with Bekenstein and Hawking's calculation of the black hole entropy. Loop quantum gravity predicts that the entropy of a black hole is proportional to the area of the event horizon, but does not obtain the Bekenstein-Hawking formula S = A/4 unless the Immirzi parameter is chosen to give this value. A prediction directly from theory would be preferable.

Vandalism 180.149.8.81

Main article: History of loop quantum gravity

In 1986, "someone" reformulated Einstein's general relativity in a language closer to that of the rest of

changed that to twitch

(cur | prev) 02:18, 14 May 2013‎ AnomieBOT (talk | contribs)‎ . . (112,172 bytes) (+53)‎ . . (Rescuing orphaned refs ("ReferenceA" from rev 554904443)) (undo) (cur | prev) 16:08, 13 May 2013‎ 180.149.8.81 (talk)‎ . . (112,119 bytes) (+4)‎ . . (→‎History) (undo) (cur | prev) 16:01, 13 May 2013‎ 180.149.8.81 (talk)‎ . . (112,115 bytes) (-9)‎ . . (→‎History) (undo) (cur | prev) 15:56, 13 May 2013‎ 180.149.8.81 (talk)‎ . . (112,124 bytes) (-9,375)‎ . . (→‎An overview) (undo) (Tag: section blanking) (cur | prev) 15:54, 13 May 2013‎ 180.149.8.81 (talk)‎ . . (121,499 bytes) (+7)‎ . . (→‎An overview) (undo)

i think someone should undo 180.149.8.81 vandals and then lock the article only ibyan and rovelli may add content ban 180.149.8.81

Time in general relativity

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)

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/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)

The loop quantum gravity diffusion limit

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)

MathML problem

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)

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Another citation needed?

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)

Multiple redundant footnotes

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)

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)

My intro altered

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 Misplaced Pages 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} 15:29, 4 October 2019 (UTC)

I have edited my comments to tone things down User: IBayn.

I have altered the intro - now a compromise between accuracy and reader-friendliness. Please note there is an important difference between:

"incorporation of the matter of the standard model into the framework established for the pure quantum gravity case"

and

"unifying gravity with the other forces at the same time."

Unifying forces has a specific meaning, for instance, the electric and magnetic forces were understood as different aspects of the same force, i.e. the electromagnetic force. This unified the electric and magnetic forces. Loop quantum gravity does not attempt to explain gravity and the other forces as being different aspects of an all encompassing single force. In fact gravity is not a force User: IBayn.

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} 22:02, 8 October 2019 (UTC)

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} 22:08, 8 October 2019 (UTC)

What does 3! mean?

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)

Make paragraph: Probabilistic loop quantum gravity

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)

Last part about granulation of spacetime is misleading?

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)

Loop Quantum Cosmology and its links with LQG

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)

Theory and hypothesis

It would help very much if theory and hypothesis are not used interchangeably.

Loop quantum gravity is still a hypothesis. It might be described mathematically, but as far as I understand, it still explains nothing, can not be used for predictions and it is not yet possible to test it.

Proposed Overview for the Page - However, It Requires Citations

Quantum gravity is a field of theoretical physics that aims to describe gravity according to the principles of quantum mechanics. This complex topic encompasses various theories and models: String-net liquid: A condensed matter physics model that involves only closed loops. It provides a potential explanation for the emergence of photons, electrons, and other elementary particles as excitations of the string-net liquid. String theory: A theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. It is a candidate for the theory of everything, aiming to unify all fundamental forces of nature, including gravity. Supersymmetry: A principle that proposes a type of symmetry between bosons (particles that follow Bose-Einstein statistics) and fermions (particles that follow Fermi-Dirac statistics). This symmetry could solve various problems in particle physics, such as the hierarchy problem. Topos theory: A branch of mathematical category theory that provides a foundation for geometry and logic. It has applications in the study of quantum mechanics and theoretical computer science. Einstein–Cartan theory: A classical theory of gravitation that extends general relativity by incorporating the intrinsic angular momentum (spin) of matter. It predicts different spacetime structures in the presence of spin-torsion interactions. These concepts are part of the broader quest to develop a coherent theory of quantum gravity. 184.147.220.93 (talk) 19:19, 21 October 2024 (UTC)

The suggestion introduces various theories and concepts (such as string-net liquid, string theory, supersymmetry, topos theory, and Einstein–Cartan theory) that are not directly related to Loop Quantum Gravity. While LQG is a theory of quantum gravity, the other theories mentioned are distinct and generally belong to different areas of theoretical physics. For example:

String theory is an alternative approach to quantum gravity, not specifically related to LQG.
String-net liquid is a condensed matter model. There is a subtle but noteworthy connection between string-nets and LQG, however, it is not central to LQG.
Supersymmetry is a concept in high-energy physics, not directly part of LQG.
Topos theory and Einstein-Cartan theory are also not central to LQG, though they could intersect with broader discussions in theoretical physics.

The suggestion is trying to cover a broad range of topics in theoretical physics without focusing specifically on LQG itself. A Misplaced Pages page's "overview" should provide a concise, focused summary of the subject in question—in this case, LQG—without straying into unrelated theories unless there is a specific connection. For example, while LQG does deal with quantum gravity and the quantization of spacetime, it is not directly concerned with supersymmetry or topos theory, so bringing them up here creates confusion.

Mentioning concepts like string theory, supersymmetry, and Einstein-Cartan theory without clearly explaining their relationship (or lack thereof) to LQG could mislead readers into thinking these are all part of the same theory or framework. This can detract from the clarity of what Loop Quantum Gravity is and how it distinguishes itself from other approaches. Ibayn (talk) 00:19, 8 November 2024 (UTC)

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