Talk:Loop quantum gravity

/Archive 1 - up to May 2004
/Archive 2 - created 29 November 2004
/Archive 3 - As of August 2005

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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. :-)

I just pray this does not reignite the flame/editwar.

--Hfarmer 00:49, 23 August 2005 (UTC)[reply]

unverified

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.

string theory does not predict or allows for post-diction calculation of masses. extradimensions remains unverified as of 2005.

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 Wikipedia: http://en.wikipedia.org/wiki/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” Wikipedia (http://en.wikipedia.org/wiki/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.

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 $i={\sqrt {(}}-1)$ 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

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.

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. --Hfarmer 01:56, 3 November 2005 (UTC)</math>[reply]

Why Heyting algebra?

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.

-- hendrik@pooq.com

Stop opinionating!

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

"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. Avriette 01:50, 12 December 2005 (UTC)[reply]

"LQG has failed to gain support in the physics community" is an unsupported generalization.

If one wishes to opinionate or preach, they can place their opinions HERE, like this:

Problems

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.

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.

Other problems associated with LQG can be found in Talk:Loop Quantum Gravity Archive 3

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.

Also, as Hfarmer said, Wikipedia is to be read by the educated layman. "Nonperturbative quantization of diffeomorphism-invariant gauge theories" indeed!

J M Rice 20:47, 25 November 2005 (UTC)[reply]

Criticisms to LQG, Shortening the Article, and issues around.

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. Wikipedia 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 Criticisms and Notes on Loop Quantum Gravity What do you people think of it? nihil 20:29, 29 November 2005 (UTC)[reply]

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

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.

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? --Hfarmer 03:49, 7 December 2005 (UTC)[reply]

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.

- - - 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.

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. --Egg ✉ 17:53, 30 December 2005 (UTC)[reply]

It has become clear that this article needs rewriting

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.) --66.92.130.180 00:24, 3 January 2006 (UTC)[reply]