Talk:Quantum gravity/Archive for 2013

Cleanup
"However, gravity is nonrenormalizable.[13] Also in one loop approximation ultraviolet divergencies cancel on mass shell."

What is that second sentence trying to say? RJFJR (talk) 14:51, 13 January 2012 (UTC)


 * This article omits all references to 5 peer-reviewed published papers which used quantum gravity to accurately predict dark energy in 1996, two years prior to discovery. Even if mainstream consensus completely ignores the facts with documented lies about spin-2 gravitons this doesn't mean they must forever main unreferenced in Wikipedia, which is "supposed" to be better than other sources, for its whole point is in bringing together a wide range of different facts that can't be found in sources produced by smaller editorial teams. 81.157.42.222 (talk) 22:46, 19 November 2012 (UTC)

What does "However, it is not yet clear what the full field equation will govern the dilaton in higher dimensions." mean? The construction "...what the X will govern the Y in Z" confuses me grammatically (unless X="heck" or something like that). --Fatio de Duillier (talk) 13:27, 1 May 2013 (UTC)
 * I hope the revised sentence is more clear.TonyMath (talk) 04:36, 7 June 2013 (UTC)

New flow diagram of physical theories


Although File:Quantum gravity.png is very nicely made, how about a more complete one in SVG? M&and;Ŝc2ħεИτlk 08:21, 8 May 2013 (UTC)


 * It's prettier, but much larger in filesize. --Rpresser 05:41, 15 June 2013 (UTC)


 * Yours will stay, after a discussion at Wikiproject physics my proposal didn't seem to get far, and it's fair enough. Indeed byte size is important also.
 * Good work, I still like your version. ^_^ M&and;Ŝc2ħεИτlk 05:50, 15 June 2013 (UTC)

Yikes!
I went ahead and rewrote the lead of this article after noticing that that it repeats a lot of widespread misconceptions about quantum gravity. Specifically, the problems are the following:

1. It treats "quantum mechanics" and "general relativity" as two theories that need to be "unified" when in fact these two subjects are not "theories" in the same sense. General relativity is a theory that postulates a specific equation for describing the gravitational field, while quantum mechanics is more of a general formalism for fundamental physics. It's more correct to say that the aim of quantum gravity is to describe gravity according to the principles of quantum mechanics. It's also problematic to say that a theory of quantum gravity should "yield the same predictions as ordinary quantum mechanics in conditions of weak gravity" since quantum mechanics is really more of a language, not a predictive theory.

2. In a couple of places, the article says that quantum gravity is all about "quantizing" general relativity, but this is not quite right. When you talk about "quantizing" a theory, you mean deforming a classical theory by replacing the classical algebra of observables by a noncommutative algebra of operators represented on a Hilbert space. In string theory, the most mainstream approach to quantum gravity, one does not quantize general relativity; rather, one constructs a quantum mechanical theory that reproduces general relativity in a certain low energy limit.

3. The article states that motivation for quantum gravity comes from "the remarkable success of the quantum theories of the other three fundamental interactions, and from experimental evidence suggesting that gravity can be made to show quantum effects". The real reason for studying quantum gravity is that you cannot couple a classical theory to a quantum theory. Since matter behaves quantum mechanically and can be described by superpositions of quantum states, the gravitational field must also be described quantum mechanically.

I also removed the "Beyond the Standard Model" template since this term usually refers to things like supersymmetry and grand unified theories, not quantum gravity per se. Polytope24 (talk) 17:40, 25 August 2013 (UTC)

Breakthrough?
This article was just published. I'm not an expert but it looks like something new....http://www.mpg.de/7513900/quantum-gravitation-Big-Bang The most interesting man in the world (talk) 17:55, 5 September 2013 (UTC)

Virtual Micro-Black Hole (VMBH) GUP
Virtual Micro-Black Holes (VMBH) were proposed by Fabio Scardigli in 1999 (http://arxiv.org/pdf/hep-th/9904025.pdf). Scardigli proposes that the vacuum can be entirely modeled as virtual-micro black holes. These virtual micro black holes produce a modification of the Heisenberg uncertainty relations, thereby resulting in a Generalized Uncertainty Principle (GUP), which can be a useful effective theory to describe a low energy limit of quantum gravity, both for quantum loop and string theories. Eladganl (talk) 04:46, 18 November 2013 (UTC)