Talk:Canonical general relativity

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[edit] Several Points

I intend to attempt a reasonably comprehensive rewrite of this article over the next few days. There are a few important reasons why I think that the article needs this:

1) The article opens by stating "In physics, canonical quantum gravity is an attempt to quantize the canonical formulation of general relativity." While this is perfectly correct, it's hardly a great first sentence for an article which is ostensibly concerned with canonical gravity.

2) The majority of the article seems to obfuscate the distinction between canonical gravity and the canonical quantisation of gravity (the first half of the article is particularly at fault in this). These are distinct topics, although canonical quantisation of gravity obviously draws heavily on the canonical formulation of gravity.

3) The article probably needs to be renamed. As it currently stands, it is a description of the canonical picture of general relativity. There exist several other theories of gravity which admit straightforward canonical descriptions. Furthermore, physicists who actually work in this area always make a distinction between canonical general relativity and canonical versions of other theories such as Brans-Dicke or relational models. (I have already corrected this.)

4) Although the article begins by talking about canonical quantum gravity, the author apparently quickly lost steam and all mention of this topic has disappeared by the time the article finishes.

5) The references are a mess. The important work on constrained systems is Dirac's, not Bergmann's. Furthermore, the idea that an article on canonical general relativity can succeed without, for example, referencing the original ADM paper is ridiculous.

Given that the talk page for this article is a graveyard, I'm simply going to go ahead and make what I believe to be the necessary changes. I shall spend the next week or two writing an article on paper before uploading it here. Should anyone object, I'd appreciate if we could discuss any further changes or reverts here on the talk page. St Cyrill 02:07, 18 August 2006 (UTC)

I wrote this article, and I agree with the broad thrust of your points. I think you're missing the point that the article is a "stub" (i.e. a sketch or an incomplete article) which you are welcome to expand. Let me say that
  1. Canonical quantum gravity redirects to this article.
  2. I don't really understand this point. The article doesn't discuss the quantization. That bit was left out.
  3. Fine, but instead of having been renamed it could have been expanded to include those theories.
  4. True. It also fails to discuss Hartle-Hawking, which would have been nice, among many other things.
  5. Read it again. Dirac's contribution is perfectly clear. ADM wasn't referenced because, in the existing text, there is no occasion to. –Joke 04:07, 27 September 2006 (UTC)

There is no formula in this headword discovered by B. DeWitt. All is work of Dirac and ADM. —Preceding unsigned comment added by 89.103.146.30 (talk) 08:07, 24 February 2008 (UTC)

[edit] Foliation

The article does not mention the foliation of space-time into space and time, in the sense that every manifold is descomposed in the form (T,M) where T is a "time" dimension and M is the spatial part of the Manifold (x,y,z) hence for the Riemann scalar inside the Einstein-Hilbert Lagrangian you have:

R00 + R(3)

R00 = T00 = ρ

and R00

R(3)

are "energy" densities so when you integrate them respect to the measure \sqrt-g^(3) you get the energy of the system.