Talk:Hamiltonian constraint
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It is incomprensible. It is with no doubt copied from somewhere and is excerpted from somewhere as clear from the sentence "So, using Occam's razor again (we used it the first time ...) ...".
It is obviously copied from a (may be copiright or may be free copirighted) article, book or note of an advanced course of theoric physics. I have a degree in Physics but I can not understand it, in the sense that I could neither read it. It is only an excerpt. It does not explain the argument. It is ruther far from the article wanted in wikipedia. For me, as well maybe copyvio it is a candidate to WP:VFD AnyFile 12:04, 12 Nov 2004 (UTC)
[edit] Copyedit
I have cleaned up a bit. Anyone who fancies the challenge of further improving should probably at least read Hamiltonian mechanics first, unless they know this stuff already. Rich Farmbrough 21:56, 25 Mar 2005 (UTC)
[edit] June 28 Editing
I basically removed the text and replaced it with a short description of the Hamiltonian constraint, which is a technical term for a specific operator in general relativity, in particular in quantum gravity. The older article appeared to mix a some notes on it, with nonsense, with parts of a general discussion of constrained hamiltonians, which are different. Salsb 29 June 2005 15:33 (UTC)
[edit] Article too narrow
I feel that the archived version is actually better than the present one in some aspects, since the Hamiltonian constraint arises from any theory that admits a Hamiltonian and is reparametrisation-invariant. The present article only talks about loop quantum gravity while even classical general relativity has this constraint. Even non-relativistic particle dynamics has this, for example, if you consider the Jacobi action. Of course, in all but the quantum gravity case the constraint does not pose real problems for the theories and is rarely discussed (many books on classical GR doesn't even mention the Hamiltonian formulation at all), but that doesn't mean they are not important (since you have to understand them before going to the quantum gravity case).
It is nonetheless very obvious that the archived version is simply a lifting from some paper or book that a person who would want to look it up has almost no hope of comprehension at all. My idea is to first write something brief about it in the Hamiltonian mechanics article and then refer to this article where here it is explained in more details, including its significance in the quantum case. Anyone has any comments or different ideas? Amadeoh 15:32, 8 May 2007 (UTC)
I'm studying up on this, and from my understanding it's specifically any gauge invariance is the time reparametrization invariance that has a Hamiltonian constraint if the time component of the canonical position transforms as a scalar. It can transform as a connection, and then the Hamiltonian wouldn't be zero, and there would still be gauge invariance...but this is not really used in physics, it's just a mathematical example from my understanding. (See Henneaux and Teitelboim's Quantization of Gauge Theories chapter 4 "Generally Covariant Systems"). I think this approach of having a classical explanation using Hamiltonians and Poisson brackets, etc. then Dirac Quantize it is the best approach. I'll try to help as best as I can. pqnelson —Preceding comment was added at 20:15, 28 November 2007 (UTC)
