Title:	Canonical gravity, diffeomorphisms and objective histories
Authors:	Samuel, J.
Issue Date:	Nov-2000
Publisher:	IOP Publishing Ltd.
Citation:	Classical and Quantum Gravity, 2000, Vol.17, p4645-4654
Abstract:	This paper discusses the implementation of diffeomorphism invariance in purely Hamiltonian formulations of general relativity. We observe that, if a constrained Hamiltonian formulation derives from a manifestly covariant Lagrangian, the diffeomorphism invariance of the Lagrangian results in the following properties of the constrained Hamiltonian theory: the diffeomorphisms are generated by constraints on the phase space so that: (a) the algebra of the generators reflects the algebra of the diffeomorphism group; (b) the Poisson brackets of the basic fields with the generators reflects the spacetime transformation properties of these basic fields. This suggests that in a purely Hamiltonian approach the requirement of diffeomorphism invariance should be interpreted to include (b) and not just (a) as one might naively suppose. Giving up (b) amounts to giving up objective histories, even at the classical level. This observation has implications for loop quantum gravity which are spelled out in a companion paper. We also describe an analogy between canonical gravity and relativistic particle dynamics to illustrate our main point.
Description:	Restricted Access.
URI:	http://hdl.handle.net/2289/3257
ISSN:	0264-9381
Alternative Location:	http://dx.doi.org/10.1088/0264-9381/17/22/305
Copyright:	2000 IOP Publishing Ltd.
Appears in Collections:	Research Papers (TP)

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