Pitts, J. Brian (2019) What Are Observables in Hamiltonian Einstein-Maxwell Theory? [Preprint]

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Abstract

Is change missing in Hamiltonian Einstein-Maxwell theory? Given the most common definition of observables (having weakly vanishing Poisson bracket with each first-class constraint), observables are constants of the motion and nonlocal. Unfortunately this definition also implies that the observables for massive electromagnetism with gauge freedom (Stueckelberg) are inequivalent to those of massive electromagnetism without gauge freedom (Proca). The alternative Pons-Salisbury-Sundermeyer definition of observables, aiming for Hamiltonian-Lagrangian equivalence, uses the gauge generator G, a tuned sum of first-class constraints, rather than each first-class constraint separately, and implies equivalent observables for equivalent massive electromagnetisms.

For General Relativity, G generates 4-dimensional Lie derivatives for solutions. The Lie derivative compares different space-time points with the same coordinate value in different coordinate systems, like 1 a.m. summer time vs. 1 a.m. standard time, so a vanishing Lie derivative implies constancy rather than covariance. Requiring equivalent observables for equivalent formulations of massive gravity confirms that G must generate the 4-dimensional Lie derivative (not 0) for observables.

These separate results indicate that observables are invariant under internal gauge symmetries but covariant under external gauge symmetries, but can this bifurcated definition work for mixed theories such as Einstein-Maxwell theory? Pons, Salisbury and Shepley have studied G for Einstein-Yang-Mills. For Einstein-Maxwell, both the electromagnetic field strength F and the metric g are invariant under electromagnetic gauge transformations and covariant (changing by a Lie derivative) under 4-dimensional coordinate transformations. Using the bifurcated definition, these quantities count as observables, as one would expect on non-Hamiltonian grounds.

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Item Type:	Preprint
Creators:	Creators Email ORCID Pitts, J. Brian jbp25@cam.ac.uk 0000-0002-7299-5137
Additional Information:	Forthcoming in _Foundations of Physics_
Keywords:	gauge freedom, constrained Hamiltonian dynamics, problem of time, observables
Subjects:	General Issues > Scientific Metaphysics Specific Sciences > Physics > Cosmology General Issues > Operationalism/Instrumentalism Specific Sciences > Physics > Quantum Gravity Specific Sciences > Physics > Relativity Theory Specific Sciences > Physics > Symmetries/Invariances
Depositing User:	Dr. Dr. J. Brian Pitts
Date Deposited:	25 Jul 2019 04:01
Last Modified:	25 Jul 2019 04:01
Item ID:	16260
Subjects:	General Issues > Scientific Metaphysics Specific Sciences > Physics > Cosmology General Issues > Operationalism/Instrumentalism Specific Sciences > Physics > Quantum Gravity Specific Sciences > Physics > Relativity Theory Specific Sciences > Physics > Symmetries/Invariances
Date:	July 2019
URI:	https://philsci-archive.pitt.edu/id/eprint/16260

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