Physical Review · 1963 · 232 citations · 3 references
Natural SciencesPhysicsGravitationGravityRelativityCoordinate SystemsCoordinate TransformationsGauge TheoryGeneral RelativityGravitational FieldsLorentz TransformationsConstraint EquationsCoordinate Transformation InvarianceGauge ConditionsGauge SymmetriesGauge TransformationsLocal Coordinate SystemsLocal Gauge InvarianceSpacetime Coordinates
Four field variables lack canonical partners due to differential constraint equations, interpretable as space‑time coordinate displacements. The authors construct a gravitational action operator invariant under general coordinate and local Lorentz transformations. They restrict arbitrariness by imposing gauge and coordinate conditions, defining a time gauge that locks local time axes to the general coordinate time axis. The action operator identifies canonical pairs, shows that in a distinguished coordinate class the gravitational field variables are independent of coordinate displacement parameters, preserves Lorentz transformation freedom, and that generators of spatial translations and rotations obey correct commutation relations, though Lorentz invariance remains undecided because the energy density operator is only implicit.
A gravitational action operator is constructed that is invariant under general coordinate transformations and local Lorentz (gauge) transformations. To interpret the formalism the arbitrariness in description must be restricted by introducing gauge conditions and coordinate conditions. The time gauge is defined by locking the time axes of the local coordinate systems to the general coordinate time axis. The resulting form of the action operator, including the contribution of a spinless matter field, enables canonical pairs of variables to be identified. There are four field variables that lack canonical partners, in virtue of differential constraint equations, which can be interpreted as space-time coordinate displacements. In a physically distinguished class of coordinate system the gravitational field variables are not explicit functions of the coordinate displacement parameters. There remains the freedom of Lorentz transformation. The generators of spatial translations and rotations have the correct commutation properties. The question of Lorentz invariance is left undecided since the energy density operator is only given implicitly.
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