Accelerating photons with gravitational radiation

Abstract

The nature of superluminal photon propagation in the gravitational field describing radiation from a time-dependent, isolated source (the Bondi-Sachs metric) is considered in an effective theory which includes interactions which violate the strong equivalence principle. Such interactions are, for example, generated by vacuum polarisation in conventional QED in curved spacetime. The relation of the resulting light-cone modifications to the Peeling Theorem for the Bondi-Sachs spacetime is explained.

Constructing Time Machines

“…Many examples of the Drummond-Hathrell effect in a variety of gravitational wave, black hole and cosmological spacetimes have been studied [11,38,39,15] etc. The black hole cases are particularly interesting, and it is found that for photons propagating orbitally, the light cone is generically modified and superluminal propagation occurs.…”

“…Outgoing radial null geodesics are associated with ℓ µ while incoming null geodesics have tangent vector n µ in the obvious Newman-Penrose basis [41,15]. The metric functions have asymptotic expansions near I + for large luminosity distance r. We just need those for the functions γ ± δ, which correspond to the two independent gravitational wave polarisations:…”

“…To sharpen this discussion, Dolgov and Novikov [14] have proposed a construction, again involving two gravitational sources in relative motion, in which Drummond-Hathrell superluminal propagation is claimed to allow signals to be sent into the past light cone of the emitter. In section 5, we analyse the Dolgov-Novikov proposal in the context of superluminal propagation in gravitational radiation spacetimes of Bondi-Sachs type [15]. We conclude once more that causality-violating trajectories, although apparently occurring when the two gravitational sources are assumed to act entirely independently, do not arise when the full spacetime involving both sources is considered consistently.…”

Quantum mechanics versus equivalence principle

“…On the other hand, Einstein's equivalence principle (EEP), which locally encompasses both the principles mentioned above, can be understood as the requirement that spacetime is Riemannian and, as a consequence, has at each point a local inertial frame [1]. Accordingly, the EEP is a statement about purely local effects.…”

Quantum gravitational optics: Effective Raychaudhuri equation

“…The Newman-Penrose (NP) formalism has been found to be an elegant way of analyzing the results in the SEP violating cases. Quantum gravitational optics attributes velocity shift and null cone modification at each point to only a single NP scalar for each of the Ricci and Weyl tensors, namely Φ 00 and Ψ 0 respectively [6]. The question is what would be the role of other NP scalars in determining the forms of Ricci and Weyl tensors?…”