Response to 'On negative refraction in classical vacuum'

摘要

An analysis [McCall, M.W.J. Mod. Opt. 2007, 54, 119-128] based on the electromagnetic energy-momentum tensor, to explore the prospects for negative-phase-velocity (NPV) propagation in gravitationally affected vacuum, did not consider (i) the total energy-momentum tensor and (ii) the global perspective of curved spacetime. Also, the appearance of NPV was wrongly attributed to a change in signature of the spacetime metric.