Can light signals travel faster than c in nontrivial vacua in flat space-time? Relativistic causality II
In this paper, we show that the Scharnhorst effect (vacuum with boundaries or a Casimir-type vacuum) cannot be used to generate signals showing measurable faster-than- c speeds. Furthermore, we aim to show that the Scharnhorst effect would violate special relativity, by allowing for a variable speed of light in a vacuum, unless one can specify a small invariant length scale. This invariant length scale would be agreed upon by all inertial observers. We hypothesize the approximate scale of the invariant length.