Fran,
The important paper in this fine write-up is from Barton in 1990 - "Faster-than-c light between parallel mirrors" . the Scharnhorst effect rederived. Definitely an "oldie but goody". it is the essence of the entire piece. http://www.sciencedirect.com/science/article/pii/037026939091224Y The most interesting subset of this phenomenon could be a situation where the "mirrors" are the reflective walls of hollow nanoparticles. From: Roarty, Francis The thread below found on a 2007 forum thread <http://lofi.forum.physorg.com/Speed--Of-Light-Depends-On-Vacuum-Permittivit y-_16713.html> makes reference to a paper http://www.ldolphin.org/setterfield/vacuum.html THE VACUUM, LIGHT SPEED, AND THE REDSHIFT.
