On the interpretation of Michelson-Morley experiments

Recent proposals for improved optical tests of special relativity have rene wed interest in the interpretation of such tests. In this Letter we discuss the interpretation of modem realizations of the Michelson-Morley experimen t in the context of a new model of electrodynamics featuring a vector-value d photon mass. This model is gauge invariant, unlike massive-photon theorie s based on the Proca equation, and it predicts anisotropy of both the speed of light and the electric field of a point charge. The latter leads to an orientation dependence of the length of solid bodies which must be accounte d for when interpreting the results of a Michelson-Morley experiment. Using a simple model of ionic solids we show that, in principle, the effect of o rientation dependent length can conspire to cancel the effect of an anisotr opic speed of light in a Michelson-Morley experiment, thus, complicating th e interpretation of the results. (C) 2001 Elsevier Science B.V. All rights reserved.