Cosmic Microwave Background and the issue of a fundamental preferred frame

The possibility to correlate ether-drift measurements in laboratory and direct CMB observations with satellites in space would definitely confirm the existence of a fundamental preferred frame for relativity. Today, the small residuals observed so far (from Michelson-Morley onward) are just considered typical instrumental effects in experiments with better and better sensitivity. Though, if the velocity of light propagating in the various interferometers is not exactly the same parameter c of Lorentz transformations, nothing would really prevent to observe an ether drift. Thus, for the Earth cosmic velocity v = 370 km/s, we argue that a fundamental 10(-)(15) light anisotropy, as presently observed in vacuum and in solid dielectrics, is revealing a 10(-9) difference in the vacuum effective refractivity between an apparatus in an ideal freely falling frame and an apparatus on the Earth surface. In this perspective, the stochastic nature of the physical vacuum could also explain the irregular character of the signal and the observed substantial reduction from its instantaneous 10(-)(15) value to its statistical average 10(-)(18) (or smaller). For the same upsilon = 370 km/s the different refractivities, respectively, O(10(-4)) and O(10(-5)) for air or helium at atmospheric pressure, could also explain the observed light anisotropy, respectively O(10(-)(10)) and O(10(-11)). However, for consistency, one should also understand the physical mechanism which enhances the signal in weakly bound gaseous matter but remains ineffective in solid dielectrics where the refractivity is O(1). This mechanism is naturally identified in a non-local, tiny temperature gradient of a fraction of millikelvin which is found in all classical experiments and might ultimately be related to the CMB temperature dipole of +/- 3 mK or reflect the fundamental energy flow associated with a Lorentz-non-invariant vacuum state. The importance of the issue would deserve more stringent tests with dedicated experiments and significant improvements in the data analysis.