  Correlating ether-drift measurements in laboratory and CMB observations in
space would confirm the existence of a preferred reference frame. To this end,
however, the velocity of light in the interferometers cannot be the same
parameter 'c' of Lorentz transformations. Thus, for the earth velocity of 370
km/s, a fundamental 10^(-15) light anisotropy, as presently observed in vacuum
and in solid dielectrics, could reveal a 10^(-9) difference in the vacuum
refractivity between an ideal freely-falling frame and an apparatus on the
earth surface. In this perspective, the stochastic nature of the vacuum could
explain the irregular character of the signal and the substantial reduction of
its statistical average (10^(-18) or smaller). For the same v=370 km/s the
different refractivity, about 10^(-4) and 10^(-5) for air or helium at
atmospheric pressure, could also explain the observed anisotropy, respectively
about 10^(-10) and 10^(-11). The mechanism enhancing the signal in gaseous
matter, but ineffective in solid dielectrics, is naturally identified in a
non-local, temperature gradient of a fraction of millikelvin. This is found in
all classical experiments and might ultimately reflect the CMB temperature
dipole or the fundamental energy flow in a Lorentz-non-invariant vacuum.
Clarification requires dedicated experiments and improvements in the data
analysis.
