  The condensation of elementary quanta and their macroscopic occupation of the
same quantum state, say k=0 in some reference frame Sigma, is the essential
ingredient of the degenerate vacuum of present-day elementary particle physics.
This represents a sort of `quantum ether' which characterizes the physically
realized form of relativity and could play the role of preferred reference
frame in a modern re-formulation of the Lorentzian approach. In spite of this,
the so called `null results' of the classical ether-drift experiments,
traditionally interpreted as confirmations of Special Relativity, have so
deeply influenced scientific thought as to prevent a critical discussion on the
real reasons underlying its alleged supremacy. In this paper, we argue that
this traditional null interpretation is far from obvious. In fact, by using
Lorentz transformations to connect the Earth's frame to Sigma, the small
observed effects point to an average Earth's velocity of about 300 km/s, as in
most cosmic motions. A common feature is the irregular behaviour of the data.
While this has motivated, so far, their standard interpretation as instrumental
artifacts, our new re-analysis of the very accurate Joos experiment gives clear
indications for the type of Earth's motion associated with the CMB anisotropy
and leaves little space for this traditional interpretation. The new
explanation requires instead a view of the vacuum as a stochastic medium,
similar to a fluid in a turbulent state of motion, in agreement with basic
foundational aspects of both quantum physics and relativity. The overall
consistency of this picture with the present experiments with vacuum optical
resonators and the need for a new generation of dedicated ether-drift
experiments are also emphasized.
