http://philsci-archive.pitt.edu/arch.../Minkowski.pdf
Harvey R. Brown and Oliver Pooley: "What has been shown is that rods
and clocks must behave in quite particular ways in order for the two
postulates to be true together. But this hardly amounts to an
explanation of such behaviour. Rather things go the other way around.
It is because rods and clocks behave as they do, in a way that is
consistent with the relativity principle, that light is measured to
have the same speed in each inertial frame."

More explanation:

http://philsci-archive.pitt.edu/arch...ontraction.pdf
Harvey Brown: "The FitzGerald-Lorentz (FL) hypothesis was of course
the result of a somewhat desperate attempt to reconcile the null
result of the 1887 Michelson-Morley (MM) experiment with the hitherto
successful Fresnel-Lorentz theory of a stationary luminiferous ether,
a medium through which the earth is assumed to move with unappreciable
drag. The MM experiment is rightly regarded today as one of the
turning points in physics, and although it is discussed widely in
textbooks, it is remarkable how much confusion still surrounds its
structure and meaning. In order then to understand the FL hypothesis,
it is necessary first to go over some welltrodden ground; sections 2
and 3 below are designed to show what the 1887 null result does and
does not imply. In particular it is shown in section 3 that IN THE
CONTEXT OF A THEORY OF LIGHT IN WHICH THE LIGHT-SPEED IS INDEPENDENT
OF THE SPEED OF THE SOURCE, A CERTAIN MOTION-INDUCED DEFORMATION OF
RIGID BODIES, OF WHICH CONTRACTION IS A SPECIAL CASE, IS REQUIRED."

Harvey Brown is the President of the British Society for the
Philosophy of Science so there can be no doubt: the MOTION-INDUCED
DEFORMATION OF RIGID BODIES is the fundamental effect, the constancy
of the speed of light is just a consequence. If this is not a genuine
revolution in Einstein criminal cult, what else coud be?

Pentcho Valev