  The Einstein postulates assert an invariance of the propagation speed of
light in vacuum for any observer, and which amounts to a presumed absence of
any preferred frame. The postulates appear to be directly linked to
relativistic effects which emerge from Einstein's Special Theory of Relativity,
which is based upon the concept of a flat spacetime ontology, and which then
lead to the General Theory of Relativity with its curved spacetime model for
gravity. While the relativistic effects are well established experimentally it
is now known that numerous experiments, beginning with the Michelson-Morley
experiment of 1887, have always shown that the postulates themselves are false,
namely that there is a detectable local preferred frame of reference. This
critique briefly reviews the experimental evidence regarding the failure of the
postulates, and the implications for our understanding of fundamental physics,
and in particular for our understanding of gravity. A new theory of gravity is
seen to be necessary, and this results in an explanation of the `dark matter'
effect entailing the discovery that the fine structure constant is a 2nd
gravitational constant.
