Flatlandia : a flat spacetime description of gravitation

The proof that a consistent theory of gravity cannot be constructed in a flat spacetime rests on the {\it assumption} that atoms be equal in every conditions. However special relativity and the principle of equivalence impose that atoms are equal only when relatively at rest and in equivalent gravitational positions. This is further backed up by implementing in QM the mass variation for moving objects and for bodies in a gravitational field.