It is emphasized that Einstein's theory of gravitation has its physical
and logical roots, firstly, in Newton's theory, namely in the existence
of Newtonian tidal forces, and, secondly, in the requirement that these
forces be compatible with the theory of relativity. Furthermore, it is
pointed out that the nonexistence of any covariant description of energy
in Einstein's theory is deeply rooted
... [Show full abstract] in a local 'unidentifiability' of
the gravitational force in Newton's theory, although this fact is
irrelevant in that theory.