The different roles and natures of spacetime appearing in a quantum field
theory and in classical physics are analyzed implying that a quantum theory of
gravitation is not necessarily a quantum theory of curved spacetime. Developing
an alternative approach to quantum gravity starts with the postulate that
inertial energy-momentum and gravitational energy-momentum need not be the same
for virtual quantum states. Separating their roles naturally leads to the
quantum gauge field theory of volume-preserving diffeomorphisms of an inner
four-dimensional space. The classical limit of this theory coupled to a
quantized scalar field is derived for an on-shell particle where inertial energy-momentum
and gravitational energy-momentum coincide. In that process the symmetry under
volume-preserving diffeomorphisms disappears and a new symmetry group emerges:
the group of coordinate transformations of four-dimensional spacetime and with
it General Relativity coupled to a classical relativistic point particle.
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