There can be true relative velocities and apparent relative velocities. A true velocity requires that there is a relation between two actualized things, parts, or phenomena, or parts thereof, that are co-existing. That is within the same and only existing entire universal configuration. If one reference object is actualized but the comparison is with a manifestation formed from received signals then the velocity calculated for the manifestation is attributed to the material object it appears to be but is not in essence the same as the true relative velocity which is the relation between the two actualized things or phenomena.
It is said that Newtonian gravity is an approximation of Einsteinian gravity. However Newton is dealing with two actualized bodies in space, whereas Einstein is dealing with a space-time manifestation ( necessarily formed from received EM radiation or calculation of that ). Therefore the solution is an attribution which although it may be similar in numerical value is in essence something fundamentally different. The difference is between what is actually happening and what is seen to have happened,
Re. Einsteins field equations "The equations must be wrong! Although the theory and the equations have passed every test, they are intrinsically incompatible with quantum theory (which has also passed every experimental test). The problem is that the equations require the energy and momentum to be defined precisely at every space time point, which contradicts the uncertainty principle for quantum states. This is not a just a problem at high energies or short distances, it is a conceptual incompatibility that applies in every lab." From"Einstein Field Equations (General Relativity)" via https://warwick.ac.uk/fac/sci/physics/intranet/pendulum/generalrelativity/ Retrieved 7 jun 2018
Quantum theory is dealing with what is (unitemporal material existence) that is prior to the making of a contextual observation, without context; that providing a singular value or state. Whereas space time represents a manifestation, the product of observation, and that product is of definite states and or values., Contextual manifestation, results, not externally real (actualized) source reality.
The solutions to these equations are the components of the metric tensor g_{munu}, which specifies the space-time geometry. The inertial trajectories of particles can then be found using the geodesic equation. From"Einstein Field Equations (General Relativity)" via https://warwick.ac.uk/fac/sci/physics/intranet/pendulum/generalrelativity/ Retrieved 7 jun 2018
The inertial trajectories mentioned are trajectories of a manifestation of an object ( formed from EM processing ) and not a material object in unitemporal space being affected by the distribution of the existing content of space unobserved.