Is it really impossible that gravity can be modeled non-geometrically? I read the following in Weinberg paper Gravity: "An alternative way to conceive of gravity would of course be to follow the lead of other theories, and regard the gravitational field as simply a distribution of properties (the field strenghts) in flat spacetime. What ultimately makes this unattractive is that the distinctive properties of this spacetime would be completely unobservable, because all matter and fields gravitate. In particular, light rays would not lie on the "light cone" in a flat spacetime, once one incorporated the influence of gravity. It was ultimately the unobservability of the inertial structure of Minkowski space that led Einstein to eliminate it from his theory of gravitation and embrace the geometric approach." I'd like to know: 1. Is gravity in flat spacetime means the same as force based gravity or is force based gravity another method where there is no spacetime but fixed space and time? If so, this means gravity in flat spacetime is fields based gravity in contrast to force based gravity? 2. How come light rays won't lie on the "light cone" in a flat spacetime gravity theory? 3. What is meant by the "unobservability of the inertial structure of Minkowski" that makes impossible gravity based on flat spacetime? 4. Is it totally impossible to model gravity that is not based on spacetime curvature? Maybe there is another way or is Gravity Geometry forever? Thanks.