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]]>The momentum of anything free-moving will change over time in a gravitational field as seen by an outside observer. If there is no exchange of energy or momentum with gravitational field in such a situation, where did these (conserved) quantities go? For instance a photon of light loses a bit of momentum climbing out of […]

Why do you think it needs to be conserved? In any conservative (central) force field, the energy/momentum would ‘appear’ to conserve, and in newtonian limit GR boils down to conservative forces therefore the apparent energy conservation doesn’t entail actual energy conservation. It is just a low speed/low gravity limit phenomenon.

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]]>V. Petkov, “Physics as Spacetime Geometry.” In: A. Ashtekar and V. Petkov (Eds), *Springer Handbook of Spacetime* (Springer, Heidelberg 2014), pp. 141-163.

Personally, I prefer to respond to published criticism because editors make sure that only relevant criticism is published.

The reason I wrote the above is that not only is the essence of your comment pre-relativistic, but the same applies also to the terminology used. There is no gravitational field in general relativity. What is there is spacetime curvature; can energy and momentum be exchanged with the non-Euclidean geometry of spacetime? And, indeed, the worldline of a particle or a photon in the vicinity of the Earth’s worldtube is geodesic which means that the particle / photon does not exchange any energy and momentum with anything (its energy-momentum 4-vector is parallel-transported along its geodesic worldline).

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]]>In fact, you restated the present view in GR. I am afraid you have not tried to understand the arguments for questioning this view.

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