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Comments are due on a recent paper by McGruder III (2017) in which the authordeals with the concept of gravitational repulsion in the context of theSchwarzschild-Droste solution. Repulsion (deceleration) for ingoing particlesinto a black hole is a concept proposed several times starting from Drostehimself in 1916. It is a coordinate effect appearing to an observer at a remotedistance from the black hole and when coordinate time is employed. Repulsionhas no bearing and relation to the local physics of the black hole, andmoreover it cannot be held responsible for accelerating outgoing particles.Thereby, the energy boost of cosmic rays cannot be produced by repulsion.

Comment on "Acceleration of particles to high energy via gravitational repulsion in the Schwarzschild field" [Astropart. Phys. 86 (2017) 18-20]