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

TL;DR

This paper critiques a previous work on gravitational repulsion in Schwarzschild black holes, clarifying that such repulsion is a coordinate effect and cannot accelerate particles or explain cosmic ray energies.

Contribution

It clarifies the misconception that gravitational repulsion can accelerate particles, emphasizing that it is a coordinate effect without physical acceleration implications.

Findings

Gravitational repulsion is a coordinate effect, not a physical force.

Ingoing particles decelerate due to coordinate effects, not real repulsion.

Repulsion cannot account for cosmic ray energy boosts.

Abstract

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