  The possibility of an extrinsic origin for inertial reaction forces has
recently seen increased attention in the physical literature. Among theories of
extrinsic inertia, the two considered by the current work are (1) the
hypothesis that inertia is a result of gravitational interactions, and (2) the
hypothesis that inertial reaction forces arise from the interaction of material
particles with local fluctuations of the quantum vacuum. A recent article
supporting the former and criticizing the latter is shown to contain
substantial errors.
