No correction for the light propagation within the cube: comment on "Relativistic theory of the falling retroreflector gravimeter"

Abstract

Although the equation of motion developed in the paper (Ashby 2018 Metrologia 55 1) depends on the parameters of the falling cube, such as depth and refraction index, the parameters are only associated with powers of time no greater than one, and so do not affect the acceleration. The paper's correction due to the light propagation within the cube is therefore not supported by the equation of motion, and probably caused by omissions in data analysis. The 'speed of light' component of the acceleration that follows from the equation, agrees with the results obtained by other authors.