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

TL;DR

This paper critiques a previous work on relativistic gravimetry, arguing that the correction for light propagation within the cube is unsupported by the derived equations and likely due to data analysis omissions.

Contribution

It clarifies that the correction for light propagation within the cube is not justified by the equation of motion, challenging prior assumptions.

Findings

The correction depends only on parameters associated with powers of time no greater than one.

The correction is not supported by the derived equations of motion.

The 'speed of light' component of acceleration aligns with other authors' results.

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.