Measurement of thespeed-of-lightperturbation of free-fall absolute gravimeters

Abstract

We report on a direct measurement of the relativistic Doppler shift with a commercial free-fall absolute gravimeter of the type FG5X. The observed Doppler shift, which is commonly called speed-of-light perturbation, can be well described by the relativistic Doppler formula, where the constant object velocity is replaced by a time-dependent velocity with constant acceleration. The observed speed-of-light perturbation stands in contrast to other publications, which predict a higher frequency shift. It has been be measured with a relative uncertainty of 1.1 × 10 −3 .

Comment on ‘Measurement of the speed-of-light perturbation of free-fall absolute gravimeters’

“…The result is caused by other perturbations not accounted in the analysis. We have analyzed only one perturbation and found that its magnitude is about 10 times higher than reported in [1]. It's possible that the analysis of other perturbations can also benefit from the review by other researchers.…”

“…The formula for the speed-of-light perturbation of the acceleration [2] used in the analysis yields 14.18 µGal ‡ for the longest drops in both sets, so the one-third of the correction is 4.73 µGal. However, on the fig.4 of [1] (FF set) this difference reaches only 2.2 µGal, and on the fig.5 (LF set) it is only 1.1 µGal. Besides being much lower than the right value, the LF and FF results disagree between themselves, even though the longest drops are the same in both sets.…”

“…However, on the fig. 4 of [1] (FF set) this difference reaches only 2.2 µGal, and on the fig. 5 (LF set) it is only 1.1 µGal.…”

“…According to [1], one of the harmonics present in the stacked residuals has the amplitude of 0.025 nm and the frequency of 7 Hz. The fig.…”

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The paper (Rothleitner et al 2014 Metrologia 51, L9) reports on the measurement of the speed-of-light perturbation in absolute gravimeters. The conclusion that the perturbation reaches only 2 3 of the commonly accepted value violates the fundamental limitation on the maximum speed of information transfer.

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