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

Abstract

Abstract. 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. The conclusion was deluded by unaccounted parasitic perturbations, some of which are obvious from the report.

Experimental assessment of the speed of light perturbation in free-fall absolute gravimeters

“…First the uncertainties related to ∆ ℎ and ∆ are estimated. Then the uncertainty for , obtained by least square on (18), is calculated.…”

“…To focus on the speed of light perturbation in the measured value of the gravitational acceleration, we subtracted from 𝑔 𝑚𝑒𝑎𝑠 (𝑇, 𝑣 0 ) the minimum value of the set to obtain ∆𝑔 𝑚𝑒𝑎𝑠 (𝑇, 𝑣 0 ). These values were then least square fitted to ∆𝑔 𝑚𝑒𝑎𝑠 (𝑇, 𝑣 0 ) = 𝑎 𝑐 • ∆𝑔 𝑡ℎ𝑒𝑜 (𝑔, 𝑇, 𝑣 0 ), (18) with ∆𝑔 𝑡ℎ𝑒𝑜 (𝑔, 𝑇, 𝑣 0 ) = (𝑔 • 𝑣 0 + 0.5 • 𝑔…”

“…The controversy was deepened after the claim in [16] of the first measurement of the 'speed of light perturbation' that apparently confirmed the calculations in [15]. The results and methods of [15,16] were questioned in a series of works [17,18] (see also [19]) as well as more recently in [20].…”

The speed of light perturbation in absolute gravimeters from the viewpoint of ‘relativistic geometry’

“…In the past few years, a relativistic treatment of the finite speed based on the Lorentz transformation was proposed in corner-cube absolute gravimeters [11], which was criticized [12]. It arose a series of debate on the perturbation due to the finite speed of light [13][14][15][16]. The issue actually boils down to the value of k in the expression of the perturbation [14]…”

“…v 0 and g 0 stand for the initial velocity and acceleration of the test body, respectively. Some people insist that k equals 2 [11], while the others stick out k equals 3 [16]. Given a freefall corner-cube absolute gravimeter with a ~20 cm drop length, the magnitude of the discrepancy (k = 2 versus k = 3) will be about 6 µGal.…”