Classical Physics


The "Missing" Measurements of the Gravitational Constant

Authors: Maurizio Michelini

The G measurements are made with torsion balance in "vacuum" to the aim of eliminating the air convection disturbance. Nevertheless, the accuracy of the measured G values appears unsatisfying. In 2000 J.Luo and Z.K.Hu first denounced the presence of some unknown systematic problem in high vacuum G measurement. In this work a new systematic effect is analysed which arises in calm air from the non-zero balance of the overall momentum discharged by the air molecules on the test mass in the vacuum chamber. This effect is normally negligible, but the disturbing force becomes comparable to the gravitational force when the chamber pressure drops to about 10-5 bar , at which the molecule mean free path equals the thickness of the meatus facing the test mass. At the epoch of Heyl's measurement at 1 millibar (1927), the technology of vacuum pumps reaching void levels up to 10-9 bar was developed, but this chance was not used. The recent G measurements used high vacuum techniques up to 10-10 bar and 10-11 bar, so the effect of the air meatus results very little. What happened to the "missing" measurements made at vacuum pressures in the "forbidden" interval between millibar and nanobar ? As a matter of fact, we were not able to find the related papers in the literature. This lack appears embarrassing in absence of an adequate physical explanation.

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Submission history

[v1] 23 Sep 2008

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