A new mine determination of the newtonian gravitational constant

Abstract

Recent theoretical interest in the possibility of observing a non-newtonian component of gravity arises from the lead that such observations will give to unification theories¹. Absolute determinations of the newtonian constant G by geophysical methods, at mass separations several orders of magnitude greater than those available in the laboratory, provide information not obtainable in any other way. Stacey² drew attention to the fact that modern geophysical measurements were precise enough in principle to provide an important check on G and Stacey et al.³ revived the mine method first used by G. B. Airy. Subsequently Stacey analysed a set of overlapping sea-floor and sea-surface gravity survey data made available by the Exxon Oil Co., to avoid the problem of density uncertainty that beset the mine measurements, and Stacey and Tuck⁴ compared the results with values of G calculated from published mine and borehole data. The striking conclusion was that the values of G were all systematically high. Residual doubts, especially concerning the adequacy of density sampling and the possibility of bias by regional gravity anomalies, left the conclusion as a rather tentative one. We report here a new determination of G, which is also high, but in which the doubt about density is substantially reduced. This information makes it implausible to explain the high value of G in terms of an inadequate knowledge of density. The possible effect of regional gravity anomalies is not as securely discounted.