Search for non-Newtonian gravitation-a gravimetric experiment in a hydroelectric lake

Abstract

In August 1988 gravity measurements were made during 22 days in the Hornberg pumped-storage reservoir in the southern Black Forest, SW Germany. Water-level changes with daily variations of 5-22 m and the Earth tides produced gravity signals which were recorded digitally with six LaCoste-Romberg field gravimeters above and below the water level in a 60m high tower. The reservoir geometry is well known, and water level could be measured continuously with high accuracy. The purpose of the experiment was to search in the gravity signals for deviations from Newton's gravitational law due to a newly postulated interaction ('fifth force') whose range is somewhere between 1 and 1OOOm. The search technique is to construct residual signals, i.e. to subtract from observed gravity known effects such as the Newtonian attraction of the moving water masses and the Earth tides, and to search by regression analysis in the residual signal for a residual component proportional to the Newtonian attraction; this component could be of non-Newtonian origin. Residual water signals with amplitudes of 0 . 2 5 f 0 . 4 per cent of the Newtonian water signal were found. This value implies negative evidence for a residual water signal and, hence, for non-Newtonian gravitation. The experiment can also be considered as one for the measurement of the gravitational constant at effective mass separations of 40-70m. The deviation from the laboratory value is also 0.25 f0.4 per cent and thus not significantly different from zero. The main limitation of the Hornberg experiment is due to calibration errors of the gravimeters used of 0.2-0.4 per cent, which were revealed by comparison of the records of neighbouring instruments.

The Newtonian gravitational constant: recent measurements and related studies

“…As we have seen in section 4, a number of interesting measurements of G were carried out by these methods. Some of the more recently reported studies include that of Müller et al (1990) who made gravimetric measurements of the Hornberg reservoir in Germany. Their experiment set a limit on the departure of G from the laboratory value of no more than (0.25 ± 0.4)% over the range 40-70 m, i.e.…”