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No. 62: Mar-Apr 1989

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More challenges to newton's law of gravitation

Two experiments reported at the 1988 meeting of the American Geophysical Union in San Francisco can be added to the others that question Newton's venerable Law of Gravitation. The abstracts of these papers are short and to-the-point, so we quote them:

"We have performed an experimental test of Newton's inverse-square law of gravitation. The test compared accurately measured gravity values along the 600 m WTVD tower near Raleigh, North Carolina, with upward, continued gravity estimates calculated from ground measurements. We found a significant departure from the inverse-square law, asymptotically approaching -547 36 microGal at the top of the tower. If this departure is derived from a scalar Yukawa potential, the coupling parameter is alpha = 0.023, the range is lambda = 280 m, and the Newtonian Gravitational Constant is G = (6.52 0.01) x 1011 m3 kg-1 s-2. We do not yet have adequate resolution to discriminate this scalar model from a scalarvector model."

(Eckhardt, D.H., et al; "Experimental Evidence for a Violation of Newton's Inverse-Square Law of Gravitation," Eos, 69:1046, 1988.)

"In the late summer of 1987, an ex periment was performed to determine the value of the Newtonian gravitational constant, G, by measuring the variation of the earth's gravity, g, with depth in the Greenland icesheet. The site for the experiment - the radar station at Dye-3, Greenland - was selected because of the existing 2000- m-deep ice borehole there. Previous analysis of ice-cores from the borehole indicate that the ice density can be accurately modeled. Gravity measurements were made to a depth of 1673 meters in the ice, the sub-ice topography was mapped with high-precision radar echo sounding over a 10-km-diameter region, and a series of 24 locations in a 32-km-diameter network around the hole were surveyed with gravity, leveling, and GPS positioning.

"When corrected for the sub-ice topography, a gravity anomaly that accumulated to nearly 4 mGal in 1.4 km was observed. We find measured anomalies can be taken as evidence for non-Newtonian gravity, but can also be accounted for in terms of Newtonian physics if a suitable distribution of high densiity masses exist beneath the borehole."

(Zumberge, Mark Al, et al; "Results from the 1987 Greenland G Experiment," Eos, 69:1046, 1988.)

The paper on the Greenland experiment led to a short article in Science in which differing opinions among the re-search team members about the experiment's significance were aired. Some opted for an unusual density distribu-tion of the rock beneath the experiment to explain the results; others thought that the required density distribution was too unlikely and contrived and consequently favored a modification of Newton's inverse-square law.

(Poole, Robert; "'Fifth Force' Update: More Tests Needed," Science, 242:1499, 1988.)

Comment. Should we permit this tiny residue of anomalous observations to cast doubt upon a law verified in count-less experiments and astronomical observations? Those who believe in the "residue fallacy" will say, "No! Discard the wild points!"

From Science Frontiers #62, MAR-APR 1989. 1989-2000 William R. Corliss