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Dead end for a fifth force.

Dead end for a fifth force

Precise measurements of the gravitational force at various heights on a 300-meter tower in Erie, Colo., furnish the best evidence yet that Newton's law of gravity accurately predicts the magnitude of the attractive force between two objects. In effect, the new findings rule out the existence of a "fifth force" of nature strong enough to make itself felt in such an experiment. If a fifth force exists at all, it would have to be much weaker than theorists had imagined.

Newton's law gravity specifies that increasing the distance between two objects should reduce the gravitational force between them in a well-defined way. Several years ago, however, a number of measurements of the gravitational force at different heights on a tower and depths in a borehole hinted that the measured attractive force may be somewhat less than expected, suggesting the influence of a small, additional force acting on a scale of 10 meters to 10 kilometers (SN: 7-26/86, p.55). Those disturbing fragments of data prompted an intensive, four-year quest for evidence of a new force of nature to join the four types already known: gravity, electromagnetism, and the strong and weak nuclear interactions.

Data from the latest tower experiment closely mirror the Newtonian predictions, leaving little room for the existence of anything but an extremely weak fifth force. "Agreement of the measured values with the Newtonian predictions is clearly excellent and the validity of [Newton's law of gravity] under the conditions of the experiment is confirmed," report James E. Faller of the Joint Institute for Laboratory Astrophysics in Boulder, Colo., and his colleagues in the Oct. 15 PHYSICAL REVIEW LETTERS.

Various other experiments have produced similar null results (SNd 9/22/90, p.183).
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Title Annotation:gravity and physical forces
Publication:Science News
Date:Nov 17, 1990
Words:291
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