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Physicists discover fifth force

By David P. Hamilton

technolog

Physicists at Purdue University believe they have discovered a fifth elementary force of nature. This postulated force, named hypercharge, may oppose the force of gravity.

Dr. Ephraim Fischbach and his colleagues have reinterpreted the results of the experiments of Roland von E"otv"os, a Hungarian scientist of the early 20th century. E"otv"os' work involved a test of the principle of equivalence, an Einsteinian postulate stating that gravity affects objects independently of their composition. E"otv"os found a small but systematic error in his calculations and declared a null experiment.

The principle of equivalence is one of the fundamental assumptions of Einstein's General Theory of Relativity. Even the verification of hypercharge is unlikely to seriously affect the principle, according to Peter Saulsan, a principle research scientist for the MIT Department of Physics.

Fischbach declared in the Jan. 6 issue of Physical Review Letters that E"otv"os' error is systematic enough to prove the existence of an ephemeral force opposed to that of gravity.

Saulson said that Fischbach had found an "astoundingly good" correlation between the degree of the error and the baryon number of the tested materials. The baryon number of a material is equal to the total number of protons and neutrons in its nucleus.

The extremely localized effect of the hypercharge force would not significantly damage the theory of relativity, Saulsan said.

The principal differences between hypercharge and gravity appear to lie in the forces' effective range and strength, Saulsan said.

Unlike gravity, whose effects seem to extend to an infinite distance, hypercharge appears to have a finite range of approximately 200 meters, he continued.

Two other elementary forces, the strong and weak nuclear forces, also have finite ranges, although the range of these forces is more on the order of the diameter of the atomic nucleus, Saulsan said.

Fischbach also quoted the results of more recent experiments which seem to support the existence of hypercharge, Saulsan said.

Experiments conducted as far as one kilometer underground by Frank D. Stacey of the University of Queensland in Australia indicate that the force of gravity varies by as much as seven-tenths of one percent at different depths in the earth.

Other scientists have reported the apparent effects of another elementary force in experiments conducted at the Fermi National Accelerator Laboratory in Batavia, Illinois, according to a Jan. 8 article in the New York Times.

The theory of hypercharge could still face some problems, Saulsan claimed. For instance, E"otv"os' "systematic trend" of error is greater than Stacey's reported gravitometric anomaly by a factor of more than 20.

Reasonable explanations for this disagreement exist, Saulsan suggested. He elaborated on the difficulty of E"otv"os' original experiment, which involved the use of a torsion balance which would respond to gravity while taking the rotation of the earth into account.

Interpreting data from a 60-year-old experiment is also rather difficult, Saulsan said. In addition, Stacey's work required him to estimate the density of the rock above him as he conducted his experiments. These estimates could easily have been in error, he continued.

Four elementary forces have already been identified. In order from weakest to strongest, they are: gravity, electromagnetic, the weak nuclear force, and the strong nuclear force. Scientists believe that these forces can explain any phenomenon, including the creation of the universe.

If hypercharge actually does exist, it would be a step away from physicists' attempts to mathematically unify the elementary forces of nature, Saulsan said. But widespread acceptance of the theory would not threaten any physicist's "dearly-cherished notions," he added.

The theory would still be a "first-rate" discovery if verified, Saulsan said.