Military scientists trying to confirm the existence of a fifth fundamental force of nature that would oppose gravity say they have found that and more: evidence for a sixth force that would act in concert with gravity.
Until two years ago, it was widely believed that there were only four forces--gravity, electromagnetism, and the strong and weak forces that hold the atom together--and that together they explain all things in nature.
But in January, 1986, physicist Ephraim Fischbach of Purdue University claimed to have seen evidence for a fifth force, one that acts over short distances--about 600 feet or less--in opposition to gravity. Such a force would mean, for instance, that in a vacuum, a feather would fall faster than a lead weight.
Last week, Air Force geophysicists said they had found evidence for a sixth force, one that acts with gravity but is slightly stronger than the fifth force.
The finding was announced by Donald H. Eckhardt and his colleagues at the Air Force Geophysics Laboratory at Hanscomb Air Force Base, Mass., last week at a meeting of the American Geophysical Union in San Francisco.
Using extremely sensitive instruments to measure the force of gravity along the side of an 1,800-foot-tall television tower in Garner, N.C., the researchers found that the force of gravity did not change in the way it should if there were only four forces--or even five.
Their results are "very exciting because they could resolve some of the contradictory evidence about the existence of the fifth force, if they are confirmed," Fischbach said.
One near-term impact of the discovery could be increased accuracy of inertially guided ballistic missiles and aircraft, Eckhardt said.
The study was undertaken, "at least in part," he said, because such missiles are not as accurate at hitting targets as scientists thought they should be. Small deviations in the effects of gravity could account for some of the inaccuracy, he said.
At least 35 groups of researchers around the world are now engaged in experiments designed to prove--or disprove--the existence of the fifth force.
The results of the four groups that were reported before last week have been equivocal. Two of them reported evidence supporting its existence; the other two reported they had found no such evidence.
Eckhardt's is the first research team to report evidence of a sixth force.
His group hoped to shed light on the existence of the fifth force by measuring the force of gravity at regular intervals alongside WTVD's transmission tower in Garner, N.C. Conventional theory predicts that the force of gravity should diminish at a constant, but very small, rate with increasing height.
If a short-range fifth force exists, the force of gravity should decline even more slowly than expected at the base of the tower. But what they found, Eckhardt said, was that gravity declined slightly faster than conventional theory predicts.
For measurements over the whole height of the tower, he said in a telephone interview, "a clear pattern emerged indicating that not only is there a fifth force, but also a sixth force as well." The sixth force, he theorized, acts in support of gravity and over slightly longer distances than the fifth force, perhaps to as much as 1,200 feet.
A sixth force in combination with a fifth force would explain why gravity along the base of the tower declined slightly faster than expected.
Respected in Field
Eckhardt also said that the discrepancies he observed in the force of gravity were at least 10 times as large as the estimated error of his measurements. Fischbach and other researchers noted that Eckhardt is a well-known researcher whose studies are always carefully conducted.
The possibility that a sixth force exists does not come as a surprise to some researchers. In the last few months, physicists Frank D. Stacey of the University of Queensland in Australia and Michael Nieto of the Los Alamos National Laboratory have independently proposed that the conflicting experimental results could be reconciled by invoking an additional force.
But scientists have not been eager to jump on such a bandwagon. "You have to . . . use only the simplest possible explanation," said physicist Eric G. Adelberger of the University of Washington. "You would like to adopt such a picture (a sixth force) only when you are forced to. I don't think we are to that point yet."
Nonetheless, Fischbach noted, "There are a lot of conflicting data in the literature and there is no evidence that anybody has made a mistake. So it is not unexpected that the theory is going to be more complicated than we first thought."
And if it is that complicated, said physicist Paul Boynton of the University of Washington, "it is going to take many, many more experiments to understand what is going on."