Scientists Contesting Newton’s Gravity Law Fall on Their Faces

Isaac Newton would have loved it.

International teams of scientists trying to find gravitational forces that they believe Newton overlooked three centuries ago are just having a devil of a time proving him wrong.

One team announced last summer that it had succeeded with an ambitious research project in Greenland. But this week, during the fall meeting of the American Geophysical Union, members of the team conceded that their announcement had been premature at best, and quite possibly just wrong.

“We now say our results do not mean new forces in nature,” said Robert Parker, a geophysicist with Scripps Institution of Oceanography. “We’ve gone back” to where they were before the announcement last summer, he added.

Falling Rocks, Feathers

Newton formulated his laws of how the universe works in the 1600s. Until recently the laws have been adequate, and every school child has learned that a ton of rocks and a ton of feathers would fall at the same speed in an absolute vacuum.

But in recent years some scientists have challenged the long-held belief that there are only four forces in nature--the weak and strong forces of the subatomic world, plus electromagnetism and gravity.

At the least, they suggested, gravity is far more complicated than Newton had realized and it might affect some materials more than others.

That led, a couple of years ago, to claims of a fifth force, which slightly retarded the force of gravity in a way that suggested that a ton of rocks and a ton of feathers might not fall at the same speed. But there has been no convincing follow-up evidence of that.

That claim was followed a few months later by reports of yet a sixth force, which slightly enhanced gravity.

The postulated non-Newtonian forces galvanized scientists who saw a possibility of tying all the forces of nature into one grand unified theory, the Holy Grail of modern science.

They came here to discuss their successes and their failures, and they will leave the meeting like warriors who have been through a bitter war that no one has won.

“There was blood all over the floor,” one scientist said after heated discussions in a technical session.

“We have found tantalizing but not compelling evidence,” bemoaned Christopher Stubbs of the University of Washington.

An international team of 22 scientists thought they had success within their grasp last July when they announced the results of an experiment in a deep well in Greenland just south of the Arctic Circle. The scientists had journeyed to that frozen land in hopes that a gravimeter, which measures gravity, would detect the sixth force when it was lowered into a well in the ice.

The ice was known to be relatively homogeneous, so nothing in the ice would interfere with the experiment. That would avoid the problems encountered in a previous experiment in an old mine shaft, where the results were skewed by the fact that variations in the ground through which the shaft passed could account for the minuscule changes in gravity measured by the gravimeter.

The Greenland experiment at first seemed to have been a roaring success because the meter detected evidence of what was believed to be the sixth force.

The announcement was made last July. But this week Parker threw ice water on the parade.

Parker produced evidence that variations in density in the bedrock below the ice could account for the changes in gravity measured by the meter. Exceptionally dense rocks, he said, would cause the meter to fluctuate, falsely indicating that the force of gravity had been enhanced.

Although it is not known for certain that the dense rocks are there because the well does not go down far enough, other scientists conceded that Parker’s point made the evidence for a sixth force highly questionable.

The density required to throw the experiment off is plausible for the area, Parker said, so it would be ridiculous to “throw out Newton’s law” on the basis of the data.

Meanwhile, scientists have begun a new series of experiments in an area where there should be no variations in density: the ocean.

“It is much more difficult to screw up the data with density variations” in the ocean, said Alan Chave, an oceanographer with Bell Laboratories.

John A. Hildebrand, a physicist at Scripps, has designed a system to measure gravity caused by a 5,000-foot column of water. Hildebrand, who was also a member of the Greenland team, made a series of measurements last May, 400 miles off the coast of the Monterey Peninsula.

That work, funded by the Office of Naval Research at a cost so far of about $250,000, has not been conclusive, and the team plans to return to the same area next summer and complete the experiment.

The system uses two gravimeters, one on the surface of the ocean and the other on the ocean floor. By determining the difference in the readings, scientists should be able to pinpoint the gravitational force exerted by the water column between the two gravimeters.

The experiment can be repeated over and over at different locations, thus providing data over a wide area.

Best Chance

Seawater, like anything else, varies in density and pressure, but the variations are so slight that the effect on the experiment will be negligible, Chave said.

The ocean experiment has the best chance of succeeding, Parker said.

But like a good scientist, he added: “I will try my darndest to disprove the results.”

Some scientists involved in the various research projects believe that in the end, Newton will prevail.

“Read my lips,” said theoretical physicist Richard Hughes of the Los Alamos National Laboratory. “No new forces.”

Newton, not noted for his sense of humor, would probably at least chuckle.