Question of a Possible ‘Fifth Force’ Baffles Scientists

Like storied thinkers and ascetics through the ages, physics professor Paul Boynton sometimes goes to a cave to ponder some of life’s biggest questions.

The cave--really an abandoned mine shaft in the Cascade Range--is Boynton’s laboratory for studying a question that has baffled physicists for at least two decades:

Is there a fifth physical force, a different kind of gravity, that could better explain observable events in the universe?

Current scientific wisdom holds that there are four forces of nature: electromagnetism; the “strong force” that holds atomic nuclear material intact; the “weak force” responsible for nuclear decay; and gravity, which keeps everything on Earth in place and the stars tethered in their galaxies.

Ring Suspended in Cave

In the mouth of the mine shaft, the physicist has suspended a special ring--half copper, half polyethylene--to test whether a different kind of physical force may be detected between the ring and the immense mass of granite in the cliff side.

Normal gravitational force that makes one body attract another is certainly there. But might there be another force working against gravity? Or, perhaps, one that adds to it?

The ring in the cave and dozens of other experiments being conducted by scientists around the globe are shots in the dark in the quest for the fifth force.

Eminent thinkers freely admit that they are not sure what they are looking for.

Although the existence of a fifth force was posited early this century, the modern hunt for it began in earnest when Australian physicist Frank Stacy took gravitational measurements in mile-deep mines of central Australia. Stacy reported differences in the gravitational pull that were not predicted by standard theory. His conclusions, however, and others since were found to be in error because they were based on an imperfect model of the Earth’s gravitational pull.

The hunt goes on.

“We’re exploring,” says Eric Attleburger, another University of Washington physicist using a different means of searching “for whatever it is.”

Attleburger, who performs most of his experiments on the University of Washington campus, uses tiny disks of copper, beryllium and aluminum suspended by metal filaments to determine whether the disks are attracted by a nearby mound of lead.

Precise instruments are trained on the disks to measure whether oscillations occur that could indicate the presence of a fifth force.

“So far, there is no sign of anything out of the ordinary,” Attleburger said. But he adds: “Essentially, everybody in physics thinks that there has to be more to it.”

This quest appears to stem largely from a scientific hunch that something is missing in our knowledge about the four known universal forces.

The vague but nagging feeling is that although the four forces do a good job of explaining physical events, they lack coherence. They do not, as Attleburger says, “make up a pretty package.”

The relationships among three of the forces--the strong, the weak and electromagnetism--are at least partially understood and tied together neatly under a unifying theory.

A Different Approach

“Gravity is still out there all by itself,” says Jim Thomas, a physicist doing fifth-force experiments at Lawrence Livermore Laboratories in California.

Thomas takes a different tack from Attleburger and Boynton in his experiments. He measures gravitational force over a wide area and then measures whether the force changes in relation to the distance one climbs up a high tower.

Thomas’ experiments are “range dependent.” Boynton’s and Attleburger’s are “composition dependent.”

The consensus of the three experimenters, as well as thinkers who attended a recent conference in the French Alps on “fifth force” work, is that there is no clear evidence that another force exists.

Thomas states that he is not even looking for a force apart from gravity, but rather a modification of gravity that may depend on distance from an attracting object.

Boynton, working at the mouth of the old mining tunnel near Index, Wash., observed during experiments two years ago what he believed were small differences in the attractive force between the massive granite cliff and various materials used in his suspended rings.

But he concluded that the statistical differences recorded were “too close” to the degree of possible error in his measuring equipment.

“The differences measured were only three times bigger than the (margin of) error,” he said. “This time we’re trying it with better equipment that is more accurate. If there is any force there, attractive or repulsive, it’s small.”

Several well-known scientists and theoreticians have postulated the existence of a yet-undiscovered force--most dealing with either attraction or repulsion between bodies.

“There are a number of reasons for speculating,” says Attleburger. “But the question is that you’ve got to look and see. It’s really exploring.

“Maybe there is a layer of nature we’ve been ignorant of for all these years. It would terribly exciting if there were.”