Physicists Test Laws of Universe in Bid to Discover a ‘Fifth Force’
Somewhere just south of the Arctic Circle in Greenland, where pale-white ice is the only landscape for thousands of miles, a small team of scientists will scud out on snowmobiles this summer and lower a long, steel tube down a narrow hole in the ice.
The operation could be likened to the delicate threading of a giant needle: The hole in the ice is just four inches wide but nearly a mile deep. The steel tube will contain an instrument that is extraordinarily fragile and valued at a quarter of a million dollars.
The unorthodox experiment is designed to yield new insights into one of the most provocative questions in contemporary physics: Is there a fifth force in the universe?
So far, only four are known. They are gravity, electromagnetism and the strong and weak forces that govern the structure of the atom. Traditionally, the four forces have been thought to explain all things in nature.
Classical Tenets
But the classical tenets were questioned 18 months ago by Purdue University physicist Ephraim Fischbach. In a January, 1986, report, Fischbach claimed to have found evidence of a fifth force called hypercharge.
Fischbach said the force acts more strongly on chemical elements, such as iron and lead, than it does on heavier or lighter elements. He also concluded that this force influences objects over relatively short distances, for example, less than 600 feet.
Such a force, in effect, would act in such a way that a lead weight would fall at a slightly slower speed than a feather.
The aim of the Greenland experiment--and many others taking place around the world--is designed in part to explore the possible existence of a fifth force.
It seeks to measure the force of gravity as a specially designed gravity meter moves up and down the hole. The researchers will then compare those measurements to what would be predicted through Sir Isaac Newton’s law of gravitation.
Any differences may suggest that the so-called gravitational constant changes with distance, contrary to traditional thought. If it does, some believe that it may point to the existence of the new force, working against gravity.
Some physicists believe that discovery of a fifth force could help tie together the other four forces in a single, long-awaited “unified theory.” Difficulties fitting gravity into such a theory had prompted speculation in the past that there might be such a missing link.
Some contend that it could also affect astrophysics and cosmology because the fifth force could have a role in the birth of stars and planets.
“The implications are astounding,” said Mark Ander, a geophysicist from Los Alamos National Laboratory in New Mexico who is heading the Greenland expedition. “This has implications for the age of the universe and the particular model (we use) of the Big Bang (theory).”
Already, about 35 research groups worldwide are exploring the fifth force theory in what to the layman might look like a bizarre series of stunts involving television transmission towers, mine shafts, cliffs, the ocean and 400 tons of lead submarine ballast.
- In a small town off U.S. 70, just south of Raleigh, N.C., two U.S. Air Force physicists intend to haul a gravity meter up the side of a 1,800-foot-tall TV transmission tower. From there, they plan to measure gravity at intervals of 150 feet.
- In the Pacific Ocean 250 miles north of Hawaii, a group from Scripps Institution of Oceanography in La Jolla plans to conduct similar tests next year. The group will make their measurements through water at intervals down to four to six kilometers.
- Other scientists are working with tools called torsion balances in a Nevada mine shaft, in a tunnel in the Cascade Mountains in northern Washington and at the Grand Canyon. One is using an instrument capable of measuring a force a billion times smaller than the weight of a postage stamp.
Fischbach, while searching for the evidence of a fifth force, had come across a classic paper published in 1922 by Hungarian physicist Roland von Eotvos.
Eotvos was trying to prove that gravity has the same effect on all materials. He also had used a torsion balance because he had no way of measuring the acceleration of falling objects. Testing various materials--including metals, asbestos and talc--Eotvos concluded that gravity exerted the same pull on all of them, within the limits of experimental error.
But when Fischbach looked at Eotvos’ original data, he concluded that Eotvos’ “experimental error” was in fact a manifestation of the fifth force.
But many scientists now attribute the discrepancies not to a fifth force but to factors such as air currents disturbing the torsion balance in Eotvos’ laboratory. The doubters also believe that the gravity of nearby buildings had perhaps altered the results by causing the torsion balance to twist.
All objects exert a gravitational effect on other objects. For example, a refrigerator would exert a minute gravitational effect on a marble nearby. But the effect would be insufficient in comparison to other forces to actually move the marble.
Researchers are trying to replicate Eotvos’ work with more sensitive tools.
University of California, Irvine, physicist Riley D. Newman is using a torsion balance enclosed in a vacuum chamber. An electric eye trained on the suspension beam can detect movements as small as one-millionth of the thickness of a piece of paper.
He will place a 220-pound copper ring on either side of the balance and measure its gravitational pull on beryllium and copper spheres. If a fifth force exists, the beryllium should be pulled toward the ring more strongly. If not, the spheres will be pulled equally.
Newman hopes to install the device in an abandoned mine shaft in Nevada, where the presence of soil on all sides would cancel out any fifth force due to the Earth.
Other scientists favor large land masses to tug at their balances.
Sealed Tunnel
One University of Washington physicist, Eric G. Adelberger, intends to take his balance to the Grand Canyon and also to place it next to 400 tons of lead submarine ballast. Another, Paul Boynton, has sealed his in a 15-foot tunnel at the base of a 400-foot-high granite cliff in the Cascade Mountains.
Peter Thieberger of Brookhaven National Laboratory on Long Island, N.Y., the only scientist to report observing the effects of a fifth force, uses a hollow copper sphere floating in a large pan of water. A video recorder shoots the sphere every hour to record its motion.
Thieberger placed the device atop the Palisades above the Hudson River in New Jersey. In many experiments, he observed that the copper sphere always moved in a straight line away from the cliff at a speed of about 0.25 of an inch per hour, repelled, he said, by the fifth force.
James E. Faller and Tim Niebauer of the University of Colorado have studied objects falling in a vacuum using a device known as a laser interferometer. They found the acceleration rates of uranium and copper balls over a nine-inch drop were identical, indicating that no fifth force was acting.
Because of the experiment’s design, however, it would only detect a fifth force that acted over a distance of more than 0.6 miles. Since the fifth force is thought to act over only shorter distances, their results are not considered definitive.
In mid-July, three researchers from Scripps Institution of Oceanography at the University of California, San Diego, set off for Greenland to set up their experiment. They were armed with 1,000 pounds of equipment; a wardrobe of goggles, face masks and gloves, and a compact disc player to play Mozart and Huey Lewis.
Ensconced in an Air Force radar facility on the 65th parallel that is jointly operated by the United States and Denmark, the team will be using a hole bored in the early 1980s by glaciologists studying “thousand-year-old air” from samples trapped deep in the ice.
But first, the researchers must measure the strength of Earth’s gravity along the surface of the ice in the vicinity of the bore hole. By measuring how it changes laterally, they expect to be able to predict how gravity should change vertically down the hole.
“When we actually measure how it changes vertically, the difference between that and (what) we predicted will be perhaps indicative of some breakdown in Newton’s law,” said Mark Zumberge, a 32-year-old Scripps geophysicist leading the expedition with Ander.
In August, a team of British researchers will join Zumberge to map the topography of the mountains beneath the ice using radar equipment. That should enable the group to predict and take into account the gravity effect from rock around the hole.
Meanwhile, Ander has spent much of the past two weeks a mile deep in the Earth in the shaft of a silver mine between Kellogg and Wallace, Ida., “seasoning” the wire cable that is to be used to lower the bore hole gravity meter into the ice with the help of a giant winch.
Using a 300-pound weight to simulate the gravity meter, Ander repeatedly let out and pulled in the full length of cable. Using lasers and infrared signals to measure the cable’s stretch under the tension of the weight, he hopes to have calibrated the cable precisely so as to eliminate any distortion as a result of using unflexed cable during the actual experiment.
Another team of Scripps researchers intends to do a similar experiment next summer in the North Pacific. They plan to spend a week there lowering a specially designed gravity meter over the side of a ship in a part of the ocean called the Central Gyre.
The advantage of the ocean experiment is that it will allow measurements over a greater distance, perhaps four to six kilometers. The team hopes to explore theories that the fifth force may operate over short ranges and gradually fade out.
Unfortunately, each medium--a mine shaft, the ocean, ice--has its peculiar drawbacks.
The earliest measurements to test for variations in gravity over distance were done in Australian mine shafts in the late 1970s. There, variations in the density of the rock around the shaft led to questions about the validity of the calculations.
So scientists turned their attention to the ocean, which has the most uniform density of any accessible part of the Earth. But there, ocean currents and movements make tracking the descent of a gravity meter difficult. In addition, most ships make unstable platforms.
That is why Zumberge and Ander began looking for ice bore holes: Ice might have the advantages of water without the disadvantages. But ice also is not without its potential drawbacks, and even hazards, Zumberge acknowledged.
“This gravity meter hasn’t been operated in an ice bore hole before,” he said. “The hole is filled with anti-freeze consisting essentially of jet fuel. . . . The temperature is on the order of minus 20 degrees Centigrade. The diameter of the hole is not that much greater than the diameter of the instruments we’ll be putting in it,” he added. “And people who (work) in holes in rock always have nightmares about things getting stuck in holes.
“So there’s a lot of things to keep me up at night.”
