Study Shows the Force Is With Newton : Science: Scripps Institution’s three-year ocean study supports 300-year-old law of gravity against new theory of a ‘fifth force.’

Rest assured, Isaac. Your 300-year-old law of gravity still holds water.

Scientists at the Scripps Institution of Oceanography have confirmed Isaac Newton’s formula for determining the effects of gravity, despite some theoretical physicists who argue that a mysterious “fifth force” of nature somehow counteracts or diminishes gravity.

“We still haven’t found a kink in Newton’s law, even after hundreds of years of trying to,” remarked Mark A. Zumberge, who, with John A. Hilderbrand, led the Scripps team of 10 scientists and the nearly 100 or so support crew members who undertook three years of studies.

Newton’s law predicts the gravitational attraction between two masses, based on the size of the masses and the distance between them.

The scientific challenge was to conduct an experiment involving masses too large, and distances too great, to test in a laboratory, where most gravitational experiments have been undertaken.

Supporters of the “fifth force” theory have said the phenomenon would be most evident in situations involving larger masses and greater distances than can be accommodated in a lab.

For their laboratory, the Scripps scientists took to the ocean--in this case, a 40-square-mile region of the Pacific halfway between San Diego and Hawaii.

Aboard Scripps’ own research vessels, the Thomas Jefferson and the New Horizon, the scientists on the water’s surface measured the gravitational pull of both the earth and the ocean water.

Then, using the Navy’s research submersibles Sea Cliff and Dolphin, the scientists studied the gravitational pull from various depths of the ocean--and ultimately on the ocean floor, 16,400 feet below the surface.

Because the influence of the earth’s own gravity was essentially constant, scientists were able to then measure the ocean water’s own gravitational pull. First, they determined the pull of gravity on the ocean surface--a gravity force that reflected both the mass of the earth and the mass of the ocean.

Then, they measured the gravity on the ocean floor. That lesser gravity force reflected the upward gravitational pull of the ocean. The difference, then, between the gravity readings taken on the water’s surface and on the ocean floor reflected the gravitational pull of the ocean.

The net findings, Zumberge said, could have been predicted by Newton himself. His theory was correct and if there is a “fifth force” at all, it is scant.

The findings by the Scripps scientists are published in today’s issue of Physical Review Letters, the journal of the American Physical Society.

Ocean water proved a good lab, researchers found, because the mass of the ocean could be accurately determined, especially because the ocean floor at the selected site is relatively flat and removed from seismic activity.

“This was the most fun experiment I’ve ever done,” said Zumberge, the 37-year-old San Diego physicist. “We use a lot of the techniques we’ve learned in physics to learn about the earth, and here was a case where we could turn that around, and use the earth itself to learn about physics.”

Scientists have waffled in debating the “fifth force”--with some experiments suggesting its existence, then a reanalysis of those experiments forcing a reassessment of the original findings. The Scripps experiment was perhaps the grandest yet in debunking the “fifth force” theory, according to Zumberge.

So, why do we care?

“There’s no immediate, direct application or new product we can build now that we couldn’t build before,” Zumberge said. “But there are many examples in the history of physics, where we simply try to understand the laws of physics and, in doing so, learn to use them better.”