Newton's Constant -- Not So Constant?

Article ID: 29511

Released: 8-May-2002 12:00 AM EDT

Source Newsroom: Weekly Scientist

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Newton's cherished constant may not beBy Mike Martin and copyright 2002, United Press International

CAMBRIDGE, Mass. May 3 (UPI) -- A Russian physicist at MIT -- the Massachusetts Institute of Technology -- has announced experimental data that may topple one of science's most cherished dogmas -- that Newton's constant of gravitation, famously symbolized by a large "G," remains constant wherever, whenever and however it is measured.

"My colleagues and I have successfully experimentally demonstrated that the force of gravitation between two test bodies varies with their orientation in space, relative to a system of distant stars," Mikhail Gershteyn, a visiting scientist at the MIT Plasma Science and Fusion Center, told United Press International from Cambridge.

The idea that forces on bodies may vary relative to the orientation of distant stars has a powerful historical precedent in "Mach's Principle," a term Einstein coined in 1918 for the theory that eventually led him to his biggest breakthrough -- general relativity.

Swing a bucket of water at the end of rope and centrifugal forces pull it up and away. These forces result from the combined gravitational pull of all the distant stars and planets, Austrian physicist Ernst Mach wrote. Any change in the orientation of heavenly bodies would affect forces on matter everywhere, so powerful is their combined effect. The idea that G may change with respect to the way a body is positioned relative to the rest of the universe is simply an example of Mach's adage: matter out there affects forces right here.

Newton's gravitational constant G "changes with the orientation of test masses by at least 0.054 percent," according to Gershteyn's experiments, a remarkable and unprecedented finding that has landed his paper on the subject in the June issue of the journal Gravitation and Cosmology.

"The fact that G varies depending on orientation of the two gravitating bodies relative to a system of fixed stars is a direct challenge to Newton's Universal Law of Gravitation," Gershteyn told UPI. "The existence of such an effect requires a radically new theory of gravitation, because the magnitude of this effect dwarfs any of Einstein's corrections to Newtonian gravity."

Isaac Newton first described G in 1687 as a fundamental component of his universal law of gravity. Two masses, Newton said, attract one another with a force proportional to their mass that falls off rapidly as the bodies move farther and farther apart. Albert Einstein later used G in his own field equations that fine-tuned Newton's original laws.

The constant G puts precise limits on gravity's attractive force and appears in equations that describe any gravitational field, whether the field is between planets, stars, galaxies, microscopic particles or rays of light. Centuries of measurement have firmly fixed the value of G at 6.673 x 10 raised to the power minus 11 cubic meters per kilogram per square second.

If G varies under any circumstances, scientists would have to rewrite virtually every physical law and a long-accepted feature of the Universe -- isotropy, or the condition that a body's physical properties are independent of its orientation in space.

"Gershteyn and his coworkers lay an extraordinary and very interesting claim which -- if proven true -- would change our view of the universe," Lev Tsimring, a research physicist with the Institute for Nonlinear Science at the University of California San Diego, told UPI. "In a well-controlled experiment, the authors proposed to measure the gravitational force between two bodies with respect to the orientation of the experimental setup to distant stars," Tsimring explained. The experiment, he said, would seek to detect gravitational anisotropy -- the condition that the attractive force between bodies would vary with respect to their spatial orientation, not their separating distance.

"The latest paper by the authors -- in collaboration with an experimentalist who is a well-respected specialist in precisely that kind of measurement -- provides strong evidence in favor of the validity of the author's original claim," Tsimring said.

Gravitation and Cosmology editor Kirill Bronnikov agreed.

"The evident merit of the paper by Mikhail Gershteyn et. al. is the information of a possible new effect, discovered experimentally -- the effect of anisotropy related to Newton's constant G," Bronnikov, told UPI from Moscow, Russia. "So far the possibility of such an effect has only been discussed theoretically."

"The authors of this paper make some extraordinary claims in a legitimate journal," George Spagna, chairperson of the physics department at Randolph-Macon College, told UPI from Ashland, Va. "But they do not provide enough of their data or theoretical justification. They must provide much more information to be convincing."

Other scientists will need to provide "more detailed and independent experiments to confirm and elaborate the experimental results obtained in Gershteyn's paper," Lev Tsimring told UPI. "I cannot exclude that there might be other ways of explaining this anisotropy within conventional theory, but I believe that Gershteyn's results are convincing."

Mike Martin, Science

ScienceNewsWeek -- United Press International --



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