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Newton's gravitation constant stands challenged
A RUSSIAN physicist at the Massachusetts Institute of Technology (MIT) has announced experimental data that may topple one of science's most cherished dogmas that Newton's constant of gravitation, famously symbolised by a large `G,' remains constant wherever, whenever and however it is measured.
Mikhail Gershteyn, a visiting scientist at the MIT Plasma Science and Fusion Centre and his colleagues have successfully and experimentally demonstrated that the well-known force of gravitation between two test bodies varies with their orientation in space, relative to a system of distant stars.
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 per cent, according to Gershteyn's experiments, a remarkable and unprecedented finding that has landed his paper on the subject in the journal Gravitation and Cosmology.
"The existence of such an effect requires simply 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 co-workers 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.
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.
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