Posted on 05/08/2002 7:29:49 AM PDT by Nebullis
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."
My dear fellow, I did do as you suggested, and my head still hurts. However, nowhere in there did I find anything to back up the journalist's claim that the pull you feel when you "swing a bucket of water at the end of rope" is caused by centrifugal force, which is merely a convenient layman's notion, or so I was told in school.
More importantly, the journalist reporting on Gestheyn's findings wrote that "These [centrifugal] forces result from the combined gravitational pull of all the distant stars and planets, Austrian physicist Ernst Mach wrote." I never doubted that there is a "combined gravitational pull of all the distant stars and planets": this has always seemed a given to me because there is no range limitation to gravitational force. However, I always believed that for practical purposes, we earthlings need only take into account the gravitational force exerted by the Earth, the Sun and the Moon. What the journalist is suggesting is the exact opposite.
But as we all know, journalists never lie.
They also tell us that Clinton was a great president and that GWB is an uneducated moron, which I naturally have always taken for the gospel truth.
But if this journalist is not telling the truth then...
Oh my! Please say it isn't so.
Right, my understanding is that the force you feel is the force you exert towards the center in order to draw the bucket out of its desired straight path. Note that the direction of force (inwards) is the same as the direction of the acceleration (that being the 2nd derivative of the position as a function of time)
s(t) = ( cos(t), sin(t) )
v(t) = s'(t) = ( -sin(t), cos(t) )
a(t) = s''(t) = ( -cos(t), -sin(t) )
Sorry - couldn't help myself :-)
But for "G" to be non-invariant with respect to direction, it would seem that there would have to be a corresponding anisotropy in the matter distribution of the Universe. But as far as I know, no such anisotropy has been observed.
What gives?
I'm glad I never comitted the value of G to memory.
Sounds good to me. Things should be more scrunched up along the axis where the pull is stronger. And they're not that anyone's said so far.
It's not clear to me that an anisotropic G would lead to any anisotropy in the distribution of matter. But if it did, the matter distribution would have been used to set a limit on the anisotropy of G. Presumably this experiment was more sensitive than any existing limit, else it wouldn't have been mounted.
My thinking was that if the initial condition were an isotropic matter distribution AND an anisotropy for the gravitational constant, then one would expect over time that matter would preferentially cluster around the direction of maximum "G" value, thus resulting in a matter distribution anisotropy.
My reaction is that matter either averages somewhat denser viewed in one direction than in another or else it doesn't. But not too many people are agreeing with longshadow and me that the problem should produce so visible a result.
Perhaps the problem is that a 0.054 percent difference just doesn't model out to be enough to produce visible effects.
Anyway, the one thing people agree on is that this area needs more study. Does the max gravity perhaps lie along our galactic plane, with the peak toward the center? If not, where and what is the anisotropy producting the difference in G?
I'm having trouble visualizing that.
You want me to save the world again? I'm already fully engaged on the other thread.
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