Posted on 08/21/2004 1:31:57 AM PDT by ScuzzyTerminator
Gravitational anomalies
An invisible hand?
An unexplained effect during solar eclipses casts doubt on General Relativity
“ASSUME nothing” is a good motto in science. Even the humble pendulum may spring a surprise on you. In 1954 Maurice Allais, a French economist who would go on to win, in 1988, the Nobel prize in his subject, decided to observe and record the movements of a pendulum over a period of 30 days. Coincidentally, one of his observations took place during a solar eclipse. When the moon passed in front of the sun, the pendulum unexpectedly started moving a bit faster than it should have done.
Since that first observation, the “Allais effect”, as it is now called, has confounded physicists. If the effect is real, it could indicate a hitherto unperceived flaw in General Relativity—the current explanation of how gravity works.
That would be a bombshell—and an ironic one, since it was observations taken during a solar eclipse (of the way that light is bent when it passes close to the sun) which established General Relativity in the first place. So attempts to duplicate Dr Allais's observation are important. However, they have had mixed success, leading sceptics to question whether there was anything to be explained. Now Chris Duif, a researcher at the Delft University of Technology, in the Netherlands, has reviewed the evidence. According to a paper he has just posted on arXiv.org, an online publication archive, the effect is real, unexplained, and could be linked to another anomaly involving a pair of American spacecraft.
Three different types of instrument have been used to detect the Allais effect. The first are conventional pendulums, such as the one Dr Allais used originally. The second are torsion pendulums, which work by hanging a bar that has weights at each end from a wire. As the wire twists back and forth, the bar rotates in pendulum-like motion. The third are gravimeters, which are, in essence, very precise scales. All of these instruments measure the acceleration due to gravity at the Earth's surface, a quantity known as g. The Allais effect is a small additional acceleration, so tiny that it would take an apple about a day to fall from a tree branch if it were the only gravitational effect around.
Dr Duif has examined various conventional explanations for the Allais effect. He finds the most obvious suggestion—that it is a mere measuring error—unlikely, because similar results have been found by many different groups, operating independently and, in at least one case, without knowledge of Dr Allais's results.
He also discounts several explanations that rely on conventional physical changes that might take place during an eclipse. One of these is that the anomaly is caused by the seismic disturbance induced as crowds of sightseers move into and out of a place where an eclipse is visible. That seems unlikely, given that one of the experiments with a positive result was conducted in a remote area of China while another that had a negative result took place in Belgium, one of the most crowded parts of the planet. Dr Duif also considered the possibility that, because the moon's shadow cools the air during an eclipse, this cooler, and thus denser, air might exert a different gravitational pull on the instruments. This change could, he reckons, affect a gravimeter, but it cannot account for the results from the pendulums.
Dr Duif rules out a third explanation, too: that cooling of the Earth's crust due to the eclipse shadow causes the ground to tilt slightly, and thus distorts the results. He notes that although a detectable tilt is caused when the temperature drops by a few degrees, that tilt is too small to explain the anomalies and, in any case, it would lag roughly 30 minutes behind the shadow (because it takes time for the ground to cool) while the experimental measurements show a change in g instantaneously during an eclipse.
Although Dr Duif discounts each of the conventional explanations on its own, he admits that they might, in combination, account for the Allais effect. But the possibility also remains that General Relativity—Einstein's sacred child—is wrong.
This suggestion would fit in with another odd phenomenon: the fact that the Pioneer 10 and 11 space-probes, launched by NASA, America's space agency, in the early 1970s, are receding from the sun slightly more slowly than they should be.
According to a painstakingly detailed study by the Jet Propulsion Laboratory, the part of NASA responsible for the craft, there is no conventional explanation for this. There may, of course, be no relationship with the Allais effect. But Dr Duif points out that the anomalous force felt by both Pioneer probes (which are travelling in opposite directions from the sun) is about the same size as that measured by some gravimeters during solar eclipses.
So what are the alternatives? One possibility (though it could not account for the Pioneer observations) is known as Majorana shielding. This eponymous theory is that large masses (such as the moon) partially block the gravitational force from more distant objects (such as the sun). Another idea is “MOND”, or Modified Newtonian Dynamics, a theory put forward in 1983 by Moti Milgrom of the Weizmann Institute in Israel. MOND suggests that at very low accelerations gravity gets a bit stronger. An even stranger suggestion, made in 2002 by Mikhail Gershteyn, then at the Massachusetts Institute of Technology, is that the force of gravity is different in different directions. Most physicists do not like that one at all. It requires that the conceptual “frames of reference” against which movement, acceleration and so on are measured, are not uniform in all directions. But it was a similarly radical idea—that there is no absolute frame of reference in the universe, only local frames that can be measured relative to one another, which put the “relativity” into relativity theory in the first place...
Hahahahaha! - I love it! <:D
ping!
bump!
Can't the force of g be somewhat dependent upon the distance from gravitational bodies? Certainly there is a gravitational pull on the earth from the sun (hence our orbit) - why couldn't the moon shield us from that momentarily, even when you consider diffraction of the gravitational force?
Seems as though the results of the current mission to Saturn have shown that gravitational forces can be planar as well.
Huh? Traveling in opposite directions from the sun? I did not realize the sun traveled. Help me out here (/snicker).
This is a very silly post. The Allais effect is only puzzling to someone who fails to view the Earth, the moon, and the sun as a single system.
All objects with mass exhibit gravitational force. The force of gravitational attraction between 2 objects is inversely proportional to the square of the distance between those two objects, so the farther away the objects are from each other, the weaker the attraction is, but it is still there. The Earth, for example, has a gravitational attraction for Pluto, and vice-versa, even though they are billions of miles apart. So, the gravitional force that an observer measures is related to his distance from the center of mass of all those objects that are exhibiting gravitational force on him.
When the moon is on the opposite side of the earth from the sun, the center of mass of that system is slightly farther away from the observer on the surface of the earth, than if the moon is in line between the earth and the sun. When the moon eclipses the sun, it is directly in line between the earth and the sun, so the center of mass (and the center of gravitational attraction) will have its maximum shift sunward along a line stretching between the earth and the sun...and near which the observer of the eclipse will be. (I am ignoring the effects of variations in the moon's orbital radius). The pendulum swings faster because it is closer to the center of gravitational attraction of the system, making gravity ever-so-slightly greater.
For your perusal.
If the change in the rate is due to a distortion of spacetime, I don't see why an atomic clock wouldn't measure the effect far more accurately.
That doesn't work, because the Earth is in free-fall with respect to the combined sun-moon system. The only part that doesn't cancel is the gravitational gradient, AKA the tidal force, and this definitely is greater during an eclipse.
The earth,s atmosphere is finite. Thus its mass is the same, no matter what its density might be.
Gravity is said to be inexorably tied to mass, not density. Giant gas planets have a gravitational pull that correlates with their mass, not their density. Although, that is not necessarily correct, in that their mass has been back calculated based upon the strength of their gravitational pull.
bump
> So what are the alternatives?
> ... Majorana shielding ...
> Another idea is “MOND” ...
Suppose gravity is a push, and not a pull?
_____________
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Thanks for the ping!
Interesting post. Thanks for putting it up.
MOND means “moon” in German, by the way.
If so, then the effect should also be observed whenever the moon is more-or-less in line with the sun (ie, once every month), rather than exclusively being seen during an eclipse
This article should have been available to "The Economist" had their reporter been scientirically literate. The paper was even in the references to Duif's paper. It's worthwhile to iterate the bibliography operator.
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