Gravitational anomalies: An invisible hand?

From The Economist print edition ^ | Aug 19th 2004

[my_pointy_head_is_sharp]

Hahahahaha! - I love it! <:D

[swilhelm73]

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.

Well, air, as all matter, does exert a gravitational pull, though an incredibly tiny one. And yes, cooler air, being denser, will exert slightly more pull.

But that being said, isn't the effect of concern here air resistance instead? The ambient temperature will have a much greater effect on air resistance then the gravitational pull exerted by said air...

[my_pointy_head_is_sharp]

ping!

[griffin]

bump!

[datura]

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.

[NetValue]

"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."

Huh? Traveling in opposite directions from the sun? I did not realize the sun traveled. Help me out here (/snicker).

[Renfield]

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.

[Junior]

For your perusal.

[Physicist]

If the change in the rate of the pendulum is due to a change in the force of gravity, I don't see why a scale wouldn't measure the effect far more accurately.

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.

[KarlInOhio]

If that were the cause, there would be a gradual change during the day as the point of measurement changed distance from the center of mass. The maximum and minimum times would change as the location of the moon changed during the month. However the paper the article references shows a definite spike during the eclipse. If the measurements are correct, something stranger is going on.

[Physicist]

The pendulum swings faster because it is closer to the center of gravitational attraction of the system, making gravity ever-so-slightly greater.

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.

[steve in DC]

A finite amount of air (or steel, or water, or whatever) has a given mass, no matter what temperature it may be.

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.

[sionnsar]

bump

[Boundless]

> So what are the alternatives?
> ... Majorana shielding ...
> Another idea is “MOND” ...

Suppose gravity is a push, and not a pull?

_____________
Believe it or not ST, I bought a SCSI
adaptor two weeks ago - 50HD female to
50LD male - probably the last SCSI
component I'll ever buy.

[PatrickHenry]

Maybe nutty. Science list Ping! This is an elite subset of the Evolution list.
See the list's description in my freeper homepage. Then FReepmail me to be added or dropped.

[Alamo-Girl]

Thanks for the ping!

[B-Chan]

Interesting post. Thanks for putting it up.

MOND means “moon” in German, by the way.

[SauronOfMordor]

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.

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

[Doctor Stochastic]

Explanation (PDF Alert): Phys Rev D 2003

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.