Gravitation Anomaly Measured

Rob Riggs writes "Is there a hole in Einstein's Theory of Relativity? A story in The Economist talks about an apparent gravitation anomaly recorded during solar eclipses. According to Chris Duif at the Delft University of Technology, the 'Allais effect' is real, unexplained, and could be linked to another anomaly involving a the Pioneer spacecraft. More detailed information can be found in the paper he has just posted on arXiv.org."

Comments

3rd body problem?

[Bill, Shooter of Bul]

My limited understanding of interstellar phsyics is that einstins equations have never really been solved for the third body problems. Am I wrong? If I remeber correctly we can only aproximate third body forces (tidal forces) even when using the newtonian model.

Re:3rd body problem?

[Anonymous Coward]

Einstein's equation hasn't even been exactly solved for two-body problems; that's why black hole and neutron star collisions are such a hot topic in numerical relativity.

Nevertheless, for solar system dynamics, this is irrelevant. Newtonian gravity works quite well, and even if you did need to go to relativistic corrections, you can do that within the perturbation scheme of linearized gravity to more than sufficient accuracy.

Re:3rd body problem?

[bluephone]

Well, we _can_ but the interactions of 9 planets, a hundred moons, thousands of asteroids, etc., becomes so complex that our ability to accurately model it for (cosmically) significant periods of time is limited by computational power, thus we have to simplify the equations, and get accuracy to a more limited extent. Essentially, it's Hard(tm).

Einstein would not be surprised

[tarranp]

Einstein once said something along the following lines:

Testing theories is a very thankless task, because nature never says "yes." Usually nature says "no," meaning that a measurement contradicts a theories predictions.
Sometimes, nature says, "maybe," indicating that while the measurements are consistent with the theory.
But nature never says "yes," because your theory could be incomplete or erroneous but your instruments are either too inaccurate to detect the error, or you are not doing the right experiment.

Newtonian dynamics makes good enough predictions for alot of phenomena.

General Relativity is more precise in its predictions.

Given our difficulties in unifying it with quantum mechanics, it is likely that we don't have the right theory. As our instruments get more precise and we conduct more experiments, eentually we'll get a hint as to where we are going wrong.

Good reason for a mission to the Moon

[Engineer-Poet]

If gravity is blocked by mass, this effect would be much easier to measure on the Moon during lunar eclipses than on Earth: the entire Moon is shadowed during many lunar eclipses whereas only part of the Earth is fully shadowed during even total eclipses, and the effect should be easier to measure against the smaller gravity of the Moon.

For real confirmation, an experiment on one of the Jovian moons would do nicely.

Yes, I'm serious about this. This is fundamental to our understanding of physics, which is in turn fundamental to our understanding of the origins, processes and fate of the universe. A billion to put a pendulum on the Moon would be money well spent.

Re:One possible explanation

[Carnildo]

This could be a confirmation of one of the competing theories of gravitation: the "MOND" theory, that at very low accelerations, gravity gets stronger.

As I recall, MOND solves some of the more annoying problems of astronomy: missing matter, and the apparent need for a period of faster-than-light expansion early in the history of the universe.

Possible explanation

[Cassander]

Let's assume for the sake of argument for a second that gravity is a wave...

Could this be constructive interference caused by the collision of the gravity wavefronts from the sun and the moon when they are lined up just right?

Just a thought, the real explanation is probably much crazier.

From Chris Duif's paper:

[dexter riley]

Although, despite all proposed conventional explanations fail to explain the observations either qualitatively or quantitatively, it is likely that the reported anomalies will turn out to be due to a combination of some of these effects and instrumental errors. The judgement of some of the experimental results is hampered by the lack of a statistical analysis and/or data of sufficient length. Nevertheless, there exist some strong data which cannot be easily explained away.

And here's a point not covered in the paper: if these experimental effects occur when the moon is between the pendulum and the sun, then shouldn't they also occur every time the earth is between the pendulum and the sun...say, every night? If this effect is due to a large mass's ability to block gravity, then surely someone should have detected this effect from the earth blocking the sun's gravity by now!

On the other hand, if the effect is because moon cheese acts as a form of Cavorite, well, then I can't help you with that.

Re:Anomaly in Gravity During Sun Eclipses?

[mangu]

I work in satellite control systems. Satellites not only go through the moon's shadow, but through the earth's shadow as well. Geostationary satellites, such as most of the commercial communications satellites, go through eclipse periods twice each year, when for several weeks they cross the earth's shadow every day.

To answer your question, the effect, if it exists, hasn't been noticed because there are many other perturbing effects on the orbit. The most important, by decreasing magnitude, are: earth's gravitational attraction, moon attraction, oblateness of the earth (that is, the flattening at the poles), sun gravitational attraction, solar radiation pressure, tri-axiality of the earth (that is, the east-west irregularity in the gravitational attraction), albedo (that is, the pressure exerted by the sunlight reflected by the earth), dynamic solid tide (the gravitational effect of the earth's deformation caused by the moon's attraction), gravitational attraction by venus, gravitational attraction by jupiter, relativistic effects caused by the earth's gravitation.

So, you can see that there are so many other effects that it's pretty hard to separate each one. In particular, the effects of solar radiation and albedo change more or less randomly, so in the end, whatever cannot be explained otherwise in a satellite's orbit is normally attributed to "solar radiation".

It's only when a probe goes so far from the sun as Pluto that solar radiation becomes small enough for other perturbations to be measured.

Gravitational Anomalies in Greece

[unikron]

Well, in Penteli mountain, there are verified gravitational anomalies (there are also a hell lot more noted in the Hellenic space by physicists).

For example, you put your car in neutral in the outskirts of the mountain and instead of gravity to pull it down, it is tractored upside. Expert physicists claim there is another energy in the mountain area that is more powerful than the gravity itself, thus creating the effect.

NATO was interested (and presumambly is still) in that particular area. It's part of Greece's x-files :)

Re:If gravity is blocked by mass, then...

[Tired and Emotional]

A very nice point. However I am not sure it works. Some of the earth's own mass is shielded so the orbit is slightly larger than it ought to be, so the gravitational pull on the sun side is slightly lower and that on the shielded side slightly higher than it should be. This will at least reduce any effect.

I see no discussion in the article of the fact that the moon distorts the space around it so that when it is between us and the sun we are slightly further away from the sun than when it is not in line. This effect has to be incredibly small but it appears the allais effect, if it exists at all, is quite small, so perhaps this is the cause. Somebody should at least calculate it out.

I have seen this theory that they mention about gravity being less effective when weak. The usually more reliable Scientific American allowed an article on it to sneak in some months ago.

Its a very silly idea because it breaks the principle of equivalence - you can now tell if you are in an elevator or a gravitational field by bringing a mass close to a test mass to almost cancel out the field and observing whether or not you see the weak gravity effect.

This in turn means physics is not covariant and that there are preferred frames of reference. So its not a "small adjustment" but a total do-over of physics.

Re:Anomaly in Gravity During Sun Eclipses?

[mikael]

The individual effect of each of the Sun or the Moon on the Earth is to cause two tidal bulges of the oceans/lakes/rivers of the Earth
(one facing the object, and the other on the opposite side). These lead to diurnal (24 hour cycle) and semi-diurnal (12 hour cycle) tides.

When the Moon and Sun are aligned together, you have Spring tides. Neap tides are caused when th e Moon and Sun are perpendicular to one another. There is also the Proxigean Spring Tide, when the moon is at its closest point to the Earth (perigee). This time is known as the "proxigee", and causes even higher tides than ordinary Spring Tides. Fortunately, these only occur once every 1.5 years.

The gravitational acceleration at the Earth's surface is 9.8 metres/second per second (towards the centre of the Earth).

The gravitational acceleration on Earth due to the Sun is 0.0059 metres/second per second.
Or about 5.9 millimetres/second.

The gravitational acceleration on Earth due to the Moon is 0.000033 metres/second per second.
Or about 0.033 millimetres/second.

Source: Space Talk Forum

These amounts are small, but research groups at one of the particle accelerator rings actually noticed a distortion in the targeting of the beams due to the stretching/squashing of the surrounding land caused by the changing positions of the Sun and Moon. This caused the beam to periodically go off target.

Intuitively, one would assume that gravity would be less when the Sun and Moon were overhead, and the pendulum would swing slightly higher and slower. Plus the behavior of the pendulum should vary according to the positions of the Sun and Moon.

If the "shielding effect" occurred with large objects, then it would also apply to Earth's ocean tides. The closest side of the Earth one should shield the opposite side, but the bulging effect can be explained by simple vector addition/subtraction.

Einstein is safe

[TheLastUser]

The paper is talking about effects on the order of 0.5*10^-10 m/s^2. I don't know how anyone could measure this with a pendulum. Also, the paper doesn't show that this effect isn't accounted for by Einstein's theory. I think they need to solve the equations for the Earth/Moon/Sol system before saying that the effect disproves the theory. The only theory they talk about is Newton's theory, eg. a = gm/r^2, which we already know doesn't hold for the scales that they are talking about.

Seems to me like the effect is most likely due to someone walking their dog a couple blocks away.

More interesting is how everyone wants to prove that Einstein's theory is wrong. Seems to me like a bit of brain-envy.

Nice try, but this article only goes about 0.5*10^-10 of the way to convincing me the chuck the field equations.