[Physicist]

The "gravity is instantaneous" crowd is the suffering party in this instance.

You could hardly put Peter van Nieuwenhuisen ("Mr. Supergravity" we called him, when I was at Stony Brook) in that category.

I'm a little perplexed at the controversy, as this experimental methodology has been "on the table" for some time. You'd think these objections would have been raised from serious quarters sooner.

[Mind-numbed Robot]

If it were true, a big door would open to wild theories of how the universe might work on the grandest scales, including its possible interaction with other universes or other dimensions. Even a slight difference in the speeds of light and gravity would give theorists nifty wiggle room to craft bizarre ideas about the mechanics of the unseen universe.

So why not just assume away and come up with all these other wonderful possibilities then check them for validty (even though based on possibly a false asumption)? Aren't many mathematical principles (theorems and such) assumptions which lead to seemingly valid conclusions?

[Lonesome in Massachussets]

Could you offer a précis of the observations, and how they are used to measure the speed of gravity, and the arguments against this interpertation?

[Paradox]

I'm a little perplexed at the controversy, as this experimental methodology has been "on the table" for some time. You'd think these objections would have been raised from serious quarters sooner.

I read their results in "New Scientist" magazine. Perhaps the establishment is a bit miffed that they went ahead and "published" in a non-technical weekly such as that one?

I also wonder how much this has to do with the work by Kopeikin. To quote New Scientist:

"He reworked the equations of general relativity to express 
the gravitational field of a moving body in terms of its mass, 
velocity and the speed of gravity. If you could measure the 
gravitational field of Jupiter, while knowing its mass and 
velocity, you could work out the speed of gravity". 

Is Kopeikins work generally regarded as valid? I admit I dont keep up on physics.

[atlaw]

I just dropped a flashlight on the kitchen floor. It broke, but as far as I could tell, the light and the flashlight got there at the same time.

[William Tell]

Physicist said: ' I'm a little perplexed at the controversy, as this experimental methodology has been "on the table" for some time. '

Physicist, I haven't had time to read up on this and I can't handle any General Relativity content. However, I have a perhaps simplistic view of what might be observable here.

Einstein's prediction that light would be affected by gravity predicts that light from a distant star will not follow a straight line when passing close to our sun but will be slightly bent toward the sun. Thus, the apparent position of a star which appears near the sun during an eclipse can be different than it would be without the effect of the sun's gravity.

I am imagining that Jupiter's gravity would have the same effect on the light from a distant star ( or galaxy ), and thus the light coming from the star would bend toward Jupiter if it passed through the stronger gravity near its surface.

Since the measurement of time has become so accurate with cesium beam clocks and such, it would be possible to chart the apparent position of the star versus time.

If gravity was instantaneous, then the symmetry of Jupiter's shape would result in equal bending of light on either side as Jupiter passes in front of the star. For the sake of my description, imagine that Jupiter is passing from right to left.

As Jupiter nears the path of light from the star, the light is bent such that the star would seem to shift toward our left as Jupiter nears it. The light would be travelling on a more and more curved path which would pass closer and closer to Jupiter's surface, until it would finally have to pass through Jupiter to get to us. At that instant, the star would disappear behind Jupiter.

As Jupiter moves further to the left, the star will appear on the right of Jupiter. Its position will be shifted to the right from where it would be without the presence of Jupiter. As Jupiter continues to pass to our left, the apparent position of the star will move to the left until it once again occupies the position in the sky expected in the absence of Jupiter.

Since the travel times to earth are virtually the same for all of these light rays, and assuming that gravity is instantaneous, I would predict that the apparent movements of the position of the distant star would be symmetrical with respect to both time and position of Jupiter. Or, in other words, if a movie of this event were filmed and run backwards, the events would be just as if we were viewing the original event in a mirror.

Now, finally, for my question. Is the experiment alluded to here one of measuring asymmetry in the apparent shifting of the position of the star? I can imagine that this event might have an asymmetrical appearance in both time and space if the gravitational field being generated by Jupiter was slight lower in the direction in which Jupiter is advancing because of a finite propogation speed for "gravity waves" or "gravitons" or whatever is interacting with the photons from the distant star.

Is this roughly what is happening? I am trying to save myself the disappointment of looking up the source materials and finding that I can't follow it.

Thanks for any tutoring.