h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Although no evidence from the Voyager craft has yet proven it conclusively, the Pioneer 10 and 11 craft that preceeded them (heading in opposite directions to each other) appear to be acceperating out of the solar system.

This has lead many to speculate whether the current theory of gravity is correct.

I don't think that it justifies serious doubts.

Do you have Internet references for that?

Sadly no. I read it in "New Scientist"
They have a web-page, but only the current articles are available. The others require a subscription to access.

However, it is a well known phenomenon and you should have no trouble searching for it on the web.

The acceleration, BTW, is miniscule. The only reason anyone noticed is because of the distance the Pioneers have travelled is so huge. One day someone noticed the distance was slightly huger than it should be.

Unfortunately, one of the Pioneers (I forget which) has stopped functioning, so the part they use for a distance check (essentially bouncing a signal off it, but it needs to amplify the signal back) is no longer working.

In my opinion everything else (beginning with deep space mass distribution) is put in question before one tries to find an alternative to today's gravitation theory.

Well the interesting thing that I read recently was that although Einstein's theories cover gravity, no-one knows whether they work over large distances, say between galaxies.

And the only alternative (Newton's mechanics) have been shown to be only an approximation to gravitational attraction. They are not perfectly accurate.

Maybe they do not know the value of the so called Cosmological Constant. It's equal to a global slightly repulsive force between all masses.

But if this is not meant, I find it too speculative.

At the risk of being accused of self-promotion;

Check out my entry on The De Sitter Horizon: A1109576

It has a bit at the end about the cosmological constant.