A modified theory of gravity that incorporates quantum effects can explain a trio of puzzling astronomical observations ? including the wayward motion of the Pioneer spacecraft in our solar system, new studies claim.

The work appears to rule out the need to invoke dark matter or another alternative gravity theory called MOND (Modified Newtonian Dynamics). But other experts caution it has yet to pass the most crucial test ? how to account for the afterglow of the big bang.

Astronomers realised in the 1970s that the gravity of visible matter alone was not enough to prevent the fast-moving stars and gas in spiral galaxies from flying out into space. They attributed the extra pull to a mysterious substance called dark matter, which is now thought to outweigh normal matter in the universe by 6 to 1.

Now, Joel Brownstein and John Moffat, researchers at the Perimeter Institute for Theoretical Physics and the University of Waterloo in Ontario, Canada, say another modified gravity theory can account for both galaxies and galaxy clusters.

The theory, called scalar-tensor-vector gravity (STVG), adds quantum effects to Einstein's theory of general relativity. As in other branches of physics, the theory says that quantum fluctuations can affect the force felt between interacting objects.

For the entire article:
http://www.newscientistspace.com/article.ns?id=dn8631

Uncle Al - 'There is no reason to believe that gravitation propagates via quantized carriers.'

DA Morgan - 'But there is every reason to believe that gravity propagates via quantized carriers: Everything else does. Likely time and space too are quantized.'


Blacknad.

I cannot remenber where, but I have seen somewhere that scientists have claimed to have mapped the presence of dark matter. Does anybody know about this?

That is correct ... it has been mapped ... in a manner of speaking. What might be more correctly stated is that they have mapped the gravitational anomalies that are currently explained by reference to dark matter.

Thanks D A

Does this not then imply that dark matter can explain these anomalies perfectly. It sounds to me a simpler explanation than gravitons; the effects of which can only be derived via complicated perturbation analysis. I have always had a feeling that perturbation calculations lead to a "virtual reality" picture of what is really happening.

Dark Matter can't explain anything perfectly as we don't know if it exists ... and if it exists what it actually is. "Dark matter" is just a label for a specific type of gravitational anomaly we can detect but for which we have no specifically identified root cause.

That said current Dark Matter theories are consistent with what has been observed. But there are other theories, as you can see, that may also explain it.

Your analysis is of course, as usual, logical. It is, however, interesting to me that the same logic has initially been used to criticize the statistical theories (on thermodynamic phenomena) of Ludwig Boltzmann; the critical scientists argued that we "do not know if molecules and atoms exist". In quantum field theory it is postulated that the force is transmitted by the emission and absorption of "virtual particles". How do we know that they actually exist? I do not think that the Casimir effect gives any conclusive evidence.

Given that we can now build microscopes capable of imaging both molecules and individual atoms whatever "logic" has been used to argue they do not exist is obviously deficient.

Exactly. Maybe, at present, we have not the technology to "observe" dark matter?

In a sense we can observe it ... but we don't know what causes it.

An analogy I would use is like watching leaves moving on a tree when you don't know about wind. You can see the wind's effect. You can propose that the air is moving. But until you actually climb up the tree and measure wind movement you can't be sure.

Like observing Brownian motion before Einstein came along? Even Einstein's modelling of this effect has not made molecules observable, but it fitted so well that everybody accepted their existence afterwards. Dark matter gives a simple explanation except for the fact that it seems that other matter moves freely "through" it. Could dark matter not be large entangled boson-waves with mass?