> > Going back to basics, it seems to me that our experience with orbital > mechanics for spacecraft and satelites and our use of the "slingshot > effect" to propel interplanetary missions to the outer solar system > are pretty good evidence that we have a good theory and a good grasp > of it.
Well, the fact that we can use it is always a good confirmation. Very precise measurements of this effect, more precise than needed to use the effect, will allow us to test the predictions of GR. So that's a good thing. > We have had discussions here of the Pioneer Anamoly in the past, and > IIRC the question is still open so it isn't like we need to abandon > current theory as unrealistic. The last thing that I read was that the anomalies were consistent with at least one possible mundane cause. This is, almost universally, considered a lack of evidence supporting an unknown force in science. Even, as with the orbit of the moon, there appears to be no mundane explanation for observed phenomena, the explanation almost always ends up being mundane. So, the Pioneer Anamoly, while probably worth continued investigation, does not offer any evidence for new physics. Dark matter is only quazi-new physics....its existence can be explained within the standard model. For the lurkers, I might mention that dark matter is needed to explain gravitational attraction in galaxies...which is higher than one would expect from the gravitational attraction of the observed matter. Dark energy, on the other hand, is not explicable in terms of the standard model. It postulates a new force...an anti-gravity force. This force is sufficient to overcome gravity and accelerate the expansion of the universe. As an aside, the first results of GP-B will be given at the APS meeting in April. My guess is that they are not earth shattering....or they'd be pre-announced in the press. Dan M. _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
