Red Shift.
One thing that has been ruled out with the observation of the red shift is that dust picking up the higher frequencies has caused the red shift in the sky where expansion is concerned. What has not been rulled out is whether or not high frequency light in night sky over long distances decays to lower frequency light due to long term interation with quatum noise.
One way to test for this would be further analaysis on light from our galaxy and learn better to identify expansion redshift from other redshift types and see if it appears as if out own galaxy seems to be moving away from itself in some way. If this is the case and It is distance related then light indeed is decaying across a quantum vacuum in such a way.
Galatic Gravitation.
Calculating the mass of our galaxy it seems as if there is not enough to hold it all together.
The current explaination is that the galaxy has invisible mass with gravitational properties. Although to a small degree this may be true there doesn't still seem to be enough mass.
An alternative explaination to this is that all the mass around solar systems is pulling on the star or binary ect star in such a way that causes a gravitational sail like effect and that the solar system is simply more suceptable to gravity due to this effect.
One way this effect could be tested for is by deep analysis of stella movement around the galaxy as to calculate the impact of system mass on the stars overall volicity in relation to the galaxy.
It think here especially polytheism will be key to an accurate answer.