Ignition said:
What about the Arp's theories? I've seen the photos of the Stephan's quintet. What about them? Seems that the quasars are near other objects that look to be nearer to us than the quasars.
I see three levels to Halton Arp's work on anomalous red-shifts:
1. Are his observations and interpretations correct (for example about galaxies and quasars with different red-shifts being connected)?
I find many of them very interesting and plausible, and his weird suggestion that quasars are apparently ejected in pairs from galaxies does seem to be supported by his evidence. I feel this looks as if it could be a real anomaly which requires a physical explanation, despite the fact that at first glance it seems incompatible with current physical theory.
2. Is he correct that there is some physical effect which increases red-shifts not only for very large masses but also apparently over a whole region near to those masses?
I'm inclined to agree that some additional non-cosmological red-shift could explain many anomalies, but it's difficult to envisage a mechanism that could lead to a gravitational red-shift apparently affecting a region the size of a galaxy; this is certainly not possible with standard GR, but then neither are the observed galactic rotation curves without assuming something else such as dark matter or MOND. (I've been wondering whether there's some mechanism by which the large-scale redshift could be an illusion, for example if a quasar or galactic nucleus could be "lighting up" its environment in some way which caused red-shifted spectral features to be re-emitted by the surrounding material, or even if the instruments for measuring red-shift don't focus accurately enough to be able to measure the red-shift of light which is too close to a bright central point with a different red-shift).
3. What about his theory to explain these results through "continuous mass creation" processes, and the idea that "new matter" behaves differently from "old matter"?
As far as I'm concerned, I don't find this even the slightest bit plausible, although his logical line of reasoning which led to this conclusion is quite interesting and could eventually be a useful part of the puzzle of how gravity works on a galactic scale and above.
If we were confident about gravity theory and General Relativity in particular as providing a complete explanation to the dynamics of systems on the scale of galaxies and above, then I think that it might be possible to dismiss Arp's observations as coincidences. However, at the moment GR at that scale is not working well, requiring dark matter or something like MOND at the galactic scale to fix it and dark energy at the cosmological scale, so I think it reasonable to include Arp's observations as something which might be valid and require a physical explanation, like galactic rotation curves.