Well I was being rhetorical, C&L tried to explain away all DM as non-linear GR efects because in a galaxy the gravitational mass is itself in orbit. Even if this did work for the galactic rotaiton curve it would not work for a galaxy cluster as the dynamics are different and the inferred DM mass is so large. I do not see how the non-linear effect of a rotating galaxy could lens light, passing at a distance from its mass, through the cluster's IGM.Tommy Anderberg wrote:Garth Antony Barber wrote:You are the relativist; you tell me. My intuitive answer would be that any GR effect which reduces the need for DM with regard to orbital motion should also mimic the effect of the replaced DM on test particles, zero mass ones included.Cluster DM has also been observed by gravitational lensing of distant quasars, do the GR non-linear effects achieve this effect without extra mass?
But suppose it didn't work out that way. If galaxies are 20% less massive than we thought, but we insist that Newtonian gravity is fine for clusters, the missing mass problem just got 20% worse for clusters. So we throw in - let me guess, 20% more dark matter at the cluster scale. What does that do to structure formation?