Is there an alternative theory to dark matter?

[PAllen]

I am pretty sure neither Cooperstock (in a classical GR framework) or Deur (in a quantum gravity framework) are actually applying mainstream GR to get their results and actually subtly deviate from mainstream interpretation of GR. But, the fact that both investigators can get such impressive results with such very, very subtle tweaks to GR interpretation is in my view very promising. It is not at all obvious that conventional GR does not have a subtle flaw or two that make a big difference at large scales in weak gravitational fields.

Everyone agrees that Newtonian gravity has to be modified. GR is a Newtonian gravity modification. The question is whether GR has to be modified.

Cooperstock, without doubt, believes he is applying absolutely conventional GR. His series of papers is certainly interesting after a skim, but I probably will not have time to study them.

 

[nikkkom]

The fact of the matter is that there is no theory of dark matter consistent with all the data.

Are nuMSM sterile neutrinos ruled out?

 

[ohwilleke]

Are nuMSM sterile neutrinos ruled out?

Yes. Any theory with sterile dark matter is inconsistent with the evidence.

 

[ohwilleke]

Cooperstock, without doubt, believes he is applying absolutely conventional GR.

Agreed. But, I think he is probably incorrect.

 

[strangerep]

[...] I think [Cooperstock] is probably incorrect.

Why? Have you tried to reproduce his computations and found an error?

 

[nikkkom]

Yes. Any theory with sterile dark matter is inconsistent with the evidence.

I did read your long post with links, but none of the papers seem to be ruling out nuMSM neutrinos.

Specifically, ~2-10keV sterile right-handed neutrinos with very small Yukawa coupling to active neutrinos. They do decay into active neutrinos, but lifetime is many orders of magnitude larger than age of the Universe. The resulting X-ray line is not expected to be easily seen. Tentative detection of 3.5 keV line might be it, though.

 

[Adrian59]

I seem to remember that although I was quite excited by the abstract of the Cooperstock paper, the conclusion that Newtonian and GR theory could be so different was totally implausible, and on closer inspection the results seemed to be spurious artifacts related to the use of a rotating coordinate system which didn't appear to be self-consistent, which was quite disappointing. I don't remember the details, but there are probably papers out there which discuss the problems; I think it was discussed in a thread on PF at the time.

I searched PF for the thread you alluded to regarding the Cooperstock paper; it did appear to raise some interest. I agree that it would be “implausible’ for Newtonian mechanics to differ widely from GR but the question remains open as to which is in error. There have been a few papers suggesting that Newtonian gravity can be applied successfully to spiral galaxies and give the observed profiles; please see my other reference given in post 10, Jalocha, J., Bratek, L. and Kutschera1, M. (2008). ‘Is Dark Matter Present in NGC 4736? An Iterative Spectral Method for Finding Mass Distribution in Spiral Galaxies.’ Astrophysical Journal, vol 679, pp 373–378. Though, one point of interest is that both these papers use a Bessel function.

 

[Adrian59]

No you can't. It is observable via gravity, specifically lensing. It is easy to imagine a scenario (that hasn't happened) whereby placement needed to explain dynamics is contradicted by lensing observations. Then you would be pretty much forced to look at modified gravity of some sort.

Just to remind you this comment was in response to a suggestion that dark matter distribution could be a free parameter. However, whilst I fully agree with your point that the dark matter has to be detectable by lensing or dynamics, it is not the case that all experimental data concur that there is a large discrepancy. Even some galaxy cluster studies appear to show that one does not require dark matter. Ref: Lu et al (2010). ‘Large-scale structure and dynamics of the most X-ray luminous galaxy cluster known – RX J1347−1145’. Mon. Not. R. Astron. Soc. 403, 1787–1800.

 

[ohwilleke]

I did read your long post with links, but none of the papers seem to be ruling out nuMSM neutrinos.

Specifically, ~2-10keV sterile right-handed neutrinos with very small Yukawa coupling to active neutrinos. They do decay into active neutrinos, but lifetime is many orders of magnitude larger than age of the Universe. The resulting X-ray line is not expected to be easily seen. Tentative detection of 3.5 keV line might be it, though.

The problem wiht nuMSM neutrinos is that they are collisionless.