Is there an alternative theory to dark matter?

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Discussion Overview

The discussion revolves around alternative theories to dark matter, particularly focusing on modified gravity and other explanations for gravitational phenomena attributed to dark matter. Participants explore the implications of these theories, the current state of experimental evidence, and the challenges in reconciling observations with existing models.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants mention modified gravity as an umbrella term for theories that attempt to modify general relativity at large scales, noting that experimental evidence does not favor one approach over another.
  • Others argue that the number of publications on dark matter significantly outweighs those on modified gravity, suggesting that no modified gravity theory is consistent with all data.
  • There is a contention regarding the consistency of the dark matter hypothesis with experimental data, with some asserting that it is not falsifiable due to the flexibility in positing unobservable matter distributions.
  • Participants discuss the implications of small cross sections for dark matter candidates like WIMPs, raising questions about the limits of detection and the ongoing search for these particles.
  • Some propose that alternative explanations, such as the possibility of ordinary matter or undiscovered massive particles, are less likely, while others highlight the potential for new models of gravity.
  • A few participants reference specific papers that propose alternatives to dark matter, suggesting that these ideas are often overlooked due to the prevailing dark matter paradigm.
  • Concerns are raised about the circular reasoning in measurements of mass density and stellar velocities, questioning whether these measurements truly support the dark matter hypothesis.

Areas of Agreement / Disagreement

Participants express a range of views, with no consensus reached on the validity of dark matter versus alternative theories. Disagreements persist regarding the interpretation of evidence and the viability of modified gravity theories.

Contextual Notes

Limitations in the discussion include the dependence on definitions of dark matter and modified gravity, as well as unresolved questions about the experimental detection of dark matter and the implications of small cross sections for proposed particles.

  • #31
ohwilleke said:
One can't absolutely rule out either modified gravity or dark matter theories, and neither has a perfect and well validated solution yet.

Thanks for your comprehensive analysis of the current status of dark matter research. It has taken me a while to get through it all. The main findings that I took to be is that the LHC and Planck do not show physics beyond the standard model; and CDM appears to be inconsistent with astronomical observations. I note you have given a published reference for the Cooperstock paper that I mentioned first in this thread and in doing so I presume mfb should be more happy

(mfb said: ↑
Sure.Submitted to arXiv 2010. Where is the publication? If that would be a solid result clearly they would have tried to publish it? Why didn't it get published?)

but in doing so are you in any way convinced by the argument that galaxy rotation curves could be explained without recourse to exotic matter or modifying Newtonian gravity..
 
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  • #32
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.
 
  • #33
I've been reading some work by Hartnett on Carmeli's treatment of SpaceTime, using the Hubble Law as an axiom, with rapid acceleration of the universe, including a bounded, possibly isotropic universe, which is interesting because, as our choice of cosmological philosophy is purely personal, we find that the regular working out of Hartnett and Carmeli's approach avoids the need for dark matter or dark energy to solve for the excess velocities of stars, or more accurately, hydrogen atoms, in distant galaxies. The number of critically selected parameters is very low, according to Hartnett, while the data-fit with actual Galaxies is very good.

As I'm not competent at that level of physics, I wonder if anyone more advanced can offer a critique of Hartnett's working?
I have no question about his choice of cosmology, only about the veracity of his physics working.
The publication I have read about Hartnett and Carmeli's work in, is ISDN 978-0-949906-68-7 'Starlight Time and the New Physics', Dr John Hartnett, PhD 2007

International Journal of Theoretical Physics carries some of the work, by JG Hartnett, issue 45, page 11.:2118-2136, 2006. It's online in the archive at arxiv.org/abs/astro-ph/0511756, I can't find it at reuters...but it must be legit enough surely? Article titled 'Spiral galaxy rotation curves determined by carmeli...'
 
  • #34
Adrian59 said:
but in doing so are you in any way convinced by the argument that galaxy rotation curves could be explained without recourse to exotic matter or modifying Newtonian gravity.

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.
 
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  • #35
Graham P said:
[...] International Journal of Theoretical Physics [...] I can't find it at reuters...
It's on the Reuters list. (Do a search on the full journal title.)

[Edit: ... and then I looked up Hartnett on Wikipedia. His extracurricular activities send cold shivers down my spine.]
 
Last edited:
  • #36
ohwilleke said:
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.
 
  • #37
ohwilleke said:
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?
 
  • #38
nikkkom said:
Are nuMSM sterile neutrinos ruled out?

Yes. Any theory with sterile dark matter is inconsistent with the evidence.
 
  • #39
PAllen said:
Cooperstock, without doubt, believes he is applying absolutely conventional GR.

Agreed. But, I think he is probably incorrect.
 
  • #40
ohwilleke said:
[...] I think [Cooperstock] is probably incorrect.
Why? Have you tried to reproduce his computations and found an error?
 
  • #41
ohwilleke said:
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.
 
  • #42
Jonathan Scott said:
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.
 
  • #43
PAllen said:
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.
 
  • #44
nikkkom said:
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.
 

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