Adrian59 said:
That is what I thought. I don't know if you have seen the Barker et al paper (arxiv.org/abs/2303.11094) but it appears to get bogged down in minutiae. They, as I said, spend a whole section refuting a 'scalar model' which would appear irrelevant wrt Deur's papers. They then spend time refuting a gravito-electro- magnetic approach which is also irrelevant wrt Deur's papers. They only get around to discussing Deur's paper directly in section IV where they write, 'it seems difficult to understand how factors of order 10^3 in the lensing could arise’. They seem to be suggesting that this is what Deur does, but I can not see how the ΛCDM model and Deur can be three orders of magnitude different.
I have quickly skimmed Barker, et al., but still haven't given it the deep dive that it deserves.
On the whole it is a sincere and fair minded effort. But I do have some issues with their approach, which is basically an attempt to reproduce Deur's claims from scratch using the same assumptions, rather than looking at Deur's analysis on a step by step basis like a geometry proof and then identifying where they think Deur made a misstep.
As readers, we are left to puzzle that out ourselves. But, it matters quite a lot.
For example, even though Deur wrote one truly classical GR paper, his original work as a quantum gravity inspiration in a weak field domain of applicability where the failure to quantum gravity efforts to remain mathematically sound in the ultraviolet doesn't matter. If he has actually picked up on a quantum gravity deviation from classical GR as conventionally applied, for example, that's a less discouraging problem than a problem with dimensional analysis or an overlooked cancellation of terms.
Another place that could be ripe for a disconnect is that in the spiral galaxy case, he picked the parameter kappa of the self-interaction term in the spiral galaxy geometry case to fit observations originally fitted for MOND rather than deriving it from first principles as a function of Newton's constant G and the geometry and mass scales involved.
Refuting a scalar model is an appropriate strategy, but by using the method of trying to reinvent it from scratch and concluding that it comes to a different result, it isn't entirely clear what the source of the problem with the scalar model is other than that they can't make one that works.
What is the tensor formulation bringing to the party that the scalar model doesn't?
Naively, the hypothesis that one can safely ignore contributions from linear momentum, angular momentum, electromagnetic flux, and pressure in the context of galaxy scale astronomy, just as the scalar Newtonian approximation of GR does, doesn't seem unsound.
Does Deur have the GR Lagrangian wrong (he does expand it into a series in a somewhat unusual way)?
Baker doesn't seem to really pick up on the strong importance conceptually of self-interaction being a second order effect that declines in magnitude more slowly with distance than the first order Newtonian term - making it irrelevant since it starts out so weak, in fields comparable in strength to those where MOND does not apply, while making it important beyond that point with a naturally realized interpolation function.
Is the main issue, in the spiral galaxy context anyway, not the GR Lagrangian itself, but the kappa parameter used for the self-interaction term which they find to be too large calculating from first principles of GR?
Also, while refuting a scalar approximation is an important step, it doesn't explain how the result could seemingly be replicated by Deur with classical GR in one paper.
In short, while Baker et al. is not confirming, it also doesn't provide much insight into why that should be the case.
I would also welcome a paper dissecting different layers of Deur's analysis to again, pin point what is problematic and what might be salvageable.
For example, most of the large scale structure and Hubble constant conclusions that Deur reaches require only a far more general model in which dark matter phenomena are actually gravitational effects, and where increased dark matter phenomena magnitudes in a galaxy or galaxy cluster translate into reduced attraction between galaxies and/or galaxy clusters. Is there any promise to this very general class of gravitational explanations of dark matter and dark energy?
As far as I can tell, there is similarly no analysis of the notion of gravitational field flux tubes, by analogy to QCD, in galaxy clusters.
