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Physics
Beyond the Standard Models
Deur Gravitational self-interaction Doesn't Explain Galaxy Rotation Curves
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[QUOTE="ohwilleke, post: 6866767, member: 19562"] Citation #27 addresses Cooperstock–Tieu and not Deur. It isn't breaking news. Citation #26 isn't available in preprint so the jury is out on it. Nothing in the rest of the paper discusses Deur - the rest of the paper discusses GR GEM effects (which I agree don't get it done). Cooperstock-Tieu and Deur are closer in method to each other than GEM approaches, but they are far from identical and are not even all that similar. Nothing published even in preprint form let alone a peer reviewed journal article has actually shown Deur is wrong, although a preprint may be out soon to look at and I welcome that. Presumably it would assert that the GR Lagrangian was done in the wrong way or that the effects with a parameter calculated from first principles rather than empirically determined is too weak. If his empirically fitted new parameter that he assumes can be derived from Newton's constant without actually doing so is too large and that is the only problem, it would imply the gravitons in weak fields couple to each other more strongly than to other particles with equivalent mass-energy, which I've never seen proposed by anyone before explicitly, but which wouldn't be an insurmountable feature to incorporate rigorously into a modified gravity theory. Deur discusses in multiple papers the choices he made in expressing the GR Lagrangian the way that he does and why it captures aspects of GR assumed away, for example, in linearized theories and the Post-Newtonian approximation and in spherically symmetric approximations, but can be captured in a lattice calculation comparable to lattice QCD that are not spherically symmetric, and he also discusses why the effects are present in large mass systems (like galaxies) but implicitly are not in small mass systems (like wide binary star systems). Often early critics find that a theory is invalid (which it may or may not be) because they misunderstand the new theory. Since Deur is relying on mathematical approaches widely used in QCD (his day job) and little used in astrophysics, it wouldn't be surprising if an astrophysicists criticism of the math got some of the QCD based methods that Deur relies upon wrong. But, ultimately, suppose that it turns out the Deur is a subtle modification of GR rather than the genuine article, but his equations and methods (which are not actually true GR) still explain all dark matter and dark energy phenomena and do it without the mass-energy conservation issues of LambdaCDM and GR with a cosmological constant. Who cares? It could be that he's actually identified a purely quantum gravity effect and made a mistake in his classical analysis papers, or it could be that his theory is just an outright modification that abridges a GR axiom in some subtle way. I've always been unsure over whether his approach really is truly GR but not as conventionally operationalized, as opposed to being a GR modification. But, if it works in the complete domain of applicability of all evidence about gravity, which it appears to so far, makes novel predictions so far confirmed by new astronomy data, does it without dark matter or dark energy, and isn't mathematically pathological (there has never been a hint that it is), and can do it with a tensor theory rather than the tensor scalar of LambdaCDM and GR with a cosmological constant (which also makes generalization to quantum gravity easier), and possibly has one less free parameter (which Deur has claimed but not proven by deriving an additional parameter that is used on the assumption that it could be derived), then that's still great, Nobel prize class stuff, even if he inaccurately assumed that it was equivalent to GR and even if it actually has an additional free parameter. It could be that quantum gravity has been so hard to devise because standard GR isn't quite the right theory to quantize. Still, any realistic GR modification that explains dark matter phenomena and dark energy phenomena is still going to look a whole lot like GR, because of all of the places where GR works and is proven to work (especially in strong gravitational fields). Likewise, even toy-model MOND implicitly assumes GR in gravitational fields stronger than its a[SUB]0[/SUB] physical constant and in terms of gravitational fields affecting photons and not just baryonic matter. [I]The material below until the arXiv abstract and citation, is a self-quotation from a blog post I made elsewhere, which I have given myself permission to make here:[/I] My first impressions of refracted gravity are that it has issues, although I welcome all new serious efforts to find gravitational solutions to dark matter phenomena and possibly also dark energy phenomena (which LambdaCDM does explain in the GR gravitational equation not with a new substance): (1) the shape of the matter distribution doesn't seem to be important and it doesn't seem to have a source of isotropy violation, which are both problematic; (2) like GR with a cosmological constant and many other gravity modifications, it is a scalar-tensor theory (Deur's GR-SI is a pure tensor theory as is GR without a cosmological constant) - an important downside of a scalar-tensor v. a tensor theory is that it makes generalization to a quantum gravity theory harder; (3) unlike Deur's approach, it doesn't appear to resolve the conservation of energy issues associated with the lion's share of gravity theories with a dark energy component, but this calls for closer inspection and isn't entirely clear from the abstract; (4) further inspection of the permittivity-mass density relationship proposed is necessary for me to really understand it; (5) it appears to have one more experimentally fixed parameter than GR with a cosmological constant, similar to relativistic MOND with a cosmological constant; (6) there are lots of key areas (early galaxy formation, CMB peaks, cluster dynamics, Bullet cluster, cluster collision rate expectations, tendency of satellite galaxies to line up in planes, Hubble tension) where it isn't clear what is predicted although other papers may develop the theory more fully; (7) all development of gravity based solutions to dark matter and dark energy phenomena are a welcome change, even though I'm skeptical that this will get the job done and the core assumption about permittivity isn't very well motivated (at least in the abstract). (8) Refracted gravity (with apologies to Sabine Hoffenfelder) is a fairly ugly theory (worse than toy model MOND). Deur's GR-SI (for GR self interaction) methods are very beautiful and elegant. That counts for something. The abstract and paper on refracted gravity that I've read is as follows, although I am aware that there are several more out there. Andrea Pierfrancesco Sanna, Titos Matsakos, Antonaldo Diaferio, "Covariant Formulation of refracted gravity" [URL='https://arxiv.org/abs/2109.11217']arXiv:2109.11217[/URL] (September 25, 2021) (submitted to Physical Review D). [/QUOTE]
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Deur Gravitational self-interaction Doesn't Explain Galaxy Rotation Curves
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