Sunday, September 8, 2019

A New Paper By Deur On Gravity

Alexandre Deur has a new paper out on gravity with some collaborators. I'll comment when I have time to read it more carefully (if ever). The conclusion, followed by the abstract and citation information are below.
CONCLUSION Our findings support the possibility that GR’s self-interaction effects increase the gravitational force in large, non-isotropic mass distributions. When applied to disk galaxies, the increased force on the observed matter transposes to the missing mass needed in the traditional Newtonian analyses. We have thus proposed a plausible explanation for the correlation between the luminous mass in galaxies and their observed gravitational acceleration shown in MLS2016. That this correlation is encapsulated in our basic, parameter-free, models indicates its fundamental origin. 
The explanation proposed here is natural in the sense that it is a consequence of the fundamental equations of GR and of the characteristic magnitudes of the galactic gravitational fields, and in the sense that no fine tuning is necessary. This contrasts with the dark matter approach that necessitates both yet unknown particles and a fine tuning in galaxy evolution and baryon-dark matter feedbacks [see e.g. 2]. We used several approaches that are quite different, thus leading to a robust conclusion. 
The work presented here adds to a set of studies that provide straightforward and natural explanations for the dynamical observations suggestive of dark matter and dark energy, but without requiring them nor modifying the known laws of Nature. This includes flat rotation curves of galaxies [3], the Bullet cluster [3, 6], galaxy cluster dynamics [3], and the evolution of the universe [5]. The Tully-Fisher relation [8] also finds an immediate explanation [3]. There are compelling parallels between those observations and QCD phenomenology, e.g. the equivalence between galaxies’ Tully-Fisher relation, and hadrons’ Regge trajectories [3, 4], plausibly due to the similarity between GR’s and QCD’s underlying fundamental equations. The fact that these phenomena are well-known for other aspects of Nature that possess a similar basic formalism; the current absence of natural and compelling theory for the origin of dark matter (supersymmetry being now essentially ruled out); and the yet unsuccessful direct detection of a dark matter candidate or its production in accelerators despite coverage of the phase-space expected for its characteristics; all support the approach we present here as a credible solution to the missing mass problem.
The paper is:

Significance of Gravitational Nonlinearities on the Dynamics of Disk Galaxies

The discrepancy between the visible mass in galaxies or galaxy clusters, and that inferred from their dynamics is well known. The prevailing solution to this problem is dark matter. Here we show that a different approach, one that conforms to both the current Standard Model of Particle Physics and General Relativity, explains the recently observed tight correlation between the galactic baryonic mass and its observed acceleration. Using direct calculations based on General Relativity's Lagrangian, and parameter-free galactic models, we show that the nonlinear effects of General Relativity make baryonic matter alone sufficient to explain this observation.
Subjects:Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc)
Cite as:arXiv:1909.00095 [astro-ph.GA]
(or arXiv:1909.00095v1 [astro-ph.GA] for this version)
The is Sargent's only pre-print, but Balsa Terzic is a published dark matter researcher with eight papers published in peer reviewed journals from 2002-2007.

Along similar lines is this new paper:

Dynamical Regularities in Galaxies

Galaxies are observed to obey a strict set of dynamical scaling relations. We review these relations for rotationally supported disk galaxies spanning many decades in mass, surface brightness, and gas content. The behavior of these widely varied systems can be summarized with a handful of empirical laws connected by a common acceleration scale.
Comments:8 pages, 6 figures; invited review for IAU Symposium 353: Galactic Dynamics in the Era of Large Surveys
Subjects:Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
Cite as:arXiv:1909.02011 [astro-ph.GA]
 (or arXiv:1909.02011v1 [astro-ph.GA] for this version)


neo said...

so how do you learn about these papers?

jd said...

Go to Google Scholar and type in Deur. Or use any other science literature search engine. To understand the general idea just read the papers. Deur has been publishing for a number of years. To understand details will take some effort, but that is always the case. (General relativity and perhaps some QFT.) There is another author, recently published, who does everything classically. Deur may be doing that in this latest work.

andrew said...

@neo I read the pre-prints from arXiv (almost) every day they are updated.

neo said...

that's dedication. reminds me of old marcus at PF.

so if Deur's correct here, there's no need to modify GR to give rise to MOND, and this paper, unlike earlier ones, is on the classical level.

i wish GR experts and QCD would evaluate this.

andrew said...

"if Deur's correct here, there's no need to modify GR to give rise to MOND"

Deur is not really accurate on this point if, by modify GR, you mean "modify GR as it is operationally defined by physicists who work with GR today.

He has applying a fairly naive GR Lagrangian, based upon assumptions that are at the core of what GR is derived from, but not Einstein's equations. As a result, is modeling the self-interaction of the gravitational field in a manner different than conventional GR does. In particularly, Einstein's equations model gravitational self-interaction indirectly, rather than as part of the stress-energy tensor like all other sources of mass-energy, while Deur models gravitational fields on an equal footing with non-gravitational fields as an input.

I'm also not convinced that the Lagrangian that he devises is strictly classical even if it looks superficially like a more classical set of equations. And, I believe that he is still using a scalar graviton approximation in the weak field case, although I haven't had time to read the latest article closely enough to be sure, which is a quite satisfactory approximation in weak fields but doesn't work in the dynamic case or when a significant share of inputs are things other than ordinary matter and fluxes in Standard Model fields.

The big point made by this article is that it can robustly fit large data sets of galaxies even if some parameters and assumptions are tinkered with.

There are qualitative differences between Deur's theory and MOND, the two most notable of which are that (1) the shape of a mass distribution is important (the more spherically symmetric a mass distribution is the less of an effect there is, which in the other direction explains the excess of apparent dark matter in galaxy clusters), and (2) dark energy effects arise because gravitons diverted to creating dark matter phenomena aren't leaving the galaxy and hence reducing the strength of the gravitational facts between galaxies that have lots of apparent dark matter - a qualitative factor that almost makes possible lots of nice theoretical properties like mass-energy conservation and localization of gravitational energy.

neo said...

do you find Deur's conclusions persuasive then?

i recall there was a paper that took into account gravitational binding energy as a way to explain mass discrepancy.

there's also the issue of mass discrepancy in galaxy clusters as well.

i know that dark energy results in negative pressure, but since it is a source of energy, shouldn't that energy also result in gravitational attraction like any other source of energy, perhaps explaining MOND

andrew said...

I find Deur's conclusions to be extremely persuasive. My gut instinct is that there is a more than 75% chance that his approach will ultimately be found to be the correct solution of the problems of quantum gravity, dark matter and dark energy, albeit, possibly with some refinements.

One way in which Deur's approach is superior to MOND is that it accurately estimates (to back of napkin precision, at least) the mass discrepancy in galaxy clusters, which is something which MOND understates.

Deur's approach to dark energy is particularly revolutionary (even relative to other gravitationally based explanations of dark matter and dark energy phenomena), because rather than considering it to be "negative pressure", or an integration constant in the equations of general relativity, or a substance as in quintessence, or an inherent property of space-time, he explains it very differently, as a diminution of the strength of the gravitational attractions between systems in which dark matter phenomena are significant in a form (basically) of gravitational shielding. In his analysis, gravitons in galaxies and galaxy clusters are diverted from their would be paths outside the system that pull it towards other galaxies and galaxy clusters, and instead diverted towards pulling masses at the fringes of the system towards it more tightly giving rise to a phenomena that looks like it is a dark matter halo in a galaxy or galaxy cluster.

There is almost no other dark energy hypothesis along this line that is currently receiving active investigation. But, it is really the only way that it is possible to reconcile the experimental results attributed to dark energy or the cosmological constant, and conservation of mass-energy. It also explains the "coincidence problem" (i.e. why the inferred amount of ordinary matter, dark matter and dark energy in the universe according to lambdaCDM cosmology are about the same).

andrew said...

"i recall there was a paper that took into account gravitational binding energy as a way to explain mass discrepancy."

This isn't a horrible way of describing what is going on in Deur's approach, which most fundamentally differs from conventional GR in the way it considers interactions between gravitons (at the quantum level) or gravitational fields (at the classical level).

neo said...

Deur's approach posits gravitons, and the main problem w/ this is pertubative gravitons is non-renormalizable. i don't see Deur changing this.

string theory, at least according to some, is uv-completion

neo said...

i had in mind this paper

A new perspective on galactic dynamics
Matteo Tuveri, Mariano Cadoni arXiv:1904.08209

"We derive the radial acceleration of stars in galaxies by using basic features of thermodynamics, statistical mechanics and general relativity. We assume that the "dark" component of the radial acceleration is originated from the reaction of dark energy to the presence of baryonic matter."

here dark energy interacts with baryons is what causes MOND like effects, reminds me of Smolin's paper.

i like this idea since the scale of a0 can be derived from the cc.

Mordehai Milgrom just published this paper

Noncovariance at low accelerations as a route to MOND

In particular, we do not know that all the principles underlying ND or GR apply below a0. I discuss possible breakdown of general covariance (GC) in this limit.

andrew said...

"Deur's approach posits gravitons, and the main problem w/ this is pertubative gravitons is non-renormalizable. i don't see Deur changing this.

string theory, at least according to some, is uv-completion"

From a practical perspective, Deur solves the non-renormalization problem by using a scalar graviton approximation and demonstrating that the magnitude of the difference between a scalar graviton system (which is also equivalent to the static solution in the tensor case) and a tensor graviton theory is small in weak fields in relativity stable systems.

A stringy type graviton is a possibility in Deur's approach and while sting theory's graviton was developed in the course of research on that theory, it is an idea that is severable to a significant extent from the larger edifice of string theory.

Re the other papers, I certainly don't disagree that there are other approaches being considered and it is important that none of them be quashed entirely, although some are more promising than others. As a category, I find the gravitational explanations, in general, to be considerably more plausible than the dark matter particle proposals.