A Erik Verlinde's new view on dark matter

[ohwilleke]

Just curious: a lot of these approaches rely on weak field approximations. Could it be that because of that we're overlooking non-linear effects which could explain the data? I'm thinking in the spirit of e.g. monster/rogue-waves, caused by non-linear effects of the hydrodynamical equations underlying them.

Probably too naive, but just wondering :)

I think that it is highly likely that there are non-linear effects in weak fields that are giving rise to phenomena interpreted as modified gravity or dark matter, and that some of the non-linearities get ignored inappropriately because of simplifying assumptions that aren't justified or a failure to recognize how a very slight effect can have a cumulatively important consequence in large scale systems when a force is always attractive.

 

[PeterDonis]

Could it be that because of that we're overlooking non-linear effects which could explain the data? I'm thinking in the spirit of e.g. monster/rogue-waves, caused by non-linear effects of the hydrodynamical equations underlying them.

Do you have any references for this type of model being applied in cosmology?

I think that it is highly likely that there are non-linear effects in weak fields

Based on what theoretical model?

Everyone, please bear in mind the PF rules about personal speculations.

 

[ohwilleke]

A summary of some of the empirical data can be found, for instance, at Federico Lelli, et al., "One Law To Rule Them All: The Radial Acceleration Relation of Galaxies" (October 27, 2016). Examples models addressing this data or exploring non-linear extensions of GR include: J.W. Moffat and M.H. Zhoolideh Haghighi, "Modified gravity (MOG can fit the acceleration data for the cluster Abell 1689" (November 16, 2016); Borut Bajc and Francesco Sannino, "Asymptotically Safe Grand Unification" (October 30, 2016); Sascha Trippe, "Can Massive Gravity Explain the Mass Discrepancy - Acceleration Relation of Disk Galaxies?" (May 28, 2013); Sacha Trippe "A Derivation of Modified Newtonian Dynamics" (March 28, 2013) (using a massive graviton approach); Dagoberto Escobar, "Born-Infeld type modification of the gravity" (September 28, 2012, last revised November 5, 2012); Max I. Fomitchev, "Dark Matter and Dark Energy as Effects of Quantum Gravity" (September 7, 2010); M. Wellmann, "Gravity as the Spin-2 Quantum Gauge Theory" (March 6, 2001); Leonardo Modesto, "Tree Level Gravity - Scalar Matter interactions in Analogy with Fermi Theory of Weak Interactions using Only a Massive Vector Field"(January 4, 2004).

 

[haushofer]

Do you have any references for this type of model being applied in cosmology?
Based on what theoretical model?

Everyone, please bear in mind the PF rules about personal speculations.

All I'm saying is that when one applies the linear approximation, non-linear effects could possible give rise to phenomena one cannot account for without doing a full numerical analysis.

I don't see how remarks like this contradict PF rules.

 

[haushofer]

I was asked to give a 1-hour talk about it at my university for future physics teachers; in Holland, where I work, it was quite a media hype. Maybe I could turn the talk into an insight later on. Details are still not clear to me, which is not strange of course, but it is also nice to put the story into a historical context. E.g. regarding the question about Dark Matter whether the theory is incomplete, or the observation. As Carroll says, the first one is much cooler and more interesting for the media to speculate upon :P

 

[ohwilleke]

Another new paper supporting the importance of non-linear quantum gravity effects in weak fields.*

We study two self-interacting scalar field theories in their strong regime. We numerically investigate them in the static limit using path integrals on a lattice. We first recall the formalism and then recover known static potentials to validate the method and verify that calculations are independent of the choice of the simulation's arbitrary parameters, such as the space discretization size. The calculations in the strong field regime yield linear potentials for both theories. We discuss how these theories can represent the Strong Interaction and General Relativity in their static and classical limits. In the case of Strong Interaction, the model suggests an origin for the emergence of the confinement scale from the approximately conformal Lagrangian. The model also underlines the role of quantum effects in the appearance of the long-range linear quark-quark potential. For General Relativity, the results have important implications on the nature of Dark Matter. In particular, non-perturbative effects naturally provide flat rotation curves for disk galaxies, without need for non-baryonic matter, and explain as well other observations involving Dark Matter such as cluster dynamics or the dark mass of elliptical galaxies.

A. Deur, "Self-interacting scalar fields in their strong regime" (November 17, 2016).

* Deur's reference to the strong field regime in gravity is to fields generated by large masses, not to large gravitational forces. Usually a weak gravitational force generated by a large mass would be called the weak field regime, while the term of "strong field" regime in gravity would be limited to cases where the strength of the gravitational field in absolute terms was very large at a given point (e.g. near black holes).

This paper builds on previous papers (both published in peer reviewed journals) in 2009 and in 2014.

What Deur does in all three papers is to overcome the mathematical difficulties involved in analytically solving a full self-interacting spin-2 graviton equation by modeling a self-interacting spin-0 graviton which captures the physics of the static case. He then convincingly argues that his conclusions (suggested by a scalar simplification of QCD which is matched in full spin-1 gluon QCD) would not be eliminated by generalizing his self-interacting spin-0 graviton model to the spin-2 case, because in the systems studied, the tensor contributions of angular momentum, linear momentum, pressure and electromagnetic flux that are present there are modest compared to the self-interaction effects observed in the spin-0 case.

(Newtonian gravity is a non-self-interacting spin-0 graviton model except that the non-interacting spin-0 graviton couples to energy (including photons) as well as to rest mass and propagates at the speed of light rather than instantaneously.)

Both Deur's work and the MOG papers by Moffat refute the claim of Clowe, et al. in their 2006 paper that: "An 8-sigma significance spatial offset of the center of the total mass from the center of the baryonic mass peaks cannot be explained with an alteration of the gravitational force law, and thus proves that the majority of the matter in the system is unseen."