Evidence of Strong Equivalence Principle Violations?

[ohwilleke]

TL;DR Summary

A group of authors in a September 2020 pre-print accepted for publication in a peer reviewed journal find strong evidence that MOND's external field effect which violates the strong equivalence principle is real.

This paper appears to be a major break though in observational evidence of a strong equivalence principle violation, something predicted in MOND and contrary to general relativity. The analysis is model dependent, but it seems to rule out the most plausible conventional GR based alternatives. Are there other problems with this analysis?

The paper is:

[Submitted on 24 Sep 2020]
Testing the Strong Equivalence Principle: Detection of the External Field Effect in Rotationally Supported Galaxies
Kyu-Hyun Chae, Federico Lelli, Harry Desmond, Stacy S. McGaugh, Pengfei Li, James M. Schombert

The Strong Equivalence Principle (SEP) distinguishes General Relativity from other viable theories of gravity. The SEP demands that the internal dynamics of a self-gravitating system under free-fall in an external gravitational field should not depend on the external field strength. We test the SEP by investigating the external field effect (EFE) in Milgromian dynamics (MOND), proposed as an alternative to dark matter in interpreting galactic kinematics. We report a detection of this EFE using galaxies from the Spitzer Photometry and Accurate Rotation Curves (SPARC) sample together with estimates of the large-scale external gravitational field from an all-sky galaxy catalog. Our detection is threefold: (1) the EFE is individually detected at 8σ to 11σ in "golden" galaxies subjected to exceptionally strong external fields, while it is not detected in exceptionally isolated galaxies, (2) the EFE is statistically detected at more than 4σ from a blind test of 153 SPARC rotating galaxies, giving a mean value of the external field consistent with an independent estimate from the galaxies' environments, and (3) we detect a systematic downward trend in the weak gravity part of the radial acceleration relation at the right acceleration predicted by the EFE of the MOND modified gravity. Tidal effects from neighboring galaxies in the ΛCDM context are not strong enough to explain these phenomena. They are not predicted by existing ΛCDM models of galaxy formation and evolution, adding a new small-scale challenge to the ΛCDM paradigm. Our results point to a breakdown of the SEP, supporting modified gravity theories beyond General Relativity.

Comments:	ApJ, accepted, 14 figures, 2 tables
Subjects:	Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
Cite as:	arXiv:2009.11525 [astro-ph.GA]
	(or arXiv:2009.11525v1 [astro-ph.GA] for this version)

 

[robwilson]

The only problem I see with it is that it is a classical analysis, not a quantum analysis. If you are looking at a regime in which the gravitational field is very weak, then it seems to me self-evident that you have to consider the possibility that the gravitational field is quantised, and that this affects what is going on. In electromagnetism, the effects of charge are inverse square, but the effects of spin (magnetism) are inverse linear, and surely something of the same nature is going on in quantum gravity to produce the MOND effects. This means that the crossover point comes where the (inverse-square) bosons become so weak that the (inverse linear) fermions take over. At a local level, it does not matter whether the bosons arrive from a local source or from outside, if there are enough of them, they dominate. They sweep up the local neutrinos, so that they forget the gravitational mass of the electrons they came from, and put their energy into a bosonic graviton, where it has much less effect than if it was allowed to hunt on its own.
Well, that's my theory, based on the framework for quantum gravity that is sketched in arxiv:2009.14613v5.

 

[strangerep]

The only problem I see with it is that it is a classical analysis, not a quantum analysis. If you are looking at a regime in which the gravitational field is very weak, then it seems to me self-evident that you have to consider the possibility that the gravitational field is quantised, and that this affects what is going on. In electromagnetism, the effects of charge are inverse square, but the effects of spin (magnetism) are inverse linear, and surely something of the same nature is going on in quantum gravity to produce the MOND effects.

Sorry, but,... you say "surely", yet this is completely upside-down speculation. QG effects would be expected for short-distance interaction, or ultra-strong fields.

This means that the crossover point comes where the (inverse-square) bosons become so weak that the (inverse linear) fermions take over. At a local level, it does not matter whether the bosons arrive from a local source or from outside, if there are enough of them, they dominate. They sweep up the local neutrinos, so that they forget the gravitational mass of the electrons they came from, and put their energy into a bosonic graviton, where it has much less effect than if it was allowed to hunt on its own.
Well, that's my theory, based on the framework for quantum gravity that is sketched in arxiv:2009.14613v5.

You say in your abstract that you "leave open the question of whether [your group theoretical ideas] can be implemented in physical theories".

Also, please note the rules on this forum prohibiting discussion of personal theories that have not passed peer review.

 

[robwilson]

Sorry, but,... you say "surely", yet this is completely upside-down speculation. QG effects would be expected for short-distance interaction, or ultra-strong fields.You say in your abstract that you "leave open the question of whether [your group theoretical ideas] can be implemented in physical theories".

Also, please note the rules on this forum prohibiting discussion of personal theories that have not passed peer review.

Mea culpa. I'm not interested in what is "expected", I am interested in what is actually seen in experiments, especially if it is unexpected. And the unexpected effects of gravity are seen in ultra-weak fields, not in ultra-strong fields.