Wednesday, November 11, 2020

Strong Observational Evidence Supports The Existence Of the External Field Effect

This September 2020 paper accepted for publication in a peer reviewed journal makes a strong empirical case that the external field effect predicted by MOND is real and that the strong equivalence principle of general relativity is violated.

Testing the Strong Equivalence Principle: Detection of the External Field Effect in Rotationally Supported Galaxies


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.

Pub Date:
September 2020
E-Print Comments:
ApJ, accepted, 14 figures, 2 tables


jd said...

If gravitons self interact, is strong equivalence principle violated? If self interaction is put into Einstein-Hilbert, is strong equivalence violated?

andrew said...

I think it is in the former case, but I haven't analyzed the question rigorously. I don't think that it is violated in Standard GR but I'm not sure if this is rigorously established either.