Verlinde's Emergent Gravity Doesn't Work

[ohwilleke]

Verlinde sought to reproduce the successes of other modified gravity theories in a variant of his entropy based gravity theories called "emergent gravity". Unfortunately, it doesn't reproduce the observed data.

Verlinde (2016) has recently proposed that spacetime and gravity may emerge from an underlying microscopic theory. In a de Sitter spacetime, such emergent gravity (EG) contains an additional gravitational force due to dark energy, which may explain the mass discrepancies observed in galactic systems without the need of dark matter. For a point mass, EG is equivalent to Modified Newtonian Dynamics (MOND). We show that this equivalence does not hold for finite-size galaxies: there are significant differences between EG and MOND in the inner regions of galaxies. We confront theoretical predictions with the empirical Radial Acceleration Relation (RAR). We find that (i) EG is consistent with the observed RAR only if we substantially decrease the fiducial stellar mass-to-light ratios; the resulting values are in tension with other astronomical estimates; (ii) EG predicts that the residuals around the RAR should correlate with radius; such residual correlation is not observed.

Federico Lelli, Stacy S. McGaugh, and James M. Schombert "Testing Verlinde's Emergent Gravity with the Radial Acceleration Relation"(February 14, 2017).

Another study also looking at a different set of data with different investigators reaches basically the same conclusion.

It was recently proposed that the effects usually attributed to particle dark matter on galaxy scales are due to the displacement of dark energy by baryonic matter, a paradigm known as emergent gravity. This formalism leads to predictions similar to Modified Newtonian Dynamics (MOND) in spherical symmetry, but not quite identical. In particular, it leads to a well defined transition between the Newtonian and the modified gravitational regimes, a transition depending on both the Newtonian acceleration and its first derivative with respect to radius. Under the hypothesis of the applicability of this transition to aspherical systems, we investigate whether it can reproduce observed galaxy rotation curves. We conclude that the formula leads to marginally acceptable fits with strikingly low best-fit distances, low stellar mass-to-light ratios, and a low Hubble constant. In particular, some unobserved wiggles are produced in rotation curves because of the dependence of the transition on the derivative of the Newtonian acceleration, leading, even in the most favorable case, to systematically less good fits than MOND. Then, applying the predicted transition from emergent gravity in a regime where it should be fully applicable, i.e. in spherical symmetry and outside of the bulk of matter, we show that the predictions for the secular advances of Solar System planets' perihelia are discrepant with the data by seven orders of magnitude, ruling out the present emergent gravity formalism with high confidence.

Aurelien Hees, Benoit Famaey, and Gianfraco Bertone, Emergent gravity in galaxies and in the Solar System (February 14, 2017).

 

[kodama]

Verlinde's specific proposals may not work

but on theoretical grounds, should there be an additional gravitational force due to dark energy, one that reproduces MOND ?

Verlinde also proposes that dark energy interacts with baryonic matter.

is this theoretically sound idea?

Lee Smolin, which also posits an additional gravitational force due to dark energy, could work.

the scale of MOND and dark energy are surprisingly close.

if there is an additional gravitational force due to dark energy, and interactions between baryonic matter and dark energy, then it's a question of getting the details correct.

 

[Chronos]

IIRC it has already been concluded that DE must contribute to the stress energy tensor, which renders it indistinguishable from the contributions of the gravitational field to Lambda.

 

[kodama]

IIRC it has already been concluded that DE must contribute to the stress energy tensor, which renders it indistinguishable from the contributions of the gravitational field to Lambda.

if there is an additional gravitational force due to dark energy, and interactions between baryonic matter and dark energy,reproduces MOND ?

 

[kodama]

A Covariant Version of Verlinde's Emergent Gravity
S. Hossenfelder
(Submitted on 4 Mar 2017)
A generally covariant version of Erik Verlinde's emergent gravity model is proposed. The Lagrangian constructed here allows an improved interpretation of the underlying mechanism. It suggests that de-Sitter space is filled with a vector-field that couples to baryonic matter and, by dragging on it, creates an effect similar to dark matter. We solve the covariant equation of motion in the background of a Schwarzschild space-time and obtain correction terms to the non-covariant expression. Furthermore, we demonstrate that the vector field can also mimic dark energy.
Comments: 14 pages, no figures
Subjects: General Relativity and Quantum Cosmology (gr-qc)
Cite as: arXiv:1703.01415 [gr-q

Hossenfelder Bee paper on this