SciPost Commentary Page
Original publication:
| Title: | Emergent Gravity and the Dark Universe |
| Author(s): | Erik Verlinde |
| As Contributors: | (none claimed) |
| Journal ref.: | SciPost Physics 2, 016 |
| DOI: | https://doi.org/10.21468/SciPostPhys.2.3.016 |
| Date: | May 16, 2017 |
Abstract:
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional 'dark' gravitational force describing the 'elastic' response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton's constant and the Hubble acceleration scale a_0 =cH_0, and provide evidence for the fact that this additional `dark gravity~force' explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
Youngsub Yoon on 2025-05-02 [id 5434]
I, Youngsub Yoon, and my collaborator, Ho Seong Hwang wrote a comment on "Emergent Gravity and the Dark Universe" as a pdf file, and attached it to this post. Here is the abstract:
In "Emergent Gravity and the Dark Universe," Verlinde justifies a formula by three different derivations. However, we discovered that all these three derivations miss the same factor "2/3." If this factor is taken into account, Milgrom's constant used in Verlinde's emergent gravity must be given by cH_0/9=0.76\times 10^-10 m/s^2 instead of Verlinde's original value cH_0/6=1.1\times 10^-10m/s^2, which roughly agrees with 1.2\times 10^-10 m/s^2, Milgrom's constant used in Modified Newtonian Dynamics. However, fitting galaxy rotation curves with Verlinde's emergent gravity shows that the most preferred value for Milgrom's constant in Verlinde's emergent gravity is also 0.76\times 10^-10 m/s^2, smaller than its most preferred value in MOND. This confirms that the missing factor 2/3 is real.
Attachment:
CommentonEmergentGravityYYHSH.pdf