Emergent Gravity and the Dark Universe

• Published in: SciPost physics Vol. 2; no. 3; p. 016
• Main Author: Verlinde, Erik P.
• Format: Journal Article
• Language: English
• Published: SciPost 16-05-2017
• ISSN: 2542-4653; 2542-4653
• DOI: 10.21468/SciPostPhys.2.3.016

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
a
0
=
c
H
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.