Erik Verlinde published his paper on gravity as an emergent property, not unlike temperature, making the need for dark matter obsolete. It’s tempting to look for this kind of solutions, as it’s never a satisfying proposition to need 95% of your explanations depending on something unknown. Time will tell.
Recent theoretical progress indicates that spacetime and gravity emerge \break 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 a0=cH0, 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. … (ArXiv)