A thermodynamic motivation for dark energy

Abstract

It is argued that the discovery of cosmic acceleration could have been anticipated on thermodynamic grounds, namely, the generalized second law and the approach to equilibrium at large scale factor. Therefore, the existence of dark energy -or equivalently, some modified gravity theory- should have been expected. In general, cosmological models that satisfy the above criteria show compatibility with observational data.

Comments: 22 pages, 7 eps figures; Key words: dark energy, thermodynamics, modified gravity. Comments added and arguments sharpened