  A curvature self-interaction of the cosmic gas is shown to mimic a
cosmological constant or other forms of dark energy, such as a rolling tachyon
condensate or a Chaplygin gas. Any given Hubble rate and deceleration parameter
can be traced back to the action of an effective curvature force on the gas
particles. This force self-consistently reacts back on the cosmological
dynamics. The links between an imperfect fluid description, a kinetic
description with effective antifriction forces, and curvature forces, which
represent a non-minimal coupling of gravity to matter, are established.
