The effective evolution of an inhomogeneous cosmological model may be described in terms of spatially averaged variables. We point out that in this context, quite naturally, a measure arises which is identical to a fluid model of the Kullback-Leibler relative information entropy, expressing the distinguishability of the local inhomogeneous mass density field from its spatial average on arbitrary compact domains. We discuss the time evolution of “effective information” and explore some implications. We conjecture that the information content of the Universe—measured by relative information entropy of a cosmological model containing dust matter—is increasing.

• Received 17 August 2003

DOI:https://doi.org/10.1103/PhysRevLett.92.141302