The quantum theory of near horizon regions of spacetimes with classical
spatially flat, homogeneous and isotropic Friedman-Robertson-Walker geometry
can be approximately described by a two dimensional conformal field theory. The
central charge of this theory and expectation value of its Hamiltonian are both
proportional to the horizon area in units of Newton's constant. The statistical
entropy of horizon states, which can be calculated using two dimensional state
counting methods, is proportional to the horizon area and depends on a
numerical constant of order unity which is determined by Planck scale physics.
This constant can be fixed such that the entropy is equal to a quarter of the
horizon area in units of Newton's constant, in agreement with thermodynamic
considerations.Comment: 11 pages, no figure
