  We show that there are implications on thermodynamics that come from the
existence of the initial cosmic singularity. At present time this is more a
conceptual change than an observable one. However at very early cosmic times
there is a big difference between the actual behavior of thermodynamic
quantities and the behavior assumed in the standard cosmological model. We
present the discussion of two systems: an ideal monatomic gas at present, and a
photon gas at the early Universe. We show the striking result that the entropy
density goes to zero as the cosmic time goes to zero. This in turn, provides an
explanation for the so called horizon problem.
