  In this paper we study the near-field thermodynamics of a photon gas at
equilibrium as well as out-of-equilibrium in the presence of dissipative
effects. As a consequence of Heisenberg's uncertainty principle, we are able to
eliminate the low-frequency modes in both cases, providing an analytical
expression for the near-field entropy. In addition, we obtain the
entropic-force contributions to the Casimir effect. At zero temperature the
well-known $l^{-4}$ behavior of the pressure is obtained. In the nonequilibrium
case, we compute the entropy production, showing that the excess of heat in
each bodies must be dissipated into the respective thermal reservoirs.

Mesoscale and Nanoscale Physics