KIRCHHOFFS THEOREM AND THE CASIMIR EFFECT

Kirchhoff's thermodynamically based classical theorem (the energy dens ity of the radiation in equilibrium is a function of T only) is used t o obtain a relation relevant to study of the Casimir effect. We use it to obtain the zero-temperature Casimir energy without recourse to reg ularization. The intimate connection between the zero-point energy and the thermal Bose occupancy expression noted by Einstein and Stern at the turn of the century is invoked to account for the results.