在热力学中,固定体积和温度的封闭系中的均匀光子气体具有如下性质:对平衡时的粒子数取确定值,非平衡时的粒子数变化.前者的化学势为零,后者的化学势非零.
In thermodynamics, the photon gas for a given the volume and the temperature has following proper- ties: the number of photons is fixed once in an equilibrium and is variable once out of the equilibrium, and thechemical potential is zero for the former whereas it is non-zero for the latter.