Hi Guys While studying physics for my masters (doing it in material science engineering), huge amount of questions appeared. First, lets imagine two experiments 1) One enclosure with perfect reflective walls (R=1 over the entire thermal radiation spectra) at a temperature T1 and a body inside with Temperature T2 (T2 higher than T1). Lets say there is vacuum inside so energy can only be exchanged through radiation After some time, since the reflected photons have the same energy of the incoming ones, there is no energy left for increasing temperature of the wall? If that statement is true, this system will never eventually reach thermal equilibrium 2) The same enclosure but now the walls are perfect black bodies. The walls will absorb thermal radiation until it reaches the same temperature of the body inside. Is that true so the system will reach thermal equilibrium?