Hi everyone. I have here a problem understanding the stability of heat transfer through radiation. I'll give you some background, and later on I'll describe the physical problem. Background I am simulating the unsteady radiative heat transfer between mutually visible surfaces of objects through FEM. I am using the method of panels, which considers constant temperature on each panel. Depending on the material properties, an instability issue might arise while integrating in time. When this happens, surfaces begin to transfer heat from one region to another, with an increasing amplitude. Problem The mechanism of instability is as follows: one surface becomes slightly warmer than the other one, and as consequence, it emits more power; so in the next time step, it tends to become colder. The other surface, being slightly colder at the beginning, gets the energy and then becomes warmer. The cycle cannot be stopped unless there is some sort of damping. Question As far as I can think, this instability looks quite reasonable. It does happen here due to the discrete numerical integration; but does anybody knows why this doesn't happen in reality? Or it does happen?