A friend of mine heard a popular science show on the radio. A caller asked what is better to wear on a hot day, white clothes or black clothes. The answer given was that it did not matter because although black absorbs more readily it also radiates it more readily. My friend said of course that is true, because these things should be symmetric. My thoughts were that although I do not know about rates of heat radiation, it does not seem to me that processes must be symmetric. For instance, in thermodynamics, entropy always increases, which does not seem symmetric to me. My question has two parts In this specific case, are the two processes symmetric? In general, are physical processes symmetric?