Gravity and Thermodynamics I was thinking about something today. Einstein's equations famously said that matter can neither be created nor destroyed, only converted from one form to another. Does this sort of equilibrium apply to temperature as well? One thing we can observe is that the universe is expanding and as so becoming increasingly colder by the light year, and that stars and black holes are forming creating immense temperatures. Is the formation of the stars and black holes consistent with the expansion of the universe and the over all temperature of matter? To say, as space gets greater and further apart, does matter become more dense in order to remain consistent with a constant that provides thermal equilibrium in a changing universe?