In a closed system, heat transfer is a losing game. All energic transactions are headed for absolute zero. The physicists always throw that in, like some kind of legal rider, some incantatory caveat. The thing is, they don't really know, and this is the place they have to admit it. They're talking about the universe, you know.
Science is so cool.
Not like religion, which is so mysterious and all, so unnecessarily complicated by the things you get to know and the things you don't. Since the Enlightenment, we get to know it all. Except, of course, those bits we can't. Like, for instance, whether the universe is open or closed. If it was all just energy and mass, it wouldn't really matter much.