Ok this may or may not sound like a very stupid idea. But having read the Black Hole War by Leonard Susskind, he makes a claim that as the Earth gets closer and closer to the center, squeezed by gravity, it loses potential energy. The lost potential energy is then radiated as heat, and therefore the Earth loses energy. And since energy and mass are inter-related, the Earth thereby loses mass. However, if my understanding is correct, potential energy is a relative measure [ P.E = mgh]. So would that also make mass a relative aspect as well, since energy is really mass? My understanding of the General Theory of Relativity is somewhat weak, so if anyone could just clear this up I would greatly appreciate it.