Black hole thermodynamics
This chapter provides a brief overview of the relationship between black holes and thermodynamics discovered in the 1970s, and which has continued as an active field of research ever since. A black hole is a region of spacetime having a gravitational field sufficiently strong that nothing can escape from it. Are black holes in states of thermodynamic equilibrium? That begs the question of how a black hole interacts with its environment. Is a black hole a James Clerk Maxwell demon, with the event horizon being the trap door. S. W. Hawking showed that the environment of a black hole is the quantum vacuum in the vicinity of the event horizon. Black hole evaporation is not in conflict with the area theorem—a proviso of the theorem is that it holds for positive energies; antimatter—the driver of Hawking radiation—is in a negative energy state. Absolute temperature and entropy go together—fraternal twins from the same mother: Carnot's theorem.