trinitree88: The energy that that occurs in the Heisenberg Uncertainty Principle is real and therefore positive.

dcl: That is certainly true in most situations of pair production. But how about Hawking radiation? As I understand it, the energy that is converted into a particle pair just outside the event horizon is said to be borrowed temporarily from space itself as opposed to pair production via conversion of energetic radiation and is called "negative energy". If you know the above to be incorrect in any way, I'll appreciate your explaining what is wrong with it. I'm a physicist, but not a particle physicist.