Something I don't understand is how the energy is subtracted from the black hole. So lets say one pair of virtual particles pop up on the event horizon, the particle goes in, the antiparticle goes out. Then lets say that a second pair does the opposite. My first question is why is the antiparticle from the first pair colliding with the particle from the second pair any different than colliding with its original partner? Has it just had enough time to become a real particle and therefore emits a photon to conserve energy? If so, wouldn't the two particles colliding inside the event horizon give off light as well? How is the energy removed from the black hole?