Will black holes evaporate, if they evaporate? When and why do they evaporate? What are the conditions for evaporation? Under what principle do they evaporate?
The evaporation occurs through Hawking radiation. This is a very slow and low energy process. So low that the cosmic microwave background radiation, which is just a few degrees above absolute zero, pours far more energy into the black hole than Hawking radiation takes away. So in principle a black hole cannot evaporate.
With the exception of conjectured atomic sized black holes, that is, as Hawking radiation would be more pronounced then.
Edit: See this answer on the physics SE: https://physics.stackexchange.com/a/26607/55483 The black hole would need to be less massive than the moon to radiate more energy than it absorbs. Bigger than atomic size, as I suggested.
hawking radiation. electrons and positrons created from the vacuum must 'repay' their energy, usually through annihilation of each other. however, if one crosses through the event horizon of a black hole and the other escapes, the energy from the black hole as well as that of the particle will 'repay' and the escaped particle becomes real. this is a very slow process and in most circumstances I would assume that a black hole would accumulate more energy than it loses.