What caused the big bang of our universe?

If the big bang was a black hole that exploded how is it possible for matter to escape from a black hole? I am aware that black holes can "evaporate" over time and eventually theory says they will explode and cease to be a black hole. But if the whole universe was a single black hole, then there is no where for it to evaporate into, so how could it explode? I think that supposing that quantum fluctuations are the cause of the big bang is as improbable as supposing that quantum fluctuations could teleport a person to mars. It's just not going to ever happen.