In the popular imagination, the Big Bang is a great explosion; at one time there was nothing, then matter erupted into previously empty space. However, the Big Bang is the beginning of spacetime itself, not an event in time.
Taner EdisPhysicists use 'God' as a metaphor more often than other scientists-- especially in popular writing, but in the technical literature as well. Of course, this is just a metaphor for order at the heart of confusion. A rational or aesthetic pattern underlying reality is far from a theistic God.
Taner EdisAsking about a time before the beginning of our spherical spacetime is like asking what lies north of the North Pole. There is no such thing.
Taner EdisWhen confronted with a demand that the universe have a cause, infidels have usually pointed out that God was not much of an explanation. This is true enough, but not really a positive argument. After mechanistic explanation became popular, infidels liked to restrict causality to the chain of causes in an eternal material universe, pointing out that no supernatural cause was then necessary. Plausible, but still rather defensive. Today's skeptic can do better. In all likelihood, the universe is uncaused. It is random. It just is.
Taner Edis