A little clarification: atheists don't usually bring up the argument of the Big Bang, except as a counter to the theists' asserion that their god did it. Also, the originator of the model which came to be christened the Big Bang Theory, Georges Lemaître, was a Catholic priest as well as an astronomer and professor of physics.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'