First off, spontaneous generation was a question raised based off of maggots "spontaneously" appearing in the carcass of a dead animal. Now, The Big Bang is not an event when something just blew up in nothing. It was an expansion of our universe from a singularity. Our universe used to be the size of a grain of salt, maybe smaller, as there was nothing outside of it. But then it started to expand, as all the crammed up energy help without spread outward into what we know as our universe.