I do not understand this argument. Because we theorize there was a Big Bang then this means God does not exist? I do not understnd. At what point does science and creation conflict?
As I understand it, Stephen Hawkings made a statement that the current state of scientific knowledge is such that mankind now knows so much about the universe, its development and functioning that gods are not needed to explain anything. This indeed does start from the Big Bang.
This then would leave only the Big Bang to be explained. I say this as nothing that any holy book says about the universe, its development and functioning is true unless it agrees unambiguously with science.
If that is the case, then all holy books can be disregarded as far as the advancement of mankind is concerned and the gods within their pages vanish.
Based upon what holy books say about natural events after creation - plagues, droughts, earthquakes, storms, floods, etc., we can say they are wrong.
If they are all wrong, why should the statement made by those books about a god who brought a universes into existence be considered true?
Consider a person who tells you about his life. It is a fascinating story filled with adventure, riches, adversity and many wonderful places. However, you later find proof that he has consistently lied. You go back to him. You remonstrate with him. He says,
"I'm sorry, I let my imagination carry me away. Everything was indeed a lie. Did I ever tell you about how I was born a Prince of the House of Hapsburg and am entitled to the Throne of Hungary?"
Are you going to accept this? Or do you fear that he has lapsed into his old ways?
Gods are what we do not, as yet, know. They are ignorance. The origin of the Big Bang is unknown. Gods fit in here because we do not know. There are those who worship that ignorance. There are others who try to discover the answer.
So yes, "Because we theorize there was a Big Bang then this means God does not exist." is not quite true, it is simply the billions of years thereafter that make gods fictitious.
So, what seems more likely, some undetectable, immortal invisible, all-knowing, etc., being, who looks like us, flicking his fingers or some tremendous reaction of a form of energy?