The physics of the universe is rather conclusive on the big bang. Not 100% obviously, but alternatives aren't many; and conclusive enough that many theists and atheists have come to accept it, with their own "spin".
And that "spin" is funny in that a lot of folks make an assumption that there was nothing before the big bang. No evidence has been shown that there was nothing, and no evidence has been shown that there was something. So it's all assumptions, conjecture, speculation, and guesswork for all the arguments.