As an athiest and as some one that isn't on top of all the latest scientific discoveries and what not. I just try to evaluate the situation based on life's experiences and some basic scientific knowledge.
I'm not even sure the big bang took place personally. They claim it did because 9f the red shift and the large amounts of energy toward the epicenter(could be off).
To me this brings up alot of questons and speculations. I mean this is suggesting that the universe has bouderies for starters. We have no evidence to my knowledge of any bounderies. Which would lead me to believe the universe is just an immensely big universe, which I'd hard for people to grasp. An ever existing infinity.
Thus doesn't negate the possibility of a multi verse. Within this infinity there could very well be segments that behave entirely different then Other segments of the infinite universe based on changes in the physics.
As far as the big bang and the shift. Perhaps massive explosions happen in large segments in the iniinty.
I'm no scientist, I'm just some basement dweller. It's seems more logical that the universe was always here, rather then some magical long beard and robe man in "heaven"(whereever that is) has been here for an infinite time and has created an infinity simply to fool the people on earth.
Tldr; santa clause isn't real, neither is god, grow up