After the explosion, once the smoke had all faded and the dust had settled, a countless number of galaxies, systems, stars, and planets covered a presumed infinite amount of space.
What the hell?
"Well, just pick from the existing ones."
"We could do that, but, uh, sir..."
"They all involve the supernatural and/or some sort of deity(s)."
"Holy crap! Heaven (which I don't believe exists) forbid we actually believe there are greater forces in the world than ourselves (arrogant brats aren't we?)! Quick, make something up!"
"How about... I know! A massive explosion created everything! We'll call it the 'Big Bang'."
"Think anyone will buy that?"
"If we come up with a bunch of nonsensical yet complex equations to back it up, yes."