I'm far from clued-up on the matter, but I'm of the opinion that the big bang was born from a black hole. Which I discussed here on SN. Many credible astronomers believe something similar, but the question would then be whether that black hole came from THIS universe or another.
  1. The black hole could have gotten too dense, too heavy and too tightly compacted that it would explode and unwind.
  2. The other option is it was formed from a black hole in another universe, with energy passing through a wormhole.
Either way, we need more attention on this subject! For too long we have questioned the existence of the big bang, when to me it just seems obvious that human's current understanding & theories surrounding spacetime is incomplete. I would also like to see more people trying to break it down into layman's terms. This subject should be approachable to everyone with a curious mind.