Big bang for the Big Bang.

What we see as the Big Bang was simply something happening to our little piece of space-time 13.7 billion years ago. There could be multiple "sheets" of space-time (sometimes called "branes" floating around in an infinitely large multi-dimensional Universe, with everything we see being confined to just one).
When these sheets bump into each other, they become very hot and expand, so to anyone living on a sheet today it would look like their Universe began at the point of collision.