The Big Bang did not happen inside our universe, at least that's what our best understanding of physics seems to be telling us during the last 70 years!

The fact of the matter is that we do not really understand how the universe came about. We cannot revisit that time, so obviously any scientific descriptions we form have to be based on how the rest of the universe operates and our detailed understanding of the constitution of matter and the laws governing its interaction. The hardest features of the universe for us to intuitively understand are the relativistic theories which seem to govern how matter, energy and space-time operate under extreme conditions of temperature, density and energy.

The issues of where the Big Bang occurred and how it happened seems to be locked up in these unfamiliar and very subtle features of the physical world. It is impossible for a non-mathematician, using the best crafted essays, to completely understand what it has taken decades of mathematical/logical abstraction and intense experimental analysis to create.

The best, non-mathematical description that any cosmologist can create for describing the Big Bang is that it occurred in every cubic centimeter of space in the universe with no unique starting point. In fact, it was an event which our mathematics indicate, actually brought space and time into existence. It did not occur IN space at a particular location, because it created space ( and time itself) as it went along. There may have existed some state 'prior' to the Big Bang, but it is a state not described by its location in time or space. This state preceded the existence of our time and space.