According to the Standard Models of Cosmology concerning the Big Bang. Space and Time itself came into creation by the singularity. There is no "before" the Big Bang within the property of Time in our natural universe. And there is no "outside" within our spacial system.
This is very counter-intuitive of course. It is hard to get a mental image in one's mind to how this works. It can really only be understood by abstract conceptions and mathematical formulas and such.
But an image that has helped me is to image the universe like an expanding balloon, with the galaxies being buttons on the balloon being pushed apart. The surface of the balloon would be our three dimensional space in this analogy. The galaxies are getting further apart as the balloon expands. And the balloon keeps expanding endlessly from its apparent beginning as a single point that seemingly came out of nowhere. Of course this image has the balloon within a 3 space already, and we are missing a dimension, so its not a perfect analogy.
What is outside the universe is outside of space and time. It is not in any way subject to the space and time of our universe. It is like the relationship between an author and a story the author and the fictional world the author creates in a book. The characters in the book can travel to any time or place within their universe, but they will not find the author as a phenomena in that universe...and yet the author in another sense is found everywhere in their universe.
“In the beginning God created the heavens and the earth. 2 Now the earth was >formless and empty<, darkness was over the surface of the deep....”
Anyway...
Weird to think that space-time is actually moving... so as not to violate the Theory of Special Relativity. If it applies to the early universe — the physical laws may not work or apply??
Also, what is happening at the boundary where space-time doesn't exist yet as the universe expands — just outside the surface of the balloon?
Thinking classically and using your balloon example, as space-time is expanding it is filling the nothingness — the nothingness that existed before the big bang?