As I understand what science is telling us both time and space did not exist before the big bang. That’s hard to make sense of – I struggle with that idea. The theory is that space grew out from the centre of the big bang, wherever that was. So the big bang sort of happened nowhere and every at the same time. Fantastic question and I hope my answer is not misleading.
The universe as we know it, all those 13.7 billion years ago, didn’t exist in a way that we can define it now in terms of space and time. The popular belief is that all the matter that exists today made made up of a singularity of infinite density and temperature. Now, a lot of people think the big bang was an explosion but it was actually an expansion faster than the speed the of light much like the thought of a balloon inflating. That might make you think that there was a starting point, and graphically it if often shown like that as the universe expands in a sphere, and we see it like that from our view of the universe here on Earth. In reality, the universe is though of to be flat and it is the same in every location and in every direction suggesting that the big bang happened everywhere at the same time. It’s a difficult concept to warp your head around, I struggle with it, but I hope that’s a least made some sort of sense!