Where in the universe did the Big Bang start from?
Everywhere! The current best theories say the universe is infinite and flat. This has the mind-bending consequence that the big bang happened everywhere in an infinite universe all at once and then the whole lot began to expand (or another way of looking at it is that it all stayed where it was and the “standard unit of length measure” began to shrink). It’s easier to think of a closed universe, like the surface of a baloon, which expands from an infinitesimally small size until it is so big that from a spot on its surface it all looks pretty infinite. Actually inflation theory says that the universe is so very very much bigger than we can ever see, that it may actually be like a very very large baloon after all.
