One of the great problems in thinking about cosmology is trying to picture what the Universe looks like. It is important to remember that the Big Bang was the expansion of all Space, Time, Matter and Energy. It was not an explosion in a vast pre-existing "shoebox" of Space. There was no point "outside" the Big Bang from which you could watch it all unfold. In other words there is no Universe outside of the Universe even during the Big Bang!
Another point to keep in mind is that when Einstein invented his cosmolgical models, he thought he needed a static universe. To keep his model Universe from collapsing on itself (via gravity) he needed to add a special term which he called the Cosmological Constant. The Cosmological Constant corresponded to an energy that filled all space and which kept everything apart. After Hubble discovered that the Universe was expanding, Einstein abandoned his Cosmological Constant and called it the worst mistake of his life. Now it seems that Einstein may have been right after all. There may be an invisible energy that permeates all space and is causing the Universe to accelerate its expansion. For simplicity we have not included a discussion of the Cosmological Constant in this interactive.