(February 23, 2018 at 6:57 pm)polymath257 Wrote: In the standard BB description, there are no 'outer limits'. The universe is always spatially homogeneous: the same in all directions. Even if space is finite in extent, there are no boundaries in the way you seem to be asking.
If space extends beyond the universe, into which it is supposed to be expanding, then it must have caused that space in the first instance, or even while it is currently expanding.