(February 23, 2018 at 8:09 pm)Banned Wrote:(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.
Once again, you have an image of some boundary expanding outwards. That is NOT what the BB model says. There is no 'beyond the universe' spatially. Instead, wherever you are, the basic 'look and feel' is the same: galaxies in all directions.
The universe isn't 'expanding into' some space beyond the universe (even in models where space is finite). Instead, the distances between galaxies *within* the universe are getting larger over time.
In a technical sense, the universe is literally expanding into the future, not into more space.
