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From the point of cosmology *THIS* Universe (there may be many others) was
"created" ex nihilo ~15billion years ago -- at a *point* of zero volume.
Since then, this Universe has been expanding BUT it is not expanding into
some extant space -- it is creating its OWN space ie space is expanding as
well and the stuff of this Universe is expanding into this expanding space.
....
There is a debate as to whether the things (galaxies, etc) of the Universe
will catch up or not OR if the things of the Universe will collapse in
several billion years OR if space will collapse back to a point.
....
Is there any hope of talking about "where" this occurred for this Universe
as opposed to "where" it might of occurred for any other Universe? Or for
that matter "when"?
.... Things seem already out of hand, but could one ask how
a "quantum fluctuation" could occur in a point/place of zero (or near zero)
volume? -- I guess not.
... . Extrapolating backward
(with large uncertainties due to the uncertainties in current distances
and the unknown deceleration rate) leads us to believe that everything
in the observable universe was much closer together, more or less in
the same place, about 10-15 billion years ago.
... . The observable
universe is limited in size not by the size of our telescopes, but by
the finite amount of available lookback time: if the universe as we
know it is only 10 billion years old, we can't look out farther than
10 billion light years. (The practical limit is very slightly less
because at high temperatures the universe was opaque to light.) Hence
we have no idea what lies beyond our 10-15 billion-light-year horizon.
It's possible that space goes on forever in all directions, or that it
curves back on itself to make a finite total volume. Or something
much more complicated and bizarre.
And if we can say something helpful to lay people about the first
(relatively long) minute or so, (after all National Geographic did it) how
do we answer the question of what happened before that minute -- Is it that
here was NO such thing as time or was it that nobody was around to start
counting. (:-)
Your phrase
"ex nihilo" seems to imply a time before the beginning when there was
nothing, and this bothers me.
Well, it bothers everybody -- or at least ought to -- but then some people
are willing to talk about other universes -- which presumably *could* have
been created billions of years before ours -- I confess to really stretching
things here.
"Moving apart" and "distance between them is getting bigger" are
synonymous, though neither is a "reason" in the causal sense.