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[Phys-l] FW: expansion of the universe



One of my students forwarded to me a quote & link to its context,
included below. Most of it need not concern us here, but I am intrigued
by the statement that an accelerating expanding universe must
necessarily be infinite. That does not seem to me to follow at all, but
perhaps someone here with more of a background in cosmology would care
to comment on it?



The model I was introduced to in college and graduate school was that
the universe was very probably spatially finite, but bets were still
being made whether or not it was temporally finite: starting with a Big
Bang and ending with a Big Crunch, or starting with a Big Bang but
openended futureward, or one temporally finite bead in an eternal
sequence of universes, or .... We spoke of an "open" or "closed"
universe, but I thought what was meant was unending/ending temporally
while spatially finite. Of course, one person's "time" has components
of both time and space for another, so perhaps no such distinction is
possible. I must admit to not having given this much thought in the
intervening years. Perhaps the only choices are finite or infinite (in
spacetime).



Now does the apparent increasing rate of expansion eliminate some of the
previously considered models? Or have some (for instance, the spatially
finite, unending temporal model) been eliminated for other reasons?



Thanks,



Ken Caviness

Physics @ SAU







"You're not going to find anyone who does not believe that the universe
is spatially infinite. And what happened in 1998 is they observed two
quasars that were accelerating at a faster pace than they should have
been according to the previous theory. And the explanation of that is
that the expansion of space is accelerating at an ever increasing rate
and that implies that the universe will expand forever. Now it follows
from Einstein's general theory of relativity, particularly the solutions
by Friedman, that if the universe expands forever it is spatially
infinite."



This is a quote from Quentin Smith in a debate with William Lane Craig
at Harvard about the existence of God. (It's available at
http://www.leaderu.com/offices/billcraig/docs/craig-smith_harvard07.html
; other debates and articles at
http://www.leaderu.com/offices/billcraig/)