(December 16, 2012 at 2:58 am)SpecUVdust Wrote: Aren't you familiar with a cyclic model like "the Big Crunch"?basically, average density of the universe is enough to slow, stop, and reverse expansion. The end result: BIG CRUNCH ... Followed immediately by a Big Bang. Heat death would still eventually occur but we couldn't know when or better- we don't know how many times this has happened.
This has been argued due to (the extremely minute amount of) what we know of dark energy being the cause for the initial cosmic inflation. But cosmic inflation stopped and became what we call expansion which was a huge change. So basically: one more odd change in the " equation of state" and things could stop expanding and start "retracting."
This remains one possibility, though there is little in the way of observational evidence to support it, and it does not appear that there is sufficient mass density to cause it to happen. Some unknown mechanism could exist, of course - similar to the inflation/expansion transition, which as far as I know also has no known cause (if the models are correct). The case for that is stronger as it appears that it did occur (even if we don't know the cause). The "big crunch" doesn't appear to be necessary (though it remains an unknown).
I sincerely hope that we learn a great deal more about this in what remains of my lifetime - we certainly have since I was born.
