[Stone Mountain]

I thought we already decided our universe is destined to expand forever; in which case such a universe is not that similar to ours.

I'm not sure that there's a consensus on that. I think it depends on the amount of "black matter" in the universe - if there is enough, then eventually, the universe will cease to expand and eventually retract into intself because of gravity. If there isn't enough matter for gravitation to do this, then the universe will keep expanding. At least this was the way I remembered it...

[Gandalf_The_Gray]

I think it depends on the amount of "black matter" in the universe - if there is enough, then eventually, the universe will cease to expand and eventually retract into intself because of gravity. If there isn't enough matter for gravitation to do this, then the universe will keep expanding. At least this was the way I remembered it...

You are right but there three possible results.
1) not enough matter and the universe keeps expanding without bound
2) too much matter and the universe eventually stops expanding and begins to contract into the "big crunch"
and (kind of like the three bears)
3) just the right amount of matter so that the expansion slows at an ever decreasing rate that approaches (but never reaches) zero. This results in a non-cyclic universe with a finite, bound volume.

Observational data seems to indicate that the rate of expansion is slowing, which eliminates number one. My personal favorite is number three because it seems to me to be the sort of thing G_d might do. Put in just the right amount of mass to blow a permanent bubble of space time.

Regards,
GtG