[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

[Gandalf_The_Gray]

PS I have long suspected that G_d is a young child playing in a sand box, several dimensions up the road from here. The reason we haven't seen him around lately is his parents have called him in from play time for supper, and then off to bed.

Our universe is the sand castle he build to while away a sunny afternoon.

Regards,
GtG

[GeraldP]

>>>Observational data seems to indicate that the rate of expansion is slowing, which eliminates number one.

Actually, the expansion seems to be accelerating (increasing rate), hence the postulation of "dark energy". Dark energy would presumably be antigravitational. If I am not mistaken, string physicists suggest this could be an effect of gravitational particles from an adjacent universe or p-brane, leaking into ours.

[Stone Mountain]

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.

Good point - I forgot about option 3. The way I see it, though, is that there would have to be just enough volume to keep things relatively consistent or at least cyclic - in a cycle of slightly expanding and contracting as the ratio of the matter in the universe keeps changing with respect to the size of the universe. It seems to me that if expansion is constantly slowing, at some point in the future, it will hit zero - of course this would be on the scale of billions of years... At that point, it seems to me that the universe would eventually start to contract - the logic being that if there is enough matter in the universe to slow the expansion, the expansion will eventually stop or at least stop expanding at any significant rate. At that point, since the amount of matter in the universe should still be constant (conservation of mass), wouldn't that imply that the existing matter in the universe would act on the universe and reverse the process and start it contracting?