The universe is flat with only a 0.4% margin of error. ~ NASA
The cosmos seems to be currently swelling at a comfortable clip. Whether the expansion will go on endlessly, or cyclically reverse course and contract into a singularity, depends upon the shape of the universe, and the nature of energetic forces that govern cosmologically.
3 topological alternatives exist: open, flat, or closed. If the cosmos is open or flat, the fan out will continue (open) or eventually halt (flat).
We live in an accelerating universe now and so, as time goes on, the density of galaxies is going to thin out. ~ English astronomer Tony Hewish
In the eventuality termed the Big Freeze, cosmic energy is spread so thin that entropy succeeds in turning the universe into an enormous popsicle. Star formation has already started to fizzle.
Stars are formed in galaxies. There was a peak in the rate at which galaxies formed, and that time has passed. ~ English astronomer Alan Heavens
The universe is curling up on the sofa and becoming a couch potato. ~ German astronomer Jochen Liske
Under the Big Rip scenario, cosmic expansion gets the upper hand. All matter and light energy will be ripped apart.
Under the rip scenario, you get this wild expansion that essentially rips spacetime apart. The universe would vanish. ~ English Mexican cosmologist Carlos Frenk
If the universe is a single shot of existence in a closed container, a Big Crunch will be the symmetrical opposite of the Big Bang. The universe collapses into a dimensionless singularity.
The latest research shows that the universe’s expansion is accelerating, so there is no reason to expect a collapse from cosmological observations. Thus, it will probably not be a Big Crunch that causes the universe to collapse. ~ Danish physicists Frederik Colding & Jens Krog
Cyclic cosmology posits a Big Bounce. Universes go through endless incarnations. Cosmic contraction follows the current expansion if there is a phase transition that causes matter to take on a bit more mass; a result of fundamental bosonic forces, especially the Higgs field, changing the key of their tune.
The phase transition will start somewhere in the universe and spread from there. Maybe the collapse has already started somewhere in the universe and right now it is eating its way into the rest of the universe. ~ Jens Krog
While the shape of the universe and semblance of forces applied appears to be comprehensible, this facile understanding is an illusion of our quite limited perspective, and of feeble mental capabilities overcome by overconfidence.