Question: is there going to be a point where the universe has a reverse big bang and disappears?

Oliver Gordon answered on 4 Mar 2019:

I learnt about this when I did my degree!

Basically, the universe can have any one of three “shapes.” It can be flat, spherical (closed), or shaped like a horseshoe (open). We have this number, “k”, which describes this shape. If its 0, it’s flat. If it’s bigger than 0, it’s closed. If it’s smaller than 0, it’s open. A closed universe is the less old than a flat universe, which is less old than an open one.

A closed universe will grow and grow and grow, and eventually at some point in time start shrinking again.

The reason I mentioned this “k” number is that it can be any number from minus infinity to infinity. We think it’s anywhere from -0.0002 to +0.0008. So we don’t know the shape, so we don’t know what will happen!

HOWEVER: If dark matter exists, then no, the universe will get to a point where it starts expanding ridiculously quickly ridiculously quickly. But this is one of the problems with proving if dark matter exists!