Ah, if I had THAT answer, I'd earn a Nobel Prize. Not an Al Gore Nobel Prize, but a REAL ONE worthy of respect.
My understanding is that the point is still being debated. Depending on how much “dark matter” is out there, it is possible that the universe will collapse again due to gravity.
Asimov had an interesting theory about this- if the universe contains enough mass to collapse due to gravity, then that gravity is also sufficient to prevent light from escaping. Ergo, the universe is a black hole.
1) The universe may have an elasticity to it like water. I forget the name of it, but you know when you pour a puddle of water onto a desktop, and look at it from the side, you see the water has a depth and curves down to the desktop. It has a thickness, but it also retains shape. Same as we dee a drop of water in a spaeship, being round or oblong etc and spinning, but these droplets retain their shape until they interact with something, yes? Well, if the universe were like that, it would expand endlessly until it reached the limit of that elasticity, though it doesn't explain a reason to contract.
Which leads me to 2> Dark Matter. They're discovering many things about Dark Matter, and I wonder: perhaps dark matter has gravitation forces to it. This would allow for elasticity, and could also somehow cause a it to retract, to collapse....
Anyhow, it seems the basic theory of physics would apply to the universe as they would to a puddle of water on a desktop, or a droplet in a spaceship.