[prettydeep]

Roger Penrose has a theory about a cyclical conformal universe, which requires that the universe eventually only contains photons. As photons travel at the speed of light, they do not experience the passage of time, so they also do not experience distance (space). So in the deep remote future, when only photons are left, the difference between the very large and miniscule disappears, and you get all photons in the universe existing at the same point at the same time, which causes a new big bang. At least, that is Penrose's theory. I believe they found some evidence in the CMB supporting it.

[AlexAndScripts]

https://en.m.wikipedia.org/wiki/Conformal_cyclic_cosmology

It seems the paper made mistakes, using a non-standard model of the CMB that failed upon replication. It's an interesting theory thoughb.

[cmsj]

As a non-Physicist, I absolutely love the CCC hypothesis and I really hope it turns out to be true. It seems like such a beautiful alternative to the idea of the heat death of the universe just lasting forever and nothing ever happening again.

[Kranar]

This is some absolutely crazy idea. I mean I'm in no position to analyze it critically but that is pretty mind blowing.