Back at the start of this thread you were looking for a “theory”. I don’t have theories; I lack the necessary maths/science to formulate one effectively. However, I’m willing to have a go at an idea. If nothing else, I can learn from having it dismantled.
Why do we not have runaway gravity?
This is the wrong question; it should be, “Do we have runaway gravity”. This has a straightforward answer: “Yes”.
Notwithstanding the fact that the Universe is expanding at an increasing rate, gravity is operating locally to cause matter to aggregate. One of the ways in which we see this happening is by black holes accreting material. True, this is a slow process, but on the timescale of the Universe processes do not need to be fast. The range of gravity is infinite, so however far apart the galaxy groups become, gravity will eventually catch up. This may be indistinguishable from the closed universe concept, but it has nothing to do with the basic geometry of the Universe. It is runaway gravity, caused by the fact that gravity creates more gravity, so gravity will eventually overcome any basic geometry.
