It seems rather simple to me.
The farther out the masses (galaxies) are from the Big Bang’s center, the less outside force (other galaxies) there is to slow them down, so they accelerate. A mass in motion tends to stay in motion, unless acted upon by an outside force, so as they move farther and farther, the distance between galaxies on the outside edge of the Universe, increases at an exponential rate, like the spokes on a wheel. This motion will continue until every star in every galaxy eventually burns out and the Universe approaches absolute zero.
Every atom in the entire Universe falls apart, and disperses its subatomic parts into a cloud of uniform massless particles that stretches to every corner of the Universe.
The cloud will then begin the process of collapsing in on itself, which would take trillions of trillions of years until the original mass of the entire Universe is gathered together in one place and the Umpteenth re-creation begins anew................
“A mass in motion tends to stay in motion, unless acted upon by an outside force, so as they move farther and farther, the distance between galaxies on the outside edge of the Universe, increases at an exponential rate, like the spokes on a wheel.”
Would this then indicate that the Universe is also spinning like a Galaxy and centrifugal force is also affecting that mass as it moves further out on the spokes of that wheel? Honestly that would make a lot of sense and explain a lot. From our perspective how could we tell if the whole Universe is spinning? We would have to have something “outside” the Universe to have reference to detect movement. It could be but we don’t have that outside reference to indicate the spin moment.
Only God knows for sure...
I’ll have to remember to ask Him!.................