The universe expands at an accelerating rate, which makes me wonder if at a certain point the speed of expansion between two points will exceed the speed of light. In that case, it might eventually become impossible for two gravitationally bound clusters of the universe to exchange light. I recall reading that future civilizations born after a certain point would be unable to observe the distant galaxies that we can now, and would have no way of knowing galaxies besides their own exist.
My question: Is this possible, and if so could it have already happened; the entire observable universe is one of multiple clusters that have since sped away from each other? Or can this be ruled out by other known facts about the history of the universe?