Expansion of the universe and visibility of distant galaxies 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?
(My answer here isn't correct, as pointed out by the first comment on this post, please refer to it.)

Yes, it certainly is possible - and it already has happened. The age of the universe is 13.8 billion years, yet it is something like 90 to 100 billion light-years in diameter. This means that we definitely can't see all of it, not because of our own observational limitations, but because the light from those parts of the universe just hasn't reached us yet - and perhaps it never will.

As for the future, yes, if cosmological expansion overpowers gravity at close range (i.e. the Milky Way and Andromeda, and the world "close" is relative here) then eventually many galaxies and clusters will disappear out of view due to light not being able to "keep up" with the expansion.