I understand that our local galaxy group is considered “gravitationally bound” and therefore exempt from the expansion from each other ((, but we don’t seem to have other galaxies collected into their own “local groups” of gravitationally bound clusters, so are we saying we’re somehow unique? Is there a trick of perception taking place?)) <—edit:this is wrong
I found this quote in the Wikipedia article on the Expansion of the universe.
While objects cannot move faster than light, this limitation applies only with respect to local reference frames and does not limit the recession rates of cosmologically distant objects.
It seems to me that if we can perceive at cosmological distance something that cannot exist, perhaps we are falsely observing an expanding universe. Maybe everything IS gravitationally bound and we’re just seeing expansion because… Relativity?
The short simple version is that if galaxies happen to be close enough to each other they fall toward each other faster than the space between them expands. That’s what “gravitationally bound” means.