system
Given the following post, respond as if you're commenting on Reddit:
human
If the universe is expanding at an accelerating rate, does that imply that certain parts of the universe are in principle unobservable/unknowable?
gpt
Yes. Although more and more galaxies will continue to enter our observable universe, any galaxy that is currently farther than about 65 Gly will never be seen at all. (For reference the current radius of the observable universe is about 47 Gly.) This occurs because of the acceleration of the expansion. Without dark energy, all galaxies would eventually enter the observable universe.

There is also a so-called cosmological event horizon, beyond which any signal emitted right now will never reach us. The current distance to the event horizon is 16 Gly, and this distance shrinks over time. Eventually the only galaxies with which we will be able to communicate will be those within our own local cluster.