[zawsaanj] Limits of colonization

For which of the objects in the night sky, if we emitted an electromagnetic signal now, would the signal eventually reach it or its remnants, taking into account the expansion of the universe? This distance represents the threshold for interstellar colonization, the colonizable universe, the farthest we could travel even if we had nearly lightspeed ships launched today. (No wormholes or warp drives.)

There exist objects in the night sky that we can see, but never reach, which we can see (its past) but not (our present) be seen from. We might observe a signal from an alien civilization from one of those distant worlds, but never be able to respond.