Even light-speed signals can’t reach galaxies beyond 18 billion light-years due to space expanding too fast.

TL;DR

In an expanding Universe, galaxies beyond 18 billion light-years are unreachable, even if we send a light-speed signal today. The expansion of space, not objects themselves, causes these galaxies to appear as though they’re moving faster than light. As space expands, light is stretched, a process called redshift, making galaxies seem to accelerate away from us. This phenomenon doesn’t break the laws of relativity since space itself isn’t bound by the speed of light. The farther we look, the more we realize that many galaxies will remain beyond our reach forever.