I looked at this question. There's one answer that alludes to what I'm asking, but I don't find it satisfactory, because to me the following is still a paradox:
The most distant galaxies we have ever observed appear to be around 13 billion light years away. Here's my question: Suppose the universe were not expanding, and suppose an observer in a galaxy 10 billion light-years away from us RIGHT NOW were to look directly at our planet (or rather at least the section of space our planet is occupying) with some magical telescope powerful enough to do such a thing. In this hypothetical scenario, both our planet and this galaxy would be static. The physical distance between the two doesn't change throughout all time. If we can observe such a far away galaxy (albeit as it was 10 billion years ago), could an observer in this supposed galaxy see earth? You'd say no, because light from our earth hasn't had enough time to reach the galaxy, with Earth being only 4.5 billion years old. But how is it that we could see such a galaxy from our viewpoint? Agreed that when light left that galaxy the earth was still a twinkle in the Milky Way's eye. But the light made the distance. At the same instant the distant observer looks at us and finds nothing?
Why is it that we can see them and they can't see us? Again, static environment. Light works one-way only?
What are the conditions for simultaneous mutual observation??