A story in The New Yorker quotes the following explanation from Arthur Eddington regarding relativity and the speed of light.
Suppose that you are in love with a lady on Neptune and that she returns the sentiment. It will be some consolation for the melancholy separation if you can say to yourself at some—possibly prearranged—moment, “She is thinking of me now.” Unfortunately a difficulty has arisen because we have had to abolish Now … She will have to think of you continuously for eight hours on end in order to circumvent the ambiguity of “Now.”
This reminded me of The Book of Strange New Things. This science fiction novel has several themes, but one is the effect of separation on a relationship. Even if you have faster-than-light communication, how does it effect you to know that your husband or wife is light years away? The communication delay might be no more than was common before the telegraph, but the psychological effect is different.
Related post: Eddington’s constant