system
Given the following post, respond as if you're commenting on Reddit:
human
According to the theory of relativity, do all observers agree on causality?

This is a question that I posed to my astronomy 101 teacher, but I don't think she understood my question. So, as I've heard relating to the theory of relativity, if observer A is on Earth, and observer B goes at ½c to the nearest star and back, observer B will have experienced far less time than observer A. But that's from the perspective of observer A. From the perspective of observer B, observer A is receding at ½c away from them, and so observer A should be experiencing less time. How is this resolved within the theory, or am I just not getting it?
gpt
Events which are causally related must have a definite ordering in time that all observers agree on. Pairs of events like this are called *timelike-separated*. Events that are not causally related don’t have a definite ordering in time. Pairs of these events are called *spacelike-separated*.