Our space wizards have studied space-time for centuries. I believe there are a set of mathematical equations that prove how it works, but I can't recall off the top of my head.

[Vague hand gestures. By his time, everyone assumes that the universe just works.]

We first study how the sun and planets move, then move onto the stars, then all cosmos. From there, we learn how to use these movements to our advantage, and that involves understanding space-time.