> If you're comparing two physically separated frames of reference it makes sense to talk about "this many seconds here corresponds to that many seconds over th

> If you're comparing two physically separated frames of reference it makes sense to talk about "this many seconds here corresponds to that many seconds over there" Even that comparison doesn't make much sense because, as raattgift already pointed out in the comments[0], > Reciprocity in Minkowski space is relevant. So from observer A's point of view the clock in observer B's frame of reference will tick more slowly, but from observer B it will appear the other way around. This is sounds contradictory but the reason for this is that observers in different frames won't even agree on what a valid time measurement is. This is called relativity of simultaneity[1]. [0]: https://news.ycombinator.com/item?id=37250897 https://news.ycombinator.com/item?id=37250897 [1]: https://en.wikipedia.org/wiki/Relativity_of_simultaneity https://en.wikipedia.org/wiki/Relativity_of_simultaneity