Recent content by zytsang

How come there is a preferred frame? I thought the geometry of 2-torus is flat, and every point on 2-torus has infinite radius, or am I mistaken?

Thank you very much for your reply. But I think in this problem Observer B is always traveling at speed of 0.9c, so there shouldn't be any change of velocity. Can you explain a bit more on "There are obvious problems with synchronizing clocks when the spatial coordinate is periodic"?

The problem statement Suppose the universe is a 2-torus, thus there exists a spatial path that you will go back to where you start eventually. Let Observer A and Observer B travel on this closed path. Observer B is traveling at a constant speed of 0.9c relative to Observer A, where c is the...