Your third paragraph is a nice way to think about FTL. Actually it causes quite interesting problems to define FTL, since nothing special happens locally. > Bu

Your third paragraph is a nice way to think about FTL. Actually it causes quite interesting problems to define FTL, since nothing special happens locally. > But one thing I could not really figure out is whether this so-called FTL travel has the potential to violate causality, because I don't fully understand how causality and FTL are related. They are not directly related, as I wrote above, nothing special happens except you find a 'shortcut.' So at every point there is still a nice lightcone ( locally) and every event is caused by events in its past lightcone. However, you can have global causality violation, that is closed timelike curves, a fancy way to talk about timetravel. The idea is, that you travel always forward in time and you reach the same space time point at which you started. Much in the same way that you can travel always forward on a tire (torus) and still reach your starting point. Something like this may or may not happen on a metric which permits FTL, for example the Alcubierre metric does not permit travel on such curves. [1] But it would actually be easy to perform the same analysis on a Godel solution [2], which would permit closed timelike curves. Edith: Added the comment about the Godel solution. [1] Alcubierre, 2000 http://arxiv.org/pdf/gr-qc/0009013v1.pdf http://arxiv.org/pdf/gr-qc/0009013v1.pdf [2] https://en.wikipedia.org/wiki/G%C3%B6del_metric https://en.wikipedia.org/wiki/G%C3%B6del_metric