[Spaceships] Real Life Non-Super Science Reactionless Engines

[Agemegos]

Originally Posted by malloyd

The problem is that if some observer can see something move FTL, some other observer can see it arrive long enough before it departs to send a signal to abort the departure.

Not a lightspeed signal. And if the FTL mechanism has properties that are not invariant between frames of reference it can work out that an FTL signal won't do it either. That's why you can choose "causality" and "FTL" out of the "causality, relativity, FTL: choose only two" trilemma.