>>11375337Misconception of what FTL means in GR. Nothing can LOCALLY go faster than light.
Imagine you're outside a black hole. You shine a light to the right, where a detector is 10 meters away. At the same time, you shine another light to the left, so it has to curve around the black hole the long way to reach the detector.
Did the right beam go at a faster speed than the left beam? No, they both locally travelled at the speed of light. But the distance along one path was greater than that along the other. This is precisely what happens with Alcubierre. If you look at any local patch, nothing is FTL, so causality isn't broken. But the net effect is that you can move between two places along one path in less time than a light beam following a different path.
"FTL violation" means LOCAL faster than light, which is what matters for causality.
Things get tricky like that when working in the presence of curvature
