Krasnikov tube vs Worm Holes and Alubierre Drive

[Drashner1]

So, would an Alcubierre metric traveling faster than light also only collapse if it was being steered in a direction where it could run into itself?

Alcubierre metrics travelling faster than light would run into causality problems under a wide set of circumstances, since they could be used to send messages back in time, especially between observers who are travelling relativistically with respect to one another. I don't know if they would collapse, but in OA void bubbles (which are based on the Alcubierre metric) are limited to subliminal speeds so the problem doesn't arise.

To expand on Steve's response a bit:

In OA, warp bubbles can (in principle) reach or exceed the speed of light - however, if they try, virtual particle creation inside the bubble ramps up exponentially until the bubble is destroyed. This is actually based on a RL theory referenced in one of the reference papers listed at the end of the article. For OA purposes we presume it to be true as a way to make use of warp bubbles without running into causality issues.

So it's not really a matter of where the warp is going as whether or not it reaches or exceeds the speed of light.

Todd