Krasnikov tube vs Worm Holes and Alubierre Drive

[Rynn]

Small nitpick: You can accelerate a wormhole mouth to relativistic speeds, but if you put them close enough together to create a time machine, then they destabilize.
Come to think of it, such a concept of chronology protection would probably destroy Krasnikov tubes only if they are in a time-travel configuration, making them possible.

This is why the Nexus grows outwards, wormholes travelling at relativistic speeds shift into the future from the perspective of the wormhole that stays at home. That doesn't violate causality because even if home (Hw) is in the global past relative to colony (Cw) it's outside of Cw's light cone. A krasnikov tube would have the same issue I'd think, though I don't know much about them.