Krasnikov tube vs Worm Holes and Alubierre Drive

[Rynn]

It's been a while since I've read up on Kraznikov tubes. Bringing up the wiki article has a succinct explanation of how two tubes can be used to make a time machine, just like wormholes. Matt Visser's hypothesis that gravity fluctuations would lead to a collapse at the moment of Closed Timelike Curve creation is, again, just like the wormholes OA uses.

While one Krasnikov tube can be seen to present no problems with causality, it was proposed by Allen E. Everett and Thomas A. Roman of Tufts University that two Krasnikov tubes going in opposite directions can create a closed timelike curve, which would violate causality.[3]

For example, suppose that a tube is built connecting Earth to a star 3000 light years away. The astronauts are travelling at relativistic velocities, so that the journey through this Tube I only takes 1.5 years from their perspective. Then the astronauts lay down tube II rather than travelling back in tube I, the first tube they produced. In another 1.5 years of ship time they will arrive back on Earth, but at a time 6000 years in the future of their departure. But now that two Krasnikov tubes are in place, astronauts from the future can travel to the star in tube II, then to Earth in tube I and will arrive 6000 years earlier than their departure. The Krasnikov tube system has become a time machine.

In 1993, Matt Visser argued that the two mouths of a wormhole with an induced clock difference could not be brought together without causing quantum field and gravitational effects that would either make the wormhole collapse or the two mouths repel each other.[4] (See Time travel using wormholes and the Chronology protection conjecture.) It has been suggested that a similar mechanism would destroy time-machine Krasnikov tubes. That is, vacuum fluctuation would grow exponentially, eventually destroying the second Krasnikov tube as it approaches the timelike loop limit, in which causality is violated.