So, I haven't looked closely at it, but he does mention that your clock remains (almost) the same as an earth clock. That implies that there is no frame of reference that shows him traveling faster than the speed of light. I'm not sure that this can be used to violate causality.
>I'm not sure that this can be used to violate causality.
If you can transmit any information from point A to point B faster than light would travel from point A to point B in a vacuum, then there are inertial frames of reference in which the information arrived at point B before it left point A.
It's really just as simple and plain as that. You need consider nothing further once you know the above facts.
Based on this effect though, it doesn't travel from point A to point B faster than the speed of light. Point A and point B are literally much closer together. Perhaps the space time distortion makes impossible to think of it in terms of static frames of reference.
If you've somehow made A and B closer together, then you've made a wormhole, not a warp drive. Wormholes also come with "closed time-like loops", which allow for time travel.
Yes, there are parts of the universe traveling away from us at faster than the speed of light. In fact, it's quite likely that the universe is infinitely big and an infinitely large part of it is traveling away from us at faster than the speed of light.
This fact, however, does not allow information to be transmitted between two points in space at faster than the speed of light. That's the important constraint here. Causality is only violated when you transmit INFORMATION between TWO POINTS at faster than the speed of light.
