I have a few questions about CTC:

  • What would CTC look like from the outside?
  • Would every loop be the same?
  • What would happen if the cause of CTC disappear? (e.g. Tipler cylinder stopped spinning)

A diagram is the best way to illustrate this. This diagram has time in the vertical direction. At the bottom are two observers in a comoving frame. Then one observer moves to enter a "tube" colored red. This could be a wormhole boosted into a time machine, or a Kraznikov tube so a "star gate of some sort. The red region is considered isolated from the outside world, but if the reader wants they can ignore that. The diagonal green lines are signals transmitted to the observer who remains stationary in the initial frame.

Clearly that observer on the right sees the observer on the left occur twice after the left observer emerges from the tube. There are then duplicates of the left observer the right observer witnesses up until the original version dives into the tube.

We may think of the two openings of this red tube as the same opening, but where the top opening is the time evolved version. If this tube disappears in the future of this diagram it just means this time looping is no longer possible.

enter image description here

  • $\begingroup$ From what I've read, I got the impression that the time-travelling observer goes back to the same point in space-time, which would make him always go again in the tube, and not further in time along the right observer (though maybe that's not the case, since universe is not deterministic), wouldn't that make the right observer see infinitely many left observers, as every instance would go back through the tube again? $\endgroup$ – Jecke Aug 24 '17 at 16:02
  • $\begingroup$ Also, what happens in this case: s30.postimg.org/wr63hrjld/image.png ? It seems like the left observer can message the right observer information from his future. $\endgroup$ – Jecke Aug 24 '17 at 16:03

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