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)
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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.