Abstract The theory of general relativity predicts the existence of closed time-like curves (CTCs), which theoretically would allow an observer to travel back in time and interact with their past self. This raises the question of whether this could create a grandfather paradox, in which the observer interacts in such a way to prevent their own time travel. Previous research has proposed a framework for deterministic, reversible, dynamics compatible with non-trivial time travel, where observers in distinct regions of spacetime can perform arbitrary local operations with no contradiction arising. However, only scenarios with up to three regions have been fully characterised, revealing only one type of process where the observers can verify to both be in the past and future of each other. Here we extend this characterisation to an arbitrary number of regions and find that there exist several inequivalent processes that can only arise due to non-trivial time travel. This supports the view that complex dynamics is possible in the presence of CTCs, compatible with free choice of local operations and free of inconsistencies. --https://iopscience.iop.org/article/10.1088/1361-6382/aba4bc
This generally has been known for a while. GR allows for time travel as well as wormholes. Of course we have yet to observe or do either! Future time travel is actually pretty easy, but time travel into the past, is another matter...possible paradoxes etc make that doubtful, even considering GR allows for it. a couple of interesting videos you may find interesting...a few years old, before the discovery of gravitational waves but still interesting..... The mind boggles at the still rather speculative, yet possible achievements, that an advanced civilisation may be possible to achieve. The two Kip Thorne ones are what I'm referring to. https://www.closertotruth.com/serie...L_CLbickxoZm2ske7itmTH7GF-cyy2choCz5UQAvD_BwE https://www.closertotruth.com/serie...L_CLbickxoZm2ske7itmTH7GF-cyy2choCz5UQAvD_BwE
The new result apparently resolves the grandfather paradox; if you travel to the past you can't do anything to alter the future you come from. But travelling to the past, or someone else's past, is 'doing something', and so the past can be changed if travelling in time is possible. This result shows that the past can't be altered enough to change the future (the one in the traveller's past), whether the traveller can return to it or wants to.
