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by KenoFischer
3732 days ago
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Let me try to phrase this a different way. Suppose the universe is a database, where (t,x,y,z) are the unique keys. For every key there is some value of "physical reality" at that point in spacetime. All the original statement is saying that if you want to generate such a database by starting with only some of the entries and applying the laws of physics, then in the presence of CTC, there are some very strict conditions on what those initial rows can be if you don't want to run into a situation where you'd want to assign two different values to the same key (e.g. by getting to the same point forwards in time and backwards in time). |
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Then, the (t,x,y,z) coordinates could all be parametric functions of observer_id and subjective_observer_time. If you follow a CTC and meet your younger self, then convince your younger self to not follow the CTC, you may simply be reassigning your younger self to a new observer_id, rather than creating a paradox that destroys the database integrity.
As long as all observers obey the rules of causality locally, your elder time-twin will never remember meeting their own elder time-twin, and your younger time-twin will never remember not meeting their own elder time-twin. The CTC has no way of knowing whether anyone ever followed it or not, because it isn't an observer. So if you ever meet yourself, you're no longer meeting yourself, because the person you meet is from that moment no longer you. If you do anything at all within the past half of your own light cone that interrupts causality, you are just creating a new observer.
So the photograph doesn't change itself, like in Back to the Future. Marty can't erase himself, but he could erase all references to himself from the historical record, except for whatever he carried through the CTC. He could then take a DNA test that proves him without a doubt to be the child of two people who cannot recall ever even touching one another. Even if he mostly restores causality, upon reversing through another CTC to a time before he entered the first CTC, there will be a different third child of his parents living with them when he gets back--someone who might not ever traverse a CTC.
If that's how it works, time travelers could do no worse than completely erase themselves from all historical records and the memories of every living person. They would be considered people who never previously existed, who spontaneously appeared, complete with memories of future events that might never come to pass. In that case, almost anything even remotely plausible could come out of either end of a CTC.