Does the Grandfather paradox rule out time travel?
It is not inevitable that time travel will result in a Grandfather Paradox. There is no acceptable resolution to the paradox if time travel happens. None of your proposals works: “What about infinite timelines; “Copenhagen interpretation” of quantum mechanics; “multiple universes interpretation” of quantum mechanics; a single timeline.” A single timeline is what gives you the Grandfather paradox. The Copenhagen Interpretation of QM applies to what happens NOW, not time travel. Bell’s “quantum splitting” (what you call “multiple universes interpretation”) might have some bearing. Under quantum splitting, the universe splits each and every time that there is a decision, so that EVERY decision happens. So you would have the universe split at the moment the time traveller decided to take his journey, and in one of those universes the journey wouldn’t happen — no Grandfather Paradox. The universe would split again at the decision to actually kill the grandfather. In one universe the time t