Without having given it too much thought, I like to think that it’s just the anthropic principle on really good crack. Any Everett branch containing a paradox simply ceases to exist / ceased to exist / has never existed (I think time-travel science fiction should adopt as its official idiom one of those East Asian languages that do not employ verb tenses).
I think that branch “never existed in the first place”. It is something like a triangle with four sides.
I agree with your assessment, but the question that puzzles me is unitarity. How do we maintain the idea that the sum of the probabilities of all things that can happen add up to 1 at every point in spacetime?
Or, to put it in macroscopic terms, just before Dumbledore read the parchment, how should an observer estimate the probability that the message will be “No” rather than “Don’t count on it”.
Or, to put it in macroscopic terms, just before Dumbledore read the parchment, how should an observer estimate the probability that the message will be “No” rather than “Don’t count on it”.
There’s been work specifically on this question about expectations for simplified cases when one has a 2D Newtonian system with wormholes violating causality. Kip Thorne discusses this in some of his books although I don’t remember if the results are due to him or to someone else. The upshot is that at least in limited circumstances, one can make meaningful statements.
Without having given it too much thought, I like to think that it’s just the anthropic principle on really good crack. Any Everett branch containing a paradox simply ceases to exist / ceased to exist / has never existed (I think time-travel science fiction should adopt as its official idiom one of those East Asian languages that do not employ verb tenses).
I think that branch “never existed in the first place”. It is something like a triangle with four sides.
I agree with your assessment, but the question that puzzles me is unitarity. How do we maintain the idea that the sum of the probabilities of all things that can happen add up to 1 at every point in spacetime?
Or, to put it in macroscopic terms, just before Dumbledore read the parchment, how should an observer estimate the probability that the message will be “No” rather than “Don’t count on it”.
There’s been work specifically on this question about expectations for simplified cases when one has a 2D Newtonian system with wormholes violating causality. Kip Thorne discusses this in some of his books although I don’t remember if the results are due to him or to someone else. The upshot is that at least in limited circumstances, one can make meaningful statements.