So, I don’t know how these stable time loops are supposed to work. My working model is that they function by trial and error, that time iterates through a universe until it encounters paradox, at which point it returns to pre-paradox, inserts some change into the world through prophecy or whatever, and tries again. This continues until a stable timeline is found, with an unknown number of them being discarded/destroyed. It appears from within that things worked on the first pass, but they did not. Our viewpoint never follows into one of those dead ends, but they exist(ed).
If the world really works that way, Harry would be potentially throwing his victory away by forcing a paradox. Time would have to reset to before the paradox and insert a change into the world to ensure a different outcome. He may or not be victorious in that new timeline. Harry dying was already a high probability and it would certainly resolve things to Time’s satisfaction. His best chance of securing his immediate past as part of the real and continuing world would be to make sure this timeline remains self-consistent.
(Plus, he’s prophesied to destroy the stars and creating a time-paradox seems like a really obvious possible way to do that.)
The only other possibility I can think of for these apparently stable timelines is that the whole universe is pre-determined and no one has any free will at all. I read something from EY about universes with time travel and he seemed to be in support of this second possibility. Any other possibilities for how this would work?
I think that the trial and error model is implausible; in which “time” are these trials and iterations occurring? The global determination of the whole universe seems much simpler.
I don’t think it necessarily conflicts with free will, when free will is understood in a compatibilist way (which is how EY and most LWers understand it). If we agree that one can have free will in a completely deterministic universe with ordinary past-to-future causal chains, then why can’t one have it in a universe where some of the chains run future-to-past?
That’s a good link, thanks. I’m warm to compatibilism. I think I’ve confused the conversation by using the wrong terms, though. Instead of pointing at a lack of free will I should have pointed at the complete lack of causality, which is more constraining. You can read EY on it here.
My interpretation of this would be that space-time would be a fixed object that exists in it’s entirety. In the same sense that you could take a cross sectional scan of a sneaker and play it from rear to front, there would be a logical consistency to how the slides transformed as you progressed through the shoe, but it would not make any sense to say that one part caused another. In this analogy, 4-dimensional space-time is the shoe, and the cross section is 3-dimensional space. We play it from back to front, watching a movie of the universe, but the entire universe from beginning to end already existed; we’re just looking at a slide of it at a time. Everything is consistent as the cross section passes through, but there’s no causality in play, it’s just an object being viewed in sequential slices. Much like EY’s modified game of Life with time-travel.
This actually seems pretty unsatisfying because there is a strong impression that the world is being run mostly on causality in the normal direction, with reverse causality coming in occasionally. This seems to me to work better with the iterating model.
Regarding the time for trials and iterations, I would refer to simulation as an analogy. “World time” is happening in the simulation, and this is what the characters are aware of. From within the simulated world, how much “Meta time” has elapsed outside of the simulation (i.e. the time stream that the computer is in), or how many failed attempts have been dumped from RAM is not very relevant in the sense that these facts don’t have any impact on “the world” (the simulated one) and are in fact probably unknowable to its inhabitants unless access to that meta-information has been somehow granted. To a denizen of the world, the fact that we switched from world version 721.213 to world version 779.344 last Tuesday at 9:41am is unknowable, the transition seamless, the lost attempts erased from world time even though they still occurred in meta time.
I’m not saying HPMOR is a simulated world. That’s just a model I’m using to think about timelines being destroyed and recalculating.
The nature of causality is controversial, but in my opinion it should be understood as a feature of the second law of thermodynamics. That causes precede their effects is an empirical law, not a logical necessity. Time turners can violate this in certain ways, but they don’t throw it out entirely.
As you look through the block universe, you can observe various features corresponding to causality: the increase in macroscopic entropy, the expansion of radiation, the human creatures inside that remember the past and plan for the future. The block universe model doesn’t eliminate causality; it is a physical feature within that universe.
So, I don’t know how these stable time loops are supposed to work. My working model is that they function by trial and error, that time iterates through a universe until it encounters paradox, at which point it returns to pre-paradox, inserts some change into the world through prophecy or whatever, and tries again. This continues until a stable timeline is found, with an unknown number of them being discarded/destroyed. It appears from within that things worked on the first pass, but they did not. Our viewpoint never follows into one of those dead ends, but they exist(ed).
If the world really works that way, Harry would be potentially throwing his victory away by forcing a paradox. Time would have to reset to before the paradox and insert a change into the world to ensure a different outcome. He may or not be victorious in that new timeline. Harry dying was already a high probability and it would certainly resolve things to Time’s satisfaction. His best chance of securing his immediate past as part of the real and continuing world would be to make sure this timeline remains self-consistent.
(Plus, he’s prophesied to destroy the stars and creating a time-paradox seems like a really obvious possible way to do that.)
The only other possibility I can think of for these apparently stable timelines is that the whole universe is pre-determined and no one has any free will at all. I read something from EY about universes with time travel and he seemed to be in support of this second possibility. Any other possibilities for how this would work?
I think that the trial and error model is implausible; in which “time” are these trials and iterations occurring? The global determination of the whole universe seems much simpler.
I don’t think it necessarily conflicts with free will, when free will is understood in a compatibilist way (which is how EY and most LWers understand it). If we agree that one can have free will in a completely deterministic universe with ordinary past-to-future causal chains, then why can’t one have it in a universe where some of the chains run future-to-past?
That’s a good link, thanks. I’m warm to compatibilism. I think I’ve confused the conversation by using the wrong terms, though. Instead of pointing at a lack of free will I should have pointed at the complete lack of causality, which is more constraining. You can read EY on it here.
My interpretation of this would be that space-time would be a fixed object that exists in it’s entirety. In the same sense that you could take a cross sectional scan of a sneaker and play it from rear to front, there would be a logical consistency to how the slides transformed as you progressed through the shoe, but it would not make any sense to say that one part caused another. In this analogy, 4-dimensional space-time is the shoe, and the cross section is 3-dimensional space. We play it from back to front, watching a movie of the universe, but the entire universe from beginning to end already existed; we’re just looking at a slide of it at a time. Everything is consistent as the cross section passes through, but there’s no causality in play, it’s just an object being viewed in sequential slices. Much like EY’s modified game of Life with time-travel.
This actually seems pretty unsatisfying because there is a strong impression that the world is being run mostly on causality in the normal direction, with reverse causality coming in occasionally. This seems to me to work better with the iterating model.
Regarding the time for trials and iterations, I would refer to simulation as an analogy. “World time” is happening in the simulation, and this is what the characters are aware of. From within the simulated world, how much “Meta time” has elapsed outside of the simulation (i.e. the time stream that the computer is in), or how many failed attempts have been dumped from RAM is not very relevant in the sense that these facts don’t have any impact on “the world” (the simulated one) and are in fact probably unknowable to its inhabitants unless access to that meta-information has been somehow granted. To a denizen of the world, the fact that we switched from world version 721.213 to world version 779.344 last Tuesday at 9:41am is unknowable, the transition seamless, the lost attempts erased from world time even though they still occurred in meta time.
I’m not saying HPMOR is a simulated world. That’s just a model I’m using to think about timelines being destroyed and recalculating.
The nature of causality is controversial, but in my opinion it should be understood as a feature of the second law of thermodynamics. That causes precede their effects is an empirical law, not a logical necessity. Time turners can violate this in certain ways, but they don’t throw it out entirely.
As you look through the block universe, you can observe various features corresponding to causality: the increase in macroscopic entropy, the expansion of radiation, the human creatures inside that remember the past and plan for the future. The block universe model doesn’t eliminate causality; it is a physical feature within that universe.