Time appears to stretch backward infinitely, because local causality still looks nice. But actually it only stretches backward to now. If time was actually a straight line rather than a cycle, then one could intervene in this system and it would only change the future. But if you intervened in a cyclic system, you would find that you had changed what looks like the past.
In fact, self-consistency constraints would kick in and logically prevent you from some sorts of intervention that would make perfect sense if time stretched off to infinity—it’s like using quantum mechanics instead of classical mechanics, where classically it seems like you should be able to have any amount of energy you want.
More philosophically, we’ve run into Aristotle’s distinction between self-cause and infinite regress. And also why Bayesian networks are typically defined as directed acyclic graphs, thus putting cyclic graphs outside of the hypothesis-space.
I think I understand your distinction between infinite regress and cyclical causation, but I don’t understand why that implies a cyclical universe violates causality. To rephrase jimrandomh: that isn’t a violation of causality, it’s just a universe with cyclical time.
Well, one can still think of it causally—you can still draw a graph with arrows, at least. But it’s atypical causality.
Typical causality is like kicking a ball. The ball sits still until you kick it, and you can kick it however you like and it will roll away. But once you have loops, it’s like if the ball had to go through a portal to the past and kick itself. As soon as you try to kick the ball, the ball you would have kicked has already gone back to the past and hit itself in a way consistent with the motion of your foot, so it will feel quite unlike kicking the first ball. And in fact it is physically impossible to move your foot in a way inconsistent with the ball being the cause of its own motion, even though trying to kick the ball restricts the possibilities—or rather, being able to try to kick the ball tells you that the possibilities were already restricted...
In typical causality, the ball has a reason for moving the way it does—you can trace the motion backwards to some acceptable starting point, like “I kicked it as hard as I could toward the fence.” When you add cycles, tracing the chain of arrows back does not need to end at anything you find remotely satisfactory or even unique—“the ball moved because it hit itself because it moved because it hit itself...”
When you add cycles, tracing the chain of arrows back does not need to end at anything you find remotely satisfactory or even unique—“the ball moved because it hit itself because it moved because it hit itself...”
This is a problem with your personal intuitions as a medium-sized multicellular century-lived mammalian tetrapod. No event in this chain is left uncaused, and there are no causes which lack effects in this model. Causality is satisfied. If you are not, that’s your problem. Hell, the energy is even conserved. It runs in a spatial as well as a temporal circle, what with the ball hitting itself and skidding to a stop exactly where it was sitting to wait for the next hit. On the other hand, in such a universe quantum mechanics does not apply, because worldlines cannot split, which also removes any possibility of entropy. ALL interactions are 100% efficient.
Time appears to stretch backward infinitely, because local causality still looks nice. But actually it only stretches backward to now. If time was actually a straight line rather than a cycle, then one could intervene in this system and it would only change the future. But if you intervened in a cyclic system, you would find that you had changed what looks like the past.
In fact, self-consistency constraints would kick in and logically prevent you from some sorts of intervention that would make perfect sense if time stretched off to infinity—it’s like using quantum mechanics instead of classical mechanics, where classically it seems like you should be able to have any amount of energy you want.
More philosophically, we’ve run into Aristotle’s distinction between self-cause and infinite regress. And also why Bayesian networks are typically defined as directed acyclic graphs, thus putting cyclic graphs outside of the hypothesis-space.
I think I understand your distinction between infinite regress and cyclical causation, but I don’t understand why that implies a cyclical universe violates causality. To rephrase jimrandomh: that isn’t a violation of causality, it’s just a universe with cyclical time.
Well, one can still think of it causally—you can still draw a graph with arrows, at least. But it’s atypical causality.
Typical causality is like kicking a ball. The ball sits still until you kick it, and you can kick it however you like and it will roll away. But once you have loops, it’s like if the ball had to go through a portal to the past and kick itself. As soon as you try to kick the ball, the ball you would have kicked has already gone back to the past and hit itself in a way consistent with the motion of your foot, so it will feel quite unlike kicking the first ball. And in fact it is physically impossible to move your foot in a way inconsistent with the ball being the cause of its own motion, even though trying to kick the ball restricts the possibilities—or rather, being able to try to kick the ball tells you that the possibilities were already restricted...
In typical causality, the ball has a reason for moving the way it does—you can trace the motion backwards to some acceptable starting point, like “I kicked it as hard as I could toward the fence.” When you add cycles, tracing the chain of arrows back does not need to end at anything you find remotely satisfactory or even unique—“the ball moved because it hit itself because it moved because it hit itself...”
This is a problem with your personal intuitions as a medium-sized multicellular century-lived mammalian tetrapod. No event in this chain is left uncaused, and there are no causes which lack effects in this model. Causality is satisfied. If you are not, that’s your problem. Hell, the energy is even conserved. It runs in a spatial as well as a temporal circle, what with the ball hitting itself and skidding to a stop exactly where it was sitting to wait for the next hit. On the other hand, in such a universe quantum mechanics does not apply, because worldlines cannot split, which also removes any possibility of entropy. ALL interactions are 100% efficient.