I am having my doubts that time travel is even a coherent concept. Actually, I have my doubts about time itself. At non-relativistic speeds and over small distances we can kid ourselves that two events not in the same place can both happen “at” a particular time. But we know that in general that’s only a convenient simplification. There’s no objectively real “t” axis in spacetime independent of the observer’s frame of reference.
Understandable. Your brain shipped with a built-in module that models time as a property of reality in order to simplify other processes. Most people have to bludgeon it to near-death in order to just barely avoid the basic failure modes of thinking about time travel.
There’s no x,y, or z axis independent of the observer’s frame of reference either. Does that mean that spatial travel is not a coherent concept?
If the coherent concept is ‘spacetime travel’, why is it required that there exist an ordering over all points in spacetime? Every pair of points (A,B) falls into one of three categories: events at point A can directly or indirectly have an effect/be observed at point B, but not vice versa; events at point A cannot have an effect or be observed at point B, directly or indirectly; events at point B can be observed or have an effect at point A, directly or indirectly.
It is difficult for different observers to communicate where points are, but they divide all points in spacetime into the same three categories.
I am having my doubts that time travel is even a coherent concept. Actually, I have my doubts about time itself. At non-relativistic speeds and over small distances we can kid ourselves that two events not in the same place can both happen “at” a particular time. But we know that in general that’s only a convenient simplification. There’s no objectively real “t” axis in spacetime independent of the observer’s frame of reference.
But Eliezer gave you a constructive example in the post!
OK then, I am having doubts that my mind is coherent enough to discuss time travel usefully.
Understandable. Your brain shipped with a built-in module that models time as a property of reality in order to simplify other processes. Most people have to bludgeon it to near-death in order to just barely avoid the basic failure modes of thinking about time travel.
In fairness, his example assumed a universal timeframe (experienced by the simulators.)
There’s no x,y, or z axis independent of the observer’s frame of reference either. Does that mean that spatial travel is not a coherent concept?
If the coherent concept is ‘spacetime travel’, why is it required that there exist an ordering over all points in spacetime? Every pair of points (A,B) falls into one of three categories: events at point A can directly or indirectly have an effect/be observed at point B, but not vice versa; events at point A cannot have an effect or be observed at point B, directly or indirectly; events at point B can be observed or have an effect at point A, directly or indirectly.
It is difficult for different observers to communicate where points are, but they divide all points in spacetime into the same three categories.