My hypothesis is that universes that allow macroscopic time travel are very unlikely to have life intelligent enough to exploit the time travel. The hypothesis depends on two points: 1) policing time travel is likely to be extremely difficult or impossible, and 2) at least some members of the species will want to cause trouble with a time machine, including the sort of trouble that causes the entire species to have never evolved in the first place. Therefore I take the fact that we exist as evidence that arbitrary amounts of time travel aren’t possible in our universe...
Larry Niven once commented that, if past-changing time travel is possible, the most stable universes will be those in which time travel is never invented...
Therefore I take the fact that we exist as evidence that arbitrary amounts of time travel aren’t possible in our universe...
Doesn’t follow. The fact that you exist in a certain way isn’t evidence about prior probability of your existing in this way. (Your points (1) and (2) are arguments about prior probability that don’t have this problem; using observations that depend on the value of prior probability also works.)
My hypothesis is that universes that allow macroscopic time travel are very unlikely to have life intelligent enough to exploit the time travel. The hypothesis depends on two points: 1) policing time travel is likely to be extremely difficult or impossible, and 2) at least some members of the species will want to cause trouble with a time machine, including the sort of trouble that causes the entire species to have never evolved in the first place. Therefore I take the fact that we exist as evidence that arbitrary amounts of time travel aren’t possible in our universe...
Larry Niven once commented that, if past-changing time travel is possible, the most stable universes will be those in which time travel is never invented...
Doesn’t follow. The fact that you exist in a certain way isn’t evidence about prior probability of your existing in this way. (Your points (1) and (2) are arguments about prior probability that don’t have this problem; using observations that depend on the value of prior probability also works.)
Hm. It looks like my intuition has a bug. I’ll have to think about it more.