Vladimir_Nesov comments on Causal Universes - Less Wrong

60 Post author: Eliezer_Yudkowsky 29 November 2012 04:08AM

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Comment author: lavalamp 28 November 2012 08:22:01PM 1 point [-]

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...

Comment author: Vladimir_Nesov 28 November 2012 09:16:20PM 1 point [-]

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.)

Comment author: lavalamp 28 November 2012 10:14:04PM 1 point [-]

Hm. It looks like my intuition has a bug. I'll have to think about it more.