The Open Thread posted at the beginning of the month has gotten really, really big, so I've gone ahead and made another one. Post your new discussions here!
This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.
Makes perfect sense to me if you assume a single time-line. (This might be a big assumption, but probably less big than the truth of sufficiently strange prophecies.) You can think of this time line as having stabilized after a very long sequence of attempts at backward time travel under slightly different conditions. Any attempt at backward time travel that changes its initial conditions means a different or no attempt at time travel happens instead. Eventually you end with a time-line where all attempts at backward time travel exactly reproduce their initial conditions. We know that we live in that stabilized time-line because we exist (though the details of this timeline depend on how people who don't exist, but would have thought they exist for the same reasons we think we exist, would have acted, had they existed).
By the way, that sort of time-travel gives rise to Newcomb-like problems:
Suppose you have access to a time-machine and want to cheat on a really important exam (or make a fortune on the stock marked or save the world or whatever. The cheating example is the simplest). You decide to send yourself at a particular time a list with the questions after taking the exam. If you don't find the list at the time you decided you know that somehow your attempt at sending the list failed (you changed your mind, the machine exploded in a spectacular fashion, you were c... (read more)