To me, the fact that we all exist hints at the fact that we haven't (won't have) messed things up with time travel. The fact is, if it gets (at any point in the future) mass-produced, or even somewhat available to the public, there'll be one wacko who'll go back and destroy humanity as some early stage. The fact that we still exist says to me that this never (will never) happened. Not that there was some sort of spiffy "time cop" stopping the guy - I think that's silly. If you have time travel, you can evade anyone very easily. Just go back and tell yourself where you saw him/her, and avoid those places/times.
PS: Anyone noticed how inadequate English tenses are for expressing even simple loops in a worldline? If time travel ever happens, I'm sure its practitioners will speak a language more suited to their needs.
PS: Anyone noticed how inadequate English tenses are for expressing even simple loops in a worldline? If time travel ever happens, I'm sure its practitioners will speak a language more suited to their needs.