Yay, everyone's favourite topic!

Okay, so you may have seen a number of methods in fiction shows used to represent how it would work, eg you get duplicated when you time travel.  Let's take this duplication principle - would it allow you to make arbitrary number of copies of yourself?  Perhaps get each copy to go to different time periods so that you exist throughout time (and thus, live forever / be invincible)!

Anyway, ignoring that, here's a problem.  If you time travel into the future, then back into the past, and get killed in this past.  Assume the future you knows of your death in the past.
If that's the case, when in the future, you would not travel back into the past since you know you'll die.  But if you never make the trip, the event never occurs, and thus you'd make it (for one reason or another)...


(this is subtly different from the well known "go back and kill grandmother" issue)