I was going to write a short story on a very similar idea once- you can travel back in time, but you can’t do anything to change history.
“If we don’t know your father is alive right now – if there is only a 90% chance that he is alive right now, then there is a chance that you can go back and kill him.
“But if you know he is alive, there is no chance you can kill him.”
In other words, even if you take a trip back in time with the specific intention of killing your father, so long as you know he is happily sitting in his chair when you leave him in the present, you can be sure that something will prevent you from murdering him in the past. It is as if it has already happened.
Technorati tag: Time travel