posted on Oct, 21 2007 @ 09:07 PM
Ah, but if a time traveller were unable to go back and stop the event (due to not knowing about it) then the event would in fact occur, giving them
the ability to know about it so they could go back and stop it.
It's called the grandfather paradox, which asks the question of what happens if you go back in time and kill your grandfather before you are born.
There are lots of answers to this question, not one of which has a shred of evidence to support it.
One thing you could do, if you were really intent on stopping an event in the past, is find some way to make sure that you still go back and stop it
later on. Maybe you could go back and stop 9-11, then mail yourself a letter with instructions to be delivered the day before you finish your time
machine in the future saying, "hey, go back and stop these flights when you're done building that!"