Time travel is a tricky fish, but I'm of the belief that you cannot change the past, otherwise the thing that you were going to do would have already happened. So, one year, as a joke, knowing that it wouldn't change a thing, I went back to 1979 and found my future wife playing in a park. I snuck up behind her, grabbed her by the hand, pulled out my pliers and chopped off her little finger. Sure enough, when I got back to the present my wife still had all of her fingers. Sometimes I wonder if I got the wrong girl, but I'm pretty sure it was her.