"grandfather paradox"
let's say you are a time traveler, you went back in time and ought to murder your grandfather. After successfully killing him, one of your parents will cease to exist and so will you. If you did not exist then you won't be able to grow, be a time traveler and murder your Grandfather and that makes your Grandfather alive.
Answers & Comments
Answer:
Another theory exist if you k*ll your grandfather in the past, that past will not continue. That time your grandfather was dead but at your present you still exist you're not going to disappear. That time the generation will not continue. But the present generation you have will still continue. Because some scientists believe that we have many dimensions of our past maybe you murder your grandfather In that dimension but your dimension will still exist and you will still continue to exist.
There's so many theory about it the other theory was the infinity one but I'm to tired to explain. bye.