A thing that contrary to popular belief, cannot cause paradoxes. The only way you would be able to
kill your grandfather would be to
kill him after your father was born, in which case you never met him in the first place and that will be how it'
s always been. In any other case, you are physically unable to, for you will inevitably be stopped or change your mind. When you go back in
time, you are only able to do what has already happened.