Grandfather Paradox

Please tell me if it is so. OK now people tell me that you cannot go back in time due to a Grandfather Paradox that keeps us from changing events that happen in past years. Basically, reason is because you could go back and off your grand pop. Then you were never born, so how did you come.

Steven Gibbs has talked about the HDR Grandfather Paradox. It is basically a long and complicated process. He says you go to an alternate time line that is not the same as our own.