The Grandfather Paradox

They had told Christopher that time travel was impossible, that it violated the laws of physics. It took twenty years of obsession, but he proved them wrong.

Christopher had always been that way. Whatever walls surrounded him, he knocked them down. He remembered what Grandfather Warren had said, that he would never amount to anything. The insult burned at him every day, spurring him on.

So it was with great regret he discovered there was one law of physics he would never be able to break. No matter how hard he tried, Christopher was never able to kill Grandfather Warren.