Okay. This is random. So I was watching Haven- an amazing TV show, by the way (you should totally watch it, seriously)- and a character (who I will not name because of spoilers) went back in time. There, he met his grandfather, who he'd never met in real life until that point. He gave his grandfather a gold coin. His grandfather later gave it to his son. His son then gave it so HIS son, being the character in the beginning. How does this work? 

Like, where did the original coin come from? Wouldn't the coin technically not exist?