What is the Grandfather Theorem?
The Grandfather Theorem is a time paradox that states if you have a time machine, and you travel back in time and kill your grandfather before he had kids, then you were never born. But if you were never born, then who killed your grandfather? A classic paradox, really.
Or, in simpler terms: if your granddad is a time-traveling assassin, you might be a temporal orphan.
Read about the time-traveling assassin who killed your grandfather Visit the Temporal Orphanage, where you can learn more about being a non-entity