Imagine you build a time machine. Is it possible for you to travel back in time, meet your grandfather before he produces any children, and kill him?  Time travel is a sci-fi staple. Is Back to the Future philosophically accurate? Did J.K Rowling crack the secret of time travel in Harry Potter and the Prisoner of Azkaban? As a bonus we explain why Rick and Morty's The Vat of Acid Episode isn't about time travel.