Chronology protection conjecture

The Chronology Protection Conjecture is an idea about time travel. It suggests that it is impossible for time travelers to change the past, because if they do, it would make the timeline (or chronology) of events not make sense. For example, if a time traveler went back in time and killed their own grandfather when he was a child, then they would never have been born! So, according to the Chronology Protection Conjecture, it simply isn't possible for time travelers to go back in time and change things, so that our timeline makes sense.