The grandfather paradox refers to a situation where a time traveler goes back in time and alters an event that ultimately makes their own existence impossible. Some synonyms for this paradox include the time travel paradox, the causal loop paradox, and the predestination paradox. The time travel paradox refers to the idea that time travel itself may not be possible if altering the past can change the future. The causal loop paradox states that an event that appears to be the cause of itself creates a self-contained loop in time. The predestination paradox occurs when a time traveler's actions in the past are predetermined and cannot be changed, ultimately leading to their own existence.