The bootstrap paradox is a type of time travel paradox that occurs when an object, information, or person is sent back in time and becomes the cause of its own existence in the present. This creates a circular loop of causality, where the origin of the object, information, or person is unknown or self-created. Here are some examples of the bootstrap paradox: In the movie Somewhere in Time (1980), a man travels back in time to meet a woman he fell in love with after seeing her portrait. He gives her a pocket watch that she had given him in the present, which he later realizes was the same pocket watch he had seen in the portrait. The pocket watch has no origin, as it was passed from the present to the past and back again. In the TV series Doctor Who, the Doctor receives a transcript of a conversation he will have in the future from Sally Sparrow, who got it from a DVD that the Doctor recorded in the past. The Doctor then reads the transcript into a camera in the past, which becomes the DVD that Sally finds in the present. The transcript has no origin, as it was created from itself. In the book A Journey Through Time by H.G. Tannhaus, which appears in the Netflix series Dark, the author writes about time travel and wormholes based on a copy of his own book that he received from a time traveler. The book has no origin, as it was written from itself. The bootstrap paradox is also known as an ontological paradox, because it involves questions about the nature and origin of being and existence. Some possible ways to resolve or avoid the paradox are: The Novikov self-consistency principle, which states that any event that causes a paradox cannot happen, and that time travelers can only act in ways that are consistent with their own history. The multiple worlds interpretation, which states that every time travel event creates a new parallel universe where the paradox does not exist, and that time travelers can never return to their original universe. The causal loop theory, which states that time is not linear but circular, and that events are predetermined and fixed by their own existence in the loop.