The Philosophy of Time Travel

The way I see it, works of fiction present four time travel scenarios.

1. Parallel Universes: When you time travel it creates a new, parallel universe that is changed based on the time traveler's actions. Includes fortune-telling, where knowing the future changes the future. Examples: Back to the Future, Donnie Darko, The Minority Report. Problems: Grandfather paradox still a problem. For instance, we are told that Michael J. Fox in the first Back to the Future created Rock-N-Roll, which creates a loop where Michael J. Fox learned about Rock-N-Roll from himself.

2. Single Universe: Like parallel, except there is only one reality that can be changed. Examples: Terminantor 1-2, Southland Tales, 12 Monkeys. Problems: Same grandfather paradox. In Terminator 1, John Connor's father is from the future. How could John Connor exist if his father isn't born until after him. This is also the case in Futurama, where Fry is literally his own grandfather. Also, running into yourself may (Southland Tales) or may not (Back to the Future) result in the end of the world.

3. Inevitable Fate: Like the single universe except that fate cannot be changed. Trying to change the events of the past will still result in the same outcome; only the circumstances change. Examples: Terminantor 3, The Time Machine (movie). Problems: Why would only certain events like the rise of machines or the death of a loved one have to occur, while you crossing the street can be changed. Assumes some kind of intelligent designer.

4. No Causality: All events in the history of time have already occurred. Time traveling results in the replaying of predetermined events. Examples: Slaughterhouse-Five. Problems: Difficult to comprehend a reality where there is no causality. This would be Hume's idea of time travel, I assume.