In preparation for his new book, about a time traveler who tries to alter the Kennedy assassination, Stephen King spoke to Wired about his views on how time travel works. (io9. provides a nice distillation of his answers.) According to King, time is watched over by guardians and history is changeable, but “larger” events require more effort to change.
One thing that makes time travel stories so interesting, and also probably infuriating, is that each author has his or her own views on how the “rules” work. Therefore, each work can tell its story differently and can use storytelling devices differently. For example, if the traveler can go back and forth, a “ticking clock” is probably not a viable motivator for the traveler to act as fast as possible. Also, the tension is much different in stories in which time is changeable, such as this King story or Back to the Future as opposed to stories in which time is fixed, like LOST and Harry Potter. In the former, the traveler has to be very careful not to mess anything up, while the latter allows for more uses of irony (I’m looking at you, killer of Daniel Faraday).
I will always love Back to the Future and the (first two) Terminator movies, but I’ve always taken the “whatever happened, happened” approach to how things would work if time travel really were possible. In fact, that is the rules set I am using in the story I’m writing for NaNoWriMo. What are your preferred time travel rules, and what is your favorite time travel story?