Genres
Time travel in fiction
A common speculative-fiction theme since the late 19th century: travel to the past or future, and its consequences.
Time travel is a common theme or trope in science fiction and speculative fiction, mainly since the late 19th century; the field is sometimes labeled time-travel fiction or chrono fiction. H. G. Wells's The Time Machine (1895) popularized mechanical time travel, and stories typically explore the consequences of changing, or failing to change, the past or future. Standard machinery includes time slips, portals, messages from the future, precognition and time loops; standard themes include the grandfather paradox, the butterfly effect and alternate histories.
Time travel is the most continuity-hungry setting in fiction: every trip rewrites what every character can know. Long time-travel serials lean on timeline tracking, and in-story changes must be handled deliberately or the plot collapses into the retcon problem from the inside.