What is it called when something is out of place in time, like a jet stream in a movie about ancient Rome?

When something or someone appears outside of its proper time in a story, an anachronism has occurred. Anachronisms are abundant in movies and are generally considered mistakes. For example,
  • In the movie Titanic, Jack (Leonardo DiCaprio) says that once, when he was younger, he and his father went ice fishing on Lake Wissota. Lake Wissota is a man-made reservoir that was created five years after the Titanic sank, so it would have been impossible for someone who went down with the Titanic to have fished there.
  • More recently, in the movie Indiana Jones and the Kingdom of the Crystal Skull, Mutt (Shia LaBeouf) rides in on a Harley Davidson motorcycle with front disc brakes and a twin cam engine, neither of which was available until 1974.

Although some people make a game out of finding anachronisms, not all anachronisms are mistakes; instead, they can lend an endearing or more approachable quality. The majority of William Shakespeare's anachronisms fall into this category:

  • In Act II, Scene 1 of Julius Caesar, a clock strikes three. Romans would not have had such chiming clocks. But the audience of Shakespeare's time would have, and the late-night chiming of the clocks helped to make this tragedy feel more current to them. Such poetic license helped turn Julius Caesar into a great tragedy instead of a tedious and exact history.
  • In Hamlet, which takes place in the seventh century, we learn that Prince Hamlet has been studying and plans to return to Wittenberg. But the University of Wittenberg wasn't founded until 1502. This anachronism helped Shakespeare's audience to identify with the play and its characters. The audience would recognize that Hamlet is a scholar, and that he would most likely be a skeptic — not a believer in spirits and ghosts.