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A floating timeline (also known as a sliding timescale) is a device used in fiction, particularly in long-running serials such as comics and animation, to explain why characters age little or not at all over a period of time – despite real-world markers like notable events, people and technology appearing in the works and correlating with the real world. A floating timeline is a subtle form of retroactive continuity. This is seen most clearly in the case of comic book characters who debuted as teens in the 1940s or the 1960s but who are still relatively young in current comics. Events from the characters' pasts are alluded to, but they are changed from having taken place years ago to having taken place more recently.
A floating timeline is usually accomplished by avoiding referencing specific dates for events in the character's lives. Instead, all references are relative to the "present" of the story. For example, instead of referencing an event as happening in 2017, the story would refer to it happening "two years ago". A floating timeline is uncommon in live action movies and television where the aging of the actors usually renders the floating timeline moot. However, floating timelines are often used on soap operas, where it has become acceptable to replace actors, allowing for many characters to exist for decades without aging much.
A floating timeline is usually abstracted from that of actual historical events, but may contain subtle references to the real world timelines. There may also be attempts made to maintain certain characters' historic timelines if it is felt to be essential to the character's personality, while allowing the rest of the world's timelines to continue to develop. For example, in the 2000s comic book miniseries The Punisher and its subsequent continuation, the title character is shown to be a Vietnam War veteran, just as he was in his earliest appearances in the Marvel comics of the 1970s. However, the stories place him in contemporary New York, where he meets fellow Marvel characters such as Spider-Man, who is barely much older than he was when introduced in 1962.
An example taken from novels is the case of mystery writer Rex Stout, who created a floating timeline for master detective Nero Wolfe and other principal characters in the corpus, while the stories take place contemporaneously with their writing and depict a changing landscape and society. Nero Wolfe's age is 56. "Those stories have ignored time for thirty-nine years," Stout told his authorized biographer John McAleer. "Any reader who can't or won't do the same should skip them. I didn't age the characters because I didn't want to. That would have made it cumbersome and would seem to have centered attention on the characters rather than the stories." In the early novels, Wolfe dated himself somewhat by discussing his life before World War I and his combat service in that war, but in later stories he was less explicit about his past.
Children's writer Antonia Forest (1915–2003) set her later Marlow family stories (published between 1948 and 1982) at the time they were written, so her characters experience aspects of 1970s popular culture in her timeline only a couple of years after they experienced the London Blitz.