Editing Alternate history (section)

====Rival paratime worlds====
{{Unreferenced section|date=October 2023}}
The concept of a cross-time version of a world war, involving rival paratime empires, was developed in [[Fritz Leiber]]'s Change War series, starting with the [[Hugo Award]] winning ''[[The Big Time (novel)|The Big Time]]'' (1958); followed by [[Richard C. Meredith]]'s ''Timeliner'' trilogy in the 1970s, [[Michael McCollum]]'s ''A Greater Infinity'' (1982) and [[John Barnes (author)|John Barnes']] ''Timeline Wars'' trilogy in the 1990s.

Such "paratime" stories may include speculation that the laws of nature can vary from one universe to the next, providing a science fictional explanation—or veneer—for what is normally fantasy. [[Aaron Allston]]'s ''Doc Sidhe'' and ''Sidhe Devil'' take place between our world, the "grim world" and an alternate "fair world" where the Sidhe retreated to. Although technology is clearly present in both worlds, and the "fair world" parallels our history, about fifty years out of step, there is functional magic in the fair world. Even with such explanation, the more explicitly the alternate world resembles a normal fantasy world, the more likely the story is to be labelled fantasy, as in Poul Anderson's "House Rule" and "Loser's Night". In both science fiction and fantasy, whether a given parallel universe is an alternate history may not be clear. The writer might allude to a POD only to explain the existence and make no use of the concept, or may present the universe without explanation of its existence.