Literally, "double-walkers". To meet one's own supernatural double (or Scots "fetch") was traditionally an unlucky or fatal portent. Even when rationalized through sf devices – typically Time Travel – such encounters can still seem ominous, as when the protagonist of Isaac Asimov's The End of Eternity (1955) is filled with irrational dread by almost meeting his earlier self. Likewise, characters in Dragonflight (fixup 1968) by Anne McCaffrey inadvertently trouble their younger selves with perceived portents. Participants in the Changewar of Fritz Leiber's The Big Time (March-April 1958 Galaxy; 1961 dos) are known as Doublegangers, having been split off from their timebound lives (which continue) to operate outside consensus reality. More genuinely alarming are doppelgangers which permanently replace human characters: Alien "pod people" in Invasion of the Body Snatchers (1956) or Robots in The Stepford Wives (1974). A minor version of this frisson accompanies characters' sighting of human doubles which are about to be substituted for nefarious purposes, as in E E Smith's First Lensman (1950), James H Schmitz's A Tale of Two Clocks (1962; vt Legacy 1979), and very many Pulp magazines and Comics scenarios.
Exact doubles generated by side-effects of Matter Transmission or intentional Matter Duplication – as in Algis Budrys's Rogue Moon (1960) – raise more genuinely disturbing questions of personal Identity, as perhaps does the potential coexistence of multiple instances of an Uploaded personality in Cyberspace. Apparent doppelgangers may also be found in Parallel Worlds, although their presence on a Counter-Earth in the film Doppelganger (1969) seems wildly implausible. [DRL]
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