This sf trope is a logical spinoff from the concept of Matter Transmission (which see). A malfunctioning matter transmitter may produce duplicates of the persons or objects transported, as has happened more than once with the Star Trek transporter: there is a duplicate Captain Kirk in the original-series episode "The Enemy Within" (1966) and an evil duplicate Spock in James Blish's Spock Must Die! (1970). In other matter transmission scenarios, the production of duplicates may be integral to the process. Living beings transmitted in Clifford D Simak's Way Station (June-August 1963 Galaxy as "Here Gather the Stars"; 1963) and Christopher Priest's The Prestige (1995) leave dead copies of themselves behind; Simak's galactic transport terminals include elaborate facilities for disposing of these bodies. A living female Doppelganger produced by matter duplication is central to William F Temple's The Four-Sided Triangle (November 1939 Amazing as "The 4-Sided Triangle"; exp 1949), which became the film Four-Sided Triangle (1952).
Classic examples of the Economics of matter duplication include "Pandora's Millions" (June 1945 Astounding) and other late stories in George O Smith's Venus Equilateral (stories October 1942-November 1945 Astounding; coll of linked stories 1947; exp 1975 UK 2vols; vt The Complete Venus Equilateral 1976), and Damon Knight's "A for Anything" (November 1957 F&SF; exp as The People Maker 1959; vt A for Anything 1961). Both examine the disastrous impact of universal cheap duplication of goods. Smith felt it necessary to introduce an unduplicatable metal – the new Element "identium" – to provide a stable medium of exchange (> Money). But Ralph Williams's "Business as Usual, During Alterations" (July 1958 Astounding) optimistically assumes that after the coming of the duplicator, the US would readily switch from a economy of scarcity to one of abundance.
In Algis Budrys's Rogue Moon (1960) such duplication is calculated, the transmitted "clones" of a single explorer being continually sacrificed to the task of exploring a hazardous alien artefact. In Thomas M Disch's Echo Round his Bones (December 1966-January 1967 New Worlds; 1967) ghostly duplicates, perceptible only to one another, are an unintended though theoretically deducible consequence of the use of Matter Transmitters. Both of these last-named stories sensitively exploit the bearing which the Imaginary-Science device has on the philosophical problem of Identity.
The Rogue Moon technique of transmitting "expendable" duplicates into hazardous situations is echoed in other sf, one example being the opening section "Doomship" (March/April 1973 If) of Farthest Star (1975) by Frederik Pohl and Jack Williamson. A succession of personal duplicates offers a form of Immortality without continuity in Thomas M Disch's "Now Is Forever" (March 1964 Amazing). Backup selves are routinely recorded and recreated by matter duplication in Wil McCarthy's The Collapsium (2000) and Charles Stross's Glasshouse (2006). A more currently fashionable means of achieving sf matter duplication is via Nanotechnology, as in the "A-gate" transmitter/duplicators of Glasshouse and, earlier, in Neal Stephenson's The Diamond Age (1995). [DRL/BS/MJE]
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