In Physics, a thought experiment or Gedankenexperiment is a common means of exploring the implications of scientific assumptions without resorting to actual apparatus. Einstein's development of Relativity employed thought experiments about light signals exchanged between observers whose relative speed was a significant fraction of the speed of light, not easily attained by any real observer or (at that time) measuring device. In science fiction, any story which uses sf devices to expound or illuminate a scientific principle may be described as a thought experiment.
Such stories range from the didactic whimsy of George Gamow's Mr Tompkins in Wonderland; Or, Stories of C, G & H (stories 1938-1939 Discovery; 1939 chap) – dealing with Relativity, Gravity and quantum physics – to Hal Clement's less obtrusive exposition of high gravity in Mission of Gravity (April-July 1953 Astounding; cut 1954; text restored with additions and one added story, as coll 1978) and of variously chaotic weather and quasi-weather systems in Close to Critical (May-July 1958 Astounding; 1964), Star Light (June-September 1970 Analog; 1971) and Still River (1987). A K Dewdney's The Planiverse: Computer Contact with a Two-Dimensional World (1984) downplays storytelling in favour of gleefully imagined Flatland science – the design, for example, of a workable two-dimensional steam engine. John E Stith's Redshift Rendezvous (1990) develops one of the Mr Tompkins conceits with a version of Hyperspace whose very low speed of light makes Relativity effects an aspect of everyday life; Stephen Baxter's Raft (September/October 1989 Interzone; much exp 1991) outdoes Mission of Gravity with its depiction of an Alternate Cosmos whose gravitational constant is so large that humans can sense one anothers' pull and Stars are only a mile or two across.
In Mathematics, sf thought experiments can give a sense of the vastness of numbers. The concept of how long a team of randomly typing monkeys might take to generate the works of Shakespeare is amusingly dramatized in R A Lafferty's "Been a Long, Long Time" (December 1970 Fantastic), whose experiment stretches over an almost unimaginable Time Abyss; the same thought experiment is spoofed in Russell Maloney's "Inflexible Logic" (February 1940 The New Yorker). Similarly vast and hard to comprehend is the titular library of Jorge Luis Borges' "The Library of Babel" (in El jardín de senderos que se bifurcan, coll 1942), which in effect contains all possible outcomes of the monkeys' stochastic efforts. Everything is there and nothing can be found (> Information Theory), even when the hypothetical library is digitized and made computer-searchable as in David Langford's "The Net of Babel" (February 1995 Interzone).
Sociological and cultural-anthropological thought experiments in sf are very numerous and diverse. Unusual human societies – of which Jack Vance is a particularly prolific creator – are regularly encountered on remote Islands, Space Habitats, and planets settled during the Colonization of Other Worlds.
A "real" thought experiment which has fascinated many sf authors is the Schrödinger's Cat paradox. This dramatizes the quantum-physics concept that the wave function representing a physical system is a superposition of possible outcomes which does not "collapse" into a particular state until observed. Should the cat in the box, whose death may have been triggered by an unpredictable quantum event (radioactive decay whose detection releases Poison gas), be regarded as in a mixed state – neither alive nor dead until the box is opened by an observer? Sf explorations of the theme include Douglas Adams's whimsical Dirk Gently's Holistic Detective Agency (1987), Greg Bear's "Schrödinger's Plague" (29 March 1982 Analog), George Alec Effinger's "Schrödinger's Kitten" (September 1988 Omni), Ursula Le Guin's "Schrödinger's Cat" (in Universe 5, anth 1974, ed Terry Carr), F Gwynplaine MacIntyre's "Schrödinger's Cat-Sitter" (July/August 2001 Analog) and Rudy Rucker's "Schrödinger's Cat" (30 March 1981 Analog). Robert Anton Wilson's 1979-1981 Schrödinger's Cat trilogy deals with a labyrinth of Parallel Worlds. A large "Schrödinger cat box" is used for randomly delayed human execution in Dan Simmon's Endymion (1996). In a chapter of Flatterland: Like Flatland Only More So (2001), Ian Stewart examines and debunks the seeming paradox, explaining that the cat/box quantum system is sufficiently large that any mixed state would almost instantaneously collapse or "decohere".
Notable twenty-first-century examples of thought-experiment sf include Ted Chiang's "Exhalation" (in Eclipse 2, anth 2008, ed Jonathan {STRAHAN}), with its melancholy evocation of how a mechanical sentience might deduce the nature of Entropy, and Greg Egan's Incandescence (2008), demonstrating in unsparing detail how low-tech dwellers in a closed environment where conventional astronomical observations are unavailable could nevertheless reason their way to general Relativity. Such ambitious sf thought experiments can convey an austere, almost purely intellectual Sense of Wonder.
A relevant anthology is Gedanken Fictions: Stories on Themes in Science, Technology, and Society (anth 2000) edited by Thomas A Easton. [DRL]
see also: Feminism; Metaphysics; Satire.
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