There's a genre of chess problems called "retrograde analysis" tasks wherein the goal is to figure out how an apparently-impossible position might appear in a legal game. As in chess, some real-life situations can never occur because there's no way to reach them from a previously existing state. They're the opposite of dead ends, which lead to extinction in the next generation. In Conway's cellular automaton Life such patterns are called "Garden of Eden" configurations; like that idyllic site, they can't evolve but have to be created.

Thinking backwards, with consistency, is a special skill that's not easy to develop. Science fiction writers are, alas, prone to conjure up self-contradictory worlds when they fail to consider how a key plot element might have arisen. Consider mystical patterns that, upon viewing, cause a brain to lock up ... or societies that lack any infrastructure for raising children ... or giant creatures that somehow live without any ecosystem to meet their immense energy requirements (as Paulette noted long ago concerning the sandworms in Dune; see also Why Big Fierce Animals Are Rare by Paul Colinvaux).

Such a place can't happen in Nature. You can't get here from there!

TopicLiterature - TopicScience - TopicRecreation - 2002-09-28

(correlates: PartOfTheProverb, PyramidBuilding, BozoBit, ...)