Term occasionally used in sf criticism for a crucial forking-place in Time, whose manipulation via Time Travel can radically affect the future that follows. "Jonbar hinge" has also been used synonymously. The name derives from Jack Williamson's The Legion of Time (May-July 1938 Astounding; rev 1952), which deals with Changewar between the potential future empires of Jonbar (good) and Gyronchi (bad). The former is named for the character John Barr: the fiercely contested jonbar point is the moment when as a small boy Barr picks up either a magnet, inspiring him to a life of science which ultimately brings Jonbar into existence, or a pebble, leading Barr to obscurity and the world to Gyronchi. In Isaac Asimov's The End of Eternity (1955), such key points are carefully calculated by watchful Time Police to achieve maximal effect from minimal interference: thus, for example, a brief delay caused by minor sabotage eliminates a Future War in the following century.
Most works of Alternate History develop their changed future from a single explicit or implied jonbar point, as do most quasi-fictional Thought Experiments in historical extrapolation, like If It had Happened Otherwise: Lapses into Imaginary History (anth 1931; vt If: or History Rewritten 1931; exp 1972) edited by J C Squire, or What Might Have Been: Imaginary History from Twelve Leading Historians (anth 2004) edited by Andrew Roberts (1963- ). [DRL]
see also: Chrononauts.
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