The pseudo-Element or alloy unobtainium – sometime spelt unobtanium – is a traditional, half-serious joke of physics and engineering dating from the mid-twentieth century: it denotes an ideal material from which frictionless bearings, massless levers and other desirable but unfeasible experimental components might be made. It was first formally defined in the US Air Force Air University's Interim Glossary, Aero-Space Terms (1958) by Woodford Heflin, as "A substance having the exact high test properties required for a piece of hardware or other item of use, but not obtainable whether because it theoretically cannot exist or because technology is insufficiently advanced to produce it." Related terms include handwavium and unaffordium. The Star Trek universe's equivalent of unobtainium is the Imaginary-Science dilithium.
In sf, unobtainium is introduced by name as the basis of an exotic Weapons system in Startide Rising (1983) by David Brin, and mentioned along with its sister non-element impossibilium in Wil McCarthy's The Collapsium (2000), whose programmable quantum-technology material "wellstone" can simulate any conceivable element including "imaginary substances like unobtainium, impossibilium, and rainbow kryptonite." In The Core (2003), unobtainium is an implausibly tough metal which can resist the extreme heat and pressure of Earth's molten core. The term has also been applied to room-temperature superconductors, another elusive dream of engineering. This is the meaning implied in Avatar (2009), with its floating mountains and apparent Antigravity, since superconductors notoriously "levitate" in strong magnetic fields such as are encountered on Pandora, the film's Gas-Giant moon setting. [DRL]
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