and the B-1 bomber required relatively large amounts of it as well). Contemporary popularization By 2010, the term had had been used in mainstream news reports to describe the commercially useful rare earth elements (particularly terbium, erbium, dysprosium, yttrium, and neodymium), which are essential to the performance of consumer electronics and green technology, but whose projected demand far outstrips their current supply. 'Unobtainium' has come to be used among people who are neither science fiction fans nor engineers to denote an object that actually exists, but which is very hard to obtain either because of high price (sometimes referred to as "unaffordium") or limited availability. It usually refers to a very high-end and desirable product. Examples are rear cassettes in the mountain biking community, parts that are no longer available for old-car enthusiasts, parts for reel-to-reel audio-tape recorders, and rare vacuum tubes such as the 1L6 or WD-11 that can now cost more than the equipment in which they were fitted. There have been repeated attempts to attribute the name to a real material. Space elevator research has long used "unobtainium" to describe a material with the necessary characteristics, but carbon nanotubes might have these characteristics. The eyewear and fashion wear company Oakley, Inc. also frequently denotes the material used for many of their eyeglass nosepieces and earpieces, which has the unusual property of increasing tackiness and thus grip when wet, as unobtanium. Science fiction Unobtainium was mentioned briefly in David Brin's 1983 book Startide Rising, and plays a role in the 2003 film The Core and the 2009 film Avatar. Similar terms The term handwavium (suggesting handwaving) is another term for this hypothetical material, as are raritanium, and hardtofindium. The term (also spelled with variants such as illudium) has been used to describe a material which has "eluded" attempts to develop it. This was mentioned in several Looney Tunes cartoons, where Marvin the Martian tried (unsuccessfully) to use his "Eludium Q-36 Explosive Space Modulator" to blow up the Earth. Another largely synonymous term is wishalloy, although the sense is often subtly different in that a wishalloy usually does not exist at all, whereas unobtainium may merely be unavailable. A similar conceptual material in alchemy is the philosopher's stone, a mythical substance with the ability to turn lead into gold, or bestow immortality and youth. While the search to find such a substance was not successful, it did lead to