Elementary, My Dear Watson

It's fun to watch lawyers crawling from the woodwork when someone scents a big pot of money. Philip K. Dick didn't sue the British SF Association for titling one of its magazines Nexus in 1980, and his heirs weren't bothered about Nexus the 1980s comics character, or Nexus the 1996 online gameworld ... but when Google called its new phone Nexus One, this triggered a shock-horror threat of lawsuits to defend the Nexus 6 replicant brand name in Dick's Do Androids Dream of Electric Sheep? (1968) and the film Blade Runner. Because – note the subtle legal difference – Google has a big pot of money.

No one is likely to prove their ownership of a Latin word that's been part of the English language for centuries, but maybe the Dickoids hope for a nuisance-value settlement. Who knows? Meanwhile, some pundits are frothing about the number of familiar sf ideas in James Cameron's Avatar, and never mind that you can't copyright ideas. The film's smoking-gun equivalent of Nexus is the magic antigravity element unobtanium. A Hugo-winning sf novel, Startide Rising by David Brin, used unobtainium (note the slightly different spelling) for an arcane weapons system back in 1983. Could Brin be consulting his lawyers?

No: he has more sense. Unobtainium is a traditional physics/engineering joke dating from the mid-20th century. It's the stuff you use to make massless levers and frictionless bearings for ideal lab experiments. It gets another sf namecheck in Wil McCarthy's The Collapsium (2000), where the programmable quantum-tech material called "wellstone" can simulate any conceivable element including "imaginary substances like unobtainium, impossibilium, and rainbow kryptonite." Of course unobtainium has long been part of the Star Trek universe, wearing false whiskers and pretending its name is dilithium.

The most famous antigravity element – unobtainium's first incarnation – is Cavorite (actually an alloy), which in H.G. Wells's The First Men in the Moon acts as a gravity screen allowing his spacecraft to float free of Earth. Though Einstein's general relativity made it clear that Cavorite is indeed impossibilium, the idea is so tempting that a US crank set up the Gravity Research Foundation in 1948 to find a "gravity shield" alloy. Eventually the GRF became all respectable and switched to awarding gravitational-physics essay prizes, several to Stephen Hawking.

Cavorite rip-offs are common, as in Joseph Kitchell's 1924 The Earl of Hell, which subtly disguises Germany as Hunovia and the magic element as Nilgrav. More imaginative names include Disney's flubber and the Rocky and Bullwinkle cartoon show's upsidaisium. Magellanium, from David Duncan's Dark Dominion (1954), has a nice name but unusually daft properties: it's gravitationally attracted only to the dwarf companion of the star Sirius, so a spaceship built of Magellanium automatically falls off Earth and continues falling towards Sirius. I forget exactly how they get it home again.

The most plausible imaginary elements tend to lurk in hoped-for "islands of stability" somewhere beyond the end of the known Periodic Table, and are usually mindboggling power sources – like the "trans-Plutonian isotopes" making up the doomsday explosive PyrE in Alfred Bester's The Stars My Destination (1956), or the "trans-three-hundred elements" of the ultimate fuel Illyrion in Samuel R Delany's Nova (1968).

Some other elements that never were:

Celestium, in a forgotten 1907 sf novel called The Mystery, explains the puzzle of the Mary Celeste – this dangerous stuff emits a highly specialized radiation that makes sailors jump overboard. Tell that, as they say, to the marines.

Nipponanium, a Japanese discovery in Margery Allingham's detective novel The Mind Readers (1965), causes telepathy and lets schoolkids trawl the minds of classmates for information – just like downloading your essay from the web.

Orichalcum, the fabulous metal mentioned in such ancient texts as Plato's story of doomed Atlantis, is rediscovered by a famous fictional airman in Biggles – Charter Pilot (1943) by Captain W.E. Johns. But this orichalcum spontaneously catches fire when exposed to air, a point that Plato didn't mention, and Biggles fails to get rich.

Lastly: George O Smith's short "Pandora's Millions" (1945) features a slew of brand-new elements created by tinkering with the settings of a matter-duplicator, and named after assorted story characters. We never learn what these are good for, but the great discovery is identium – a synthetic element that can't be matter-duplicated. This instantly replaces gold as an ideal currency standard, saving the solar system's economy from rapacious bankers. If only! So we end as we began, with a big pot of money.

David Langford hopes to acquire wealth and fame by discovering Langfordium.

Later: this column must have been written too late to allow a mention of Tom Holt's imaginary element aposiderium in Blonde Bombshell. Or maybe, since an important property of aposiderium is that it mysteriously causes amnesia, I just forgot.