Making yourself invisible: could it leap from fiction to fact?

Jimmy Lee Shreeve does a disappearing act
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Whether we're inspired by the The Invisible Man or the more recent Harry Potter series, the ability to vanish at will is something that most of us would love to possess. Not only could we duck out of embarrassing situations, but we could spy on our friends and enemies - or even sit in on conversations between Tony Blair and Gordon Brown. Not to mention the nefarious uses to which an invisibility cloak could be put, such as shoplifting and robbing banks.

Until now, such ideas were the preserve of fantasy fiction, movies and daydreams. But according to scientists, writing in the 25 May edition of the journal Science, an invisibility cloak is not only possible, but early versions, that would mask microwaves and other forms of electromagnetic radiation, could be as close as 18 months away.

One of the authors of the paper, Professor Sir John Pendry, a physicist at Imperial College London, stresses that he and his fellow-researchers just need to perfect the manufacture of new materials - called "metamaterials" - that have the ability to steer light and other electromagnetic radiation around an object. "It's theoretically possible to do all of these Harry Potter things," he says. "But what's standing in the way is our engineering capabilities."

Metamaterials can be tuned to bend electromagnetic radiation (radio waves and visible light, in particular) in any direction. A cloak made of these materials would neither reflect light nor cast a shadow. Instead, light and other forms of electromagnetic radiation would hit the cloak and simply flow around it.

Another of the authors of the paper, David R Smith, a professor of engineering at Duke University, North Carolina, gives the analogy of running water: "You place a rock in [a] stream, the flow lines of the stream circle around the rock, and that's essentially what's happening in this cloak. As light comes in, it's directed around the object that you're looking to conceal."

Unlike a rock in a stream, however, the onlooker would see right through the invisibility cloak - everything covered by it would be hidden from view, just like in Harry Potter. To create the formula for metamaterials, the authors of the paper drew on earlier research that they had conducted into the way refracted light travels. Not long ago, scientists believed that it always travels in a predictable direction. But in 2000, Smith's team introduced a grid-like material that bends it in unexpected ways. Many physicists were sceptical, even critical. But in 2003, after several laboratories confirmed the finding, Science listed it as one of the 10 research breakthroughs of the year. The team had found a way to defy the laws of nature, and out of that came the blueprint for the invisibility cloak.

Clearly, one of the obvious uses for an invisibility cloak is in the military (unsurprisingly, Smith's team is part-funded by the US Department of Defense). Metamaterials could hide a spy plane or be used by special forces to go unobserved behind enemy lines. Smith and his team also suggest using cloaking materials to keep ugly buildings, such as factories or refineries, from spoiling the view. Other forms of cloaks, they say, could deflect destructive seismic waves or dangerous radiation from buildings.

Currently - even in the theoretical models - there are limitations. For one thing, if you were concealed beneath the cloak, the trade-off for vanishing would be you wouldn't be able to see out (but Smith and his team are working on overcoming this). Smith also freely admits that you couldn't do much inside an invisibility cloak - you'd have to stay still. "It can't change its shape," he explains. "If a person is moving around, lifting or waving their arms, that becomes very difficult to cloak."

And what about bumping into objects? That could be quite an issue if you cloaked large ugly buildings. "I suppose that's always a danger," Smith concedes. "But I think nearly everyone has bumped into a closed sliding glass door once in their lives."

The idea of making objects invisible is nothing new. It has long been a mainstay of conjuring. In 1918, for example, the escapologist and magician Houdini marched a 6,000lb Asian elephant called Jennie on to the stage at the New York Hippodrome. He then enticed Jennie into a specially constructed cabinet and shut the doors. The orchestra whipped up a frenzied climax, whereupon Houdini pulled open the doors to reveal that Jennie had vanished. In reality, she hadn't vanished at all; she was simply hidden behind a mirrored screen that made it look as if the cabinet was empty.

In those terms, it sounds easy. But as the conjuring expert Jim Steinmeyer makes clear in his book, Hiding the Elephant (Arrow, 2005), a great deal of precision goes into making such illusions believable: "Houdini's vanishing elephant was the result of over 50 years of careful experiments by stage magicians in France, England and the States." He goes on to point out that magicians have accumulated a large body of scientific knowledge on how we humans perceive things, which they exploit to create illusions that befuddle even the most sceptical of observers.

But when the invisibility cloak outlined by Smith's team eventually goes into production, it won't be an illusion or trick of the light. Anyone would be able to throw it over themselves and become invisible. This raises alarm bells with some.

"This technology is terrifying in the wrong hands and could create numerous new victims," says the true-crime writer Carol Anne Davis, author of Couples Who Kill (Allison & Busby, 2005). "After all, we currently warn women to park in well-lit areas, to look around their vehicle before unlocking it. Such safeguards would be useless if the rapist or mugger was invisible. There would be horrendous implications for the most vulnerable members of society."

Professor Smith, however, dismisses such worries: "There are enough practical fundamental science issues that need to be sorted out before we see even the first demonstration of the technology - so I imagine it will be a while before we need to worry about it falling into the wrong hands."

Despite Smith's assurances, the fact remains, an invisibility cloak would have huge appeal, not just to intelligence and military agencies, but to those involved in organised crime and industrial espionage. It might be a while before the capes hit the streets, but you can be sure that it won't just be the good guys wanting to get their hands on them. In Harry Potter terms, it's the Voldemorts of this world donning invisibility cloaks that we have to worry about.

Just sci-fi fun - or the face of the future?

Matter transporters

Beaming from one place to another using a matter transporter, as in Star Trek, may seem a long way off, but scientists believe that they have worked out how to transport one atom. If we can transfer one, they argue, perhaps we'll soon be able to do two, and so on. They may achieve their goal this century.

Replicators

One of the most intriguing devices featured in Star Trek was the replicator. It could scan the molecules of any object and produce a shiny new copy at the flick of a switch. The beginnings of replicators are being developed by the Massachusetts Institute of Technology's Center for Bits and Atoms

(CBA). Nicknamed "Fab Labs", the devices (essentially machining tools) can't assemble things from component atoms but can be used to make anything with features bigger than those of a computer chip.

Flying broomsticks

One of the most amazing items in Harry Potter's magical toolkit is his Nimbus 2000 broomstick. Scientists believe that such a flying vehicle could be created using anti-gravity research. A decade ago, physicists in Russia used magnetic forces to shield objects from gravity., and this is being studied closely by Nasa's Breakthrough Propulsion Physics Project. It could power a new generation of planes and shuttles.

Phaser guns

For years, the US military has explored firepower using beams of electromagnetic energy, which can be throttled up or down - much like the phaser guns in Star Trek could be set to kill or stun. George Gibbs, of the Marine Expeditionary Rifle Squad Program, which oversees "directed-energy" projects, says they would be ideal to stop suicide bombers, without harming the innocent.

Terminator strength

Natick's Future Warrior Concepts Lab, in the US, has been developing technologies for soldiers for some time, and is now looking to use nanotechnology on uniforms to give soldiers superhuman strength. Staff Sgt Robert Atkinson, of Natick, says: "The technology is there, and once we get it all into place, the soldier will be unstoppable."

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