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Now you see me, now you don’t

Rupert Coy reports on research out of sight, but not of mind.

invisibility-cloak

invisibility-cloak

The concept of invisibility has occupied human imaginations for millennia. From Greek mythology to Harry Potter, we are endlessly fascinated by the possibilities and moral ambiguities of being unseeable. It now seems that the Ring of Gyges or invisibility cloaks might be closer than we think.

Disappearing cats and headless fish have featured in recent footage from China’s Zhejiang University. The effect of invisibility was achieved using specially designed small-scale materials called metamaterials that cause light and other radiation to bend in extraordinary ways.

Light naturally bends when it traverses different mediums. For example, when you put a ruler in water it appears crooked because light changes direction as it goes from air to water. Metamaterials take this principle to the next level, curving radiation around entire objects.

But there’s a catch: according to Sydney University’s Dr Boris Kuhlmey, “if you were inside [an invisibility cloak], you wouldn’t be able to see outside.” Just as light can’t get in, it also can’t escape. He explained that metamaterials “convert light to heat, [so] the cloak will appear black, rather than invisible.”

With less absorptive substances, scientists may overcome this, but it is not guaranteed. This is one of several reasons why this technology has been tested more at radiowave and microwave frequencies than in the visual light spectrum.

Other scientific developments are also making invisibility technology look like a possible reality. Onlookers were shocked when a nearly invisible car toured around Germany for a week in late 2012. The Mercedes Benz F-cell echoed James Bond’s camouflage car in Die Another Day, minus the machine guns and ejector seat (look up the car on YouTube: you won’t regret it).

This method of invisibility involves cameras capturing images and then projecting them on to screens. Tanks and fighter planes are already using similar designs to hide their heat signature and hence avoid missiles. They’re installed with tiny heat sensors and heaters.

Dr Kuhlmey believes this to be the most promising invisibility process. “The only technology I could see evolving into actual personal invisibility cloaks would be camouflage, using cameras and displays in the form of textiles,” he said.

Although it’s currently a rather expensive exercise to cover oneself with HD cameras and retina displays, it may not be in the future. Shadows make concealment difficult over short distances, argues Dr Kuhlmey, but the success in nature of squids, chameleons, flower mantises and others gives us hope.

Making fabrics can be difficult at the best of times, but it’s a lot harder for USyd researcher Dr Alessandro Tuniz: his fabric is invisible. Having developed models of invisible metamaterial fibres which have some properties identical to air, his team is now working on producing physical examples of this.

Also at Sydney, a team under Professor Ross McPhedran is analysing ‘wands’ which makes surrounding objects invisible. If brought to the skin, it could reveal what was just underneath, potentially a huge development for non-invasive detection of various medical conditions.

Perhaps invisibility research will initiate scientific progress in unintended areas. Penicillin, saccharin, and the internet were all created by scientists working on other projects. So often, the most incredible discoveries are accidental.

Dr Kuhlmey explained that research in metamaterials has opened up a range of possibilities. “Both at the University of Sydney and elsewhere [it] extends much beyond achieving invisibility…the incredible diversity of properties that metamaterials can yield also provides novel avenues for miniaturisation of optical telecommunications components.”

They have also been used for making superlenses: special lenses which go beyond traditional laws of optics and could facilitate early cancer detection, observation of DNA molecules, or the manufacturing of even smaller computer chips. This remarkable range of applications ensures that metamaterial research will continue to grow, which may well act as a catalyst for invisibility technology.

While the wizarding world’s technology remains out of reach for the moment, top Muggle scientists are certainly catching up.