IT IS rare for arcane physics and childhood fantasy to come together in the same sentence. Yet this week, newspapers, radio and TV could not help comparing two scientific papers on invisibility shields to Harry Potter鈥檚 invisibility cloak, the fantastic garment that lets Harry and his pals go places undetected and have adventures that no muggle could conceive of. The scientific papers are lucid, and the ideas they propose, if not the technologies, are simple. However, the analogy with Harry鈥檚 most prized possession is not so straightforward.
First, for the immediate future invisibility is likely to be constrained to the microwave spectrum, perhaps for hiding from radar. This is because the essential ingredient of the technology is a 鈥渕etamaterial鈥�, a 3D array of copper coils and wires that can influence only electromagnetic radiation with wavelengths larger than the array鈥檚 components (see 鈥淚nvisibility cloak leaves the realm of magic at last鈥�). At radar wavelengths of 3 centimetres, the metamaterial needs coils of around 3 millimetres, which is eminently achievable. For visible light, the wires and coils would have to measure around 10 nanometres, and this is at or beyond the limit of our present abilities.
There are other differences between what science and art propose. Existing metamaterials are not light, so don鈥檛 expect to throw an invisibility shield over your shoulder without breaking your back. And in the real world, a cloaking device would work better in substances with a high refractive index, which means it will be easier to shield a submarine in water than a battle tank in air.
Advertisement
Perhaps the biggest dislocation between reality and fantasy is what invisibility would be used for. Harry wields his cloak for the best of motives: to fight evil. What about in real life? Much of the existing research on metamaterials is paid for by the US Defense Advanced Research Projects Agency. All鈥檚 fair in war, after all. But organised crime and industrial spies would pay huge amounts to go places unseen. And what would overzealous law enforcement agencies do with it?
Within hours of the scientific papers being published, The Nanoethics Group called for a public debate on these issues. Without wishing to hit the panic button (there are more pressing things to worry about), they have a point. Society can take decades to resolve ethical issues surrounding new technology, and delay is not always advisable. US citizens have found in recent weeks that a programme of monitoring who they call on the phone has started without any public debate.
Invisibility would pose new challenges to security and privacy. While the technology is imaginative and exciting, who should use it and how are questions that need to be answered. It鈥檚 hard not to wonder how Professor Dumbledore would resolve this one鈥�
