WHAT IT IS Disappearing into the background
WHY YOU WON’T DO IT The science is lagging far behind the idea
In the absence of a Harry Potter-style cloak of invisibility, making yourself disappear seems like a tall order. Fortunately, however, some of our brightest thinkers have been coming up with alternative methods, some of which seem just as magical. Using technology instead of magic or superpowers might seem like a cheat, but if the end result is the same, does it really matter?
When we see an object, what we are actually seeing is light rays bouncing off the object and into our eyes. If something allows light to pass through it without absorbing or reflecting any of it, the object becomes invisible to the viewer. While there are certain natural materials that are transparent to a lesser or greater degree, none is 100 per cent – so developing more transparent materials is one aspect of the invisibility challenge faced by researchers, while finding ways to conceal non-transparent objects within them is a second, even more difficult problem.
The defence industry has long had an interest in developing technology that allows objects (from personnel to aircraft, tanks and submarines) to move around without being detected by radar. This has given rise to stealth technology, also known as ‘low observable technology’. In some respects, this is the closest we have yet come to achieving invisibility – though a stealth bomber, for instance, may still be very obviously visible to the human eye even if it goes undetected by radar. (The bombers are painted in dark colours and usually operate at night to ameliorate this problem.)
A radar-detecting system relies on being able to detect radar waves being reflected off an object. A stealth bomber’s invisibility to radar is thus achieved by several means, including:
• A distinct shape that redirects the electromagnetic waves from radars.
• Metal plates that reduce reflection of radar waves.
• A ‘skin’ that absorbs radar waves, bouncing them around internally until the waves lose their energy.
• Special radar-absorbent paints that convert radar rays into heat.
In the same way that stealth technology aims to stop reflection of radar waves, those looking to develop invisibility to the human eye seek to prevent objects from reflecting light rays. This has led to the development of new ‘metamaterials’ – materials that have been engineered to have properties not seen in nature.
A team at the University of California, Berkeley, has created a fishnet-style material by stacking together silver and metal dielectric layers and then perforating them with holes. This material refracts light negatively to make things appear where they are not. For instance, a fish in a stream might appear to float above the water’s surface. Meanwhile, another team at the same university created a metamaterial that sends light around an object, much as water passes round a rock in a river. By bending the light rays round an object, the rays are not reflected off it, thus rendering it invisible.
Both of these developments take us considerably closer to the point where we really may be able to call upon invisibility cloaks. However, the technology remains in its infancy and while they prove that light can be ‘bent the wrong way’ to fool the eye, it will be a good while before we will be able to effectively hide objects of any great size. As Jason Valentine, one of the Berkeley researchers, has admitted: ‘I don’t think we have to worry about invisible people walking round anytime soon.’
Indeed, perhaps that is something we should be grateful for. While invisibility cloaks can’t come soon enough for military personnel who wish to slip in and out of conflict zones unseen, think of the implications in the wider world: fare-dodgers sneaking onto buses and trains without paying; rogues left to commit their crimes in the knowledge that no witness will be able to supply a photofit; embittered ex-paramours secretly joining you as you re-enter the dating scene. And as or nudist beaches, it hardly bears thinking about!
