The year is 2050, and a group of criminals is meeting in a disused warehouse to plan a major robbery. The warehouse looks empty, but on the landing above them, six invisible figures stand silently by, listening to every word and watching every move. If the criminals would look very closely they might see an odd phenomenon – like six pairs of unconnected eyes. But they are engrossed in their planning and so notice nothing until the police drop their cloaks and move in on an arrest.
In this day and age, yesterday’s science fiction has a knack of turning into tomorrow’s everyday technology. Jules Verne’s trip to the moon, Buck Rogers’ interplanetary explorations and ray-gun weaponry, and Frankenstein’s body-part transplants are just a few examples of this.
And now, HG Wells’ ‘Invisible Man’, written over a century ago, is about to reach reality as a team of internationally-renowned physicists have not only devised a theoretical ‘invisible cloak’, but appear to be only months away from demonstrating this as a reality, using a cloak made from exotic artificial composite materials called ‘metamaterials’.
In fact, several groups of scientists around the world are already having a credible tilt at solving this problem and the prestigious publication, ‘The Economist’, which is not normally given to flights of fancy, reported on this work in their Science and Technology feature of May 27, 2006.
As early as the year 2000, a Japanese professor, Susumu Tachi of Tokyo University, was experimenting with a way to make people or objects ‘invisible’. He did this with an elaborate and very interesting system of optical camouflage, which, though quite successful under certain conditions, needed a great deal of preparation. His principle was based on a special material called RPT, ‘retro-reflective material’, which had to be used to make a cloak. This material, covered with very small beads, ensures that light is only reflected in the same direction as it is projected, in the same manner as reflective road signs and cats’ eyes reflectors. Such material reflects an image efficiently, even in daylight.
Professor Tachi, who recently demonstrated his principle to admiring conferences around the world, has worked out a special system whereby a camera is placed behind the object that is to be rendered ‘invisible’. This camera photographs the ongoing scene behind the ‘invisible’ cloth, while another camera, linked to it and in line with the viewer, projects the image onto the cloth. The result is visually amazing. The cloth and whatever it hides seem to totally disappear and the viewer can only see the projection of exactly what is being filmed on the other side of the cloth. Effective? Yes! But also extremely limiting, more akin to a Las Vegas magician’s ‘smoke and mirrors’ repertoire than to practicality in everyday use. Because, without the cameras being placed in precisely the right positions and angles, the system does not work. And the moment someone walks around in such a cloth and moves out of the exact camera range and angle, the invisibility ceases.
A somewhat similar system, also restricted to static objects, has been patented by Professor Oleg Gadomsky of the Ulyanovsk State University in Western Russia. Gadomsky claims that his sub-micron stratum of microscopic colloid golden particles will also render static objects invisible under limited conditions.
So far, so good, but very complicated and somewhat limiting. Limiting, that is, until the work announced by a team of British and US scientists of great eminence. Their experimentation and research is based on a theory that is hardly new. One hundred and fifty years ago, a scientist named James Clerk Maxwell published a paper on four mathematical expressions that explained the concise way that electric and magnetic fields interacted with matter.
An Anglo-US team of researchers began with the principle that light is an electromagnetic wave, longer than x-rays and ultra-violet and shorter than radio waves, microwaves and infra-red light. Yet all of these are bound by Maxwell’s equations. The team’s research, funded by the US Department of Defense and carried out by Sir John Pendry of London’s Imperial College and Professors David Smith and David Schurig of Duke University in North Carolina concluded that, using certain materials – known as metamaterials – light could be made to flow around these materials. It would then meet up at the back in much the same way as river water flows smoothly around the piers of a well-designed bridge. These metamaterials have to be of a structure that is smaller than the wavelength of electro-magnetic radiation.
Such metamaterials will, it is hoped, shortly be able to steer light and other types of electro-magnetic radiation around objects, rendering them invisible and producing neither shadows nor reflections. Basically, they bend the light completely around the object, rendering the object invisible without the use of cameras, projections, or other extraneous technology. The end result is that a person or object covered in a cloak made of this material would become invisible to the naked eye, regardless of the movement of the person or object cloaked in this material. “There are still some problems that need to be overcome”, Dr David Smith explained. “At this point our method only works over a very small spectral range, and to get complete invisibility we would need a much larger bandwidth: 400/700 nanometers. At this point we can cloak red rays with the very narrow band available, but not yet blues or greens, but we are working hard on getting around the bandwidth limitation. Once we have done this, the results should be really exciting.”
“The cloak would act like you’ve opened up a hole in space”, says Professor Smith, Augustine Scholar and Professor of Electrical and Computer Engineering at the prestigious Pratt School at Duke University, USA. “All light or other electromagnetic waves are swept around the area, guided by the metamaterial to emerge on the other side as if they had passed through an empty volume of space.”
Sir John Pendry explains it this way: “Such metamaterials will allow light to flow around an object and rejoin on the other side, so that the object virtually ‘disappears’, leaving no shadow and producing no reflection. Such light-bending materials will rely on their physical structure rather than their chemical composition”. The team is working on materials that can bend light around any object, regardless of where it is coming from. “This means”, says researcher Smith, “that you can apply it to any shape and cloak virtually anything. And the breakthrough is tantalisingly close. It’s fair to say that this year there will be a demonstration on the basic physics of cloaking”.
According to Sir John Pendry, this will introduce a new class of designer materials which refract light in an entirely novel manner. These new metamaterials will open new vistas in optics and offer the possibility of super-high resolution lenses that can resolve details finer than the wavelength of light. The concepts have application across much of the electromagnetic spectrum.
Needless to say, such technology immediately becomes very interesting to the defence industry, and much of this kind of work has been supported by the Pentagon’s Defense Advanced Research Projects Agency.
Imagine, for instance, tanks or troop carriers covered in such material being able to cross open country without being seen, or stealth planes circling overhead when all the ground observer can see is open sky. Of course, the eyes – or window slits of the troop carriers or aircraft would not be invisible, but these would be unlikely to be noticed.
Sadly for the H.G. Wells battlefield technicians, there is a drawback. Other types of reflective waves like radar would immediately ‘see’ the object behind the cloak. And there is another big problem. Once you take the ‘invisible’ cloak off, how are you ever going to find it again? No doubt, once this is in actual production, scientists will come up with an answer for that also.
So stand by for the invisible cloak. It’s virtually reality already! Move over, Harry Potter!!!
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