One step closer to the Invisible Man

Aug. 17, 2008

One Step Closer to the Invisible Man
Shades of Harry Potter and his cloak of invisibility! The gee whiz scientists are buzzing with experiments in invisibility.
There have been other stories of invisibility, as in the book The Invisible Man, in which drinking a chemical rendered the hero invisible as long as he went around naked, and the radio series The Shadow, in which Lamont Cransten could hypnotize people so they could not see him. In the Star Trek science fiction series it was the Romulans and Klingons who used a cloak of invisibility. That’s fiction, too.
But what about some sort of paint that bent light? What if, for instance, a tank could be made invisible? Now it’s looking like invisibility is possible and not merely fiction.
Light striking an object scatters and bounces back. But what if light could be made to bend around an object like water flowing around a rock in a river? After the water passes the rock it closes up, leaving no downstream impression. That’s the analogy: to make light work like the flowing water instead of reflecting. That’s the theory behind the research at the University of California by Xiang Zhang and reported in the journals Nature and Science.
So far, Xiang Zhang has been working at the nano level, ultra small. A multi-layered fishnet structure he created has “negative refractive” properties, so light bends around it instead of passing through or reflecting.
Xiang Zhang isn’t the only one experimenting with invisibility. In Britain two mathematicians, Nicolae Nicorovici and Graeme Milton, have reported their own theory in the Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. Their theory is that a super lens such as that developed by Professor Sir John Pendry, of Imperial College London, could make light behave in unusual ways.
The theory used by the British scientists is that a cloaking effect is created that prevents the light from bouncing back from an object. Instead of bending the light around an object, their idea is to get the light to stop reflecting.
So far, those experiments haven’t gotten beyond making a speck of dust stop reflecting light. Even so, their experiment applies only to certain wavelengths of light.
Professor Pendry of the Imperial College in London has a different approach – a “metamaterial” made of rings of fiberglass covered with copper elements. The cloak consists of 10 fiberglass rings covered with copper elements. It’s made to affect electromagnetic waves and is intended to make microwaves pass around an object, making it invisible to radar. This isn’t the same as the Stealth bomber, which depends on its shape and a radar absorbing paint to make a minimal radar reflection. In the laboratory Pendry’s method has made a copper cylinder apparently disappear.
Maybe the scientists are on the wrong track. In nature, the way to be invisible is not to be seen. Living creatures have adapted camouflage because what predators and prey look for is motion. If you stand perfectly still, a deer might not see you. You can demonstrate this with your car in a WalMart parking lot. A motionless object on your car antenna is hard to spot, but a ribbon blowing in the wind is quickly noticed, even at a distance. A motionless object in a laboratory, whether it’s dust or a copper cylinder, might be rendered invisible, but what if it’s moving?
Whether it takes one of professor Pendry’s super lenses, or his metamaterial, or Xiang Zhang’s fishnet lattice of nano materials to successfully create a cloak of invisibility outside the laboratory remains to be seen -- or unseen. Whichever theory proves to be practical, don’t yet count on being able to run around naked and invisible. The invisible man of fiction found the experience to be pretty cold and hard on his bare feet.
Harley Sachs is also an author of science fiction. Visit his web site www.hu.mtu.edu/hlsachs.