Having done a bit of research on the matter, invisibility is an interesting subject. While a variety of animals possess the ability to appear invisible as such by ‘cloaking’ themselves in the colour and pattern of their surroundings, (see this video: http://youtube.com/watch?v=OQWxIrSRDQQ) it has never been achieved on the same scale by human will or technology. Although there have been reports of various inventions, none of these claims have ever been proven.
You can read a 2006 article from Daily Tech purporting this to be the case (http://www.dailytech.com/article.aspx?newsid=475) but the scientist in question has never presented his research for analysis. (In my opinion, the photos he has taken appear very much like projections onto a plain jacket, and I’d be thrilled if I’d managed to get such a prank to be published.)
The closest credible science has come to achieving objective invisibility is the creation of a form of glass that reflects no light whatsoever. Glass is special, in the sense that a portion of light energy is lost as it reflects off the material’s surface. Researchers at Japan’s Institute of Physical and Chemical Research (http://www.riken.jp/) developed a prism of engineered material — metamaterial (http://en.wikipedia.org/wiki/Metamaterial) comprised of an arrangement of nano-coils of precious metals such as gold or silver — embedded in a solid glass-like material. The prism structure has a negative refractive index, which makes it truly transparent to light, allowing it to pass freely through with no reflection.
Perhaps the most significant progress has been made by a group of physicists in the US:
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From New Scientist:
(http://technology.newscientist.com/article.ns?id=dn12722&feedId=online-news_rss20)
“The world’s first true invisibility cloak – a device able to hide an object in the visible spectrum – has been created by physicists in the US. But don’t expect it to compete with stage magic tricks. So far it only works in two dimensions and on a tiny scale.
“The new cloak, which is just 10 micrometres in diameter, guides rays of light around an object inside and releases them on the other side. The light waves appear to have moved in a straight line, so the cloak – and any object inside – appear invisible.”
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Interestingly, even if we did develop a method to become invisible, the distinct possibility exists that the whole process would be a two way barrier. In other words, to be invisible to others you would probably have to be temporarily blind.
From Wikipedia:
(http://en.wikipedia.org/wiki/Invisibility#Sight_while_invisible)
“According to the laws of physics as presently understood, a perfectly invisible person would necessarily be blind, no matter how their invisibility were achieved. In order to see light, it must be absorbed by the retina, but in order for a person to be invisible, the body must not absorb light. So to retain sight at least pupil sized holes in the cloak would be necessary in front of the pupils and directly behind them on the back of the person as light isn’t being transmitted through. In fact, according to the no cloning theorem of quantum mechanics, they could not even make a copy of the photons so they could see one copy and allow the other copy to pass through or around them.
This physical barrier appears to offset the advantage of any perfect invisibility method, unless one’s intent was simply to hide and be still, letting the danger pass.
“On the other hand, a practical invisibility method need not allow light of all frequencies to pass all the time, so there may be ways around this limitation.”
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Hope this has been informative.
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