The concept of invisibility has fascinated the public and intrigued scientists for millennia. But now, as we’re entering the age of so-called ‘meta-materials’ we’re starting to discover materials with curious optical properties that may make the fantasy a reality. Some of these nano- or micro-fabricated artificial composite materials (designed down to levels of about a billionth of a metre) have enabled scientists to cloak very small items; much smaller than the thickness of a human hair.
But, recently in 2011, scientists from the University of Birmingham and colleagues from Imperial College, London, and Technical University of Denmark, have built an ‘invisibility cloak’ using calcite crystal, that can make objects as large as pins and paper clips disappear from sight. The light enters the calcite and splits into two rays of different polarisations travelling at different speeds and in different directions. Although the crystal ‘cloak’ is visible, it is transparent and yet still hides objects placed underneath it.
Meanwhile, Professor Susumu Tachi at Tokyo University has created a coat made with a special type of ‘retro-reflective’ material containing microscopic glass beads, which acts as a photographic screen. ‘We have a camera behind the person wearing the coat,’ he explains. ‘The image from the camera is then projected onto the front of the coat, so that the wearer appears to be virtually transparent’. However, the real purpose of this new technology is not to make a person invisible but to augment reality. For example, it may be useful for pilots lading planes if the floors and walls of their cockpits appear to be transparent.
In 2002, an American named Hasan Elahi was grabbed and questioned by the FBI concerning the September 01 terrorist attacks. He turned out to be one of the very many people who have mistakenly ended up on the USA’s infamous watch lists.
After long questioning, and nine lie detector sessions, he was let go but he was unable to get himself removed from their lists. So he decided to help the FBI out - and set up a website detailing his position at all times to all who cared to know. The site also lists all his financial transactions, and includes a photograph of every loo he ever uses. He did eventually manage to get taken off the million-strong ’No fly’ list.
Vision is the art of seeing what is invisible to others.
The Royal Society was originally known as the Invisible College - the name referred to the natural philosophers who met in the mid-1640s:
'to discuss the new philosophy of promoting knowledge of the natural world through observation and experiment',
which we now call science.
In the sixteenth century it was commonly (and erroneously) believed that ferns must reproduce by seed. But since they couldn’t be found, it was concluded that fern seeds must therefore be invisible. And according to the ‘doctrine of signatures’ (plants which looked like bits of the body could cure those same bits, so kidney vetch was good for the kidney, liverwort for the liver, and so on), it followed that carrying invisible fern seed would make the bearer invisible.
Traditionally, fern seed could be collected on midnight on Midsummer Night’s Eve, but only by catching it as it fell from the plant onto twelve pewter plates. It would supposedly pass through the first eleven plates and be caught by the twelfth. Needless to say not everyone believed it, but it does seem to have been a real superstition: the character Gadshill in Henry IV, part I, says, ‘We have the receipt of fern seed, we walk invisible’.
In Greek and Roman mythology agate was supposed to confer invisibility, and to turn an enemy's sword upon himself.
In Ancient Rome, black was worn when in mourning to make the bereaved invisible and so protect them from vengeful spirits.
Lord Curzon said of Gladstone's oratory that it gave him a feeling 'as though the air was fanned by invisible wings'.
You can buy invisible ink to use in your inkjet printer. This is used a lot for printing information on business forms for the processor of the forms without cluttering the form itself with visible information.
The fish Malacosteus niger, otherwise known as the Lightless Loosejaw, can hunt its prey with an essentially invisible beam of light. It generates long-wavelength infra-red, which is invisible to other deep-sea animals.
80-year-old recipes for invisible ink in the US are still secret information, the CIA will not allow access to the information.
Polar bears are nearly invisible to infrared cameras.
To drive fast enough make your number plate invisible to speed cameras, you would need to be doing 119 million mph.
British Secret Service agents used their own semen as invisible ink during WWI. They adopted the motto ‘Every man has his own stylo’.