Inventor plans 'invisible walls'

The invisible material is made of thousands of tiny beads

The inventor of an "invisibility" cloak has said that his next project will be to develop the technology to allow people to see through walls.

Susumu Tachi, who showed off the cloak at an exhibition in San Francisco earlier this month, said he was hopeful of providing a way to provide a view of the outside in windowless rooms.

"This technology can be used in all kinds of ways, but I wanted to create a vision of invisibility," he told BBC World Service's Outlook programme.

"My short-term goal would be, for example, to make a room that has no outside windows appear to have a view to the outside, then the wall would appear to be invisible."

Use and misuse

Professor Tachi's cloak works by projecting an image onto itself of what is behind the wearer.

A computer generates the image that is projected, so the viewer effectively sees "through" the cloak.

Invisibility material may allow pilots to see through the floor of their planes

The key development of the cloak, however, was the development of a new material called retro-reflectum.

"This material allows you to see a three-dimensional image," Professor Tachi said.

"This material is the key to our technology."

There are many potential uses of the cloak, ranging from espionage and military purposes to helping pilots see through the floor of the cockpit to the runway below.

However there are massive questions of potential misuse too, particularly surrounding the huge crime implications.

It would become incredibly difficult to spot a thief, for example, if the items they were taking were simply disappearing under the cloak.

Professor Tachi said that he had first had the idea of developing something to make objects invisible in 1977.

But he said it was "hard to make it into reality," as the image looked flat and unrealistic.

"It didn't work at all when we just projected the image onto a normal screen," he added.

"We tried hard, but it took a while before we came up with this retro-reflective material."