Two separate research teams at the University of Birmingham and MIT have made breakthroughs in the quest to achieve workable invisibility by using a material called calcite, a common crystallized type of calcium carbonate found in most seashells. Calcite’s unique refractive qualities have been known for years.
From micro to macro
Other invisibility research around the world have approached desire to achieve a disappearing act using meta-materials. These exotic experiments have had limited success wrapping light waves around an object and making is disappear from sight, but all the objects have been microscopic. Ramp up the process to the “real world”—the macro scale—and meta-materials don’t work.
Now a common substance as been shown to make objects visible to the unaided eye invisible and the researchers scaled invisibility up from the microscopic to a gigantic object (in a relative sense): a paperclip.
Now you see it, now you don’t
Using calcite, the Birmingham team glued crystals with diametrically opposed refractive properties and placed them over a paperclip. Like magic the paperclip disappeared. The light bent around it in such a way that an observer essentially saw what was behind the paperclip, but not the paperclip itself.
Their breakthrough study is available in the journal Nature Communications
The team at MIT’s Singapore-MIT Alliance for Research and Technology Center conducted a more modest experiment successfully making a small piece of metal—about the size of a pencil point—optically vanish.
Interviewed by the UK Telegraph, Dr. Shuang Zhang, a physicist and lead investigator from the University of Birmingham said: “This is a huge step forward as, for the first time, the cloaking area is rendered at a size that is big enough for the observer to ‘see’ the invisible object with the naked eye.”
From 2D to 3D
While the process is restricted in many ways to a 2D view, the Birmingham team believes that techniques can be developed to make the process work in the 3D world. It may also be possible to scale up the process making much larger objects effectively invisible to the naked eye. The ability to make the process work without the use of exotic meta-materials is a huge leap forward.
“By using natural crystals for the first time, rather than artificial meta-materials, we have been able to scale up the size of the cloak and can hide larger objects, thousands of times bigger than the wavelength of the light.” Zhang explained.
Pencil points and paperclips are one thing, but what about people, tanks, aircraft?
According to Zhang, the process is limited only by the size of the crystals. And since some calcite crystals can grow nore than 20 feet long, the new invisibility method could theoretically be used to make soldiers and military assets invisible now. The Birmingham team also thinks it will be possible to make the crystals artificially.
The MIT press release quotes Dr. Ulf Leonhardt, chair in theoretical physics at Scotland’s University of St. Andrews who led a team and authored one of the first papers investigating the invisibility potential of meta-materials. Concerning the Birmingham-MIT experiments he says, [These] “are two beautiful experiments. I particularly like their simplicity. Cloaking has been inspired by research on metamaterials,” he observes, “but, ironically, these cloaking devices are almost ‘home-made.’ Instead of sophisticated optical meta-materials that are difficult to make and have many problems of their own, they use simple calcite crystals.”
George Barbastathis, the Singapore Research Professor of Optics and Professor of Mechanical Engineering and one of the co-authors of the MIT study believes the results of the invisibility breakthrough are “closer to science fiction.” Science fiction made fact.