Think of the possibilities if warriors were really able to approach – or penetrate– an enemy force unseen. Tales of invisible warriors have long been the stuff of dreams.   Greek myths talked about a helmet of invisibility that would render the warrior imperceptible and Star Trek (as well as Frodo) fans know that the ability to become invisible is a great option when under or planning an attack.

Although many veterans have long felt invisible, a new technological breakthrough may make them invisible for real.  Most scientists attempting to make things invisible have focused on metamaterials, materials that blend polymers and miniscule wires to distort electromagnetic radiation paths.  The resulting fabrics would bend light so that it would curve around an object making the viewer “see” right through it (or around it). This has been successful in microscopic experiments, but hasn’t really be effectively demonstrated on larger objects.

The newest technique, however, uses naturally occurring crystals instead of metamaterials.  Two independent research teams, from the Singapore-MIT Alliance for Research and Technology (SMART Centre) and the other comprised of researchers from the University of Birmingham, Imperial College, London and Technical University of Denmark, have shown  that there is a technology that can cloak larger objects within a broad range of wavelengths normally visible to the naked eye.

The two teams used the transparent mineral calcite that has birefringence, an optical property known as double refraction. Birefringence is when light splits into two separate rays with different polarizations.  The two rays travel at different speeds in different directions causing the eye to see two double when viewed through a clear piece of calcite.

The scientists from the University of Birmingham placed on a mirror two pieces of calcite with opposing optical paths that they had glued together.  They them looked at them – or attempted to – in air and liquid.

The SMART Centre team did something similar.  They glued the calcite together into a wedge that they placed over an object.  The object disappeared when viewed from either the right or left sides, but not from other views.

Depending upon the size of the crystals, different objects disappear.  Thus far, the cloak has only hidden items like pins and paperclips.  In January, SMART Centre’s research was published in Physical Review Letters and in February Birmingham’s research was published in the journal Nature Communications.