Smith, Pendry and their colleagues realized that for metamaterials to really take off, they’d have to demonstrate what their invention could do. Because metamaterials offer such a large amount of freedom, however, they weren’t sure where to start.

Pendry took to his archives to find an answer, dusting off a computational tool he created in 1996 for transforming coordinate systems. Think of drawing a grid on a sheet of rubber, stretching it out and needing to know exactly how the squares are going to look afterward.



Pendry realized that this conceptual trick of changing the coordinate system could be used as a design tool: You imagine controlling the trajectory of light by simply changing the coordinate system. Once you have things the way you want them, you can use that transformation to obtain the exact material properties needed to make the device.



“The idea was elegant and conceptually simple,” Smith said. “The material properties are extremely challenging, but they were a perfect match for metamaterials.”



The transformation calculation allowed the researchers to design metamaterials where each cell was not identical. By subtly changing each cell’s properties, they could steer electromagnetic waves along a gradient — a concept called transformation optics — which led to an even crazier idea: A sheet of metamaterial cells could be tailored in this way to move far beyond the way a simple glass lens bends light; they might actually bend electromagnetic waves around an object to rejoin on the far side as if the object were never there.

“Somewhere along the way John decided we could make an invisibility cloak out of this,” said Smith. “He said it partially as a joke, I think. But the math held up, and you could write down the prescription for a cloak that was actually fairly simple.”

“David said ‘We have to build this!’” Pendry recalled. “We wrote the theory paper in 2006 and it came out pretty fast in Science. Now, normally there might be some interest in such a paper, but it doesn’t change your life. The response to this was simply astounding.”

Media worldwide stampeded to Smith and Pendry, eager to draw comparisons between their somewhat crude theoretical proposal and the famous fictional invisibility cloaks of Harry Potter and Star Trek. With the level of attention the theory paper received — including some genuine surprise from the scientific community — the team knew they’d have to act quickly to be the first to build a working device. As with most things in science, however, this proved easier said than done.