The Cloak of Invisibility

By now you may have heard news reports suggesting that Harry Potter’s invisibility cloak may actually be possible, because sufficiently advanced nanotechnology (to paraphrase Arthur C. Clark) is indistinguishable from magic. The rash of news reports stems from a Science online article co-authored by Sir John Pendry of London’s Imperial College. Pendry’s idea is that light could be bent around objects and reconstituted on the other side. Light would appear to just flow through, instead of reflecting back, hence the objects would be invisible. Many transparent materials such as water or crystal can bend light, but only in one direction. To create a viable invisibility cloak, you need to be able to bend it back the other way on the other side of the object. Materials with a negative refractive index do not exist in nature, but nanostructured “meta-materials” as Pendry calls them, can be manufactured with such a property. Well, maybe.

“It's theoretically possible to do all these Harry Potter things, but what's standing in the way is our engineering capabilities," said John Pendry, as quoted by AP. Pendry has developed a theoretic framework for an invisibility device.

Using meta-materials, Pendry has also invented something possibly more useful, a perfect lens that should have sub-wavelength resolution. Standard light microscopes are limited cannot resolve objects smaller than the wavelength of light, which is why it takes an electron microscope to visualize molecules or atoms (an electron has a wavelength, but it is sub-atomic in size).

Meta-materials are not yet something you can buy from a catalogue—building three-dimensional nanoscale objects to order is not easily done, so far. We still need that hypothetical molecular assembler.

TRN has published a lengthy interview with Pendry, if you would like more information.

What are the odds that DARPA would fund a grant proposal to build a nanotech-enabled invisibility cloak? Pretty good, probably. And think of the commercial spin-offs!