The index of refraction must vary within the material making up a cloak to raise the phase speed sufficiently to make light waves passing through the cloak match with those passing by the cloak (Image: B. Dodson)
Wavefronts of a beam of light passing through an invisibility cloak; the red lines indicate the largest positive electric field intensity, and the blue lines the largest negative fields, while lime green indicates regions having little or no electric field. (Image: B. Dodson)
While one would hope to make an invisibility cloak that performs like the central image, it appears that basic laws of physics may cause a result more like that of the image on the right (Photo: B. Dodson)
It's often a case of swings and roundabouts. If you save money by buying a house out of town, you spend more time and money commuting. If you really measure the momentum of an electron, you have no idea where the little guy is located. And now, according to a new analysis by a pair of University of Texas electrical engineers, the better an object is hidden by an invisibility cloak at a given wavelength of light, the easier it is to see at other wavelengths. Swings and roundabouts.
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