Archive for March 2016
Hopes are not yet dashed, but they clearly have taken a body blow:
A pair of researchers from the Ludwig Maximilian University of Munich, and the University of Otago have carried out theoretical modelling in an attempt to understand how an invisibility cloak might actually work in real life. There are different ways to make invisibility cloaks, all of which have to contend with the fact that diverting light around something introduces time delay problems — because the light can’t pass straight through the object that’s being cloaked.
The most realistic way to do it using an “amplitude cloak.” This approach discards information about the phase of light, instead recreating its color and attempting to introduce a time delay to make up for the differences in path length along which the light travels. The good news is that the cloaks create a compelling representation of reality. In fact, labs have already been able to show off amplitude cloaks that kind of work.
But the new research brings some bad news, too. Sadly, it seems this kind of cloak would only work when the hidden object and its observer are stationary. The reason is to do with something known as Fresnel-Fizeau drag. When light propagates through a moving medium — like, say, a raindrop — it is dragged along with the medium. So a moving invisibility cloak — or a moving observer — would drag light with it.