At the moment the idea of an invisibility cloak remains theoretical, and scientists are spending their time on theoretical models to see how a device designed to ‘hide’ an object could be rendered. Last year on Digital Journal Owen Weldon described how attempts to hide three dimensional objects from scanners had been developed in China, leading to a prototype invisibility covering. The new project discussed takes a different route.
There are different ways to make an invisibility cloak, however each idea is met by the problem of light. Attempts to divert light around a object, Gizmodo explains, creates a time delay problem, because the light can’t pass straight through the object that’s being cloaked, meaning that the presence of an object, however well obscured, will sometimes be detected by a scanner or the human eye.
The new way being considered is termed an “amplitude cloak.” This approach, outlined in a research note, seeks to discard information about the phase of light and alternatively seeks to recreate color and attempts to introduce a time delay account for the differences in path length along which the light travels. In essence the cloak would seek to create a different representation of reality through appearing transparent.
While this works well in theory, it would only function with stationary objects. This is because of physical concept called the Fresnel-Fizeau drag. With this, when light hits a moving object it is pulled along with the medium. Here, an invisibility cloak over a moving object or person would drag light with it, revealing itself to an observer.
The research was a collaboration between scientists based at Ludwig Maximilian University of Munich and the University of Otago. The research is published in the journal Physical Review A, and it is titled “Fresnel-Fizeau drag: Invisibility conditions for all inertial observers.”
