Asked by: Anonymous
The answer is no time soon, if ever, despite recent progress by the US military. An invisibility cloak must carry light around an object, with the light emerging on the opposite side, travelling in its original direction. For this to happen the cloak must have a negative refractive index, so that the light entering it bends away from an imaginary line perpendicular to the surface, rather than towards that line.
Getting the light to flow around an object is one thing; getting it to emerge travelling in its original direction is quite another, since it would have to ‘remember’ the direction from which it came. Until this problem (among others) is solved, true invisibility cloaks will remain in the fictional world of Harry Potter.
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