more on The Economist: How to weave a cloak that makes you invisible

[David Farber <dave () farber net>]

Begin forwarded message:

From: Denis Russell <D.Russell () ukerna ac uk>
Date: May 26, 2006 4:07:53 PM EDT
To: dave () farber net, Ed Gerck <egerck () nma com>
Subject: Re: [IP] more on The Economist: How to weave a cloak that  
makes you invisible

At 15:47 -0400 26/5/06, David Farber wrote:
> Begin forwarded message:
>
> From: Ed Gerck <egerck () nma com>
> Date: May 26, 2006 2:10:32 PM EDT
> To: dave () farber net
> Cc: ip () v2 listbox com
> Subject: Re: [IP] The Economist: How to weave a cloak that makes  
> you invisible
>
> >  From The Economist print edition
> > http://www.economist.com/science/displaystory.cfm?story_id=6971134
> > How to weave a cloak that makes you invisible
>
> The invisibility claim does not follow from the theory. The  
> electromagnetic,
> waves, even if they maintain the exact same path and polarization  
> after the
> object, will be delayed by "going around". Since the speed of light  
> cannot
> increase beyond c, there is no way to make up for the delay. The  
> object can
> be seen by a simple interferometer arrangement.
...

Well the body would act much like a lens, with the thicker bits  
delaying the light more, but the delay would depend not just on the  
thickness (and refractive index), but on the extra delay running  
round the object. In the "perfect" case, the interferometer effect  
would act at the emitting surface, with the slightly phase shifted  
adjacent emitting points interfering with each other and sending the  
light off at an angle rather than straight out. (Think of all those  
elementary illustrations of how the wave theory of light predicts  
refraction at the interface between two materials of different  
refractive indices, and remember that refractive index=>speed in the  
material => delay on the optical path). The effect would be visible  
to the naked eye as a distortion of the image of the stuff behind the  
invisible body - like looking through a polythene bag of water with a  
funny (and high) refractive index.

        Denis


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