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

[David Farber <dave () farber net>]

Begin forwarded message:

From: Valdis.Kletnieks () vt edu
Date: May 26, 2006 4:08:36 PM EDT
To: dave () farber net
Cc: ip () v2 listbox com
Subject: Re: [IP] more on The Economist: How to weave a cloak that  
makes you invisible

On Fri, 26 May 2006 15:47:33 EDT, David Farber said:

> 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

> 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.

Only if you have a baseline to calibrate the interferometer against.  
Yes,
the object can be detected by an interferometer *if* it's standing in  
front
of a nicely calibrated wall where you *know* what the values should be:

http://www.digitalblasphemy.com/dbgallery/2/chamelea.shtml

However, if the object is in front of a bush or a field of grass or
similar, it becomes a *lot* harder to do the interferometry trick:

http://www.michaelbach.de/ot/cog_dalmatian/index.html

(The page isn't about this, specifically - but does demonstrate the
difficulty of dealing with a "noisy" background....)

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