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

[David Farber <dave () farber net>]

Begin forwarded message:

From: Brad Templeton <btm () templetons com>
Date: May 26, 2006 5:37:18 PM EDT
To: David Farber <dave () farber net>
Cc: ip () v2 listbox com
Subject: Re: [IP] more on The Economist: How to weave a cloak that  
makes you invisible


I believe he is noting that if you have two sensors (such as two  
eyes, but
further apart) then the light from behind the "invisible" object will
reach one eye directly and reach the other eye by going through the  
object,
at the edges.   Proper interferometry should show this clearly, I  
believe.

In general it's unlikely you could make anything so invisible as to
hide from somebody with detection equipment designed to find it.
Being invisible to the human eye would be amazing enough on its own.

However, the technology cited in the article is for narrow wavelengths.
It's not indicated, but I suspect it means we would have the cloak
be invisible in the blue, but not in the red.   Cute, but not invisible
to the human eye, except perhaps against a clear blue sky.

It is also false to say this would not work (if it worked at all) for
spyplanes, because the invisibility need not be two way, nor need it
be 100% at all locations.   The spyplane could be very visible from
above (and thus be absorbing as much light from the ground as it
wishes) and invisible from below.   Or it could have small circles
for camera lenses that absorb 1% of the light and still be an
excellent spyplane, invisible to the human eye.   The human eye
would not see a small slightly dimmed circle against just about
any background, even one as simple as sky.

Furthermore, planes fly blind all the time, so I can't fathom why
the author suggested this as an issue.


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