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

[David Farber <dave () farber net>]

Begin forwarded message:

From: "William S. Duncanson" <caesar () starkreality com>
Date: May 30, 2006 1:54:54 PM EDT
To: dave () farber net
Cc: btm () templetons com
Subject: RE: [IP] more on The Economist: How to weave a cloak that  
makes you invisible

It's not really narrow wavelengths, rather, it's a small range of
wavelengths.  The metamaterials that they discuss have to be built  
smaller
than the wavelength of the electromagnetic wave that they're trying do
deflect; for light wavelengths this would be difficult with todays
technologies; longer wavelengths are easier since the size of the  
particles
needed is larger.  So it would be feasable to do this with radar,  
which has
a relatively long wavelength, and would require particles in the (close
order of) centimeter scale, but not necessarily visible light, which  
would
metamaterials with particles on the nanometer scale.

This is really nothing more than Stealth 3.0...and just because  
something
works on paper or in the lab just means that the problem moves from the
realm of the scientists to that of the engineers.

-----Original Message-----
From: David Farber [mailto:dave () farber net]
Sent: Saturday, May 27, 2006 5:59
To: ip () v2 listbox com
Subject: [IP] more on The Economist: How to weave a cloak that makes you
invisible



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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