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Invisibility unmasked

Last week's report on the quest for invisibility sparked some pretty intriguing comments, including numerous claims that the military has already developed real-life invisibility cloaks. It sounds a little too much like "The X-Files" to me — but hey, sometimes the truth really is out there. A couple of readers also noted additional limitations on invisibility technology. Read on for a selection of the e-mail feedback:

David Reid, Denver: "Wouldn't a person inside an invisibility cloak be 'blind'? If light is bent around their eyes (so their eyes are invisible along with their body) then they wouldn't be able to see. At least that's my theory on it."

John Boyle (no relation): "I think you left out one more catch: No part of an invisible object, including the eyes, absorbs light.  So if you're covered by an invisibility sheath of some sort, you'll be just as blind as everyone else.  Although that only applies to the wavelength you block, so you could use infrared goggles or something."

You're both right on target. A total invisibility shield might be good for hiding objects you don't want found, but not so good for hiding observers who want to look out of the cloak. It's important to remember that, realistically, the shield would be invisible only to specific wavelengths. Therefore, you could have a ship or underwater monitoring station that was "cloaked" from radar soundings but still able to see out (and be seen) in other wavelengths.

Robert Cutshaw: "Several weeks ago, Military.com contained an article regarding a company, Advanced American Enterprise, that claims it has invented a cloaking device. I don't know if you have already seen this article and dismissed it, but thought that you might find it interesting.  This is a link to another article regarding the same device and other technologies developed for military use. ... While digital technology makes it very easy to create fake photographic evidence, Advanced American Enterprise also claims it has a video available that shows the device in action. So far I have been unable to locate a copy of that video on the Internet.  So at this point the jury is still out on this particular device."

David B. Buffalo: "Thirty years ago (yep, when I was at Georgia Tech), I knew two Air Force ROTC students who had been doing research in what was then the Electrical Engineering Department. One claimed, and I had no reason to doubt this guy (because he was no B.S. artist and he was incredibly intelligent), that the Department of Defense had developed four different refractive/reflective cloaking devices late in 1974. If someone in academia like Mr. Pendry [one of the researchers behind the latest studies] is just now discussing such ideas, I truly believe it is a smoke screen or he is just lost in the laboratory working on projects no one cares about.

"I have to believe that American and Russian scientists (who quite frankly have had superior optical research projects on the books when compared to the U.S.) have long since developed cloaking technologies and are probably deploying them now. The stealth bomber technology of the last decade was pretty much finished in the middle 1970s, and one Australian engineering outfit had already figured out how to defeat it within a couple of years of our deployment. One of the things that worries engineers currently with regard to 'Star Wars' anti-missile technology is that Chinese or Russian scientists have already begun testing radar and other kinds of cloaking that would make it impossible to knock down missiles or satellites, in ways similar to how thermal decoys are used to fool heat-seeking missile technology in anti-aircraft defenses.

"If we are not much farther along with cloaking technology than what Mr. Pendry is describing, then I am truly worried about American defense capabilities. Given the last few presidential administrations' penchants for giving away technological advantages to our enemies, your most recent article really gives me the chills. I don't listen to Art Bell either. I just know that in the past, we have had technological breakthroughs that did not emerge into the public domain for decades. If what Mr. Pendry is describing is the best the West has, we are in trouble deep."