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Invisibility Cloak Hokum At Duke University

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by Andy, cross-posted from The Charlotte Capitalist™



The Capitalist Daughter hooked me on the Harry Potter series. I just finished the fourth book "Goblet Of Fire". I originally thought I would not like the series because of all the spells, ghosts, and other mystical aspects.

Oh, contraire. The books are a lot of fun and they focus upon Harry Potter's heroic efforts against evil.

One of Harry's tools is his invisibility cloak. By placing the cloak over his body, Harry is able to move where he chooses without anyone seeing him. The cloak allows others to see completely through itself and Harry as if they weren't there. It is a lot of fun in the book and I can understand why kids would like the idea of such a cloak. Didn't you want the power to be invisible when you were a kid?

Now, along comes an article from The National Geographic which says that scientists are near to developing an invisibility cloak:

The theoretical breakthrough is made possible by novel substances called metamaterials.

Invented six years ago, the man-made materials are embedded with networks of exceptionally tiny metal wires and loops.

The structures refract, or bend, different types of electromagnetic radiation--such as radar, microwaves, or visible light--in ways natural substances can't.

"[Metamaterials] have the power to control light in an unprecedented way," said Sir John Pendry, a theoretical physicist at England's Imperial College London.


Sorry, I am not buying into this. In fact, their analogy is way off-base:

Schurig likens the effect to a rock in a stream. The rock symbolizes a metamaterial cloaking shell. The water plays the role of electromagnetic radiation flowing around the cloaking shell.

"Downstream you can't necessarily tell that there was an object distorting the flow," he said, adding that, even from the side, the disturbance is hard to discern.


When you perceive something visually, say a table, one of your senses (sight via the eyes) is picking up reflected light rays, interpreting them, and sending signals to your brain. If you take a step in another direction, the table will look slightly different to you because your eyes are picking up light which is reflected differently than the light you were seeing before you moved.

For an invisibility cloak to work, that is, an object would appear not to exist and you could see what is behind is undistorted, would require at least the following:

1. The cloak would have to be able to re-reflect the light which is coming from behind the cloaked object in an undistorted manner. It would have to be able to act almost like a computer program and manage incredibly small "pixels" so that they are arranged in a way that copies the objects behind the cloak.

A cloak is of course soft and if the person or object under the cloak moves, then the cloak would have to interpret all of those movements in order to keep the pixels properly arranged and then reflect them out instantaneously and without distortion.

2. The invisibility cloak would have to know not only where the perceiver and his eyes are, the cloak would have to also track the movements of the perceiver because again, as you you move, you see the reflected light from an object differently.

Thus, the overall process for the cloak would have to be to "read" reflected light from objects which would normally be blocked from the perceiver if the cloak did not exist. Track those "pixels" of light, take into consideration movements in the cloak, perceive the position of the perceiver's eyes and re-reflect the light out to the perceiver in the exactly "pixel" formation. In the end, the meta-materials of the cloak have to track 1. the object in the distance behind the cloak, 2. the cloak and the object it is covering, 3. the position of the perceiver and what his eyes are perceiving.

The water analogy is faulty because one drop of water looks like another. As a stream of water rushes by a perceiver, it makes no difference if one molecule is in place of another. But with reflected light if a "pixel" is out of place, then what the perceiver perceives is distorted.

The above, I believe, is an objective way of looking at this issue. There are several non-objective ways of looking at the cloak.

An idealist would simply say, "The cloak is a gift from God. God works in mysterious ways including using miracles. The cloak is a miracle." I can't go for that, no-oh-oh.

The materialist approach would be to say, "Consciousness is a myth anyway. So whether you see something or say it is invisible is irrelevant. We can't really know anything."

Now, there may be some value to these meta-materials. My guess this whole thing is a publicity campaign for these guys to get funding. But for a magazine such as National Geographic to go along with this cloak hokum is embarrassing.



http://ObjectivismOnline.com/blog/archives/000865.html
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