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Is Invisibility possible according to physics? Is there any backing theory to prove it true or false?

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Invisible to what? You seem to be implying invisibility in the visible spectrum, but things can also be invisible at certain wavelengths but not others. Radar absorbing material (RAM) on stealth aircraft for example. –  tpg2114 Jan 3 '13 at 13:38
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Can you see the air? What about viruses? Radio-waves? –  zhermes Jan 3 '13 at 18:08

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up vote 2 down vote accepted

This is an active area of research in both optics and acoustics using diffractive elements.

You can think of these diffractive elements as guiding all the incoming light around them, thus reproducing the input radiation at the output, resulting in invisibility. The are often referred to as "cloaks."

The current reason why they don't work in practice is because they have only been shown to work at specific wavelengths (or colors), and not over a wide band of wavelengths simultaneously.

See this Wikipedia page for more details.

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Interesting link..I had seen a video of quantum revolution where i saw experiments about diffractive elements and meta materials. Can existent materials be engineered to be invisible? –  DarkHorse Jan 4 '13 at 9:21
    
In 2006 a 2-d experimental cloak that worked in the microwave was made by Schurig et al sciencemag.org/content/314/5801/977.short Recently at Duke, Landy and Smith improved upon Schurig's design here nature.com/nmat/journal/v12/n1/full/nmat3476.html, still in the microwave. –  daaxix Jan 4 '13 at 14:17
    
Thanks for all those links, you gave a in-depth analysis :) –  DarkHorse Jan 6 '13 at 2:36

Yes it is possible

If the object has the same refractive index as a surrounding fluid it is not visible.

If the object does not produce or reflect light (such as a black hole) it is invisble.

complex systems are being produced to create nanoscale invisible objects now.

http://www.sciencedaily.com/releases/2012/05/120521104637.htm

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the nano scale objects mentioned in the article above do work over a comparatively wide range of the visible spectrum. Still, it is far away from being useful to harry potter or wonder woman. –  kaine Jan 3 '13 at 15:18
    
Nice:). Your answer does satisfy invisibility in concepts of vision. How about engineering an existent object having no transparency properties and having size visible to human-eye to become invisible? –  DarkHorse Jan 4 '13 at 9:07
    
Physically possible by surrounding the opaque object with a complex structure involving metamaterials with negative refractive indices. Has not been done for an object that can be viewed in three dimentions. Please note, if you expect to make the device capable of "seeing" out and not having everything else be invisible, the engineered device must consume power. It does not break the laws of physics but is is extremely difficult and seems like it would be very impractical for, say, an invisible tank. –  kaine Jan 4 '13 at 18:45
    
Thanks for proving invisibility is possible :) –  DarkHorse Jan 6 '13 at 2:34

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