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September 8, 2008 | by  | in Opinion |
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Invisibility: one power closer to becoming a supervillan

Have you ever played the “what superpower would you have” game? Did you eschew flashier powers like the ability to fly or a cool admantium skeleton and claws (not actually a superpower, but possible because of Wolverine’s quick-healing power) for the ability to become invisible at will? Do you think that Harry’s invisibility cloak would be just perfect for making daring daylight bank robberies a little less daring, or for sneaking into the changing room of people of your sexual preference (you have heard there’s free porn on the internet, right)? If so, scientists are at work developing what could one day become the product of your dreams.

How we see

We see stuff when the lens of our eye focuses an image onto the light-sensitive retina, located at the back of our eyeballs. The retina is made up of cells which absorb photons (light particles). When stimulated, the cells produce electrical impulses which travel to the visual cortex at the back of the brain, where they are interpreted.

So what makes this ‘image’ in the first place? As well as having characteristics of particles (as a stream of photons), light has wave properties. Light visible to the human eye is part of the electromagnetic spectrum, which also includes radio waves, microwaves, infrared and ultraviolet light, x-rays, and gamma rays – none of which we can see. (And, even though gamma rays transformed Susan Storm into the Invisible Girl in the Fantastic Four, don’t try this approach, because gamma rays will actually just kill you).

When we see, it is not the objects themselves that we see per se. The light that hits an object gives it its visible characteristics by what happens next: the light that is reflected off the object and reaches our eyes is what we see; light that is absorbed by the object, and therefore not reflected, gives it its colour. For example, leaves that absorb (and therefore do not reflect) light from the red and blue part of the visible spectrum appear green to us because of the wavelength of light that is reflected.

Light is ‘refracted’ – a phenomenon we’re most familiar when an object like a straw sticking into a glass appears to be bent or broken – when the light wave alters when travelling from one medium (air) to another (water).

So what does all this have to do with invisibility?

Scientist Xiang Zhang and the rest of his team of researchers at the University of California Berkeley recently published accounts in Nature and Science of a ‘metamaterial’ they have engineered that can be used to cover objects to make them invisible. A ‘metamaterial’ is a material with properties that do not occur naturally, and which gains those properties from its structure, rather than from its composition as such.

A phenomenon called ‘negative refraction’ is responsible for ‘bending’ the light waves around the object cloaked with the metamaterial.

Although negative refraction has previously been achieved in the microwave and infrared regions of the electromagnetic spectrum, with 2D objects, this is the first time it has been demonstrated in the visible region of the spectrum, and the first time it’s been used with 3D objects.

So what all this means is that when objects are cloaked in the metamaterial developed by Zhang and team, light is neither absorbed nor reflected, but ‘bends’ around the object. As a result, only the light from behind the object can be seen – which makes the object invisible!

But, before you start getting measured up for your invisibility suit, keep in mind that so far, this has only worked on a tiny, nanometer scale (a nanometer is a billionth of a meter). It’ll be years until scientists will be able to render large objects invisible. And the research at the University of California at Berkeley is funded by the American military, which means that it’s likely to be cloaking soldiers and tanks long before it’ll be available at your local comic-book store.

Nevertheless, now that it looks like scientists are well on their way to achieving invisibility on scale that’d be good for, say, a skin-tight suit and cape that could be quickly changed into in a phonebox, we’ve just got to get them working on the essential superpowers that should accompany invisibility, like the ability to walk through walls … and that (not so daring) daylight bank robbery is one step closer.

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