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Surprising Science

Small-Scale Invisibility Cloaks

For generations, the topic of invisibility has been of great interest. Although it was once dismissed as science fiction, it has now become reality on a small scale. Physics textbooks around the world must be rewritten and scientists must admit that they were wrong.

For the first time, scientists in Germany announced that they have been able to create a cloaking device that can render a three-dimensional object invisible (at near optical frequencies). Previously in 2006, scientists at Duke University created a substance called metamaterials which could render an object invisible by absorbing all the light that hits it, but only in two-dimensions and only at microwave frequencies.

This time, scientists were able to make a cloaking device that could make a tiny three-dimensional object disappear under infrared light, which is almost in the visible range. Infrared by definition has a longer wavelength at a lower frequency than that of visible light. These scientists in fact made a small invisibility carpet, and if you place an object under this carpet (made of gold), then the bump made by this carpet disappears. Light hits the bump, which modifies the path of the beam so that the beam bounces off just as if the bump weren’t even there. This process can be scaled up and in principle you could put one of these carpets over a person, a car, or even a house and make it disappear. This technology of course raises many moral concerns, as discussed in Plato’s Republic, which argues that a person with such a power (a ring that makes you invisible) would use it for unjust means if given the opportunity.

There are many hurdles to overcome before we have something similar to and as technologically advanced as Harry Potter’s cloak.

a) First, scientists have to make a cloak that works in the visible range, which might come very soon.

b) The object under the bump is very tiny (a few microns wide), smaller than a human hair, so small it cannot be seen with the naked eye. But, in principle, in the future it can be scaled up to cover a person or any object for that matter. The process of building such a cloak would be very expensive and time-consuming, since it’s done via nanotechnology.

c) From a distance, the carpet/cloak looks like a mirror. The bump in this carpet/mirror disappears if we use metamaterials. Scientists have to demonstrate this effect without the object looking like a mirror, which may take a bit of time. 

This type of research in general is both fast-paced and competitive, and other groups working on invisibility include both UC Berkeley and Cornell. An invisibility cloak (or carpet) similar to the one worn by Harry Potter is certainly a distinct possibility but will take many years of hard work to perfect. Still, it may be here sooner than you think, and as I’ve stated before, “The more we know, the faster we can know more.”


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