Invisibility is one of the oldest concepts in our mythology. Years before Harry Potter put on his cloak or Tom Cruise pranced behind an invisibility tarp, Plato recounted the myth of the ring of Gyges, a poor and honest shepherd who discovers a ring that makes him invisible. Ptolemy’s quintessential work “Optics”, with its definitions of light and color, also discusses invisibility, and Tolkien made a magic ring of invisibility the centerpiece of his fantasy novels.
The idea of becoming invisible is anything but new, and has inspired not only our imagination and culture, but also more recently opened up our understanding of the universe and its mysterious origins.
Mostly though, invisibility is a common plot device in science fiction, fantasy and mythology. The military dreams of one day perfecting stealth technology, as do scientists, writers, artists and children alike. Yet here we all are, it’s the year 2012, and we’re still left asking ourselves: is this really possible?
The answer is: probably, and it involves a new type of artificial substance called metamaterials. When he first theorized them in 1967, the Russian physicist Victor Veselago predicted that these new artificial materials would interact in completely opposite to the way that all other materials did. His landmark paper, “The Electrodynamics of Substances with Simultaneously Negative Values of ε and μ," posited that a substance could have negative refraction, so long as both the (electric) permittivity and themagnetic permeability of a material are negative — an idea that practically shits on what every textbook on optics says is possible.
It wasn’t until 1999 that Dr. John Pendry at the Imperial College London started working with refractive indexes and electromagnetism to begin constructing these new materials. The most promising new development involving invisibility and metamaterials was achieved in a DARPA-funded experiment in 2006 at Duke University in Durham, NC where they successfully used metamaterials to render an object invisible to microwave radiation.
The secret to metamaterials lies in the manipulation of how light bends when traveling through a transparent medium, or what is known as the “index of refraction.” The scientists at Duke embedded tiny circuits in copper bands that were arranged in a flat, complex pattern of circles in order to bend light in unorthodox ways. Think of the way a river flows around a tree trunk or large stone. As the water quickly wraps itself around it, the edges of the object become washed out downstream.
The sophisticated results of these new metamaterials were that they were able to channel and bend a path of microwave radiation in a specific way that would never happen naturally. Research into metamaterials is on the march, but many problems still remain in trying to render an object completely.
To create invisibility — to construct a material with negative refraction — the internal structures implanted inside it must be smaller than the wavelength of the light it’s trying to be invisible from. Since light waves are normally very short (300 to 800 nanometers), one solution could involve constructing ‘tiny machines’ that could manipulate the wavelengths of light at the atomic level. By instantly processing the incoming light and changing individual atoms inside the metamaterial accordingly, you could modify and bend light at your discretion. You could be invisible.
Scientists believe that building such an invisibility cloak will depend upon the promise of nano-technology. Other solutions include holography, or maybe the use of an entirely different technology known as “plasmonics.”. While we’re nowhere near the invisible assassin or the light-cloaked tank, “invisibility” is no longer a dirty word in science. There is good reason to think that what was once considered an impossibility will in fact be entirely possible.
In the meantime, metamaterials may promise a bounty of other applications in the future, from detecting biological agents and chemical explosives to creating smaller and stronger antennas. A “photonic” computer chip that utilizes a combination of a metamaterial with a semiconductor to turn trapped light on or off would be up to 10 times faster than our current silicon-based chips. Researchers in China have even claimed to have created a tunable “electromagnetic gateway” that could block electromagnetic waves while allowing other entities to pass.
Forty-five years after Veselago first theorized metamaterials, science is actually beginning to manufacture them in laboratories. Einstein famously said that “If at first, the idea is not absurd, then there is no hope for it.” Science isn’t about what we perceive to be possible. It’s what happens when we begin with the assumption that nothing is impossible. These days, that involves looking less at what we can see and more at all the stuff that’s invisible.