Can you imagine what would it be like to bend light in such a way that you are rendered totally invisible? Imagine evading Voldemort’s clutches, winning an intergalactic battle, or at the least, easily slipping into class whenever you’re late. But of course, invisibility is absurdly impossible – or is it?
We can refract, diffract, and polarize light. We now know even the once previously mysterious properties of light. If the very nature of invisibility stems from how light works, can we be so quick to say that invisibility is theoretically inconceivable? In fact, we actually already see forms of pseudo-invisibility, from transparent objects and camouflage to stealth technology for radars and chroma keying in filmmaking.
Even the invisibility seemingly real only to science fiction is actually the work of metamaterials, the latest in the Peverell brothers’ concoctions. Metamaterials, artificial composites with properties not found in nature, can, by way of their negative refractive index, bend light backwards. Unlike naturally occurring material, metamaterials derive their characteristics from structure rather than chemical composition, which makes them useful in interacting with and manipulating electromagnetic waves, opening them up to many potential applications, such as imaging, optical communications, and of course, invisibility.
Duke researchers initiated the first development of a two-dimensional metamaterials cloaking effect for microwave beams. In this setup, light flows around an object, as if they object really weren’t there, thus mimicking the characteristics of free space. Berkeley researchers have been able to extend into three dimensions for near-infrared and invisible light. While these advances have been in metamaterials made of metal, more recently this year, a cloaking device for infrared light was developed from metamaterials of glass.
Despite these advances, the age of Harry Potter’s invisibility cloak is well ahead of us. Metamaterials cloaking devices are still limited in size, and their effect is distinct from total invisibility, as they only reduce the shadow and reflection of an object. Whether of glass or metal, current cloaking devices scarcely resemble the wieldier cloak in fiction.
Even in the skeletal theory of invisibility, however, physical constraints aren’t the only limitations. An invisible person would have to be effectively blind in order for the invisibility to take. While this is not much use for our own fanciful ambitions, it does render equity to an otherwise easily exploitable contrivance. Until further breakthroughs, we’ll just have to settle for the fantasy books.
For more information, check out:
http://www.dukenews.duke.edu/2006/10/cloakdemo.html; http://berkeley.edu/news/media/releases/2008/08/11_light.shtml; http://news.nationalgeographic.com/news/2008/08/080812-invisibility-cloak.html; http://news.bbc.co.uk/2/hi/7553061.stm; http://www.sciencedaily.com/releases/2010/07/100721164007.htm; http://www.cnn.com/2006/TECH/science/08/09/feature.invisibility/; http://www.nytimes.com/2007/06/12/science/12invis.html