Invisibility - To Bend or Break from the Ether
Can Scientists Bend Light to Achieve a State of Being Invisible?
Oct 22, 2009
At one end of the spectrum, things that are unimportant, mundane, and drab are sometimes characterized as being invisible. Terence Stamp emphasized this when he stated: "As a boy I believed I could make myself invisible. I'm not sure that I ever could, but I certainly had the ability to pass unnoticed." At the other end of the spectrum, things that are spiritual, supernatural, and god-like are also characterized by their invisibility.
It is this context of invisibility that has always romantically mystified and fascinated humankind. To become invisible is to mingle with the spirits or the gods. The famous French aviator and author of The Little Prince, Antoine de Saint Exupery, touched on this when he said, "And now here is my secret, a very simple secret; it is only with the heart that one can see rightly, what is essential is invisible to the eye." So, is it actually possible to become invisible? As discussed above, the state of invisibility actually characterizes diametrically opposed concepts at opposite ends of the spectrum.
Wave Nature of Light
"Spectrum" is the key word here. Visibility requires light, and light exists as an entire spectrum of colors: purple-blue-green-yellow-orange-red, as revealed by their differential refraction in a rainbow, for example. Therefore, perhaps one way to become invisible would be to selectively refract or filter-out a certain color of light, thereby making things of that color disappear or become invisible. Light can be modeled as electromagnetic waves and the properties of waves include constructive and destructive interference, so if scientists could selectively destruct or cancel-out just those light waves that make things visible, those things would be invisible. One can imagine all sorts of scenarios with different lenses, wavelengths, refractions, diffractions, reflections, filters, holographs, etc. that could be engineered to make the light that makes things visible deconstruct or disappear; in effect, to make things invisible.
Light Bending Research
Researchers at the University of California at Berkeley and Imperial College in London seem to be doing just that. These scientists are using special materials that bend light around objects, rendering them invisible. The British group is revisiting Maxwell's equations and also studying the bending using microwaves because their short wavelengths optimize the actual bending process, but the same principles apply to light in the visible spectrum. Xiang Zhang of the American group says, “In the case of invisibility cloaks or shields, the material would need to curve light waves completely around the object like a river flowing around a rock.” The assumption is that the complete bending of light around objects will make them invisible. How much is complete?
Invisibility in Culture
In Greek mythology, Athena and Hermes hid from others using a cap of invisibility. Plato in The Republic, provided Gyges with an invisible ring to perform his treacheries. H. G. Wells' Invisible Man achieved his hidden state by changing his refractive index to match that of air, while Marvel Comic's Invisible Woman achieved hers by bending the light waves around her, not unlike what today's scientists are trying to do. Michelangelo once said that his great sculptures already existed in the stone, and his work merely freed them from their cryptic hiding place. Similarly, the writer Vladimir Nabokov said, "The pages are still blank, but there is a miraculous feeling of the words being there, written in invisible ink and clamoring to become visible."
Medium or Ether for Invisible Objects
Not unlike these cultural examples, perhaps visibility is merely an indication that an object is free from some unknown medium, clutter, noise, or other cryptic device that would otherwise cloak it and make it completely invisible. While the scientists are synthesizing new artificial materials that do not exist in nature to bend light and make things invisible, perhaps there already exists some natural medium within which objects exist, not unlike the classical ether invented by 19th century physicists to provide a medium for light waves to travel through space. Such a medium might be capable of cloaking people and objects, rendering them just as invisible as Michelangelo's sculptures before he freed them from their native stone.
References
Valentine, Jason, et al., An Optical Cloak Made of Dielectrics, Nature Materials, Vol. 8, 568, (2009).
Marco Rahm, et al., Design of Electromagnetic Cloaks and Concentrators Using Form-Invariant Coordinate Transformations of Maxwell's Equations, Photon. Nanostruct.: Fundam. Applic. 6, 87 (2008).
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