Scientific Magic: Invisibility

Invisibility has influenced mankind in many mythological stories and fairy tales. In Greek mythology, Hades, the king of the underworld, owned the “Cap of Invisibility” which can make the wearer invisible. Also Athena, Hermes and Perseus used this cap in order to fight the Titans. Plato discussed invisibility with The Ring of Gyges, in his famous book The Republic [Plato. The Republic. Trans. by Benjamin Jowlett, Book II, 358d—361d]. We see traces of invisibility in a fairy tale from Hans Christian Andersen, The Emperor’s New Clothes. More recent examples of invisibility include J.R.R. Tolkien’s fiction, in this book the ring of invisibility stolen by the hobbit Bilbo, Harry Potter’s Cloak of Invisibility, Star Trek’s cloaking device, which is supposed to be Romulan technology described in 2266.

Of the brief descriptions given above, two of them catch my attention: they are “The Ring of Gyges” and the “Emperor’s New Clothes.” Let me explain them in more detail. For the “Ring of Gyges,” Plato discussed invisibility, used a philosophical thought experiment from the perspective of ethics with the Ring of Gyges. According to this story, Gyges, who is a shepherd, finds a ring and becomes invisible and anonymous. Then he deceives a queen, kills the king and Gyges becomes a king. “The Ring of Gyges” is a story about a man, who uses a talismanic ring unfairly. According to Plato every person would be unjust if they had the ring of invisibility. The Emperor’s New Clothes is about a situation called “The elephant in the room,” which everyone is aware of, but no one discusses, because having this debate is bad for those who argue.

Invisibility can be considered the elephant in the room but not now, in the future, and Plato would probably be right about unjustness in the usage of invisibility. Now let’s look at the scientific improvements since several material scientists around the world have been studying invisibility.

To put it simply, to make an object invisible means to make it undetectable to electromagnetic waves. This is possible when you can control the electromagnetic waves of your object. Work in transformation optics strives to make such control a possibility. In Figure 1, we see a circular object with a radius R1 in red, and around this object we see a cloaking with a radius R2 in blue. As can be seen, the light lines bend around the red object in the blue area and in this way the red zone is hidden from the observer. This “magic” is possible when material properties of the blue region are purposely changed. These cloaking regions are all engineered by material scientists, which means they do not exist naturally. These regions can be plastic, metal, glass or dielectric.

 

Figure 1: From the article J. B. Pendry, D. Schurig, and D. R. Smith, Controlling electromagnetic fields, Science 312, 1780 (2006).

John Pendry and his team first studied an invisibility cloak in 2006 at visible light region and around a 2D-tiny object. After 12 years of research, only small steps have been achieved.

That is to say, a perfect, real invisibility cloak which makes a 3D moving object invisible for all light spectrums hasn’t been invented yet. But this promising technology has many potential uses for both the military: e.g., invisible radars, planes, tanks, and soldiers -for camouflage; and for the medical sciences:, e.g. new generation bio-medicines, surgeons’ ability to see through their own hands as they operate, extraordinary lenses to closely examine DNA, see unborn children clearly and check for early defects or diseases, and also for use in in energy harvesting and even in computing.

In conclusion, within the next ten to twenty years, invisibility will come into our lives as a promising camouflage technology. Nothing will ever be secret again in the room with an elephant.

Author: Neslihan Eti

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