As a society that really wants to be seen, make a scene and individuals wanting to be noticed for something, we seem to be putting a bit of effort for the opposite! Ever wonder if not being seen is possible? Reader, I'm talking about invisibility. Using a device to hide oneself from other people's vision. Kind of like the Invisibility Cloak from Harry Potter.
*key idea: you need 2 main things for vision to occur. Object to be seen and an observer. Without either one, nothing can be seen*
For invisibility to work, the material being used must not be seen by the observer. As shown in the picture to the right, the material has to be able to reflect of the material, hit another above the object and bounce off the back. Unfortunately, this is very hard and maybe even impossible to do (have something follow you from above).
Let's take a step back for a second though. Light is an electromagnetic wave (we also know now, that it is a particle). That is, it changes from an electric field to a magnetic field very quickly. We know this thanks to James Maxwell. He also had thoughts about invisibility.
We know that most liquids and gases are "invisible" (transparent), but why is that? Atoms in higher excited states (due to heat, pressure or a bigger volume) have more spaces between them. This is a key role for such visibility problems. If the spaces between the atoms are greater than the wavelength of the light, then light is not given off. What about diamonds? Why can I see right through them? Some solids have special properties.they are called Lattices'. The atoms are arranged so that there are equal spaces between each other and is organised!
So how do we use such properties to become unseen? New materials are being worked on in laboratories called Metamaterial. These are materials that can bend light waves. So far, we are able to bend microwaves (smaller than infrared).
Light have a property called the index of refraction. If you have ever gone fishing and saw a fish in the water and decided to put a net over the fish, you know that you didn't catch it. this is because the index of refraction is responsible for the bending of light. This concept needs to be applied to an invisibility device. Metamaterial is special, in which it actually has a negative value for the index of refraction (everything you can see will always have a positive value).
This is quite close to the concept of Fibre Optics. In a fibre optic tube, light is bent at a 90 degree angle so nothing passes through it but stays contained in the tube. The US military has a device that uses fibre optics for an "invisible" cloaking device. this is the closest we are to such a cloaking device.
In Michio Kaku's book, Physics of the Impossible, he rates invisibility a class 1 impossibility. This means that it is not possible now, but will be in a matter of a decade.