by Zeus Kabob » Sat Jun 02, 2012 8:06 am
I'll start at the top.
Light is made up of photons, which have a wavelength and a direction. The wavelength of light determines its visibility (380-750 nm is visible light), and the direction determines where it goes.
A device that changes the frequency of light is possible, but it would have to use one of a few different methods. The only method I can think of would be to vibrate a physical reflector in order to change the frequency of light. This would take advantage of the Doppler effect, the only problem being that to shift red light upwards out of the visible light spectrum, the device would have to be moving at about half the speed of light (1.5e8 m/s). This speed is entirely impractical.
As well, this only makes the object "invisible" in the way that a blackboard is "invisible". To make something truly invisible, you must simulate the action of having all light pass through the object. If all light only moved one direction, this would be easy, but light moves in many directions. A potential setup is a suit made of cameras and an as of yet unknown device that can release light in various directions. The suit would collect light with the cameras, and a piece of software would use the locations of the cameras, the dimensions of the person wearing the suit, and the light input to simulate the light passing through the figure.
As far as I can tell, the technical implications of this setup are ridiculously complex and fraught with error. This is the "invisibility cloak" that is currently being developed, and its current stages are not "invisibility", but "active camouflage" (think fatigues, not Halo).
Another way to cause invisibility is to surround the "invisible" object with a metamaterial that has a negative refractive index for light in the range of 380-750 nm. A proof-of-concept has been made for a metamaterial with a negative refractive index in the 50 cm - 1 m range, so it's theoretically possible to make this material, but it requires nanoscale engineering that we don't have.
I've rambled a bit, but you can probably interpret the ideas here.
Sorry for the wall o' text.