Invisible Cloaking Device You must have dreamed of being a invisible man and sneak into a bathroom. I was one of a boy dreaming of such a thing. I majored in physics at university and I am now studying about invisible cloaking device. The device makes a object cloaked with it invisible by deflecting light. The interesting point is the deflected light goes back to the path where if there weren't the device it would go. Let me give you a brief explanation about the mechanism of the invisible cloaking device. It is known that light takes the shortest optical path. This is a Fermat's principle. In the media that has a reflective index larger (smaller) than 1, the optical path gets longer (shorter) than in a vacuum. The invisible cloaking device has a artificial reflective index profile. This is because the light takes such a weird path, that is the shortest path for the light. This means that light propagates as if there is nothing, so you cannot see the object cloaked with it. However I realized a very important fact that if you are cloaked with the device, you cannot see anything! Even if you could sneak into a bathroom, you cannot see anything! It was very disappointing, but I don't give up. Physics must realize your dream.