“Harry looked down at his feet, but they had gone. He dashed to the mirror. Sure enough, his reflection looked back at him, just his head suspended in mid-air, his body completely invisible.”
(Harry Potter and the Philosopher’s Stone – J.K. Rowling)
J.K. Rowling invented Harry Potter’s invisibility cloak, but a recent Science paper suggests that physicists are close to developing their own invisibility cloaks.
Technology Review explains how it works: Electromagnetic radiation can be diverted around an object using a “metamaterial”, recreating the original path of the radiation as if there was no object present. The cloaking devices that are currently being developed can only bend microwaves, and not yet visible light, but the developers predict that bending visible light will be possible too. That means that Harry Potter’s invisibility cloak could theoretically be made using these metamaterials. However, a cloak like this would still differ from Harry’s cloak in several ways: it would be bulkier, invisible when not being worn, and you would not be able to see where you’re going if you pulled a metamaterial cloak over your head.
A few years ago, scientists in Japan found another way to make invisibility cloaks. They use a video camera to capture what is behind the coat-wearer and project it on the front of the coat. It’s explained in detail and with all its impracticalities on “How Stuff Works“.