Two magicians physicists at the University of Rochester in New York have created an invisibility cloak capable of hiding large objects, such as humans, buses, or satellites, from visible light. Surprisingly, rather than relying on exotic and hard-to-manufacture materials, this invisibility cloak is fashioned out of conventional mirrors. This isn’t theoretical, like some of the other invisibility cloaks we’ve covered — you could build this cloak today from off-the-shelf parts and hide yourself from view.

Before you get too excited, though, this invisibility cloak — created by John Howell at the University of Rochester and his 14-year-old son Benjamin — is unidirectional. This means that it only cloaks objects that are being observed from a single, fixed position; if you move more than a few degrees to the side, or above, you can clearly see the object that’s being cloaked. With that said, though, if you’re far enough away from the object — say, if you’re cloaking an orbiting satellite or military spy plane — then the very narrow field of view means that unidirectional cloaking works just fine. It should work reasonably well at medium range, too; at a range of a few hundred meters, a human (or tank) could be fairly well hidden by this invisibility cloak.

The unidirectional invisibility is fashioned out of two right-angle mirrors. As you can see in the diagram to the right, this arrangement of mirrors bounces the light around an object, so that the light striking your eye comes from the scene behind the object. The invisibility isn’t perfect, but due to the finicky nature of electromagnetic radiation we’ll probably never have perfect invisibility. That’s basically all there is to it.

If this sounds vaguely familiar, it’s because it’s the same setup that magicians have been using for years to vanish people and objects. “The point we wish to emphasize is not the novelty,” Howell & Son admit in their research paper, “but the ease of scaling to nearly arbitrary size.” Here they are referring to the fact their mirror-based invisibility cloak can be scaled up indefinitely, while other invisibility cloaks — such as those based on metamaterials — currently operate on the centimeter scale or smaller.

While this current approach with flat, rectangular mirrors placed at right angles will always be limited to unidirectional cloaking, exotic mirrors and interesting angles might allow for multi-directional and -dimensional invisibility. A cloak with spherical symmetry could perhaps be constructed out of retroreflecting spheres — spheres that reflect almost all of the light back to its source with minimal scattering, such as a cat’s eyes. In recent years, there have been numerous theoretical studies and a few practical demonstrations of mirrored invisibility that move us towards methods of cloaking that would be useful in everyday life. For now, though, the prospect of satellites that are almost invisible from Earth is fairly chilling…

Now read: Invisibility cloak made from simple mirrors can stop time indefinitely

Research paper: arXiv:1306.0863 – “Simple, broadband, optical spatial cloaking of very large objects”