Something like Harry Potter’s invisibility cloak might actually be the best way to become invisible in real life. Unfortunately, it surely won’t be here for your next Christmas gifts, although scientists are trying (with some success) to understand how to make one.

To understand how to be invisible, we’ve got to understand the problem first: how are we visible? A visible object does two main things: it reflects at least part of the light that hits it, and it doesn’t let through light coming from behind it. So if a ball is hiding behind a big box, I can’t get the light bouncing off the ball, instead I only see the box.

The big visible box blocks the light bouncing off the ball. So we only see a boring box.

An easy way to be invisible, then is camouflage: make it so that the light bouncing off of us looks a lot like the one from around. It doesn’t quite solve the problem, but it effectively makes us less visible. As long as we stand still.

The hard way, the Potter way, is also where science is going: show those in front of the obstacle the light that comes from behind it. Basically become transparent. The main idea is to develop cloaks or devices that bend and guide light around what needs to become invisible. For example, a cloak to wrap around the box that makes it invisible and shows the ball behind it.

Research is still going in several directions: from composite materials (metamaterials) to thin coatings that bend light making three dimensional things look flat, hiding their features. However, most successful experiments only worked for specific wavelengths of light, or for tiny objects, or only if looking from a specific angle. A true invisibility cloak should work from all angles, with all light (at least the visible part), be light, and relatively thin. So there’s still quite a way to go.

Then there’s a more practical, but very hard problem: if the cloak bends around us all light, we don’t get any at all inside. We might as well be invisible, but we’ll immediately get caught by walking into everything!

If you want more

• Some time ago, phys.org collected a few researches on metamaterial cloaking
• If you’d rather have X-Ray vision as a superpower, a while ago we talked about how that works
• DNews also tackled invisibility cloaks:

Cover photo: Invisibles, CC-BY-NC-ND Sergio/Flickr