You don’t look through an invisibility cloak; you look around it.
To make something invisible, hide the light that bounces off of it. That’s the basic concept of an invisibility cloak, Harry Potter or otherwise. But since it’s difficult to corral the innumerable photons ricocheting off of literally everything you can see (when we do, the materials turn out blacker than the blackest black), recent cloaking devices instead bend rays of light around objects so that the incriminating light rays never meet our eyes.
Earlier this month, researchers at the University of Rochester did this in maybe the simplest way possible – simple, but effective.
The team – consisting of PhD student Jospeh Choi and professor of physics John Howell – achieved this optical misdirection by bending light rays with a series of lenses into a small beam so that any object passing around this tight beam would be effectively cloaked. The cloaking area is a ring-shaped region on the outside of the lenses, not in the middle.
The lenses pass the optical information for the background through a small visual bottleneck, and expand it at the viewer’s end. Blocking the very center of the lenses’ line-of sight will disengage the cloak, but across a decently large angle the cloaking works on the periphery.
“There have been many high-tech approaches to try an achieve cloaking, but it’s really just an optical illusion,” says Howell in a video outlining the project.
The advantage to Howell and Choi’s cloaking device is that it works for a decently wide viewing angle (around 15 degrees), works for the whole visible spectrum of light, and it doesn’t distort the background (you can see that the grid matches up in the video). Other high-tech cloaking devices don’t work at this range of angles or shift they shift background dramatically, giving away the distortion. That’s something that would kill a Klingon warbird.
“This is the first device that we know of that can do three-dimensional, continuously multidirectional cloaking, which works for transmitting rays in the visible spectrum,” said Choi, a PhD student at Rochester’s Institute of Optics in a press release.
The beauty of this cloaking device is that the researchers simply used the science of optics to come up with a more elegant solution than motion-tracking cameras and projectors. Based on the math, they knew what kinds of lenses they would need and at what distance from each other they would have to be in order to bend and refocus the rays of light around the object they wanted to cloak.
It’s simple enough that you could build your own, though if you wanted to sneak into a chamber of secrets you’ll need a pretty expensive set up.
Kyle Hill is the Chief Science Officer of the Nerdist enterprise. Follow the stream of geekery on Twitter @Sci_Phile.