If you could have any superpower, what would it be? The ability to fly? Walk through walls? Super-strength? No doubt, many of us would be tempted by invisibility. Just think of it: sneaking in and out of rooms undetected, listening in on conversations like a fly on a wall. Humans have been captivated by the idea of invisibility for ages, and this fascination has permeated popular culture, from Harry Potter's magic cloak to Frodo's mystical ring, which renders him undetectable. But how close are we to creating an actual invisibility cloak?
"Invisibility may seem like magic at first, but its underlying concepts are familiar to everyone. All it requires is a clever manipulation of our perception," says Boubacar Kanté, a professor in the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering.
Rendering something invisible without the use of wizardry requires changing how light reacts when it hits an object. The reason we can see things at all is because light bounces off of them and into our eyes. If we can prevent this, or change how light reacts around an object, we could change how it looks. No natural material can manipulate light in this way, but researchers are busy concocting their own "meta-materials" made of tiny electronics that have special properties to reroute light and "cloak" an object from our view.
For example, last year, researchers at UC Berkeley created an "ultra thin invisibility cloak" that, when activated, can make a 3D object appear entirely flat, like a mirror. It's made out of microscopic gold nanoantennas just 80 nanometers thick (as Jesse Emspak at Live Science notes, "an average strand of human hair is about 100,000 nanometers wide"), which means it's flexible and could be wrapped around an object, like a blanket. The gold nanoantennas can be "tuned" to make the material look like something else, which has big implications for disguise in the military. "You could cover a tank with it and make it look like a bicycle," the study's director, Xiang Zhang, told the Los Angeles Times.
The catch? The material has to be "tuned" to a specific background, meaning that if I'm standing in front of a forest, this cloak would need to be tuned to match the trees behind me, and would only really work if I stayed in one place. That's not particularly practical for anyone hoping to wander the halls of Hogwarts, but Zhang says making the cloak adaptive is the next step. Also, the prototype is incredibly small, just the size of a few cells. But the research offers a proof of concept and could be scaled up.
Meanwhile, at the University of Rochester, researchers have found a way to use lenses to bend light so that it avoids an object, making it disappear. This is a more low-tech cloaking method, but it could do things like let a surgeon "look through his hands to what he is actually operating on," said John Howell, a professor of physics at the university.
To prepare for a time when cloaking is a reality, a team of Swedish researchers has been studying how being invisible affects the body and the mind. "The prospect of using these techniques on humans raises important neuroscientific questions," the researchers write. "How does invisibility affect self-perception of one's body? Are there any cognitive 'side effects' of having an invisible body?" Interestingly, they found that owning an invisible body could actually help treat social anxiety.