It doesn’t take that much to convince us we’re invisible, according to a new report.
Scientists from Sweden's Karolinska Institutet revealed in a study last week that, with a few manipulations, they were able to trick participants into believing their bodies were no longer visible.
To create the illusion of invisibility, the scientists equipped each participant with a head-mounted display (HMD). The authors explain:
“The participants were asked to stand in an upright position with their head tilted and to look down at their body. They were then fitted with a set of HMDs…. The HMDs presented the participants with video streams of two high-performance, industrial, digital cameras…that were attached side by side with a custom-made tripod mounted on the wall at the level of the participant’s head and that faced the floor.”
The head displays showed the participants an empty space where their bodies should be. Experimenters prodded the participants and the space below the cameras, creating the illusion that the physical sensations felt by participants were applied to bodies they couldn’t see. The scientists later asked participants to describe how that felt by identifying with figures in varying states of invisibility:
Dark green represents how participants felt when researchers prodded both their bodies and the corresponding videotaped space at the same time ("synchronous touching"). Light green represents how they felt when the prods didn't match up with what participants saw ("asynchronous touching"). Red refers to a previous experiment.
The paper’s authors conclude: “Our results demonstrate that healthy individuals can experience the illusion of owning an invisible full-body.”
Lead author Arvid Guterstam told Fusion in an email that the results were unexpected. "I was personally surprised that the illusion actually works. Considering that we are born with and have a lifelong experience of having a physical body, it is quite astonishing that the brain in the matter of ten seconds can be fooled into accepting an invisible body as part of the self."
We, too, were surprised by the results—but also by the researchers' premise for conducting the study in the first place. In the abstract, they write: “Recent advances in materials science suggest that invisibility cloaking of the human body may be possible in the not-so-distant future.” Come again?
Guterstam confirmed, "Materials science has over the last decade made several major advancements in the development of invisibility cloaking materials."
When asked whether these cloaks will resemble those of science fiction, Guterstam said they come closest to the model imagined in H.G. Wells's The Invisible Man—but he hopes real-life invisibility cloaks will do more good. "In Wells’s book, the power of invisibility results in rather negative cognitive consequences," he said, "such as megalomania and a breakdown of our sense of morality, which I hope will not be the case if genuine invisibility cloaking of the human body becomes reality."
Rather than triggering megalomania, Guterstam and his colleagues hope invisibilty cloaks could help ease a common ill—social anxiety. Guterstam explained that, currently, cognitive behavioral therapy is used to train people out of feeling stress in response to social situations. Tricking people into feeling invisible could pair with a virtual-reality therapy to treat anxiety.
Intrigued by the advances in cloaking materials Guterstam mentioned, we took a look at previous reports—and what we found didn't disappoint.
A decade ago, National Geographic reported on a study that proposed a cloaking device that would prevent objects from reflecting light, the way visible objects do. Under the cloak, the objects would appear so small that they would be very difficult to see:
Electronic engineers at the University of Pennsylvania in Philadelphia are researching a device they say could make objects "nearly invisible to an observer." The contrivance works by preventing light from bouncing off the surface of an object, causing the object to appear so small it all but disappears.
National Geographic added that the device was still rather crude:
[Imperial College physicist John Pendry] said that light-shielding covers would have to be customized to match the properties of each and every object they hide. It would be still more difficult to devise shields that could cope with all wavelengths of the visible spectrum—from red to violet light—and not just a single color.
Since then, researchers have explored different types of cloaking devices. And while Guterstam told us that "many fundamental challenges remain before we can cloak macroscopic objects," science has come close. Notably, in 2013, a team of researchers from Zhejiang University in China showcased an "invisibility box." In the abstract to their study, the authors described a "cloak design to be made in large scale using commonly available materials." Their achievement? "We successfully report cloaking living creatures, a cat and a fish, in front of human eyes."
"The box is basically a set of prisms made from high-quality optical glass that bend light around any object in the enclosure around which the prisms are arrayed."
This, too, however, needed more work:
As well as being visible themselves, these cloaks only work for certain viewing directions. A sophisticated observer would also be able to measure that different rays of light have travelled different distances inside the device.
Then in September 2014, a team of researchers from the University of Rochester revealed another cloaking device in the works:
This one, explained researcher Joseph Choi, 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." It's imperfection? “This cloak bends light and sends it through the center of the device, so the on-axis region cannot be blocked or cloaked."
Guterstam predicts that, for the immediate future, the invisibility cloaks of fiction will remain fictional. “Many fundamental challenges remain before we can cloak macroscopic objects," he told Fusion. "Genuine invisibility cloaking of an entire human body might therefore lie decades into the future, if science will ever achieve it.”
Frankly, decades sounds pretty close.
Danielle Wiener-Bronner is a news reporter.