Scientists Say We'll Never Have a Real-Life Invisibility Cloak

Wednesday, 06 July 2016 - 12:26PM
Wednesday, 06 July 2016 - 12:26PM
Scientists Say We'll Never Have a Real-Life Invisibility Cloak
Sadly for Harry Potter fans, it looks like J.K. Rowling lied to us. Researchers have investigated the physical limitations of so-called "invisibility cloaks," and based on current technologies, it will be virtually impossible to create one for humans in real life.

Real-life "invisibility cloak" technology has recently involved metamaterials, special substances which are capable of "bending" light away from them so they appear invisible to the naked eye. But while the researchers confirmed that metamaterials are capable of perfectly cloaking smaller objects from specific wavelengths of light, they found that it becomes more difficult to cloak objects across multiple wavelengths, especially as the objects get larger.
Opening quote
"The question is, 'Can we make a passive cloak that makes human-scale objects invisible?'" lead researcher Andrea Alù said in a statement. "It turns out that there are stringent constraints in coating an object with a passive material and making it look as if the object were not there, for an arbitrary incoming wave and observation point."
Closing quote

For the new study, published in the journal Optica, the team of researchers created a mathematical framework in which the capabilities of hypothetical cloaking devices can be tested on different-sized objects before they're even built. They found that the capabilities of a passive cloak, meaning a cloak made from metamaterials that don't draw power from an external energy source, are largely based on the size of the object. And further, it's much easier for metamaterials to hide objects from longer wavelengths, such as radio waves, but shorter wavelengths, such as visible light, are much more difficult for larger objects. 

Opening quote
"We have shown that it will not be possible to drastically suppress the light scattering of a tank or an airplane for visible frequencies with currently available techniques based on passive materials," Monticone said. "But for objects comparable in size to the wavelength that excites them (a typical radio-wave antenna, for example, or the tip of some optical microscopy tools), the derived bounds show that you can do something useful, the restrictions become looser, and we can quantify them."
Closing quote

But that being said, these conclusions are based on very specific technologies that already exist, so there's no telling whether we'll find another method for cloaking humans from visible light. Furthermore, even based on the technologies we have, active metamaterials may be more promising. The researchers propose that the next step is exploring options involving external power sources, for which these limits wouldn't apply. We could also adjust our definition of "invisibility," and rather than cloaking objects by scattering the light, we could create a material that delays the light as it's transmitted, giving an optical illusion of transparency.

Opening quote
"Even with active cloaks, Einstein's theory of relativity fundamentally limits the ultimate performance for invisibility," Alù said. "Yet, with new concepts and designs, such as active and nonlinear metamaterials, it is possible to move forward in the quest for transparency and invisibility."
Closing quote
Science
NASA

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