A team of researchers has moved invisibility cloaks into the real-life classroom.
Real-life invisibility cloaks do exist, in a manner of speaking: researchers have engineered systems that bend light around an object, shielding it from detection. But most are very tiny and only work at very small wavelength ranges, rendering them less impressive to the average observer.
Researchers from the Karlsruhe Institute of Technology (KIT), in Karlsruhe, Germany, has developed a portable invisibility cloak that can be taken into classrooms and used for demonstrations. It can't hide a human, but it can make small objects disappear from sight without specialized equipment.
Scientists hoping to divert light around an object to render it invisible must find a way to compensate for the increased distance the light must now travel. On a road trip, you might solve this problem by changing your speed. The greater distance is offset by the higher speed limit.
Unfortunately, light is a bit more challenging than a station wagon and because relativity prevents mass from traveling faster than the vacuum speed of light, there's no way to further speed up the detoured light in a vacuum or in air.
To address this challenge, the KIT team constructed their cloak from a light-scattering material. By scattering light, the material slows down the effective propagation speed of the light waves through the medium. Then the light can be sped up again to make up for the longer path length around the hidden object.
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Lead researcher Robert Schittny said that the cloak takes advantage of the much lower effective propagation speed in light-scattering media, adding they seemingly slow down the light everywhere, speeding it up again in the cloak to make up for the longer path around the core is not a problem.
If the average time it takes light to travel through the polydimethylsiloxane block is in just the right proportion to the average time it takes to travel through the cloak, the core will become invisible.
Schittny noted that it is a macroscopic cloak that you can look at with your bare eyes and hold in your hands and with a reasonably strong flashlight in a not too bright room, it is very easy to demonstrate the cloaking.