Invisibility cloak hides objects in a gap in time

Researchers come up with invisibility cloak that's more Dr. Who than Harry Potter

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Just in time for the film finale of Harry Potter, whose best deus ex machina was a cloak that made him invisible, researchers at Cornell invented one that combines invisibility and time travel.

Well, not time travel – as in travelling through time into the past. The device actually creates a spot between two time lenses in which anything that happens is undetectable because the light that should be hitting it has taken a detour, through time, around it.

That's not the kind of time travel that will get you to the court at Camelot in time to become revered for predicting an eclipse, but it's not too shabby.

It's a much more elegant approach than the earliest "cloaks" that provided camouflage, not invisibility, by projecting on one side of the cloak the image of what was on the other side. To make a truck invisible, tiny cameras on one side take in the image of a truckless landscape and send the image to the other side, which displays it as a high-def movie of a truck not being in that spot.

A 2008 paper theorized the ability to do something similar without the cameras and movie screen by using materials that erase the effect on light of passing through a space or bouncing off an object.

Metaphorically that would mean catching the light, erasing the image and then sending it on its way without delaying it. Like live-action Photoshop at relativistic speeds.

More recently physicists specializing in the behavior of light have designed "metamaterials" that bend light around an object so it appears not to be there (no light bouncing off it means you can't see it, but you'd think there would be a dark spot where the invisible you was supposed to be).

Metamaterials are fabrics, metals or other materials designed (usually with something clever operating on a nano scale) to have properties normal materials don't. Like being able to bend light around themselves.

The problem with that approach, other than the tendency to be stolen by English boarding-school children with a penchant for trouble, is that they're difficult and expensive to build.

The metamaterials used have a lattice structure – like woven cloth – with gaps between the strands of material that are smaller than the wavelength of the light you're trying to bend.

That's ridiculously small, but not enough to give the material the ability to bend light in a controlled way.

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Source: Cornell Univ

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