Invisibility cloak hides objects in a gap in time

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

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.

That, in one experiment, required 10,000 gold resonators that were attached to a piece of silk one centimeter square.

Try doing that on the kitchen table with a pair of tweezers and some Elmer's.

At Cornell the approach relied relied only on beams of light and the odd common behavior of light being refracted – bent as it passes through a medium like water, which is why a fish you see from the surface is never quite where it looks like it is if you try to poke it with a stick.

Light refracts not only in space, but in time as well, because the two are part of the same uber-thing according to Dr. Einstein.

Send a focused beam of light through a lens that modulates it optically (using the material in the lens) and with electromagnets and you can take a beam of light moving in a straight line, cause it to bend around an object, and return to its straight line as if nothing ever happened.

Except it doesn't bend just in space, as is would if it hit an angled mirror; it bends in time, then returns to its original course without having to bounce off anything first.

Bend light around all sides of an object and you create a spherical space that still exists in normal space and time, but you can't see it because all the light that should be hitting it is taking a detour though a part of the physical dimensions we normally can control only to the point that we can alter whether we're late to a meeting or not.

Researchers at Imperial College in London published a paper in February describing a similar experiment in invisibility using "A Spacetime Cloak, or a History Editor," the result is not only repeatable, it also has a brand name.

You'll probably be able to pick one up at your local Big Box store in a year or two, along with technology able to accomplish all the other magical things in Harry Potter, Lord of the Rings and all the other fantasy novels that apparently created a yen for magical powers in the kid brains of what are now top physicists.

I'm sure they'll keep on in that path until, in a decade air traffic will be complicated by dragon flights but you'll never miss an appointment because the airline will have a time portal for you to jog through on your way down to baggage claim (you'll have had to check the battle axes and armor; sorry, no one has invented a way to make the TSA invisible or unnecessary).

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