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Saturday, April 19, 2014

Pentagon Use ‘Time Hole’ to Mask Events

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Soldiers could one day conduct covert operations in complete secrecy, now that Pentagon-backed physicists have figured out how to mask entire events by distorting light.

A team at Cornell University, with support from Darpa, the Pentagon’s out-there research arm, managed to hide an event for 40 picoseconds (those are trillionths of seconds, if you’re counting). They’ve published their groundbreaking research in this week’s edition of the journal Nature.

This is the first time that scientists have succeeded in masking an event, though research teams have in recent years made remarkable strides in cloaking objects. Researchers at the University of Texas, Dallas, last year harnessed the mirage effect to make objects vanish. And in 2010, physicists at the University of St. Andrews made leaps towards using metamaterials to trick human eyes into not seeing what was right in front of them.

Masking an object entails bending light around that object. If the light doesn’t actually hit an object, then that object won’t be visible to the human eye.

Where events are concerned, concealment relies on changing the speed of light. Light that’s emitted from actions, as they happen, is what allows us to see those actions happen. Usually, that light comes in a constant flow. What Cornell researchers did, in simple terms, is tweak that ongoing flow of light — just for a mere iota of time — so that an event could transpire without being observable.

The entire experiment occurred inside a fiber optics cable. Researchers passed a beam of green light down the cable, and had it move through a lens that split the light into two frequencies, one moving slowly and the other faster. As that was happening, they shot a red laser through the beams. Since the laser “shooting” occurred during a teeny, tiny time gap, it was imperceptible.

Sure, the team’s got a ways to go before they’re able to mask 30 seconds of action, let alone several minutes. But the research certainly opens up new possibilities. For one, masking super-quick events, like those that occur with data transmission, could help conceal covert computer operations.

In the words of Nature editors, the research marks “a significant step towards full spatio-temporal cloaking.” But it could be decades before military personnel will basically be able to zap history, as it happens: According to Cornell scientists, it’d take a machine 18,600 miles long to produce a time mask that lasts a single second.

Source: Wired


The laboratory device manipulates the flow of light in such a way that for the merest fraction of a second an event cannot be seen, according to a paper published in the science journal Nature.

It adds to experimental work in creating next-generation camouflage -- a so-called invisibility cloak in which specific colours cannot be perceived by the human eye.

"Our results represent a significant step towards obtaining a complete spatio-temporal cloaking device," says the study, headed by Moti Fridman of Cornell University in New York.

The breakthrough exploits the fact that frequencies of light move at fractionally different speeds.

The so-called temporal cloak starts with a beam of green light that is passed down a fibre-optic cable.

The beam goes through a two-way lens that splits it into two frequencies -- blueish light which travels relatively fast, and reddish light, which is slower.



The tiny difference in speed is then accentuated by placing a transparent obstacle in front of the two beams.

Eventually a time gap opens up between the red and blue beams as they travel through the optical fibre.

The gap is tiny -- just 50 picoseconds, or 50 millionths of a millionth of a second.

But it is just long enough to squeeze in a pulse of laser at a different frequency from the light passing through the system.

The red and blue light are then given the reverse treatment.

They go through another obstacle, which this time speeds up the red and slows down the blue, and come to a reverse lens that reconstitutes them as a single green light.

But the 40-picosecond burst of laser is not part of the flow of photons, and thus cannot be detected.

In a commentary, optical engineers Robert Boyd and Zhimin Shi of New York's University of Rochester, likened the experiment to a level crossing on a busy road.

When a train comes, the cars are stopped, and this causes a gap in the traffic.

When the train has passed, the stopped cars speed up until they catch up with the traffic in front of them. To the observer, the flow seems quite normal, and there is no evidence that a train has crossed the intersection.

After proving that the "cloak" is possible, the next step for the researchers is to expand the time gap by orders of magnitude, firstly to microseconds and then to milliseconds, said Boyd and Shi.

The time cloak has a potential use in boosting security in fibre-optic communications because it breaks up optical signals, lets them travel at different speeds and then reassembles them, which makes data hard to intercept.

Last year, scientists reported a step forward in so-called metamaterials which act as a cloaking of space, as opposed to time.

Metamaterials are novel compounds whose surface that interacts with light at specific frequencies thanks to a tiny, nano-level structure. As a result, light flows around the object -- rather like water that bends around a rock in a stream -- as opposed to being absorbed by it.

Fridman's work was part-supported by the Defense Advanced Research Project Agency, or DARPA, a Pentagon unit which develops futuristic technology that can have a military use. Its achievements include DARPANet, a predecessor of the Internet. - spacedaily

 
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