January 5, 2012
Scientists Make Time Disappear
Physicists working with the support from the US government said on Wednesday they had devised a “time cloak” that can make time disappear, albeit briefly.
The device manipulates the flow of light in such a way that an event cannot be seen for about 40 trillionths of a second -- or 40 picoseconds -- by speeding up and slowing down different parts of a light beam.
The research, published in the journal Nature, adds to experiments in creating next-generation camouflage that restricts the human eye from perceiving specific colors.
“Our results represent a significant step towards obtaining a complete spatio-temporal cloaking device,” said the study, led by Moti Fridman of Cornell University in New York.
The breakthrough exploits the fact that frequencies of light move at fractionally different speeds. The time cloak starts by using a beam of green light passed down a fiber-optic cable. The beam then travels through a two-way lens that splits it into two frequencies -- a bluish light which travels relatively fast, and a reddish light, which travels slower. The small difference in speed is then emphasized by placing a transparent obstacle in front of the two beams. This obstacle creates a time gap between the blue and red beams as they travel through the optical fiber.
But this time gap 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 reconnects the two lights into a single green light.
The key is that the 40 picosecond burst of laser is not part of the flow of photons, and thus cannot be detected. And since the technology only works on periods of time so minute, lawmen should not worry much, since evildoers would have to move far faster than human beings ever could to ℠conceal´ their actions.
Instead, the hidden fractions of time could be used for ultra-secure communications. The technique could also be combined with recent advances in optical cloaking in order to hide an event in both space and time.
Professor Robert Boyd and Dr Zhimin Shi, of Rochester University in New York, reviewed the paper for the journal. “As if the idea of a device that makes an object seem invisible was not mind-boggling enough, researchers have now demonstrated a system that can conceal an event in time,” they told Daily Mail Online reporter Rob Waugh.
“Because spatial and temporal cloaking work in different physical dimensions - space and time, respectively - there is no fundamental reason why the two techniques cannot be combined so that full spatial-temporal cloaking could be turned on or off at will,” he said.
For example: say you are watching surveillance cameras at a bank when a burglar enters and steals the contents of the bank vault. You do not see him enter the bank, open the vault or steal the money, yet he does in fact do this. It isn´t just that the thief is invisible -- the whole event is. It would appear as that area of time had been erased from history, the Cornell researchers said.
“You kind of create a hole in time where an event takes place,” said study co-author Alexander Gaeta, director of Cornell´s School of Applied and Engineering Physics. “You just don´t know that anything ever happened.”
This is the first time that scientists have been able to mask an event in time, a concept first theorized by Martin McCall, a professor of theoretical optics at Imperial College in London. The Cornell team, who had been working on time lenses, decided to see if they could make McCall´s vision a reality.
Surprisingly, it only took them a few months, a blink of an eye in scientific research time.
“It is significant because it opens up a whole new realm to ideas involving invisibility,” McCall told the Associated Press (AP).
Scientists can already cloak objects by bending light, but until now, cloaking time has been science fiction. And between the two approaches, the idea of full invisibility will work its way into useful technology, McCall predicted.
The science, although legitimate, only works on a fraction of a second, added City College of New York physicist Michio Kaku, who specializes in the physics of science fiction.
“That´s not enough time to wander around Hogwarts,” Kaku told AP in an email. “The next step therefore will be to increase this time interval, perhaps to a millionth of a second. So we see that there´s a long way to go before we have true invisibility as seen in science fiction.”
Gaeta believes he can make the cloak last a millionth or even a thousandth of a second. But McCall said the mathematics dictate that it would take too big a machine -- one 18,600 miles long -- to make a cloak last a full second.
“You have to start somewhere and this is a proof of concept,” said Gaeta.
The researchers said there are numerous possible applications for this research. There may be good uses of this technology, but “for some reason people are more interested in the more illicit applications,” added Gaeta.
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