Physicists set sights on `spacetime cloak`
Paris: Jewellery robbers, magicians, exam cheats and practical jokers everywhere will have an interest in an offbeat idea launched by physicists on Tuesday to make the passage of time invisible.
The scientists have conceived of a "spacetime cloak" which manipulates light and, in essence, conceals whole events from a viewer.
The theory is based on censoring the flow of events, which we perceive as a stream of light particles, also called photons, which strike the retina.
By exploiting a characteristic of fibre optics, the flow of photons can be slowed, events edited out and stitched back together, say the team from Imperial College London and Salford University, northwestern England.
"A safecracker would be able, for a brief time, to enter a scene, open the safe, remove its contents, close the door and exit the scene, whilst the record of a surveillance camera apparently showed that the safe door was closed all the time," according to their paper.
The theory is expounded in a daunting series of equations and diagrams in the Journal of Optics, published by the Institute of Physics.
It would work thanks to different light intensities that affect the refractory index in optical fibre, the cable widely used in telecoms today.
The refractory index is a determinant of the speed with which the light is transported in the cable.
In the example of the safe cracker, the "leading" segment (the image of the unmolested safe) would be slowed down.
The middle segment, of the robber opening the safe and making off with the contents would be edited out, disappearing into a "spatio-temporal void".
The final segment -- of the safe room apparently untouched -- would be accelerated so that it catches up with the leading segment and dovetails seamlessly with it.
"By manipulating the way the light illuminating an event reaches the viewer, it is possible to hide the passage of time," said Martin McCall, an Imperial College professor who headed the work.
"Not only can specific events be obscured, but it is possible for me to be watching you, and for you to suddenly disappear and reappear in a different location."
The paper appears in the Journal of Optics, published by Britain`s Institute of Physics.
The theory has yet to be tested or confirmed in a lab, but the authors are confident that this will not be too far ahead.
The physicists are keen to point out that their notion of "invisible events" differs from the fast advancing realm of "invisible materials".
These are so-called metamaterials, whose nano-metric surface interferes with light at specific wavelengths. As a result, light deviates around an object, making it invisible -- or, more accurately, invisible in specific colours of the light spectrum.
"It is unlike ordinary cloaking devices because it does not attempt to divert light around an object," said co-author Alberto Favaro.
"Instead, it pulls apart the light rays in time, as if opening a theatre curtain -- creating a temporary corridor through which energy, information and matter can be manipulated or transported undetected."
Beyond its sci-fi potential, the "spacetime cloak" could have benefits for quantum computing, which depends on the manipulation of light to transport huge amounts of data.
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