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Monday, January 9, 2012

Temporal cloaking

Physicists from Cornell University have managed to create what they call a ‘temporal cloak’.  Their proof of concept demonstration shows that events can be made invisible to normal observation.  If you have a nefarious deed to hide that takes place in less than 50 picoseconds (trillionths of a second), this may be the system for you.

Briefly, the researchers took advantage of the fact that different frequencies of light (colors) move at different speeds.  The team, led by Alex Gaeta, shot a laser through a fiber optic cable.  That beam of light passed through a ‘split-time lens’, a device that increases the speed of the blue elements of the light beam and decreases the speed of the red elements.  As the light beam progressed through the cable, a gap opened up between the red and blue parts of the light. The beam then passed through a second split-time lens that reversed the effects of the first lens, stitching the light beam back together. Any event that occurred at the precise time and place of that light gap was undetectable.

Top: Experimental configuration for cloaking an event in time using two identical split time-lenses (STLs).
Bottom: The wavelength of the probe beam as a function of time.
(a)   before first STL
(b)  after the first STL;

(c)   temporal hole
(d)  before second STL
(e)   after the second STL.
When both STL's are in operation the event becomes invisible.
Used by permission.

By the way, the event you're attempting to conceal must not only occur within only a few trillionths of a second, but must be illuminated only by the beam of light you're using.  Not exactly a recipe for bank robbing.

For a much more detailed (and probably clearer) explanation, check out Skull in the Stars and a video made by Rose Eveleth.

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