Punching a Hole in Time

Anyone who has ever watched Star Trek knows what a cloaking device is. In that case, an object–a star ship, for instance–could be cloaked from view. The idea of cloaking a period of time with an invisibility cloak is a concept engineers and physicists have been working on recently. Moti Fridman and Alexander Gaeta, Cornell University scientists, developed a rudimentary time cloak that creates a gap in laser beams. Anyone can create a similar gap by placing a hand over a flashlight beam. However, the scientists learned to stitch the light beam together again after a period of time, so whatever happens during the gap will not be seen in the beam and will not be detected, effectively punching a hole in time.

To create the gap, a device was used that has the ability to shift light frequencies. The scientists first shifted the light to a higher frequency, and then suddenly lowered it. The altered light frequency was then sent through an optical fiber that caused some light wavelengths to speed up and move faster than others. When some of the wavelengths raced ahead of others, a gap opened in the light beam. Then when the light passed the place where the hidden action occurred, they reversed the process, and the gap closed. An observer would see a continuous beam of light and not know that part of the action was blocked from sight.

According to physicist Martin McCall of Imperial College London, who was not involved in the study, the effect is similar to a chicken crossing the road. When it enters the roadway, traffic slows down to let it pass, and when the chicken gets to the other side, the cars that slowed speed up to close the gap between them and the cars ahead. Anyone watching from a distance would not see the chicken or the slowing of traffic. They would simply see cars passing in a continuous stream. The chicken was effectively “cloaked” from sight, similar to the cloaking action the scientists created in the gap in the light stream, caused by slowing and then speeding up the frequency of the light waves.

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