A team at Cornell University has succeeded in actually building a ‘temporal cloak’ which makes events invisible.
Last year, researchers at Imperial College London said they’d demonstrated the possibility of such a device – and now it’s been shown off for real.
The device is based on two so-called ‘time lenses’. While a normal lens focuses light in space through diffraction, a time lens focuses in time through dispersion. It essentially either speeds up or slows down light.
If two time lenses are placed in series, it’s possible to make the first compress the light in time, while the second decompresses it, or slows it down. The light emerges from the second lens undistorted, just as it went in to the first.
This creates a sort of hole in time, during which any event can’t be observed. The viewer sees a seamless shift from the point at which the light goes int the first lens and the point at which it emerges from the second. What happens in between is invisible.
The team demonstrated their device by modifying the spectrum of a probe beam between the two lenses. “We… show that the event is observed when the cloak is turned off but becomes undetectable when the cloak is turned on,” they say.
Unfortunately, the device can only hide very, very short events – just 110 nanoseconds. And the Cornell team says this can’t be improved to any longer than 120 microseconds.
It’s more likely to come in useful for physicists and other scientists than for budding Harry Potters.