A team of physicists at Cornell University has created a wrinkle in time. Actually, it’s more like a teeny tiny moth hole in time. Inside it, things can occur that are entirely undetectable, at least to ordinary observers. It’s as if they never happened.
This phenomenon, known as “temporal cloaking,” is the latest addition to a world that once existed only in children’s literature and science fiction — a place where objects are invisible and events are unrecorded.
The physics community let out a small gasp six years ago when researchers reported the first successful “spatial cloaking,” in which light is bent around an object in a way that makes it disappear from view. The new report in the journal Nature shows how they can play with something that would seem to be even harder to manipulate: the perception of time.
“We think of time in the way that other people think of space. What other people are doing in space, we can do it in time,” said Moti Fridman, a researcher at the School of Applied and Engineering Physics at Cornell University .
Temporal cloaking, like spatial cloaking, is not magic. It follows all the ironclad laws of physics and is to some extent a parlor trick, albeit performed in a highly unusual parlor. Whether it will have a use isn’t known, as the hole in time created by the Cornell team lasts only 50 trillionths of a second.
Cloaking things, either in space or in time, requires the manipulation of light. Light carries information; it bounces off objects, defining their shape and sending those details to detectors such as our eyes. If an object can prevent light from doing that, it will become invisible.
But because light travels and has speed, it also defines when something happens. The lightening and darkening that occurs when a beam of light illuminates an event marks the event in time. If something can happen and yet leave the light unperturbed, which is the essence of temporal cloaking, then the event can become as invisible as a cloaked object.
Temporal cloaking depends on special lasers and optical fibers that disperse or undisperse light in predictable ways.
In their experiment, Fridman and his collaborators sent a laser beam of light down a fiber- optic cable. At the starting end, they pulsed the beam with a second laser that changed the light from a single wavelength to a range of wavelengths, essentially different colors.
The beam then entered a section of cable that had the property of carrying light of different wavelengths at different speeds, specifically blue light faster than red. As a consequence, the two colors separated until there was a space between them where there was no light at all. This blip of total darkness — 1 centimeter wide and lasting 50 picoseconds — is what the researchers called a “time gap” or “time hole.”
The beam was then reassembled by reversing the steps.
To show that an event occurring in the “time gap” was undetected, the researchers pulsed a ray of light through it. Normally, that would perturb the first beam in a way that was obvious when the light came out the far end of the cable. But when the ray went through the time gap and then the beam was reassembled successfully, the detector at the end of the cable perceived no change.
In the experiment , it appears an impossible event has transpired. But of course, that’s not the case. All that’s happened is that detection of an event through ordinary means has been made impossible.
“It is not enough time to steal a painting from a museum,” Fridman said, joking. He added that there might nevertheless be practical uses of the technology.
Such uses might include more efficient solar collectors and “super-resolution” of images.
