Take some light bending metamaterials, incorporate them into flexible fabric and you have yourself an invisibility cloak. That's the theory anyway, and it doesn't stop at hiding objects. Building on the optical invisibility research of Professor Sir John Pendry, researchers from Imperial College, London, have now proposed that similar metamaterials could be used to conceal entire events – get ready for the "Spacetime Cloak".
According to Prof. Martin McCall, leader of the research project, it should be possible to use metamaterials to "open up" light by speeding up the leading half of the light waves while slowing down the trailing half. This would create a “corridor” between the two halves, at which point their source would not be observable – this is the point in spacetime at which energy, information or matter could be secretly moved or manipulated. The leading light waves would then be slowed back down to normal speed, while the trailing waves would be sped up, so they could catch up and seamlessly close the gap. To an observer’s eyes receiving those light waves, it would look like one continuous, uneventful scene.
The Imperial College team use the analogy of a pedestrian crossing a busy road. If the lead cars speed up and the trailing cars slow down, a gap opens between them which the pedestrian could run through. If the trailing cars then catch back up to the lead cars, all that someone watching the traffic head-on would observe is a steady stream of cars, with no pedestrian to be seen.
While it’s questionable whether we’ll be seeing spacetime cloaks anytime particularly soon, the technology could also be used in signal processing and computing. An optical data channel, for instance, could be interrupted so that a calculation could be performed for a parallel channel. That interruption would then be hidden, allowing for continuous processing.
“We're sure that there are many other possibilities opened up by our introduction of the concept of the spacetime cloak,” said McCall, “but as it's still theoretical at this stage we still need to work out the concrete details for our proposed applications.”
The research was published this week in Journal of Optics.