Researchers around Martin McCall, Imperial College London, UK, introduce a type of electromagnetic cloak, the spacetime cloak (STC), which conceals events rather than objects. Non-emitting events occurring during a restricted period are never suspected by a distant observer.

The cloak works by locally manipulating the speed of light of an initially uniform light distribution, whilst the light rays themselves always follow straight paths: Illuminating light is divided into a leading part which is sped up and passes before an event, and a trailing part which is slowed down and passes after. Light is then stitched back together seamlessly, so as to leave observers in ignorance.

It is unlike ordinary cloaking devices because it does not attempt to divert light around an object. Instead it pulls apart the light rays in time, as if opening a theatre curtain – creating a temporary corridor through which energy, information, and matter can be manipulated or transported undetected.

Besides the science-fiction capabilities of the event cloak, signal-processing applications will play a key role in driving research forward on this topic.

• A spacetime cloak, or a history editor,
  Martin W McCall, Alberto Favaro, Paul Kinsler, Allan Boardman,
  J. Opt. 2010.
  DOI: 10.1088/2040-8978/13/2/024003