A spacetime cloak, or a history editor

We introduce a new type of electromagnetic cloak, the spacetime cloak (STC), which concealsevents rather than objects. Non-emitting events occurring during a restricted period are neversuspected by a distant observer. The cloak works by locally manipulating the speed of light ofan initially uniform light distribution, whilst the light rays themselves always follow straightpaths. Any ‘perfect’ spacetime cloak would necessarily rely upon the technology ofelectromagnetic metamaterials, which has already been shown to be capable of deforming lightin ways hitherto unforeseen—to produce, for example, an electromagnetic object cloak.Nevertheless, we show how it is possible to use intensity-dependent refractive indices toconstruct an approximate STC, an implementation that would enable the distinct signature ofsuccessful event cloaking to be observed. Potential demonstrations include systems thatapparently violate quantum statistics, ‘interrupt-without-interrupt’ computation on convergentdata channels and the illusion of a Star Trek transporter