If we Earthlings are not alone in the Universe, why have we yet to detect signals from an extraterrestrial civilisation? Two physicists have come up with an intriguing solution to this lingering possible puzzle, suggesting a way in which aliens could send messages to each other across space that not only disguises their locations but also makes it impossible for a casual observer to even distinguish the messages from background noise, criss-crossing the Milky Way without our ever knowing.
At first glance, sending a message without giving away your location appears impossible. If a signal -- a stream of photons -- comes from a single source, its origin can always be determined by measuring the direction of recoil of a detector struck by the photons. But Walter Simmons and his colleague Sandip Pakvasa from the University of Hawaii at Manoa have come up with a cunning way around this.
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