Researchers at Purdue University may have created the first practical way to communicate with absolute secrecy by concealing messages in time using tricks of laser light and fiber optics.

The technique, called “temporal cloaking,” conceals not just the content of a message, but even the fact that it was sent, by tucking messages into a gap in the flow of photons sent by one of two lasers down a single strand of fiberoptic cable.

The effect is similar to putting a stick in a stream of water, creating a gap on the downstream side; water flows around the stick, closes the gap and eliminates any evidence it existed. Look closely enough, however, and it’s possible to see that the individual molecules of water that hit or detoured around the stick lag slightly behind those that didn’t, and now carry a few molecules of stick along with them.

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