An experimental device has been unveiled in a paper in the journal Nature that promises to be able to keep accurate time for the next 5 billion years. 

"We demonstrate a many-atom system that achieves an accuracy of 6.4×10−18," the authors write, noting that "more stable and accurate atomic clocks will benefit a wide range of fields, such as the realization and distribution of SI units, the search for time variation of fundamental constants, clock-based geodesy and other precision tests of the fundamental laws of nature."

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