Fiber-optic cable - the result of long years of French and German scientists - tied clock located in Paris (France) and Braunschweig (Germany). With this connection, you can compare the frequency of electromagnetic waves, which is taken into account when adjusting the clock. A report on this work was published in the journal Nature Communications.
Over the past few years, optical atomic clocks have been noticeably improved: they have become a hundred times more accurately, even in comparison with the best cesium clocks. However, this precision is lost in the propagation of the signal due to imperfect means of communication.
Now for two accurate clocks in different cities in Europe, this problem is resolved. The two halves of the cable whose total length is greater than 1400 km, there are about half way - in the IT-center of the University of Strasbourg, where he compares the signals of both devices.
Monitoring the hours with such precision opens new opportunities for astrophysics, geodesy and metrology, as well as allows for a wide range of very sensitive physics experiments, to which applies, for example, the search for changes in the time-dependent constants.