Resumen de Networked atomic clocks seek untimely behaviour
Pacome Delva of the Paris Observatory and his colleagues have used strontium clocks to test time dilation. Two optical fibre links, one between London and Paris and another between Paris and Braunschweig, Germany, were used to compare devices in these locations. These clocks are moving at different velocities because of their position on the Earth's surface, and relativity makes precise predictions about the extent of time dilation they experience. To compare them, the team synchronized lasers to the frequency of the radiation from each clock's strontium atoms. Then they transmitted the beams over the fibre-optic links, allowing them to superimpose the lasers to detect any telltale differences in frequency indicating one clock ticking faster than the other. With the measurements, the team calculated a parameter called alpha, which should be zero if there is no violation of Lorentz invariance. The latest results show that alpha is less than 10^sup -8^--a result two orders of magnitude better than from experiments using cesium clocks, and twice as accurate as the previous best limit, obtained by studying electronic transitions in lithium ions moving at one-third the speed of light.
