Physicists have for the first time recorded periodic changes in the flow of time on Earth under the influence of the Moon and the Sun

Time on Earth flows unevenly — and this is now measurable

The Moon and the Sun affect not only ocean tides: their gravity causes extremely small fluctuations in Earth's gravitational potential, which make time flow at slightly different rates in different places on the planet. An international group of physicists has, for the first time, recorded these periodic changes using a network of optical clocks, the publication reported Kun.uz citing a description of the experiment, published on arXiv.

How the experiment was conducted

The group included scientists from Europe's leading metrology centers: the Physikalisch-Technische Bundesanstalt (Germany), the National Physical Laboratory (United Kingdom), the LNE-Laboratoire National de Métrologie et d'Essais laser laboratory (France), and the National Metrology Research Institute (Italy). Their devices were connected by roughly 800 kilometers of dedicated fiber-optic communication lines; both stationary laboratory optical clocks based on strontium and ytterbium atoms and innovative mobile clocks were used.

What exactly is new

The fundamental difference from previous experiments lies in the nature of the measurements. Earlier experiments with optical clocks targeted static, time-invariant differences in gravity between points. Now, periodic changes in these indicators have been recorded for the first time. The gravitational pull of the Moon and the Sun creates potential fluctuations equivalent to a change in an object's height of 10 centimeters for two stations separated by about 800 kilometers. The new European network makes it possible to detect such fluctuations in measurements lasting less than a day, and the results obtained agree well with theoretical calculations.

Practical implications

Such high precision of optical clocks imposes new requirements on time measurement: when comparing readings from remote instruments, scientists must now take into account how periodic changes in the gravitational potential caused by the Moon and the Sun affect the relative rate of the clocks. Without the appropriate corrections, as Kun.uz notes, the results of ultra-precise experiments, tests of fundamental physical theories, and the construction of unified time scales could be distorted. In addition, the combined network of clocks could become a tool for studying the planet itself: such sensitive systems make it possible to track in real time the redistribution of water and ice masses, changes in groundwater levels, tectonic shifts, and volcanic activation.