The Earth is speeding up, and over the past 40 days, the atomic clocks that measure the Earth’s rotation cycle have recorded the shortest days on record since they began doing their job in the 1960s. Last July 26, the planet shaved 1.5 milliseconds off its daily journey of 86,400 seconds. Before that, June 28 was an even faster day: it ended the spin 1.59 milliseconds ahead. Two such marks express a trend: over the past two decades, fast rotations abound. However, if we zoom in, the trend is the opposite: rotations have been slowing down for millions of years, albeit at an inconsistent rate. In the remote and vaguely defined past, a day lasted a couple of hours less.

The deviation of 1.59 milliseconds remains so small that it does not challenge the conventionality of the day, nor does it express any significant cosmic disorder. Reality owes us nothing, it has no commitment to the idealizations we have constructed to represent it (hours, days, years…) and, for that reason, the Earth has always deviated minimally, by excess or defect, from the commitment of the right 24 hours. Just six years ago, this natural unpunctuality led the International Earth Rotation and Reference Systems Service (IERRS) to add a second ghost to June 25, 2005, the so-called leap second. That day lasted 86,401 seconds because that was the way to normalize an accumulated gap between our time and the rhythm of the planet, between astronomical time and atomic time. During the previous 45 years, the world gave itself 37 seconds like that; The stricter and better documented answer explains that the poles dance in 433-day cycles in irregular circles between three and 15 meters in diameter, according to a pattern called «Chandler’s wobble» and known since 1891. The reason for this oscillation, according to a 2000 study, is due to «fluctuating pressure on the ocean floor, caused by changes in temperature and salinity, and changes in the direction of ocean currents.»

There are other hypotheses that extend the certain knowledge of the Chandler wobble. First theory: the melting of glaciers is changing the distribution of mass over the Earth’s surface, shifting it from the poles towards the center, which conditions the fluctuation. Second theory: the inner core of the planet, its solid center, is displaced by the outer core of liquid substance and alters the rotation. And third theory: seismic movements affect the wobbling of the poles. In fact, the recent tendency to have short days has been linked to the 2004 Indian Ocean earthquake.

Atomic clocks were the breakthrough of the last century in time measurement. In short: instead of relying on a mechanical cycle, it is based on an atomic resonance frequency. In the internal rhythm of cesium, a chemical element that oscillates between two states (calm and excited) in a cycle that, through a treatment of cold and radiation, is perfectly predictable and gives the surest measure there is of what a second is.

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