In theory, the Earth needs 86,400 seconds for a day, which corresponds to exactly 24 hours. But the planet does not always move at the same speed. In recent decades, the Earth usually needed one to three milliseconds longer, but since 2020 at the latest it has been traveling faster than 24 hours.
That is “somewhat surprising,” says geophysicist Roland Pail from the Technical University of Munich. Because actually all signs point to a slowdown. Both the moon and climate change would slow down the Earth rather than drive it forward, which is why Pail assumes a short-term phenomenon.
Handbrake and pirouette figure
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Because: “The moon acts like a handbrake on the earth,” says Pail. The mutual attraction of the two masses leads to a gradual slowing down of the earth. Data from coral reefs and sediments show that 500 to 600 million years ago a day was 21 hours long. The earth was spinning around its own axis much faster. Since then, the “lunar handbrake” has slowly slowed down the Earth’s spin, explains Pail.
The experts would also have expected that climate change would further slow down the earth. Because when the polar ice melts, large masses of water shift from the poles to the equator. When a figure skater extends her arms in a pirouette, she slows down, Pail explains. This is what one would have expected for Earth.
The Earth’s mantle and core dance out of sync
But she doesn’t seem to want to stick to theories and predictions. Instead of slowing down, it has become faster in recent years, as measurements from the Vienna University of Technology show, among other things. “My guess would be that processes occurring in the Earth’s interior actually have this opposite effect,” says Pail.
He thinks that the Earth’s mantle and core are not currently rotating at the same speed. The phenomenon is basically known, but can hardly be investigated or modeled. “What the long-term behavior will be is absolutely unknown,” says Pail.
Hundredth of a blink of an eye
This has imperceptible effects on us humans. “We’re talking about a hundredth of a blink of an eye, which in itself has no significance for everyday life,” says Pail. Fluctuations in the rotation speed in one direction or the other have also occurred again and again throughout Earth’s history.
However, the precise atomic clocks, which are used, among other things, to determine the global standard time, do detect the shorter days. Because days in the past were typically longer than 86,400 seconds, leap seconds had been added to time at regular intervals since the 1970s. Similar to February 29th in the calendar, the leap second synchronized artificial time with natural time. The last time the leap second was needed was at the turn of the year 2016 to 2017.
Computer crash feared
For the first time since the introduction of the leap second, there is now a discussion about a negative leap second, says Pail. But giving a system a second is one thing, stealing a second is something completely different, says the expert: “Nobody is prepared for that.”
The concern is particularly about computer systems that may not be able to handle negative time calculations. For Pail, the fears are justified: “No one can foresee how big the consequences would be,” he says, and the consequences of a divergence in time calculation in the millisecond range are less dramatic than a possible computer crash caused by a negative leap second.