Earth’s Rotation Speed Has Increased Over the Past 50 Years

Compensating for the lost time may prove challenging for scientists.

Ever experience the sensation that time is slipping away faster? It’s not just a feeling. Earth is currently rotating at a pace quicker than it has in the past fifty years, leading to a minor reduction in the length of our days. Although the difference is infinitesimally small, it has posed challenges for physicists, computer programmers, and even stockbrokers.

Why Earth Rotates

Approximately 4.5 billion years ago, our solar system took shape when a dense cloud of interstellar dust and gas underwent gravitational collapse, initiating a spinning motion. The remnants of this initial movement persist in Earth’s current rotation, sustained by angular momentum—a property defined as “the tendency of the body that’s rotating to carry on rotating until something actively tries to stop it,” as elucidated by Peter Whibberley, a senior research scientist at the UK’s National Physical Laboratory.

This enduring angular momentum has kept our planet spinning for billions of years, governing the occurrence of night and day. However, the rate of Earth’s rotation has not remained constant throughout its history. Hundreds of millions of years in the past, Earth completed approximately 420 rotations during one orbit around the Sun, a phenomenon evidenced by the growth lines on fossil corals, which reflect the presence of additional days in each year. While the duration of days has gradually extended over time, influenced in part by the gravitational effects of the moon on Earth’s oceans, humanity has witnessed a relatively consistent 24-hour rotation during our observational span—equivalent to about 365 rotations per orbit around the Sun.

Nevertheless, as scientific advancements have allowed for more accurate monitoring of Earth’s rotation and timekeeping, researchers have discerned subtle fluctuations in the duration of a complete rotation.

A New Way to Track Time

In the 1950s, scientists pioneered atomic clocks that gauged time based on the descent of electrons in cesium atoms from a high-energy, excited state to their normal states. The unswerving periodicity of atomic clocks, rooted in this consistent atomic behavior, shields them from disruptions caused by external factors such as temperature variations, setting them apart from traditional clocks.

However, over time, an issue surfaced: the unwaveringly precise atomic clocks exhibited a slight deviation from the universal time standard. Judah Levine, a physicist at the National Institute of Standards and Technology’s time and frequency division, explains that as time progresses, a gradual disparity emerges between the readings of atomic clocks and time as determined by astronomical observations, including the position of Earth, the moon, and stars. Essentially, a year measured by atomic clocks proved to be marginally faster than the same year calculated based on Earth’s celestial movements.

To mitigate this growing discrepancy, a decision was made in 1972 to periodically introduce leap seconds to atomic clocks. Leap seconds function analogously to leap days added to February every four years to compensate for the fact that Earth’s orbit around the Sun takes roughly 365.25 days. Unlike leap years, which occur regularly every four years, leap seconds are unpredictable.

The International Earth Rotation and Reference Systems Service monitors Earth’s rotational speed using laser beams directed at satellites, among other methods. When the time derived from Earth’s rotation approaches a one-second misalignment with atomic clock time, scientists worldwide synchronize to pause atomic clocks for precisely one second at 11:59:59 pm on either June 30 or December 31. This pause allows astronomical clocks to catch up, effectively introducing a leap second.

Unexpected Change

Since the introduction of the first leap second in 1972, scientists have periodically inserted leap seconds into our timekeeping system. The irregularity of these additions stems from the unpredictable nature of Earth’s rotation, characterized by intermittent fluctuations in speed that disrupt the planet’s ongoing, millions-of-years-long deceleration.

“The rotation rate of Earth is a complex phenomenon, involving the exchange of angular momentum between Earth and the atmosphere, as well as the influences of the ocean and the moon,” explains Levine. “Predicting future events in this regard is challenging.”

However, in the past decade, Earth’s gradual slowdown has experienced a deceleration of its own. Notably, no leap second has been added since 2016, and currently, our planet is rotating at a pace faster than it has in the last fifty years. The reason behind this unexpected trend remains unclear.

“This absence of the need for leap seconds was not anticipated,” notes Levine. “The prevailing assumption was that Earth would continue its deceleration, necessitating ongoing adjustments with leap seconds. Therefore, this outcome is quite surprising.”

The Trouble With Leap Seconds

Depending on the extent and duration of Earth’s acceleration in rotation, scientists may need to take corrective measures. “There is currently a concern that if Earth’s rotation rate continues to increase, we might need to implement what’s called a negative leap second,” explains Whibberley. Essentially, instead of adding an extra second to allow Earth to align, a second would be subtracted from the atomic timescale to synchronize it with Earth.

However, introducing a negative leap second would pose a novel set of challenges. “There has never been a negative leap second before, and the concern is that the software required to handle this situation has never been operationally tested,” adds Whibberley.

Whether it involves a regular leap second or a negative one, these minor adjustments can create significant complications for various industries, spanning from telecommunications to navigation systems. The interference caused by leap seconds disrupts the continuous flow of time, crucial for the functioning of computer systems. For instance, the foundational principle of the internet relies on the continuity of time, and any disruption can lead to system breakdowns. Leap seconds also pose challenges for the financial sector, where each transaction requires a unique timestamp, potentially causing issues when the 23:59:59 second repeats itself.

Some companies have devised their own solutions to address leap seconds, such as the “Google smear.” Instead of halting the clock to synchronize Earth with atomic time, Google slightly extends each second on a leap second day. However, this approach does not align with the international standard for time definition, as highlighted by Levine.

Time As a Tool

In the larger context, however, we’re dealing with exceedingly small increments of time—just one second introduced every few years. You may have experienced numerous leap seconds without even being aware of them. When considering time as a tool to measure natural transitions, like the shift from one day to the next, an argument can be made for adhering to the time determined by Earth’s movement, as opposed to the precision of atomic clocks.

Levine suggests that leap seconds might not be worth the challenges they pose: “My personal opinion is that the remedy might be more troublesome than the issue itself.” If we were to cease adjusting our clocks for leap seconds, it could take a century to deviate even a minute from the “true” time recorded by atomic clocks.

However, he acknowledges that while time is a human construct—an attempt to comprehend our experiences in a vast, enigmatic universe—there is also a connection to astronomical time. “It’s true that at 12 o’clock noon, the Sun is overhead. So, although we may not often reflect on it, we do maintain a link to astronomical time. Leap seconds serve as a minuscule, nearly imperceptible means of preserving that connection.”

This article is republished from DiscoverMagazine under a Creative Commons license. Read the original article.

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