The leap second, added to the world’s clocks 27 times since 1972 to keep atomic time in step with the Earth’s rotation, is very likely never to be added again. Representatives of the International Bureau of Weights and Measures (BIPM) are considering abolishing it permanently at a meeting in Versailles that ends on Thursday, ABC reported.
If the proposal is approved, the leap second could be replaced by a “leap hour”, which people might need to add many centuries from now.
Why clocks need correcting
A second has traditionally been defined as 1/86,400 of a day. However, the Earth does not spin at a perfectly steady rate, and the length of a day can vary by about a millisecond.
Over the long term, the Earth’s rotation is slowing, mainly because of the Moon’s gravitational pull. Over shorter periods, however, it can speed up, and it has been doing so since 2020.
The speed of rotation is affected by the atmosphere, winds, ocean currents, melting glaciers, volcanic eruptions and the movement of mass inside the Earth, according to Lucia McCallum, a geodesist at the University of Tasmania. These tiny variations matter for technologies such as GPS, which rely on extremely precise time measurements.
In the late 1960s, a more precise definition of the second was adopted, based on the properties of caesium atoms. It underpins Coordinated Universal Time (UTC), which is measured by atomic clocks. Leap seconds were introduced in 1972 to keep UTC in line with the Earth’s actual rotation. The most recent was added on 31 December 2016.
A problem for computers
Adding a second is almost unnoticeable in daily life, but it can cause serious problems for computer systems.
Many programs assume that time only ever moves forward and that every minute has exactly 60 seconds, said Darryl Veitch, a researcher at the University of Technology Sydney. Leap seconds break those assumptions, causing malfunctions and service outages. Platforms such as Reddit and Cloudflare have been affected in the past.
Unlike the clocks going forward or back, leap seconds do not follow a fixed schedule and are announced only six months in advance. In 2022, a decision was taken to scrap them by 2035.
The recent speeding up of the Earth’s rotation, however, has raised the possibility that a “negative leap second” will be needed, removing a second rather than adding one. This has never happened, so nobody knows how computer systems would react. That risk has sped up the move to abolish leap seconds.
A leap hour centuries away
The leading proposal would allow UTC to drift gradually away from the Earth’s rotation until the gap reaches one hour. A single large correction, a “leap hour”, could then be made.
As the gap currently grows by less than a second a year, it could take more than a thousand years before such a correction is needed. By then, timekeeping technology is likely to have changed radically.
(information from cnn.gr)
