On Wednesday, March 27, a paper by the geophysicist appears in the prestigious scientific journal “Nature”. Duncan Agnew (Duncan Agnew) from the University of California with the somewhat strange title: “Melting ice solves leap-second problem – for now”, immediately making the rounds of the world. With dozens of reports and analyzes on the Internet. But which ice melts? What is this naughty second causing trouble? And do we control it or can it get away?
It takes some patience to understand what happens to time that drags us along while we unconsciously swim in it. Here on Earth we already had, since the last century, at least two different ways of measuring the exact length of 24 hours and by extension the basic unit of time, i.e. the second.
24 hours is the time that elapses between two successive passages of the sun from the highest point in the sky of a place. The second came out as (1/86400) of that time (since 1 day = 24 hours x 60 minutes x 60 seconds = 86,400 seconds). But this was approximate because the duration of 24 hours had and still has some fluctuations.
In 1967, however, with the advent of individual watches, the word “approach” disappeared. They operated using an isotope of the element cesium with 1 second being the (very accurate) time required to emit 9,192,631,770 wavelengths of electromagnetic radiation. Radiation emitted when an electron transitions from an energy band of this element to a very, very neighboring one. Obviously the above was chosen so that we still have 86,400 seconds in 24 hours.
The erratic behavior of the Earth
So perfect invention this “second”, technologically advanced. But our planet, during its rotation, turned out not to be the perfect timekeeper. There were three reasons for this:
- The friction of the water with the seabed has a slowing effect on the rotation speed of the planet (tidal dissipation).
- The melting of ice has contributed to the transformation of the Earth’s volume. As the poles are freed from the weight of the ice, the lands there rise, while at the equator the movement of large amounts of water has helped the planet acquire a more spherical shape with the end result of decreasing the rotation speed.
- The liquid metallic core of the Earth showed a deceleration in its rotation, and since this is an internal motion in the Earth’s sphere, it must be compensated by the motion of its outer material, in the mantle and the crust, with exactly the opposite behavior, and therefore with increasing rotation speed.
From earlier, for the universally accepted rotation time and the duration of one second by extension, it was decided to make the following compromise. To have the so-called Coordinated Universal Time (UTC) in which the unit of time will be determined based on two components.
One will come from the seconds as derived as an average of the values from the 450 certified individual watches of 80 laboratories scattered around the world. But as a second ingredient “something” will be added (sometimes removed) (on the last day of June or December preferably).
This “something” will be time based on the changing period of rotation of the Earth which results in the duration of each second being a quantity subject to changes in rotation time due to the causes described before. That’s what he needed every now and then to the fixed units of time resulting from the atomic clocks some leap seconds were added since the rotation of the Earth was constantly slowing down.
Just as one day is added to February every four years. The first such vaccine second was added in 1972 and for the first ten years it was added almost every year by a. Since 2016, however, not even 1 has been added, because overall the time for a complete rotation of the Earth is decreasing and we are approaching the moment when, for the first time, 1 full second must be subtracted from the “inelastic time” resulting from the atomic watches.
And some fear that not all machines are ready for such a thing. GPS, Linux, for example, may be in a first approach to the affected. Meta is already pissed off and making their own patents.
What has emerged from the work in Nature is how the speed-up in Earth’s rotation due to the counter-behaving “liquid core-solid shell” twin is contrasted with the slowdown caused by the melting of the ice caps at the end of the 20th century. So the forced subtraction of a second is pushed back with relief to 2029. Without it making us proud of what we accomplished by melting the ice.
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