We all know that if the time goes to 23:59:59 every day, the next second is 00:00:00 the next day. But from 1972 to the present, in 49 years, there are 27 days, and when the time reaches 23:59:59, the next second is 23:59:60, and then the next day 00:00:00.
Interestingly, late at night on June 30, 2012, many websites around the world, including LinkedIn, suddenly crashed, with slow or even direct unopenable web pages. As for the reason, it was later investigated that the next second at 23:59:59 on June 30, 2012 was 23:59:60, and the next second was 00:00:00 on July 1, 2012. Because this extra second directly causes many websites to overload the servers.
So the question is, why do you have 27 days to add this "second"? What's the point of doing that?
It starts with how we time it. During the Spring and Autumn Period and the Warring States Period in China, there was a scholar called Corpse In the Hundred Sons of Zhuzi, who was called Corpse Zi by the Jianghu people, and his representative work was "Corpse Zi", which recorded a very profound sentence in this classic, which is the definition of the universe:
The four directions are known as the universe, and the ancient and the present are known as the universe.
The meaning of this sentence is that the "universe" of the universe represents space, the "universe" of the universe represents time, and the universe is the collection of time and space.
This definition is very close to the definition of the universe in cosmology today. And the ancients came to such a conclusion with a basis. This is based on the fact that their judgment of time comes from the celestial signs.
For example, a year is the time it takes for the sun to circle once in the celestial sphere, and a month is the time it takes for the moon to circle in the celestial sphere. And a day and night is a day.
Later people also basically inherited the views of the ancients. However, due to the development of science, our understanding of celestial phenomena is deeper than that of the ancients. We know that it is one year for the Earth to circle the Sun, one month for the Moon to circle the Earth, and one day for the Earth to rotate.
The reason why we still base our rotation on the Earth is because the Earth is massive enough and stable enough to measure "the time of day" as a "clock", and the time of day is 24 hours, which is also known as: universal time. Because a day is 24 hours, 86400 seconds. Therefore, the definition of one second is 1/86400 of the Earth's rotation period.
But the problem is that with the advancement of science and technology, scientists began to make more accurate measurements of the Earth's rotation cycle, and found that the Earth's rotation period was not exactly 86,400 seconds. Therefore, it is not accurate to define the second in terms of the Earth's rotation period, and other more precise ways must be found to define it. Until now, the most accurate clock invented by scientists is actually the atomic clock. The specific principle of atomic clocks is:
Timing is performed using electromagnetic waves emitted when atoms absorb or release energy.
Because this electromagnetic wave is very stable, and scientists have designed very sophisticated instruments to control it. Therefore, the accuracy of the atomic clock is super high, and the error is only 1 second in 20 million years.
In 1967, the 13th International Congress of Weights and Measures used a cesium atomic clock to define the second:
The transition between the two ultrafine energy levels of the cesium-133 atomic ground state corresponds to the duration of 9,192,631,770 cycles of radiation.
After that, the world began to use this definition. This definition is also known as: atomic time.
As new definitions emerged, so did new troubles. That's because scientists have found that the Earth's rotation is not constant, but has been slowing down. For example, scientists have found that in the era of dinosaur dominance, that is, 200 million years ago, the earth rotated in a circle of about 23.5 hours, faster than it is now. So what's going on?
There are many reasons for the Earth's rotation speed, but the biggest influence comes from the Moon. The moon rotates around the earth for a month, while the earth rotates for only 1 day, a difference of nearly 30 times.
Therefore, when the moon rotates around the earth, because the earth rotates more slowly, this causes the gravitational pull of the moon to drag the earth, the sea water will friction with the earth's crust, and friction will occur between rocks and rocks and magma, which will indirectly reduce the energy of the earth's rotation, resulting in the earth's rotation speed becoming slower.
In the long run, the Rotation of the Earth will become slower and slower, but in the short term, it may also be suddenly faster due to certain factors.
In order to correct the difference between the change in the earth's rotation and the new definition of "seconds", scientists proposed that when the difference between the "world time" represented by the earth's rotation and the "atomic time" defined by the cesium atomic clock on the second is greater than 0.9 seconds, a global scale adjustment should be carried out. For convenience, this kind of meter adjustment behavior is mainly concentrated on the evening of June 30 or December 31 every year.
If the self-transformation is 1 second slower, it is after 23:59:59 and a 23:59:60, which is also called a positive leap second; if the Earth's rotation suddenly becomes faster, it is after 23:59:58, the next second is directly to 00:00:00 the next day, that is, subtracting one second, which is also called negative leap second. So far, there has been no negative leap second, and the scales that have occurred in the past have been positive leap seconds.
In the Chinese New Year's Eve night of 2012, the major websites actually went down because of the global meter adjustment, this time it was a leap second, and it was a second to add a second, which led to the server overload of many websites on these platforms.