Can you kill me in 17 cards (manual dog head)? Speaking of spikes, let me ask you a question that strikes straight into the depths of your soul, do you know what "seconds" are? How are seconds measured? How long is each of these seconds? In this issue, I will tell you about the origin of the second.
According to the Vinaya of the Sangha, "The momentary is one thought, twenty thoughts are one moment, twenty moments are one finger, twenty fingers are one lo- pre-approval, twenty-lo-ru pre-is one-whisker, and one day and one night are thirty-whiskers." Then a "snap finger" is 7.2 seconds, a "moment" is about 0.36 seconds, and our commonly used "moment" should be 0.018 seconds.
The "second" of time is a concept that did not appear until the mid-fourteenth century, and although it was short, it could do many things. For example, one second can determine the ownership of the 100-meter champion in the Olympic field; one second the cheetah can fly 28 meters on the grassland; one second the hummingbird can flap its wings 55 times; one second the athlete's heart can beat once can transport about 60 milliliters of blood; one second it can run 300,000 kilometers.
So where do seconds come from?
This is consistent with people's cognitive processes. Due to the rotation of the earth, sunrise and sunset occur, giving rise to the concept of "heaven". With the development of astronomy, people realized that the earth rotated around the sun while rotating, so the concept of "year" was created; and the moon's orbit around the earth formed the concept of "moon".
With the progress of society, people gradually need to divide the "heavens" into smaller units in order to carry out social production and carry out various social activities. This has been documented in the history of the world. The ancient Egyptians initially divided the day into 10 hours, and they made A-shaped sundials that used the sun's shadow to measure the 10 hours of the day. For more convenient equal time, 10 was not used directly, but 12 was used as an aliquot, probably because 12 has more factors than 10, so that 12 hours are formed during the day. Later, they found that the time division of the day had been completed, but the time of the night had not yet been divided, and many things fell into chaos. So they observed the stars in the night sky, using astrological signs to divide the night time into 12 hours. In this way, 24 hours a day was determined, spread all over the world and continues to be used today.
With the continuous development of science and technology, it is necessary to continue to make a more precise division of "hours". More than 1,800 years ago, the ancient Greek astronomer Claudius Ptolemy defined a circle as 360 degrees, each degree as 60 minutes, and each minute as 60 seconds, which was widely used in geometric mathematics and astronomy. Many people have divided "hours" differently, but astronomy has always been closely related to time measurement, and in the mid-fourteenth century someone introduced the method of dividing radians directly into time measurements, which divided the hour into 60 minutes, and each minute was also defined as 60 seconds. As for why it is 60, it is probably because 60 has more integer factors and is easier to divide it into more equal parts.
Although the concept of "minutes" and "seconds" had already appeared in the fourteenth century, due to the limitations of the technical conditions at that time, it was difficult for time measurement methods or devices to achieve the resolution of the accuracy of minutes and seconds, so the concepts of "minutes" and "seconds" were not widely used at that time. Until the seventeenth century, the determination of geographical longitude in navigation put forward higher requirements for precise time measurement. On the other hand, the science of time measurement was also well developed at that time. Therefore, minute and second hands began to appear on pendulum clocks or mechanical clocks at that time. In 1675, the Italian scientist Tor Rivio Blatini published the "World Survey" for the first time, he explicitly said that a second is 1/86400 of a "solar day".
Astrometry in the twentieth century has developed by leaps and bounds. Astronomers first defined "solar time" based on the Rotation of the Earth, defining one second as 1/86,400 of a "flat solar day." Later, astronomers introduced a time system based on the rotation of celestial bodies in the solar system, the almanac. In 1955, the International Astronomical Union (IAU) defined the second as 1/31556925.975 of the length of the regression year at 12 o'clock on January 0, 1900. The result was officially adopted at the Eleventh International Congress of Weights and Measures (CGPM) in 1960, and 1/31556925.9747 after refining in 1956 was used as the official result of the second definition.
Cesium atomic clock developed by the British NPL in 1955
The development of quantum mechanics has led to the emergence of a new type of time measurement device - atomic clocks. In 1955, the Royal Physical Laboratory (NPL) pioneered the development of an operable cesium atomic clock. Just three years later, scientists at the U.S. Naval Observatory (USNO) and the British NPL compared the transition of the cesium atom to the almanac seconds from observing the motion of the moon, and determined 9192631770 transitions of the cesium atom to new second values. At 4:30 p.m. on October 13, 1967, the 13th International Conference of Weights and Measures (CGPM) decided to officially adopt the 9192631770 of cesium atomic transitions as the new definition of the second, the atomic second. This definition has been used to this day, and it has been widely used in our daily lives and various scientific research.
Author: Wu Wenjun
Adaptation, Reading: Wang Xiang
Planners: Chen Lin, Liu Yongxin
Editor, Producer: Chen Lin, Wei Dong
Scientific Advisor: Li Xiaohui
Producer: Dou Zhong
The reproduced content represents the views of the author only
Does not represent the position of the Institute of Physics, Chinese Academy of Sciences
Original title: Reflecting the world of the Earth's rotation: The origin of the second
Source: National Timing Centre
Edit: Garrett