Nine billion, one hundred ninety-two million, six hundred thirty-one thousand, seven hundred seventy is the number of periods of radiation of a caesium atom. So what? Well, that is the number of periods that define one official second. You can read the chapter "Time" in Steven Johnson's book "How We Got to Now" or watch the episode in the tv show "How We Got to Now" on Amazon tv. You can look at Alanna Mitchell's New York Times article "Get Ready for the New, Improved Second".
In her "Improved Second" article, Mitchell writes:
Nowadays the bureau regulates the seven base units that govern time, length, mass, electrical current, temperature, the intensity of light and the amount of a substance. Together, these units are the language of science, technology and commerce.
Scientists are constantly refining these standards. In 2018, they approved new definitions for the kilogram (mass), ampere (current), kelvin (temperature) and mole (amount of substance). Now, with the exception of the mole, all of the standards are subservient to one: time.
The meter, for example, is defined as the distance light travels in a vacuum during one-299,792,458th of a second. Likewise, the new definition of the kilogram rests on the second, in a manner too complicated to explain in fewer than several paragraphs.
It seems that strong efforts are made to find something in nature that is very reliable, for purposes of measurement and standard units.
I went to graduate school just as computers were emerging. We were studying analysis of experimental data and we had to learn about using a computer. Our tricky professor gave one assignment that we worked on for three years: Given two dates, tell the number of days between them. We knew he was tricky and we learned about Pope Gregory and his adjustment of the calendar. His adjustment was only about two weeks. He ruled that tomorrow would be a date 10 days away. There were riots and demands to return our days and don't shorten our lives.
Humans started with the day-night cycle as a basis for time measurement but the rotation of the earth is slowing, to the point of losing 3 hours in 2,000 years. Try not to panic.
