Time is a concept formed in the development of human civilization, and its essence can be understood as a regular summary of environmental changes. With the development of civilizations, the continuous refinement of the concept of “time” is actually the continuous development of human civilization and technological levels. Nowadays when we ask “What time is it now?”, we already have a clear quantitative unit to determine the time, and almost everyone can get the answer to the time through their watches, mobile phones, and others. But have you ever thought about this question – how is the time we are accustomed to now determined?
Don’t underestimate this problem. When we think about whether the time on watches, mobile phones, and other devices is “accurate”, we have actually subconsciously recognized the concept of standard time. Because of the existence of standard time, people can take time to clarify their schedules and plan their lives.
Standard time is a time determined based on the international standard time system, and the Beijing time we use is a time calculated based on standard time. Shortly, standard time gives countries in different regions a unified time at the physical level and a fixed reference “coordinate” based on local time. But in fact, even standard time was once not standard. The standard time in the past was Greenwich Mean Time (GMT), which was based on the earth’s rotation time and the prime meridian as 0 o’clock. However, since the Earth’s orbit is actually an ellipse, the Earth’s daily rotation is somewhat irregular and is slowly decelerating. Therefore, GMT was quickly replaced by Coordinated Universal Time (UTC) determined by atomic clocks.
It can be said that atomic clocks redefine the standard of “time”.
An atomic clock is a timing device designed based on the basic principles of physics. It was originally designed to explore the universe, and its accuracy can reach an error of 1 second every 20 million years. With the birth of atomic clocks, great changes have taken place in communications, transportation, finance and other fields – because we have more accurate time measurement methods. This is the reason that the atomic clocks have subtly improved our quality of life.
At the same time, today’s very mature satellite navigation systems actually rely on atomic clocks to provide us with accurate positioning services – you know, even an error of one billionth of a second will bring a distance of 0.3 meters error. In fact, we can now obtain the authoritative channel of Beijing time, which is also generated through the atomic clock group and the universal time measurement system, and is broadcast throughout the country.
So how accurate can atomic clocks be today? A deviation of only 1 second in 7.2 billion years!
Not long ago, our country’s scientific research team successfully developed a strontium atomic optical lattice clock with stability and uncertainty of 10,000 seconds better than 5×10^(-18) (equivalent to an error of no more than 1 second in billions of years). On this basis, the system frequency shift factors of the strontium atom optical lattice clock were evaluated item by item, and finally, the uncertainty of the system was determined to be 4×10^(-18), which is equivalent to 7.2 billion years to produce 1 seconds deviation. Don’t underestimate this number. The birth of this technology is equivalent to stepping one foot into the category of redefining the “second”, providing the important technical foundation and a basis for the subsequent construction of a new generation of global time benchmarks and even providing new methods for gravitational wave detection and dark matter search.
Of course, the development of atomic clock technology is not just about accuracy. It includes how to accurately convey the time determined by the atomic clock, or install the atomic clock on complicated equipment. One certain thing is that atomic clocks have become an important and necessary technology in our lives. Perhaps we will not come into contact with these products personally, but these instruments and equipment are affecting us all the time as they continue to develop. We are accepting time that is constantly “defined” by atomic clocks.