So it's not surprising that since ancient times, all localities have started to track time, measure time, record time and establish time scales.
Reliable timestamps need to be based on repeatable periodic events.
In ancient times, the most easily observed cycle was nothing more than day and night (the rotation of the earth), so there was a "day"; Secondly, the moon's profit and loss (the revolution of the moon), so there is a "month"; And the periodic alternation of climate (the revolution of the earth), so there are years, seasons and solar terms. ...
On this basis, when society needs a smaller time scale, we also slowly stare at a cup of tea and a wick, and then evolved regular timing tools such as copper pot dripping, pendulum and lever gear.
In the early society, such a time scale was enough for life scenes such as farming and transportation. However, with the development of human civilization, the scales of these timing methods are neither precise nor high enough, and they are easily disturbed and unstable by external factors.
Today, the timing of human society is no longer based on macroscopic phenomena and instruments, but on microscopic particles.
For example, the clock used to test Einstein's theory of relativity in the 1940s was not a mechanical/electronic clock in our home, but was based on the decay of muons. Because the particle decay is an autonomous random process, the decay speed is fixed and is not affected by external factors, we can track the time flow according to the muon decay process.
Later, at 197 1, the physicist changed a cesium atomic clock to verify it again.
What is the principle of cesium atomic clock? Today, we know that electrons in atoms are in discontinuous energy levels (orbits); When electrons jump from one energy level to another (that is, electron jump), corresponding electromagnetic waves will be released/absorbed.
Each atom has its own series of electromagnetic wave frequencies, and the frequency of the same atom is fixed. For example, one of the characteristic frequencies of cesium-133 atom is 9 192, 63 1 770 Hz (microwave band), which can be observed on any cesium-133 atom-this has become the metronome that defines "second" internationally.
In 200 1 year, based on similar principles and advanced laser technology, scientists developed an all-optical atomic clock on mercury atoms, also known as an optical clock.
Because the characteristic frequency of cesium atom is mainly in microwave band, and the new atomic clock is based on radiation in higher frequency band, the optical clock can provide a finer time scale. If the world's most accurate light clock has been running since BIGBANG, it will only deviate by 0.5 seconds until today.
Therefore, in 20 15, the international time-frequency advisory Committee put forward a roadmap to modify the definition of "second", and a new round of second definition based on light clock may be ushered in around 2026.
At present, similar atomic oscillations are the most stable periodic events observed by scientists-but atomic clocks can be more accurate.
Theoretically, an atomic clock can be timed by the oscillation of a single atom. However, on the microscopic scale, a single atom is limited by the uncertainty of quantum mechanics, and its "real" vibration frequency can only be reflected through a large number of measurements and averages, which is the so-called standard quantum limit.
Therefore, in practice, atomic clocks generally measure thousands of similar atoms and then count the correct values. However, even in thousands of atoms, the uncertainty of the standard quantum limit still exists-at this time, the quantum entanglement that once troubled scientists has the help of God.
A study by MIT at the end of last year pointed out that the oscillation of atoms in quantum entanglement will be tightened around a * * * same frequency, which is smaller than that of atoms not in quantum entanglement, so that we can measure the accuracy beyond the standard quantum limit.
In this new atomic clock, scientists entangled 350 ytterbium atoms, the accuracy is four times that of the version without quantum entanglement, and the deviation can be less than 0. 1 second in the long life of the universe of/kloc-0.4 billion years.
From the past to the present, we have tracked time more closely and meticulously, not only serving life, but also decoding the universe; So will the future.
In life, more and more sophisticated human civilization, such as many scenes and possibilities in the 5G era, can be blessed with more accurate time and space positioning.
In scientific research, scientists can discover more physical laws about time that could not be detected in the past, such as gravitational waves and even dark matter. They can further ponder over some counter-common sense and "destroying three views" issues, such as the specific influence of gravity on the flow of time and whether time itself changes with the aging of the universe.
However, the road to further development is not endless.
A paper in Physical Review X 2065438+07 points out that better timing comes at a price: the higher the accuracy of the clock, the greater the energy consumed and the entropy generated. An ideal clock with perfect period will theoretically burn infinite energy and produce infinite entropy, but this is impossible in reality. In other words, the accuracy of the clock is fundamentally limited.
Fortunately, up to now, most clocks, including the world's most advanced atomic clocks run by the JILA Institute in Boulder, Colorado, have not reached the relevant basic limits, and they burn far more energy than the minimum energy required to tell the time.
However, Jun Ye, a physicist at JILA, said that watch manufacturers are accelerating the use of quantum information science to make more accurate clocks, and the basic restrictions will become more and more important in the future.
On October 20-24, 20265438+01kloc-0, teachers and students of Gaoshan College will visit Xi 'an, the birthplace of Jingshi, and explore the most familiar and unfamiliar essence of Shishi with scientists.
Author | Qiu
Editor Zhu Zhen
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Special thanks to Professor Gou Lijun, researcher of the National Astronomical Observatory of Chinese Academy of Sciences, head of the stellar black hole research and innovation team of the National Astronomical Observatory and executive editor of the Journal of Astronomy of China, for his professional review of this article.