In 1967, atomic clocks appeared. They determined time with such precision that scientists were able to calculate that the Earth was rotating more and more slowly (by fractions of a second!). But how can we guarantee that our time is synchronized with the rotation of the Earth?

How often do we promise to “make time” for cleaning the balcony or meeting up with friends we haven’t seen in a long time? And every time our intentions are hampered by a lack of time. The latter is no longer a problem for scientists. They have the ability to create time (with periodicity, of course)!

While philosophers and physicists continue to argue about the origin of time and its existence, other scientists quietly create seconds that are embedded in the temporal nebula. And that’s what they’ve been doing for the past 46 years. The origins of this magic lie in the invention of the atomic clock. The latter, by the way, are plentiful in Switzerland.

A SCIENTIFIC DISCOVERY

Since antiquity, time has been determined by observing the stars. For many centuries, one second was equal to 1/86 400 of an average solar day. Thus, one complete passage of the Sun (two consecutive passes through the zenith) takes 86,400 seconds.

This unit of universal time was in effect until the 1960s, when new discoveries changed our time system.

Since 1967, in the international system of SI units it has been accepted to define one second as 9,192,631,770 periods of electromagnetic radiation corresponding to the transition between the two superfine levels of the ground state of the cesium-133 atom.

Long ago astronomers said that the interval between the two zeniths is not constant, based on the fact that the Earth does not revolve around the Sun in a circle, but rather in an ellipse. Moreover, the angle of the Earth is 23.3 degrees relative to the level of its solar orbit. As a result, the length of the solar day varies. It may be 16 minutes 23 seconds shorter on November 4 and 14 minutes 22 seconds longer on February 11. Connoisseurs of fine watchmaking recognize this as the famous equation of time.

The measurement of time by atomic clocks is independent of the stars, so scientists made a startling discovery: they were able to prove that the Earth’s rotation slows down. They explained this phenomenon by the small amount of friction between electromagnetic waves and the rotating Earth and the fact that the Moon is moving away from our planet.

The slowing of the Earth’s rotation means an increase in the length of the day. So far it is imperceptible, but today, for example, the day is two milliseconds longer than it was 100 years ago. Such a difference implies a periodic adjustment that helps to be closer to the average solar day.

WHAT ARE ATOMIC CLOCKS FOR?

The extra second as a time correction system was introduced in 1972. Since then, 27 seconds have been added, most recently on December 31, 2016. That evening one second after 23:59:59 the time was not 00:00:00, but 23:59:60. It is impossible to know the date of the next correction in advance, but it will be carried out when the synchronization between the Universal Coordinated Time and the rotation of the Earth is out of sync by more than 0.6 seconds.

So where does Coordinated Universal Time come from? Every day the International Bureau of Weights and Measures collects information from the Web of 350 atomic clocks located in different parts of the world and calculates the average value. This is Coordinated Universal Time, and there is a demand for it.

For example, Google responds to 7 billion automatic requests every day to synchronize computer time and world time. And this figure will increase as the number of connected devices grows rapidly: it is predicted that by 2020 there will be 20 billion.

GPS and Galileo also need accurate time. After all, how does GPS work? The system provides the possibility to obtain the exact coordinates at any time of the day. It is based on the fact that there are three satellites in space in geocentric orbit with atomic clocks that are about one nanosecond accurate. They measure the time that a radio signal travels from the satellites to the receiver. In this way, the coordinates are determined using time. The latter will be correct if the accurate clocks on the satellites do not lag behind each other.