Time is getting faster and faster? It's not an illusion, it's a fact...

Review expert: Qian Hang, aerospace science expert of the First Academy of China Aerospace Science and Technology Corporation

As we all know, the earth has been revolving around the sun for 4.6 billion years . While the earth is revolving, it is also rotating. The earth rotates once a day, 24 hours.

Solar system diagram source: Baidu pictures

1Time is going by faster and faster, is it true?

****Whether the Earth is revolving or rotating, it will be affected by the interstellar forces and will adjust in a constant process of acceleration and deceleration. As far as the present is concerned, the Earth's rotation is accelerating, which means that the day is getting shorter. In other words, "time is passing faster and faster" is not an illusion, but a fact .

"Professional data shows that time is passing faster now than at any time in the past half century. This is because the Earth's rotation rate is the fastest in 50 years." Dou Zhong, a popular science expert and secretary of the Party Committee of the National Time Service Center of the Chinese Academy of Sciences, said that relevant scientific research has found that since mid-2020, the Earth's rotation rate has shown an accelerating trend.

Changes in the Earth's rotation speed from January to December 2020. Since mid-2020, the Earth's rotation has begun to accelerate. Image courtesy of the National Time Service Center of the Chinese Academy of Sciences

2 Why is the Earth rotating faster ?

This phenomenon may be related to changes in the Earth's surface morphology. Just as a figure skater or ballet dancer can rotate faster when the body is closer together during a turn, the Earth's rotation will also speed up when matter is gathered closer to the center. Take global warming as an example. When glaciers and ice sheets melt and flow into the ocean, the mass of the Earth is redistributed, and matter is closer to the center than before, so the Earth's rotation will speed up.

In mid-2020, the Earth's rotation accelerated Source: Science Popularization China

However, observations over the past few hundred years have found that changes in the speed of the Earth's rotation are based on a long-term slowdown.

"The changes in the Earth's surface are only temporary. In the long run, the general trend of the Earth's rotation speed slowing down will not change." Dou Zhong said that because of the tidal gravitational force of the sun and the moon, it is equivalent to gently tapping the "brakes" for the Earth's rotation. If the slowdown reaches a critical point, time workers around the world will have to use the trump card of "leap seconds".

**3 leap seconds 1,** What is a leap second?

In the old days, time seemed to pass at a constant speed, but in fact, time has been adjusted for decades - a leap second is inserted every few years. First, let's understand the timekeeping system.

To determine the time, there are now three common time systems: universal time based on the Earth's rotation period; calendar time based on the Earth's revolution period around the sun; and atomic time based on the frequency of electromagnetic oscillations emitted by the transition of electron energy levels inside atoms.

Cesium atomic clock Image source: Wikipedia

A leap second is the addition or subtraction of one second from the universal time. It is the product of the coordination between astronomical time and atomic time.

When does 2 leap seconds occur?

Leap seconds are usually inserted at 23:59:59 , which means that the next second should be 0:0:0:0, but after adding the leap second, the clock displays 23:59:60 and then 0:0:0:0.

1972 - Year of Leap Second Insertion in 2021

The date for inserting leap seconds is usually June 30 or December 31, or March 31 or September 30. There is no fixed rule. The specific date is uniformly determined and announced by the International Earth Rotation Service through monitoring the rotation speed of the earth. Generally, countries are notified six months in advance when to add or subtract leap seconds.

What impact will 3 leap seconds have?

The adjustment of leap seconds has little direct impact on our daily lives, and we often cannot feel the changes brought about by leap seconds. However, leap seconds have an important impact on technical systems and application fields that rely on precise time synchronization, such as computers, finance, aerospace, etc. For example, the addition or deletion of leap seconds requires global synchronization, which poses a challenge to the time management of computer systems.

In July 2022, Google, Microsoft, and Amazon jointly advocated the abolition of leap seconds. After all, the adjustment of leap seconds has brought a lot of trouble to the technology industry.

In 2012, several large websites crashed their servers due to time synchronization errors, resulting in a brief service interruption; the social news site Reddit had a system crash caused by a leap second, which lasted for more than half an hour. In 2015, when the leap second came again, engineers fixed some of the problems that occurred in 2012, but discovered new problems.

4 Leap seconds will be eliminated

Although the original intention of leap seconds was to keep the universal time synchronized with the Earth's rotation time UT1, the adjustment of leap seconds, especially the potential uncertainties behind it, has made the time synchronization system increasingly complex. There are different opinions on whether to keep or remove leap seconds. Perhaps larger corrections should be implemented, such as leap minutes and leap hours, to extend the adjustment time to hundreds or thousands of years. Or perhaps the correction should be stopped and the growing time difference between universal time and international atomic time should be announced.

The 27th General Conference on Weights and Measures in 2022 decided to abolish leap seconds and replace them with leap minutes no later than 2035, allowing the difference between the International Atomic Time and the World Time to be within 1 minute. It also required all parties to negotiate and propose a new plan that can maintain the "Coordinated Universal Time" for at least a hundred years.

It seems that time does not flow in a constant manner. Doing unlimited things in a limited time is what we should consider now. I also believe that with the continuous development of science and technology, new time synchronization technology will continue to be updated. Let us wait and see!