The theory of time relativity was founded by Einstein. "Time relativity" means that the speed of time is relative, that is to say, it is different in different speed motion systems. In a relatively high-speed moving system, time will become relatively slow.

Time will slow down, which is often mentioned in China's ancient fairy tales, but this is the imagination in China's fairy tales after all. It is far from easy to establish the theory of time relativity in science. Not only have a lot of experimental data, but also have good mathematical cultivation and analytical ability. More importantly, we should be able to jump out of the mindset caused by traditional habits. The uniform passage of time is absolutely the same at any time and any place. This is the mindset of people for thousands of years, no doubt. The great scientist Newton's "absolute time theory" has ruled the scientific community for more than 300 years. It was only at the beginning of the twentieth century that Einstein introduced the theory of time relativity to the world, and the mindset of "time absolutism" was questioned until it was broken. Einstein's theory of time relativity has since become another great scientific and technological achievement in the history of human science.

Einstein's theory of relativity was introduced, which caused a sensation in the world, just as Copernicus discovered Heliocentrism, where the earth revolves around the sun. The so-called sensation is hard for ordinary people to imagine and understand. As a result, people criticized Einstein's theory of relativity, and many physicists and philosophers criticized Einstein's theory of relativity fiercely and mercilessly. They accused Einstein of "violating scientific common sense", "being unconventional and not serious" and "playing with mathematical games". Later, it even developed into slander. 1920 February 12, some students of Berlin University deliberately made trouble during Einstein's lecture, and Einstein was forced to quit the classroom and left school angrily. Not counting this, just 25 years after the publication of the theory of relativity, 193 1 year, someone published a book, "One Hundred People Against Einstein". This book lists 100 scholars and experts who oppose Einstein's theory of relativity. Einstein was very calm after knowing it, and quipped: "Since this theory is wrong, it only needs an expert to refute it."

Let's see how Einstein deduced the theory of relativity of time:

On the constant-speed train, a passenger threw a ball in the carriage. At this time, although the train is traveling at a constant speed of 60 kilometers per hour, the ball seen by the passengers in the train moves vertically up and down. At this time, if a person standing outside the train also sees the people in the train throwing the ball, the phenomenon that he sees the ball moving up and down is different from that of the passengers in the train. The throwing point and landing point of the ball, people in the train see that the ball is in the same place, while people outside the train see that the ball is thrown and dropped in different places; People in the train see that the trajectory of the ball moving up and down is a vertical line, while people outside the train see that the trajectory of the ball moving up and down is a zigzag line.

When we imagine such an experiment in a high-speed spacecraft, it is not the ball that moves up and down, but the optical signal. A beam of optical signal is emitted upward on the floor at the bottom of the space capsule perpendicular to the cabin roof, and a mirror receives the optical signal on the cabin roof. At this time, the light seen by astronauts in the flight cabin is reflected vertically downward from the mirror, while the light seen by static observers outside the flight cabin is different from that seen by astronauts. The movement of light is a combination of up-and-down movement and forward movement, just like the trajectory of the ball moving up and down in the above-mentioned moving train. The light emitted and reflected in the spacecraft cabin is ∧-shaped, that is, the light propagates diagonally from the cabin bottom to the cabin top instead of vertically. As we all know, in a right-angled triangle, the hypotenuse is always longer than the right-angled side, that is to say, for the static observer outside the cabin, the light travels longer in a high-speed spacecraft. The speed of an optical signal is equal to the distance traveled by light divided by time. Obviously, either the speed of light in the spaceship is slow, or the speed of time passing in the spaceship is slow. Einstein's conclusion is that in a high-speed moving system, time goes slower. This is Einstein's theory of time relativity.

Einstein's theory of scientific relativity is based on two premises. The first premise is that uniform linear motion has no effect on physical phenomena, and this principle can be understood by middle school students. The example of throwing the ball on the train mentioned above has shown that the uniform motion of the train does not affect the up-and-down motion of the ball. The second premise is that the speed of light is constant, and the speed of light is 299,792.458 km/s, both of which have been confirmed in classical physics. Under these two premises, it can only be that time slows down in a high-speed spaceship, which is Einstein's conclusion. Thus the theory of relativity of time was born.

According to Einstein's conclusion, in a high-speed moving system, the clock will go relatively slowly, the astronaut's heartbeat will also slow down, the biochemical process in the body will also slow down, the electron oscillation frequency in the atom will also slow down, and all physical processes will slow down. Therefore, time itself will become slower. The faster a high-speed moving system is, the slower time goes. If the speed of a high-speed moving system reaches the speed of light, the time in the system will tend to stop, and all physical process changes will become infinitely long.

After Einstein became famous, many countries invited him to give lectures, and Peking University in China also invited him. Some articles say that Einstein has never been to China, which is wrong. He has not only been there, but also been there twice. He came with his wife, but not to Beijing as originally agreed with Cai Yuanpei, president of Peking University, but to Shanghai. The first time I went to Japan to give a lecture, I passed through Shanghai, and the time was 1922, 165438+ 10, 65438+March. He won the Nobel Prize of 192 1, and the Swedish consul in Shanghai officially informed him at this time. His second trip to Shanghai was at the end of 1922. He arrived in Shanghai by boat after his speech in Japan. 1923 On New Year's Day, he attended a tea party hosted by Jews living in Shanghai. In the afternoon, at the invitation of Shanghai Jewish Youth Association, he gave a lecture on relativity in the auditorium of Shanghai Ministry of Industry (now hankou road 193). Jews in Shanghai show great enthusiasm for outstanding scientists in their country. It's a pity that Einstein came to Shanghai, and the Chinese people are looking forward to loving Weng. Einstein came to Shanghai, but nothing happened in China's scientific and academic circles. This is really a difficult mystery.