/kloc-in the 6th century, Copernicus, a Polish astronomer, put forward a new theory of cosmic system-Heliocentrism. 16 10, Italian astronomer Galileo made astronomical observations with a telescope for the first time, observing sunspots, the surface of the moon, the planets' losses and the four moons of Jupiter. Now, more and more historical facts prove that the reason why human civilization exists today is the same. Among them, Galileo and Newton, who created classical mechanics, and Einstein, who created special and general relativity, are the most representative. When we review these epoch-making scientists, we will find that although they lived in very different times, great changes have taken place from classical mechanics to modern physics, we can see many similarities in these people. First of all, they are explorers who are not bound by prejudice or traditional ideas. Their scientific research work tends to widen the gap from those places that are considered to be conclusive. The problems they studied, even if we look at them today, will feel too basic and too abstract. For example, what is time? What is space? What is relative? What is absolute? What is the law of celestial motion? What is the origin of the universe? Wait a minute. These problems, from Newton's law to Einstein's theory of relativity, from people's daily concerns to the real world, seem to belong to another world. However, it has been proved that the technological progress brought about by the progress of these "academic" problems is irreplaceable by anything else. Secondly, they all adhere to the research methods of natural science. Although they care about abstract problems, they don't make speculative empty talk. On the contrary, they use the method of comparing theory with physical experiment or astronomical observation to examine every concept and hypothesis, so as to judge the success or failure of theory. Thirdly, most of them are not only natural scientists in a narrow sense, but also lofty people. For example, Einstein is a representative who advocates rationality, science and democracy. He once said, "Only by dedicating yourself to society can one find the meaning of a short and risky life." He is also indignant at the attitude that he dare not talk about the scientific spirit because he is afraid of power. He said, "What if Giordano? Bruno, Spinoza, Voltaire and Humboldt all think so. If we do this, where will we be? " Because of this, they and their theories were often not tolerated by the rulers at that time. Galileo was persecuted by the Inquisition, and Einstein was persecuted by German fascists. Ironically, even in the 1970s when the illiterate Gang of Four engaged in fascist cultural absolutism, the theory of relativity was besieged in China! Although these histories have passed like nightmares, it is not only beneficial but even necessary to revisit them today. Because, if we only know the academic details, but we don't grasp the spirit of science and science becomes the soul of real science, then we can't really transplant science and let it take root, blossom and bear fruit. The purpose of this booklet is to introduce some main development clues from Newton's law to Einstein's theory of relativity. Due to the limited space and lack of (or only a few) mathematical tools, we just want to explain the most basic ideas and concepts clearly. Perhaps this is also a subjective wish, but it has not been realized, or it has not been fully realized. I hope readers will criticize and correct me. This booklet was only planned to be published at the suggestion of the editorial board of this series last autumn. Later, Comrade Chu Yaoquan and I wrote the first draft one after another. Now, when I was teaching in Italy, I spent some time rewriting it from scratch. These days, I live in Linchenko College, and what I see outside the window is the school emblem of Linchenko College printed in Galileo's Dialogue. Although the emblem of the world's oldest academy of sciences is very old, whenever you write about Galileo, it can't help but make you respect. Tomorrow is1March, 979 14, which is the full100th anniversary of Einstein's birth. Today, I finally finished reading the whole book as a memorial to Galileo and Einstein, two great scientists who should be respected forever!