According to Einstein's prediction, the structure of space-time will change with the fluctuation where gravitational waves pass. Imagine a square in space, and the length of each side is the same. When gravitational waves pass by, they will squeeze or stretch the square, making its side length change very, very slightly. Measuring the distance change in two directions is the basic principle of measuring gravitational waves. However, because this change is very small, it is very, very difficult to measure, so that sometimes scientists wonder whether gravitational waves can be detected. It is said that the person in charge of a laser interference gravitational wave observatory project once said in a lecture, "Sometimes I lie next to my wife in bed and think, God, I have spent so much money in the country in the past 20 years, but I have not detected gravitational waves. Why do I still live here? I really should commit suicide! " After more than 20 years of hard work, I couldn't find the result. I was really desperate. However, scientists have been persevering because they have a little confidence. 1974, russell hulse went to Arecibo Observatory of Cornell University as a visiting scholar in the last year of his doctoral thesis, during which he cooperated with joseph taylor to do a lot of research on pulsars and found the pulse binary star PSRB1913+16. Through long-term observation and in-depth study, they found that the distance between binary stars is shortening at a rate of about 7.42mm per day, and the period is slowly decaying, indicating that energy is being dissipated. Energy dissipation is indirect evidence of gravitational waves! Because of this achievement, they were awarded the 1993 Nobel Prize in Physics.