The law of parity non-conservation refers to the asymmetry of the motion of substances that are mirror images of each other under weak interaction, which was verified by Wu Jianxiong with cobalt 60. Before 1956, the scientific community always thought that parity was conserved, that is, the mirror image of a particle was exactly the same as its own properties. 1956, scientists found that the spin, mass, lifetime and charge of θ and γ mesons are exactly the same. Most people think it is the same particle, but θ decay produces two π mesons and γ decay produces three π mesons. This shows that they are different kinds of particles. 1956, Li Zhengdao and Yang Zhenning boldly asserted that τ and θ are exactly the same particles (later called k mesons), but their motion laws are not necessarily exactly the same in the weak interaction environment. Generally speaking, if these two identical particles look at each other in a mirror, their decay mode is. In scientific language, the "θ-τ" particle is parity-nonconservative under weak interaction. At first, the "θ-τ" particle was only regarded as a special case, and people are still reluctant to give up the parity conservation of the whole microscopic particle world. Shortly thereafter, Wu Jianxiong, an experimental physicist of Chinese descent, verified the "parity non-conservation" with a clever experiment. Since then, "parity non-conservation" has really been recognized as a basic scientific principle with universal significance. Wu Jianxiong used two sets of experimental devices to observe the decay of cobalt 60. At a very low temperature (0.0 1K), she used a strong magnetic field to make the spin direction of cobalt 60 in one set of devices to the left, and the spin direction of cobalt 60 in the other set of devices to the right. Cobalt 60 in these two devices is a mirror image of each other. The experimental results show that the number of electrons emitted by cobalt 60 in these two devices is very different, and the directions of electron radiation cannot be symmetrical with each other. The experimental results show that parity is not conserved in weak interaction. We can use a similar example to illustrate this problem. Suppose two cars are mirror images of each other. The driver of car A sits in the front left seat with the accelerator pedal close to his right foot. The driver of car B sits in the right front seat with the accelerator pedal close to his left foot. Now, the driver of car A turns on the ignition key clockwise, starts the car, and presses the accelerator pedal with his right foot to make the car move forward at a certain speed. The driver of car B did exactly the same thing, but switched from left to right-he turned on the ignition key counterclockwise, stepped on the accelerator pedal with his left foot, and the inclination of the pedal was consistent with that of A. How will car B move now? Perhaps most people will think that two cars should move at exactly the same speed. Unfortunately, they made a mistake of course. Wu Jianxiong's experiment proves that in the particle world, car B will travel at a completely different speed and in a different direction! The particle world is an incredible proof that parity is not conserved. The discovery that the universe originated from non-conservative parity is not isolated. In the microscopic world, there are three basic symmetry ways for elementary particles: one is that particles and antiparticles are symmetrical to each other, that is, for particles and antiparticles, the law is the same, which is called charge (C) symmetry; One is spatial reflection symmetry, that is, the same kind of particles are mirror images of each other and have the same motion law, which is called parity (P); One is time reversal symmetry, that is, if we reverse the motion direction of particles, the motion of particles is the same. This symmetry is called time (T) symmetry. That is to say, if antiparticles are used instead of particles, left turns to right, and the flow of time is reversed, then the transformed physical process still follows the same physical laws. However, since the law of parity conservation was broken by Li Zhengdao and Yang Zhenning, scientists soon found that the behavior of particles and antiparticles is not exactly the same! Some scientists have further suggested that it may be because of the slight asymmetry of the laws of physics and the asymmetry of the charge (C) of particles, which led to a little more matter produced at the beginning of the Big Bang than antimatter. Most of the matter and antimatter were annihilated, and the rest of the matter formed the world we know today. If the laws of physics were strictly symmetrical, the universe and ourselves would not exist-the same amount of matter and antimatter should be born after the Big Bang, but the positive and negative matter would be annihilated immediately after they met, so there would be no chance for galaxies, the earth and even human beings to form. Next, scientists found that even time itself is no longer symmetrical! Perhaps most people thought that time could not be turned back. In daily life, the arrow head of time always has only one direction, "the deceased is like this", the old man becomes young, the broken vase cannot be restored, and the boundary between the past and the future is clear. However, in the eyes of physicists, time is always considered reversible. For example, a pair of photons collide to produce an electron and a positron, and a pair of photons are also produced when the positive and negative electrons meet. These two processes conform to the basic laws of physics and are symmetrical in time. If one of the processes is filmed with a video camera and then played, the viewer will not be able to judge whether the video tape is played forward or backward-in this sense, time has no direction. However, at the end of 1998, physicists first discovered the events that violated the symmetry of time in the micro-world. Researchers at CERN found that there is time asymmetry in the transformation process of positive and negative K mesons: the rate of anti-K mesons transforming into K mesons is faster than its inversion process, that is, K mesons transforming into anti-K mesons. At this point, the symmetry of the physical laws of the particle world has been completely broken, and the world has been proved to be imperfect and flawed in essence. The Discovery Process Yang Zhenning, Li Zhengdao and Wu Jianxiong are all familiar names in China, and the peak of their careers is closely linked with "parity". In the words of scientists, parity is short for intrinsic parity. It is a physical quantity that represents the transformation properties of particles or particle systems under spatial reflection. Under the spatial reflection transformation, the field of a particle only changes by one phase factor, which is called the parity of the particle. We can also simply understand that parity is the image of a particle in the mirror when it looks at it. It used to be thought that parity must be conserved according to the symmetry recognized by the physical world. Just as there is a positron, there must be a negative electron. Professor Yang Zhenning cooperated with Professor Li Zhengdao in 195 1 and put forward the law of "parity non-conservation in weak interaction" in 1956 * *. This truth is actually very simple. Symmetry reflects the * * * relationship between different material forms in motion, and the destruction of symmetry makes them show their own characteristics. Just like buildings and patterns, only symmetry without its destruction looks regular, but at the same time it looks monotonous and boring. Only basic symmetry and incomplete symmetry can form beautiful buildings and patterns. Nature is such an architect. When constructing macromolecules like DNA, nature always follows the principle of replication, connecting molecules together according to a symmetrical spiral structure, and the spatial arrangement of the spiral structure is consistent. However, in the process of copying, a slight deviation from the exact symmetry will create new possibilities in the arrangement order of macromolecular units, thus making those styles that are more convenient to copy develop faster and form a development process. So the destruction of symmetry is the reason why things continue to evolve and become colorful. The close cooperation between Yang Zhenning and Li Zhengdao is the basis for their great achievements. Yang Zhenning recalled: I received my doctorate from the University of Chicago in June, 1948, and I spent that summer at the University of Michigan. After the fall, I returned to the University of Chicago and was hired as a lecturer in the Department of Physics. During my teaching, I continued to study nuclear physics and field theory. At the end of 1948, Li Zhengdao and I cooperated to study decay and capture, and found that these interactions and decay have very similar intensity. Li Zhengdao 1946 went to the University of Chicago for postgraduate study in the fall. We may have met in China earlier, but we didn't really know each other until we got to Chicago. I found him both talented and diligent. We got along well and soon became good friends. I am a few years older than him and a few years earlier than him in graduate school, so I try my best to help him. Later, Fermi became his thesis supervisor, but he always asked me for guidance. Therefore, in those years in Chicago, I actually became his physics teacher. 1953, Li Zhengdao went to Columbia University. In order to continue our cooperation, we have established a system of mutual visits. I stay in Colombia one day a week, and he stays in Princeton or Brookhaven one day a week. This routine exchange of visits has been maintained for six years. During this period, our interest is sometimes basic particle theory and sometimes statistical mechanics. This is a fruitful cooperation, which is deeper and wider than my cooperation with others. Over the years, we have known each other very well, and even seem to know what each other is thinking. However, we have great differences in temperament, feelings and tastes, which are conducive to our cooperation. Our communication started at 1946, which is intimate and based on mutual respect, trust and care. Then 1957, our success (both won the Nobel Prize). During the 16 years when I made friends with Li Zhengdao, I treated him as a brother. This cooperation has made a great contribution to physics, which is enviable. Li Zhengdao himself claimed that this cooperation had a decisive impact on his career and growth. When it comes to Yang Zhenning, Li Zhengdao and parity, there is an outstanding China woman who cannot be forgotten. This is Wu Jianxiong. Dr Wu Jianxiong has made great contributions to this revolution in the United States, and is called "parity non-conservation" by the physics circle. Yang Zhenning and Li Zhengdao doubt the correctness of parity law in the weak interaction of elementary particles in theory, and propose that if parity is not conserved under weak exchange, then a group of β rays with directed nuclei should be asymmetrically distributed in the axial direction. In order to prove the correctness of their prediction, two scientists found Dr. Wu Jianxiong. Wu Jianxiong has many novel and ingenious physics experiment techniques, which are widely adopted by other physicists. Many physicists will ask her for help when they encounter difficulties in their experiments. At Yang Li's request, Dr. Wu Jianxiong discussed the possibility of cooperation with Dr. Abel of the American National Bureau of Standards. The actual work will begin in three months. She observed the decay of cobalt 60 into nickel 60 at extremely low temperature (0.0 1 degree Celsius above absolute zero) and the weak exchange of electrons and antiparticles in the magnetic field. Sure enough, neither electrons nor antiparticles obey the principle of parity conservation. The experiment was successful. Dr. Wu proved the theory of sum and overturned the law of parity conservation that existed in physics for 30 years. This discovery made the Royal Swedish Academy of Science award the 1957 Nobel Prize in Physics to Dr. Yang Zhenning and Dr. Li Zhengdao immediately.