Yang Zhenning, Li Zhengdao and Wu Jianxiong are well-known names in China, and their career peaks are 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 jointly put forward the law of parity non-conservation of weak interaction in 1956.
This truth is actually very simple. Symmetry reflects the commonness of 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 spent that summer in the University of Michigan after receiving my Ph.D. from the University of Chicago. 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 the American revolution, which physicists call "parity non-conservation".
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 enabled the Swedish Academy of Royal Science to immediately award the 1957 Nobel Prize in Physics to Dr. Yang Zhenning and Dr. Li Zhengdao, because they corrected the serious mistakes made by scientists in the past, and even started the research on some laws of the "weak exchange" of elementary particles, which made mankind's understanding of the inner layer of material structure take a big step forward. American writer Li Edison said: The doctor did many difficult and complicated experiments, and Yang and Li made theoretical breakthroughs and experimental proofs. Wu Jianxiong discovered the phenomenon that electrons tend to turn left, which not only changed the basic belief of parity conservation in physical science, but also affected the development of chemistry, biology, astronomy and psychology. Although Dr. Wu Jianxiong didn't win the Nobel Prize, the importance of her work didn't decrease. On the contrary, she was more brilliant because of other honors and honors. When Princeton University awarded her an honorary doctorate in philosophy, the president solemnly announced that Dr. Wu Jianxiong had completely gained the right to be called the greatest physical experimenter in the world. The principle of parity non-conservation completely changed people's understanding of symmetry, which contributed to the concern of physics circles for symmetry in the following decades.
The three scientists have made such great achievements, and they have one thing in common, that is, they love their motherland and strive to draw nutrition from the cultural essence of China.
Professor Zhou, president of China Academy of Sciences and physicist, summed up his academic achievements with "a great scientist who made the Chinese nation proud". He said that Professor Yang Zhenning has a very profound cultural tradition in China, and at the same time, he has integrated the excellent parts of western cultural traditions, forming his unique style of rigorous scholarship and unpretentious, which is admirable and exemplary.
1June 1996, someone asked Yang Zhenning, "You are a world-famous scientist, and now you are awarded the honor of being a foreign academician of China Academy of Sciences. How do you view this honor? " Mr. Yang Zhenning pondered for a moment and said with emotion, "I am still from China. I cherish the honor of being a foreign academician of the China Academy of Sciences, and I am proud of it. " From the bottom of my heart, this famous Chinese-American physicist at home and abroad has a deep China complex ―― Yang Zhenning 1922 was born in Hefei, Anhui Province, and his family background made him receive a good education from an early age. During the Anti-Japanese War, he obtained a Bachelor of Science degree from Kunming Branch of National Southwest Associated University, and a Master of Science degree from 65438 to 0944 in Tsinghua University. /kloc-0 went to study in the United States in the winter of 1945, and/kloc-0 received a doctorate in physics from the University of Chicago in the winter of 1948. After that, he worked in Princeton Institute for Advanced Studies for a long time, and then presided over the Institute of Theoretical Physics of the State University of New York at Stony Brook.
The development of many fields of modern theoretical physics is inseparable from Yang Zhenning's name. 1949, together with Fermi, a world-famous physicist, proposed the structural model of elementary particles, namely Fermi-Young model. In cooperation with Mills, gauge field theory established Yang Zhenning's position as the founder of physics in the second half of the 20th century. 1956, Yang Zhenning and Li Zhengdao put forward the theory of parity non-conservation of weak interaction. This great achievement broke through the traditional concept of physics at that time and promoted the development of elementary particle theory. It was called "a turning point in the history of science" by scientists, and together with Li Zhengdao, it won the Nobel Prize in Physics with 1957. From beginning to end, Yang Zhenning believed that the traditional culture and education of China received in China as a teenager were very important to his career. Therefore, at the ceremony of winning the Nobel Prize in Physics, Yang Zhenning said, "Although I have devoted myself to modern science, I am proud of the China tradition and background I have endured."
As a descendant of the Chinese people, Yang Zhenning lives in America, but he loves his old country. His lifelong pursuit of scientific truth, strong interest and enthusiasm for science are inseparable from his concern for the development of science and technology in China. From 197 1 returning to China for the first time to today's reform and opening up, he deeply felt the ever-changing changes in the motherland. Now he goes back to China to give lectures and visit every year, and spares no effort to strengthen the scientific and technological exchanges between China and the world and promote the scientific and technological development of China. In this regard, he said, "Because it is rooted in the cultures of China and the United States, it has a special responsibility to enhance friendship and understanding between the two countries."
1994 when yang Zhenning returned to China, he told thousands of students "the 500-year history of scientific and technological development in China" at China university of science and technology, which once infected and inspired countless students. When the reporter talked to Yang Zhenning about his influential speech "Historical Review and Prospect of Modern Science Entering China" and asked him to talk about how China's scientific and technological development faces fierce competition and meets the challenges of the 2 1 century, Yang Zhenning said with emotion and confidence: "China used to stand still and lag behind the West, but now it is developing rapidly. Only by relying on science education can we revitalize China. China has countless outstanding talents and thousands of years of excellent traditions. Coupled with the current reform and opening up and economic development, China will certainly catch up. "
12 years ago, when Yang Zhenning visited China, he happily wrote a poem, "The world has been in turmoil for two hundred generations, and the situation is changing rapidly; If you ask about the future of that mountain, you will fight for the sky and seize the day. " Poems written by physicists are clearly his earnest expectation for the day when China will take off. Yang Zhenning firmly believes that at the turn of the century, with the implementation of China's strategy of "rejuvenating the country through science and education", China will certainly catch up; With the rapid development of the Chinese nation, China will soon stand proudly among the world's technological powers and become a giant of oriental science.
On May 25th, 1997, China Academy of Sciences and Jiangsu Provincial People's Government held a naming conference for Yang Zhenning's Star in Ning. "Yang Zhenning Star" is an asteroid with the international number of 342 1. The Purple Mountain Observatory of China Academy of Sciences discovered 1975+065438+ on June 26th.
Li Zhengdao is over 70 years old. He has been engaged in physical science research for 50 years. In his scientific career of half a century, he has made outstanding achievements in the fields of high-energy physics, astrophysics, fluid mechanics, statistical physics, condensed matter physics and general relativity with his genius and diligence. Since 1972, he has devoted himself to supporting the development of science education in the motherland with deep patriotic feelings, actively promoting scientific exchanges and cooperation between China and foreign countries, suggesting the establishment of a postdoctoral system and helping to establish and improve the natural science fund system. He devoted a lot of efforts to the construction and operation of the Beijing Electron Positron Collider. Ten years ago, he proposed to establish modern physics research centers in China Advanced Science and Technology Center and Beijing. In the past ten years, under the auspices of Professor Li Zhengdao, the two centers have carried out a large number of academic research exchanges between China and foreign countries, achieved many important research results, and continuously cultivated senior scientific and technological talents. Professor Li Zhengdao's fifty years are the fifty years when he used his intelligence to explore the mysteries of science and devoted himself to the scientific development of the motherland and mankind. However, this outstanding scholar, who is too old and rare, is never satisfied. He still looks forward to the future with vigor and vitality, hoping to make new contributions in the coming 2 1 century. The asteroid with international number 3443 discovered by Purple Mountain Observatory of China Academy of Sciences has been approved by relevant international organizations and officially named as "Li Zhengdao Star". 1997 On May 30th, China Academy of Sciences held a grand naming ceremony for the Star of Li Zhengdao. Since then, Li Zhengdao's name has been embedded in the stars in space, traveling with asteroid 3443 and shining in the Milky Way. "Li Zhengdao Star" (international number 3443) was discovered by Purple Mountain Observatory of China Academy of Sciences on September 26th, 1979/kloc-0. "Li Zhengdao Star" orbits the sun in an elliptical orbit with an eccentricity of 0.3. The average distance to the sun is 359 million kilometers, and it takes 3.70 years to go around the sun.
Wu Jianxiong 1934 graduated from the Department of Physics of Central University, and then went to the United States to study, and successively obtained doctor of science degrees from California University, Princeton University, Yale University, Harvard University and other institutions. 1954 American citizenship. 1973, she was elected President of american physical society, an honorary member of the Royal Society of Edinburgh, a member of the National Academy of Sciences, and a member of the American Academy of Arts and Sciences. 1994 won the Outstanding Achievement Award of Chinese in the United States.
Professor Wu Jianxiong has always been concerned about the development of science and technology in China. Since 1973, I have visited relatives and lectured in China many times. She is an honorary professor of Peking University and Nanjing University, and established Wu Jianxiong Laboratory in Southeast University. 1990, an asteroid discovered by Nanjing Purple Mountain Observatory was named "Wu Jianxiong Star". 1June 1994, she was elected as the first foreign academician of China Academy of Sciences. 1February, 1997 16, Professor Wu Jianxiong died of a stroke again at the age of 85. Accompanied by her husband, physicist Professor Yuan Jialiu and other relatives, her ashes were buried in the newly-built "Wu Jianxiong Cemetery" of Mingde School in Liuhe Town, Taicang City, Jiangsu Province, realizing her long-cherished wish of returning to her hometown.
On the occasion of Professor Wu's 80th birthday, he briefly introduced the doctor's resume at the birthday ceremony, and said that he had a strong interest in history and geography during his studies, and his literary attainments were extraordinary. Later, she made some achievements in physics, which made ordinary people ignore her literary talent. Dr Wu Jianxiong, who was retired at that time, delivered a speech at the birthday party, saying that there is no shortcut to scientific research, and "basic literacy begins with hard work such as interest, observation, experiment and perseverance".
Western scientists called Dr. Wu China's wife, and Dr. Imirie Shogley, who also won the Nobel Prize, praised her as the "queen of nuclear physics".
The influence of parity non-conservation principle is far-reaching. Many people say, "Without the work of Yang and Li, it is hard to imagine what theoretical physics would be like today. ! At the end of 1998, physicists discovered the first event that violated the symmetry of time. Researchers at CERN found that the positive and negative K mesons have time asymmetry in the conversion process. Although this discovery is helpful to improve the Big Bang theory, it shakes the view that the basic laws of physics should be symmetrical in time.
As people often sigh, time cannot go back. In daily life, the arrow head of time always has only one direction. Old people can't become young, broken vases can't be restored, and the past and the future are clearly defined. But in the eyes of physicists, time has always been 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. This process conforms to the basic laws of physics and is symmetrical in time. If you shoot one of the two processes with a video camera and then play it, the audience will not be able to judge whether the video tape is played forward or backward. In this sense, time has no direction.
In physics, this characteristic of not distinguishing between the past and the future is called time symmetry. The classical laws of physics all assume that time has no direction, and they have indeed passed the test in the macro world. But in recent decades, physicists have been studying whether time symmetry is equally applicable in the microscopic world. After three years of research, a team at CERN finally made a breakthrough. Their experimental observations prove for the first time that at least in the process of neutral K meson decay, time violates symmetry.
This group, composed of nearly 100 researchers from 9 countries, studied the process of K meson anti-K meson transformation in experiments. Mesons are particles whose mass is greater than that of electrons, but less than that of protons and neutrons. Spins are integers and participate in strong interactions. According to the internal quantum number, it can be divided into π meson, ρ meson and K meson. In the experiment, researchers found that the rate of anti-K meson transforming into K meson is faster than its time reversal process, that is, K meson transforming into anti-K meson. This is the first time in the history of physics that time asymmetry has been directly observed.
Modern universe theory once thought that BIGBANG should produce the same amount of matter and antimatter at the beginning, but today's universe is dominated by the material world, which has always been confusing. The new experiment of CERN proves that antimatter can be transformed into matter faster than the opposite process, thus providing a partial answer to why the mass of matter in the universe is far more than antimatter. In addition, the new results are also of great significance to the study of the basic symmetry laws in physics. Physicists have always believed that besides the basic laws of physics are not affected by the directionality of time, the physical reflection process of objects in space and the transformation process of particles and antiparticles should also follow symmetry. The laws of time, parity and charge conservation are considered as one of the foundations supporting modern physics.
Since 1950s, physicists have found that some conservation laws sometimes do not completely satisfy symmetry. Chinese-American physicists Yang Zhenning and Li Zhengdao once put forward the theory of parity non-conservation of weak interaction, which was confirmed by experiments. Later, Americans james cronin and Val Fitch discovered that the decay process of the K meson violated the laws of parity and joint symmetry of charges, and both of them won the Nobel Prize in physics. Because time, parity and charge should be conserved as a whole, physicists speculate that time will violate symmetry in some cases. CERN's results confirmed this conjecture for the first time.
1March 999 Scientists said that direct observation proved that the law of charge parity was wrong. Fermilab announced that it has proved with unprecedented accuracy that the neutral K meson directly violated the law of joint symmetry of charge parity in the process of decay. This result is regarded as an important progress in the field of matter and antimatter research.
At present, it is generally believed that every elementary particle has a corresponding antiparticle. For example, corresponding to negatively charged electrons, there are positrons with the same mass and opposite charges. Since the antimatter theory was put forward, scientists have always believed that there is symmetry in characteristics between particles and antiparticles, just like people look at themselves through a mirror. These symmetry features mainly include that the basic laws of physics are not influenced by the directionality of time, and the physical process under spatial reflection and the transformation process between particles and antiparticles follow symmetry, which are called the laws of time, parity and charge conservation respectively.
1964, American physicists Cronin and Fitch found that there was a violation of parity and the law of joint conservation of charges between the K meson and its antimatter anti-K meson. However, two physicists observed the violation of the conservation of charge parity mainly through the quantum mechanical fluctuation effect of K mesons and anti-K mesons, so they were regarded as indirect observations. Since the 1960s, physicists all over the world have come to some similar results, but they basically belong to the category of indirect observation. In order to directly prove that K mesons violate parity and the law of joint conservation of charges, the main way is to study the process of K mesons decaying into other particles. K mesons can decay into two mesons. Physicists theoretically point out how many k mesons decay into mesons through experiments. If this ratio is not close to zero, it can be regarded as a direct proof of the non-conservation of parity and charge joint law.
It is reported that in recent years, scientists all over the world are engaged in the calculation of the ratio of K meson decay to meson, but the obtained results can not be considered as exact proof. The latest numerical results obtained by Fermilab (error of 0.00280 is 0.0004 1) are more accurate than previous experiments, which directly proves that parity and the law of charge conservation are indeed limited.
1980 Professor Cronin, one of the earliest discoverers of the laws of parity non-conservation and charge conservation, who won the Nobel Prize in physics, said in his evaluation of the new achievements of Fermilab that this was the first time that people had a really new understanding of this issue since the violation of the laws of parity and charge conservation was discovered 35 years ago. Val Fitch, a professor at Princeton University, said: "This result is extremely surprising. It was completely unexpected. This is very, very interesting. "
Scientists plan to continue experiments and calculations in Fermilab to verify whether these latest observations are true. At the same time, if you want to know why the world is like this, the answer lies entirely in the difference between left and right-all you have to do is look in the mirror.