Paul dirac's main experience

Paul dirac (1August 8, 902-19841October 20), male, a British theoretical physicist, was one of the founders of quantum mechanics and made important contributions to the early development of quantum electrodynamics. He served as Lucas Professor of Mathematics at Cambridge University and spent the last fourteen years of his life at Florida State University. Dirac died in Tallahassee, Florida on 1984.

The Dirac equation he gave can describe the physical behavior of fermions and predict the existence of antimatter.

1933, Dirac and Erwin Schr?dinger both won the Nobel Prize in physics for "discovering new forms that are very useful in atomic theory" (namely, the basic equations of quantum mechanics-Schrodinger equation and Dirac equation).

Chinese name: paul dirac.

paul adrie maurice dirac

Nationality: UK

Place of birth: Bristol, southwest England

Date of birth:1August 8, 902

Date of death:1984 65438+1October 20th.

Occupation: theoretical physicist

Graduate institutions: Bristol University (Bachelor's degree), St. John's College, Cambridge University (Master's degree, Doctor's degree)

Main achievements: 1933, Erwin Schr?dinger won the nobel prize in physics.

One of the founders of quantum mechanics

Masterpiece: Principles of Quantum Mechanics

Gender: male

Education: Doctor.

family background

Charles Dirac, the father of P.A.M Dirac, 1866 was born in Montaigne, a French-speaking country, and did not become a British citizen until 19 19. At the age of 20, Charles betrayed his family and went to study at the University of Geneva. Later, he came to England about 1890 and settled in Bristol, teaching French for a living. 1896, he got a teaching position in Bristol Commercial Vocational and Technical School, met Florence Holden in Bristol (she is a captain's daughter, younger than Charles 12 years old), and married her in 1899. One year after their marriage, their first child, Reginald Dirac, was born, and two years later,1802, Paul Dirac was born. At that time, their family lived in monk street. Four years later, Beatrice Margaret Dirac was born. She was the third child of the Dirac family. Paul, like his brothers and sisters, was born with Swiss citizenship, and did not acquire British citizenship until1917.

The life of the character

Studying in early years

Paul dirac, 1902, was born in Bristol, southwest England, and grew up in Bishop. His father, Charles Ezron Radislav Dirac, is a French teacher who once taught in Bristol. He immigrated to England from saint maurice in the Swiss state of Valais. His mother, Florence Hannah Dirac, whose original name was Holden, was the daughter of a captain and worked as a librarian in Bristol Central Library. Paul has a sister named Beatrice Isabel Margaret, her name is Betty, and a brother named Reginald Charles Felix. Felix committed suicide in March 1925. Dirac later recalled: "My parents were very sad. I didn't know they were so concerned ... I never knew that parents should take care of their children, but since this incident, I have known about it. "

Charles and his children were registered as Swiss citizens, and they were not naturalized as British citizens until19101October 22nd. Although Dirac's father disapproves of corporal punishment, he is a strict and autocratic man. Dirac's relationship with his father was so tense that after his father died, he wrote, "I feel more free. I want to be myself. " In order to let the children learn French, Charles forced them to speak only French. But Dirac found himself unable to express what he wanted to say in French, so he chose silence.

Dirac's first education was at Bishop Road Primary School, and then at the joint venture technical college for men and businessmen (later Kautham School). His father is a French teacher there. This school is an affiliated school of Bristol University. They like the space and staff here. This university emphasizes technical courses, such as bricklaying, shoemaking, metalworking and modern languages. This was an unusual arrangement in British secondary education, which was still mainly teaching classical literature at that time. Dirac later expressed gratitude for these arrangements.

After that, Dirac studied electronic engineering at the School of Engineering, Bristol University. Although his favorite subject was mathematics, Dirac later claimed that engineering education had a profound influence on him:

"At first, I was only interested in completely correct equations. However, the engineering training I received taught me to allow approximation, and sometimes I can find amazing beauty from these theories, even if it is based on approximation ... Without these training from engineering, I may not be able to make any achievements in my future research ... I will continue to use these incomplete and rigorous engineering mathematics in my future work, and I believe you can see from my future articles ... Mathematicians who require all calculations to be completely accurate can hardly go very far in physics. "

Shortly before 192 1 got his degree, he took the entrance examination for St. John's College of Cambridge University. He passed the entrance examination and won a scholarship of 70 pounds, but it was not enough to cover the huge expenses needed for studying and living in Cambridge. Although I graduated with a first-class honours bachelor's degree in engineering, I still couldn't find a job as an engineer in the post-war economic recession in Britain. Therefore, he chose to accept the opportunity to study for a bachelor's degree in mathematics at Bristol University for free. Because he has finished his engineering degree, he is allowed to take the first-year course.

1923, dirac graduated with first class honors again and won a scholarship of 140. Plus 70 pounds from John College, the money is enough for him to live and study in Cambridge.

Cambridge suiyue

At first, Dirac wanted to study the theory of relativity that he had always been interested in. However, under the guidance of Ralph Fowler, Dirac began to contact atomic theory. Fowler introduced Dirac to the latest concepts in atomic theory, such as the theory of niels bohr and others. Dirac once recalled:

"I remember the first time I saw Bohr's theory. I'm surprised ... surprisingly, under certain conditions, we can actually apply Newton's law to electrons in atoms. The first condition is to ignore electron radiation, and the second condition is to add quantum. I still clearly remember how shocking Bohr's theory was. I believe that the concept introduced by Bohr is the biggest breakthrough in the development of quantum mechanics. "

Later Dirac also tried to expand Bohr's theory. 1925, Werner Heisenberg put forward a theory centered on observable physical quantities, which involved the non-commutativity of matrix multiplication. Dirac didn't particularly appreciate it at first, but about two weeks later, he realized the significance of noncommutativity and found the similarities between poisson bracket and Heisenberg's matrix mechanics rules in classical mechanics. Based on this discovery, he proposed a clearer quantization rule (i.e. rule quantization). This paper, Quantum Mechanics, was published in 1926, and Dirac received his doctorate for this work.

At the same time, Erwin Schr?dinger put forward his own quantum theory according to the wave equation of matter wave. Dirac soon discovered that Heisenberg and Schrodinger's theories were complementary, so he began to study Schrodinger's wave mechanics.

1926 In September, at Fowler's suggestion, Dirac went to the niels bohr Institute in Copenhagen for a period of time. During his stay in Copenhagen, Dirac continued to study quantum mechanics and developed a generalized theory covering wave mechanics and matrix mechanics. This method is similar to the canonical transformation of classical Hamiltonian mechanics and allows different groups of variable bases to be used. In addition, in order to deal with continuous variables, Dirac introduced a new mathematical tool-Dirac δ function.

Dirac also began to study radiation theory. In his article Quantum Theory of Absorbing and Emitting Radiation, he quantized the wave function by using the technology of secondary quantization, and further linked photon radiation with bose-einstein statistics. In this method, the quantum state of a particle set is represented by the distribution of its particles in various energy States, and the quantum state is changed by the generation and elimination of particles. Dirac shows that the two methods are equivalent, and the electromagnetic field is regarded as photon or quantized field. In fact, this work has led to a new physical topic-quantum field theory, and secondary quantization has become the basis of quantum electrodynamics.

1927 In February, Dirac came to G? ttingen, where he stayed for several months and met Herman Weil, Max Born, Robert Oppenheimer and others.

During the second world war

After the beginning of World War II, Dirac's teaching burden increased due to the shortage of teachers. In addition, he must instruct many graduate students. Before, Dirac always tried to avoid this responsibility, preferring to do research alone. The exception is 1930.

193 1 year, he took over and guided Fowler's student Chandraseka. 1935- 1936, Max Born left Cambridge for Edinburgh and accepted two students who had been instructed by Born. Dirac has supervised less than 12 students in his life (mostly11940s and 1950s).

During the war, Dirac invested in the research and development of isotope separation to obtain uranium 235. This is a key technology in the application of atomic energy. He and Peter Capicha tried to develop a method of separating gas mixture by centrifuge, but their experiment was later stopped because Capicha was trapped in Russia.

194 1 year, dirac cooperated with Francis Simon of Oxford University and provided many practical opinions on statistical methods. These methods are still in use today.

In addition, he is an informal consultant of Birmingham Group to calculate critical mass.

(of a respected person) leave this world forever.

Dirac died in Tallahassee, Florida on 1984, and was buried in the local rossland Cemetery. Dirac's childhood house in Bristol was decorated with a blue plaque, and the road where the house was located was also named Dirac Road to show his connection with this area. There is a sign on the wall of the local Bishop Road Primary School, which reads Dirac's most famous Dirac equation.

1 991August1day, a memorial stone was erected in saint maurice Garden in Dirac's father's hometown. 1995165438+1October 13 A memorial slate made of Burlington green slate and engraved with Dirac equation made its debut in Westminster Abbey. Edward Carpenter, the head of the priest, once opposed this matter, because Dirac was an atheist and his opinion was ignored.

From 65438 to 0975, Dirac gave five series of lectures at the University of New South Wales. This series of lectures was later compiled and published as a book "Direction of Physics" (1978). He donated the royalties of this book to the University of New South Wales and set up a series of Dirac lectures. Dirac Silver Medal is an award awarded by the school on this occasion.

Immediately after Dirac's death, two research institutions set up annual awards in memory of Dirac: the British Physical Society awarded Dirac medals and prizes in recognition of "outstanding contributions in theory (including mathematics and calculation methods) physics". The top three winners are Stephen Hawking (1987), John Stewart Bell (1988) and roger penrose (1989). The International Center for Theoretical Physics (ICTP) awards the ICTP Dirac Medal on August 8th every year (Dirac's birthday). In addition, the publishing headquarters of the British Physical Society in Bristol was named Dirac Bookstore.

The Dirac-Herman Award of Florida State University was established by Dr. Bruce Herman (the last doctoral student of Dirac) in 1997 to reward the outstanding performance of theoretical physics researchers in the university.

Paul dirac Science Library, located in Florida State University, was founded by Manch on 1989. There is a collection of Dirac's papers before his death, and there is a bronze statue outside the museum. The road where Tallahassee National High Intensity Magnetic Laboratory in Florida is located is named "PaulDiracDrive". In his hometown of Bristol, a road in Digert Town was named "DiracWay". The BBC named an image compression format it developed after Dirac.

Major achievements

Scientific contribution

Dirac won the 1933 Nobel Prize in Physics for establishing an effective new atomic theory.

Dirac developed quantum mechanics, put forward the famous Dirac equation, and theoretically predicted the existence of positrons.

Dirac first engaged in the study of relativistic dynamics. Since Heisenberg 1925 visited Cambridge University, Dirac was deeply influenced and turned his energy to the study of quantum mechanics. 1928, he introduced relativity into quantum mechanics and established the Schrodinger equation in the form of relativity, namely the famous Dirac equation. This equation has two characteristics: first, it meets all the requirements of relativity, no matter how fast the electron moves; Second, the conclusion that electrons have spins can be automatically deduced. The solution of this equation is very special, with both positive energy states and negative energy states. Dirac therefore predicted the existence of positrons, believing that positrons are mirror images of electrons, with exactly the same mass but opposite charge signs. According to this image, Dirac also predicted that there was a process in which an electron and a positron annihilated each other and released photons. On the contrary, the reverse process of this process, that is, a photon annihilation produces an electron and a positron, may also exist. 1932, when American physicist Anderson (1923-) was studying the trajectories of high-energy electrons emitted from cosmic ray clusters, he found strangely that half of the electrons in the strong magnetic field were deflected in one direction and the other half in the opposite direction. After careful identification, this is the positron predicted by Dirac. It was soon discovered that gamma rays produced electron pairs, and the positive and negative electrons collided and "annihilated" into photons, which fully confirmed the correctness of Dirac's prediction. Dirac's work initiated the theoretical and experimental study of antiparticle and antimatter.

Dirac is the founder of quantum radiation theory, and once independently discovered Fermi-Dirac statistics with Fermi. Dirac also published a large number of cosmological papers in Florida State University, which promoted the development of cosmological research. In particular, Dirac predicted the possible existence of magnetic monopoles in theory as early as 1930s. The theoretical research and experimental detection of magnetic monopole have made rapid development in modern physics. There are reports from 65438 to 0982 abroad, claiming that some people have found evidence of the existence of magnetic monopoles. Of course, if the existence of magnetic monopole can be proved by experiments, it will definitely lead to profound changes in physical theory.

To sum up, Dirac's main contributions to physics are as follows: the quantum mechanical equation (Dirac equation) describing relativistic Fermi particles is given, and the antiparticle solution is given; Predicting magnetic monopole; Fermi-Dirac statistics. In addition, basic work has been done in quantum field theory, especially in quantum electrodynamics. He also made outstanding work in the theory of gravity and the quantization of gravity.

electrodynamics

By 1927, Dirac had become a famous figure in the field of science due to many pioneering work. Proof is that he was invited to attend the 5th Solvay Conference (Electrons and Photons). In the same year, Dirac was elected as an academician of St. John's College, and was appointed as a senior lecturer in mathematical physics on 1929. At this time, Dirac is studying the relativistic quantum theory of electrons. Although Klein-King equation was established at that time, Dirac thought that the problem had not been solved. This equation may give a negative probability, which cannot be explained by quantum mechanics.

In 1928, Dirac put forward a relativistic equation describing electrons-Dirac equation. Independent of Wolfgang Pauli's work, he found a 2x2 matrix describing spin. Abraham Pais once quoted Dirac as saying, "I believe I got it independently, and Pauli may get this result independently of me." But Dirac equation and Klein-Gordon equation have the same problem, and there is an unexplained negative energy solution. This prompted Dirac to predict the existence of antiparticle positrons of electrons. He explained that positrons come from the Dirac Sea full of electrons. 1932 carl anderson observed and confirmed positrons in cosmic rays. Dirac equation can also explain that spin is a relativistic phenomenon.

Because Enrico Fermi's β decay theory in 1934 involves the destruction and creation of particles, Dirac equation is interpreted as the field equation of particles with arbitrary spin _/2, in which the process of field quantization includes the anti-exchange law. Therefore, in 1934, Heisenberg reinterpreted the Dirac equation as the field equation of all elementary particles (quarks and leptons)-Dirac field equation. In theoretical physics, this field equation is in the same core position as Maxwell equation, Young-Mills gauge theory and Einstein field equation. Dirac is regarded as the founder of quantum electrodynamics and the first person to use this term.

In addition, in the early1930s, he also put forward the concept of vacuum polarization. This work is the key to the development of quantum electrodynamics by the next generation of theoretical scholars such as Schwinge, Feynman, Ichiro Asanaga and Dyson.

1930, Dirac published his book Principles of Quantum Mechanics, which is an important milestone in the history of physics and is still a classic textbook of quantum mechanics. In this book, Dirac integrates Heisenberg's work in matrix mechanics and Schrodinger's work in wave mechanics into a mathematical system, and links the relationship between observable measurements and actors in Hilbert space. Dirac δ function, which is widely used in quantum mechanics, is also introduced. Continuing Dirac's article in 1939, he added his mathematical symbol system-Dirac symbol to the third edition of this book in 1939. Until today, Dirac symbol is still the most widely used symbol system in quantum mechanics.

1932 dirac succeeded Joseph larmor as Lucas professor of mathematics at Cambridge university. Dirac and Schrodinger both won the Nobel Prize in Physics in 1933. He told Rutherford that he didn't want to be famous and he wanted to refuse the honor. Rutherford said to him, "If you do this, you will be more famous and people will bother you more." 193365438+February 65438+February, Dirac delivered a Nobel Prize-winning speech in Stockholm entitled "The Theory of Electrons and Positrons".

Magnetic monopole

193 1 year, Dirac discussed the idea of magnetic monopole in an article entitled Singularity in Quantized Electromagnetic Field. 1933 Continuing his paper 193 1, Dirac proved that the existence of a single magnetic monopole can explain the quantization of charge. In 1975, 1982 and 2009, the research results show that magnetic monopole may exist. But so far, there is still no direct evidence of the existence of magnetic monopoles. Even so, some grand unified theories still contain magnetic monopoles to explain the formation of the structure of the universe. Dirac's magnetic monopole is the first time to use the concept of topology to deal with physical problems

Large number hypothesis

1937, Dirac put forward the hypothesis of large numbers. He compared two dimensionless values: the ratio of fundamental forces (here, gravity and electromagnetic force) and the scale of the age of the universe, and found that both of them decreased by about 39 orders of magnitude. Dirac guessed that this may not be a coincidence, and there may be some connection between the two. According to Edward Arthur Milne's theory, the gravitational constant is allowed to change with time. Based on these assumptions, he designed his own cosmological model.

academic research

Create quantum mechanics

1925 began to study quantum mechanics founded by Heisenberg and others. 1926 published a paper entitled "quantum mechanics", obtained a doctorate in physics from Cambridge University, and was invited to be a researcher at St. John's College. There are two kinds of geniuses. One is an ordinary genius, whose achievements can be achieved by others, as long as he works hard enough and has a little luck. The other is extraordinary genius (mathematician Mark Carker called them "magicians"). They have amazing irrational insight, and it is difficult for others to achieve that kind of wisdom. Einstein was a genius. Paul dirac, who died on 1984, was also an extraordinary genius. His equations predicted the existence of antimatter, and he was the greatest theoretical physicist in England after Newton. Dirac became one of the founders of quantum mechanics at the age of 23. The theory was developed in the 1920s and 1930s, and many seemingly odd conclusions were put forward, including the basic fact that the world could not be fully understood. But while his colleagues were still puzzled by the philosophical significance of this equation, Dirac thought that language was dangerous and only paid attention to the mathematical value. For him, this equation is beautiful. As he grew older, he became more and more convinced that beauty was the guide of truth. He believes that basic physics can be picked up from elegant mathematics, and this view has now penetrated into the whole field of exploring nature.

The pursuit of physical beauty

Quantum electrodynamics has obtained some infinite results in high-order perturbation calculation. This is unreasonable in the physical system. Therefore, a computing technology called renormalization was developed as a stopgap measure, but Dirac could not accept it. In a speech at 1975, he expressed this view:

"I must say that I am quite dissatisfied with this situation. Because such a' good theory' ignores the infinite divergence from the equation in a random way. This is not sensible math. Wise mathematics can ignore a small value, but it cannot be abandoned because a value is infinite. "

He refused to accept the reorganization, which made him gradually move away from the mainstream in his research.

Starting from the Hamiltonian form he wrote, he tried to establish quantum electrodynamics on the "logical basis". He found an updated method to calculate the abnormal magnetic dipole moment, and re-deduced Lamb displacement with Heisenberg's painting scene. But despite great efforts, Dirac failed to develop a satisfactory theory all his life.

In the late 1950s, Dirac applied the Hamiltonian method developed by Dirac to Einstein's general theory of relativity. This involves the quantization of gravitational field.

In order to live closer to his daughter Mary, Dirac resigned from Cambridge University on 1969 and accepted a teaching position offered by Florida State University. In the last fourteen years, Dirac spent most of his time in Miami University and Florida State University.

From 65438 to 0982, Dirac's health began to deteriorate. 1984, 10/0 On October 20th, Dirac died of illness in Tallahassee, and his body was buried in the local cemetery according to his family's wishes.

family status

The political chaos in Europe led to World War II, which also split the originally complete European academic environment. Quantum mechanics was born in such an environment. Dirac maintained a loyal friendship with each side in this conflict. He tried to rescue Russian physicist Peter Kapicha who was detained by the Soviet regime, but failed. He also sincerely treated Werner Karl Heisenberg, a German physicist suspected of being a Nazi supporter.

Dirac is famous for his silence. He seldom speaks, and silence has become his label. He doesn't want to argue with others. He is withdrawn and seems to have lost his sensitivity to society. In the eyes of many of his colleagues, he had no interest in anything other than mathematics, so that his colleagues were surprised when he got married. However, as GrahamFarmelo said in his biography, Dirac is more than just a boring calculator. He likes reading comic books and Mickey Mouse movies, and later he fell in love with an American female singer, Cher.

Famelo sympathetically described Dirac's unfortunate family background. His parents seemed to hate each other and his brother committed suicide. Dirac blamed his father's fault for his brother's death, and of course some of his father's actions also confirmed this. When Dirac won two scholarships at Cambridge University, he only needed 5 pounds to leave this place. His father gave money to his son, making him think that his father had let him start his own business. Dirac didn't know the truth until later. 1936 after his father died, he discovered that the important 5 pounds was not given by his father, but by a local educational institution, while his father had accumulated 7,500 pounds, equivalent to 15 times his annual salary.

Character monograph

Personality assessment

Bonus; prize

Dirac and Erwin Schr?dinger both won the 1933 Nobel Prize in Physics for "discovering a new form of atomic theory". In addition, Dirac was awarded the Royal Medal in 1939 and the copley Medal and Max Planck Medal in 1952.

1930 was elected as an academician of the Royal Society, and 1948 and197/kloc-0 were elected as honorary academicians of the american physical society and the British Physical Society respectively. Dirac was awarded the Medal of Meritorious Service in 1973, which is a very high honor in Britain. He refused to be knighted because he didn't want to change his name.

Research style

One of his students, John Pogue kinghorn, once recalled, "Once he was asked about his core beliefs about physics, he went to the blackboard and wrote,' The laws of nature should be described by beautiful equations'".

Dirac was asked about his personal philosophy of physics when he was lecturing in the Physics Department of Moscow University on 1955. He replied: "A physical law must have mathematical beauty." The blackboard where Dirac wrote this sentence is still preserved today.

Based on the requirement of mathematical beauty, Dirac cannot accept renormalization to solve the infinite divergence of quantum field theory. In a speech, he said:

"If you truncate the integral range, you will introduce a non-relativistic situation and destroy the invariance of relativity. If the price only destroys the invariance of relativity, quantum electrodynamics can still be within a reasonable mathematical framework. But compared with ignoring divergence from basic mathematical principles, the damage of relativistic invariance is much smaller. "

Dirac often talks about giving priority to finding beautiful equations instead of worrying about their physical meaning. Steven weinberg once commented on this:

"Dirac told physics students not to worry about the physical meaning of the equation, but to pay attention to the beauty of the equation. This suggestion is only useful for physicists who are very sensitive to the pure beauty of mathematics, and they can rely on it to find the way forward. There are not many such physicists-maybe only Dirac himself. "

physicist

For Dirac, Bohr once said: "Among all physicists, Dirac has the purest soul."

Max Born once recalled the first time he read Dirac's article:

"I remember very clearly that this is one of the biggest surprises in my life's research experience. I don't know who Dirac is. I can guess that he is probably a young man, but every part of his article is quite perfect and respectable. "

Chinese-American physicist Yang Zhenning published Symmetry Physics in 199 1 and mentioned his views on Dirac:

"In quantum physics, the concept of symmetry exists. I once compared Dirac's bold and original prediction to the first introduction of negative numbers. The introduction and expansion of negative numbers have improved our understanding of integers and laid the foundation for the whole mathematics. Dirac's prediction expanded our understanding of field theory and laid the foundation for quantum electrodynamics field theory. "

Yang Zhenning once mentioned that Dirac's article gives people the impression that "autumn water articles are dust-free" and go straight to the depths and mysteries of the universe without dross.

Summarizing Dirac's life, abdul sallam said, "Paul Ezron Morris Dirac is undoubtedly one of the greatest physicists in this century or any century. His three key works 1925, 1926 and 1927 laid the foundation for his first quantum physics, the second quantum field theory and the third elementary particle theory ... No one, even Einstein, has the means to have such a decisive influence on the development of physics in this century in such a short time.