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In 1928, Dirac published his first paper on electronic quantum theory. In that article, he constructed a wave equation for electrons, interpreting spin as the result of a combination of quantum mechanics and relativity. The Dirac equation also reveals the antimatter counterpart of electrons, that is, antielectrons or positrons.

Based on the success of the Dirac equation, researchers in quantum mechanics try to quantify the electromagnetic field by creating quantum field theory. But all attempts in this area have failed because the calculation result according to this theory is infinity. Their solution to this problem is to use a mathematical technique called renormalization to ignore these infinities. But Dirac said: "I am very dissatisfied with this situation. It is not wise mathematics to simply ignore the infinity in the equation."

In June 1947, the first international physics conference since World War II was held on Shelter Island, which brought together 24 physicists from the Manhattan Project. At this meeting, two important experiments appeared. In the first paper, Lamb proposed an experiment that shows that the 2S_1/2 and 2P_1/2 energy levels of hydrogen atoms are not the same, on the contrary, they differ from 1058Mhz. Another experiment showed that the hyperfine structure of hydrogen had an anomaly of 0.1%, which Brett later interpreted as the g factor of the electron.

The problem is that both equations contradict the Dirac equation, so participants assume that Dirac's electronic theory must be incomplete and propose that these effects are caused by the quantization of the electromagnetic field. They also assume that quantum field theory can be used to calculate these differences, and renormalization techniques can be used to correct theoretical infinity, which is the origin of quantum electrodynamics. However, Dirac is not optimistic about this, saying that reorganization is only an expedient measure, and we must have some fundamental changes in our thinking, rather than hoping to get a good theory by tampering with numbers.

A few months after the meeting, Bette published a paper outlining the equation of the first experimental Lamb shift. In its equation, the K value diverges to infinity, so Bette decided to use renormalization: by replacing the infinite value with the finite value of the electron energy K=mc ². The problem is that there is no physical reason for this change, and the only reason to use it is that the final conclusion is close to the experiment.

A few months later, Schwinger gave the formula of the g factor of the electron: Gao 1 + α / 2 π, where α is the fine structure constant. Using this formula, the theoretical value of the g factor calculated by him is very close to the previously published experimental results. However, he never explained how he got the equation and said he would publish a paper outlining the details of his theory. Schwinger's equation has had a great impact on the scientific community because of its simplicity and accuracy, and everyone is looking forward to Schwinger's theory.

The following year, in 1948, a second physics conference was held. In addition to those who attended last time, Bohr, Dirac and Fermi also attended. The focus of the meeting was on Schwinger's speech, and there were high hopes that he would explain how he calculated the g factor. In the end, Schwinger gave a five-hour speech and came up with a series of complex and incomprehensible formulas. Oppenheimer later commented: "others gave speeches to show how to do calculations." and Schwinger's speech showed that only he could do it. "

On the second day of the meeting, Feynman delivered his speech and showed the famous Feynman diagram for the first time. However, one of the reasons why most participants did not respond positively at the time was that they thought it was impossible for positrons to go backwards in time. Although Schwinger's theory is difficult to understand, it is still thought to be closely related to known quantum electrodynamics. Later, Chaoyong Zhenichiro also put forward a third new theory.

Now there are several competing theories, and British physicist Freeman Dyson has found a way to unify them. Dyson proposed that the g factor of the electron can be calculated by using the Heisenberg scattering matrix: it is converted into a series now known as the Dyson series, in which the first two terms happen to be Schwinger's formula for the g factor, and each term can be calculated by solving a certain number of Feynman diagrams.

In 1949, these people held a third meeting. Feynman takes Dyson's theory as the final form of quantum electrodynamics. Since then, Feynman diagram has become a popular tool for American physicists and has since become famous and become the leader of a new generation of scientists. Further research leads to the formation of quantum chromodynamics, electroweak theory and the standard model of particle physics, which depend to a large extent on the use of Feynman diagrams.

In the same year, Gardner and Purcell obtained more accurate experimental values of the g factor. At this time, the g factor calculated by Schwinger's formula is quite different from the experimental value, and the factor is no longer considered to be accurate. It was a famous opportunity to test Dyson's theory. Physicists made complex calculations and published the value of the third term of the Dyson series, when the theory coincided with the experiment again.

After that, the experimental value of g factor is constantly updated, and the Dyson series calculated by Feynman diagram is also consistent with the experimental results. Feynman, Schwinger and Chaoyong Zhenichiro also won the Nobel Prize in Physics in 1965.

This article comes from the official account of Wechat: Vientiane experience (ID:UR4351), author: Eugene Wang

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