Image source: wikipedia.org
Written by | Shi Yu (Professor, Department of Physics, Fudan University)
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Modern Democritus
The ancient Greek Democritus proposed that matter consists of inseparable basic units called "atoms" . Chinese does have the meaning of the basic unit of matter, and the English atom is derived from the Greek word ἄτομος, which means "indivisible".
In the 19th century, Dalton proposed that matter is composed of atoms according to the laws of chemical reactions. Later, atomism was also supported by Boltzmann, Albert Einstein, Piran and others from the perspective of statistical physics.
Physicists further discovered that atoms are made up of electrons and nuclei and are described by quantum mechanics. This perfectly explains Mendeleev's periodic table of elements, unifying chemistry into physics, but also showing that atoms in modern science are separable.
However, in the current scientific theory, there is indeed an inseparable basic unit of matter, which is the quark. The quark is the modern counterpart of the Democritus "atom" (ἄτομος).
Murray Gell-Mann (15 September 1929 – 24 May 2019), the originator of Quark's theory, has just died at the age of nearly 90. In 1969, at the age of 40, he was awarded the Nobel Prize in Physics "for his contributions to the classification of elementary particles and their interactions." In my opinion, Gell-Mann can be called the modern Democritus.
Prior to the 1930s, theoretical predictions and experimental discoveries of new particles were difficult things to do.[1] In 1932, Chadwick discovered neutrons. Since then, it has been known that the nucleus of an atom is composed of protons and neutrons, collectively known as nucleons or baryons. In 1934, Hideki Yukawa predicted mesons that would transmit forces between nucleons. This is the π meson discovered by Powell in the cosmic ray in 1947. Prior to this, in 1937, a muse was discovered in cosmic rays, which was once considered a meson, and later learned that it belonged to the same class as electrons, called leptons. In 1949, Fermi and Yang Zhenning considered that mesons were not elementary particles, but models consisting of nucleons and their antiparticles.
In the early 1950s, many "exotic" particles were discovered, first in cosmic rays and later in Cosmotron, a new accelerator at Brookhaven Lab, which were also classified as baryons and mesons. In the face of these new particles, the Nobel laureate rabbi lamented: "Who ordered it?" Another Nobel laureate, Lamb, said in his Nobel Prize speech: "I heard that there is a saying that the discovery of new elementary particles that previously won the Nobel Prize should now be fined ten thousand dollars." ”
He brought order to the complex and disordered world of particles
In 1953, Gell-Mann proposed a new index (quantum number) called the singular number. In the production of particles dominated by strong interactions, the singular number is conserved. In the decay process dominated by weak interactions, the singular number is not conserved. In the process, Gell-Mann also predicted that neutral K-mesons also have antiparticles.
Prior to this, Pais advocated the search for new quantum numbers, conservation laws, and symmetries, and had proposed a quantum number in which parity must be conserved, so there was a union of particles. Gell-Mann's theory of singular numbers replaced Pais's theory. In the early days of his ideas, Gell-Mann gave a report at Princeton, which Pais disagreed with, saying it was an example of his own ideas. Later, Gell-Mann completed two papers, and Pais found that it was exactly the theory he was looking forward to, so he invited Gell-Mann to collaborate on a conference article, which Pais presented at the conference, summarizing the situation in the field. In the process, they also collaborated on a paper proposing that both positive and negative neutral K mesons are quantum superposition states of two different lifespans of K mesons. Gell-Mann felt that he had been used afterwards, and the two turned against each other.
In 1961, Gell-Mann proposed the "periodic table" of particle physics at the time, calling it the Noble Eightfold Path (a term borrowed from the Buddhist language, but only as a word, Gell-Mann was not religious). According to the charge and singular number of elementary particles at that time, baryons and mesons are arranged into regular geometry. The 8 lightest baryons form a hexagon, and the other 2 baryons are in the center, forming the baryon 8-fold state. The 8 lightest mesons also form a hexagon, with another 2 in the center, forming the 8-fold state of the meson. In addition, the 9 baryons form a triangular pattern, and another vertex is vacant, where the particles should have an electric charge -1, the singular number -3, called negative omega (Ω-). Three years later, the particle was found.
The success of the Noble Eightfold Path demonstrates the so-called SU(3) symmetry between these elementary particles. Each pattern is an indication of this symmetry. As a basic representation of this symmetry, Gell-Mann proposed a quark model in 1964, containing 3 types of quarks. Each meson consists of 2 quarks and each baryon consists of 3 quarks. Quarks have fractional charges. But usually quarks cannot exist freely, and can only be confined to mesons or baryons. Later, it was discovered that there were 6 kinds of quarks, or rather, quarks had 6 flavors.
It is worth mentioning that the Israeli military attaché in London, Niman, independently proposed a theory similar to the Noble Eightfold Path, and Feynman's student Zweig independently proposed the aces theory similar to the quark theory while working at CERN. Moreover, Gell-Mann originally did not think of quarks as real particles, and Zweig thought of aces as real particles from the beginning. But Zweig was reluctant to publish it in European journals (for which it clashed with the director of CERN), and the American Physical Review did not accept his paper, so his first article was not published, and the second was published in a collection of essays more than a decade later. Ironically, Gell-Mann's paper was published in the European journal Physical Communications.
In 1962, Gell-Mann also proposed the so-called flow algebra, using symmetry, through the algebraic relationship of the physical quantity of "flow", without understanding the dynamics of quarks, can give predictions of quark models. In 1964, Greenberg proposed that quarks also have "color" freedom. In 1972, Fritzsch and Gell-Mann proposed the Yang-Mills theory to describe strong interactions through color, called quantum chromodynamics. In 1973, Gross and Verczek, as well as Pulitzer, discovered that the Young-Mills theory has the nature of progressive freedom, that is, the shorter the distance, the weaker the interaction. This determines the physical significance of quantum chromodynamics.
Since Nobel Prizes are not generally awarded to people who have already won them, Gell-Mann's death may increase fritzsch's chances of sharing the Nobel Prize with others.
Fermi: "I've given you physics"
Gell-Mann made many other contributions to particle physics. In 1952, he collaborated with Goldberg on dispersion relations. In 1953, he collaborated with Francis Low on the reorganization of groups and found that the intensity of interactions depended on energy and spatial scales (after the 1970s, the reorganization groups became very important in both particle physics and statistical physics). In 1957 , after the establishment of the term non-conservation of the weak interaction , he and Feynman proposed the V-A theory ( which was also proposed by Sudashan and Marschak ) .
In 1954, in order to find the interaction law behind the production of a large number of exotic particles, the Young-Mills theory was proposed. Gell-Mann was intrigued and suggested that Feynman study its quantization. In the early 1960s he and Glashow studied the Young-Mills theory under the Lie group other than SU(2), and he also tried to unify electromagnetic and weak action, but without success. In 1960, Gell-Mann collaborated with Levi et al. to study partial conservation of axial vector flows. In the 1960s, he also did a lot of work on the Reich theory of strong interactions (the theory before the advent of quantum chromodynamics that studied the mathematical properties of scattering as a function of angular momentum). Gell-Mann's leadership in particle theory continued for many years.
Gell-Mann was born into Jewish civilians in New York, as did Feynman. Both parents were from Austria and met in the United States. His father had run a language school in New York, and his mother believed that Gell-Mann could do great things. From an early age, Gell-Mann showed extraordinary language skills, as well as an interest and profound knowledge of birds, plants, evolution, archaeology, and history, which lasted a lifetime. Probably closely related to this trait, he later made outstanding contributions to particle classification in particle physics, and named many things. His later turn to complexity research is probably related to this broad interest.
Gell-Mann entered Yale University at the age of 15, entered the Massachusetts Institute of Technology for a doctorate at the age of 19, and received his doctorate at the age of 22. After that, he went to Princeton as a postdoctoral fellow at the Institute for Advanced Study, which was in 1951. In the summer, I also visited the University of Illinois. A year later, Goldberg (Fermi's student) returned to the University of Chicago as an assistant professor, helping Gell-Mann get in touch with him as a lecturer there. This was a position that Yang Zhenning had held, so Gell-Mann consulted Yang Zhenning and learned that this position only required one class per semester and would certainly be promoted to assistant professor. He accepted the position. In Chicago, Gell-Mann made important work on singular numbers, dispersion relations, and reorganized groups, and became an academic star.
In the autumn of 1954, Fermi became seriously ill. Gell-Mann had just arrived at Columbia University as a visiting associate professor. He called Yang Zhenning and flew to Chicago to visit Fermi. As they left, Fermi was heard behind them saying, "I've given you physics." ”[6]
Although both Chicago and Columbia gave Gell-Mann permanent positions, he chose to join caltech in 1955 as a colleague of Feynman's. In 1971, Schwartz et al. founded superstring theory in Princeton. In 1972, Gell-Mann hired Schwartz for continued support, even though superstring theory was still at its low point. In the 1980s, Schwartz and Green made great strides, and superstring theory became popular.
In 1984, Gell-Mann, along with Anderson, Pines, and others, founded the Santa Fe Institute, which focuses on complexity. After retiring from Caltech in 1993, he moved to Santa Fe. I think his interest in complexity is probably related to his long-term interest in a wide range of interests. Gell-Mann once had a "notorious" joke calling solid physics squalid physics. And his mentor, Veskov, had previously said that particle physics is fundamental physics and solid state physics is extended physics. Both claims annoyed Anderson. According to the author's understanding, Gell-Mann agrees that there are laws that emerge at each level, but that this is similar to symmetry breaking, and does not agree with Anderson's statement that it cannot be reduced to a lower level of law. During this period, Gell-Mann also studied decoherence with his former student Hartl, i.e., how the classical world appeared in quantum mechanics, and used it in quantum cosmology. Their theory is based on the multi-world and self-consistent historical interpretation of quantum mechanics.
There is a lot of affection between geniuses
According to Goldberg, Gell-Mann was a popular candidate for the Nobel Prize for 6 years before winning the award. In 1969, he received a research prize for his prediction of Ω, which foreshadowed that he was likely to receive the Nobel Prize, because many Nobel laureates won the prize before winning the Nobel Prize. When someone asked him if he was free in December, he said yes. Li Zhengdao asked unpredictably, "Are you sure?" ”
After Gell-Mann won the Nobel Prize, Feynman gave it great praise: "This marks a public recognition of the fact that we have known for a long time, that Gell-Mann is today's leading theoretical physicist." In the past 20 years, no fruitful idea has progressed in our knowledge of basic physics without his contribution. ”[3]
Gell-Mann was a young genius, very conceited, and sharp-edged, and annoyed many people, including the aforementioned Pais. He has many ideas, but writes slowly, especially for fear of publishing the wrong article. So there will be situations where others will preempt him and say similar ideas. Before the discovery of the weak interaction of cosmology non-conservation, Lee Jeong-do and Yang Zhenning had tried to solve the θ-τ mystery with the so-called cosmological duality, and of course later knew that it was wrong. Gell-Mann had similar ideas, but did not publish them. Seeing Lee and Yang's article (published on April 1), Gell-Mann began attacking them. Goldberg (who was also a classmate of Yang Zhenning's) advised him that you wouldn't get credit for the idea of writing it in a notebook. When Lee and Yang found out, they wrote to warn Gell-Mann. Gell-Mann apologized. Lee and Yang wrote back to Gell-Mann's apology.
In the late 1950s, at a meeting of physics professors at the Institute for Advanced Study in Princeton, Oppenheimer said he considered inviting Gell-Mann to join the institute. Yang Zhenning said that if Gell-Mann came, he would leave. Oppenheimer did not mention it again.[6]
This is just a small episode. Gell-Mann and Yang Zhenning, although they each have a certain competitive mentality, believe that they are very strong in theoretical physics. I have noticed that when Gell-Mills referred to the Young-Mills theory in his speech, he liked to say "My friend Frank Young..."
In 1989, Lee attended the Gell-Mann 60th Birthday Celebration in Pasadena. In 2002, Gell-Mann attended Yang Zhenning's 80th birthday celebration at Tsinghua University. In 2009, Yang Zhenning attended the 80th birthday celebration of Gell-Mann in Singapore.
After learning of Gell-Mann's death, Mr. Yang Zhenning wrote in an email to this writer:
"Living physicists over the age of 90: Steinberg, Young, Anderson, Lee. ???."
bibliography:
Shi Yu. The Neutrino Hypothesis spawned by the Crisis of Life, Southern People Weekly, No. 12, 2019, No. 12, 2019, 58-63.
https://mp.weixin.qq.com/s/0BI0SkXmbY5kMb5w2PJEEg
[2] Johnson G. Strange Beauty.
Shi Yu. One Hundred Years of Normative Theory, Intellectuals, March 31, 2019.
https://mp.weixin.qq.com/s/YmFQRDGnb4vE8DWygCF5WQ
Shi Yu. Feynman Centenary (Part 2). Intellectuals, November 18, 2018.
https://mp.weixin.qq.com/s/qYKTh0o6R4GA1xOu1SzI7w
[5] Gell-Mann M. Interviewed by S. Lippincott.
[6] Yang C N. Selected Papers with Commentary II.
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![The father of Quark, Gell-Mann[fig]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)