This article is from WeChat official account:Principle (ID: principle1687), author: Takeko, from the head of FIG: visual China
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One hundred years ago, on January 18, 1921, Nanbu Yoichiro was born in Tokyo, Japan.
In the same year, Japanese physicist Nishina Yoshio went to Copenhagen and then brought quantum mechanics back to Kyoto. Japanese physics circles began to get involved in the field of modern physics.
Decades later, the “Kyoto-Copenhagen School” came out of many important figures, such as Japan’s first Nobel Laureate in Physics, Hideki Yukawa, and Asa Yongzhen, who made outstanding contributions in the field of quantum electrodynamics Ichiro wait. Nanbu Yoichiro grew up to be one of the most influential theorists in physics in the 20th century.
Southern’s research is very forward-looking. He played a key role in the development of the Standard Model of particle physics. He is also one of the founders of string theory. In 2008, Nanbu won the Nobel Prize in Physics for discovering the mechanism of spontaneous symmetry breaking in subatomic physics. His scientific career spans more than half a century, reflecting the rapid development of theoretical physics in the 20th century.
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In 1942, when Nanbu graduated from Tokyo University, Japan was mired in the Second World War. However, the Japanese physics community was extremely active at this time. A group of outstanding Japanese physicists are developing the framework of quantum field theory.
The spark of this kind of thinking comes from the research of Hideki Yukawa in the 1930s. Yukawa predicted that in the nucleus, the force between nucleons is caused by the exchange of a mass of particles. This particle is now called a piion. It laid the foundation of modern particle physics. Soon, Japan’s research in the fields of particle physics and quantum field theory showed great potential.
1In 949, Yukawa became the first Nobel Prize winner in physics in Japan. During the same period, Nanbu joined Osaka City University. Early in his career, many studies in the South involved quantum field theory. For example, in a famous paper, Nanfang introduced the derivation of the precise mechanics laws in nuclear physics and drew an equation describing the combination of particles. This equation was later developed by Bethe (Hans Bethe) and Sarpit (Edwin Salpeter) is derived independently and is now often referred to as the Bette-Salpet equation.
Nanbu himself has always felt that his time in Osaka shaped his unique personal philosophy in physics research. Influenced by other Japanese physicists, Nanbu, as a theorist, also paid close attention to experimental physics.
A few years later, Southern was invited to the University of Chicago. There, he was exposed to an exciting academic atmosphere, which is Fermi’s (Enrico Fermi) “boundaryless physics” style miniature. Here, regardless of the so-called particle physics, metal physics or nuclear physics, everything is discussed in a unified way.
Under the influence of this atmosphere, while working in a completely different field, the South discovered one of the milestones in the history of particle physics in the 20th century.
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The symmetry of the laws of nature is often the guiding principle in physics. However, in some cases, symmetry is spontaneously broken. Magnets are an example. The molecules inside the magnet are themselves small magnetic dipoles. If we turn on a small magnetic field, the rotational symmetry will be broken, and all dipoles will line up along the direction of the magnetic field. Interestingly, even after the external magnetic field is turned off, the dipoles will continue to be arranged in the same direction, and the rotational symmetry is spontaneously broken.
The existence of rotational symmetry will also cause another phenomenon: if we slightly disturb one of the neatly arranged dipoles, this dipole will gently move the adjacent dipoles, thereby By analogy, the result is a wave propagating inside the magnet. This wave has very low energy and is called a spin wave.
When Nanbu tried to understand the BCS superconductivity theory, he proposed an idea to spontaneously break the symmetryThe concept has been raised to a new level. Nanbu realized that analogous to the situation inside a magnet, in the absence of electromagnetic interaction, the superconducting state would spontaneously break the symmetry, which is related to the conservation of charge.
Shortly after completing superconductivity research, the South returned to particle physics. He first noticed that the Bogoliubov equation describing the excitation near the Fermi surface in a superconductor is very similar to the Dirac equation describing nucleons. The energy gap in the superconductor becomes the mass of the nucleon, and the spontaneously broken charge symmetry in the superconductor corresponds to the sign symmetry.
If the energy gap in a superconductor is the result of the spontaneous breaking of charge symmetry, will the mass of the nucleus be the result of the spontaneous breaking of chiral symmetry? In the 1960s, a revolutionary idea was proposed in the South. Unlike the charge symmetry in superconductors, chiral symmetry is a kind of global symmetry that can be broken spontaneously. He believes that the particles caused by such breaking are π mesons.
In the eyes of many theoretical physicists, the revolutionary nature of this view cannot be overemphasized. The southern part is saying that spontaneous symmetry breaks in a vacuum; the mass of elementary particles has an origin, and this origin can be calculated. This spontaneous breaking of symmetry later became the key to establishing the standard model of particle physics, and affected our understanding of electromagnetic and weak forces.
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We can now confirm that the chiral symmetry in strong interactions is spontaneously broken, and this is also inseparable from another study in the south.
In 1964, Gellman(Murray Gell-Mann) and Zweig(George Zweig) were independently proposed. All hadrons (particles affected by strong forces) are all made of quarks Constituted.
However, this idea soon ran into “big trouble”. The quarks that make up the nucleus have ½ spin. According to the spin statistics theorem, they should be fermions that obey the exclusion principle. However, if quarks are indeed smaller particles that make up hadrons, then they seem unlikely to be fermions.
To resolve this contradiction, SouthThe Ministry proposed that quarks have an attribute, which is now called “color”(color). In a paper co-authored with Han Wurong, they proposed the three-color model. Once people realize that the colors of quarks are different, these particles are no longer exactly the same, and the usual incompatibility of fermions no longer applies.
Nanbu believes that color is like another kind of “charge.” Quark not only produces an ordinary electric field, but also a new “generalized electric field”. This field creates a new force between the quarks, which binds the quarks in the nucleus. This proved to be basically correct, and now it is also called Quantum Chromodynamics(QCD).
In order to better understand the color of quarks, Nanbu subsequently devoted himself to the development of string theory and made a foundational contribution to string theory. He and other physicists put forward a new point of view that subverts Newtonian view of (Newtonian). In the Newtonian theory, the basic laws of nature are expressed by particles or point-like components. Scientists such as Nanbu believe that the basic physical object is a one-dimensional string, not a point particle.
The southern part also provides a dynamic principle, which has large local symmetry to achieve continuous string propagation. He published the famous paper “Duality and Hadron Dynamics” (Duality and hadrodynamics) on string models. Today, string theory is considered to be one of the most promising basic physical frameworks covering gravity.
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Many people recall that Nanbu himself was shy and humble, and always spoke softly. But in contrast, in science, he boldly and “radically” put forward one after another unique ideas that transcended the times.
It’s not uncommon for scientists to insist on their own creative theories sometimes. In contrast, the southern mind is very open. For him, his research is like putting a few pieces in a huge puzzle. He never thought that he had discovered the so-called “ultimate truth.” This humility was deeply imprinted on hisCharacter.
In Nanbu’s own words, “The basic rules are simple, but the world is not boring.”
Reference source:
https://cerncourier.com/a/yoichiro-nambu-breaking-the-symmetry/
https://www.nature.com/articles/524416a
https://news.uchicago.edu/story/yoichiro-nambu-nobel-winning-theoretical-physicist-1921-2015
https://www.nobelprize.org/prizes/physics/2008/nambu/photo-gallery/
This article is from WeChat official account:Principle (ID: principle1687), author: Takeko