Hideki Yukawa and Richard Feynman

1. Feynman diagrams and Yukawa coupling

Yukawa with Feynman in Kyoto (1954). Courtesy of Saito Hayakawa.

Without vertices, Feynman diagrams would be straight lines telling nothing about physics. This was not what Feynman intended. Those diagrams tell physics because of the vertices. Who then invented the vertex? In 1934, Hideki Yukawa wrote an article telling that the force between two nucleons is due to exchange of mesons between them. In 1947, mesons were observed in laboratories. In 1949, Yukawa received the Nobel prize in physics. These days, this aspect id known to us as the Yukawa coupling.

The day after Yukawa's death in 1981, Japan's Mainichi Shinbun (One of Japan's major newspapers) had this front-page article about him. If you can read Japanese, it is OK. If you cannot read, it is still OK. This page gives a photo of Yukawa in is his latest year.

2. Harmonic oscillators

Like all great physicists, Feynman was fond of harmonic oscillators. Before inventing a new physical theory, it is absolutely necessary to test it for harmonic oscillators. If it works there, we can continue. If it does not, we do not know what to do.

In 1970, Feynman gave a very controversial talk on at the APS meeting in Washington, DC, U.S.A. It was about the quark model in the Lorentz-covariant regime. Feynman was telling us that we should use harmonic oscillators instead of Feynman diagrams for bound states. Everybody said Feynman became absolutely crazy, but I said it was the greatest talk I have ever heard. Then, I also became a crazy man. Indeed, Feynman gave me enough courage to develop my own independent research line. Here is a detailed story from my home page.

I then started reading papers written by others. The first paper I read was a short note by Hideki Yukawa published in the Physical Review. I also noted that the paper of Fujimura, Kobayashi and Namiki [Prog. Theor. Phys. vol.43, 72 (1970)] who use the Yukawa oscillators to calculate the dipole-cutoff of nuclear form factors. I still do not know why they do did not refer to Yukawa's work in their paper.

In 1973, with Marilyn Noz, I published my first paper on this subject. We were interested in combining the wisdoms of Yukawa and Feynman. Since then, we are still continuing our collaboration and still writing papers on covariant harmonic oscillators. One of the most rewarding results in this venture was to see Paul A. M. Dirac was working along the same logic. Click here for a detailed story.

V. I. Man'ko, Y. S. Kim, and M. A. Markov (Maryland 1984).

After 1973, I learned that M. A. Markov of the Soviet Union published a paper on Yukawa oscillators. He was interested in deformation of extended particles. Academician Markov was kind enough to send me a reprint of his paper published in Nuovo Cimento Suppl. vol.3, 760-772 (1956). I was fortunate enough to have a photo with him in 1984.

On my right is Vladimir Man'ko, who wrote a paper with V. L. Ginzburg in 1965 (Nucl. Phys. vol.74, 577-588). They were interested in possible application of the Yukawa oscillators to the quark model soon after Gell-Mann's 1964 paper on the quark model.

Vladimir Man'ko is a very resourceful man, and I still meet him often, and I have many photos with him. Here is a photo taken at the Covent Garden (London) in 1993 with young musicians.

In his article of 1965, Yukawa stated that Markov attempted to use the concept of extended particles to deal with singularities in particle theories [J. Phys. (USSR) vol2, 453 (1940)]. In the same article, Yukawa formulated harmonic oscillators in terms of step-up and step-down operators and constructed a set of operators known today as the generators of squeezed states.

3. Feynman's "one physics" and Yukawa's harmony of the universe. Both as Kantian physicists like Einstein.

According to R. P. Feynman, the adventure of our science of physics is a perpetual attempt to recognize that the different aspects of nature are really different aspects of the same thing.

I studied this aspect of physics extensively starting from the philosophy of Immanuel Kant, which influenced Einstein in his formulation of relativity. I then concluded that, like Einstein, Feynman was also a Kantianist. The purpose of my Feynman page is to emphasize this point.

I was so excited about the Kantian influence on modern physics that I went to the Russian city of Kaliningrad in 2005. This place was a German city called Koenigsberg before World War II. Kant was born and spent 80 years of his entire life in this city, and it is widely believed that his philosophy was formulated from the city's geographical environment. The best way to study this aspect is to go there and look at the place and talk to the people. Here is my Kaliningrad webpage.

I was also interested in whether Hideki Yukawa was a Kantianist. It is well known that Yukawa studied Taoism systematically in his early years. The question then is whether Kantian base and Taoist base have the common ground. I developed this suspicion while talking with Professor Eugene Wigner during the period 1985-91.

Yukawa with Einstein in Princeton (1953). Photo from Mainichi Shinbun.

While I was in Kaliningrad, I was able to confirm this point. There are many Kantian philosophers in Japan, and there are many Japanese books on Kant. It is because Japan traditionally has a strong Taoist base. Indeed, like Einstein and like Feynman, Yukawa was a Kantianist. I am very happy to present to you a photo of Yukawa with Einstein taken in 1953.

Why do Kantianism and Taoism have the same ground? After coming back from Kaliningrad, I was able to provide the following answer. Both are products of their own geography. Kantianism is product of Koenigsberg now called Kaliningrad. Its geography is the same as that of Venice with large lagoons providing a natural harbor for ships from many different places. People used to come to this place with different backgrounds and different opinions. Kantianism was developed to accommodate those different viepoints.

Taoism is the philosophy developed by ancient Chinese. After the ice age, many people came to the river banks of the two great rivers of China. They all came with different languages and different ways of thinking. In order to communicate, they started drawing pictures. That is how Chinese developed their characters. In order to talk to other people, they started singing. That is why spoken Chinese has tones. How about thinking? If there is one opinion, there is a different or opposite opinion. That is how Chinese developed the concept of Yang (plus) and Ying (minus), and the harmony between them. You may be interested my archived article on this subject.

4. Yukawa and Dirac

Yukawa and Dirac (1953).

• Dirac met Hideki Yukawa in 1953, probably in New York. They met again in 1955. It appears that they met in Kyoto (Japan) in 1955. I assume they talked about physics. In 1953, Yukawa published a short paper entitled Structure and Mass Spectrum of Elementary Particles. II. Oscillator Model while he was visiting Columbia University. In 1955, Yukawa became more intensely interested in harmonic oscillators, while Dirac was using the oscillator language throughout his life.

  However, there does not seem to be any published material to indicate that they talked about harmonic oscillators. With one of my co-workers, I was able to able to compose a paper on what they could talked to each other on the oscillator issue, and published the paper in the Progress of Theoretical Physics, the Japanese Physics Journal established by Hideki Yukawa.

  Dirac, Yukawa, and their wives in Kyoto (1955).

  In either case, both of them received their Nobel prizes for predicting new particles by writing mathematical poems.

  It is my pleasure to post a photo of Dirac and Yukawa (Kyoto 1955). Their wives are also in the photo. I never met Professor Yukawa, but I once received a letter from Mrs. Yukawa. Click here for her handwritten letter. In this letter, she talks about Mrs. Margit Dirac. I met Mrs. Dirac in 1978 (in Florida) and in 1988 (in Princeton). I met Paul A. M. Dirac in 1962 and in 1978.

5. Yukawa Hideki

Yukawa Hideki from the AIP Niels Bohr Libray

In Japan, Hideki Yukawa is known as Yukawa Hideki (last name first). He became a national hero for Japanese when he got the 1949 Nobel prize in physics. Japan needed him because the Japanese morale was at the rock bottom because of the disastrous defeat in the Pacific War with nuclear baptism. Japanese were not allowed to sing or play their national anthem until the San Francisco peace treaty signed in 1952. Nobel prize in physics meant to Japanese that they are smart enough to make nuclear bombs.

In addition, there are two female contributors to Japan's morale boost. One was Misora Hibari (pop singer like Elvis Presley) and Suwa Nejiko (violinist like Isaac Stern). Click here if you like to hear more about them.

While I was in Stockholm (Sweden) in 2005, I dropped in the City Hall where the Nobel banquet is held evry year in December. I met there a group of Japanese tourists at the banquet hall, and pretended not to know whether Japan ever produced Nobel laureates. They asked me what my profession is, and then asked me whether I ever heard of Yukawa Hideki. We all laughed and produced this photo. I even told them I have a photo of Dr. Yukawa dancing with Mrs. Yukawa on "this floor" (with my finger pointing down). Would you like to see this photo?

Feynman with the Yukawas in Kyoto (1954). Courtesy of Hayakawa Saito.

1. Yukawa Hideki dancing with his wife after the Nobel dinner in Sotockholm (1949). Scanned from Nihon Keizai Shinbun.

2. Yukawa Sumi (Mrs. Yukawa) next to Feynman (1954).

3. Handwritten Letter from Yukawa Sumi. I was fortunate enough to receive a handwritten letter from Mrs. Yukawa in 1981.

Mrs. Yukawa had enough personality to lead women's organizations for world peace and women's liberation. She was positive and dynamic. She was a nontraditional Japanese lady, called "wagamama." These days, the Wagamama is known as a rapidly-spreading Japanese restaurant chain throughout the world.

I would like to thank my Japanese colleagues who constantly sent me informative materials on Professor Hideki Yukawa.

Y. S. Kim (2008.9.8)

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copyright@2008 by Y. S. Kim, unless otherwise specified.

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