The German physicist Sommerfeld came to New York to promote the English version of his academic monograph "Atomic Structure and Spectral Lines".

The first edition of Atomic Structure and Spectral Lines was published in 1919, in which Sommerfeld systematically expounded his theoretical system.

At the Solvay Conference in 1921, the experiment of space quantization was recognized by the heads of physics and named the "Woodgate-Lee Experiment".

The Woodgate-Lee experiment was a strong evidence for Sommerfeld's theoretical system, so at the end of 1921, Sommerfeld revised Atomic Structure and Spectral Lines, adding new content such as the Woodgate-Lee experiment and alkali metal lines, and at the same time carried out the translation of the English version.

The promotion of the English version of the second edition of "Atomic Structure and Spectral Lines" is one of the purposes of Sommerfeld's visit to the United States.

As early as 1921, Li Kangping established a correspondence with Sommerfeld, and Einstein said, "You can tell Mr. Sommerfeld whatever you want to say to me", so Li Kangping visited Mr. Sommerfeld's hotel on Fifth Avenue with gifts.

The 55-year-old Sommerfee, who has a thick beard above his lips, warmly received Li Kangping and presented him with an English version of "Atomic Structure and Spectral Lines".

"Dr. Li, I have wanted to meet you for a long time, I thanked you in my letter for your contribution to the theory of space quantization, and now, in front of you, I thank you again." Sommerfeld said sincerely, and as he spoke, he couldn't help patting Li Kangping's thigh.

Before this, although the two had not met, they had been friends for a long time. Sommerfeld expressed his affection for Li Kangping, a young physicist, with affectionate gestures.

Compared with the Göttingen School and the Copenhagen School, the Munich School led by Sommerfeld is not so famous, but the Munich School specializes in a "martial art" and is unique in this "martial art".

The Woodgate-Lee experiment proves the only existence of quantum states, is conclusive evidence for the theory of spatial quantization, and is a strong agent for quantum theory.

However, the Woodgate-Lee experiment also poses serious difficulties for quantum physicists, revealing significant shortcomings in the old quantum theory.

The major shortcomings of the old quantum theory are mainly two problems, one of which is the problem of birefringence. Second, the problem of steady-state transition.

Einstein, at the Solvay Conference in 1921, raised both questions when he endorsed the Woodgate-Lee experiment.

Not only Einstein, but also physicists including Sommerfeld and Bohr, the founders of the theory of space quantization, also found it difficult to explain the problem of birefringence and the problem of steady-state transitions under the premise that the theory of space quantization is established.

In terms of running enterprises, Li Kangping put forward the idea of "rolling development".

In fact, physics is also moving forward in a rolling development mode.

Although the old academic problems have not been completely solved, this does not prevent the rolling development of physics.

Li Kangping knows very well that the birefringence problem and the stationary transition problem can be perfectly explained through a theory.

This theory is called "electron spin".

Li Kangping pinched his fingers and calculated, the concept of "electron spin" was almost time to appear.

But not today.

Sommerfeld made a rare trip to the United States, and Li Kangping chatted with Sommerfeld about material waves.

Particles of matter must have particles, so do particles of matter have fluctuations?

Li Kangping elaborated on the wave nature of material particles in the article "Matter Waves", and published "Nickel Crystal Electron Diffraction Experiment", in which he conjectured and verified by himself, and obtained experimental evidence of material waves.

Sommerfeld, who had read the papers "Waves of Matter" and "Experiments on the Electron Diffraction of Nickel Crystals", said: "The 'faithful believers' have received neither much glory nor much success in trying to oppose the current trend of quantum theory." In my opinion, there is great hope for positive progress through this pathway. Dr. Lee, I am glad to see that you have made such a bold hypothesis and have found plausible evidence for your hypothesis. One is certainly far from being able to say anything last, and we are only at the very beginning here. Dr. Lee, you've got involved some philosophical thinking, and you've moved significantly away from that pure formality. So, I wish you every success in your endeavors. ”

With that, Sommerfeld smiled and slapped Li Kangping's sturdy and elastic thighs again.

In terms of material waves, it seems difficult to get Sommerfeld to make a clear statement.

To be a man at the level of a bigwig like a school leader, of course, he knows how to be cautious.

"Mr. Sommerfeld, let's change the subject."

Resting no longer on Sommerfeld's attitude towards material waves, Li Kangping took out two copies of his dissertation from his bag, one from Compton and the other from Duane.

"Professor Compton and Professor Duane both carried out two experiments and wrote two papers on the basis of quantum theory and optical quantum theory. These two papers have not yet been published, and Professor Compton and Professor Duane are currently in a situation of convincing each other. I think these two papers are very important, and with the consent of Professors Compton and Duane, I would like to ask Mr. Sommerfeld to take a look at them. ”

"Which Compton?"

"Arthur Compton."

"Arthur Compton? I don't know this person. As for Professor Duane, I have met with him, and I will give him a copy of "Atomic Structure and Spectral Lines". Put the paper with me first, and now or tomorrow, Dr. Lee, I want to visit the lab where the Woodgate-Lee experiment was made, can I do it? ”

"Professor Woodgate went to Michigan for some personal matters, so Professor Woodgate was not able to come with me here to visit you. Professor Woodgate has commissioned me to accompany you to the Woodgate Laboratory, so, Mr. Sommerfeld, let's go to Columbia University now. ”

Li Kangping personally drove Sommerfeld to the Woodgate Laboratory at Columbia.

The experiment of space quantization has long been completed, and the experimental equipment of space quantization is completely preserved in the laboratory.

Sommerfeld carefully observed the complete set of space quantization equipment, and it was the experimental data generated by this device that proved his theory of space quantization.

"Professor Otto Stern of Germany--- you may not have heard of that name, but he did almost identical molecular beam experiments a few months ago. It seems to me that Professor Otto Stern copied your experiments and got the same data. Lee, please don't have any worries, no one can take credit from you, Professor Otto Stern repeated your experiment out of pure academic interest, and he started and completed his experiment after reading your paper on the Woodgate-Lee experiment. Sommerfeld said, and he immediately said with great interest: "Professor Otto Stern's experimental equipment is a little more advanced than yours, but it is really remarkable that you designed and manufactured this equipment in the first half of 1921 and obtained convincing experimental evidence!" ”