Li Zhengdao's explanation of the source of parity non-conservation thought
Q: According to the general view, the crux of Li Yang's split lies in the following argument between you: Who was the first to put forward the idea of the Nobel Prize-winning paper, that is, the breakthrough of weak function parity non-conservation? It is said that it was he who "at the critical moment, I (referring to Yang himself) thought of ..." and said that you opposed this view first and agreed after his persuasion [1]. Do you think this statement is true? Can you tell me the truth you know?
(Editor's Note: Pointing the mouse to the position of [1] will pop up the footnote [1]. The same below. )
A: Yang Zhenning's statement is inconsistent with the facts. In fact, the breakthrough of parity non-conservation thought was completed by me independently in the first ten days of April of 1956, which had nothing to do with Yang Zhenning.
The situation at that time was like this:
1954 and 55 years, the mystery of θ-τ became the focus of physics. Here I want to briefly explain the mystery of θ-τ at that time. Two new particles θ and τ were observed from cosmic rays in the early 1950s. They decay in very different ways. θ decays into two π mesons and τ decays into three π mesons. Because the total parity of odd π mesons is negative, and the total parity of even π mesons is positive. Therefore, from the decay modes of θ and τ, it can be determined that the parity of θ is positive (called scalar) and that of τ is negative (called pseudo-scalar). Strangely, in 1954 and 55 years, it was found that two particles with different parity, θ and τ, had exactly the same life and mass within the experimental precision range.
At that time, from the decay mode of θ and τ, we can not only determine the parity difference between them, but also know that this decay is realized by weak force, so we can estimate their life by theoretical calculation. If τ and θ are different particles, the lifetime of τ should be much longer than θ, about one hundred times. However, the experimental results show that the lifetimes of τ and θ are almost the same. Moreover, if τ and θ are different particles, why are their masses almost identical? If you think it's the same particle, how can it have completely different parity?
In order to solve this problem, physics put forward various ideas, but none of them succeeded. In 1950s, in the field of particle physics, an international comprehensive academic conference was held every year at the University of Rochester in new york, USA. Therefore, this very important meeting is called the Rochester Conference. Anyone who wants to attend the meeting must receive an invitation letter. At the Rochester meeting on April 3-7, 1956, the problem of θ-τ was also discussed. At that time, some people at the meeting, including Yang Zhenning and me, asked whether parity might not be conserved in the decay of θ and τ. However, none of these discussions at the meeting came to any conclusion. To understand why this happened, I need to introduce the background of parity conservation at that time.
Parity conservation was recognized as an important physical law at that time. Parity conservation is based on "left-right symmetry", which has always been regarded as an axiom of physics. From classical physics to modern physics (including mechanics, electromagnetism, gravitational field, weak interaction theory, atomic, molecular and nuclear structures, etc.). ), all physical theories were symmetrical before April 1956. Because every physical theory has a lot of experiments to prove it, physicists naturally think that "left-right symmetry" has also been fully proved in particle physics, which is very correct and the truth of nature. Parity conservation is natural.
1During the discussion at the Rochester Conference in early April, 956, all physicists realized that all known physics is left-right symmetry and parity conservation. There is no need to discuss this. The problems discussed at the meeting are: whether parity may not be conserved in the decay process of θ and τ; Aside from all the known physics at that time, whether θ and τ can be used as special cases is an isolated point.
What happens if θ and τ are the same particle and parity is not conserved during its decay? The result is that the same particle (θ-τ) can decay in positive θ mode or negative τ mode. However, this result is exactly the same as the θ-τ puzzle phenomenon known from the beginning. Therefore, although the hypothesis that the θ-τ decay parity may not be conserved is put forward, this hypothesis has not produced any new physical results. This assumption has nothing to do with all other physics. Before this hypothesis was put forward, the mystery of θ-τ was an isolated point; After making this assumption, θ-τ is still an isolated point. Because this hypothesis can't produce any new conclusions, it can't be regarded as a breakthrough of parity non-conservation. This is recognized by the physics community.
At that time, I was also concerned about this problem and made some attempts, but failed. I remember that on April 3-7, one or two days after the meeting of 1956 in Rochester, that is, on April 8 or 9, my colleague J. Steinberger came to my office to ask questions. At that time, he was conducting experiments on the generation and decay of unstable heavy particles. His problem is how to determine the spin of such heavy particles, which has nothing to do with the mystery of θ-τ and parity non-conservation. In the process of speaking, I was inspired and suddenly enlightened. To solve the mystery of θ-τ, we must first leave the θ-τ system, assuming that particles other than θ-τ may also have a new phenomenon of parity non-conservation. I found that in Steinberg's experiment, a new pseudo-scalar can be easily organized by using several momentum generated and decayed by heavy particles. Using this pseudo scalar other than θ-τ, we can test whether the parity of the system other than θ-τ is not conserved. These pseudo-scalars, obviously, have not been measured by any previous experiments. Using these new pseudolites, we can systematically study the big problem of whether parity is not conserved. The mystery of θ-τ is no longer an isolated point, it can be related to the heavy particles that Steinberg is experimenting with, or it may be related to all other physics as a whole. To solve the mystery of θ-τ, it is necessary to measure pseudo-scalars other than θ-τ in weak interaction. I guess parity non-conservation is probably a universal basic scientific principle. This is a breakthrough in parity non-conservation.
At that time, I told Steinberg this idea and asked him to tell the people in his experimental group to reanalyze the experimental data according to my suggestion. Steinberg is also very excited. He said that all the original experimental data you need have been recorded in the journal of his experimental group, but because you don't know how to analyze it, you haven't put it together for analysis. After that, he and his experimental group immediately analyzed their experimental data according to the method I suggested. Although there are signs that parity is not conserved, there is not enough data to draw a conclusion. 1in September, 956, their papers on heavy particle experiments were published in Physical Review, namely R. Budd, M. Chretien, J. leitner, Samuel (N.P. Samios) and M. Schwartz. Part of the article is to discuss my breakthrough idea and its analysis. They also thanked me for my "very helpful discussion" in the article, that is, my breakthrough thought on parity non-conservation, which is the source of the breakthrough thought of parity non-conservation [3]. Schwartz, one of the participants in this experiment, later published a recall article.
Schwartz (1988 Nobel Prize winner) remembers the above situation vividly. He has a clear memory and written record of my suggestion at that time, the breakthrough of parity non-conservation thought and what happened. Its course and time are completely consistent with my memories published in 1986. Schwartz said:
"In any case, I remember very clearly that after the Rochester meeting (April 3-7), Steinberg immediately returned to the Nevis laboratory and told us that he had just discussed with Li () and that Li had a very important idea. Li suggested Steinberg divide the data from φ = 0 to φ = 2π. ..... If there is asymmetry, it will be an obvious example of parity destruction "[4].
All this fully proves that the breakthrough of parity non-conservation thought was first made independently by me in early April of 1956, and had nothing to do with Yang Zhenning.
In mid-April, 1956, Steinberg and his experimental team have obtained the preliminary analysis results. He told me that there are seven cases of heavy particle ∧0 decay from φ = 0 to π, but there are 15 cases from φ = π to 2π, which is about twice. There are 13 cases of heavy particle Σ-decay from φ = 0 to π, and only 3 cases from φ = π to 2π, which is about 4 times smaller. Of course, these data are not enough to draw the conclusion that parity is not conserved. Steinberg added that he estimated that within one year, they could use the accelerator of Brookhaven Laboratory to produce ten times more cases. Then we can complete the decisive experiment of whether parity is conserved in the decay process of ∧0 and ∑-equal-weight particles. (In fact, one year later, in 1957, Steinberg and his collaborators did complete the decisive ∧0, ∧-parity non-conservation experiment and published it in Physical Review. )
I was very excited at that time. This preliminary experiment of parity non-conservation has fully proved that my breakthrough in parity non-conservation is correct and feasible. The question of whether parity is conserved no longer stays at the isolated point of θ-τ mystery. Unstable heavy particles ∧0 and ∑-have been included except θ-τ!
From mid-April to the end of April, 1956, I made great efforts to complete the theoretical analysis and thesis writing of the parity non-conservation in θ-τ, ∧0, ∑-and all weak interaction decay fields called "exotic particles". I made an appointment with Steinberg, and my theoretical analysis article was published at the same time as the experimental analysis article of his experimental group at that time, that is, the article published by Budd, Schwartz, Steinberg and others on1September 5, 956. Of course, apart from exotic particles, there is a larger field of weak interaction decay, that is, β decay with a research history of more than 50 years. This includes neutrons, pions, muons and more particles. I'm going to start analyzing exotic particles in early May, 1956, after writing the paper on parity non-conservation.
At the beginning of May, 1956, Steinberg came to my office in Columbia University and said that he had just reported their experimental results and analysis at the academic report meeting of Brookhaven Laboratory, and also reported my suggestion on parity non-conservation. Yang Zhenning also attended and listened to the report. But he strongly opposes my view that audience parity is not conserved. During that time, I didn't work with Yang Zhenning. After the meeting in Rochester in early April, I returned to new york and never saw Yang Zhenning again. After listening to Steinberg's words, I called Brookhaven Laboratory and told Yang Zhenning that since I broke up with him at the Rochester meeting, I had made a theoretical breakthrough, and asked him not to make public his objection before discussing it with me. The next morning, as Yang Zhenning said, in late April and early May, Yang Zhenning came to my office. After a brief conversation, Yang Zhenning said that he had come by car and forgot the difficulty of parking in new york. He had to walk into the street to move his car.
In all the streets around Columbia, it is stipulated that parking is not allowed every morning from 1 1 to 2 pm because the streets are cleaned. Because Yang Zhenning is not familiar with these rules in new york, I left the campus with him and went to125th Street in the north of new york. The rule of street cleaning there is that no parking is allowed from 8 am to 1 1 every morning. There are two China restaurants at the intersection of125th Street and Broadway, which I often go to. Because it was eleven o'clock in the morning and the hotel was not open yet. Let's go to the cafe next to Tianjin Hotel for a cup of coffee. I told Yang Zhenning all my recent work, my breakthrough idea about parity non-conservation and Steinberg's new experimental results according to my suggestion.
Yang Zhenning strongly opposes it. He said that he had just heard Steinberg's report two days ago. Steinberg measured the "dihedral angle" he (Yang Zhenning) studied, and will never get any new results of parity non-conservation. While we were arguing, the Tianjin Hotel next door opened.
As an old customer of Tianjin Hotel, I borrowed a pen and paper from the waiter. I wrote down the equation, drew a picture, and explained all this to Yang Zhenning again. I pointed out to him that the angle φ used in Steinberg's new analysis is not the dihedral angle imagined by Yang Zhenning, but the new pseudo-scalar referred to by my ideological breakthrough. The dihedral angle is a scalar, which can only be from 0 to π. Of course, it is parity conservation. This new φ angle is a pseudo-scalar, which can range from 0 to π, and then it can also range from π to 2π. When φ is in the range of 0 ~π, φ is the same as dihedral angle, but it is completely different in the range of π~ 2π. With such a new pseudo scalar φ, through the decay process of ∧0 and ∑-,if the number of cases in these two φ regions is different, it is a clear proof of parity non-conservation, so we can measure whether particles other than θ-τ are also parity non-conservation. This is something that others have never thought of before. This is a breakthrough in my idea of parity non-conservation.
According to my suggestion, Steinberg experimental group analyzed the number of cases in the range of 0 to π and π to 2π in ∧0 and ∑-decay. This analysis was completed in April. As a result, these two quantities are very different, and we can already see the signs of parity non-conservation. Unfortunately, the number of examples in the whole experiment is not enough to draw a conclusion, but it can already prove that my ideological breakthrough is feasible. Then, I repeatedly wrote down the preliminary analysis details of Steinberg's experimental group, which I just dictated in the cafe. Yang Zhenning slowly stopped opposing.
After lunch, when we returned to my office in Columbia University, Yang Zhenning was completely convinced. He is also very excited. On my desk, he saw an article I was writing about the possibility that parity might not be conserved in the decay of θ-τ, ∧0, ∑-and other strange particles. I told him that this article would be published at the same time as Steinberg's experimental article. I also told him that I began to prepare to extend this analytical application to the field of beta decay.
Yang Zhenning said that he was willing to cooperate with me. At the same time, he advised me not to publish the article on parity non-conservation of singular particles that I had almost finished writing. He said that this is a very popular breakthrough, and it is necessary to occupy the whole weak field at once with the fastest speed, so as to be more complete.
Yang Zhenning has a highly critical vision. He is an excellent physicist and a good friend of mine. Parity non-conservation will involve all fields of physics. I think Yang's participation will undoubtedly make the final result more fruitful. Therefore, I accepted his request for cooperation and welcomed it.
My decision is correct, and our cooperation is very successful. Before 1956 was symmetric physics from classical physics to modern physics. After 1956, it is found that most physical phenomena are asymmetric. Not only parity is not conserved, but also positive and negative charges, time reversal and vacuum are asymmetric, so quarks can be confined, different neutrinos can change each other, and even protons may be unstable. Of course, it wasn't 1956 that suddenly changed the outside universe, but the article on parity non-conservation published by Yang Zhenning and me in 1956 changed all the traditional, deep-rooted, wrong and blind old ideas about the concept of "symmetry" in the whole physics field!
1956 Our article on parity non-conservation brought the Nobel Prize of 1957. For me, the greater significance is that I have this opportunity to make a fundamental and revolutionary contribution to the parity non-conservation in the history of human thought development. This makes me deeply feel my luck and the great significance of my life that can make a breakthrough contribution.
The decisive experiment to prove that weak interaction parity is not conserved was completed by Wu Jianxiong and her collaborators in 1957 1 year. About how I made a breakthrough in the idea of parity non-conservation and how their decisive experiment started from me, Wu Jianxiong also has her very clear recollection article [5], published in 1972:
"... 1956 One day in early spring, Professor Li Zhengdao came to my office on the 13th floor of Puping Physics Laboratory. He explained the mystery of τ-θ to me first. He went on to say that if the answer to the mystery of τ-θ is parity non-conservation, then this kind of destruction should also be observed in the spatial distribution of β decay of polarized nuclei: we must measure pseudo-scalars.
"... after Professor Li came, I thought about it from beginning to end. It is a precious opportunity for a scholar who is engaged in beta decay physics to do this crucial experiment. How can I give up this opportunity? ..... That spring, my husband Yuan Jialiu and I planned to attend a conference in Geneva and then go to the Far East. We all left China on 1936, exactly twenty years ago. We have booked tickets for the Queen Elizabeth. But I suddenly realized that I must do this experiment at once and do it well before other physicists realize the importance of this experiment. So I asked Jia Xiang to let me stay and let him go alone. ..... At the end of May, after the end of the spring semester, I began to prepare this experiment seriously. ……
On the afternoon of 1 month 15, the physics department of Columbia University held a press conference, announcing that a basic law of physics had been unexpectedly overturned. ..... The news broke out among the public and quickly spread all over the world. As o·r· Frish, a professor at Cambridge University, described in a speech at that time, the incomprehensible statement that parity is not conserved spread all over the world like a new gospel. "
The following is Yang Zhenning's memory of 1982 parity nonconservation 1956 [6]:
"In early April, the spring semester of the Institute for Advanced Studies (Princeton) ended, and my family and I went to Brookhaven for the summer vacation in April 1956+07. Li Zhengdao and I continue to exchange visits twice a week. During this period, we met Brooke Haven in Colombia. As in the past, we were interested in all kinds of problems, but at that time we were most concerned about the mystery of θ-τ. We are particularly interested in the angular distribution in the following reaction chains:
π-+ p → ∧0+θ0 ( 1)
∧0 → π-+ p (2)
R.P. Shute, Steinberg and W.D. Walker have studied these reactions. They reported their research results at the Rochester Conference, at which the exact range of dihedral angle variables used by these three groups of physicists was disputed.
"One day in late April or early May, I drove to Colombia for a weekly visit. I took Li Zhengdao out of his office and got on the bus. It is difficult for us to find a parking space. Later, I parked my car at the corner of Broadway and125th Street. It's time for lunch, but the restaurant nearby hasn't opened yet. So we went to the nearby "White Rose" cafe and continued our discussion there. Later, we had lunch at "Shanghai Restaurant" (I remember this restaurant, but Li Zhengdao said that he remembered "Tianjin Restaurant"). Our discussion focuses on the mystery of θ-τ. At a key point, I thought that the symmetry of production process should be separated from the decay process. Therefore, if people assume that parity is conserved only in strong interaction, but not in weak interaction, then θ and τ are the same particle, and the conclusion that spin and parity are 0- (inferred from strong interaction) will not encounter difficulties. This separation is of special significance for reaction chains (1) and (2). Li Zhengdao first opposed this view. I tried to convince him, because this idea can be tested by (1) and (2) the possible asymmetry in the reaction, and it is more attractive. Later, he agreed with me.
"... At that time, Li Zhengdao was not familiar with beta decay. He can't help it. He advocates that the research on reactions (1) and (2) should be written into short articles and published first. I don't agree to do this, because I have to finish the calculation of β decay. "
At that time, Steinberg's experimental group was studying the reaction chain (1) and (2) recalled by Yang Zhenning. Yang Zhenning's breakthrough in the idea of parity non-conservation is the same as my memory, that is, the idea I described in the memory article published by Schwartz in 1986, which is what Schwartz said. In early April of 1956, "Li suggested Steinberg that we divide the data from Ф = 0 to Ф = 2 π". So Yang Zhenning's memory published in 1982 is consistent with my memory published in 1986. What is the breakthrough of parity non-conservation thought at the beginning of 1956? However, Yang Zhenning and I have completely different memories of how the breakthrough of parity non-conservation thought came about. The time difference between the two statements is about three weeks, and the location and situation are completely different.
The breakthrough of parity non-conservation is completely focused on the reaction process of ∧0 and ∑-heavy particles. The feasibility of this idea can only be determined by analyzing the generation and attenuation of ∧0 and ∑-. If any theoretical physicist suddenly makes such an important breakthrough, he will immediately go to the team that did ∧0 and ∑-experiments to convince them to reanalyze their data according to the suggestion of this breakthrough. However, Yang Zhenning 1982' s reminiscence articles and his later biographies have no such recollection and narration at all. It can be seen that Yang Zhenning's above memories are unreasonable. Why? Because in early May of 1956, when Yang Zhenning came to see me in new york, he clearly knew that Steinberg's experimental group had made an analysis based on my breakthrough in parity non-conservation. Therefore, Yang Zhenning can't mention this experimental analysis in his memory.
Steinberg (1988 Nobel Prize winner), Yang Zhenning and I were classmates of the University of Chicago in the 1940s, and we all knew each other very well. 1956 Steinberg and I are both full professors in the Physics Department of Columbia University. Our office is very close, only one floor away. At that time, most of the ∧0 and ∑-cases in the whole physics field were in the hands of Steinberg experimental group, with about 40 cases, which is not a small number. Yang Zhenning learned all these things at the meeting in Rochester in early April. Steinberg, Yang Zhenning and I were all invited to attend the Rochester meeting. If, as Yang Zhenning said,1early May, 956, he suddenly thought of a key point in the generation and decay reaction chain of ∧0 at lunch, and the idea of parity non-conservation had such an important breakthrough, we could not return to Columbia University after lunch, and he did not go to find a friend who was close to my office and was also his close friend Steinberg. It is impossible for him not to tell Steinberg immediately that his important ideas ∧0 and ∑-decay may be parity-nonconservation. At the same time, it is impossible for him not to rush to ask Steinberg to do an experiment as soon as possible to see if his own ideological breakthrough is feasible.
Why didn't Yang Zhenning go to Steinberg? Because Yang Zhenning fully realized that Steinberg not only knew my breakthrough at that time, but also made an analysis according to my thoughts. At the same time, Yang Zhenning also knows that he just listened to Steinberg's report two days ago, and he also objected. At the beginning of May, when Yang Zhenning was having lunch at Tianjin Hotel, 1956, he was fully aware that the analysis results of Steinberg experimental group showed signs of parity non-conservation. Although there is no conclusion, it can completely prove that my ideological breakthrough is feasible. In the three weeks after the meeting in Rochester in April 1956, these extremely important facts were completely blank in Yang Zhenning's memory. Why? Because in the memory of Yang Zhenning 1982, the narrative about the breakthrough of parity non-conservation thought is false. He knew that he wanted to turn my ideological breakthrough into his and his opposition into mine. There are many other plots of 1982 in Yang Zhenning's memory that are not true. Give two examples. 1At the beginning of May, 956, when he saw an article I was writing in my office about the non-conservation of parity of exotic particles such as θ-τ, ∧0 and ∑-,it was he who asked me to participate in the analysis of β decay field. He also told me not to publish articles about exotic particles. However, in the memory of 1982, he even said: "He (referring to Li) was a little irrepressible, and advocated that the research on (1) and (2) should be written into short articles and published first, but I don't agree with this" [6]. Yang Zhenning said that I "couldn't help it" and it didn't match the facts. This is completely presumptuous and immoral.
Before we co-wrote the paper on parity non-conservation, in the eight years of 1948-56, Yang Zhenning and I co-wrote only six papers, which was a small part of my papers published in the same period. After 1956 we published a paper on parity non-conservation, Yang Zhenning and I started close cooperation. From the second half of 1956 to 1962, we have written 26 articles.
1April 1956, Yang Zhenning and I didn't have any cooperation projects, nor did we meet twice a week as Yang Zhenning recalled in 1982. When he came to my office in early May, 1956, he hadn't been to Columbia University for some time. Otherwise, he won't drive around eleven o'clock in the morning, because he can't forget the problem of parking near Columbia University around noon. I haven't seen Yang Zhenning in April. In fact, the so-called twice-weekly meeting in Yang Zhenning's memory 1982 began after we published a paper on parity non-conservation in June 1956+00. Yang Zhenning's memory 1982 said that he and Li Zhengdao exchanged visits twice a week in April 1956, which was also not true.
Because of my breakthrough in thought, Budd, Christine, Retnell, Samuel, Schwartz and Steinberg analyzed the parity non-conservation in their experimental articles at that time (April 1956). Therefore, they thanked me in the paper [3]. They didn't mention Yang Zhenning because it had nothing to do with Yang Zhenning.
As mentioned above, Schwartz, one of the participants in this experiment, clearly stated in the memory of parity non-conservation breakthrough in April 1986 that this idea was put forward by me and Yang Zhenning was not mentioned at all, because it had nothing to do with Yang Zhenning.
It can be seen that all this completely proves that the breakthrough of parity non-conservation thought was made by me independently, and it has nothing to do with Yang Zhenning.
After I made a breakthrough in the idea of parity non-conservation in early April of 1956, it was not until May that Yang Zhenning joined in and made a systematic theoretical analysis of parity non-conservation with me, and jointly wrote a paper that won the Nobel Prize. The above description does not belittle Yang Zhenning's contribution to cooperation with me, nor does it deny his qualification to win the Nobel Prize, let alone the honor he has won for it.
Although we won the Nobel Prize together, it is an objective fact that I independently made a breakthrough in parity non-conservation, which is documented and known to my colleagues. But I have never emphasized this point. I have never hurt Yang Zhenning, and I have never belittled his contribution to completing the paper on parity non-conservation in cooperation with me. But the crux of the problem is that from 1982 to now, Yang Zhenning always wants to erase the fact that I independently completed the breakthrough of parity non-conservation. His account of this problem has no factual basis and is completely inconsistent with historical facts.