Ding Zhaozhong: Science is that the majority obeys the minority

China Newsweek reporter/Huo Siyi

Published on May 2023, 5, the 29rd issue of China Newsweek magazine

"I don't think Professor Ding Zhaozhong needs more introduction." On the morning of May 5, at the "High Energy Forum" held by the Institute of High Energy Physics of the Chinese Academy of Sciences, director Wang Yifang "introduced" like this, and the audience applauded.

Ding Zhaozhong nodded to the audience. In the eyes of those familiar with him, Ding Zhaozhong does not seem to have changed much in the past ten years. He was dressed in his usual black suit, his hair was gray but neatly groomed, he spoke slowly and softly, his Chinese voice was not loud, but he was determined, and he used to put his hands together in front of his chest when he spoke, showing a calmness and ease. Time seemed to freeze on him.

Unlike most physicists, the 87-year-old is still active in scientific research. He is not retired and is the chief scientist of a very large international collaborative project Alpha Magnetic Spectrometer (AMS). The project was proposed by him and went through twists and turns until 2011, when Ding Zhaozhong was 75 years old.

For the past 12 years, Ding Zhaozhong has woken up at seven in the morning and worked until seven or eight in the evening, regardless of weekends, rarely socializing, and he has devoted almost 100% of his energy to the physics experiment "this one thing". He frequently appears at conferences, forums and television programs, regularly presents the latest results of AMS, and publishes papers.

As an old man, the wrinkles on Ding Zhaozhong's face are increasing, and his waist is bending even more, but physicist Ding Zhaozhong has not changed. For decades, he has been telling about his discoveries and views on physics.

The Economist once said of him: "There are many super-intelligent and super-ego scientists in high-energy physics, and Ding Zhaozhong has few opponents in both aspects." In his speech on May 5, Ding Zhaozhong said in his usual resolute tone: "The development of natural science is that the majority obeys the minority, and science can move forward only after a very small number of people overturn the views of the majority." ”

"The very small minority that overthrows the majority"

Ding Zhaozhong is "a very small minority that overthrows the majority", and his method is simple, that is, experimentation.

"Experiments are the basis of natural science, and theories are meaningless without experimental proof. When the experiment overturns the theory, it is possible to create a new theory, and the theory cannot overturn the experiment. Over the past 400 years, most of what we know about the structure of matter comes from experimental physics. At the beginning of the May 5 speech, Ding Zhaozhong emphasized. He had said the exact same thing too many times.

At the award ceremony of the 1976 Nobel Prize in Physics, Ding Zhaozhong decided to use Chinese speech. He said that there is an old saying in China: "Those who work hard rule people, and those who work hard rule people." Because of this thinking, many students in developing countries prefer theoretical research to avoid experimental work. In fact, natural science theories cannot be separated from the basis of experiments, in particular, physics arises from experiments.

Everyone at the top of the pyramid in physics knows that Ding is a staunch experimentalist, and experimentation is both his basic value and methodology. He said that he has done a total of five important experiments so far, which can be classified into two categories: the first is to explore the most basic structure of the universe; The second is to search for the origin of the universe, spanning the most microscopic and macroscopic levels.

The first experiment is to measure the radius of electrons. In 1965, Ding returned to the United States as a lecturer at Columbia University just after completing his postdoctoral work at CERN. At this time, he was only 29 years old, still a very young and "nameless" physicist, but he wanted to challenge authority.

According to quantum electrodynamics (QED) theory, electrons have no volume, but in 1964, two teams from Harvard and Cornell universities in the United States came to an unexpected result through experiments: the electron radius is 10-13~10-14 cm, that is, electrons have volume, quantum electrodynamics is wrong.

As soon as this conclusion came out, the physics community immediately shocked, and many people stood opposite QED, but Ding Zhaozhong was skeptical of this tempting "new result". He believes that this is an experiment on the basic idea of physics, because QED is the most accurate theory in all of physics. From Faraday to Maxwell to Dirac, all previous experiments are consistent with theory, are they all wrong? To test QED more carefully, he decided to design a new protocol to remeasure the radius of electrons.

He took the new plan to Professor Leon Lederman, a Nobel Prize-winning physics winner and later director of the Fermi National Accelerator Laboratory, who poured cold water on him, saying that "the idea is interesting but very difficult to implement" and "it will take at least three or four years", and that he has never used many of the electronic instruments used in the experiment before and lacks sufficient experience. "I don't think you can do it." Lederman said categorically, gambling $20 with him.

But that didn't change Ding's mind. As many times since, he chose to believe in himself. He ran to the German Institute for Electron Synchrotron (DESY), which was willing to receive him, and only eight months later, the results were available: the radius of the electron is smaller than 10-14 centimeters, which means that the electron still "has no volume", or more accurately it is impossible to measure, and quantum electrodynamics is correct. A few months later, at an international high-energy physics conference to discuss QED, the Harvard and Cornell teams each made long reports, and Ding Zhaozhong suddenly stood up and asked the host if he could give him 10 minutes to give a short report. He successfully refuted the Harvard and Cornell teams with solid experimental data. Later, Ding Zhaozhong received $20 from Lederman.

At that high-energy physics conference, one of the people who were successfully persuaded was a physicist named Richard Feynman. Ten years later, Feynman, who remained childish at the end of his life, wrote a letter to Ding Zhaozhong in which he "asked": "Why is the Nobel Prize awarded to you?" Are you discovering new phenomena that I did not anticipate or understand? "I challenge you to discover something I can understand."

This was October 1976, 10, three days after Ding Zhaozhong won the Nobel Prize in Physics for his discovery of J particles, and Ding Zhaozhong became the third Chinese scientist to win the Nobel Prize after Yang Zhenning and Li Zhengdao. That year, he was only 21 years old.

The discovery of the J particle was the second important experiment in Ding's physics career. Now, we all know the basic makeup of matter, with layers of negatively charged electrons spinning around each atom, the first member of the family of elementary particles to be discovered. The nucleus of an atom, composed of protons and neutrons, is further dissected, and the units that make them up are called quarks, that is, quarks are the smallest indivisible units that make up the basic elements of nature. Of course, this is only the conclusion for now, and a popular saying among physicists is that particles are like onions, and after peeling off one layer, there will always be another layer below.

In the 20~50s of the 70th century, only three kinds of quarks were discovered. Ding Zhaozhong felt very strange, why is there no fourth and fifth kind? In the eyes of the mainstream physics community at the time, this idea was neither meaningful nor difficult to break through. A physicist said to him: "These three quarks can already explain all known phenomena, why look for a fourth, there is no need." ”

From the level of experimental design, it is extremely difficult to find new quarks, and the sensitivity of the detector and the accuracy of the experiment are extremely high, Ding Zhaozhong himself described as "equivalent to finding a red raindrop in 100 billion raindrops per second when it rains in Beijing". In presenting the award, the Nobel Prize committee also described the difficulty of the matter as "trying to hear the cricket call of a cricket while a jumbo jet takes off."

Ding Zhaozhong said: "Every experiment I have done has two characteristics: people who study theory say that this experiment is meaningless, and people who study experiments think that no one can make such a difficult experiment." But he doesn't care about that, "Do what you think is right, and don't change your right mind because of the opposition of the majority." Ding Zhaozhong said.

After being rejected by almost all laboratories, Brookhaven National Laboratory in the United States agreed to his request. In 1974, he discovered the existence of a fourth quark, the J particle, which has a lifespan 1,12 times longer than known particles, a peculiar property. Later, the fifth and sixth quarks were also discovered. Now, the basic structure of the microscopic material world is clearly displayed before our eyes, this structure is very simple, composed of <> kinds of elementary particles, three generations of elementary particles, including six quarks and six leptons.

Compared with other scientists who have waited decades to win the Nobel Prize, Ding Zhaozhong won the prize two years after discovering the J particle and is considered "one of the fastest winners in history."

Regarding his award, Ding Zhaozhong believes that "excitement blinded their (the Nobel Committee's) judgment". He always remembers the words in Feynman's letter to him: "Don't think you've become an expert just because you've won an award." This sentence had a profound impact on him. At the High Energy Forum, a questioner asked him to talk about the future of the collider and which areas might lead to new discoveries, saying, "I don't know." "He never talks about things he doesn't understand.

"The most important thing is to think that your abilities are capped, to doubt your abilities, and to be cautious at all times." Ding Zhaozhong said, for example, to know when the instrument has abnormal phenomena, so that this piece of data can be canceled. "Assuming the instrument is faulty and you don't know it, you get the wrong result."

Burton Richter, who shared the Nobel Prize with him, described Ding as "an extremely cautious man who cared about all the details of the experiment." On the other side of the coin, Nature magazine commented that Ding's obsession with detail led to his controlling management style.

On May 5, Ding Zhaozhong attended the "High Energy Forum" of the Institute of High Energy Physics, Chinese Academy of Sciences. Photo/Zhongxin

"Scientific things cannot be solved by voting"

With his "glorious achievements" again and again, Ding Zhaozhong has built up a global influence. By 1979, the MARK-J experiment led by Ding Zhaozhong had found gluons on the PETRA positron collider in Germany.

If elementary particles are the "bricks" that make up the material world, gluons are "cement", responsible for "bonding" particles, and their role is to transmit the interaction between particles. However, unlike the J particles that no one expected, the existence of gluons has long been predicted, but it was finally verified by Ding Zhaozhong's experiments.

At this time, he was a tenured professor in the physics department at the Massachusetts Institute of Technology (MIT). When he joined MIT in 1969, his only condition was "permission to do experiments anywhere." With this support, he was able to work in Europe for a long time while working at MIT. At this time, his third major experiment was launched, and it was also the first global cooperation project he led and involved institutions in five countries: China, the United States, Germany, Spain and the Netherlands. In September 1979, the New York Times reported on the discovery of gluons on the front page, specifically mentioning: "9 Chinese scientists participated in this experiment, which is the first time in the history of international cooperation projects on nuclear particles, and it is also a major contribution of China." ”

The discovery of gluons opened the cooperation between Ding Zhaozhong and Chinese physicists for the next half century, and nearly 1000,1977 Chinese scientists participated in his experiments, including Tang Xiaowei, Chen Hesheng, Zheng Zhipeng, Wang Yifang and others, who became the backbone of China's high-energy physics research after returning to China. It all started in August 8, when Deng Xiaoping, who had just made his comeback, suggested to Ding that 10 Chinese scientists be sent to his lab every year. Since January 1978, groups of Chinese scientists have been sent out. In January 1, China and the United States formally established diplomatic relations, and during Deng Xiaoping's "ice-breaking" trip to the United States, the two countries formally signed the "Sino-US High Energy Physics Cooperation Implementation Agreement".

After graduating from Nanjing University in 1984 with a major in nuclear physics, Wang Yifang was selected to join Ding Zhaozhong's L3 experimental group at CERN. At this time, Ding's research site had moved from Germany to the suburbs of Geneva, Switzerland, where a 27-kilometer-long electron-positron collider (LEP) was officially put into use in 1989. When running, positive and negative electrons with energy of 1000 billion electron volts collide, and the temperature at the time of collision is 4000 billion times the surface temperature of the sun, and it is also the temperature of the first 1000 billion billionths of a second of the birth of the universe. Ding's team designed a very huge L3 detector, six stories high, with the aim of finding the most basic particles in the universe and studying the origin of the universe.

From 1982~2003, Ding Zhaozhong spent 20 years in the L3 experiment, which was his fourth important experiment. In the end, two important experimental results were obtained: there are only three different electrons and six quarks in the universe; Neither electrons nor quarks are bulky and both have radii of less than 10-17 cm. The L3 experiment published 300 articles and 300 people received PhDs as a result, but Ding still finds it "quite unfortunate" because all the results are consistent with the Standard Model, which he does not want. When experiments agree with theory, he says, there's a limit to what we learn. Only when there is inconsistency can science make new progress.

　　尤其令他不甘心的一点是，电子仍无法被测量。从1965年起，历经40多年，丁肇中才把电子半径的范围从10-14厘米缩小到10-17厘米，直到现在，他仍对此念念不忘。5月16日的采访中，丁肇中对《中国新闻周刊》说，这是一个很简单但却非常奇怪的现象，我们每天都在使用电，但你去测电子的体积，却永远找不到，永远比粒子的尺度要小。

　　L3实验中，丁肇中的国际合作团队更加庞大，共有美国、中国、苏联等19个国家的600多名科学家参与，中国的主要贡献是精密仪器制造和物理分析。王贻芳参与了L3实验中重要的物理分析工作。5月16日下午，高能所举办的一场对谈活动中，王贻芳说，MARK-J实验中，丁肇中有意把每个中国科学家分到实验的不同层面，覆盖到整个高能物理实验的各种领域方向，这也是后来北京正负电子对撞机(BEPC)建设相对顺利的原因。参与MARK -J实验的第一、二批人，日后都成为了BEPC和北京谱仪的核心骨干人员。“每个子系统的人都是从MARK-J训练出来的。”王贻芳说。

　　王贻芳指出，中国高能物理的发展得益于国际合作，从丁肇中领导的MARK -J实验开始，中国科学家迅速掌握了国际上最前沿的方法、技术和思想，并以最快速度融入到国际高能物理研究的大环境中。丁肇生在对谈中还强调，中国不仅要积极参与别人主导的国际合作，还要主动出击，“在什么地方合作也是非常重要的”。

　　5月16日上午的演讲尾声，他主动提起对撞机。他说，美国芝加哥的Tevatron正负质子对撞机周长6.3公里，发现了第六种夸克。CERN的大型强子对撞机(LHC)周长27公里，实验过程中促发了互联网的诞生，找到了希格斯粒子。美国的超导超级对撞机(SSC)周长是86公里，因为管理不善，1993年被国会终止，之后很多美国优秀的高能物理人才去了CERN，有的去了中国和日本。

　　“对我而言，中国高能所正在讨论的100公里环形正负电子对撞机(CEPC)是一个非常重要、超前的目标，原因很简单，对撞机的能量越高，越能发现意想不到的东西，这将会改变我们对宇宙的基本认识。”

　　尽管丁肇中的前辈、诺奖得主杨振宁对此持反对意见。杨振宁认为，在一个发展中国家，花费数百、上千亿元去寻找“只存在于猜想中的粒子”不是一个聪明的做法。显然，丁肇中不同意这点。

　　目前，为了对撞出更多希格斯粒子的CEPC仍停留在纸面上。按照初步设计方案，工程造价约400亿元人民币的第一阶段建设原本应在2022年开工，如果一切顺利，第二阶段将会升级为超级质子对撞机(SppC)，能量超过LHC的7倍。

　　丁肇中说，“做新的事情总有人有不同的意见，不同的意见不是坏事。永远记住，人是向前走的，你不做，别人就会做，你就只能跟在别人后面。科学上的事情不能用投票来解决，我的每一个实验都遭到很多人反对，你去做，才能站到大家的前面。”

　　“我拒绝你的拒绝”

　　“回顾你整个职业生涯，哪个实验是最重要或者说最基础的？”

David Ziegler, an oral historian at the American Physical Union, asked Ding in an interview in July 2020. Without hesitation, he replied: "In 7 or 20 years, if people look back at what I did, the only thing worth mentioning might be the Alpha Magnetic Spectrometer (AMS) experiment." This is his fifth major experiment, and the only work he still devotes himself to in his old age.

In 1993, the US Superconducting Super Collider (SSC) program was completely canceled by Congress, which was a huge setback for the American high-energy physics community, and for Ding Zhaozhong personally, it was an important turning point in his career. Ziegler asked him if he would never participate in AMS if the SSC went through, and he said it was quite possible.

In order to observe more unexpected particles, ground-based accelerators must move towards higher energies. After the SSC failed, Ding Zhaozhong was walking in the garden near Geneva one day and suddenly thought that the energy of cosmic rays is much higher than the energy of any collider on Earth, why can't we try to turn from the ground to space and directly detect cosmic rays? The strongest accelerator of the universe is the universe itself.

In 1994, Ding Zhaozhong made a big decision and chose to do AMS. "There are no more than 10 people in the world who can see this process." Wang Yifang said this during a conversation on the afternoon of May 5. As a former student and long-term partner of Ding Zhaozhong, Wang Yifang told China Newsweek that after Ding Zhaozhong decided to do cosmic ray experiments, he considered two options, one is space and the other is ground, and he also studied the surface cosmic ray experiment in Yangbajing in Tibet, China. In the end, he made a decision beyond everyone's imagination, that is, "go to heaven".

Wang Yifang explained that Ding Zhaozhong believed at that time that ground-based cosmic ray experiments had considerable difficulties, because cosmic rays had mass and would be absorbed by the atmosphere after entering the earth, and ground experiments could not be directly measured, only through model backwards, and it was not easy to draw reliable and quantitative scientific conclusions. Although space is technically difficult, the measurement accuracy is very high, so in the ground and space of the Pacific space, he chose space.

Although Ding Zhaozhong's every experiment has been opposed by many people, AMS has encountered the greatest resistance in the previous objections, partly because of its difficulty, Ding Zhaozhong himself has concluded: "This is the most complex and technically challenging experiment he has ever done." On the other hand, it was because of his overly bold experimental idea: sending a magnetic spectrometer into space, which no one had ever dared to think about before Ding Zhaozhong.

In order to "go to heaven", Ding Zhaozhong designed a new experimental protocol, first of all, the experimental goal is to accurately measure the charge, mass and momentum on cosmic rays. The method is to send a magnetic spectrometer, that is, a magnet, to the International Space Station, and after the charged particles pass through the magnetic spectrometer, their mass and charge trajectories will be bent by the magnetic field.

But an inescapable problem is that after the magnetic spectrometer is sent into space, it will be deflected by the influence of the earth's magnetic field, as if there is a large compass in the sky, "one pointing north, the other guide, which is why for many years everyone has wanted to put the magnetic spectrometer in the sky but has not succeeded." In his speech at the "High Energy Forum", Ding Zhaozhong explained.

In order to keep the magnetic spectrometer from rotating in the sky, Ding Zhaozhong's team created a unique approach in the design of the magnet: there is a clockwise magnetic field in the upper part, and a counterclockwise magnetic field in the lower part, combined together, from the outside, the magnetic field disappears, which is the permanent magnet. As the core equipment in the AMS experiment, the permanent magnet was designed, developed and simulated by the Institute of Electrical Engineering, Chinese Academy of Sciences, the Institute of High Energy and the China Academy of Launch Vehicle Technology in Beijing.

AMS is the first magnetic spectrometer launched into space and the most powerful and sensitive particle physics detector currently operating in space, its ultimate goal is to find dark matter and antimatter universes, and if successful, it will truly unravel the mystery of the origin of the universe.

In April 1995, the first flight test of the AMS was approved by NASA. In June 4, the U.S. space shuttle Discovery flew AMS-1998 in space for 6 days and successfully collected 01 hours of data. It was just a flight experiment, but it proved the feasibility of detecting high-energy particles in space.

After the Columbia crash in 2003, NASA decided to shift its focus to Mars exploration. In 2005, the AMS launch plan was removed from the Space Shuttle's mission list, but Dante did not abandon it. According to David Steelland, a CERN physicist who participated in the L3 experiment, Ding Zhaozhong once asked the U.S. Department of Energy to upgrade the LEP experiment, and the proposal was rejected, "Ding Zhaozhong stood up and said, I refuse your refusal."

While Ding has partners around the world continue to build AMS modules, he rents a room for a long time at the Mayflower Hotel in downtown Washington as his "lobbying office." He invited many members of parliament into the room, and in front of them, he opened a notebook full of documents and diagrams, and used a finished PowerPoint to explain the significance of AMS. In 2005, before a Senate committee, he also persuaded many of the members present with five minutes and nine transparencies.

Wang Yifang told China Newsweek that Ding Zhaozhong's eloquence was outstanding, and his content was never popular, sometimes very unexpected. And he can often explain a complex scientific problem in an easy-to-understand way, so that people have no doubt. "Especially when he reports to government officials, his ability to convince the U.S. Department of Energy and NASA is rare."

In 2007, at Ding's request, the U.S. Department of Energy organized a review meeting. "I asked that I have to find the world's top scientists, such as Nobel laureates, academicians of the National Academy of Sciences or top aerospace engineers, to discuss with me face-to-face, because first-class scientists can look forward and have a sense of the future. The first reaction of ordinary scientists is that the money is given to you, what should I do. As expected, many of the people involved in the judging meeting competed with me, but they all agreed to do AMS. Ding Zhaozhong recalled in his speech at the "High Energy Forum".

In 2008, an estimated $15.72 billion was spent on AMS worldwide. Ding Zhaozhong received a reporter from Nature magazine in his room at the Mayflower Hotel and told him: "At present, I do nothing but this (AMS), I am responsible for all the problems that arise in the project." After that, "Nature" tells the story of Ding Zhaozhong and AMS, titled "Ding Zhaozhong's Last Fight", this year, he was <> years old.

On June 2008, 6, the United States Congress unanimously passed H.R. Proposition 18, which requires NASA to "add an additional flight to carry AMS-6063 to the International Space Station." A few days before AMS-02 took off, Ding Zhaozhong asked all the staff in the launch pad to stay away from him, and he thought alone for hours, recalling every important decision in the past 02 years, whether there were wrong decisions, whether there were doubts, and if it was not sure that everything was foolproof, it could not be allowed to take off. On May 16, 2011, a space shuttle carrying AMS-5 was officially launched.

12 years later, Ding Zhaozhong recalled this past at the "High Energy Forum", pointing out that dark matter is the main body of the universe, accounting for more than 90% of the total weight of the universe, but human beings have not yet observed. In the 12 years of AMS operation, we have obtained 390.1 million data, the energy range is from 1~1 trillion electron volts, the experimental accuracy is 100%, the data error is very small, and the observed high-energy positron energy distribution is "basically consistent" with the dark matter theory, "but it cannot be said that <>% of dark matter has been found".

He explained to China Newsweek that there are many theories of dark matter, one theory assumes that dark matter is a heavy mass particle, and the experimental results are currently consistent with this theory, but based on the error of the data, it cannot exclude all other theories, and more data is needed in the future to determine the existence of dark matter. As a result, AMS is being upgraded, with plans to increase the reception of data by 300%, "and in another decade, it should be possible to rule out the vast majority of theory."

Wang Yifang speculated that if AMS really discovered dark matter, it would mean the birth of new physics beyond the Standard Model, and whether dark matter exists in the form of particles is just a possibility.

As the retirement of the ISS is delayed from 2024 to 2030, AMS-02 will also continue to operate until 2030. This also means that Ding Zhaozhong will not be able to retire until at least 2030. His wife, Susan, told China Newsweek that Ding, now based at the AMS office in Geneva and returning to MIT every few weeks, has continued his daily habit of meeting on Zoom for hours with colleagues around the world to review every aspect of the experiment, since the pandemic. "You can't take it for granted. Just because there are no problems for ten years does not mean that there will be no problems tomorrow. Ding Zhaozhong said in an interview with Ziegler.

"So, now every day you're preparing for possible problems?" Ziegler asked.

"Yes."

China Newsweek, Issue 2023, 19

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