How did you end up coming to Michigan?
I was born in Ann Arbor, Michigan. And three months after I was born, war between Japan and China broke out. My parents decided to return to China.
So I grew up during wartime in China. I never had a chance to go to school. In 1948, we went to Taiwan. Then, my father was a professor of engineering, and my mother was a professor of psychology. Both of them had come to graduate school in Michigan. My mother was very active in the University of Michigan alumni association. I think she was the president.
One day, I think the trustees of Michigan, together with the dean of engineering, visited Taiwan. My mother arranged the program for them, and that’s how I met G.G. Brown [George Granger Brown, Edward DeMille Campbell University Professor of Chemical Engineering and Dean of the College of Engineering]. It must have been my sophomore year in high school.
After I graduated from high school, I returned to Michigan. So I went to pay my respects to G.G. Brown. He said, “Well, you don’t have a place to stay. Why don’t you come stay with us?”
I stayed in their house, and I learned a lot of things from the Browns. The most important thing I learned, I think, was football. They said, “You need to go to a football game with us!”
I had no idea what they were talking about, but I vaguely remembered when I was in Taiwan, my parents were describing football, and they showed no interest. Now, I said to myself, “Now that I am a student at the University of Michigan, I want to be what everyone else is.”
So I went to the game. It was University of Michigan versus UCLA. It took me a very short time to figure out the rules. In my six years at Michigan, I probably did not miss any games. I always went to the games.
But more important, because G.G. Brown was the dean of engineering, many accomplished scholars came to visit. So I had the chance to meet many people. I am very grateful to the Browns. George and his wife were very kind to me. At that time, I really didn’t understand what was going on.
How good was your English?
Wow. How did you go through school without understanding English?
That’s very interesting because in 1956, the University of Michigan was quite different from the University of Michigan today. There were very few foreign students.
I decided now that I’m here in the United States, if I want to stay here, it’s better I learn all the customs and the language. In order to try to accomplish something, you really have to assimilate yourself to the society. So that’s why I made an effort to learn English.
The first week, because of the time change, I normally fell asleep in class. And the teacher would call my name, and everybody would laugh because I was asleep. But after a month, people began to take notice of me.
Every month, there was a blue book exam. Even at that time. Students, my classmates, began to notice: Well, there’s this guy, hardly speaks English, but somehow he always gets his blue book back first. Which meant I was the guy who got the highest grade. And people began to borrow my notes and talk to me, and I made an effort to talk to them. That’s how I gradually learned English.
But of course, the courses I took were mostly physics, chemistry and mathematics, and those are somehow easier for me. You don’t really need to know the language to figure that out.
You’ve said that the University of Michigan had a great influence on your career. Can you expand on that a little bit?
I had very good teachers in physics and mathematics. The six years I was at Michigan were really the happiest moments of my life – when I was free, and I could take whatever courses I wanted. It helped me to learn to think freely. And the university was very supportive. They gave me a scholarship.
Before Michigan, I had a very limited education. Six years of high school in Taiwan. I didn’t have any grade school in China.
I went to the University of Michigan on September 6, 1956. And I enrolled in the school of engineering – in mechanical engineering. After the year is over, I had an advisor. Actually it was a very well known professor, Robert White. He took a look at my grades and he said, “You are no engineer.”
At that time, there were no computers. So you had to look at a mechanical object from the top, from the front, and from the side. You had to do a three dimensional drawing, and I was absolutely no good at that. I also couldn’t draw a line straight. You know, a line is supposed to have uniform thickness, and I never seemed to be able to do that.
And then Professor White said, “Well, why don’t you go to physics and math? Why don’t you try to get two degrees at the same time? And why don’t you take courses in graduate school? I’ll help you to skip some requirements such as sociology and social science.”
So that’s how I started taking courses in physics and math, and that turned out to be quite easy for me. I got my degrees rather quickly. Entered in ’56, I think I got my degrees in engineering physics and engineering math in ’59.
At that time, there was still a draft for the war in Vietnam. I was classified as 1A, ready to be drafted. Fortunately, the Atomic Energy Commission had a national competition to select a few physicists and mathematicians and give them a full scholarship and a live-in stipend of $2,000 a semester – at that time it was worth quite a bit of money.
So I participated in the test. Luckily, I was selected. Then the Atomic Energy Commission wrote a letter to my draft board claiming that I’m important to national defense, so I was exempt, and I was able to go to graduate school at Michigan.
Because I had good grades, I started working with George Uhlenbeck. He was the one who discovered that an electron spins – it rotates around itself. So I studied with him.
After about a month, he had a tea with me and a few other of his students. He remarked that, if he were to do his life over again, he would rather be an experimental physicist than a theoretical physicist. I was quite surprised because he was one of the great theoretical physicists of the early 20th century.
So I asked him why and he said, well, an average experimental physicist is very useful because you always measure something. An average theoretical physicist is not. Look at the early 20th century. You have Einstein, you have Dirac, you have Heisenberg, and so forth, you can count them on your fingers how many really made a contribution.
After this little conversation, I decided to leave theoretical physics. I was wondering what to do. Then I met Professor Larry Jones, who is retired but still living in Ann Arbor, and Marty Perl, who recently passed away as a professor at Stanford [and who received the Nobel Prize in 1995 for his 1975 discovery of the tau lepton particle]. They mentioned their experiment in the Lawrence Radiation Laboratory at Berkeley [now the Lawrence Berkeley National Laboratory]. If you join us, they said, you get a trip to California. And I had nothing else to do, so I joined them.
At first, it was really quite difficult. I had no idea what they were doing. But after a while, I begin to learn things. So that’s how I became a particle physicist.
Speaking of particle physics, can you tell me about the importance of the j/psi particle?
When you break the atom apart, you have a nucleus. And if you break the nucleus apart, there are some things that we thought were elementary particles. Pions, protons, kaons, rho mesons, omega mesons, and so forth. There are a few hundred of them.
All of them have a very short lifetime. In 1974, I discovered this J particle. Soon after this, a family of similar particles were observed by many, many groups worldwide. Their unique feature is their lifetime is 10,000 times longer than all the known existing elementary particles. The significance of which you can visualize as follows.
Everybody lives on Earth to about 100 years. But you find some village in the Upper Peninsula where people live 1 million years. And then these people are somewhat different from ordinary people. And this discovery means our understanding of physics is totally incomplete. New models had to be made. That is why I received a Nobel Prize – mainly because the J particle changed the basic concept of physics.
How did you feel when you realized that you’d seen something that was really groundbreaking?
Basically, you have a feeling that you are really very small. There are so many things you do not know. You thought you understood everything. Not the case at all.
Did it make you more interested in trying to be the first to find something else?
Yes. I am now doing an experiment on the International Space Station. The idea is very simple. You have heard of the Big Bang origin of the universe. Now, at the beginning of the Big Bang, there is a vacuum. So then suddenly you have a big bang. The universe begins to expand. After 14 billion years, we have the University of Michigan, we have a football team, we have you and me.
Now the question is, at the very beginning of the Big Bang, there must be equal amounts of matter and antimatter because otherwise it would not have come from a vacuum. Nothing exists in a vacuum.
So once you have a big bang, the positive and negative must be the same amount.
Can you tell me more about antimatter?
Antimatter exists on Earth. If you go to the hospital, you have a PET scan. That’s Positron Emission Tomography. That positron is a positively charged electron, that’s the antimatter of the electron.
You also have protons and antiprotons. You have neutrons, you have antineutrons. So every particle has an antiparticle. So the existence of antiparticles is not a question. The question is: If the universe comes from a big bang, where is the universe made out of antimatter? And that’s the question I’m asking on the International Space Station.
How are you doing that?
Matter and antimatter have opposite charges. Protons have a positive charge, antiprotons have a negative charge.
To distinguish charge, you need a magnet. So when particles go through a magnetic field, positive bends one way, negative bends the opposite way. So you need to put a magnetic device on the space station. This is a difficult thing because, as you know, a magnet always points north, the other end points to the south. If you’re not careful, the space station will spin like a magnetic compass.
For many years, nobody can put a magnetic detector in space. And then one day, I figured out a way, together with a group of collaborators at MIT. A magnet that doesn’t turn. All the magnetic field stays inside the magnet. It’s a very simple idea, but it took us 40 years to figure out. And so after we figured it out, we put it in space. So now we can detect matter going one way, antimatter going the opposite way.
Dark matter is also a target of the alpha magnetic spectrometer, right?
Yes. What is dark matter? If you look at a galaxy, there are thousands of galaxies that have been examined, every galaxy has a closed orbit. A closed orbit means it is a balance of gravitational force and centripetal force. Only when you have forces that are balanced do you have a closed orbit.
Gravitational force is the product of the mass of the galaxy and the mass of the entire universe. Centripetal force is the mass of the galaxy and the speed. And so if you put all this together, you examine the galaxy, you find out the amount of material – the amount of matter you need in the universe – is 10 times more than what you see in the universe. In other words, 90 percent of the universe you cannot see.
This is not only true for our galaxy, it’s true for thousands of galaxies that have been examined. That’s why it’s called dark matter. It’s called dark matter because you cannot see it. Nobody knows what dark matter is like. But the collisions of dark matter become energy. Energy can change into matter from relativity. And so you can produce positrons and antiprotons. So by measuring these particles, you can try to get a hint of what is going on with the origin of dark matter. In fact that’s what we’re doing now. We are measuring cosmic rays, particles shooting through space.
And this shows up as an excess of antimatter in your detector? As in, much more than you would expect?
Huge excess! Enormous excess of positrons and antiprotons. Much more than from ordinary collisions of cosmic rays. So something new – some new phenomena is there.
It will take some time for us to pin it down. But up to now, we have collected more than 100 billion cosmic rays, up to an energy of a trillion electron volts [in other words, a particle with the same kinetic energy as a flying mosquito]. And all this phenomena, all the things we have collected, cannot be understood by the knowledge of existing cosmic ray physics.
Why hadn’t other cosmic ray experiments caught this?
Before us, there have been many experimental measures of cosmic rays by balloons and small satellites. Balloons, you can send to space, but not to 400 kilometers above earth. They normally fly to about eight kilometers. So you still have atmosphere above.
Also at night, when the temperature cools down, the balloon tends to fall to the ground. Balloons tend to stay aloft for a few days to a maximum of a month or two. So you cannot make a precise measurement.
Small satellites normally do not carry a magnet. If you don’t carry a magnet, you cannot distinguish positive charge and negative charge. So this is the first time you have a very large particle physics type detector in space. So basically we open the door into a new territory. There are now hundreds of theories to explain what we have observed.
What are you favorites?
Oh, when they ask me, I always tell them they are all correct. Some people say, oh, it’s because the origin of the positrons or antiprotons come from a different form of supernova explosion. Some people say it’s because of the propagation through space, some of them have been accelerated. There are many, many theories.
But to me, that’s really not important. The important thing is to do the measurement very accurately. This is a very precise experiment, so we need three or four more years to finish all the measurements.
So far, though, we have made measurements of positrons, antiprotons, helium, lithium, elements across the periodic table. These measurements are very, very accurate. I run a collaboration of about 600 physicists. We normally have two teams, sometimes four teams, analyze the same data. Only when all agree within one percent, we will publish.
Yeah, because it took us nearly 20 years to put this device in space. And in the foreseeable future, there are probably no similar detectors in space. So we have an obligation to get it right because nobody else can perform the same measurements.
This is the same data, same detector. But to achieve an accuracy of one percent, a judgment call is needed. What is a real particle signal, what is background from the detector itself? There is always a human element. Most of the time people don’t agree. But I want to understand why. Eventually, people reach agreement.
How did it feel when your experiment launched and was installed on the space station?
I was quite scared because before that, I used to do experiments in accelerators. And in accelerators, if you have something you’re worried about, you can shut down the accelerator and go in and take a look. I remember when the space shuttle took off, I was quite, quite concerned. Because suddenly, I could not check anything.
Fortunately, most of the elements are redundant. The electronics and the computers sometimes have fourfold redundancy, and the minimum is twofold redundancy. So if one goes bad, another one can switch and replace it.
And finally, for the football fans, what are your feelings about Ohio State?
When I was at Michigan, the first thing I learned was not physics – the first thing I learned was, “Beat Ohio State!”
I remember one year, Michigan did not do well. The Michigan-Ohio State game was always the last game. The stadium had a capacity of 100,000 people, but that year, because Michigan had done so badly, and it was raining hard, there were only about 5,000 people in the stadium. And I was one of them.
A few years ago, I went to visit Ohio State. They invited me to give a speech about my experiment. They announced I was from Michigan, and I heard this “Booooo” noise. When it was my turn to do the talk, I told them I came from Michigan, and today is the first day I actually realized that Ohio State has classrooms on its campuses!
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