Tiếng Việt | Français   rss
Web link
The Road to the Nobel Prize (23-07-2008 08:36)
It is a great pleasure and honor to have been invited to Vietnam and have the opportunity to speak at Hue University. Vietnam has one of the most rapidly developing economies in the world. But to sustain this progress, it will have to continue developing its science and technology. And those students of Hue University and other Vietnamese universities who will develop professional expertise in these areas will play an essential role advancing the welfare of the Vietnamese people. It is a special privilege to speak to the students here because you are the ones who will ultimately help shape the future of your country. You have the potential to accomplish great things.

The message I want to convey to the students here is that with a good education, dedication and hard work, you can accomplish things well beyond your hopes and have a future that can even exceed your dreams. I was such a young person many years ago and I would like to tell you how this came about for me. To do this, I should tell you a little about my background and how I chose physics as a career, a career that gave me the opportunity to probe the wonders of nature. I would also like to describe some of my efforts to uncover nature’s secrets. I do this not because I consider myself so important as an individual. Rather, I do this because my career demonstrates how any student can work toward a productive and satisfying career in science, or in any other field. I also hope that some of the lessons I learned along the way may be useful to you.

I was born in the city of Chicago, in the United States. My parents were immigrants from Russia. My father came to the United States in 1913 and my mother arrived in the United States in 1914 on one of the last voyages of the Lusitania, which was sunk during World War 1. My parents had little formal education, except for courses in English after they arrived in the United States. But they were self taught and had wide ranging interests.

I grew up in difficult times. When I consider the kind of environment in which I grew up, I think it would have been totally inconceivable to anybody who knew me that someday I would be awarded the Nobel Prize. I was raised in a poor neighborhood in the west side of Chicago. The public schools were inadequate and there were bad influences on the streets. It was the Great Depression and my parents had severe financial problems. I received my primary and secondary education in Chicago. As a child, I liked to draw and paint. In high school, I entered a special art program, which allowed me to draw and paint a few hours a day; and my ambition was to become an artist.

While I always had some interest in science, I only developed a strong interest in physics when I was in my fourth year in high school. This came about as a result of my reading a short book entitled Relativity, by Albert Einstein.

You might wonder what attracted me to this book. Of course, Einstein was greatly admired by my parents, as he was by people throughout the world. I had read a little about relativity and what I read fascinated me. I thought that this book might give me some understanding of the mysteries of how meter sticks shrink and clocks slow down when they move fast – things that I had read about in popular articles. I read the book carefully and tried my best to understand these matters; but in the end, I really didn’t understand the basic concepts of special relativity. This only made me more curious and more determined to try to understand these perplexing ideas. It was clear to me that I would have to study physics to really understand the theory of Relativity.

This book opened new vistas for me and deepened my curiosity about the physical world. When I completed high school, I received a scholarship to the museum school of the Art Institute of Chicago. My art teacher strongly encouraged me to accept this scholarship. However, I decided to continue my formal education and sought admission to the University of Chicago because of its excellent reputation and because Enrico Fermi taught there. Enrico Fermi was one of the greatest physicists of the 20th century.

I spent my first two years at the University in a highly innovative and intellectually stimulating liberal arts program. I am happy that I had that exposure to the liberal arts because they opened the world to me in many areas that have given me great satisfaction throughout my life. I entered the Physics Department in 1950.

The Physics Department was a very exciting place. I had a wonderful education, but I found it very difficult. My high school background in mathematics and physics was inadequate, and at times I had to struggle. Sometimes, I wondered if I had made the right choice. But I refused to be discouraged because I truly loved what I was studying. I worked with great dedication and passed all of my exams.

When I was ready to start my doctoral research, I decided to ask Fermi whether he would supervise my research. While I wasn’t optimistic about him accepting me as one of his students, I thought I had nothing to lose by asking him. I certainly could accept being turned down by such a great man. So I went to ask him; and to my great surprise, he said yes immediately. I was overjoyed. This taught me an important lesson. Be willing to risk failure. Reach high even if you think you don’t have a chance. You might succeed! Being supervised by Fermi was a remarkably stimulating experience that shaped the way I think about physics.

After I received my PhD, I continued working in Fermi’s laboratory, which had been taken over by an outstanding young faculty member, Val Telegdi, after Fermi’s tragic death in 1954. At about that time there were some puzzling observations of the decay of a newly discovered particle that were causing much controversy and speculation in the particle physics community. In a bold paper, two young physicists, T. D. Lee and C. N. Yang proposed that this apparent paradox was due to the non-conservation of parity in the weak interactions and suggested some experimental tests of this hypothesis. The so-called weak force is one of the four basic forces of nature and is responsible for igniting energy production in the sun and also for radioactivity. And Parity is a quantum mechanical concept. Its conservation is equivalent to the idea that a physical system should behave in the same way when observed in a mirror.

While most of the community considered the conservation of parity to be a sacred principle, Professor Telegdi asked me to join him in making a measurement to test the bold hypothesis of Lee and Yang, who had been students at the University of Chicago. Most of the others in our lab thought that this was a waste of time. I remember giving a seminar at our Institute on the measurements we were going to make. After the seminar, a distinguished older member of the faculty came up to me and said that I had given a nice talk, but that I should realize that we were not going to find anything.

As it turned out, we were one of the first three groups that demonstrated the non-conservation of parity in the weak interactions; and as result of these experiments, a new theory of the weak interactions was developed. Lee and Yang were awarded Nobel Prizes in 1957 for their work. The lesson that I learned from this is that one should be willing to test new ideas, even if they are rejected by others. Progress in science only comes about when old theories give way to new ideas.

1960, I was hired as a faculty member in the Physics Department of the Massachusetts Institute of Technology. In 1963, Henry Kendall and I started a collaboration with Richard Taylor and other physicists from the Stanford Linear Accelerator Center and the California Institute of Technology to design and construct electron scattering facilities for a physics program at a two mile long, 20 Billion electron-volt, electron linear accelerator that was being constructed at Stanford University, called SLAC. We soon set up a small MIT group at SLAC and for extended periods of time one of us was always there.

From 1967 to about 1975 the MIT and SLAC groups carried out a series of measurements of inelastic electron scattering from the proton and neutron that provided the first direct experimental evidence that the proton and neutron are made up of quarks. This work confirmed the quark model and provided the experimental foundations for Quantum Chromodynamics, the theory of the so-called strong force. It was a very exciting time for me.

It was for this work that Henry Kendall, Richard Taylor and I were awarded the Nobel Prize in Physics in1990. What a surprise and joy that was! It was a magical week in Stockholm filled with the kind of grandeur and excitement that I had never had experienced before. There were talks, press conferences, receptions, gala parties, and sumptuous banquets, one of which was held in the royal palace. But the most stunning event was the ceremony in which the Nobel Prizes were presented to us by the King of Sweden. It was held in a beautiful concert hall, bedecked in flowers, with an audience of a couple of thousand men and women in formal wear and evening gowns. Between the presentations of the awards, there were interludes of beautiful music. It is a memory that my family and I will always cherish. But sometimes I wonder to myself how was it possible that this really happened to me.

When we started this experiment for which we so honored, many physicists told us that it was a waste of time. In fact, members of our collaboration who had participated in the design and construction of the apparatus dropped out of the experiment because they wanted to do something more productive. Let me now tell you about this work.

But to start, I should put this work in the context of what is known about matter. Looking at the top of the first slide, we see just ordinary matter, consisting of atoms and molecules. Everything here is made up of such matter, this table, us and everything around us. If we increase the magnification a 100 million times, we see the atom. The atom consists of electrons going around a positively charged small object in the center called the nucleus. This picture was proposed by a Japanese physicist, Hantaro Nagaoka in 1904. It was confirmed in 1911 by Rutherford in a famous series of experiments using the scattering of alpha particles. If we now increase the magnification another 100,000 times, we see the nucleus which is composed of neutrons and protons. That picture started unfolding in 1919, when Rutherford identified the proton as the nucleus of the hydrogen atom, and culminated with the discovery of neutrons in 1932 by Chadwick. If we increase the magnification further, we see that the proton and neutron are composed of other particles called quarks. That story started unfolding in 1968 and goes on to the present. That’s the story I want to tell you. *

The beginning of this story was the discovery of a new kind of particle called the pi meson or pion. The existence of this new particle was theoretically predicted by a Japanese physicist, Professor Hideki Yukawa, in 1935. Physicists started searching for this new particle because the theory was very compelling. In 1947, it was discovered; and Professor Yukawa was awarded the Nobel Prize in Physics in 1949 for this outstanding theoretical work. When the pion was discovered, there was great elation in the physics community because there was a feeling that there was some understanding of the subatomic world. But this elation was short lived because enormous complexity soon developed in this field. *

By 1960 a large number of different particles had been discovered, and it was unclear how these various particles were related to one another. These newly discovered particles were the result of new and higher energy accelerators and new types of particle detectors.

In 1961 a classification scheme was developed for these many newly discovered particles. It was like the periodic table of the elements except that it was for particles. This classification scheme not only provided an order for these newly discovered particles, but it also predicted the existence of particles that not had yet been discovered. And all of these particles predicted by this scheme were later discovered. But the question arose: Why is this classification scheme so successful?*

In 1964, two physicists independently proposed quarks as the building blocks of particles, because they found that quarks could be the basis of this classification scheme. Initially, the quark model had three types of quarks: the UP quark, the DOWN quark and the STRANGE quark. But quarks had a very peculiar property that was very surprising and troubling. They all have fractional charge, and no particle in nature has ever been found with a fractional charge. The UP quark has a charge +2/3, the DOWN quark is -1/3 and the STRANGE quark is -1/3. *

Now the proton, you see is made up of 2 UP quarks and a DOWN quark, giving the proton a charge +1 and the neutron is made up 2 DOWN quarks and an UP quark, giving a charge 0. You see that is basically how the proton and neutron are constructed in this theory. *

What do physicists do to find out if something is real? They will look for it. Well, there were many attempts to find these quarks. But not a quark was found. To many physicists this was not surprising. Fractional charges were considered to be a really strange and unacceptable concept, and the general point of view in 1966 was that quarks were most likely just mathematical representations - useful but not real.

So most physicists at that time did not think that quarks existed. There were, however, a few physicists who would not give up the quark model, and they persisted in making calculations of applications of the quark model. But few physicists paid attention to them.*

In 1966, there was an important development in this story. The Stanford Linear Accelerator at SLAC was completed and brought into operation. This is a very long high energy linear accelerator for accelerating electrons. Inelastic electron-proton scattering experiments started in 1967 and continued until 1974 by an MIT-SLAC collaboration, which included Henry Kendall, Richard Taylor, and myself along with other physicists. Conceptually this was a very simple experiment. You would shoot electrons at protons. Electrons would scatter off and many other particles would be produced. You would only detect and measure the electrons and this provided the first direct evidence for quarks. Let me explain how, because the scientific methodology is really quite simple. I will explain it by an analogy. *

I give you a fish bowl with a certain number of fish in it and put it in a dark room. I ask you: Tell me how many fish are in the bowl ? I also ask that you not put your hand in the fish bowl. But I do give you a flashlight. Well, what you would do is turn on the flashlight and look, right? You would see how many fish there are in the fishbowl. That would be the sensible thing to do.

Well, you see, the experiment was basically the same idea. Instead of having a light beam, you have an electron beam. Instead of using your eyes, you use particle detectors. Instead of having a brain to reconstruct the images, you do that with a computer, programmed by human intelligence. And, of course, instead of looking for fish inside the fishbowl, you are looking for what is inside the proton. So it’s basically that idea. You are looking inside the proton with the equivalent of a very powerful electron microscope. The effective magnification that this experiment provided was a factor of 60 billion times greater that that of an ordinary microscope.

This is the picture of the Stanford Linear Accelerator. It’s two miles long and you can see there’s a road going over it. The electrons are bent into three beam lines. These are the two experimental halls. The experiment was done in the larger of the two halls. The electron beam is bent and it enters this hall that houses the experimental apparatus. The linear accelerator delivered an electron beam of 20 billion electron volts, which was a very high energy in those days.*

Here is a picture of the magnetic spectrometers used to measure the energy of the scattered electrons. The larger of the two is the 20 billion electron volt spectrometer. It was 50 meters long and weighed 3000 tons. The other one could measure up to 8 billion electron volts and it was 25 meters long. The beam comes in from the left, and hits the target at the pivot in front of the spectrometers. The spectrometers can move on the rails that run around the pivot. These were the biggest instruments in physics at that time. *

Now what are the characteristics of scattering that you would expect on the basis of the quark model as compared to that from a proton whose electric charge is smeared out, which was the model of the proton at that time? In a certain sense, this is really the crux of the matter from a physical point of view. If you had the old model, in which the charge was quite diffuse you would expect the electron to come in and not be deviated too much because the charge is smeared out and there’s nothing hard inside to really scatter it in a hard collision. The incoming electron comes in and goes through the proton without too much deviation. This is shown in the upper image. But if you have constituents inside the proton, then occasionally an electron comes in and scatters with a large angle from one of the constituents, as you can see in the lower image.

So, an excessive amount of large angle scattering would imply much smaller objects inside the proton. Consequently, by looking at the scattering probability distribution you can determine what is inside the proton, and this is how the experiment was analyzed. I want to show you what was found.

Here in this slide, we show the probability distributions of scattering from the experiment as compared to that expected from old model of the proton. The top curves here are the measurements. The rapidly falling curve is the type of distribution you would expect from the old model of the proton. And you see the difference, as much as a factor of a thousand between what the old model would have predicted in scattering probability and what the experiment produced. Basically what these measurements showed was that an unexpectedly large amount of large angle scattering was observed. Now, the experimenters went on to try to analyze and reconstruct the images, in terms of what was measured.

How big were the objects inside? The results indicated that they were point-like. They were smaller than could be measured with the resolution of the system. But this was a very strange point of view. It was so different from what was thought at the time that we were reluctant to discuss it publicly.

So using these instruments, we found that both the proton and neutron were composed of point-like constituents. We called them point-like because they are so small we were not able to measure their size. We were also not able to determine if they had the correct fractional charges.

Fractional charge was a much more difficult problem; and to really resolve that problem another type of scattering had to be brought into the picture. Neutrino scattering had to help provide the answer. *

First of all, what are neutrinos? Neutrinos basically are particles that are almost ghost-like. They have a very small amount of mass, they have no charge and they barely interact. Neutrinos interact so weakly that a 100 billion volt neutrino, has on the average to go through 4 million kilometers of iron before it scatters once.

How do determine the charges of the constituents? You can find out about the charges of the constituents by making comparisons of electron and neutrino scattering from the proton and neutron. Comparisons of our electron scattering results and neutrino scattering measurements from CERN, a laboratory in Switzerland, demonstrated without a doubt that the quark model was correct. And physicists who strongly doubted the existence of quarks finally had to accept their existence.*

One question remains - what is the size of the quark? Well, the size of the quark is still smaller than we can measure. So we say it’s point-like.

We don’t necessarily believe that it’s a point, but as far as our tools of measurement can go, we only see points. The upper limit of its size from current measurements is exceedingly small. If we take a carbon atom, which is much, much smaller than a virus, and expanded it to the size of the earth, a quark would be less than a half of centimeter in comparison. And that’s the upper limit of its size. But even if we can’t measure their size, I hope that you are convinced that you are made up of quarks and that your quarks are very well held together. *

You might wonder what lessons I have learned about life during my career? Here are some of the things that I learned:

Dream and work hard and your highest aspirations may come true. When you choose your career, go into a field that you truly love. Only when you have a deep interest and passion in a field can you make the commitment that is necessary to accomplish something important. What drew me into physics was a sense of awe about the wonders of nature and a deep curiosity about how nature works.

When I was a student and throughout my career I have worked hard, but I have never felt that I was working hard because I love physics so much. I feel that I have one of the best jobs in the world. I get paid for trying to solve puzzles of my choice and teaching a subject that I love.

My profession is a source of great pleasure. When I develop an insight into a problem that has been puzzling me, I experience a great sense of joy. And making a discovery brings even a greater joy. Just think, in making a discovery, you may be the first person in the history of humankind to observe or understand the secret of nature that you have just uncovered.

I have also learned in my career that to accomplish something important you often have to take risks in pursuing your ideas and goals, even if others discourage you from doing so. You must have the courage of your convictions. I would never have received a Nobel Prize without going against the well intentioned advice from respected people in my field.

I would now like to conclude with some general remarks about the importance of science and technology. What we have learned from science has profoundly shaped the way we view our place in the universe. It has provided us with some understanding of how the universe works from the basic building blocks of the subatomic world to the outer reaches of the cosmos. And evolutionary biology has given us an understanding of our place in the natural order of life.

But science also has an immense impact on how we live. The world is changing very rapidly, driven to a large extent by science and technology. The development of humankind has been strongly linked to the innovations arising from human creativity, from the earliest crude tools to the modern technological society of today. In the modern era, science and technology have provided innovations that have enhanced our standard of living, improved our health and driven the economies of nations. But science and technology must be used by society with wisdom and humanity. The great theoretical physicist Victor Weisskopf, said “ Society is based on two pillars, knowledge and compassion. Compassion without knowledge is ineffective. And knowledge without compassion is inhumane.”

You, students here, are receiving an education that will provide a strong foundation for your futures. Remember, a good education is something on which you can build on throughout your life and which can provide you with a satisfying career.

All of you will have much to offer your nation and the world. Your help is needed to create a bright future, a future based on both knowledge and compassion. I have great confidence that you are well up to the task. So do all that you can do to fulfill your potential, and your accomplishments and your future may even exceed your dreams.

Thank you.

Jerome I. Friedman (MIT)


Web link