二十世纪理论物理学的主旋律_杨振宁_杨振宁（In twentieth Century the main melody of physics theory _ _ Chen Ning Yang Chen Ning Yang）

二十世纪理论物理学的主旋律_杨振宁_杨振宁（In twentieth Century the main melody of physics theory _ _ Chen Ning Yang Chen Ning Yang） 二十世纪理论物理学的主旋律_杨振宁_杨振宁(In twentieth Century the main melody of physics theory _ _ Chen Ning Yang Chen Ning Yang) The theme of theoretical physics in the twentieth Century Speaker: Chen Ning Yang Time: 2005-2-22 Chen Ning Yang: Distinguished guests, dear students, I am very pleased to have this opportunity to so many students talk about some development in twentieth Century in theoretical physics, from any viewpoint, twentieth Century is a very big progress for a period of time. Since our ancestors discovered fire, in twentieth Century the first human found second kinds of energy, nuclear power stronger than the fire, another man has learned to control electronic action, thereby creating a semiconductor, leading out of the computer, leading out of Communications Engineering, greatly enhance the human productivity. Human beings have discovered the method of studying minimal structure, thus discovered the structure of double helix, and guided the biological engineering technology. For the first time human beings left the gravitational field of the earth and landed on the moon. The major events of this century are closely related to the development of physics, but a few minutes ago I have been talking about some developments that have something to do with real life. And there is a great deal of progress in physics, and these great developments are that we have a deeper understanding of the most basic and primitive ideas of time, space, motion, energy, and strength. And if you want to speak at once, some of the developments I have been talking about have to do with applications that are actually based on these primitive, basic, conceptual revolutions. The simplest, for example, is a computer, and without the development of semiconductors, it would not be possible to have today's computer industry; without the development of quantum mechanics, it would not be possible for semiconductors to be produced. The discovery of quantum mechanics, of course, leads us to a deeper understanding of time, space, motion, energy, and power. So if we say that the whole development of the twentieth Century is based on the development of basic theoretical physics, this is not a word too far. What I'm going to talk to you today is like the theme of the symphony, themetic melody. Well, let's say, what about themetic melody in physics in the twentieth Century? It is a quantum, symmetrical and phase factor. The three concepts change, evolve and become entangled, which led to the development of theoretical physics in the twentieth Century. The first is quantization, which was introduced in an article written by a German named Marx Planck in 1900 twentieth Century. You may not see it clearly. I copied it from the first page of his article. If you read this article later this page, to this place, under a you may see clearly, is "B = minus twenty-seven square 6.885 x 10 ergs. This is the first time he introduced such a constant, the constant is today called Planck 's Constant (Planck constant), and if you look at this very accurate value of this constant with more than 100 years ago, Planck decided that this value is only 4%. Planck was very bold in writing such an article, saying that the absorption and emission of this light is not a continuous one, Until then, it was considered a continuous step to light out or absorb it, he said, not for a while, every time it was called a quantum. When he had published this article, the more he thought about it, the more he thought it was wrong, so he became very timid. If you went to see his articles for the next few years, you found him retreating backwards and backwards. Why does he want to retreat? Because he wanted to write him out very boldly, the article was put together with traditional physics, and he felt he could not be compatible with each other. But in 1905, the 26 year old Einstein wrote an article, he not only did not retreat, he took a step further, his bold was very impressive, it is also a feature of Einstein's works. He would have grabbed the most subtle, but it was a very important field, a big step forward. After a few years of their work, another young man, Niels Bohr, took another step in 1913, drawing Planck's ideas and constants into the direction of the atomic structure. I want you to go to high school physics, may have heard or learned something Bohr was thinking of Bohr, after the work out, because there are a lot of places with the agreement, so shocked the entire academic circle. He used to talk about hydrogen atoms, but when it was applied to more complex problems, such as helium atoms, with two electrons, a very difficult problem came up at once. This difficult problem at first thought is a mathematical problem, but studies many years not just math problems found, although no rigorous mathematical problems and solutions, but can approximate solution, the approximate solutions with experimental results far away. A dozen years after that, at the beginning of physics in a very disordered state, at that time the workers are very curious psychology, sometimes guess, guess a result with the experimental results, then two days to be in an ecstasy of joy, but to feel completely wrong, is very depressed. So, a few years ago, a famous expert on the history of science was called Edwin Peers. He wrote a book to discuss the development of that time. Then he quoted Charles Dickens in "Shuangcheng" inside story, "said It was the spring is of hope, It was the winter of despair", it was the spring of hope, it is the future of winter, this is indeed described that after ten years of physics family mentality. Bohr, for example, gave Rutherford, Rutherford, the world's most important experimental physicist, and Bohr was his postdoctoral fellow. Bohr said in a letter to Rutherford in 1918 that I am now optimistic about the future of this theory. Why did he say that? It was because before that everyone made a terrible noise, and I wonder if the whole direction was wrong. Another example is Pauli (Pao Li), was a famous physicist, he gave two West a letter on May 1925, the letter says "physics into a dead end, for me too difficult physics". But after five months later to krohe West wrote a letter, He said Heisenberj (Heisenberg) mechanical recovery makes me. As I mentioned above, I am going to make it clear to you that the ups and downs of success and failure were very large. This phenomenon is very rare in the history of physics. For instance, Kramers wrote a letter to Klein, this is 1927, this is after some articles of basic quantum mechanics has been published, in time to discuss the interpretation of quantum mechanics to argue the Henxiong, Bohr and Heisenberg two people argue. Then Kramers gave Klei a letter, he said: "we are too generous, not to be involved in this dispute, Boolean and Heisenberg are expert insisted, step by step, we will put pressure into pieces". So I think we can look at this and know the air at that time. In 50s, you may know that the R - Oppenheimer (Robert Oppenheimer) is a theoretical physicist at wartime atomic bomb in the United States, after the war from the beginning of 1949 he became director of the Princeton Center for advanced studies. I have been working in the place for 17 years, I told him very well, he said he is the description of that era, but also can be said to be twenty years before 1925, he said, "that is the patient in the laboratory work of the times, there are many key experiments and bold decisions, have tried many wrong and premature to assume that it is a dispute communication and frantic meeting times, there are many fierce debate and relentless criticism, filled with a mathematical method of clever. For those participants, it is the era of innovation, since the new understanding of the structure of the universe, they got excited also tasted fear." (please note the words "also tasted fear"), "this period of history will never fully recorded, to write this history to write like Oedipus (Audi Paz), or Cromwell (Cromwell) wrote that book, but due to the distance of knowledge in daily life is so far away, really it is hard to imagine any poet or historian can do". What I have just introduced to you is the beginning of the development of quantization in twentieth Century. Let me introduce the symmetry to you. The idea of symmetry is very ancient in the history of mankind, and it has its history in every civilization and in ancient times. Symmetric reference to science is relatively late, but a large amount of reference to physics is a phenomenon that occurred in the twentieth Century. Symmetry is closely related to invariance in mathematical language. For example, when you say that a thing is symmetrical, it can be interpreted as a photograph taken and you turn it in the opposite direction. To put it in reverse, this thing has invariance, and this is an exact historical language to describe symmetry, so symmetry and invariance are essentially the same thing in mathematical language. The introduction of symmetry to physics in the twentieth Century was also the beginning of Einstein, and Einstein's other great essay in 1905 was the special relativity theory. There is a symmetry in the article of his special theory of relativity, which, from the later on, has a symmetry, but Einstein himself does not understand it. Einstein's article in 1905 contained neither the idea of Symmetry symmetry nor the idea of invariance. The introduction of this concept is two years later a mathematician Minkowski (Minkowski) bring it in, Minkowski (Minkowski) pointed out Einstein's 1905 article has invariance very important, and this is the time and space invariant connected together. The idea of Einstein at first resisted, he once said, he said Minkowski (Minkowski) the mathematical concept of special relativity is Superfluous learnedness, I can translate into difficulties Austria is useless. But soon Einstein thought for a while and realized that the idea was wrong. Not only that, but later he found the idea not only right, but also to study it more deeply. On this point we can see from the following sentence, he in 1950, he wrote an Article 71, discussed above his scientific research life history, "he said in 1908, I realized that Lorentz is the special theory of relativity (Lorentz invariant) the transformation is too narrow the". This can be said to be generalized started relativity, is this sentence you will know to 1908 he has learned that he could resist Minkowski (Minkowski), the invariance to special relativity. This view is wrong on the lead. And not only do you think Minkewski (Minkowski)'s idea is right, it's obvious that you read this sentence and know that he began to expand it in 1908. What did he expand to? He hoped that a invariance could be in a very large space, and that this study lasted seven to eight years, and that general relativity was written around 1915 or 1916. So you can say, by 1925, 1926 there have been known for the symmetry in physics is a step further, but this further step far enough, which is the main reason is because of the symmetry and invariance to lead to theoretical physics, need more mathematical tools, the tools of mathematics when there is no physicist, this mathematical tool called a group of the most important (Group Theory). The group is basically in nineteenth Century by some mathematicians developed by physicists, for years, Yijiuyiji group until the nineteen twenties, don't know, few people study group. But in 1925, Heisenberg, Dirac, Pauli and Bohr, a few of them after the introduction of quantum mechanics, physicists gradually understand the Group Theory group is a very important application in quantum mechanics. At that time the most important physics theory to promote the Group inside the two, one is a great mathematician Hermann Weyl (Herman ear), one is a physicist called Wigner (Wegener), from 1925 to 1970, this symmetry will gradually become a theme, this contains the group theory understanding, understanding with the symmetric invariance. There is another thing in the 1956 to 1958 discovery of parity nonconservation, Parity violation phenomenon is found in the past because we feel that the symmetry since it is so important, so the universe must be extremely symmetric. The idea, of course, was later changed, but there was no question of the importance of symmetry, or did everyone continue to accept it?. But between 1954 and 1956, there was a mystery, called -r. I don't need to explain this is like a mystery, it is said that the development of the idea of not too, according to the original idea, there are some basic particles inside the phenomenon can not understand, then later found the reason, although the universe very symmetrical, but slightly a little wrong place called. So this is a bit slightly asymmetric place called parity nonconservation, then this experiment was made by Wu Jianxiong with a group of experimental workers she led in early 1957 found. She once said she would not believe that parity violation, so that she can play just how much money to bet, Wu Jianxiong said the experiment proved the parity is conserved. So until it is not conserved after it, she said "fortunately no one bet, otherwise today I have no enough money to lose, so I lost some face, but I have enough reputation to lose". For this reason, so in 1957, 1958 to 1959 between the two years, the importance of symmetry in physics has reached the very peak, and that the symmetry is not so simple, is not only the symmetry often have small asymmetry. Just now, I'd like to introduce the development of symmetry to physics in the first half century. Here are some other third themes: phase factor. The idea of phase factor phase factor is not, of course, the beginning of the twentieth Century. It is the idea that any theory with a wave of ideas has a phase, but there is not enough knowledge of the importance of this aspect. Dirac (Dirac) was one of the founders of quantum mechanics. In 1972, he said such a thing. Before that, all of us thought that the most important thing about quantum mechanics was the "noncnmmutaive algebra" which could not be translated. But in 1972, in Dirac (Dirac) has septuagenary. He said: "if someone asked me the main features of quantum mechanics, I would say today, not noncnmmutaive algebra, but the phase (Phase)". Then he talked about the importance of this phase in quantum mechanics, and, in sum, he meant that in a wave there must be the idea of phase. For example, you can put the peak of 90 degrees, 270 degrees to wave, and then to a peak of 360 degrees and 90 degrees, a phase that the change of the fluctuation of any movement, this is obviously a very important concept. However, in a particle, an electron in go, or a proton in taking the time not obviously have the concept of phase, but by quantum mechanics, we know that the theory of fluctuations with particle theory is one thing, so the whole physics concept becomes inside phase very important. But the importance of the phase Dirac mentioned the Kuantien in quantum mechanics was enough importance for today we describe phase factor of understanding, the development is in 1918 by Hermann Weyl (Herman ear) by the introduction of. At that time, Hermann Weyl was influenced by Einstein, and Einstein shocked the whole physics world by publishing the general relativity in the past two years. Then Einstein said, the general theory of relativity has some understanding of the gravitational field, general relativity had some understanding for Maxwell equations of electromagnetism, should put the two together into a unified theory of unified field theoryti. So, this is a direction Einstein put forward, and this direction in the next few decades, Einstein has been trying to contribute to a research direction. So today, Einstein is still one of the central problems of theoretical physics. Weyl (ear) about six years younger than Einstein, he was influenced by Einstein this idea, he would like a way out, to put together with the electromagnetic gravitational field, so he developed the theory now called norm theory. The specification means "size", "gauge" means "quantity", and "normative theory" is "gauge theory". Why is it called "gauge theory"? Since the Weyl (outer ear) was trying to measure a thing, then the I was added, and the volume became phase. So by the Fock (Fokker) and London (London) and later Weyl (outer ear) after come back to write an article, this theory is actually called phase theory and the basic theory of phase center thought is under a word, that is the random phase factor is given to the electromagnetic equations, electromagnetic Maxwell equation is written down Maxwell in 1865, this is certainly a great contribution to human history. The symmetry of Maxwell but there was a meaning, the symmetry until I into the 1918, 1927, 1929, Weyl, Fock, London, a few of them work makes you understand this, understand the use of words is the phase factor of randomness, what is random? That is to say, the phase factor can be changed, and after you have modified it, it does not affect the electromagnetic equation. This idea is the central idea of the normative theory. Just half an hour I introduce three main melody, quantization, with symmetrical phase factor, in twentieth Century to the second half of the century, can be said to be the main theme of the basic theory of the development of physics is the three theme of the expansion and variation with interleaving. Developments, variation, and, intertrance, and very interesting is that they're intertwined. I'm entangled with this. I want to be like development in Symphony music. The one I particularly want to give everyone out there is a formula, this formula is the idea of Feynman, the Feynman foundation of quantum mechanics to rewrite a method, he introduced a concept of Propagator, and the Popagator as a Path path integral, integrate is written like this, I think this is not a problem, Feynman is life's most important contribution, there are a lot of contributions to Feynman, graduate students most likely to notice his contribution to Feynman diagrams. The contribution of Feynman diagrams is important, I think this is far better than the equation is important, because this equation caught the quantum mechanics of the spirit, and this equation is very interesting, the three main melody I speak are intertwined. First, you see, there's a h, and that's Planck's constant, so this equation has a direct relationship to quantization. Moreover, this equation is a integral whole of this kind, and this exp[i/h (activn)] is a phase factor, a phase factor of a more complex idea. And what does this have to do with symmetry? Having a very close relationship; closely related to gauge symmetry. Because I just say in gauge symmetry changed when its physical constant, so that through this path integral is fully displayed, so I think this is the main theme of the three equations mentioned together as a formula, this is a very wonderful equation. And I feel so this equation is important because it is, because the mathematical meaning of this equation is not yet understood, this line integral what thing is defined, up to now has not a strict mathematical. So I think it's just a few years before twenty-first Century when a young physicist can spread his world in his hair. The specification of symmetry in 1929 to 50s, we all know it is very wonderful, but by the middle of the 50s, the need to promote the promotion of gauge symmetry, the p-eA (p-eA is an important concept of gauge symmetry equation was slightly changed into p-eB). A is a field, and B is a matrix field, so B is a little more complicated than A. This equation is called a non Abel gauge field. Abel was a great mathematician. He was a Norwegian in the early nineteenth Century. Unfortunately, he was in his twenties. Then he made a very important work in the early group, so a lot of the group called Abel group, Abel group is characterized by its two elements which can change, AB is equal to BA, AB is equal to BA the group called Abel group. Then the electromagnetic field becomes a phase factor, and that phase factor is a Abel group. I just said to turn A into B, the B is a square matrix (the matrix) after it becomes square (matrix) after it could be reversed, so it becomes non Abel group, the generated Abel group called non-Abelian gauge field gauge field. Over the last twenty-five years, all of these experiments in high-energy physics have been described by non Abel gauge fields, but a new one has been added here, which is symmetry breaking. For this reason, I summed it up at the end of the 70s, and I say this can be described as symmetric dominating interaction. That is, the fundamental equations of all interactions are determined by symmetry, and the method of decision is the non Abel gauge field. Everyone agrees now, but there is still nothing left, How can Einstein's general theory of relativity be turned into a non Abel gauge field?. Everyone knows that the two structure is very similar, so it must be a non Abel gauge field, but there are some still can not solve the problem, it can be said that the twenty years of basic theory of physics center problem, and this problem I want to continue until twenty-first Century. In addition, I think everyone deserves special mention is given symmetric phase factor and fiber bundle concept, wait for the phase factor of non Abel physicists from the comparison of the actual, more understanding and then, suddenly found the original in 70s, and the mathematical structure of mathematicians have developed a concept called twenty or thirty years. There is a close relationship between fiber bundle. I first learned of the two relations, because in 1968 1969, before and after I was teaching of general relativity in the Stohg Brech, I wrote a formula, called Rieman curtcnre, which is the general theory of relativity is the basic concept of Geomely Riman. After I had the idea of writing on the blackboard, I suddenly discovered that this equation with more than 20 years ago Mills and I wrote in 1954 non Abel gauge field equations like, so after class I would like to study carefully how, after research found that it is not as clear, it is simply a return things, just to give some idea of slightly altered, changed after completely different. So I went to a Stohy Broch at the math department, called J Simance, he was a famous mathematician, I told him these things, he said these are what I said is a fiber bundle, fiber bundle? He gave me a book, this book is a man named Stinront wrote, a very famous book, so I just take a look back to see, then, do not understand, because the language is now very dry mathematician (boring). So then one in South Korea in a speech I was telling this story, I now say this math book is only two, one of you reading the first page you will not look down, and one you read the first sentence and you can't go on. But surprisingly, this can not be read until then I understand the fiber bundle, give it is absorbed into the gauge field and the development of spirit, speaking from the mathematician's position is very natural. So the relationship between mathematics and physics is a very delicate relationship, but there are different values and different traditions. The introduction of fiber bundles naturally introduces topology into physics. Topology was one of the mainstream mathematics of the twentieth Century, and it could be said that there was no such major idea in mathematics. To sum up, I introduce these three themes to you. These three themes directly influence our basic understanding of time, space, movement, energy and power. This very interesting thing is that in the very long run, these three themes have been discussed sporadically in the early history of mankind. Quantization, for example, The Democritus (de Muck Ritter) has discussed the atom, Zeno (Zeno) is discussed with continuous discontinuous division, China Chuang-tzu in 300 BC years are also discussed with continuous discontinuity between the philosophical problems. But these quantization is similar to the quantization in twentieth Century, but there is a major difference. In twentieth Century this quantization is quantized to exercise, this is not an atom, molecule, then this is the quantized concept so that adds an important change to it, this is a very element about the development of physics in twentieth Century. About symmetry, then the Greeks for symmetry is very attention, from 600 BC to 500 BC, especially Pythagoras, they for the symmetry of a circle, think this is the domination of the universe all the most basic elements. Then the symmetry to the development to the development of today, this symmetry is the most important non Abe Lie group, so an important concept which is from a very long term everyone recognized inside, after understanding the details of it, put it into another example of accurate mathematical language. Now then phase, of course we know the phases of the moon, the cycle of the seasons, these are any ancient culture inside some ideas, but especially important today is the phase factor of randomness, its scalability, although it does not affect the result of expansion but it equation. This is the basic gauge field the concept of. And this concept has been injected into the phase factor, which has slowly generated the physics of today's twentieth Century, thank you.