Maxwell is mainly engaged in electromagnetic theory, molecular physics, statistical physics, optics, mechanics and elasticity theory. In particular, his electromagnetic field theory, which unifies electricity, magnetism and light, is the most brilliant achievement of the development of physics in the19th century and one of the greatest complexes in the history of science. He predicted the existence of electromagnetic waves. This theory has been fully verified by experiments. He erected a monument to physics. Radio technology for the benefit of mankind is developed on the basis of electromagnetic field theory.
Maxwell began to study electromagnetism around 1855. After studying Faraday's new theory and thought about electromagnetism, he firmly believes that Faraday's new theory contains truth. So he held the desire to "provide the foundation of mathematical methods" for Faraday's theory and determined to express Faraday's genius thought in clear and accurate mathematical form. On the basis of predecessors' achievements, he made a systematic and comprehensive study of electromagnetic phenomena, and with his profound mathematical attainments and rich imagination, he successively published three theoretical papers on electromagnetic fields: On Faraday's magnetic field lines (from 1855 to1856); The line of force in physics (186 1 to1862); Electromagnetic field dynamics theory (1864 65438+February 8). Summarizing predecessors' and own work comprehensively, the electromagnetic field theory is expressed in a concise, symmetrical and perfect mathematical form, and after finishing and rewriting by later generations, it becomes Maxwell equations as the main foundation of classical electrodynamics. On this basis, in 1865, he predicted the existence of electromagnetic waves, which can only be shear waves, and calculated that the propagation speed of electromagnetic waves is equal to the speed of light. At the same time, he came to the conclusion that light is a form of electromagnetic wave and revealed the relationship between light phenomenon and electromagnetic phenomena. 1888 German physicist Hertz verified the existence of electromagnetic waves through experiments. Maxwell published his scientific masterpiece Electromagnetic Theory in 1873. The electromagnetic field theory is systematically, comprehensively and perfectly expounded. This theory has become one of the important pillars of classical physics. Maxwell also made important contributions to thermodynamics and statistical physics. He is one of the founders of gas dynamics theory. 1859, he obtained Maxwell's velocity distribution law for the first time by using statistical laws, thus finding a more accurate method to calculate the statistical average from two microscopic aspects. In 1866, he gave a new method to deduce the molecular distribution function by velocity, which was based on the forward and backward collision analysis. He introduced the concept of relaxation time, developed the general transport theory and applied it to gas diffusion, heat conduction and internal friction. The term "statistical mechanics" was introduced in 1867. Maxwell is a master who uses mathematical tools to analyze physical problems and accurately express scientific ideas. He attaches great importance to experiments. The Cavendish laboratory established by him, under the leadership of him and several subsequent directors, has developed into one of the world-famous academic centers. He is good at starting from experiments, after keen observation and thinking, using skillful mathematical skills, starting from careful analysis and reasoning, boldly putting forward hypotheses with experimental basis, establishing new theories, and then making the theories and their predicted conclusions tested by experiments, gradually perfecting and forming a systematic and complete theory. Especially, Thomas W's effective use of analogy inspired Maxwell to become an expert in establishing various models and studying different physical phenomena by analogy. In his three papers on electromagnetic field theory, he used analogy research methods many times to find the connection between different phenomena, thus gradually revealing scientific truth.
Maxwell's rigorous scientific attitude and scientific research methods are extremely valuable spiritual wealth of mankind.
maxwell
Father's influence
In the history of science, some important theories often depend on the unremitting efforts of many people. /kloc-the electromagnetic theory that led to the physics revolution was founded in the 0/9th century, and it is like this. More than half a century has passed since Oster and Ampere discovered the magnetic effect of current, and Faraday laid the foundation stone and completed the theory. James clerk maxwell, an outstanding British mathematician and physicist, finally completed this theory.
The paper "On Faraday's magnetic field lines" is basically the mathematization of Faraday's magnetic field lines.
Translation is a very important step. Because Maxwell used mathematical methods from the beginning, and chose the essence of Faraday's theory-the line of force thought as the starting point of his research. This shows that Maxwell's scientific insight is really extraordinary. He determined the main direction of attack, and he unswervingly continued his research. His later series of papers followed this correct path step by step. This is where he is better than Thomson. Thomson has come to the edge of truth, but he hesitated; Maxwell grasped the truth and persisted. So Maxwell started late, but he was the first to reach the peak of glory.
The road to science is always uneven. Just when Maxwell's research was promising, an unfortunate event interrupted his plan. One day, he was immersed in studying some recent electrical materials when the postman came from home. When he received the letter, he was surprised to find that it was not his father's handwriting. What he had been worried about for a long time finally happened. My father was old and weak, and his health went from bad to worse. He was suddenly ill in bed. That letter was written by my father on behalf of others. Maxwell was very anxious and sad after reading the letter. He has deep feelings for his father. My father was his mentor since I was a child, and he was the pillar of the whole family. For more than ten years, they have lived together day and night and lived in harmony. After Maxwell left home to study, they corresponded almost every day, exchanging various scientific ideas and views on society, and talking about interesting daily life.
In order to take care of his father, Maxwell had to leave Cambridge University and work in Aberdeen, which is close to home. A college in Aberdeen, a port city in northern England, promised Maxwell to be a lecturer in natural philosophy, but it will take some time. Maxwell stayed in front of his father's bed all night, trying to alleviate the old man's illness. But no matter how carefully he served, he still failed to stop the arrival of death. When the spring of 1856 came, my father finally left this world. This is undoubtedly an irreparable loss in Maxwell's life. His sorrow has not subsided for a long time.
Soon, maryse Kyle College in Aberdeen officially hired him as a professor of natural philosophy. Before taking office, Maxwell went back to Cambridge University to deal with some affairs and stayed for several months. He is in a very ambivalent mood. He misses his alma mater, his father has passed away, and it is of little significance for him to stay in Aberdeen. More importantly, his electromagnetic research has just begun, and I wonder if Aberdeen has suitable research conditions. However, maresca College has already offered him a letter of appointment. It is said that the dean appreciates him very much, and he can't shirk it, so he has to take office. This time, his electromagnetic research was postponed for four years.
Faraday's inspiration
1860 In the early summer, the physics lecture of Mali College was suspended for some reason. Maxwell left Aberdeen at the age of 28 to teach at Royal College London. His wife also went with him. This job transfer is a turning point in Maxwell's career.
Before that, there was an episode. Maxwell's original alma mater, Edinburgh University, will also hire a professor of natural philosophy. He was going there. There are three people who should be selected, the other two are his classmates at Cambridge University, and one is a middle school classmate. Which of these three people should be taken away, the authorities decided to decide through examination. When it comes to learning, Maxwell is definitely the first, but compared with eloquence, he suffers. As a result of the exam, Maxwell came last, and even the examiner doubted his speech ability. At that time, a magazine in Edinburgh commented on this matter and felt sorry for him. As the saying goes:
"A blessing in disguise is a blessing in disguise." Unfortunately, Maxwell was not selected by the University of Edinburgh, but because of this, he transferred to the Royal College and made the most important contribution in his life.
During Maxwell's four years in Aberdeen, he always had a heart to express Faraday's theory with mathematical tools. His wish was shelved only once in 1855. Even in the bitter struggle of studying Saturn, as long as you see an article about electromagnetism, it will attract his close attention. He often wrote to Faraday to explore the mysteries of electromagnetism. His desk is full of "Experimental Research on Electricity". Every time he opens this brilliant masterpiece, he is very excited. Faraday, a great man he had never seen at that time, painted a vivid picture for physics! What laws are hidden behind electricity, magnetism, light, lines of force, fluctuation ...
Maxwell paid a special visit to Faraday after he arrived in London. This is an unforgettable meeting. The young physicist handed in his business card, and soon Faraday came out with a smile. The experimental master is nearly seventy years old and his temples are gray. He and Maxwell hit it off and started a cordial conversation.
These two great men are not only 40 years apart in age, but also very different in personality, hobbies and specialties, but their views on the material world have produced a * * * sound. This is a wonderful combination: Faraday is cheerful and kind, and Maxwell is serious and witty. Teachers are warm fires, and students are sharp swords. Maxwell is not good at words, but Faraday speaks beautifully. One is not proficient in mathematics, but the other is familiar with it. Their scientific methods are just the opposite: Faraday is mainly experimental exploration, and Maxwell is good at theoretical generalization. It can be said that they complement each other in many ways; Einstein once called them lovers, saying that they were like Galileo and Newton, and they brought out the best in each other. Maxwell himself talked about this point: "Because there are different types of people's minds, scientific truth should be expressed in different forms, whether it is in a qualitative form with distinctive physical colors or in a simple and simple symbol, it should be regarded as the same science." This is natural, and there is respect for Faraday between the lines. However, the depth of exploring science often varies with different scientific methods. Faraday expressed the truth in an intuitive and vivid way, and Maxwell finally summed it up with amazing mathematics, which mentioned the height of theory, so his understanding was deeper and deeper into the essence of things, so it was more universal.
Four years ago, Faraday praised the paper "On Faraday's Force Line". He didn't expect the author of the paper to be so young. When Maxwell asked him what he thought of the paper, Faraday said, "I don't think my theory is necessarily true, but you are the one who really understands it."
"Sir, can you point out the shortcomings of this paper for me?" Maxwell said modestly.
"This is an excellent paper." Faraday said thoughtfully, "But you should not stay in explaining my point of view with mathematics, you should break through it!" "
Faraday's words are like a bright light, illuminating the way forward for young physicist Maxwell. He immediately threw himself into the new battle with the greatest enthusiasm.
He designed a theoretical model to further explore Faraday's concept of magnetic field lines. This model is based entirely on the analogy of mechanical structures. Some people call it "ether model", but now it looks boring and difficult to understand. A British historian of modern science spent a whole page without making it clear. In fact, Maxwell also abandoned this model in his later works. Strangely, Maxwell used this as a springboard and successfully reached the other side of truth.
The building is finally finished.
When discussing the ether model, Maxwell paid great attention to an important fact he found. After analyzing Faraday's research on dielectric, he confirmed that there is also current in the dielectric with changing electric field, which he called "displacement current". In addition, he calculated the speed of this water flow. Maxwell was surprised to find that the speed of displacement current is exactly equal to the speed of light!
Is this a coincidence? There is no such coincidence in the world. He was so excited that he didn't sleep well for several days. His wife checked it carefully for him several times, and the data was really correct. This means that he calculated that the propagation speed of electromagnetic waves is equal to the speed of light, which is a very remarkable discovery, although he didn't fully realize it at that time. A few days later, he wrote to Faraday and reported the results. In his letter, he said that his calculated electromagnetic wave propagation speed is "3 10740 km/s", while the speed of light measured by direct experiments in the free soul (186,5438+09 ~1896) is 14858 km/s. The mailing time of the letter is1861110/0/9. Whether Faraday wrote back to him is not recorded in the historical materials. But there is no doubt that it is this discovery that prompted Maxwell to come to the conclusion that light is electromagnetic wave four years later.
1862, Maxwell published the second electromagnetic paper "On the Force Line of Physics" in the 23rd issue of Volume 4 of the British Journal of Philosophy. As soon as the article was published, it immediately aroused widespread concern. Joseph Thomson, a famous British physicist and discoverer of electronics, later recalled: "I still remember that paper clearly. At that time, I was a child of 18 years old. As soon as I read it, I was very excited It was a long article, and I copied it all. "
This is indeed an epoch-making paper, and it is a qualitative leap compared with the Faraday line in 1855. This paper is no longer a simple mathematical translation of Faraday's viewpoint, but an important extension and development. One of the decisive steps is to introduce the concept of "displacement current". Before that, people including Faraday always mentioned conduction current when discussing the magnetic field generated by current, that is, the current formed by the movement of free electrons in a conductor. Maxwell felt that there was a great contradiction in this old concept in his research. For example, in a capacitor connected to an AC power supply, there is no free charge in the dielectric, that is, there is no conduction current, but the magnetic field still exists. After repeated thinking and analysis, Maxwell resolutely pointed out that the magnetic field here is formed by another kind of current, which exists in any dielectric with changing electric field and forms a closed total current together with the conduction current. Maxwell obtained the equation representing this current through strict mathematical derivation and called it displacement current.
The concept of displacement current is introduced in theory, which is indeed a major breakthrough in electromagnetism after Faraday electromagnetic induction. According to this scientific hypothesis, Maxwell derived two highly abstract differential equations (the equations were not perfected until 1865), which are the famous Maxwell equations. This set of equations develops Faraday's achievements from two aspects. One is displacement current, which shows that not only the changing magnetic field produces an electric field, but also the changing electric field produces a magnetic field; Secondly, the equation not only perfectly explains the electromagnetic induction phenomenon, but also summarizes it theoretically. That is, where the magnetic field changes, there is an induced electric field around both the conductor and the dielectric. After Maxwell's creative summary, electromagnetic phenomena's law was finally revealed in his unshakable mathematical form. Only then did electromagnetism begin to become a scientific theory.
In the history of natural science, only when a certain science reaches its peak can it be expressed as a law by mathematics. These laws can not only explain known physical phenomena, but also reveal some undiscovered things. Just as Newton's law of universal gravitation foresaw Neptune, Maxwell foresaw the existence of electromagnetic waves in the Force Line of Physics. He pointed out that since the alternating electric field will produce an alternating magnetic field, and the alternating magnetic field will produce an alternating electric field, then this alternating electromagnetic field will spread to space in the form of waves. Maxwell was only 3 1 year old at that time, which was the most brilliant year of his life.
Maxwell continued to go deep into the field of electromagnetism. 1865 published the third electromagnetic paper "electromagnetic field dynamics". This paper was published in the journal of the Royal Society of London. In this important document, the form of Maxwell's equation is more perfect. He adopted the mathematical methods founded by French mathematician and mechanic Lagrange (1736 ~ 18 13) and Irish mathematician and physicist Hamilton (1805 ~ 1865), and directly deduced the wave equations of electric and magnetic fields from those equations. The propagation speed of electromagnetic wave is based on wave equation. This is exactly the same as the ratio calculated by Maxwell four years ago. Until this time, the existence of electromagnetic waves is certain! So he boldly concluded that light is also an electromagnetic wave. Faraday's hazy conjecture about the electromagnetic theory of light changed from Maxwell to scientific theory. The names of Faraday and Maxwell have been linked together ever since, just like the names of Galileo and Newton, which will shine forever in physics.
Maxwell taught at Royal College London for five years. These five years were a productive period in his life. In addition to establishing electromagnetic theory, he also made contributions to molecular physics and gas dynamics.
1865, shortly after Maxwell officially announced the electromagnetism of light, he resigned as the chairman of the Royal Academy of Sciences and returned to his hometown Glenlai Manor to systematically summarize the research results and write a monograph on electromagnetism. After several years' efforts, his General Theory of Electromagnetism was published in 1873. This is a classic work on electromagnetic theory. Maxwell systematically summarized the research achievements of Coulomb, Ampere, Oster, Faraday and himself on electromagnetic phenomena around the middle of19th century, and established a complete electromagnetic theory. The significance of this masterpiece can be exactly the same as Newton's Principles of Mathematics (Mechanics) and Darwin's Origin of Species.
Compared with biology, it is also the crystallization of human wisdom.
The magnificent building of electromagnetic theory, after several generations of efforts, stands tall! The publication of General Theory of Electromagnetism became a great event in the field of physics at that time. Maxwell returned to teach at Cambridge University, and his friends and students have been looking forward to this book for a long time. People rushed to the bookstore to buy, and the first edition was sold out in a few days.
Final evaluation
Although the General Theory of Electromagnetism has been robbed, few people really understand it. Soon, I heard someone criticize it for being difficult to understand. Of course, the highly abstract Maxwell differential equation is not as simple as 2×2=4 after all. Only two formulas and a few mathematical symbols contain all the laws of electromagnetic phenomena in nature, such as charge, current, electromagnetism and light, which is really incredible to ordinary people. In addition, there is a more important reason, that is, since Maxwell published his theory, no one has ever discovered electromagnetic waves. Whether electromagnetic waves can be proved is the key to test Maxwell's theory. So many physicists are skeptical. Even william thomson, who had warmly encouraged Maxwell before, was not sure whether Maxwell's prediction was reliable.
Maxwell's electromagnetic theory is of epoch-making significance in physics. It's a pity that Maxwell himself failed to prove his theory (to some extent, it can be said that there is no proof). There are both objective and subjective reasons for this. Due to the limitation of environment and working conditions, Maxwell never had more opportunities to engage in electromagnetic experiments. The study of thermodynamics and molecular physics consumed most of his time and energy. Besides, he is mainly a theoretical physicist. As his student Fleming (1849 ~ 1945) later said, "He predicted the existence of electromagnetic waves in theory, but it seems that he never thought of using any experiment to prove it." Faraday has never left the experiment in his life, so it can be said that there is no Faraday without the experiment. On the contrary, Maxwell only conducted some limited experiments during his five years in London, most of which were in gas dynamics. There is a long and narrow attic near the roof of his apartment, which is his laboratory. His wife often works as his assistant, lighting the stove and adjusting the indoor temperature. The conditions are quite simple. Later, in the laboratory of the Royal College, he did some electrical experiments, mostly just measuring the standard resistance. After the completion of General Theory of Electromagnetism, Maxwell was busy building Cavendish laboratory and sorting out Cavendish's works (1731~1810).
For these reasons, the electromagnetic theory has not been recognized for a long time after it came out. At first, only some young physicists at Cambridge University supported it. Many people, including a group of prestigious scientists, hold a wait-and-see attitude towards the new theory that has not yet been proved. Laue (1879 ~ 1960) once commented in the History of Physics: "Although Maxwell's theory is perfect in essence and consistent with all experiences, it can only be gradually accepted by physicists. Its thinking is so unusual that even people with extraordinary talents like Helmholtz and Boltzmann (1844 ~ 1906) have spent years trying to understand it. "
Several spring and autumn years have passed. Maxwell silently dedicated his efforts to Cavendish laboratory. The laboratory broke ground on 1872 and was completed on 1874. The construction funds were donated by a duke who encouraged science. In order to acquire instruments, Maxwell also took out his own savings. In the whole preparation process, Maxwell personally asked questions from the design, construction, instrument purchase to the inscription on the gate. It is the founder and the first director of the laboratory. Later, his successors were Rayleigh (1842 ~ 19 19) and Joseph Thomson, followed by Rutherford (187 1 ~ 1937), both of whom were world-class physicists. The period of flowering and fruiting in this laboratory was in the 20th century. From here, a large number of outstanding scientific talents have been trained, especially those in atomic energy physics.
Maxwell's main job in the last few years was to sort out a lot of information left by Cavendish. The task entrusted to him by the duke is quite arduous. Cavendish was a famous eccentric British physicist and chemist in the18th century. He once found that hydrogen, the chemical composition of water, was the first substance to calculate the mass of the earth, and he also made good research on electrostatics. He has never been married, he is shy and likes to live alone. After his death, he left 20 unpublished scientific manuscripts of Dozza, mostly involving mathematics and electricity, many of which were buried for nearly half a century. It is a very meticulous and difficult job to sort out these materials. Maxwell made great sacrifices to finish this work: he gave up his research and ran out of energy.
In addition to the daily affairs of Cavendish laboratory, Maxwell will give a lecture on electromagnetism or thermodynamics every semester. He enthusiastically publicized electromagnetic theory and popularized new theories on the platform. Unfortunately, there are not many listeners. He is not good at giving lectures, what's more, electromagnetic theory is so profound that it is very different from traditional physics! 1In May, 878, he gave a popular science lecture on telephone. The telephone was a new thing at that time and just broke out. Bell invented the telephone in 1875 and obtained the patent the following year. Edison announced the impedance microphone in 1877. These new inventions in the history of human telecommunications aroused Maxwell's great interest. Perhaps, he had a premonition that his theory would one day give wings to these inventions and spread all over the world.
Maxwell's later life was full of troubles. No one understands his theory. His wife has been ill for a long time. This double misfortune exhausted him. After his wife's illness, the whole family life was out of order. Maxwell has always been considerate to his wife In order to take care of his wife, he hasn't slept in bed for three weeks. Nevertheless, his lectures and laboratory work never stopped. Excessive anxiety and fatigue eventually damaged his health. Colleagues noticed that the selfless scientist was getting thinner and paler. However, he still works so doggedly.
1879165438+1On October 5th, Maxwell died of cancer at the age of 49. In the history of physics, a star that can shine with Newton has fallen. It is a great pity that he died young. His theory opened up a brand-new road for modern science and technology, but his achievements were not taken seriously when he was alive. Maxwell's life is a life of omnipotence and self-sacrifice. The honor of this great scientist is far less than Faraday's. It was not until many years after his death that Hertz proved the existence of electromagnetic waves that people realized that he was recognized as "the greatest mathematical physicist in the world after Newton".