Einstein's student days
Albert Einstein was born in the German town of Ulm on March 0879 1879. His parents are Jews. Einstein had a happy childhood. His father was a calm, docile and kind man who loved literature and mathematics. His mother had a strong personality and loved music, which influenced Einstein. Einstein began to learn the violin at the age of six, and the violin became his lifelong companion. Einstein's parents had a good influence on him and his family education, and the spirit of freedom and the atmosphere of peace permeated his home.
Like Newton, Einstein did not show extraordinary intelligence when he was young. On the contrary, he has been unable to speak since he was over four years old, and his family even worried that he was an imbecile. At the age of six, he entered a national school. He is a very quiet child and likes to play games that require patience and perseverance, such as building a house with pieces of paper. 1888 after entering middle school, his studies are not outstanding. I am good at all subjects except math, especially Latin and Greek. He is not interested in classical languages. At that time, German schools had to receive religious education. At first, Einstein was very serious, but after reading popular science books, he realized that many stories in religion were untrue. /kloc-at the age of 0/2, he gave up his religious belief, doubted all authority and beliefs in the social environment, and developed into a free thought. Einstein found that there is a huge natural world around him, which exists independently of human beings, just like an eternal mystery. He saw many people whom he greatly respected and admired found inner freedom and peace when they devoted themselves to this cause. As a result, Einstein chose a scientific career in his teens, hoping to master the mystery of nature. Once he chose this road, he went on without mercy and never regretted it.
1895, Einstein came to Zurich, Switzerland, intending to enter the Federal Institute of Technology in Zurich. Although he did well in math and physics, he failed in other subjects. The principal of the school recommended him to study in the middle school in Arau, Switzerland for one year to catch up on his lessons. Einstein felt very happy during his stay at Arau State Middle School. He tasted the free air and sunshine in Switzerland and decided to give up his German nationality.
From 65438 to 0896, Einstein officially became stateless and was admitted to the Federal Institute of Technology. During his college years, Einstein was fascinated by physics. On the one hand, he read the works of famous German physicists Kirchhoff and Hertz, studied Maxwell's electromagnetic theory and Mach's mechanics, and often went to the home of theoretical physics professors for advice. On the other hand, he spends most of his time doing experiments in the physics laboratory, obsessed with direct observation and measurement. 1900, graduated from Einstein University. 190 1 acquired Swiss nationality. 1902, with the help of his friend Grossman, Einstein finally found a stable job as a technician in the Swiss Federal Patent Office in Bern.
The establishment of special relativity
As early as 16 years old, Einstein learned from books that light is a very fast electromagnetic wave. He has an idea. If a person moves at the speed of light, what kind of world scene will he see? He will not see the advancing light, but only the electromagnetic field that oscillates in space but stagnates. Is this possible?
In connection with this, he would like to discuss the so-called ether problem related to light waves. The word ether comes from Greece and is used to represent the basic elements that make up objects in the sky. /kloc-Descartes introduced it into science for the first time in the 0/7th century as a medium for spreading light. Later, Huygens further developed the theory of ether, thinking that the medium carrying light waves is ether, which should fill all spaces including vacuum and penetrate into ordinary matter. Unlike Huygens, Newton put forward the particle theory of light. Newton believed that the luminous body emitted a stream of particles moving in a straight line, and the impact of the particle stream on the retina caused vision. Newton's particle theory prevailed in18th century, but the wave theory prevailed in19th century, and the theory of ether developed greatly. At that time, the view was that the propagation of waves depended on the medium, because light can propagate in a vacuum, and the medium that propagates light waves is the ether that fills the whole space, also called optical ether. At the same time, electromagnetism has developed vigorously. With the efforts of Maxwell, Hertz and others, a mature electromagnetic phenomena's dynamic theory-electrodynamics was formed, which unified light and electromagnetic phenomena in theory and practice, and regarded light as electromagnetic waves in a certain frequency range, thus unifying the wave theory of light and electromagnetic theory. Ether is not only the carrier of light waves, but also the carrier of electromagnetic fields. Until the end of 19, people tried to find ether, but they never found it in the experiment.
But electrodynamics has encountered a big problem, which is inconsistent with the relativity principle followed by Newtonian mechanics. The theory of relativity existed as early as Galileo and Newton. The development of electromagnetism was originally included in the framework of Newtonian mechanics, but it encountered difficulties in explaining the electromagnetic process of moving objects. According to Maxwell's theory, the speed of electromagnetic waves in vacuum, that is, the speed of light, is a constant. However, according to the principle of speed addition in Newtonian mechanics, the speed of light in different inertial systems is different, which leads to a question: Is the principle of relativity applicable to mechanics applicable to electromagnetism? For example, there are two cars, one is approaching you and the other is leaving. You see the lights in the front car approaching you and the lights in the back car are far away. According to Maxwell's theory, the speed of these two kinds of light is the same, and the speed of the car doesn't work in it. But according to Galileo's theory, the measurement results of these two items are different. The car coming towards you will accelerate the light, that is, the speed of light in front of the car = speed of light+speed; Light leaves the car more slowly, because the speed of light behind the car = speed of light-speed of light. Maxwell and Galileo's statements about speed are obviously opposite. How can we resolve this disagreement?
Theoretical physics reached its peak in the19th century, but it also implied a huge crisis. The discovery of Neptune shows the incomparable theoretical power of Newtonian mechanics. The unification of electromagnetism and mechanics makes physics present a formal integrity, which is known as "a solemn and majestic architectural system and a touching and beautiful palace". In people's minds, classical physics has reached the point of near perfection. Planck, a famous German physicist, told his teacher when he was young that he would devote himself to theoretical physics. The teacher advised him: "young man, physics is a completed science, and there will be no further development." It is a pity to dedicate his life to this subject. "
Einstein seems to be the man who is going to build a brand-new physics building. During his stay in Berne Patent Office, Einstein paid extensive attention to the frontier dynamics of physics, thought deeply about many problems and formed his own unique views. During ten years of exploration, Einstein studied Maxwell's electromagnetic theory seriously, especially the electrodynamics developed and expounded by Hertz and Lorenz. Einstein firmly believes that the electromagnetic theory is completely correct, but there is one problem that makes him uneasy, and that is the existence of the absolute reference frame ether. He read a lot of books and found that all the experiments that proved the existence of ether failed. After Einstein's research, it was found that ether had no practical significance in Lorentz theory except as an absolute reference system and the load of electromagnetic field. So he thought: Is it necessary to have an absolute frame of reference? Do electromagnetic fields have to be loaded?
Einstein likes reading philosophical works and absorbing ideological nutrition from philosophy. He believes in the unity of the world and the consistency of logic. The principle of relativity has been widely proved in mechanics, but it cannot be established in electrodynamics. Einstein questioned the logical inconsistency between the two theoretical systems of physics. He believes that the principle of relativity should be universally established, so the electromagnetic theory should have the same form for each inertial system, but there is a problem of the speed of light here. Whether the speed of light is constant or variable becomes the primary question whether the principle of relativity is universally established. Physicists at that time generally believed in ether, that is, there was an absolute frame of reference, which was influenced by Newton's concept of absolute space. /kloc-At the end of 0/9, Mach criticized Newton's absolute view of time and space in Mechanics in Development, which left a deep impression on Einstein. 1905 One day in May, Einstein and a friend Bezo discussed the problem that had been explored for ten years. Bezo expounded his point of view according to Mahism, and they had a long discussion about it. Suddenly, Einstein realized something, went home and thought about it again and again, and finally figured it out. The next day, he came to Bezo's house again and said, thank you, my problem has been solved. It turned out that Einstein thought clearly about one thing: there is no absolute definition of time, and time is closely related to the speed of optical signals. He found the key to the lock, and after five weeks of hard work, Einstein showed people the special theory of relativity.
1905 On June 30th, the German Yearbook of Physics accepted Einstein's paper "On Electrodynamics of Moving Objects" and published it in September of the same year. This paper is the first article about special relativity, which contains the basic ideas and contents of special relativity. Special relativity is based on two principles: the principle of relativity and the principle of invariability of light speed. Einstein's starting point for solving problems is to firmly believe in the principle of relativity. Galileo first expounded the idea of relativity principle, but he did not give a clear definition of time and space. Newton also talked about relativity when he established the mechanical system, but he also defined absolute space, absolute time and absolute motion. He contradicts himself on this issue. Einstein greatly developed the principle of relativity. In his view, there is no absolute still space, and there is no absolute constant time. All time and space are connected with moving objects. For any reference system and coordinate system, there is only space and time belonging to this reference system and coordinate system. For all inertial systems, the physical laws expressed in space and time of the reference system are the same in form, which is the principle of relativity, strictly speaking, the principle of relativity in a narrow sense. In this article, Einstein did not discuss too much about taking the constant speed of light as the basis of the basic principle. It is a bold assumption that the speed of light is constant, which is put forward from the requirements of electromagnetic theory and the principle of relativity. This article is the result of Einstein's thinking about ether and electrodynamics for many years. At the same time, he established a brand-new space-time theory from the perspective of relativity, and gave a complete form of electrodynamics of moving objects on the basis of this new space-time theory. Ether is no longer necessary and ether drift does not exist.
What is the relativity of simultaneity? How do we know that events in two different places happen at the same time? Generally speaking, we will confirm by signal. In order to know the simultaneity of events in different places, we must know the speed of signal transmission, but why didn't we get this speed? We must measure the spatial distance between the two places and the time required for signal transmission. The measurement of spatial distance is simple, but the trouble lies in the measurement time. We must assume that every place has an aligned clock, and the propagation time of the signal can be known from the readings of the two clocks. But how do we know that the clocks in different places are right? The answer is that another signal is needed. Can this signal set the clock right? If we follow the previous thinking, it needs a new signal, so it will retreat indefinitely, and the simultaneity of different places cannot be confirmed. But one thing is clear, simultaneity must be associated with a signal, otherwise it is meaningless to say that these two things happen at the same time.
Optical signal may be the most suitable signal for a clock, but the speed of light is not infinite, which leads to a novel conclusion that two things happen at the same time for a stationary observer but not for a moving observer. Let's imagine a high-speed train, its speed is close to the speed of light. When the train passed the platform, A stood on the platform, and two lightning flashes appeared in front of A's eyes, one at the front end of the train and the other at the back end, leaving traces at both ends of the train and the corresponding parts of the platform. Through measurement, the distance between A and both ends of the train is equal, and the conclusion is that A saw two lightning flashes at the same time. Therefore, for A, two received optical signals travel the same distance in the same time interval and reach his position at the same time. These two things must happen at the same time, and at the same time. But for B in the center of the train, the situation is different, because B moves with the high-speed train, so he will intercept the front-end signal that propagates to him first, and then receive the optical signal at the back end. For B, these two events are different at the same time. In other words, simultaneity is not absolute, but depends on the observer's motion state. This conclusion denies the framework of absolute time and absolute space based on Newtonian mechanics.
Relativity holds that the speed of light is constant in all inertial reference frames, and it is the maximum speed at which an object moves. Due to the relativistic effect, the length of the moving object will become shorter and the time of the moving object will expand. However, due to the problems encountered in daily life, the speed of motion is very low (compared with the speed of light) and the relativistic effect cannot be seen.
Einstein established relativistic mechanics on the basis of completely changing the concept of time and space, pointing out that the mass increases with the increase of speed, and when the speed approaches the speed of light, the mass tends to infinity. He also gave a famous mass-energy relation: E=mc2, which played a guiding role in the later development of atomic energy.
The establishment of general relativity
1905, Einstein published his first article on the special theory of relativity, which did not immediately arouse great repercussions. But Planck, the authority of German physics, noticed his article and thought that Einstein's work could be comparable to Copernicus's. It is precisely because of Planck's promotion that relativity quickly became a topic of research and discussion, and Einstein also attracted the attention of academic circles.
1907, Einstein listened to his friend's suggestion and submitted the famous paper, and applied for the position of supernumerary lecturer at Federal Institute of Technology, but the answer was that the paper was incomprehensible. Although Einstein is very famous in the German physics field, in Switzerland, he can't find a teaching post in a university, and many famous people began to complain about him. 1908, Einstein finally got the position of supernumerary lecturer and became an associate professor the following year. 19 12 years, Einstein became a professor, 19 13 years, at the invitation of Planck, he became the director of the newly established Institute of Physics of Emperor William and a professor at Berlin University.
At the same time, Einstein is considering expanding the accepted theory of relativity. For him, there are two problems that make him uneasy. The first is the problem of gravity. Special relativity is correct for the physical laws of mechanics, thermodynamics and electrodynamics, but it cannot explain the problem of universal gravitation. Newton's theory of gravity is beyond distance, and the gravitational interaction between two objects is instantaneous, that is, at infinite speed, which conflicts with the view of field on which relativity is based and the limit of light speed. The second problem is the non-inertial system, and the special theory of relativity, like the previous physical laws, only applies to the inertial system. But in fact, it is difficult to find the real inertial system. Logically speaking, all natural laws should not be limited to inertial systems, and non-inertial systems must also be considered. It is difficult for special relativity to explain the so-called twin paradox. Paradoxically, there are two twins. My brother is traveling near the speed of light in a spaceship. According to the effect of relativity, the high-speed clock slows down. By the time my brother came back, he was very old, because he had been on the earth for decades. According to the principle of relativity, the spacecraft moves at a high speed relative to the earth, and the earth also moves at a high speed relative to the spacecraft. Brother looks younger than brother, and brother should look younger. This question can't be answered at all In fact, special relativity only deals with uniform linear motion, and my brother has to go through a process of variable speed motion to come back, which relativity can't handle. While people are busy understanding the relative special relativity, Einstein is accepting the completion of the general relativity.
1907, Einstein wrote a long article about the special theory of relativity, "On the Principle of Relativity and Its Conclusions". In this article, Einstein mentioned the principle of equivalence for the first time, and since then, Einstein's thoughts on the principle of equivalence have been developing continuously. Based on the natural law that the inertial mass is directly proportional to the gravitational mass, he proposed that the uniform gravitational field in an infinitely small volume can completely replace the frame of reference for accelerating motion. Einstein also put forward the view of closed box: no matter what method is used, the observer in closed box can't be sure whether he is still in the gravitational field or in the accelerating space without gravitational field. This is the most commonly used viewpoint to explain the equivalence principle, and the equality of inertial mass and gravitational mass is the natural inference of the equivalence principle.
1915438+01In June, Einstein submitted four papers to the Prussian Academy of Sciences. In these four papers, he put forward a new viewpoint, proved the precession of Mercury's perihelion, and gave the correct gravitational field equation. At this point, the basic problems of general relativity have been solved, and general relativity was born. 19 16 years, Einstein finished his long paper "The Basis of General Relativity". In this article, Einstein first called the theory of relativity that once applied to the inertial system as special relativity, and called the principle that only the physical laws of the inertial system are the same as the principle of special relativity as special relativity, and further expressed the principle of general relativity: for any moving reference system, the physical laws must be established.
Einstein's general theory of relativity holds that space-time will be curved due to the existence of matter, and the gravitational field is actually a curved space-time. Einstein's theory that space is bent by the sun's gravity well explains the unexplained 43 seconds in the precession of Mercury's perihelion. The second prediction of general relativity is gravitational redshift, that is, the spectrum moves to the red end in a strong gravitational field, which was confirmed by astronomers in the 1920s. The third prediction of general relativity is that the gravitational field deflects light. The gravitational field closest to the earth is the solar gravitational field. Einstein predicted that distant starlight would deflect 1.7 seconds if it passed through the surface of the sun. 19 19, encouraged by British astronomer Eddington, Britain sent two expeditions to observe the total solar eclipse in two places. After careful study, the final conclusion is that the starlight does deflect around the sun for 1.7 seconds. The Royal Society and the Royal Astronomical Society officially read out the observation report, confirming that the conclusion of general relativity is correct. At the meeting, Tang Musun, a famous physicist and president of the Royal Society, said, "This is the most significant achievement of gravity theory since Newton's time" and "Einstein's theory of relativity is one of the greatest achievements of human thought". Einstein became a news figure. 19 16, he wrote a book "On Special Relativity and General Relativity", which was reprinted 40 times by 1922, and was also translated into more than a dozen languages and widely circulated.
The significance of relativity
Special relativity and general relativity have been established for a long time. It has stood the test of practice and history and is a recognized truth. Relativity has a great influence on the development of modern physics and modern human thinking. Relativity logically unifies classical physics and makes it a perfect scientific system. On the basis of the principle of special relativity, special relativity unifies Newton's mechanics and Maxwell's electrodynamics, pointing out that both of them obey the principle of special relativity and are covariant to Lorentz transformation, while Newton's mechanics is only a good approximate law of low-speed motion of objects. On the basis of generalized covariation, general relativity establishes the relationship between local inertia length and universal reference coefficient through equivalence principle, obtains the generalized covariant forms of all physical laws, and establishes the generalized covariant gravity theory, and Newton's gravity theory is only its first-order approximation. This fundamentally solved the problem that physics was limited to the inertia coefficient in the past, and got a reasonable arrangement in logic. Relativity strictly examines the basic concepts of physics such as time, space, matter and motion, and gives the time-space view and material view of scientific system, thus making physics a perfect scientific system logically.
Special relativity gives the law of high-speed motion of objects, and puts forward that mass and energy are equivalent, and gives the relationship between mass and energy. These two achievements are not obvious to macroscopic objects moving at low speed, but they are extremely important in the study of microscopic particles. Because the speed of microscopic particles is generally relatively fast, and some of them are close to or even reach the speed of light, the physics of particles cannot be separated from relativity. The mass-energy relationship not only creates the necessary conditions for the establishment and development of quantum theory, but also provides the basis for the development and application of nuclear physics.
General relativity has established a perfect theory of gravity, mainly involving celestial bodies. Today, relativistic cosmology has further developed, and gravitational wave physics, compact astrophysics and black hole physics, which belong to relativistic astrophysics, have made some progress, attracting many scientists to study.
A French physicist once commented on Einstein: "Einstein will be at the forefront of physicists in our time." He is and will be one of the most outstanding superstars in the human universe. "In my opinion, he may be greater than Newton, because his contribution to science has entered the structure of the basic essence of human thought more deeply."