Introduction to Einstein: March 14, 1879, was a memorable day for the small town of Ulm, Germany. On this day, Einstein, the greatest scientist of the 20th century, was born here.
Einstein’s parents were Jewish. As early as the 16th century AD, Einstein's Jewish ancestors wandered to Germany from unknown places. But for unknown reasons, they suddenly gave up the ancient tradition of Jewish migration, and instead fell in love with the mountains, rivers and forests of Germany, and began to settle down. By the generation of Einstein's parents, apart from some minor religious habits, they had actually become authentic Germans. They spoke German, loved Germany, regarded Germany as their motherland, and took themselves as Germans for granted.
Einstein’s father, named Hermann Einstein, was an unsuccessful small businessman. His favorite thing in life was to read Schiller and Heine in the living room every night. Works by others. Her mother’s name was Pauline Coker. She was born into a famous family, received a good education, and had a high level of cultural accomplishment. She loved literature and music even more.
Einstein was born into such a family. In addition, the era when he grew up was the most rapid development of physics in human history. When Einstein entered his youth, it was Thomas Alva Edison, Hendrik Antoon Lorentz, Pierre Curie and Marie Sklodowska Curie and others. most active period. At this time, the theoretical system of classical physics established by Galileo, Newton and others, after nearly 200 years of ups and downs, has undergone tremendous changes due to the discovery of the laws of energy conservation and conversion, the establishment of thermodynamics and statistical physics, especially due to the work of Faraday and Maxwell. The discovery of electromagnetism is increasingly becoming the greatest subject in human history.
The young Einstein was not bound by old traditions. Based on the research work of Lorenz and others, he made fundamental changes to some basic concepts such as space and time. This fundamental breakthrough in theory opened up a new era of physics.
This theory is the symbol of Einstein's lifelong career and is his theory of relativity. Prior to this, Einstein was the first to expand Planck's quantum concept to the propagation of light in space in his article "On the Generation and Transformation of Light" written in 1905, and proposed the "Light Quantum Hypothesis" , it is believed that: for time average values ??(i.e., statistical average phenomena), light behaves as fluctuations; while for instantaneous values ??(i.e., fluctuation phenomena), light behaves as particles. This is the first time in history that the unity of wave and particle properties of microscopic particles, known as "wave-particle duality", has been revealed. Subsequent developments in physics have shown that wave-particle duality is the most basic feature of the entire microscopic world. Einstein won the 1921 Nobel Prize in Physics for this discovery.
The birth of the theory of relativity was marked by "On the Electrodynamics of Moving Bodies" published in 1905 when Einstein was 26 years old. To be honest, few people can understand Einstein's paper, but it is the greatest paper of the 20th century. The special theory of relativity proposed by Einstein in this paper largely solved the crisis of classical physics that emerged at the end of the 19th century and promoted the revolution of the entire physical theory. The end of the 19th century was a period of change in physics, with new experimental results impacting the classical physics system established since Galileo and I. Newton. The older generation of theoretical physicists represented by H.A. Lorenz tried to resolve the contradiction between old theories and new things based on the original theoretical framework. Einstein believed that the way out lay in fundamental changes to the entire theoretical foundation. Based on the two universal generalizations of the relativity of the inertial reference system and the invariance of the speed of light, he transformed the basic concepts of time, space and motion in classical physics, denying the existence of absolutely static space and the concept of simultaneity. of absoluteness. This theory also successfully explained why radioactive elements (such as radium) can release large amounts of energy, laying the theoretical foundation for the invention of atomic bombs and hydrogen bombs in the 20th century.
Einstein's third contribution was his "theory of molecular kinetics." In his article "Study of the Movement of Suspended Particles in Stationary Liquids on the Basis of Molecular Kinetic Theory", Einstein used atomic theory to explain "Brownian motion". "Brownian motion" is the irregular motion of some very small particles suspended in a liquid. It was first discovered by R. Brown.
Three years after Einstein proposed this theory, French physicist J.B. Perrin confirmed Einstein's theoretical predictions with precise experiments, thus solving the question of whether atoms exist that has been debated in the scientific and philosophical circles for more than half a century. , making the atomic hypothesis a scientific theory with a solid foundation.
Three great discoveries in the history of science are enough to put Einstein on par with Copernicus, Newton, Darwin and others. But what Einstein is more praised by future generations is that in his later years, he devoted himself to society with great enthusiasm, cared about politics, opposed war, and called for peace. At this point, Einstein was not only a great scientist, an outstanding thinker with a spirit of philosophical exploration, but also an upright man with a high sense of social responsibility. During World War I, he participated in public and underground anti-war activities. After the Nazis seized power in Germany in 1933, Einstein was the primary target of persecution in the scientific community. Fortunately, he was lecturing in the United States at the time and was not persecuted. In 1939, he learned of the discovery of uranium nuclear fission and its chain reaction. Under the impetus of the Hungarian physicist L. Szilard, he wrote to President Roosevelt suggesting the development of an atomic bomb to prevent Germany from taking the lead. So Roosevelt was determined to build an atomic bomb, and successfully tested it in New Mexico in 1945. On the eve of the end of World War II, the United States dropped atomic bombs over Hiroshima and Nagasaki, Japan, and Einstein was strongly dissatisfied with this. After the war, unremitting struggles were carried out to launch a peaceful movement against nuclear war and against the danger of fascism in the United States.
Einstein died of illness at Princeton University in the United States on April 18, 1955. His name and achievements will be immortal!
Einstein’s student days
Albert Einstein was born on March 14, 1879, in the small German town of Ulm. His parents were both Jewish. Einstein had a happy childhood. His father was a calm, gentle and kind-hearted man who loved literature and mathematics. His mother had a strong personality and loved music, which influenced Einstein. Einstein started learning the violin at the age of six, and the violin became his lifelong companion. Einstein's parents had a good influence and family education on him, and the family was filled with a free spirit and a peaceful atmosphere.
Like Newton, Einstein did not show any superior intelligence when he was young. On the contrary, he could not speak when he was more than four years old, and his family even worried that he was an imbecile. When he was six years old, he entered the national school. He was a very quiet child who liked to play games that required patience and tenacity, such as building houses with paper. After entering middle school in 1888, he was not outstanding academically. Except for being good at mathematics, he was not very good at other subjects, especially Latin and Greek. He had no interest in classical languages. At that time, German schools had to receive religious education. Einstein was very serious at first, but when he read popular science books, he realized that many stories in religion were untrue. At the age of 12 he gave up his belief in religion and became suspicious of all authority and belief in social settings, developing a free mind. Einstein discovered that there is a huge natural world around him, which exists independently of human beings like an eternal mystery. He saw many people he greatly respected and admired find inner freedom and peace when they devoted themselves to this career. Therefore, as a boy, Einstein chose a career in science, hoping to master the mysteries of the natural world. Once he chose this path, he persevered and never regretted it.
In 1895, Einstein came to Zurich, Switzerland, and prepared to apply for the Federal University of Technology in Zurich. Although he did well in mathematics and physics, he did not do well in other subjects. The principal of the school recommended that he go to Switzerland. I studied at Aarau State High School for a year to make up for my homework. Einstein felt happy during his time at the Aarau State High School. He tasted the free air and sunshine of Switzerland and was determined to give up his German citizenship.
In 1896, Einstein officially became a stateless person and was admitted to the Federal University of Technology. During college, Einstein became obsessed with physics. On the one hand, he read the works of famous German physicists Kirchhoff, Hertz and others, studied Maxwell's electromagnetic theory and Mach's mechanics, and often went to theoretical physics. Ask the professor's home for advice. On the other hand, he spent most of his time going to physics laboratories to do experiments, and was obsessed with direct observation and measurement. In 1900, Einstein graduated from university. In 1901, he obtained Swiss citizenship.
In 1902, with the help of his friend Grossmann, Einstein finally found a stable job as a technician at the Swiss Federal Patent Office in Bern.
The Creation of Special Theory of Relativity
As early as 16 years old, Einstein learned from books that light is an electromagnetic wave traveling at a very fast speed. He had an idea, if If a person moves at the speed of light, what kind of world will he see? He will not be able to see the light moving forward, but can only see the electromagnetic field oscillating but stagnant in space. Is this possible?
In connection with this, he very much wanted to explore the so-called ether problem related to light waves. The term ether originates from the Greeks and is used to represent the basic elements that make up celestial objects. Descartes first introduced it to science in the 17th century as a medium for transmitting light. Later, Huygens further developed the ether theory, believing that the medium carrying light waves was ether, which should fill all space including vacuum, and be able to penetrate into ordinary matter. Different from Huygens' view, Newton proposed the particle theory of light. Newton believed that the luminous body emits a stream of particles moving in a straight line, and the particle stream impacts the retina to cause vision. In the 18th century, Newton's particle theory prevailed. However, in the 19th century, the wave theory gained absolute dominance, and the theory of ether also developed greatly. The view at that time was that the propagation of waves depends on the medium, because light can propagate in vacuum, and the medium for propagating light waves is the ether that fills the entire space, also called light ether. At the same time, electromagnetism has developed vigorously. Through the efforts of Maxwell, Hertz and others, a mature dynamic theory of electromagnetic phenomena—electrodynamics—has been formed, and unified light and electromagnetic phenomena in theory and practice. It is believed that Light is an electromagnetic wave within a certain frequency range, thus unifying the wave theory of light with the electromagnetic theory. Ether is not only the carrier of light waves, but also the carrier of electromagnetic fields. Until the end of the 19th century, people attempted to search for ether, but it was never discovered experimentally.
However, electrodynamics has encountered a major problem, which is that it is inconsistent with the principle of relativity followed by Newtonian mechanics. The idea of ??the principle of relativity existed as early as the time of Galileo and Newton. The development of electromagnetism was initially integrated into 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 speed addition principle of Newtonian mechanics, the speed of light in different inertial systems is different. This raises a question: Is the principle of relativity applicable to mechanics Applicable to electromagnetism? For example, there are two cars, one approaching you and one driving away. You see the lights of the car in front of you approaching you and the lights of the car behind you moving away. According to Maxwell's theory, the speed of the two kinds of light is the same, and the speed of the car does not play a role in this. But according to Galileo's theory, these two measurements are different. The car coming towards you will accelerate the light emitted, that is, the speed of light of the car in front = speed of light + speed of car; while the speed of light of the car driving away is slower, because the speed of light of the car behind = speed of light - speed of car. Maxwell's and Galileo's statements about speed clearly contradicted each other. How do we resolve this disagreement?
Theoretical physics reached its peak in the 19th century, but it also contained huge crises. The discovery of Neptune showed the extremely powerful theoretical power of Newtonian mechanics. The unity of electromagnetism and mechanics made physics show a formal integrity, and it was praised as "a solemn and majestic architectural system and a touching and beautiful temple." In people's minds, classical physics has reached an almost perfect level. When the famous German physicist Planck was young, he told his teacher that he would devote himself to theoretical physics. The teacher advised him: "Young man, physics is a science that has been completed and will not be much more important." It is a pity to devote his life to this subject."
Einstein seems to be the person who will build a new edifice of physics. During his days at the Bern Patent Office, Einstein paid extensive attention to the cutting-edge developments in physics, thought deeply about many issues, and formed his own unique insights. During the course of ten years of exploration, Einstein carefully studied Maxwell's electromagnetic theory, especially electrodynamics as developed and elaborated by Hertz and Lorentz. Einstein firmly believed that the electromagnetic theory was completely correct, but there was one problem that made him uneasy, which was the existence of the absolute reference system ether. He read many works and found that all attempts to prove the existence of ether had failed.
After research, Einstein discovered that, apart from serving as an absolute reference system and a load of electromagnetic fields, ether had no practical significance in Lorentz's theory. So he thought: And is an absolute frame of reference necessary? Does the electromagnetic field have to have a load?
Einstein liked to read philosophical works and absorb ideological nourishment from philosophy. He believed in the unity of the world and the consistency of logic. The principle of relativity has been widely proven in mechanics, but it cannot be established in electrodynamics. Einstein raised doubts about the logical inconsistency between the two theoretical systems of physics. He believed that the principle of relativity should be universally true, so the electromagnetic theory should have the same form for each inertial system, but here the problem of the speed of light arises. Whether the speed of light is a constant quantity or a variable quantity has become the primary question of whether the principle of relativity is universally valid. Physicists at that time generally believed in the ether, that is, they believed in the existence of an absolute reference system. This was influenced by Newton's concept of absolute space. At the end of the 19th century, Mach criticized Newton's absolute view of space and time in his book "Developing Mechanics", which left a deep impression on Einstein. One day in May 1905, Einstein discussed this issue that had been explored for ten years with a friend Besso. Besso elaborated on his views based on Machism, and the two discussed it for a long time. Suddenly, Einstein realized something. After thinking about it over and over again when he got home, he finally figured out the problem. The next day, he came to Besso's house again and said: Thank you, my problem is solved. It turns out that Einstein thought one thing clearly: there is no absolute definition of time, and there is an inseparable connection between time and the speed of light signals. He found the key to the lock, and after five weeks of hard work, Einstein presented the special theory of relativity to people.
On June 30, 1905, the German "Annals of Physics" accepted Einstein's paper "On the Electrodynamics of Moving Bodies" and published it in the journal in September of the same year. This paper is the first article on the special theory of relativity. It contains the basic ideas and basic content of the special theory of relativity. The special theory of relativity is based on two principles: the principle of relativity and the principle of the constant speed of light. The starting point for Einstein's solution to the problem was his firm belief in the principle of relativity. Galileo was the first to clarify the idea of ??the principle of relativity, but he did not give a clear definition of time and space. Newton also talked about the idea of ??relativity when he established the mechanical system, but he also defined absolute space, absolute time and absolute motion. He was contradictory on this issue. Einstein greatly developed the principle of relativity. In his view, there is no absolutely static space at all, and there is no absolutely identical time. All time and space are related to 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 by the space and time of this reference system are all in the same form. This is the principle of relativity, strictly speaking, the principle of relativity in a narrow sense. In this article, Einstein did not discuss much about the basis for the constant speed of light as a basic principle. He proposed that the constant speed of light was a bold assumption, which was based on the requirements of electromagnetic theory and the principle of relativity. This article is the result of Einstein's many years of thinking about the issue of ether and electrodynamics. He used the relativity of simultaneousness as a breakthrough to establish a new theory of time and space, and based on the new theory of space and time, he gave the theory of moving bodies Electrodynamics in its complete form, the ether is no longer necessary, ether drift is non-existent.
What is the relativity of simultaneity? How do we know that two events in different places happened at the same time? Generally, we confirm via signals. In order to know the simultaneity of events in different places, we need to know the speed of signal transmission, but how come this speed is not exceeded? We must measure the spatial distance between two places and the time required for signal transmission. Measuring spatial distance is very simple. The trouble lies in measuring time. We must assume that there is a clock in each place that has been adjusted. From the readings of the two clocks, You can know the signal propagation time. But how do we know that the clock in a different place is correct? The answer is that a signal is also needed. Can this signal set the clock correctly? If we follow the previous line of thinking, it would require a new signal, which would lead to infinite retreat and the simultaneity of different places cannot actually be confirmed. But one thing is clear, simultaneity must be related to a signal, otherwise it would be meaningless for us to say that these two things happened at the same time.
The light signal may be the most suitable signal for the clock, but the speed of light is not infinite, which leads to a novel conclusion. For a stationary observer, two things happen at the same time, and for a moving observer, two things happen at the same time. It's not at the same time. We imagine a train running at high speed, its speed is close to the speed of light. When the train passed the platform, A stood on the platform. Two lightning bolts flashed in front of A's eyes, one at the front end of the train and one at the rear end, leaving traces on both ends of the train and corresponding parts of the platform. Through measurement, A and The distance between the two ends of the train is equal, and the conclusion is that A saw two lightning bolts at the same time. Therefore, for A, if the two received light signals travel the same distance within the same time interval and arrive at his location at the same time, the two events must occur at the same time, they are simultaneous. But for B, who is in the center of the train, the situation is different. Because B moves with the high-speed train, he will first intercept the front-end signal propagating towards him, and then receive the optical signal from the back-end. For B, the two events are not simultaneous. That is to say, simultaneity is not absolute but depends on the motion state of the observer. This conclusion denies the absolute time and absolute space frameworks underlying Newtonian mechanics.
The theory of relativity holds that the speed of light is constant in all inertial reference systems and is the maximum speed at which objects move. Due to relativistic effects, the length of a moving object will become shorter and the time of a moving object will dilate. However, due to the problems encountered in daily life, the movement speed is very low (compared to the speed of light), and no relativistic effect can be seen.
Einstein established relativistic mechanics based on a radical change in the view of space and time, stating that mass increases with speed and approaches infinity as speed approaches the speed of light. He also gave the famous mass-energy relationship: E=mc2. The mass-energy relationship played a guiding role in the subsequent development of atomic energy.
The establishment of the general theory of relativity
After Einstein published his first article on the special theory of relativity in 1905, it did not immediately arouse a great response. However, Planck, an authority in German physics, noticed his article and believed that Einstein's work was comparable to that of Copernicus. It was precisely because of Planck's promotion that the theory of relativity quickly became a topic of research and discussion. Einstein also attracted academic attention.
In 1907, Einstein followed the advice of his friends and submitted his famous paper to apply for a non-staff lecturer position at the Federal University of Technology, but the reply he received was that the paper was incomprehensible. Although Einstein was already very famous in the German physics community, he could not get a university teaching position in Switzerland. Many famous people began to complain about him. In 1908, Einstein finally got a non-staff lecturer. position and became an associate professor in the second year. In 1912, Einstein became a professor. In 1913, at Planck's invitation, he served as director of the newly established Kaiser Wilhelm Institute of Physics and professor at the University of Berlin.
During this period, Einstein was considering extending the established theory of relativity. For him, there were two problems that made 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 gravity. Newton's theory of gravity is at a distance. The gravitational effect between two objects is transmitted instantaneously, that is, at an infinite speed. This conflicts with the field view based on the theory of relativity and the limit of the speed of light. The second is the problem of non-inertial frames. The special theory of relativity, like the previous laws of physics, only applies to inertial frames. But in fact it is difficult to find a real inertial frame. Logically speaking, all natural laws should not be limited to inertial systems, but must consider non-inertial systems. It is difficult for special relativity to explain the so-called twin paradox. The paradox is that there is a pair of twin brothers. The brother is sailing in the spacecraft at a speed close to the speed of light. According to the effect of relativity, the high-speed clock slows down and waits for the brother. Back, the younger brother has become very old, because the earth has experienced decades. According to the principle of relativity, the spaceship moves at a high speed relative to the earth, and the earth also moves at a high speed relative to the spacecraft. The younger brother sees that the elder brother is getting younger, and the older brother sees that the younger brother should also be younger. There is simply no answer to this question. In fact, the special theory of relativity only deals with uniform linear motion, but for my brother to come back, he must go through a process of variable speed motion, which the theory of relativity cannot handle. While people were busy understanding the special theory of relativity, Einstein was completing the general theory of relativity.
In 1907, Einstein wrote a long article on the special theory of relativity, "On the Principle of Relativity and Conclusions Drawn from It". In this article, Einstein mentioned equivalence for the first time. Since then, Einstein's ideas about the equivalence principle have continued to develop. He used the natural law that inertial mass and gravitational mass are proportional as the basis of the equivalence principle, and proposed that a uniform gravitational field in an infinitely small volume can completely replace the reference frame of accelerated motion. Einstein also proposed the concept of a closed box: no matter what method is used, an observer in a closed box cannot determine whether he is at rest in a gravitational field or in a space that is accelerating without a gravitational field. , this is the most commonly used statement to explain the equivalence principle, and the equality of inertial mass and gravitational mass is a natural corollary of the equivalence principle.
In November 1915, Einstein submitted four papers to the Prussian Academy of Sciences. In these four papers, he put forward new ideas, proved the precession of Mercury's perihelion, and gave Get the correct gravitational field equation. At this point, the basic problems of general relativity have been solved, and general relativity was born. In 1916, Einstein completed a long paper "The Foundation of General Relativity". In this article, Einstein first called the theory of relativity that was previously applicable to inertial frames special relativity, and classified the physical laws that are also true only for inertial frames. The principle is called the principle of special relativity, and further states the principle of general relativity: The laws of physics must hold true for any frame of reference that is moving in any way.
Einstein’s general theory of relativity believes that due to the existence of matter, space and time will be curved, and the gravitational field is actually a curved space-time. Einstein's theory of using the sun's gravity to curve space well explains the unexplained 43 seconds of Mercury's perihelion precession. The second major prediction of general relativity is gravitational redshift, that is, the spectrum moves toward the red end in a strong gravitational field. In the 1920s, astronomers confirmed this in astronomical observations. The third major prediction of general relativity is that gravitational fields deflect light. The largest gravitational field closest to the earth is the gravitational field of the sun. Einstein predicted that if the light of distant stars passes over the surface of the sun, it will be deflected for 1.7 seconds. In 1919, at the instigation of the British astronomer Eddington, the United Kingdom sent two expeditions to two places to observe the total solar eclipse. After careful research, the final conclusion was that starlight did indeed occur near the sun at 1.7 seconds of deflection. The Royal Society and the Royal Astronomical Society officially read out the observation report, confirming that the conclusions of general relativity are correct. At the meeting, famous physicist and President of the Royal Society Thomson said: "This is the most significant achievement in the theory of universal gravitation since Newton's time." "Einstein's theory of relativity is one of the greatest achievements of human thought." one". Einstein became a news figure. In 1916, he wrote a popular book on relativity, "A Brief Introduction to Special and General Relativity." By 1922, it had been reprinted 40 times and translated into more than a dozen languages. spread widely.
The significance of the theory of relativity
A long time has passed since the establishment of the special theory of relativity and the general theory of relativity. It has withstood the test of practice and history and is a truth generally recognized by people. The theory of relativity has had a huge impact on the development of modern physics and the development of modern human thinking. The theory of relativity unifies classical physics logically and makes classical physics a perfect scientific system. The special theory of relativity unifies the two systems of Newtonian mechanics and Maxwell's electrodynamics on the basis of the special principle of relativity, pointing out that they both obey the special principle of relativity and are covariant to the Lorentz transformation. Newtonian mechanics is nothing more than the movement of objects at low speeds. A good approximation for motion. On the basis of general covariance, the general theory of relativity established the relationship between the local inertial length and the universal reference coefficient through the equivalence principle, obtained the general covariant form of all physical laws, and established the general covariant gravity theory, and Newton's theory of gravity is only its first approximation. This fundamentally solves the previous problem of physics being limited to inertial coefficients, and provides a logically reasonable arrangement. The theory of relativity strictly examines the basic concepts of physics such as time, space, matter and motion, and provides a scientific and systematic view of time, space and matter, thus making physics a logically perfect scientific system.
The special theory of relativity gives the laws of motion of objects moving at high speeds, and suggests that mass and energy are equivalent, and gives the mass-energy relationship.
These two results are not obvious for macroscopic objects moving at low speeds, but they show extreme importance when studying microscopic particles. Because microscopic particles generally move very fast, with some approaching or even reaching the speed of light, particle physics is inseparable from the theory of relativity. The mass-energy relationship not only creates necessary conditions for the establishment and development of quantum theory, but also provides a basis for the development and application of nuclear physics.
General relativity has established a complete theory of gravity, which mainly involves celestial bodies. Up to now, relativistic cosmology has further developed, and gravitational wave physics, compact astrophysics, and black hole physics, all branches of relativistic astrophysics, have made certain progress, attracting many scientists to conduct research.
A French physicist once said of Einstein: "Among the physicists of our time, Einstein will be at the forefront. He is and will remain the most influential physicist in the human universe. "One of the shining stars", "In my opinion, he may be greater than Newton, because his contribution to science has penetrated more deeply into the structure of the basic essentials of human thought."