Einstein's scientific career began in the winter of 1900, when he was in the pain of unemployment after graduating from college. From 1900 to 1904, he writes a paper every year and publishes it in the German journal of physics. The first two articles are about the thermodynamics of liquid level and electrolysis, trying to give chemistry a mechanical basis. Later, I found that this road could not be taken, and I changed to the mechanical basis of thermodynamics. Independent of J.W. Gibbs' work in 190 1, some basic theories of statistical mechanics are put forward. Three papers from 1902 to 1904 all belong to this field. 1902' s paper deduces the heat balance theory and the second law of thermodynamics from the laws of mechanics and probability operation. 1904 discusses the fluctuation phenomenon predicted by statistical mechanics and finds that energy fluctuation (or thermal stability of the system) depends on Boltzmann constant. He not only applied this result to mechanical systems and thermal phenomena, but also boldly applied it to radiation phenomena, and obtained the fluctuation formula of radiation energy, thus deducing Wien's displacement law. The study of fluctuation phenomenon made him make a major breakthrough in both radiation theory and molecular motion theory in 1905.
Miracle 1905 1905, Einstein created a miracle without precedent in the history of science. This year, he wrote six papers, and during the half year from March to September, he made four epoch-making contributions in three fields in his spare time besides working eight hours a day in the patent office.
photon
In the paper "A Speculative Viewpoint on the Generation and Transformation of Light" written in March of 1905, the quantum concept put forward by Planck in 1900 was extended to the propagation of light in space, and the optical quantum hypothesis was put forward, which was recognized as: for time average (i.e. statistical average phenomenon), light showed fluctuation; For instantaneous values (that is, fluctuations), light appears as particles. This is the first time in history to reveal the unity of fluctuation of microscopic objects and particles, that is, wave-particle duality. The later development of physics shows that wave-particle duality is the most basic feature of the whole microscopic world. This paper also named L. Boltzmann's "Entropy of a system is a function of its state probability" as "Boltzmann principle". At the end of the paper, he explained the photoelectric phenomenon with the concept of optical quantum, and deduced the relationship between the maximum energy of photoelectrons and the frequency of incident light. It took 10 years for this relationship to be confirmed by R.A. Millikan's experiments. Einstein won the Nobel Prize in Physics in 192 1 year for discovering the law of photoelectric effect.
kinetic theory
1In April, May and February of 905, he wrote three theories about the motion of suspended particles in liquid. This movement was first discovered by British botanist R. Brown in 1827, and is called Brownian movement. Einstein's purpose at that time was to determine the actual size of molecules by observing the random motion of suspended particles caused by the fluctuation of molecular motion, thus solving the problem of whether atoms exist in scientific and philosophical circles for more than half a century. Three years later, the French physicist J.B. Perrin confirmed Einstein's theoretical prediction with accurate experiments. This made F.W. ostwald, the German chemist who was the most firmly opposed to atomism at that time and the founder of "Energetics", take the initiative to announce in 1908: "The atomic hypothesis has become a scientific theory with a solid foundation.
Special relativity in the era of innovation
1in June, 905, Einstein wrote a long article about electrodynamics of moving objects, which initiated a new era of physics and thoroughly put forward the special theory of relativity. This is the result of his brewing and exploration in 10, which largely solved the crisis of classical physics at the end of 19 and promoted the revolution of the whole physics theory. In order to overcome the contradiction between the new experimental facts and the old theoretical system, the older generation of physicists, represented by Lorenz, adopted the method of mending loopholes and put forward numerous hypotheses, which made the old theoretical system even more stretched. Einstein believes that the way out lies in fundamentally changing the whole theoretical basis. Starting from the belief of the unity of natural boundaries, he investigated the following questions: Why does the principle of relativity (the laws of mechanics are unchanged for any inertial system) which is generally established in the field of Newtonian mechanics not hold true in electrodynamics? According to M Faraday's electromagnetic induction experiment, this inconsistency is obviously not inherent in the present phenomenon, and the problem must be based on the theory of classical physics. He absorbed the empiricism philosopher D Hume's criticism of transcendentalism and E Mach's criticism of I Newton's concepts of absolute space and absolute time. Starting with the "simultaneity" of two spatially separated events, he denied the absolute simultaneity without empirical basis, and then denied the existence of absolute time, absolute space and "ether", and thought that the traditional concept of time and space must be revised. He promoted the relativity of mechanical motion discovered by Galileo, a basic experimental fact with universal significance, to the basic principle that all physical theories must follow; At the same time, all the "ether drift" experiments show that light always travels at a certain speed in vacuum as a principle. If the principle of relativity and the principle of invariability of light speed are established at the same time, then the transformation between coordinates of different inertial systems can no longer be galilean transformation, but should be another transformation similar to that developed by Lorenz in 1904. In fact, Einstein didn't know Lorenz's work in 1904 at that time, and their original transformation form was consistent only in the first power of □/□; Lorentz transformation now essentially refers to Einstein's form. For Lorentz transformation, the length of space and time is no longer the same, but the physical laws including Maxwell's equations are the same (covariant). Newton's laws of mechanics are covariant to galilean transformation, and must be modified to meet the covariant under Lorentz transformation. This transformation is actually a generalization, which regards classical mechanics as the limit case of relativistic mechanics at low speed. So mechanics and electromagnetism are unified on the basis of kinematics.
Mass energy equivalent
1905 In September, Einstein wrote a short article, is the inertia of an object related to the energy it contains? As an inference of the theory of relativity, the equivalence between mass (□) and energy (□) is revealed: □ =□□□□□, which explains why radioactive elements (such as radium) can release a lot of energy. Mass-energy equivalence is the theoretical basis of nuclear physics and particle physics, and it also paved the way for the release and utilization of nuclear energy in the 1940s. The further development of quantum theory Einstein put forward the theory of light quantum, which was opposed by almost all physicists of the older generation. Even Planck, who first put forward the concept of quantum and enthusiastically supported the special theory of relativity, seriously thought it was a "mistake" of Einstein until 19 13. Nevertheless, Einstein worked alone and developed quantum theory unremittingly. 1906, he extended the quantum concept to the vibration inside the object, and basically explained the relationship between the specific heat capacity of the solid and the temperature at low temperature. 19 12 years, he applied the concept of light quantum to photochemical phenomena and established photochemical laws. 19 16 published the paper "Quantum Theory of Radiation", which synthesized the development results of quantum theory, put forward the statistical theory of radiation absorption and emission process, and deduced the Planck radiation formula from the concept of quantum transition in N Bohr 19 13. The concept of stimulated emission put forward in this paper provided a theoretical basis for the booming laser technology in the 1960s. Inspired by the concept of wave-particle duality revealed by optical quantum theory, the theory of matter wave was put forward by L.V. de Broglie 1923. This theory was first enthusiastically supported by Einstein. Not only that, when he received a paper on the quantum statistical theory of light from the young physicist S Bose in 1924, he immediately translated it into German and recommended it for publication. Combining this theory with the concept of matter wave, he put forward the quantum statistical theory of monoatomic gas. This is about the bose-einstein statistics of integer spin particles (see quantum statistics). Inspired by Einstein's work, E. Schrodinger extended De Broglie wave to bound particles and established wave mechanics in 1926 (see representation theory and quantum mechanics). Therefore, American physicist A. Pais believes that "Einstein is not only one of the three elders of quantum theory (Planck, Einstein, N. Poe), but also the only godfather of wave mechanics." M born also believes that "he is a pioneer" and "our leader and standard bearer" in the struggle to conquer the wasteland of quantum phenomena.
Exploring the equivalence principle of general relativity
After the establishment of the special theory of relativity, Einstein was not satisfied and tried to extend the application of the principle of relativity to non-inertial systems. He found a breakthrough from Galileo's old experimental fact that the acceleration of all objects in the gravitational field is the same (that is, the inertial mass is equal to the gravitational mass), and put forward the equivalence principle in 1907: "The equivalent strength of the gravitational field and the reference system is completely equivalent in physics." It is concluded that in the gravitational field, the clock should go fast, the wavelength of light wave should change and the light should bend. This year, H. Minkowski, his university teacher and famous geometer, put forward the four-dimensional representation of special relativity, which provided a useful mathematical tool for the further development of relativity. Unfortunately, Einstein didn't realize its value at that time and used it.
The tortuous course of continuing exploration
The discovery of the principle of equivalence was regarded by Einstein as the happiest thought in his life, but his later work was very hard and he took a big detour. 19 1 1 year. According to the equivalence principle and Huygens principle, he calculated the deflection value of light passing near the sun as □. At the beginning of 19 12, he analyzed the rigid rotating disk and realized that Euclidean geometry in the gravitational field was not strictly effective. At the same time, he also found that Lorentz transformation is not universal and needs to seek a more universal transformation relationship; In order to ensure the conservation of energy and momentum, the gravitational field equation must be nonlinear; The principle of equivalence is only valid for infinitesimal areas. He realized that the theory of Gaussian surface studied in college should be useful for establishing the equation of gravitational field, but he was not familiar with this set of mathematical tools and could not start at the moment. 19121kloc-0/0 in October, he left Prague and returned to work at his alma mater in Zurich. With the help of M. Grossman, a classmate who was then a professor of mathematics at his alma mater, he studied Riemannian geometry and the absolute differential calculus of G. Rich and T. Levi-Chevita (that is, tensor analysis). After a year of hard cooperation, they published an important paper "Outline of General Relativity and Gravity Theory" in 19 13, and put forward the gauge field theory of gravity. Here, the gravitational field is not a scalar, but a metric tensor, that is, the gravitational field is determined by 10 gravitational potential functions. This is the first time that gravity and scale are combined to give Riemann a real physical meaning. However, the gravitational field formula they got at that time was only covariant to linear transformation, and did not have the covariant under arbitrary coordinate transformation required by the principle of general relativity. This is because Einstein was not familiar with tensor operation at that time, and mistakenly thought that as long as he obeyed the conservation law, he had to limit the choice of coordinate system. In order to maintain the principle of causality, he had to give up the requirement of universal covariation.
The second peak of scientific achievements
The three years from 19 15 to 19 17 are the second peak of Einstein's scientific achievements, similar to 1905, and he has also made historic achievements in three different fields. In addition to the general theory of relativity, which is recognized as one of the greatest achievements in the history of human thought, it was finally built in 19 15. 19 16 years, a major breakthrough was made in radiation quantum theory, and in 19 17 years, modern scientific cosmology was founded. The mistake of giving up the requirement of covariation of all things when the general theory of relativity was established made Einstein continue to take a detour for more than two years, and it was not until July of 19 15 that he gradually realized this mistake. After returning to the requirement of the covariation of all things, he concentrated on exploring new gravitational field equations from June 19 15 to June10,165438. In the first paper, he obtained the universal covariant gravitational field equation satisfying the conservation law (see general relativity), but added an unnecessary restriction, that is, only unimodal transformation was allowed. In the third paper, according to the new gravitational field equation, it is calculated that the deflection of light passing through the surface of the sun should be □, which is twice the previous value; At the same time, the remaining age difference of Mercury perihelion every 100 years is calculated to be 43□, which is completely consistent with the observation results, completely solving a major problem in astronomy for more than 60 years and giving Einstein great encouragement. In his paper "Gravity Field Equation" on191/kloc-5125 October, he gave up unnecessary restrictions on transformation groups, established a truly universal covariant gravitational field equation, and declared that "general relativity as a logical structure has finally been completed". At the same time, the German mathematician D. Hilbert also independently obtained the universal covariant force field equation at1915438+065438+1October 20th in Gottingen. 19 16 In the spring, Einstein wrote a concluding essay "The Basis of General Relativity"; At the end of the same year, he wrote a very popular booklet "On Special and General Relativity".
gravity wave
Einstein completed the summary of general relativity in March 19 16, and studied the approximate integral of gravitational field equation in June, and found that when a mechanical system changes, it will inevitably emit gravitational waves that travel at the speed of light. He pointed out that the existence of radiation-free stable orbits in atoms is mysterious from both electromagnetic and gravitational perspectives. Therefore, "quantum theory should not only transform Maxwell's electrodynamics, but also transform a new theory of gravity." In autumn, he returned to the problem of quantum radiation, with this intention, he put forward the concepts of spontaneous transition and stimulated transition, and made a new derivation of Planck radiation formula. The existence of gravitational waves caused some scientists to disagree, and Einstein later discussed its existence and nature many times. Gravitational waves are too weak to be detected and have not attracted people's attention for a long time. Since the 1960s, the experiment of detecting gravitational waves has gradually formed a craze, but none of them have reached the minimum accuracy required for detection. The announcement of 1979 indirectly confirmed the existence of gravitational waves through four-year continuous observation of the periodic changes of the radio pulse binary star PSR1913+16 discovered in 1974.
The establishment of cosmology
19 17 Einstein used the results of general relativity to study the space-time structure of the whole universe and published a groundbreaking paper, An Overview of Cosmology Based on General Relativity. This paper analyzes the traditional concept of "the universe is infinite in space" and points out that it is incompatible with Newton's gravity theory and general relativity gravity theory. In fact, people can't give reasonable boundary conditions for the gravitational field equation at infinity in space. He believes that the possible way out is to regard the universe as a "self-enclosed continuous area with limited space (three-dimensional) volume". It is a bold pioneering work in human history to infer that the universe is finite and unbounded in space with scientific arguments, which makes cosmology get rid of pure speculative speculation and enter the field of modern science, and is a revolution in cosmology. According to the fact that the speed of stars observed in astronomy at that time was very small, Einstein thought that the distribution of matter was quasi-static. To ensure this condition, he introduced an unknown universal constant (cosmological term) into the gravitational field. During this period, W. De Sitt, a Dutch astronomer who frequently communicated with Einstein, proposed another model of the universe with zero average mass density. 1922, A.A. Friedman, a Soviet physicist, pointed out that the cosmological term was unnecessary, and thus the expanded cosmological model with non-zero material density was obtained directly from Einstein's original results. Einstein didn't agree at that time, but a year later he publicly retracted his wrong criticism and admitted that Friedman's theory was correct. Due to the discovery of the red shift of the spectral lines of extragalactic galaxies in 1929, the theory of cosmic expansion has been strongly supported. After 1946, it developed into big bang cosmology, which is the most successful cosmology theory so far.
The long and difficult exploration of unified field theory
After the completion of general relativity, Einstein still felt unsatisfied. It is necessary to extend the general theory of relativity to include not only the gravitational field but also the electromagnetic field, that is, to seek a unified field theory. He believes that this is the third stage of the development of relativity, which not only unifies the gravitational field and electromagnetic field, but also unifies relativity and quantum theory, providing a reasonable theoretical basis for quantum physics. He hopes to get a solution without singularity in the unified field theory he tries to establish, which can be used to represent particles, that is, to explain the structure and quantum phenomena of matter with the concept of field. The original unified field theory was popularized by mathematician H. Weil in 19 18. Einstein appreciated this, but pointed out that the linear elements given by this theory are not constant, but related to their past history, which contradicts the fact that all hydrogen atoms have the same spectrum. Then in 19 19, mathematician T.F.E kalucha tried to realize the unified field theory with five-dimensional manifolds, which was highly praised by Einstein. The first paper on unified field theory completed by Einstein in 1922 was about Karucha theory. After 1925, Einstein went all out to explore the unified field theory In the first few years, he was very optimistic and victory was in sight; Later, I found many difficulties and felt that the existing mathematical tools were not enough; Exploration of 1928 to pure mathematics. He tried to use various methods, sometimes in five dimensions and sometimes in four dimensions, but he didn't get any results with real physical significance.
During the 30 years from 1925 to 1955, except for the completeness of quantum mechanics, gravitational waves and general relativity, Einstein devoted almost all his scientific creative energy to the exploration of unified field theory. 1937, with the cooperation of two assistants, he deduced the equation of motion from the gravitational field equation of general relativity, further revealing the unity among time and space, matter and motion, which was a major development of general relativity and the last major achievement Einstein made in scientific creation activities. However, he never succeeded in unifying the field theory. He has met with numerous failures, but he has never been discouraged and always starts from scratch with confidence. Because he was far away from the mainstream of physics research at that time, he tackled the problems that could not be solved at that time by himself, which was in sharp opposition to the Copenhagen School, which was dominant at that time. Because of this, contrary to the situation in the 1920s, he was very isolated in the physics field in his later years. But he remained fearless and unswervingly explored the truth along his own path. Until the day before his death, he was still preparing to continue his mathematical calculation of the unified field theory in his hospital bed. He realized in 1948, "I can't finish this work; It will be forgotten, but it will be rediscovered in the future. " The development of history has not failed him. Because a series of experiments in 1970s and 1980s strongly supported the theory of electric weak unification, the idea of unified field theory showed its vitality in a new form, which provided a hopeful prospect for the future development of physics.