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What is Einstein's main contribution?
1, relativity and Einstein's mass-energy equation

Einstein put forward two basic postulates of special relativity in his paper "On Electrodynamics of Moving Objects": "The speed of light is constant" and "the principle of relativity". According to these two postulates, when the speed of motion is close to the speed of light, some important amendments are made to classical mechanics, thus solving the contradiction between Maxwell's equations and the laws of classical mechanics. After finishing, these pioneering works became Einstein's special theory of relativity.

Recognizing the relativity of time and space and the invariance of light speed, several inevitable inferences are drawn. First of all, a moving object will shrink in length in its direction of motion. Second, moving objects will experience time expansion. In other words, a moving clock goes slower than a stationary clock. Third, the concept of ether is actually redundant and useless.

Einstein expressed the equivalence of mass and energy in his paper, and deduced the mass-energy equation E from the equation of special relativity. =? Mc2. This means that energy and mass are actually the same thing and can be converted to each other. For any object, its mass will increase with its speed.

Einstein's theory of relativity has been controversial for many years. He won the Nobel Prize in Physics 192 1 year not because he praised his great contribution to the theory of relativity. Planck is one of the most enthusiastic physicists who support the theory of relativity.

2. Photons and energy quanta

Einstein put forward the light quantum hypothesis in the article "An enlightening view on the generation and transformation of light", that is, light is composed of discrete energy quanta, which is called light quantum, and is hereinafter referred to as photon. At first, the light quantum hypothesis was strongly questioned by physicists, including Max Planck and niels bohr.

Later, robert millikan's experiment confirmed the equation of photoelectric effect, and arthur compton's Compton scattering experiment showed that light would show particles in some cases. The light quantum hypothesis was not widely accepted until 19 19.

Einstein concluded that the light beam with frequency f consists of light quantum with energy hf; Where h is Planck constant. Einstein did not give many explanations for this conclusion. In fact, he is not sure about the relationship between light quantum and light wave. However, he did suggest that this idea could explain some experimental results, especially the photoelectric effect.

3. Quantized atomic vibration

In 1906, in Planck's radiation theory and specific heat theory, Einstein proposed a new physical model to describe matter, called Einstein model. In this model, each atom in the lattice structure is regarded as an independent quantum harmonic oscillator, and each atom makes a simple harmonic vibration with the same frequency like a spring, so it has discrete energy levels.

Duron-Roland law predicts that the specific heat capacity is constant, and the model gives the same theoretical results at the high temperature limit; When the temperature tends to zero, the specific heat predicted by the model also tends to zero, which is consistent with the experimental results. This is the third important quantum theory discovered in the early 20th century.

Einstein's model predicts that the specific heat capacity tends to zero as an exponential function of temperature, because it assumes that the vibration frequency of all harmonic oscillators is the same. Peter debye modified this assumption. In his Debye model, the vibration frequency is different, so the specific heat capacity tends to zero as a cubic function of temperature.

4. Wave-particle duality

In Einstein's light quantum hypothesis, light quantum only shows the discontinuity of energy and is not endowed with the properties that particles should have, so it cannot be strictly considered as particles. 1909, in two papers published by Einstein, The Present Situation of Radiation and The Development of Our Views on the Nature and Composition of Radiation, Einstein clarified that light quantum has a clearly defined momentum and shows the physical behavior of point particles in some aspects.

These two papers introduced the concept of photon (Gilbert Lewis named the term photon in 1926), which inspired the concept of wave-particle duality in quantum mechanics. He also said that the next stage of theoretical physics will develop a theory that can combine the wave theory of light with the particle theory of light. The "fusion" here refers to the wave-particle duality, or more extension, which is the complementary principle put forward by niels bohr later.

5. Critical opalescence theory

Near the critical point, the light beam irradiated on the medium will be strongly scattered by the medium, which is called critical opalescence. 1908, the Polish physicist Marion Smoluchowski first showed that the mechanism of critical opalescence is the fluctuation of medium density, and he did not give the relevant equation.

Two years later, Einstein strictly discussed the density fluctuation formed by the molecular structure of the medium with statistical mechanics, and derived the related equation, and used this equation to give another method to calculate Avogadro constant. More interestingly, this key opalescence mechanism can explain the phenomenon that the sky is blue.

According to Rayleigh scattering theory, the irradiance of Rayleigh scattered light is inversely proportional to the fourth power of incident light wavelength. Rayleigh scattering is used to explain the blue phenomenon in the sky. Blue light with shorter wavelength is more likely to produce Rayleigh scattering than red light with longer wavelength. Therefore, the sky is blue. Rayleigh scattering equation can accurately describe the Rayleigh scattering behavior of light beam to gas, but it is not suitable for liquid.

Einstein's critical opalescence theory is more generally applicable to liquids and gases; Rayleigh scattering is only a special case of critical opalescence. Later, Bruno Zimm analyzed the randomness of particles in gas and liquid, and extended Rayleigh scattering theory to describe the scattering behavior of light in liquid.

6, zero energy

Zero-point energy refers to the energy possessed by a quantum system when it is in the ground state, and the energy possessed by a quantum system cannot be lower than zero-point energy. Planck put forward the concept of zero point energy when he restated his quantum theory191to 19 13.

Einstein and his assistant Otto Sting were very interested in this idea. They developed a method to prove the existence of zero-point energy. They assume that the rotational energy of diatomic molecules contains zero point energy, and all diatomic molecules rotate at the same angular velocity, and then calculate the specific heat capacity of diatomic molecular gas.

7. General relativity

Einstein's general theory of relativity, founded between 1907- 19 15, is a theory of gravity. According to the general theory of relativity, the gravitational force observed between mass and mass comes from the space-time bending caused by these masses. In modern astrophysics, general relativity is an important tool.

When Einstein accepted the Nobel Prize in Physics at 192 1, he said that the preference of special relativity for inertial motion is not satisfactory, and its theory of not favoring any motion state (whether it is uniform motion or acceleration motion) from the beginning should be more satisfactory, so he will strive to develop general relativity.

In 1907, he pointed out that free fall is actually an inertial motion, and the rules of special relativity should be applied to the observers of free fall. Einstein did not make a detailed analysis of this topic, which was later called the equivalence principle.

In addition, he also preliminarily predicted the gravitational red shift, that is, the light injected into the gravitational potential well will shift blue, while the light emitted by the gravitational potential well will shift red; It also roughly predicts the deflection of light in the gravitational field, that is, the path of photons will deflect in the gravitational field. These predictions were later confirmed by experiments.

Einstein expanded the paper of 1907 and wrote the paper "On the Influence of Gravity on Light Propagation" at191. In this paper, he re-analyzed the deflection of light in gravity field in detail, and obtained a result that can be strictly tested, that is, the deflection angle of light when it passes through the gravitational field generated by the sun. This prediction can be strictly tested in the experiment, so he called on the experimenters to pay attention to it and complete the experiment as soon as possible.

8.gravitational waves

Gravitational waves are ripples of curvature of spacetime, which propagate outward from the wave source in the form of waves and transmit energy outward at the same time. 19 16, Einstein predicted the existence of gravitational waves. According to the general theory of relativity, Lorentz invariance makes the existence of gravitational waves possible, because gravitational interaction must propagate in space at a limited speed. Newton's law of universal gravitation cannot predict this result, because it assumes that gravitational interaction propagates at infinite speed in space.

Physicists Russell hoels and joseph taylor of Princeton University discovered the first pulse binary system PSRB1913+16 in/974. Through the in-depth study of it, indirect quantitative evidence of the existence of gravitational waves was discovered for the first time. 201June 1 1 A century after Einstein's paper was published, the LIGO team announced that it had directly detected gravitational waves, which originated from the fusion mechanism of double black holes.

9. Cosmology

Fully equipped with the super-powerful general theory of relativity, Einstein is ready to show his talents in the dream field of cosmology. 19 17 years, he applied general relativity to model the whole universe structure. Inferred from the experimental observation at that time, he thought that the scope of the universe was limited and there was no boundary, because the mass of the universe would bend space-time back to itself, just like the surface of a sphere, with limited area and no boundary.

This kind of universe is called the static universe. But according to Einstein's field equation, the static universe cannot exist, and the universe can only expand or contract. In order to keep the universe still, Einstein added a cosmological constant term to his equation, and then the cosmological constant term and the cosmological mass term canceled each other, so that the cosmological constant term could resist the action of gravity and realize a static universe.

However, Edwin Hubble determined that the universe expanded in 1929. Einstein had to give up the cosmological constant, which he thought was "the biggest mistake in his life" to introduce the gravitational equation.

Later, people found that the universe was expanding at an accelerated pace. The simplest statement of this phenomenon is that the cosmological constant is not zero, but a very small value. Einstein's intuition may be correct in the end.

10, bose-einstein statistics

Indian physicist satyendra bose completed his paper Planck's Law and the Photoquantum Hypothesis in 1923, and sent it to the British Journal of Philosophy, but it was refused to be published. Bose was not discouraged at all, and the next year he forwarded the paper to Einstein for advice.

In this paper, Bose puts forward a new statistical model. According to this model, the light beam can be regarded as a gas composed of a group of indistinguishable particles, so all photons with the same energy should be combined when doing statistical operations. Einstein noticed that the statistical model of bose was not only applicable to photons, but also to many other particles, which were later called bosons. Einstein translated Bose's paper into German and published it in the German Physical Age.

Einstein extended the Bose theory to particles with mass, and published a paper "Quantum Theory of Monoatomic Ideal Gas" in 1924. The following year, he published a paper, predicting that when the boson is cooled to a very low temperature, it will condense to its lowest energy quantum state, so a new state of matter will appear, called Bose-Einstein condensed state.

1995, Eric Cornell and Carl Weiman of the University of Colorado at Boulder in170 NK (1.7×10? 7? Bose-Einstein condensation was first observed at the low temperature of k). Four months later, wolfgang ketterle of MIT independently realized Bose-Einstein condensation by using sodium atom gas.

1 1, miracle year paper

Einstein published four epoch-making papers in the Yearbook of Physics in 1905. No one has ever made so many great contributions to modern physics in such a short time. This year is therefore called "Einstein miracle year". These four papers are: the enlightening viewpoint on the generation and transformation of light, the motion of suspended particles in still liquid required by the theory of thermomolecular motion, and the electrodynamics of moving objects. Is the inertia of an object related to the energy it contains? 》

Extended data:

When Adolf Hitler became German Chancellor in 1933, Einstein was visiting the United States. Because Einstein was a Jew, even though he was a professor at the Prussian Academy of Sciences, he didn't return to Germany. /kloc-settled in the United States in 0/940 and became an American citizen.

On the eve of World War II, he signed a letter to then-American President franklin roosevelt, in which he mentioned that Germany might develop a new and powerful bomb, so he suggested that the United States should also conduct relevant research as soon as possible, and therefore the United States launched the Manhattan Project. Einstein supported the strengthening of the Allies, but condemned the idea of using the newly discovered nuclear fission for weapons. Later, Einstein and the British philosopher Bertrand Russell signed the Russell-Einstein Declaration, which emphasized the danger of nuclear weapons.

Einstein published more than 300 scientific papers and 150 non-scientific works in his life. Einstein, known as the "father of modern physics", was one of the most important scientists in the world in the 20th century. His outstanding and unique scientific achievements made the word "Einstein" synonymous with "genius".