1, relativity

The establishment of special relativity;

As early as 16 years old, Einstein learned from books that light is a fast electromagnetic wave. Related to this, he would like to discuss the so-called etheric 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 in the 0/7th century and christiaan huygens later initiated and developed the theory of ether, believing that ether is the medium of light wave propagation, which is full of all spaces including vacuum and can penetrate into matter.

Different from the ether theory, 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, and wave theory prevailed in19th century. The theory of ether has also been greatly developed: wave propagation needs medium, and the medium through which light propagates in vacuum is ether, also called optical ether.

At the same time, electromagnetism has developed vigorously. With the efforts of Maxwell, Hertz and others, a mature electromagnetic phenomena dynamics theory-electrodynamics was formed, and it was proved theoretically and practically that light is electromagnetic wave 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. On the contrary, Michelson-Morey experiment found that ether was unlikely to exist.

The development of electromagnetism was originally contained in the framework of Newtonian mechanics, but when explaining the electromagnetic process of moving objects, it was found that it was inconsistent with the relativity principle followed by Newtonian mechanics. According to Maxwell's theory, the speed of electromagnetic wave in vacuum, that is, the speed of light, is a constant; However, according to the principle of velocity addition in Newtonian mechanics, the speed of light in different inertial systems is different.

For example, 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 Galileo's theory, the car coming to you will emit light with a speed greater than C (vacuum light speed of 3.0x10 8m/s/s), that is, the light speed in front of the car = light speed+speed; The speed of light leaving the car is less than c, that is, the speed of light behind the car = speed of light-speed.

However, according to Maxwell's theory, the speed of the car does not affect the propagation of light. To put it bluntly, regardless of cars, the speed of light is equal to C. Maxwell and Galileo's views on speed are obviously opposite!

Einstein seems to be the man who is going to build a brand-new physics building. Einstein carefully studied Maxwell's electromagnetic theory, 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.

Einstein likes reading philosophical works and absorbing ideological nutrition from philosophy. He believes in the unity of the world and the consistency of logic. During the period of "Olympia Academy of Sciences", david hume's doubts about the universal validity of causality had an impact on Einstein.

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 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 relativity principle.

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 how to measure 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 = MC 2, which played a guiding role in the later development of atomic energy. ?

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 thought.

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 inertial system 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.

At that time, most physicists on earth, including Lorenz, the founder of relativistic transformation relation, found it difficult to accept these new concepts introduced by Einstein.

Some people even said that "at that time, only two and a half people in the world understood the theory of relativity". The obstacle of the old way of thinking makes this new physical theory not familiar to physicists until a generation later. Even in 1922, when the Swedish Academy of Royal Sciences awarded Einstein the Nobel Prize in Physics, it just said, "Because of his contribution to theoretical physics, but also because he discovered the law of photoelectric effect."

Einstein's Nobel Prize in Physics was awarded, but Einstein's theory of relativity was not mentioned. (Note: Relativity didn't win the Nobel Prize. One of the important reasons is the lack of a large number of facts. )

2, photoelectric effect

1905, Einstein put forward the photon hypothesis and successfully explained the photoelectric effect, so he won the 192 1 year Nobel Prize in Physics.

When light irradiates a metal, the electrical properties of this substance will change. This photochromic phenomenon is collectively called photoelectric effect.

The photoelectric effect can be divided into photoelectron emission, photoconductive effect and photovoltaic effect. The former phenomenon occurs on the surface of an object, which is also called external photoelectric effect. The latter two phenomena occur inside the object, which is called internal photoelectric effect.

Hertz discovered the photoelectric effect in 1887, and Einstein was the first to successfully explain the photoelectric effect (the effect that a metal surface emits electrons under the action of light irradiation, and the emitted electrons are called photoelectrons). Only when the wavelength of light is less than a certain critical value can electrons be emitted, that is, the limit wavelength, and the corresponding frequency of light is called the limit frequency.

The critical value depends on the metal material, and the energy of emitted electrons depends on the wavelength of light, which has nothing to do with the intensity of light and cannot be explained by the fluctuation of light. And the fluctuation of light is also contradictory, that is, the instantaneity of photoelectric effect. According to the fluctuation theory, if the incident light is weak and the irradiation time is long, the electrons in the metal can accumulate enough energy and fly out of the metal surface.

But the fact is that as long as the frequency of light is higher than the limit frequency of metal, no matter the brightness of light, the generation of photons is almost instantaneous, no more than ten MINUS nine seconds. The correct explanation is that light must be composed of strictly defined energy units (i.e. photons or optical quanta) related to wavelength.

In the photoelectric effect, the emission direction of electrons is not completely directional, but most of them are emitted perpendicular to the metal surface, regardless of the irradiation direction. Light is electromagnetic wave, but light is an orthogonal electromagnetic field with high frequency oscillation, and its amplitude is very small, which will not affect the emission direction of electrons. ? [ 1]?

3. Law of Conservation of Energy

E=mc？ , the law of material immortality, said the immortality of the material quality; The law of conservation of energy is about the conservation of energy of matter.

Although these two laws have been discovered one after another, people think that they are two unrelated laws, each of which explains different natural laws. Some people even think that the law of immortality of matter is a chemical law, and the law of conservation of energy is a physical law, belonging to different scientific categories.

Einstein thought that the mass of matter is a measure of inertia and energy is a measure of motion. Energy and mass are not isolated from each other, but are interrelated and inseparable. The change of the mass of the object will change the energy accordingly; And the change of the energy of the object will change the mass accordingly.

Einstein put forward the famous formula of mass and energy in the special theory of relativity: e = MC 2 (where e stands for energy, m stands for mass, and c stands for the speed of light, and the approximate value is 3×10.8m/s, indicating that reducing mass can create energy).

Einstein's formula of mass-energy relationship correctly explains various nuclear reactions: Take Helium 4(He4) as an example, its nucleus consists of two protons and two neutrons. In principle, the mass of helium 4 nucleus is equal to the sum of the masses of two protons and two neutrons.

In fact, this arithmetic doesn't hold water. The mass of helium nucleus is 0.0302u (atomic mass unit) less than the sum of the mass of two protons and two neutrons! Why is this? Because when two deuterium [dāo] nuclei (each deuterium contains 1 proton and 1 neutron) are polymerized into 1 helium 4 nuclei, a large amount of atomic energy is released.

When 1g helium 4 atom is generated, about 2.7× 10 12 joules of atomic energy is released. Because of this, the mass of helium 4 nucleus decreases.

This example vividly shows that when two deuterons are polymerized into 1 helium 4 nucleus, it seems that the mass is not conserved, that is, the mass of helium 4 nucleus is not equal to the sum of the two deuterons. However, according to the formula of mass-energy relationship, the mass lost by helium-4 nucleus is exactly equal to the mass reduced by releasing atomic energy during the reaction.

Einstein expounded the essence of the law of immortality of matter and the law of conservation of energy from a newer height, and pointed out the close relationship between the two laws, which made human beings further understand nature. ?

4. Cosmic constant

Einstein used the cosmological constant when he put forward the theory of relativity (in order to explain the existence of a static universe with non-zero density of matter, he introduced a term in the gravitational field equation that is proportional to the metric tensor, which was represented by the symbol λ. This proportional constant is very small and can be ignored at the galactic scale. λ is only meaningful at the cosmic scale, so it is called the cosmological constant.

The so-called fixed value of antigravity) into his equation. He believes that there is an anti-gravity that can balance gravity and make the universe finite and static. When Hubble showed Einstein the astronomical observation results of the expanding universe, Einstein said, "This is the biggest mistake I made in my life."

The universe is expanding. Hubble and others believe that anti-gravity does not exist, and the expansion speed is getting slower and slower due to the gravity between galaxies. There is a twisting force between galaxies, which makes the universe expand continuously. This is dark energy. 7 billion years ago, they "conquered" dark matter and became the masters of the universe.

The latest research shows that dark matter and dark energy account for about 96% of the universe in mass composition (only real mass, no virtual matter). It seems that the universe will continue to accelerate its expansion until it collapses and dies. There are other arguments, which are controversial.

Although the cosmological constant exists, the value of anti-gravity far exceeds gravity. Linde said humorously: "I finally understand why he (Einstein) likes this theory so much and is still studying the cosmological constant after many years." Cosmic constant is still one of the biggest problems in physics today. "

Extended data:

Albert. Einstein (1March 87914-1April 955 18) was born in Ulm, Wü rttemberg, Germany, and graduated from Federal Institute of Technology in Zurich as a Jewish physicist.

Einstein was born in a Jewish family in Ulm, Germany on 1879. 1900 graduated from the Federal Institute of Technology in Zurich and became a Swiss citizen.

1905 received a doctorate from the University of Zurich. Einstein put forward the photon hypothesis and successfully explained the photoelectric effect. So he won the Nobel Prize in physics at 192 1 and founded the special theory of relativity at 1905. General relativity was founded in 19 15. 1April 1955 18 died at the age of 76.

Einstein laid a theoretical foundation for the development of nuclear energy and initiated a new era of modern science and technology, and was recognized as the greatest physicist after Galileo and Newton. 199965438+On February 26th, Einstein was selected as "the great man of the century" by American Time magazine.

In memory of the people:

Albert Einstein Prize is an award for theoretical physics. It was first awarded by Princeton Institute of Advanced Studies on 195 1 with a prize of 15000 USD. Later, the bonus was reduced to 5000 dollars. Einstein was a judge of this award.

1955 In August, four months after Einstein's death, the 99th element was named "Einstein" to commemorate Einstein's contribution.

From 1965 to 1978, the US Postal Service issued a set of "American celebrities" stamps, including Einstein, with a face value of 8 cents.

1The asteroid 200 1 discovered on March 5, 973 was named Einstein.

Albert einstein institution in Bonn established and awarded the Albert Einstein Medal. It was first awarded in 1979 to reward people who made outstanding contributions to Einstein's related affairs.

Einstein satellite is an X-ray observation satellite, which is jointly manufactured by Harvard Smithsonian Center for Astrophysics and NASA. It was launched in June1978165438+10/3. Its original name was HEAO-2, and it was named after Einstein to commemorate the 0/00th anniversary of his birth.

The Albert Einstein World Science Prize was established by the World Cultural Council and was first awarded in 1984. Its purpose is to stimulate scientific research and technological research and development, and the prize is $65,438+$00,000.

Anecdotes of characters:

1, discerning.

At the age of sixteen, Einstein applied for the engineering department of the Federal Institute of Technology in Zurich, Switzerland, but failed in the entrance examination. Mr. Weber, a physicist, read his papers on mathematics and physics. He was very discerning and praised him: "You are a very clever boy, Einstein, a very clever boy, but you have a big shortcoming: you don't want to show yourself."

Einstein can be said to be a "genius" in mathematics. He taught himself analytic geometry and calculus at the age of 12 to 16. He is also "unrepentant" for not wanting to show his "shortcomings".

In his letter to friends in his later years, he said: "When I was young, my needs and expectations for life were that I could do research quietly in a corner, and the public would not pay full attention to me, but now I can't."

2. Citizens of the world

When Einstein was young, one day, the German emperor's army passed through the streets of Munich. Curious people flocked to the window to cheer, while children yearned for the soldiers' shining helmets and neat steps. But Einstein hid in fear. He despised and feared these "monsters in war" and asked his mother to take him to a country where he would never be such a monster.

Einstein gave up his German citizenship in middle school, but he didn't apply for Italian citizenship. He wants to be a world citizen who doesn't want any attachment. After World War II, Einstein tried to establish his dream of world peace on the basis of reality, and delivered a series of "peace" speeches in "enemy countries".

Albert Einstein's name also appeared on the blacklist of German right-wing assassins, and Hitler offered a reward of 20,000 marks for his head. In order to keep himself in harmony with the world, Einstein had to move from Italy to Holland. He emigrated from Holland to America and became an American citizen. He believes that in the United States, people from all walks of life can survive in a barely passable friendship. ?

3, indifferent to fame and fortune

1948 14 in may, the state of Israel was born, but soon war broke out between Israel and neighboring Arab countries. Einstein, who has lived in the United States for more than ten years, immediately declared to the media: "Now, the Israelis can't retreat any more. We should fight. Jews can only survive in a world hostile to them if they rely on themselves. "

1952165438+1On October 9th, Weizmann, an old friend of Einstein and the first president of Israel, passed away. The day before, the Israeli ambassador to the United States handed Einstein a letter from Israeli Prime Minister David Ben-Gurion, formally asking Einstein to become the Israeli presidential candidate.

That night, a reporter called Einstein's residence and asked if Einstein would become the president of Israel. "No, I can't." Einstein rejected the proposal. I just put the phone down when it rang again.

This time it's the Israeli ambassador to Washington. The ambassador said, "Professor, I was instructed by Israeli Prime Minister Ben Gurion. Are you willing to accept your nomination as a presidential candidate? " Einstein was moved by the goodwill of his compatriots, but he was more concerned with how to politely refuse the ambassador and the Israeli government without disappointing or embarrassing them.

Soon, Einstein issued a statement in the newspaper, formally refusing to be the president of Israel. In Einstein's view, "being president is not an easy task." At the same time, he quoted himself again: "Equation is more important to me, because politics is present, but equation is eternal."

4. The secret of success

Einstein often told people that learning time is a constant, but its efficiency is a variable. It is unwise to simply pursue study time. The most important thing is to improve learning efficiency. He believes that only through cultural and sports activities can we gain abundant energy and keep a clear head. Einstein also summed up a formula according to his own personal experience, that is, A = X+Y+Z Y+Z.

A stands for success, X stands for the right method, Y stands for hard work, and Z stands for less nonsense. He summed up the content of this formula in two sentences: the combination of work and rest is the ladder of success, and cherishing time is an important condition for making achievements.

References:

Baidu Encyclopedia-Albert Einstein