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Quantum theory is one of the two cornerstones of modern physics. Quantum theory provides us with a new way to express and think about nature. Quantum theory reveals the basic laws of the microscopic material world and lays a theoretical foundation for atomic physics, solid state physics, nuclear physics and particle physics. It can well explain the atomic structure, the regularity of atomic spectrum, the properties of chemical elements, the absorption and radiation of light and so on.

From 65438 to 0928, Dirac applied the theory of relativity to quantum mechanics, and after the development of Heisenberg and Pauli, quantum electrodynamics was formed. Quantum electrodynamics studies the interaction between electromagnetic field and charged particles.

1947, Lamb displacement was discovered by experiment.

1948- 1949, richard phillips feynman, J.S. Schwinge and Asanaga Ichiro developed quantum electrodynamics with the concept of renormalization, thus winning the 1965 Nobel Prize in Physics.

2. Scientists who have contributed to the creation and development of quantum theory.

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wilhelm carl werner otto fritz franz wien

Lord Rayleigh (Lord Rayleigh)

max karl ernst ludwig planck

Paul Adrian Morris Dirac.

Niels bohr (niels bohr)

Prince Louis-Victor de Broglie

Schrodinger (Irving Schrodinger? Dingge)

Werner Karl Heisenberg

Max Born

Richard feynman.

H. Hertz (heinrich rudolf hertz)

Robert Andrews Millikan

[Name] Albert Einstein (Jewish theoretical physicist)

bohr

3. The development of quantum theory.

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The creation of quantum theory is a magnificent epic;

The early days of quantum theory;

1900, Planck introduced the concept of energy quantum in order to overcome the difficulty of classical theory in explaining the law of blackbody radiation, which laid the foundation for quantum theory.

Subsequently, Einstein put forward the light quantum hypothesis in view of the contradiction between the photoelectric effect experiment and the classical theory, and successfully applied the concept of energy quantum to the specific heat of solids, which opened up a new situation for the development of quantum theory.

19 13, Bohr put forward Bohr's atomic theory based on Rutherford nuclear model by using the concept of quantization, and gave a satisfactory explanation of hydrogen spectrum, which made quantum theory a preliminary victory. Later, Bohr, Sommerfeld and other physicists made great efforts to develop quantum theory, but encountered serious difficulties. The old quantum theory is in trouble.

The establishment of quantum theory;

1923, de Broglie put forward the hypothesis of matter wave, which applied wave-particle duality to particle beams such as electrons and developed quantum theory to a new height.

1925-1926 Schrodinger first successfully established the wave equation of electrons along the concept of matter wave, found the basic formula of quantum theory, and thus established wave mechanics.

Almost at the same time as Schrodinger, Heisenberg wrote a paper entitled "Re-interpretation of quantum theory on the relationship between kinematics and mechanics" and founded a matrix method to solve quantum wave theory.

1In September, 925, Born cooperated with another physicist, Jordan, and developed Heisenberg's thought into a systematic theory of matrix mechanics. Soon, Dirac improved the mathematical form of matrix mechanics and made it a theoretical system with complete concept and consistent logic.

1926, Schrodinger found that wave mechanics and matrix mechanics are completely equivalent in mathematics, so they were collectively called quantum mechanics. Schrodinger's wave equation became the basic equation of quantum mechanics because it was easier to understand than Heisenberg's matrix.

4. Debate in the development of quantum mechanics.

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Although quantum mechanics has been established, its physical explanation is always abstract, and everyone's opinions are different. What is the so-called wave in the wave equation?

Born believes that the wave in quantum mechanics is actually a probability, and the wave function represents the probability that an electron appears at a certain time and place. 1927, Heisenberg put forward the uncertainty relation in the micro field. He believes that the position and momentum of any particle cannot be accurately measured at the same time. If one of them is to be measured accurately, the other is uncertain. This is the so-called uncertainty principle Together with Born's explanation of wave function probability, it laid the physical foundation of quantum mechanical explanation. Bohr is keenly aware that the uncertainty principle represents the limitations of classical concepts, so he put forward the "complementary principle" on this basis. Bohr's complementary principle is regarded as the orthodox Copenhagen explanation, but Einstein disagreed with the uncertainty principle and thought that everything in nature should have its definite causal relationship, while quantum mechanics is statistical, so it is incomplete, and the complementary principle is an expedient measure. So Einstein and Bohr argued for thirty or forty years until their death.

Roulette in the microscopic world discovered in the 20th century-quantum theory

If the propagation of light in space is the key to the theory of relativity, then the emission and absorption of light bring about the revolution of quantum theory. We know that objects emit radiation when heated, and scientists want to know why. For the convenience of research, they assumed a perfect radiator, called a "black body", which itself does not emit light and can absorb all the light that shines on it. During the research, scientists found that the energy of the ultraviolet part of the blackbody spectrum calculated according to Maxwell's electromagnetic wave theory is infinite, which is obviously wrong. This is an "ultraviolet disaster" that provides a foundation. 1900, the German physicist Planck proposed a new model of vibrating atoms in matter. He borrowed the concept of discontinuity from the molecular structure theory of matter and put forward the quantum theory of radiation. Regarding the discontinuity in quantum theory, we can understand it as follows: if the temperature rises or falls, we think it is continuous, and it must go through 0. 1. 1 degree before it can rise from one degree to two degrees. However, quantum theory holds that there cannot be 2 degrees between two values, such as 1 degree and 3 degrees. Just like we spend money on things, a penny is the minimum amount. You can't take out 0. 1 cent, although you can calculate money in centimeters. This penny is the minimum number of coins. This minimum quantity is quantum. He believes that electromagnetic waves of various frequencies, including light, can only be emitted from the vibrator with the energy of its own determined composition. This kind of energy particle is called quantum, and the quantum of light is called light quantum, or photon for short. The blackbody spectrum calculated by this model is consistent with the actual observation. This has turned a new page in physics. Quantum theory not only naturally explains the law of radiation energy distribution according to wavelength, but also puts forward the whole problem of interaction between light and matter in a brand-new way. Quantum theory not only provides a new concept to optics, but also to the whole physics, so its birth is usually regarded as the starting point of modern physics.

Quantum theory: the pioneer of the nuclear world

The quantum hypothesis is in direct contradiction with the belief that nature has not jumped for hundreds of years, so many physicists will not accept it after the emergence of quantum theory. Planck himself was very shaken, regretted his bold move, even gave up quantum theory and continued to use the continuous change of energy to solve the radiation problem. However, history has pushed quantum theory to the vanguard position in the new era of physics, and the development of quantum theory is imminent.

Einstein was the first to realize the universal significance of quantum concept and apply it to other problems. He established the light quantum theory to explain the new phenomena in the photoelectric effect. The quantum theory of light has brought the historical debate about the nature of light into a new stage. Since Newton, the particle theory and wave theory of light have come and gone. Einstein's theory reiterated the importance of particle theory and wave theory in describing the behavior of light. Both of them reflect one aspect of the essence of light: sometimes light appears as fluctuation and sometimes as particle, but it is neither classical particle nor classical wave, which is the wave-particle duality of light. Mainly due to Einstein's work, quantum theory was further developed in the first decade after it was put forward.

19 1 1 year, Rutherford proposed a planetary model of atoms, that is, electrons move around a tiny but massive nucleus at the center of the atom, that is, the nucleus. In the next 20 years, a lot of research in physics focused on the peripheral electronic structure of atoms. This work created a new theory of micro-world-quantum physics, which laid the foundation for the application of quantum theory to macro-objects. But the tiny nucleus at the center of the proton remains a mystery.

The nucleus is an important level in the microscopic world. Quantum mechanics is a theory to study the movement law of microscopic particles, one of the theoretical foundations of modern physics, and an indispensable tool to explore the mystery of nuclear. Shortly after the atomic quantum theory was put forward, physicists began to explore the tiny mass nucleus in atoms-nucleus. In atoms, positively charged nuclei attract negative electrons under static conditions. But what holds the nuclei together? The nucleus contains positively charged protons and uncharged neutrons, and there is a huge repulsive force between them, and protons repel each other (uncharged neutrons do not have this repulsive force). It is a new powerful force that unites the nuclei and overcomes the repulsive force between protons, which only works inside the nuclei. The great energy of the atomic bomb comes from this powerful nuclear force. The study of nuclear properties and nuclear forces had a great influence on the 20th century. Radioactivity, isotopes, nuclear reactions, fission, fusion, atomic energy, nuclear weapons and nuclear drugs are all by-products of nuclear physics.

Danish physicist Bohr first applied the quantum hypothesis to atoms and explained the discontinuity of atomic spectrum. He believes that electrons only move around the nucleus in a certain circular orbit. When running in these orbits, it does not emit energy, but only emits radiation when it transitions from a higher energy orbit to a lower orbit, otherwise it absorbs radiation. This theory not only solves the problem of atomic stability on the basis of Rutherford model, but also completely accords with the experimental results obtained by spectral analysis when applied to hydrogen atoms, thus causing a shock in physics. Bohr instructed physicists from 19 to 1920 to understand the basic structure of quantum theory, which sounds contradictory. In fact, he is both a midwife and a nurse of this theory.

Bohr's quantized atomic structure obviously violates the classical theory, and also attracts many scientists' dissatisfaction. However, its unexpected success in explaining the empirical law of spectral distribution has earned it a high reputation. But Bohr's theory can only be used to solve the simple case of hydrogen atom, which can't be explained for multi-electron atom spectrum. The old quantum theory faced a crisis, but it was soon broken through. The first breakthrough in this respect was made by French physicist De Broglie. He majored in history at university, but his brother is a famous physicist who studies X-rays. Influenced by him, after graduating from De Broglie University, he changed to physics and studied the fluctuation and particle properties of X-rays with his brother. After a long time of thinking, de Broglie suddenly realized that Einstein's theory of light quantum should be extended to all matter particles, especially photons. From September 1923 to September 10, he published three papers in succession, put forward the theory that electrons are also a kind of wave, and introduced the concept of "standing wave" to describe the radiation-free static state of electrons in atoms. Standing waves are contrary to traveling waves moving on lakes or lines, and the vibration on guitar strings is standing waves. In this way, the position of electrons can be described in the form of wave function. But what it gives is not the familiar certainty, but the statistical "distribution probability", which well reflects the distribution and operation of electrons in space. De Broglie also predicted that the electron beam will also diffract when it passes through the small hole. 1924, he wrote his doctoral thesis "research on quantum theory", which systematically expounded the theory of matter wave, and Einstein appreciated it very much. Within a few years, experimental physicists really observed the diffraction phenomenon of electrons, which confirmed the existence of de Broglie matter wave.

It was the Austrian physicist Schrodinger who continued to advance along the concept of matter wave and founded wave mechanics. He learned about De Broglie's concept of matter wave from a paper by Einstein, and immediately accepted this view. He suggested that particles are just bubbles on fluctuating radiation. 1925, he deduced a wave equation of relativity, but it was not completely consistent with the experimental results. 1926, he changed to non-relativistic electronic problems, and the wave equation obtained was confirmed in the experiment.

1925, a young german physicist Heisenberg wrote a paper entitled "reinterpretation of quantum theory on the relationship between kinematics and mechanics" and established a matrix method for solving quantum wave theory. Classical but unmeasurable concepts such as electron orbit and operation period in Bohr's theory are replaced by radiation frequency and intensity. With the joint efforts of Heisenberg and Dirac, a young British scientist, matrix mechanics has gradually become a theoretical system with complete concepts and consistent logic.

Supporters of wave mechanics and matrix mechanics have been arguing endlessly, accusing each other of defects in their theories. It was not until 1926 that Schrodinger discovered that the two theories were mathematically equivalent that the hostility between the two sides was eliminated. From then on, these two theories are collectively called quantum mechanics, and Schrodinger's wave equation becomes the basic equation of quantum mechanics because it is easier to master.

Quantum theory full of uncertainty

Heisenberg's uncertainty principle is one of the most important principles in quantum theory. It is pointed out that it is impossible to accurately measure the momentum and position of particles at the same time, because the instrument will interfere with the measurement process, and measuring its momentum will change its position, and vice versa. Quantum theory has crossed the dead end of Newtonian mechanics. When explaining the macroscopic behavior of things, only quantum theory can handle the details of atomic and molecular phenomena. However, this new theory produces more paradoxes than the wave-particle duality of light. Newtonian mechanics answers questions with certainty and decisiveness, and quantum theory answers questions with possibility and statistical data. Traditional physics tells us the exact location of Mars, while quantum theory lets us bet on the position of electrons in atoms. Heisenberg's uncertainty absolutely limits human's understanding of the micro-world, telling us that it can't be measured without completely affecting the results. Schrodinger, one of the founders of quantum mechanics, recognized the uncertainty in quantum mechanics in 1935, and assumed a famous cat thinking experiment: "A cat is kept in a steel box with the following extremely cruel device (it must be ensured that this device is not directly interfered by the cat): there is a small piece of radioactive material in the Geiger counter, which is very small and may be in 65438. Perhaps no atom decays with the same probability. In the case of decay, the counter tube discharges and releases a hammer through the relay, crushing a small cyanide bottle. If people leave the whole system free 1 hour, then people will say that if there is no atomic decay during this period, the cat is alive. The first atomic decay will definitely poison the cat. "

Common sense tells us that cats are either dead or alive. But according to the rules of quantum mechanics, the whole system in the box is the superposition of two States, one is a live cat and the other is a dead cat. But in real life, who has ever seen a cat alive and dead? Cats should know whether they are alive or dead, but quantum theory tells us that this unfortunate animal is in a state of uncertainty until someone peeks into the box to see what is going on. At this point, it either becomes alive or dies immediately. If the cat is replaced by a human, the mystery will become more acute, because in this way, friends who are imprisoned in boxes will realize whether they are healthy from beginning to end. If the experimenter opens the box and finds that he is still alive, he can ask his friend how he felt before this observation. Obviously, this friend will answer that he is absolutely alive at any time. But this is contrary to quantum mechanics, because quantum theory holds that friends are still in a state of superposition of life and death before the things in the box are observed.

Bohr is keenly aware that it represents the limitations of classical concepts, so he puts forward the "complementary principle" on this basis, arguing that there are always two mutually exclusive classical characteristics in the quantum field, and it is their complementarity that constitutes the basic characteristics of quantum mechanics. Bohr's complementary principle is called the orthodox Copenhagen explanation, but Einstein has always disagreed. He always thinks that statistical quantum mechanics is incomplete and the principle of complementarity is a kind of appeasement philosophy, so he has repeatedly put forward hypotheses and experiments to accuse quantum theory, but Bohr always gives self-consistent answers to defend quantum theory. The struggle between Einstein and Bohr lasted for half a century until their death.

Einstein's Query on Quantum Theory

Schrodinger's cat experiment tells us that the paradox of reality in the atomic field has nothing to do with daily life and experience, and the quantum ghost is confined to the shadow micro-world of atoms in some way. If we follow the logic of quantum theory until its final conclusion, most of the physical universe seems to disappear into a vague fantasy. Einstein will never accept this logical conclusion. He asked: Is the moon real when no one is looking? Science is an impersonal objective cause, and the idea that observers are the key elements of physical reality seems to contradict the whole scientific spirit. If there were no "external" concrete world for us to experiment and measure, wouldn't all science be a game of chasing imagination?

The revolutionary characteristics of quantum theory caused a heated debate about its correctness and explanation content from the beginning, which lasted until the 20th century. Will the laws of nature be fundamentally random? Are there any entities in our observation? Are we affected by the observed phenomenon? Einstein took the lead in questioning quantum theory from several aspects. He denied that the laws of nature were random. He doesn't believe that "God is playing dice with the world". In a series of famous debates with Bohr, Einstein once again criticized and tried to consolidate the potential loopholes, mistakes and shortcomings of quantum theory. Bohr cleverly foiled all Einstein's attacks. In a paper in 1935, Einstein presented a new evidence: he asserted that quantum theory could not completely describe nature. According to Einstein, some physical phenomena that cannot be predicted by quantum theory should be observed. This challenge eventually led Aspat to do a series of famous experiments, which he intends to use to solve this dispute. Aspat's experiment proved the correctness of quantum theory in detail. Aspat believes that quantum theory can predict but cannot explain some wonderful phenomena, and Einstein asserts that this is impossible. Information seems to travel faster than the speed of light-this obviously violates relativity and causality. Aspat's experimental conclusions are still controversial, but they have led to more strange theories about quantum theory.

Bohr's and Heisenberg's development theories and Copenhagen School's viewpoints are still controversial, but they are gradually recognized by most physicists. This school believes that the laws of nature are neither objective nor certain. Observers cannot describe reality that is independent of them. As the uncertainty law and uncertainty law tell us, the observer can only be influenced by the observation results. Experimental predictions based on the laws of nature are always statistical rather than definitive. There is no law to be found, just the distribution of possibilities.

The obvious contradiction between the fluctuation of electrons and the particle nature in two different experiments is an example of the complementary principle. Quantum theory can correctly and continuously predict the fluctuation of electrons or the properties of particles, but not both at the same time. According to Bohr's point of view, this contradiction is produced in the process of our brain constantly exploring the nature of electrons, and it is not a part of quantum theory. Moreover, only limited and statistical information provided by quantum theory can be obtained from nature. Quantum theory is complete: what it fails to tell us may be interesting guesses or metaphors. But these things are neither observable nor measurable, so they have nothing to do with science. The Copenhagen interpretation failed to meet Einstein's requirements about what the completely objective and decisive laws of physics should be. A few years later, he challenged Bohr through a series of thinking and reasoning experiments. These experimental plans are used to prove that the predictions of quantum theory are inconsistent and wrong. Einstein challenged Bohr with contradictions in dilemma theory or quantum theory. Bohr thought about this problem for several days, and then he could propose a solution. Einstein paid too much attention to something or ignored some effects. Ironically, Einstein once forgot to consider his own general theory of relativity. Finally, Einstein acknowledged the subjective consistency of quantum theory, but he still stubbornly insisted on a fatal criticism: EPR thinking experiment.

1935, Einstein and two colleagues, Podolski and Rosen, wrote a paper refuting the completeness of quantum theory, which was widely circulated among physicists and scientific thinkers. This kind of paper is called EPR paper and has the initials of three surnames. They assume that there are two electrons: electron 1 and electron 2 collide. Because they have the same charge, this collision is elastic and conforms to the law of conservation of energy. After the collision, the momentum and motion direction of two electrons are related. Therefore, if the position of electron 1 is measured, the position of electron 2 can be inferred. Suppose that the position of the electron 1 is accurately measured after the collision, and then its momentum is measured. Because only one quantity is measured at a time, the measurement result should be accurate. Because of the correlation between electron 1 and 2, although we did not measure electron 2, that is, we did not interfere with it, we can still accurately infer the position and momentum of electron 2. In other words, we know the position and momentum of electrons through a measurement, which is impossible according to quantum theory and not foreseen by quantum theory. Einstein and his colleagues proved that quantum theory is incomplete.

After a period of thinking, Bohr retorted that EPR experiment not only failed to prove quantum theory, but also proved the complementary principle of quantum theory. He pointed out that the measuring instrument, electron 1 and electron 2 *** constitute a system and an inseparable whole. In the process of measuring the position of electron 1, the momentum of electron 2 will be affected. Therefore, the measurement of electron 1 cannot explain the position and momentum of electron 2, and one measurement cannot replace two measurements. These two results are complementary and incompatible. We can neither say that one part of the system is influenced by another, nor try to relate two different experimental results. EPR experiment assumes the existence of objectivity and causality, and draws the conclusion that quantum theory is incomplete. In fact, this objectivity and causality is only a speculation.

Quantum theory in the real world

Although people are not clear about the significance of quantum theory, its achievements in practice are surprising. Especially in the scientific research of condensed matter-solid and liquid. It is necessary to explain how atoms combine to synthesize molecules with quantum theory, so as to understand these states of matter. Bonding is not only the main reason for the formation of general compounds such as graphite and nitrogen, but also the main reason for the formation of symmetrical crystal structures of many metals and gems. Studying these crystals with quantum theory can explain many phenomena, such as why silver is a good conductor of electricity and heat but not light, and why diamonds are not a good conductor of electricity and heat but light? More importantly, in practice, quantum theory well explains the principle that semiconductors are between conductors and insulators, laying the foundation for the emergence of transistors. 1948, American scientists john bardeen, William Shockley and walter brattain invented the transistor according to the quantum theory. It can work effectively under very small current and power, and its volume can be made very small, thus quickly replacing bulky and expensive vacuum tubes and creating a brand-new information age. These three scientists won the Nobel Prize in Physics from 65438 to 0956. In addition, quantum theory is also applied to the invention of laser and the explanation of superconductivity.

Moreover, the application prospect of quantum theory in the industrial field is also very bright. Scientists believe that the theory of quantum mechanics will have a great impact on the electronic industry, and it is an undeveloped new field of physics with broad prospects. At present, the miniaturization of semiconductors is close to the limit. If it is smaller, the theory of microelectronics technology is powerless and must rely on the theory of quantum structure. Scientists predict that by 20 10, people can make the width of etched lines on semiconductors as small as one tenth of a micron (one micron equals one thousandth of a millimeter). When an electric signal passes through such a narrow circuit, it will only be a few electrons. It is very different to increase or decrease one electron.

According to the theory of quantum mechanics, Max Lagall, a material scientist at the University of Wisconsin in the United States, has made some tiny structures called "quantum dots" which can hold a single electron. This kind of quantum dot is so tiny that a needle tip can hold billions. Researchers use quantum dots to make transistors, which can be controlled by the movement of a single electron. They also made this arrangement possible by cleverly arranging quantum dots and became the heart of a tiny and powerful computer. In addition, Texas Instruments, IBM, Hewlett-Packard and Motorola are all interested in this tiny structure composed of molecules, support the research in this field, and believe that the progress made in this field "will definitely get great returns".

The main goal of scientists studying quantum structure is to control the movement of very small electron groups, that is, to make them not conflict with quantum effects through "quantum constraints". Quantum dots may achieve this goal. Quantum dots are composed of a cluster of substances with a diameter of less than 20 nanometers, which is about the length of a string of 60 silicon atoms. Using this quantum confinement method, it is possible to manufacture small and efficient lasers used in many optical disc players. This kind of quantum well laser is made of two layers of other materials and an ultra-thin semiconductor material. The middle electron is enclosed in a quantum plane, and the electron can only move in two dimensions. In this way, it becomes easier to inject energy into electrons. As a result, electrons can generate more lasers with less energy.

Researchers at AT&T Bell Labs are studying quantum more deeply. They try to reduce the quantum plane by one dimension and make lasers based on quantum wires, which can greatly reduce the number of repeaters needed on communication lines.

James tours's chemistry laboratory at the University of South Carolina has produced quantum structures from a single organic molecule. Using their method, people can compress billions of molecular devices in an area of one square millimeter. The number of transistors that can be accommodated in a square millimeter may be 65,438+0,000 times that of current personal computers. Konstantin Garev, a physicist at new york State University, made a memory chip model with quantum storage points. Theoretically, his design can store 1 terabit data on a chip about the size of the chip used today, and the capacity is1.5000 times that of the current chip. Many research groups have made the single-electron transistors necessary for Likharev model devices, and some have also made single-electron transistors that work at room temperature. Scientists believe that there are still many problems to be solved in the application of quantum mechanics theory in electronics industry. Therefore, most scientists are trying to study new methods instead of designing quantum devices like computers now.

Can quantum theory and relativity be unified?

Quantum theory provides the ability to solve countless things such as atoms, lasers, X-rays, superconductivity and so on accurately and consistently, and almost completely discredits the ancient classical physical theory. But we still use Newtonian mechanics in our daily ground movements and even space movements. There is always a conflict between this old familiar viewpoint and this new revolutionary viewpoint.

The laws of the macro world are still stubbornly verifiable, while the laws of the micro world are random. Our dynamic description of projectiles and comets has obvious visual characteristics, but the description of atoms does not. The world like tables, stools and houses seems to be under our observation all the time, but the actual or physical state of electrons and atoms has not alleviated this contradiction. If these explanations have any effect, it is that they widen the gap between the two worlds.

For most physicists, it doesn't matter whether this contradiction is solved or not. They only care about their own work and ignore philosophical arguments and conflicts. After all, physics work is to accurately predict natural phenomena, so let us control these phenomena, and philosophy is irrelevant.

General relativity has achieved brilliant success in large-scale space, and quantum theory has also achieved brilliant success in the microscopic world. Elementary particles follow the laws of quantum theory, while cosmology follows the laws of general relativity. It is hard to imagine that there will be a big difference between them. Many scientists hope to combine the two to create a new theory and unify all physical laws from macro to micro. But so far, all efforts to seek unity have failed, because these two major disciplines of physics in the 20th century are completely contradictory. Can we find a new theory, which is better than the existing two theories, and make both of them obsolete, just as we encountered before various theories became popular?