What Is Quantum Theory?

At the end of the 19th century and the beginning of the 20th century, physics was in a period of alternation between old and new. The development of production and the improvement of technology led to a series of major discoveries in physics experiments, which made the classic physics theory building at that time stronger and more prosperous. What was inconsistent was only the small "two dark clouds" on the physics sky. But it was these two dark clouds that kicked off the physics revolution: one dark cloud descended from quantum theory, and then another dark cloud descended from relativity. The birth of quantum theory and relativity theory has completely changed the face of physics.

Overview

Quantum theory is one of the two cornerstones of modern physics. Quantum theory gives us a new expression of nature

At the beginning of the 20th century, new experimental facts continued to discover that classical physics had difficulty in explaining some phenomena. The most obvious and prominent ones were the following three problems:

1. Blackbody radiation problem

2. Photoelectric effect

3. Atomic stability and atomic spectrum.

The quantum concept was put forward as a hypothesis in the theoretical explanation of these three issues.

Study of Blackbody Radiation

Thermal radiation is a new discipline developed in the 19th century. Its research is supported by thermodynamics and spectroscopy, and it also uses emerging technologies in electromagnetics and optics, so it has developed rapidly. By the end of the 19th century, a gap had been opened in this field, that is, the study of black body radiation led to the birth of quantum theory. In order to come up with the black body radiation law consistent with the experiment, many physicists have made various attempts.

In 1893, the German physicist Winhelm Wein (1864-1928) proposed a law of black body radiation energy distribution, which is the Wien formula. This formula is more consistent with the results observed in the experiment in the short-wave part, but it is obviously inconsistent with the experiment in the long-wave part.

In the 1920s, the study of physics theory focused on the following three aspects:

First, from the study of classical electrodynamics to the study of relativity. In 1905, Einstein proposed the special theory of relativity, and in 1915 he introduced the general theory of relativity. From then on, relativity was not only the object of theoretical physicists' study, but also attracted worldwide attention.

2. The statistical physics established by Maxwell, Boltzmann, Gibbs and others at the end of the 19th century is one of the widely studied contents in theoretical physics. By the 1920s, Bose Einstein statistics and fees The emergence of Midirak statistics.

3. Research on atomic structure. In 1897, Thomson discovered electrons and began to study the structure of atoms; in 1911, Rutherford proposed a nucleated model of atoms; in 1913, Bohr proposed the quantum theory of atomic structures. Since then, research in this area has become more and more active. Quantum mechanics begins with the study of some unexplainable problems in atomic physics. Therefore, it can be said that quantum mechanics starts from the discussion of atomic structure. Its development has two routes. One is the matter wave proposed by De Broglie. Later, Schrodinger introduced the concept of wave function and proposed the Schrodinger equation to establish wave dynamics. The other route was Heisenberg's matrix mechanics. Born et al. Proposed the notation of mechanical quantity operators. The same problem was solved from two different paths, that is, the laws of motion of microscopic particles in terms of mechanics. The unified work of the two was mainly completed by Dirac and extended, and finally the relativistic quantum mechanics was completed.

De Broglie matter wave

As a prelude to quantum mechanics, De Broglie's material wave theory has special importance. As early as 1905, Einstein implied in his light quantum hypothesis the idea that volatility and particleness are the two manifestations of light, and predicted that a new theory will emerge that unifies wave theory with particle theory . At the beginning of the 1920s, when modern physics was facing a major breakthrough, De Broy, who had a vision of beauty, stood out from the crowd. How does light consist of particles and oscillations? In 1923, the French nobleman and the insightful physicist Prince Louis de Broglie made this particle-wave image more confusing in his doctoral dissertation. He proposed that physical particles should behave like waves!

De Broglie's research on the wave-particle duality benefited from the revelation of Einstein's theory of relativity and the concept of light quantum, on the other hand, he was influenced by Brillouin's view and relationship between physical particles and waves. Brillouin's attempt was unsuccessful, but his thinking had a beneficial effect on De Broglie, who was pursuing a doctorate.

De Broglie intends to remove the concept of "Ether", and directly give the electrons the volatility of Ether, and further explore the theory of atoms. The hard work of the predecessors in the physics community has cleared the way for successors to explore. De Broglie examined the history of the particle theory and wave theory of light, noting that in the nineteenth century WR Hamilton (1805-1865) had expounded the similarity between geometrical optics and classical mechanics. He therefore thought that just as geometric optics could not explain the interference and diffraction of light, classical mechanics could not explain the laws of motion of microscopic particles. So he had this idea from the beginning: "It seems necessary to create a new mechanics with wave characteristics, and its relationship with the old mechanics is like the relationship between wave optics and geometric optics." He boldly guessed the mechanics and There is an analogy between certain principles of optics, and an attempt has been made to adapt a theory to both of these fields of physics (this theory was later completed by Danish physicist Schrodinger).

In 1922, with the publication of a paper on black body radiation as a landmark, De Broglie took an important step forward. In this article, he used the quantum theory of light and thermodynamic molecular motion theory to derive the Wien radiation law, and from the hypothesis of photon gas, he obtained Planck's law, which shows that he has a deep understanding of the particle nature of radiation. This article put him at the forefront of physics at the time.

The interest in quantum theory led De Broglie to move in the right direction to unify the undulating aspect of matter and the aspect of particles. In the summer of 1923, De Broglie's thoughts suddenly sublimated to a new level: Planck's energy theorem and Einstein's light quantum theory proved that the radiation that was once considered to be a wave has a particle nature, then the past was considered to be Are particle things volatile? De Broglie later recalled that after such long periods of lonely thinking and reverie, I suddenly thought in 1923 that the discovery made by Einstein in 1905 should be extended to include everything The entire field of matter particles, especially electrons. Since the fall of this year, his creative ideas about material waves have been continuously revealed, and he has published three short articles on waves and quantum in the Bulletin of the French Academy of Sciences from September to October. The idea that the particles unify.

In the doctoral dissertation "Research on Quantum Theory" submitted to the Faculty of Science of the University of Paris in 1924, De Broglie expressed his new ideas more systematically and clearly. He pointed out in the thesis: "For the entire century, compared with the wave research method, we have neglected the research method of particles too much. Has the opposite error occurred in the theory of physical particles? Did we put the Think of an image that is too much and ignore the image of the wave too much? "He believes that" any object is accompanied by a wave and it is impossible to separate the motion of the object from the propagation of the wave. " This means that the wave-particle duality is not only a property of light, but a property common to all particles, that is, what was originally considered a particle also has volatility. This kind of wave associated with physical particles is called matter wave or De Broglie wave. This wave-particle duality of particles can be further revealed by the De Broglie relationship p = frca. This relationship will be considered for a long time as two physical concepts with completely different propertiesmomentum and wavelength are organized using Planck constant h. The ground is connected together, so that the particle and the wave are fused in the same object. Although De Broglie's doctoral dissertation was highly appraised by the defense committee and considered very original, he was considered too mysterious and was not taken seriously.

After De Broglie's thesis was published, the theory of matter waves did not attract the attention of the physics community at the time. The reasons for this were roughly as follows:

(1) Although the weekly report of the French Academy of Sciences is a widely circulated magazine in Europe, not many people take it seriously;

(2) DeBro's reputation for controversy is also a reason. He has participated in the interpretation of the correspondence principle between Bohr and Sommerfeld, the role of quantum numbers, the number of energy levels, the application of quantum conditions, etc. A series of issues.

If it weren't for his mentor Lang Zhiwan, who sent his thesis to Einstein and persuaded Einstein to study it seriously, maybe his thesis would not leave a deep impression on the physics community. After Einstein read De Broglie's thesis, things changed dramatically. Because Einstein had a superhuman aesthetic literacy in science, he always loved the symmetric view that the physical world should be harmonious in the final analysis. De Broglie proposed that the physical particles have fluctuations just like the light particles have. correspond.

DeBro intends to use the analogy of Fermat's principle in geometrical optics and Morpheus's variational principle in classical mechanics in the process of proposing material waves, and was inspired by Einstein's wave-particle duality of light. The establishment of this new concept shows the harmonious and symmetrical nature of nature, and also provides an important basis for the establishment of wave dynamics. In addition, Einstein understands that De Broglie's doctrine is not easy to accept, because when he himself proposed the granularity of light in 1905, he had to struggle to accept this view with his colleagues. Therefore, Einstein gave De Broglie strong support and appealed to other physics workers one by one. Don't underestimate the young man's work. In this way, De Broglie's thesis was strongly recommended by Einstein and caused widespread concern in the physics community. De Broglie conceived that the experiment of crystals diffracting electron beams, it is possible to observe the fluctuation of electron beams. Later, Davidson and GP Thomson each proved the existence of matter waves from the diffraction of electrons in the crystal. For their outstanding work in this area, they jointly won the Nobel Prize in Physics in 1937.

Establishment of wave dynamics

After the introduction of De Broglie's matter wave theory, people hope to establish a new theory of atomic mechanics to describe the motion of microscopic objects. The Austrian physicist Schrodinger completed this work. In the past, a new quantum theorywave dynamicswas established in the form of a wave equation.

In the summer and fall of 1925, Schrodinger was working on quantum gas research, at a time when Einstein and Bose's work on quantum statistical theory was published shortly. In the article "Quantum Theory of Single Atom Ideal Gas" published by Einstein in 1924, Schrödinger stated that he could not understand it, so he often communicated with Einstein for discussion. It can be said that Einstein was the direct leader of Schrodinger, and it was this article by Einstein that guided Schrodinger's research direction. Einstein strongly recommended De Broglie's dissertation, so Schrodinger managed to find a De Broglie dissertation to read. After in-depth research, Schrodinger germinated the idea of using new perspectives to study the structure of the atom. The idea of matter waves was immediately extended to describe atomic phenomena. In addition, the famous chemical physicist Debye also had a positive impact on Schrödinger. Schrödinger introduced De Broglie's work to the participants at a lecture at the University of Technology Zurich. Professor Debye, the moderator of the meeting, asked Schrödinger: Since the particles of matter are waves, is there a wave equation? No wave equation! Schrödinger understood that this was indeed a problem and an opportunity, so he immediately reached out to seize the opportunity and finally succeeded. It can be seen that being able to persist in preparation for a long time and seize it as soon as possible is a key to success. Schrödinger argues that De Broglie's work "has not been illustrated universally." So he tried to find a more general law, and at the same time, he saw that matrix mechanics used a very abstract and difficult transcendental algebra, so he decided to explore new ways when he lacked intuitiveness. At the beginning, Schrödinger tried to establish a relativistic equation of motion. After intense research, he overcame many mathematical difficulties. Starting from the theory of relativity, he finally got a wave associated with electrons moving in an electromagnetic field in 1925. Wave equation. However, he immediately discovered that the results of this wave equation when calculating the spectrum of hydrogen atoms were not consistent with the experimental values, nor could the fine structure of the hydrogen atom spectrum be obtained. He was very frustrated at the time, thinking that his line was wrong, and it took a few months before he recovered from the frustration and returned to the job. ^[3]