Classical physics

A period in the history of physics

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synonym Classical physics (classical physics) generally refers to classical physics

Classical physics is based on classical mechanics , Classic Electromagnetic field theory And classic statistical mechanics It is a classical physical system with three pillars.

By Galileo (1564-1642) and Newton (1643-1727) and others founded the classical physics in the 17th century. After the expansion in various basic departments in the 18th century, the classical physics got comprehensive, systematic and rapid development in the 19th century, reaching its brilliant peak. By the end of the 19th century, a grand and complete Theoretical system 。 Especially its three pillars - classical mechanics, classical electrodynamics, classical thermodynamics and statistical mechanics ——They have reached maturity and perfection. They are not only very rigorous and perfect in theoretical expression and structure, but also contain very clear and profound basic concepts of physics Scientific knowledge It also has a far-reaching impact.

Chinese name: Classical physics
Foreign name: Classical physics

founder: Galileo 、 Newton wait forsomeone
Creation time: seventeenth century

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The development of physics is divided into several periods according to the characteristics of its own development Representativeness Characteristics of. This is mainly based on the internal logic of the development of physics, which can take into account Social production and Socio economic form And can reveal the inherent nature throughout the development of physics Regularity 。

According to the development law of physics itself, combined with the characteristics of social and economic periods, and taking into account that different periods have different research method The history of the development of physics is roughly divided into three periods.

Empirical physics

During the period of empirical physics (before the 17th century), China and ancient Greek Form a cultural center where two things complement each other. Empirical science From productive labor The main methods of this period were intuitive observation and philosophical speculative speculation. Astronomy, force, heat, sound and light related to production activities and people's own direct feelings（ geometrical optics ）And so on. Except Greek statics In addition, China was in a leading position in the above aspects at that time. At this time, physics was still in its infancy.

Classical physics

During the period of classical physics (from the beginning of the 17th century to the end of the 19th century) capitalism Production has promoted the development of technology and science, forming a relatively complete system of classical physics. The combination of systematic observation experiments and rigorous mathematical deduction was introduced into physics, which led to“ scientific revolution ”。 Newtonian mechanics The establishment of the system marks the birth of classical physics. After preparation in the 18th century, physics gained rapid and important development in the 19th century. At the end of the 19th century classical mechanics , Thermodynamics and Statistical Physics , Classic Electromagnetic field theory As a pillar, the development of classical physics reached its peak.

Modern Physics

Modern Physics Period (20th century First break At the end of the 19th century, a series of major discoveries in physics made classical physics Theoretical system It has encountered an insurmountable crisis, which has caused modern Physics revolution 。 because Production technology With the development of, the creation of precision and large-scale instruments and the reform of physical thought, the physical theory in this period showed a rapid development. The research object goes from low speed to high speed, from macro to micro, and deep into the deep universe and the interior of the material structure Macro world The understanding of the structure, the law of movement and the law of movement of microscopic materials has produced significant changes.

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The 19th century was a great time for classical physics, a construction scientific theory The era of the mansion is the era of perfect combination of theory and experiment, which has produced many famous physicists. The rapid development of science and technology has produced a wide range of social impacts Dynamics , electromagnetics heat Optics and acoustics form the building of classical physics. It can also be said that the 19th century was a glorious era of classical physics.

By the end of the 19th century, physics had reached a perfect and mature level. The brilliant achievements of physics have made many physicists complacent and intoxicated with joy, so they came to the view that the building of physics has been completed, and physicists don't need to do anything in the future, they just need to measure various data more accurately. However, there are two dark clouds floating in the clear sky of physics at the moment, and a series of new discoveries have emerged in physics. These new discoveries, which can not be explained by classical physics, put classical physics into crisis. The first flower and Michelson Experiment related, the second one is related to Blackbody radiation of It was these two black clouds that led to the 20th century Physics revolution The whole natural science has entered a new stage due to the violent storm. These "two dark clouds" became the great physics revolution of the 20th century Fuse 。

It was born from the first dark cloud less than a year later relativity And then came from the second dark cloud Quantum theory 。 The edifice of classical physics was completely shaken. In fact, at the end of the nineteenth century, photoelectric effect 、 Atomic spectrum And the stability of atoms and other experimental facts have also been in sharp opposition to the theory of classical physics. The establishment of quantum theory makes human's understanding of matter enter from the macro world Microcosm 。

The appearance of "dark clouds"

In the spring of 1900, a famous physicist Kelvin Lord In his farewell speech to the old century, he said: "The physics building has been completed in the 19th century, and the task of physicists in the future is to decorate and perfect this building." At the same time, he also mentioned that there are two small, disturbing clouds floating in the sky of physics, one is the negative result of the etheric drift experiment, and the other is Blackbody radiation Of Ultraviolet disaster 。 In fact, "dark clouds" not only include these two, but also gas specific heat in Energy equipartition Failure of laws photoelectric effect Experiment, atom Line spectrum Etc. However, it was these dark clouds that brought a revolutionary storm that shocked the whole physics world and led to the birth of modern physics.

The First Dark Cloud "Ether" Theory

The first dark cloud follows the light wave theory And began to appear. fresnel and Thomas Young Having studied this theory, it includes such a question: how does the earth pass through Light ether In this way Elastic solid And sports? The second dark cloud is Maxwell Boltzmann's theory of equal distribution of energy. These two dark clouds involve two aspects of experimental discoveries, including mechanics, electromagnetism Kinetic theory of gas molecules Theoretical difficulties. Principle of relativity It is one of the most basic principles of classical mechanics, which believes that absolute static and absolute Uniform motion All are nonexistent, all measurable, and therefore there are Physical meaning The motion of object of reference Of relative motion 。 Newton I am fully aware of the determination“ Absolute motion ”The difficulty of“ Absolute space ”Exists as refuge 。 maxwell After the success of the electromagnetic field theory of, electromagnetic wave The carrier of ether becomes the absolute space of materialization, and the ether resting in the universe constitutes the background frame of "absolute motion" of all objects. Since the ether is also a kind of material existence, or it represents the materialized absolute space, of course, the absolute motion of objects relative to the ether background can be measured through precise experiments. However, in 1881, American physicist Michelson and Morey used Interferometer The precision optical experiments carried out failed to observe the expected movement of the ether relative to the earth.

The second dark cloud "ultraviolet disaster"

The second dark cloud involves another branch of classical physics, thermodynamics and Theory of molecular motion An important issue in. The Kelvin civilization did mention "Maxwell Boltzmann's theory of equal distribution of energy". It actually refers to the late 19th century Blackbody radiation Serious difficulties encountered in the research. To explain Blackbody radiation experiment As a result, physicists rayleigh Heggins believes that energy is a continuous change physical quantity The blackbody radiation formula that is more consistent with the experimental facts when the wavelength is relatively long and the temperature is relatively high is established. However, this formula deduces that in the short wave region（ ultraviolet Area) as the wavelength becomes shorter, radiation intensity Can be increased endlessly experimental data It is impossible to make a difference of one hundred and eight thousand li. So this failure was called "ultraviolet disaster" by Ellen Feist. These two dark clouds at the beginning of the 20th century finally led to a great change in physics. The first dark cloud "ether" theory led to relativity The birth of. The second dark cloud "ultraviolet disaster" caused quantum mechanics Generation of. Therefore, it can also be said that the study of these two "dark clouds" marks that Modern Physics The arrival of the times.

Basic concepts

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Classical mechanics and Mechanical determinism

Newton summarized it in a rigorous unified theory, realizing the first theoretical synthesis in the history of modern physics. Published in 1687《 Mathematical Principles of Natural Philosophy 》Newton proposed three basic principles of dynamics and Law of universal gravitation 。 utilize Variational method Of Mathematical method And“ Principle of minimum action ”And Newton kinetic equation Equivalent Euler - Lagrange equation And finally in 1834 by the British Hamilton (1805-1865) proposed Hamilton principle and Canonical equation , established“ Analytical mechanics ”The theory has realized the biggest leap of post Newtonian mechanics theory.

thermodynamics And energy and entropy

Principle of conservation of energy It is a great victory in natural science in the 19th century and the second theoretical synthesis in the development of modern physics. Entropy principle The discovery of Irreversibility And historic.

In classical mechanics and Electromagnetic field theory Medium, basic Laws of physics The time in is symmetric and reversible basic equation yes Time inversion All have Symmetry The movement has no essential difference between the past and the future. Time is only a parameter to describe the movement from the outside, and its change has no effect on the nature of the movement. thus Time arrow Not there Substantive The meaning of.

The name "statistical mechanics" was first proposed by American physicist Gibbs in 1884. Gibbs in Maxwell and Boltzmann On the basis of thinking“ Ensemble ”Concept, creating the ensemble statistical method 。 So as to heat The phenomenological sum of Theory of molecular motion The two basic research directions of Organic entirety Middle, finished statistical mechanics This is another theoretical synthesis of classical physics.

classic electrodynamics

In 1862, Maxwell introduced an electromagnetic ether standard mechanical model And“ Displacement current ”It is assumed that electrodynamics was proposed in 1864 Equations , predicted electromagnetic wave Well reveals the electromagnetic wave nature of light. Maxwell's scheme makes the concept of media delivery contact fully realized, and electromagnetics The whole theory physical base It became the third theoretical synthesis in the development of modern physics.

Completion and Limitations of Classical Physics

Around 1895, classical mechanics Classical thermodynamics The classical physics, which is supported by statistical mechanics and classical electrodynamics, has been combined into a magnificent architectural system and a moving "beautiful palace", reaching its peak.

In mechanics, related to the mechanical concept Absolute time 、 Absolute space The concept of gravity and the definition of mass have been widely criticized, and Newton also adopted an evasive attitude towards the essence of gravity. and Newtonian mechanics In fact, the theoretical framework of Action at a distance , which is fundamentally opposite to the field physics developed in the 19th century.

In terms of heat, Principle of entropy increase Revealed and Thermal phenomenon Irreversibility of relevant natural processes reflects Thermodynamic principle And the principles of classical mechanics and classical electrodynamics statistical mechanics Introduced in probability statistics Thought and the statistical properties of thermodynamic laws have made classical mechanics rigorous certainty There is a gap.

In optics and electromagnetics Media The special nature of "ether", which is difficult to understand, and the detection of its existence have made scientists hard at work. According to electromagnetic theory Spatial coordinates Of continuous function The described field has energy and can't be simplified any more Physical reality This is also contrary to the view of classical mechanics that the moving particle is regarded as the only type of energy.

Newton made extraordinary achievements on the basis of previous studies. The three laws of motion and the law of universal gravitation successfully describe the planets, satellites Comet movement , and fully explained the movement of tides and other objects on the ground. Since then, people have believed that all known movements in nature can pass through Newton (classical) mechanical laws. So Newtonian (classical) mechanics is regarded as Scientific interpretation The highest authority and final standard of. The process of establishing classical mechanics is essentially an experimental method, logical thinking The establishment and development of methods and mathematical methods. From this we can see the meaning of "classic" in classical physics. It was proposed by a famous physicist, and after repeated experimental verification, the most authoritative, standard and classic conclusion was finally reached.

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