Statistical Physics

A discipline

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synonym statistical mechanics (Physical concept) generally refers to statistical physics (a discipline)

Statistical Physics Microstructure and Microparticle Understanding of interaction, using probability statistics The method of particle Constituent Macroscopic object Of physical property And macro laws Theoretical physics Branch. also called statistical mechanics 。 The so-called large amount is based on 1 mole of material Molecular number (its Order of magnitude 10 ^ 23).

Chinese name: Statistical Physics
Foreign name: statistical physics

Methods: probability statistics
Object: Material Microstructure and Micro particle Interaction
Historical origin: Since 1960s

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Research object

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The research object changed from a small number of individuals to a group composed of a large number of individuals, resulting in the regular nature and research method Fundamental changes, a large number of particle system Followed Statistical law It cannot be reduced to mechanical laws. Statistical physics is composed of microcosmic As a bridge to the macro, it provides the basis for various macro theories, and has become a gas, liquid, solid and plasma And plays a role in the research of chemistry and biology. Kinetic theory of gas (once called Kinetic theory of gas molecules ）It is an early statistical theory. It reveals the pressure , temperature, internal energy, etc Macroscopic quantity The microscopic essence of Microscopic quantity average value Relationship between. Mean free path Formula derivation, gas molecule rate or velocity distribution The establishment of laws, Equipartition theorem of energy The presentation of, and the drawing of relevant data, enable people to Equilibrium state lower ideal gas Molecular Thermal movement , collision Energy distribution And so on have clear physical images and quantitative understanding, and also show the probability statistical distribution And so on.

theoretical basis

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wrong Equilibrium state Distribution function and its evolution equation The establishment of H function And its compliance H theorem Understanding the macro process Irreversibility And the process of approaching balance has played an important role. Clarification of the statistical significance of entropy, Principle of entropy increase The micro statistical interpretation of, shows that statistical theory has changed from equilibrium state to Nonequilibrium state Development has gone from micro statistical interpretation of some macro concepts and macro laws to The second law of thermodynamics Such a general law can be explained by micro statistics. But, Kinetic theory of gas Taking molecules as statistical individuals, it is necessary to make groundless guesses or assumptions about the molecular structure and the interaction between molecules, which is the fundamental difficulty and limitation of its further development.

research method

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J. W. Gibbs Taking the whole system as a statistical individual, it is proposed to study the Ensemble stay Xiangyu Distribution in the, overcoming Kinetic theory of gas The difficulty of establishing statistical physics. stay Equilibrium state In statistical theory, for energy and Number of particles changeless Isolated system , using Microcanonical ensemble ； For systems that can exchange energy with large heat sources but have a fixed number of particles Canonical ensemble ； It can exchange energy and particle System, using Giant canonical ensemble 。 These are three commonly used systems, and the distribution of each ensemble in the phase universe density function All have obtain. Quantum statistics And Classical statistics And research method Similarly, the concept of ensemble is still applicable in quantum statistics. The difference is that quantum statistics believes that Microparticle The movement of follows quantum mechanics Regularity instead of classical mechanics Law, Micro motion state have Discontinuity , required quantum state Rather than Xiangyu.

wrong Equilibrium state Statistical physics has a wide range of contents and is still developing rapidly and far from mature. For the system near the equilibrium state, study its equilibrium Relaxation time And temperature Dependencies ； Not too far from equilibrium, maintain temperature difference, concentration difference Potential difference Systems that have undergone various transport processes linear Transport coefficient In addition, it also studies Fluctuation Phenomenon. Relaxation , transport and fluctuation are the main non-equilibrium processes near the equilibrium state.

Historical origin

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Since the 1960s Far from equilibrium Of physical phenomenon A wide range of studies have been carried out, the most important of which is the mutation far away from equilibrium, Ordered structure The emergence of, established Dissipative structure theory , but not complete Theoretical system 。

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