Document Type

Course

Journal/Book Title/Conference

Physics 3710 – Introductory Modern Physics

Publication Date

8-28-2017

First Page

1

Last Page

5

Abstract

Bare essentials of statistical mechanics

Atoms are examples of many-particle systems, but atoms are extraordinarily simpler than macroscopic systems consisting of 1020-1030 atoms. Despite their great size, many properties of macroscopic systems depend intimately on the microscopic behavior of their microscopic constituents. The proper quantum mechanical description of an N -particle system is a wavefunction that depends on 3N coordinates (3 ways of moving, in general, for every particle) and 4N quantum numbers (3 motional quantum numbers and 1 spin quantum number for every particle). (If the “particles” are molecules there might be additional quantum numbers describing rotations and internal vibrations.) The latter is referred to as a microstate. In a macroscopic solid or liquid there are about 1023 atoms per cm3; in a gas there are about 1020. Thus, the amount of information required to specify the wavefunction for such a system is scandalously large. A fundamental theory of macroscopic systems cannot be based on all of the microscopic details. Instead, a new way of thinking is required. This is known as statistical mechanics.

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