Skip to main content Accessibility help
×
×
Home
  • Print publication year: 2013
  • Online publication date: September 2014

6 - Entropy of fermion systems

Summary

Symmetries and wave functions

An important difference between the classical and quantum perspectives is their different criteria of distinguishability. Identical particles are classically distinguishable when separated in phase space. On the other hand, identical particles are always quantum mechanically indistinguishable for the purpose of counting distinct microstates. But these concepts and these distinctions do not tell the whole story of how we count the microstates and determine the multiplicity of a quantized system.

There are actually two different ways of counting the accessible microstates of a quantized system of identical, and so indistinguishable, particles. While these two ways were discovered in the years 1924–1926 independently of Erwin Schrödinger’s (1887–1961) invention of wave mechanics in 1926, their most convincing explanation is in terms of particle wave functions. The following two paragraphs may be helpful to those familiar with the basic features of wave mechanics.

A system of identical particles has, as one might expect, a probability density that is symmetric under particle exchange, that is, the probability density is invariant under the exchange of two identical particles. But here wave mechanics surprises the classical physicist. A system wave function may either keep the same sign or change signs under particle exchange. In particular, a system wave function may be either symmetric or antisymmetric under particle exchange.

Recommend this book

Email your librarian or administrator to recommend adding this book to your organisation's collection.

A Student's Guide to Entropy
  • Online ISBN: 9780511984556
  • Book DOI: https://doi.org/10.1017/CBO9780511984556
Please enter your name
Please enter a valid email address
Who would you like to send this to *
×