Editing Degenerate matter (section)

== Concept ==
{{Main|Fermi-Dirac statistics}}
[[Quantum mechanics]] uses the word 'degenerate' in two ways: [[degenerate energy levels]] and as the low temperature ground state limit for states of matter.<ref name=TaylorZafiratosDubson2014>{{Cite book |last1=Taylor |first1=John Robert |title=Modern physics for scientists and engineers |last2=Zafiratos |first2=Chris D. |last3=Dubson |first3=Michael Andrew |date=2004 |publisher=Pearson Education |isbn=978-0-13-805715-2 |edition=2|location=Upper Saddle River, NJ |oclc=1319408575}}</ref>{{rp|437}} The electron degeneracy pressure occurs in the ground state systems which are non-degenerate in energy levels. The term "degeneracy" derives from work on the specific heat of gases that pre-dates the use of the term in quantum mechanics.

Degenerate matter exhibits quantum mechanical properties when a [[fermion]] system temperature approaches [[absolute zero]].<ref name=AshcroftMermin/>{{rp|30}} These properties result from a combination of the [[Pauli exclusion principle]] and [[quantum confinement]].  The Pauli principle allows only one fermion in each quantum state and the confinement ensures that energy of these states increases as they are filled. The lowest states fill up and fermions are forced to occupy high energy states even at low temperature. 

While the Pauli principle and Fermi-Dirac distribution applies to all matter, the interesting cases for degenerate matter involve systems of many fermions. These cases can be understood with the help of the [[Fermi gas]] model.  Examples include electrons in metals and in white dwarf stars and neutrons in neutron stars.<ref name=TaylorZafiratosDubson2014/>{{rp|436}} The electrons are confined   by Coulomb attraction to positive ion cores; the neutrons are confined by gravitation attraction.  The fermions, forced in to higher levels by the Pauli principle, exert pressure preventing further compression.

The allocation or distribution of fermions into quantum states ranked by energy is called the [[Fermi-Dirac distribution]].<ref name=AshcroftMermin>{{Cite book|url=https://archive.org/details/solidstatephysic00ashc/page/39|title=Solid state physics|last1=Neil W.|first1=Ashcroft|last2=Mermin|first2=N. David.|date=1976|publisher=Holt, Rinehart and Winston|isbn=0030839939|location=New York|pages=[https://archive.org/details/solidstatephysic00ashc/page/39 39]|oclc=934604|author-link=Neil Ashcroft|author-link2=N. David Mermin|url-access=registration}}</ref>{{rp|30}} Degenerate matter exhibits the results of Fermi-Dirac distribution.