Also found in: Wikipedia.
Wigner's theorem[′wig·nərz ‚thir·əm]
The theorem that, if ψ is an eigenfunction of the Hamiltonian operator and R is a symmetry element of the Hamiltonian, then R ψ is an eigenfunction of the Hamiltonian having the same eigenvalue as ψ.
Angular momentum of the electron spin is conserved in a collision of the second kind.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.