Lamb shift

Etymology
Named after American physicist (1913-2008).

Noun

 * 1)  A small difference between the energy levels 2S½ and 2P½ of the hydrogen atom, not predicted by the Dirac equation, whose detection in the Lamb–Retherford experiment of 1947 foreshadowed the development of quantum electrodynamics (in which the discrepancy is explained to be an effect of the emission and re-absorption of virtual photons); such a difference between otherwise expectedly equal energy levels of hydrogen or any other type of atom.

Translations

 * French:, déplacement de Lamb
 * German: Lamb-Verschiebung
 * Italian: spostamento di Lamb
 * Portuguese: desvio de Lamb