Editing Lamb shift (section)

{{Short description|Difference in energy of hydrogenic atom electron states not predicted by the Dirac equation
}}
{{Use American English|date=January 2019}}{{Quantum field theory}}
[[File:Hydrogen_fine_structure2.svg|thumb|[[Fine structure]] of energy levels in hydrogen – relativistic corrections to the [[Bohr model]]]]

In [[physics]], the '''Lamb shift''', named after [[Willis Lamb]], is an anomalous difference in energy between two electron orbitals in a [[hydrogen atom]]. The difference was not predicted by theory and it cannot be derived from the [[Dirac equation]], which predicts identical energies. Hence the Lamb ''shift'' is a deviation from theory seen in the differing [[energy|energies]] contained by the  <sup>2</sup>''S''<sub>1/2</sub> and <sup>2</sup>''P''<sub>1/2</sub> [[energy levels|orbitals]] of the hydrogen atom.

The Lamb shift is caused by interactions between the [[virtual photon]]s created through [[Quantum fluctuation|vacuum energy fluctuations]] and the electron as it moves around the hydrogen nucleus in each of these two orbitals. The Lamb shift has since played a significant role through vacuum energy fluctuations in theoretical prediction of [[Hawking radiation]] from [[black hole]]s.

This effect was first measured in 1947 in the '''Lamb–Retherford experiment'''<!--boldface per WP:R#PLA--> on the hydrogen microwave spectrum<ref name=Aruldhas>
{{cite book |title=Quantum Mechanics |chapter=§15.15 Lamb Shift |chapter-url=https://books.google.com/books?id=4HLB6884s9IC&pg=PA404 |page=404 |edition= 2nd |publisher=Prentice-Hall of India Pvt. Ltd. |author=G Aruldhas |year=2009 |isbn=978-81-203-3635-3}}
</ref> and this measurement provided the stimulus for [[renormalization]] theory to handle the divergences. The calculation of the Lamb shift by [[Hans Bethe]] in 1947 revolutionized [[quantum electrodynamics]].<ref name=":0">{{Cite book |last=Brown |first=Gerald E. |url=https://archive.org/details/hansbethehisphys0000unse/page/15 |title=Hans Bethe and His Physics |last2=Lee |first2=Chang-Hwan |publisher=[[World Scientific Publishing]] |year=2006 |isbn=978-981-256-609-6 |pages=15–16, 116–118, 161}}</ref> The effect was the harbinger of modern quantum electrodynamics later developed by [[Julian Schwinger]], [[Richard Feynman]], [[Ernst Stueckelberg]], [[Sin'ichirō Tomonaga|Sin-Itiro Tomonaga]] and [[Freeman Dyson]]. Lamb won the [[Nobel Prize in Physics]] in 1955 for his discoveries related to the Lamb shift. [[Victor Weisskopf]] regretted that his insecurity about his mathematical abilities may have cost him a Nobel Prize when he did not publish results (which turned out to be correct) about what is now known as the Lamb shift.<ref>{{cite web |url=https://www.nasonline.org/wp-content/uploads/2024/06/weisskopf-victor.pdf|first1=Kurt |last1=Gottfried |first2=J. David |last2=Jackson |title=Victor Frederick Weisskopf, 1908–2002, A Biographical Memoir |page=16 |quote=I might even have shared the Nobel Prize with Lamb}}</ref>