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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.
Willis Lamb had found when probing hydrogen atoms with microwave beams that one of the two possible quantum states had slightly more energy than predicted by the Dirac theory; this became known as the Lamb shift. Lamb had discovered the shift a few weeks before (with Robert Retherford), so this was a
Willis Eugene Lamb Jr. (/ l æ m /; July 12, 1913 – May 15, 2008) was an American physicist who won the Nobel Prize in Physics in 1955 "for his discoveries concerning the fine structure of the hydrogen spectrum."
The Lamb shift is a small difference in the energies of the 2 S 1/2 and 2 P 1/2 energy levels of hydrogen, which arises from a one-loop effect in quantum electrodynamics. The Lamb shift is proportional to α 5 and its measurement yields the extracted value: α −1 = 137.0368(7).
In 1947, Willis Lamb and Robert Retherford measured the minute difference in the 2 S 1/2 and 2 P 1/2 energy levels of the hydrogen atom, also called the Lamb shift. By ignoring the contribution of photons whose energy exceeds the electron mass, Hans Bethe successfully estimated the numerical value of the Lamb shift.
A major talking point at the conference was the discovery by Willis Lamb and his graduate student, Robert Retherford, shortly before the conference began that one of the two possible quantum states of hydrogen atoms had slightly more energy than that predicted by the theory of Paul Dirac; this became known as the Lamb shift.
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The 1947 measurements by Willis Lamb of the Lamb shift, and by Polykarp Kusch of the electron's anomalous magnetic dipole moment, both of which were instrumental in the development of Quantum Electrodynamics and Quantum Field Theory.