= Lamb shift
{c}
{tag=The most important physics experiments}
{title2=1947}
{wiki}
2s/2p energy split in the <hydrogen emission spectrum>, not predicted by the <Dirac equation>, but explained by <quantum electrodynamics>, which is one of the first great triumphs of that theory.
Note that for atoms with multiple electrons, 2s/2p shifts are expected: <Why does 2s have less energy than 1s if they have the same principal quantum number?>. The surprise was observing that on <hydrogen> which only has one <electron>.
Initial experiment: <Lamb-Retherford experiment>.
On the return from the train from the <Shelter Island Conference> in <New York>, <Hans Bethe> managed to do a <non-relativistic> calculation of the <Lamb shift>. He then published as The Electromagnetic Shift of Energy Levels by Hans Bethe (1947) which is still paywalled as of 2021, <academic publishing>[fuck me]: https://journals.aps.org/pr/abstract/10.1103/PhysRev.72.339 by <Physical Review>.
The Electromagnetic Shift of Energy Levels <Freeman Dyson> (1948) published on <Physical Review> is apparently a <relativistic> analysis of the same: https://journals.aps.org/pr/abstract/10.1103/PhysRev.73.617 also paywalled as of 2021.
TODO how do the infinities show up, and how did people solve them?
\Video[https://www.youtube.com/watch?v=jPKEuiUNJIk]
{title=<Lamb shift> by Dr. Nissar Ahmad (2020)}
{description=Whiteboard Lecture about the phenomena, includes description of the experiment. Seems quite good.}
\Video[https://www.youtube.com/watch?v=WcyMfgj9psQ]
{title=<Murray Gell-Mann> - The race to calculate the relativistic <Lamb shift> by <Web of Stories> (1997)}
{description=Quick historical overview. Mentions that <Richard Feynman> and <Julian Schwinger> were using <mass renormalization> and cancellation if infinities. He says that French and Weisskopf actually managed to do the correct calculations first with a less elegant method.}
https://www.mdpi.com/2624-8174/2/2/8/pdf History and Some Aspects of the Lamb Shift by G. Jordan Maclay (2019)
\Video[https://www.youtube.com/watch?v=062GN3RdH1c]
{title=Freeman Dyson - The Lamb shift by <Web of Stories> (1998)}
{description=
Mentions that he moved to the <USA> from the <United Kingdom> specifically because great experiments were being carried at <Columbia University>, which is where the <Lamb-Retherford experiment> was done, and that <Isidor Isaac Rabi> was the head at the time.
He then explains <mass renormalization> briefly: instead of calculating from scratch, you just compare the raw electron to the bound electron and take the difference. Both of those have infinities in them, but the difference between them cancels out those infinities.
}
\Video[https://www.youtube.com/watch?v=YP6TGj-yL7Y]
{title=<Hans Bethe> - The Lamb shift (1996)}
{description=
Ahh, Hans is so old in that video, it is sad to see. He did live a lot tough. Mentions that the shift is of about 1000 MHz.
The following video: https://www.youtube.com/watch?v=vZvQg3bkV7s Hans Bethe - Calculating the Lamb shift.
}
\Video[https://www.youtube.com/watch?v=-0DDUyR0200]
{title=<Lamb shift> by Vidya-mitra (2018)}