kurt101 said:
What about the lamb shift?
Feynman was too successful - people think, even some professionals, virtual particles exist. His good friend, Dyson, sorted it out - they are simply the pictorial representation of a Dyson series:
https://en.wikipedia.org/wiki/Dyson_series
They do not really exist. It's one of the many misconceptions we have to often deal with here:
https://arxiv.org/abs/quant-ph/0609163
This is a B level thread - we do not of course expect you to know this advanced material, simply be aware what you read in popularization's, beginner texts etc is sometimes/even on occasion often - not correct - especially in Quantum Field Theory. Also strictly speaking they are not valid references here which are well respected textbooks and peer reviewed papers, but of course we are all willing to help a beginner with what is really going on so it's OK to mention in passing that's where you got it from and then we explain what's really happening.
The Lamb Shift can be explained without Virtual Particles - Bethe essentially explained it in a back of the envelope calculation he did while on the train returning from the conference where Lamb presented his results:
https://www.ias.ac.in/article/fulltext/reso/010/10/0033-0048
But Schwinger and Feynman decided to try for a more general framework to explain it - Feynman with Bethe as his Mentor - they were at Cornell together - and Dyson was there as well. Feynman came up with a pictorial way to view it, but its physical basis left something to be desired. However it was computationally very efficient in calculating such results. Schwinger went down a different path that was computationally quite hard - but still got the correct answer. Dyson showed they were the same - but since Feynman's methods were more efficient his ideas won out. They included imagery like virtual particles and positrons as electrons traveling backwards in time. It all helped with the calculations - but as Dyson proved their existence in any kind of usual sense was mistaken - they are simply mathematical 'tricks' to make calculation easier.
Interesting story. Dyson never got a PhD - he actually can't be called doctor. There is something higher than a PhD called a DSc - Doctor of Science that also entitles it's holder to be called Doctor. To get one you present your papers to a committee and if they think they are of the caliber to get the degree then you get it. Dyson made many important contributions to physics so it would be a mere formality for him to get one. But you know what - he never bothered - if fact he doesn't even like the whole system:
http://blogs.sciencemag.org/pipeline/archives/2014/04/01/freeman_dyson_on_the_phd_degree
While Dyson was presenting his results showing the equivalence of the two methods Feynman was in the audience down the back cracking jokes and leaving everyone in stitches. He of course knew of Dysons work so had no need to hear the lecture. At the end he said - your in Doc - a reference to the fact he did not have a PhD, but after work of that caliber it was just a formality. Its likely, secretly, Feynman would have liked to not bother with a PhD either - he would have liked to have said, in his Brooklyn accent (strange since he was borne in Far Rockaway - not Brooklyn - just more of Feynman's mystique), hey buddy - even I know that and I don't have a PhD. On his death bed Heisenberg was asked about physicists he knew. When asked about Feynman he said - Feynman, oh that Feynman - he talks like a gangster. When told of it Feynman laughed his head off.
Thanks
Bill
