I’m currently revising the book chapter based on the original “Bunnies Made of Cheese” post, which deals with virtual particles and Quantum Electro-Dynamics. The best proof of the power of QED is the measurement of the anomalous magnetic moment of the electron, where experiment and theory agree to something like thirteen decimal places.
In double-checking things this morning, I find that the Gabrielse group has released yet another improved measurement of the electron g-factor since the last draft of this chapter. I’ve updated the current draft accordingly, and continue to be amazed by the whole field. The bastards will probably push it out another decimal place or two before the book sees print, too.
Interestingly, the analogous quantitiy for the muon seems to show a small discrepancy between the experimental and theoretical values, with the theoretical value being slightly larger than the experimental (2.00116592287 vs. 2.00116592080, if I’m reading this preprint correctly). It’s not entirely clear to me whether this is a possible sign of new physics (as a 3.3-sigma effect, it’s not that definitive), or just a sign that the calculations and experiments are really tricky.
Anybody with relevant knowledge of the muon situation, please leave me a comment. Otherwise, I’m moderately likely to say something silly when I try to add this to the book.