It is well-known that quantum electrodynamics is the flagship of all quantum field theories. The article in Wikipedia has been flagged good article after an important review process and so it is worthwhile to read. I received as usual the table of contents of Nature for this week and I have found a striking paper. You will need a subscription to read it in full but the first part is readable for free and the conclusions by these authors are striking. The idea is smart as they consider an atom formed by a proton and a muon rather than the usual hydrogen atom. If you remember standard Bohr formula for the radius, this goes as 1/m and so this is smaller for the muon atom making possible a more direct probing of the finite size of the proton. These authors do fine spectroscopy on it measuring the Lamb shift. What they find is in disagreement with QED computations and so it is possible to conclude that this discrepancy may arise either directly from the theory or, for some reason, one has to shift Rydberg constant. This is a relevant crack into a cherished theory and so, it will appear interesting to work out a possible understanding. It should be said, even if on a more complex side, that muon g-factor could be a possible clue for new physics departing from the Standard Model. Indeed, it seems that, in some way to be clarified, muons are the key.
Update: There is a nice article at Physics World. A worthwhile reading.