Schwinger has on his grave (it seems) the relation between the g-factor of the electron and the fine structure constant:
$g = 2 \ + \ \alpha / \pi \ + \ ... $
Did Schwinger or somebody else ever give a simple explanation for the second term of the right hand side? The 2 appears from Dirac's equation. The second term is due to the emission and absorption of a photon. Is there a simple way to see that this process leads to the expression alpha/pi?