and 
. Energy shifts are infinite...
wheeee.... The only thing that matters is energy differences, so the
infinities get subtracted.
More precisely, it is the electron interaction with zero-point energy of the quantized electromagnetic field.
To first order, this is interactions like emission and absorption
of a photon. This is consistent if and . Energy shifts are infinite...
wheeee.... The only thing that matters is energy differences, so the
infinities get subtracted.
The lamb shift is 
. This is nonzero for s-wave states. This is about
. so 
The lamb shift further splits 
from 