theorists to develop Quantum ElectroDynamics. The correction increases the energy of s
states. One may think of the physical origin as the electron becoming less pointlike as virtual
photons are emitted and reabsorbed. Spreading the electron outa bit decreases the effect of being
in the deepest part of the potential, right at the origin. Based on the energy shift, I estimate that
theelectron in the 2s state is spread out by about 0.005 Angstroms, much more than the
size of the nucleus.
Theanomalous magnetic moment of the electron,gā2, which can also be calculated in field
theory, makes a small contribution to the Lamb shift.