In quantum electrodynamics (QED), the electron 'g' factor, also known as the electron magnetic moment anomaly, arises from the interaction between the electron's spin and its surrounding electromagnetic field, including virtual photons. The Dirac equation predicts the value of the electron 'g' factor to be exactly 2 in the absence of any quantum corrections. However, through calculations in QED, it is found that there are quantum fluctuations and interactions with virtual particles that modify the electron 'g' factor.
The virtual photons involved in the calculation of the electron 'g' factor are associated with the electromagnetic field fluctuations and vacuum polarization effects. Virtual particles, including virtual photons, are temporary and transient entities that do not have the same properties as real particles. They exist only as intermediate states in quantum calculations.
The energy level of virtual photons involved in the electron 'g' factor calculation is not a well-defined quantity like the energy of real photons. Virtual particles, including virtual photons, do not have distinct energy levels in the same way that real particles do. The concept of energy associated with virtual particles is tied to the mathematical formulation of quantum field theory, rather than a direct physical interpretation.
Instead of referring to specific energy levels of virtual photons, the calculation of the electron 'g' factor involves the integration of virtual particle contributions over a range of momenta and energies. These contributions are expressed as mathematical expressions in terms of Feynman diagrams and involve integrals over various momentum variables.
In summary, while virtual photons play a crucial role in the calculation of the electron 'g' factor through their interactions with the electron's spin and the surrounding electromagnetic field, the concept of energy levels for virtual photons is not applicable in the same way as for real photons. The electron 'g' factor is determined through complex calculations involving integrals over momenta and energies of virtual particles in the context of quantum electrodynamics.