SteveKlinko said:
Since this Theoretical Construct can be used to calculate predictions for multiple disparate phenomena then it would seem to me that the Theoretical Construct begins to become more and more a real Phenomenon and less and less just a Theoretical Construct.
But anyway, I suppose then I should restate my original question as to how we might measure QVFs to: Putting aside whether QVFs actually exist, what existing devices use the Theoretical Construct of QVFs in some aspect of their operation? Do you know if there are any effects in SETs or TFETs that use the Theoretical Construct of QVFs to explain the effects?
The point is that the words "vacuum fluctuations", "virtual particles", "vertex corrections", etc. are just names (abbreviations) for the perturbative series (in this case of QED).
I always emphasize that relativistic QT should be formulated as relativistic QFT, and relativistic QFT can only be solved in terms of perturbation theory (let alone ab initio numerical approaches like lattice to solve certain aspects of QCD, but that's off-topic here).
So the modern solution of the hydrogen problem starts with QED at tree level in the Coulomb gauge. That's particularly convenient for this problem, because you come already very close to the empirically correct solution. The tree level always boils down to the solution of the classical field equations, which in this case is the Dirac equation for an electron in the staticc Coulomb field of a nucleus. This leads to the famous result already found (by shear luck) in the "old quantum theory" by Sommerfeld and later lead Dirac, among other issues, to the discovery of his famous relativistic wave equation for spin-1/2 particles which bears his name, the Dirac equation.
Now this cannot be the whole truth since it doesn't take into account the quantization of the fields, and indeed one has to go to higher orders in perturbation theory. Thanks to the genius of Feynman we have a short-hand systematic notation for these calulations looking almost pictorial, the Feynman diagrams. The Feynman diagrams are, however, not more thatn precisely that, namely very clever symbolism for cumbersome calculations of corrections to the leading-order perturbative result (at "tree level", i.e., represented by Feynman diagrams without loops). The corrections symbolized by Feynman diagrams with loops are thus sometimes also called "radiative corrections", because they go beyond the tree-level result for atomic energy levels where no "radiation" is taken into account but only the static Coulomb field of the perturbative formulation of QED in the Coulomb gauge.
At one-loop level (i.e., at corrections of order ##\mathcal{O}(\hbar)##) there are
-electron self-energy corrections: these are corrections describing the interaction of an electron with the quantum-fluctuating electromagnetic field, but note that we have a real electron in the game, i.e., we do not deal with the perturbative vacuum! The self-energy corrections should rather be interpreted of the electron interacting with its own flucuating em. field than thinking as if there were "vacuum fluctuations"
-photon polarizations: This is the analogy of self-energy corrections for the photon. The modern terminology would call the corresponding diagram "photon self-energy" rather than "vacuum polarization" or "photon polarization". Note again: We deal with a photon here, i.e., it's again not the perturbative vacuum, but the correction is due to the quantum fluctuations of the Dirac field due to the presence of a photon (i.e., an electromagnetic field).
-vertex corrections: This describes the fact that two electrons (or an electron and a positron) interact and this interaction is also corrected for quantum fluctuations of the electromagnetic field, but again it's not the perturbative vacuum that fluctuates, but the em. field due to the presence of the interacting charges. Among other things (charge renormalization) this diagram also corrects for the gyro-factor of the electron, not being exactly 2 as is only true at tree-level. This correction of the gyro-factor is, as the Lamb shift, among the most precise agreements between theory and experiments in the history of physics.
Anyway, all these effects together contribute to the Lamb shift, and nowhere are "vacuum fluctuations" the reason. Nowadays the evaluation of the perturbative series for the Lamb shift of the hydrogen atom (and also the muonic hydrogen-like bound state of a proton and a muon) are driven to 5th loop order, and theory and experiment agree very well.
