Do the Lamb shift and Casimir-Polder forces prove that vacuum fluctuations really exist and can be changed ?
Probably NOT, because the same results can be obtained without invoking vacuum fluctuations but by using the so-called radiation reaction field (or source field). In the case of the Lamb shift, it is possible to show that quantum mechanics predicts the existence of fluctuations of the atom’s electric dipole moment, yielding a fluctuating electric field emitted by the atom. This field can then interact with the emitting atom – it is the reason why it is called a reaction field – yielding an energy shift of the atomic energy levels that coincides exactly with that obtained when using the vacuum fluctuations argument. A similar reasoning can be applied to Casimir-Polder forces. The Lamb shift and Casimir-Polder forces can thus be deduced with equal forcefulness by two completely different methods : as a consequence of vacuum fluctuations or of a radiation reaction field. Yet again, we are confronted with a deep-rooted example of complementarity in the quantum world where phenomena can be
