renormalization ....
the polite way to say this is that one removes non-observable properties from a theory so that one can realistically interpret an experiment. since an electron's mass (which appears IN these theories) depends on its energy which depends on its (energetic) interaction with the particles in the vacuum, one can NEVER measure the "bare mass" of the electron ever. one can only observe the mass of the electron in the lab (via interaction) as it concurrently interacts with this vacuum. therefore clever summation techniques were developed so that all these vacuum interactions effects could be included (added up) in such a way as to connect the observable electron mass with the "true" electron mass appearing in various fundamental theories.
the summation techniques were developed in stages. first is a set of mathematical approximations which Feynmann and others did to first order to get sensible and ultimately very accurate results. renormalization is a procedure that ensures the summation process can be carried out to higher and higher orders of approximation. some theories give sensible results to first order, but cannot be renormalized. Freeman Dyson showed that quantum electrodynamics can be renormalized. 't Hooft and Veltman showed that electro-weak (electromagnetism plus the weak force) theory is renormalizable. there is no quantum gravity yet that is renormalizable, hence superstrings and all that kind of effort.
weird as all these summation efforts sound, the predictions which arise from them are incredibly accurate for quantum electrodynamics.
> Some features of the world revealed by physics simply have no corresponding or even
> analogous features in the 'visible' world which common language deals with.
for example, the "real", "true" electron mass, unaffected by any
interactions with anything.
at first sight, the math developed for renormalization doesn't have any inherent elegance. its not part of the fundamental structure of the theories. but it was developed as a sort of mopping up operation to make things clean, tidy and workable, to connect the theory WITH experiment.
this changed, as it's methods were extended into something called the renormalization group, which is now used in other branches of physics in an elegant fashion.
Les Schaffer