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Nuclear super-allowed $\beta$ decay has been used to obtain tight limits onthe value of the CKM matrix element $V_{ud}$ that is important for unitaritytests, and therefore important for tests of the standard model. Currentrequirements on precision are so intense that effects formerly thought toosmall to matter are now relevant. This article is a brief review of personalefforts to include the effects of strong interactions on Fermi $\beta $ decay.First I examine the role of isospin violation in the decay of the neutron. Thesize of the necessary correction depends upon detailed strong-interactiondynamics. The isospin violating parts of the nucleon wave function, importantat the low energy of $\beta$ decay, can be constrained by data taken at muchhigher energies, via measurements, for example, of $ed\to e'\pi^\pm +\rm X $reactions at Jefferson Laboratory. The next focus is on the role of nuclearshort-ranged correlations, which affect the value of the correction needed toaccount for isospin violation in extracting the value of $V_{ud}$. The netresult is that effects previously considered as irrelevant have become relevantfor both neutron and nuclear $\beta$ decay.

Strong Interaction Dynamics and Fermi $\beta$ decay in the nucleon and the nucleus