A question I'm sure I've seen asked here and/or elsewhere is why there doesn't seem to be any classical force corresponding to the weak interaction. I came up with the following, and am wondering whether this seems correct and satisfying to others. Basically, being able to write down a Lagrangian density isn't the same thing as being able to describe the classical theory that is the counterpart of a quantized system. In particular, it seems like this can't possibly work for unstable particles. For example, the Lagrangian density for muon decay has a constant in it, GF, the Fermi coupling constant. The half-life of the muon goes like [itex]h/G_F^2[/itex]. In the classical limit, the half-life goes to zero, so the classical theory of muons is a theory with no muons in it.