A possible inconsistency in the renormalization procedure that appears at very high energies in quantum electrodynamics (QED) and other quantum field theories in which there is not asymptotic freedom. It was shown in the mid-1950s by Lev Davidovich Landau and others, using approximation techniques, that in the limit of extremely high energies the relation between the unrenormalized and actual electric charges is such that the observed charge should fall to zero, thus making the procedure of renormalization impossible. This difficulty is called the Landau ghost (or sometimes the Moscow zero). It has not been established whether or not it is true in general, for the consistency of QED. This difficulty is theoretical rather than practical for QED as, at the energies at which the problem arises, electromagnetic interactions are thought to unify with weak interactions and strong interactions. The opposite situation to the Landau ghost is asymptotic freedom, which occurs in quantum chromodynamics.