2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/91719Relying on the variational principle, it is proved that new contradictions emerge from an analysis of the Lagrangian density of the Klein-Gordon field: normalization problems arise and interaction with external electromagnetic fields cannot take place. By contrast, the Dirac equation is free of these problems. Other inconsistencies arise if the Klein-Gordon field is regarded as a classical field.11 pages, 0 figuresQuantum Physicstext