2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/92355The Dirac equation is compared with the Klein-Gordon one. Unlike the Dirac case, it is proved that the Klein-Gordon equation has problems with the Hamiltonian operator of the Schroedinger picture. A special discussion of the Pauli-Weisskopf article and that of Feshbach-Villars proves that their theories of a charged Klein-Gordon particle lack a self consistent expression for this Hamiltonian. Related difficulties are pointed out.13 pages, 0 figuresQuantum Physicstext