  The mystery that the real scalar Klein-Gordon field has vanishing current
densities is resolved. The scalar field is shown to be a complex field due to
the condition of possessing a proper non-relativistic limit. Like the
Schr\"odinger field, one component complex Klein-Gordon field corresponds to a
boson with one flavor, and therefore there exists no physical real scalar
field. As a good example, we present the Schwinger model Hamiltonian which is
naturally described by the complex scalar field with one flavor. The
non-existence of the real scalar field indicates that the Higgs mechanism
should be reconsidered.
