  As currently understood since its discovery, the bare Klein-Gordon theory
consists of negative quantum probabilities which are considered to be
physically meaningless if not outright obsolete. Despite this annoying setback,
these negative probabilities are what led the great Paul Dirac in 1928 to the
esoteric discovery of the Dirac Equation. The Dirac Equation led to one of the
greatest advances in our understanding of the physical world. In this reading,
we ask the seemingly senseless question, "Do negative probabilities exist in
quantum mechanics?" In an effort to answer this question, we arrive at the
conclusion that depending on the choice one makes of the quantum probability
current, one will obtain negative probabilities. We thus propose a new quantum
probability current of the Klein-Gordon theory. This quantum probability
current leads directly to positive definite quantum probabilities. Because
these negative probabilities are in the bare Klein-Gordon theory, intrinsically
a result of negative energies, the fact that we here arrive at a theory with
positive probabilities, means that negative energy particles are not to be
considered problematic as is the case in the bare Klein-Gordon theory. From an
abstract-objective stand-point; in comparison with positive energy particles,
the corollary is that negative energy particles should have equal chances to
exist. As to why these negative energy particles do not exist, this is
analogous to asking why is it that Dirac's antimatter does not exist in equal
proportions with matter. This problem of why negative energy particles do not
exist in equal proportions with positive energy particles is a problem that
needs to be solved by a future theory.
