  From the ancient Einstein-Podolsky-Rosen paradox to the recent Sorkin-type
impossible measurements problem, the contradictions between relativistic
causality, quantum non-locality, and quantum measurement have persisted. Based
on quantum field theory, our work provides a framework that harmoniously
integrates these three aspects. This framework consists of causality expressed
by reduced density matrices and an interpretation of quantum mechanics that
considers quantum mechanics to be complete. Specifically, we use reduced
density matrices to represent the local information of the quantum state and
show that the reduced density matrices cannot evolve superluminally. Unlike
recent approaches that focus on causality by introducing new operators to
describe detectors, we consider that everything--including detectors,
environments, and humans--is composed of the same fundamental fields, which
prompts us to question the validity of the derivation of Schrodinger's cat
paradox and leads us to propose an interpretation of quantum mechanics that
does not require any additional assumptions and is compatible with relativity.
