Does Decoherence Theory Imply the Existence of Hidden Variables?

Relying on decoherence theory, I present arguments in favor of the existence of hidden variables. Specifically, I examine, first, a system in a pure state whose subsystem is in a mixed state and, second, a setting in which the state-vector assignment may depend on the experimental context. It is well known that any viable hidden-variable theory must be nonlocal and contextual. Building on contextuality, I conjecture that certain systems are non-detectable, and I use this conjecture to formulate hypotheses about the nature of dark matter and dark energy.