Whenever a quantum environment emerges as a classical system, it behaves like a measuring apparatus

There exist two closely-related questions about the quantum mechanical nature of our universe that keep being intriguing after decades of thought processing: how is it that we do not experience state superpositions, and why we cannot even see them when observing quantum systems. As for the latter question, it is somehow assumed that this is due to the continual measurement process acted upon by the environment. However, despite often being considered as an acceptable answer, this argument is not a formal result, and attempts to make it such have been only recently proposed. In fact, the current analysis of the quantum measurement process, its Hamiltonian description, as well as its characterization in the framework of the open quantum systems (OQS) dynamics has revealed the qualitative nature of the above argument, thus making it ever more urgent to develop a rigorous approach to the original question. This is the main goal of our work, where we consider a quantum principal system ?, with an environment ? made of N elementary quantum components. By using properties of generalized coherent states for the environment we demonstrate that whenever ? behaves according to an effective classical theory such theory emerges from the quantum description of a measuring apparatus in the large-N limit, regardless of the actual interaction between ? and ?. In fact, we show how to construct a Hamiltonian model for the dynamical process that rules the coexistence of any two quantum systems whenever one of them is macroscopic and behaves classically. This result wears two hats: on the one hand it clarifies the physical origin of the formal statement that, under certain conditions, any channel from ?? to ?? takes the form of a measure-and-prepare map; on the other hand, it formalizes the qualitative argument that the reason why we do not observe state superpositions is the continual measurement performed by the environment