# Emergence of classicality and chaos from within quantum theory

*Fields: quantum foundations, many-body physics*

A question all approaches to quantum gravity face is: given the more fundamental quantum theory, how does the classical spacetime physics of general relativity emerge from it? More generally, even in quantum foundations the question of how classical physics emerges from within quantum theory is not settled. Despite the development of approaches such as decoherence, quantum Darwinism, coarse-grained measurement schemes and others, it remains an open problem, e.g., to fully explain the emergence of classical chaos from quantum theory. In particular, how do classical trajectories featuring a high sensitivity to initial values emerge from a quantum dynamics which a priori does not feature such sensitivity (e.g., due to uncertainties)? Sensitivity to initial values leads to an information generation: repeated coarse-grained phase space measurements give more and more precise information about the initial state. This property is crucial for characterizing classically chaotic dynamics (formalized through various entropies) and applies also to generally covariant systems.

We are currently working on a scheme to explain the emergence of such properties from within quantum theory.