Quantum theory lives in abstract, infinite-dimensional, complex, linear Hilbert space, is unitary and non-dissipative, and has been proven not to be embeddable in spacetime for N 2 quantum entities. It is per definition unobservable (in itself). Classical physics describes the causal, nonlinear dynamics of actual events, which lie in, and also define, four-dimensional spacetime. The ``Born Rule" maps abstract quantum theory into events, i. e. real outcomes, in classical spacetime. It must be postulated separately and cannot be deduced from quantum theory, as it is both non-unitary and irreversible, i. e. dissipative. Hence, the ``Born Rule" is ultimately and fundamentally responsible for dissipation, i. e. friction, and therefore all evolving complex systems, in the classical, observable world.
Hansson et al. (Thu,) studied this question.