  The conceptual setting of quantum mechanics is subject to an ongoing debate
from its beginnings until now. The consequences of the apparent differences
between quantum statistics and classical statistics range from the
philosophical interpretations to practical issues as quantum computing. In this
note we demonstrate how quantum mechanics can emerge from classical statistical
systems. We discuss conditions and circumstances for this to happen. Quantum
systems describe isolated subsystems of classical statistical systems with
infinitely many states. While infinitely many classical observables "measure"
properties of the subsystem and its environment, the state of the subsystem can
be characterized by the expectation values of only a few probabilistic
observables. They define a density matrix, and all the usual laws of quantum
mechanics follow. No concepts beyond classical statistics are needed for
quantum physics - the differences are only apparent and result from the
particularities of those classical statistical systems which admit a quantum
mechanical description. In particular, we show how the non-commuting properties
of quantum operators are associated to the use of conditional probabilities
within the classical system, and how a unitary time evolution reflects the
isolation of the subsystem.
