  Position and momentum observables are considered and their correlation is
studied for the simplest quantum system of a free particle moving in one
dimension. The algebra and the eigenvalue problem for the correlation
observable is presented and its possible relevance for the solution of the
Pauli problem is analysed. The correlation provides a simple explanation of the
shrinking and spreading of wave packets in an interpretation of quantum
mechanics based in an ontology suggested by quantum field theory. Several
properties and speculations concerning position-momentum correlations are
mentioned.
