The fundamental problem considered is that of the existence of a joint probability distribution for momentum and position at a given instant. The philosophical interest of this problem is that for the potential energy functions (or Hamiltonians) corresponding to many simple experimental situations, the joint "distribution" derived by the methods of Wigner and Moyal is not a genuine probability distribution at all. The implications of these results for the interpretation of the Heisenberg uncertainty principle are analyzed. The final section consists (...) of some observations concerning the axiomatic foundations of quantum mechanics. (shrink)

We prove the existence of hidden variables, or, what we call generalized common causes, for finite sequences of pairwise correlated random variables that do not have a joint probability distribution. The hidden variables constructed have upper probability distributions that are nonmonotonic. The theorem applies directly to quantum mechanical correlations that do not satisfy the Bell inequalities.

The program of a physical concept of information is outlined in the framework of quantum theory. A proposal is made for how to avoid the intuitive introduction of observables. The conventional and the Everett interpretations in principle may lead to different dynamical consequences. An ensemble description occurs without the introduction of an abstract concept of information.