This paper considers states on the Weyl algebra of the canonical commutation relations over the phase space R 2n . We show that a state is regular iff its classical limit is a countably additive Borel probability measure on R 2n . It follows that one can "reduce" the state space of the Weyl algebra by altering the collection of quantum mechanical observables so that all states are ones whose classical limit is physical. lemmas to characterize the countably additive Borel measures on R 2n in terms of algebraic structure, and I apply Thm. 1 to the purely classical system with phase space R 2n . Finally, in Section V, I prove the main result and discuss its significance. The results of this paper involve little, if any, mathematical novelty. I hope, however, that the perspective I provide on the construction of new quantum theories is of interest.
II. PRELIMINARIESThe Weyl algebra over R 2n is formed by deforming the product of the C*-algebra AP (R 2n ) of complex-valued almost periodic functions on R 2n . The C*-algebra AP (R 2n ) is generatedfor all y ∈ R 2n , where · is the standard inner product on R 2n . Polynomials (with respect to pointwise multiplication, addition, and complex conjugation) of functions of the form W 0 (x) for x ∈ R 2n are norm dense in AP (R 2n ) with respect to the standard supremum norm. 59The Weyl algebra over R 2n , denoted W h (R 2n ), for h ∈ (0, 1] is generated from the same set of functions by defining a new multiplication operation. The symbol W h (x) ∈ W h (R 2n ) is used now to denote the element W 0 (x) as it is considered in the new C*-algebra. Define the non-commutative multiplication operation on W h (R 2n ) by W h (x)W h (y) := e ih 2 σ(x,y) W h (x + y)for all x, y ∈ R 2n , where σ is the standard symplectic form on R 2n given byfor a, b, a ′ , b ′ ∈ R n and · is now the standard inner product on R n . The Weyl algebra is the norm completion in the minimal regular norm 9,51,66 of polynomials of elements of the form W h (x) for x ∈ R 2n with respect to the non-commutative multiplication operation.It is this C*-algebra (sometimes known as the CCR algebra, or the Weyl form of the CCRs) that is often used to model the physical magnitudes, or observables, of a quantum mechanical system constructed from a classical system with phase space R 2n . One can then take the positive, normalized linear functionals, or states, on the C*-algebra of physical magnitudes to model the physically realizable states of the quantum system. 11,12,34,38