Correlation between Measurements in Quantum Theory

An attempt to extend the postulational basis of quantum theory by introducing correlations between the results of measurements, developed in this article, leads to negative joint probabilities for otherwise meaningful sets of measured values. Since, so far as can be seen, the attempt made is the only one compatible with the theory of random variables, and is incompatible with the structure of Hilbert space, we conclude that correlations are absent. This result, though it is tantamount to a denial of von Neumann's projection postulate and the “reduction of wave packets” on measurement, is nevertheless shown to be entirely satisfactory from the physical point of view.