The basic operational devices in a particle theory are detectors which show that a particle is “here, now” rather than “there, then.” Successful operation of these devices requires a limiting velocity. Given auxiliary devices which can change particle velocities in both magnitude and direction, the Lorentz-invariant mass can be defined. The wave-particle duality operationally required to explain the scattering of particles from a diffraction grating then predicts fluctuations in particle number (the Wick-Yukawa mechanism), if we postulate a smallest mass. We (...) show that this suffices to establish the conventional quantum mechanical scattering formalism without postulating either “interactions” or “analyticity.” By introducing the phase change due to external electromagnetic fields, we can describe the auxiliary devices assumed above to an accuracy ofe 2/hc, thus completing the operational definition to that accuracy. (shrink)

We assume, in the first place, that two kinds of processes occur in nature: the strictly continuous and causal ones, which are governed by the Schrödinger equation and those implying discontinuities, which are ruled by probability laws. In the second place, we adopt a postulate ensuring the statistical sense of conservation laws. These hypotheses allow us to state a rule telling, in principle, in which situations and to which vectors the system's state can collapse, and which are the corresponding probabilities. (...) The way our proposed approach works is illustrated with some examples and with the analysis of the measurement problem. We obtain the exponential decay law. A comparison with other attempts to solve the measurement problem is performed. (shrink)