On the unpredictability of quantum measurement outcomes

The paper addresses the issue of stochastic behavior in quantum systems. The causes of the unpredictability of measurement outcomes in quantum mechanics are analyzed. The fundamental postulate of quantum mechanics is formulated, and on its basis a clear and consistent general concept of measurements in quantum mechanics is developed. The principles of designing an instrument that operates in accordance with Bohr's postulates are outlined. A model of the corresponding measurement process is proposed in the simplest case of a spin 1/2 particle in a constant magnetic field. It is shown that there is no difference between the nature of the stochastic behavior of quantum and classical systems.