On the quantum foundations of the exponential decay law

Abstract

By assuming that in every actual decay process the unstable system is subject to repeated processes of measurement which ascertain whether the system is decayed or not, we prove that the decay law is exponential, obtaining a consistent reconciliation of the quantum and the classical statistical descriptions of decay experiments. We also show that the measurement process is a localization of the decay products and that, consequently, the unstable system is reduced to a unique quantum state. We are able to give, within the framework of ordinary quantum mechanics, a natural definition of the wave function of the unstable system.