With the help of an analogy with a double-slit experiment, it is shown that
the standard method of calculation of the rate of an interaction process by
adding the rates of production of all the allowed final states, regardless of a
possible coherence among them, is correct. It is a consequence of causality.
The claims that the GSI time anomaly is due to the mixing of neutrinos in the
final state of the electron-capture process are refuted. It is shown that the
GSI time anomaly may be due to quantum beats due to the existence of two
coherent energy levels of the decaying ion with an extremely small energy
splitting (about 10^{-15} eV) and relative probabilities having a ratio of
about 1/99.Comment: 7 page