On the uniqueness of the Dirac theory in curved and flat spacetime

In this work a number of examples are used to illustrate uniqueness of physical prediction of the Dirac theory in a curved and a flat spacetime. Dirac Hamiltonians in arbitrary, including time‐dependent, gravitational fields uniquely determine physical characteristics of quantum‐mechanical systems irrespective of the choice of the tetrad fields. Direct spin‐rotation coupling that occurs with a certain choice of tetrads does not manifest itself in final physical characteristics of the systems and therefore does not represent a physically relevant effect.