Abstract. The linearity of quantum mechanical wave equations (Schrödinger equation as well as Dirac equation) has been considered as an argument that there can be no deterministic mechanism like a susceptibility to initial conditions behind the apparent quantum indeterminacy and it is generally assumed that this indeterminacy is fundamental. In 1927 Fermi developed a model where he took radiation reaction force due to the oscillations in charge density distribution in nonstationary states as a nonlinear term into the account. Similar semiclassical theories were developed in 1970's Although such models are insufficient in describing the interaction of radiation with matter when compared with quantum electrodynamics(QED) they contain important clues how susceptibility to initial conditions of a certain degree and a related quasi-indeterminacy may emerge as a consequence.

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