  The state vector evolution in the interaction of initial measured pure state
with collective quantum system or the field with a very large number of degrees
of freedom N is analysed in a nonperturbative QED formalism. As the example the
measurement of the electron final state scattered on nucleus or neutrino is
considered.In the nonperturbative field theory the complete manifold of the
system states is nonseparable i.e. is described by tensor product of infinitely
many independent Hilbert spaces. The interaction of this system with the
measured state can result in the final states which belong to different Hilbert
spaces which corresponds to different values of some classical observables,i.e.
spontaneous symmetry breaking occurs. Interference terms (IT) between such
states in the measurement of any Hermitian observable are infinitely small and
due to it the final pure states can't be distinguished from the mixed ones,
characteristic for the state collapse. The evolution from initial to final
system state is nonunitary and become formally irreversible in the limit of
infinite time. The electromagnetic (e-m) bremmstrahlung produced in the
electron scattering process contain the unrestricted number of soft photons
which radiation flux become classic observable. Analoguous processes which
occurs in the second kind phase transitions in ferromagnetic and phonon
excitations in cristall lattice are considered briefly.
