  We consider particle creation (the Dynamical Casimir effect) in a uniformly
contracting ideal one-dimensional cavity non-perturbatively. The exact
expression for the energy spectrum of created particles is obtained and its
dependence on parameters of the problem is discussed. Unexpectedly, the number
of created particles depends on the duration of the cavity contracting
non-monotonously. This is explained by quantum interference of the events of
particle creation which are taking place only at the moments of acceleration
and deceleration of a boundary, while stable particle states exist (and thus no
particles are created) at the time of contracting.
