  In recent decades it was established that the quantum measurements of
physical quantities in space-time points divided by space-like intervals may be
correlated. Though such correlation follows from the formulas of quantum
mechanics its physics so far remains unclear and there is a number of different
and rather contradictory interpretations. They concern particularly the
so-called Einstein-Podolsky-Rosen paradox where the momentary action at a
distance together with non-local entangled states is used for the
interpretation.
  We assume that the quantum theory can be formulated as local and look for the
consequences of this assumption. Accordingly we try to explain the correlation
phenomena in a local way looking for the origin of correlation. To exclude a
presupposed correlation of participating quantum particles we consider two
independent particle sources and two detectors that are independent as well. We
show that the origin of the correlation is the feature that the occupation
number of a particle (and other its measurable quantities) is formed by a pair
of complex conjugated wave functions with in general arbitrary phases. We
consider this point as crucial as it provides interpretation of the observed
correlation phenomena that may otherwise look puzzling.
  We briefly discuss a special type of noise that is typical for the quantum
correlation phenomena.
