  It is a well known fact that quantum fields on Minkowski spacetime are
correlated for each pair of spacetime regions. In Robertson-Walker spacetimes
there are spacelike separated regions with disjoint past horizons but the
absence of correlations in that case was never proved. We derive in this paper
formulae for correlations of quantum fields on Robertson-Walker spacetimes.
Such correlations could have reasonably influenced the formation of structure
in the early universe. We use methods of algebraic and constructive quantum
field theory.
