  The vacuum expectation values (VEVs) of the field squared and energy-momentum
tensor for a massless scalar field are investigated in the Milne universe with
general number of spatial dimensions. The vacuum state depends on the choice of
the mode functions in the canonical quantization procedure and we assume that
the field is prepared in the conformal vacuum. As the first step an integral
representation for the difference of the Wightman functions corresponding to
the conformal and Minkowski vacua is derived. The mean field squared and
energy-momentum tensor are obtained in the coincidence limit. It is shown that
the Minkowski vacuum state is interpreted as a thermal one with respect to the
conformal vacuum. The thermal factor is of the Bose-Einstein type in odd
dimensional space and of the Fermi-Dirac type in even number of spatial
dimensions.
