  All differences between the role of space and time in nature are explained by
proposing the principles in which none of the spacetime coordinates has an {\it
a priori} special role. Spacetime is treated as a non-dynamical manifold, with
a fixed global $\mathbb{R}^D$ topology. Dynamical theory of gravity determines
only the metric tensor on a fixed manifold. All dynamics is treated as a Cauchy
problem, so it {\em follows} that one coordinate takes a special role. It is
proposed that {\em any} boundary condition that is finite everywhere leads to a
solution which is also finite everywhere. This explains the $(1,D-1)$ signature
of the metric, the boundedness of energy from below, the absence of tachyons,
and other related properties of nature. The time arrow is explained by
proposing that the boundary condition should be ordered. The quantization is
considered as a boundary condition for field operators. Only the physical
degrees of freedom are quantized.
