  Classically general covariance is found from the idea that a vector is a
physical quantity which exists independently of choice of coordinate system and
is unchanged by a change of coordinate system. It is often assumed that there
exists some form of absolute mathematical space or space-time, and that in a
flat space approximation vectors can be imagined between defined points in this
space-time, much as we can imagine an arrowed line drawn on a piece of paper.
However, while classical vector quantities can be represented on paper, in the
quantum domain physical quantities do not in general exist with precise values
except in measurement; a change of apparatus, for example by rotating it, may
affect the outcome of the measurement, so the condition for general covariance
does not apply. The purpose of this paper is to re-examine covariance within
the context of an orthodox, Dirac-Von Neumann interpretation of quantum
mechanics, to replace it with a new condition, here called quantum covariance,
and to show that quantum covariance is the required condition for the
unification of general relativity with quantum mechanics for non-interacting
particles.
