Can spacetime collapse a wavefunction?

Hi,
I beleive that the effect of general diffeomorphisms of a spacetime
over which a quantum field is defined is strictly unitary on the
quantum field. You can't use spacetime to collapse a wave function.
Below is a little explanation of why. Does anyone know exactly how to
identify transforamtions of a quantum system or field with
diffeomorphisms of the spacetime over which it is defined?
I have been wondering about how diffeomorphisms affect quantum fields
and quantum systems without departing into quantum gravity. I imagine
a flat minkowski background in which is embedded some quantum process,
perhaps mapped out by feynman diagram, or perhaps just a quantum system
evolving according to some hamiltonian. Now imagine a diffeomorphism
applied to the background. This diffeomorphism should affect the
quantum field, interaction or system. One might imagine a conformal
expansion of the spacetime that is faster than the speed of light,
separating two entangled particles in such a way that they cannot
communicate and are essentially isolated from one another. It is
standard practice that one traces out one of the systems. This assumes
that the diffeomorphism is having a non unitary effect. It is this
point that I think is ad hoc and false. In other words, I believe that
all diffeomorphisms will induce only unitary transformations. The
reason is that the set of observables is diffeomorphism invariant. If
you know about superoperators, you know that in order to perform a non
unitary transformation one essentially increases the size of the
hilbert space, entangles and then traces out the extra stuff, sort of.
However, if the observables are diffeomorphism invariant, where did
this extra bit come from?

.

Relevant Pages