I've been thinking to myself and being unable to get to talk to a Professor in Maynooth (due to being ignored) I was wondering if anybody here could help me.
Is this the main incompatibility between QM and General Relativity:
({} indicates subscript)
A property of Quantum Field theory in Minkowski space-time is that the field operator, which corresponds to an integer-spin classical field, evaluated at spacelike related points must commute with itself.
Since Relativity can be seen as a spin-2 self-interacting field, by anology with with flat-spacetime Quantum theories it would be natural to expect the metric field operator g{ab}to satisfy the commution relation:
[g{ab}(x),g{cd}(x')] = 0
for x and x' being spacelike related
However if we do not know the metric, we cannot say that the above equation is valid and if valid must hold independently of the metric's value.
i.e.,causality is ill-defined if the notion of a classical spacetime metric is abandoned.
In other words a fundamental result which seems to hold for all QFT is non-applicable to General Relativity.
Insert phrase said by somebody else.
  