Schrodinger's cat and the clock: lessons for quantum gravity

I review basic principles of the quantum mechanical measurement process in view of their implications for a quantum theory of general relativity. It turns out that a clock as an external classical device associated with the observer plays an essential role. This leads me to postulate a 'principle of the integrity of the observer'. It essentially requires the observer to be part of a classical domain connected throughout the measurement process. Mathematically this naturally leads to a formulation of quantum mechanics as a kind of topological quantum field theory. Significantly, quantities with a direct interpretation in terms of a measurement process are associated only with amplitudes for connected boundaries of compact regions of spacetime. I discuss some implications of my proposal such as in-out duality for states, delocalization of the 'collapse of the wavefunction' and locality of the description. Differences to existing approaches to quantum gravity are also highlighted.