 All approaches to the problem of quantum gravity agree that something must be said about the relationship between gravitation and quantized matter. These various approaches can be catalogued in various ways, depending on the relative weight assigned to general relativity and quantum field theory. Some approaches view general relativity as in need of correction and quantum field theory as generally applicable, while others view quantum field theory as problematic and general relativity as having a more universal status. Still others view the theories in a more even-handed manner, perhaps with both simply amounting to distinct limits of a deeper theory. It has often been suggested, since the earliest days of quantum gravity research, that bringing quantum field theory and general relativity together might serve to cure their respective singularity problems (the former resulting from bad high frequency behaviour of fields; the latter resulting from certain kinds of gravitational collapse). This hope does seem to have been borne out in many of the current approaches. Roger Penrose has even argued that the joint consideration of gravitation and quantum theory could resolve the infamous quantum measurement problem (see Penrose 2001; see also the section on the measurement problem in the entry on  philosophical issues in quantum theory).  The basic idea of Penrose’s proposal is fairly simple to grasp: when there is wave-packet spreading of the centre of mass of some body, there results a greater imprecision in the spacetime structure associated with the spreading wave-packet, and this destroys the coherence of the distant parts of the wave-function. There are difficulties in distinguishing the gravitationally induced collapse that Penrose proposes from the effective collapse induced by quantum theory itself, thanks to decoherence—Joy Christian (2005) has suggested that by observing oscillations in the flavor ratios of neutrinos originating at cosmological distances one could eliminate the confounding effects of environmental decoherence.