the equations of quantum mechanics, when cast in terms of the variable that is really measured by a clock in the laboratory, will differ from the traditional Schrödinger description. Although this is an idea that arises naturally in ordinary quantum mechanics, it is of paramount importance when one is discussing quantum gravity. This is due to the fact that general relativity is a generally covariant theory where one needs to describe the evolution in a relational way. One ends up describing how certain objects change when other objects, taken as clocks, change. At the quantum level this relational description will compare the outcomes of measurements of quantum objects. Quantum gravity is expected to be of importance in regimes (e.g. near the big bang or a black hole singularity) in which the assumption of the presence of a classical clock is clearly unrealistic. The question therefore arises: is the difference between the idealized version of quantum mechanics and the real one just of interest in situations when quantum gravity is predominant, or does it have implications in other settings? We will argue that indeed it does have wider implications. Some of them are relevant to conceptual questions (e.g. the problem of 