(RQM) is the most recent among the interpretations of quantum mechanics which are most discussed today. It was introduced in 1996, with quantum gravity as a remote motivation (Rovelli 1996); interests in it has slowly but steadily grown only in the last decades. RQM is essentially a refinement of the textbook “Copenhagen” interpretation, where the role of the Copenhagen observer is not limited to the classical world, but can instead be assumed by any physical system. RQM rejects an ontic construal of the wave function (more in general, of the quantum state): the wave function or the quantum state play only an auxiliary role, akin to the Hamilton-Jacobi function of classical mechanics. This does not imply the rejection of an ontological commitment: RQM is based on an ontology given by physical systems described by physical variables, as in classical mechanics. The difference with classical mechanics is that (a) variables take value only at interactions and (b) the values they take are only relative to the (other) system affected by the interaction. Here “relative” is in the same sense in which velocity is a property of a system relative to another system in classical mechanics. The world is therefore described by RQM as an evolving network of sparse relative events, described by punctual relative values of physical variables.
The physical assumption at the basis of RQM is the following postulate: The probability distribution for (future) values of variables relative to S ′ S′[/sup depend on (past) values of variables relative to S′[/sup but not on (past) values of variables relative to another system S″.
