Relational Quantum Mechanics

Relational quantum mechanics (RQM) is an interpretation of quantum mechanics developed by Carlo Rovelli in 1996, which holds that quantum states are not absolute but relational — a system's quantum state is only defined relative to another system that interacts with it. There is no view from nowhere; every description of a physical system is always a description from the perspective of another physical system. On this account, the measurement problem dissolves: 'collapse' is just the relational update of one system's state relative to another, and the question 'what really happened?' has no observer-independent answer. What makes RQM uncomfortable is also what makes it rigorous: it treats ontology as irreducibly perspectival, which conflicts with the physicist's instinct that the world must have a state that is not relative to anything. That instinct may simply be wrong.