Summary
Relational quantum mechanics is a reading of quantum theory in which a physical system has no properties on its own, only relative to another system it interacts with. The physicist Carlo Rovelli proposed it in 1996. The comparison its proponents use is velocity, always the speed of one thing relative to another: on this reading the same holds for every quantity the theory describes. In Rovelli’s words, quantum mechanics is about the “physical description of physical systems relative to other systems”.
The ‘observer’ needn’t be a mind; any physical system will do. It is one of several competing interpretations, not settled physics, and Rovelli revised it in 2023.
Rationale
We keep this entry as an analogy, not evidence. Physics that finds properties only in relations echoes what Part 1 says of relational traditions, that nothing “exists independently”; it can’t tell us how cultures work.