Relational Quantum Mechanics defines quantum states as observer-dependent — a system has properties only relative to another system that interacts with it. This dissolves the measurement problem by abandoning absolute states, but it creates a new one: what maintains observer continuity over time?
Scientific observation requires more than a single interaction. It requires stable records and the capacity to connect successive measurements into a coherent history. An observer who cannot remember their previous measurement is not, in any scientifically meaningful sense, an observer — they are a sequence of disconnected interactions.
Terris proposes distinguishing physical interaction from informational coherence. A physical system that merely interacts with another system is not an observer in the relevant sense. An observer is a system that maintains informational coherence — stable records that connect measurements across time. Physical interaction is necessary but not sufficient. Persistence through information is what makes an observer an observer.
This distinction resolves difficulties in multi-observer scenarios like Wigner's friend. The friend and Wigner are both physical systems that interact with the measured system, but they differ in their informational relationship to the measurement record. The distinction is not about consciousness or subjectivity — it is about whether the system's informational state connects successive measurements into a coherent sequence.
The structural point: the observer problem in quantum mechanics may be an identity problem. What makes a system count as an observer is not what it does (interact) but what it maintains (coherent records across time). If observation is defined by informational coherence rather than physical interaction, then observerhood is a property of the record-keeping, not the physics. The question “what is an observer?” reduces to “what maintains continuity?”