Measurement is fundamentally relational. No quantity can be defined in isolation; it must be compared, exchanged, or detected through interaction.
These interactions occur at boundaries.
When light strikes a detector, when particles collide, or when fields interact with measurement instruments, information flows across an interface. Through these interactions, the observer gains access to properties of the system.
Because measurement occurs at boundaries, the surfaces separating systems become central to physical description. Boundaries determine how information is exchanged and how observable structure is encoded.
This perspective shifts attention away from volumes and toward interfaces, where information becomes accessible.
