observers

An observer is an entity that perceives, monitors, or records information about a system, event, or phenomenon. Observers can be people, measuring instruments, software agents, or other processes that acquire data and report it for analysis.

In science, observation is a core method. An observer gathers measurements such as position, time, intensity, or state. In physics, observers are often described by reference frames; different observers may disagree on measurements due to relativity. In quantum mechanics, observation is linked to measurement, and the act of observing can influence the system, a notion known as the observer effect; however, the precise mechanism remains debated and depends on interpretation.

In computer science, the Observer pattern is a design where objects (observers) subscribe to a subject to receive notifications of state changes. This decouples data producers from consumers. Observers are also used in monitoring systems to track performance and health of software and hardware.

In research methods, naturalistic observation and participant observation involve watching subjects in their natural environment. Researchers must address observer bias and reliability, using practices such as inter-observer agreement and standardized protocols to ensure data quality.

The term is used across disciplines, from meteorological weather observers to astronomers recording celestial events. The concept of an observer emphasizes the role of perception and measurement in understanding complex systems.