Observation

Observation in the natural sciences^[1] is an act or instance of noticing or perceiving ^[2] and the acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data via the use of scientific instruments. The term may also refer to any data collected during the scientific activity. Observations can be qualitative, that is, the absence or presence of a property is noted and the observed phenomenon described, or quantitative if a numerical value is attached to the observed phenomenon by counting or measuring.

For other uses, see Observation (disambiguation).

Relativity: In which deals with velocities close to the speed of light, it is found that different observers may observe different values for the length, time rates, mass, and many other properties of an object, depending on the observer's velocity relative to the object. For example, in the twin paradox one twin goes on a trip near the speed of light and comes home younger than the twin who stayed at home. This is not a paradox: time passes at a slower rate when measured from a frame moving concerning the object. In relativistic physics, an observation must always be qualified by specifying the state of motion of the observer, its reference frame.

relativistic physics

Quantum mechanics: In , which deals with the behavior of very small objects, it is not possible to observe a system without changing the system, and the "observer" must be considered part of the system being observed. In isolation, quantum objects are represented by a wave function which often exists in a superposition or mixture of different states. However, when an observation is made to determine the actual location or state of the object, it always finds the object in a single state, not a "mixture". The interaction of the observation process appears to "collapse" the wave function into a single state. So any interaction between an isolated wave function and the external world that results in this wave function collapse is called an observation or measurement, whether or not it is part of a deliberate observation process.

quantum mechanics

In some specific fields of science, the results of observation differ depending on factors that are not important in everyday observation. These are usually illustrated with apparent "paradoxes" in which an event appears different when observed from two different points of view, seeming to violate "common sense".