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Physical system
Portion of the universe chosen for analysis / From Wikipedia, the free encyclopedia
A physical system is a collection of physical objects under study.[1] The collection differs from a set: all the objects must coexist and have some physical relationship.[2] In other words, it is a portion of the physical universe chosen for analysis. Everything outside the system is known as the environment, which is ignored except for its effects on the system.
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The split between system and environment is the analyst's choice, generally made to simplify the analysis. For example, the water in a lake, the water in half of a lake, or an individual molecule of water in the lake can each be considered a physical system. An isolated system is one that has negligible interaction with its environment. Often a system in this sense is chosen to correspond to the more usual meaning of system, such as a particular machine.
In the study of quantum coherence, the "system" may refer to the microscopic properties of an object (e.g. the mean of a pendulum bob), while the relevant "environment" may be the internal degrees of freedom, described classically by the pendulum's thermal vibrations. Because no quantum system is completely isolated from its surroundings,[3] it is important to develop a theoretical framework for treating these interactions in order to obtain an accurate understanding of quantum systems.
In control theory, a physical system being controlled (a "controlled system") is called a "plant".