In Physical, the term system has a technical significance with the direction where it is identified with part of the selected Univers physical for the analysis. Any thing apart from the system is called environment and is not taken into account in the analysis except for its influence on the system. Separation system/environment is arbitrary and is generally made in order to simplify the analysis as well as possible. A system is known as insulated if it can exchange neither energy nor matter with outside, closed if it can exchange energy (and only of energy) with open outside and if it can exchange matter and energy with outside.
Generally a physical system is selected to correspond as well as possible to what is called usually Système, that is to say for example a particular machine in macroscopic thermodynamics, or a reactional medium in Thermochimie. But the physical systems can be very varied: an atom, the water of a lake or water in a half of the known as lake can be studied like physical systems. In the study of the quantum Décohérence, the “system” will be able to refer to the macroscopic properties of an object (for example the position of a heavy pendulum) while “the environment” corresponding will be able to represent its internal degrees of freedom, described classically by the thermal vibrations of the known as system (for example in the case of a solid vibrations of Phonon S).
Complexity of the physical systems
The Complexité of a physical system is equal to its probability of being described by a Vecteur of particular state, i.e. to be described by a whole of physical sizes caractéristiques.
Thus, if one considers the situation of a Newtonian ball among a whole of mobile physical objects rebounding on the walls of a container, the probability of state of the system does not vary during time. The Entropie varies but not the probability of the vector of state, which it is possible to evaluate périodiquement.
In a physical system, a vector of state of weak probability self-sustained is equivalent to a strong complexity. A vector of self-sustained state of weak probability makes it possible the physical system to remain with an high level of complexity. The study of such physical systems applied to our universe in remainder still with the premises of research, and is speculative by nature, but it appears that there exist systems with weak probabilities which are able car-to discuss. One speaks then about Métastabilité.
In the mathematical systems (abstract), one can more easily consider complexity relative in particular states. For example, if one considers a Machine of Turing which generates random symbols and then uses them like algorithm to create new series of symbols, the complexity of the final symbol string is almost mathematically equivalent to the minimal size of the necessary chain to produce a longer chain as defined by the algorithmic Information theory.
- Conceptual vs Physical Systems
- Research in simulation and modeling off various physical systems
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