An '''Isolated system''', is a [[physical system]] thatdoesnot[[interaction|interact]]with its [[surroundings]]. Itobeysa number of [[conservation law]]s: itstotal[[energy]]and[[mass]]stayconstant. Theycannotenterorexit,butcanonlymovearoundinside. Anexampleisinthestudyof[[spacetime]],whereitisassumedthat[[asymptoticallyflat spacetime]]sexist.

+

A '''closed system''' or '''Isolated system''', is a [[system]] inthe"stateof being isolatedfrom its surrounding environment."<ref>[[Bela H. Banathy]] (1992). ''Asystemsview of education: conceptsandprinciplesforeffectivepractice''.p.184</ref>Thetermoftenreferstoanidealizedsysteminwhichclosure is perfect. Inrealitynosystemcanbecompletelyclosed;thereareonlyvaryingdegreesofclosure.

−

Truly isolated physical systems do not exist in reality, but real systems may behave nearly this way for finite (possibly very long) times. The concept of an isolated system can serve as a useful [[scientific modeling|model]] approximating many real-world situations. It is an acceptable [[idealization]] used in constructing [[mathematical model]]s of certain natural [[phenomenon|phenomena]]; e.g.,the [[Sun]] and [[planet]]s in our [[solar system]], and the [[proton]] and [[electron]] in a [[hydrogen atom]] are often treated as isolated systems. But from time to time, a hydrogen atom will [[absorption (optics)|interact]] with [[electromagnetic radiation]] and go to an [[excited state]].

+

Truly isolated physical systems do not exist in reality, but real systems may behave nearly this way for finite (possibly very long) times. The concept of an isolated system can serve as a useful [[scientific modeling|model]] approximating many real-world situations. It is an acceptable [[idealization]] used in constructing [[mathematical model]]s of certain natural [[phenomenon|phenomena]].

−

−

Another reason no system can be truly isolated is that even in [[Interstellar medium|interstellar space]], there is the [[Kelvin|2.7 K]] background [[black body|blackbody]] radiation left over from the [[Big Bang]]. This [[heat]] permeates every [[physical body]] in the [[Universe]].

−

−

In the attempt to justify the postulate of [[entropy]] increase in the [[second law of thermodynamics]], Boltzmann’s [[H-theorem]] used [[Ludwig Boltzmann#The Boltzmann equation|equations]] which assumed a system (e.g., a [[gas]]) was isolated: i.e., that all the mechanical [[Degrees of freedom (physics and chemistry)#Example: classical ideal diatomic gas|degrees of freedom]] could be specified, treating the walls simply as [[mirror]] [[boundary condition]]s. This inevitably lead to [[Loschmidt's paradox]]. However, if the [[stochastic]] behavior of the [[molecule]]s in actual walls is considered, along with the [[random]]izing effect of the ambient, background [[thermal radiation]], Boltzmann’s assumption of [[molecular chaos]] can be justified.

−

−

==Closed system==

−

−

By contrast, a '''closed (but not isolated) system''' can exchange [[heat]] and [[mechanical work|work]], but not [[matter]], with its surroundings. This is a basic concept in '''[[thermodynamics]]''', where it is assumed that a ''thermally'' isolated (insulated) system can be realized. It is a useful idealization, even if it can only be [[asymptote|asymptotically]] approximated.

==See also==

==See also==

−

* [[Dynamical system]]: Has components and/or flows that change over time.

* [[Dynamical system]]: Has components and/or flows that change over time.

+

* [[Glossary of systems theory]]

* [[Open system]]: Can be influenced by events outside of the actual or conceptual boundaries.

* [[Open system]]: Can be influenced by events outside of the actual or conceptual boundaries.

A closed system or Isolated system, is a system in the "state of being isolated from its surrounding environment."^{[1]} The term often refers to an idealized system in which closure is perfect. In reality no system can be completely closed; there are only varying degrees of closure.

Truly isolated physical systems do not exist in reality, but real systems may behave nearly this way for finite (possibly very long) times. The concept of an isolated system can serve as a useful model approximating many real-world situations. It is an acceptable idealization used in constructing mathematical models of certain natural phenomena.