In thermodynamics, an isolated system, as contrasted with a closed system, is a physical system that does not interact with its surroundings. It obeys a number of conservation laws: its total energy and mass stay constant. They cannot enter or exit, but can only move around inside. An example is in the study of spacetime, where it is assumed that asymptotically flat spacetimes exist. Thermodynamics (from the Greek thermos meaning heat and dynamis meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... In thermodynamics, a closed system, as contrasted with an isolated system, can exchange heat and work, but not matter, with its surroundings. ... A physical system is a system that is comprised of matter and energy. ... Interaction is a kind of action which occurs as two or more objects have an effect upon one another. ... In a thermodynamics problem, the surroundings, or environment, are anything not part of the system. ... In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves. ... Mass is a property of a physical object that quantifies the amount of matter and energy it contains. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... This article is in need of attention from an expert on the subject. ...

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; e.g., the Sun and planets 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 interact with electromagnetic radiation and go to an excited state. Scientific modeling is the process of generating abstract or conceptual models. ... Idealization is the process by which scientific models assume facts about the phenomenon being modeled that are certainly false. ... A mathematical model is an abstract model that uses mathematical language to describe the behaviour of a system. ... A phenomenon (plural: phenomena) is an observable event, especially something special (literally something that can be seen from the Greek word phainomenon = observable). ... The Sun is the star at the center of Earths solar system. ... A planet is generally considered to be a relatively large mass of accreted matter in orbit around a star. ... The solar system comprises the Earths Sun and the retinue of celestial objects gravitationally bound to it. ... In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ... A hydrogen atom is an atom of the chemical element hydrogen. ... Absorption, in optics, is the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electrons make a transition between two electronic energy levels. ... wave f[o[Image:Light-wave. ... It has been suggested that this article or section be merged with quantum state. ...

Another reason no system can be truly isolated is that even in interstellar space, there is the 2.7 K background blackbody radiation left over from the Big Bang. This heat permeates every physical body in the Universe. The distribution of ionized hydrogen (known by astronomers as H II (aitch two) from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible from the Earths northern hemisphere (from the Wisconsin H-Alpha Mapper Survey) In astronomy, the interstellar medium (or ISM) is the matter (interstellar... The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... According to the Big Bang theory, the universe emerged from an extremely dense and hot state (bottom). ... In physics, heat is defined as energy in transit. ... A physical body is an object which can be described by the theories of classical mechanics, or quantum mechanics, and experimented upon by physical instruments. ... The deepest visible-light image of the cosmos, the Hubble Ultra Deep Field. ...

In the attempt to justify the postulate of entropy increase in the second law of thermodynamics, Boltzmann’s H-theorem used equations which assumed a system (e.g., a gas) was isolated: i.e., that all the mechanical degrees of freedom could be specified, treating the walls simply as mirror boundary conditions. This inevitably lead to Loschmidt's paradox. However, if the stochastic behavior of the molecules in actual walls is considered, along with the randomizing effect of the ambient, background thermal radiation, Boltzmann’s assumption of molecular chaos can be justified. Ice melting - a classic example of entropy increasing Entropy is a concept in thermodynamics, statistical mechanics and information theory. ... The second law of thermodynamics states that The Second Law is a statistical law and thus applicable only to macroscopic systems. ... In thermodynamics, the H-theorem describes the increase of entropy of an ideal gas in an irreversible process, solving the Boltzmann equation. ... Ludwig Boltzmann Ludwig Eduard Boltzmann (Vienna, Austria-Hungary, February 20, 1844 – Duino near Trieste, September 5, 1906) is an Austrian physicist famous for his founding contributions in the fields of statistical mechanics and statistical thermodynamics. ... A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... // Degrees of freedom in mechanics In mechanics, for each particle belonging to a system, and for each independent direction in which movement is possible, two degrees of freedom, are defined, one describing the particles momentum in that direction, the other describing the particles position along an axis defined... A mirror is a surface with good specular reflection that is smooth enough to form an image. ... In mathematics, boundary conditions are imposed on the solutions of ordinary differential equations and partial differential equations, to fit the solutions to the actual problem. ... Loschmidts paradox states that if there is a motion of a system that leads to a steady decrease of H (increase of entropy) with time, then there is certainly another allowed state of motion of the system, found by time reversal, in which H must increase. ... Stochastic, from the Greek stochos or goal, means of, relating to, or characterized by conjecture; conjectural; random. ... In chemistry, a molecule is an aggregate of at least two atoms in a definite arrangement held together by special forces. ... In ordinary language, the word random is used to express apparent lack of purpose or cause. ... Thermal radiation is electromagnetic radiation from the surface of an object which is due to the objects temperature. ... In kinetic theory in physics, molecular chaos is the assumption that the velocities of colliding particles are uncorrelated, and independent of position. ...

See also

• Dynamical system: Has components and/or flows that change over time.
• Open system: Can be influenced by events outside of the actual or conceptual boundaries.