X-Nico

Closed system

In nonrelativistic classical mechanics, a closed system is a physical system which doesn't exchange any matter with its surroundings, and isn't subject to any force whose source is external to the system.

Philosophy of thermal and statistical physics

This law follows simply from statistics: if a physical system is given (is allowed to occupy) new energy states which are equivalent to the existing states (say, a gas is expanding into a larger volume), then the system will occupy "new" states on equal footing with the existing ("old") ones.

see also

Entropy in thermodynamics and information theory

There are close parallels between the mathematical expressions for the thermodynamic entropy, usually denoted by S, of a physical system in the statistical thermodynamics established by Ludwig Boltzmann and J. Willard Gibbs in the 1870s, and the information-theoretic entropy, usually expressed as H, of Claude Shannon and Ralph Hartley developed in the 1940s.

Maupertuis' principle

In classical mechanics, Maupertuis' principle (named after Pierre Louis Maupertuis), is that the path followed by a physical system is the one of least length (with a suitable interpretation of path and length).

Quantum reference frame

It, like any reference frame, is a physical system which defines physical quantities, such as time, position, momentum, spin, and so on.

Theory of Dynamic Interactions

Dynamics is the part of classical mechanics that describes the evolution in time of a physical system in relation to the causes that provoke the changes of physical state and/or movement.

Zero energy

Zero-point energy, the lowest possible energy that a quantum mechanical physical system may have