Entropy, in thermodynamics, is a property originally introduced to explain the part of the internal energy of a thermodynamic system that is unavailable as a source for useful work.

Look up entropy in Wiktionary, the free dictionary.

Entropy may also refer to:

• Entropy (classical thermodynamics), thermodynamic entropy in macroscopic terms, with less emphasis on the statistical explanation
  • Entropic force. The product of temperature and the gradient of the entropy density is viewed an effective force, yielding a gradient in the energy density of a system.
  • Entropy production. Development of entropy in a thermodynamic system.
• Entropy (statistical thermodynamics), the statistical explanation of thermodynamic entropy based on probability theory
  • Configuration entropy, the entropy change due to a change in the knowledge of the position of particles, rather than their momentum
  • Conformational entropy, the entropy change due to a change in the "configuration" of a particle (e.g. a right-handed vs. a left-handed polyatomic molecule)
• Tsallis entropy, a generalization of Boltzmann-Gibbs entropy
• von Neumann entropy, entropy in quantum statistical physics and quantum information science

• Entropy (information theory), also called Shannon entropy, a measure of the unpredictability or information content of a message source
• Differential entropy, a generalization of Entropy (information theory) to continuous random variables
  • Entropy of entanglement, related to the Shannon and von Neumann entropies for entangled systems; reflecting the degree of entanglement of subsystems
• Algorithmic entropy an (incomputable) measure of the information content of a particular message
• Rényi entropy, a family of diversity measures generalising Shannon entropy; used to define fractal dimensions
• Measure theoretic entropy, a measure of exponential growth in dynamical systems; equivalent to the rate of increase of Shannon entropy of a trajectory in trajectory-space
• Topological entropy, a measure of exponential growth in dynamical systems; equivalent to the rate of increase of α->0 Renyi entropy of a trajectory in trajectory-space.
• Topological entropy in physics
• Volume entropy, a Riemannian invariant measuring the exponential rate of volume growth of a Riemannian metric
• Maximum entropy (disambiguation)
• Graph entropy, a measure of the information rate achievable by communicating symbols over a channel in which certain pairs of values may be confused.

• Entropy encoding, data compression strategies to produce a code length equal to the entropy of a message
• Entropy (computing), an indicator of the number of random bits available to seed cryptography systems
• Entropy (anesthesiology), a measure of a patient's cortical function, based on the mathematical entropy of EEG signals
• Entropy (ecology), measures of biodiversity in the study of biological ecology, based on Shannon and Rényi entropies
• Social entropy, a measure of the natural decay within a social system

• Entropy (choreography), the difference between a transcription and a performance

• Entropy (package manager), a Sabayon Linux package manager

• Information entropy, relating to disruptive actions taken in Internet vigilantism

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