# What is entropy?

• (noun): (communication theory) a numerical measure of the uncertainty of an outcome.
Synonyms: information, selective information

## Entropy

Entropy is a thermodynamic property that is the measure of a system’s thermal energy per unit temperature that is unavailable for doing useful work. Perhaps the most familiar manifestation of entropy is that, following the laws of thermodynamics, entropy of a closed system always increases and in heat transfer situations, heat energy is transferred from higher temperature components to lower temperature components. In thermally isolated systems, entropy runs in one direction only (it is not a reversible process). One can measure the entropy of a system to determine the energy not available for work in a thermodynamic process, such as energy conversion, engines, or machines. Such processes and devices can only be driven by convertible energy, and have a theoretical maximum efficiency when converting energy to work. During this work, entropy accumulates in the system, which then dissipates in the form of waste heat.

### Some articles on entropy:

Configuration Entropy - Calculation
... The configurational entropy is related to the number of possible configurations by Boltzmann's entropy formula where kB is the Boltzmann constant and W is the number of ... be in states n with probabilities Pn, the configurational entropy of the system is given by which in the perfect disorder limit (all Pn = 1/W) leads to Boltzmann's ... This formulation is analogous to that of Shannon's information entropy ...
Logrithm - Applications - Entropy and Chaos
... Entropy is broadly a measure of the disorder of some system ... In statistical thermodynamics, the entropy S of some physical system is defined as The sum is over all possible states i of the system in question, such ... Similarly, entropy in information theory measures the quantity of information ...
Streaming Algorithm - Some Streaming Problems - Entropy
... The (empirical) entropy of a set of frequencies is defined as , where. ...
Configuration Entropy
... In statistical mechanics, configuration entropy is the portion of a system's entropy that is related to the position of its constituent particles rather than to their velocity or momentum ... The configurational entropy is also known as microscopic entropy or conformational entropy in the study of macromolecules ... In general, configurational entropy is the foundation of statistical thermodynamics ...
Interdisciplinary Applications of Entropy - Science Fiction About Entropy
... with and potentially reverse the process of entropy ... people asks a super-computer named AC(Multivacs) again and again" How can the net amount of entropy of the universe be massively decreased?" Each time AC's ... AC discovers the answer and decides to show it by demonstrating the reversal of entropy "And AC said"LET THERE BE LIGHT!" And there was light." ...

### More definitions of "entropy":

• (noun): (thermodynamics) a thermodynamic quantity representing the amount of energy in a system that is no longer available for doing mechanical work.
Example: "Entropy increases as matter and energy in the universe degrade to an ultimate state of inert uniformity"
Synonyms: randomness, S

### Famous quotes containing the word entropy:

Just as the constant increase of entropy is the basic law of the universe, so it is the basic law of life to be ever more highly structured and to struggle against entropy.
Václav Havel (b. 1936)