# Entropy vs. Atrophy

## Difference Between Entropy and Atrophy

#### Entropynoun

strictly thermodynamic entropy. A measure of the amount of energy in a physical system that cannot be used to do work.

*The thermodynamic free energy is the amount of work that a thermodynamic system can perform; it is the internal energy of a system minus the amount of energy that cannot be used to perform work. That unusable energy is given by the entropy of a system multiplied by the temperature of the system.*

^{[http://en.wikipedia.org/wiki/Thermodynamic_free_energy]}(Note that, for both Gibbs and Helmholtz free energies, temperature is assumed to be fixed, so entropy is effectively directly proportional to useless energy.)#### Atrophynoun

(pathology) A reduction in the functionality of an organ caused by disease, injury or lack of use.

#### Entropynoun

A measure of the disorder present in a system.

*Ludwig Boltzmann defined entropy as being directly proportional to the natural logarithm of the number of microstates yielding an equivalent thermodynamic macrostate (with the eponymous constant of proportionality). Assuming (by the fundamental postulate of statistical mechanics), that all microstates are equally probable, this means, on the one hand, that macrostates with higher entropy are more probable, and on the other hand, that for such macrostates, the quantity of information required to describe a particular one of its microstates will be higher. That is, the Shannon entropy of a macrostate would be directly proportional to the logarithm of the number of equivalent microstates (making it up). In other words, thermodynamic and informational entropies are rather compatible, which shouldn't be surprising since Claude Shannon derived the notation 'H' for information entropy from Boltzmann's H-theorem.*

#### Atrophyverb

(intransitive) To wither or waste away.

#### Entropynoun

The capacity factor for thermal energy that is hidden with respect to temperature [http://arxiv.org/pdf/physics/0004055].

#### Atrophyverb

(transitive) To cause to waste away or become abortive; to starve or weaken.

#### Entropynoun

The dispersal of energy; how much energy is spread out in a process, or how widely spread out it becomes, at a specific temperature. [https://web.archive.org/web/20060702234316/http://www.entropysite.com/students_approach.html]

#### Atrophynoun

a decrease in size of an organ caused by disease or disuse

#### Entropynoun

A measure of the amount of information and noise present in a signal.

#### Atrophynoun

any weakening or degeneration (especially through lack of use)

#### Entropynoun

(uncountable) The tendency of a system that is left to itself to descend into chaos.

#### Atrophyverb

undergo atrophy;

*Muscles that are not used will atrophy*

#### Entropynoun

(communication theory) a numerical measure of the uncertainty of an outcome;

*the signal contained thousands of bits of information*

#### Entropynoun

(thermodynamics) a thermodynamic quantity representing the amount of energy in a system that is no longer available for doing mechanical work;

*entropy increases as matter and energy in the universe degrade to an ultimate state of inert uniformity*