# entropy

Pronunciation: say "EN-truh-pee" /ˈɛntɹəpi/

## Noun

1. The tendency of a system, when left to itself, to break down into chaos.
   - Simple: The way things fall into disorder and mess when no one looks after them.
   - _Left without maintenance, the abandoned rail line surrendered to entropy within a decade._
   - _Every organization fights entropy; without steady attention, its procedures drift into disarray._
2. In thermodynamics, a quantity measuring the disorder of a system, or how far its energy has spread out and is unavailable for doing useful work.
   - Simple: In physics, a measure of how disordered a system is, or how much of its energy has spread out and cannot work.
   - _Mixing two gases raises the total entropy, because the mixed state can be realized by vastly more microstates than the separated one._
   - _Statistical physicists calculate the entropy of a crystal by counting the microstates consistent with its measured energy._
3. In information theory, the average amount of information, or uncertainty, in each symbol or message a source produces, usually measured in bits.
   - Simple: In information science, a measure of how unpredictable a message is, which is also how much information it carries.
   - _Shannon defined the entropy of a source as the average information carried by each symbol it emits._
   - _Password strength is often estimated from the entropy of the process that generated the password._

## Origin

Attested in English by 1866, as a translation of German Entropie, coined in 1865 by Rudolph Clausius on the model of Energie (“energy”), replacing the root of Ancient Greek érgon (“work”) with Ancient Greek tropḗ (“transformation”).

Source: DictionaryAI, https://dictionaryai.com/define/entropy (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).