diff --git a/entropy.tex b/entropy.tex index c365ce3..900fb07 100644 --- a/entropy.tex +++ b/entropy.tex @@ -8,7 +8,8 @@ \usepackage{tikz} \usepackage{float} \usepackage{amsmath} -\PassOptionsToPackage{hyphens}{url}\usepackage{hyperref} % allows urls to follow line breaks of text +\PassOptionsToPackage{hyphens}{url} +\usepackage{hyperref} % allows urls to follow line breaks of text @@ -20,6 +21,30 @@ \begin{document} \maketitle \section{What is entropy?} +Across disciplines, entropy is a measure of uncertainty or randomness. +Originating in classical thermodynamics, +over time it has been applied in different sciences such as chemistry and information theory. +%As the informal concept of entropy gains popularity, its specific meaning can feel far-fetched and ambiguous. +The name 'entropy' was first coined by german physicist \textit{Rudolf Clausius} in 1865 +while postulating the second law of thermodynamics. +The laws of thermodynamics are based on universal observation regarding heat and energy conversion. +Specifically, the second law states that not all thermal energy can be converted into work in a cyclic process. +Or, in other words, that the entropy of an isolated system cannot decrease, +as they always tend toward a state of thermodynamic equilibrium where entropy is highest for a given internal energy. +Another result of this observation is the irreversibility of natural processes, also referred to as the \textit{arrow of time}. +Even though the first law (conservation of energy) allows for a cup falling off a table and breaking +as well as the reverse process of reassembling itself and jumping back onto the table, +the second law only allows the former and denies the latter, +requiring the state with higher entropy to occur later in time. + +Only 10 years later, in 1875, \textit{Ludwig Boltzmann} and \textit{Willard Gibbs} derived the formal definition +that is still in use in information theory today. +\begin{equation} +S = -k_B \sum_i p_i \ln(p_i) +\end{equation} +It gives statical meaning to the macroscopical phenomenon by defining the entropy $S$ of a macrostate as +the result of probabilities $p_i$ of all its constituting micro states. + \section{Definitions across disciplines} %- bedingte Entropie %- Redundanz