Entropy: A unifying path for understanding complexity in natural, artificial and social systems

Energy and entropy are basic concepts in thermodynamics and elsewhere. The concept of energy emerged in mechanics, the branch of physics which studies the motion of bodies and their causes. In contemporary physics, it appears in classical, relativistic and quantum mechanics. The concept of entropy emerged quite later than that of energy. It was introduced by Rudolf Julius Emmanuel Clausius around 1865 in order to further understand the roles of heat and work in thermodynamics. A decade later, Ludwig Eduard Boltzmann gave an interpretation of entropy in terms of the microscopic world – atoms, molecules, and their motion --, whose existence was at the time very controversial – in January 1897, at the Viennese Academy of Sciences, Mach brazenly lambasted Boltzmann with his sadly famous, and ignorant, “I do not believe that atoms exist!” --.