Thermodynamics – Past, Present and Future Werner Ebeling Institute of Physics, Humboldt-University Berlin, Newtonstr. 15, 12489 Berlin, Germany Summary. We begin with historical remarks on the basic contributions to thermo- dynamics and statistics with some bias to scientists working in Berlin as Helmholtz, Clausius, Nernst and Einstein. We underline the key role of thermodynamic ideas in the scientific revolutions in the 20th century. Further we discuss several recent applications to natural, evolutionary and informational systems, exotic applications as well as perspectives and open problems. 1 Foundation of the Three Fundamental Laws Thermodynamics as a branch of science was established in the 19th century by Sadi Carnot (1796-1832), Robert Mayer (1814-1878), Hermann Helmholtz (1821-1894), William Thomson (1824-1907) and Rudolf Clausius (1822-1888). Evidently Mayer was the first who formulated the law of energy conserva- tion. His paper “Bemerkungen ¨ uber die Kr¨ afte der unbelebten Natur” pub- lished 1842 in Liebig’s Annalen is expressing the equivalence of work and heat. Joule’s conclusions on this matter were based on direct measurements of the conversion of work into heat. A great role in the foundation of ther- modynamics played physicists working in the middle of the 19th century in Berlin. We will discuss their contribution here in some more detail, just to illustrate the genius loci. In particular it was Hermann Helmholtz who de- termined the direction of thermodynamic research [1, 2]. At 27 years of age Helmholtz – at that time still working as a military surgeon in Potsdam – reported 1847 to the “Berliner Physikalische Gesellschaft” about a new prin- ciple of conservation of energy. The underlying experimental research which he carried out in the laboratory of his adviser Professor Magnus was primarily devoted to the conversion of matter and heat in such biological processes as rotting, fermentation and muscular activity. From experiments and brilliant generalization emerged the principle of conservation of energy or what is now called the first law of thermodynamics. Neither Mayer nor Joule recognized its fundamental and universal character as clearly as Helmholtz. The work of Mayer and Joule was unknown to Helmholtz at that time. Helmholtz had to fight hard for the recognition of his work. Professor Poggendorf, the editor of the “Annalen der Physik und Chemie”, rejected the paper which seemed to him too speculative. Professor Magnus also did not like the work, but at B. Kramer (Ed.): Adv. in Solid State Phys. 45, 3–14 (2005) c  Springer-Verlag Berlin Heidelberg 2005