Einstein and complexity

We study Einstein's contributions to thermodynamics and statistical physics and their influence on some fields of physics which have led to current studies on complexity. We focus our attention on the use of fluctuations and entropy as a common framework for light and matter, whcich leds him to some of his fundamental contributions (phtoelectric effect, Brownian motion, specific heat of solids, stimulated light emission, Bose-Einstein condensation). We underline some aspects of Einstein's research style: extrapolations, analogies, simplifications. We underline the relationship between light and matter as a common link of his researches in statistical physics.