"The groundwork for [Einstien's] understanding of Brownian motion was laid by Boltzmann, Maxwell, and others." #readingToday
The groundwork for the understanding of Brownian motion was laid in the decades that followed Brown's work, by Boltzmann, Maxwell, and others. Inspired by Quételet, they created the new field of statistical physics, employing the mathematical edifice of probability and statistics to explain how the properties of fluids arise from the movement of the (then hypothetical) atoms that make them up. Their ideas did not catch on for several more decades, however. Some scientists had mathematical issues with the theory. Others objected because at the time no one had ever seen an atom and no one believed anyone ever would. But most physicists are practical, and so the most important roadblock to acceptance was that although the theory reproduced some laws that were known, it made few new predictions. And so matters stood until 1905, when long after Maxwell was dead and shortly before a despondent Boltzmann would commit suicide, Einstein employed the nascent theory to explain in great numerical detail the precise mechanism of Brownian motion.34 The necessity of a statistical approach to physics would never again be in doubt, and the idea that matter is made of atoms and molecules would prove to be the basis of most modern technology and one of the most important ideas in the history of physics.
The Drunkard's Walk: How Randomness Rules our Lives, Leonard Mlodinow