Then, in 1905, theoretical physicist Albert Einstein published a paper where he modeled the motion of the pollen particles as being moved by individual water molecules, making one of his first major scientific contributions. In 1900, almost eighty years later, in his doctoral thesis The Theory of Speculation (Théorie de la spéculation), prepared under the supervision of Henri Poincaré, the French mathematician Louis Bachelier modeled the stochastic process now called Brownian motion. This motion is named after the botanist Robert Brown, who first described the phenomenon in 1827, while looking through a microscope at pollen of the plant Clarkia pulchella immersed in water. The kinetic energies of the molecular Brownian motions, together with those of molecular rotations and vibrations, sum up to the caloric component of a fluid's internal energy (the equipartition theorem). More specifically, the fluid's overall linear and angular momenta remain null over time. Within such a fluid, there exists no preferential direction of flow (as in transport phenomena). This pattern describes a fluid at thermal equilibrium, defined by a given temperature. Each relocation is followed by more fluctuations within the new closed volume. This pattern of motion typically consists of random fluctuations in a particle's position inside a fluid sub-domain, followed by a relocation to another sub-domain. Random motion of particles suspended in a fluidĢ-dimensional random walk of a silver adatom on an Ag(111) surface Simulation of the Brownian motion of a large particle, analogous to a dust particle, that collides with a large set of smaller particles, analogous to molecules of a gas, which move with different velocities in different random directions.
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