What is Brownian Motion?
Brownian motion is a phenomena whereby small particles suspended in a liquid tend to move in psuedo-random or stochastic paths through the liquid, even if the liquid in question is calm. It is the result of asymmetry in the kinetic impacts of molecules that make up the liquid. The liquid phase, by definition, must have some temperature, meaning its molecules or atoms must be thermally excited, bumping into each other and objects suspended within them. To idealize Brownian motion, imagine the motion of golf balls on a table filled with thousands of ball bearings moving in quick trajectories. The phrase Brownian motion can also refer to mathematical models used to describe the phenomenon, which have considerable detail and are used as approximations of other stochastic motion patterns. Mathematical Brownian motion is related to, but more structured than, the random walk, in which the displacement of a particle is entire randomized. Brownian motion has the Markov property, a term from pro
Small particles suspended in a liquid wiggle around furiously. It took the mind of Albert Einstein to change this from a curious observation to important evidence for the then controversial atomic theory of matter. Einstein realized that the random motions (called Brownian motion) could be explained by the molecular kinetic theory of heat. In 1905, Einstein published a paper that predicted a relationship between the mean squared magnitude of Brownian excursions and the size of molecules. Now all that remained was to do the experiment. Jean Perrin won the Nobel Prize in 1926 for his work confirming Einstein’s hypothesis. Perrin’s experimental confirmation of Einstein’s equation was an important piece of evidence to help settle a debate about the nature of mater that had begun nearly 2000 years earlier in the time of Democritus and Anaxagoras. Since then, a thorough understanding of Brownian motion has become essential for diverse fields ranging from polymer physics to biophysics, aerody
