Brownian motion
Brownian motion is the completely random, zigzag motion of minute particles of matter in fluids and gases. It can be seen in all types of suspensions: solid-in-liquid, liquid-in-liquid,
gas-in-liquid, solid-in-gas, and liquid-in-gas. [Observe the irregular movement of dust particles seen in the path of sunlight streaming in from the window into your house…essentially, you will be seeing the Brownian motion].
The motion is named after the botanist Robert Brown* who observed [in 1827] the movement of plant spores in water under a microscope. The effect is caused by the thermal motion of the molecules in the fluid or gas. These molecules are in continual random motion with a velocity proportional to the temperature of the liquid or gas.
The first satisfactory mathematical explanation of Brownian motion was made by Einstein in 1905. Later, Jean Perrin did a quantitative experiment of how Brownian motion was dependent on temperature and particle size. This verified Einstein’s mathematical formula.
ONELINER: Brownian motion
OTHER CONNECTIONS: None
BIBLIOGRAPHY:
www.bartleby.com, www.hyperdictionary.com, Web dictionary of Cybernetics and Systems,
www.sciences.demon.co.uk[Brian J. Ford science website]
Wikipedia (see animations)
History
Reproduced from the book of Jean Baptiste Perrin, Les Atomes, three tracings of the motion of colloidal particles of radius 0.53 µm, as seen under the microscope, are displayed. Successive positions every 30 seconds are joined by straight line segments (the mesh size is 3.2 µm).[8]
The Roman philosopher-poet Lucretius' scientific poem "On the Nature of Things" (c. 60 BC) has a remarkable description of the motion of dust particles in verses 113–140 from Book II. He uses this as a proof of the existence of atoms:
Observe what happens when sunbeams are admitted into a building and shed light on its shadowy places. You will see a multitude of tiny particles mingling in a multitude of ways... their dancing is an actual indication of underlying movements of matter that are hidden from our sight... It originates with the atoms which move of themselves [i.e., spontaneously]. Then those small compound bodies that are least removed from the impetus of the atoms are set in motion by the impact of their invisible blows and in turn cannon against slightly larger bodies. So the movement mounts up from the atoms and gradually emerges to the level of our senses so that those bodies are in motion that we see in sunbeams, moved by blows that remain invisible.
Although the mingling, tumbling motion of dust particles is caused largely by air currents, the glittering, jiggling motion of small dust particles is caused chiefly by true Brownian dynamics; Lucretius "perfectly describes and explains the Brownian movement by a wrong example".[9]
While Jan Ingenhousz described the irregular motion of coal dust particles on the surface of alcohol in 1785, the discovery of this phenomenon is often credited to the botanist Robert Brown in 1827. Brown was studying pollen grains of the plant Clarkia pulchella suspended in water under a microscope when he observed minute particles, ejected by the pollen grains, executing a jittery motion. By repeating the experiment with particles of inorganic matter he was able to rule out that the motion was life-related, although its origin was yet to be explained.
The first person to describe the mathematics behind Brownian motion was Thorvald N. Thiele in a paper on the method of least squares published in 1880. This was followed independently by Louis Bachelier in 1900 in his PhD thesis "The theory of speculation", in which he presented a stochastic analysis of the stock and option markets. The Brownian motion model of the stock market is often cited, but Benoit Mandelbrot rejected its applicability to stock price movements in part because these are discontinuous.[10]
Albert Einstein (in one of his 1905 papers) and Marian Smoluchowski (1906) brought the solution of the problem to the attention of physicists, and presented it as a way to indirectly confirm the existence of atoms and molecules. Their equations describing Brownian motion were subsequently verified by the experimental work of Jean Baptiste Perrin in 1908.