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Brownian motion (named in honor of the botanist Robert Brown) is either the random movement of particles suspended in a fluid or the mathematical model used to describe such random movements, often called a Wiener process.

The mathematical model of Brownian motion has several real-world applications. An often quoted example is stock market fluctuations. Another example is the evolution of physical characteristics in the fossil record.[citation needed]

Brownian motion is among the simplest continuous-time stochastic processes, and it is a limit of both simpler and more complicated stochastic processes (see random walk and Donsker's theorem). This universality is closely related to the universality of the normal distribution. In both cases, it is often mathematical convenience rather than the accuracy of the models that motivates their use.

The concept has also been applied in the field of cultural studies. In Michel de Certeau's The Practice of Everyday Life, the concept of "Brownian motion" is used to describe the tactical maneuvers of the Other. In reference to the rise of a "cybernetic society," de Certeau suggests that this society will be "a scene of Brownian movements of invisible and innumerbable tactics" (PEL, 40). Building on de Certeau's theorizing, Constance Penley elaborates on the concept in "Brownian Motion: Women, Tactics and Technology" (an essay that appeared in Penley and Andrew Ross's Technoculture, 1991).

History
Jan Ingenhousz had observed the irregular motion of coal dust particles on the surface of alcohol in 1785 but Brownian motion is generally regarded as having been discovered by the botanist Robert Brown in 1827. It is believed that Brown was studying pollen particles floating in water under the microscope. He then observed minute particles within the vacuoles of the pollen grains executing a jittery motion. By repeating the experiment with particles of dust, he was able to rule out that the motion was due to pollen particles being 'alive', although the origin of the motion was yet to be explained.

The first person to describe the mathematics behind Brownian motion was Thorvald N. Thiele in 1880 in a paper on the method of least squares. This was followed independently by Louis Bachelier in 1900 in his PhD thesis "The theory of speculation." However, it was Albert Einstein's independent research of the problem in his 1905 paper that brought the solution to the attention of physicists, and presented it as a way to indirectly confirm the existence of atoms and molecules. (Bachelier's thesis presented a stochastic analysis of the stock and option markets.)

At that time the atomic nature of matter was still a controversial idea. Einstein and Marian Smoluchowski observed that, if the kinetic theory of fluids was right, then the molecules of water would move at random. Therefore, a small particle would receive a random number of impacts of random strength and from random directions in any short period of time. This random bombardment by the molecules of the fluid would cause a sufficiently small particle to move in exactly the way described by Brown. Theodor Svedberg made important demonstrations of Brownian motion in colloids and Felix Ehrenhaft, of particles of silver in air. Jean Perrin carried out experiments to test the new mathematical models, and his published results finally put an end to the two thousand year-old dispute about the reality of atoms and molecules.

詳情 : http://en.wikipedia.org/wiki/Brownian_motion

懸浮在液體或氣體中的微粒　
受到液體或氣體粒子不斷的撞擊而作出的不規則運動
Aerosol receives the irregular movement in the liquid either the gas particle
which the liquid or the gas granule unceasing hit makes
中一科學

好似係f1教
如果我冇記錯既話
應該係 指氣體或液體 會由濃度高向濃度低擴散
就布朗運動

Brownian motion

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This article is about the physical phenomenon; for the stochastic process, see Wiener process. For the sports team, see Brownian Motion (Ultimate).


圖片參考：http://upload.wikimedia.org/wikipedia/en/thumb/a/a7/Brownian_hierarchical.png/180px-Brownian_hierarchical.png



圖片參考：http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png
Three different views of Brownian motion, with 32 steps, 256 steps, and 2048 steps denoted by progressively lighter colors.


圖片參考：http://upload.wikimedia.org/wikipedia/en/thumb/f/f8/Wiener_process_3d.png/180px-Wiener_process_3d.png



圖片參考：http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png
A single realization of three-dimensional Brownian motion for times 0 ≤ t ≤ 2.
Brownian motion (named in honor of the botanist Robert Brown) is either the random movement of particles suspended in a fluid or the mathematical model used to describe such random movements, often called a Wiener process.
The mathematical model of Brownian motion has several real-world applications. An often quoted example is stock market fluctuations. Another example is the evolution of physical characteristics in the fossil record.[citation needed]
Brownian motion is among the simplest continuous-time stochastic processes, and it is a limit of both simpler and more complicated stochastic processes (see random walk and Donsker's theorem). This universality is closely related to the universality of the normal distribution. In both cases, it is often mathematical convenience rather than the accuracy of the models that motivates their use.
The concept has also been applied in the field of cultural studies. In Michel de Certeau's The Practice of Everyday Life, the concept of "Brownian motion" is used to describe the tactical maneuvers of the Other. In reference to the rise of a "cybernetic society," de Certeau suggests that this society will be "a scene of Brownian movements of invisible and innumerbable tactics" (PEL, 40). Building on de Certeau's theorizing, Constance Penley elaborates on the concept in "Brownian Motion: Women, Tactics and Technology" (an essay that appeared in Penley and Andrew Ross's Technoculture, 1991).

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http://en.wikipedia.org/wiki/Brownian_motion