Brownian Motion: Langevin Equation
As an illustration of the rather abstract results of the previous chapter we discuss a theory of Brownian motion going back to Langevin [14.1]. We consider a Brownian particle that has a momentum p(0) at time t = 0. The collisions of this particle with other particles of the heat bath will lead to random fluctuations of its momentum that cannot be predicted in detail. On the average, however, it must relax to its equilibrium value 〈p〉 = 0.
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