The Black-Scholes equation is an economical tool used in financial contracts. Following Ian Stewart (via Alexandre Borovik), this equation caused the economic crash and crisis. We can immediatly say that we must not use mathematics to describe the financial system, but the problem isn't in the equation, is in his use:
The formula was fine if you used it sensibly and abandoned it when market conditions weren't appropriate. The trouble was its potential for abuse. It allowed derivatives to become commodities that could be traded in their own right. The financial sector called it the Midas Formula and saw it as a recipe for making everything turn to gold. But the markets forgot how the story of King Midas ended.The equation was derived by Black and Scholes in 1973, in the paper The Pricing of Options and Corporate Liabilities. In the same year Robert Merton in the paper Theory of Rational Option Pricing develop the mathematics under the equation and the options, starting from the model of Fischer Black and Myron Scholes. For their work Scholes and Morton won the Noble Prize in economics in 1997 (Black died in 1995).
Now, one of the background ideas in Black and Scholes original model is the brownian motion, a mathematical model used to describe the random motion of a particle in a fluid. So it could be right use a brownian model in the study of the financial networks, but is also a great simplification of the problem:
Large fluctuations in the stock market are far more common than Brownian motion predicts.