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Question:
What is the Monte Carlo Technique? And why it is so frequently apply to simulations of experiments in particle physics?


Replies:
Hello,

Monte Carlo technique (named after the gambling haven (or hell) in the European country of the same name) is the most powerful computational technique invented to tackle the widest range of problems in physical and even social sciences (e.g., economics), problems that are too complex, difficult, and often impossible to solve in any other way.

This is a statistical method, relying on random numbers, probability and statistics to solve problems. Its beauty is in its simplicity and its accuracy, accuracy in the sense that at the expense of a prolonged computational time, as accurate a result as desired can be obtained. It is best to illustrate my response with an example. Suppose on wishes to study how sun rays scatter through a particular kind of cloud and reach an observer on the ground. To a casual observer looking habitually and everyday at clouds, this seems trivial. But behind what he sees there is a complex set of interactions that are next to impossible to study where it not for the Monte Carlo method. While formulating the problem and solving it for some simple cloud geometry and content may be possible, it is impossible to do the same for an arbitrary shaped cloud with arbitrary kinds of particulates in it. In such a case, one simulate the problem by taking, say, 100, 1000, 10,000, or more photons, following their paths as they enter the could, scatter around according to the laws of scattering, end up getting absorbed or ejected out of the cloud, and reach an observer's eyes. If one follows enough of these photons, one obtains a reasonable picture of what is going on. If one wants more accurate results, then more photons are followed.

Simple, elegant, and powerful.

AK

Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory



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