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What do we need to characterize a system in an ensemble?

Classical answer: coordinates and momenta of *all*
particles!^{}

*N* particles, each has 3 coordinates and 3
momenta--6*N*-dimensional space. This is called *phase
space* . Each system is a point in this space. The time evolution is
a flow in the phase space!

**Mechanical approach:**- Describe each trajectory in phase space
**Statistical approach:**- Describe the flow in the phase space, averages, distribution, deviations, etc. This is the problem we will discuss in this course.

© 1997

Wed Sep 3 22:38:51 EDT 1997