1. Collective Behavior, from Particles to Fields Part 1

The following content is provided under a Creative Commons license. Your support will help MIT OpenCourseWare continue to offer high quality educational resources for free. To make a donation, or view additional materials from hundreds of MIT courses, visit MIT OpenCourseWare at ocw.mit.edu. PROFESSOR: Alright. So what we are doing is covering 8.334, which is statistical physics.

ANd let me remind you that basically statistical physics is a bridge from microscopic to macroscopic perspectives. And I'm going to emphasize a lot on changing perspectives. So at the level of the micro, you have the microstate that is characterized, maybe, by a collection of momenta and coordinates of particles, such as particles of gas in this room.

Maybe those particles have spins. If you are absorbing things on a surface, you may have variables that denote the occupation-- whether a particle or site is occupied or not. And when you're looking at the microscopic world, typically you are interested in how things change as a function of time. You have a kind of dynamics that is governed

by some kind of a [INAUDIBLE] which is dependent on the microstate that you are looking at, and tells you about the evolution of the microstate. At the other extreme, you look at the world around you and the macro world. You're dealing with things that are described by completely different things. For example, if you're thinking about the gas,

you have the pressure. You have the volume. So somehow, the coordinates managed to define and macrostate, which is characterized by a few parameters in equilibrium. If you have something like a collection of spins, maybe you will have a magnetization. And again, another important thing that characterizes the equilibrium we describe as temperature. And when you're looking at things