1. Fundamental Postulate Revisited

2. Statistical Distributions (10 huge number particles)
As we know, statistical mechanics deals with the behavior of systems of a large number of particles. But, we give up trying to keep track of individual particles.
If we can’t solve Schrödinger’s equation in closed
form for helium (4 particles) what hope do we have
of solving it for the gas molecules in this room?
(10 huge number particles)
Statistical mechanics handles many particles by
calculating the most probable behavior of the system as a whole, rather than by being concerned
with the behavior of individual particles.

3. In statistical mechanics, we assume that the more ways there are to arrange the particles to give a particular distribution of energies, the more probable is that distribution. (Seems reasonable?)
6 units of energy, 3 particles to give it to
6 ways
3 2 1
3 1 2
2 1 3
2 3 1
1 2 3
1 3 2
1 1 4
4 1 1
1 4 1
3 ways
more likely

4. In statistical mechanics, we assume that the more
ways there are to arrange the particles to give a
particular distribution of energies, the more
probable is that distribution. (Seems reasonable?)
We begin with an assumption that we believe
describes nature. We see if the consequences of the
assumption correspond in any way with reality.
It is not “bad” to begin with an assumption, as
long as we realize what we have done, & discard
(or modify) the assumption when it fails to
describe things we measure and observe.