# Lecture 28: Boltzmann Hypothesis | Summary and Q&A

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October 23, 2023
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Lecture 28: Boltzmann Hypothesis

## TL;DR

Boltzmann's entropy formula describes the relationship between entropy and the number of microstates, while the Boltzmann distribution function determines the occupancy of different states based on their energy levels.

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### Q: How does Boltzmann's hypothesis connect stability and the number of microstates?

Boltzmann's hypothesis states that the state with the maximum number of microstates is the most stable. This is because a state with more microstates has a higher probability of occurring and is less likely to change.

### Q: What is Boltzmann's entropy formula?

Boltzmann's entropy formula states that entropy is proportional to the logarithm of the number of microstates, with a pre-factor known as Boltzmann's constant. It explains how the stability of a system is related to the number of microstates it can occupy.

### Q: How does the Boltzmann distribution function determine occupancy of different states?

The Boltzmann distribution function expresses the fractional occupancy of each state as a function of its energy level. It is derived through the maximization of entropy under the constraint of fixed energy and particle number.

### Q: What is the significance of the partition function in the Boltzmann distribution?

The partition function is a sum over all possible states and their associated energies. It normalizes the distribution function and describes all the different ways energy can be partitioned in the system.

## Summary & Key Takeaways

• Boltzmann's hypothesis connects stability to the number of microstates, stating that a state with the maximum number of microstates is the most stable.

• Boltzmann's entropy formula defines entropy as a function of the number of microstates, with entropy monotonically increasing with the number of microstates.

• The Boltzmann distribution function describes the fractional occupancy of each state, which is exponentially dependent on the energy of that state.