Statistical mechanics
Theory · 1860s to 1900s, Britain, Austria, and the United States · Physics, stage 2: Map the theories
Statistical mechanics derives the laws of thermodynamics from the mechanics of the huge numbers of particles a substance is made of. Maxwell worked out how the speeds of gas molecules are distributed, and Boltzmann showed that entropy counts the number of microscopic arrangements matching a given macroscopic state. Gibbs later gave the subject its general formalism. The move was contested for decades, because atoms had not been observed and many physicists regarded them as a calculating fiction; Einstein's 1905 analysis of Brownian motion settled the argument. The framework explains why the second law holds statistically rather than absolutely: entropy decreases are not forbidden, only overwhelmingly unlikely.
What it claims
- Large-scale properties such as temperature and pressure are averages over microscopic motion.
- Entropy counts the microscopic arrangements consistent with an observed macroscopic state.
- The second law is a statistical statement, not an absolute prohibition.
- Matter is made of discrete particles, and their statistics are measurable.
Key ideas
People
Sources
- Statistical mechanics English Wikipedia
- Philosophy of Statistical Mechanics Stanford Encyclopedia of Philosophy
- Boltzmann's Work in Statistical Physics Stanford Encyclopedia of Philosophy
