Fluctuation-Dissipation Theorem

The jiggle and the drag are one: thermal noise in a system is set by how it dissipates energy.

Core Principles & Analysis

• Einstein’s 1905 Brownian-motion relation between diffusion and friction is its earliest special case.
• Johnson-Nyquist resistor noise obeys it: hotter and more resistive means noisier.
• Callen and Welton proved the general quantum version in 1951.

Specifications & Metrics

• SYMBOL: S(ω) ↔ dissipation