A particle in a double-well potential undergoes thermally-activated Kramers transitions. Escape rate r ~ exp(-ΔU/D) where D is noise strength — Arrhenius law. Stochastic resonance occurs when noise matches signal.
Kramers (1940): escape rate r ≈ (ω₀ω_b/2πγ) exp(-ΔU/kT). Noise-induced transition (Horsthemke-Lefever): multiplicative noise can shift stable states. Stochastic resonance enhances weak signals.