Fermi's golden rule is a way to calculate the transition rate between two states of a system using perturbation theory, which means it's an approximation. The transition probability per unit of time is given by:
where ρ is the density of final states, δ is the Dirac delta function, and < f | V | i > is the matrix element (in bra-ket notation) of the potential, V, between the final and initial states.
Although named after Enrico Fermi, most of the work leading to the Golden Rule was done by Dirac.
External links