Perturbation theory[0] is an algorithmic way to find approximate solutions to problems you don't know how to solve. The idea is to perturb a known solution to a

Perturbation theory[0] is an algorithmic way to find approximate solutions to problems you don't know how to solve. The idea is to perturb a known solution to a closely related problem. It is pivotal in quantum mechanics. [0] http://www.cmls.polytechnique.fr/perso/paul/6paul2.pdf http://www.cmls.polytechnique.fr/perso/paul/6paul2.pdf