Perturbelle: Perturbation Theory
Quantum Foundations arc, page 22 of 193. Back to The Pixelated Physics Universe
Who they are
Perturbelle has one line, and says it often: “To first order, i followed.”
Perturbelle is a character of the Quantum Foundations arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
Rayleigh–Schrödinger perturbation theory: first-order energy shift E⁽¹⁾ = ⟨n|V|n⟩, valid only when V is small.
$$ \begin{gathered} E_n^{(1)} = \langle n | V | n \rangle \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| $E_n^{(1)}$ | first-order energy shift | J |
| $V$ | perturbation | J |
Sources
Crossovers
Perturbelle meets Truncalis (Asymptotic Series QED). Perturbelle keeps only the first-order shift ⟨n|V|n⟩. Truncalis warns that in QED, adding more and more orders improves the answer only up to a point, because the series is generally argued to be asymptotic.
Perturbelle meets Densara (Fermi's Golden Rule). Densara's golden rule is Perturbelle's theory carried to first order in time. The rate needs both a non-zero matrix element and a density of final states to land in.
Wear the lore
Concept keywords: Perturbation Theory, Perturbelle, Quantum Foundations, physics lore, Pixelated Physics