---
slug: convergence-encyclopedia-c02
title: Convergence Encyclopedia: C02 — Least Action / Variational Principles
canonical: https://miscsubjects.com/a/convergence-encyclopedia-c02
---

**F1 — Tier.** T0 (mathematical theorem for classical mechanics) / T1 (ubiquitous instantiation across domains). CRITICAL NOTE: This is definitional universality, not surprising universality. Almost any smooth dynamical law can be written as an extremum principle (inverse problem of calculus of variations). The convergence here is formal, not necessarily substantive. Flagged honestly.

**F2 — Sources.** 
- Fermat, P. de (1662). Principle of least time (unpublished; posthumous formulation in Methodus ad disquirendam maximam et minimam).
- Maupertuis, P.L.M. de (1744). “Accord de plusieurs lois naturelles qui avaient paru jusqu’ici incompatibles.” Memoires de l’Academie des Sciences, 417–426.
- Euler, L. (1744). Methodus inveniendi lineas curvas maximi minimive proprietate gaudentes.
- Lagrange, J.L. (1788). Mecanique analytique.
- Hamilton, W.R. (1833). “On a general method of expressing the paths of light, and of the planets, by the coefficients of a characteristic function.” Report of the Fourth Meeting of the British Association for the Advancement of Science, 513–518.
- Feynman, R.P. (1948). “Space-time approach to non-relativistic quantum mechanics.” Reviews of Modern Physics, 20(2), 367–387.

**F3 — Domains.** All of physics (classical mechanics, electromagnetism, general relativity, quantum mechanics), economics (utility maximization), AI (policy gradient methods, reinforcement learning).

**F4 — Scale.** Quantum (action in units of ℏ) → cosmic (gravitational action of the universe).

**F5 — Falsifier.** Discovery of a fundamental physical law that cannot be expressed as an extremum principle. (Note: due to the inverse problem in calculus of variations, this is formally difficult; the substantive falsifier would be a law for which the extremum formulation requires more complexity than the direct formulation.)

**F6 — Rival (strongest form).** The universality of least action is a mathematical artifact, not a deep fact about nature. The inverse problem of calculus of variations shows that virtually any sufficiently smooth differential equation can be derived from a Lagrangian. The “convergence” is that mathematicians have a powerful tool, not that nature prefers economy. This is formal universality masquerading as substantive universality. (Source: philosophical consensus in foundations of physics; explicit in Hanc, Taylor & Tuleja 2004 Am. J. Phys. 72:514.)

**F7 — Independence.** HIGH — with caveat. Fermat (optics), Lagrange (mechanics), and Feynman (quantum) arrived from unrelated physical problems. BUT: all employ the calculus of variations — this is a hidden common cause. The shared mathematical framework may explain the convergence. Independence assessment: MODERATE for the formal principle; HIGH for the physical instantiations.

**F8 — Pattern type.** Mathematical.

**F9 — Maps.** A2 (thermodynamic/computational), A9 (mathematical foundations).

---

## Corpus map
- Previous: [Convergence Encyclopedia — C01](/a/convergence-encyclopedia-c01)
- Next: [Convergence Encyclopedia: C03](/a/convergence-encyclopedia-c03)
- Encyclopedia start: [The Schema](/a/convergence-encyclopedia-schema)
- Same node, other planes: [Catalogue node C02](/a/oip-node-c02-least-action-variational-principles) · [Catalogue hub](/a/oip-convergence-public-article)
- Edges touching C02: [convergence edge 2](/a/oip-convergence-edge-2) · [disconfirming edge 3](/a/oip-disconfirming-edge-3)
- Kin corpora: [Total Structure](/a/oip-total-structure) · [Signature of the Grain](/a/oip-sog-preamble-axioms)
