---
slug: wilson-1971
title: Wilson 1971 — Renormalization Group and Critical Phenomena
canonical: https://miscsubjects.com/a/wilson-1971
---

## The Source

Wilson, K.G. "Renormalization Group and Critical Phenomena. I." *Physical Review B* 4(9), 3174–3183 (1971). DOI: 10.1103/PhysRevB.4.3174.

Wilson, K.G. "Renormalization Group and Critical Phenomena. II." *Physical Review B* 4(9), 3184–3205 (1971). DOI: 10.1103/PhysRevB.4.3184.

## The Claim

At criticality, correlation length shoots to infinity. The system forgets its atoms. Symmetry alone picks the numbers.

## The Context

1971. Cornell. Magnets, fluids, and alloys share the same exponents. Landau's theory fails. Experiments defy prediction. Wilson takes Kadanoff's block-spin idea and builds the machine. Coarse-graining erases the small. The large survives.

## The Evidence

Wilson writes the renormalization group as a flow. Repeated rescaling drives the Hamiltonian toward fixed points. At those points, ξ → ∞. Finite scales wash away. Critical exponents emerge as eigenvalues. Part I maps Kadanoff scaling to field theory. Part II runs the phase-space cell analysis. The epsilon expansion debuts. The numbers match experiment.

## The Convergence

This instantiates **C05 — Criticality** and **C10 — Scale Invariance**.

Wilson proves that criticality and scale invariance are one face. No characteristic scale means power laws. The same exponents rule magnets, fluids, and sandpiles. The renormalization group is the bridge. It links Bak's avalanches [SOURCE:bak-1987|type:empirical] to fractal geometry to metabolic scaling. One engine. Many bodies.

GRAIN scores this edge at convergence strength 8. Four fields. Four methods. Same statistics.

## The Honest Limits

Wilson addresses equilibrium. He does not touch self-organized criticality. Bak's sandpiles find criticality alone. Wilson needs a dial.

The epsilon expansion lives near four dimensions. Low dimensions break it. The Kosterlitz-Thouless transition escapes his net.

Wilson gives math. He does not give the why. Why do brains, markets, and quakes sit near criticality? That waits for Beggs, Kauffman, and GRAIN.

Rival: power laws are fitting artifacts. Log-log plots make them appear. Finite systems show cutoff effects. Pure scaling is an idealization.

## The Receipt

> "At criticality, correlation length ξ → ∞; the system becomes scale-invariant."

This is Wilson's core payload. The Hamiltonian flows to H* under rescaling. Microscopic details vanish. Different systems land on the same fixed point. Same exponents. Same numbers. That is the proof.

## Related Sources

- [Bak, Tang & Wiesenfeld — Self-Organized Criticality (1987)](/articles/bak-1987): Wilson's math meets systems that tune themselves.
- [Schrödinger 1944 — What Is Life?](/articles/schrodinger-1944): Physics crosses into biology. Wilson's machinery follows.
- [Noether 1918 — Invariante Variationsprobleme](/articles/noether-1918): Symmetry begets conservation. Wilson's fixed points inherit this law.
- [Wiener 1948 — Cybernetics](/articles/wiener-1948): Feedback and control. The engineering cousin to scaling.
- [Barabási & Albert 1999 — Scale-Free Networks](/articles/barabasi-1999): Power laws in links. Wilson's math in graph space.
- [Prigogine 1977 — Dissipative Structures](/articles/prigogine-1977): Non-equilibrium order. The thermodynamic cousin to criticality.

