Encyclopedia Galactica · bounded analogue

Psychohistory: a bounded engine for predictable social dynamics

Weather prediction worked because the atmosphere has conservation laws, weak coupling at the forecast scale, and indifference to the forecast. Society has partial, local, conditional analogues of each — and the engine reports its own scope as a first-class output.

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Four ways in

This site is split into a guided tutorial, a worked-out account of the mathematics, and the full empirical record of every test run against real data. Pick a door.

The thesis

Three structural properties, three partial repairs

Numerical weather prediction is the existence proof that a system of comparable apparent difficulty can be forecast — not because of compute, but because of three conditions. The conditions, not the compute, are the theory.

P1 · Conservation laws

Mass, energy, momentum are conserved; trajectories are confined to low-dimensional manifolds. Social analogue: attention is a conserved normalized measure — allocated, never created. Belief is a drift field riding on top, not a stock.

P2 · Weak coupling at forecast scale

Ensemble statistics over quasi-independent regions are meaningful. Social analogue: Simon near-decomposability — dense within communities, sparse between. The statistical unit is the block; Neff ≈ K, not the population.

P3 · Non-reflexivity

The atmosphere does not read the forecast. Social analogue: reflexivity is dissolved at mean-field-game fixed points — a forecast is publishable iff it reproduces itself once everyone acts on it.

The running example · SVB, March 2023

Attention concentrated in days; the forecast of failure caused the failure; the run propagated within one professional block before jumping; a single deposit-guarantee announcement at peak sensitivity halted the cascade. Every component appears in one week.

The objections and their repairs

ObjectionRepairMechanism
No conservation — belief appears freely Attention conserved; belief = drift Total media time is ~flat; composition churns. Continuity equation ∂ρ/∂t + ∇·J = s; belief is a direction on transport, not a sub-measure. ▸ the math
Reflexivity — the forecast is an input Dissolves at MFG fixed points Lasry–Lions equilibrium ρ* reproduces itself under best-response. Publishable set = equilibrium set; deposit insurance is the engineered fixed point. ▸ the math
Correlated agents — small effective N Simon blocks, Neff ≈ K Near-decomposable hierarchies; model communities, not persons. Neff read from the macro variance-ratio, never Pearson-of-fluctuations. ▸ the math
The canon spine

Asimov concept → real-math analogue

The framework is a literal, bounded reading of the Foundation machinery. Each canonical concept maps to a piece of mean-field / control theory.

Asimov conceptReal-math analogueLives in

Seldon inverts secrecy: he published the Plan's existence (the fixed-point components) and hid its contents. Information release is itself a control input. ▸ the full tutorial