Absence of critical scaling in the Schelling segregation model

Abstract

We find no evidence of critical scaling in the Schelling segregation model, in either the Moore neighborhood or its dense-spectrum extension to Chebyshev radii up to $r_0=6$ ($k=168$ neighbors). On periodic grids up to $L=320$ with 50 trials per point (> 12,500 runs), every finite-size scaling diagnostic in the Moore baseline fails: the per-$L$ $T_c$ does not drift, Var$(S)\sim L^{-2.02\pm 0.09}$ matches trivial averaging, $\gamma /\nu \approx 0$, and the scaling collapse never reaches a finite optimum. The 8-site Moore neighborhood restricts satisfaction to ratios $j/k$ with $k\le 8$, giving $S(T)$ a staircase structure with 23 rational thresholds; discreteness alone does not forbid criticality (cf. the Ising model), but the scaling evidence rules it out empirically. A branching-ratio calculation predicts subcritical cascades of mean size $1/(1-R)$ and is validated by perturbation experiments to within 15%; the multiscalar dissimilarity length stays finite across the transition. The dense-spectrum extension strengthens the negative verdict: across $r_0\in 3,4,5,6$ on $L\in 40,80,160$ the Binder cumulant has no $L$-curve crossing and the per-$L$ $T_c$ drift is monotonic and unsaturated; at $r_0=4$, extending to $L=320$ gives $\alpha =-2.70$, below the critical boundary $\alpha =-2$, dissolving an apparent $\alpha =+0.81$ signal visible only on $L\in 40,80$. The mechanism is the absence of long-range correlation in equilibrium plus deterministic high-$k$ dynamics, not the staircase structure. With a Beta-distributed heterogeneous tolerance, the intolerant tail drives segregation even at moderate population-average tolerance. The staircase theorem and cascade mechanism together account for the Schelling transition without invoking critical phenomena.

24 pages, 16 figures, 6 appendices. Over 12,500 simulation runs on periodic grids up to L = 320; Chebyshev radii r_0 up to 6 (k = 168 neighbors)