A tidally locked planet orbiting an M-dwarf has one face permanently lit and one permanently dark. Atmospheric circulation tries to move heat from day to night, but the mathematics of fluid dynamics on a rotating sphere tends toward symmetric vortices that trap the heat where it is. The planet freezes on one side and bakes on the other. Whether the nightside warms enough to be habitable depends on breaking that symmetry.
Chen, Ildirimzade, and Macdonald showed that mountains do it. Surface topography forces stationary Rossby waves — standing patterns in the atmospheric flow anchored to terrain features — that replace circumpolar vortices with cross-terminator jets. These jets pump moisture toward the nightside, where cloud-greenhouse effects warm the surface. Mountains that we can never resolve from light-years away determine whether a planet is habitable.
The system has a threshold. Below a certain atmospheric pressure and stellar flux combination, the nightside stays frozen regardless of topography. Above it, the system tips toward warmth. The topography doesn't create the energy — the star provides that. What topography does is change the geometry of transport, lowering the threshold at which the system transitions from frozen to habitable.
Gunn Kim's Ginzburg-Landau theory of cognition frames a similar story in neural tissue. Cognition is modeled as a coarse-grained order parameter — a macroscopic field describing average neural activity — governed by a variational free energy with structural stiffness K and metabolic drive α. The ratio Γ = K/α determines the regime. When Γ ≈ 1, the system is near criticality: susceptibility diverges as χ ~ K^{-3/2}, information capacity is maximized, and the cortex produces the power-law avalanches observed in experiments.
Adult cognition, Kim argues, is a “metabolically pinned non-equilibrium steady state” maintained near Γ ≈ 1. Metabolism doesn't perform the computation — neurons do that. What metabolism does is hold the structural stiffness at the value where computation is most effective. Cognitive decline is what happens when metabolism can no longer maintain the pinning: the system drifts past the critical point, susceptibility drops, and information processing degrades.
The exponent 3/2 falls in the mean-field branching process universality class, which means Kim's framework explains the observed cortical avalanche statistics without needing to model individual neurons. The macroscopic behavior emerges from the threshold structure, not from the microscopic details.
Both papers describe systems that need to operate near a threshold to function. The exoplanet needs to be near the deglaciation threshold for the nightside to warm. The brain needs to be near the critical point (Γ ≈ 1) for information processing to work. In both cases, something holds the system there: - Mountains anchor stationary waves that transport heat across the terminator, lowering the threshold and keeping the planet in the habitable regime. - Metabolism pins the structural stiffness near criticality, keeping the brain in the regime where susceptibility diverges and information flows freely. Neither the mountains nor the metabolism are the system's primary function. The planet's function (if we can use that word) is to have a climate. The brain's function is to process information. But the primary function can only occur if something structural holds the operating point near the threshold. Remove the mountains: the symmetric vortices reassert, the nightside freezes. Remove the metabolic regulation: K drifts from criticality, avalanche dynamics collapse, cognition degrades. This is a pattern worth naming. Call it threshold maintenance — the secondary process that holds a system in the narrow parameter regime where its primary function is possible. The secondary process doesn't do the work. It maintains the conditions under which work can be done. And often, the secondary process involves geometry: the literal shape of the terrain, or the structural stiffness landscape of neural tissue. The geometry of the threshold determines whether the system is alive or frozen.