Why do capitalist economies recurrently generate crises whose severity is disproportionate to the size of the triggering shock? This paper proposes a structural answer grounded in the evolutionary geometry of production networks. As economies evolve through specialization, integration, and competitive selection, their inter-sectoral linkages drift toward configurations of increasing geometric fragility, eventually crossing a threshold beyond which small disturbances generate disproportionately large cascades. We introduce Sandpile Economics, a formal framework that interprets macroeconomic instability as an emergent property of disequilibrium production networks. The key state variable is the Forman--Ricci curvature of the input--output graph, capturing local substitution possibilities when supply chains are disrupted. We show that when curvature falls below an endogenous threshold, the distribution of cascade sizes follows a power law with tail index $α\in (1,2)$, implying a regime of unbounded amplification. The underlying mechanism is evolutionary: specialization reduces input substitutability, pushing the economy toward criticality, while crisis episodes induce endogenous network reconfiguration and path dependence. These dynamics are inherently non-ergodic and cannot be captured by representative-agent frameworks. Empirically, using global input--output data, we document that production networks operate in persistently negative curvature regimes and that curvature robustly predicts medium-run output dynamics. A one-standard-deviation increase in curvature is associated with higher cumulative growth over three-year horizons, and curvature systematically outperforms standard network metrics in explaining cross-country differences in resilience.

翻译：为什么资本主义经济体反复产生危机，其严重程度与触发冲击的规模不成比例？本文提出了一个基于生产网络演化几何学的结构性解释。随着经济体通过专业化、整合和竞争选择不断演化，其产业间联系逐渐趋向于几何脆弱性日益增大的结构，最终跨越一个阈值，在此之后微小扰动会引发不成比例的巨大级联效应。我们提出沙堆经济学这一正式框架，将宏观经济不稳定性解释为非均衡生产网络的一种涌现属性。关键状态变量是投入产出图的Forman-Ricci曲率，它捕捉了供应链中断时局部替代的可能性。我们证明，当曲率降至内生阈值以下时，级联规模的分布遵循尾部指数α∈(1,2)的幂律，这意味着一个无限放大的机制。其潜在机制是演化性的：专业化降低了投入替代性，将经济推向临界状态，而危机事件则引发了内生的网络重构和路径依赖。这些动态本质上非遍历，无法被代表性主体框架所捕捉。在实证方面，利用全球投入产出数据，我们证明生产网络持续运行在负曲率区间，且曲率能够稳健地预测中期产出动态。曲率一个标准差提升与三年期累积增长率的上升相关，且在解释国家间韧性差异方面，曲率系统地优于标准网络指标。