Assessing Rational Expectations: Sunspot Multiplicity and Economic Fluctuations
回顾了太阳黑子均衡概念如何挑战传统理性预期模型，揭示自我实现预期可能引发内生经济波动，并与凯恩斯“动物精神”及真实经济周期理论形成对比。
The idea of sunspot equilibrium has been one of the most important ones in macroeconomics and in economic theory in general over the last twenty years. It has made us reassess our understanding of economic fluctuations, of dynamic economies, and of the rational expectations hypothesis. A sunspot is a random expectational shock unrelated to the real fundamentals of the economy. Sunspots were introduced by David Cass and Karl Shell who questioned the strong stationary results that seemed to come out of the rational expectations models in macroeconomics, such as Lucas's 1972 paper. As rational expectations equilibria are essentially self‐fulfilling equilibria, the idea was to see what is the entire class of such equilibria or in other words, whether there can be self‐fulfilling equilibria other than the stationary equilibria. Sunspots or extrinsic uncertainty is a shorthand device to introduce an expectational coordinating variable to see the potential for these additional equilibria. The presence of such equilibria would also indicate the potential for endogenous self‐fulfilling fluctuations, and tie in with Keynes's idea of ‘animal spirits’ affecting economic outcomes. As such it is a counterpart to the real business cycles view of fluctuations where economic fluctuations are due to exogenous real shocks to the economy.