Jean-Philippe Bouchaud will present an online talk within the seminar “Analysis of Complex Systems” on Friday, December 11, 2020 via Zoom.
If you would like to attend, please email email@example.com
Title: Marginally stable economies?
Will a large economy be stable? Building on Robert May’s original argument for large ecosystems, we conjecture that evolutionary and behavioural forces conspire to drive the economy towards marginal stability. We study networks of firms in which inputs for production are not easily substitutable, as in several real-world supply chains. We argue that such networks generically become dysfunctional when their size increases, when the heterogeneity between firms becomes too strong, or when substitutability of their production inputs is reduced. At marginal stability and for large heterogeneities, we find that the distribution of firm sizes develops a power-law tail, as observed empirically. Crises can be triggered by small idiosyncratic shocks, which lead to “avalanches” of defaults characterized by a power-law distribution of total output losses. This scenario would naturally explain the well-known “small shocks, large business cycles” puzzle, as anticipated long ago by Bak, Chen, Scheinkman, and Woodford.
Jean-Philippe Bouchaud is Professor of Physics at Paris École Polytechnique and Co-Director of the CFM-Imperial Institute of Quantitative Finance at Imperial College London.