We show that the intelligence of a swarm of cooperative units (birds) emerges at criticality, as an effect of the joint action of frequent organizational collapses and of spatial correlation as extended as the flock size. The organizational collapses make the birds become independent of one another, thereby allowing the flock to follow the direction of the lookout birds. Long-range correlation violates the principle of locality, making the lookout birds transmit information on either danger or resources with a time delay determined by the time distance between two consecutive collapses. DOI: 10.1103/PhysRevLett.107.078103 PACS numbers: 87.23.Cc, 64.60.fd, 89.70.Àa, 89.75.Hc In the recent few years, there has been intense activity to explain why a swarm of birds behaves as a single individual [1,2]. How is it possible that when a predator comes, the swarm changes direction to escape from danger? How is it possible that a subset of a swarm becoming aware of the right direction toward a resource [3] convinces the whole flock to pursue that specific course? In which sense, using a metaphor made popular by Couzin [4], can we interpret the swarm as a cognitive mind?The main purpose of this Letter is to prove that this form of intelligence is the effect of the joint action of frequent organizational collapses, allowing the single birds to recover independence of the others, and of a correlation length as extended as the flock size. Although the environment perceiving units are a small fraction of the total number of units, they exert a determinant action on the swarm during the short rearrangement phase after an organizational collapse, which makes each unit free to select a new direction. This freewill condition allows the swarm to select the new flying directions that are transmitted to all the units by the few danger-or resource-perceiving birds, thanks to the criticality-induced long-range correlation. The connection between dynamic instability and information transfer has been recently observed in locust nymphs [3]. The results of this Letter confirm the importance of this observation, establishing at the same time that the information transfer is made possible by the nonlocal nature of the criticality condition, with a time delay depending on the time distance between two consecutive organizational collapses. The correlation length between birds becomes as extended as the finite swarm size, thereby allowing the lookout birds to transmit their flying direction to the whole swarm. Thus, the mean value hi, proportional to the correlation length, remains finite.To afford a convincing proof that the swarm's intelligence is determined by the joint action of organizational collapses and criticality-induced nonlocality, we proceed in two main steps. In the first step we use a model of bird organization, referred to in this Letter as the bird model, to illustrate the concept of temporal complexity. The second step is based on a simpler model, where the relative positions of the birds are fixed and they have only to ch...

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We build a novel interregional computational input–output model to assess the economic impact of lockdowns in Italy. Lockdowns are modeled as shocks to labor supply, calibrated on regional and sectoral employment data coupled with the prescriptions of government decrees. When estimated on data from the first lockdown, our model closely reproduces the observed economic dynamics during spring 2020. We also show that the model delivers a good out-of-sample performance during fall and winter 2020 and demonstrate that it can be used to analyze counterfactual scenarios.

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