Heterogeneity extends criticality

TL;DR

This paper demonstrates that heterogeneity in complex systems extends the range of parameters where criticality occurs, reducing the need for fine-tuning and facilitating the emergence of complexity, robustness, and adaptability.

Contribution

It shows that introducing heterogeneity into homogeneous models broadens criticality, enabling systems to naturally reach phase transitions without precise parameter tuning.

Findings

Heterogeneity extends criticality in dynamical models.

Criticality can be achieved without fine-tuning parameters.

Heterogeneity enhances the evolution of complexity.

Abstract

Criticality has been proposed as a mechanism for the emergence of complexity, life, and computation, as it exhibits a balance between robustness and adaptability. In classic models of complex systems where structure and dynamics are considered homogeneous, criticality is restricted to phase transitions, leading either to robust (ordered) or adaptive (chaotic) phases in most of the parameter space. Many real-world complex systems, however, are not homogeneous. Some elements change in time faster than others, with slower elements (usually the most relevant) providing robustness, and faster ones being adaptive. Structural patterns of connectivity are also typically heterogeneous, characterized by few elements with many interactions and most elements with only a few. Here we take a few traditionally homogeneous dynamical models and explore their heterogeneous versions, finding evidence that heterogeneity extends criticality. Thus, parameter fine-tuning is not necessary to reach a phase transition and obtain the benefits of (homogeneous) criticality. Simply adding heterogeneity can extend criticality, making the search/evolution of complex systems faster and more reliable. Our results add theoretical support for the ubiquitous presence of heterogeneity in physical, social, and technological systems, as natural selection can exploit heterogeneity to evolve complexity "for free". In artificial systems and biological design, heterogeneity may also be used to extend the parameter range that allows for criticality.