Emergence: A Unifying Theme for 21st Century Science

David Pines

When electrons or atoms or individuals or societies interact with one another or their environment, the collective behavior of the whole is different from that of its parts. We call this resulting behavior emergent. Emergence thus refers to collective phenomena or behaviors in complex adaptive systems that are not present in their individual parts.

Examples of emergent behavior are everywhere around us, from birds flocking, fireflies synchronizing, ants colonizing, fish schooling, individuals self-organizing into neighborhoods in cities – all with no leaders or central control – to the Big Bang, the formation of galaxies and stars and planets, the evolution of life on earth from its origins until now, the folding of proteins, the assembly of cells, the crystallization of atoms in a liquid, the superconductivity of electrons in some metals, the changing global climate, or the development of consciousness in an infant.
Indeed, we live in an emergent universe in which it is difficult, if not impossible, to identify any existing interesting scientific problem or study any social or economic behavior that is not emergent.

From emergence to complexity to emergence

The Santa Fe Institute began exploring emergent behavior in science and society at its 1984 founding workshops, “Emerging Syntheses in Science,” during which every speaker dealt with an aspect of emergent behavior as well as the search for the organizing principles that bring about that behavior [1]. However, in the early days of SFI, SFI’s scientists often focused on defining and understanding the ways these systems were complex, rather than focusing on the organizing principles responsible for the emergent behavior these systems exhibited. Indeed, some members of the Institute’s growing scientific community dreamed of creating a unified science of complexity through which complexity itself could be defined and quantified – and thus classify complex systems in some kind of grand hierarchical schema.

In 1993 SFI held a major workshop to define complex adaptive systems and assess the status of its initial quest for a science of complexity. As the title of the resulting proceedings – “Complexity: Metaphors, Models, and Reality” – suggests, in the course of that workshop the dream of a unified theory of complexity was abandoned [2]. As it turns out, we might have heeded our friend, the great mathematician Stanislaw Ulam, who, prior to his death in 1984 just as the Institute was forming, had dismissed the predecessor of complexity science, nonlinear science, as “the study of non-elephants” – by which he meant that nonlinear is not a useful descriptor because everything is nonlinear (a.k.a. complex). By the end of the workshop the participants agreed that while complexity is difficult to define, and that there can be no unified science of complexity, it is highly useful to devise models of a wide variety of systems and ask to what extent the ideas behind a model that describes complex behavior in one system might be applicable to understanding another system.

In arriving at this realization, we were endorsing the pursuit of emergence as a unifying theme for science at SFI – but without using the language of emergence. To paraphrase the character M. Jourdain in Molière’s Le Bourgeois Gentilhomme (1670) – who remarks, “Good heavens! For more than forty years I have been speaking prose without knowing it” – we were studying emergent behavior in complex adaptive systems without being explicit about doing so.

Flocking, the collective motion of many birds in flight, is an emergent behavior arising from individuals following simple rules without central coordination or leadership.

Flocking, the collective motion of many birds in flight, is an emergent behavior arising from individuals following simple rules without central coordination or leadership.

But our lexicon began to change within a few years. In what was perhaps the first general-audience book to focus on emergent behavior, Emergence: From Chaos to Order (Helix Books, 1998), John Holland, one of SFI’s early intellectual leaders, wrote about systems (e.g. games, simple molecules, etc.) in which the organizing principles responsible for emergent behavior are a set of comparatively simple rules. His book was soon followed by The Emergence of Everything: How the World Became Complex (Oxford University Press, 2002), in which another early SFI intellectual leader, Harold Morowitz, addressed emergent behavior from the perspective of a theoretical biologist. He considered systems for which the rules are not yet known, and wrote about emergence in nature, from the Big Bang to the emergence of humans on earth and the development of agriculture.

Still another SFI perspective on emergence, that of the theoretical physicist, can be found in two articles addressed to a general scientific audience. In a remarkably prescient article, “More Is Different” [3], written more than a decade before SFI’s founding, Philip Anderson (who spoke at our 1984 founding workshops and later co-chaired, with fellow Nobel laureate Ken Arrow, the Institute’s initial foray into economics) questioned the way fundamental research was characterized by many leading scientists. He also discussed the role of hierarchies and symmetry in complex systems from what we would today describe as an emergent perspective. A companion piece, “The Theory of Everything” [4], was written 28 years later by Stanford physicist R.B. Laughlin and myself. Both perspectives emphasized the limitations of a reductionist approach to complex systems in which one seeks to explain them by studying their components in ever-finer detail [5].