Recently I have posted about such topics as econophysics and the physics of societal and cultural change, as well as similarities in network structures of the Internet and al Qaeda. I am personally fascinated by the relatively new field of study of complexity and emergent behavior, although I am the first to admit I am an absolute beginner in my understanding of what has been done at the cutting edge over the last ten to twenty years. Some of the comments to my posts as well as questions in emails and additional reading I have done (including a book I have just started: check out “A Different Universe” by Robert Laughlin, Nobel laureate in physics…it is a page turner) have only increased my desire to learn more and develop a deeper understanding of what complexity and emergent behavior means, as well as where physics and science in general is headed in the future.
What I want to do in this post is list some examples of what is meant by “emergence,” and in future posts develop a way of explaining what it might mean for the path science takes in this century. A working definition of emergence: refers to the principles of organization for a many-body system. Such systems consist of individual entities that can act/move randomly, but then the system spontaneously exhibits some sort of collective organized behavior. The details of the individual components are not necessary to understand the system’s behavior. In fact, the emergent behavior is typically not predictable with only the rules of the individual components of a larger system. All of the following are examples of emergent behavior I’ve come across in some of the literature devoted to the study of complex systems.
- magnetism: in most materials individual domains are directed randomly but then can spontaneously be redirected by an external magnetic field so they align, causing the emergence of macroscopic fields.
- When you splash water on a surface and those little beads develop: water molecules inside the bead move randomly, but the bead emerges because of surface tension, giving a fixed structure
- Gases in closed systems: molecules move around randomly, but collectively the system follows set statistical rules such as the ideal gas law, PV = nRT
- Synchronization: there are lots of examples of this, such as an audience that begins clapping randomly, but then the clapping organizes into clapping in unison
- Emergent behavior can refer to phase transitions, such as cooling a liquid so the random motion of molecules stops and those molecules then become fixed in some lattice; a solid emerges from the randomness
- Social networks: individuals meet and know others randomly, but what emerges is a network of fixed mathematical structure, such as a scale-free network
- Galaxies: stars begin by moving randomly and are affected most just by other stars in the local neighborhood, but a swirling structured system emerges
- Random motions of vibrated granular materials can spontaneously form structured patterns such as oscillons
- Mix of people with diverse, varying skills emerge as an economy; the individuals can be free to do what they wish with their money, but the collective behavior is a system with fixed mathematical structure and statistical rules
- Art: think of a Monet painting of flowers…look at it closely and the individual brush strokes are imperfect and essentially random, but collectively structures appear and we have a masterpiece. The details of the individual stroke are not necessary in understanding what the emergent behavior, i.e. the global emergence of the form of the flowers, is
- Music: an instrument such as a violin has a continuum of sounds it can make, and played randomly we would recognize as noise. But some random sounds placed in particular order with timing structure emerges as pleasing music
- Radioactivity: individual uranium atoms decay at random. An individual atom can spontaneously decay as easily in a few seconds from now as tens of thousands of years from now. Collectively, however, millions of uranium atoms emerge as a system that follows select statistical rules with well-defined characteristic times such as a half-life. The individual atoms no longer are important, but rather the emergent statistical behavior, which gives predictable results, matters.
What all of these examples show is that the rules for the individual members of each system become less important, and can actually become irrelevant, to understanding the collective behavior of the system. Rather, what is important for the system is the principle of organization that leads to the collective behavior that has emerged. Statistical rules normally dominate to describe the way the system behaves, and predictable results can be obtained for the system, even though the nature of the individual members of the system can act at random. This is the essence of research in complexity and emergence fields of study, and brings about important changes in the way we think about the science of the natural world as well as social sciences. What are the fundamental rules and laws that help describe and explain what we observe? The rules of the individuals (microscopic, local) or of the emergent behaviors of the collective system (macroscopic, global)? Which are more important to understand? Are the rule sets for the local more important than those for the global? Historically most physical science has been geared in a reductionist mindset, breaking problems down further and further to understand the microscopic system of individual components (that is the essence of my days of research in particle physics, for example). Studies of complex systems, however, have been showing the need to step out of the reductionist mindset many scientists have been in and develop an entirely new way of approaching the science. What’s more, the focus needs to be placed on identifying principles and rules of organization, which are more fundamental for the system’s behavior, than the rules of individual components of the system. In addition, what has been observed is that the organizational rules of what are entirely different systems, such as numerous physical systems and numerous models of economics, are nearly identical. This has allowed for unprecedented collaboration between physicists and economists and has lead to new areas of research in econophysics. Most who work in these new areas of study believe we have only scratched the surface in our understanding of emergent behavior of complex systems.